'■"■mumS »i<'miiii,n<(ilimin.i 'l!!||'f!l!!;!ljl;„ fyxmW mmxmxii» f ifc«g BOUGHT WITH THE INCOME PROM. THE SAGE ENDOWMENT FUND THE GIFT OF Heni^g M. Sage 1S91 hMi.ifo \aM\ii 3777 ENGINEERING LIBRAR^-^ Cornell University Library TN 500.T48 Stamp milling and cyaniding, 3 1924 004 121 715 Cornell University Library The original of tiiis bool< is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31 9240041 21 71 5 STAMP MILLING AND CYANIDING McGraw-Hill DookCompaip^ Puj6Cis/iers oif3ooJ^/br Electrical World The EnginGeiingandMining Journal EngineGring Record Engineering News Railw^ Age Gazette American Machinist Signal Engineer American Engjneei' ElectricUailway Journal Coal Age Metallurgical and Chemical Engineering Power im^ Frontispiece FiQ. 1. 10-Stamp Mill with Cast-iron Anvil Blocks. STAMP MILLING AND CYANIDING BY FRANCIS ANDREW THOMSON, E.M. HEAD OF DEPARTMENT OP MINING ENGINEEKING, STATE COLLEGE OF WASHINGTON, PULLMAN, WASHINGTON FiBST Edition McGRAW-HILL BOOK COMPANY, Inc. 239 WEST 39TH STREET, NEW YORK 6 BOUVEEIE STKEET, LONDON, E. C. 1915 COPTHIGHT, 1915, BY THE McGRAW-HILL BOOK COMPANY, Inc. Stanbope iprese F. H.GILSON COMPANY BOSTON, U.S.A. SJo fife mrmorg OF J. A. T. AND J. K. R. HIS FATHERS IN ENGINEEEING, THE AUTHOR DEDICATES THIS WORK PREFACE This book is designed for use as a text. It is, therefore, prop- erly and of necessity a compilation. The subject matter and method of presentation have been developed from my lectures on the metallurgy of gold and silver, and will, I trust, meet with the approval of other students of the metallurgic art. While every effort has been made to avoid errors, it is scarcely to be hoped that none will be found, and I shall appreciate having my attention called to such as are discovered. I have levied freely upon all available sources of information. Especially am I beholden to the files of the Mining {and Scientific) Press, the Engineering and Mining Journal, . the Mining and Engineering World, the Mining Magazine (of London), the Trans- actions of the American Institute of Mining Engineers and of the Institution of Mining and Metallurgy. I have also made use of all available texts, and lastly have drawn in many cases from my own ten years of professional practice. In every case I have tried to acknowledge the source from which information has been taken, but doubtless I have failed to do so in certain instances; for even as "we are part of all whom we have met, " so our knowledge is part of all that we- have read, and after many years of reading full acknowledgment is no longer a possibility. For aid in illustrating this book my thanks are due to the fol- lowing manufacturers: Allis-Chalmers Co., Milwaukee; Blaisdell Co., Los Angeles; Braun-Knecht-Heimann Co., San Francisco; Chalmers and Williams, Chicago; Chrome Steel Works, Brooklyn; Colorado Iron Works, Denver Engineering Works, and Dorr Cyanide Machinery Co., Denver; Fairbanks-Morse and Co., Chicago; Hammond Mfg. Co., Portland, Ore.; Hardinge Conical Mill Co., New York; Joshua Hendy Iron Works, San Francisco; Mine and Smelter Supply Co., Denver; Monarch Engineering Co., Baltimore; Moore Filter Co., New York; Oliver Continuous Filter Co., and Pacific Pipe and Tank Co., San Francisco; Power viii PREFACE and Mining Machinery Co., Cudahy, Wis.; Stearns-Roger Mfg. Co., Denver, and L. C. Trent Engineering Co., Los Angeles; also to the publishers of the Engineering and Mining Journal, and to the secretary of the American Institute of Mining Engineers. I desire to acknowledge aid received from the following mining engineers and metallurgists: Messrs. W. B. Chidester, Edgar A. Collins, David Goodale, Henry Hanson, J. W. Hutchinson, Merrill Metallurgical Co., A. R. Parsons, Lloyd Robey, Harry C. Robinson, and R. Wheeler. For faithful and invaluable help in typing the manuscript I am indebted to Miss Helene T. Bruckman; and for aid in proof- reading the bibliography, to my assistant Mr. Henry E. Doelle. To Mr. Frank A. Ross I am particularly obligated for valuable suggestions and for reading the typescript. To my colleague Prof. Hallet R. Robbins, especial thanks are due for critical scrutiny of the final proof. FRANCIS A. THOMSON. State College of Washington, February, 1915. CONTENTS PAGEa Preface vii-viii PART I MILLING AND AMALGAMATION CHAPTER I Gold and Silver 3-7 Gold; Physical and Chemical Properties; Occurrence, 3. Metallurgical Properties; Silver; Physical and Chemical Properties, 4. Occurrence; Metallurgical Properties, 5. Bibli- ography, 6. CHAPTER II Principles op Amalgamation 8-12 Amalgams, 8. Amalgamation, 9. Flouring and Sickening, 11. Bibliography, 12. CHAPTER III The Stamp Mill and Its Accessories 13-55 The Stamp and Its Mechanism, 14. The Mortar, 23. The Foundation and Frame Work, 25. Accessory Apparatus and Operation, 38. Starting the Mill, 46. Lubrication, 47. Order, Height, and 'Speed' ot Drop, 48. Power, 50. Bibli- ography, 51. CHAPTER IV Stamp Mill Amalgamation 56-78 General Principles; Inside Amalgamation, 56. Outside Amal- gamation, 57. Position of Plates, 61. Plate Materials; Plate-Frames, 62. Care of Quicksilver, 63. Treatment of Amalgam, 64. Aids to Amalgamation, 66. Cleaning Plates, 69. Battery Clean-up, 71. Cleaning Battery-Sand; Clean- ing-up of Odds-and-Ends, 72. Clean-up Room; Retorting, 73. Melting, 75. Bibliography, 76. CHAPTER V Variations in Practice 79-87 Gilpin County Practice, 79. The California Practices, 80. South African Practice, 81. Individual Stamps, 82. Stamp Milling Costs, 83. Bibliography, 86. ix X CONTENTS CHAPTER VI Pages Other Mills and Grinders 88-109 Modified Gravity-Stamps; Steam-Stamps, 88. Arrastras and Pans, 91. Centrifugal and Edge-Runner Mills, 93. Tube-Mills and Ball-Mills, 102. Bibliography, 104. CHAPTER VII Comparisons op Various Mills 110-119 Crushing Efficiency, 110. Suitability of Product; Wear and Tear; Bibliography, 118. PART n CYANIDING CHAPTER VIII History and Chemistry op Cyaniding 123-136 History, 123. Chemistry, 127. Cyanides of Gold and Silver; Other Metallic Cyanides, 129. Solution of Gold in Cyanide, 130. Precipitation of Gold and Silver, 132. Bibliography, 133. CHAPTER IX Preparation op Ores for Cyanide Treatment 137-145 Crushing, 137. Classification and Dewatering, 138. Amal- gamation and Concentration, 141. Roasting, 142. Bibli- ography, 145. CHAPTER X Dissolving the Gold and Silver 146-177 Strength of Solution, 146. Temperature of Solutions; Condi- tion of the Gold Particles, 148. Presence of Cyanicides, 149. Amount of Solution; Method of Application; The, Leaching Method, 152. The Agitation Method, 163. Effect of Extra- Solutions and Oxidizers, 172. Bibliography, 173. CHAPTER XI Separating Solution and Pulp 178-205 Gravity Filtration; Assisted Gravity Filtration; Decantation, 178. Filter-Presses, 182. Vacuum Filters, 186. Pressure Filters, 194. Bibliography, 201. CHAPTER XII Precipitation op Gold and Silver 206-216 Precipitation with Zinc Shaving, 206. Precipitation with Zinc- Dust, 208. Precipitation with an Electric Current, 211. Bibliography, 212. CONTENTS xi CHAPTER XIII Pages Recovery and Treatment of Precipitate 217-224 The Acid Treatment, 218. Roasting; Direct Smelting, 219. Treatment of Solution after Precipitation, 220. Bibliography, 222. PART ni THE TREATMENT OF GOLD AND OF SILVER ORES CHAPTER XIV Treatment of Gold Ores 227-254 Amalgamation; Amalgamation and Concentration, 228. Amal- gamation and Cyanidation; Amalgamation, Concentration and Cyanidation; Cyanidation, 229. Plow-Sheets, 231-246. Bib- liography, 247. CHAPTER XV Treatment of Silver Ores 255-265 Application of Cyanide to Silver Ores, 255. Flow-Sheets, 258- 261. Bibliography, 262. MiSCBLLANEOtrS BIBLIOGRAPHY 266-269 Costs, 266. Cyaniding Concentrate, 267. Miscellaneous, 268. Index , 271-285 PART I MILLING AND AMALGAMATION STAMP MILLING AND CYANIDING CHAPTER I GOLD AND SILVER The modem metallurgy of gold, taking the term in its purely commercial sense, and excluding from consideration the recovery of the precious metals as a by-product of smelting, concerns itself with the three processes, amalgamation, cyanidation, and — to a continually decreasing extent — chlorination. The metallurgy of silver, which for many years has lagged far behind that of its sister metals, is now making rapid strides and, while at the present time amalgamation still plays an important part, it seems destined to yield almost entirely to cyanidation. GOLD Physical and Chemical Properties. Gold is the one metal that is yellow in color, malleable, and of high specific gravity (19.6) ; these properties serve at once to distinguish it from all others. Gold melts at about 1060° C. and is sensibly volatile above 1200°. It has high electrical conductivity (76.7), crystaUizes in the iso- metric system (usually in octahedra), alloys readily with nearly all other metals, and has at least one allotropic form, and possibly two. Chemically, gold forms compounds with the halogens, oxy- gen, sulphur, and silica, also with the salts of thiosulphuric and hydrocyanic acids. Occurrence. In nature only two forms are positively recog- nized. Native, or free, gold is by far the most common occurrence. Less frequently it is found associated with tellurium in various combinations. Selenide of gold is said to have been discovered but its existence is still a matter of doubt. 3 4 STAMP MILLING AND CYANIDING Metallurgical Properties. From the metallurgist's point of view five properties of gold are of prime importance. These are: 1. High specific gravity. 2. Formation of alloys with mercury. 3. Formation of alloys with lead, copper, and copper sulphide. 4. Solubility in solutions of cyanide salts. 5. Formation of a soluble chloride by contact with chlorine gas. The first property is purely physical. It finds an important application in the recovery of gold in riffles, on blankets, etc., in connection with placer mining and is a distinct aid in the milling of gold ores. The second property — the formation of an alloy, or so-called amalgam, with mercury — is the basis of the amalgamation pro- cess, and was for many years the most important factor in gold metallurgy. The third property is utilized in lead and copper smelting, and while extremely important in point of production, will not be fur- ther discussed in this work. The fourth property — the solubility of gold in salts of hydro- cyanic acid — is the fact upon which the cyanide process is based; known, but unused, twenty-five years ago, this chemical fact has revolutionized the art of gold recovery. The fifth property — the formation of a soluble gold chloride by means of the action of chlorine gas upon moist gold — was for many years second only to amalgamation as a means of gold re- covery. In spite of many ardent advocates, however, the process has been steadily losing ground.* SILVER Physical and Chemical Properties. Silver, next to platinum and gold, is the most valuable of the more common metals. It is distinguished by its white color, brilliant luster, malleability, and hardness. In electrical conductivity silver excels all other metals. It melts at 962° C. and is readily volatile at higher temperatures. Its specific gravity (10.5) is about half that of gold. Chemically, silver is much more active than gold. Nitric acid attacks it readily, and it is soluble in hot concentrated sulphuric * One of the most interesting controversies in metallurgical literature is to be found in the Eng. and Min. Jour., Vols. 78 and 79, where Phillip Argall and W. E. Greenwalt debate at great length the comparative merits of cyanida- tion and chlorination. GOLD AND SILVER 6 acid. Owing to the insolubility of the chloride, hydrochloric acid attacks it only superficially. Many salts of silver are soluble in water and this fact has led to numerous proposals for extracting it from its ores. Occurrence, Silver occurs in nature in a greater variety of forms than any other well known metal. Native silver in threads and crystals is frequently found either alone or associated with gold, or with native copper. Native silver-amalgam is not unknown. Argentite AgaS containing 86 per cent silver is one of the commonest silver minerals. The sulph- antimonides and sulpharsenides of silver are next in importance; among the most usual are the light and dark ruby silvers, proust- ite AgsAsSs and pyrargyrite AgsSbSs, also stephanite AgSbS4. The haloid silver minerals, especially cerargyrite the chloride, and emboUte the chlorobromide, are important in the upper, oxidized portions of most silver veins. Nearly all copper minerals, and practically all lead minerals, carry more or less silver; such ores, however, are treated almost altogether by smelting. Metallurgical Properties. Probably more processes have been proposed for the extraction of silver from its ores than for any other metal. To mention all of the properties upon which these have been based would be useless. The most important are as follows: 1. The property possessed by silver and its halogen compounds of forming an alloy or amalgam with mercury. 2. The property possessed by copper, copper sulphides and metalUc lead of dissolving or alloying with silver in various forms. 3. The solubility of silver chloride in a solution of sodium hypo- sulphite. 4. The solubility of nearly all silver minerals in cyanide solu- tions. The first-mentioned property has, even more than is the case with gold, been responsible in the past for a large part of the world's supply of silver. Aside from the smelting methods men- tioned under the second heading, it is safe to say that amalgama- tion, until the last few years, has supphed over 90 per cent of the silver production of the world. For some years hyposulphite leaching was in vogue but wet processes were crude then and mechanical difficulties, coupled in 6 STAMP MILLING AND CYANIDING many cases with the necessity of a preliminary roast with salt, — to convert other silver compounds into chlorides, — gradually led to its abandonment. The mechanical perfection of the present- day cyanide plants would solve many of the problems of hypo- sulphite lixiviation, but it is doubtful if the latter has any advan- tages over cyaniding, and its revival does not seem likely. Cyaniding of silver ores is a new field. Ten years ago it was scarcely heard of. To-day Mexico and Nevada are producing millions annually by this means. GENERAL BIBLIOGRAPHY ON TREATMENT OF GOLD AND SILVER ORES * Especially Desirable for Students' Use. Books on Milling and Amalgamation. Adams, W. J. Hints on Amalgamation and the Care of Gold Mills, 120 pp., San Francisco, 1907. * Del Mab, Algernon. Stamp MiUing, 134 pp.. New York, 1912. EissLBB, Manuel. The Metallurgy of Gold, 524 pp., London, 1901. * Locke, C. G. W. Principles and Practice of Gold MiUing, 823 pp., London, 1906. * Louis, Henry. A Handbook of Gold Milling, 599 pp., London, 1903. McFarren, H. W. Practical Stamp Milling and Amalgamation, 166 pp., San Francisco, 1910. O'Dbiscoll, Florence. Notes on the Treatment of Gold Ores, 200 pp., London, 1886. Preston, E. B. California Gold Mill Practices, Bull. No. 6, Calif. State Mining Bureau, San Francisco, 1895. * Richards, R. H. Ore Dressing, Vols. I (1903) & III (1909), New York. * RicKARD, T. A. Stamp Milling of Gold Ores, 260 pp., New York, 1898. * Rose, T. K. The Metallurgy of Gold, 547 pp., London, 1906. Books on Cyaniding. * Bain, H. Foster. More Recent Cyanide Practice, 420 pp. (Cyaniding Articles Appearing in Min. & Sci. Press from Oct., 1907 to July, 1910), San Francisco, 1910. Clbnnell, J. E. The Chemistry of Cyanide Solutions, 198 pp.. New York, 1909. BosQDi, Francis L. Practical Notes on the Cyanide Process, 200 pp., New York, 1900. * Clennell, J. E. Cyanide Handbook, 526 pp.. New York, 1910. James, Alfred. Cyanide Practice, 225 pp., London, 1901. * Julian and Smart. Cyaniding Gold & Silver Ores, 405 pp., London, 1907. GOLD AND SILVER 7 * McFaeren, H. W. Text-book of Cyanide Practice, 290 pp., New York, 1912. * McCann, Ferdinand. Beneficio de Metales de Plata y Ore per Cianuracion, 400 pp. (Treatment of Silver and Gold Ores by Cyanid- ing), Mexico, 1909 (Spanish). * McCann, Ferdinand. Cyanide Practice in Mexico, 194 pp., Mex- ico, 1912. * Megraw, Herbert A. Practical Data for the Cyanide Plant, 90 pp., San Francisco, 1910. Park, James. The Cyanide Process of Gold Extraction, 240 pp., London, 1906. * RicKARD, T. A. Recent Cyanide Practice, 350 pp. (Cyaniding articles appearing in Min. & Sci. Press from Jan., 1906 to Oct., 1907), San Francisco, 1907. ScHBiDEL, A. The Cyanide Process, 140 pp.. New York, 1901. . A Textbook of Rand Metallurgical Practice, Vol. I, 468 pp.; Vol. II, 438 pp. Johannesburg, 1911. CHAPTER II PRINCIPLES OF AMALGAMATION Amalgams. An amalgam is an alloy of mercury with other metals. The word amalgam is derived from the greek ' mcdagma' — poultice — referring, of course, to the pasty nature of mercury alloys. On account of the low fusing point of mercury —42° F., its al- loys with other metals were early investigated, but so far as we are aware no commercial uses were made of them for many years after their existence was known. Tin and bismuth amalgams are used for silvering mirrors and silver-tin amalgams with small additions of other metals are much used in dental work. The amalgams of gold and silver, however, are those most important for the metal- lurgist. While much remains to be learned concerning the exact consti- tution of these precious-metal amalgams, it may be safely said that there are certain definite chemical compounds of both gold and silver with mercury. These compounds, in turn, form solid solu- tions with an excess of mercury, so that, while gold and silver are only to an extremely . limited degree soluble in mercury, their amalgams will remain in suspension in it to almost any extent. Recent investigations into the constitution of gold and silver amalgams by T. T. Read * have demonstrated the following inter- esting facts': 1. That there are two definite compounds of gold and mercury, one carrying 13.62 atomic per cent of mercury, corresponding nearly to the formula AuigHgs, and the other 17.44 atomic per cent, corresponding nearly to AuioHg^. 2. That gold is soluble in mercury at 20° C. to the extent of about 0.06 per cent; that this solubility increases to about 0.25 per cent at 100° C. and probably decreases to zero at the freezing point of mercury. * Trans. A.I.M.E., Vol. 37, page 64 et seq. 8 PRINCIPLES OF AMALGAMATION 9 3. That while no definite results have been obtained with silver it is probably the case that compounds of silver and mercury exist similar to those mentioned for gold. Amalgamation is, of course, the art of forming or making amal- gams, but in metallurgical parlance, the word is limited to the means adopted for the recovery of gold and silver from its ores with the aid of mercury. The use of mercury for this purpose is one of the ancient arts. Vitruvius and Pliny both mention its employment for the extraction of gold from gold cloth. As it had long been the custom to recover gold from both lode and placer mines with the aid of hides or long-napped cloth, it would be but a short step to connect these two ideas and make the mercury com- plete the extraction of gold from the hide or blanket concentrates. This knowledge of amalgamation as applied to gold ores was so well nigh lost sight of in the middle ages, that it reappears in the six- teenth century as a secret art. For the application of the amalgamation process to the recovery of silver, we are indebted to Bartolome de Medina, a Mexican miner, who, at Pachuca, in 1557, invented the 'patio process.' This was the first and, for many hundreds of years, the most important silver amalgamation method. The fact that silver usually occurs not native, but in combination with other ele- ments, explains why amalgamation was not applied to silver ores until long after gold amalgamation was an established art. The ignorant Mexican miner solved, probably by accident, the prob- lem that had bafiied the European metallurgists. In order that amalgamation or union between gold (or silVer) and mercury can take place, they must be brought into intimate contact. Presuming that by previous treatment the particles of gold have been freed from adhering gangue-matter, there are three methods by which the desired contact may be secured: 1. By grinding-contad. 2. By surface-contact. 3. By immersion-contact. (1) The first method, grinding-contact, is the oldest, and if we lay aside the commercial considerations of time and mercury consumed, it is probably the most efficient. It is still practiced exclusively for the amalgamation of silver ores. The grinding in contact with mercury is accompHshed in iron or copper pans, or in areas enclosed by masonry, all of which lend themselves conven- 10 STAMP MILLING AND CYANIDING iently to the addition of chemicals and in most cases to the use of hot water. (2) The surface-contact method of amalgamation did not ap- pear until the happy idea of the California millmen, in 1860, led them to coat with mercury the surface of sloping copper tables, over which the crushed ore and water (pulp) was allowed to flow in a thin film. T. K. Rose suggests that this idea came from the knowledge gained in silver amalgamation with copper pans, where it had been found that the amalgam formed crusts on the sides of the copper vessel. In any event the introduction of copper amal- gamating-plates revolutionized the milling of gold ores. The action of the copper plate coated with quicksilver is ex- tremely simple. As the sheet or film of pulp flows over the plate the heavier particles of gold naturally seek the bottom of the film and come in contact with the mercury surface. The mercury at once seizes upon the gold particles and causes them to adhere to the plate. If, as has been pointed out by Read {loc. cit.), the par- ticle of gold is smaller in diameter than the thickness of the mercury film, no disturbing effect is produced; if the diameter of the par- ticle be greater than the thickness of the film, then the surface tension of the mercury causes it to pull the gold particle down to the plate with considerable force, which of course is assisted by the attraction of gravity upon the gold particle itself. One of the most important points in favor of plate amalgamation is, that amalgam is a much more efiicient gold catcher than barren mer- cury, and with the thin film existing on the copper plate, the gold is always exposed to the attraction of amalgam when once the operation has been started. Another feature of value in connec- tion with plates is that they are readily accessible for inspection or for removal of accumulated amalgam. This last feature has at times, of course, been provocative of theft. (3) Probably no generally discredited method has been the subject of more patents and inventions than the scheme of forcing previously crushed ore to immerse itself for a brief moment in a mercury bath, in the belief that by so doing, the gold would be taken up by the mercury in the form of amalgam. These appliances are not in use in standard mills in the United States or Canada, and while European and Australian practice favored them for many years, they are gradually giving way to copper plates, or to other, usually less efficient, surface-contact PRINCIPLES OF AMALGAMATION 11 amalgamators. The reasons why immersion-amalgamators are less successful than plates may be summarized as follows: (o) It is practically impossible to get any such path of contact as is afforded by a long copper plate. (6) With an ore carrying sulphides or other heavy minerals, these collect on the surface of the bath and complicate the operation, (c) The time of con- tact is so short and the likelihood of the gold particles being surrounded with a film of air or of other ore particles is so great, that the gold is not readily 'wetted' by the mercury and hence amalgamation does not take place, (d) Amalgam is a more effi- cient gold-saver than mercury, and in a mercury bath the tendency for the gold amalgam to settle away from the balance of the quick- silver is sijfficient to make the contact mainly one of ore and mercury, instead of one of ore and amalgam as in plate work, (e) Large amounts of mercury, are kept tied up in the machine and a large loss due to mechanical subdivision of mercury into small particles is inevitable. Comparing and summarizing we find: 1. That grinding-contact is efficient but expensive and consumes much mercury. As a final amalgamation treatment it has been abandoned for all but silver ores and rich gold concentrates. 2. That surface-contact with copper plates is efficient and inex- pensive and is almost universally employed for gold ores. 3. That immersion-contact has little to recommend it and has practically been abandoned. Flouring and Sickening. Reference has been made to loss of mercury by its being broken up into small globules which will not recoalesce; this is known technically as 'flouring.' 'Sickening' of mercury is a term closely connected with flouring and by many writers not clearly distinguished from it. T. A. Rickard * defines flouring "as the minute subdivision of mercury by mechanical causes, and sickening as the rendering of such a condition per- manent, by the intervention of a coating of some foreign substance, effectually preventing the coalescence or reunion of the globules previously formed." This illuminating distinction has been generally accepted and will be adhered to throughout this work. * Stamp Milling of Gold Ores, 1st Ed., page 219. 12 STAMP MILLING AND CYANIDING BIBLIOGBAPHY FOR PRINCIPLES OF AMALGAMATION. • Especially Desirable for Students' Use. Bangle, H. W. Pan Amalgamation, 3 pp. Min. & Sci. Press, Vol. 94, p. 826 (1907). * BusTAMENTE, MiQUEL, Jr. Study of Amalgamation Methods, espe- cially the Patio Process, 13 pp.' Trans. A.I.M.E., Vol. 32, p. 484 (1902). * Del Mar, Algernon. Amalgamation, 5 pp. Pac. Min., Vol. 17, p. 249 (1910). Hatnbs, Justin H. The Pierce Amalgamator, IJ pp. Min. & Min., Vol. 29, p. 524 (1909). Hatnes, Justin H. Plate Amalgamation. West. Chem. & Met., Vol. IV, p. 233 (1908). HoPMAN, H. O. Amalgamation in the Black Hills of South Dakota. Trans. A.I.M.E., Vol. 17, p. 526 (1889). * HoFMAN & Hatward. Experiments in Pan Amalgamation, 17 pp. Trans. A.I.M.E., Vol. 40, p. 382; abstract in Min. & Sci. Press, Vol. 99, p. 529 (1909). Jones, Henry Chapman. Investigation of Silver Amalgams, 3 pp. Jour. Chem. Soc, Vol. 98, p. 336 (1910). JoRT, J. H. Electrolytic Amalgamation. Min. Wld., Vol. 30, p. 885; Vol. 31, p. 687 (1909). LoRiNG, W. J. Amalgamation Details at the Utica Mills, California. Trans. A.I.M.E., Vol. 28, p. 553 (1898). McGraw, D. F. Ailing Process of Electrochemical Amalgamation. Min. & Sci. Press, Vol. 98, p. 897 (1909). Morgan, Percy. The Position of Amalgamating Plates in the Stamp Mill. Min. & Sci. Press, Vol. 93, p. 379 (1906). . * Ortega, Manuel Valeric. The Patio Process, 9 pp. Trans. A.I. M.E., Vol. 32, p. 276 (1902). * Read, T. T. Amalgamation of Gold Ores. (Historical and Experi- mental.) Trans. A.I.M.E., Vol. 37, pp. 64 to 84 (1906); Min. Rep., Vol. 53, p. 612 (1906); Min. & Sci. Press, Vol. 93, p. 15 (1906). Rice, C. T. Silver Mill Amalgamation. Eng. & Min. Jour., Vol. 86, p. 401. Richards, R. H. Use of Silver Amalgam in Dressing New Plates. Trans. A.I.M.E., Vol. 7, p. 362 (1880). Rickard, T. a. Discussion of Plate Amalgamation, Slope and Surface of Plates. Trans. A.I.M.E., Vol. 23, p. 143 (1893). RicKAED, T. A. Silver Mill Amalgamation. "Journeys of Observa- tion," (S. F., 1909). Thibault, E. E. Thibault Gold Amalgamator. 1 column. Min. & Sci. Press, Vol. 105, p. 848 (1912). Thomson, Francis A. Disadvantages of Mercury Wells. West. Chem. & Met., Vol. 4, pp. 272-74 (1907). McKelvey Process of Amalgamation, (Adv.) Min. Sci., Vol. 59, p. 313 (1909). CHAPTER III THE STAMP MILL AND ITS ACCESSORIES The gravity stamp mill is at once the most primitive and the crudest crushing machine in existence, while at the same time the most satisfactory all-round milling-and-amalgamating device yet contrived. In its modern form the stamp mill (Fig. 1) consists essentially of a series of hammers (the stamps) falhng upon a mixture of ore and water, inside a cast-iron box (the mortar). The resulting crushed ore (the pulp) is splashed out through a screen or grating in the end or side of the box. Originating in Saxony, and first used in the Uiiited States in Virginia and Georgia, the stamp mill, in a primitive form, found its way to California and then to Gilpin County, Colorado. Here, free from the trammels of tradition, it speedily developed from an affair of wood, shod with iron and operated with the crudest gear- ing, to substantially its present form. The difference in conditions led, however, to a development along vastly different lines. The easily treated ores of California led the millmen to design their plants for the greatest crushing efficiency since amalgamation was a comparatively simple matter. In Gilpin County, however, the situation was reversed and crushing capacity had to be- made de- cidedly secondary to the successful amalgamation of a compara- tively refractory ore. From the California practice, since it has been found the more generally applicable, have grown the modern methods of stamp milling as employed in practically all parts of the world, with the exception of Australia where development has proceeded along somewhat independent Unes. The important parts of the stamp mill may conveniently be discussed under the following heads. (1) The stamp and its mechanism. (2) The mortar. (3) The foundation and framework. (4) Accessory apparatus and operation. 13 14 STAMP MILLING AND CYANIDING (i) THE STAMP AND ITS MECHANISM The stamp proper constitutes the hammer which falls upon the particles of ore on the die or anvil, thus breaking the ore into frag- ments. It consists of the following parts as lettered in Fig. 2: Fig. 2. Sectional Elevation of California Stamp Mill. A. The Stem is the central shaft or spindle upon which are mounted the tappet, boss, and shoe. The stem is usually of soft steel from 3 to 4 in. in diameter and from 9 ft. 6 in. to 14 ft. 6 in. in length. It is cylindrical throughout, except the last 4 to 6 in. at each end, which are tapered to a diameter from j to J in. less than the diameter of the stem proper. ./. The Boss, Boss-Head, or Head (Fig. 2J), as it is variously called, is the cylindrical connection between the stem and the shoe. THE STAMP MILL AND ITS ACCESSORIES 15 h-G- FiG. 2/. The Boss. It is of the same diameter as the latter and from 15 to 30 in. long. The upper end has a centrally located, accurately drilled, conical hole for the reception of the stem. At the lower end of the boss is a similar conical opening, larger and less accurately made, for the accommodation of the shoe-shank. At the small end of each of the conicallDpenings is a rectangular hole at right angles to the axis of the cone, through which a key, or drift, may be driven to loosen either stem or shoe. Cast-iron bosses are commonly employed, but the tendency is toward the use of some higher grade material, such as chrome or manganese- steel. K. The Shoe (Fig. 2K) consists of a cylinder surmounted by a truncated cone or shank. The shoe is usually from 8 to 10 in. in diameter and from 6 to 10 in. high, exclusive of the shank. The shank is usually 5 to 6 in. high and tapers from a diameter of 4| or 5 in. at the bottom to 3^ or 4 in. at the top. The shank is secured in the boss by means of wooden wedges ranged around it. These wedges are preferably made of medium-hard wood and should be so cut as to allow a space of about J in., between the top of the shoe and the bottom of the boss, when the former is driven up tight. Shoes are made of cast-iron, chrome-steel, man- ganese-steel, and other special steel alloys. The choice of material is a matter of the hardness of the ore and the facilities of the market. Where a mill has its own foundry and can use scrap-iron from about the plant, home made cast-iron shoes and dies' are frequently economical. Where transport- ation charges are high, then the very best material, regardless of first cost, is advisable and chrome or other steel should be employed for both shoe's and dies. C. The Tappet serves to transmit the lifting power of the cam to the stamp. In principle it is simply a collar secured to the stem by a gib and keys. Formerly tappets were secured to the stem by being screwed upon an upset thread. 1 1 I Fig. 2Z. The Shoe. 16 STAMP MILLING AND CYANIDING This is scarcely, if ever, seen now-a-days. The detailed con- struction of a two-keyed tappet is shown in Fig. 2C, where iS is the stem, G is the gib, and KK the keys. The projecting por- tions at the top and bottom of the tappet are the surfaces against which the cam operates; when one end is worn the tappet is turned upside down. As in the case of the boss, tappets are frequently of cast iron, but the tendency is toward the use of some one of the special steels already mentioned. L. The Die while not properly a part of the stamp may be conveniently dis- cussed under this heading. It is a cylin- drical anvil, slightly larger in diameter than the shoe, and is usually provided with a square or octagonal base to secure it from movement when placed in the mortar. Dies may advantageously be made of somewhat softer material than the shoes, owing to the fact that the ore lying upon them protects them from the blow. As pointed out in discussing shoes, wherever freight is a serious item the dies should be of the best material available. Table I, taken from the catalogue of the Stearns - Roger Mfg. Co., Denver, Colo., shows the usual variations in weights and dimensions of stamp parts constructed by them, where the complete stamp varies from 850 to 1600 lb. in weight. The stamp is lifted by means of a double-armed cam from which it drops when the full lift is reached. Single- and triple- armed cams have been used but are no longer seen; the Saxon and Cornish stamp mills used a shaft of large diameter with pro- jecting teeth for cams. These may still be seen in the countries of their origin. The important features of the lifting mechanism are the cam, the cam-shaft, and the pulley, or 'bull-wheel' as it is often called. The Cam (E, Fig. 2, page 14) consists of a circular hub, from which project two arms. The face of each arm is curved to an Fig. 2C. Two-key Tappet. THE STAMP MILL AND ITS ACCESSORIES 17 TABLE I Dropping weight of stamp in lb. Stem, diam in. Stem, length ft. Stem, weight lb. Tappet lb. Bosshead lb. Shoe, weight lb. Shoe, dimensions, diam. X height in. Bosshead, dimensions in. Die, dimensions, diam. X height in. Die, weight lb. Cam shaft (10 stamps), dimen- sions in. diam. X ft. length . . . Cam shaft, weight lb. Cam shaft pulley (10 stamps), dia. Xfaoe in. Cam, 5 in. to 7 in.drop, diam. X weight Cam, 6 in. to 8 in. drop, diam. X weight Cam, 7 .in. to 9 in. drop, diam. X weight Cam, 8 in. to 10 in. drop, diam. X weight 14 365 135 225 145 8iX8 8JX18 81X6 106 5iX14i 1115 72X13 26X155 28X165 30X175 32X185 950 3i 14 395 135 252 170 9X8 9X17J 9iX6 115 6JX14J 1170 78X15 26X165 28X165 30X175 32X185 14 458 156 270 170 9X8 9X19 9iX7 140 6X14J 1400 84X17 27X180 29X192 31X205 33X220 1250 31 14i 545 178 342 185 9X9 9JX22 9iX7 140 6}|X14i 1740 84X19 28X210 30X230 32X248 34X260 4 15i 661 212 420 207 9X10 9iX26J 9iX8 160 84X22 28X220 30X242 34X278 1600 4 16 683 212 498 207 9X10 91X30} 9iX8 160 6 }8X15 1800 84X22 28X220 30X242 32X263 34X278 involute of a circle, the raciius of which is the distance from center to center of cam-shaft and stem. The exact shape of this cam- curve is a matter of extreme importance. Much of the noise, vibration, and breakage in poorly designed mills is due to errors in the design of the cams or in the setting of the shaft. The cam- curve must be so constructed as to fulfill the following conditions: First. The engaging surfaces of cam and tappet must remain parallel throughout the entire lift to insure the minimum of jar and friction and to avoid excessive thrust from the cam. Fig. 3 illustrates this point.* Second. The velocity of lift must be constant and -the amount of lift must be directly proportional to the arc traversed by the cam- shaft. Third.. For two-armed- cams this arc must be considerably less than 180°. The normal involute mentioned fulfills the first two conditions.! This normal involute is the curve generated by the end of a tight string as it is unwound from a circle. The string is always tan- gent to the circle, consequently the curve it generates must be normal to the tangent at each point. It is also evident that the * Mark R. Lamb, Eng. & Min. Jour., Vol. 88, page 66. t For complete discussion see Henry Louis' " Handbook of Gold Milling," 2nd Ed., pages 200-206 and 557-569. 18 STAMP MILLING AND CYANIDING extension of the string is equal to the length of the arc from which it has been unwound. Considering Fig. 3 in which the cam- curve is the normal involute of a circle whose radius is ^ + B + C, where A is the shaft radius, B the clearance between shaft luacrlbed Circle ;^= £ad!us of Cam Shaft ^a CluaranCQ Ca Badlus of Stem i Z)=> KadiuB oflnscribed Circle I for Involute Fig. 3. Position of Cam. and stem, and C the radius of the stem; we find the axis of the stem tangent to the inscribing circle; and since the curve of the involute is normal to the tangent of its inscribing circle, the cam- curve at the point of contact is normal to the stem axis and parallel to the tappet face. This fulfills the first condition. We have said that the string in generating the involute increases by the length of arc unwound, i.e., the point of the string has moved along the tangent and away from the center of the circle, a distance equal to the rectified arc. Applying this to the cam in Fig. 4 it means that while the cam is revolving through the angle m, the tappet will have moved up to the position bj the dis- tance ab being equal to the length of the arc xy of the inscribing circle, thus fulfilling the second condition. The third condition means that for two-armed tappets the semi- circumference of the inscribing circle must be greater than the lift, or if r is the radius of inscribing circle and h is the lift or drop, tt must be greater than h, or approximately r must be greater than X , that is, the diameter of the inscribing circle must be greater than two-thirds the drop. THE STAMP MILL AND ITS ACCESSORIES 19 From the above discussion it is evident that a cam-curve de- signed for a certain distance between cam-shaft and stem, and for a certain drop, does not fulfill the conditions imposed when it is used for any other drop. A small range of drop is necessary to accomo- jDiameter of Steiu 3% in. Dla'meter of Cam Bhaft 5H iu. Diameter of Hub 10 ia. Average Drop 7 in. Clearance between Stem and Sliaft IH in. Clearance between Hub and Tappet 1% in. Diameter of Inscribing Circle '^ 6H + 3% + 2ii = llJSln. " ["'Circumference of Circle = ll>i X 3.14ie = 35.7 in. Upper Position ^.< — ■ t of — ^^, Tappet I Dr(p Partof Circumference Equal to Drop = 7/35.7 = .197 Degrees of Arc Equivalent to 7 in. Drop=380x .197— 70°30' Tapp^ Degrees of Arc Equivalent to ,1 in. Drop=m=lO''05 ' Fig. 4. Cam Construction. date the wear of shoes and dies, but this range should not exceed 2 or 21 in. at the most. Of course, it is impossible to use a cam for a longer drop than it is designed for. To use it for a shorter drop means loss of efficiency since the cam must engage the tappet at a point where it is traveling with greater velocity and conse- quently strikes the tappet a heavier blow; the lever arm is longer than necessary and more power is required; also the cam-curve is longer for the same amount of lift near its point, than it is near the hub and the friction loss between cam and tappet is thereby increased. A simple method of construction is shown in Fig. 4, the dimen- sions being about standard for a 900- to 1000-lb. stamp with a drop of 6 to 8 in. The curve upon the outer end of the cam is slightly modified to allow the upward motion to cease as soon as the tappet leaves the cam. The end of the cam is beveled to correspond to the rim of the tappet, so that the tappet is released 20 STAMP MILLING AND CYANIDING from an arc 2^ in. long, instead of from a sliarp point, as would be the case if the end of the face were square with the sides. The inner end of the cam-curve is filleted to meet the hub. The face of the cam is from !§ to 3 in. wide and of about the same thickness. It is supported by a rib or web usually from 1 to 1§ in. tliick. Cams are made right- and left-handed, the term being used to designate the side of the stem upon which the cam operates when viewed from the 'hang-up' position. For attaching the cams to the shaft, keys and keyways were formerly much used. Where, as is commonly the case, a number of stamps are operated from the same shaft, this means that in order to distribute the work uniformly the cams must be ranged Fig. 5. Blanton Cam, around the shaft at a uniform distance apart. For example, with five stamps to a shaft they must be set 36° apart, with ten stamps 18° apart. To accomplish this with keyed cams, each cam must have its keyway cut in a different place, and before a broken cam can be replaced, the old key must be driven out and a keyway cut in the new cam, unless a large stock is kept on hand with renewals for each position. A better way is to remove the entire cam- shaft and substitute another with cams in place. To obviate this difficulty of the keyways the Blanton cam was invented, and this, together with the modifications introduced by com- THE STAMP MILL AND ITS ACCESSORIES 21 peting firms, has practically displaced the old form of keyed cams in up-to-date mills. In the Blanton cam an eccentric wedge (Fig. 5), fitting tightly in a corresponding eccentric recess cut out of the cam-hub, replaces the key and kejrway. By this" means the cam is secured to the shaft by a powerful friction grip, from which, however, it may be readily loosened by a few blows of the hammer in a direction opposite to the lifting reaction. The wedge is held in position by a couple of small dowel pins which fit into corresponding holes drilled in the shaft. The Cauda cam (Fig. 6) is similar in principle, having the added advantage of preventing any lateral motion along the shaft. Other fasteners of this type are on the market. One point about the circular wedges worth not- ing is that both the eccentric recess and the circular wedge must be made with great exac- titude, otherwise the cams will not be uniformly disposed about the shaft. Therefore if cams are to be made in local shops it will usually be more satisfactory to use keys than eccentric wedges. Cams may be made of good cast-iron, in which case a wrought- iron band is usually shrunk on the hub. Special-steel cams are frequently used. Cam-Shaft. The cam-shaft (D, Fig. 2) is an extremely im- portant part of the mill and should be of the best material avail- able. It is perhaps exposed to more severe conditions than any other piece of shafting. Mild steel, chrome-nickel-steel, and ham- mered iron are the preferred materials. The Union Iron Works make their cam-shafts by forging down old iron propeller-shafts from large steamships. Hollow shafts have been used in South Africa and the practice is a sound one mechanically. Cam-shafts range from 4| to 7 in. in diameter according to the weight of the stamps. Where, as is commonly the case, the stamps are arranged five to each mortar, cam-shafts are often made sufficiently long to drive ten stamps, with the necessary overhang for the pulley. The Drive-Pulley or Bull- Wheel (Z, Fig. 2) is made of wood on account of the jar and vibration to which it is subjected by the Fig. 6. Canda'Cam. 22 STAMP MILLING AND CYANIDING cams striking the tappets. The wooden portions are placed radially, the thickness of the pulley being built up of several layers, secured together by bolts and a cast-iron hub with wide flanges, one of which is removable, as shown in Fig. 7. Cam-shaft pulleys vary from 6 to 8 ft. in diameter by 12 to 18 in. face. In a few instances the cam-shaft pulley is replaced by a gear-wheel. The cam-shaft boxes or bearings are mostly of the open type, and since the speed Fig. 7. Bull-Wheel. of rotation is not great and the friction of steel on cast-iron is low, babbiting is uncommon. Covers of canvas are preferred to cast- iron as the latter frequently work loose due to the jar. Owing to the fact that the cams operate only on one side of the stem, there is a decided lateral thrust between the tappet and the cam (Fig. 8). This thrust is lessened by running the cam close to the stem and by keeping the center of gravity of the stamp as far down as possible, i.e., by concentrating the weight in the boss and shoe. This thrust is also controlled by guides on the stem, and by placing collars on the cam-shaft to prevent it moving lengthwise. A frequently used corrective is to make part of the cams left- handed and part right-handed, thus balancing the thrust from each direction. THE STAMP MILL AND ITS ACCESSORIES 23 An incidental but none-the-less important feature of cam-driven stamps is, that the stamp is partly rotated at each lift by the friction of the cam-face on the tappet. This serves admirably to equalize the wear on the shoes. (2) THE MORTAR The mortar or mortar-box is the vessel within which the crushing and frequently part of the amalgamation of the ore takes place. The capacity and efficiency of the stamp mill depends to a large degree upon the form and internal dimensions of the mor- tar. Especially is this true of the width and depth of the lower part of the mortar in the immediate vicinity of the dies. The mortar is usually of cast-iron, although in some of the Gilpin County mills, and in cases where mills are built 'sectional' for mountain transport, the bases only are of iron, the sides and ends being of wood or Fig- 8. Effect of Cam light sheet-steel. ^*^'*- Fig. 9 shows a standard type of 5-stamp mortar, the various parts being designated by letters. A is the feed-throat or feed-slit, made smaller at the opening than below, in order that any piece of rock which once enters may not wedge and hang-up before reaching the dies BB. C is the screen, set in a wooden frame and held in place by the keys D. E is the chuck-block by changing which, the height from the bottom of the screen to the top of the die may be varied; this distance, designated the 'discharge' or 'issue,' is an important factor in regulating the character of crush- ing done by the stamps. F is an inside copper plate designed to catch gold within the mortar. G, G, G, are cast-steel liners to protect the inside of the mortar from being worn by the constant abrasion of sharp pieces of ore. H is the base and I the founda- tion or holding-down bolts. The base which rests upon the founda- tion should be machine finished to give a true bearing, as should also the faces against which the screen-frames are fitted. All other comers should be well rounded with fillets. The dies are fre- quently placed upon a false bottom-plate or liner. Such a mortar as shown will usually be from 4 ft. 6 in. to 5 ft. high. 24 STAMP MILLING AND CYANIDING The weight of the mortar is from 6 to 10 times that of each stamp; for example, in a mill erected by the writer some years ago the stamps weighed 850 lb., the mortars 5200 lb., or 6.1 times the weight of the stamp. In the mill of the Goldfield Consoli- dated Company, with 1050-lb. stamps, the mortars weigh 10,5001b. The weight of the mortar must be concentrated in the base to absorb the shock of the shoe striking the die, and to give solidity to the blow struck. If we make the discharge low, i.e., if we bring the screens down close to the level of the die, other conditions remaining the same. H -I Fig. 9. Medium Width Mortar with Heavy Pig. 10. Narrow Mortar for Base for Concrete Foundation. Fast Crushing. the pulp when struck by the descending stamp will be forced against the screens more violently, and with the same screen aper- ture we will get a coarser product and greater capacity. Simi- larly as we narrow the mortar immediately above the dies, so we increase the violence of the splash of pulp when the stamp strikes the surface of the water, and again a coarser product is discharged. Thus, a narrow mortar with low discharge tends to high crushing- capacity, while a wide mortar with deep discharge gives low capacity and a finer product. These conditions should be borne in mind as they have an important bearing upon stamp-mill amalgamation to be discussed later. Double-discharge mortars, originating in the dry-crushing silver mills, have at times been used for gold-milling. The energy of the THE STAMP MILL AND ITS ACCESSORIES 25 splash, however, seems to be lost by this arrangement and it usually results merely in an increased consumption of water, without an increased capacity of the mill. I have usually found better results to follow the closing of the back discharge in such mills. In Fig. 9 is shown a mortar of medium width and discharge. Fig. 10 shows a narrow mortar with low discharge for fast crushing. In Fig. 11 is shown a high-discharge wide mortar, verging toward the Gilpin County type. (3) THE FOUNDATION AND FRAMEWORK The heavy mortar in order to serve as an anvil subject to the incessant pounding of the stamps must have an extremely solid, secure founciation. The mortar-block, as the foundation is called, has until recent years always been of timber but after much dispute it is now gener- ally acknowledged that concrete is superior to wood for this pur- pose. Mortar-Blocks may, for con- venience, be divided into three classes: (A) Wooden, (7) solid, (77) built-up. (B) Concrete. pio. n. High Discharge Wide Mortar (C) Concrete surmounted with Front and Back Plates. hy cast-iron anvils. {A) Wooden Mortar-Blocks were for many years considered the only suitable foundation for a stamp mill, great stress being laid upon the resihence of the wooden block under the blow of the stamp. This and other claimed advantages have been proved to be largely hypothetical. Where timber is readily available, hpw- ever, it is much cheaper than concrete in first cost and for a small or temporary plant is undoubtedly to be preferred. (7) Solid-timber mortar-blocks (Fig. 12) are rarely of one piece of timber. For a 5-stamp battery * two timbers about 30 inches * The unit of a mill, i.e., stamps and mortar, is spoken of as a "battery," for example, "a 5-stamp battery," "a 2-stamp battery," etc. 26 STAMP MILLING AND CYANIDING square, or three 18 by 30 in., are bolted together, making a block from 10 to 15 ft. high when placed on end in a previously pre- pared pit. The bottom of this pit, which should be upon bed- rock if possible, is leveled with concrete or tailing, and the block placed on end upon this. In cases where bed-rock is not easily Fig. 12. Solid-timber Mortar-Blocks. reached a foundation of concrete at least 3 ft. deep and of area proportioned to the character of the ground should be used be- neath the wooden block. The sides of the pit around the block may be filled in with concrete, although tailing makes a satisfactory fining. THE STAMP MILL AND ITS ACCESSORIES 27 (77) Built-up wooden blocks (Fig. 13), constructed of 2 by 12 in. planks, spiked and bolted together, with joints broken, are pre- ferred by some millmen, owing to the greater care which can be exercised in the selection of sound wood. I have used blocks of this character where large timbers were unobtainable. They are much more expensive than the solid block, and it is questionable if their use is advisable on the score of longer life as has been claimed. Where this is a consideration and cement is obtainable, concrete is a better and cheaper material. After having been set in place, the top of the wooden block, be Fig. 13. Mortar-Seotion Showing Built- up, Wooden Mortar-Block. Fig. 14. Mortar on Concrete Block. it solid or sectional, must be carefully dressed to a horizontal plane, bolt holes drilled, and pockets cut for the holding-down bolts. These bolts are usually from IJ to If in. in diameter and about 2 ft. 6 in. to 3 ft. long. Between the mortar-base and the top of the block it is usual to place several layers of tarred blanket or strips of rubber belting. Some manufacturers supply a felt pad and others a mat of j-in. rubber for this purpose. (B) Concrete Mortar-Blocks seem to be rapidly gaining in favor and it is now exceptional to find a large mill in process of 28 STAMP MILLING AND CYANIDING erection provided with wooden blocks. It was for a long time feared that increased stem breakage and other difficulties would follow the use of the concrete mortar-block, but this does not seem to have been proven. Crumbling of the concrete beneath the mor- tar base has been remedied in two ways, first, by making the mortar base wider, and second, by interposing some sort of cushion be- tween the mortar and concrete, both to give an even bearing and to absorb part of the impact (Fig. 14). Most mills use a thin Maple Base Cnrefullyy Surfaced and Laid / up in Tar Fig. 15. Mortar on Concrete Block with Wooden Cushion. rubber pad or mat; others prefer a cushion of hard wood upon the concrete (Fig. 15). Another difficulty has been to make the hold- ing-down bolts secure; this has been accomplished by placing them in a pipe bedded in the concrete, leaving both ends accessible. The lower ends of the bolts are made to bear against a 4 by 6-in. timber instead of against the concrete. As in the case of the wooden blocks, if bed-rock can be reached so much the better, but any reasonably solid ground is sufficient, provided the area of the base of the foundation is made great enough. The advantages of permanency, solidity, and consequent greater stamp-capacity are THE STAMP MILL AND ITS ACCESSORIES 29 all with the concrete mortar-blocks and their use promises to be- come practically universal. (C) Concrete Mortar-Blocks with Cast-iron Anvils- have many advocates. Two-thirds of the bat- teries in the great stamp mills of the Alaska Treadwell Company are mounted on this type of foundation, supplied by the Allis-Chalmers Com- pany, see Fig. 16. (Also shown in elevation in Fig. 1, page 1.) The Gold King Company's mill, probably the most up-to-date plant of its kind in Colorado, has iron anvil-blocks, built on the principle described by the Denver Engineering Works Company, as a ' sub-base ' block (Fig. 17 and 18). The anvil-block offers a means of hav- ing a base of ample width and weight for the mortar without the initial stresses and strains which would be estabhshed in casting a base of similar proportions as a part of the mortar. The same means of securing the sub- base or anvil-block to the concrete should be employed as would be used in the case of a mortar setting directly on the concrete. The Frame is designed to support the cam-shaft and to guide the stamp stems as they rise and fall; frequently also, but not necessarily, the main line-shaft is carried thereon. The great majority of battery frames are built of timber, although frames of structural steel (see Fig. 18) are gaining in favor and cast-iron frames for small installations are often seen. All wooden frames have in common the large vertical post on each side of the mortar, called the battery-post, usually 12 or 14 by 24 in. in section and from 18 to 20 ft. long. Where wooden mortar-blocks are employed, these posts rest on cross-sills each side of the mortar-block; in the case of concrete blocks a cast-iron base frequently provided with a rubber cushion, takes the foot of the post. My attention has been recently called to the fact that Fig. 16. Mortar on Cast-iron Anvil Block. 30 STAMP MILLING AND CYANIDING this is frequently a point of failure in stamp-battery frames. The base or shoe should be heavy, and the post should be secured to it by a stout bolt on each side, attached to the post by a soUd lug or bracket. Between the battery-posts run the girts, to which the guides are secured. The cam-shaft boxes or bearings are usually set in niches cut in the battery-posts, about two-thirds of their length from the bottom. In accordance with the manner in which Fig. 17. Mortar with Sub-base Block. these battery-posts are secured to, and supported by, the other members, the types of frames are classified. The 4-frame (Fig. 19) is used for small portable installations. It is not convenient where plates are used, but is light and in- expensive. Frames of either the back-knee or front-knee type are the most commonly used. The back-knee (Fig. 1) is the one preferred in THE STAMP MILL AND ITS ACCESSORIES 31 the larger plants. It gives greater light about the plates and a full view of the mill from the front of the batteries. The line-shaft, however, is not so well placed as in the case of the front-knee frame. Many mills are practically a composite between the two types, having a front-knee frame connected with bins behind the stamps (Fig. 20), or more rarely a back-knee frame connected with the posts of the building in front. By placing the line-shaft level Fig. 18. Steel Battery-Frame. (Courtesy of Denver Engineering Works.) with the cams, a horizontal belt-drive is secured, but the belts are in the way and light is sacrificed. Most large stamp mills are driven from a line-shaft behind and below the mortar, a belt- tightener being used to prevent slipping. This also serves prac- tically as a friction-clutch, since upon releasmg the stram of the tightener the belt sUps on the drive-pulley. 32 STAMP MILLING AND CYAN I DING Fig. 19. "A "-type Battery-Frame. Fig. 20. Front-Knee Frame Connected with Bins. Fig. 21. Composite Steel and Timber Frame. Fig. 22. Boss Cantilever Battery-Frame 34 STAMP MILLING AND CYANIDING These various types of frames are, of course, subject to modifica- tion and may be combined with each other or with the ore-bin framing in various ways. Where not otherwise provided for, brackets are secured to the battery-posts in front to support the platform or runway giving access to the cams, cam-shaft, and boxes. Fig. 23. Cast-iron Battery-Frame. Steel frames are not at the present time in extensive use. The incessant jar and vibration to which the battery-post is subjected is considered sufficient reason for the non-employment of a metal so elastic as steel for this member. This objection could un- doubtedly be overcome by the employment of a sufficiently heavy section, but, except for durability, it would offer little advantage over the wooden post, particularly in the matter of weight. There is no reason, however, why steel should not be used for the balance of the frame, including ore-bins, and the Goldfield Consolidated THE STAMP MILL AND ITS ACCESSORIES 35 frame, shown in Fig. 21, is as satisfactory a scheme as can be de- vised at present. A steel frame on the cantilever principle (Fig.' 22), in which I-beams projecting from the bin foundations form the supports for the cam-shaft, thus ehminating battery-posts and all Fig. 24. All-iron Frame Battery in Sections. other obstructions about the battery, has not proved entirely satisfactory. Cast-iron frames are used in the United States for small portable mills and they are admirably adapted for this purpose (Fig. 23). A frame with cast-iron columns and brackets, tied by steel tension bolts, was furnished for a 100-stamp mill in Bolivia by the Umon 3& STAMP MILLING AND CYANIDING Iron Works Company (Fig. 24). Wherever timber is scarce this form of frame would seem to be commendable. Cast-iron frames and heavy columns without tie-rods are extensively used in Aus- tralia. In the City Deep Mill in South Africa reinforced-concrete pillars have been substituted for the usual battery-posts. On top of the pillars rests a heavy girder which carries the guides on its Pig. 25. All-wood Guides. lower edge, and on the upper side are set cam-shaft bearings be- tween each cam and its neighbor. Guides. The function of the guides is to prevent the stems from deviating from their vertical path when being raised by the cams. They are, of course, a hindrance to the stamp in falling and unless they are kept reasonably loose and well lubricated, interfere seriously with the efficiency of the blow struck by the stamp. Guides are made either of wood or iron, or of a combina- tion of both of these materials. Two sets of guides are used; the THE STAMP MILL AND ITS ACCESSORIES 37 first is placed about 6 in. above the highest point reached by the tappet, the second, or lower guide, is set as close to the top of the mortar as will allow access thereto, the lower the better. A Fig. 26. Sectional Wooden Guide in Iron Frame. Fig. 27. AU-iron Solid Sectional Stamp Gtlides. satisfactory guide should allow adjustment in all directions. This is necessary to take up the wear due to a thrust, which is the re- P»B«" N IM 1 K -' r-' /"^ ^ — .ri^— -^^^^E-c^rr- :':::z: :>^^ ..,.„:_:■ ^ _^4 - i^^-. - g 1 L— J- ■ \ ^ftS: P ' wqrMa; ',. • WORK*/ "oai^i » Fig. 28. AU-iron Guides. sultant of the direct thrust of the cam-face and of the eccentric lift which the cam gives to the tappet. The simplest form of wooden guide consists of two hardwood 38 STAMP MILLING AND CYANIDING timbers bolted to the guide girt, with semi-cylindrical grooves cut in the face of each timber (Fig. 25). This guide is much used, its' simplicity compensating for the lack of endwise adjustment.. Ad- justment laterally is provided for by starting with shims, or liners between the guides; these are gradually removed as the wood wears away, and later the faces are planed off as the stems con- tinue to cut into the wood. Individual wooden guides are used to some extent, see Fig. 26. These permit adjustment of separate stems without stopping the Fia. 29. Iron Gmdes on Wood Girt. entire battery. All-iron guides are employed in some of the larger mills, both plain and babbitted boxes being common; see Fig. 27, 28 and 29. (4) ACCESSORY APPARATUS AND OPERATION " Hanging-up " stamps. For the purpose of supporting the stamps so that the tappets shall be clear of the cams, finger-bars or latch-fingers, as they are called, are provided (0, Fig. 2) ; these are shod at each end with iron and provided with hand grips in front. They are pivoted on the jack-shaft (usually of about 3 in. diameter), which in turn is carried on brackets on the inner side of the battery posts. When the stamps are to be hung up, a cam- • stick (Fig. 30) is placed on the cam, thus causing the stamp to rise higher than usual, and permitting the latch-finger to be swung under the tappet, which is thus kept at a height beyond the reach of the cam. Various ingenious mechanical devices have been used at times to replace the old-fashioned cam-stick and latch-finger, but none of these has found general acceptance. The Overhead Track and Crawl, to which is attached a chain- block, is indispensable for picking up stamps requiring repairs, for handling cam-shafts, and other heavy lifting on the cam floor. THE STAMP MILL AND ITS ACCESSORIES 39 The Screens, in conjunction with the height of discharge, regulate the maximum size of the crushed product turned out by the stamps. Upon the mesh * and character of the screen used depends, to a large extent, the capacity and the extraction of the mill. Screens are of two classes, punched and woven. Cam Stick Latch Finger wlieii uot in use Latch Finger lin Foaition to Support Stamp Ucl,l„^^A'//Miif -iTaclE Shaft Fig. 30. Method of Hanging up Stamps. Punched screens, as their name would indicate, are made by punching holes in thin metal plates. Steel or iron is usually the metal, but copper ' gratings, ' as they are called, are used in Austra- ha. Some American millmen attach great virtue to tin-plate screens from which the tin is burnt in the forge. Punched screens are designated by the shape of the hole punched in them. ' Round- hole' and 'slot' designate the shape of the hole; 'burr-punched' denotes the plate is indented in the cutting, ' clear-punched ' that the piece is taken clear out, leaving no indentation. Burr-punched diagonal-slot screens are great favorites in some camps, the burr being placed inside, with the idea that as the screen wears the in- dentation will flatten out and thus keep the size of the opening from growing larger. Horizontal and vertical slot screens, both clear and burr, may be purchased. Punched screens are desig- nated as to the width of their apertures by an arbitrary system of numbers, for common sizes if a; = trade number, (a; — 1) 5 = linear mesh. * In American practice screen aperture is designated by the number of holes to the linear inch, but in South Africa by the number of holes to the square inch. Ten mesh in Goldfield is 100 mesh in Johannesburg. 40 STAMP MILLING AND CYANIDING Woven screens are made of wire; brass or iron being the usual material. In all but the finer meshes the diameter of the wire and the diameter of the hole are practically equal, thus making the ratio of opening to total screen average about 25 per cent.* Brass- wire is preferable as it does not rust, but its use is out of the ques- tion where quicksilver is fed into the battery. Comparing punched and woven screen the following points may be noted : Punched screens wear longer, do not bag or become distorted in shape, have a smaller percentage of opening, and deliver a less uniform product than wire screens. In general, high capacity demands the use of cloth or woven screens with consequent higher screen-cost per ton than would be the case if punched screens were used. Screen Frames are practically always of wood. In a five- stamp battery the screen opening is from 10 to 20 in. wide by 48 to 50 in. long. With wire-cloth screens of fine mesh (20 or under), the opening is divided into two, or sometimes three, panels by vertical bars, to support and stiffen the cloth. With punched plate screens this is unnecessary. Screens are tacked to the inner side of the frame, which is made secure and tight against the planed faces of the mortar. To accomplish this the inner edges of the frames are covered with belting or blanket, and the frames are held in place by keys at each side of the mortar, see D in Fig. 9. Keys at the bottom of the frame, on the mortar lip, are also used. Screens are sometimes placed in separate panels, thus malting a double frame. Provision should always be made for a handhole above the screen or higher up on the sloping front of the mortar, for the re- moval of chips and other 'trash' which will accumulate against the screen, impairing its efficiency and frequently causing break- age. Screens usually incline outward from 10° to 15° from the vertical. Splash-Boards or Canvas Curtains are frequently placed in front of the screen to confine the spray from the mortar. Where a board is used it should incline outward at about 45° to allow ready inspection, and should come to within about an inch of the screen frame along the bottom edge. Such a board covered with a cop- per plate forms an efficient gold and amalgam catcher. * See page 113 for table of apertures and wire diameters in standard screens. THE STAMP MILL AND ITS ACCESSORIES 41 Housing or Cover Boards are placed at the top of the mortar, resting on ledges cast for the purpose. They are made in two pieces with notches cut along the inner edge to fit the stems, and serve to confine the splash within the mortar. Rock-Breakers have gradually come to* be regarded as indis- pensable prerequisites for the treatment of ore by stamp milling. It is not proposed to enter into any description of the various types of breakers, but merely to point out that the stamp mill is not designed to crush coarse rock and that to attempt to make it do so is fatal to its capacity and efficiency. Nevertheless, it seems to be possible to go too far in the opposite direction, and some mill- men have found that beyond a certain point there is no gain but an actual loss in too fine crushing previous to stamping.* It is undoubtedly true that there should exist a definite ratio between the weight and drop of the stamp and the diameter of the particle to be crushed. Present knowledge would seem to indicate' yV-in. diameter for each 100 pounds of stamp-weight, as about right for average ore, standard drops, and fine crushing. Breakers of the Blake and gyratory types have displaced all others. Gyratories are gaining favor as they require less attention in feeding; and for the same reason the grizzlies or sloping bar- screens, formerly so much in evidence, are going out of fashion, and are being replaced where necessary by shaking or revolving plate- screens or trommels. Rolls in some few instances have been included as part of the accessory crushing plant for stamps, but the practice is unusual. As a preliminary to certain other crushing devices, to be mentioned later, they have attained a certain degree of popularity. Their preeminent field is, of course, that of fine and intermediate crushers for concentrating mills. The Hterature on rolls is voluminous and should be consulted if further information is desired. Ore-Feeders. In the early days of stamp milling all feeding was done by hand, and even after the introduction of mechanical feeders, it was still claimed that hand-feeding was the more efficient. In Gilpin County, where, strange to say, hand feeding is commonly used, I have seen the feeder shovel in a hundred pounds or so of rock and go home, to his dinner, leaving the battery to "pound herself out" as he expressed it. In all mills making any pretense * W. Beaver, J. C. & M. M. Soc, S. A., Vol. 6, page 215, Jan., 1906. 42 STAMP MILLING AND CYANIDING to efficiency, however, automatic ore-feeders are in use. These feeders, as long as no marked variation occurs in the character of the ore, will work day and night, practically without attention, giv- ing maximum capacity, requiring almost no repairs and saving the wages of an attendant for every 20 stamps. Feeders are of two general types; both' of these, at one time, were patented, but they have long been open to manufacture by any one. Tulloch Feeder. The simplest feeder is known as the Tulloch,- although for the principle upon which it operates, we are indebted to C. P. Stanford, a CaUfornian, who used it in 1855. It consists of an inclined tray, set beneath a hopper. A reciprocating motion is given to the tray by means of a system of levers connecting with a bumper-rod actu- ated by one of the stamps, usually the center one. By reference to Fig. 31 it will be seen that as ore accumu- lates on the die, the tappet will not descend far enough to strike the Fig. 31. Tulloch Feeder. As soon as the tappet A reaches A', the shoe B will have reached B'; the lower edge of the tappet then engages the bumper C, pushing down the rod D; this bumper and the feeder does not work; in turn depresses the end of the as the supply on the die is crushed rod ^; by this means the system ^nd discharged through the screen of levers jerks the tray G back- ,, , , i _l , ward and the contents of the tray *^® ^^^^ descends to a lower pomt, are spiUed into the mortar. The ^^^ consequently the tappet striking spring F returns the tray to its the bumper causes the ore to be de- position. The hopper H carries livered by the feeder. Although ex- the supply of ore and feeds to the ^remely simple in operation, the tray G. J is the hand wheel rr n t ol j; j r j •„ which controls the position of the Tulloch or Stanford feeder will only rod E and hence the height of C. ''^^ork with the driest and most gran- ular ore; wet, sticky, or talcose material often hangs in the tray, and is not dislodged by the blow of the stamp on the bumper. THE STAMP MILL AND ITS ACCESSORIES 43 The Challenge Feeder (Fig. 32) has, for the reasons cited, prac- tically replaced all others. Originally built and patented by Joshua Hendy of San Francisco, this feeder, modified in recent years as to the details of the operating mechanism, is without a serious rival. Like the preceding type, it is operated by a 'blow from the stamp, the amount of the blow being regulated by the quantity of ore within the mortar. In this case, however, the hopper feeds to an inclined circular cast-iron plate (a), the revolution of which carries the ore to the mortar. The underside of this revolving plate gears with a bevel pinion (e) which is revolved by a system of levers {m,n,p,k), connecting the bumper (r) with a friction ratchet (h) mounted on the same shaft as the pinion. As the ore is Fig. 32. Challenge Feeder. brought around by the plate it is scraped into the mortar by the wing plates (c). The amount of ore to be fed is regulated by the hand wheel (s) which raises or lowers the bumper, thus caus- ing the tappet or collar to engage it sooner or later as the case may be. In place of the rod and rubber bumper of the Tulloch feeder operated by the tappet, the newer forms of Challenge feeders are driven by a collar on the center stem striking against a forked bumper-rod. The suspended feeder (Fig. 33) is hung from a light track on the underside of the cam floor, thus leaving a clear space behind the battery. The great superiority of the mechanical feeder hes in its per- fect regularity of action, and in the automatic adjustment of feed to depth of layer of ore on the die. The thinner this layer, 44 STAMP MILLING AND CYANIDING other things being equal, the less cushion there will be to the blow struck by the shoe and the more effective will the blow be. Evi- dently this depth cannot be less than the diameter of the particles to be crushed, and this, as already pointed out, should depend upon the weight of the stamp. The importance of this is recognized by Fig. 33. Suspended Challenge Feeder. all good millmen. I have had men on opposite shifts, when the competition was keen, change the adjustment of the feeder when going off shift, to make the layer of ore deeper and consequently to cut down the tonnage put through by the other shift. A good millman will, of course, detect this by taldng hold of the stem and thereby judging of the nature of the blow being struck. The blow if dead indicates too heavy feed. If "iron strikes iron" the feed is too light. The right blow is soon learned and an educated ear can detect from some distance whether conditions are right in any particular battery. Water Service. An ample water-supply is one of the most important items in stamp milUng work. Where water is scarce, as is often the case in the arid regions of the southwestern states, the mill tailings are discharged into impounding systems or settling tanks and the supernatant liquid — for in extreme cases it can scarcely be termed water — is used over again in the batteries. THE STAMP MILL AND ITS ACCESSORIES 45 In any event, of course, an adequate piping system is necessary, and the water-supply must be under a constant head to avoid the necessity of continually adjusting battery-cocks, etc. The main for the stamp-service is usually laid in front of the batteries just below the cam-floor level, and pipes for each battery lead from it. Occasionally this main service pipe is placed below the plate-floor, in front of the mortar blocks. As to the manner of feeding the water into the mortar itself, a variety of practices is seen. There are three places where water may be introduced. (1) Through holes in the housing boards. (2) Through the feed throat. (3) Through special openings usually at, or below, the level of the dies. When the first method is used, some millmen prefer one pipe as near the center stamp as possible; others place a pipe beside every stem. The majority following this method, however, use one pipe between stems No. 2 and 3, and one between No. 3 and 4. In some mills these individual jets are pointed straight toward the back of the mortar. A single pipe or even a piece of hose pushed a short distance into the feed throat has many advocates, and occasionally a pipe at each end of the feed throat is seen. In a Nova Scotia mill, Richards describes the use of a jet in front of and between each pair of dies, and in a recent South African mill individual jets are placed behind each die.* In every case it is essential that there be a suitable hose connection for every bat- tery or pair of batteries for washing down plates, hosing-off lip of mortar, and for general utihty. The flow through the smaller individual pipes about the battery is best controlled by double cocks, one near the battery to regulate the flow, the other to turn water off and on; in this way adjustment is not necessary every time the mill is started. Globe and gate valves will not stay set, owing to the vibration. The water fed to the battery has two functions : (1) To give a medium that will aid the splash, and hence the discharge of the battery. (2) To dilute and give mobility to the pulp, and to allow separation of gold from gangue, both inside and outside of the mortar. The quantity used varies with the character of the ore, the fineness of crushing, and the slope of the outside plates. The * E. M. Weston, Eng. & Min. Jour., Vol. 89, page 172. 46 STAMP MILLING AND CYAN I DING amount is stated in various ways, tons of water per ton of ore being a common method of measurement. Richards states that twenty-five mills throughout the United States show an average of 6.17 tons of water per ton of ore. Gallons of water per stamp per minute is a popular but decidedly unsatisfactory method of expressing the water consumption. The quantity varies from as low as 1.3 gallons in some of the Gilpin County mills to as high as 6.6 gallons in the South African mills. Other things being equal, the water consumption of course depends upon the stamp duty and varies with it. This consumption, as has been already stated, may be decreased, as far as supply of new water is concerned, by settling-tanks and the like. In one case I was able by this means to keep a stamp mill operating for some time on about 0.5 gallon of fresh water per stamp per minute, corresponding to 2.1 tons of new water per ton of ore. For transposing from one system to the other it is convenient to re- member, that gallons per minute multiplied by six equals tons per day. Starting the Mill. Presuming the battery-frame and guides for each battery to be in place, the stems, with the tappets keyed lightly in their approximate positions, are lifted into their places with the aid of the crawl and chain-block, and the caps are placed loosely on the guides. The latch fingers are set under the tappets. If not done previously, the dies should now be placed in the mortar with ^- to J-inch of clean sand beneath them to make an even bed. If false dies or bottom liners are used sand should be placed below and above them also. The dies should then be packed about with sand and fine rock to keep them in place until the ore has bedded itself about them, although this precaution is often omitted.* A 2- in. plank is then put on top of the dies and one boss at a time is set on the plank and in line with its stem, which is lowered into the socket in the boss, and tapped at the top end with a heavy copper hammer to drive it home. (An ordinary slfedge hammer may be used if care is taken to protect the stem from abrasion.) This is repeated for each stamp until all stems are set. To make more secure, the shoeless stamp is raised and dropped several times, allowing the boss to strike on the plank. The shoes are set in place, and wedges, as described, ranged round the shanks; each boss is dropped over its corresponding shoe shank and thus picks up the shoe which is driven home by several drops on the plank as before. * Setting the dies in place with cpncrete is an interesting departure that seems to [jromise well. THE STAMP MILL AND ITS ACCESSORIES 47 A few shovels of ore are placed on the dies, and the battery is run slowly or by hand for a moment or two till all is secure. The height of drop is then arranged by placing a block of wood, the height of the proposed drop, on the die and lowering the shoe upon it.* The corresponding cam is then revolved until its point is at the top center, and the tappet is set resting upon it and the keys driven home. If inside plates are used they are sprinkled with mercury and set in place, and screen frames are put in and keyed. The feeders are inspected, the water-feed is looked over, and as soon as the outside plates are in condition and the rest of the mill is in shape, the stamps are ready to begin crushing ore. When all these points have been attended to, the millman starts up one battery at a time, dropping first the center stamp as this works the feeder, and then the two others on each side of it and lastly turning on the water- feed. The water-feed is then adjusted until the proper wave motion is seen on the plate; the feeder is adjusted by the 'feel' of the stems until the minimum feed which will prevent the shoes from striking the naked die is found. If the ore is inchned to bank under one stamp, that stamp is given a slightly greater drop by lowering the tappet; or if one stamp constantly 'pounds iron,' its drop is decreased by setting the tappet higher on the stem. As shoes and dies wear away the drop becomes greater and thus compensates for the loss in weight. It is usual to correct the greater drop by adjustment of the tappets. Lubrication. The stamp mill in common with all other forms of machinery requires lubrication, but the fact that grease is the arch enemy of both- amalgamation and concentration, renders this a peculiar problem. There are two solutions. Either make it im- possible, by extra precautions, for oil or grease to get into the bat- tery, or else substitute something in place of grease or oil as a lubricant. The first method is the most commonly used; drip boxes are placed under all shafting, oil wells are provided on cam- shaft bearings and a canvas curtain is hung between the cam-shaft and the top of the battery. Among the substitutes for grease, compounds of soft soap and graphite, or of molasses and graphite, are urged by some authori- * In regiilar operation the height of drop is easily regulated without shut- ting down other stamps or opening the mortar, a chalk-mark on the stem, or even the ring of lubricant which marks the lowest point of the stem-travel in the guide, giving all the index required. 48 STAMP MILLING AND CYANIDING ties. In warm weather the latter compound is excellent for at- tracting flies and other insects, so that in a short time the cams and cam-shaft bearings look like a heavily-loaded, sticky fly-paper. As in all other work the least amount of lubricant which will suffice should be used. The Order or Sequence of Drop is an important factor in the capacity of a five-stamp battery. Both the splash on the screen and the distribution of the ore on the dies are largely affected by it. It is usually conceded that adjacent stamps should not faU in suc- cession and that as one stamp is falling its neighbor should be striking. The wave motion produced should not result in carry- ing the ore to one end of the battery. The California drop is much in favor. Numbering the stamps from left to right, the sequence is 1-4-2-5-3. This fulfills the condition imposed and does not give rise to any marked accumula- tion of ore at either end. A sequence known as the Black Hills drop, 1-3-5-2-4, has many advocates and discussion as to the com- parative merits of each order has at times waxed warm. It has been pointed out by J. E. Collie * that one of these is simply the left-handed version of the other. California numbers 1-2 -3 -4 -5. Designated by letter A-B-C-D-E. Black Hills numbers 5-4 -3 -2 -1. Using letters in place of numbers and carrying out the sequence we get: California drop ADBECADBEC Black Hills drop ECADBECADB so that it is not easy to see why the fact that one man counts from the left, and the other from the right should have any marked effect upon the efficiency of the mill. The Gilpin County drop, 1-5-2-4-3, violates the law of non- adjacent sequence. It is quite common, however, especially in the 'slow-drop' mills of the district from which it takes its name. The perfect symmetry of the arrangement is attractive. T. A. Rickard says that this sequence promotes rapid crushing, but causes scouring of the inside plates.f * Pacific Miner, Vol. 16, page 50. t Stamp Milling" of Gold Ores, 1st Ed., page 89. (This may be true in high-speed mills with heavy stamps; it of course neither promotes rapid crush- ing nor causes scouring in Gilpin Co.) THE STAMP MILL AND ITS ACCESSORIES 49 Other sequences are used elsewhere but are rarely seen in the United States. It is said that in many of the AustraUan mills the stamps drop in pairs simultaneously, 1 and 5, 2 and 4, followed by the middle stamp. Height of Drop. The height of drop multiplied by the weight of the stamp is roughly constant, that is to say a light stamp is used with a long drop and a heavy stamp with a short one. With the aver- age stamp weight of 1000 pounds a drop of 5 to 7 inches is common. ' Speed ' of Drop. The mmiber of drops per minute depends, of course, upon the weight of the stamp and distance through which it falls. The acceleration of gravity, retarded by the friction of the guides, determines the minimum interval between blows. Any attempt to lessen this interval results in ' camming,' that is, in the Pomt of Eeleai 0am -^ : 'oiut Bel ofCi m ,i' \ \ '/ f \ ; \ / L ,/ \ , ^a / *\ / "'■• Vi - {' \ n a 1 / \ .2 J4 / '" \\ .9 1 \ CO "3 a o .1 o 1 / \\ 1 / /• . Poi It of Eng -gem !nt \ .3 .7 .» 1.0 .4 .5 .6 Scale of Time In Second. Fig. 34. Morison Indicator Diagram for 900-lb. Stamp dropping 65 in. 97 times per Min. cam catching the tappet before its descent is complete. D. B. Morison, an eminent English mechanical engineer, made an ex- haustive investigation concerning the velocity of the stamp in its rise and fall and has computed from the data thus obtained, a table showing the maximum number of drops possible with any given height of drop.* The inscribing circles given in the table with the shorter drops are less than the sum of the diameters of stem and cam-shaft plus the clearance. No account is taken of the fact that the friction of the guides is a variable quantity, dependent upon conditions of * Richards, Ore Dressing, Vol. 1, page 216. 50 STAMP MILLING AND CYANIDING lubrication, and that the guide friction will retard a heavy stamp less than a light one. With well lubricated guides the writer has run a battery of 900-lb. stamps with 6-in. drop at the ra,te of 115 drops per minute with only an occasional 'pamming.' In the chapter on "Variations in Practice" will be found a number of examples of height and ' speed ' of drop. Fig. 34 shows an indicator diagram taken by Mr. Morison which represents graphically the cycle of progress in the rise and fall of the stamp. Power. The power required for driving stamps is used in two ways: (1) In raising the stamps, (2) in overcoming friction of the J 22 20 18 IG 14 12 10 Horse Power for 10 Stamp Battery 100 Drops per Minute Includes Friction of Cam Shaftin Bearinss ^Friction of Cams against Tappets Friction of Stamp Stems against Guides Raising Stamps ^ ^^ ^^ ^^ -pto?^ .-^^^ ^^-^ ^^ ^^ ,^ -"^ 1,^ .^^ ^ ^^ a ^^ \ ^-^ l^^e^ £0? ■ ^^ -"^ ' J "^ ^--^ f -lo* OlO?^ "^ ^^^ ,t1io? — " ^,.^- -^ -■^ at*; . .— — ^,^- ■-^ ^ ii ts2i — ' . 750 800 850 950 1000 1060 Weight ol Stamp Lbs Fig. 35. 1100 1150 1260 operating parts. The first item is easily calculated by figuring foot-pounds of work done and transposing into H. P., thus: Wt. of stamp X lift in ft. X number of drops 33,000 = H. P. The second factor is somewhat indeterminate. After the power is transmitted to the cam-shaft, there remain in addition to the work already calculated, the following items; (1) the friction of the cam-shaft in its bearings, (2) the friction of the cam-face against the tappet, and (3) the friction of the stem within the guides. THE STAMP MILL AND ITS ACCESSORIES 51 Accurate data is lacking as to the total percentage of power thus wasted. With the increasing use of electric motors in individual units, it should not be difficult to obtain exact figures. It is probably between ten and twenty per cent of that required to raise the stamps. The diagram in Fig. 35, taken from the Denver Engineering Works catalogue, shows approximately the power required for various drops with different weights of stamps. BIBLIOGRAPHY FOR THE STAMP MILL AND ITS ACCESSORIES * Especially Desirable for Students' Use General. , Boss, M. P. Has the Stamp a Future? 1| pp. Mines & Methods, Jan., 1910, p. 198. * Boss, M. P. Historical Notes on the Stamp Mill, 3 pp. Trans. A.I.M.E., Vol. 33, p. 244 (1902). Christensen, C. C. Modern Stamp Mills. Eng. Mag., Vol. 34, p. 29 (1907). * DeKalb, Couhtenay. Stamp Mill Practice, 2 pp. Eng. & Min. Jour., Vol. 82, p. 245 (1906); Min. Sci., Vol. 54, p. 11 (1906); Min. & Min., Vol. 27, p. 135 (1906); abst. 31, Can. Min. Inst., Mar., 1906. Del Mar, Algernon. Some. Experiences in Stamp Milling. Min. & Sci. Press, Vol. 93, pp. 138, 379, 634, 566 (1906)". Del Mah, Algernon. MiUing Gold Ores, 2 pp. Min. & Sci. Press, Vol. 93, p. 597 (1906). Del Mah, Algernon. Practical Working of the Stamp Mill, If pp. Eng. & Min. Jour., Vol. 88, p. 548 (1909). Del Mar, Algernon. A Case for the Stamp Mill, J p. Min. & Sci. Press, Vol. 102, p. 633 (1911). * FooTE, A. D. Stamp Mill. (Answer to DeKalb q.v.) Eng. & Min. Jour., Vol. 82, p. 886 (1906). Gordon, H. P. Milling Gold Ores, 1 p. Min. & Sci. Press, Vol. 93, p. 685 (1906). * Harnum, Dana. Discussion of General Principles of Stamp Milling and Amalgamation. Rev. in Min. Ind., Vol. IX, p. 356; Min. & Sci. Press, Dec. 1, 1900. HoFMAN, H. O. Detailed Description with Costs of Milling Practices in Black Hills, also reprinted as Bulletin No. 1420 by the Allis-Chalmers Go. Trans. A.I.M.E., Vol. 17, p. 49 (1888-89). Louis, Henry. Discussion of Morison's Results on Stamp-efficiency. Trans. A.I.M.E., Vol. 28, p. 355 (1898). RaTmond, R. W. An Early and Complete Discussion of Stamp Efficiency. Trans. A.I.M.E., Vol. 1, p. 40 (1871). * Semple, Clarence C. Milling the Homestake Ore. Eng. & Min. Jour., Vol. 91, p. 661 (1911). 62 STAMP MILLING AND CYANIDING Sanford, C. p. History of California Stamp-mill. Min. & Sci. Press, Vol. 67, p. 262 (1893). . "Heavy Stamps." West. Chem.; & Met., Vol. 6, p. 233 (1910). The Stamp and Its Mechanism. * Boss, M. P. Low Mortars and High Heads, li p. Min. & Sci. Press, Vol. 101, p. 866 (1910). Von Bernbwitz, M. W. Stamp Milling, — The Berrill Cam, J p., illus. Min. & Sci. Press, Vol. 106, p. 995 (1913). Berry, S. L. Stamp-mill Cam Curves and Speeds. 2 pp. Min. & Sci. Press, Vol. 106, p. 831 (1913). Cka-wfoed, a. J. F. A Keyless Tappet. Min. & Min., Vol. 29, p. 258. Del Mar, Algernon. Position of Driving Power for Stamp Mills. Eng. & Min. Jour., Vol. 89, p. 7 (1910). Del Mak, Algernon. Cushioning Vibrations of Cam-shafts. J p. Min. & Sci. Press, Vol. 97, p. 877 (1908). Deming, J. J. Details of Stamp-mill Construction. Min. & Sci. Press, Vol. 85, p. 188 (1902). * Hutchinson, Charles T. Stamp Battery Cam-shafts, 2 pp. Min. & Sci. Press, Vol. 103, p. 767 (1911). Jones, Martin. Weight of Stamps, | p. Min. & Sci. Press, Vol. 98, p. 748 (1909). * Lamb, Mark R. The Proper Design of Cams, IJ pp. Eng. & Min. Journal, Vol. 88, p. 66 (1909). * Randall, A. Z. Material for Stamp-mill Parts. Eng. & Min. Jour., Vol. 90, p. 1144 (1910). Foundation and Framework. * Barbour, Percy E. Foundations of the Goldfield Consolidated Mill, 3 pp. Eng. & Min. Jour., Vol. 87, p. 1173 (1909). BiNCKLEY, Geo. S. Concrete Mortar Blocks. Eng. & Min. Jour., Vol. 76, p. 514 (1903). Boss, Ira C. Concrete Battery Foundation and Cantilever Frame at Tonopah. Eng. & Min. Jour., Vol. 77, p. 404 (1904). Boss, M. P. Concrete Battery Blocks, i p. Min. & Sci. Press, Vol. 103, p. 82 (1911). Del Mar, Algernon. Quick Mill Construction for Fort Bidwell Mines, 1 p. Min. & Sci.- Press, Vol. 102 (1911), p. 139. Del Mar, Algernon. Battery Posts of Reinforced Concrete, | p. Eng. & Min. Jour., Vol. 88, p. 598 (1909). FisoN, G. B. Some Notes on the Construction and Operation of the Gravity Mill. (From London Min. Jour., Vol. 86, p. 297), 2 pp. Min. Sci., Vol. 60, p. 469 (1909); Eng. & Min. Jour., Vol. 88, p. 1131 (1909). FooTE, Arthur B. Masomy Foundations for Mortars of Stamp Mills, 1 p. Eng. & Min. Jour., Vol. 82, p. 886 (1906). Haynes & Warwick. Cost of Concrete Battery Blocks. Western dhem. & Met., Vol. VI, pp. 139, 237; abst. Min. Sci., Vol. 61, pp. 34, 445; Min. Wld., Vol. 32, p. 928 (1910). THE STAMP MILL AND ITS ACCESSORIES 58 * Kaeding, Charles D. Battery Foundations of the Kuk-San-Dong MiU, Korea. Min. & Sci. Press, Vol. 94, p. 598 (1907). Perkins, F. E. A Concrete Battery Block, J p. Min. & Sci. Press, Vol. 103, p. 483 (1911). Robertson, G. A. "Reinforced Concrete for Stamp Mills." Min. Wld., Vol. 33, p. 617 (1910). (From So. Afr. Min. Journ.) Thomson, F. A. Light Stamp-battery Frame. Bulletin Colo. School of Min., Vol. 4, p. 7 (1907). Washburn, W. H. Mortar Foundation for Soft Clay. Min. & Sci. Press, Vol. 84, p. 246 (1902). . Altering Stamp-mill Foundations. Eng. & Min. Jour., Vol. 89, p. 763 (1910). . A Battery Frame. Min. & Sci. Press, Vol. 92, p. 104 (1906). . Concrete Mortar Blocks. Min. & Sci. Press, Vol. 89, p. 120 (1904). . Concrete Mortar-block at Oroville. (An early example.) Min. & Sci. Press, Vol. 75, p. 505 (1897). . Various Forms of Battery Frames. Min. & Sci. Press, Vol. 75, p. 45 (1897). . Concrete Battery Blocks, 1 p. Min. & Sci. Press, Vol. 103, p. 19 (1911). . Battery Block and Posts of Concrete, Benoni Mill, J col. Eng. & Min, Jour., Vol. 92, p. 160 (1911). City Deep Battery Foundation, 1 p. Eng. and Min. Jour., Vol. 95, p. 951 (1913). Accessory Apparatus and Operation. Aaron, C. H. Discussion of Stamp Details, Weights, Screens and Opera- tion. Eng. & Min. Jour., Vol. 48, p. 140 (1889). Ball, R. "Stamp Drop Sequence." Eng. & Min. Jour., Vol. 89, p. 204, 597 (1910). Beaver, W. Stamp Mill Notes. Effect of Fine Feed, 1 p. J. C. M. & M. Soc. S. A., Vol. 6, p. 215 (1906). Behr, H. C. Behr Battery Feeder, J column. Eng. & Min. .Tour., Vol. 95, p. 854 (1913). Bell, Ralston. Stamp Drop Sequence, f p. Eng. & Min. Jour., Vol. 89, p. 204 (1910). Bell, Ralston. Stamp Drop Sequence, i p. (Reply to Mark R. Lamb's criticism of art. on " Stamp Drop Sequence " by Ralston Bell, in Journal of Jan. 22, 1910.) Eng. & Min. Jour., Vol. 89, p. 597 (1910). Brown, R. Oilman. Some Taihng Samplers, 1 p. Min. & Sci. Press, Vol. 93, p. 542 (1906). Chalmers, Alex. Power in Stamp Milling. (Reply to Criticism of H. Haas.) i p. Min. & Sci. Press, Vol. 98, p. — (1909). Chase, Charles A. Feeder Mechanism. Eng. & Min. Jour., Vol. 89, p. 1053 (1910). Clark, J. E. Re-setting Tappets, 5 p. Min. & Sci. Press, Vol. 98, p, 748 (1909). 54 STAMP MILLING AND CYANIDING CoLUE, J. E. The Order of Stamp Drop, 1| p. Pac. Min., Vol. 16, p. 50 (1910). Del Mar, Algernon. Screen-wear in Single-stamp Mills, 4 p. Eng. & Min. Jour., Vol. 92, p. 836 (1911). Haas, H! Power in Stamp Milling. (Criticism of Art. "Stamp- Mill Practice on the Mother Lode" by Alex. Chalmers, Min. & Sci. Press, Vol. 97, p. 785 (1908), i p. Min. & Sci. Press, Vol. 98, p. 216 (1909). * Hebsam, Ernest A. Conditions in the Mortar of the Stamp MiU, 2 pp. Pac. Min., Vol. 15, p. 81 (19'09). Htjntoon, Lotris D. Stamp Milling in 1910 (li pp.) ; Stamp Milling in 1911. Eng. & Min. Jour., Vol. 91, pp. 42, 46 (1911); Vol. 93, p. 52 (1912). Johnston, A. McArthur. High Stamp Duty in Gold MiUing, 1 p. Eng. & Min. Jovii., Vol. 82, p. 1016 (1906). Kenneb, Alvin R. Ore Feeder — Battery Ore Feeder, Bio Plata MiU, li columns. Eng. and Min. Jour., Vol. 95, p. 423 (1913). Lamb, Mark R. Stamp Drop Sequence, | p. (Criticism of Ralston Bell's article in previous Eng. & Min. Jour.) Eng. & Min. Jour., Vol. 89, p. 354 (1910). McDoNAU), Bernard. Method of Feeding Water to Stamp Batteries by Holes through the Mortar at Level of the Dies. Reviewed in Min. Ind., Vol. VIII, p. 296. Trans. C. M. I., Vol. Ill, p. 64 (1899)." MuNROE, Henry S. Stamp Drop Sequence, | p. Eng. & Min. Jour., Vol. 90, p. 1271 (1910). Peplbr, D. J. Metallurgy. Battery Feeders and New Driving Device Therefor, 1 p. Min. Rep., Vol. 56, p. 445 (1907); (J. C. M. & M. Soc, S. A.). Pitt, H. T. Stamp Milling Water Feed, | p. Eng. & Min. Jour., Vol. 86, 386 (1908). * Potter, W. C. Devices for Saving Water in Stamp MiUing. Eng. & Min. Jour., Vol. 72, p. 225 (1901). Reed, H. S. A New Amalgamation Trap, | p. Min. & Sci. Press, Vol. 100, p. 297 (1910). RiCKARD, T. A. Salt Water in Stamp MiUs, If pp. Min. & Sci. Press, Vol. 98, p. 860 (1909). ScHMiTT, C. O. Stamp Battery Water Supply. Taken from a textbook on Rand Metallurgical Practice, Vol. II. Eng. & Min. Jour., Vpl. 95, p. 473 (1913). Stacpoolb, A. R. Notes on Battery Practice, 6 pp. J. C. M. & M. Soc. S. a.. Vol. 11, p. Ill, 253 (1910). Stewart, John A. Increasing Milling Capacity at Small Cost, f p. Min. & Sci. Press, Vol. 94, p. 147 (1907). Storms, W. H. "Stamp Drop Sequence." Eng. & Min. Jour., Vol. 90, p. 109 (1910). Strickland, Herbert. Rapidly Adjustable Battery Screen-frame. Min. Sci., Vol. 61, p. 33 (1910). Warwick, A. W. Discussion of Power Required for Stamps. Min. & Sci. Press, Vol. 82, p. 103 (1901). THE STAMP MILL AND ITS ACCESSORIES 55 Weston, E. M. Individual Jets for Water Peed. Eng. & Min. Jour., Vol. 89, p. 172 (1910). Weston, R. Diverting Battery-discharge during Clean-up, | p. Min. & Soi. Press, Vol. 93, p. 566 (1906); (from Journal Chem., Met. & Min. Soc, S. Africa). Westwood, E. H. W. "Power Required for Stamp Batteries." Min. & Sci. Press, Vol. 100, p. 222; Eng. & Min. Jour., Vol. 89, p. 258; Min. Science, Vol. 61, p. 205; from Aus. Min. and Eng. Rev., Oct. 5, 1909. Individual Stamps. " Amalqamatob." Individual Stamps, 1 p. Min. & Sci. Press, Vol. 94, p. 115 (1907). Berry, S. L. The Pinder Berry Stamp Mill, 2 pp., illus. Min. & Sci. Press, Vol. 106, p. 739 (1913). Del Mar, Algernon. Single-stamp Mills, i p. Mini. & Sci. Press, Vol. 94, p. 303 (1907). Del Mar, Algernon. Single and Five Stamp Batteries, | p. Min. & Sci. Press, Vol. 100, p. 640 (1910). Nissen, Peter N. Nissen Stamp Mill at Boston Consolidated Mining Co., 1 p. Min. & Min., Vol. 27, p. 71 (1906). Nissen, Peter N. The Nissen Stamp, f p. Min. & Sci. Press, Vol. -93, p. 240 (1906). * Nissen, Peter N. High Duty Gravity Stamps. Min. & Sci. Press, Vol. 103, p. 840 (1911). Nissen, Peter' N. High Duty Gravity Stamp-miUs, 151 pp. J. C. M. & M. Soc, S. A., Vol. 12, p. Ill (1911). Pinder, J. W. Single Stamp Batteries. Min. & Sci. Press, Vol. 94, pp. 115, 147, 303 (1907). . Nissen Stamps at Cobalt. Can. Min. Jour., Vol. 31, p. 87; Min. Mag., Vol. II, p. 224 (1910). CHAPTER IV STAMP MILL AMALGAMATION General Principles. In standard stamp mill amalgamation two of the amalgamating methods outlined on page 9 are utilized; viz., amalgamation by grinding-contact, and amalgamation by surface-contact. That by grinding-contact is accomplished by feeding mercury, or as the millmen call it 'quick,' into the mortar with the ore, allowing the mercury to become broken up by the agitation and to come in contact with the newly liberated gold particles, thus serving the purpose of catching and retaining them within the mortar, or else of rendering them more readily caught by the out- side plates acting on the . surface-contact principle. The first method is generally referred to as 'inside amalgamation,' the second as 'outside amalgamation.' Outside amalgamation is used almost invariably; inside amalgamation is quite frequently omitted. Inside Amalgamation. There are two ways of accomplishing amalgamation inside the battery; these we will designate as the 'loose-quick' method and the 'inside-plate' method. In the first-named, mercury is fed to the battery in propor- tion to the amount of gold being handled and is expected to form amalgam. A certain portion of this amalgam will pass out through the screens; the balance will sink into the quiet spaces and between the dies, and there unite with other particles similarly deposited. If conditions are suitable amalgam may begin to form on the iron surfaces, and these may thus become centers for amal- gam collection. This is not depended on, however, and the amalgam is looked for in the 'battery-sands' which collect between and around the dies. From these it is recovered on clean-up days when the mortar is emptied. In the inside-plate method suitably shaped copper plates are placed within the mortar in the vicinity of the dies, serving thus to collect the mercury fed into the battery with the amalgam 56 STAMP MILL AMALGAMATION 57 formed by it. Practically all the pulp must come in contact with these amalgamated surfaces and in this case there is established within the mortar both grinding and surface-amalgamation con- tact. The use of inside-plates entails the use of wider and deeper mortars, and this for two reasons : first of all, for the accommodation of the plates and their wooden backing and, secondly, because it is useless to operate inside-plates with a shallow, narrow mortar, for the splash, under these conditions, is too violent. With the narrow mortar it is practically impossible for amalgam to accumulate on the plates, or if it does accumulate, there is serious danger that it will be scoured off with the least sign of over-feeding or other derangement within the battery. This has been overcome in some cases by covering the inside plates with a coarse screen, which, in turn, means greater mortar width and consequently less capacity. It has therefore come to be recognized that where a high stamp-duty is required, i.e., where capacity is of greater importance than close amalgamation, inside plates are undesirable. Also where the gold is coarse, so that both from weight and size, there is Httle chance of its escaping through the screen, inside plates are unnecessary. There can, however, be no question that with an ore in which the gold is difficult to amalgamate, better results can usually be obtained by the employ- ment of inside amalgamation-plates, or 'coppers' as they are' some- times called. These plates are placed most commonly between the dies and the screen (Fig. 9, page 24). Sometimes both back and front plates are used (Fig. 11, page 25), in which case a pro- jecting ledge is necessary to protect the back plates from abrasion by the coarse ore dropping from the feeder. End plates are rarely used. The inside plates are not usually open to inspection and in consequence much depends upon the millman's judgment and experience; if allowed to become too dry, amalgam is likely to break off, become pulverized, and pass out through the screen, where it may or may not be caught on the outside plates. If the amalgam becomes too soft, it may meet a similar fate, in which case, however, it is more likely to be caught on the outside plates. Outside Amalgamation. An almost universal adjunct of the amalgamating stamp mill is the outside plate, or table as it is termed. This consists usually of a sheet of specially selected soft copper, in most cases silver-plated, with its surface covered with mercury or preferably amalgam; it is often by far the most suitable 68 STAMP MILLING AND CYANIDING means for the recovery of free gold in the pulp delivered by the stamps. These plates for a 5-stamp battery are usually from 5 to 6 ft. wide and from 8 to 24 ft. long. In spite of many prejudices to the contrary, it is now generally conceded that silver plating of these copper-plates is a distinct advantage especially in starting a new mill. One ounce of silver per square foot is the usual thickness of plating, but two or even three ounces are sometimes specified. The area of the plate should, of course, be in proportion to the tonnage and value of the ore pass- ing over it; from 3 to 4 sq. ft. per ton of ore per day will be found to accord closely with standard practice. The grade of the plates is regulated by the character of the ore, the fineness of crushing, and the amount of water .available. From 1| to 2 in. per ft. is about the average slope, although some authorities — notably the late W. J. Adams, a man of wide mill- ing experience — insist that no plate should have less than 2| inches per foot slope.* Adams' argument is, that with less slope . so much water is required that the film of pulp passing over the plates is too deep to allow the gold to come in contact with the plate, and also that it is possible to have too much mercury on the plate. The first argument loses weight when we consider the much slower progress of the pulp waves when the plate is com- paratively flat, and the second point- is weakened by the fact that with a good millman too soft a plate will not occur. The proper appearance of the pulp when passing over the plate is shown by Fig. 36, the successive waves serving to turn the pulp over and over and thus to bring every particle in contact with the amalgamated surface. The progress of these waves should be as slow as possible, consistent with keeping the pulp moving and pre- venting the accumulation of 'sulphurets' (as the millmen call the sulphide minerals of iron, copper, etc.), magnetic iron, or other heavy particles on the plate. This means, that with a certain character of ore, the grade of the plate and the quantity of water used are mutually interdependent, and since, within the battery, a certain quantity of water is necessary to insure a satisfactory splash and discharge, the slope of the plate must evidently be such as to suit the pulp delivered by the stamps. Several drops or breaks in the length of the plate are often used; while formerly as much as 4 to 6 in. high, these are now seldom made to exceed * Hints on Amalgamation, page 24. STAMP MILL AMALGAMATION 59 1 in, in height. Their efficiency is usually proven by the accum- ulation of amalgam at the foot of the drop or fall. The condition of the amalgamated surface of the outside plates, or 'apron-plates' as they are called, is the most important single factor in the satisfactory recovery of gold in stamp mill amalga- FiG. 36. Plate-Waves. mation. If too hard the gold will not be caught; if too soft it is likely to be carried off by quicksilver flowing down the plate. The same thing is true if dry amalgam is discharged from the battery, in which case, as aptly pointed out by H. W. McFarren,* condi- tions are analogous to a flake of snow blown across a sheet of ice; if the ice is hard the flake will not catch, but the moment it strikes a soft or plastic spot it is at once arrested and held. The exact condition most suitable for any ore must be determined by experi- ment; coarse gold will usually be readily caught by a hard plate; finely divided gold, however, requires a soft plate. In general a white frosty appearance of the plate, and a consistency of the amalgam such that it will just yield to the pressure of the fore- finger, is about right; but here, as indeed in almost every de- partment of rnetallurgy, the ore in hand must be studied and suited. * Min. & Sci. Press, Vol. 97, pages 814r-816. 60 STAMP MILLING AND CYANIDINO Where, as is usually the case, quicksilver is fed inside the battery, the plates are kept soft between dressings by this means. In fact the condition of the outside plates is usually the criterion for feed- ing mercury to the stamps. Where inside amalgamation is entirely omitted more frequent dressings are necessary. In some mills, operating under this condition, mercury is sprinkled on the plate while the pulp is going over it. This should only be permitted where the work is in the hands of an extremely expert amal- gamator. It must ever be kept in mind that amalgam is the best gold saver and that in consequence the plates must never be so thor- oughly 'skinned' that a long period of inefficient gold saving must ensue before the plates are again in good shape. At the same time, when the amalgam begins to get thick on the plates it be- comes difficult to prevent losses of amalgam by attrition. The medium here is determined mainly by the grade of the ore and the character of its gold, but it is found that, in the majority of cases, the amalgam which can be readily taken up with a rubber scraper should be removed every twenty-four hours and that the plates should be dressed every twelve hours. In dressing the plates the stamps are hung up, or in some mills the pulp is diverted to another plate, and the plates to be operated on are washed clear of all adhering sand and dirt; then beginning at the bottom with a whisk broom or stiff paint brush, the plate is rubbed over thoroughly, loose pieces of amalgam are picked up, or bedded down, and where necessary fresh quicksilver is sprayed on the plate from a bottle the mouth of which is covered with canvas. Any spots which may show discoloration or coating are carefully cleaned, sometimes using a weak cyanide solution for the purpose. Some good millmen object to the use of cyanide and it will often be found that borax soap and 'elbow grease' are the only chemicals necessary to put a plate in good shape. Amalgam is taken from the plate by the aid of a piece of rubber belting, or a plain rubber cut to a square edge. The amalgam is pushed from each side to form a ridge in the center, from this ridge it is collected in a small scoop, and then cleaned to await retorting. Supplementary outside plates are often used in addition to the large expanse of apron-plate, and are usually placed close to the mortar. Lip-plates, secured to the projecting ledge of the mortar STAMP MILL AMALGAMATION 61 below the screen (Fig. 9, page 24), are good amalgam catchers, as are also splash-plates which are placed in front of the screen on an inclined splash-board (Fig. 9, page 24). Splash-plates have the advantage that a large proportion of the pulp impinges against them with considerable violence. Sluice-plates, a survival of placer mining methods, are seldom seen nowadays ; they are narrow plates in the bottom of the launder or sluice leading from the apron, and it is ridiculous to expect a narrow plate, deeply covered with fast-rushing pulp, to catch gold which has passed over the broad plate under so much more fa- vorable conditions. Plates in the distributing boxes of shak- ing tables' and vanners are occasionally quite efficient due to the agitation they undergo. Mercury-traps at the foot of every apron plate are prac- tically indispensable, as it is impossible to prevent quick- silver dripping from the lower end of the plate. Various forms of traps are used, that shown in Fig. 3.7 being the most common. The pulp is led through a pipe to the bot- tom of a well, from which it must rise to the overflow. Any mercury particles of appreci- able size are arrested and re- main in the trap, the bottom of which is provided with a drain or outlet. These mercury-traps act in some measure as a balance-wheel to steady the amalgamating conditions, and if the plates become dry or amalgam escapes, the trap often saves what would otherwise be lost. They should not be depended on for this purpose, however, and a large recovery of either quick-silver or amalgam from the traps is an indication of poor amalgamation on the plates or in the battery. Position of Plates. In the majority of American mills the apron plates are placed immediately beneath the lip of the mor- tar, without the intervention of any distributing devices. In this' Fig. 37. Mercury Trap. 62 STAMP MILLING AND CYANIDING manner, the pulsating discharge from the battery screen is syn- chronous with the wave motion on the plate. When distributors are interposed between the mortar and its corresponding plate this is lost, and the wave motion must establish itself inde- pendently. The apron plates should not be directly connected with the battery timbers as the vibration is thought to interfere with amal- gamation. In many of the South African mills where amalgamation follows the tube-mills, the plates are divorced entirely from the crushing machinery and placed in a separate building. It is a significant fact that under these circumstances the shaking copper-plate, which has never found much favor in this country, is extensively used and found to be more efficient than the stationary plate; especially should this be true with the thick, heavy pulp discharged by the tube-mills. Plate Materials. Three materials for apron-plates are in common use: Raw-copper, silver-plated copper, and Muntz-metal. Silver-plates have been suggested as efficient; gold would be more so; neither are likely to become fashionable. Raw-copper plates are cheaper than the silver-plated oneSj but they are harder to get in shape, i.e., to coat with amalgam, and in consequence, they do not become efficient gold catchers as soon as the silvered plates, and are more subject to discoloration and coat- ing. They absorb more gold, but when once in good working order are certainly as good, and some authorities maintain even better gold savers than the silvered plates; Silver-coated plates are more generally used than any other kind; they are, of course, expensive, but their promptness in getting into condition is usually sufficient compensation. Muntz-metal is nothing more than a special brass (copper 60 per cent, zinc 40 per cent) formerly much used for plating ships' bottoms. It has long been popular in Australia and its use may perhaps become more general in the United States, especially where, as is not infrequently the case, cyanide solution takes the place of battery water. Under this condition Muntz-metal has been demonstrated to have a longer life than either plain or silvered copper. Plate-Frames. The tables supporting the outside plates should preferably be of metal, if of wood the construction should be STAMP MILL AMALGAMATION 63 thoroughly substantial. The grade should be adjustable and provision made for moving the plates away from the battery for repairs to the latter. The plates are secured to the table-top by means of cleats running along the sides. No screws should be put through the plate. Turning up the edges of the plate avoids any possibility of mercury leaking past the cleats. Care of Quicksilver. The mercury used about the stamp mill must be kept free from impurities, if good amalgamation is desired. Only mercury which has been retorted is fit for use, and in some cases, this is not a sufficient guarantee of purity, as lead, zinc, and other readily volatile metals are distilled over with the mercury from the retort. In this event 'pickling,' usually with nitric acid, is resorted to, although both hydrochloric and sulphuric acid are used, the latter especially for removal of zinc. This pick- ling is accomphshed by agitating the quicksilver with the acid until by its action the mercury is seen to be free from impurity. A simple mechanical test is sufficient in the majority of cases to detect harmful impurities. If the mercury is lively, and the glob- ules in rolling about, retain their spherical shape, little need be feared, but if the particles are 'dead' and on rolling, drag behind them a tail, or are elongated, purification is necessary. Another test is to dissolve some of the suspected quicksilver in nitric acid; upon evaporating to dryness and igniting with sulphur, there should be no residue. The supply of mercury for the mill should be issued in weighed amounts, and placed in a stout glass bottle or jar, the surface of the mercury being kept covered with dilute nitric acid or with a solution of potassium cyanide. From this receptacle the mercury to be fed to the battery is taken. Mechanical mercury-feeders have been devised, but they save no time in a gold-mill, and as the feeding of the quicksilver to the battery is a matter of judgment, based upon the condition of the lip or apron-plates, automatism is out of place. The quantity of mercury used is, of course, proportional to the number of ounces of gold or silver amalgamated; usually from 2 to 4 oz. of mercury per ounce of gold is considered sufficient, but, as already suggested, much depends upon the character of the gold. The finer the particles the larger the amount of mer- cury required to form a suitable amalgam. The loss of quicksilver is difficult to prevent. It is caused 64 STAMP MILLING AND CYANIDING by flouring and accelerated by sickening, the fine particles of mercury being carried out to the tailing pond. From 0.2 to 0.5 oz. per ton of ore are common figures for mercury loss. A book should be kept for the mercury account in which the quantities issued and recovered are entered. Not only in the de- termination of cost are the figures of mercury consumption im- portant, but in checking the work of the millmen. Excessive mercury consumption means one of two things, either the amal- FiG. 38. Clcan-up Barrel. gamator is careless or he is dishonest. If the former, he may be spilling and slopping it about the mill or overfeeding the batteries, causing loss of gold. Otherwise the high consumption is due to gold, with its accompanying mercury, being stolen from the mill either by the millman or his accomplices. Treatment of Amalgam. The soft, pasty amalgam, taken from the plates or elsewhere, is mixed with an excess of quicksilver and ground in a Wedgwood mortar, or a gold-pan, or in large mills in a clean-up barrel (Fig. 38), or pan (Fig. .39). After this treatment the impurities rise to the surface and are skimmed off and put aside STAMP MILL AMALGAMATION 65 for future treatment. This grinding and skimming is repeated, adding in some cases hot water, until the mercury solution of amal- gam shows a clean surface. It now remains to separate the amal- gam from its excess mercurj'; this is done by pouring as much of it as can be conveniently handled into the center of a cloth pre- viously wetted and so placed over a vessel as to form a suitable depression. The ends of the cloth are then gathered up and the mercury is squeezed through the pores of the cloth, leaving behind a solid lump of amalgam. The lump is rolled about over the cloth Fig. 39. Clean-up Pan. to pick up any small, detached particles adhering to the folds, and is then placed in the safe to await retorting. The process is re- peated until the entire batch is squeezed. The quantity of mercury left in the squeezed amalgam is de- pendent upon its temperature, the extent to which it has been squeezed and worked, and the character of the gold. From one- third to one-fourth bullion is expected from any given weight of hard amalgam. Where large quantities of amalgam are to be squeezed the work is done by the plunger of an hydraulic or other power press (Fig. 40). The mercury thus recovered from the 66 STAMP MILLING AND CYAN I DING amalgam solution always carries an appreciable quantity of gold, the amount depending upon the size of the gold particles, the kind of medium used for the squeezing, and the temperature of the water. This gold (or silver), far from being a detriment to the quicksilver, is a positive advantage, and provided the mercury contains no other impurity it may be used again in the battery. It should be tested however. Canvas or the so-called 'outing flannel' of a stout quality is generally employed for the filtering medium. ^ Almost all writers on the subject mention chamois skin, bub it is seldom used, and my own experience has been that it rots with the repeated wetting and drying and soon becomes too weak to stand the pressure. The dross and skimmings are allowed to accumulate along with other odds and ends from about the mill, until a sufficient quantity is on hand to justify cleaning and retorting sepa- rately. The quicksilver recovered from such material needs special hand- ling before being returned to the mill supply. Aids to Amalgamation. The num- ber of nostrums, ' dopes,' etc., which have been proposed as infallible aids to the recovery of gold by amalgama- tion is endless; few of them are worth the space required to discuss them. Sodium-amalgam, first proposed according to Rose * by Sir Robert Crookes, seems to be efficacious in preventing the accumu- lation of a layer of metallic oxides on the surface of the plates. This preventive action is probably due to the hydrogen released by the decomposition of the water in contact with the metaUic sodium. The resulting caustic soda is also of use in 'killing' the grease which is a serious hindrance to amalgamation. The ma- jority of millmen do not care to use sodium-amalgam, owing to the great avidity with which it amalgamates with iron, for when too much is used the inside of the battery, as well as the shoes, dies, and screens speedily become coated with amalgam. Where * Metallurgy of Gold, 3rd Ed., page 144. Fig. 40. Amalgam Press. STAMP MILL AMALGAMATION 67 much difficulty is encountered in keeping the plates bright, a small amount may prove beneficial, and for this reason the method of preparing it will be given. A 20-gram assay crucible is half filled with mercury and placed in a support over a Bunsen burner or on a laboratory hot-plate. When thoroughly heated to about the boiling point of water, cover the crucible with a scorifier or cru- cible-cover, then, cautiously raising the cover, drop in a piece of metalUc sodium about the size of a pea, and at once replace the cover. When the pyrotechnic display has ceased, more sodium is cautiously added in the same way, until the amalgam is in such condition that it will just begin to adhere to a freshly filed iron surface. When this point has been reached the amalgam is cooled, and placed in a tightly stoppered bottle; it may be substi- tuted for plain mercury both inside and outside the battery. Cadmium- and zinc-amalgams have both been investigated by C. H. Aaron,* who found cadmium-amalgam especially to be re- markably free from tarnish under conditions where mercury- coated copper plates were quickly discolored. Both of these amalgams should be investigated more fully.f It is possible that the claimed superiority of Muntz-metal plates may be due in part to the zinc-amalgam which will naturally be formed on their surfaces. Electrolytic Amalgamation has, from time to time, been heralded as another panacea for all the amalgamator's ills.J The results would seem, in so far as they are beneficial, to resemble those pro- duced by sodium-amalgam, the electrolysis Uberating hydrogen by decomposing water and depositing metallic sodium, when, as is often recommended, salt-water is fed to the batteries. As the cyanider has found to his cost, however, electrolysis is likely to quicken the action of those reagents which are valuable to us be- cause of their selective tendencies, with the result that they be- come more promiscuous, taking to their bosom substances we do not wish to recover by their aid. Practically, electrolytic amal- gamation has a tendency to amalgamate everything in sight and * Eng. & Min. Jour., Vol. 48, page 118. t Recent investigations give following results: Amalgams in order of ability to resist coating by FeSOa and MnS04 : Cd, Pb, Sn, Au, Ag, Na, Zn and Hg. Amalgams in order of their ability to save gold in presence of sulphates : Sn, Pb, Na, Ag, Zn, Cd, Hg. (Unpublis.hed thesis of R. Keffer, State College of Washington.) t Min. Sci., Vol. 60, pages 30-32. 68 STAMP MILLING AND CYANIDING hence has never found general favor. As in the case of sodium- amalgam, there are probably special cases where an extremely weak galvanic action will prove beneficial in keeping the plates bright and free from tarnish. This may easily be arranged by placing a few iron strips lengthwise on the amalgamated copper plate. The Alaska-Treadwell company reports an increased- saving by amalgamation when using sea-water in the stamp batteries. That this is probably due to electrolytic action is suggested by the fur- ther statement that the corrosion of the mortars is so great that the net result is undesirable financially. Chemical Aids. Lime, caustic soda, caustic potash, wood ashes, and other substances of like character are fed to the battery in cases where the ore, due to partial oxidation, contains free acid. Their use under this condition is logical and to be commended. Potassium cyanide is almost universally condemned by writers on stamp milUng, and almost as generally believed in by skilled amalgamators. As a plate dressing solution it is more commonly used than any other chemical. It is sufficiently alkaline to remove any film of grease, is a strong reducing agent, and dissolves most metals and metallic oxides. It has a tendency, however, the reason for which has never been explained, to harden the amalgam by causing the excess of mercury to exude from the plate and run down to the lower end, thus leaving the amalgam dry and hard. In moderation and in weak solution its use is justified. The fact, however, must not be lost sight of that both gold and gold-amal- gam * are soluble in cyanide solutions. Ammonium chloride has many of the properties of cyanide in this connection with the added advantage of not being a solvent of gold. It is frequently of de- cided benefit with discolored plates. Extremely dilute solutions of hydrochloric and sulphuric acid are at times of benefit. Ferro and ferricyanide of potassium as a mixture for dressing plates is highly recommended by W. J. Adams,t the compound being made by adding 1 part of a saturated solution of ferrous sulphate to 4 parts of a 2.5 per cent cyanide solution. This is a good example of the prescriptions so sacredly guarded by the older generation of millmen. The fact that many of these compounds * According to Roskelley 4.65 oz. of amalgam lost 0.025 oz. in 12 days in 3 per cent KCy solution. I Hints on Amalgamation. STAMP MILL AMALGAMATION 69 were known only to a few in nowise enhanced their value, for a more general knowledge of them would have led to more severe trials and the abandonment of all but the best. The greatest enemies to successful amalgamation either inside or outside the battery are the films either preexisting on the gold in the ore, or created artificially on the gold, on the mercury globules, or on the plate. These films, often of infinitesimal thick- ness, are sufiicient to prevent contact without which, of course, no amalgamation can be expected. Grease and various metaUic oxides are the main film-forming substances; the former is, of course, saponified by the alkalies. The metallic oxides may be dissolved by the alkali, but are more likely to be removed by a solvent such as cyanide or a mineral acid. Since cyanide is decidedly alkaline and at the same time a good solvent for most of the oxide films, its popularity as a plate dressing seems logical enough. Increased Temperature has been claimed to be an aid to amal- gamation. T. T. Read, whose work on amalgams has already been mentioned (page 8), concludes that increased amalgamation temperature, which, of course, is accomplished by increasing the temperature of the battery water, has the following effects: It increases the solubility of harmful salts existing in the ore, and hence the precipitation of base metals into the amalgam. It de- creases the viscosity and surface tension of the mercury and flour- ing is thereby increased. The power of the mercury to hold the gold particles to the plate is also diminished. Increase of tempera- ture is beneficial in that quicksilver is more lively when warm, catches the gold more readily, and separated particles are more easily made to coalesce. Read says: "A comparatively low tem- perature is better where the influence of soluble salts is to be con- sidered, but when tMs may be neglected as high a temperature as can economically be maintained without variation * is most favorable to successful amalgamation." The gist of the above quotation is in the italicized words "without variation." In the vast majority of cases any temperature within reasonable limits will give satisfactory results, provided there is but little fluctuation. Cleaning Plates. The daily clean-up, by means of rubber scrapers, fails in the majority of cases to remove completely the amalgam adhering to the plates. This result is cumulative and * The italics are mine, F. A. T. 70 STAMP MILLING AND CYANIDING eventually in every mill a point is reached where more drastic measures must be used. While it is universally admitted that amalgam is the best gold catcher, it is not expedient from any point of view to allow a large amount of gold to remain on the plates indefinitely. In a custom mill, of course, practically all amalgam must be removed from the plates at the end of every run. Hard-wood scrapers are frequently substituted for the rubber ones, and will remove more amalgam. Steel scrapers are made by forging each end of an old file to a chisel edge, one end being turned down to a hoe-shape. In Gilpin county a better form of scraper is employed. This consists of a piece of steel 12 by 3 by | in. thick, turned down for about f in. at one end. The edge of the turned end is ground perfectly square, and the square edge thus made is depended upon for the scraping effect. In this form the corner of the scraper is not so likely to dig into the plate and make an objectionable groove. The steaming of plates for the removal of hard amalgam is in- creasing in favor, and is a much cleaner and neater method than the old system of taking the plates from the table and placing them over a charcoal fire, after which they were seldom fit for anything but the scrap heap. Rickard * in describing the operation of cleaning the plates at the Alaska-Treadwell Mill says: " Their surface is first washed with a jet of water to remove particles of ore. A wooden cover is laid over the copper plates, resting on the cleats that fasten the plates to the table; this leaves a IJ-in. space between the cover and plates. All openings along the sides and at the top and bottom are closed with strips of burlap; a hose is inserted at a point one-third the way from the head of the plate and live steam is admitted at a pressure of 36 to 65 lb. The steam is allowed to act for 20 min. and is then turned off. The wooden cover is removed and the softened amalgam is scraped off with chisels. The amalgam has become as soft as Swiss cheese and about as brittle. The mercury is partly volatilized by the heat, and the men are careful to stand back when the cover is raised. Warning is given by the fact that the brass sockets of the electric lights hanging over the tables become amalgamated. In cleaning the tables the men wear a wet sponge at their nostrils. When the amalgam has been scraped off, the plate is washed with a weak cyanide solution; it is then dressed with fresh mercury, using whisk-brooms to spread the globules of mercury uniformly." * Min. & Sci. Press, Vol. 98, page 861. STAMP MILL AMALGAMATION 71 All such methods, however, should be regarded in much the same way that the general public regards a surgical operation — ■ as a thing of the last resort. Eventually all amalgamating-plates that have been long in use find their way to the copper smelter for extraction of absorbed gold and silver. Battery Clean-up. Wherever mercury is fed into the battery, a periodical cleaning out of the mortar must be made to remove accumulated amalgam. If coarse gold is present in the ore part of it will accumulate inside the mortar whether mercury is used or not, and this alone would make a periodical clean-up necessary. The interval for this operation is dependent entirely upon the richness of the ore. In low-grade mills the battery clean-up is made once or twice a month. In contrast with this I have had to make a clean-up every day when milling exceptionally high- grade material. The method of cleaning-up is usually as follows: When ready to close down the mill, the feeders are shut off and the battery is allowed to continue running. This is continued as long as is con- sistent with the safety of the shoes and dies; the water is then turned off and the stamps are hung up on the latch-fingers. The screen-frames are taken out, carefully washed over the apron- plates, and examined for adhering amalgam, which, if present, is removed and placed in a granite-ware kettle. If inside plates are used they are removed to a place of safety and their amalgam removed by scraping. If the plate-frames are portable they are moved from the front of the mortar, if not the workmen stand or squat on planks placed across the plate-frame, and the remaining battery-sand is taken from between the dies and put aside for future treatment. A sharp look-out is kept all the while for loose lumps and balls of amalgam. The dies are worked loose with a crowbar (not usually an easy operation), cleaned of adhering amalgam and set aside. The bottom of the mortar is carefully scraped, crevices and corners are examined, and when all is perfectly clean, a layer of taihng is spread on the mortar-bottom, and the dies, if not worn out, are set in place again and the tappets are re-adjusted. If the dies have worn irregularly they are put back in the mortar in a reversed position to equalize the abrasion. The inside-plates having been cleaned of their amalgam are dressed with quicksilver and set in place. Screens and screen-frames are renewed if neces- 72 STAMP MILLING AND CYANIDING sary, keyed in position and the mill is again ready to begin crush- ing ore. One unit, usually of ten stamps, is thus cleaned up at a time and is started miming before the next one is stopped. The time consumed is from 45 min. to one and a half hours per five- stamp battery. A small trolley-track suspended from the cam- shaft floor, upon which a bucket may be run in front of the batteries, is a convenience in moving the material to be handled. Cleaning Battery-Sand< The removal of amalgam and coarse gold from the battery sand is accomplished in various ways. In small plants the material is usually panned or run through a sluice- box provided with riffles, the tailing from the process being re- turned to the battery. In larger mills three methods are in use: (1) Returning the sand from the different batteries to one mortar, which is cleaned-up last of all. (2) Charging all battery-sand into a clean-up barrel, rotating about a horizontal axis. (Fig. 38.) In this the battery residue is ground for 6 to 12 hours, with an excess of mercury. Cast-iron balls are used to loosen the amalgam from all particles to which it has been adhering. It is collected by the excess mercury and is drawn out and taken to the clean-up room and panned to free it from gangue matter. In some mills the material from the clean- up barrel is discharged into a riffled sluice, the riffles being depended upon to catch the heavy particles. Mechanically operated pans or bateas take the place of the gold pan in some large mills. (3) Grinding the material collected from the mortars in a small pan, on the principle of that used in the silver mills (Fig. 39). This last, however, is better suited for cleaning large quantities of amalgam previously freed from all but the finest impurities. Battery-sand is likely to contain pieces of iron, such as pick-points, ends of drill-steel, particles of shoes or of dies which would inter- fere with grinding it. When the grinding-pan is used a gentle stream of water is kept flowing into the pan. This serves to carry away the finely ground ore or slime leaving only the heavy sulphides, iron and mercury to be dealt \\'ith by hand. The final collection of amalgam is treated, as previously de- scribed, with a large excess of quicksilver to free it from impurities and is then squeezed through cloth or by an amalgam-press, Fig. 40. Cleaning-up of odds-and-ends. Nothing which is used about the clean-up room or around the batteries, where amalgamation STAMP MILL AMALGAMATION 73 is practised, should be destroyed. Whisk-brooms, plate-rubbers, old screen-frames, chuck-blocks, amalgam-cloths, chips from in- side the battery, dross and scum from amalgam, and a thousand other little scraps, should be carefully kept, and if combustible, burned and the ashes either returned to the battery or placed in the clean-up pan or barrel. Iron scraps should be thoroughly rusted with the aid of salt or sal-ammoniac to loosen any adhering films of amalgam, and may then be similarly charged into a barrel although preferably made a separate charge. Clean-up Room. The clean-up room need not be large. It should be kept securely locked whether in use or not. The win- dows should be inside the mill and heavily barred, or should be omitted altogether, provision being made for ventilation through the roof, and light being furnished by electricity. The fittings shpuld consist of a deep sink or two for panning, and a flat-top table each side of the sink and sloping slightly to- ward it. Concrete is the best substance for the sink and table-tops and the floor should be of the same material. The amalgam-press, if one is used, should be placed here. A small safe for temporary disposal of amalgam is useful. Whether the retorting and melting is done in this room or not is a matter of individual prefer- ence; usually where a stamp mill is operated with a cyanide plant in conjunction, retorting, melting, and refining are done in a special building. Retorting. The hard amalgam, whether squeezed by the press or by hand, must be heated to free it from mercury before it is fit to be melted into bullion. To do this it is handled in some form of retort, the distilled mercury being condensed and recovered. In small mills the pot-shaped retort (Fig. 41) is used. In large mills a retort in the form of a cast-iron muffle is built, and the amalgam is placed therein on small trays or pans. When using Fig. 41. Pot-Retort and Condenser. 74 STAMP MILLING AND CYANIDING the pot-retort, the amalgam should not more than two-thirds fill the vessel, which should be chalked inside, or lined with tissue paper. The cover secured by a key and clamp is made tight with a lute of salt and bone-ash, or of fine slmie. Heat is applied gradually and water is turned into the jacket on the condensing pipe. As soon as mercury begins to distill, the heat should be checked slightly and should then be regulated according to the Retort and Bullion Furnace. flow of mercury. When no more quicksilver is given off, the heat should be raised to bright red to expel the last traces, and the re- tort allowed to cool. The spongj- mass, called by millmen the re-tort, is turned out and is ready for melting. It always retains a small amount of mercury, but if reasonably free from sulphides and other impur- ities, will be a characteristic golden-yellow. The built-in retorts (Fig. 42) have, of course, a stationary fire box. The smaller retorts may be heated in any convenient manner. An ordinary gaso- line assay furnace serves ad- mirably, and special retort furnaces (Fig. 43), designed for the use of crude oil or gasoHne, may be bought. There are two sources of danger in retorting; Fig. 43. Gasoline Retorting-Fuinace. STAMP MILL AMALGAMATION 75 the pipe may become plugged with particles of amalgam, due to the violent boiling which takes place when the retort is heated too rapidly; or the end of the pipe may be carelessly allowed to dip under water, with the result that should the heat be decreased, the condensation of the vapor will draw water into the retort. Either of these accidents is almost certain to result in an explosion, scat- tering the valuable contents of the retort in all directions and exposing the workman to danger of salivation by mercury vapor. Melting. The product of the retorting operation is melted in graphite crucibles, usually in an ordinary coal or coke-fired wind- furnace, although crude-oil or gasoline is infinitely superior for the purpose, on account of the readiness with which the heat may be controlled, as well as the efficiency and convenience in their use. Mills seldom do any extensive refining of their gold; a little borax or occasionally a mixture of borax and niter is added to the crucible by means of a small metal spout. While the elaborate precautions described by the older authorities for the preparation and annealing of the graphite crucibles are scarcely necessary now- a-days,* it is well to store the crucibles in a warm place, such as the top of a furnace, to ensure complete elimination of moisture; they should also be tested by fairly slow heating in the furnace before the bullion is placed in them. Pouring-molds are usually rectangular in shape, and before the molten gold is poured into them they should be given a coating of graphite on the inside and placed on the furnace to heat. A piece of tallow or paraffine candle is allowed to melt in the mold, till the bottom is covered about J in. deep. This should be smoking slightly when the gold is poured. If a large amount of slag is formed in the crucible it is skimmed off; otherwise it is poured with the gold, and subsequently knocked off with a hanuner, or de- tached by throwing the bar, while hot, into water. If the bar is not smooth, either the mold was too cold, there was not enough grease, or too much slag was poured with it. If desired it may be re- melted without appreciable loss. A high poUsh may be given to a bar by dropping it into dilute sulphuric acid before it has time to cool. In small melts the crucibles are handled by hand-tongs. With larger quantities a pair of scissor-tongs with a small crane is necessary.. * I have, as an experiment, actually taken a new crucible, filled it two-thirds full of retorted gold, and placed it in the full heat of a crude-oil burner without the least injury to the melting pot. 76 STAMP MILLING AND CYANIDING BIBLIOGRAPHY FOR STAMP MILL AMALGAMATION * Especially Desirable for Students' Use Aaron, C. H. Gold Losses in Amalgamation and Remedies, mentions Zn & Cd Amalgams. Eng. & Min. Jour., Vol. 48, p. 118 (1889). Adams, W. J. Hints on Amalgamation and the Care of Gold Mills. San Francisco (1907). BAKBOtiB, Percy E. Amalgam Traps. Eng. & Min. Jour., Vol. 92, p. 152 (1911). Batth, Wm. H. The Amalgamation of Copper Ore, | p. Mia. & Sci. Press, Vol. 94, p. 146 (1907). * Batliss, R. T. Accumulation of Amalgam on Copper Plates and Dis- tribution of Gold and Silver thereon. Trans. A.I.M.E., Vol. 26, pp. 338, 1039, 1047 (1896); Vol. 27, p. 1003 (1897). BuRFEiND, J. H. Potassium Cyanide in Gold Amalgamation, 1 p. Min. & Sci. Press, Vol. 58, p. 64 (1908). Caldecott, W. a. Silver Coating of Amalgamating Plates, f p. Min. & Sci. Press, Vol. 98, p. 92 (1909). Carey, Elmer Ellsworth. The. Electrochemical System of Extract- ing Gold Values, 2| pp. Min. Sci., Vol. 60, p. 31 (1909). * Clark, A. J. and Sharwood, W. J. Amalgamation at the Home- stake, 2 pp. Min. and Sci. Press, Vol. 105, p. 762 (1912); (abst. from Bull. 28, I. M. M.). Dennis, Clifford G. Position of Amalgamating Plates in the Stamp Mill, i p. Min..& Sci. Press, Vol. 93, p. 566 (1906). ' DowuNG, W. R. Amalgamation on the Rand, 4 pp. Min. & Sci. Press, Vol. 102, p. 785 (1911). * DowLiNG, W. R. Amalgamation of Gold in Banket Ore. I. M. M., 24 pp.. Vol. 20, p. 270*(1911); I. M. M., 2 pp.. Vol. 21, p. 700 (1911). * DowLiNG, W. R. Area of Amalgamation Plates. (Excerpt from paper read at a meeting of C. & M. Soc, S. A.), f p. Eng. & Min. Jour., Vol. 91, p. 1148 (1911). Editorial. Shaking Tables, i p. Pac. Min., Vol. 18, p. 40 (1911). Eissler, M. The Metallurgy of Gold. Chaps. II and III, London (1896). Goddard, Sydney F. Scaling and Sweating of Copper Battery Plates, i p. Min. & Sci. Press, Vol. 99, p. 368 (1909). Hardy, J. W. Some Notes on Amalgamation. Pac. Min., Vol. 16, p. 107 (1909). Halse, Edw. Plate Absorption, Etc., Amalgamation. Min. & Sci. Press, Vol. 96, p. 806 (1908). * Halse, E. Comparison of Plain Copper and Silver-plated Copper Plates. Rev. in Min. Ind., Vol. 9, p. 353. Inst. M. & M., Jan. 16, 1901. Hornsby, Thomas E. Diagnosing Amalgamating Troubles, 1 p. Pac. Min., Vol. 18, p. 96 (1911). Hubbard, J. D. Electroplating Battery Plates, IJ pp. Min. & Sci. ■ Press, Vol. 103, p. 135 (1911). STAMP MILL AMALGAMATION 77 Joky, J. H. Uses and Limitations of Electrolytic Amalgamation, 1 p. Min. & Soi. Press, Vol. 99, p. 476 (1909). * MacFareen, H. W. Amalgamation Methods, 3J pp. Min. & Sci. Press, Vol. 97, p. 814 (1908). MacFarren, H. W. Hints on Amalgamation. Min. Wld., Vol. 30, p. 891 (1909). Merton, a. M. Mexican Method of Retorting Amalgam, 1 p., illus. Eng. & Min. Jour., Vol. 96, p. 263 (1913). O'Brien, C. Some Notes on Amalgamation. Pac. Min., Vol. 17, p. 19 (1910). Parsons, A. R. Muntz Metal Plates. (Bamberger Delamar Mines.) Min. & Sci. Press, Vol. 92, p. 281 (1906). Pierce, Lucius S. Amalgamation Methods. Min. & Soi. Press, Vol. 98, p. 216 (1909). * PiTCHFORD, J. H. Use and Care of Mercury. Eng. & Min. Jour., Vol. 83, p. 467 (1907). Preston, E. B. Calif. Gold Mill Practices. Bull. No. 6, Calif. State Mining Bureau (1895). Rickard, T. a. Cleaning Plates at the Alaska Treadwell Mill. Min. & Sci. Press, Vol. 98, p. 860 (1909). Sears, J. R. The Position of Amalgamating Plates, J p. Min. & Sci. Press, Vol. 93, p. 534 (1906). * Semple, Clarence C. Area of Amalgamation Plates, 1 p. Eng. & Min. Jour., Vol. 92, p. 837 (1911). * Smart, G. O. Dressing Plates as Affecting Amalgamation, 1 p. (Abstract of Art. in J. C. M. & M. Soc, S. A., June, 1909). Eng. & Min. Jour., Vol. 88, p. 556 (1909); Min. & Sci. Press, Vol. 99, p. 503 (1909). * Smith, Alfred Merritt. Amalgamation in Cyanide Solution, 3i pp. Pac. Min., Vol. 15, p. 212 (1909). * Spaulding, C. F. Amalgamation following Fine Grinding, 3 pp. Min. & Sci. Press, Vol. 101, p. 872 (1910). "Special Correspondent." A New Idea in Saving Fine Gold by Ad- hesion, I p. Min. Sci.^ Vol. 60, p. 33 (1909). * Stacpoolb, a. R. Amalgamation Practice. J. C. M. & M. Soc, S. A., Vol. 11, p. Ill, etc., abst., Min. Wld., Vol. 33, p. 811 (1910). Stanley, G. H. and Murray, M. T. Gold Absorption by Amalgama- tion Plates, 1 p. Min. & Eng. Wld., Vol. 36, p. 1103 (1912); abs. from J. C. M. & M. Soc, S. A. * Tays, E. a. H. Distribution of Gold and Silver in Bullion from Plate Amalgamation and Plate Absorption of Gold and Silver. Trans. A.I.M.E., Vol. 30, p. 318 (1900). * Thomae, W. F. a. Plate Absorption. Eng. & Min. Jour., Vol. 86, pp. 709, 996 (1908). . Amalgamation Tables at Homestake, 1 p. Eng. & Min. Jour., Vol. 93, p. 739 (1912). . Amalgamation Tables at Alaska-Treadwell. Eng. & Min. Jour.,_ Vol. 93, p. 835 (1912). 78 STAMP MILLING AND CYANIDING . Amalgamation Tables at Argonaut, Calif., J p. Eng. & Min. Jom:., Vol. 93, p. 983 (1912). . Verdigris on Amalgamation Plates, | column. Mex. Min. Jour., Vol. 15, p. 35, No. 2 (1912). . Shaking Amalgamation Tables for Tube Mill Circuit, 2 pp. Eng. and Min. Jour., Vol. 94, p. 63 (1912). . Mercury Trap for Amalgamating Tables, I5 columns. Eng. and Min. Jour., Vol. 94, p. 443 (1912). . Methods of Fastening Amalgamating Plates at Homestake, i column. Eng. and Min. Jour., Vol. 95, p. 22 (1913). . Area of Amalgamation Plates, 5 column. Eng. and Min. Jour., Vol. 95, pp. 180, 375 (1913). CHAPTER V VARIATIONS IN PRACTICE ^ For the purpose of discussing the modifications and appUca- tions of the stamp mill, the various practices will be classified as follows: (1) Gilpin County Practice, using light stamps, high discharge, and high drop with slow speed, relying largely on inside amalgamation with the aid of inside plates. (2) Original California Practice, using a medium weight stamp, moderately high discharge, inside plates, short drop, and high speed. (3) Modified California Practice, using a heavy stamp, low dis- charge, short drop, and high speed, feeding quicksilver into the battery but using no inside plates. (4) South African Practice, using the stamp mill primarily as a crusher, with extremely heavy stamps, short drop, high speed, and low discharge and omitting inside amalgamation altogether. Table II, giving important features of typical mills in each class, will exemplify the points of difference. TABLE II r; "2*1 1 Wt. of stamp Height of drop No. of drops per min. Height of discharge Area of inside plates Stamp duty Screen used o s lb. in. in. sq.ft. tons meah 1 500 to 600 16 to 18 25 to 30 11 to 16 61 ItoJ 50 J 2 850 to 950 6 to 8 90 to 100 7to8 lito2 2.5to4 30 to 50 -tof 3 850 to 1200 6 to 8 90 to 110 2to4 none 3 to 9 20 to 40 -to J 4 1200 to 2000 4to7 90 to 115 2 to 4 none 7 to 20 4 to 10 none (i) GILPIN COUNTY PRACTICE Gilpin County practice developed at a place where milhng was first done with the California stamp mill. Gradually the ores be- came more complex and the mills, failing to make the extraction, gave way for a time to the smelters. Eventually, however, the 79 80 STAMP MILLING AND CYANIDING millman triumphed, by adapting and modifying iiis amalgamation practice to suit the ore. He found that a roomy mortar, with plenty of inside-plate surface, and fine-grinding, assisted by deep discharge and long contact of the pulp with the plates and the quicksilver in the mortar, would give a satisfactory extraction from an ore, in which the gold was intimately associated with pyrite, and so fine as to be rarely visible to the naked eye. In short, the Gilpin County millman is successfully treating by amalgamation, aided by the crudest kind of concentration,* an ore which practi- cally every other millman in the world would declare could not be handled by stamp milling. The capacity per stamp is far lower than elsewhere, but the cost per ton bears favorable comparison with costs in other plants and the extractions are good. For various reasons, however, the method of milling developed in the ' Little Kingdom ' of Colorado has not been extensively used, away from its birthplace. The following experience in a small mill in the Southwest is of interest in this connection: The mill was equipped with 850-lb. stamps, making 104 to 106 five-inch drops per minute. The discharge was 4 in., no inside plates were used, and loose quicksilver was fed to the battery. Pending the in- stallation of a cyanide plant, one battery was made as nearly as possible a Gilpin County mill. The discharge was made 9 in., the drop 10 in., and the speed was reduced to 50 drops per minute. Inside-plates were arranged in both back and front of the mortar. Under the first condition we were saving 40 per cent by amalgamation and our concentrate assayed $200; using the 'Gilpin County Mill,' our amalgamation extraction went up to 65 per cent and our concentrate dropped to 875 per ton. This illus- trates the essential feature of the Gilpin County practice, viz., that it saves gold by amalgamation which would usually go to the concentrator or to some other form of treatment. And, therefore, we may safely say, that the Gilpin County stamp mill, with its apparently pettifogging ways, its small tonnage, and its conserv- atism, is without question — outside possibly of the arrastra — the best amalgamator in the world. (2 and 3) THE CALIFORNU PRACTICES The California type of mill antedates the Gilpin County Mill and is more nearly representative of the usual, standard practice * The Gilpin County bumper can only be called a concentrator by courtesy. VARIATIONS IN PRACTICE 81 throughout the world to-day than any other style of milling. In the design of the mortar, the aim has constantly been to harmonize capacity with inside amalgamation. A narrow, deep mortar has been found to combine these two essentials (see Fig. 9, page 24). The front plate is placed above the level of the dies to avoid the scouring action at that point. The California milUng fraternity is, however, far from being united as to this being the better practice, and that which I have designated the 'modified California' practice has many adherents. Faster crushing is possible where inside plates can be omitted, owing to the decreased height of discharge. There are good rea- sons, however, for feeding quicksilver into the battery whether inside plates are used or not. In the first place, the particles of gold as they are liberated, brightly burnished from their quartz matrix, are in excellent condition for instant amalgamation. Once amalgamated they become pasty and malleable and are less likely to be broken up by the blow of the stamp; furthermore, should they then be broken, they are more likely to be caught by the plate than the corresponding particles of gold would be if unamalgam- ated. There is further a strong tendency for particles of amal- gam within the mortar to coalesce, and so protect each other from abrasion and from being carried out with the swash of the pulp. It is, moreover, an axiom in milling, that the gold should be saved as early in the process as possible. If one saw a $50 gold nugget in the ore bin, he would be foolish to let it go into the mill and take a chance of its being broken up and in part floured. Simi- larly that which can be saved within the battery should not be allowed to run the risk of loss on the plates outside and so on. As to whether inside plates should be used or not depends upon the ore. With high-grade ores they undoubtedly should be used; with low-grade ores, it would seem less desirable and- yet we have the examples of the Homestake and the Alaska-Treadwell mills both using inside plates with the lowest-grade gold ores that are being treated at the present time. (4) SOUTH AFRICAN PRACTICE South African practice has come, in recent years, to an entire omission of inside amalgamation. The stamp mill thus becomes a crusher of rock, pure and simple, and it is at once on debatable ground as to its supremacy over all other machines. As a com- 82 STAMP MILLING AND CYANIDING bined amalgamator and crushing machine the stamp is without an equal. Remove the amalgamating feature and the superiority of the stamp over other devices is a matter of doubt. However, at the present time in South Africa, heavy stamps are extremely popular. The tendency is to make the stamps crush only to a coarse product, from | to ^V in. diameter, relying on the tube- mills or other devices to reduce the ore to the sizes deemed essen- tial for cyanide treatment. Here, amalgamation in many cases follows not the stamps but the tube-mills. Each of these practices shades and blends into the other, so that whereas a particular mill may not fall into any one of the four classes specified, at the same time it is likely to approximate closely to one or the other. INDIVIDUAL STAMPS All of the preceding discussions have presumed that the batteries under consideration were of the five-stamp type. In the last few years nnportant installations of one- and two-stamp mills have been made and much valuable data has been collected on the subject. The advantages claimed for stamps operating in individual mortars are: (1) Greater screen area and consequently greater tonnage. (2) Absence of interfer- ence by waves from other stamps and consequently more efficient crushing, resulting in less power per ton stamped. (3) Less slime produced. These mills, however, have not fully justified anticipa- tions. They take more labor per ton than the five-stamp batterj', for screens, feeders, and other apparatus are vastly increased in number. The swash within the individual mortars is so great that inside amalgamation by plates or otherwise is out of the question. The tonnage per stamp is undoubtedly greater and the power consumption per ton is less than for the same weight of stamp in a five-stamp battery. Where the conditions discussed under ' South African practice ' are Fig. 44. Nissen Mortar. VARIATIONS IN PRACTICE 83 to be met it would seem that single-unit stamp mills might have a .field.* The Nissen stamp (Fig. 44) and the three-stamp individ- ual-mortar mill, of the Joshua Hendy Co. (Fig. 45), are the best known representatives of this class. Two-stamp batteries (Fig. 46) are sold but seem to have little to commend them; they have Fig. 45. Three-stamp Mill Indi- vidual Mortars. Fig. 46. Two-stamp Triple Dis- charge Mill. neither the capacity of the unit-stamp, nor the amalgamating advantages of the five-stamp, mill. STAMP MILLING COSTS Stamp milling costs are made up of the following items: (1) power, (2) labor, and (3) repairs and supplies. (1) Power. This item is, of course, dependent upon the kind of prime-mover used. It may be a steam-engine, an oil or other * Recent reports of Nissen stamp performances in South Africa appear to justify this opinion. 84 STAMP MILLING AND CYANIDING internal combustion engine, or it may be a water-motor. Any of these may drive the mill direct or may serve to operate" an electric generator. The cost per horse-power per annum will vary with electric or steam power from $40 under unusually favorable cir- cumstances to as much as $150 in small plants using expensive fuel. Take as an example a 1050-lb. stamp dropping 6 in., 100 times per minute. This means a consumption of 2 h-p. (see Fig. 35, page 50). Assuming a stamp-duty of 3 tons we get 0.66 h-p. per ton per 24 hours. Figuring 300 working days to the year and $60 per annum as a good average, our power cost is 20 cents per h-p. per day or 13| cents per ton. Similar calculations will enable the power cost to be readily determined for any given data. (2) Labor is not so easily calculated since it is often difficult to segregate the service rendered in different parts of the plant. Taking a 60-stamp mill, one amalgamator, and half of the time of one helper per shift (the rest of the helper's time being devoted to the rock-breaker, etc.) with half the time of the mill foreman will cover the actual stamp mill labor. If, as is common, 8-hour shifts are used, the cost is, of course, more than where two shifts only are necessary. 12-hr. Shifts 8-hr. Shifts I Foreman @ $4.00 $2.00 $2.00 1 Amalgamator per shift @ $3.50 7 . 00 10 . 50 i Helper per shift @ $2.75 2.75 4.12i $11.75 $16.62i With our stamp duty as before this gives 65 cents for labor where two shifts are employed or 9 J cents with three shifts. As the size of the mill decreases the cost for labor will of necessity in- crease. On the other hand, increasing the size of the plant does not decrease the labor cost but rather tends to increase it until another point of maximum economy is reached. The lowest labor cost for milling is probably that of the Alaska-Treadwell Co., 2.9 cents per ton. (3) Repairs and Supplies. Wear and tear on the stamp parts, lubricants, water, and quicksilver are the important items under this head. Shoes and dies — the parts subjected to abrasion — are, of course, the heaviest items of expense. Rickard,* writing fifteen years ago, summarizing practice in Colorado, California, and * Stamp Milling of Gold Ores, 1st Ed., pages 206-209. VARIATIONS IN PRACTICE 85 Australia, gives the wear of the shoes as from 0.24 to 1.33 lb. per ton of ore crushed; of the dies from 0.19 to 0.5 lb. per ton. The costs correspondingly range from 2.02 to 7.64 cents for shoes, and from 0.7 to 5.5 cents for dies. The combined cost for both shoes and dies he gives as ranging roughly from 4 to 13 cents per ton. The minimum cost for dies in the examples cited by Rickard occur with wrought-iron, chrome-steel giving the lowest cost for shoes. The Alaska-Treadwell mills, using Koppel-steel shoes and locally- made cast-iron dies, reports wear per ton as 0.27 and 0.16 lb. respectively. The cost of material for shoes and dies will vary from 3 cents per lb. for cast-iron, under exceptionally favorable cir- cumstances, to 6 or 7 cents for chrome, or other good quahty steel at an average western railroad point. Richards * gives as the aver- age cost for shoes and dies of various kinds in 14 mills, 5.03 cents per ton. This is probably high. The wear and tear in other parts of the stamp mill, of course, vary greatly with operating condi- tions. Including everything about the battery not otherwise specified, it will probably run from 2 to 5 cents per ton in a well- operated plant. Screen-cost will run from a maximum of 3 cents per ton, under the severe conditions of fine screen and low dis- charge, to as low as 0.15 cent (estimated screen-cost at Alaska- Treadwell mills), thus making the total for wear and tear on stamp parts average as follows: Shoes and dies 2 to 13 jS per ton Other stamp parts 2 to 5i per ton Screens 0.2 to 3 j« per ton 4.2 to 21 (i per ton The variation in the total would probably not be as great as this, since some of the factors will tend to balance one another. Lubricants, water, and quicksilver are hkely to be the most variable items in the operating cost. The first, however, is so small as to be insignificant. The water cost may vary from prac- tically nothing to as much as 10 cents per ton of ore in arid regions even when every precaution for saving and re-use is taken. Quick- silver consumption per ton of ore is also a variable factor but will average between 0.1 and 1 oz. per ton of ore, or from 0.3 to 3 cents per ton. * Ore Dressing, Vol. 1, page 206. 86 STAMP MILLING AND CYANIDING Summarizing the actual running expenses under the usual range of conditions, and omitting such items of general expense as super- intendence and lighting, depreciation and interest on the money invested in the plant, we have as follows: Cost in cents per ton milled Item Maximum Minimum Power 25 5 Labor 20 3 Stamp parts, shoes, dies, and screens 21 4^ Water 10 Quicksilver and lubricants 4 1 Totals 80 131 BIBLIOGRAPHY FOR VARIATIONS IN PRACTICE * Especially Desirable for Students' Use Gilpin County. Collins, G. E. Gilpin County, Colorado, Milling Practice. Bull. Colo. School of Mines, Vol. 5, p. 139; Min. & Sci. Press, Vol. 101, p. 366; Min. Science, Vol. 62, pp. 52, 79 (1910). Morse, W. S. Gilpin Co. Stamps in Arizona. Trans. A.I.M.E., Vol. 35, p. 130 (1905). Newell & Newell. Comparison of Fast and Slow-drop Batteries in Penn City Mill, Gilpin Co., Colo. Min. & Sci. Press, Vol. 74, p. 153 (1897). Paul, Almarin B. Comparison of Colo, and Calif. Systems of Stamp Milling. Min^. & Sci. Press, Vol. 68, p. 260 (1894). " Wascott." Comparison of Slow Drop and Rapid Drop Mills in Gilpin Co., Colo. Min. & Sci. Press, Vol. 74, p. 49 (1897). . Milling in Gilpin County, Colorado. Min. & Sci. Press, Vol. 91, p. 344 (1905). California. Chalmers, Alex. Stamp Mill Practice on the Mother Lode, f p. Min. & Sci. Press, Vol. 97, p. 785 (1908). DbKalb, C. California Stamp Mill. Min. & Sci. Press, Vol. 100, p. 736 (1910). Del Mar, Algernon. Stamp Milling in Northern California. Min. & Sci. Press, Vol. 92, p. 143 (1906). Preston, E. B. California Gold Mill Practices. Bull. No. 6, Calif. State Mining Bureau (1895). Storms, W. H. Milling Practice on the California Mother Lode. Min. Wld., Vol. 32, p. 3 (1910). S. Africa. * Caldecott, W. a. Development of Heavy Stamps. Reviewed in Min. Ind., Vol. XVIH, p. 370. Eng. & Min. Jour., Vol. 88, pp. 694, 1157 (1909); Min. Sci., Vol. 60, p. 272 (1909); Min. Wld., Vol. 31, p. 543 (1909); from Inst. M. & M., Bull. 59, and J. C. M. & M. Soc, S. A., Vol. 10, p. 108 (1909). VARIATIONS IN PRACTICE 87 * Denny, H. S. The Development of Heavy Gravitation Stamps. Eng. & Min. Jour., Vol. 88, p. 1157 (1909). Editorial. Stamp Mills as Coarse Crushers, i p. (Regarding " Stamp Mill Evolution" in S. African Min. Jour., Oct. 9, 1909.) Eng. & Min. Jour., Vol. 88, p. 1231 (1909). Gascoyne, Rowland. The Question of Stamps vs. Tube Mills on the Witwatersrand, f p. Min. and Eng. Wldi, Vol. 38, p. 1194 (1913). London Cokrespondbncb. Latest South African Stamp Mill Practice, i p. Eng. & Min. Jour., Vol. 90, p. 958 (1910). Roberts, F. C. Stamp-mill Practice in South Africa. Eng. & Min. Jour.; Vol. 78, p. 304 (1904). Roberts, F. C. Notes on Crushing of Metalliferous Ores in the Stamp Battery in Africa. Min. & Sci. Press, Vol. 90, pp. 10, 72, 91, 105, 119 (1905). * Roskelley, I. Rand Milling Practice and Construction, from J. C. M. & M. Soc, S. A., Feb., 1904; Eng. & Min. Jour., Vol. 77, p. 841 (1904). * ScHMiTT, C. O. Development of Gravity Stamps. (Inst. M. & M., Feb. 10, 1910), 5i pp. Min. & Min., Vol. 30, p. 625 (1910). . Troubles at City Deep Mill, 1 p. Eng. & Min. Jour., Vol. 93, p. 795 (1912). * . Changes in So. African Stamp Design, | col. Eng. & Min. Jour., Vol. 93, p. 1032 (1912). . The Gravity Stamp on the Witwatersrand, 2 col. Min. & Eng. Wld., Vol. 37, p. 675 (1812). , Australia. Boydell, H. C. Stamp Milling at Bendigo, Australia. Aust. Inst. Min. Eng., Vol. VIII, part II, p. 236; reviewed in Min. Ind., Vol. XI, p. 299. CHAPTER VI OTHER MILLS AND GRINDERS The other mills in use may be divided into: (1) Modified gravity-stamps. (2) Steamr-stanips. (3) Arrastras and pans. (4) Centrifugal and edge-runner mills. (5) Tvbe-mills and ball-mills. (i) MODIFIED GRAVITY-STAMPS From time to time attempts have been made to assist and in- crease the speed of the stamp-drop with the aid of coiled springs, air-chambers, or vacuum-chambers in connection with the stems. The main object has, of course, been to enable a greater number of blows per minute to be struck than is possible with the gravity stamp. The use of coiled springs has not been successful for mechanical reasons, the springs soon wearing out and losing their resilience. Acceleration with compressed air seems to promise better results and work along this line in South Africa is being carried on vigorously. The Morison stamp, which is driven by cranks in place of cams and is equipped with a hydro-pneumatic accelerating rig, was operated for several months in the Meyer and Charlton mill; S. A. With 1600-pound stanips dropping 135 times per minute a duty of over 9 tons per day was maintained-* The Holman pneumatic-stamp is also of this type. Another air- accelerated stamp weighing 1670 pounds, invented by H. C. Behr on the Rand, is said to have given 140 drops per minute and to be mechanically efficient.f (2) STEAM-STAMPS Michigan Steam-Stamps. It is not often that we find the use of a highly successful machine confined to one particular district, but the immense, single, steam-stamp, used almost to the exclus- * H. S. Denny, Eng. & Min. Jour., Vol. 88, pages 1157-58. t C. O. Schmitt, Min. & Min., Vol. 30, page 630. 88 OTHER MILLS AND GRINDERS 89 ion of other crushing machinery in the Michigan copper country IS seen nowhere else. These machines, one of which is shown in Fig. 47, consists of a mortar and stamp, the stem of the latter ter- P'lG. 47. Michigan Steam-Stamp. minating in a steam cylinder which serves to raise and lower the stamp. Richards,* comparing the California gravity stamp with the Michigan steam-stamp, gives the energy in foot-pounds of each * Ore Dressing, Vol. 1, page 132. 90 STAMP MILLING AND CYANIDING as 439 and 32,913 respectively. Each 'head,' as a stamp is called, crushes from 350 to 400 tons in 24 hours through a i^-in. screen. Steam-stamps were tried for crushing and amalgamating gold ores in the Black Hills, S. Dakota,* but for various reasons, many of which could have been remedied, they were a failure from the amalgamating viewpoint. In- side amalgamation was not pos- sible and facilities for outside amalgamation were not properly provided. Where coarse crush- ing is desired, without regard to amalgamation, the use of steam- stamps would give a compact plant. The power consumed per ton of ore crushed is practi- cally equal in steam and gravity mills. Small steam-stamps equiva- lent in size to the ordinary gravity stamp have been on the market for a number of years, but have not come into general use. The Tremain Steam-Stamp, shown in Fig. 48, is the best known and most used. It con- sists of a two-stamp battery with the stamps actuated by steam cylinders. The mortar is fitted with screens on the front and at each end. Inside amalgamation is provided for, but does not appear to have been used with much success. The number of drops ranges from 140 to 200 per minute according to the steam pressure. E. W. Sperry j found the mill a good amalgamator, with a capacity of from 10 to 19 tons per day for the two stamps, using about 12 * T. A. Rickard, Stamp Milling, page 97. t Trans. A.I.M.E., Vol. 26, page 545. Fig. 48. Tremain Steam-stamp Mill. OTHER MILLS AND GRINDERS 91 h-p. Repair costs were low. In Rhodesia, S. A., these mills are popular on account of their portability * and they appear to be easily kfept in repair. The fuel consumption is high, but in some localities this is of little consequence. (3) ARRASTRAS AND PANS The Arrastra. The forerunner of the grinding-pan was the arrasta (Fig. 49). This is probably the oldest milling device in America. When intelligently operated it is at least as efficient as .Sfee/ Pin Sfee/ Pin SECTION Stone Pavement 1 I HALF PLAN Fig. 49. Arrastra. a first-class stamp mill, so far as amalgamation is concerned. It is still valuable for prospecting and for the working of small de- posits of rich ore. The arrastra consists of a circular enclosure paved with stones; upon this pavement, heavy mullers, also of stone, are dragged by means of arms extended from the central spindle. The spindle is revolved either by animal or mechanical * C. E. Parsons, Min. & Sci. Press, Vol. 97, pages 386-89. 92 STAMP MILLING AND CYANIDING power. The pavement is composed of flat hard rocks about a foot thick, preferably set in cement, but as cement is seldom available in regions where arrastras are used, clay is generally substituted. A rim or wall of rock or wooden pickets is built around the outside of the ring, which is usually from 10 to 20 ft. in diameter. The mullers, from 2 to 8 in number, are as heavy as can conveniently be handled. They often weigh about 600 to 700 lb. and are set with their forward edges slightly raised in order to ride over the coarse grains in the ore. The charge of ore, usually from 1000 to 3000 lb., is placed in the arrastra-bed and is ground with a small amount of water for several hours. Mercury is then sprinkled over the entire charge. The exact dilution of pulp at this point is all-important as it must be sufficiently thin to work readily and yet thick enough to keep the mercury in suspension. The mill is again started, and is run until no more free gold is seen on panning. The pulp is then diluted and the muller is revolved rapidly to keep in sus- pension the worthless gangue matter, which is run out through plug-holes in the side, into a sluice-box, or over copper-plates to catch escaping amal- gam. Tlie great bulk of the amalgam is left behind with the con- centrate on the bed of the arrastra from which it is gathered up and cleaned by panning. The Grinding-Pan is the modern succes- sor of the arrastra, in which the stone pave- ment is replaced by a cast-iron pan, and the heavy stone mullers by shoes which gain their grinding action not by weight but by pressure of a screw feed (Fig. 50). These pans are much less used than formerly, when they were an important feature in the amal- Fio. 50. Grinding Pan. OTHER MILLS AND GRINDERS 93 gamating of silver ores. The grinding action was often omitted in this case, the mullers being used mainly to assist in agitation and amalgamation. In recent years the pan, as a fine-grinder preliminary to cyanide treatment, has been used extensively in Australia and good results are reported. In the United States and Mexico, however, it has met with less favor than the tube-mill. The figure shows the Australian type of pan known as the Wheeler, the drawing being that of a mill furnished to the Home- stake Company of S. Dakota by the Colorado Iron^Works. (4) CENTRIFUGAL AND EDGE-RUNNER MILLS The Huntington Mill is perhaps the strongest competitor the stamp mill ever had in its field of combined crushing and amalgam- Huntington Mill. ating. In this mill (Fig. 51) the crushing is done by the centri- fugal force of steel rollers or mullers operating on the inside of a steel die-ring. These rollers or mullers are hung on a spider and are free to revolve on their own axes as well as to rotate about the 94 STAMP MILLING AND CYANIDING main, central spindle. The die-ring is keyed with wooden wedges inside a cast-iron pan. The pan is surmounted by a Ught cast-iron housing with suitable screen and feed openijigs. In the center of the pan-bottom is a conical pillar for the reception and guid- ing of the spindle, which is rotated from below by a bevel-gear and belt-drive. As the spider, yoke, and muUers revolve, the latter are thrown out pendulum-like against the die-ring and crush the ore both by pressure and by impact. To aid the pressure of the muUers against the die-ring, the muUer spindles incline inward and the faces of the muUers are correspondingly beveled. The mill is made in several sizes, particulars of which are given in the accom- panying table: TABLE III Size of mill, nominal diameter Diam. of die ring Diam. of 1 muller Wt. of mill Capacity on i-ia. material Power required Speed ft. 31 5 6 6 (heavy) ft. in. 3 4 4 9 5 5i 5 5i in. 14j 161 19 19 lb. 7,000 15,000 25,500 44,600 tons 5 to 10 10 to 20 • 20 to 40 40 to 80 h.p. 5 to 10 10 to 12 12 to 20 15 to 30 .p.m. 70 55 55 When used as an amalgamator a large quantity (25 to 50 lb.) of mercury is charged into the mill, which is usually provided with a quicksilver-outlet in the pan-bottom. The Huntington is a good amalgamator as long as there are no derangements within the mill, but loosening of any of the parts, coarse pieces of rock, over- feeding or other irregularities are likely to result in the amalgam being swept through the screen. For crushing soft, clayey ores it is superior to the stamp. If hard ]ore is fed, it must be crushed to at least ^ in. diameter. The Huntington mill is efficient in its own field when intelligently looked after, but it requires much closer supervision than the stamp mill and is by no means fool- proof. For this reason it is losing popular favor. Huntingtons should be stopped a few minutes at the end of every shift, the interior of the mill rapidly but thoroughly inspected and bolts, mullers, and die-rings sounded with a hammer to detect looseness. If anything is wrong with one of the mullers, do not attempt to repair it in place, but lift it out with the chain-block and put a spare one in its place. In this way little time is lost, and the defec- tive muller can be repaired at leisure and to much better advan- tage than in the interior of the mill. In the case of a large plant OTHER MILLS AND GRINDERS 95 where a complete shutdown is out of the question an extra mill is provided so that the repair gang can go over the entire series of Huntingtons every day. The upkeep of these mills is higher than that of stamps; screen repairs are excessive and only punched-metal screens are suitable. In first cost Huntingtons are cheaper than stamps; they are also more readily erected and more easily moved from place to place. Edge-runner or Chilean Mills have greatly increased in popu- larity in recent years. In primitive times crude mills of this type were used to prepare the ore for the arrastra. At present they are used in some cases to replace stamps, but usually follow the stamps as regrinding machines. In principle, the 'Chile' mill, as it is popularly called, consists of two or more large steel rollers rotating about a central spindle and Fig. 52. High-speed Chilean Mill. rolling on a circular steel track. The discharge is by centrifugal force through peripheral screens similar to those in the Huntington mill. The middle of the tires does pure crushing; the edges do both crushing and grinding. Chilean mills may be separated into the high-speed and low-speed tj'pes. A typical high-speed mill (Fig. 52) will have from three to four rollers, 4 to 6 ft. in chameter by 8 in. face, making 2.5 to 35 rev. per min. The die or track will be from 5 to 7 ft. internal dia- 96 STAMP MILLING AND CYANIDING meter. The capacity of such a mill is from 25 to 75 tons per day, using 25 to 40 h. p. High-speed mills are used for regrinding in concentrating mills and to follow the stamps in some cyanide plants.* They are unsuited for inside amalgamation but may be advantageously followed by plate amalgamation. The best-known slow-speed machine of this type is the Lane Chilean mill (Fig. 53). C. C. Lane gives the following data of a successful mill of this kind in operation at Barron, Washington: Six runners, diameter 42 in., width at center 9 in., at edge 5 in. Weight of each runner or wheel 900 lb. Diameter of track out- side 10 ft., speed 6 to 8 rev. per min. Size of feed j in., size of Lane Slow-speed Chilean Mill. product 70 mesh, average capacity 40 tons per 24 hours, using 12 h. p. The pan above the wheels is loaded with stones or scrap-iron to give weight to assist the grinding. These slow- speed mills have given satisfaction as inside amalgamators, the action in this respect being not unlike that of the arrastra. The discharge in the slow-speed mill is by overflow through a coarse (10-mesh) screen, the size of product being regulated by the height of discharge and not by a change of screens. (5) TUBE-MILLS AND BALL-MILLS The Tube-Mill, long a popular machine in the cement industry, has, in recent years, become an important factor in the fine-grinding of ore preliminary to cyanide treatment. Mechanically, the tube-mill is extremely simple. It consists of a sheet-steel cylinder, from 3 to 6 ft. in diameter by 10 to 20 ft. * J. W. Hutchinson, Min. & Sci. Press, Vol. 102, pages 617 and 619. OTHER MILLS AND GRINDERS 97 long, set with its axis at a slight angle with the horizontal. This cylinder is given a suitable lining and after being half filled with hard pebbles, from f to 4 in. in diameter, is slowly revolved by suitable mechanism. Thick pulp (when, as is usually the case, wet crushing is employed) is fed into the upper end of the mill and Fig. 54. Trunnion-type Tube-Mill with Scoop Feed. Fig. 55. Tire-type Tube-Mill showing Spiral Feed. after being reduced to a fine state of division by the action of the pebbles is discharged at the lower end. The feeding is accom- plished either through a scoop communicating with a hollow trunnion (Fig. 54) or by a spiral feed on the principle of an Archi- medean screw, see Fig. 55. 98 STAMP MILLING AND CYANIDING Enlarged Section The proportion of water to solid is an important factor in tube- mill efficiency, and, up to a certain point, as the water in the pulp decreases the capacity of the mill increases rapidly. This point of 'critical dilution,' as it has been called, apparently varies slightly with different ores, but a pulp with from 35 to 45 per cent moisture seems to give the best results. To ensure the proper consistency, tube-mills are almost always fed from a classifier, which serves also to remove the material that is already crushed to the proper fineness. The chscharge is usually by means of a hollow trunnion, al- though in some mills a spiral similar to the feeding spiral is used. In this event, slots in the end of the mill communicating with the spiral allow the pulp to flow out while the pebbles are retained. The trunnion dis- charge has the effect of a classi- fier and heavy mineral grains are necessarily crushed finer than the grains of gangue before they are discharged. This would usually be a distinct advantage where the pulp is to be cyanided. No attempt is made to screen the tube-mill product; instead it is generally sent to a classifier and the sand product returned to the mill for regrinding. ^me ' •^■^ i \':t^ m 1 Fig. 56. El Oro Tube-mill Lining. For lining, cast-iron, cast-steel, and flint blocks have been used; preference is given to the fining of flint or ' silex, ' as it is called. The pebbles are frequently a variety of flint, found in Greenland, though where hard ores are found locally, their use would seem to be desirable for this purpose. An extremely ingenious device, known as the El Oro fining, has recently been placed on the market. It consists, see Fig. 56, of a series of ribbed plates secured to the inside of the mill; the projecting ribs form tapering channels into which the pebbles are forced and wedged into place by the action of the mill. As the pebbles wear they drop out of the slots and are Tube-mill 5 ft. diam. half full of pebbles, speed 30 rev. per min. Lin- ing 4i in. thick, peobles assumed as 3-in. spheres. For any pebble centrifugal force = —— \m = mass, V = velocity, r = radius) and gravi- tational force when resolved along the radius is opposed to centrifugal force and is equal to mg sin e. (The tan- gential component of gravity, mg cos 8, is overcome by the work done in revolving the mill and serves to keep the pebbles pressed together.) When =mg sine, Pebble Action in Tube-Mill. the pebble is no longer forced outward but is free to take the tangential push imparted to it by the wall of the mill and bjr the pebble following it; and is launched into space as a projectile with an initial velocity Vo equal to its rotational speed, and at an angle c = 90 — 9. (1) To find 0. mV = mg sin d, but V = (2 irmy, where r = radius and n = rev. per sec. Therefore sin $ = sin B = 0.308 r. (2) To find the parabola. a = -jp-Sin 2e, -T-T ' Directrix ^ g /3 = :^sitf £ A = TT^ cos^ e. 2? 4?*2„2 (? = 32.2, 7r2 = 9.9, re = I) and For each ball Fo = 2 vm, e = 90° - e. PARABOLAS FOR BALLS A TO E Ball Angle e sin 9 = 0.308 r Angle £ e = 90°-9 a = 7^1 sin 2 e ■ig ^=|^^in^. A = ^cos». A B C D E 38 32 27i 18' 52 58 62i 67i 72° 0.592 0.422 0.279 0.163 0.090 0.378 0.338 0.267 0.196 0.140 0.231 0.132 0.072 0.034 0.015 From an inspection of the figure it is evident that balls A, B and C will not be free to fall in their natural parabolic paths, owing to the crowding of the balls nearer the center. For example the ball E will rise to position E' and will crowd its predecessor which is on the way down, over to position E"; this in turn crowds D" and so on, with the result that A" occupies a position outside of its normal parabola. If we consider balls G and H, this crowding will be still more marked. The general result, therefore, is a rolling of tjie outer pebbles down a slope much flatter than the parabola and a crowding together of the pebbles on the interior of the mass. (99) 100 STAMP MILLING AND CYANIDING automatically replaced. This lining is cheaper and better than its next-best competitor the silex blocks, which are cut key-fashion and are cemented around the interior of the mill. The action of the tube-mill is somewhat as follows: In the rota- tion of the mill the pebbles next to the shell, see Fig. 57, cling to the side, the height to which they rise being regulated by the speed of the mill. As long as the centrifugal force is greater than the gravity component, these pebbles will continue to revolve with the walls of the tube-mill until a point is reached — indicated by the angle d in the figure — where these pebbles leave the wall and fall in a parabolic path, striking and rolling over the other pebbles below and crushing, both by impact and by attrition. Each suc- ceeding layer of pebbles nearer the center of rotation has less centrifugal force and does not rise as high. The pulp fed into the mill is also carried up as a coating on the pebbles, and by the con- stant rubbing and striking of the pebbles against each other and against the lining is reduced to an extremely fine state of division. From the figure, however, it is evident that impact is a less im- portant factor in the work of the mill than would at first be sup- posed. If the speed of a tube-mill is increased to a point where the entire mass of pebbles distributes itself evenly about the walls, i.e., where the centrifugal force throughout the mill ex- ceeds the component of gravity, crushing ceases, and the power- consumption of the mill drops to almost nothing. Table IV shows the performance of the tube-mill in various cyanide plants. The Hardinge * Pebble-Mill differs from the foregoing in that the cylinder is replaced by two cones, placed base to base, with a short cylinder between, see Fig. 58. It is claimed for this mill, since the pebbles range themselves in decreasing size from the maxi- mum mill-diameter to the minimum mill-diameter, that the size of the pebbles, and hence their crushing effect, is in proportion to the size of the particles to be crushed in the various parts of the mill. In other words, the coarse particles are crushed by the large pebbles and the fine particles are crushed by the small pebbles. While ' the machine has not been tested sufficiently in competition with the cylindrical tube to allow of any decided comparison, it seems to promise well for all but extremely fine grinding. Tube-mills are not usually considered as amalgamating ma- * Trans. A.I.M.E., Vol. 39, pages 336-341. OTHER MILLS AND GRINDERS 101 *" E2 72!5SlS*2£3*iP So i>. o» os as •* cm ^ C« U3 t« Ol C3 U3 (N us C« t^ to CO l> ^ «0 eC US fiai|iii||||||||||||||| oo goo o -ioc«tf-t- o e^T^to ^i«d ■*34»43 ;g +3'* -. -, ,«)M»c>iM -CN] O40DC4 XXX X XXXXXXXXXXXXXxXiS n XXX ^lOtO iO -^ ■« '« «S lO U3 U3 -^ U3 '^ U3 >- !>• r^ (D CQtOCOCO hQ """"M«Mf . . . ^ " a a p. bc S) Si'= '-' ^ 'H ooo _r_r^ S S " ^^OOO Pi Oi Q> ■Pop o'^"-' - a p.a >t :»*;>>>_■_;_ , oJ - - ^ooogooo c S ffi EB SSSSg StOOOMCQ.J • , . S S £ ^^ • . . ^3 (D ^i^is:oo 0) V d) I ] Cb p. p,0) g^ >goOOoo-o6QO- . SsSf^ ^ aSa.S.S.SS ««" .a a a awSB . i(Meo-Oi- S >3 e d SS$ S Pi O, O. rt p O " p; o s ^ rtt -ii u ri 1 8 I J s 102 STAMP MILLING AND CYANIDING chines, but recently several metallurgists * have claimed an in- creased extraction, due to feeding quicksilver into their tube-mills. Ball-Mills are in principle similar to, but not identical with, tube-mills. Forged-steel balls and manganese-steel plates are Compdj"&tive peripKer&ll speeds at different zones of mi 1 1 500 I per mm o per mm. 20O' per n\\i\. pebble crushir\g '^4" particle =M36.000 Comparative relatiorv] of sizes of crushing mediomsto particle being crushed 1:4- division pebble crushing Vjg" particle =1:16384 ■ 3" pebble crushing V4." particle =1:896 Fig. 58. Hardinge Conical Pebblo-Mill. substituted for pebbles and silex "linings. The action within the mill is also to some extent different, in that the balls are compara- tively large, few in number, and do not rise as iiigh as the pebbles in the tube-mill. The ball-mills are usually larger in diameter and shorter than the tube-mills and do not revolve as rapidly. They are generally used for dry-crushing. Discharge is provided for by slots between the overlapping edges of the lining-plates. These slots communicate with an annular space around the mill, which is covered with two layers of screen, a coarse screen to take the heavy wear, and a fine screen to limit the mesh of the product, see Fig. .59. The oversize is returned to the mill in the course of its revolution. Ball-mills have never been popular in the United States, but in Australia they have done good service as grinders following coarse rock-breakers. The advantages of the ball-mill, as summarized by Eissler f in 189.5, still seem to hold good. They are: * Min. & Soi. Prosa, Vol. 100, pa(;c 008. t The Metallurgy of Gold, 4th Ed., page 148a. OTHER MILLS AND GRINDERS 103 (1) "Comparatively large-sized pieces of ore, the size of a double-fist, can be fed into it." (2) "It requires little or no supervision and very small horse-power." (3) "The wear and tear of the mill ... is relatively very small for the work done by it." (4) "The internal parts of the mill are always easily got at." (5) "It crushes very regularly to any mesh of sieve required and does not make too many slimes." (The last statement is less cogent to-day than in 1895.) To this" list might be added, that the moment the ore is crushed Fig. 59. AUis-Chalmers Ball-Mill. fine enough, it must pass out of the mill owing to the efficiency and large area of the screen-surface. It is strange that a machine apparently so efficient should not be in more general use, but American manufacturers are beginning to invade the ball-mill field, which heretofore has been almost entirely in the hands of the German iron-works, and several promin- ent metallurgists are projecting plants involving the employment of these evidently efiicient comminutors. , 104 STAMP MILLING AND CYANIDING The data for the following table are taken from AustraHan practice, mainly as outlined in an excellent article on 'Ball-mill Practice' by M. W. von Bernewitz.* TABLE V 53 6^ n Character of feed Character of product No. 5 No. 5 No. 5 No. 8 No. 8 No. 8 2350 2800 4400 4480 4480 33 40 100 95-100 80-90 0.5 0.32 0.47 0.65 0.47 0.64 (Fairly soft, calcite and ( quartz 75%, 2-iii. ring. . "Hard schistose 3-in. feed" "Hard 60% SiOj, 3-in. I feed." S Schistose, 3-in. feed. Schistose, 3-in. feed. ("Very hard cherty, 3-in. ] feed." 24%-|- 40 mesh r46%-200 mesh 143% -150 mesh 55%- 150 mesh 54% -150 mesh 55% -150 mesh 1%-|- 30 mesh 52% -150 mesh Wet crushing No. 5 No. 5 2200 2400 25 30 93-100 (1) "Hard dense quartz" ( 23%+ 30 mesh 1 25% -150 mesh ( 10%-|- 40 mesh 158% -150 mesh All mills are of Krupp manufacture. No. 5 is 89 by 46 in., is driven at 25 rev. per min., and has 70 sq. ft. screen area. No. 8 is 106 by 54 in., is driven at 24 rev. per min., and has 100 sq. ft. screen area. (I) Double the wear when dry-crushing. BIBLIOGRAPHY FOR OTHER MILLS AND GRINDERS General. * Especially Desirable for Students' Use Hanson, Hbnry. The Development of Fine Grinding in Connection with Gold Ore Treatment, 1 p. Mex. Min. Jour., April, 1912, p. 18; from Trans. Can. Min. Inst. (1912). Lamb, Mark R. Crushing Machines for Cyanide Plants, 5 pp. Dis- cussion ibid., p. 913; Trans. A.I.M.E., Vol. 41, p. 672 (1910). Preston, E. B. California Gold Mill Practices, pp. 58-64. Bull. No. 6, Calif. State Mining Bureau. San Francisco (1895). Sperrt, Edwin a. Classification and Comparison of Crushing and Grind- ing Machines. West. Chem. & Met., Vol. IV, p. 192 (1908). Webber, Morton. Dry Crushing and Direct-cyaniding, 1| pp. Mex. Min. Jour., Vol. 13, p. 25, No. 1 (.1911). * Min. & Sci. Press, Vol. 103, page 68. OTHER MILLS AND GRINDERS 105 Modified Gravity Stamps. Denny, H. S. The Morison Stamp Operated in S. Africa. Eiig. & Min. Jour., Vol. 88, pp. 1157-58 (1909). * MuNBOE, Henry S. Efficiency of Gravity and Other Stamps. Trans. A.I.M.E., Vol. 9, p. 84 (1880). . "Comparative Test of Pneumatic and Gravity Stamps." Eng. & Min. Jour., Vol. 89, p. 809 (1910). . Data on Holman Pneumatic Stamp, J col. Min. & Sci. Press, Vol. 103, p. 320 (1911). Steam Stamps. GooDALE, C. W. Use of Steam Stamps on Butte Ores. Trans. A.I. M.E., Vol. 26, p. 608 (1896). Parsons, Cyril E. Tremain Steam Stamps, 3| pp. Min. & Sci. Press, Vol. 97, p. 386 (1908). * Sperry, E. a. Amalgamation in Tremain Steam Stamp Mill. Trans. A.I.M.E., Vol. 26, p. 645 (1896). . Steam Stamps on the Rand. Eng. & Min. Jour., Vol. 89, p. 305 (1910). Arrastras and Pans. * VON Bernewitz, M. W. Grinding Pans at Kalgoorlie, 2| pp., illus. Min. & Sci. Press, Vol. 106, p. 734 (1913). * Brett, H. T. Use of Pans for Regrinding Raw Sands. Min. & Sci. Press, Vol. 93, p. 745 (1906). Clarke, Robert. Pans vs. Tube-mills, J p. Min. & Sci. Press, Vol. 94, p. 430 (1907). James, Alfred. Crushing and Grinding Practice at Kalgoorlie, 2 p. Min. & Sci. Press, Vol. 93, p. 109 (1906). KoHNCKE, Ilodobo. Home Made Arrastra in Central America, 1 p. Min. & Sci. Press, Vol. 97, p. 185 (1908). Mitchell, D. P. Pans vs. Tubes, J p. Min. & Sci. Press, Vol. 93, p. 136 (1906). Simpson, W. E. Grinding Machines at Kalgoorlie. Eng. & Min. Jour., Vol. 76, p. 733 (1903). * Sohnlein, M. G. F. Economical Fine Grinding in Pans, 2f pp., illus. Eng. & Min. Jour., Vol. 96, p. 581 (1913). Walker, Edward. The Cobbe-Middleton Pan, | p. Pac. Min., Vol. 15, p. 218 (1909). * Williams, G. W. Tube Mill and Pan Costs. Eng. & Min. Jour., Vol. 85, p. 345 (1908). . The Cobbe-Middleton Grinding Pan. Min. Mag., Vol. I, p. 213 (1909). Centrifugal and Edge-runner Mills. * Bayldon, H. C. Chilean Mills in Russia, 3 p. Min. & Min., Vol. 32, p. 177; abst. from Bull. 75, Inst. M. & M. (1911). von Bernewitz, M. W. Huntington Mill Practice at Kalgoorlie, 4 pp. Min. & Sci. Press, Vol. 105, p. 618 (1912). 106 STAMP MILLING AND CYAN I DING Carter, E. E. Amalgamation in Slow Speed Chilean Mills, 1 p. Min. & Sci. Press, Vol. 102, p. 370 (1911). * Carter, E. E. Slow Speed Milling (Chilean), 2 pp. Min. & Sci. Press, Vol. 106, p. 863 (1913). * Empson, J. B. The Slow Speed Chilean Mill, 3 pp. Eng. & Min. Jour., Vol. 93, p. 259; abst. from Mex. Inst. Min. & Met. (1912). * Gahl, Rudolf. Comparative Grinding Experiments with a Chilean MiU and a High-speed Roll at the Detroit Copper Company's Concentrator, Morenci, Ariz., 1 p. Pac. Min., Vol. 19, p. 31 (1911). Hutchinson, J. W. Chilean Mills at Goldfield Cons. Min. & Sci. Press, Vol. 102, pp. 617, 619 (1911). Lamb, M. R. The Chile Mill, 1 p. Eng. & Min. Jour., Vol. 87, p. 1182 (1909). Lane, C. C. The Development of Chilean Mills, f p. Min. Rep., Vol. 65, p. 515 (1907). * McLaren, Alexander. Crushing with Slow Chilean Mills, If pp. Eng. & Min. Jour., Vol. 92, p. 305 (1911). * Megraw, Herbert A. Some of the Characteristics of Chilean Mills, li pp. Eng. & Min. Jour., Vol. 90, p. 967 (1910). Rice, Claude T. Huntington Mills and Their Operation, 1 p., illus. Eng. & Min. Jour., Vol. 96, p. 215 (1913). Sackett, B. L. Chilean Milling in Peru, 2f pp. Eng. & Min. Jour., Vol. 92, p. 943 (1911). * Semple, Clarence Carlton. Notes on Huntington Mills in Nicara- gua, 12 pp. Trans. A.I.M.E., Vol. 42, p. 799 (1911). Simmons, Jesse. Crushing in Slow-speed Chile Mills in S. Dak., 2 pp. Min. and Eng. Wld., Vol. 37, p. 813 (1912).. Stewart, J. A. Conclusive Test of Lane Mill, IJ p. Min. Rep., Vol. 55, p. 543 (1907). Storms, W. H. How to BuUd an Arrastra, 2 pp. Eng. & Min. Jour., Vol. 91, p. 1053 (1911). Tats, E. A. H. The Bryan (Chile) Mill Compared with the Stamp- Battery. Trans. A.I.M.E., Vol. 29, pp. 776 and 1054 (1899); discussion ibid.. Vol. 31, p. 999. Comparative Cost of Milling with Stamps and Huntingtons. Min. & Sci. Press, Vol. 53, p. 86 (1886). Tube-Mills. Allen, A. W. Pebble Efficiency in Tube-milling. Min, & Sci. Press, Vol. 104, p. 19 (1912). * Ball, H. Standish. The Economics of Tube-milling. Min. & Sci. Press, Vol. 103, p. 383; abs. from BuU. Inst. M. & M., 3 pp (1911). * Banks, E. G. Grinding in Tube Mills, 4 pp. Trans. A.I.M.E., Vol. 38, p. 196 (1907); abstr. in Min. & Min., Vol. 27, p. 492 (1907). Bell, Jno. W. Critical Moisture in Tube-mill Peed. Min. Mag., Vol. IV, p. 263 (1911); Min. Mag., Vol. V, p. 223 (1911). * BosQui, F. L. Recent Improvements in the Cyanide Process: Early Methods — Tube Mills — Filter Presses — Vacuum Filters. Paper read OTHER MILLS AND GRINDERS 107 at Denver, 1906 Meeting American Mining Congress, 1 p. Min. & Min., Vol. 28, p. 298 (1907). Bradley, WalteS W. Tube-Mill Lining, f p. Min. & Sci. Press, Vol. 94, p. 17 (1907). * Brett, H. I. Tube-Mills and Grinding Pans in W. Australia, 2 pp. Min. & Sci. Press, Vol. 93, p. 744 (1906). * Brown, Frederick C. The Importance of Fine-grinding in the Cyanide Treatment of Gold and Silver Ores, 9 pp. Trans. A.I.M.E., Vol. 36, p. 654 (1906). * Brown, F. C. Tube-Mill Practice, 2 pp. Min. & Sci. Press, Vol. 104, p. 206 (1912). * Burt, E. Details of El Oro Tube-Mills. (Complete data.) Min. Wld., Vol. 27, P..699 (1907). * Caetani (G.) & Bukt (E). Fine Grinding by Tube-Mills at El Oro, 10 pp. Trans. A.I.M.E., Vol. 37, p. 3; abstr. Min. & Min., Vol. 26, p. 511 (1906). Caldecott, W. a. Weight of Tube-Mill Pebble Loads (Table). J. C. M. & M. Soc, So. A., Vol. 13, p. 363 (1913). Del Mar, A. Efficiency of Tube-MiUs. Min. Wld., Vol. 32, p. 371 (1910). Del Mar, Algernon. Conical Tube-Mill Results, 2 pp. Min. & Sci. Press, Vol. 101, p. 614 (1910). Dowling, Walfobd R. Critical Moisture in Tube-mill Feed, i p. Min. Mag., Vol. IV, p. 439 (1911). Dhuckeb, a. E. Tube-Milling in Korea, 1 p. Min. & Sci. Press, Vol. 93, p. 348 (1906). Drtjcker, a. E. Tube-Mill Lining, li pp. Min. & Sci. Press, Vol. 93, p. 594 (1906). Editorial. " Tube-Milling," i p. Eng. & Min. Jour., Vol. 93, p. 677 (1912). * Fischer, Hermann. The Mechanics of Tube-mill Operation. Eng. & Min. Jour., Vol. 78, p. 791; abstr. iiom Zeitsch. d. Ver. Devtsch. Ingen., Mar., 1904. * Fox, H. W. Tube Mills (General), 4 pp. Min. & Min. Vol. 28, p. 537 (1908). Fulton, Charles H. El Oro or Brown Tube-MUl Lining. Min. Ind., Vol. 16, p. 546. Groch, N. C. & Nagel, F. J. Feeder for a Tube-mill, 1 p. Min. & Sci. Press, Vol. 94, p. 541 (1907). Hardinge, H. W. (with Editor's Note). Tube Mill Lining, 1 p. Min. & Sci. Press, Vol. 96, p. 418 (1908). * Hardinge, W. H. Pebble-mill Amalgamation, 1 p. Min. & Sci. Press, Vol. 100, p. 608 (1910). Hardinge, H. W. The Conical Pebble-mill, 6 pp. Trans. A.I.M.E., Vol. 39, p. 336 (1908); see also Min. Wld., Vol. 27, p. 1005, IJ PP. (1907); Min. & Sci. Press, Vol. 96, p. 223, 1| pp. (1908); Eng. & Min. Jour., Vol. 89, p. 221, U pp. (1910);. Min. & Sci. Press, Vol. 101, p. 478, 2J pp. (1910); Eng. & Min. Joum., Vol. 90, p. 1057, If pp. (1910). 108 STAMP MILLING AND CYANIDING * Kennedy, J. Notes on Tube-mills, | p. (J. C. M. & M. Soc, S. A., Aug., 1907.) Min. & Sci. Press, Vol. 95, p. 555 (1907). Kidder, S. J. Regrindiug at the Pittsburg Silver Peak Mfll, 2 pp. Min. and Sci. Press, Vol. 106, p. 306 (1913). Lamb, M. R. Tube Mill Practice in American Cyaniding. Mines & Methods, Vol. 1, p. 74 (1909). McMiKEN, S. D. Tube Mill Lining, J p. Min. & Sci. Press, Vol. 93, p. 534 (1906). * Mbhton, a. M. Selection and Operation of Tube MUls, 3 pp., iUus. Min. & Engr. Wld., Vol. 38, p. 1129 (1913). * Neal, Walter. Experiment in Critical Moisture for Tube-mill Feed. Min. & Sci. Press, Vol. 100, p. 483 (1910). * QtTARTANO, A. G. Use of Quartz in Tube Mills, IJ pp. Eng. & Min. Jour., Vol. 91; p. 1017 (1911). * Qttartang, a. Critical Moisture in Tube-miU Feed, 1 p. Min. Mag., Vol. V, p. 223 (1911). RoTHERHAM, G. H. A New Tube Mill Lining. Min. Wld., Vol. 32, p. 846 (1909). * Sherrod, V. B. Grinding Tests at Pachuca, 3i pp. Min. & Sci. Press, Vol. 100, p. 357 (1910). * Tod, Stuart. " Comparison Conical and Cylindrical Tube-mill Results, i p. Min. & Sci. Press, Vol. 101, p. 243 (1910). * Truscott, S. J. Economics of Tube Milling, 2 pp. Min. & Sci. Press, Vol. 104, p. 533; abs. from BuU. Inst. M. & M. (1912). Van Law, C. W. Tube MUls at Guanajuato, 4 p. Min. & Sci. Press, Vol. 95, p. 205 (1907). * Warwick, A. W. The Influence of Fine Grinding on the Metallurgy of the Precious Metals. West. Chem. & Met., Vol. 1, p. 37 (1905). West, H. E. Tube-mill Lining, | p. Min. & Sci. Press, Vol. 96, p. 418 (1908). West, H. E. Power for Tube-miUing, IJ pp. Eng. & Min. Jour., Vol. 90, p. 1243 (1910). * Williams, G. W. Tube Mill Capacities. Eng. & Min. Jour., Vol. 85, p. 345 (1908). * Wilson, E. B. Tube-milling. Min. & Min., Vol. 29, p. 8 (1908). . Smooth Lining for Tube-mills. Eng. & Min. Jour., Vol. 89, p. 905 (1910). . The Osborn Tube-mill Lining (a modified El Oro type). Eng. & Min. Jour., Vol. 90, p. 250 (1910). . The Economics of Tube Mills. The Capital Expenditure and Tonnage Aspects, J p. (Abstracted from Jl. S. A. Mines, Oct. 27, 1906.) Min. &'Min., Vol. 28, p. 297 (1907). . Komata Tube Mill Liner, 2 columns. Eng. and Min. Jour., Vol. 94, p. 1135 (1912). Ball-Mills. * VON Bernewitz, M. W. Ball-mill Practice at Kalgoorlie, 4 J pp. Min. & Sci. Press, Vol. 103, p. 68 (1911). OTHER MILLS AND GRINDERS 109 * VON Bbrnewitz, M. W. Ball Mill Practice at Kalgoorlie. Min. Mag., Vol. V, p. 139; Min. Mag., Vol. VI, p. 59. * . The Allis-Chalmers Ball Mill, 1 p. Min. & Sci. Press, Vol. 94, p. 317 (1907). * . The Giesecke Ball-tube Mill. Pac. Min., Vol. 19, p. 40 (1911). CHAPTER VII COMPARISONS OF VARIOUS MILLS A discussion of this kind would be somewhat pointless without some comparison of the various crushing devices mentioned. It is obvious that the most efficient crushing machine is that which produces the desired result with the least expenditure of energy for operation, and of time and money for repairs and renewals. Furthermore, comparisons can only be made between pieces of apparatus that cover in some part at least the same or similar territory. It is scarcely reasonable to compare the work of a gyratory crusher, reducing mine-run ore to 3-in. size, with that of a tube-mill, reducing 20-mesh material to 200-mesh. Between the machines discussed in the last two chapters, however, com- parison is legitimate and, as has been said, necessary. Three points of relative merit may be established for purposes of discussion: (1) Reduction in size effected per unit of power. (2) Suitability of product for purposes in hand. (3) Wear and tear on various parts, and loss of time incident thereto. (1) Reduction in Size Effected per Unit of Power — this is commonly referred to as 'crushing efficiency.' An adequate Sis- cussion of this extremely important question cannot be here at- tempted. Certain work done during the last few years in connection with the efficiency of pre-cyanide crushing * has placed in our hands a simple and apparently logical basis for rough comparisons. Stadtler's hypothesis, briefly stated, is, that in crushing an ore, the area of fracture, multiplied by a coefficient determining the resistance, represents the force required to cause the fracture. * R. W. Chapman, Prod. Aust. Inst. Min. Eng., Oct., 1909; aba. Min. Mag., Vol. 2, page 64. H. Stadtler ' Grading Analyses,' Inst. Min. & Met., May, 1910; J. C. M. & M. See. S. A., May, 1910; abs. Min. & Min., Vol. 31', page 344. 110 , COMPARISONS OF VARIOUS MILLS 111 In order to perform mechanical work this force has to move through a distance represented by the deformation which the body can stand before reaching the breaking point. It is in this con- nection, immaterial that this distance of deformation — -within the limits of elasticity and plasticity — is, for non-homogeneous bodies, subject to variations, because for highly elastic and unplastic bodies, as quartz, glass, etc., these variations are too insignifi- cant to be considered. In addition they are by the nature of our crushing appliances averaged to such an extent, that these averages are as good as exactly defined figures, and dealing with relative values only, we do not need to know the exact extent of this deformation. It is sufficient for our purpose that this factor is a constant function of the diameter of the particles to be crushed. The mechanical work done is represented by the product of the force by the distance; but, as in a regular scale of reduction by volume, in which r = J, the diameters of the particles decrease at the same ratio as the area of fracture increases; the product, or the mechanical ^York required for reducing the volume (or weight) of the unit from one grade to the next following, is a constant for each grade, called the crushing or energy unit (E. U.). The same conclusion is also arrived at by the application of Kick's Law, which reads : " The energy required for producing analogous changes of configuration of geometrically similar bodies of equal technological state, varies as the volumes or weights of these bodies." The volumes of the particles decrease from grade to grade, at the same ratio as the number of the particles increases, said par- ticles constituting in their total the volume of the unity; and the product of the volume into the number of the particles of that grade is, therefore, constant for each grade. Since, in conformity to the above law, the amount of energy absorbed is proportional to the volume of the body to be crushed, it follows again also that the total energy required for reducing the weight of the unit is constant for each grade. The ordinal numbers of any arithmetical progression given to these grades represent consequently the relative values of the energy which has to be spent upon producing the respective grade from the initial unit; i.e., the mechanical value of the grade in energy units (E. U.). 112 STAMP MILLING AND CYANIDING For obtaining the mechanical value of mixed sands we need only to multiply the percentages of the gradings by the number of the energy units of the respective grade and add the products. This possibility of having the grading of pulps condensed and expressed in one representative figure proves to be of great value. The useful work done per unit by any crushing machine is de- termined by the difference between the mechanical values of the samples taken at the inlet, and at the discharge of the machine, and for obtaining the total work done this difference has to be multiplied by the tonnage handled. The relative mechanical efficiency is the value obtained by dividing the total work done by the unit of energy (for instance horse-power) : Relative mechanical efficiency _ Tonnage X work done per unit in E. U. Unit of energy (h. p.). The appended table shows the data compiled by Mr. Stadtler for his work and is self-explanatory. The right-hand side of the table is of value in other connections also, in giving the data of the now generally adopted 'I.M.M. screens.' COMPARISONS OF VARIOUS MILLS 113 TABLE VI Standard Grades and Screens Mines Trials Committee -(M.T.C.) standard grades Institution of Mining and Metallurgy. Standard laboratory screens Ordi- nal num- ber or mecli. value Mesh aper- ture (=side3 of theoret. cubes) Volume (or weight) of theoret. cubes Area of fracture from unit Commercial denomina- tion of screens Ordin. number or mech. value of grade No. of mesh Mesh aper- ture Dia. of wire Area dis- ch'ge Approx. num- ber of meshes E.U. 30 in. .00098 mm, .02480 cu. in. .000000 cu. mm. .00002 sg. in. 3072.0 p lin.in. P:„=0- 1 -200 grade 1 incl. washed slimes E 30.0 29.0 28.0 27.0 26.0 .U. 26.02 lin. in. 200 in. .0025 .0033 .0042 .005 .0065 .0062 in. .0025 .0033 .0041 % 26.0 24.50 25.40 25.0 24.50 24.60 24.70 24.80 25.0 29 .00123 .00155 .03125 .03937 .000001 .000003 .00003 .00006 2438.1 1935.4 28 27 .00195 .00246 .04961 .06250 .000007 .000016 .00012 .00024 1536.0 1219.1 26 200 40000 25 .00310 .00391 .07875 .09922 .000030 .000069 .00049 .00098 967.68 768.0 160 130 22500 17000 25.0 24.0 24.81 23.77 23.01 160 120 100 90 80 24 23 .00492 .00620 .1250 .15760 .000119 ,000238 .00196 .00391 609.52 483.84 110 90 12000 8000 23.0 22.0 .006 .0065 .0063 .0071 .0083 .01 22 21 22.60 22.08 .00781 .00984 .19844 .250 .000477 .000954 .00781 .01662 384.0 304.76 75 60 5500 3500 21.0 20.0 21.49 TO 60 50 .0071 .0083 .01 20.81 20.0 20 19 .01240 .01562 .3160 .39688 .001907 ,003815 .03126 .06250 241.92 192.0 60 40 2500 2000 19.0 18.0 19.03 17.80 16.99 40 30 26 20 .0125 .0166 .020 .025 .0125 .0167 .020 .025 25.0 24.8 25.0 25.0 24.92 24.92 18 17 .01969 .0248 .50 .630 ,007629 ,015259 .1260 .260 152.38 120.96 35 30 1200 900 17.0 16.0 16 16.02 IS .03126 .03937 .7038 1.0 .030617 .061035 .50 1.0 96.0 76.19 25 20 . 600 400 15.0 14.0 15.06 13.81 13.01 16 12 .0312 .0416 .0312 .0417 u 13 .04961 .06250 1.260 1.6875 .122070 .244140 2.0001 4.0002 60.480 48.0 18 14 300 200 13.0 12.0 10 8 .05 .062 .05 .063 25.0 24.60 12 12.08 11 .07875 .09923 2.0 2.620 .488281 .976562 8.0003 16.000 38.102 30.240 11 8 120 65 11.0 10.0 10.0 6 .10 .10 25.0 10 9 .1250 .15750 3.1750 4.0003 1.9530 3.9060 32.001 64.003 24.0 19.051 6 4 35 15 9.0 8.0 8 7 .19850 .250 5.040 6.350 7.8120 16.626 128.02 266.03 15.120 12.0 3.6 Ap'rt're i" 12 9 7.0 6.0 6 5 .3150 .39690 8.0005 10.080 31.250 62.50 612.06 1024.1 9.526 7.560 A" r 6 4 6.0 4.0 4 3 .50 .630 12.70 16.0 125.0 250.0 2048.3 4096. S 6.0 4.763 i" 1" 3 2 3.0 2.0 a 1 .79370 1.00 20.160 25.4 600.0 1000.0 8193.0 16386.0 3.780 3.0 i" 1 inch. 1 1.0 0.0 g a R = 1 ).7937 R= i 0.5 1.2599 The M.T.C. grades are tion of a successive re weight) of the screen based on the assump- duction in volume (or products by one-half Geometrical pr ogression fronr grade to g rade. 1 114 STAMP MILLING AND CYANIDING As examples of the application of this crushing efficiency calcul- ation we have: (1) A stamp mill, with 1150-lb. stamps consumes 2.6 h-p. per stamp with a duty of 9 tons per 24 hours. Battery screen 8-mesh, aperture 0.097 in. TABLE VII Feed Discharge pulp Denomi- nation of screen Mechani- cal value ot mean grade Grading analyses Mechanical value ot discharge Number E. U. Per cent E.U. + 12 13 Subject to variations, but 19.9 2.59 + 20 15 by practical experience it 12.1 1.82 + 30 17 has been ascertained that 9.7 1.65 + 50 19 the grade (1-inoh screen) 11.5 2.19 + 80 21 represents a fair average 10.9 2.29 +120 23 size. 2.6 .50 +200 25 4.2 1.05 -200 28 29.1 8.15 100% 20.34 Less Mech. value of feed 0.0 Total wo rk done p Voik done by stamp per unit (say 1 ton) er stamp in 24 hours = 9 tonsX20.34 E.U. 20.34 = 183.06 E.U. . Relative mechani , „ . , 9tonsX20.34E.U. cai einciency per n-p. = s~st; ^ . n~p. = 70.40% COMPARISONS OF VARIOUS MILLS 115 (2) a; 22 by 5|-ft. tube-mill, 30 rev. per min., 100 h-p. Feed, 290 tons pulp + 6.75 tons coarse ore of 30 E. U. value when crushed. TABLE VIII Intake Discharge -Denomina- tion of screen Mechani- cal value of mean grade Grading analyses Mechanical value of intake Grading analyses Mechanical value of discharge No. E. U. Per cent E. U. Per cent E. U. + 12 + 20 + 30 + 50 + 80 +120 +200 -200 13 15 17 19 21 23 25 28 27.6 '3.59 15.7 2.36 13.7 2.33 7.4 19.9 3.78 22.5 15.5 3.26 29.0 2.0 .46 6.0 1.6 .40 7.7 4.0 1.12 27.4 100% 17.30 100% Less mechanical value of intake Work done per unit, say 1 ton 1.26 4.28 6.09 1.38 1.93 7.67 22.61 , 17.30 5.31 E.U. 1539.2 202.5 1742.4 17.42% Total Work Done by Tube-Mill in 24 Hours Reduction of pulp feed = 290 tons X5 . 31 E.U. = Reduction of banket ore = 6.75 tonsX30 E.U. = Total work done in 24 hours Relative mechanical efficiency per h-p. = — ^ ", — '- — '- = These results, while cited for the purpose of illustrating the method of calculating, give also a striking comparison in this in- stance at least in favor of the mechanical efficiency of the stamp as compared with the tube-mill, the ratio being 70.4 per cent for the stamp and only 17.4 per cent for the tube. It is evident that comparative efficiencies can only be obtained by this method upon identical ores, but it is quite generally true- that after we get down to the finer sizes, there is less difference in the grinding or crushing characteristics of ores than oiie would expect. The following table of comparisons then, while subject to criti- cism from lack of uniformity of conditions, is at least suggestive: 116 STAMP MILLING AND CYANIDING X h- 1 pa «i H.g ■ o q I as S H t- ^H i-t 00 lO M ^-too>u^oooococl^e4 oous §(M usuacoeooeo Tl ** i-l i-« ^H i-l iH 83 HC4 C4 .-H a a an "■gssags|g t-"* OO'-t a s 0} a CO O B^« t ea .s 1 ^--^ d ^ = w ^ te rS - i"^ ll.a.--«9 CO -^ U9 CD t« CO o O^ en CO -^ ui to i>- oo siaaaa^l' ^"Jla-Ssag. ".a-ll^-sll |^533l&83 S d t' «"9 a J"^ * a Is. 06 CO 03 00 Sua^ '« « sg!" to -^^M lO«e«TK •*■* M^OO XI .an a & -ta I III ^^ •i ■si, o;g g £■* 3 fi S fe1 § g.S.S COMPARISONS OF VARIOUS MILLS 117 "— — ^ — ^ — ~r^ ^ § i i 6? ^ 1 Ui g s ^ 09 a CO O O ■* ^ 00 CD t* ui CO ui t> o "^ C4 '-' M ^ '^ ce o o CO o CO O us ■^ ++ 11 8 e>4 CO r^'— . -HCON^WCO MOO «M -icq cq 1-1 coc<]i-ii-4 eo CO^^OU3CO-4< >o prt OtJ O-^ O'T) C3 n 6 ^ o CO C3 a' a' CO 2 § il £ a £ a •S «£^ P^ XXX »o ^ — § a 6 d s a a *- o o V S W N M c« ^ *; ■3-1 ■e ■= Sf.S --J 0*0 (I a* M s is ^ B S 5 « o COCO . " 3 g gg a "a .- -: -S .00-7S ffl .^ o ■ *• 6 .>^£ o ooooo Oi a Qi Oi a 4) d) Q) O Q) .33223 ^3 GO OS C8 ^ n jlllll S^- § § 3 - a ^ fe o il § |5t--|a - g gl ss^-ss-s-s^ >'^0»0 ,-^rH PqcO C"^ >0 CO tn t>I 00 0» O rH c-a •-nM K^eq Da(N rjoie^cM ►>,(Niw(ncqcoco C4 C4 e>) CO 'A I S . J . CO CD I ■o CQ 6t% »^COCO . a CDU3 . g a d a o^^ iS ^ . .^ iH^iotot^QO a> ^-«o i-H M e4 09 ^ tn o r. 00 ■| n la 5 -i &s S ISo V aa -t^ a o MOO lis .S aja a a^ « S -J "* m a> ^ si W-S"-" A 3 SbO g S- ffl 5S-|g -J Q S a r5.g-§ o !>.a si.sl cd u^ ■^ « aa S='3'i 118 STAMP MILLING AND CYAN I DING (2) Suitability of Product for Purposes in Hand. This is a less serious question for either amalgamation or cyanide treatment than for concentration, in which the minimum comminution that will liberate the mineral is the desired end. From the point of view of the amalgamator, the stamp mill, the slow-speed Chilean mill, and the Huntington mill would stand about in the order named. For cyaniding, where the ore must be finely crushed to permit satisfactory extraction, the stamp mill, the ball-mill, and the Huntington mill can hardly be expected to furnish a sufficiently finely-ground product when operating at reasonable efficiency. The tube-mill, the slow-speed Chilean, the grinding-pan, and the high-speed Chilean mill would appear to take rank, so far as popularity is concerned, in the order named. The tube-mill is always used following stamps or other suitable primary crush- ing machines; this also applies to the use of grinding pans. The Chilean mill appears, from the data available at present, to cover a wider range of comminution at high efficiency than any other machine on the market. It is not as yet, however, being exten- sively used as an ultimate fine grinder. (3) Wear-and-tear on Various Parts and Loss of Time Inci- dent Thereto. On this basis, the stamp mill for coarse-crushing, the ball-mill in its wide range, and the tube-mill in its field of final reduction seem to stand preeminent. The slow-speed Chilean should perhaps be included in this class. The high-speed Chilean and the Huntington mill, together with their variants, are constantly exposed to the criticism of not being foolproof, and of delaying the rest of the plant due to shut-down, or else of requiring a duplicate or spare equipment if continuous operation is to be ensured. BIBLIOGRAPHY FOR COMPARISON OF VARIOUS MILLS * Especially Desirable for Students' Use VON BehnewItz, M. W. Comparison of Tube-mills, Ball-mills and Other Grinding Devices, IJ pp. Min. & Sci. Press, Vol. 101, p. 777 (1910). * Bell, John W. Grading Analyses and Their Application to Cyaniding. Eng. and Min. Jour., Vol. 95, p. 1044 (1913). VON Bernewitz, M. W. Dry vs. Wet crushing at Kalgoorhe, 1| pp. Min. & Sci. Press, Vol. 106, p. 409 (1913). Browne, R. Stuabt (Editorial). Single-stage or Two-stage Crushing? 1 p. Pac. Min., Vol. 17, p. 202 (1910). COMPARISONS OF VARIOUS MILLS 119 Chapman, R. W. Pre-cyanide Crushing. Proc. Aust. Inst. Min, Engrs.; abs. Min. Mag., Vol. II, p. 64, Oct., 1909. * Denny, G. A. Efficiencies of Crushing Plants, 5i pp. Mex. Min. Journ., p. 34, July, 1912. * Del Mar, Algernon. Mechanical Efficiency in Crushing, 6 pp. Eng. and Min. Jour., Vol. 94, p. 1120,(1912). Gates, Abthdr 0. The Crushing-surface Diagram, 2i pp. Eng. & Min. Jour., Vol. 95, p. 1039 (1913). Heesam, Ernest A. Screens for Sizing, 25 pp. Trans. A.I.M.E.,Vol. 37, p. 265 (1907). Megraw, Herbert A. Efficiency of Fine Grinding Machinery, J p, Eng. & Min. Jour., Vol. 92, p. 387 (1911). * Megraw, Herbert A. Grinding Ores for Cyaniding, 8 pp. Eng, and Min. Jour., Vol. 96, p. 821 (1913). * Pearce (S. H.) & Caldecott (W. A.) Crushing Efficiency of Tube- mills, li pp. Min. Rep., Vol. 64, p. 545; abstr. from Jl. C. M. & M Soc, S. A. (1906). * Quartano, a. Criticism of Stadtler's Hypothesis, 1 p. Min. Mag. Vol. V, p. 223 (1911). * Speak, S. J. The Application of Kick's Law to the Measurement of Energy Consumed in Crushing, 8 pp. Bull. 116. Inst. Min. & Met. (May, 1914); also Bull. 119 (Aug., 1914). * Stadtlbr, H. Crushing Efficiency of Pine-grinding Machines, f p. (Abstract from J. S. African Ass'n of Engrs.) Min. & Sci. Press, Vol. 100, p. 900 (1910). * Stadtler, H. Grading Analyses, 5 pp. (Paper submitted for joint discussion to the Inst, of Mining and Metallurgy, read May 19, 1910, in London, and at M. & M. Soc, S. A., May 21, 1910, in Johannesburg. Min. & Min., Vol. 31, p. 344 (1911). * Stadtler, H. High Duty Gravity Stamps, 3 pp. Min. & Sci. Press, Vol. 104, p. 274 (1912). * Stadtler, H. The Law of Crushing, 7 pp. Eng. & Min. Jour., Vol. 98, pp. 905 and 945. * Taggaht, Arthur P. The Work of Crushing, 19 pp. Bull. 85 A.I.M.E. (Jan., 1914; also June, 1914). Ubbitbr, Walter H. Efficiency of Fine Grinding Machinery, 2 pp. Eng. & Min. Jour., Vol. 92, p. 257 (1911). * Wainwright, W. E., and McBride, W. J. Fine Grinding Tests. Trans., Aus. Inst. Min. Eng., Vol. 13, p. 38; Min. Mag., Vol. 2, p. 316; Met. & Chem. Eng., Vol. 8, p. 544 (1909). * Yates, Arthur. Screen Analysis and Grinding Efficiency, 2 pp. (Abstract from paper read before C. M. & M. Soc, S. A., Dec. 19, 1908.) Min. & Sci. Press, Vol. 98, p. 624 (1909). ■ . Comparison of Nissen Single Stamp and Heavy 5-Stamp Bat- teries. Eng. & Min. Jour., Vol. 92, p. 1219 (1911); Eng. & Min. Jour., Vol. 93, p. 354 (1912). . Grading Analyses and their Application to Cyaniding, 2 pp. Eng. and Min. Journal, Vol. 95, p. 1044 (1913). PART II CYANIDING CHAPTER VIII HISTORY AND CHEMISTRY OF CYANIDING History From the majority of gold and silver ores, when properly pre- pared, the precious metals may be dissolved by an extremely dilute solution of a cyanide salt. It then remains to separate the gold and silver-bearing, or "pregnant," solution, as it is called, from the ore and to precipitate the metals. This last is readily accomplished by the action of zinc. This process, so extremely simple and easily comprehended in principle, is at tipaes rendered exceedingly complex by mechanical difficulties and chemical interferences. It is strange, nevertheless, that the long-known fact, that gold is soluble in cyanide solution, should have remained so long im- utilized. The discussion of the cyanide process of gold and silver extrac- tion begins, naturally, with the history of the cyanides themselves. Authentic information in regard to cyanogen compounds dates from the accidental discovery of prussian blue in 1704 by Dies- bach, a German chemist interested in the dyeing industry. Owing, however, to the extremely poisonous nature of many cyanides, and to the ease with which they are prepared from organic material, it is more than likely that many of the poisons which ancient and medieval intriguery prized so highly were, in part at least, cyanide compounds. In any event, Diesbach was the first to 'place the cyanides upon an investigational basis, and from his work Macquer and Guyton, in France, and Bergman and Scheele, in Germany, were led to important discoveries. Scheele, in 1782, succeeded in isolating prussic acid (HON) and found that gold, silver, and copper were precipitated by cyanide solution and that the pre- cipitates were soluble in an excess of the reagent. This, however, is not a recognition of the fact that gold and silver are themselves soluble in cyanide solutions. Hagen, another German, is credited with having announced in 1805 or 1806 that gold is soluble in 123 124 STAMP MILLING AND CYAN I DING a solution of prussiate of potash, as potassium cyanide was then called. Ten years later the brilliant Frenchman Gay-Lussac announced the discovery of a compound, having in many respects the proper- ties of a single element, and gave its composition as carbon and nitrogen in equal units. He proposed the name of 'cyanogen' for the new radical — from the Greek 'Kyanos' blue, referring to the blue color of the ferrocyanide salt of iron. From this point, the history of the cyanogen radical comprises the investigation of its various compounds and their properties; only those, however, which relate to the application of cyanides to the solution of gold and silver will be followed. In a patent specification covering an electroplating process the Elkington brothers, in 1840, clearly state their recognition of the solubility of gold and silver in cyanide solution, and Bagration, a Russian nobleman, pubhshed some researches to the same effect in 1843. According to Philip Argall * Bagration's conclusions may be summarized as follows: (1) That cyanide of potassium dissolves metallic gold. (2) That if the gold is fine it will pass rapidly into solution. (3) That the electric current does not assist solution. (4) That heat does assist solution. (5) That the dissolved gold can be precipitated on metallic sur- faces without the aid of electricity. (6) That air has a marked quickening effect on the solution of gold in cyanide. All of these generalizations have stood the test of time. Truly a remarkable record, and one that stamps Bagration as one of the fathers of cyanide. Turning again to the Germans, we find Eisner, in 1844, enun- ciating the now universally recognized fact that oxygen is essential to the solution of gold and silver in cyanide. This fact was again emphasized by Faraday in 1856. Concerning the equation, ex- pressing the solution of gold in' cyanide and known by Eisner's name, there appears to be some doubt as to whether Eisner, Bag- ration, or the compilers of Watt's Chemical Dictionary are en- titled to the credit. This equation is usually written as follows: 2Au -f- 4KCy -)- -|- H2O = 2 AuKCyz -|- 2K0H. * Miu. & Sci. Press, Vol. 95, page 655. HISTORY AND CHEMISTRY OF CYANIDING 125 At this point we will turn to the history of the application of cyanide solutions to the treatment of ores. It would seem highly probable that the discovery of the fact that gold and silver were soluble in cyanide, must have been followed by attempts to apply this principle to the treatment of ores, but if so only one record of such an experiment has been found to date.* In 1846 Dr. Duflos, a German, following Bagration's discovery, tried to treat an arsenic- al gold ore with potassium ferrocyanide but failed to make an extraction. The investigator considered the use of potassium cyanide but abandoned the idea owing to the fact that the ore carried considerable ferrous oxide, and his experiments had already indicated that ferrocyanide was without action. Thus, did a piece of apparently plausible, a priori reasoning ensnare and lead away an investigator, from the threshold of a great discovery. We know of no additional metallurgical researches in this line for almost 20 years until, in 1867, J. H. Rae, an American, appears with a patent process for the treatment of gold and silver ores by means of potas- sium cyanide aided by the electric current. There is reason to believe that this was tried on a commercial scale, but of this we have no positive proof, and the process appears to have died in its infancy. With the exception of statements by Hahn, in 1870, that gold and silver sulphide are soluble in cyanide, and by Skey, in 1875, warning millmen against the too liberal use of cyanide as an aid to amalgamation, owing to its solvent action on gold, we have nothing more until 1881, when we find Faucett and S&nders, within six months of each other, taking out patents for the use of cyanide as an aid to amalgamation. It is to be noted that up to this point no process has been introduced or patented for the extraction of gold and silver from their ores by the solvent action of cyanide salts unaided by electrolysis. Now comes Jerome W. Simpson of Newark, New Jersey, in 1885, with a patent entitled a "process for extracting gold, silver, and copper from their ores." In his description he specifies the crush- ing of the ore, agitation with a solution of potassium cyanide, sodium chloride and ammonium carbonate, settUng, and then placing in the supernatant solution, a piece of sheet zinc to precipit- ate the metals. The solution specified is one with about 3 per cent KCy, 0.2 per cent NH4CO3, and 0.1 per cent NaCl. He dis- tinctly states in his patent that he does not wish to be understood * J. E, Clennell, The Cyanide Hand Book, page 12. 126 STAMP MILLING AND CYANIDING as broadly claiming the exclusive use of potassium cyanide as a solvent, or of zinc as a precipitant. This patent, while covering nearly all the points of present practice, was never followed up, but as the English judge wisely remarked in a decision in regard to the Mac Arthur-Forrest patent to be discussed later: "if the (MacArthur-Forrest) patent were held valid would not Rae's and Simpson's processes, if now used, be Uable to be stopped as 'in- fringements? I think they certainly would." Quoting again, Philip Argall says: * "If we rely on the almost unanimous verdict of the courts we must award the palm of discovery to the inventive genius of Rae and of Simpson." This brings us, naturally, to the MacArthur-Forrest patents of 1887 in England and of 1889 in the United States.f After at- tempting to cover the entire use of cyanide salts for gold and silver recovery and, as has been indicated, being defeated in this owing to the priority of the Rae and Simpson patents, the Mac- Arthur-Forrest patents had, by 1890, been reduced to the distinct- ive use of extremely dilute cyanide solution "not exceeding 8 parts of cyanogen in 1000 parts of water t and of filiform or 'shav- ing' zinc for precipitation." MacArthur and Forrest claim that such dilute solutions have a selective action, such as to dissolve the gold and silver in preference to the baser metals. Eventually, in almost every country the MacArthur-Forrest patents were can- celed on grounds of lack of novelty. Argall § points out the entire invalidity of the solution patents in that, in all of them, MacArthur-Forrest limited themselves to the use of cyanide alone, excluding the necessary agent, oxygen. The fight over the MacArthur-Forrest patents was a long and a bitter one, and in litigation so fierce almost every one interested was forced to take sides pro or con, with the result that it is difficult, although the smoke of the battle has cleared, to find a historian free from prejudice in the matter. This much, hdwever, must be said, that whether the patents of the two vaHant Scotsmen and their associates were technically valid or not, their work was quantitative, where that of their predecessors was merely qualita- tive, so that no one can dispute the statement that, "To these men, * Min. & Sci. Press, Vol. 95, page 682. t Louis Janin, Jr., has recently called attention to a caveat granted him in 1886, following the lines afterward covered by MacAithur and Forrest. i Equivalent to 1.9 per cent KCy. § Loc. cit. HISTORY AND CHEMISTRY OF CYANIDINO 127 MacArthur and Forrest, is due the praise, not that they were the first discoverers, but that they pushed their invention and enabled a recovery of $14,000,000 in five years by their process, which otherwise would be irrevocably lost," and "that they made what had before been regarded as a pretty chemical scheme, into a sound commercial success." New Zealand, in 1889, was the first country to see cyaniding commercially successful, but South Africa was the more fertile field for the new process. In 1890, the first year that MacArthur and Forrest report a pro- duction by their process in the Transvaal, they recovered $6000 from taihngs and in 1891, $60,000. By 1§93 over $6,000,000 in round numbers was the cyanide production from the South African mines. Since the termination of the litigation referred to, the process has advanced at a rapid rate, mainly, however, by the improve- ment of existing mechanical devices, or by introducing and adapt- ing to the cyanide process, appliances already in use in other industries. Chemistry Cyanogen and Its Compounds. Cyanogen, CN, nitride of carbon, is a colorless gas with a peculiar, characteristic odor, re- sembling that of bitter almonds. It is extremely poisonous. Cyanogen gas is given off from the dry distillation of silver or mercuric cyanides. Although a compound, it has many of the properties of a single element aiid in many ways resembles the halogens, iodine, chlorine, and bromine. The compound symbol CN is somewhat awkward and must be bracketed for use with subscripts; for this reason I shall follow the British usage of writ- ing the symbol Cy except where a decomposition of the cyanogen radical is involved. Combined with hydrogen, cyanogen forms prussic or hydrocyanic acid HCy. This is most readily prepared by treating a cyanide salt with a dilute mineral acid. KCy + HCl = KC1 + HCy. Hydrocyanic acid is a colorless volatile liquid, which boils at 26° C. and is extremely poisonous. It is soluble in water. With the halogens, cyanogen forms several compounds; of these the chloride CyCl is a gaseous compound, while CyCU is a soUd. CyBr and CyBra are both soUds as is also the iodide Cyl. These haloid cyanides are important in certain modifications of the cyanide process to be discussed later. 128 STAMP MILLING AND CYANIDING The metallic cyanides and double cyanides are of extreme im- portance in the process. The cyanides of the aljkalis are used as solvents. The importance of the precious metal cyanides is obvious enough. The cyanides of the base metals are unfortun- ately formed to a greater or less extent during the solution of the gold and silver, and are either precipitated later or remain to foul the solution. The following table of properties is useful : Cyanides of alkalis and alkaline earths Cyanides of other metals Soluble Alkaline Extremely poisonous Colorless Insoluble (except Cd and Hg) Unite with alkaline cy- anides to form soluble double salts. Usually highly colored. The cyanides of the alkalis and alkaline earths are the substances which have been used and proposed for use as the solvent salts in the process under discussion. Potassium and sodium cyanides are practically the only ones that have been utilized on a commer- cial scale. The following table is adapted from Julian and Smart: * TABLE X Cyanides Molecular weights Equivalent amount per unit gold Dissolving power in terms ofKCy NHiCy NaCy. , KCy.., MgCya. CaCyj. SrCva.. Ba(Jy2. 18+26=44 23+26 = 49 39+26=65 24+52=76 40+62 = 92 87.5+52 = 140 136.8+52=189 88 98 130 76 92 140 189 148 133 100 171 141 93 70 Owing to instability of the alkaline earth cyanides, only the cyanides of the alkali metals and of ammonium are possible as commercial solvents. Of these, ammonium cyanide is too un- stable for present use. The sodium salt, while more powerful than that of potassium and to be preferred on that account, is deli- quescent and subject to decomposition. Much, if not most, of the * Cyaniding Gold and Silver Ores, 2nd Ed., page 104. HISTORY AND CHEMISTRY OF CYANIDING 129 so-called '98% potassium cyanide' commonly specified is in reality impure sodium cyanide. The cyanides of the metals and their properties are important in a process in which complex ores are subjected to cyanide solu- tion. As previously mentioned, the simple cyanides of mercury and cadmium are alone soluble; many of the other metals, however, form simple cyanides which, uniting with the excess of cyanide salt in the solution, become themselves soluble compounds. The three metals which of necessity are the most important in the process, viz., gold and silver as solutes, and zinc as a precipitant, belong to this class. Cyanides of Gold and Silver. The following compounds are known and have been investigated:* TABLE XI Symbol Name Properties AuCy Aurous cyanide Auric cyanide Auro-potassic cyanide Auro-zincic cyanide Auro-argentic cyanide Argento-cyanide Argento-potassic cyanide • insoluble soluble soluble in 4 pts. cold water insoluble solubleiin 8 pts. cold water AuCya KAuCy2(AuCy+KCy) .... ZnfAuCvz)!.. AsAuCvj AiCy. . . . KAgCy^CKCy+AgCy) Other metallic cyanides of importance in the treatment of ores, with their properties, are given in the following table: TABLE XII Metal Cyanide . Properties Cuprous cyanide Cu2Cy2 insoluble Cupric cyanide CuCy2 partly soluble Double cyanides of copper Copper and ammonium x(NH4Cy)y(CuCy2)z(Cu2Cy2) soluble, feeble solvents of gold Cuprammonium cyanides slightly soluble, powerful sol- x(NH3)y(CuCy2)z(Cu2Cy2) vent of gold Mercury Mercuric cyanide HgCy2 Double cyanide of mercury soluble in 8 pts. cold water and potassium K2HgCy4 soluble in 4 pts. cold water Zinc... Zinc cyanide ZnCyz Zinc potassium cyanide insoluble KjZnCyi readily soluble * Clennell, op. cit., pages 71-81. 130 STAMP MILLING AND CYANIDING Complex cyanogen compounds, in which the radical is composed of a metal of the iron group with cyanogen, are of interest chemi- cally, but are not usually of importance in the treatment of ores. Of this group the ferrocyanides of the type M4FeCy6 and the ferri- cyanides MsFeCye are the most important and best known. Cyanogen unites with oxygen in some cases to form an acid radical CNO; such compounds are called cyanates. Other mem- bers of the oxygen group sometimes replace the oxygen, for example sulphur in the sulpho- or thio-cyanates, potassium sul- phocyanate KCyS being a common laboratory reagent. Solution of Gold in Cyanide. The general truth of Eisner's equation 2 Au + 4 KCy + H- H2O = 2 AuKCya -|- 2 KOH, as expressing the results accompanying the solution of gold in cyan- ide solution, is now almost universally accepted. "It is doubtful, however, whether the complete chemistry of these changes is understood even by those who have made it a careful study." The hypothesis offered by Julian and Smart seems the most logical explanation of the matter yet presented. This may be briefly summarized as follows: The solution of gold in cyanide is effected by electrolytic action, the difference of potential set up being due to other minerals in electrical contact in the same solution with gold, or to gold of different densities being in electrical contact. The common minerals, e.g., pyrite and arsenopyrite, are electro- negative to gold; so that if we take the case of gold associated with pyrite and immersed in cyanide solution, the gold becomes the anode of a simple cell, pyrite being the cathode. A current is established with the result that KCy is ionized to K cations and Cy anions. (Fig. 60.) At the anode Au + Cy = AuCy. AuCy + KCy = AuKCyz At the cathode K -f- H2O = KOH + H. This last explains why oxygen in some form or other is essential to continuous solution, for without it the cathode becomes covered with bubbles of hydrogen (polarized) and no further current can flow. Strictly speaking, therefore, it is the negative pole (pyrite) which requires the oxygen and not the gold as commonly supposed. There is indeed some reason to think that free oxygen retards the HISTORY AND CHEMISTRY OF CYANIDING 131 solution of the gold in spite of its indispensable secondary effect. Atmospheric oxygen has proven the most satisfactory depolarizer. Artificial oxidizers have not been wholly successful, due probably to the fact that they add to the density of the solution and so re- tard the migration of the ions. Reducing agents are, of course, manifest hindrances to the solution of gold and silver in potassium Fig. 60. Ionization of Cyanide by Gold and Pjn^te. cyanide. Experimentally, however, it has been proven that certain compounds in cyanide solution will make it an active solvent of , gold and silver in the absence of oxygen. The use of halogen-cyanides has been mentioned in this con- nection; according to Professor Christy,* the reaction is as follows: BrCy+KCy = KBr-|-2 Cy and 2 KCy-|-2 Au-|-2Cy = 2 KAuCya or combining the two: 3 KCy + BrCy H- 2 Au = 2 AuKCya + KBr. Christy also states that practically the same result is produced by the addition of bromine water to potassium cyanide solution. 2 KCy -I- Au + Br = KAuCya + KBr. Similar 'reactions probably hold for chlorine and iodine. Com- paring this equation with the Eisner reaction, it will be noted, * S. B. Christy, Trans. A.I.M.E., Vol. 26, page 740. 132 STAMP MILLING AND CYANIDING that, weight for weight, oxygen causes solution of more gold than any of the halogens. Double cyanides and copper-ammonium cyanides are likely to break up with a liberation of nascent cyanogen, thus possibly assisting solution in the following manner: Au + KCy + Cy = KAuCyj. Ferricyanides have at times proven of assistance in dissolving gold and silver. 2 KCy + KaFeCye + Au = KAuCya + KiFeCye. Direct oxidizers, such as alkaline peroxides, peroxides of the metals, peroxide of hydrogen, ozone, and numerous other com- pounds, have been tried. Some of . them will probably prove efficient under special circumstances, but as a rule their use is to be discouraged. Precipitation of Gold and Silver. Both gold and silver when in cyanide solution are electro-negative to zinc and hence are precipitated by it. The exact nature of the reaction is not known. We do know, however, that hydrogen is evolved, that KOH is formed, and that plenty of free cyanide is essential for complete precipitation. The following reaction has been suggested as meeting all the preceding conditions: KAuCys -f- 2 KCy + Zn -fHaO = K2ZnCy4 -|- Au -j- H -f- KOH, or, as modified by Christy: * 2 KAuCya + 4 KCy -|- 3 Zn -|- 2 H2O = 2 Au + 2K2ZnCy4 + ZnKaOa -^ 4 H. Other reactions consuming both zinc and cyanide doubtless occur without any useful result except perhaps that of furnishing alkali in a most expensive manner. Among these may be men- tioned : Zn -h 4 KCy + 2 H2O = KjZnCyi -j- 2 KOH + H2 and Zn -I- -F H2O = Zn (0H)2. The latter compound sometimes forms a white deposit in the »zinc boxes, when there is an insufficiency of free cyanide to dis- solve it. Electrolytic precipitation is the term applied to precipitation * Op. cit., page 764. HISTORY AND CHEMISTRY OF CYANIDINO 133 where the electric current is suppUed from an external source. The chenaistry of the process is simply one of ionization. KAuCya + H2O = Cya + Au + KOH + H. The liberated cyanogen attacks the anodes and the gold is de- posited on the cathode. Countless other precipitation schemes have been tried with more or less success as laboratory methods — -such as the use of charcoal, aluminium, sodium amalgam, and various metallic chlor- ides, nitrates, sulphates, etc.: of these aluminium seems to give the best promise of eventual success and we have at least one recent example of its successful use.* The zinc and the electrolytic pre- cipitation methods, however, are the only ones that are at present in general use. * E. M. Hamilton, Eng. & Min. Jour., Vol. 95, page 935. BIBLIOGRAPHY FOR HISTORY AND CHEMISTRY OF CYANIDING * Especially Desirable for Students' Use History. Abgall, Philip. Steps in Cyaniding, f p. (Brief History of Cyaniding, by same author.) Min. & Min., Vol. 28, p. 368 (1908). * Akgall, Philip. History of Cyaniding, 6i pp. Min. & Sci. Press, Vol. 95, pp. 655, 682 (1907). Hunt, Bertram (Adair, Alfred). (Comments on Mr. Jaiies' article on "Cyanide History," by Alfred Adair, from S. A. Min. Jour.) Min. & Sci. Press, Vol. 99, p. 421 (1909). James, Alfred. Cyanide History, 1 p. Min. & Sci. Press, Vol. 99, p. 420 (1909). MacArthur, J. S. Reminiscences of the Early Rand, Ij pp. (J. C. M. & M. Soc, S. A., Dec, 1908.) Eng. & Min. Jour., Vol. 88, p. 357 (1909). McCoMBiE, J. History of Cyanide Process, 1 p. Min. & Sci. Press, Vol. 102, p. 850 (1911). ■ Malcolmson, James W. The History and Progress of Gold and Silver. (Paper read Am. Min. Con., Joplin), 2i pp. Min. Wld., Vol. 27, pp. 973 and 1011 (1907). Power, Fredk. Danvbrs. History of Cyaniding, | p. Min. & Sci. Press, Vol. 96, p. 319 (1908). RoLFE, F. Percy. History of Cyaniding, i p. Min. & Sci. Press, Vol. 96, p. 93 (1908). * Traphagen, F. W. The Cyanide Process — A Review, 6 pp. • West. Chem. & Met., Vol. Ill, p. 181 (1907). ' Reviews of Progress. Argall, Philip Henry. Metallurgical Progress in Colorado. Min. & Sci. Press, Vol. 100, p. 35 (1910). 134 STAMP MILLING AND CYANIDING * Argall, Philip. Review of Cyaniding in 1910, 3f pp. Eng. & Min. Jour., Vol. 91, pp. 42 and 506 (1911). Argall, Philip. Review of Cyaniding in 1912, IJ pp. Eng. & Min. Jour., Vol. 95, p. 108 (1913). Barbour, Percy E. Developments in Cyanide Practice, 4 pp. Minea & Minerals, Vol. 31, p. 597 (1911). * Browkb, R. Stuart. Review of Cyano-metallurgy in 1910, 2i pp. Pac. Min., Vol. 18, p. 10 (1911). Browne, R. Stuart. Progress of Cyano-metallurgy in 1911, 6 pp. Min. & Eng. Wld., Vol. 36, pp. 287, 348, Feb. 3 and 10, 1912. BosQUi, F. L. Recent Improvements in the Cyanide Process, 2j pp. Min. & Sci. Press, Vol. 93, p. 719 (1906). * Browne, R. Stuart. Progress in Cyano-metallurgy During 1909, 4 pp. Pac. Min., Vol. 16, p. 13 (1910). Carter, T. Lane. High Extraction Processes in the Metallurgy of Gold and Silver, 25 pp. Eng. Mag., Vol. 42, p. 615 (Jan., 1912). * Editorial. American Progress in Cyaniding, 3| pp. Min. & Sci. Press, Vol. 102, p. 67 (1911). Haley, C. S. Progress in Slime Filtration, 2^ pp. Min. & Sci. Press, Vol. 103, p. 16 (1911). Hamilton, E. M. Alfred James' Annual Cyanide Letter, f p. Min. & Sci. Press, Vol. 100, p. 328 (1910). James, Alfred. Annual Reviews of Progress. Eng. & Min. Jour., Vol. 83, p. 17 (1907); Min. & Sci. Press, Vol. 94, p. 18 (1907); Min. & Sci. Press, Vol. 97, p. 41 (1908); Min. & Sci. Press, Vol. 98, p. 47 (1909); Min. Sci., Vol. 60, p. 247 (1909); Eng. & Min. Jour., Vol. 87, p. 1194 (1909); Min. & Sci. Press, Vol. 100, p. 41 (1910); Min. & Sci. Press, Vol. 102, p. 52 (1911); Min. & Sci. Press, Vol. 104, p. 37 (1912). James, Alfred. Progress in Gold-Silver Ore Treatment During 1912, 5f pp., iUus. Min. & Sci. Press, Vol. 106, p. 23 (1913). Lamb, Mark R. Cyaniding in America, 1 p. Mines and Methods, Oct. (1909). Lamb, Mark R. Progress and Development in Cyanide Practice, 2f pp. Eng. & Min. Jour., Vol. 89, p. 178 (1910). Lamb, Mark R. Present Tendencies in Cyanide Practice, 4 pp. Eng. & Min. Jour., Vol. 90, p. 855 (1910). Mackenzie, Geo. Progress in Cyaniding, 1 p. Min. & Sci. Press, Vol. 99, p. 86 (1909). * Megraw, H. a. Analysis of Cyanide Practice, 2f pp. Eng. & Min. Jour., Vol. 95, p. 110 (1913). NicoL, John M. Alfred James' Annual Cyanide Letter, IJ p. Min. & Sci. Press, Vol. 100, p. 328 (1910). Occasional Contributor, An. American Progress in Cyaniding. Min. & Sci. Press, Vol. 102, p. 67 (1911). * Robinson, Burr A. Cyaniding in 1911, 2 pp. Eng. & Min. Jour., Vol. 93, p. 45 (1912). HISTORY AND CHEMISTRY OF CYAN I DING 135 Chemistry. Browne, R. Stuart. The Making up of Cyanide Solutions, 3 pp. Pac. Min., Vol. 16, p. 130 (1910). Bell, Ralston. Spurious Potassium Cyanide, 1 p. Eng. & Min. Jour., Vol. 89, p. 1049 (1910). * Christy, S. B. Solution and Precipitation of Gold, 37 pp. Trans. A.I.M.E., Vol. 26, p. 740 (1896). * Christy, S. B. Electromotive Force of Metals in KCy solution. 82 pp. Trans. A.I.M.E., Vol. 30, p. 864 (1900). * Clennell, J. E. Lead Salts in Cyanide Treatment, 3 pp. Eng. & Min. Jour., Vol. 94, p. 597 (1912). CoGHiLL, Will. G. Copper and Sulphur in Cyanide Solution, 2| pp. Min. & Sci. Press, Vol. 105, p. 203 (1912). Chosse, Andrew F. The Action of Mineral Sulphates and Arsenates on Cyanide Solutions, li pp. Min. & Sci. Press, Vol. 105, p. 16 (1912). Ekeley & Tatum. The Electrochemistry of the solution of gold in KCy, 4 pp. West. Chem. & Met., Vol. 5, p. 19 (1909). . Gross, John. Rate of Dissolution of Free Gold in Cyanide Solution, i p. Eng. & Min. Jour., Vol. 96, p. 749 (1913). HoLBROOK, E. A. Sodium Cyanide. Min. & Sci. Press, Vol. 96, p. 660 (1908). Johnston, A. McA. Iron in Mill Pulp, 3 pp. Min. & Sci. Press, Vol. 105, p. 463 (1912). * Julian, H. F. Action of Oxygen in Cyanide Solutions. Min. & Sci. Press, Vol. 91, p. 446; same in Vol. 93, p. 512; abst. from J. C. M. & M. Soc, S. A., (1906). * LowDEN, H. B. The Phase Rule in Cyaniding, 1 p. Pac. Min., Vol. 19, p. 35 (1911). Magenau, William. A Negative Experience with Sodium Cyanide, 1 p. Eng. & Min. Jour., Vol. 82, p. 363 (1906). * Megraw, H. a. Oxidation and cyaniding, 2 pp. Eng. & Min. Jour., Vol. 88, p. 645 (1909). * Megraw, Herbert A. Ores Amenable to Cyaniding, 4J pp. Eng. and Min. Jour., Vol. 96, p. 629 (1913). * Megraw, Herbert A. Chemicals used in the Cyanide Process, 6i pp. Eng. & Min. Jour., Vol. 97, p. 265 (1914). * Neil, William. Manufacture of Cyanide, 1 p. Eng. & Min. Jour., Vol. 91, p. 902 (1911). Shabwood, W. J. Commercial Sodium and Potassium Cyanide, 2i pp. Eng. & Min. Jour., Vol. 89, p. 614 (1910). * Stuart, J. B. Theory of the Dissolution of Metals by Cyanide, 2 pp. Min. & Sci. Press, Vol. 101, p. 180 (1910). Weber, M. G. Effect of Electric Current on Cyanide Solution, 1 p. Min. and Eng. Wld., Vol. 37, p. 340 (1912). . Cyanogen Compounds from Distillation of Coal, 1 p. Min. & Sci. Press, Vol. 105, p. 272 (1912). 136 STAMP MILLING AND CYANIDING Poisoning. Brown, H. L. Cyanide Poisoning, | p. Eng. & Min. Jour., Vol. 82, p. 835 (1906). Kennedy, A. P. Cyanide Poisoning, J p. Min. & Sci. Press, Vol. 94, p. 303 (1907). Kbitzek, W. H. First Aid for Cyanide Poisoning, f p. Min. and Sci. Press, Vol. 106, p. 148 (1913). Masson, Orne. Cyanide Poisoning, I p. From Queensland Govern- ment Mining Journal. Min. & Sci. Press, Vol. 98, p. 562 (1909). . Cyanide Poisoning, IJ p. Pac. Min., Vol. 15, p. 52. . Cyanide Immunity, | p. Eng. & Min. Jour., Vol. 94, p. 290 (1912). CHAPTER IX PREPARATION OF ORES FOR CYANIDE TREATMENT The preparation of ores for cyanide treatment is dependent not only upon the method of cyaniding to be used but also upon the processes which are to precede cyanide treatment. The condi- tions governing the choice of methods to be used will be discussed later. In the meantime, certain preliminary processes of import- ance will be discussed in their relation to cyaniding. The most important of these are: Crushing, and classification and dewater- ing which are essential in the cyanide treatment of nearly all ores; and amalgamation, concentration, and roasting which are more limited in their application. Crushing. In crushing for cyanide treatment the aim is, of course, to Uberate the gold and silver particles and to expose 4/hem to the solvent action of the solution. Anything beyond this is a waste of money and time. It is evident, however, that to fulfill this condition with one ore may require an entirely different degree of crushing than would be necessary with another, as the follow- ing extremes will show: In the Stonewall district. Lower California, I have seen ore crushed by a Dodge rock-breaker and loaded direct into leaching tanks; in other cases tube and ball-mills are used to produce an impalpable slime before cyanide treatment. Where the primary and sole purpose of the crushing is to prepare the ore for cyanide treatment it may be accomplished by either of two methods: 1. Dry crushing. 2. Wet crushing. The advantages and disadvantages of each method have formed a fruitful subject of discussion ever since the inception of the pro- cess. The chief points of comparison are: (1) First-cost of plant per ton capacity. The cost of rolls or ball- mills is less than that of wet-crushing stamps or Chilean mills. (2) Total cost of crushing per ton. Where ore can be cheaply dried, dry crushing is cheaper, but with wet ore and expensive fuel, wet-crushing will prove more economical. 137 138 STAMP MILLING AND CYANIDING (3) Percentage of slime or dust produced. In general a much more leachable product is secured by dry-crushing than by wet.- (4) Losses from dust or slime. This is not an especially serious item in any event but is probably greater in dry-crushing. (5) Percolation and leaching of 'product, and consumption of cyanide. When an ore is crushed wet and then sized, clean, leachable products are secured, in part at least, and the solvent action of the water used in crushing assists very materially in re- moval of free acid and so reduces consumption of cyanide. (6) Effect upon operatives. Dry-crushing is exceedingly dan- gerous to workmen on account of dust, and in time almost invari- ably leads to fatal lung diseases. We can never have one general, standard system of crushing, with so many different conditions to meet. An ideal system on a certain ore in one locality might be altogether unsuitable for a similar ore in another locality. A typical dry-crushing mill would operate somewhat as follows: After reduction to about J-in. cubes the ore would pass to a dryer, in order that it may be screened and so lessen the slime pro- duced in subsequent comminution. Further reduction may take place either in rolls, as is common in the United States, or in ball- mills which are coming rapidly into favor. Stamps have become obsolete as dry crushers and are seldom or never used. The pro- duct from these operations is screened and the over-size returned, preferably to a separate machine. The screened product is ready to be charged into the cyanide leaching-tanks. Wet crushing is seldom seen dissociated from either amalga- mation or concentration or both. Since tube-mills are more efficient when operated wet, however, there is no reason why a non-concentrating, non-amalgamating ore should not, where fine crushing is -necessary, be crushed wet by stamps, or ball-mills, or Chilean mills, and go thence after classification to the 'tubes' be- fore cyaniding. Where this system is followed, however, there are few gold ores which would not, repay the slight expenses of allow- ing the tube-mill pulp at least, to flow over amalgamated copper plates. Classification and Dewatering. The separation of slime from sand, or of excess water or solution from either or both of them, is in the majority of cases necessary at some stage of the cyanid- ing process. / PREPARATION OF ORES 139 In essence, classification and dewatering are practically the same, for in cyanide work classifiers with a rising current or hydraulic sorting-column are seldom used, since the problem is always to avoid dilution of the pulp, especially where the object is to prepare sand for tube-mill feed. The classifiers used in cyanide work may be divided into two classes: (1) Cone-classi- fiers and (2) Drag or conveyor-classifiers. The. Cone-Classifier, as its name implies, consists of a hollow cone of wood or preferably steel, the spigot or sand outlet being at the apex of the cone, the slime dis- charge being provided for by an annular launder or trough about the periphery. The amount of sand discharged is regulated either by a cock or gate on the spigot, or, as in the Callow tank, by an upturned gooseneck outlet. The feed to the cone-classifiers is usually central, through a pipe dipping a few inches below the level of lo'sume . , Launder the pulp m the cone. There has recently been intro- duced in South Africa * and in Mexico t the modification sug- gested by W. A. Caldecott (Fig. 61). This consists of a disc dia- phragm placed near the bottom of .the cone, together witb, in some cases, a baffle plate B to prevent ' diving ' of the incoming pulp stream. Quite remarkable results are reported as a result of the use of this apparently simple device, a slime-free sand discharge containing only 26 per cent moisture being maintained under working conditions; thus apparently it serves most effectually the dual function of dewatering and class- ification. Included under cone-classifiers should be mentioned, * G. 0. Smart, Min. Sci., Vol. 61, pages 392-396 from J. C. M. & M. Soc. S. A. t Walter Neal, Min. & Sci. Press, Vol. 100, pages 483-486. Fig. 61. Sand Outlet Caldecott Cone. 140 STAMP MILLING AND CYANIDING as of the same general varietj', pj'ramidal boxes of the surface- current box-classifier type, most of which have proven less efficient than the cone for this work. Drag or Conveyor-Classifiers. The pioneer of this type, de- signed according to its originator "in desperation * to save mill height," is the invention of J. V. N. Dorr. The Dorr Classifier, as described by the patentee and manufac- turer, and as illustrated in Fig. 62, consists of a settling box in the form of an inclined trough, open at the upper end. From this trough mechanically operated rakes remove the heavy material as fast as it settles. The hquid and slime overflow at the closed end. The rakes are suspended by suitable hangers from bell-cranks Fig. 62. The Dorr Classifier. connected by rods to levers which terminate in rollers. The latter press against cams attached to the crank shaft. The rakes arc raised and lowered at opposite ends of the stroke by the action of the cams transmitted through the levers and rods to the bell cranks. The horizontal motion is produced by cranks. The pulp is fed across the width of the trough and the sand settles to the bottom, after which it is advanced up the inclined bottom of the trough by the scrapers reciprocating with a slow raking motion. After emerging from the liquid the sand passes across a washing * Min. & Min., Vol. 28, page 541. PREPARATION OF ORES 141 device and is discharged from the open end of the machine with about 26 per cent moisture. It is claimed that if the machine be stopped while full of sand, the rakes can be raised from the bottom and, after it has been started, they can be gradually lowered while rurming until they assume their normal position. The slime is prevented from settling by the flow of liquid, as well as by the agitation near the bottom, caused by the reciprocating motion of the scrapers, and overflows at the lower end of the ma- chine. The agitation produced, while ample to prevent the slime from settling, is not sufficient to cause any sand to overflow with the slime. The Akins Classifier of the Colorado Iron Works, Fig. 63, has a semi-cylindrical trough in which a large slow-moving screw-con- FiG. 63. Akins Classifier. veyor moves the sand up the slope of the trough, the slime over- flowing at the lower end. Both of the above machines are reported as doing good work. Amalgamation and Concentration. Amalgamation and con- centration are alike, in that both of them are used to save gold or silver not readily recoverable by direct cyanide treatment. The first has been sufficiently discussed elsewhere in this book. Concentration, where it is practiced in connection with cyaniding, is hardly the fine art that it has become in the treatment of lead and copper ores. In general it comes under what is usually desig- nated as 'fine concentration,' i.e., only finely crushed material is handled. This limits the machines to be used for the work, so that Wilfley tables or other machines of the riffled-surface shaking-table type, with belt vanners occupying a less prominent 142 STAMP MILLING AND CYANIDING position, are almost the only concentrators ever seen in cyanide plants. Canvas or other stationary sloping-plane tables are some- times used. An interesting variant from this practice is shown in the Goldfield Consolidated plant, where blankets have taken the place of part of the amalgamating tables and are found efficient in recovering coarse but unamalgamable gold. Roasting. The vast majority of complex ores would be ren- dered more susceptible to cyanide treatment by a thorough pre- liminary roast, not only on account of the removal of cyanicides, but also, because of the porosity induced by subjecting them to heat and consequent dehydration. For example, clay before bak- ing is anything but porous, but after being burnt into bricks it will absorb its own weight of water almost instantly. The extra cost entailed by roasting is, however, seldom justified and only in a few cases, such as in the treatment of the sulpho- telluride ores of Cripple Creek and Kalgoorlie, or the complex arsenical-sulphides of Mercur, has it been used on a,ny large scale.* Small installations for the roasting of concentrates prior to cyanid- ing have been more common. After numerous trials of the almost endless variety of roasting fiu-naces which have been evolved in lead and copper metallurgy, standard practice of to-day has fixed upon the straight-line type of furnace as the most suitable for roasting preliminary to cyanid- ing. One thing is to be particularly noted in this cormection: the roasting must be a 'dead' or 'sweet' roast, that is, the elimination of sulphur, arsenic, and other volatile elements must be practically complete. Partial decomposition products of oxidation by roast- ing are quite as vigorous cyanicides as the same or similar com- poimds produced by natural oxidation. . There are on the market at present two furnaces which have proven particularly adapted to this work, for both of which we are indebted to Western Australia. I refer to the Edwards and the Merton furnaces. The Edwards Roaster is of two types, fixed and tilting. In the former the hearth slopes gently toward the discharge end; in the tilting type this slope is adjustable by jack-screws at one end of the furnace, the entire structure being mounted upon a pivot near * The roasting plant of the Mercur type, erected at Republic, was, in the state of the art at that time, justified by the close-grained character of the ore and not because of the complexity of the gold and silver minerals. PREPARATION OF ORES 143 its center, see Fig. 64. Rabbling or stirring of the cliarge is pro- vided for by means of rotating arms mounted upon spindles pro- jecting through the arch of the furnace and driven by suitable gearing. These rabble-arms cut each others' circles, and revolve in opposite directions, so that the ore is made to pursue a zig-zag course in traveling through the furnace. The standard simplex furnace of this type has a hearth 6| by 57 ft. In the 'duplex' furnace the hearth is double this width, 13 ft., and has a double! row of rabbles; the length is vari- able, depending upon conditions. The number and location of the fireboxes is a matter determined by the character of the ore. The furnace may be used with either wood, coal, gas, or oil. The fur- naces, 65 by 64 ft., at the Great Boulder mine have a capacity of 25 tons of ore per day, require 2 h.-p., and reduce the sulphur from 4 per cent to 0.05 per cent S and 1.8 per cent SO3. Fuel required (wood at $2.35 per ton) is 9 per cent of the weight of ore roasted. The total cost of roasting, exclusive (jf transporting the ore to and from the furnace, is in the neighbor- hood of 50 cents per ton. The Merton Furnace, Fig. 65, is similar in general principle and rabbling device to the Edwards. It is built, however, with multiple hearths, the ore dropping in its progress through the furnace from (in bO C M c3 O H GO a & a 144 STAMP MILLING AND CYANIDING hi C rt 3 o PREPARATION OF ORES 145 one hearth to the other. The multiple-hearth feature effects a saving of fuel. The costs and results, otherwise, are about the same as with the Edwards. Roasting furnaces are also used to some extent as a^means of chloridizing sulphide silver ores preliminary to cyanide treatment. BIBLIOGRAPHY FOR PREPARATION OP ORES FOR CYANIDE TREATMENT * Especially Desirable for Students* Use Classification. Ayton, Ernest F. The Ayton Pulp-Thickener for Tube-mill Feed. Pac. Min., Vol. 17, p. 403 (1910). Atton, Ernest F. Sand and Slime Separation, Ajianena Mill, 1 p. Mex. Min. Jour., Vol. 16, p. 87 (1913). DoRB, J. V. N. The Dorr Classifier, 1 p. Min. & Min., Vol. 28, p. 341 (1908). Huntley, Rollo E. . Slime Settler or Dewaterer, f p. Min. & Min., Vol. 31, p. 339 (1911). * Neal, Walter. Diaphragm Cones and Tube Milling, 3| pp. Min. & Sci. Press, Vol. 100, p. 483 (1910)., ' * Smart, G. O. The Tube MiU Circuit and Classification, 4 pp. (Ab- stract from J. C. M. & M. Soc, S. A., Feb., 1910.) Min. Sci., Vol. 61, p. 392 (1910). Roasting. * VON Bernewitz, M. W. Roasting at Kalgoorlie, 1 p. Min. & Sci. Press, Vol. 102, p. 660 (1911). Edwabds, J. E. Notes on Ore Roasting, 5 pp. Min. Sci., Vol. 61, p. 220 (1910). "Metallurgist." Roasting at Kalgoorlie, 2 pp. Min. & Sci. Press, Vol. 101, p. 50 (1910). * SciBiRD, G. H. & Mack, R. L. The Roasting of Telluride Ores. Min. & Sci. Press, Vol. 95, pp. 751, 777 (1907). CHAPTER X DISSOLVING THE GOLD AND SILVER The chemistry of solution has already been touched upon; in addition to the reactions involved, the following points are of importance in dissolving gold and silver from ores: (1) Strength of the solution. (2) Temperature of the solution. (3) Condition of the gold or silver particles. (4) Presence of cyaniddes. (5) Amount of solution. (1) Strength of Solution. Under ordinary conditions of tem- perature and pressure the solubility of gold and silver is dependent, according to Julian and Smart,* upon the following circum- stances: (1) The number and velocity of the migratory ions and oxygen molecules that take part in the dissolving of the metals. (2) The difference of potential between two parts of the metallic surface in contact with the solu- tion. Christy, whose work upon the electromotive force of metals in cyanide solutions f has become one of the few classics of cyanide literature, states it somewhat dif- ferently. According to his view the solubility of gold is depend- ent upon: (1) The electromotive force of the gold itself, which is insuffic- ient for the purpose. * Cyaniding Gold and Silver Ores, 1904, page 77. t Trans. A.I.M.E., Vol. 30, page 864-946. 146 10 20 80 40 50 Stiosgtb of Cyanide Salution laPeEoent Fig. 66. Christy's Diagram. DISSOLVING THE GOLD AND SILVER 147 (2) The electromotive force of the hydroxy! (OH) ions, which he assumes as proportional to the number of oxygen molecules, i.e., to the solubility of the oxygen in the cyanide solution. In effect the two authorities say the same thing in a different way. The curves in Fig. 66, taken from Christy (op. cit.), and based in part upon the pioneer work of J. S. Maclaurin,* regarding the effect of cyanide solutions of varying strength with and without oxygen, show clearly that the maximum solubility of gold occurs at a concentration of between 5 and 10 per cent KCy, that is where the gold voltage and the solubility of oxygen taken together form a maximum in effect. This, however, is not the same thing as the maximum efficiency of the solution, as is illustrated by the following table of com- parative solubilities :t TABLE XIII Comparative Weights Dissolved from Surfaces of Equal Area IN THE Same Time and Under Identical Conditions Metal 1 per cent sol. KCy 0.10 per cent aol. KCy Zine Gold Silver Lead Chalcopyrite Charcoal iron Pyrite and cast iron Galena Iron rust Mispickel Marcasite 282 230 127 121 101 62 50 32 20 13 100 82.5 45.5 43 36 22 18 11.5 7. 4.8 0.0 This table illustrates, also, that the dissolving power is not directly proportional to the strength of the solution. For exam- ple, under the conditions of the above tests, 230 parts of gold were dissolved in a 1 per cent solution; but in a solution iV as strong instead of Yir- = 23 parts, we have 82| parts, or almost four times this. If we take 0.01 as a unit of solution strength and compare the amounts dissolved per unit of strength in any solution we find: * Jour. Chem. Soc, Vol. 63, page 731, Vols. 67 and 68, pages 199-212. t Adopted from Julian and Smart, op. cit., page 81. 148 STAMP MILLING AND CYANIDING Strength of solution Total gold dissolved Gold dissolved per unit 1.0 0.1 0.01 230 82.5 24.0 2.3 8.25 24.0 Christy found that solution of gold in cyanide practically ceases at 0.001 per cent KCy ; hence it follows, of course, that the maximum efficiency lies between this point and Maclaurin's maximum solu- bility point. Weaker solutions are more efficient due to the re- latively larger number of free ions, and, also, because they not only hold oxygen in solution, but, being less viscous, they do not retard the migration of the oxygen (or hydroxy 1) ions. The solution required, then, is one of maximum strength con- sistent with minimum resistance to the circulation of the oxygen molecules. Time is, of course, an all important factor in the question of solution, but when, as in the case of a gold ore, solution takes place with considerable rapidity, while washing can only be accomplished slowly, we may virtually disregard the tim^ factor, and the most efficient solution for gold ore is thus usually found to be from 0.05 to 0.10 per cent KCy. In the treatment of silver ores, however, stronger solutions of 0.25 to 0.50 per cent KCy are found to give the best results. (2) Temperature of Solutions. In practice, after many re- peated trials, it has been found that only in rare cases does any advantage result from heating the solution. The solubility of the gold and silver increases from 90 units at 0° C. to 146 at 100° C. ; but the solubility of pyrite and other mineral matter increases much more rapidly, owing to the decrease in polarization, and so the advantage of increased solvent power is likely to be lost by increased consumption. Only in those climates where the solu- tion is likely to freeze has it been customary to make arrangement for heating it. The impression is gaining ground, however, that solutions when warm are more easily handled in filters, settling tanks, and thickeners, and the practice is extending among the silver mills with some rapidity. (3) Condition of the Gold Particles. The shapes and sizes of the gold particles in any ore must be numerous; but in any typical ore the chances are that the majority of particles will con- form to the same general shape, owing to the fact that they were DISSOLVING THE GOLD AND SILVER 149 probably formed at the same time and place, and under identical conditions. Take the two extreme cases: (1) The thin, flat plate or flaky gold, in which the surface ex- posed is practically constant until solution is complete. (2) The perfect sphere, in which the surface exposed to solution decreases as the action progresses. The first case calls for no further discussion; the second explains very clearly, why, in many ores, the last traces of gold are so hard to extract. If we consider a mixture of variously sized spheres the case is even more apparent; the small spheres are completely dissolved before the large ones, the remaining portions of which Unger on, dissolving at a constantly decreasing rate. The actual condition in most ores probably lies between these two extreme cases; few of the gold particles are likely to be true spheres, and hence as they approach dissolution, they tend to become slightly flattened. (4) Presence of Cyanicides. Cyanicides are substances de- structive of cyanide, that is decomposing it and becoming them- selves cyanides or derivatives of cyanide, without yielding any compounds desirable in the process. Mineral acids are — in strong solutions — absolutely destruc- tive, breaking up even the cyanogen molecule; in weak solutions hydrocyanic acid is evolved. Wood-fiber, cocoanut-fiber, jute, and similar vegetable tissues destroy cyanide in absence of alkali, when new, but the reaction soon ceases. Iron or steel decomposes cyanides but slowly. They consume much cyanide, however, as shown by the equation: Fe + 6 KCy + 2 H2O = KiFeCye + 2 KOH -|- 2 H. Their introduction is unavoidable in the course of crushing operations, due to the attrition of the grinding-machine parts. Copper may be native in the ore, or in minute amount may come from blasting-caps. It is comparatively negligible, however. 2 Cu -F 4 KCy + 2 H2O = K2Cu2Cy4 + 2 KOH -F 2 H. Lead is extremely soluble in potassium cyanide solution, but it is scarcely possible for it to come in contact with the solution, and so it remains an unimportant factor. 150 STAMP MILLING AND CYAN I DING Mercury, an important factor in treatment of amalgamation tailing, consumes cyanide and is precipitated on the zinc in ad- vance of the gold. Arsenic may occur native in gold ores, but is scarcely acted upon by cyanide. Tellurium often occurs with telluride compounds in ores; it is slowly attacked by cyanide but, Uke its sister metal selenium, (which is much more soluble) it seldom occurs in such quantity as to make its presence objectionable from the point of view of cyanide consumption. Pyrite (FeS2), unoxidized, is practically insoluble in the absence of oxygen. If partial oxidation has taken place before treatment, with formation of FeS04, then remedial measures must be taken before cyaniding. Pyrite, however, is more apt to oxidize to limonite and metallic sulphur. Marcasite is less soluble in the presence of oxygen than is pyrite. It is more likely to oxidize to FeS04, however, with consequently greater cyanide consumption, followed by complicated and unde- sirable reactions. (If much FeS04 is present it may be largely removed by a pre- liminary leach with water. The balance may be neutralized with alkali which converts it into ferrous hydrate and alkaline sulphate.) Chalcopyrite, Tetrahedrite, Chalcocite, etc., in fact, any of the copper-iron sulphide compounds, are probably the worst cyanicides we have. Much depends upon the other minerals in the ore. Chalcopyrite, for example, dissolves slowly in potassium cyanide alone. When a more negative mineral, as marcasite, is present solution is much more rapid. The presence of copper is not neces- sarily fatal to treatment by cyanide. An ore with 2 per cent of copper may be amenable to extraction of its gold content by cyanide and show a profit. On the other hand, an ore containing less than 0.5 per cent copper may not be susceptible of profitable treatment, owing to destruction of cyanide. Much depends, as before stated, upon the mineralogical association in which the copper and gold exist. Copper seems to interfere less in the ex- tracting of gold, than of silver from an ore. Mispickel (FeAsS) is a common constituent of gold ores. Its direct solubility in cyanide solutions is not great (see diagram). All the arsenic minerals, however, are soluble in alkali and the com- pounds thus formed seem to exercise a marked reducing action, DISSOLVING THE GOLD AND SILVER 151 thereby interfering seriously at times with the cyaniding of arsenic- al gold ores and causing a high consumption of cyanide. The decomposition products, hydrated oxides of iron, and arsenic are not especially active. The latter, however, in absence of free alkali decomposes potassium cyanide and liberates hydrocyanic acid. Lime or magnesia should be added to arsenical ores for this reason. Orpiment and realgar act in a similar way to the arsenic oxides mentioned above. Stibnite (Sb2S3), like arsenic, is sometimes highly injurious. Its decomposing action on cyanide is similar to that of the arsenic compounds, but it is not as readily controlled by addition of alkali. Sphalerite (ZnS), contrary to expectation, is not an active de- composer of cyanide. Like the copper sulphides, its action seems to depend in a large measure upon the associated minerals in the ore. If partly oxidized its action is much more marked, destroy- ing both cyanide and alkali. Galena is often associated with gold and silver ores. It is not an especially violent cyanicide, action following only long exposure to solution. Tellurides usually make an ore difficult to treat, the solvent action being very slow. As in the other cases, much depends upon the association of the minerals. Roasting renders most tellurides easily susceptible of treatment. Cyanicides Produced by Oxidation. Various partly oxidized products from iron and copper sulphides are active destroyers of cyanide. Ferrous and ferric sulphates unite with cyanide, forming either Prussian or TurnbuU's blue. The addition of lime or caustic soda precipitates ferric hydrate and prevents loss of cy- anide. Carbonates of copper (malachite and azurite) consume so much cyanide that ores containing even small quantities of them become unprofitable for cyanide treatment. Mineral Association. Apparently similar ores, from different locaUties, vary greatly in their action under cyanide treatment. The only explanation which can be offered is that of contact elec- trolysis varying with the minerals in association. For example, marcasite and pyrite, separately, have comparatively little effect upon cyanide. When the two minerals occur together the de- struction of cyanide may be greatly increased. Many of the complex compounds formed are decomposed in 152 STAMP MILLING AND CYANIDING the precipitating boxes, the metal being deposited or forming in^ soluble compounds with the precipitate. In this way, apparently weakened solutions are often freed of part of their impurities, and are in a measure regenerated. (5) Amount of Solution. In a thick, slimy pulp, solution of gold in cyanide cannot take place rapidly. This means that a certain ratio of liquid to solid must be maintained for the best work. The ratio varies with different ores and with different degrees of crushing. Silver ores require a greater amount of solu- tion than do gold ores. For ordinary gold-silver ores the ratio will vary from one of solid to one-half of solution in leaching, to as high as one of solid to six of solution in treatment of some silver ores, proportions in each case being by weight! Method of Application. In the MacArthur-Forrest methods of cyanide treatment, the cyanide solution was passed, usually with the aid of gravity, through a porous mass of ore, dissolving the gold and silver as it went. The cyanide solution was said to 'leach' the ore and the operation was designated the 'leaching method.' It soon came to be realized, however, that in order for the solution to leach out the gold and silver, it must percolate through the mass of ore, and that percolation, in the majority of cases, is only possible when the ore is in a comparatively .coarse state; so that leaching is impossible for ores requiring fine crush- ing to expose the gold particles to the action of cyanide. To overcome this difliculty agitation in one form or another has become a valuable adjunct to the cyanide process. (A) THE LEACHING METHOD Whenever it is possible to obtain satisfactory results by it, the leaching method, provided the time required be not too great, is to be preferred on account of its simpUcity and consequent low cost. Leaching-Tanks. The ore after suitable preparation is charged, by means to be discussed later, into the treatment 'tank' or 'vat,' as it is variously called. Leaching-tanks are almost always cir- cular and cylindrical, owing to the greater ease of construction and support when in this shape. Three materials are available, wood, steel, and concrete or masonry. Wooden Tanks are used in practically all but the largest instal- lations. California redwood, and Oregon or Douglas fir are the DISSOLVINO THE GOLD AND SILVER 153 materials most commonly employed. Tanks of redwood are to be preferred. Tanks less than 10 ft. in diameter may be made of 2-in. lumber, but 3-in. material is better. The staves of the tank, when well made, are shaped to the arc of the tank circle and the edges are beveled radially. The bottom pieces are cut to the necessary circle and are secured to each other by wooden dowel pins. The bottom of the tank is notched into the staves to a depth of § to f in., the notch or gain being known as the croze. The staves, of course, project some distance beyond the bottom of the tank, usually about 3 in. This projection is called the chine. The staves are secured to the bottom and to each other by en- circling rods of |- to f-in. round steel. Flat hoops were at one time popular but have been universally condemned. For securing the two ends of a small hoop, or the various sections of a large one. rMallcable Iron Lug Fig. 67. Hoop-Lug. to each other, various types of lugs are used. Fig. 67 shows one of the best. The threads of these hoops should be 'upset,' i.e., of the same diameter at the base of the thread as the balance of the rod, thus securing the maximum strength with minimum weight. Wooden tanks are designated by outside diameter and outside height. With 3-in. material, this means that the inside measure- ments are 6 in. less than the nominal size. Steel Tanks are popular in South Africa and in the larger instal- lations in Mexico. This is to be explained to some extent by the fact that in a tropical or semi-tropical country wooden tanks are harder to keep from leaking, as well as by the condition that, in the former country at any rate, the deposits justify a permanency of plant which is seldom aimed at in the western United States. They are more expensive than wooden tanks at the present time. 154 STAMP MILLING AND CYANIDING As lumber suitable for tank stock becomes scarcer and higher in price, steel tanks will become more widely used. They are built of the same shape as wooden tanks, the thickness of plate varying from t:\ to f in. according to height and diameter. They are stif- fened at the top and bottom by angle-irons and the bottom corner is usually formed by this means. Like wooden tanks they are shipped 'knocked down,' the plates being cut and punched for rivet-holes, and the side plates being rolled to the required tank circle, as are also the angle-iron rings. Masonry and concrete tanks have not yet come into extensive use. With the experience of hydraulic engineers in seepage through concrete stand-pipes" and reservoirs it would seem, that until more efficient means of water-proofing such materials are devised, masonry and concrete should be reserved for foundations and the like, and wood or steel used for cyanide tanks. Size of Tanks. Leaching tanks are usually made of such a size that their capacity is equal to the amount of sand to be leached per day. In this way, by providing as many tanks as there are days in the cycle of treatment, one tank is loaded and discharged each day, thus keeping conditions of labor and so forth uniform, throughout the plant. The depth of the tank to be employed is influenced mainly by the leachability of the ore; from 4 to 10 ft. will cover the range of depths generally employed. Having fixed on the depth, the diameter is a simple matter of arithmetic, as soon as the weight per cubic foot of the material is known. This last may easily be determined by experiment. The commercial size nearest the cal- culated dimensions should, of course, be selected, making allowance for the fact that the sand should not come nearer than 6 inches from the top of the tank, and also for the space occupied by the filter frame. Filter-Bottoms (Fig. 68). The filter-frame most commonly used (marked style B and style E) consists of a grating of 1-in. strips, spaced 1 in. apart, supported on a series of sill-pieces at right angles to them on the bottom of the tank. On the grating is placed a canvas filter-cloth; this in turn is often supported by cocoa- matting. In large tanks this grating is made in sectors for ease in handling. Surrounding this filter-frame is a wooden ring, of the same height as the filter-frame, so set that there is a space of f to 1 in. between it and the side of the tank; the canvas filter-cloth DISSOLVING THE GOLD AND SILVER 155 Fig. 68. FUter-Bottoms. Fig. 69. Sand Slat-Fflter. 156 STAMP MILLING AND CYANIDING is cut several inches larger in -diameter than the filter-bottom, the edges of the cloth are then tucked into this space, and a rope is caulked on top of the cloth, thus stretching the cloth on the filter-frame much as the vellum is stretched on the head of a drum. In some plants shoveling-strips of 1-in. material are Hghtly fastened to the upper side of the filter to protect the can- vas when discharging the tanks by hand. Another form of filter (style C and style D) is made of boards with numerous holes bored through them, the boards in turn being supported on cleats to give space for the filtered solution. So called 'sand-filters' (Fig. 69) are sometimes seen in leaching plants and are becoming quite popular in some mills as a means of clarifying slightly cloudy solutions from other parts of the process. They consist simply of triangular strips, supported on the tank- bottom by the usud cleats. The apex of the triangle is placed uppermost and the space between the slats filled with successive layers of gravel, until a uniform surface of coarse sand is presented. Upon this the charge to be leached is placed. Charging. The method to be used in charging the leaching- tanks depends primarily upon whether the ore is charged dry or wet. Dry-charging is, of course, only possible with a dry-crushing plant or when dealing with semi-dried tailing accumulations. It has the advantage, that there is no such stratification of coarse and fine material, as necessarily occurs when a wet-crushed pro- duct is charged, with water, directly into the leaching tank. In dry-charging for small installations the material is handled by car or other means and is dumped on a grating set over the tank. In larger plants elaborate systems of belt-conveyers either feed to centrifugal-distributors, which scatter the sand in a shower over the surface of the charge, or else pile it in the center of the tank, there to be distributed by a series of discs rotating about a vertical axis, operated and supported from a travelling bridge which spans the leaching tank and travels lengthwise of the tank-house. This distributor is similar in principle to the Blaisdell excavator shown in Fig. 74 and is put out by the same firm. In wet-charging, two methods are available. The first is to collect the sand in the tank in which it is to be treated. The second is to collect the sand in one tank and transfer it to another before applying the cyanide solution. In small plants the first method is almost always used on account of the smaller num- DISSOLVING THE GOLD AND SILVER 157 ber of tanks required. The pulp is usually charged into the leach- ing-tank by means of a distributor of the lawn-sprinkler type, (Fig. 70), the slime overflow being provided for, either by a series of holes one above the other in the side of the tank, or by a 'slat Fig. 70. Automatic Pulp-Distributor. gate' overflow, so arranged that the sUme outlet is at a practically constant distance above the sand accumulating in the tank. By this means, with general mill tailing, the sand is kept fairly free from slime; but slime in the charge and sand in the overflow are, to a certain extent, unavoidable. UsuaUy, however, a fairly leach- 158 STAMP MILLING AND CYANIDING able product is secured. If good classification precedes charging, there is no reason why ahnost clean sand should not be obtained. When the tank is sufficientlj' full, the flow of pulp is diverted, the water on the surface decanted, and that in the charge allowed to drain through the filter. The cyanide solution is then applied. When collecting tanks are used, they are filled with clear water, and the stream of pulp is turned into the tank through the dis- tributor as before; the sand at once begins to settle, and the slime overflows by means of an annular launder at the top edge of the tank. When the collecting tank is full of sand, the pulp-flow is diverted, the water drained off as before, and the sand transferred Fig. 71. Bottom Gate. to the leaching tanks. In some cases it is found advantageous to give the sand a double treatment, that is, to leach it in one tank and then transfer to another tank for a second leaching. The thorough aeration of the pulp thus induced occasionally makes a marked difference in the extraction. In this event the first treat- ment may be given in the collecting tanks. Discharging. There are two types of gates for use in dis- charging the leaching-tanks ; one is the bottom gate, the other the side gate. Bottom gates, two forms of which are shown in Figs. 71 and 72, are preferable whenever there is room below the tank to permit their use. These are made either square or circular, and a tube-like projection extends from the bottom of the tank to the DISSOLVING THE GOLD AND SILVER 159 surface of the filter. Circular discharge-doors are to be preferred. Side discharge-gates should be put in only when their use is un- avoidable; they interfere seriously with the hoop spacing, unless special provision is made for them. The form shown in Fig. 73 ^waiiiwan. Fig. 72. Bottom Gate. Fig. 73. Side Discharge-Gate. is recommended by R. Stuart Browne,* who has had much ex- perience in tank construction. For moving the material out of the tank, there are three possi- bilities: shoveling by hand, sluicing with a hose and nozzle, and excavating with machinery. Whenever water is available sluicing * Pac. Miner, Vol. 17, page 336. 160 STAMP MILLING AND CYAN I DING is the quickest and cheapest method; shoveling is, of course, ex- tremely expensive, but is often the only alternative where the size of the plant does not warrant the use of mechanical excavators. The Blaisdell excavator (Fig. 74) is only possible with a large plant; it consists of a rotary disc-harrow, the discs being suspended from arms fixed to a central revolving spindle. This spindle is supported and operated from a travelling bridge which spans the leaching-tanks as shown. The shaft is lowered as the discs cut their waj' through the charge, moving the sand before them to a central discharge-gate. ^ ; ■ 'mmk^ BMIIBi"lii iiiii''Wiwjagmtei8M— ^:^^m^^ ;: . ,■ .. '^■^■''':;;^/ RJ Fig. 74. Blaisdell 30 ft. Class A Vat Excavator. Applying Solutions. The solution may be applied at the sur- face of the ore and allowed to percolate downward by gravity, or it may be applied from below the filter-cloth, under low pressure and allowed to percolate slowly upward. There are also the inter- mittent and the continuous methods of application. In the for- mer, each solution is added after the previous one has completely drained. In the continuous method the next solution is added before its predecessor is out of the tank. There is a diversity of practice in this respect. Some metallurgists apply their solution in a few large charges, other in numerous small ones, both giving DISSOLVING THE GOLD AND SILVER 161 apparently equally satisfactory results. In the subsequent water wash, however, numerous small charges are beneficial, and this is an important point, for it is as essential that the dissolved gold should be washed out of the charge, as that it should be dissolved in the first instance. The rate of percolation varies with the size, volume, and uni- formity of the interstices between the ore particles and to some extent with the depth of the column, the temperature, and the pressure. Downward percolation takes place at a- fairly uniform rate, diminishing slightly with increased depth of ore; upward percolation diminishes rapidly in velocity as the surface is reached. Uniformity in texture of the ore is one of the chief secrets of good leaching, and to get uniformity in texture uniformly sized particles are necessary. Thus a carefully-sized ore will give not only more uniform results but better extraction, and will retain less moisture than the same ore unsized. The amount of moisture retained by an ore depends upon the character of the ore, the size of the particles, the texture, the depth of the column, the temperature, and the pressure. The first 2 to 6 in. above the filter always retains an excess of moisture. This depth is practically constant, so that the deeper the charge in the tank the less moisture proportionally is retained above the filter. Pressure, applied usually by inducing a partial vacuum below the filter, is efficient in removing the last traces of moisture. Pres- , sure, howevfer, must not be applied indiscriminately, as it is apt to result in uneven packing and settling of the charge. Bad leaching results from uneven percolation, and uneven per- colation follows want of uniformity in texture of the ore, or lack of uniformity in the pores of the filter-cloth. If ore containing slime is charged, the slime may settle unevenly on the filter-cloth and so clog part of the pores. For this reason filter-cloths should be frequently washed. In some plants there is an excellent cus- tom of covering the filter with thi-ee or four inches of clean sand; this serves to equalize the filtration rate over the whole area. If any machinery or staging is supported directly on the tank, the vibration set up may cause uneven settling, and so lead to poor leaching results. The quantity of solution required to cover the ore is evidently dependent upon the volume of the interstitial spaces. If G is the specific gravity of solid ore and g is that of the crushed 162 STAMP MILLING AND CYANIDING material, then the ratio of spaces of voids to volume occupied by , • G-g pulp IS -^■ Assume the specific gravity of sohd quartz to be 2.65, and of the 2 65 1 28 1 37 pulp 1.28, then ' ^ ' = ^— = 0.52 = proportion of voids. Therefore, the proportion of voids to sohds is as 52:48, and the relative weights are: 1.28 of sand to 0.52 of water; or 0.405 ton of water per ton of sand is required to fill the interstitial spaces. Slime. Reference has already been made to the effect of slime, and it may be well to digress somewhat on this point. The term sUme is a somewhat indefinite one; many authorities base the dis- tinction between sand and slime upon fineness of the grains alone. This is manifestly inaccurate, since pure quartz ground to 150 mesh does not form a slime with water, while a talcy, clayey rock will become plastic with far less comminution. The definition proposed by Warwick comes nearer fitting the case than any other I have seen. "A slime is all that part of a crushed product which, after settling in water for 48 hours, retains at least 40 per cent moisture and exhibits plastic qualities." * Slime is the enemy of leaching,, and as it increases in quantity, leaching becomes more and more unsatisfactory and finally im- possible. The following taken from Julian and Smart illustrates this point: To a carefully sampled pulp, freed from its own slime, various quantities of plastic clay, free from gold and silver, were added, and the samples so prepared were each submitted to a leaching test under identical conditions of treatment. Slime added Extraction to sample 0% 84.3% 5% 75.9% 10% - 62.5% 11% 31.9% 12% No percolation The slime was tested for cyanide consumption and showed prac- tically none whatever, so that the effect was purely mechanical, * This is a working definition. That the sand represents the crystalline portion, and the slime, in the main, the colloidal portion of the pulp is evident. DISSOLVING THE GOLD AND SILVER 163 due in part to coating of the gold particles, and in part to the re- tention of gold solution by the slime, up to the point where leaching was out of the question. (B) THE AGITATION METHOD While much more recent than leaching, agitation has now reached a high state of perfection and the majority of cyanide plants throughout the world are treating non-leachable material by this method. The systems of agitation in use may be divided into: 1. Agitation with mechanical stirrers. 2. Agitation with centrifugal pumps. 3. Agitation with compressed air. 1. Agitation with Mechanical Stirrers. The revolving arm or paddle-agitator (Fig. 75) is one of the simplest of this type. A Paddle-Agitator. vertical shaft or spindle is supported in the.center of a flat-bottom tank. To the lower end of the spindle are attached two horizontal arms, tapered toward the outer end. The shaft and arms are revolved by suitable bevel-gearing above or below the tank. One horizontal shaft may be arranged by suitable clutches to drive any number of agitators. This agitator does not provide for as thorough aeration of the pulp as is desirable and there is always a fendency for ore and sol- 164 STAMP MILLING AND CYANIDING ution to rotate e?i masse, thus defeating the purpose in view. In consequence it has been in some cases supplemented by baffle- boards, or by perforated pipes on the bottom of the tank through which compressed air is dehvered to the charge. One of the most recent devices for agitating cyanide pulp is the Dorr agitator (Fig. 76). In speaking of it the inventor says: "It can be operated in any flat-bottom tank, and consists of a central vertical cylinder carried by a shaft supported from the top of the tank and equipped with two arms carrying plows, as in the Dorr thickener, which travel around the bottom of the tank and draw the pulp to the center. This (pulp) is raised through the cylinder by means of air and distributed evenly over the surface of the pulp in the tank, by suitable revolving launders." It is difficult to see why this apparatus should not prove entirely successful, since it provides for thorough aeration and obviates Fig. 76. Dorr Agitator. the other difficulties of the mechanical-stirrer type of agitator as commonly used. It also makes impossible the accumulation of solids in the bottom of the tank, a defect from which even the best compressed-air agitators are not entirely free, particularly if col- DISSOLVING THE GOLD AND SILVER 165 Fig. 77. Hendryx Agitator. Fig. 78. Agitation with Centrifugal Pump. 166 STAMP MILLING AND CYANIDING loids (which assist materiality in keeping the sand in suspension) are absent from the ore. The Hendrijx agitator, see Fig. 77, consists of a conical-bottom tank -u-ith a central column in which operate several propellers. These propellers draw the pulp from the bottom of the tank into Fig. 79. Trent Agitator with Footstep Detail. the central pipe, and discharge it at the top on a flat conical apron which extends to within a short distance of the side of the tank. This apron forms an excellent aerating surface. 2. Agitation with Centrifugal Pumps. This sj^stcm (Fig. 78), which was developed shortly after the first revolving stirrer, consists DISSOLVING THE GOLD AND SILVER 167 of discharging the pulp from the bottom of a conical tank into the suction of a centrifugal pump, returning it to the top of the tank, and discharging it upon an apron, or in the form of a spray, to en- sure oxidation. A modification of this method is to allow a small amount of air to be drawn into the pump suction, thus aerating the pulp in the pump and return pipe. This method is open to the objection that the wear of centrifugal pumps when handling O" O" B/" 6sis.>i DiBcharge Plauge Fig. 80. Pachuca Agitator. pulp is excessive. To obviate the difficulty, the following scheme has been proposed by L. C. Trent, and has proven fairly success- ful in several mills: The Trent agitator (Fig. 79) is, only in a superficial sense, of the centrifugal pump type. The suction of the pump here con- nects with the upper part of the tank containing practically clear solution; this clear solution is delivered on the bottom of the tank, 168 STAMP MILLING AND CYAN I DING through the arms of a distributor of the lawn-sprinkler type, else- where discussed. Aeration is provided for by a properly-controlled 'leaky suction.' Special provision must, of course, be made for the footstep bearing carrying the distributor, in order that it may not wear out rapidly, due to the grit. 3. Agitation with Compressed Air. Developed independently in New Zealand and in Mexico, the Brown-Pachuca agitator has rapidly displaced other methods for the circulation and aeration of pulp. The extreme simplicity of the method, combined with the fact that there are no wearing parts exposed to the cutting action of the pulp, has led to its frequent application in recent slime plants. Fig. 80 shows a typical Pachuca tank, 45 ft; high by 15 ft. in diameter, consisting of a steel shell having a conical bottom. Suitable braces of angle-iron extend from the central pipe-column to the shell. In a tank of the size given the central pipe is 18 in. in diameter. It extends to within 18 in. of the bottom or apex of the cone and runs from there to within 2 ft. of the top of the tank. Into the lower end of this pipe a jet of compressed air is forced through a l§-in. pipe and the dilution by air bubbles of that part of the pulp within the pipe leads to its rising within the pipe and hence to its over-flow at the top. The following is taken from an article by A. Grothe * the father of the Pachuca tank in Mexico. "When agitation is started up, a pressure somewhat in excess of the hydrostatic head has to be used, and slime being closely packed in the con- ical part of the tank and in the air-lift, the first effect of turning on the compressed air will be to drive the contents of the lift upward, where they will overflow into the tank, leaving the air-shaft quite empty. The air- valve should then be closed to obviate the useless escape of air, but in a short time material outside the lift will have entered the lower part of it by reason of the pressure in the tank, and a slight movement of the mass outside the hft will have set in. The contents of the hft should then be blown out again by a momentary opening of the air-valve, and this opera- tion should be repeated until a narrow annular channel is formed on the outside of the lift through which the solution standing above the sand can freely enter the lift at the bottom, after which the current scours the sur- rounding sand and slime, and after a short time the cone is free from all impediment and the tank is in uniform agitation, the whole operation not having taken more than a few minutes. The pressure and quantity of air can now be considerably reduced; they do not have to be nearly so * Mex. Min. Jour., Vol. 11, No. 2 (Aug., 1910, page 3). DISSOLVING THE GOLD AND SILVER 169 great as the hydrostatic pressure, corresponding to the height of the tank and the specific gravity of the pulp, owing to- the central pipe containing a mixture of air and pulp very much lighter than the material surrounding it when the tank is in agitation.". . . . . . "It is a common mistake to take for granted that violence of agi- tation acts beneficially on the time and thoroughness of extraction. It is only necessary to keep all the pulp in constant agitation, and this is at- tained when the velocity of the current in the cone is sufficient to move every particle of material as it comes down to the inlet of the air-hft. As long as any settlement on the sides of the cone is prevented the maximum of useful agitation is obtained and anything in excess of this is sheer waste of air. The pulp brought to the top instantly commences a downward course, the particles of ore, at a somewhat greater velocity than the solu- tion, being accelerated by gravity. Particles heavier, on account of size or greater specific gravitj^ (such as the metaUic contents), reach the bottom sooner than the fine slimes and, therefore, the solid contents continually change their position in relation to the fluid contents, and in their fall of 45 feet are constantly brought into contact with fresh portions of the solu- tion. This is the fundamental difference between this kind of agitation and that in mechanical stirrers, or with ordinary and more refined air jets, all and every one of which have a- tendency to effect an appreciable amount of classification, thus producing the opposite effect to that obtained in Pachuca tanks." . . . . . . "To obtain this perfect circulation, 30 cu. ft. of free air (per minute) is sufficient for a tank 15 ft. diameter and 45 ft. height, holding a charge of 100 tons dry ore, all ground to 150 mesh, and 75 per cent to 80 per cent to 200 mesh, with a proportion of 1.2 of solution to 1 of solids. It is another matter when some peculiarity of the ore, such as a tendency to scum, has to be overcome, in which case it may be judicious to only charge the tank to a point several feet below the top of the air-lift, making use of the falling pulp to break up the scum which might otherwise accumulate and cause trouble. An instance of the successful use of this method is to be found in the San Rafael mill at Pachuca." In a recent modification the central pipe- terminates some 6 or 8 ft. below the top of the charge and better aeration is claimed for this arrangement. The Parral Tank* Fig. 81, is fundamentally the same as the Pachuca. As at present used the Parral tanks are flat-bottomed, 25 ft. in diameter by 15 to 25 ft. high; and the single 18-in. cen- tral pipe of the Pachuca is replaced by four 12-in. pipes equi- distantly spaced on a 17-ft. circle. These pipes terminate in a * Bernard Macdonald, Trans. A.I.M.E., Vol. 42, page 819. 170 STAMP MILLING AND CYANIDING tee at their upper end, so that the pulp is discharged with con- siderable tangential velocity, soon setting the entire contents of the tank in rotation. Another variation of the' compressed-air agitation is the so- called Just process, in which the bottom of a flat treatment tank Fig. 81. Parral Agitator. is lined with a porous inert material called 'silica-sponge.' Com- pressed-air is forced beneath this silica-sponge bottom, and rising through the interstices in the porous brick, ascends in innumera- ble small bubbles through the charge in the tank. Good results are reported to have followed its use in some Mexican mills, but it is hard to see that it has any advantages over the Parral or Pachuca agitator. A. Grothe {loc. dt.) makes the following interesting remarks : "It is sometimes adduced that the dissolving action of the cyanide is increased and accelerated by the quantity of air mixed with the solution, and the alleged rapidity of action in tanks with porous-brick bottoms is supposed to be due to the large quantity of air passing through the pulp in fine jets. A little reflection, however, will show the fallacy of this idea. In the Pachuca tanks the air enters the lift in a thin annular jet and mixes intimately with the pulp. There is no question of large bubbles when the tank is in uniform agitation, these only occurring at the time when it is necessary to employ more air for starting up. The air is carried down- ward for some distance with the falling pulp and rises in small bubbles to the surface. The solution in the tank is saturated with air, and it is clear DISSOLVING THE GOLD AND SILVER 171 that the chemical action in certain kinds of ore can only be exerted by such air as is in solution, and not by the small bubbles on which stress has been laid. After the saturation point has been reached, any further admixture of air is ineffective, and this reasoning is fully borne out by experiment. I have repeatedly tried the effect of ultra-violent agitation as against that of a moderate one, and have found that as long as all particles are kept in motion, no further improvement either in point of time or ultimate re- covery, can be looked for." Intermittent vs. Continuous Agitation. Until quite recently all agitators were operated on the intermittent or ' charge ' system. In this way, a tank was filled to its capacity with slime; this was agitated for the requisite time and discharged to the filter or filter storage. It then stood idle while being filled. At the mill of the Esperaiiza Mining Co., at El Oro, Mexico, using 15 by 45 ft. Pachuca tanks, M. H. Kuryla * found that over 15 per cent of the net time of agitation was lost in filling and dis- charging the tanks. In addition much inconvenience and con- siderable cost was involved in discharging the tanks from the bottom, which was nearly 40 ft. below the top of the tanks used for pulp-storage prior to filtration. To obviate these difficulties Mr. Kuryla connected the six tanks of the battery under consideration, by means of 6-in. pipe, feeding the pulp-supply to No. 1 tank,, and withdrawing it from below the level of the top of the air-lift in No. 6 tank. This method not only solved the problems mentioned, but showed a slightly increased extraction of both gold and silver, due probably to the increased time of agitation, incident to eliminating the filling and emptying of each tank. The evident advantages of this continuous method of agitation have led to its adoption in many of the large plants. It has been successfully applied not only to Pachucas but to Parral tanks, Trent agitators, and to other forms of agitating devices. Time of Treatment. The time of treatment, whether by leach- ing or by agitation is, of course, a function of the individual ore, a derivative as it were of the ore's 'personal equation, but it will usually be found that a much shorter time of agitation with air is required, than where one of the mechanical or pump-agitators is used. It is also equally true that with the same ore far less time is required where the ore is agitated with solution, than where it is * Mex. Min. Jour., August, 1910, Vol. 11, No. 2, pages 44^47. 172 STAMP MILLING AND- CYANIDING treated by leaching alone. If our electrolytic solution theory is correct the reason for this is obvious enough, for with an adequate air-supply the likelihood of polarization is much lessened. Effect of Extra-Solutions * and Oxidizers. For ordmary gold ores, air, provided it be furnished in sufficient quantity, seems to furnish oxygen enough for Eisner's reaction. But with telluride ores, cyaniding alone, without previous roasting, does not yield a satisfactory extraction. This problem has been solved in West AustraUa by the addition (in the agitator) of bromo-cyanogen to the cyanide solution after it has been in contact with the ore for 12 to 16 hours. From one-fourth to one-third the weight of cyan- ide is the amount of 'Bromo' used. The bromo-cyanide is pre- pared either by adding liquid bromine to cyanide solution packed in ice, or by agitating for a considerable period a solution of 'mixed salts' (potassium bromide and bromate) with potassium cyanide and sulphuric acid.f For various reasons this treatment has not, until recently, been followed with the telluride ores of Cripple Creek, Colorado. The new Portland mill at that place is however employing a non-roast- ing process with success, the exact details of which have not been made public. There is reason for believing that the method is dependent upon the use of a halogen cyanide. Bromo-cyanogen is "also used sparingly in the new Independence mill in the same district. The Clancy process,! — patented — designed primarily for the treatment of these ores, employs cyanogen iodide as its active reagent. A solution of potassium iodide, cyanide, and sulpho- cyanide with calcium cyanamide is used in place of the usual cyanide. The ore is agitated with this solution while a weak electric current is passed continuously through the pulp, with the result that cyanogen-iodide is liberated. (Clancy suggests also the formation of cyanamidogen iodide (I2CN2).) Regeneration is effected by further electrolysis after addition of caustic soda to increase alkalinity. * The decadence of hyposulphite Uxiviation leaves this convenient term open to appropriation. t E. W. Nardin, Min. & Sci. Press, Vol. 97, page 562. t John Collins Clancy, paper read before the American Electro-chemical Society, Dec. 16, 1910, reproduced in Eng. & Min. Jour., Vol. 90, page 1250; Min. & Sci. Press, Vol. 101, page 862; Pao. Min., Vol. 18, pages 43-117. This is an exhaustive discussion and should be read by all interested. DISSOLVING THE GOLD AND SILVER 173 With silver ores the problem is a different one; in certain complex ores — particularly when high-grade — there is some question as to whether air is a sufficiently energetic oxidizer on account of its low oxygen content. D. Mosher * has suggested ozone for this purpose, and reports good results from its use. Oxygen derived from electrolysis of water j has also been suggested for the same purpose. Other oxidizers and chemicals applied to the treatment of silver ores will be discussed elsewhere in this work. * Pac. Min., Vol. 15, page 89. . t H. A. Megraw, Eng. & Min. Jour., Vol. 88, page 645. BIBLIOGRAPHY FOR " DISSOLVING THE GOLD AND SILVER " * Especially Desirable for Students' Use Leaching. * Browne, R. Stuart. The Design of a Sand Leaching Plant. Pac. Min., Vol. 17, pp. 296, 334, 363 (1910). Banks, John H. G. Upward Leaching of Sand, 1 p. Eng. & Min. Jour., VoL 92, p. 149 (1911). * Butters, Charles & Crank, Albert F. Handling Sand for Cyanide Vats (Blaisdell Excavator, Etc.), 1| pp. (Originally read before Inst, of Mining & Metallurgy.) Eng. & Min. Jour., Vol. 76, p. 850 (1903); Min. Wld., Vol. 26, p. 46 (1907). * Caldecott, W. a. The Vacuum-pump in the Cyaniding of Sand, f p. Min. & Sci. Press, Vol. 98, p. 316 (1909). Caldecott, W. A. Continuous Collection of Sand for Cyaniding, 2 pp. Min. & Sci. Press, Vol. 99, p. 659 (1909). Deanb, a. J. Aeration of Sand Charges. Eng. & Min. Jour., Vol. 92, p. 198 (1911). DuRANT, H. T. Upward Leaching of Sand, IJ pp. Eng. & Min. Jour., Vol. 91, p. 417 (1911). Editorial. Caldecott Filter Tables, 1 p. Min. & Sci. Press, Vol. 99, p. 48 (1909). Linden, H. I. Leachmg Slimy Pulp, 2i p. Pac. Min., Vol. 15, p. 202 (1909). * Megraw, H. A. Characteristics of Sand in Cyaniding, 2 pp. Min. Wld., Vol. 32, p. 927 (1910). * Tays, E. a. H. Leaching & Aeration. Min. & Sci. Press, Vol. 93, p. 265 (1906). . An Early Account of Leaching Methods. Min. & Sci. Press, Vol. 48, pp. 254, 274, and 290. * . Caldecott Sand-filter Table, 1 p. Eng. & Min. Jour., Vol. 94, p. 15 (1912). Slime and ' Sliming.' Ashley, Harrison Everett. Slime, i p. Min. & Sci. Press, Vol. 99, p. 289 (1909). 174 STAMP MILLING AND CYANIDING * Ashley, H. E. Chemical Control of Slime, 16 pp. Trans. A.I.M.E., Vol. 41, p. 380 (1910). * Ashley, H. E. Colloid Matter of Clay, etc. U. S. Geol. Survey BuU. No. 388 (1909). Bhooks, Huxley St. J. AU-sliming. (Enquiry about E. M. Hamil- ton's Art. under same title) in Vol. 99, p. 255, I p. Min. & Sci. Press, Vol. 99, p. 760 (1909). * Caetani, Gelasio. Sand, Slime and Colloids in Ore Dressing, 5 pp. Min. & Sci. Press, Vol. 106, p. 438 (1913). * Collins, Edgak A. All Sliming, i p. Min. & Sci. Press, Vol. 99, p. 389 (1909). Editorial. All Sliming, 1 p. Pac. Min., Vol. 18, p. 150 (1911). " * Hamilton, E. M. All-sliming, 3 pp. Min. & Sci. Press, Vol. 99, p. 255 (1909). Lamb, Mark R. Sliming Ores for Cyaniding, | p. Min. & Sci. Press, Vol. 95, p. 658 (1907). Megraw, H. A. AH Slime Treatment of Ore in Cyanide Plants, If pp. Eng. & Min. Jour'., Vol. 89, p. 319 (1910). Nichols, Horace G. Treatment of Slime, 1 p. Pac. Min., Vol. 15, p. 217 (1909). Parrish, Edward. Slime, 2^ pp. Min. & Sci. Press, Vol. 99, p. 492 (1909). Salkinson, A. Effects of Heating Solutions in Treatment of SUme. Rev. in Min. Ind., Vol. XVIII, p. 354; J. C. M. & M. Soc, S. A., Vol. IX, p. 308. Spicer, H. N. Evolution of Methods of Handling Slime, 10 pp., illus. Met. and Chem. Eng'r, Vol. 11, p. 239 (1913). Whitman, P. R. All Sliming, i p. Min. & Sci. Press, Vol. 99, p. 388 (1909). Wilson, E. B. Cyaniding Slime. Min. & Min., Vol. 29, pp. 129, 187 & 224 (1908). Agitation. * Adams, Huntington. The Continuous System of Cyaniding in Pachuca Tanks, 7 pp. Bull. 56, Trans. A.I.M.E., p. 595, August, 1911. * Allen, Robert. Agitation of Slime Pulp, 4 pp. J. C. M. & M. Soc, S. A., April, 1911, Vol. 11, pp. 422, 561 (1911). Austin, L. S. Continuous Agitation and Extraction, 1 p. . Mex. Min. Jour., Vol. 16, p. 239 (1913). VON Bernbwitz, M. W. Slime Agitation at Kalgoorlie, IJ pp. Min. & Sci. Press, Vol. 102, p. 749 (1911). Bishop, L. D. The Hendryx Agitation Tank. West. Chera. & Met., Vol. 3, p. 187 (1907). * Brown, F. C; Agitation by Compressed Air, 4 pp. Min. & Sci. Press, Vol. 97, p. 424 (1908). Cabpent^ir, Jay A. Continuous Agitation at the West End Mill, Tonapah, 6 pp., illus. Min. & Sci. Press, Vol.. 106, p. 646 (1913). CoNKLm, H. R. Piping for Continuous Agitation, f p. Eng. & Min. Jour., Vol. 93, p. 587 (1912). DISSOLVING THE GOLD AND SILVER 175 Crosse, Andrew F. Assisting Solution of Gold in Cyanide process by- compressed air, i p. Min. Rep., Vol. 56, p. 420 (1907). * Editorial. Slime Agitation. Pac. Min., Vol. 16, p. 41 (1910). Editorial. A new Method of Agitating Cyanide Pulps, 2 pp. Pac. Min., Vol. 16, p. 121 <1910). Editorial. Agitation in Pachuca Tanks, IJ pp. Pac. Min., Vol. 19, p. 4 (1911). Eggers, John H., Jr. Continuous Agitation and Decantation in Pachu- cas, 2 pp. Pac. Min., Vol. 18, p. 55 (1911). Eraser, Lee. New Cyanide Device, IJ pp. Min. & Sci. Press, Vol. 101, p. 504 (1910). * Grothe, a. Principles of Agitation in Pachuca Tanks, l.p. Min. & Sci. Press, Vol. 103, p. 80 (1911). From Mex. Min. Jour. Grothe, A. Principles Governing Agitation in Pachuca Tanks, If pp. Mex. Min. Jour., p. 26, July, 1911. Geothe, a. Agitation in Pachuca Tanks. Mex. Min. Jour., Vol. 11, No. 2, p. 3, August, 1910. Hendrtx, Dr. Wilbur A. Cyaniding of Ores, 4 pp. (Paper read at Col. Sci. Soc, March 7, 1908.) Min. & Min., Vol. 28, p. 530 (1908). * Knippen, Lloyd M. Methods of Pulp Agitation, 2 pp. Min. & Sci. Press, Vol. 100, p. 824 (1910). Kueyla, M. H. Pachuca Tanks (Agitation). Mex. Min. Jour., Vol. 11, No. 2, pp. 44^47, Aug., 1910. * Kttbyla, M. H. Continuous Pachuca Tank Agitation at Esperanza Mill. (Paper presented April 28, 1910, Inst. Mexicano de Minas y Met- alurgia.) Min. Sci., Vol. 62, p. 56 (1910). Lamb, Mark R. Charge vs. Series System in Treatment of Slime by Agitation, 5 pp. Trans. A.I.M.E., Vol. 40, p. 775 (1909). LowDEN, H. B. The Akins-Rothwell Agitating Tank, 1 p. Min. Sci., Vol. 62, p. 281 (1910). * Laschingek, E. J. Air-lift agitation. Min. & Min., Vol. 32, p. 239 (1911). * McIntre, a. C. The A. Z. Agitator. Pac. Min., Vol. 16, p. 11 (1910). * MacDonald, Bernard. The Parral-Tank System of SUme-Agitation, 9 pp. Bull. 64, Trans. A.I.M.E., p. 387 (1912). * Nahvaez, Francisco. Cyaniding with the Brown Vat, 2 pp. Min. & Sci. Press, Vol. 95, p. 689 (1907). NicoL, John M. A New Method of Agitating Pulp in Cyaniding, i p. Min. & Sci. Press, Vol. 101, p. 260 (1910). NicoL, J. M. Hydraulic Agitation for Cyanide Plants, IJ pp. Min. & Eng. World, Vol. 38, p. 1133 (1913). RoTHWBLL & Akins. A New Pulp Agitator, of the Centrifugal Pump Type. Eng. & Min. Jour., Vol. 90, p. 206 (1910). Spahlding, C. F. Continuous Agitation of Slime with Barren Cyanide Solution, 2 pp. Min. & Sci. Press, Vol. 106, pp. 342 and 9S0 (1913). Spilsbury, E. Gibbon. The Just Filtration and Agitation Process, 13 pp. Trans. A.I.M.E., Vol. 41, p. 367 (1910). 176 STAMP MILLING AND CYANIDING SwAREN, J. W. Air-lift agitators (Historical). Min. & Sci. Press, Vol. 103, p. 409 (1911). Spaulding, C. F. Continuous Agitation of Slime with Barren Cyanide Solution, 2 pp. Min. & Sci. Press, Vol. 106, pp. 342, 950 (1913). Symmes, Whitman. The Symmes Agitator, 2i pp., illus. Min. & Sci. Press, Vol. 107, p. 92 (1913). * Tays and Schiertz. Cyaniding of Clay Slimes by Agitation and Decantation, 37 pp. Trans. A.I.M.E., Vol. 32, p. 179 (1902). * Trent, L. C. The Science of Agitation, 2f pp. Mex. Min. Jour., p. 26, June, 1912. Warwick, A. W. Mechanical and Air Agitation for Slime Treatment, 2 pp. Min. Wld., Vol. 34, p. 243,Jan. 28 (1911). Waterman, Douglas. Step-bearing for Slime Agitator, i p. Min. & Sci. Press, Vol. 105, p. 375 (1912). Yaeger, Amos J. A Modification of Pachuca-Tank Practice, i p. Min. & Sci. Press, Vol. 101, pp. 539, 844 (1910). — — — •. Mechanical Aids to the Cyanide Process, 2 pp. Min. Rep., Vol. 54, p. 7 (1906). . Air-lift Agitation of Shme Pulp, f p. Min. & Sci. Press, Vol. 102, p. 628 (1911.) . Nozzle for Pneumatic Agitator, i p. Pac. Min., Vol. 18, p. 122 (1911). Oxidizers and Extra Solutions. VON Bernewitz, M. W. Lead Salts in Cyaniding, 4 pp. Min. & Sci. Press, Vol. 107, p. 757 (1913). * Brockdnibr, S. H. Bromo-cyaniding of Southern Gold Ores, 5 pp. Trans. A.I.M.E., Vol. 31, p. 793 (1901). * Browne, R. Stuart. Editorial Discussion of the Clancy and Similar Processes, 1 p. Pac. Min., Vol. 17, p. 357 (1910). Clancy, John Collins. The Clancy Electrochemical Cyanide Pro- cess. A paper presented before the Dec. 16, 1910, meeting of the Ameri- can Electrochemical Society, held at the Chemists' Club, N. Y. City. Eng. & Min. Jour., Vol. 90, p. 1250 (1910); Pac. Minv, Vol. 18, pp. 43 and 117; Min. Sci. Press, Vol. 101, p. 862 (1910). Clevknger, G. H. The Function of Lead Salts in Cyanidation, 8 pp. Min. & Sci. Press, Vol. 109, p. 635 (1914). Edgerton, Ward. The new Portland Mill, 3 pp. Min. Sci., Vol. 62, p. 76 (1910). * Gbeen, Morris. Action of Oxidizers in Cyaniding, 3 pp. Eng. & Min. Jour., Vol. 95, p. 1233 (1913); Min. & Eng. Wld., Vol. 38, pp. 1056, 1108 (1913). Habgrave, C. L. Extra Solutions, Electrolysis, etc., in Cyaniding Ores of Cobalt, Canada, 2 pp. Eng. & Min. Jour., Vol. 93, p. 1133 (1912). Hunt, Bertram. Researches Upon Cripple Creek Telluride Ores, f p. Min. & Sci. Press, Vol. 100, p. 135 (1910). * Knutzen, H. The Diehl or Bromo-cyanide Process in Kalgoorlie. J. C. M. & M. Soc, S. A., Ill, IV, 41; Reviewed Min. Ind., Vol. XI, p. 320 (Aug., 1902). DISSOLVING THE GOLD AND SILVER 177 * Megraw, Herbert A. Oxidation and Cyaniding, 1| pp. Eng. & Min. Jour., Vol. 88, p. 645 (1909). MosHER, D. The Clancy Process, 1 p. Pac. Min., Vol. 18, pp. 43, 81 (1911). * MosHER, D. The Ammonia^cyanide Process, 3 pp. Pac. Min., Vol. 16, p. 83 (1910). * Nardin, E. W. Bromo-cyaniding of Gold Ores, 2| pp. Min. & Sci. Press, Vol. 97, p. 562 (1908). Worrell, S. H. The Bromocyanide Reaction. Min. & Sci. Press, Vol. 98, p. 356 (1909). Zachert, Victor. DiflBculties in the Clancy Process, 2 pp. Min. & Eng. Wld., Vol. 35, p. 913, with discussion by A. W. Warwick, from Trans. American Metallurgical Society (1911). . The Application of the Clancy Cyanide Process, IJ pp. Eng. & Min. Jour., Vol. 91, p. 904 (1911). . The Clancy Process, Ajax Mill, Cripple Creek, 1 p. Eng. & Min. Jour., Vol. 92, p. 1077 (1911). . Method of Making BrCy, J col. Eng. & Min. Jour., Vol. 92, p. 1145 (1911). CHAPTER XI SEPARATING SOLUTION AND PULP So far we have been dealing mainly with the means for causing or aiding the solution of gold and silver in cyanide, and however com- pletely we may be able to effect this vitally necessary operation, there still remains the problem — which in some cases is the most serious of all ^- of separating the valuable metal-bearing or 'preg- nant' solution from the now worthless gangue matter. Broadly, the methods for accomplishing this may be divided into four classes: For sand l\- Gravity fiUration. \II. Gravity filtration assisted by pressure or suction. T, ,. [ill. Decantation. For slime ^^^, „ , _.. ,. \IV. Forced Filtration. I. Gravity filtration is inseparably connected with the leaching method and has been already described under that process. The porous false-bottom of the tank serves as a medium through which the solution can flow and by which the sand is kept back. This is usually called 'natural filtration.' II. Assisted gravity filtration is merely an extension of the fore- going principle. To the upper surface of the charge, or to the lower surface of the filter, pressure or suction respectively is ap- plied, and there results, in some cases, a somewhat quicker and more complete separation of solution and tailing. The use of assisted filtration has been limited, however, by the tendency of the charge to pack under the extra pressure, with the consequent develop- ment of channels or fissures through which the solution would reach the filter without coming into uniform contact with the ore to be treated. On the whole, assisted natural filtration has been a thorough success in only a few cases. Recently, good reports have been received of its use in South African practice.* ///. Decantation, following a period of undisturbed settlemient, was for many years the only way known for the separation of * W. A. Caldecott, Min. & Sci. Press, Vol. 98, page 316. 178 SEPARATING SOLUTION AND PULP 179 cyanide solution from slime. It had, of course, the inherent de- fects of any system based upon the principles of Mark Twain's Calaveras frog jumping half his preceding distance at each suc- cessive attempt. Nevertheless, in South Africa, at least, decan- tatioii had an immense vogue. Its popularity, however, like that of the stone adze or the flint arrow-head, was a matter of ' nothing better known.' For small or temporary equipments, intermittent settlement and decantation may occasionally be desirable, but in Fig. 82. Decantation with Hose and Float. the main the process in its original form has passed into cyanide history. A few facts as to the details are of interest however. The settlement usually takes place in deep tanks, as it is gener- ally believed that the deeper the column of settled slime the dryer will the lower strata become, although some recent investigations would seem to prove otherwise.* It is usually estimated that slime retains its own weight of solution after agitation and settle- ment, so that one can easily approximate the value left after each washing. The amount of wash water required depends upon the * R, T. Mishler, Eng. & Min. Jour., Vol, 94, page G43 (1912). 180 STAMP MILLING AND CYANIDING value remaining in the tank after each dilution and incidentally upon the volume of solution it is possible to decant. Various reagents to promote flocculation and settlement of the slime have been used with success. Lime is the most commonly employed substance for this purpose. In crude equipments, the side of the tank is perforated with a vertical series of holes, so arranged by cocks and spigots that the outlet may be at any desired point be- low the surface. Siphons with floats to keep them drawing from the immediate vicinity of the surface may be employed, and in the South African plants a float attachment to a hose or pipe with a loose elbow (Fig. 82) near the bottom of the tank has been suc- cessfully employed. With the perfecting of appliances for the de-watering or thicken- ing of pulp, there have been many proposals of 'continuous- S. Feed 'Launder Fig. 83. Dorr Continuous Thickener. settlement,' or 'continuous decantation, ' as a means for the separation of pulp and pregnant solution. Of these proposals that made by J. V. N. Dorr, elsewhere men- tioned, and embodying the application of the Dorr continuous thickener to counter-current decantation, seems to be meeting with most success. This thickener, Fig. 83, consists of a flat- bottom tank with a peripheral-launder overflow, and a central spigot discharge, fed by the gentle rabbling action of radial arms mechanically operated. The method, as employed in supplementing the usual filtering equipment, is shown in Fig. 84, from which it will be seen that SEPARATING SOLUTION AND PULP 181 Mill 75^ of Gold recovered is dassdlved h^rre Hiiring crusliing; 100 TAn Pulp 400 T. Solution No. 1 Thickensr 100 T( 100 T. nPulp olution Agitator 100 Tdn Pulp 200 T. Solution No. 2 Thickener 100 Tin Pulp 100 T. Solution 1 r f- 100 Tin Pulp 100 T. ^olutlbn 50 T. Water Wash 100 Ton Pulp 50 T. Solution 300-T.,Pregnant 'Solution i decanted. I _The balance of Gold is dissolved here. Precipitation Plant is 300 T. Effluent Solution In many cases the Filter may be omitted with advantage. ter ) ith {• Fig. 84. Counter-current Decantation Supplementary to Filtering. 182 STAMP MILLING AND CYANIDING after the first thickener, the flow of pulp continually being impov- erished is in the opposite direction to the flow of solution continu- ally being enriched. Finally, the solution, having accompanied the ore through the crushing stage, is decanted from the first thickener and goes, after clarification, to the precipitation plant. The number of thickeners employed is, of course, a function of the strength and richness .of the solution and the character of the pulp. In certain cases, e.g., where weak solutions can be used, and where the pulp is of such character that it can be discharged from the thickeners with a low moisture content, it appears not only possible but decidedly profitable to employ continuous decanta- tion without a supplementary filter. In the cyaniding of silver ores where strong solutions are necessary, or in the treatment of an ore carrying heavy sulphides, which would have a tendency to settle and be discharged from the system before a sufficient time for treatment had elapsed, the method would hardly be applicable. These limitations, it is only fair to say, are recognized and in- sisted upon by Mr. Dorr himself. IV. Forced filtration. When we come to forced filtration we are confronted by an almost endless variety of apparatus, and it is very certain that the end is not yet. Two distinctive types are in use, which may be designated as filters of the press type and filters of the vacuum or suction type. (A) Filter-Presses. The filter-press, as first used in sugar- making and in the chemical industries, was for many years used in cyaniding, practically without change in the design. Essentially, it consists of a number of flat cells or chambers with walls of can- vas or other filtering medium. The pulp is charged into the chamber, either from a gravity-system, or from a montejus or storage-tank so arranged that the pulp is displaced by air-pressure. The liquid passes out through the pores of the cloth into suitable channels, while the sohd material remains between the cloths in the form of a cake. Provision is made for washing the cake thus formed and for displacement of the wash solution by compressed air. For details of the principles of construction reference should be made to Figs. 85 and 86 of the Merrill press, keeping in mind the fact that, aside from the manner of discharging, the two types are identical. The press is emptied by releasing the hydraulic or screw-gear keeping the different units together, the frames are slid apart, and the cake is removed by hand. The capacity of a press SEPARATING SOLUTION AND PULP 183 of this type with 50 frames, each 40 in. square, is usually from 4 to 5 tons of dry slime per 24 hours. The cost of operating is from 50 cents to $1.00 per ton, and is usually nearer the higher figure. The obvious objection to the use of hand-removal presses is their high cost, both for installation and operation. Nevertheless, they have been extensively used in Australia and South Africa. In North America, however, they never became popular, probably because of the high price of labor which would make their operation almost prohibitive. The necessity of solving the problem of treating the large amount of slime produced by the Homestake mills, which assays less than a dollar a ton, has led to the development of a filter-press which does away entirely with the hand-removal feature. The Merrill filter-press as described by Clarence G. Semple,* "consists of an iron frame in which are placed 90 cell- or chamber- frames, with distance-frames or grids between them, to control the direc- tion of the flow of solution through the cake of slime. A diagram of a cell-frame is shown in Fig. 85. It is a rectangular open casting with rounded corners, 4 in. wide, with the edges machine finished. In the four corners are two 2J-in. holes AA and BB. In the center of the upper part of the frame there is a 4-in. horizontal hole C, from which a passage D opens downward into the chamber or cell. At the bottom of the frame there is a 6-in. hole E, passing through the lug- like projection F, which projection is open through the center, as shown at G, opening into the cell upward and to both sides. The grid or distance frame is shown in Fig. 85. It is exactly the same size as the cell frame, but only 1 in. thick. The edges of the plate are machine finished. The entire frame is a soUd casting; the area within the rim H is a, httle thinner than at the rim and is grooved or fluted on both sides, like the surface of a laundress' washboard, only the grooves do not all run in the same direction. There are four 2|-in. holes AA and BB in the corners in exact juxtaposi- tion with the corner holes of the ceU frame, but the AA holes have a small channel / leading from the holes to each side of the fluted surface H: The grids have the holes C and E just like the cell frames, but are continuous through the casting without any lateral passages or channels. "The filter-cloths are cut large enough to cover both sides and hang over the top of the cell frames, as shown in Fig. 85. Discs are cut out of the cloths opposite each of the six horizontal holes in the casting. Cotton- twill cloth is used covered by 8- or 10-oz. duck. AH the frames have lugs J cast on the sides with rollers K upon which the frames rest when * Eng. & Min. Jour., Vol. 91, pages 719-722. 184 STAMP MILLING AND CYANIDING placed in the press. The method of making up a press is shown in Fig. 86. A grid frame M is placed against the head L of the press with a gasket be- tween, in which six circular holes have been cut in line with the horizontal holes in the grid; P. & B. paint is used on the edges to make a tight joint. A cell frame N, with the filter cloths in position, is then set tightly against V.VW.VV\\W.T^ H Thla Area la Iron, Thinner tban the lUm and Ohanneled on both Siaoa Cell Frame. Distance Frame. Fig. 85. Merrill Press, Plate and Frame. the grid and a second grid placed against it, but in the reverse position to the first grid so the corner holes with the channels / are on the opposite side of the press than the corresponding holes in the first grid. The second cell-frame is then placed and the third grid brought up against it, but with the channels I on the same side as the first grid. The press is- thus filled with frames, with every alternate grid with the channels on the same side of the press, until the 90 frames are in position. The frames are then drawn tightly together by draw bolts operated by capstan heads. The six horizontal holes through the frames now form six continuous passages or tubes through the press that are bhnd against the back head P, but which pass through the front head L and connect with pipes outside the press. " The Operation of the Presses. The passage C, through the upper part of the press, is connected with the pipe from the slime-storage tank. By opening a valve on this pipe the slime enters the press through C, and passes into the interior of the cells through the passages Z). When the cells have been filled, the supply valve is closed, and air at 26 pounds pressure is admitted through the passages AA, which flows through the press, as shown in Fig. 86, coming out from the opposite side of the press through the passages BB. The air removes the excess of water and aerates the slime cake. The first period of aeration takes about two hours, and is succeeded by the following operations : Treatment with strong solution 0.12 to 0.14 KCN; draining strong solution; aeration; second treatment with strong solution; draining; treatment with weak solution 0.07 to 0.075 KCN; draining; aeration; second treatment with weak solution; draining; treatment with wash water; and discharging the press. The cycle from filling to discharging takes about nine hours, the treatments SEPARATING SOLUTION AND PULP 185 with solution being a little longer than the periods of aeration, except the first blowing. "The arrangement of the piping outside the press is shown in Fig. 86. By this arrangement of the valves, air, water, strong or weak solution, may be admitted from either side of the press and drawn out from the side opposite. The usual practice is to admit the solution at one side of the press for one-half the period of treatment, and then to reverse the flow by the rearrangement of the valves. The efiluent solutions and wash water discharge into a small iron sump at the front end of the press. O N M N O N M N O N lu ^s or 10 oz Duck Filter Cloth over Twill Filter Cloth Fig. 86. Diagram of Flow through Merrill Press. " Discharging the Slime Cake. The shme cake is discharged through the bottom central passage. Through the passage E there runs a 2-in., or 2\-va.. pipe R, Fig. 85. This pipe enters the front header through a stuffing-box and enters a bearing socket in the back header of the press, and is supported outside the press, by boxes, just as a shaft would be. In each cell-compartment there is a Uttle nozzle S screwed into this pipe. Four of the cell-frames, at equal intervals along the length of the press, are tapped at the bottom to receive a short piece of 2\-va.. pipe that can be closed by valves. When the press is to be discharged these valves are opened and water under pressure enters the press through the pipe R, whichis turned back and forth through an angle of 170° by mech- anism outside the press. A jet of water enters the cells through the noz- 186 STAMP MILLING AND CYANIDING zles S, loosening the cake of slime that runs through the annular passage ,left between the outside of the pipe R and passage E, until reaching one of the cells with the discharge pipe, through which it flows into the launder leading to the creek." The presses are 46 ft. long and weigh 65 tons each; the frames measure 4 by 6 ft. outside. On the Homestake slime their capac- ity is 25 tons per charge. The recovery is about 90 per cent or 81 cents per ton at a total cost of about 25 cents, of which the actual filtering cost is less than 11 cents per ton. As used at the Homestake all the treatment is given in the presses. Where, as in the case with certain ores, a longer time of treatment is necessary, solution may be effected in the ordinary agitating-tanks, and the Merrill presses used merely for the sepa- ration of solution and pulp. Another modification * in the employment of the Merrill presses has been to avoid the formation of a solid 4-in. cake, the slime-feed being shut off, while there is a space of J in. in the middle of the frame. Water or solution is then introduced through the sluicing pipe, leaching taking place from the center outward. The general opinion seems to be that the Merrill press is highly successful in handling finely-crushed ore free from colloidal mate- rial, but that where the ore forms a tough clinging slime, difficulty is experienced in completely sluicing out the cake. (B) Vacuum-Filters. In cyaniding, the finer the product the higher the extraction; this is the case with few exceptions. To apply this principle requires two things: a satisfactory machine for fine-grinding and a filtering scheme which would be at once economical and efficient. ' Filter-pressing, while an estabUshed practice in Australia, was never popular in America and few suc- cessful installations are recorded prior to 1907, the date of intro- duction of the Merrill press. About 1903 George Moore of the Consolidated Mercur Com- pany, in Utah, devised a vacuum-filter and installed a plant at the Mercur mill. This, while faulty in design and a comparative failure so far as cyaniding is concerned, was the origin of the vacuum type of filter, recent modifications of which are in use at a number of mills in this country and in Australia, and are being introduced into South Africa. The unit of the Moore filter, as now used, is a rectangular frame * Henry Hanson, Min. & Sci. Press, Vol. 98, page 657. SEPARATING SOLUTION AND PULP 187 188 STAMP MILLING AND CYANIDING (Fig. 87) 5 by 10 ft., made of J-in. pipe,* with a wooden header. The lower member of the pipe frame has its upper surface per- forated with j-in. holes to admit the filtered solution. The filter consists of a sheet of canvas stretched over the entire pipe frame on both sides. Vertical wooden strips, spaced 4 to 5 in. apart, are used as stiffeners and to keep the filter from collapsing. Be- tween the stiffeners the two sides of the filter are sewed tightly together. In operation these frames or 'filter-leaves,' as they are called, are grouped in clusters or baskets, and in the original Moore proc- ess, several large installations of which are in operation, the basket Fig. 88. Moore Filter System. Tai/ings Conye^r of frames is lowered by suitable means into a hopper-bottom com- ipartment containing the slime pulp (Fig. 88). The vacuum is .applied to a common pipe connected with each frame, the solution is drawn through the canvas by means of a vacuum pump, and a slime cake, varying from g to 2 in. in thickness, is deposited on each side of the filter-frame. The cluster of filter-frames, carrying the charge of slime and weighing several tons, is then lifted from the pulp, and is shifted automatically to adjoining compartments con- taining the wash of weak solution and water respectively. Into * Moore's early filter did not have the pipe frame, for which idea, apparently, eyaniding is indebted to G. A. Duncan, see Min. & Sci. Press, Vol. 96, pages 769-770. SEPARATING SOLUTION AND PULP 189 each of these it is lowered in turn, the vacuum applied, and the displacing operation carried on. The load is finally raised and shifted to a bin, where the cakes are discharged by introducing air or water into the interior of the frames. The vacuum during the transfer of the cake calls for careful regulation; if too high, the cake is likely to crack; if too low, the cake may become detached from the filter surface. It was, of course, not a difiicult matter to modify this idea to the extent of keeping the filter stationary, bringing pulp, weak solution and wash-water, into the filter compartment in turn and then dis- FiG. 89. Butters FUter System. charging the spent cakes into the same tank. This, with some mechanical improvements, constitutes the Butters' modification of the Moore filter. In the Butters filter (Fig. 89) the leaves are set in a rectangular box or tank, the bottom of the box consisting of a series of pointed pockets to facilitate the discharge of the spent cakes. The frame is similar to the Moore, the filter, however, consisting of a piece of cocoa-matting, fitting inside the pipe-frame, upon both sides of which canvas is quilted by frequent sewing; stiffening ribs of wood are placed vertically outside the filter every foot or so apart. The 190 STAMP MILLING AND CYANIDING frames stand parallel in the filter box at about 4f in. centers. The slime pulp is drawn from the slime reservoir or pumped, if necessary, into the bottom of the filter box until all the frames are immersed. The vacuum is then applied until a cake of suitable thickness is deposited; and the excess of pulp is returned to the slime reservoir. This operation is repeated for the wash, and the cake is finally discharged into the bottom of the box by introduc- ing water under a low head into the interior of the leaves. The accumulated cakes from each discharge are removed by sluicing. In cost of operation the two types are about equal, running from 5 to 22 cents per ton of dry slime. This variation in cost is largely a matter of the character of the slime, which influences the time required to form a cake of suitable thickness, as well as the amount of washing required to displace the cyanide solution. The average cycle of treatment, including charging, caking, washing, and dis- charging the cake, varies from 2§ to 5 hours. On an average about 50 to 75 sq. ft. of filtering surface per ton of slime capacity per day is necessary. The Barry and Banks system, in use in New Zealand, and known as the Crush filter, is to all intents and pur- poses the same thing as the Moore. These 'immersion-filters,' as they have been termed, marked a most distinct advance in the cyaniding art, and in conjunction with the tube-mill made possible results hitherto unattainable. In common, however, with the Merrill press, with which at the present time they share the greater part of the world's cyanide tonnage, they are open to the objection of being discontinuous in operation, that is, they work intermittently, thus failing to co- ordinate nicely with the rest of the plant, where crushing, amal- gamation (if it is practiced), concentration, and even agitation in many plants are continuous processes. To obviate this objection, various vacuum-filters of a traveling or continuous type have been proposed. The Ridgeway filter, shown in Fig. 90, is one of the earliest of this type. This machine consists of a number of cast-iron filter-plates, sectors of an annulus in shape, which revolve in a horizontal plane about a hollow central spindle. Over the underside of these filter- plates, cloth or canvas is stretched, the space between the canvas and the frame forming a chamber which has suitable connections . with vacuum pump and with air-pressure at different parts of the cycle. In operation, as it revolves about the central spindle, each SEPARATING SOLUTION AND PULP 191 plate dips in turn into the part of the annular trough containing slime pulp, accumulates a cake on its surface, rises out of the slime pulp and dips into wash water which washes the cake; the plate ^^ -*— Compressed Air Wash-Solution L^UJ Strong Solution lo Vacuum Pump Fig. 90. Ridgeway Filter. then rises and descends again in its circular path to the discharge point, where, by a suitable mechanism, the vacuum-connection is shut off, and air-pressure is applied, thus releasing the cake. The 192 STAMP MILLING AND CYANIDING particular sector we have been following is then ready to begin the cycle over again. PI an Fig. 91. Hunt Filter. The Hunt filter (Fig. 91), as described by the inventor,* con- sists of a horizontal, annular chamber which is connected with a * Bertram Hunt, Min. & Sci. Press, Vol. 97, page 430. SEPARATING SOLUTION AND PULP 193 vacuum-pump, the top of the annular chamber being built on the principle of the sand-filter, described under 'Leaching-Tanks.' "This chamber forms the permanent filter-bed and is supported strongly enough to remain perfectly rigid on the apphcation of a. vacuum in the chamber underneath. This chamber is connected with a wet vacuum-pump which withdraws the solution and maintains the vacuum. "The annular vacuum-chamber is made of concrete and iron and the walls, being raised above the top of the filter-bed, constitute circular tracks on which a carriage revolves. This carriage has an iron scraper in front, which removes the layer of residue from the permanent filter-bed. Fol- FiG. 92. Oliver Continuous Filter. lowing close behind the scraper, on the carriage, is placed a distributor similar to that used on a Frue vanner, which handles the sandy portion of the pulp. Behind this is a second distributor which spreads the slimy portion of the pulp over the layer of sand just laid down by the first dis- tributor. On the central column of the machine are two concentric hoppers or funnels ; these are connected by pipes with the two distributors which receive the pulp. Before reaching the filter machine the pulp is roughly classified, so that a portion of the fine sand is separated in a clean condition, and this clean sand is fed upon the filter-bed by the first dis- tributor, the rest of the pulp going to the second. In this way the slimy portion of the pulp is always distributed over a layer of clean fine sand. 194 STAMP MILLING AND CYAN I DING Fig. 93. The Oliver Continuous Filter (End View). List of Paris. 1. Filter Drum. 2. Steel Filter Tank. 3. Cast Iron Pedestals. ' 4. Steel I-Beam Frame. 6. Manhole. 6. Cast-iron Spider Rim. 7. Channel Steel Arms. 8. Hollow Trunnion. 9. Steel Shaft. 10. Main Bearings. 11. Stuffing Boxes. 12. Worm Drive Gear. 13. Worm Shaft. 14. Oil Well for Worm. 15. Filter Drive Pulleys. 16. Pulleys for Agitator and Wiring. 17. Chain Drive for Agitator. 18. Bevel Gears on Agitator Shafts. 19. Agitator Shafts. SEPARATING SOLUTION AND PULP 195 Pig. 93A. The Oliver Continuous Filter (Side View). List of Parts. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. Agitator Shaft Bearings. 30. Wood Staves for Drum. 31. Section Division Strips. 32. Filter Medium. 33. Wire Winding. 34. Steel Scraper. 35. Scraper Adjustment. 36. Tailing Apron. 37. Vacuum Pipes. 38. Compressed Air Pipes. Regrinding Valve Seat. Automatic Valve. Adjusting Lever for Valve. Vacuum Hose Connection. Compressed Air Connection. Discharge Spray Pipe. Emergency Agitator Pipe. Drain Flange. Wash Water Pipes. 196 STAMP MILLING AND CYANIDING As the carriage moves continuously the deposited layer of sand and slime is also continuously removed by the scraper, while fresh material is depos- ited by the distributors, as described above. Pipes to spray wash-solution and wash- water follow the carriage at suitable distances, so that the residue can be thoroughly washed." Another device quite similar in general design to the Hunt is the Parrish filter* In this, however, the filter surface is of canvas or cocoa-matting protected by wire winding. The Oliver filter (Figs. 92, 93 and 93A). Probably the most suc- cessful of all the continuous filters is that perfected by E. L. Oliver at the North Star mine, Grass Valley, California. This machine consists of a drum or cylinder with open ends, revolving about a horizontal axis and dipping into a tank containing (under gentle agitation) the pulp to be filtered. Usually about half the drum is submerged. The outer surface of the cylinder forms an annular vacuum-chamber, divided into sections and covered with filter cloth protected from wear by a wire winding. By suitable valve mechanism at the end of the trunnion, and by corresponding pipes communicating with the filter-sections, vacuum is applied to form the cake during the submergence of each section; this vacuum is continued, as the section rises out of the pulp, until it passes the wash-water. Finally the vacuum con- nection is cut off and air pressure applied just as the section reaches the discharge point; the cake thus loosened is removed by a light steel scraper and the filter-section continues in its revolution into the pulp to commence another cycle. The thickness of the cake varies, according to the character of the slime, from J to 1 in. The time of one revolution is from 5 to 10 min. for the standard filter, which is 11 ft. 6 in. in diameter and of any length, up to 16 ft. From 3 to 5 sq. ft. of filter area is required per ton of daily capacity. The Portland filter of the Colorado Iron Works is substantially of the same type. As a type intermediate between filter-presses and vacuum-filters, we have the pressure-filters, 'which in general construction bear more resemblance to the submerged, vacuum type than to the presses. All of these offer the general advantage of allowing the use of a higher pressure than it is possible to obtain from the at- Pac. Min., Vol. 15, pages 124-125. SEPARATING SOLUTION AND PULP 197 S/me Preiiurt\ .Inlet mosphere, and for this reason are particularly suited to use in high" altitudes. Th& Blaisdell filter (Fig. 94) is virtually of the Moore-Butters type, consisting of vertical filter-leaves suspended in a vertical pressure-cylinder. The Kelly filter (Fig. 95) is similar in principle, except that the pressure-cylin- der is set at a slight inclination to the horizontal, and the cylinder head, carry- ing the basket of filter-frames, moves up the slope into the cylinder on a suitable track. Pressure is applied, and the cake accumulated and washed as usual; the head with its accompanying filter-frames and cakes is allowed to run down the track until clear of the cylinder, when the cakes are discharged in the usual manner. A press of this type with a cyUnder 4 by 9J ft., and halving 300 sq. ft. of filtering area, is stated to have a capacity on roasted telluride ore of 50 tons per day. The Burt pressure-filter (Fig. 96) con- sists of a pressure-cylinder inclined at 45°, with the head at the lower end operated by toggles. Within the cyUnder are suspended a number of ordinary filter-frames, set transversely to the cylinder axis. The cylinder is filled with pulp under pressure, cake accumulated, excess pulp dis- charged, wash-water introduced, cake washed, and finally . dis- charged by opening the discharge-door or lower head. At El Oro, Mexico, with cylinders containing 28 frames, each of 8 sq. ft. area, 120 tons of dry slime are filtered per 24 hours. The Burt revolving filter is a recent innovation which looks decidedly promising. It consists of a revolving cylinder similar in appearance to a tube-mill, the filter surface forming the inside walls of the cylinder. Pulp is charged into the interior, air pressure turned on and the cylinder slowly revolved. The cake accumulates about the periphery, and the solution flows out through suitable holes in the shell to a sump beneath. When all the solution has been expelled and air blows from the holes, wash- water or weak solution is turned in, and the cake is washed. Fig. 94." Blaisdell Pres- sure-Filter. 198 STAMP MILLING AND CYANIDING Fig. 96. Burt Pressure-Filter. TAI Characteristics of Vak Name or type Methods of in- tion General Bhape, usual size, position, and mate- rial of filtering surface Nature of filter support Thickness of Time of cycle Method filter and juitap Plate Pressure Rectangular, 40 in. , Corrugated or 2 to 3 in. n to 5 hr. Forced and from pump square vertical. studded C. I. ter ch frame or monte- 10-tQl2-oz.duck. plates. press. jus. Merrill. Gravity Rectangular, 3X5 Corrugated 4 in. 9 hr., includ- Gravity pressure. ft., vertical, 10- to 12-oz. duck over cotton twill. thus ing treat- ment in storaf presses. Merrill. Gravity Rectangular, 3X 5 If in. each 4hr. Gravity pressure. ft., vertical, ,10- to 12-oz. duck side storag ' over cotton twill. Moore.. Vacuum Rectangular, 5X10 Pipe frame with 1 to 2 in. 2| to 5 hr. Transfe pump. ft., vertical, 10- oz. duck. slats, between which canvas sewed together charg dischi Butters. Vacuum Rectangular, 5X10 Pipe frame, with 1 to 2 in. 2i to 5 hr. Pulp an pump. ft., to 10X10 ft., vertical, 10-oz. duck. cocoarmatting support, to which canvas stitched, or on wire netting. frome orste Ridge- Vacuum Annular sector, 3 Cast-iron frame. J to 1 in. Imin. By traB way.. pimip. sq. ft., horizon- tal, face down- ward, 10-oz. duck. canvas stretched over small Hunt... Vacuum Annular ring, hor- Triangular bars. i to 1 in. N. D. Sand an pump. izontal, sand sur- face. apex upward, with gravel cover. wash tachn Oliver. . Vacuum Barrel 11 ft., 6-in. Corrugated J to J in. 3 to 5 min. Filter n pump. diam.X7 to 16 ft., horizontal, 12-oz. duck, wire-wound. staves with burlap. in tan full of Blais- Pressure. Like Moore and Like Moore and f to U in. Similar i dell... Butters but smaller leaves in vertical cylinder. Butters. Kelly... Pressure. Narrow, rectangu- lar, vertical, canvas covered, leaves in nearly horizontal cyl- inder. Small leaves, trans- Pipe frame, co- coarmatting, or wire netting 1 to 3 in. 30 to 45 min. Pulp ch under from I galpu monte Burt . . . Pressure. Pipe frame, co- itoHin. 30 to 45 min. Pulp cht (Pres- versely set in 45° coarmatting, der pu sure) . cylinder. or wire netting sure gravit Burt . . . Pressure. Lining walls of cyl- Corrugated Up to 6 in. 60 to 90 min. Pulp ohf (Re- indrical cham- staves set in gravit tion c volv- ber, 42 in. diam. ' filter sections. ing).. X40 ft. Filter compr air. ■ in sections 26 in. X 10 ft. each. Sweet- Pressure. Small leaves, 6X4 Pipe frame, co- 1 to IJ in. 35 to 60 min Pulp chf land.. ft., in filter press frame, canvas surface. coarmatting, 15-oz. duck. into c by mo • This cost is inc usive of pulp-transfer, cloth-tenewal 1, acid-wash, etc The net Xxv Sume-fh/tebinq Devicbs oUainemg Oimemto tnitbii mlo fil- tyfwm ^bnks. tylrom Method of wash- ing Water forced into alter- nate filter spaces and tnru cake. Water forced into alter- nate filter spaces and thru cake. From center space. Method of dis- charging Reported coats per ton dry slime Hand-removal Sluicing. Sluicing. 25(ito $1.00 91^* 24«i ieniiig filter from slime to wash, to dis- iBMompartment, successively, by crane; Mge by air or steam back-pressure. aid rash solutions charged about filter nstorage: discharge in same tank by air iteamback pressure. biiiDalr, much as in preceding, but units lalltlioughout. idulilime fed on from revolving spreader, iialmi removal by similar revolving at- ickent. li slime. Spray on cake after emerg- ing from slime. Back pressure of air aided by scraper. aril ill respects to the Butters mcentrifu- [ pump or inteim. iciiarieiii un- iipimipres- iieotly [jvity. peiis»,4 *'y ia*iSltrar ffljedby 01 ir. Bcliiapd {otlinber Wash water under pres- sure. Wash water under pres- sure. Wash water in troduced and forced throughcake by air. As pulp. Basket slid_ out of cylin- der and steam or water dis- charge used. Back pressure of air, lower head opened and filtered slime slides out. End gate op- ened and cyl- inder revol- ved cake loosens slides out. Sluicing. 5to22|< 5to22f< N. D. 3 to lU Filter particularly adapted for handling 20to40|i 40 (grav- ity). 8(i (pump) Granular slime. Granular slime. Will handle finer and more col- loidal material than above. Sticky clayey slime. Sticky clayey slime. Sticky clayey slime. Sand and slime together. Slime of all de- scriptions. Sticky clayey slime with low pressures; sandy slime with high pres- sures. As above. Advantages Good washing. Great capacity, low cost. Great capacity, low cost. Capacity and low cost. Capacity and low cost. Best washing. Disad vantages Cost of op- eration and instal- lation. Cost of in- stallation. Cost of in- stallation. Poor wash- jngaQd en- richment of wash solutions. Poor wash- ing and enrich- ment of wash solu- tions. Small units, compli- cated ar- rangement Undetermined. As above. As above, at El Oro 80% pulp -200 mesh. As in other pres- sure filters. Simplicity and low cost. Higher pressures available for high altitudes- As above. As above with apparently very low cost. As above. Higher pres- sures avail- able. Washing limited. Inconven- ience and expense. As above. Probaby cost. "T^ of the actual filtering operation is probably less than 30. (Between pages 198-199) SEPARATING SOLUTION AND PULP 199 When the operation is completed, the cyUnder head is removed, a small amount of water admitted and the cyKnder revolved; the cake then rolls up hke a leaf and is discharged. The standard- size machine as used at El Oro is 42 in. in diameter by 40 ft. long and makes 15 rev. per min. The capacity of this unit is given as 13 charges per 24 hr., each charge being 5j tons dry weight; the average thickness of the cake being 4^ in., the pressure 38 lb. for forming cake, and 48 lb. for washing, with 66 per cent of the pulp finer than 200 mesh. The Sweetland filter-press* so-called, is in reality a pressure-filter, each leaf being suspended in a frame of the filter-press pattern, these frames being clamped together as usual. Discharge is pro- vided for by means of sluicing-nozzles which wash the spent cakes out of the chamber, as they drop from the leaves when the pres- sure is released. SUMMARY AND COMPARISON OF FILTERS The outstanding features of each of the types previously dis- cussed are collected for convenience in Table XIV. The cycles of operation of the various types are shown in Fig. 97, part of which is a reproduction of the scheme used by Prof. Young t in his admirable paper. The balance is an extension of the same idea to the filters not discussed by him. Of the most prominent filtering devices in present use, viz.: the Moore-Butters, the Merrill, the Oliver, and the Burt (to which should be added the Ridgeway, though its use on the western Con- tinent is rare) each has distinct merits of its own. Probably they will all survive, and each will eventually find its own field as in- deed they are, in some measure doing, at the present time. The Moore-Butters and the Burt systems seem equally well adapted to the treatment of slimy pulp. Both are open to the objection of discontinuous operation. The use of the Merrill system; ingenious and clever as it is, seems to be limited to a fairly granular material. It also is of the intermittent type. The Oliver and the Ridgeway have the great advantage of thin cake and continuous operation. * Pac. Min., Vol. 16, page 86. t Slime Filtration, Geo. J. Young, Trans. A.I.M.E., Vol. 42, pages 752-784. 200 STAMP M4LLING AND CYANIDING Bidgeway Filter 1 Mleu Cycle Sweetlaad Filter 43 M in. Cycle Fig. 97. Cycle of Operation of Various Filters. SEPARATING SOLUTION AND PULP 201 The next step of an important character in the development of filter-apparatus for cyanide work will probably be the introduction of a centrifugal filtering device. BIBLIOGRAPHY FOR SEPARATING SOLUTION AND PULP * Especially Desirable for Students' tTse Decantation. * Ashley, Harbison Evekett. Theory of the Settlement of Slime, 2 pp. Min. & Sci. Press, Vol. 98, p. 831 (1909). Ashley, Harrison E. Theory of the Settlement of Slime. Min. & Sci. Press, Vol. 99, p. 252 (1909). * Browne, R. Stuart. The Dilution System of Slime Treatment, If pp. Pao. Min., Vol. 15, p: 195 (1909). * Browne, R. Stuart. Editorial Discussion of McCann's System for SUme Treatment. Pac. Min., Vol. 15, p. 155 (1909). Brooks, H. St. J. Continuous Decantation Versus Filtration, 3 pp. Min. and Sci. Press, Vol. 106, p. 624 (1913). Demond, C. D. Settling El Tigre Slimes, | p. Eng. and Min.> Journal, Vol. 94, p. 970 (1912). Forbes, D. L. H. Use of Dorr Thickeners with Spiral Paddles, 2 pp. Eng. & Min. Jour., Vol. 92, p. 691 (1911). ' Gardiner, B. L. SUme Settlement, 5 pp. Jour. W. Aust. Chamber of Mines, May.31, 1911. Hills, Leon P. An Intermittent Pulp Continuous Solution Decantar tion System, 1 p., illus. Mex. Min. Jour., Vol. 17, p. 327 (1913). Huntley, Rollo E. An AustraUan Slime Settler, li pp. Mines & Methods, Sept., 1910. Irwin, Donald F. Continuous Decantation, 1 p. Min. & Sci. Press, Vol. 103, p. 102 (1911). Jay, Clyde H. A Continuous Dewatering, Agitation and Filtering Cyan- ide Process, IJ pp. Min. Sci., Vol. 59, p. 429 (1909). * Laschinger, E. J. The Decantation Process, 2 pp. Abstr. from J. C. M. & M. Soc, S. A., April, 1904. Eng. & Min. Jour., Vol. 78, p. 508 (1904). * McCann, Ferdinando. A Proposed New System for the Cyanide Treatment of Shmes, If pp. Eng. & Min. Jour., Vol. 88, p. 688 (1909); Min. Sci., Vol. 60, p. 324 (1909). * Megraw, Herbert A. Continuous Decantation of Slime, 2i pp. Eng. and Min. Jour., Vol. 95, p. 379 (1913), also 8i pp.. Vol. 98, pp. 683 and 792. * Megraw, Herbert A. Filtering Slimes in Cyanidation, 4J pp. Eng. & Min. Jour., Vol. 97, p. 1057. * 'Mennell, J. Leslie. Devaluing with Dorr Thickeners, 2 pp. Min. & Eng. Wld., Vol. 36, p. 607; abs. from Mex. Inst. Min. & Met. (1912). Mishler, H. T. Settling Slimes at the Tigre Mill, 4 pp. Eng. and Min. Jour., Vol. 94, p. 643 (1912). Nichols, Horace G. The Separation of Slime in Cyanide Treatment, 3J pp. Min. & Sci. Press, Vol. 96, p. 563 (1908). 202 STAMP MILLING AND CYANIDING Nichols, Horace G. Free Settlement Method of Separating Slime, li pp. Min. & Sci. Press, Vol. 99, p. 369 (1909). Parmelee, H. C. Cyaniding by Continuous Decantation in Clear Creek County, Colorado, 4i pp. Met. and Chem. Eng., Vol. 10, p. 27 (1912). * Parmelee, H. C. Cyaniding Slimy Ore by Continuous Decantation, 3| pp. Met. and Chem. Eng., Vol. 11, p. 25 (Jan., 1913). RoTHWELL, John E. A Continuous Cyanide Treatment Method for Gold and Silver Ores, li pp. Met. & Chem. Eng. (July, 1911). RoTHWBLL, John E. The Counter Current of Continuous Agitation, Decantation and Dilution Applied to the Cyanide Process, 2i pp. Met. & Chem. Eng. (Sept., 1911). * Simmons, J. Continuous Decantation with Dorr Thickeners, 1 p. Eng. and Min. Jour., Vol. 95, p. 627 (1913). Stjlman, H. L. Shme Settlement. Eng. & Min. Jour., Vol. 86, p. 854; abstr. from Jour. Inst. M. & M., Bull. 42 (1908). * Van Saun, P. E. Continuous Decantation System at Guazapares, 3 pp. Eng. & Min. Jour., Vol. 92, p. 707 (1911). Spicer, H. N. Slime Settlement, i p. Min. and Sci. Press, Vol. 106, p. 954 (1913). . The Adair-Usher Cyanide Process, 1 p. Min. Rep., Vol. 55, p. 494 (1907). . Way-Arbuckle Process at Benoni Mill, IJ pp. Min. & Sci. Press, Vol. 104, p. 723 (1912). . Adair-Usher Process. Eng. & Min. Jour., Vol. 86, p. 463 (1908). Filter-Presses. * VON Bernewitz, M. W. Filter-pressing SHmes. (Abstract from Proc. Aust. Inst. Min. Eng.) Min. & Sci. Press, Vol. 101, p. 377 (1910). BoBQUi, F. L. Cyanide Practice at the Homestake Mills, 4 pp. Min. & Sci. Press, Vol. 95, p. 21 (1907). * BosQui, Francis L. Plan for Extensive Filter-press Slime Plant, 11 pp.. Trans. A.I.M.E., Vol. 34, p. 715 (1904). * Ehlb, Mark, Jr. The Homestake Slime Plant and Merrill Filter Press, 5 pp. Min. & Min., Vol. 27, p. 358 (1907). Hanson, Henry. Merrill Filter-press. Min. & Sci. Press, Vol. 98, p. 657 (1909). Ipould, Percy. Methods of Shme Treatment in Western Australia. (From the AustraUan Mining Standard.) Min. Sci., Vol. 58, p. 308 (1908). * Semplb, Clarence C. The Homestake Cyanide Plants, 2 pp. ■ (Mer- rill Filter.) Eng. & Min. Jour., Vol. 91, p. 719 (1911). * Wallace, A. B. Filter Presses in W. Australia. Min. & Sci. Press, Vol. 92, p. 71 (1906). Wilson, J. K. Filter-press Treatment of Slime in W. Australia. Min. Ind., Vol. IX, pp. 779-782 (1902). SEPARATING SOLUTION AND PULP 203 Butters-Moore FUters. Blake, J. R. Slime Filters, | p. Min. & Soi. Press, Vol. 94, p. 564 (1907). * Brown, Gilman. "Cyanide Practice with the Moore Filter, 6| pp. Min. & Sci. Press, Vol. 93, pp. 261, 292 (1906). * Clevbnger, G. Howell. The Butters Vacuum Filter, 2i pp. Min. & Min., Vol. 86, p. 574 (1908). Dtjncan, G. a. Submerged Facts and Filters, 1 p. Min. & Sci. Press, Vol. 96, p. 769 (1908). Fkier, James. The Butters Filter, | p. Min. & Sci. Press, Vol. 94, p. 432 (1907). Guthrie, G. L. Cyanide Correspondence, 1| pp. (Written to Chas. Butters concerning installation and operation of Butters FUters.) Min. & Sci. Press, Vol. 96, p. 810 (1908). * Hamilton, E. M. The Filtration of Slimes by the Butters Method, 10 pp. Min. & Sci. Press, Vol. 94, pp. 785, 818 (1907). KiEBY, A. G. Vacuum Slime-filters, 2i pp. Min. & Sci. Press, Vol. 95, p. 46 (1907). Lamb, Mark R. The Moore and Butters Filters, 4 p. Min.- & Sci. Press, Vol. 94, pp. 54, 152, 400 (1907). * Lamb, Mark R. Butters Filter at Combination Mine, 10 pp. Trans. A.I.M.E., Vol. 38, p. 200 (1907). MacDonald, William. Vacuum Filtration at the Victoria Mill of the Waihi Gold Mining Co. Ltd., New Zealand, 12 pp., illus. Jour. C. & M. & M. Soc, So. A., Vol. 13, p. 527 (1913). Mbrton, a. M. Historical Review of Vacuum Filtration, If pp., Ulus. Min. Sci., Vol.. 68, p. 29 (1913). * Moore, George. First Moore Filter as Installed at Cons. Mercur Mines. Eng. & Min. Jour., Vol. 76, p. 855 (1903). * Nutter, Edward H. Cyanide Practice with the Moore Filter, 2 pp. Min. & Sci. Press, Vol. 93, p. 714 (1906). Nutter, Edward H. Mr. Lamb and the Butters Filter, 1 p. Min. & Sci. Press, Vol. 94, p. 210 (1907). Nutter, Edward H. The Moore and Butters Filter, IJ pp. Min. & Sci. Press, Vol. 94, p. 491 (1907). Pettis, E.S. The Butters Filter. Min.&Sci.Press, Vol. 94,p. 367 (1907). * Smith, Alfred Mberitt. Vacuum Shme-fUters at Goldfield, 1 p. Min. & Sci. Press, Vol. 99, p. 65 (1909). Smith, H. G. Operating a Stationary Filter, i p. Min. and Sci. Press, Vol. 105, p. 601 (1912). Stone, C. J. A Leaf-filter Operated by Gravity, 3 pp. Eng. & Min. Jour., Vol. 93, p. 368 (1912). Young, G. E. Testing the Filtration Rate of a Slime, 3 pp. Mex. Min. Jour., Vol. 16, No. 6, p. 36 (1912). Warwick, A. W. Conditions Governing Washing of Filter Cakes, 2i pp. Min. and Eng. World, Vol. 38, pp. 797 and 1135 (1913). * . Mr. Murphy on Slime Filters (humorous), | p. Min. & Sci. Press, Vol. 97, p. 636 (1908). 204 STAMP MILLING AND CYANIDING -. A New Filter Frame, 1^ pp. (Excerpt from an article in the Monthly Journal of the Chamber of Mines of Western Australia.) Eng. & Min. Jour., Vol. 91, p. 999 (1911). . Vacuum Filtration on the Rand. Min. Mag., Vol. 3, pp. 249 and 261; Eng. & Min. Jour., Vol. 90, p. 797 (1910). Continuous Filters. Hunt, Bertram. Continuous Vacuum-filter Machine, Ij pp. Min. & Sci. Press, Vol. 97, p. 430 (1908). Lamb, Mark R. The Ridgeway Filter, 1 p. Min. & Sci. Press, Vol. 96, p. 769 (1908). * Martin, A. H. Oliver Continuous Filter, 1 p. Min. & Sci. Press, Vol. 99, p. 715 (1909). Nicholas, Askin Morhison. Patent Specification of Continuous Filter, U p. Min. & Sci. Press, Vol. 95, p. 715 (1907). Parrish, Edward. Parrish FOter. Pac. Min., Vol. 15, pp. 124r-125 (1909). Parrish, Edward. Treatment of SUmes by Filtration with Special Refer- ence to Parrish Filter, IJ pp. Min. & Sci. Press, Vol. 94, p. 177 (1907). Parrish, Edward. Continuous Revolving Shme Filter, J p. Min; & Sci. Press, Vol. 99, p. 253 (1909). Schorr, Robert. Continuous Slime Filter, 2 pp. Min. & Sci. Press, Vol. 97, p. 194 (1908). * Tweedy & Deals. Oliver Filter at Minas del Tajo. Trans. A.I.M. E., Vol. 41, p. 349 (1910). . The Argall Filter (in " Cyaniding in Colorado"). Eng. & Min. Jour., Vol. 85, p. 219 (1908). . The Ridgeway Filter, 2 p. (Abstract from Jl. Ch. of Mines, W. Aust., Nov., 1906.) Min. & Sci. Press, Vol. 94, p. 181 (1907). . The Robinson Continuous Drum-filter. Eng. & Min. Jour., Vol. 90, p. 258 (1910). . The Portland Filter, 1 p. Min. Wld., Vol. 33, p. 1154 (1910). . OUver Filter, Cost, etc., at Minas del Tajo. Min. & Sci. Press, Vol. 99, p. 132 (1909). Pressure Filters. * Btjrt, E. The Burt Rapid Cyanide Filter, 2| pp. Min. & Sci. Press, Vol. 95, p. 717 (1907). Kelly, D. J. The Kelly Filter. West. Chem. & Met., Vol. 3, p. 153 (1907). * Kelly, D. J. TheKelly FUter Press, ;l| pp. (Abstract from Author's Art., ' 'Recent Improvements in the Art of Slimes Treatment" in Western Chemist and Metallurgist, Sept., 1907.) Min. Rep., Vol. 66, p. 173 (1907). Putman, D. G. Operation with Kelly Filter. Min. & Sci. Press, Vol. 98, p. 115- (1909). Sweetland, Ernest J. Pressure Filtration, IJ pp. Min. & Sci. Press, Vol. 99, p. 853 (1909). Sweetland, Ernest J. Improvements in Filtration Methods, 2 pp. Min. & Eng. Wld., Vol. 35, p. 863 (1912). SEPARATING SOLUTION AND PULP 205 Miscellaneous Filters. VON Bebnewitz, M. W. Eclipse Slime Filter, 1 p. Min. & Eng. Re- view (Aust.), Aug. 5, 1911; abstr. in Min. & Eng. Wld., Vol. 64, p. 985 (1911). Bishop, L. D. The Hendryx Methods of Cyaniding, 6 pp. West. Chem. & Met., Vol. 3, p. 187 (1907). * Editorial. Efficiency in Slime Washing, 1 p. Pac. Min., Vol. 16, p. 2 (1910). * Editorial. Centrifugal Filters, J p. Pac. Min., Vol. 18, p. 77 (1911). * Julian, H. Forbes. Losses in Cyaniding Incident to Filtration, 7 pp. Min. Mag., Vol. 5, p. 284 (1911). Megraw, H. a. Difficulties of Vacuum Filtration, | p. Eng. and Min. Jour., Vol. 95, p. 434 (1913). Moore, B. H. Review of the Various Sliine Filter Types, IJ pp. Min. & Eng. Wld., Vol. 35, p. 693, Oct. 7, 1911. Nichols, Askin Morrison. Vacuum Filtration, 1 p. Min. & Sci. Press, Vol. 100, p. 395 (1910). Olson, C. R. Solution Clarifier used at Tonopah-Liberty Mill, | p. Eng. & Min. Jour., Vol. 93, p. 158 (1912). Oates, J. H. Improvements to Filter Plant, f p. Mex. Min. Jour., Vol. 13, No. 3, p. 22 (1911). Spilsbory, E. G. Jiist Filtration Process. Trans. A.I.M.E., Vol. 41, p. 367 (1911). Trent, L. C. Centrifugal Slime Filter, 1 p. Eng. & Min. Jour., Vol. 93, p. 1259 (1912). Wetherald, F. H. Clarifying Cyanide Solutions, 1 p. Eng. and Min. Jour., Vol. 94, p. 884 (1912). . Nichols Slime Filter, | p. Eng. & Min. Jour., Vol. 90, p. 607 (1910). . The Rothwell Horizontal Vacuum Filter, 4 p. Min. and Eng. World, Vol. 37, p. 535 (1912). CHAPTER XII PRECIPITATION OF GOLD AND SILVER Three methods for the removal of gold and of silver from cyanide solution are in common use: 1. Precipitation with zinc-shaving. 2. Precipitation with zinc-dust. 3. Precipitation with an electric current. (1) Precipitation with zinc-shaving was first successfully used by Mac Arthur and Forrest. Zinc-plate had been tried without success, and it was not until these inventors conceived the idea of cutting the zinc into fine ribbon-like shavings, that any thoroughly successful precipitation method had been put forward. The object to be attained is, of course, to bring the pregnant solution in contact with the zinc surface, allowing contact to continue for the Pregnant Solution FilBt Compartment Filled with Coarse Sand or with ExculBior DrainJPipe Fig. 98. Zinc Box. Barren Effluent Solution minimum time consistent with commercially complete precipitat- ion. This is usually accomplished by placing the zinc-shaving in compartments in a rectangular trough as shown at A, Fig. 98. The solution slowly rises through the wide compartments and overflows at the lower end of each wide compartment into the narrow compartment B, through which it flows downward to as- cend in the next wide compartment, and so on to the end of the trough, which is set on a slight slope toward the discharge end. 206 PRECIPITATION OF GOLD AND SILVER 207 In each zinc-compartment there is a removable tray or false bottom to support the shaving, to assist in maintaining a uniform flow of solution, and to afford opportunity for settlement of precipitate, which may be withdrawn through the drain pipe along the bottom of the box by pulling out the plugs CC. The dimensions and number of the zinc-boxes are, of course, de- pendent upon the amount and character of the solution to be han- dled, varying from 12 to 24 ft. in length, and from 18 in. to 3 ft. square in cross-section. They are usually of wood, although iron boxes are not uncommon. Separate cyhndrical or rectangular compartments are occasionally used (see Fig. 99) ; each of these has a projecting lip from which the solution discharges into the descending compartment of the next box in the series. The zinc Fig. 99. Separate Zinc Boxes. used may be prepared at the plant by winding sheet-zinc on a mandrel mounted in a small but substantial lathe, and cutting spirals from this with a side-cutting tool; or if preferred, zinc- shaving may be purchased ready cut. With a large plant the first method is preferable. The thinner the shaving, the greater is the area of zinc surface exposed; at the same time extremely thin shavings break up more readily and foul the precipitated gold and silver. From 3V to | in. wide and from 5^^ to j^Vir in- thick, are the common dimensions of cross-section. Uniformity of thick- ness is an important aid in minimizing the amount of 'short-zinc' The shaving is loosely but evenly packed into each zinc-compart- ment, leaving neither open channels nor tightly packed portions 208 STAMP MILLING AND CYANIDING to accelerate or retard solution-flow through various portions of the mass. In boxes containing six or eight compartmerits it is common to omit the zinc from the compartments at each end. The first box is left empty, or filled with excelsior or some such material, to catch any slime or sediment from the leaching-tanks or filters; and the last box serves as a trap, to prevent detached precipitate from being carried out with the solution. The capacity of any zinc-box, in tons of cyanide solution per day, is a somewhat indeterminate factor, depending upon the strength of the solution, its value, and the amount of foreign metals present. From 1 to 2 tons of solution for each cubic foot of actual zinc-shaving would usually be a conservative figure. The efficiency, and frequently the capacity for precipitation, may be materially increased by dip- ping the shaving, before use, into a solution of lead acetate or other soluble lead salt. The lead thus precipitated forms with the zinc a galvanic couple that is often an extremely effective precipitant. Much the same purpose may be served by a mixture of zinc and lead shavings or by the use of zinc containing a small amount of lead. The precipitated gold and silver should be loosely adherent to the zinc and of a dark-brownish color. The development of 'channels' in the zinc-boxes should be watched for and prevented, as should also the polarization of the zinc by hydrogen bubbles. These bubbles may be removed by shaking the zinc. The accumulation of 'white-precipitate' on the shaving is a common occurrence; this may frequently be remedied by temporarily strengthening the solution by means of a strong- solution ' drip,' or by placing lumps of cyanide in the head boxes. Occasionally, white precipitates which do not yield to this treat- ment are encountered; in such cases the only thing to do is to in- vestigate the substance and find a solvent for it which can be added without detriment to the cyanide solution, or else to let the material accumulate and clean it out" periodically. Precipitation with zinc-shaving has the advantage of being simple in operation, and the apparatus is simple to erect. It is in consequence almost invariably used in small plants in preference to any other method. (2) Precipitation with zinc-dust, although proposed quite early in the development of the cyanide process, and used in several small plants, notably at Deloro, Canada, and at Marysville, Montana, did not come into general use until a few years ago. At the present PRECIPITATION OF GOLD AND SILVER 209 time it bids fair to replace the zinc-shaving method in all large plants. It is evident that the more finely divided any substance, the greater the surface it will expose and the more rapid will be any chemical reaction dependent upon it. The manifest advantages of zinc-dust in this regard were early recognized, but the difficulty of feeding the zinc, and of separating precipitate and zinc from the solution, prevented its general application. Credit for the satis- factory solution of both these problems must be given to C. W. Merrill, although other zinc-dust precipitation plants, evading his patents, are in successful use. The zinc used is a distillation pro- duct. According to W. J. Sharwood * it should conform to the following specifications: "It should be dry and fine; nearly all, say 95 per cent, should pass a sieve of 200 meshes to the linear inch (aperture 0.003) while very little, say not over 1 or 2 per cent, should remain on 100-mesh. ... It should not show any signs of caking, or contain lumps which do not break up at once when shaken on a sieve. . . . The presence of a little lead, say 2 or 3 per cent, is an advantage. . . . The presence of a little zinc oxide is appar- ently without detrimental effect, except as diminishing the percentage of active metal. ... A number of samples which have proved satisfactory in actual use have shown from 85 to over 95 per cent metallic zinc {i.e., zinc in the metallic state), most of them over 90 per cent." A recent proposal is that zinc (and lead in suitable proportion) shall be atomized at the mill, thereby lowering transportation cost and ensuring a fresh unoxidized precipitant, the composition of which is at the control of the metallurgist. In the Merrill process (see Fig. 100) the zinc dust is spread upon the belt of an automatic feeder, which is arranged by means of a float and counterweight to travel at a speed proportionate to the volume of solution treated. The dust drops into a small agitating or mixing cone where it is emulsified with air and cyanide solution, and overflows into the suction of a triplex pump, which draws its supply from the gold-tanks f of the cyanide plant. The mixed stream of pregnant solution and zinc emulsion passes up the discharge column and into the filter-press, where the precious metals and any excess of zinc remain. The clear barren * J. C. & M. Soc. S. A., Feb., 1912; abs. in Min. & Sci. Press, Vol. 104, page 659; Eng. & Min. Jour., Vol. 93, page 943. t The misnomer ' gold-tank ' is applied to the reservoir for the storage of the pregnant or gold-bearing solution before it goes to the precipitation plant. 210 STAMP MILLING AND CYANIDING solution passes through the pores of the filter-cloth and into the storage-tank. In this process fresh zinc is constantly being intro- duced, the cloths in the filter-press are coated with a layer of fine zinc, and no particle of solution can pass away without coming into precipitating-contact. The press used in the Merrill system is triangular in section but otherwise is substantially the same as Fig. 100. Merrill Zinc-dust Feeder. the other standard filter-presses. Interesting variations have been developed both in precipitation and in recovery of the pre- cipitate from this method. A tiny tube-mill charged with zinc (in one plant aluminium) granules, through which the pregnant solution flows, has the ad- vantage of continually exposing new surfaces of zinc to the solu- tion, at the same time abrading the gold-silver precipitate as soon as 'A is formed. The precipitate is then carried along by the effluent solution to be deposited in the filter. At Lluvia de Oro * a simple scheme of double canvas bags at- tached to a solution header is used to supplement the usual re- covery of precipitate by filter-pressing. The bags, when full, are removed from thecircuit and others are substituted. Burningof the bag in the precipitate-melting furnace avoids all possibiUty of loss. The main advantages of zinc-dust precipitation are the com- * H. R. Conklin, Eng. & Min. Jour., Vol. 95, page 1001. PRECIPITATION OF GOLD AND SILVER 211 pactness of the plant; the low cost for labor; and the absolute security of the precipitate, it remaining locked in the press which is opened only on clean-up days. The recovery of gold and silver is, if anything, more nearly complete than by the use of zinc- shaving, and there is less trouble from the precipitation of base metals interfering with gold recovery, since fresh zinc surfaces are constantly exposed to the incoming solution. The base metals are also more completely removed, thereby improving the tone of the solution. Exact comparison of cost between the zinc-dust and the zinc-shaving methods of precipitation is not possible. Dust can be purchased more cheaply than shaving, but this is offset by the greater operating cost in the zinc-dust precipitation plants. Figures available show a variation 'from 1.13 to 16 cents per ton of ore for precipitation with dust, and from 1.7 to 20 cents for pre- cipitation with shaving, the conditions in each case not being dis- similiar. (3) Precipitation with an Electric Current. Electrolytic pre- cipitation — using the term to describe deposition by the aid of an electric current from an external source — is an older process than either of the methods that have been discussed. It is, of course, in principle merely the extension of the electroplating process so long in use; nevertheless, it has, in the United States at least, never been popular, and there is only one American plant of consequence using the method at the present time. Contemporaneous with the introduction of MacArthur-Forrest's zinc-shaving method into South Africa, Siemens and Halske, two German chemists, brought out a process, which, with various modifications, is the most successful electrolytic precipitation method to-day. In the original Siemens-Halske method, iron anodes and lead cathodes were employed. The iron anode-plates were enclosed in canvas to prevent short circuiting and to collect the iron oxide formed during the electrolysis; the cathodes, in the form of thin sheet lead, were placed between the anodes, and at a distance of about 3 in. from them. The area of the anode and cathode sheets is merely a matter of convenience, from 4 to 6 sq. ft. being common. The iron anodes are from ^^ to | in. thick and the lead cathodes from 0.0032 to 0.01 in.; from 0.04 to 0.06 amp. per sq. ft. of anode are used, at a pressure of 5 to 10 volts. The immense area of lead foil required soon led to cutting the 212 STAMP MILLING AND CYANIDING foil into narrow strips, a few inches wide, and corrugating them in the direction of their width. Under favorable circumstances it was found that from 15 to 20 cu. ft. of tank volume were neces- sary for each ton of solution handled per 24 hours. By increasing the density of the current, and by using lead peroxide anodes in place of iron, Charles Butters has been able to reduce materially the volume of tankage required. The gold in every case, of course, is deposited as an adherent film on the lead-foil cathode. More recently Butters, at his Virginia City plant, and at Minas Prietas, in Mexico, has substituted sheets of commercial tin-plate for the lead cathodes. The gold and silver do not adhere to the tin as they do to the lead, and may be rubbed off from time to time to accumulate, as a sludge or slime, in the bottom of the tank.. In spite, however, of many ingenious improvements in electrical precipitation, it appears to be necessary, in almost every case, to send the solution to zinc-boxes for removal of the last extractable portions of gold and silver. The process can, therefore, in no case be regarded as a final one, and in view of the simplicity of zinc- boxes for small plants, and the convenience and satisfactory work of zinc-dust in the larger plants, it is hard to see how electrolytic precipitation in its present form is likely to become at all general in its application. In the treatment of solutions from certain complex ores, how- ever, electrolytic precipitation will probably continue to hold its own, because of its abiUty to remove objectionable metals from the solution, and thereby regenerate and make available the cyan- ide locked up and otherwise useless. BIBLIOGRAPHY FOR PRECIPITATION OF GOLD AND SILVER * Especially Desirable for Students* Use General. VON Bernbwitz, M. W. Graphite in Cyaniding, f p. Min. & Sci. Press, Vol. 100, p. 869 (1910). * VON Bernbwitz, M. W. Graphite — an Obstacle to Good Cyaniding, 2 pp. Min. & Sci. Press, Vol. 99, p. 758 (1909). * Browne, R. Stuart. Premature Precipitation of Gold, 4J pp. Min. & Eng. Wld., Vol. 35, p. 1108 (1911). . * Busey, a. p. Methods of Precipitation in the Cyanide Process, 21 pp. Bull. Colo. School of Min., Vol. 3, p. 247 (1907). * Caldeoott, W. A. Precipitation of Gold by the Carbonaceous Matter in Burnt Lime Used for Neutralizing. Min. & Sci. Press, Vol. 98, p. 828 (1909). PRECIPITATION OF GOLD AND SILVER 213 CowLBS, R. K. Precipitation of Gold and Silver by Carbon, 1 p. Min and Soi. Press, Vol. 105, p. 730 (1912). * Editorial. Carbon, a Precipitant? | p. Pac. Min., Vol. 16, p 81 (1910). Green, Morris. The Effect of Charcoal.in Gold Bearing Cyanide Solu- tion with Reference to the Precipitation of Gold, 14 pp. Bull. I. M. M. No. 109 (1913). Abstr. in Min. & Eng. Wld., Vol. 39, p. 873 (1913). Gross, John. Precipitation Temperatures, 1| pp. Eng. and Min Jour., Vol. 95, p. 911 (1913). MacArthur, J. S. New Method of Precipitation by Zinc, J p., 2 pp Min. and Eng. Wld., Vol. 38, pp. 433, 820 (1913). Mbgraw, H. a. Precipitation of Gold and Silver in Cyaniding, 2i pp Min. & Eng. Wld., Vol. 35, p. 685, Oct. 7, 1911. * Megraw, Herbert A. Precipitation from Cyanide Solution, 65 pp Eng. & Min. Jour., Vol. 97, p. 1232 (1914). Phillips, F. D. Notes on Precipitation, 1| pp. Mex. Min. Jour.. Vol. 11, No. 5, p. 17 (1910). * Sharwood, W. J. & Clark, A. J. Carbon and Cellulose in Cyanide Solutions, 2 pp. (Abstract C. M. & M. Soc, S. A.) Min. & Sci. Press, Vol 100, p. 554 (1910)'. Smith, E. H. Precipitation Temperatures, | p. Eng. and Min. Journal Vol. 95, p. 579 (1913). * Turner, H. W. Precipitation with Sodium Sulphide, IJ pp. Eng & Min. Jour., Vol. 93, p. 973 (1912). 'Webster, E. H. Sodium Sulphide as Cyaniding Precipitant, If p Eng. & Min. Jour., Vol. 93, p. 973 (1912). Witteveen, G. De Wilde Precipitation Process, IJ p. Pac. Min., Vol, 18, p. 32 (1911). Witteveen, G. De Wilde Precipitation Process, (Read at Institute of Mines and Metallurgy, Mexico) 1 p. Min. & Min., Vol. 31, p. 342 (1911). Zachebt, V. Precipitation of Gold and Silver from Cyanide Solutions by a Zinc-sodium Alloy, i p. Pac. Min., Vol. 18, p. 20 (1911). . A New Precipitating Process, J p. Min. & Sci. Press, Vol. 96, p. 566 (1908). . The Precipitation of Gold and Silver by Organic Substances in Nature and in Cyaniding Experiments, J p. Min. Sci., Vol. 61, p. 369 (1910) . Zinc-shaving Precipitation. BosQUT, F. L. Short Zinc, i p. Min. & Sci. Press, Vol. 98, p. 478 (1909). Browne, R. Stuart. Short Zinc, IJ pp. Min. & Sci. Press, Vol. 98, p. 718 (1909). * CooLiDGE, Roy F. Zinc-box Precipitates. Min. & Sci. Press, Vol. 99, p. 394 (1909). Guanajuato Engineer. A New Style of Zinc-box, i p. Pacific Min., Vol. 19, p. 42 (1911). Hunt, Bertram. Short Zinc, i p. Min. & Sci. Press, Vol. 98, p. 718 (1909). 214 STAMP MILLING AND CYANIDING * Lamb, K. B. Practical Hints in the Precipitation of Silver from Cyanide Solutions, li pp. Min. Sci., Vol. 60, p. 586 (1909). Phillips, F. D. Notes on Precipitation in Zinc-boxes, 1 p. Abstr. from J. C. M. & M. Soc, S. A.; Pac. Min., Vol. 17, p. 425 (1910). Rhinert, James T. Increasing the Capacity of Zinc Lathes. J p. Pac. Min., Vol. 18, p. 122 (1911). Smith, Mather. Relation Between Quantity of Solution and Amount of Zinc. J. C. M. & M. Soc, S. A., Vol. 9, p. 300 (1909). Wheatley, R. Lorin. A New Style of Zinc-box, 2 pp. Pac. Min., Vol. 18, p. 170 (1911). Willis, H. T. Short Zinc. (Enquiry about letter from P. L. Bosqui of April 3rd.) Min. Sci. Press, Vol. 98, p. 656 (1909). . Revolving Zinc-boxes, f p. Mines & Methods, Jan., 1910, p. 199. . Device for Handling Zinc Shavings, J p. Eng. and Min. Journal, Vol. 94, p. 1170 (1912). Zinc-dust Precipitation. * Clark, A. J. Comparison Zinc-dust and Zinc-shaving, Cost, etc., 3 pp. W. Chem. & Met., Vol. S, p. 182, 1909; abstr. from J. C. M. & M. Soc., S. A., Vol. 9, p. 222 (1909). * Clark, Allan J. Zinc-dust Precipitation. Min. Mag., Vol. IV, p. 289 (1911). Cleotstell, J. E. Notes on Analysis of Zinc-dust, 4 pp. Eng. and Min. Jour., Vol. 95, p. 793 (1913). CoLBATH, Jambs S. Automatic Zinc-dust Feeder, | p. Eng. & Min. Jour., Vol. 89, p. 453 (1910). ' 'Cyanide Man." Zinc-dust vs. Shaving, | p. Min. & Sci. Press, Vol. 93, p. 196 (1906). * Editorial. Zinc-dust Precipitation, ip. Eng. & Min. Jour., Vol. 92, p. 528 (1911). Hbrrick, R. L. Precipitation by Zinc-dust. Min. & Min., Vol. 28, p. 432 (1908). Irvin, Donald F. Zinc-dust Precipitation Equipment, IJ pp., illus. Min. and Sci. Press, Vol. 106, p. 861 (1913). Linton, Robert. Zinc-dust Precipitation at the Homestake Mine, f p. (Notes in J. C. U. & M. Soc, S. A.) Eng. & Min. Jour., Vol. 88, p. 199 (1909). Merrill, C. W. Zinc-dust Precipitation Comparative Costs, etc., 1 p. Eng. & Min. Jour., Vol. 92, p. 407 (1911). Merton, a. M. Zinc-dust Precipitation of Gold and Silver, If pp., illus. Min. and Engr. Wld., Vol. 39, p. 429 (1913). Morris, A. W. Zinc-dust Feeder, 1 p. Min. & Sci. Press, Vol. 104, p. 249 (1912). MuNROE, H. S. Zinc-dust Precipitation at Cerro Prieto, Sonora, Mexico, IJ pp., illus. Eng. and Min. Jour., Vol. 95, p. 1085 (1913). * MuNROE, H. S. Smelting Precipitate at Cerro Prieta, Sonora, 3 pp., illus. (Tavener Process.) Eng. and Min. Jour., Vol. 95, p. 1137 (1913). PRECIPITATION OF GOLD AND SILVER 215 Parsons, A. B. Zinc-dust Feeder, | p. Eng. & Min. Jour., Vol. 90, p. 447 (1910). Pettis, E. S. Zinc-dust Precipitation, f p. Min. and Sci. Press, Vol. 105, p. 151 (1912). Rice, Claude T. Zinc-dust Feeder, 2 pp. Eng. & Min. Jour., Vol. 91, p. 361 (1911). * Sharwood, W. J. Zinc-dust Precipitation, 2 pp. Eng. & Min. Jour., Vol. 79, p. 753 (1905). * Sharwood, W. J. Zinc-dust Specifications and Tests, 4 pp. J. C. M. & M. Soc, S. A., Vol. 12, p. 332 (1912); abstr. Eng. & Min. Jour., Vol. 93, p. 943 (1912); abstr. Min. & Sci. Press, Vol. 104, p. 659 (1912). Electrolytic Precipitation. Alderson, M. W. Electrolytic Precipitation. Min. & Sci. Press, Vol. 89, pp. 137 and 157 (1904). * Andreolb, E. Electrolytic Precipitation. Eng. & Min. Jour., Vol. 64, p. 96 (1897); Eng. & Min. Jour., Vol. 63, p. 142 (1896). Argall, Philip. Zinc vs. Electrolytic Precipitation. Min. Ind., Vol. X, p. 361 (1901). E. F. G. Electrical Precipitation from Cyanide Solutions, f p. Eng. & Min. Jour., Vol. 89, p. 598 (1910). Frary, F. C. Electro-deposition of Gold and Silver, 73 pp. Am. Electro- Chem. Soc, Vol. 23, p. 25 (1913). Lay, Douglas. Electrolysis of Cyanide Solutions at Reliance Mill, Nelson, B. C. Eng. & Min. Jour., Vol. 83, p. 801 (1907). Neumann, Bbrrik. Electrolytic Recovery of Gold in Cyanide Solu- tions. (Abstract from Zeit. fur Elektro-chemie in Aust. Electrical Record, July 31, 1907), 1 p. Min. Rep., Vol. 56, p. 237 (1907). Ogden, J. A. The Recovery from Cyanide Solutions by Electricity, i p. Min. Sci., Vol. 67, p. 545 (1908). * Rice, C. T. Butters Plant, Virginia City, Electrolytic Precipitation. Eng. & Min. Jour., Vol. 83, p. 269 (1907). * Richmond, Chas. P. Electrolytic Precipitation at San Sebastian Mine. Eng. & Min. Jour., Vol. 83, p. 612; (see also Vols. 13 & 15 Min. Ind.) (1907). * Rose, T. K. Electrical Precipitation of Gold. Inst. Min. & Met.; abstract in Min. Ind., Vol. IX, p. 377, Ap. 25 (1900). Altuninium Precipitation. * Hamilton, E. M. Aluminum Precipitation at Nipissing, Ont. Eng. & Min. Jour., Vol. 95, p. 935 (1913). Hamilton, E. M. Precipitation by Aluminum Dust, 4 pp. Mines and Methods, p. 213, May, 1913. KiRKPATRiCK, S. F. Aluminum Precipitation at Deloro, Ont., li pp., illus. Eng. & Min. Jour., Vol. 95, p. 1277 (1913). Regeneration and Care of Solutions. * Allen, A. W. Solution Control in Cyaniding, 4 pp. Min. and Sci. Press, Vol. 107, p. 448 (1913). 216 STAMP MILLING AND CYANIDING AiTOEHSON, Isaac. Regenerating Copper Cyanide Solution. Min. & Sci. Press, Vol. 100, pp. 229, 803 (1910). * Aldkich, T. H., Jr. Electrolytic Oxygen in Cyanide Solution, 6 pp. Bull. 62, Trans. A.I.M.E., p. 177 (1912). * Bullock, L. McN. B. Regenei-ation at Copala, f p. Min. & Sci. Press, Vol. 94, p. 719 (1907). Chandler, E. D. Copper in Cyanide Solutions, J p. Min. & Sci. Press, Vol. 93, p. 534 (1906). * Clennell, J. E. Electrolytic Cyanide Regeneration, 3 pp. Eng. & Min. Jour., Vol. 91, p. 1064 (1911). Clevenger, G. Howell and Hall, M. L. Electrolysis of Aqueous Solutions of the Simple Alkaline Cyanides, 19 pp. Am. Electro-Chem. Soc, Vol. 24, p. 271, Sept. (1913). Christy, S. B. Removal of Base Metal Cyanide by Acid Precipitation. Trans. A.I.M.E., Vol. 26, p. 747 (1896). Editorial. Lime in Cyaniding, J p. Eng. & Min. Jour., Vol. 93, p. 869 (1912). GuppY, R. L. and Waterman, D. Separation of Base Metals in Cyan- ide Solution for Quantitative Determination, 1 p. Min. and Sci. Press, Vol. lOS, p. S97 (1912). * Holt, Thbo. P. Lime Reaction in Cyaniding, 1 p. Min. & Min., Vol. 31, p. 475 (1910-11). Kern, Ed. F. The Electrolysis of Cyanide Solutions, 25 pp. Am. Electro-Chem. Soc, Vol. 24, p. 241, Sept. (1913). Merton, a. M. The Use of Lime in Cyanide Work, 4 pp., illus. Min. Sci., Vol. 68, p. 154 (1913). * NiCHOLL, B. George. Cyanide Regeneration, 2 pp. Min. & Sci. Press, Vol. 104, p. 406; abstr. from Min. Eng. Rev. (Aust.) (1912), Rhodes, C. E. Lime in Cyaniding, 1 p. Eng. and Min. Jour., Vol. 94, p. 251 (1912). Sharwood, W. J. Efficiency of Coarse and Fine Lime. Rev. in Min. Ind., Vol. XVII, p. 468; J. C. M. & M. Soc, S. A., Vol. VIII, p. 293 (1908). * Wheelock, R. p. Cyanide Regeneration, 1 p. Min. & Sci. Press, Vol. 104, p. 506 (1912). Wheelock, R. P. Tests on Acid Regeneration of Cyanide Solutions, 4 pp. Min. & Sci. Press, Vol. 88, p., 814 (1909); also Min. & Sci. Press, Vol. 100, p. 396 (1910). Williamson, W. D. Regeneration of Cyanide Solution, i p. Min. and Sci. Press, Vol. 105, p. 49; (Abstr. from J. C. M. & M. Soc, S. A.) (1912). CHAPTER XIII RECOVERY AND TREATMENT OF PRECIPITATE The method of handHng the precipitated gold and silver will, of course, be largely dependent upon the method of precipitation employed. With zinc-box precipitate, in order that the deposit adhering to the zinc may be thoroughly loosened, it is customary to strengthen the cyanide solution materially for a few hours before a clean-up is made. This done, the cyanide is displaced by clear water, to which alum may be added to facilitate settlement. Then beginning at the head box, the zinc is lifted out by hand and carefully sprayed to remove adhering precipitate; this may be done over the zinc-box or over a special clean-up tank. The cleaned zinc is then laid aside in water, and the next compartment is treated in the same way till all coarse zinc has been removed. There will then remain below the trays in the boxes the residue to be treated, consisting of the so-called ' short-zinc ' (pieces large enough to be removed by screen- ing), various compounds of zinc, gold (or silver), and cyanide, and the bulk of the precipitated gold, together with any other metals or substances which might have been precipitated or deposited on the zinc. This material, together with the water remaining in the boxes after siphoning off the clear liquid, is either drawn out through spigots in the bottom of the boxes or bailed out with wooden or enameled buckets, and is placed iA a clean-up tank, where the precipitate is given sufficient time to settle thoroughly ; the super- natant liquid is then carefully siphoned away. In some works the muddy precipitate is run through a 60-mesh screen by which means much short-zinc is at once separated. In other cases the material from the boxes goes direct to a small filter-press. In any event the precipitate, either before or after drying, should be freed as much as possible from short-zinc. When this has been done we have a finely-divided product of uncertain composition, but carry- ing a considerable proportion of zinc and other foreign substances, which must be removed before a satisfactory bullion can be made. 217 218 STAMP MILLING AND CYAN WING Where zinc-dust is the precipitant, a finely-divided slime is re- covered in the presses, which corresponds to the screened product from the boxes, except that it is likely to contain more zinc. The electrolytic precipitate is usually cleaner than that from either of the other processes. In many plants the finely-divided precipitate, whatever its source, is carefully sampled, sacked, and shipped by express to the smelter, the cost of refining at the plant being greater than ex- press plus treatment at the smelter. In cases, however, where treatment of the precipitate at the mill is desirable, several nfethods are available. Of these the ones in most common use will be described : I. Add treatment for removal of zinc, subsequent drying and melt- ing the residue with suitable fluxes. II. Roasting, with or without niter, to remove zinc; with treatment of residue similar to the preceding. III. Direct smelting with an oxidizing charge to flux the zinc and other impurities, the resulting bullion {usually lead) being refined for gold and silver. I. The Acid Treatment is the one most commonly used in the United States. The precipitate, after being transferred to a lead- lined tank, is treated with sufficient 10 per cent sulphuric acid to dis- solve all the zinc, arrangements being made for heating and stirring the solution if necessary. This operation should be carried out under a hood on account of the fumes evolved. Hydrochloric acid is sometimes used in place of sulphuric. When all the zinc has been dissolved, the tank may be filled with water, the precipitate allowed to settle, and the zinc sulphate solution decanted by suit- able means, although, as before, much more satisfactory results will be attained by the use of a small filter-press. In any event the residue from this treatment will be practically zinc-free and ready for direct fusion. In some plants, however, the precipitate is roasted before melting, but this would seem scarcely necessary in most cases. Before melting, the required fluxes should be thoroughly mixed with the precipitate. Many of the larger plants briquette the flux- precipitate mixture to prevent dusting during the early stages of fusion. The fluxes to be use'd vary considerably with the choice of the operator and the nature of the precipitate. From 30 to 50 parts of borax and 9 to 30 parts of bicarbonate of soda, to each 100 RECOVERY AND TREATMENT OF PRECIPITATE 219 parts by weight of precipitate, is a common charge. The melting is usually done in graphite crucibles, in coal, coke, wood, or char- coal furnaces. Recently the use of gasoline or crude-oil as a fuel has become more common and there are on the market several melting furnaces fired by this means, and so arranged to tilt on trunnions (see Fig. 101), that it is unnecessary to remove the cru- cible from the furnace in pouring. This arrangement is so con- venient that its use is bound to become quite general. II. The Roasting Method, while never very popular in the United States, has been used quite extensively elsewhere. Niter, either in the form of powder, or as a saturated solution, is fre- FiG. 101. Tilting-type Melting-Furnace. quently added to assist in oxidizing the zinc, before drying the precipitate. The roasting is usually done in some form of mufHe furnace, the precipitate being placed in roasting pans before it is put in the muffle. The whole operation must be conducted with extreme care to avoid loss by dusting, as well as to minimize the mechanical and chemical losses connected with the volatilization of the zinc. in. The Process of Direct Smelting is coming into favor in many of the larger mills. Where zinc-shaving is used the short zinc is usually removed by running the zinc-box sludge through a 20- or 40-mesh screen. When this practice is followed, the method 220 STAMP MILLING AND CYANIDING used at the Dos Estrellas mill, as described by Walter Neal,* is simple and efficient. The precipitate, after screening out the 'zinc-shorts,' is run to a filter-press, dried with compressed air, and discharged into a steam-dryer car. The material is handled as httle as possible so as not to break the cakes formed in the press. Fluxes are shoveled on top of the precipitate, the dryer car run to the furnace and precipitate and fluxes shoveled into crucibles ready for melting. The charge is made up of: Precipitate 100 parts. Borax 15 parts. Soda bicarbonate 8 parts. Sand 4 parts. Scrap iron in excess. The so-called Tavener process for treating precipitate, re- sembles the ordinary fire-assay for gold and. silver. The precipi- tate is mixed with litharge, borax (and other fluxes if necessary) and some reducing agent to ensure a lead button and the whole is fused. The lead button is cupelled, and the gold and silver are recovered as a clean bulhon. This method is especially popular in South Africa, and a number of the larger mills in the United States are reported as finding it eminently satisfactory. Another modification of the direct smelting process is in use in some of the larger Nevada mills.! The precipitate is briquetted with fluxes in the following proportions: — Parts Precipitate (dry weight) 100 Litharge 100 to 125 Concentrate (S, 35 per cent, SiOa, 30 per cent) 60 to 70 Moisture about 9 per cent. These briquettes are charged into a small blast-furnace with some old slag, cupel bottoms, etc., and smelted for lead bullion, which is later cupeled as in the Tavener process. The results are excellent and the cost is extremely low. Treatment of Solution after Precipitation. It is well to remem- ber that the precipitation plant yields two products — precipitate and effluent solution. Upon the proper disposal and treatment of the latter depends, to no small extent, the successful and economi- cal treatment of the ore. * Min. & Sci. Press, Vol. 98, page 327. t J. W. Hutchinsoi), Min. & Soi. Press, Vol. 102, page 717. RECOVERY AND TREATMENT OF PRECIPITATE 221 In standard practice the effluent solutions are run to sump tanks from which they are withdrawn as needed for re-use. These sump solutions are naturally weaker in cyanogen than they were before use, and this loss of cyanide is a serious item of cost; in some plants, indeed, it is the largest single cost-factor. If, for example, the solution, as applied to the ore, shows by titration with silver nitrate a strength equivalent to 0.52 per cent KCy and the same solution when it reaches the sump titrates 0.27 per cent KCy, then we have an apparent consumption of 0.25 per cent KCy, or 5 pounds per ton of solution which at 12 to 18 cents per pound means serious expense from this source alone. It does not necessarily follow, however, that this amount of cyanide has been irrevocably lost, the greater part of the consumption being due, not to destruction of cyanide, but to the formation of cyanides of zinc in the extractor- boxes, of cyanides of iron from the tanks and pipes, and from particles of iron abraded from crushing machines, and cyanides of various other base metals according to the character of the ore undergoing treatment. Ferrocyanides, sulphocyanides, cyanates, and numerous other compounds are also Hkely to be formed under certain conditions. If the ore is a comparatively simple one, continued re-use of the solution for long periods may cause no appreciable effect either upon solution or precipifation. With the more complex ores, how- ever, especially those containing base metals in soluble form, the accumulation of metallic cyanides has an effect both on solution and on precipitation, although usually this effect is more marked upon the latter than upon the former. In certain cases, however, as cited by Julian and Smart,* solutions which have been used have no longer the same dissolving power although raised to the original cyanide strength. These difficulties may in general be solved in one of the following ways: (1) Through keeping the solution slightly alkaline by the addi- tion of lime to the ore during crushing, or by addition of ' milk of Ume' or caustic soda to the cyanide solution itself. This, indeed, is necessary in all successful cyanide work. The proper amount of protective alkaU {i.e., alkali over and above that of the cyanide itself) is a matter of determination for each particular ore. An interesting case is cited by L. McN. B. Bullock,t in which, by an * Cyaniding Gold and Silver Ores, 1st Ed., pages 71-72. t Min. & Sci. Press, Vol. 94, page 719. 222 STAMP MILLING AND CYANIDING increase of alkalinity from 0.04 to 0.14 per cent (caustic soda), the cyanide consumption was cut from 4.5 to 1.5 pounds per ton of ore. (2) Through complete aeration of the solutions, as practiced by some of the silver cyanide mills in which the sumps solutions are kept constantly circulating through cones by the aid of centrifugal pumps. In this way various reducing agents collected from the ore, and which would affect the solvent action of the solution, are rendered innocuous. (3) Through removal of the base metal cyanides by acid pre- cipitation.* KaCuzCyi + H2SO4 = K2SO4 + CuaCya + 2 HCy. If the supernatant liquid be decanted from the Cu2Cy2 precipi- tate,, and run into a tank containing an excess of lime water we shall have: K2SO4 + 2 HCy + Ca(0H)2 = CaS04 + 2 KCy + 2 H2O. In this manner half of the cyanogen locked up may be recovered. It is possible also to recover a large portion of the cyanogen from the cupric cyanide precipitate. f Various methods, such as the addition of ferric salts for the precipitation of ferrocyanides as prussian^ blue, or of alkaline sul- phides to decompose cyanides of various metals, have been proposed and used to some extent. Electrolysis has recently been given a thorough trial, as a means of cyanide regeneration J and has been reported ineffective. In general the first two methods mentioned must be relied upon for everyday work. Acid regeneration may be advisable, but should only be used in extreme cases. * S. B. Christy, Trans. A.I.M.E., Vol. 26, page 747. t R. P. Wheelock, Min. & Sei. Press, Vol. 99, page 814. t J. E. Clennell, Eng. & Min. Jour., Vol. 91, page 1064. BIBLIOGRAPHY FOR RECOVERY AND TREATMENT OF PRECIPITATE * Especially Desirable for Students' Use * Aarons, J. Boyd and Black, Herbert. Refining and Melting Pre- cipitate, 2 pp. Min. & Eng. Wld., Vol. 35, p. 955 (1912). VON Bernewitz, M. W. Treatment of Cyanide Clean-up Matter, 1 p. Min. & Sci. Press, Vol. 104, p. 343 (1912). RECOVERY AND TREATMENT OF PRECIPITATE 223 * Clbvenger, G. Howell. Refining Zinc Precipitates. Trans. A.I. M.E., Vol. 34, p. 891 (1904). * Campbell, Bkayton F. Refining Precipitate with Sulphurous Acid. Pac. Min., Vol. 16, p. 222 (1910). Clark, Donald. Method of Refining Gold with Sulphur, 1 p. Min. Soi., Vol. 57, p. 363 (1908). Clevenger, G. H. The Shipment of Cyanide Precipitates, If pp. Eng. and Min. Jour., Vol. 95, pp. 273 and 863 (1913). * Clbvenger, G. H. A Study of Cyanide Precipitates, If pp. Eng. and Min. Jour., Vol. 95, p. 273 (1913). CoNKLiN, H. R. Smelting Precipitate with Electric Furnaces, 2 pp. Eng. & Min. Jour., Vol. 93, p. 1189 (1912). . * CoNKLiN, H. R. Handling Cyanide Precipitate at Lluvia de Oro, 1 p. Eng. and Min. Jour., Vol. 95, p. 1001 (1913). * CooLiDGE, Roy F. Cupellation of Cyanide Precipitate, 2 pp. Eng. & Min. Jour., Vol. 92, p. 756 (1911). Dewey, F. P. Shipment of Cyanide Precipitate, | p. Eng. and Min. Jour., Vol. 95, p. 961 (1913). Drtjcker, a. E. Treatment of Matte from the Cyanide Mill, | p. Min. & Sci. Press, Vol. 94, p. 638 (1907). Edmands, H. R. Smelting and Refining Zinc-box Precipitate, Ij pp. Min. and Sci. Press, Vol. 105, p. 55 (1912). HixoN, H. W. Smelting Cyanide Precipitate, 1 p. Eng. and Min. Jour., Vol. 95, p. 1027 (1913). Hutchinson, J. W. Direct Smelting of Precipitate. Min. & Sci. Press, Vol. 102, p. 717 (1911). * Megkaw, Herbert A. Treatment of Cyanide Precipitate, 11 pp. Eng. & Min. Jour., Vol. 97, p. 606 (1914). Mtjnroe, H. S. Smelting Precipitate at Cerro Prieto, Sonora, 34 pp. Eng. and Min. Jour, Vol. 95, p. 1137 (1913). * Neal, Walter. Treatment of the Gold and Silver Precipitate at Dos Estrellas, 1 p. Min. & Sci. Press, Vol. 98, p. 327 (1909). Sewell, F. W. The Refining of Gold and Silver Precipitates, li pp. Min. Sci., Vol. 60, p. 540 (1909). Smith, L. Refining at Pittsburg-Silver Peak Mill, 1| pp. Eng. and Min. Jour., Vol. 95, p. 603 (1913). * SwiNNEY, L. A. E. The Tavener Process for Gold Slimes, 2 pp. Eng. & Min. Jour., Vol. 83, p. 608 (1907). Tavener, P. S. The Tavener Process of Refining Cyanide Precipitate by Lead Smelting and Cupellation. J. C. M. & M. Soc, S. A., Vols. Ill, IV, p. 70-78 (Oct., 1902); reviewed Min. Ind., Vol. IX, p. 323 (1909). Thomas, James E. Cyanide Clean-up, 1 p. Min. & Sci. Press, Vol. 94, p. 62 (1907). Smith, Lyon. Refining at Pittsburg-Silver Peak Mill, IJ pp. illus. Eng. and Min. Jour., Vol. 95, p. 603 (1913). * Thomas, A. Smelting of Cyanide Precipitate. J. C. M. & M. Soc, S. A., Vol. 9, p. 6 (1908). 224 STAMP MILLING AND CYANIDING Thomas, James E. Cyanide Works Clean-up Practice, 1 p. (from J. C. M. & M. Soc, S. A.) Min. Rep., Vol. 55, p. 33 (1907). * Truscott, S. J. Treatment of Gold Precipitate and Manipulation of Tilting Furnaces at the Redjang Lebong Mine, Sumatra. (Read before Inst. Min. & Met.) Min. Rep., Vol. 54, p. 466 (1906). WiLMOTH, L. J. Acid Washes on Cyanide " Clean up," 1 p. Abstract from J. C. M. & M. Soc, S. A.; Pac. Min., Vol. 16, p. 98 (1910). WiNGATB, Hamilton. Treatment of Zinc-box Precipitate in N. Z., 6 pp. Trans. A.I.M.E., Vol. 33, p. 136 (1903). * Yates, Arthur. The Smelting of Gold Precipitates and Bullion with Oil Fuel, 1 p. (J. C. M. & M. Soc, S. A., June, 1909.) Min. Sci., Vol.60,.p. 203 (1909). . Comparison of Oil and Coke (as Fuel for Melting Precipitates), 1 p. Min. & Min., Vol. 27, p. 369 (1907). . Melting and Refining Precipitate at El Tigre Mill, 1 p. Eng. and Min. Jour., Vol. 95, p. 931 (1913). PART III THE TREATMENT OF GOLD AND OF SILVER ORES This portion of the text is intended to correlate the various pro- cesses which have so far been described, and to point out the rela- tions and functions of the various parts of the modern gold- and silver-milling plants. CHAPTER XIV TREATMENT OF GOLD ORES It will be at once accepted as axiomatic, that in order for the particles of gold existing in an ore to be removed from it, they must be exposed to the action of the particular process designed for their recovery. This may be accomplished in one of three ways: (1) By re- moving from the gold particles all of the enclosing envelope of rock; (2) by removing enough of the envelope, to enable the reagent to come in sufficient contact with the gold, either to hold the gold and its matrix, or to remove it therefrom by solution or otherwise; (3) by rendering the ore so porous, that to all intents and purposes the gold particle is as completely liberated as though the surrounding gangue material had been entirely removed. The first two results may be brought about as the result of crush- ing, the completeness of liberation being a function of the size of the gold particles and of the character and fineness of crushing. The third condition — in which, owing to the porosity of the matrix, complete liberation is not essential — is brought about usually as the result of natural or artificial oxidation of other minerals (usually sulphides) existing as a part of the gangue. Examples are seen in the oxidized, porous, and cellular out-crops of sulphide ore-bodies. Much the same result may be brought about by roasting sulphide ores under suitable conditions. All this presumes that the gold exists in the native state, and free from adhering films, and that it may hence be released from its matrix, much as the kernel of a nut may be set free by cracking the shell. Should the gold not exist in the native state but in combination with some other element, then it is still true that the gold compound must be similarly liberated from its envelope before any mechani- cal or chemical extraction can take place. This brings us to the point of recognizing crushing as the sine qua non of any metallurgi- cal process which is not planned, as is smelting for instance, to de- compose the rock-mass as a whole. 227 228 STAMP MILLING AND CYANIDING Having the particles liberated and exposed, there then remains to be decided the method of removing the gold or gold mineral from the rest of the ore. If the gold is coarse, free, in the sense of being native, and free from adhering films of oxide or other substance, then it is evident that it should be recovered as far as possible by amalgama- tion. In fact, we might go farther than this and say, that all gold which can be recovered by ordinary methods of amalgamation, should be so saved, and that only that portion of the precious metal not effectively and readily recoverable by this means should be subjected to cyaniding. The reasons for this are obvious enough. Coarse gold particles dissolve but slowly in cyanide- solution, thus increasing materially the time required for treatment; secondly, complete precipitation and complete recovery of solution are alike impossible, so that in no case will aU of the gold particle find its way into the cyanide clean-up. With regard to concentration the case is different. Concentrat- ion is not a final process. The product recovered by this means must be subjected to still further treatment for the recovery of any gold it may contain, and unless by concentration we can remove substances, which if left in the ore would be detrimental to cy- aniding or, unless the gold recovered in this way cannot l^e re- covered by direct cyaniding, concentration should be omitted. In the treatment of gold ores, then, we have the following pos- sibilities: (1) Amalgamaiion. (2) Amalgamation and concentration. (3) Amalgamation and cyanidation. (4) Amalgamation, concentration, and cyanidation. (5) Cyanidation. (1) Amalgamation, as a sole means of recovery, is rarely, if ever, sufficient. In a few cases, with exceptional ores in which the gold is clean and coarse, and the conditions are such that the ore is completely oxidized, it may be found that practically all of the gold is recoverable by this means, but such conditions are decidedly rare, and at best can last only until the level of oxidation is bot- tomed. Such ores are the ones referred to as 'free-milling.' (2) Amalgamation and Concentration. Prior to the advent of the cyanide process, this was the combination almost universally employed for such ores as we are discussing. Good recoveries TREATMENT OF GOLD ORES 229 were made, and immense tonnages treated by this means, and the process has by no means become obsolete. Stamps in this field have been particularly successful in the combined function of crushers and amalgamators, the plate tailing in such cases being sent to van- ners or, in the more recent plants, after classification, to Wilfley-type tables and to vanners. The concentrate is treated on the ground by cyanidation or chlorination, or shipped to smelting works. (3) Amalgamation and Cyanidation is proving itself the most rational mode of treatment for an immense tonnage of ore at the present day. Where, as previously remarked, the omission of concentration does not cause excessive cyanide consumption, and where the net recovery by cyanide treatment is as high as by concentration and shipment of the concentrate, allowing for the extra cost of the latter method, then, of course, entirely local treatment is to be preferred. It should be noted in this connection, that while gold in the form of bullion is paid for at the full value of $20.67 per ounce, that existing in the concentrate will, when shipped to a smelter, bring only $19 or $19.50 unless the con- centrate is particularly high grade, in which case as much as $20 per ounce may be realized. (4) Amalgamation, Concentration, and Cyanidation together must necessarily be employed in the treatment of the more com- plex ores, and are of course, frequently seen in older plants to which cyaniding has been added as an after-thought. Such a combination means great complexity of plant with high treatment cost, and is avoided wherever it is possible to omit one of the steps. It seems probable that, as time goes on, and we are able to handle the sulphide minerals more successfully in the cyanide plant, concentration will become a less important factor in the treatment of gold-ores than is at present the case. Much the same thing may be said of concentration followed by cyaniding without the use of amalgamation. (5) Cyanidation. Direct and unassisted cyanidation is finding many advocates, especially in South Africa, but this matter has already been discussed quite fully. Undoubtedly, there are cer- tain ores where the percentage of gold recoverable by amalgam- ation is so small, that even the slight extra expense of passing the pulp over copper-plates and recovering the amalgam from them is a matter of doubtful economy. On the other hand, it is a regrettable fact that less attention is paid to amalgamation in 230 STAMP MILLING AND CYANIDING many cyanide mills than would have been tolerated under the system in vogue before cyaniding reached its present efficiency. In fact, there are cases where there is reason to think that amal- gamation is slighted, to give the cyanide plant a chance to make a better showing. This, of course, is the height of folly. In the preceding discussion no distinction has been drawn, in cyanidation, between sand and slime treatment,* nor have other adjuncts, such as roasting or solution-oxidizers, been mentioned. It is now proposed to show, in detail, typical plants illustrative of good practice under each of the above conditions. It is not necessarily to be assumed that the process in each case is best suited to the particular ore, nor is it true that the mill arrange- ments and details of treatment are in every case such as would be approved by a jury of competent metallurgists. In the main, however, the plants chosen represent standard practice and the reader will find many of the best plants in the world included in the following diagrams. * As used in ordinary mill-parlance, ' sand ' is a product which is treated by leaching; 'slime' is a product which is not or cannot be so handled. It would generally be more exact to say, 'leachable product' and ' non-leachable product,' than to use the terms ' sand ' and ' slime ' in their usual significance. TREATMENT OF GOLD ORES 231 (i) AMALGAMATION Examples under this class are rare and I can recall but one plant, that of the Round Mountain Mining Company at Round Moun- tain, Nevada. The process there used is shown by the following diagram. Character of Ore: — The gold is associated with iron oxide lying in seams in a rhyoUtic rock. Average value $7.00 per ton. The ore would be classified as soft. Flow Sheet: Ore from Mine No. 3 D Gates Gyratory and 7 x 12 in. Dodge Crasher - 2 in. Product I Unit No. 1- Capacity 100 Tons Trommel - 1 m. Aperture Oversize Undersize T Unit No. 2 - Capacity 100 Tons Ten 900 lb. Stamps, dropping 6 in. 110 times per min.- X in. mesh - Stamp Duty 10 tons. Small lip Plate. Two.1250 Ib.Nissen Stamps, dropping 6 in. 120 times per Min. Discharge 2 in. - Tyler "Ton Cap" Screen No. 44 ?mesh. Stamp Duty 12 Tons Two Apron Plates 2 >ix5 ft. Two Apron Plates5x5 ft. between One 5 ft. Huntington Mill-70 R.P.M. Tyler "Ton Cap" Screen No. 527,? mesh. Two 5 f t.Huntington Mills-Making 70 R.P. M. Tyler "Ton Cap" n -^T «.x n . Beplaced by Hardlage Mill and Aklns GlaaBiaeis Screen No. 59, ? mesh. ^ Two Apron Plates 5 x 15 ft. in three sect: ons H in, drop T" One Akins Classifier Y Sand Slime Two 5 X 8 ft. Tube Mills' 4 Six Large Apron. Plates 5x5 ft. sections. i Riffle Box es 5x 5ft. J Sett ling Pond Waterxfor re-use Tailing Results: — Saving 88 per cent. Cost of milling, including 20ji for depreciation, is $1.00 per ton. Fig. 102. 232 STAMP MILLING AND CYANIDING (2) AMALGAMATION AND CONCENTRATION An excellent example of this practice is afforded by the immense mills of the Alaska-Treadwell Gold Mining Company.* The fol- lowing diagram shows the methods there used. Character of Ore: — Altered syenite carrying free gold, auriferous pyrite and arsenopyrite. Average value of ore $2.59 per ton (in 1912). Flow Sheet: Three Gates and Four "Comet" Gyratories Crushing to l>i inch. ^ Ore Bins ^^-"-"^^-{ Sg^ldType 240 Stamps - 850 lbs. each*- 98 drops - 8)« ( ?) in. drop - Stamp duty 4.86 tons - Wooden mortar-'blocks. 120 Stamps - 1020 lbs. each - 98 drops - 8M in. drop Stamp duty 5.73 tons - Wooden mortar-blocks. 520 Stamps - 1020 lbs. each - 98-100 drops -SH-S% in. drop - Stamp duty 5.52 tons - Concrete mortar-'blocks, with C.I. "Anvils" All in 5 Stamp batteries using chuck-plate 4-6 in. wide x full length of mortar. From 0.1 - 0.2 oz. Quicksilver per ton of ore (4 oz. per oz. Au) fed inside the mill, about 10!4 in. per ft. Plates dressed twice every 24 hrs. with 0.03 to O.OSoz.Hg. per ton ore. From 65 - 85* of the total clean-up is taken from these plates. Copper Lined Troughs (tail boxes) Quick Traps - Truncated Cone with 3 in. pipe delivering pulp within 2 in. of T)Ottom. Trom 3 - 5 ?( of clean-up is taken from traps. Erue Vanners (4 & 6 ft.) making 2 !« of Concentrate varying from $40 - $70 per ton. The value of the Concentrate decreas- es with iiner crushing in the batteries. ' — v^ Concentrates are treated by cyanidation after fine grinding. Results: — Average recovery is about 95 per cent. This recovery is equa,lly divided between amalgamation and concentration. The total cost of miUing is 21.7j5 per ton distributed as follows: crushing 2.1|i; tramming 1.4^; stamping 13.8^; concentrating 5.4^. Fig. 103; * Robt. A. Kinzie, The Treadwell Mines.Trans. A.I.M.E., Vol. 34, page 365. TREATMENT OF GOLD ORES 233 (3) AMALGAMATION AND CYANIDATION I. Sand Treatment. The earlier practice on the South African Rand was essentially of this type. \ Character of Ore: — South African "Banket." Gold, free and fine in firmly consolidated conglomerate. Value 42s. per ton. Flow-Sheet: Rock Breakers ^ 100 Stamps - 5 tons duty - thru 40 mesh- Amalgamating Plates Hydraulic Classifiers Overflow, 90 )t Distrlbuting'Tanks Collecting Tanks Slime 25l'» Sand'^ ^51l To dump Drained with Suction Preliminary Wash with 0.04 jSKCy 12 hr. Treatment " 0.08 jt " T Sand Solution Leaching Tanks Spigot, lOji Assay 15dwt. (Coarse Sand and Pyrite) 1 Leaching Tanks 3 day Treatment with 0.3 ^KCy 3 " " " 0.1^ " Tailing to dump. Solution 9 Zinc Boxes Extraction 90!^ 12 hrs. Treatment with 0.2 ^ KCy Washing " 0.08 ^ " 0.04 !« ' " " Water+Ca(OH) 7 7 Tailing to dump Strong Sol. Weak Sol."Washes Strong Sol. Zinc Boxes 1 — T~ Precipitate Solution Weak Sol. Zinc Boxes Solution Precijjitate Heturned to respective circuits Results: ■ 9s. (1894). ■Average extraction 78 per cent. Milling and cyaniding cost Fig. 104. 234 STAMP MILLING AND CYANIDING (3) AMALGAMATION AND CYANIDATION II. Treatment of Sand by Leaching and of Slime by Decantation is exemplified by the mill of the Simmer Deep Ltd.* at Johannes- burg, S. Africa. Character of Ore: — Typical South African "Banket,'' i.e., consolidated conglomerate carrying free gold and pyrite. Flow Sheet: IX in. Product fro m Mine I Three Hundred-IBTO lb. Stamps, Dropping Sii in. 100 times per Min. Stamp Duty 9.1- Tons. Screen 59x24 in. with 0.033 in. Aperture. Amalgamating Plates. T Amalgam Traps. Tailing Pits. Centrifugal Pumps 8 in. Bight Cone Classif iers ( 7 ft. deep 45 in. Diam. at Overflow) 1 '^ — ^ Underflow Overflow I Twelve Cone Classifiers in parallel FourDewatering Cones(5 f t.Deep, 36 in.D iam.) 6X f t.Deep,and 6 ft, Diam. j ' • 1 —J *^' y — „ ,1 _ ^ *jn Underflow Overflow Underflow Overflow ;- X T , CentrifugalPump(6in.) Ten Spitzkaste n I Sand Slime Four Krupp Tube Mills (22x5}ift. 30 R-P.M.V Shaking Amalgamating Tables Eight Classifying Cones ( 8x8 ft.) I 1 Underflow Overflow 30it Moisture l^Slime Amalgam I Retort Pulp J- rF Two Caldecott Sand Filter Tables' Launder Carrying 0.03 KCy Solution Centrifugal Pump ■ 1 Six Sand Collecting Vats Butters & Mein Distributors Sand 15!^ Moisture Two Cones (8x8ft.) — J ' ^ ' Sand Overflow X 70x8 .25 ft.Ov erfl owLaundei s T I Sand Overflow Solution Four Slime CoUectingVats ( 70x1 3ft) T T 7 Slime Decanted "Water & Wash Solution Storage Tank j !]. Overflow Barre n Solution Storage Tank Centrifugal Pumps 12 in. Two Wash Vats 2nd Decanted Solution Centrifugal Pump 6 in. iTwo Settling Tanks in Serie s. 70x16 ft. T— r f-(- -6 in- Barren Solution Tank Belt Conveyor 1 Blaisdell Distributor F- , . Ten Sand Leaching Tanks 50 x 1 ft. ; ^ 1 Tailing- Discharged by I Shovelling Solution Extractor Boxes (30 X 5 ft.) -J i . Precipitate Barren Solution i 1st Decanted Solution 01 ; Overflow Centrifugal Pump —J \ f. ZTZJ Vat(20x6ft.) i I Mill Storage Tanks "t: Acid Treatment by Sodium Bisulphate Smelted to Bullion g Ove?flow "^"^^"^"S^l ^""P ^^"- Two W ash'Vats 1 r- Decanted Solution Slime Centrifugal Pump To Waste 6 in. Two Filter Pre sses (82 x 32 in. T- — Frames) Steady He ad Tank . 1 Eight Extractor Boxes (30x5ft.) Precipitate _r Barren Solution Pump Results: — Average value of ore 20s. ($4.87). Recovery90%. Cost4s.6(Z.($1.08). Fig. 105. The phraseology, it will be noted, is slightly different from that in use in the cyanide plants of the United States. * Min. Ind., Vol. IS,, -bej-!? S4S TREATMENT OF GOLD ORES 235 (3) AMALGAMATION AND CYANIDATION II (a). Treatment of Sand by Leaching and of Slime by Fil- tration. The best example of this type of treatment is probably that afforded by the Pittsburg-Silver Peak Gold Mining Go's, mill at Blair, Nevada.* Character of Ore: — Quartz and alaskite containing free gold with small amounts of pyrite and galena. Flaw Sheet: No. 6 Gyratory Crusher -J" Two No. 3 Gyratory Crushers Product Passing lin. ring 120 Stamps 1050 lb. each, 96 drops, 654 - IH in. Stamp duty 4 tons thru 35 Mesh 5-6 tons Water per ton ore. Mortar on Concrete block with hardwood cushion. No inside amalgamation Amalgamating Plates, 12.859 sq. ft-, per Stamp. Grade IX in. per ft. J Via 12 X 8 in. wooden launder- Steel bottom. Tailing 40j« -200 Mesh I Distributing Sump 3 ft. Diam.x 4 ft. Two Settling Cones 8 ft. Diam. 50 sides with 4-lM in. Spigots —I : ^-f Slime Sand - "~T7 Eight Classifiers 4 ft. 3 in.Diam. 70° sides with Hydraulic S orting T T Column Slime Sand ~r ~r 9Si-2SX) mesh-14-16 Pts.Waterto 1 solid 13^-200mesh-3-4Pts.Watertol solid 1 ; Distributing Sump Sand Distributor 1 "^ ^ Five Clarifying Tanks 26 x 24 ft., with f'^^ 36 x UM f t. Leaching Tanks, with 45°Cone Bottoms, with annular overflow 4;?""'^' Launders for overflow.Capacity 500 tons Sand to each tank. Clearwater Thickenjd Slime Cycle of complete treatment 7 days 1 f^ i I Solution forced thru clke in Press. Pregnant Solution . Tfing _ Merrill Filter Press. -30 lb. pressure Sluiced to Waste Slime 64-4 in. Frames Tailing Pregnant Solution to Waste I Merrill Zinc Dust Precipitating Plant I — TT" TJT, :rzT. Precipitate Strong Sol. Weak Sol. "Low (inKCy)Sol. to Refinery to Leaching Tanks to Leaching Tanks Used to sluice out presses. Fig. 106. * Henry Hanson, Min. & Sci. Press, Vol. 98, page 657; also Min. & Min., Vol. 29, page 569. 236 STAMP MILLING AND CYANIDING Results: — Average value of ore $5.50 per ton. Extraction 92 per cent. Cost $1.04.* * Distribution of cost: Stamping $0,298 Amalgamating 0.047 Neutralizing and settling 0.074 Leaching and sluicing 0. 145 Filter-pressing 0. 104 ^ Precipitating 0.036 Refining 0.048 Assaying 0.033 Water service 0.070 Heating 0.007 Superintendent and foreman 0.053 Total direct operating $0,915 Pro-general 0.079 Suspense account 0.046 Total operating $1,040 TREATMENT OF GOLD ORES 237 (3) AMALGAMATION AND CYANIDATION III. 'All-slime ' Treatment is exemplified by the flow-sheet below which illustrates a plant designed by the writer for an ore similar to that discussed on page 244. Character of Ore: — Fine grained cherty quartz with some andesitic country rock — small amount of fine grained complex sulphides. Flow Sheet; No. 5 Gates Gyratory. 50 Stamps 1500 fbs. wt. 6 in. drop 110 per min. 4 mesh screen. Crushing inKCy Solution. '. 1 ' Chilean Mills 20 to 30 mesh r T Classifiers Sand ^ 1 Slime Tube Mills (70% thru 200 mesh.) Muntz Metal Amalgamating Plates. Classifiers r Sand Slime Pulp Thickeners. Under Flow Over Flow r"^. Merrill or Oliver Filters Pachuca Agitators < I fPailing Solution — ?zz Clarifler Zinc Dust Precipitation Results Anticipated: — Average assay of ore 0.10 oz. gold, 10 oz. silver. Ex- traction 95 per cent gold, .85 per cent silver. Estimated cost with H.P. at $50.00 per annum, 82.00 per ton. Fig. 107. 238 STAMP MILLING AND CYANIDING (4) AMALGAMATION, CONCENTRATION, AND CYANIDATION I. Cyanide Treatment of Sands only. This treatment is well exemplified by the mill of the Camp Bird Ltd. near Ouray, Colo- rado.* Character of Ore: — The ore is siliceous, carrying free gold, with galena, blende, pyrite, and chalcopyrite. Value $25 per ton, distributed about as follows: gold $23; silver $1; copper and lead $1. Flow Sheet: Crushers I Sixty - 1050 lb. Stamps flropping 5 in. 120 times per minute. Stamp duty 4.6 to 5 tons. Amalgamating plates 5 x 24 ft. to each 5 stamp battery Twenty-four 6 ft. Vanners -| 1 Tailing Concentrate 1 Classifier i 1 Spigot Overflow 5 - 5 ft. Huntington Mills (? ) Wilfley Tables crushing thru 35 to 40 mesh screens. 4(?) X 15 ft. Amalgamating Plates Taili ng Cc mcentra e i 1 Tailing + ■ i Concentrate 1 Sand Pump Concentrates united 1 15 ft. Classifier ■ ^ .k Slime Overflow Sand Waste Leaching Tanl and shipped to smelter 10 a Pb. 14 )S Zn. 13oz.Ag. 3 oz Au. ■ 1' / ^X~' ? . ' I • ci.._ ^ ^i m — .. /-!■ M!-_ ii»!ii_ Two 4 ft. box Classifiers ~l J" 1st Spigot I Six. 6 ft. Trent Chilian Mills. ,. » 4. < — Elevator ^ Distributor ~ 1 Callow Tanks i i Overflow Spigot Overflow 2nd Spig ot Six Dorr Classifiers. — ~ t ~rn ^ ".f^ — M ■• Overflow Sand Six Tube Mills 60 Primary Deister Tables "T ; r Tailing M iddling Concentrate zzn — — I — ?=;. 18 No. 3 Deister Tables Concentrate Middling Tailing 16 Secondary Deister Tables Tailing Concentrate Four 48 in. x 16 ft. Amalgamating Tables. 3 Sections Copper, One Section Blanket to each plate. Treatment Plant Distributor 16 Settling Tanks m x 12 ft. Overflow ; Two 36 X 10 ft. Clariflers t T Overflow Mill Storage ~r~i — Underflow — T-r Underflow Ten 15 x 45 ft.J,Pachuca Agitators Operated in Series. No.l Pulp Storage with Trent Agitator No 2 Pulp Storage 34 x 12 ft. Mechanical Agitator J - Butters Filter 336 leaves. T. J Pregnant Solution 3 Perrin Presses Merrill Zinc Dust precipitating Plant. f Tailing to waste Note. — Concentrates go to roasting and cyaniding plant. Results: — The total recovery is 94 per cent made up as follows: by amal- gamation 17J per cent, by concentration 54 per cent, and by cyanidation 22| per cent. The total cost of operation and repairs for the entire treatment is 81.61. The consumption of chemicals is as follows: KCy 3.1 lb.; lime 8.5 lb.; zinc dust i lb.; and lead acetate i lb. per ton. Fig. 111. * J. W. Hutchinson, Min. & Sci. Press, Vol. 102, page 616, et seq. 242 STAMP MILLING AND CYANIDING (5) CYANIDATION I. Leaching Unassisted by any other Process. It is rare to find an ore yielding a satisfactory portion of its gold and silver content by so simple a treatment. The mill of the Wasp No. 2 Mine, at Deadwood, S. Dakota,* represents the acme of simplic- ity in cyaniding. Character of Ore: — The ore is a hard close grained Cambrian quartzite, the average value being $2.50 per ton, the ratio of silver to gold being roughly 2 to 1. Flow Sheet: One No. 6 Gates Gyratory Crusher.-1>^ in. Product Two No. 4k Gates Gyratory Crushers. ->« in. Product Two 16 X 36 in. Mc Farlane Rolls. Elevator Two 2 X 9 ft. 45°Screens- ]4 in. square aperture Oversize Undersize Two 16 1 X 36 in. Mc Farlane Rolls. , , 1 Storage Bins Six Conveyor Belts Six Leaching Tanks- 32 x 12 ft. 400 tons Capa city Pregnant Solution T i Zinc Boxes ailing- To dump Barren Solution Precipitate To Storage Results: — The value of the ore is $2.50 per ton, the bullion recovered is $1.98 per ton, corresponding to 80 per cent erfraction. The cost of treatment is 53 cts. per ton. Fig. 112. * Jesse Simmons, Eng. & Min. Jour., Vol. 92, page 214. TREATMENT OF GOLD ORES 243 (5) CYANIDATION II. Applied to the Treatment of both Sand and Slime. The plant of the Trinity Gold Mining and Reduction Co.,* at Carrville, Trinity Co., California, is a good example of this class. Character of Ore: — "Oxidised soft and friable." Average value $5.00 to $5.50 per ton. Ore has changed materially since plant was built, which accounts for low extraction. Flow Sheet: One 14 X 24 in. Blake Crusher 3 in. product ¥. Grizzly I in. space TJndersize Oversize One 12x20 in. Blake Crusher 0.1WKCySol. Ore Bin lOOoWs Capacity ->4. Forty - 1100 lb. Stamps dropping 6 in. 102 times per Min. Stamp duty 8 to 9 tons thru Kia in. diagonal slot screen. [ J- Four - 48 in. Double Cone Classifiers Coarse Sand Fine Sahd and Slime Two Dorr Duplex Classifiers i *± Coarse^'Sand Fine Sand^and Slime Two Pulp Thickeners CDorr Type) 30 ft? Butters Disfanbutor -i 25 x 12 ft. ^ '■ 4 N' Four 30 X 7 ft. Leaching Tanks Overflow Two Rachuca Agitators 12 x 25 ft. Each 170 tons capacity. 3 to 6 tons \~ Agitated for eight hours Solution per ton of ore added contin uously. Total time of OontactlSO hrs. Two Clarifying I J Tanks 25 x 12 ft. Tailing Pregnant Sol, Sluiced out continuous treatment Two Dorr' Thickeners 25 X 12 ft. Oliver Filters ^. 13" Pregnant Sol. Tailing - to waste Merrill Zine Dust Precipitating Plant 1 Pre cipit ate Barre n SoL Acid Treatment ^ Bullion J TE Results: — The extraction is about 82 per cent. Cost of milling $1.01 (?). Fig. 113. * J. W. Swaren, Eng. & Min. Jour., Vol. 91, page 907. 244 STAMP MILLING AND CYANIDING (5) CYANIDATION III. Sliming the Entire Pulp. The mill of the North Wash- ington Power and Reduction Co. * at Republic, Washington, is of this type. (Fig. 114.) Character of Ore: — The ore is a fine grained cherty quartz with a small amount of complex sulphides and free gold, both in an unusually minute state of division. Average value of ore $8. Silver and gold in ratio of 10 to 1. Flow Sheet: 10 X 20 in. Blake Crusher IH in. product. 1* Ondersize ghaking* Grizzly V Oversize 1 10 X 12 in: Podge Crusher H in?' Trommel "Uhdersize 14 X 30 in. Traylor Itolls ^ in. tirodnct. Sampling IMill 6 ft. Trent Chilian Mill - 30 Mesh \ ■ Oversize Slime Akins Classifier 5 R.P.M. ■1^ Sand 5 X 22 ft. Tube mm. El Oro Lining SeoQP Feed-85!<-2003VIe3h Four Trent Agitators - 5 Arms - 7 in. Centrifugal Pump for agitation.used in series. Trent Disc Thickener Solution mp Oliver Filter 11?^ x 16 ft. Solution .T Tailmg - to waste Sand Filter Trent Zinc Dust Precipitating Plant Barren Sol. I AT Precipitate Results (Approximate only): — Extraction 90 per cent gold; 85 per cent silver; cost $4.00 per ton, — due to expensive fuel and inefficient power equipment. Fig. 114. * H. W. Newton, Min. World, Vol. 34, page 447, and private notes. TREATMENT OF GOLD ORES 245 (6) CYANIDATION IV. Following Roasting of the Ore. This practice has never been popular in the United States.* The mill of the Great Boulder Pro- prietary Gold Mines Ltd.,t at Kalgoorlie, W. A., is taken as typical. Character of Ore: — The ore is schistose in structure, its main constituents being SiOz 75 per cent, CaCOs, MgCOs, and FeCOs 15 per cent. Pyrite and various tellurides of gold also occur. Part of the gold is in the free state. Flow Sheet: One No. 5 D Gates Gyratory Crusher - 2 in. Product We r Undersize Trommel et "White Howell Dryer 1 3 Dry Oversize Four Gates Gyratory Crushers TMill Bin ^ Four No.8 Krupp Ball Mills 9 x 4 ft. 90 tons each thru 30 Mesh-50)i- 200 Mesh I > Twelve - 30 in. Griffin ■Mills. 31 tons each thru 15 Mesh 67}i- 200 Mesh. Fourteen Edwards.Roasters 64 x 6ii ft. 25 Tons per da y each for 340 sq. ft. hearth- 2.2 H.P.~| ~ EighiMerton-Eoasters - 4 Deck. 25 Tons per day each for 442 sq. ft. I hearth- 1.7 H.P. T 5 ft. Mixer with weak KCy Sol. & ij lb. Lead Acetate per ton. ~^ 12 Wheeler Pans (Ground with Hg) Overflow 10 Wheeler Pans (Ground with Hg) Amalgam t Overflow Box Classifier Amalgam Spigot Overflow — ^ — : 48x24 ft. Settler ^ ; — Spigot Overflow . Results: — The ore assays $15.00 per ton, the bulUon recovery being $14.33 or 95 per cent of- the total; the cost of treatment is esti- mated at $2.40 per ton, of which 55^ is for roasting. Amalgamation is responsi- ble for 25 per cent of the gold recovery, cyanidation for the balance. 4 x 16 ft. Settler ~I ^ . Overflow S pigot to Storage 1 T 16 Pulp Storage 5 18 Agitators 20 x 5 ft. 16 Hrs. agitation 0.1^ KCy. 10 Ridgeway Filters Solution. . Tailing -to waste Zinc Boxea - 66 Cu. ft. eacli. Fig. 115. * The largest roasting-cyanide plant in the worl(i, however, is that of the Golden Cycle Co., in Colorado, t Robert Allen, Min. Rep., Vol. 54, page 36. A. E. Drucker, Min. & Sci. Press, Vol. 101, page 401. 246 STAMP MILLING AND CYANIDING (7) CYANIDATION V. With the Aid of an Oxidizing Reagent in the Solution. As discussed elsewhere, bromine is the only oxidizer which has so far found extensive and economic application. As in the preced- ing case we must look to West Australia for the best practice in this respect. The plant of the Oroya Brownhill Co.,t at Kal- goorlie, affords a typical example of what has been usually known as the Diehl process. (Fig. 116.)' Character of Ore: — Similar to preceding. Fhw Sheet: Two No. 6 Blake Crushers. 1 Fifty Stamps - Duty 7.6 tons. ~1 Screen Coarse Sand Fine Sand & Slime T Five Grinding Pans Ten WUfley Tables ~1 ~r — Concentrate Tailing Classifier ^ I I 1st. Spigot 2nd. Spigot Overflow y T Six Wilfley Tables Six Wllfley Tables — I ; ; r Concentrate Tailing Concentrate Talllne ^ I i 1 1^^ Six Tube Mills I ~" Thickener Pulp To Roasting, Grinding, Amalgamating & Cyanlding Plant "T Overflow - to Storage Agitation with Br Cy /(probably. 20 hr. with 0.155« KCy " Fol lowed by 4 hrs.wlt h addition J ^of BrCy) Four Filter Presses "1 r~ Tailing Pregnant Sol. to waste Z TZ Zinc Boxes Results: — The ore averages $9.35 peir ton; the extraction is $8.70 or 93 per cent; the treatment cost is $2.50 per ton; 17 per cent of the recovery is made by concentration, the balance by bromo-cyanidation. Fig. 116. * A. E. Drucker, Min. & Sci. Press, Vol. .101, page 401. TREATMENT OF GOLD ORES 247 BIBLIOGRAPHY FOR TREATMENT OF GOLD ORES • Especially Desirable for Students' Use Cyaniding of Gold Ores. * Allen, H. W. The Simplification of Gold Ore Treatment by Direct Cyaniding, 2 pp. Min. & Sci. Press, Vol. 107, p. 254 (1913). Argall, Philip. Cyaniding of Ore Containing Coarse and Fine Gold, i p. Min. & Sci. Press, Vol. 95, p. 709 (1907). Cabby, Elmee Ellsworth. Amalgamation vs. Cyaniding, 2 pp. Mex. Min. Jom-n., Vol. 13, No. 1, p. 19 (1911). Dake, W. M., Jr. Extraction Difficulties, 1 p. Min. and Sci. Press, Vol. 106, p. 701 (1913). HoLDEN, Edwin C. Cyaniding of Ore Containing both Coarse and Fine Gold, J p. Min: & Sci. Press, Vol. 96, p. 62 (1908). Hamilton, E. M. Cyaniding of Ore Containing both Coarse and Fine Gold, J p. Min. & Sci. Press, Vol. 95, p. 775 (1907). Kennedy, E. P. Cyaniding of Ore Containing both Coarse and Fine Gold, i p. Min. & Sci. Press, Vol. 96, p. 62 (1908). Packard, Geo. A. Cyaniding of Ore Containing both Coarse and Fine Gold, i p. Min. & Sci. Press, Vol. 96, p. 192 (1908). Reid, Walter L. Cyaniding of Ore Containing both Coarse and Fine Gold, i p. Min. & Sci. Press, Vol. 96, p. 62 (1908). ScHOLL, George P. Treatment of Gold Ore. Changes in the Last Decade. Min. & Sci. Press, Vol. 94, p. 211 (1907). Tays, E. a. H. Cyaniding of Ore Containing both Coarse and Fine Gold, J p. Min. & Sci. Press, Vol. 96, p. 62 (1908). "Viator." Cyaniding of Ore Containing both Coarse and Fine Gold, i p. Min. & Sci. Press, Vol. 95, p. 709 (1907). Wells, Jas. S. C. Treatment of Ore Containing Coarse Gold, 1 p. Min. & Sci. Press, Vol. 96, p. 192 (1908). GOLD MILLS IN VARIOUS STATES AND COUNTRIES Colorado. Aegall, Philip. Cyaniding of Cripple Creek Ores, 3 pp. Min. & Sci. Press, Vol. 101, p. 804 (1910). Argall, Phillip. Cyaniding Sulpho-telluride Ores. Min. Ind., Vol. XI, pp. 334 to 338 (1902). Argall, P. H. MilUng at Stratton's Independence, If pp. Mines and Minerals, Vol. 32, p. 319 (1«11). Barker, F. L. Cyaniding Cripple Creek Ores, I and II. Min. & Min., Vol. 28, pp. 422, 481 (1908). Baron, H. J. The Gold Prince Mill, San Juan County, Colorado, 3j pp. Min. Rep., Vol. 54, p. 204 (1906). * Chase, Chas. A. The Liberty Bell Mill, 5 p. Min. & Sci. Press, Vol. 102, p. 840 (1911). Chauvenet, Regis. The Cyanide Process at the Portland (Colo.) Mill, 3 pp. Min. Rep., Vol. 27, p. 378 (1907). 248 STAMP MILLING AND CYANIDING * Crowe, Thos. B. Researches Upon Cripple Creek Telluride Ores. (By Portland Met. Soc, Edited by T. B. Crowe, J. C. & M. Soc, S. A.) Min. & Sci. Press, Vol. 99, p. 427 (1909>. Dodge, W. R. Retreatment of Mill Tailings at Cripple Creek, 2 pp. Min. Sci., Vol. 64, p. 528 (1911). Downey, Charles J. Cyaniding the Sulphide Ores of Idaho Springs. Min. Sci., Vol. 65, p. 268 (1912). Kdqerton, W. Portland Mill at Victor. Min. Sci., Vol. 62, p. 76 (1910). GooDALE, Stephen L. The Argo Cyanide Mill, Idaho Springs, Colo., 4i pp., illus. Eng. and Min. Jour., Vol. 96, p. 385 (1913). Hbbrick, R. L. Handling Tailings at Colorado City, 4 pp. Min. & Min., Vol. 30, p. 621 (1910). Herrick, R. L. and Scholl, Geo. P. The Gold Prince Mine and Mill, 8 pp. Min. & Min., Vol. 27, p. 337 (1907). Megbaw, H. a. Cyaniding at the Liberty Bell Mill, 5i pp. Eng. & Min. Jour., Vol. 95, p. 9 (1913). Megbaw, Herbert A. Cyaniding at Cripple Creek, Colo., 4J pp. Eng. and Min. Jour., Vol. 95, p. 313 (1913). * PuBiNGTON, Woods, & Doveton. Camp Bird Mine and Mill, 52 pp. Trans. A.I.M.E., Vol. 33, p. 499 (1903). Read, Thomas T. Cripple Creek Metallurgy, 1 p. Min. &-Sci. Press, Vol. 102, p. 263 (1911). Read, T. T. Camp Bird MiU. Min. & Sci. Press, Vol. 97, p. 669; .abstr. Min. Ind., XVII, p. 439 (1908). Tract, W. E. Cyanide Practice at the Liberty Bell Mine, Telluride, Colo. Eng. & Min. Jour., Vol. 82, p. 149 (1906). WoECESTEE, S. A. Mechanical Features of Ajax Mill (Clancy Process) Cripple Creek. Eng. & Min. Jour., Vol. 93, p. 753 (1912). WoBCBSTEB, S. A. Milling in Cripple Creek. Eng. & Min. Jour., Vol. 87, p. 956 (1909). * Warwick, A. W. The Clancy Process at Cripple Creek. Min. Sci., Vol. 64, p. 440 (1911). . Cyaniding Cripple Creek Dumps. Min. & Min., Vol. 29, p. 444 (1909). Nevada. Aybes, Ends R. The Bullfrog Cyanide Mill. Eng. & Min. Jour., Vol. 83, p. 376; (Rev. Min. Ind., XVI, p. 533) (1907). * Bakboue, P. E. Goldfield Cons. Mill. Eng. & Min. Jour., Vol. 86, p. 467 (1908). BosQUi, Peancis L. Ore Treatment at the Combination Mine, 6i pp. Min. & Sci. Press, Vol. 93, pp. 413 and 451 (1906). Collins, Edgar A. Cyaiiiding in Nevada, J p. Min. & Sci. Press, Vol. 96, p. 257 (1908). Collins, Edgab A. Cyaniding in Nevada, f p. Min. & Sci. Press, Vol. 96, p. 63 (1908). * Hanson, Henby. Mines and Plants of the Pittsburg-Silver Peak, 5 pp. Min. & Sci. Press, Vol. 98, p. 657; also Min. & Min., Vol. 29, p. 569 (1909). TREATMENT OF GOLD ORES 249 Httnt, Bertram. Cyaniding in Nevada, li pp. Min. & Sci. Press. Vol. 96, p. 256 (1908). * Hutchinson, J. W. Operation of the Goldfield Consolidated Mill, 12 pp. Min. & Sci. Press, Vol. 102, pp. 616, 652, 686, 716, 719 (1911). Kennedy, J. C. The Big Four Mill, Manhattan, Nevada, 2 p. Min. and Sci. Press, Vol. 106, p. 824 (1913). Kidder, S. J. Regrinding at the Pittsburg-Silver Peak Mill; (costs), 2 pp., illus. Min. & Sci. Press, Vol. 106, p. 306 (1913). KiRBY, A. G. Cyaniding in Nevada, 4 pp. Min. & Sci. Press, Vol. 97, p. 836 (1908). King, Lochiel M. The Treatment of Desert Ores, 1 p. Min. & Sci. Press, Vol. 93, p. 226 (1906). King, Lochiel M. Cyaniding in Nevada, 2f pp. Min. & Sci. Press, Vol. 96, p. 123 (1908). Lamb, Mark R. Milling at Combination Mill, Goldfield, Nev., 1 p. Min. & Min., Vol. 29, p. 209 (1908). Leaver, E. S. Nevada Goldfield Reduction Co. Mill. Min. & Sci. Press, Vol. 97, p. 254 (1908). Megraw, H. a. Cyaniding at Nevada Wonder Mill, 3 pp. Eng. and Min. Jom'., Vol. 95, p. 693 (1913). * Morris, H. G. Equipment and Practice at Florence-Goldfield Mill, 3i pp. Eng. & Min. Jour., Vol. 89, p. 365 (1910). Martin, A. H. Montgomery Shoshone Mine, IJ pp. Min. & Sci. Press, Vol. 100, p. 289 (1910). McKenzie, J. H. Goldfield Consohdated Mill. Min. Wld., Vol. 32, p. 276 (1910). Martin, A. H. Pittsburg-Siiver Peak Mill, Nevada. Min. Wld., Vol. 33, p. 461 (1910). Megraw, Herbert A. Cyaniding at Grass Valley, Calif. Eng. & Min. Jour., Vol. 95, p. 983 (1913). Megraw, Herbert A. The Black Oak Cyanide Plant, California, 2| pp., illus. Eng. and Min. Jour., Vol. 95, p. 1179 (1913). Parsons, A. B. Nevada Cyanide Practice, | p. Mex. Min. Jour., Vol. 13, No. 2, p. 18 (1911). Rice, Claude T. Milling at Florence-Goldfield, 2 pp. Eng. & Min. Jour., Vol. 91, p. 761 (1911). Rickard, T. a. Goldfield Consolidated Mill. Min. & Sci. Press, Vol. 96, p. 842 (1908). Rickard, T. A. Nevada-Goldfield Red. Co. Mill. Min. & Sci. Press, Vol. 96, p. 841 (1908). Van Saun, P. Edwin. Cyaniding at the Montgomery-Shoshone Mill, 2f pp. Eng. & Min. Jour., Vol. 89, p. 217 (1910). Van Saun, P. E. The Montgomery Shoshone Mill, 2 pp. Min. & Min., Vol. 28, p. 385 (1908). Wolf, J. H. G. Goldfield Consolidated Mill. Min. & Sci. Press, Vol. 98, p. 12 (1909). . Goldfield, Nev., Cyanide MiUs, 1| pp. Min. and Min., Vol. 32, p. 610 (1912). 250 STAMP MILLING AND CYAN I DING California. Alexander, G. E. Milling Practice at the North Star Mine, Nevada County, California, 2| pp. Min. Rep., Vol. 54, p. 56 (1906). ' * FooTE, A. D. North Star MiU. Min. & Sci. Press, Vol. 92, p. 240 (1906); Min. Rep., Vol. 54, p. 56 (1906). Latjdguth, Frank C. Empire Mines Cyanide Plant, 1 p. Min. & Sci. Press, Vol. 102, p. 237 (1911). Martin, A. H. Milling Practice at Grass Valley. Min. Wld., Vol. 31, p. 1107 (1909); Min. Sci., Vol. 60, p. 6 (1909). Martin, A. H. The Pioneer Gold Stamp Mills of California, 1 p. Min. and Eng. Wld., Vol. 37, p. 332 (1912). Megraw, H. a. Black Oak Cyanide Plant, California, 2J pp. Eng. and Min. Journal, Vol. 95, p. 1179 (1913). Shaw, S. P. The Standard Consolidated Cyanide Mill, 2 pp. Eng. & Min. Jour., Vol. 87, p. 487 (1909). SwAREN, J. W. Mining and Milling at Trinity Mine, 2 pp. Eng. & Min. Jour., Vol. 91, p. 907 (1911). Tyssowski, John. MiUing at North Star Mines. Eng. & Min. Jour., Vol. 90, p. 409 (1910). Urqubart, C. H. The Black Oak Mill, 5i pp. Min. and Sci. Press, Vol. 105, p. 687 (1912). Vestal, F. A. Cyanide Plant at the Empire Mines — Grass Valley, 3| pp. Min. and Sci. Press, Vol. 105, p. 586 (1912). WiLLOTJGHBY, A. A. The New Mill at the Globe Mine, Dedrick, Cali- fornia, i p. Eng. and Min. Jour., Vol. 96, p. 688 (1913). South Dakota. * Clarke, A. J. & Sharwood, W. J. Metallurgy of the Homestake Ore. Trans. Inst. M. & M. BuU. 98; abstr. in Min. & Eng. Wld., Vol. 37, pp. 1037, 1090, 1147; Eng. & Min. Jour., Vol. 95, pp. 161, 215 and 1189 (1913). * Fulton, Chas. H. Crushing in Cyanide Solution in the Black Hills, 30 pp. Abstr. in Min. & Sci. Press, Vol. 89, pp. 207, 224, 243, 260, 273, 290, 310; Trans. A.I.M.E., Vol. 35, p. .587 (1905). * Gross, John. Cyaniding at Maitland, S. D., 21 pp. Trans. A.I.M.E., Vol. 35, p. 616 (1905). Megraw, H. A. Cyanide Practice in the Black HiUs, 6 pp. Eng. and Min. Jour., Vol. 94, p. 1221 (1912). * Merrill, C. W. Metallurgy of the Homestead Ore, 14 pp.; discus- sion ibid, p. 983; Trans. A.I.M.E., Vol. 34, p. 585 (1904). O'Brien, B. D. Cyaniding Black HiUs "Blue Ores," 4 pp. Min. & Min., Vol. 29, p. 427 (1909). * Pahmelee, H. C. Cyanide Practice in the Black Hills, S. D., 7 pp., illus. Met. & Chem. Eng., Vol. U, p. 395 (1913). Simmons, Jesse. Mill of the Wasp No. 2 Mine in S. Dakota. Eng.' & Min. Jour., Vol. 92, p. 214 (1911). Simmons, Jesse. Trojan Cyanide Mill, Black Hills, If pp. Eng. and Min. Jour., Vol. 92, p. 357 (1911). TREATMENT OF GOLD ORES 251 Simmons, Jesse. Victoria Mine and Mill, S. D., 2 pp. Min. & Eng, Wld., Vol. 37, p. 571 (1912). Simmons, Jesse. Cyajiiding at the Wasp No. 2 Mill, Black Hills, 2 pp Min. & Eng. Wld., Vol. 38, p. 11 (1913). Simmons, Jesse. Mining and Milling in the Black Hills, S. D., 11| pp. 4 parts. Min. & Eng. 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Rev. in Min. Ind., Vol. IX, p. 371; Min. & Sci. Press, Vol. 80, May 21 (1900).. * KiNziE, RoBT. A. Complete Description of Treadwell (Alaska) Mines and Mills. Trans. A.I.M.E., Vol. 34, pp. 334, et seq (1904). * Lass, W. P. The Cyanide-plant at the Treadwell Mines, Alaska, 32 pp. Trans. A.I.M.E., Vol. 43, p. 183 (1912). Magenatt, Wm. Cyaniding at Mercur. Rev. in Min. Ind., IX, p.'371. Eng. & Min. Jour., Vol. 70, p. 70 (1900). Meghaw, Herbert A. Two Arizona Cyanide MiUs. Tom Reed MiU at Oatman, Vulture Mill at Wickenburg, 3f pp., iUus. Eng. & Min. Jour., Vol. 96, p. 199 (1913). Megraw, Herbert A. Cyaniding the Ores of Republic, Wash. Eng. & Min. Jour., Vol. 95, p. 835 (1913). Megraw, Herbert A. The Gold Road Cyanide Mill, Arizona, SJ pp., iUus. Eng. & Min. Jour., Vol. 96, p. 3 (1913). Morse, Edward C. The San Poll Mill, RepubUc, Wash., 6 pp. Trans. A.I.M.E., Vol. 43, p. 697 (1912). Newton, H. W. North Washington Power and Reduction Co.'s MiU. Min. World, Vol. 34, p. 447 (1911). Palmer, Lbroy A. Cyaniding at Mercur, Utah, 3i pp. Min. & Sci. Press, Vol. 98, p. 616 (1909). 252 STAMP MILLING AND CYANIDING Thomson, Francis A. Ore Treatment at Republic (Wash.), 14 pp. Trans. A.I.M.E., Vol. 43, p. 672 (1912). W. Australia. Allen, Robert. Cyaniding at Great Boulder Proprietary. Min. Rep., Vol. 64, p. 36 (1906). * ALiiEN, Robert. Reduction Plant and Process at the Oroya-Brown- hill Mines. (Abstract Jour, of Cham, of I^ines, KaJgoorlie, West Aus- 'tralia.) Min. & Sci. Press, Vol. 91, p. 366 (1905). VON Bernewitz, M. W. Slime Treatment at Kalgoorlie, 1 p. Min. & Sci. Press, Vol. 95, p. 743 (1907). * VON Bernewitz, M. W. Progress in Ore Treatment at" Kalgoorlie, 2| pp. (Abstracted from The Gold mines of Western Australia.) Min. & Sci. Press, Vol. 100, p. 926 (1910). VON Bernewitz, M. W. Two New Treatment Plants in Western Aus- tralia, 1 p. Min. & Sci. Press, Vol. 105, p. 148 (1912). Brooke, H. J. Kalgoorlie Cyanide Practice. Eng. & Min. Jour., 78, p. 632 (1904). Brooke, Harry J. Ore Milling at Kalgoorlie. Eng. & Min. Jour., Vol. 80, p. 4 (1905). Charleton, A. G. Gold Mining and Milling in W. Australia. Eng. Mag., Vol. 21, p. 405 (1901). * Drdcker, a. E. Metallurgical Practice in Western Australia, 5 pp. Min. & Sci. Press, Vol. 101, p. 401 (1910). Nardin, E. W. Bromo-cyanide in W. Aust. Min. & Sci. Press, Vol. 97, p. 562; Rev. Min. Ind., XVII, p. 444 (1908). NicoL, W. J. Treatment of Low-grade Slimes in Victoria, 2 pp. Min. and Eng. Wld., Vol. 37, p. 189 (1912). * Prichabd, W. a. & Hoover, H. C. Cyaniding Sulpho-telluride Ores at Kalgoorlie, li pp. Eng. & Min. Jour., Vol. 76, p. 156; Reviewed Min. Ind., Vol. XI, pp. 338-342 (1903.) * Stokes, Ralph. Metallurgical Methods in Western Australia. Min. Wld., Vol. 26, pp. 4 and 34 (1907). * Williams, G. W. Metallurgical Practice at Kalgoorlie, Australia, 6 pp. (Rev. Min. Ind., Vol. 16, p. 637.) Eng. & Min. Jour., Vol. 85, p. 345 (1908). S. Africa. Denny, G. A. & H. S. Metallurgy of the S. African Rand. Eng. & Min. Jour., Vol. 82, p. 1217 (1906); Min. Mag. (N. Y.), Vol. 12, p. 173 (1905). Denny, G. A. Mill Practice on the Rand. Min. & Sci. Press, Vol. 98, p. 884 (1909); Min. Mag. (N. Y.), Vol. 11, p. 401 (1905). Dickson, Gordon F. Cam and Motor Metallurgy. Method of treat- ing a Rhodesian gold ore containing arsenic and antimony, 4J pp., illus. Min. Mag., Vol. 9, p. 132 (1913). Gabcoyne, Rowland. A Modern Reduction Plant on the Rand, 2 pp. Min. & Sci. Press, Vol. 102, p. 288 (1911). TREATMENT OF GOLD ORES 253 GiESEB, H. S. Benoni Mine and Mill on the Rand, 4 pp. Eng. & Min. Jour., Vol. 94, p. 23 (1913). GiESER, H. S. Modern Metallurgy on the Rand, 10 pp., illus. Max. Min. Jour., Vol. 16, p. 72 (1913). GiLMOUR, D. Randfontein Central Mill. J. C. M. & M. Soc, S. A., Vol. 11, p. 133 (1910). * Hatch, F. H. Evolution of Rand Cyanide Practice. Eng. & Min. Jour., Vol. 92, p. 165 (1911); Min. & Eng. Wld., Vol. 35, p. 199 (1911). Hatch, Frederick H. Progress in Milling on the Rand, 2 pp. Eng. & Min. Jour., Vol. 92, p. 265 (1911). Nichols, H. G. Present Tendencies on the Rand. Min. Mag., Vol. Ill, p. 44 (1910). PiTCHFORD, J. B. Mining Conditions in South Africa, 6 pp. (A lecture delivered to the Mining Students of the U. of Cal.) Min. & Min., Vol. 28, p. 49 (1907). * PiTCHFORD, J. B. Simmer East and Knights Deep, S. Africa. Min. & Sci. Press, Vol. 94, p. 337 (1907). Schmitt, C. O. Future Economics in Rand Reduction Plants, 27 pp. Bull. 80, I. M. M., May 24, 1911; also J. C. M. & M. Soc, S. A., April, 1911. Stadtler, H. The New Metallurgy, 4^ pp. Min. and Sci. Press, Vol. 105, p. 78 (1912). Thomas, J. E. Simmer Deep & Jupiter Reduction Works. Min. & Sci. Press, Vol. 99, p. 396 (1909). * Weston, E. M. Analysis of Mine & Mill Practice on the Rand; Eng. & Min Jour., Vol. 89, p. 171 (1910); Eng. & Min. Jour., Vol. 89, p. 267 (1910). Weston, E. M. Simmer East & Knights Deep, S. Af. Eng. & Min. Jour., Vol. 85, pp. 350, 356 (1908). * Weston, E. M. Mill of the Randfontein Central Gold Mining Com- pany, f p. Eng. & Min. Jour., Vol. 90, p. 970 (1910). . Reduction Works of Simmer Deep. Min. Sci., Vol. 60, p. 126 (1909). . Hendrjrx Agitator on the Rand, 2 pp. Min. & Sci. Press, Vol. 106, p. 151 (1913); Vol. 105, p. 599 (1912). Mexico. Bullock, L. N. B. Cyanide Practice at Copala, 1 p. Min. & Sci. Press, Vol. 96, p. 63 (1908). Burt, E. Milling Practice at El Oro, Mexico. Min. Wld., Vol. 27, p. 699 (1907). * Caetani, G. and Burt, E. Fine Grinding of Ore by Tube-mills, and Cyaniding at El Oro, Mexico, 53 pp. Trans. A.I.M.E., Vol. 37, p. 3 (1907). Forbes, D. L. H. The New Mill and Cyanide Plant at El Tigre, Sonora, Mexico, 3 pp. Mex. Min. Jour., Vol. 16, p. 186 (1913). HoLCOMBE, J. p. San Francisco Mill, Pachuca Mill, Mex., 2 pp. Min. & Eng. World, Vol. 38, p. 911 (1913). 254 STAMP MILLING AND CYANIDING Lamb, Mark R. Minas Prietas Reduction Works, li pp. Min. & Sci. Press, Vol. 93, p. 147 (1906). * MacDonald, Bernard. Milling & Cyanide Practice at the San Prospero Mill, Guanajuato, | p. Min. & Sci. Press, Vol. 97, p. 253 (1908). Miller, G. N. Operation of a Cyanide MiU in Western Chihuahua. Eng. & Min. Jour., Vol. 80, p. 344 (1906). " Occasional Contributor." Dos Estrellas Mill, IJ pp. Min. & Sci. Press, Vol. 96, p. 197 (1908). RicKARD, T. A. Cyanide Practice at El Oro. Min. & Sci. Press, Vol. 93, p. 381 (1906). Shaw, S. F. Recent Cyanide Practice at the Montezuma, Costa Rica, 2 pp. Min. & Sci. Press, Vol. 102, p. 179 (1911). Shaw, S. F. Mines and Mill of Montezuma Mines, Costa Rica, 2 pp. Eng. & Min. Jour., Vol. 90, p. 715 (1910). * Van Law, C. W. Mill Practice at Guanajuato. Min. & Sci. Press, Vol. 95, p. 205 (1907). * Weston, W. The Santa Gertrudis Cyanide Mill, If pp. Eng. & Min. Jour., Vol. 92, p. 109 (1911). Miscellaneous. GoosMAN, J. G. Ore Reduction and Cyaniding at Waihi Mill, New Zealand, 1 p. Min. & Eng. Wld., Vol. 37, p. 1127 (1912). Hubbard, J. D. Chosen Mining Co.'s Reduction Plant, 3 pp. Min. 6 Sci. Press, Vol. 106, p. 510 (1913). Mbgraw, H. a. Cyanide Practice in Canadian Fields, 2 pp. Min. & Eng. Wld., Vol. 38, p. 811 (1913). Megraw, H. a. Cyaniding at the Dome Mill, 4 pp. Eng. & Min. Jour., Vol. 94, p. 983 (1912). Megraw, Herbert A. Cyanide Development at Porcupine, Ont., 7 pp. Eng. & Min. Jour. Vol. 98, pp. 385 and 477. Parmalbe, H. C. Cyanide Practice in the Porcupine District, Ont., 10 pp. Met. & Chem. Eng., Vol. 12, pp. 667 and 636. Reid, J. A. Cyaniding at the Dome Mill, i p. Eng. & Min. Jour., Vol. 94, p. 1062 (1912). RoDGBRS, C. Earl. The Motherlode Mill at Salmo, B. C, 3i pp., illus. Eng. & Min. Jour., Vol. 96, p. 629 (1913). Rogers, R. B. Building a Mill in Central America, 5| pp. Min. & Sci. Press, Vol. 106, p. 472 (1913). CHAPTER XV TREATMENT OF SILVER ORES The application of cyanide to silver metallurgy is a subject concerning which much less is known than of the corresponding treatment of gold ores. Rapid strides are being made, however, and the pioneer work done on the silver-ores of Mexico has re- 95 1 — -M ativl 3 Si Ter 1 ,■ r A- jeo ,iw — ^ ^ ^ ^ ^ y / y . / ^ / ?<' »*- ■^ '•'i'i / ^ '' §50 / ^ r- ^45 / / _^^ -" trjS MO .^ / / ' «■? -'' / ^ -^ -- --' ) / y ^ ^ -' "^ / / ^ -- / y /' ^ '" Te trab edri ce / / ... .__ — ._. ... — ^ '/. ^ ^^' -- — // / .,- -•^ t> r " 2 4 6 8 10 12 li 16 18 20 22 24 26 28 30 32 31 36 38 40 42 44 46 i8 Time of Agltati&n in Hours Fig. 117. Solubility of Various Silver Minerals. (Conditions — 50 gm. ore, lOOcc. solution containing 0.5 per cent KCy and 0.3 per cent CaO.) suited in extensive silver cyahiding plants in that country and in the State of Nevada. As previously noted, silver occurs in a far greater variety of mineral forms and associations than does gold, and the solubility of the different silver minerals in cyanide solution also varies within wide limits. The preceding diagram (Fig. 117), 255 256 STAMP MILLING AND CYANIDING by Theo. P. Holt,* shows the relative solubilities of the six most important silver minerals : embolite, native silver, argentite, prou- stite, pyrargyrite, and tetrahedrite. It is to be noted at the outset that much stronger solutions of cyanide are required in the treat- ment of silver ores than are necessary in the cyaniding of gold ores. Various . oxidizers and extra solutions seem to promise better with silver than with gold. Fig. 118, also taken from Holt,t illustrates the effect of various reagents when added to cyanide Fig. 118. E£fect of Various Reagents in Cyaniding Silver Minerals. solution in the treatment of artificially prepared mixtures of different silver-minerals and quartz sand. The main difficulty with all of the silver-sulphide minerals seems to be in the liability of the solution reaction, Ag2S + 4 KCy?=^2 KAgCy2 + KjS, re- versing itself, with the result that the silver is prematurely pre- cipitated as sulphide. The effect of lead salts is to prevent this reversal by taking up the sulphur to form lead sulphide, t^us getting *■ Min. & Sci. Press, Vol. 99, page 159. t Loc. cit. TREATMENT OF SILVER ORES 257 it out of the way. It is to be noted that these results have not always been confirmed by other experimenters,* and that Holt's conclusions contradict those of Hobson f as to the beneficial effect of mercuric salts. The complex silver-ores of Cobalt are prepared for cyanide treatment by a preliminary desulphurizing reduction to the metallic state with hydrogen generated by caustic alkali and aluminium, in contact with the ore in a small tube-miU.| In crushing the ore and agitating it with solution, and in separ- ating solution from pulp, the methods discussed herein for gold are, of course, readily applicable. The precipitation of silver from cyanide solutions is effected both by electrolysis and by zinc, the latter either in shaving or dust form. The bulk of the precipitate is, of course, many times greater than in treating a gold ore of corresponding value, and the consumption of zinc per ton of ore is also necessarily much greater. Aside from these points the pre- cipitation of silver from cyanide solutions is, if anything, simpler than that of gold. The discussion on page 227, concerning the liberation of tKe particle of gold-mineral, applies with equal force to the minerals of silver. In spite of the fact that the ores are more complex, how- ever, the variation in methods of treatment, so far as cyaniding is concerned, are much fewer. Amalgamation is practical^ never used with cyanide; leaching, on account of the long time of con- tact, and large number of washes, is only rarely resorted to, and concentration with 'all-sliming,' agitation, and vacuum-filtering, bids fair to remain for some time the standard silver cyaniding practice. Three types of plants will be shown in detail as representing the treatment methods in use: (1) Concentration, with leaching of sand and agitation of slime. (2) Concentration, followed by cyanide treatment of an ' all-slime ' product. (.3) 'All-slime' cyanidation. * W. A. Caldecott, Min. & Sci. Press, Vol. 97, page 295. t Francis I. Hobson, Min. & Sci. Press, Vol. 97, pages 159 and 182. i Jas. J. Denny, Min. & Sci. Press, Vol. 107, p. 484. 258 STAMP MILLING AND CYANIDING (i) CONCENTRATION WITH LEACHING OF SAND AND AGITATION OF SLIME The mill of the Tonopah Mining Co.,* at Millers, Nevada, com- monly known as the Desert Mill, is a good example. Character of Ore: — Siliceous andesite carrying gold and silver in the ratio of 1 to 100 by weight. The silver occurs mainly as stephanite, argentite, and polybasite with small amounts of galena, blende, pyrite, and chalcopyrite. Flow, Sheet: One No. W Gates Gyratory- 2 in. Product Trommel JH in. holes. Undersize Oversize I Two No. 4.Gates Crushers ~~f " — gampling Mill OreBins O.lSjt KCy Solution Challenge Feed ers I > >< ■ 100 - 1050 lb. stamps dropping 6J4 in. 104 times per min. duty 5 tons thru 12 mesh - ■■ ^ 2 in. discharge 30 ft. Elevator Wheel f Ten 20 in. Double Cone Classifiers j;^ ■ : — T — Overflow 50^- 100 Mesh Spigot 11)(-100 Mesh. Two 6 ft. Chilean Mills Twenty No. 5 Wil fley Tables : 'i 1 5 ft. Huntington MillNv Tailing Concentrate 9 Johnston Vanners Tailing Cone. 54^tt. Elevating Wheel. ' * Ten36in.)'L, „.;«„,„ Two60in.{tJlassifie rs TT" — :r"n ,. -r 1.1.^ m Spigot Overflow }i Ib.Lead Acetate per Ton "r ^" i 4 lbs. CaO per Ton | Four Sand Collecting TanlcB33x8ft ■ I ■ ■ "~^ Blaisdell Excavator 1 ' Tilaisdell Distributor I Overilow Spitzi^asten " Collecting Tanks 36 x 20 ft. Sa*nd Slime Slime Clear Overflow- to Zinc Boxes ^^ iZI-J I / Treatment . 18- Leaching Tanks 33x8 ft. Agitator Tank 36 x 20 ft. \ 39 hrs.0.25)(KCy lat. Treatment:- 30 tons 0.25%^ Sol. Agitation by Two 4- Arm Paddles ) 6 hr. Settlement with repeated washes with O.lB^ assisted by Centrifugal Pump \ and Decanted KCy Sol. S days, and Treatment:- T J repeated washes with strong and Overflow-Pregnant Sol. Slime weak Sol. Sand transferred to second vat and treated again, followed by wash watfer. Total time of treatment 12 or 15 days. ~~l 1 Tailing -to waste Pregnant Solution 0.03 oz. Gold l~' Seven Agitators as above-for 24 hrs. Filter Storage , Two -96 Leaf Butters Filters 1 J £1 J Pregnant Sol. Tailing - to waste ^•'"^^"^^■^ Two 24 xs'ft. Tanks 18 Zinc Boxes- Each holding 1600 lbs. Zinc Shavings Barren Sol. Precipitate to Storage Results: — 1907 ore assayed $52. Extraction 92%. Cost $2.94 per ton. 1912 ore assayed $19.97. Extraction 90.6%. Cost $2.74 per ton. Fig. 119. * A. R. Parson, Min. & Sci. Press, Vol. 95, pages 495-500. TREATMENT OF SILVER ORES 259 (2) CONCENTRATION FOLLOWED BY CYANmE TREATMENT OF AN 'ALL-SLIME' PRODUCT The mill of the Montana-Tonopah Co., at Tonopah,* Nevada, is an excellent example; since, however, one Tonopah plant has already been discussed, the mill of the San Rafael Co., at Pachuca, Hidalgo, Mexico, t will be outlined. Character of Ore: — The ore is composed of pyrite, blende, and galena, in a gangue of quartz and calcite, the silver occurring mainly as argentite. The ore assays from 4 to 5 grams gold and 900 grams of silver to the metric ton.J Flow Sheet: Blake Crushers ' I 0.25jt KCy Sol. Hand Sampled ^= 7^=5 Forty-8501b. stamps, dropping 75^^104 times per min. Stamp duty ZH tons - 10 mesh. Forty-1250 lb.stamps.dropping 6%, 104 times per min. Stamp duty 6ii tons - 10 mesh. 16 Wilfley Tables I 1 ^ Slime Tailing Concentrate- to Smelter 5 Dorr Classifiers Slime Sand (1 Sol, to 2 Sand) Slime ; Solution:: 1:10. 5-4 x 20 Krupp Tube Mills. + f 3 - 20 X- 10 ft. El Oro Linings 5 Dorr Pulp Thickeners < 2 - 24 x 10 ft I I '' Overflow Slime: Solution - 1:1.2 To Storage T^ 12 - 15 X 45 Pachuca Agitators.- i hrs. Agitation with O.Sj KCy & 250 gr.PbCCgsOQg per ton.-24 trs.Rest in Agitator. I Four - 40 Leaf Moore Filter Plant. — ^ r Pregnant Solution , | ~ , „„ + Tailing - to waste Sand Filters =- „. i . Zmc Boxes 1 T Precipitate Barren Solution - to Storage Fig. 120. * C. H. Rotherham, Min. & Sci. Press, Vol. 97, page 324. t E. Girault, Min. and Min., Vol. 30, page 618. t Grams per metric ton is the usual method of expressing assay returns in Spanish America. 1 gm. = 0.0001 per cent of a metric ton, or is equivalent to 0.2916603 oz. Troy per Avoirdupois Ton. In this ore the gold content is between 0.117 and 0.146 oz., the silver is 26.2 oz. 260 STAMP MILLING AND CYANIDING Results : — The extraction is 97% of the gold and 91.5% of the silver; 22% is made by concentration, the balance by cyanide. The cyanide consumption is 1.078 kilo of NaCy (128 per cent KCy) per metric ton. The cost is reported as follows: General expense SO. 39 Grinding and Concentrating 0.59 Cyaniding 0.66 Pumps and compressor 0.075 Filtration (with royalty) . 165 Precipitation and melting 0.22 Total , S2. 100 TREATMENT OF SILVER ORES 261 (3) 'ALL-SLIME' CYANIDATION All-slime cyanide treatment, without the assistance of concen- tration, is only possible, at present, with the simpler silver ores. As knowledge increases, it may be possible to extend this method to the more complex ores. The mill of the New York and Honduras Rosario Mining Co.,* at San Juancito, Honduras, recently aban- doned the amalgamation process in favor of cyanidation, and their scheme of treatment is shown below. Character of Ore: — Hard quartz carrying "lead, copper, iron, and antimony." Flow Sheet: (?) Crushers 2 inch product I 1 KCy Solution Mill Bin ^= =T- Fifty- 750 lb. stamps-dropping 6 in.-lOO times per min.-Stamp duty.2 tons thru 1mm Slot Screen. Three Conical Classifiers. I I Overflow Spigot ~T^ — I — ■ Settling Tanks Small Pyramidal Thickeners "I 1 I J Clear Overflow Overflow Spigot Slime 90?i-200 mesh. T 2-90 ton Receiving Tanks 2 Tube Mills (Silex Lining Life 90 days.) I I ■7 - 50 ton Agitation Tanks. 40 to 60 hr. treatment with 0.3^ KCy Sol. J 2 - Filter Storage Tanks. I 60 Leaf Butters Filter Plant. 1 1 Pregnant Solution. 14 oz. Ag. 0.12 oz. Au. per ton Tailing - to waste I Zinc Boxes 1 1 Barren Solution 0.08 oz. Ag. Trace Au. Precipitate Results: — The ore assays $24. Ratio Ag to Au, 10 to 1 by weight. The total extraction is 90 per cent. The cost of treatment is $3.46 per ton. The cyanide consumption is extremely high, — nearly 8 lb. per ton. Pig. 121. * Geo. E. Driscoll, JVfin. & Sci. Press,. Vol. 98, page 388. 262 STAMP MILLING AND CYANIDING BIBLIOGRAPHY FOR TREATMENT OF SILVER ORES * Especially Desirable for Students' Use Cyaniding of Silver Ores. * Caldecott, W. a. Cyaniding of Silver Ore in Mexico, Chap. I and II, 4 pp. (Abstracted from J. C. & M. Soc, S. A., Jan., 1908.) Min. & Sci. Press, Vol. 96, pp. 426 and 594 (1908); Min. & Sci. Press, Vol. 97, p. 294 (1908). * Caldecott, W. A. Cyaniding of Silver Ores. Min. & Sci. Press, Vol. 97, p. 806 (1908). Caldecott, W. A. Cyaniding 'of Silver Ores. Min. & Sci. Press, Vol. 97, p. 295. Clakk, J. E. Cyaniding Base Silver Ores, | p. Min. & Sci. Press, Vol. 103, p. 459 (1911). * CoGHiLL, Will. H. Refractory Manganese-silver Ores, 9 pp. Min. & Sci. Press, Vol. 104, pp. 754 and 794. Cunningham, Noel. Effect of Heating Cyanide Solutions. Min. & Sci. Press, Vol. 104, p. 315 (1912). Eye, C. M. Use of Lead Salts in Silver Cyaniding. Min. & Sci. Press, Vol. 98, p. 82 (1909). Hamilton, E. M. Cyaniding of Manganese Silver Ore, 2 pp. Min. & Sci. Press, Vol. 99, p. 756 (1909). * Holt, Theo. P. Cyaniding of Silver Ores, 2 pp. Min. & Sci. Press, Vol. 98, p. 546 (1909); Min. & Sci. Press, Vol. 99, p. 159 (1909). HoRSPALL, H. A. Treatment of Complex Silver Ores for Small Mines, 3 pp. Min. Sci., Vol. 68, p. 36 (1913). * Kniffin, Lloyd B. Cyaniding of Silver Ores, 1 p. Min. & Sci. Press, Vol. 100, p. 322 (1910). Jackson, Byron. Treatment of Manganese-silver Ores, 1 p. Min. & Sci. Press, Vol. 104, p. 732 (1912). Jones, A. H. Heating Cyanide Solution for Treatment of Silver Ores, i p. Min. & Sci. Press, Vol. 104, p. 176 (1912). MosHBR, D. Cyaniding of Silver Ores, 2 pp. Min. & Sci. Press, Vol. 98, p. 691 (1909). * MosHER, D. Ozone in the Treatment of Silver Ores in Cyaniding, 1 p. Pac. Min., Vol. 15, p. 89 (1909). MosHER, D. ChlorineintheCyanidingof Silver Ores, lip. Pac. Min., Vol. 16, p. 168 (1910). * Sharwood, W. J. Cyaniding of Silver Ores, 2J pp. Min. & Sci. Press, Vol. 97, p. 418 (1908). Van Wagenen, Theo, F. Silver, 3i pp. (Abstracted , from Popular Science Monthly, Sept., 1908.) Min. & Sci. Press, Vol. 97, p. 392 (1908). Van Wagenen, Theo. F. More Thought about Silver. Min. & Sci. Press, Vol. 98, p. 851 (1909). TREATMENT OF SILVER ORES 263 SILVER MILLS IN VARIOUS STATES AND COUNTRIES Nevada. VON Bernewitz, M. W. The McNamara Mill, Tonopah, Nev. (Costs), li pp. Min. & Sci. Press, Vol. 106, p. 182 (1913). VON Bebnbwitz, M. W. Metallurgy at Tonopah, 2 pp. Min. & Sci. Press, Vol. 105, p. 828 (1912). BoSQUi, F. L. Montana Tonopah Mill. Eng. & Min. Jour., Vol. 83, p. 805 (1907). Carpenter, Jay A. Operation of the West End Mill, Tonopah (Costs), 2 pp. Min. & Sci. Press, Vol. 107, p. 191 (1913). Fleming, J. B. Nevada Hills Surface Equipment, 2 pp. Eng. & Min. Jour., Vol. 91, p. 1001 (1911). Hart, J. P. and Williams, H. L. West End Consohdated Mill, Tono- pah, 4 pp. Eng. & Min. Jour., Vol. 94, p. 163 (1912). Irvin, Donald F. Silver Cyaniding at Tonopah, 1 p. Eng. & Min. Jour., Vol. 95, p. 912 (1913). * KiRCHEN, John G. Tonopah Extension Mill, 2 pp. Min. & Sci. Press, Vol. 100, p. 522 (1910). Martin, Al. H. Tonopah Extension Mine and Mill, Nevada, IJ pp. Pac. Min., Vol. 17, p. 363 (1910). Martin, A. H. The Mill of the To&opah Mining Company, 2 pp. Min. Sci., Vol. 61, p.. 172 (1910). * Megraw, Herbert A. Silver Cyaniding at Tonopah, 15 pp. Eng. & Min. Jour., Vol. 95, pp. 413, 455, 503, 767 (1913). Megraw, Herbert A. Cyaniding Silver at Nevada Hills Mill, 3j pp. Eng. & Min. Jour., Vol. 95, p. 645 (1913). Megraw, Herbert A. Cyaniding at the Nevada Wonder Mill, 24 pp. Eng. & Min. Jour., Vol. 95, p. 693 (1913). * Parsons, A. R. The Desert Mill (Tonopah), 5 pp. Min. & Sci. Press, Vol. 95, p. 494 (1907). * Rice, Claude T. The Butters' Cyanide Plant, Virginia City, Nev., 3 pp. Eng. & Min. Jour., Vol. 83, p. 270 (1907). * Rice, Claude T. Tonopah Mining Company's Mill, 6 pp. Eng. & Min. Jour., Vol. 91, p. 1212 (1911). Rice, Claude T. The Tonopah Extension Mill, 3 pp. Eng. & Min. Jour., Vol. 92, p. 1085 (1911). * RdTHERHAM, G. H. Milling Plant of the Montana Tonopah Mining Company, 4 pp. Min. & Sci. Press, Vol. 97, p. 324 (1908). Symmbs, Whitman. Mexican Mill, Virginia City, Nev., 5 pp. Eng. & Min. Jour., Vol. 94, p. 701 (1912). WoLCOTT, G. E. The Mines and Mills of Tonopah, Nevada, 4 pp. Eng. & Min. Jour., Vol. 87, p. 594 (1909). . New Mill of the Tonopah Extension Mining Co., 2| pp. Eng. & Min. Jour., Vol. 89, p. 1066 (1910). . Flow-sheet of New Belmont (Tonopah) Mill. Min. & Sci. Press, Vol. 104, p. 625 (1912). 264 STAMP MILLING AND CYANIDING Mexico. * Allan, Jno. F. Tests and Treatment of Silver Ores in Mexico by MacAxthur-Forrest Process, 20 pp. (Early Silver-Cyaniding.) Trans. A.I.M.E., Vol. 35, p. 12 (1905). Butler, J. S. Milling and Cyanide Practice, San Prospero Mill, Guana- juato, 2i pp. Min. & Sci. Press, Vol. 97, p. 130 (1908). * Bullock, L. N. Metallurgical Chart of Operations in the Mill of the Butters Copala Mines in Sinaloa, Mexico, 2 pp. Min. & Sci. Press, Vol. 94, p. 221 (1907). Bullock, Lawrence N. Cyaniding at Copala, Mexico, 1 p. Min. & Sci. Press, Vol. 94, p. 335 (1907). * Bordeaux, Albert F. J. Cyaniding of Silver Ores in Mexico, 12 pp.; discussion, ibid. p. 917. Trans. A.I.M.E., Vol. 40, p. 764 (1909). Chiddey, Alfred. Cyaniding of a Silver Ore at El Salvador, Mexico. Eng. & Min. Jour., Vol. 79, p. 1053 (1905). * CoNKLiN, H. R. Improvements at lluvia de Oro Mill, 4 pp. Eng. & Min. Jour., Vol. 95, p. 551 (1913). * Elwes, H. G. Application of Cyaniding to the Lower-grade Silver Ores of Zacatecas and Other Districts of Mexico. (Rev. in Min. Ind., Vol. 14, p. 282.) Eng. & Min. Jour., Vol. 79, p. 515; Vol. 80, p. 199 (1905). GiRAULT, E. Cyaniding Silver Ores in Mexico, 2 pp. (Read before Mining & Metallurgical Institute of Mexico, Aug., 1909.) Min. & Min., Vol. 30, p. 618 (1910). * HoBSON, Francis J. Cyaniding in Mexico, 6 pp. Min. & Sci. Press, Vol. 97, p. 159 (1908). Hunt, Bertram. Cyaniding in Mexico, 1§ PP- Min. & Sci. Press, Vol. 97, p. 286 (1908). Kline, R. C. Treatment of Silver Ores at Guanacevi, Mexico, 2J pp. Min. & Sci. Press, Vol. 102, p. 402 (1911). Lewis, S. J. Cyanide Practice at Ajuchitlan. Min. & Sci. Press, Vol. 100, p. 100 (1910). McDonald, Bernard. The Veta Colorado Mill and Cyaniding Plant, 7h pp. Min. & Sci. Press, Vol. 105, p. 4 (1912); Vol. 105, p. 40 (1912). Malcolmson, J. W. Cyaniding of Silver-gold Ores in the Guanajuato District, Mexico. (Sirena Mill.) Eng. & Min. Jour., Vol. 80, p. 529 (1905). * OxNAM, T. H. Cyanidatioii of Silver Ores of the Palmarejo Mine, Chihuahua, Mexico, Eng. & Min. Jour., Vol. 80, pp. 297, 339 (1905). * OxNAM, T. H. Cyanidiag Silver-gold Ores of the Palmarejo Mine, Chihuahua, Mexico, 54 pp. Trans. A.I.M.E., Vol. 36, p. 234 (1906). Rice, C. T. Veta Colorado Mill. Eng. & Min. Jour., Vol. 86, p. 120; Review in Min. Ind., Vol. XVII, p. 445 (1908). Rice, C. T. Guerrero Mill. Eng. & Min. Jour., Vol. 86, p. 648; Re-, viewed in Mm. Ind., Vol. XVII, p. 443 (1908). Rice, C. T. San Prospero Mill. Eng. & Min. Jour., Vol. 86, p. 949; Reviewed in Min. Ind., Vol. XVII, p. 441 (1908). Seamon, W. H. Yoquivo Silver Cyanide Mill, Western Chihuahua. Eng. & Min. Jour., Vol. 90, p. 811 (1910). TREATMENT OF SILVER ORES 265 Shapley, Edwin. Santa Natalie Mill, Guanajuato. Eng. & Min. Jour., Vol. 88, p. 68 (1909). Sill, H. A. and K. T. Cyaniding Zambona Low-grade Silver Ores, 2 pp. Eng. & Min. Jour., Vol. 95, p. 745 (1913). SwEETZBB, A. L. Rosario Cyanide Plant, IJ pp. Min. & Sci. Press, Vol. 105, p. 752 (1912). * Tweedy & Beals. Cyanide Plant and Practice at Minas del Tajo, 24 pp. Trans. AJ.M.E., Vol. 41, p. 324 (1910). Willis, H. T. Cyaniding of Parral Silver Ores, 2 pp. Min. & Sci. Press, Vol. 98, p. 488 (1909). . Operations of Guanajuato Development Co., 4 pp. Eng. & Min. Jour., Vol. 88, p. 651 (1909). . Construction and Operation of the Tigre Mill, J p. Eng. & Min. Jour., Vol. 94, p. 498 (1912). . The San Francisco Mill, Pachuca, Mex., 1 p. Eng. & Min. Jour., Vol. 95, p. 1104 (1913). Canada. Flynn, F. N. Metalliu-gical Conditions at Cobalt, Canada, 3 pp. (Ab- stracted from Jour. Can. Min. Inst.) Min. & Sci. Press, Vol. 97, p. 432 (1908). Johnstone, Jajmes. Mill etc. of Nipissing M. Co., Cobalt, pp. 28, Bull. 85, A.I.M.E. (Jan. 1914), and discussion, Bull.' 91 (July 1914) and 95 (Nov. 1914). Linton, Robert. Cyanidation of Silver Sulphide at Ocampo, Mex., pp. 7. Bull. 86 A.I.M.E. (Feb. 1914). Megeaw, H. a. Cyaniding in the Cobalt District, 5 pp. Eng. & Min. Jour., Vol. 94, p. 837 (1912). Megraw, H. a. Nipissing High Grade Mill, Cobalt, 2 pp. Eng. & Min. Jour., Vol. 94, p. 1127 (1912). Shaw, S. F. Mill of Montezuma Mines, Costa Rica. Eng. & Min. Jour., Vol. 100, p. 715 (1910). Tyssowski, John. Hydrometallurgical Operations at Cobalt, 5 pp. Eng. & Min. Jour., Vol. 90, p. 1253 (1910). W(ilson), E. B. Hydrometallurgy of Cobalt Ores, 5 pp. Min. & Min., Vol. 31, p. 303 (1910). Watson, R. B. Nipissing High Grade Mill, Cobalt, 4 pp. Eng. & Min. Jour., Vol. 94, p. 1077 (1912). 266 STAMP MILLING AND CYANIDING BIBLIOGRAPHY FOR MILLING AND CYANIDING COSTS. CY- ANIDING OF CONCENTRATE AND OTHER TOPICS 'NOT ELSE- WHERE SPECIFIED. Costs. Brockunibb, S. H. Costs at the Erie Mine, 2 pp. Eng. & Min. Jour., Vol. 94, p. 455 (1912). Coleman, W. N. Cost of a Small Cyanide Plant. Pac. Min., Vol. 15, p. 40 (1909). Fulton, Charles H. Costs of Cyaniding. Min. Ind., Vol. 16, p. 547; Min. Ind., Vol. 17, p. 458 (1908). Handt, R. S. Milling Costs, 2 pp. Min. & Sci. Press, Vol. 98, p. 156 (1909). Hutchinson, Charles T. Cost of Constructing Stamp-mills. Min. & Sei. Press, Vol. 103, p. 546 (1911). Merrill, C. W. Homestake Slime-plant Costs. Min. & Sci. Press, Vol. 97, p. 353 (1908). Merrill, C. W. Homestake Cost Data, i p. Min. & Min., Vol. 28, p. 364 (1908). Parsons, A. R. Costs of Cyaniding at Tonopah, | p. Eng. & Min. Jour., Vol. 95, p. 720 (1913). MouLTON, W. A. Cyanide Costs. Min. & Sci. Press, Vol. 96, p: 803 (1908). Rhodes, C. E. Cyanide Costs, i p. Min. & Sci. Press, Vol. 97, p. 523 (1908). Taylor, G. M. Construction Costs at the New Portland Mill, Cripple Creek, Colorado. Min. & Sci. Press, Vol. 104, p. 12 (1912). Weston, E. N. Rand Mining and Milling Costs, 2 pp. Eng. & Min. Jour., Vol. 95, p. 329 (1913); Vol. 95, p. 425 (1913). Wilkinson, W. Fischer. Transvaal Costs and Recoveries. Eng. & Min. Jour., Vol. 85, p. 53 (1908). . Unit Costs in 20-stamp Cyanide Plant. Eng. & Min, Jour., Vol. fl3, p. 937 (1906). . Costs at Homestake, J p. Eng. & Min. Jour., Vol. 93, p. 593 (1912). . Costs at Behnont (Tonopah) Mill. Min. & Sci. Press, Vol. 104, p. 626 (1912). . Operating Costs at the Goldfield Consolidated Mill, 4 pp. Min. & Sci. Press, Vol. 104, p. 137 (1912). . Costs: Round Mountain Co., Tigre Mining Co., West Rand Con., 1 p. Eng. & Min. Jour., Vol. 94, p. 401 (1912). . Cost: Butterfly Mine, Colo., Pittsburg Silver Peak, 1 p. Eng. & Min. Jour., Vol. 94, p. 497 (1912). . The Consolidated Mercur Costs, 1 p. Eng. & Min. Jour., Vol. 95, p. 23 (1913). . Costs: Daly West Mining Co., Bodie, Calif.; Nipissing Cyan- ide Mill, Tonopah, Belmont; French Gold Min?, Calumet and Arizona. Eng. & Min. Jour., Vol. 95, p. 1003 (1913). MISCELLANEOUS BIBLIOGRAPHY 267 . Operating Costs at the Goldfield Consolidated mill, | p. Min. and Sci. Press, Vol. 105, p. 813 (1912). . Costs at the Ivanhoe, Kalgoorlie, i p. Min. and Sci. Press, Vol. 106, p. 363 (1913). . Costs at Perseverance Mine, Kalgoorlie, | p. Min. and Sci. Press, Vol. 106, p. 614 (1913). . Cyaniding and Milling Costs given in detail each year. Mineral Industry, Annual Volume. Cyaniding Concentrate. Bkown, F. C. Cyaniding of Concentrate at Waihi, N. Z. Min. & Sci. Press, Vol. 97, p. 424 (1908). Cunningham, Noel. Cyaniding of Concentrate, f p. Min. and Sci. Press, Vol. 106, p. 634 (1912). CoLMAN, Mtjrray N. Cyaniding of Sulphides, 1 p. Min. & Sci. Press, Vol. 101, p. 307 (1910). " Cyanicide." Cyaniding of Concentrate, J p. Min. & Sci. Press, Vol. 101, p. 445 (1910). Druckeh, a. E. Treatment of a Concentrate-slime, 3| pp. Min. & Sci. Press, Vol. 96, p. 458 (1908). * Dkuckbb, a. E. Recent Cyanide Practice in Korea, 3 pp. Min. & Sci. Press, Vol. 97, p. 468 (1908). Dkucker, a. E. Cyaniding of Concentrate, 2j pp. Min. & Sci. Press, Vol. 100, p. 416 (1910). Evans, G. Chesterfield. Cyaniding of Concentrate. Min. & Sci. Press, Vol. 101, p. 844 (1910). Fell, E. Nelson. Cyaniding of Tailing at Athabasca Mine, B. C, 13 pp. Trans. A.I.M.E., Vol. 31, p. 752 (1901). * Hamilton, E. M. Cyaniding of Concentrate, 3f pp. Eng. & Min. Jour., Vol. 93, p. 839 (1912). Hartley, Z. B. Some Observations on the Treatment of Pyritic Con- centrates by Cyaniding, 1 p. Pac. Min., Vol. 17, p. 413 (1910). * Htttchinson, J. W. Treatment of Concentrate at the Goldfield Cons. MiU (Costs), 71 pp. Min. & Sci. Press, Vol. 106, pp. 170, 204 (1913). * HoLDEN, Edwin C. Cyaniding at Ymir, B. C, 9 pp. Trans. A.I.M.E., Vol. 34, p. 599 (1904). Hubbard, J. D. Cyaniding Concentrate at Taracol, Korea, IJ pp. Min. & Sci. Press, Vol. 99, p. 471 (1909). " Ingbniero K C N." Cyaniding of Concentrate, J p. Min. & Sci. Press, Vol. 101, p. 445 (1910). Lamb, Mark R. Cyaniding Sulphides, i p. Min. & Sci. Press, Vol. 101, p. 414 (1910). Linton, Robert. Cyaniding of Concentrate, IJ pp. Min. and Sci. Press, Vol. 106, p. 437 (1912). Longbottom, W. a. Cyaniding of Antimonial Tailings, U PP- Min. & Eng. Wld., Vol. 37, p. 97 (1912). * McMiken, S. D. Milling Practice at the Komata Reefs Mine, 6 pp. Min. & Sci. Press, Vol. 103, p. 4 (1911). 268 STAMP MILLING AND CYANIDING Rbece, F. B. Cyaniding of Pyritio Ores, 1 p. Min. & Sci. Press, Vol. 105, p. 77 (1912). TovBY, L. Gold Milling in Western Siberia. Eng. & Min. Jour., Vol. 82, p. 577 (1906). Tremoubeux, R. E. a Successful Treatment of Concentrates by Cyaniding, 1 p. Mex. Min. Jour., Vol. 15, No. 6, p. 18 (1912). WiNGATE, Hamilton. Direct Cyaniding of Wet-crushed Ore in N. Z., 11 pp. Trans. A.I.M.E., Vol. 33, p. 125 (1903). . Milling at La Belliere, France, Cyaniding Complex Arsenical Gold Ore. Eng. & Min. Jour., Vol. 87, p. 792 (1909). . The Nickel Plate Mine and Mill, 2 pp. Min. & Sci. Press, Vol. 101, p. 271 (1910). . Cyaniding of Concentrate, 1 p. Eng. & Min. Jour., Vol. 94, p. 682 (1912). . Agitating Concentrate, | p. Min. & Sci. Press, Vol. 105, p. 118 (1912). Miscellaneous. Additon, a. Sidney. Calculation of Extraction in Cyanide Plants, 1 p. Eng. & Min. Jour., Vol. 96, p. 31 (1913). Allen, A. W. Mill and Cyanide Plant Records, 2| pp. Min. & Sci. Press, Vol. 104, p. 708 (1911). BoEBiCKE, W. F. & Eastman, B. L. Home-made Cyanide Plant, 1 p. Min. & Sci. Press, Vol. 97, p. 712 (1908). * Browne, R. Stuaet. The Mechanical Equipment of Cyanide Plants, 3J pp. Pac. Min., Vol. 15, p. 85 (1909). Brown, A. Selwtn. The Treatment of Auriferous Antimonial Ore, J p. Min. Rep., Vol. 54, p. 133 (1906). Browne, R. S. Method of Calculating Recovery of Dissolved Values from Slime, 1^ pp. Min. & Eng. Wld., Vol. 37, p. 203 (1912). Buskett, E. W. Cyaniding of the Granite-Bimetallic TaiUngs, 4^ pp. Min. & Eng. Wld., Vol. 37, p. 287 (1912). Cadogan, a. G. Calculation of Extraction in Cyanide Plants, 1 p. Eng. & Min. Jour., Vol. 95, p. 1109 (1913). Collins, Edgar A. Tailing-wheds or Pumps? i p. Min. & Sci. Press, Vol. 97, p. 596 (1908). Del Mar, Algernon. Requirements of Small Cyanide Mills, 2| pp. Eng. & Min. Jour., Vol. 96, pp. 769, 917 (1913). DuRANT, H. T. Making Up Solutions, 2 columns. Eng. & Min. Jour., Vol. 94, p. 64 (1912). DuRANT, H. T. Pump Suctions from Cyanide Tanks, i p. Eng. & Min. Jour., Vol. 94, p. 159 (1912). Editorial. Opportunities for Research Work in Cyano-metallurgy, I p. Pac. Min., Vol. 18, p. 39 (1911). Eggers, John A., Jr. A Cyanide Plant Constructed of Masonry, 3i pp. Pac. Min., Vol. 18, p. 7 (1911). Flint, H. P. Wire Sampler for Cyanide Solution, J p. Eng. & Min. Jour., Vol. 95, p. 709 (1913). MISCELLANEOUS. BIBLIOGRAPHY 269 Gross, John. Blanket Concentration of Cyanide Solutions, 2 pp. Min. & Soi. Press, Vol. 106, p. 783 (1913). Hunter, Chas. A Cheap Cyanide Plant, f p. (Abstract of paper read before Inst, of Min. & Met., July, 1907.) Min. Wld., 27, p. 1056 (1907). Irvin, Donald F. Sampling — Adequate Sampling in Modern Mill Practice, 3J pp., illus. Min. & Sci. Press, Vol. 106, p. 514 (1913). * James, Geo. A. Preliminary Treatment of Water and Air for use in Cyaniding. Min. & Sci. Press, Vol. 103, p. 415 (1911). McKenzib, C. S. Solution Meter at the Belmont MUl, f p., iUus. Eng and Min. Jour., Vol. 96, p. 165 (1913). Megraw, H. A. Extraction Percentages in Metallurgical Plants, 14 pp Eng. & Min. Jour., Vol. 89, p. 705 (1910). Megraw, Herbert A. Cyaniding Troubles and Remedies, 12 pp Eng. and Min. Jour., Vol. 94, p. 311 (1912); Vol. 94, p. 360 (1912). * Meghaw, Herbert A. Calculation of Extraction in Cyaniding, 3 pp, Eng. & Min. Jour., Vol. 96, p. 441 (1913). Nutter, E. H. A Simple Solution Meter, 2 pp. Min. & Sci. Press, Vol 93, p. 657 (1906). Reid, Walter L. Tailing Wheels Compared with Centrifugal Pumps, 1 p. Min. & Sci. Press, Vol. 97, p. 383 (1908). Sharwood, W. J. Calculation of Extraction in Cyaniding, 4 pp. Eng. & Min. Jour., Vol. 96, p. 937 (1913). Simmons, Jesse. Charging Tanks by Conveyors, 1 p. Eng. and Min. Jour., Vol. 94, p. 1169 (1912). Simpson, Duncan. Sand Sampling in Cyanide Works, IJ pp. (Read before Inst, of Min. and Met., London, Oct. 18, 1906.) Min. Wld., Vol. 26, p. 10 (1907). Simpson, Geo., Jr. Calculation of Extraction in Cyaniding, 1 p. Eng. and Min. Jour., Vol. 95, p. 1255 (1913). Spiers, James. Solution Meter for Leaching Plants, 2 pp. Mines and Methods, Vol. 3, p. 563 (1912). Tte, a. a. and Counsblman, T. Launder Data, Cananea Consolidated, 1 p. Eng. & Min. Jour.*, Vol. 97, p. 376 (1913). Wepper, G. W. Tailing-wheels, 2 pp. Min. & Sci. Press, Vol. 97, p. 596 (1908). Wilson, J. K. Notes on the Occurrence and Treatment of an Aurif- erous Ore Containing Insoluble Arsenides. (J. C. M. & M. Soc, S. A., Feb., 1907.) Min. Rep., Vol. 55, pp. 356, 374, 394 (1907). . Method of Erecting Wood Stave Tanks, IJ pp. Pac. Min., Vol. 16, p. 56 (1910). . Air Lift for Transporting Sand, f p. Eng. & Min. Jour., Vol. 91, p. 706 (1911). . Siphon for Cyanide Vats, J p. Min. & Sci. Press, Vol. 106, p. 953 (1913). . Recording Gauge for Filter Operation, | p. Min. & Sci. Press, Vol. 105, p. 766 (1912). INDEX Acid treatment for cyanide precipitate, 218-219. Agitation, 163-171. bibliography, 174-176. continuous, 171. intermittent, 171. Agitator, centrifugal pump, 165-166. compressed air, 168-169. Dorr, 164. Hendry X, 165. mechanical stirrer, 163-166. Pachuca, 169-170. Parral, 169. Trent, 167. Akin's classifier, 141. Alaska Treadwell, costs, 85. flow sheet, 232. sea water used at, 68. steaming plates at, 70. Aluminium, precipitation with, 133. bibliography, 215. Amalgam, cadmium, 67. gold, 66. silver, 8. sodium, 9. treatment of, 64. zinc, 66. Amalgamation, principles of, 8-12. bibliography, 12. stamp mill, 75. aids to, 66-69. bibliography, 76-78. electrolytic, 67. general principles, 56. use of, in flow-sheets, 231-235, 237-240. use of cyanide in, 68. Apron plates, 59. position of, 61-62. Argall, H., quoted, 126. Arrastra, 91-92. bibhography, 105. Arsenic, as a cyanicide, 150. 271 272 INDEX Back-knee battery frame, 30. Bagration, conclusions on cyanidinig, 124. Ball-mills, 102. bibliography, 108. crushing eflBciency, 116. Battery clean-up, 71. Battery-frames, 29-36. bibliography, 53. Battery-sands, cleaning, 72. Behr, H. C, modified gravity stamp, 88. Bibliography for agitation, 174-176. amalgamation, 12, 76. arrastras, 105. ball-mills, 108. centrifugal mills, 105. Chilean mills, 105. classification, 145. comparison of mills, 118. costs, 266. cyaniding, books on, 6. cyanidation, chemistry of, 135. of concentrate, 267. history of, 133. miscellaneous, 268-269. decantation, 201. dissolving gold and silver, 173-177. filter-presses, 202. filters, Butters-Moore, 202. continuous, 204. miscellaneous, 205. pressure, 204. gold mills in California, 250. Colorado, 247. Mexico, 253. miscellaneous, 254. Nevada, 248-299. S. Africa, 252-253. S. Dakota, 250. various coim tries, 251. various states, 247-248. W. Australia, 252. gold ores, treatment of, 247-256. grinding pans, 105. leaching, 173. mills and grinders, 104-109. oxidizers and extra-solutions, 176. precipitate treatment, 222-224. precipitation, 212-216. INDEX 273 Bibliography for precipitation with aluminium, 215. electrolytic, 215. zinc-dust, 214. zinc-shaving, 213. preparation of ores for cyanide treatment, 145. regeneration of cyanide solution, 215. roasting, 145. separating solution and pulp, 201-205. silver mills in Canada, 265. Nevada, 263. Mexico, 264. silver ores, treatment of, 262. slime and sliming, 173. stamp mill accessories, 53. foundation and framework, 52. mechanism, 52. modified gravity, 105. single, 87. practice, California, 86. Gilpin County, 86. South Africa, 86. variations in, 86. steam-stamps, 105. tube-mills, 106. Black HiU stamp-drop sequence, 48. Blake rock breaker, 41. Blaisdell filter, 197. Blanton cam, 20. Boards, housing for mortar, 41. mortar cover, 41. Boss or boss-head, 14. Boss caAtilever battery-frame, 35. Bull-wheel, 21-22. Burt pressure-filter, 197. revolving filter, 197. Butters filter, 189-190. Butters-Moore filters, bibliography, 202. Cadmium amalgam, 66. California milling practice, 79, 80. bibliography, 86. stamp-drop sequence, 48. California, gold mills in, bibliography, 250. Cams, Blanton, 20. Cauda, 21. construction, 17-19. position of, 18. shaft, 21. 274 INDEX Camming, 49. Camp Bird mill, flow-sheet, 238. Canada, silver mills in, bibliography, 265. Canda cam, 21. Cast-iron battery-frame, 35. Centrifugal mills, 95. bibliography, 105. Centrifugal pump, agitation with, 165-166. Chalcocite, as a cyanicide, 150. Chalcopyrite, as a cyanicide, 150. Challenge ore-feeder, 43. Charging leaching tanks, 156-158. Chemical aids to amalgamation, 68. Chemical properties of gold, 3. of silver, 4. Chemistry of cyanidation, 127-133. bibliography, 135-136. Chilean mills, 95-96. crushing efficiency, 116. Christy, S. B., on cyanide reactions, 131. diagram showing effect of cyanide solutions, 146. Clancy process, 172. Classification and dewatering, 138-139. bibliography, 145. Classifier, Akiiis, 141. cone, 139. conveyor, 140. Dorr, 140. drag, 140. Cleaning battery-sand, 72. Cleaning plates, 70. Clean-up barrel, 64. Clean-up, battery, 71. Clean-up room, 72. Comparison, of wet and dry-crushing, 137-138. of filters, 199-201. of various mills, bibliography, 118. Compressed air, agitation with, 168-169. Concentrates, cyanidation of, bibliography, 267. Concentration, 141. Cone-classifiers, 139. Contact, grinding-, amalgamation by, 9, 11, 56. surface-, 10, 11, 56. immersion, 10, 11. Continuous agitation, 171. Contiguous filters, bibliography, 204. Conveyor classifiers, 140. Copper-ammonium cyanides, 132. INDEX 275 Copper as a cyanicide, 149. Costs, stamp milling, 83-86. bibliography, 266. Counter-current decantation, 181. Crushing, comparison of dry and wet, 137-138. for cyanide treatment, 137. efficiency, 110-112. of baU-mills, 114. Chilean mills, 114. gravity stamp, 114. grinding pans, 114. Huntington mills, 114. steam stamps, 114. tube-mills, 115. Cyanicides, 149-152. Cyanide, alkaline, 128. copper-ammonium, 132. double, 128. gold, 129. ionization, 131. metallic, 128. properties of, 129. silver, 129. solution of gold in, 130-132. use of, in amalgamation, 68. Cyanide solution, application of, in leaching, 160-162. regeneration of, 221. bibhography, 215. Cyaniding, history of, 123-127. chemistry of, 127-133. Cyaniding silver minerals, effect of various reagents in, 256. Cyanogen, compounds, 127-129. discovery of, 124. Daly Reduction Co., flow-sheet, 240. Decantation, 178-182. bibliography, 201. counter-current, 181. Desert mill, flow-sheet, 258. Dewatering, 138-139. Diehl process, flow-sheet, 246. Dies, stamp, 16. Diesbach, 123. Direct smelting of precipitate, 219-220. Discharging leaehing-tanks, 158-159. Dissolving gold and silver, 146-173. bibliography, 173-177. Dodge rock-breaker, 137. 276 INDEX Dorr agitator, 164. classifier, 140. Drag classifier, 140. Drive-pulley for stamps, 21. Duflos, 125. Edge-runner nulls, 95. Edwards roaster, 142-143. Effluent solution, treatment of, 220-222. Electric-current, precipitation with, 132, 211-212. bibliography, 215. Electrolytic amalgamation, 67. El Oro tube-mill lining, 98. Eisner reaction, 124, 131. Extra-solutions, 172-173. bibliography, 176. Faucett's patent on use of cyanide, 125. Feed throat, water service through, 45. Ferricyanide, use of, in amalgamation, 68. Ferrocyanide, use of, in amalgamation, 68. Filter, Blaisdell, 197. Burt pressure, 197-198. Burt revolving, 198. Butters, 189-190. Hunt, 192-194. Kelly, 197. Merrill, 183. Moore, 186-189. Oliver, 194^196. Portland, 194. Ridgeway, 190-192. Sweetland, 199. presses, 182. bibliography, 202. Filter-bottoms, 154^155. Filters, comparison of, 199-201. Butters-Moore, bibliography, 202. continuous, bibUography, 204. miscellaneous, bibliography, 205. pressure, bibhography, 204. Filtration, assisted gravity, 178. forced filtration, 182-199. gravity, 178. of precipitate, 210. Flouring of mercury, 11, 64. Flow-sheet, Alaska-Treadwell mill, 232. Desert mill, 258. INDEX 277 Flow-sheet, Goldfield Cons, mill, 241. Great Boulder Co. mill, 245. Montgomery-Shoshone mill, 239. New York and Honduras Rosario mill, 261. North. Wash. P. & R. Co. mill, 244. Oroya Brownhill Co. mill, 246. Pittsburg-Silver Peak mill, 235. Round Mt. M. Co. mill, 231. San Rafael, Paohuca mill, 259. South African type mill, 233. Trinity G. M. & R. Co., 243. Wasp No. 2 mill, 242. Forced filtration, 182-199. Foundation of stamp-miUs, 25-29. Frame, battery, 29. "A" type, 30. back-knee, 30. Boss cantilever, 35. cast-iron, 35. front-knee, 31. Goldfield consoUdated, 34. steel, 34. wooden, 29. Frames, screen, 40. Front-knee battery-frame, 31. Fvumaces, roasting, 142. Edwards, 142. melting, 75, 219. Merton, 143. retort, 75. Galena, as a cyanicide, 151. Gay-Lussac, discovery of cyanogen, 124. Gilpin county milling practice, 81. bibhography, 86. stamp-drop sequence, 48. Gold, amalgams of, 8. cyanides of, 129. occurrence, 3. metallurgical properties, 4. physical and chemical properties, 3. precipitation of, 132, 133. Solution of, in cyanide, 130-132. Gold mills in California, bibliography, 250. in Colorado, bibliography, 247. in Mexico, bibliography, 253. miscellaneous, bibliography, 254. in Nevada, bibhography, 248-249. 278 INDEX Gold mills in S. Africa, bibliography, 252-253. S. Dakota, bibliography, 250. various countries, 251. various states, 247-248. W. Australia, 252. Gold ores, treatment of, 227-246. bibliography, 247-254. Goldfield consolidated mill, battery-frame, 34. flow-sheet, 241. Grade ot plates, 58. Gravity-filtration, 178. assisted by pressure, 178. assisted by suction, 178. Gravity stamps, crushing efficiency, 116. modified, 88. Behr, 88. Holman, 88. , Morison, 88. Great Boulder G. M. Co; flow-sheet, 245. Grinding-contact, amalgamation by, 9, 11. Grinding-pans, 92. bibUography, 105. crushing efficiency, 116. Grothe, A., on agitation with air, 168-169, 170-171. Guides, stamp, 36-38. Gyratory rock breakers, 41. Hagen, on cyanide, 123. Hahn, solubiUty of gold and silver sulphide, 12S, Hanging-up stamps, 38. Hardinge pebble-mill, 100. Head, stamp, 14. Hendryx agitator, 165-166. History of cyaniding, 123-127. bibliography, 133. Holman pneumatic stamp, 88. Hose and float, decantation with, 179. Hunt filter, 192-194. Huntington mill, 93-95. crushing efficiency, 116. Hydrocyanic acid, 127. Immersion-contact, amalgamation by, 10-11. Individual stamps, 82. bibUography, 55. Inside amalgamation, 56. Intermittent agitation, 171. Ionization of cyanide by gold and pyrite, 131. Iron as a oyanicide, 149. INDEX 279 Julian and Smart, 128, 130, 146, 147, 162. KeUy filter, 197. Labor, stamp mill, 84. Leaching, 152-163. bibliography, 173. effect of slime on, 162. Leaching tanks, 152-154. charging, 156-158. discharging, 158-159. size of, 154. time of treatment in, 171. Lead as a cyanicide, 149. Lip-plates, 60. Lluvia de Oro, filtering precipitate at, 210. Lubrication, stamp miU, 47. MaoArthur-Forrest patents, 126-127; Marcasite as a cyanicide, 150. Masonry and concrete tanks, 154. Mechanical-stirrer agitators, 163-166. Melting bullion, 75. Melting furnaces, 219. Mercury {see quicksilver), care of, 63. cyanicide, 150. / flouring of, 11, 64. - loss of, 63. sickening, 11, 64. traps, 11. Merrill press, 182-186. zinc-dust feeder, 209-210. Merton furnace, 143-144. Metallic cyanides, 128. Metallurgical properties of gold, 4. of silver, 5. Mexico^ gold mills in, bibliography, 253. silver mUls in, bibliography, 264. Michigan steam-stamps, 88. MilUng and cyaniding costs, bibUography, 266-267. Mill, baU, 96. bibliography, 108. crushing efficiency, 116. centrifugal and edge-runner, 93-96. bibliography, 105. Chilean, 95-96. bibliography, 105. crushing efficiency, 116. 280 INDEX Mill, Huntington, 93-95. crushing efficiency, 116. Hardinge pebble, 100. crushing efficiency, 117. stamp, and accessories, 13-51. bibliography, 51-55. practice, variations in, 79-86. bibliography, 86-87. steam-stamp, 88. bibliography, 105. tube-, 96-100. pebble action in, 99. bibhography, 106-108. Mineral acids, as cyanicides, 149. Mispickel as cyanicide, 150. Modffied gravity stamps, 88. Montana-Tonopah mill, flow-sheet, 259. Montgomery-Shoshone mill, flow-sheet, 239. Moore filter, 186-189. bibliography, 202. Morison, modified gravity-stamp, 88. Mortar, the stamp mill, 13-23. Mortar-blocks, 25-29. concrete, 27-29. with anvil-blocks, 29. wooden, 25-27. Molds, pouring-, 75. Nevada, gold miUs in, bibliography, 248-249. silver mills in, bibhography, 263. New York and Honduras Rosario miU, flow-sheet, 261. North Washington P. & R. Co. miU, flow-sheet, 244. Occurrence of gold, 3. of silver, 5. Oliver filter, 194^196. Ore-feeders, 41-44. challenge, 43. suspended, 44. Tulloch, 42. Orpiment, as cyanicide, 151. Outside amalgamation, 57. Overhead track and crawl, 38. Oxidizers, effect of, in cyanidiag, 172-173. bibhography, 176. Pachuca agitator, 169-170. Pans, grinding, 92. INDEX 281 Pans, grinding, bibliography, 106. Parral tank, 169-171. Pebble action in tube-miU, 99. Pebble-miU, Hardinge, 100. Physical aids to amalgamation, 69. Physical properties of gold, 3. of silver, 4. Pittsburg-Silver Peak mill, flow-sheet, 235. Plate, apron, 69. frame, 62. grade or slope, 58. Up, 60. materials, 62. splash, 61. steaming at Treadwell, 70. Portland filter, 194. Pneumatic stamp, Holman type, 88. Position of apron plates, 61-62. cams, 18. Pouring-molds, 75. Power required for stamps,- 50. cost, 83. Precipitate, cyanide, recovery and treatment of, 217-222. bibUography, 222-224. acid treatment, 218. direct smelting process, 219. roasting method for, 219. Precipitation of gold and silver, 132-133, 206-212." bibhography, 212-215. with aluminium, 133. bibliography, 215. electrolytic, 132, 211-212. bibUography, 215. Siemens-Halske, 211. treatment of solution after, 220-222. with zinc dust, 208-211. bibUography, 214. with zinc shaving, 206-208. bibUography, 213. Preparation of ores for cyanidation, 137-146. bibUography, 145. Presses, filter, 182-183. Merrill, 183-186. Pressure filters, bibUography, 204. Prussic acid, isolation of, 123. Pulp-distributor, 157. Pyrite, as cyanicide, 150. electrolytic action with gold, 131. 282 INDEX Quicksilver (see mercury), care of, 63. Read, T. T., on amalgams, 8, 69. Realgar, as cyanicide, 151. Recovery and treatment of precipitate, 217-222. bibliography, 222-?24. Regeneration of cyanide solutions, 222. bibliography, 215. Repairs, stamp mill, cost of, 84-85. Retorting amalgam, 73. Revolving filter, Burt, 197. Ridgeway filter, 190-192. Rickard, T. A., 11, 48, 84. Roasting, pre-cyanide, 142-145. ' bibUography, 145. Roasting furnace, Edwards, 142-143. Merton, 143-145. Roasting, treatment of precipitate, 219. Rock breakers, 41. Rolls, crushing, 41. Round Mountain Mining Co. mill, flow-sheet, 231. Sand, gravity filtration for, 178. Sand-slat filter, 155-156. Sanders, patent on use of cyanide, 125. Scheele, isolation of prussic acid, 123. Scseen frames, 40. Screens, stamp-mill, 39-40. burr-punched, 39. clear-punched, 39. pimched, 39. round-hole, 39. slot, 39; woven, 40. Searwater, used in Trfeadwell mills, 68. Semple, Clarence G., Merrill press, 183-186. Shaft, cam, 21. Shaking copper-plate, 62. Sharwood, W. J., on zinc-dust, 209. Shapes and sizes of gold particles, 148-149. Shoe, stamp-, 15. Sickening, of mercury, 64. Silver amalgams, 8. cyanides, 129. metallurgical properties, 5. occurrence, 5. physical and chemical properties, 4. precipitation, 132-133, 206-212, INDEX 283 Silver precipitation, bibliography, 213-216. Silver mills, bibliography, 263-265. flow-sheets, 258, 259, 261. in Canada, bibliography, 265. in Nevada, bibUography, 263. in Mexico, bibliography, 264. Silver minerals, 5. solubility of, 255. Silver ores, treatment of, 255-261. bibUography, 262-265. Siemens-Halske, precipitation, 211. Simpson, Jerome W., cyanide patent, 125. Skey, on use of cyanide in amalgamation, 125. Slime, 162: decantation treatment of, 178-182. effect of, in leaching, 162. filtering devices, comparison of, 199. forced filtration for, 182-199. Slime and sliming, bibliography, 173. Sluice plates, 61. Sodium amalgam, 66. Solution cyanide, treatment after precipitation, 220-222. Solution of gold in cyanide, 130. Solvent power of cyanides, 128. on various metals, 147. South African type of mill, flow-sheet, 233. South African stamp practice, 81. bibUography, 86. gold mills, bibUography, 252-253. South Dakota, gold mOls, bibUography, 250. Sphalerite as cyanicide, 151. Splash-boards, 40. Splash-plates, 61. Strength of (cyanide) solution, 146-148. Stamp-drop, height, 49. sequence, 48. speed of, 49. Stamp-boss, 14. dies, 16. guides, 36-38. shoe, 15. stem, 14. tappet, 15. Stamp miU and its accessories, 13-51. bibUography, 51-55. Stamp mill amalgamation, 56-75. bibUography, 76-78, costs, 83-86. 284 INDEX Stamp mill foundation and framework, 26-38. bibliography, 52-53. labor, 84. lubrication, 47. mechanism, 13-23. bibUography, 52. power, 50, 83. repairs, 84. starting the, 46. supplies, 84. Stamp practice, variations in, 7&-86. Stamps, individual, 82. modified gravity, 88. bibUography, 105.i steam, 88-90. bibliography, 105. crushing eflSciency, 116. Standard grades and screens, table of, 113. Steam-stamps, 88-90. Steaming amalgamating plates at Treadwell, 70. Steel, as cyanicide, 149. battery frames, 34. tanks, 153. Stem, stamp, 14. Stibnite, as cyanicide, 151. Suction, gravity-filtration assisted by, 178. Supplementary outside plates, 60. Surface contact, amalgamation by, 10-11. Suspended ore-feeders, 44. Sweetland filter-press, 199. Tanks, leaching, 152-156. charging, 156-158. masonry, 154. steel, 153. wooden, 152. Tappet, stamp, the, 15. Tellurides as cyanicides, 151. Tellurium as cyanicide, 150. Temperature of solutions, 148. Tetrahedrite, as cyanicide, 150. Tilting-type melting furnace, 219. Tire-type tube-mill, 97. Tavener process for precipitate, 220. Tremain steam-stamp, 90. Trent agitator, 167. Trinity Gold M. & R. Co. mill, flow-sheet, 243. Tube-mills, 96-100. INDEX 285 Tube-mills, bibliography, 106-108. crushing efBciency, 106. lining, El Oro, 98. pebble action in, 99. performances, table of, 101. Tulloch, ore-feeder, 42. Vacuum filters, 186-197. Variations in stamp-practice, 79-86. bibliography, 86-87. Wasp No. 2 mill, flow-sheet, 242. Water-service for stamp mill, 45. West Australia, gold mills in, bibliography, 252. Weights and dimensions of stamp parts, 17. Wood-fiber, as cyanicide, 149. Wooden battery-frame, 29. Wooden tanks, 152-153. Zinc amalgams, 66. boxes, 206-208. dust, precipitation with, 208-211. bibliography, 214. feeder, 209-211. shaving, precipitation with, 206-208. bibliography, 213.