Search Documents

By Fred K. Stieler

The largest updraft sinter machine built has a roasting area of 132 sq.m. Sinter machines with an area of over 200 sq.m. are under consideration. These large machines require new techniques with regard to drive thrust and sealing mechanism. To optimize the results of sinter plants, the charge preparation systems and the return fines circuits were improved. Special crushers were developed for crushing return sinter of up to 800 ºC to a size of minus 6 mm. Strand cooling of Pb-sinter was investigated. Different methods for plant ventilation were compared. New processes, which might replace sintering in the future, are in the stage of large - scale testing.

Jan 1, 1977

By A. W. Fahrenwald

The physics and chemistry of the flotation process are not well understood. Many papers dealing with the theory of flotation have been published but most have been narrow in their viewpoint. No theory advanced has done more than explain, more or less satisfactorily, various isolated phenomena. Scientists have done little with the problem, doubtless because they have not seen sufficient of the practical side of the subject to have their interest aroused. Any attempt to explain the mechanism of flotation that considers only contact angles, surface tension, adsorption, the floating of needles, flocculation, or any other single and narrow phase of the question is sure to be disappointing. Flotation is a problem of colloid chemistry and must be studied as such. In a broad general way, flotation is a process involving and operating by virtue of surface reactions. The term "surface reactions" may be open to criticisms. Many chemists give the term "reactions" a definite and restricted meaning and to such the term may connote change in atomic grouping in strict stoichiometric ratios. While Langmuir looks upon adsorption as a reaction, and there is much evidence in support of this view, we may look on adsorption as a physcial process as far as this paper is concerned. The term seems well suited to the work in general. Presumably these reactions are reactions between the same kinds of forces (electrical) and differ only in degree and in the surface manifestations produced. This premise seems logical if we accept the theory that the atoms of dl elements are made up of grains of electricity, having mass and charge, called electrons; and that atoms differ from one another only in the number and arrangement of the electrons about a positive nuclear

Jan 1, 1924

By T. W. Bossert

MELTING is the initial step in the fabricating of all aluminum and aluminum-alloy products. Its function may be considered as threefold: to improve the metal quality, to adjust the composition, and to change the form to that required for subsequent fabrication. Because the melting operation is generally somewhat removed from the final product fabrication, its importance is frequently overlooked. Melting equipment and melting procedures can reflect materially on fabricating procedures as well as on quality and cost of final product. The selection of equipment and the establishment and control of melting procedures, therefore, should be given careful consideration. It is the purpose of this paper to present the various factors that should be considered in establishing melting procedures and in selecting melting equipment. Certain of these are the result of the inherent characteristics of aluminum and can be treated rather specifically. Others depend on the particular production requirements and hence will have to be considered more generally. This paper is intended to cover only the melting of solids, as differentiated from fines, such as borings, turnings, and sawdust. The melting of fines, in many respects, is a subject that should be treated by itself, and practices for melting fines are by no means as standardized as are those for melting solids. The melting of fines is today the subject of considerable developmental interest; hence practices discussed today may soon be replaced by new or improved ones. CHARACTERISTICS OF THE METAL THAT AFFECT MELTING Aluminum and aluminum alloys possess several inherent characteristics that affect the melting problem. Of the physical properties, density, heat content, thermal conductivity, emissivity, and melting temperatures are important because of their effect on equipment design. A list of such properties for commercially pure aluminum is given in Table r, compared with similar properties for iron and copper. The low density of aluminum as well as of the aluminum alloys is of material advantage in the design of melting equipment, in that such equipment can be considerably lighter than similar equipment for handling the heavier metals. The density, however, particularly of the molten metal, is not greatly different from that of the oxides and other nonmetallic materials that develop or become part of the melt during the melting process. Separation of such nonmetallics is not as rapid a process as with some of the other metals, and consideration of this must be made in establishing melting procedures. Sufficient holding time to permit such materials to separate out and, in some cases, fluxing treatments to aid the separation, are required. Since some of these nonmetallics settle to the bottom of the melt, provision should also be

Jan 1, 1946

By Theodore Simons

During the last half century a great amount of ingenuity and energy has been devoted to the invention of appliances for the recovery of valuable minerals from very fine sands and slimes. The reason for this is that in almost every dressing plant the greatest losses of values, considered relatively as well as absolutely, occur in the treatment of slimes. The natural aim of mill operators to minimize these losses has in recent years received another impetus, from the fact that the gradually diminishing occurrence of high-grade ores makes a more intense recovery of values from existing resources absolutely necessary for profitable operation. The results of such attempts are found in the appearance of a great number of machines and appliances which make it profitable to-day to rework old clumps, containing the tailings of older processes. A constantly growing difficulty of obtaining skilled labor and the increase in wages made it prohibitory to employ those types of machines which required much attention, and in the middle of the ninieteenth century the various concentrating tables of the percussion type, which automatically discharge their products, began to take the place of the intermittent tables, on which, when the bed had reached a certain thickness, operation had to be stopped in order to allow the skimming by hand of the separate layers formed on the table. In the course of years, two general types of machines evolved for the treatment of fine sands arid slimes: The so-called concentrators and vanners, on the one hand, and the buddles and round tables on the other.' For the profitable treatment of the very finest slimes, round tables have as a last resort proved more satisfactory and econoillical than other machines. In recent years they have agaiu become the subject of close inves-

Jan 1, 1914

By M. E. Wadsworth, L. H. Raby, A. S. Peck

Infrared spec troscopy was used to study the adsorption of oleate collector on three varieties of hematite. Each of the minerals was found to react with either oleic acid or a solution of sodium oleate to form a mineral cation-collector anion chemisorbed layer at the solid-liquid interface. The chemisorption reaction displaced surface hydroxyls and was found to be pH dependent. The infrared band characteristic of the antisymmetrical C = 0 structural group of chemisorbed oleate appears between 1520 and 1540 cm-'. Evidence is presented which shows that molecular filming of the mineral surfaces with un-dissociated oleic acid precedes chemisorption. Infrared absorbance is correlated with the flotation behavior of the mineral. Adsorption processes are usually classified into two types which are distinguished and character- ized by the nature of the bond formed between the adsorbate and adsorbent. The process in which molecules chemically bond to solid surfaces is termed activated adsorption or chemisorption. If only weak van der Waals forces bind the molecules to the surface then the process is termed physical adsorption. Chemisorption is of primary interest in flotation systems since selectivity may be obtained if a single mineral is rendered air-avid by a specific collector mineral adsorption reaction. In previous studies infrared spectroscopy was used to define the mechanisms involved in the adsorption of oleic acid and sodium oleate on fluorite, barite, and calcite. Infrared techniques were particularly useful since adsorbed monolayers were identified in situ. Further, the infrared method permitted identification of reaction products in the solid, liquid, and vapor phases of the systems. The chemisorption reactions displaced F- from fluorite, SO4 from barite, and CO3 from calcite. This investigation was pursued in an effort to characterize and interpret the adsorption processes for synthetic hematite, compact red hematite, and specular hematite (crystalline hematite). Adsorption tests were performed using either oleic acid or

Jan 1, 1967

By J. M. Callow

THE results obtained by pneumatic flotation throughout the country on all classes of ore, and. the tonnage now being treated by this particular method, speak for themselves. Its advantages over the so-called agitation process are now established by facts and data from practice. The comparative efficiency of a rapidly revolving paddle, as a means for aerating an ore pulp, and of a cycloidal or turbine blower for the same purpose, would seem to be so obvious as to leave no room for discussion. Practitioners in this art are to be congratulated on the acquisition of the valuable literary contributions that have recently been made on the theory of. flotation by Messrs. Ralston, Van Arsdale, Taggart and Beach, and others, and the very valuable and able articles, by Messrs. Laist and Wiggin on "Flotation Concentration at Anaconda, Mont.," by, Dr. Rudolf Gahl- on the "History of Flotation at Inspiration," and by David Cole on "The Advent of Flotation in the Morenci District." It is not within the province of this article to attempt an answer to the various issues raised in regard to the theory, or to defend the one advanced by me a year ago. But since discussion usually benefits the profession, a reply will be made to some of the statements made by the last-named writers. COMPARATIVE SENSITIVENESS AND ATTENDANCE Concerning 'the article, "Flotation Concentration at Anaconda, Mont.," by Laist and Wiggin, a little explanation is in order. It should be stated that; with the exception of about 24 days at the end of the testing 'period, the Callow experimental plant at Anaconda was not run under my direction. This perhaps accounts for some of the conclusions drawn on page 562 of the descriptive paper. The conclusion that the use of acid seems to be of considerable advantage, calls, for some comment. While the tests conducted by the Anaconda Copper Co. do show acid to be, of considerable benefit, this is a consequence of using acid sludge as a flotation agent. My belief has always been that the Anaconda

Jan 2, 1917

By Ancel St. John

Defects in the interior of metal objects are troublesome to both manufacturer and user. For the former, they frequently increase manufacturing cost through the rejection of material when defects appear after considerable work has been done. For the latter, they often cause damage to equipment, personal injury, or loss of life when a part, which has passed all inspections and has been put in service, gives way because of a hidden flaw. Methods of testing that locate such flaws without subjecting the specimen to possible, if not actual, destl-uction are few; x-ray examination, whether fluoroscopic or radiographic, is one. Hitherto, however, x-ray examination has been restricted to objects of nearly uniform thickness and regular outline; the inspection of such articles as those shown in Fig. 1 has been inconvenient and unsatisfactory. This figure represents a group of 5/16-in. hexagonal-head machine bolts,

Jan 1, 1923

By Ancel St. John

Defects in the interior of metal objects are troublesome to both manufacturer and user. For the former, they frequently increase manufacturing cost through the rejection of material when defects appear after considerable work has been done. For the latter, they often cause damage to equipment, personal injury, or loss of life when a part, which has passed all inspections and has been put in service, gives way because of a hidden flaw. Methods of testing that locate such flaws without subjecting the specimen to possible, if not actual, destl-uction are few; x-ray examination, whether fluoroscopic or radiographic, is one. Hitherto, however, x-ray examination has been restricted to objects of nearly uniform thickness and regular outline; the inspection of such articles as those shown in Fig. 1 has been inconvenient and unsatisfactory. This figure represents a group of 5/16-in. hexagonal-head machine bolts,

Jan 1, 1923

By G. Van Esbroeck, M. Van Weyenbergh

The copper mines of the Katanga region in the Belgian Congo lie along the same mineralized belt as those of Northern Rhodesia. There are two distinct types of deposits in that belt, the dolomitic and the quartzitic. In the dolomitic type the metallic minerals are found in a dolomitic limestone country rock. Through oxidation and enrichment, large deposits of high-grade oxidized copper ores were formed, some of which are being worked by the Union Minière du Haut Katanga. Such deposits are all in Katanga. The quartzitic deposits are found in Katanga and Northern Rhodesia. Here the primary mineralization occurred in sandstones and quartzites, in horizons stratigraphically lower than the dolomites. These rocks are not favorable to secondary enrichment and the oxidized zone is poorer than the sulphide zone, which alone contains the ore. There are also in Katanga a few ore-bearing veins. One of them is being worked in the Prince Leopold mine at Kipushi. Prince Leopold Mine The Kipushi ore body fills a fault vein and invades the wall rocks more or less extensively by metasomatic replacement. The vein strikes north-northeast and south-southwest and dips to the west. The variable dip averages 60' to a depth of 300 ft., and more uniformly 80' below 400 ft. In the upper section the average width is 200 ft. and below the width is about 150 ft. The length of the ore body is 2300 feet. The eastern side of the vein—the footwall—is dolomitic and contains irregular masses of ore sometimes extending 100 ft. or more from the main

Jan 1, 1940

By M. Van Weyenbergh, G. Van Esbroeck

The copper mines of the Katanga region in the Belgian Congo lie along the same mineralized belt as those of Northern Rhodesia. There are two distinct types of deposits in that belt, the dolomitic and the quartzitic. In the dolomitic type the metallic minerals are found in a dolomitic limestone country rock. Through oxidation and enrichment, large deposits of high-grade oxidized copper ores were formed, some of which are being worked by the Union Minière du Haut Katanga. Such deposits are all in Katanga. The quartzitic deposits are found in Katanga and Northern Rhodesia. Here the primary mineralization occurred in sandstones and quartzites, in horizons stratigraphically lower than the dolomites. These rocks are not favorable to secondary enrichment and the oxidized zone is poorer than the sulphide zone, which alone contains the ore. There are also in Katanga a few ore-bearing veins. One of them is being worked in the Prince Leopold mine at Kipushi. Prince Leopold Mine The Kipushi ore body fills a fault vein and invades the wall rocks more or less extensively by metasomatic replacement. The vein strikes north-northeast and south-southwest and dips to the west. The variable dip averages 60' to a depth of 300 ft., and more uniformly 80' below 400 ft. In the upper section the average width is 200 ft. and below the width is about 150 ft. The length of the ore body is 2300 feet. The eastern side of the vein—the footwall—is dolomitic and contains irregular masses of ore sometimes extending 100 ft. or more from the main

Jan 1, 1940

By S. B. Christy

The fact that many millions of gold have been extracted by the cyanide process, during the last five or six years, from South African tailings which could not be profitably worked by any other method previously tried upon them, lends a peculiar practical interest to this branch' of metallurgy. Numerous writers have recently made valuable contributions on the process without exhausting the many complexities of the subject. Among the first American writers on the subject in its modern aspect were two former students of the University of California, Mr. Louis Janin, Jr., and Mr. Charles Butters. Young Janin was one of the first to enter this field, and performed much useful experimental work in the early stages of the history of the process. At about the same time, Mr. Charles Butters, who had left California to erect chlorination works for the Robinson mine at Johannesburg, became interested in the cyanide process, and, after getting the chlorination plant in working order, put up, for working the tailings from the Robinson mine, a cyanide plant which achieved the first large-scale success ever made with this process. The papers which Charles Butters, together with John E. Clennell and Edgar Smart, have contributed on the chemistry of the process, were among the first to give any adequate idea of its nature.* Another important contribution to the literature of the subject is the paper of Dr. A. Scheidell, published in 1894 as a " Bulletin of the California State Mining Bureau." This contains an admirable summary of the state of the art at the time of its publication.

Jan 1, 1897

By Dorsey A. Lyon, Robert M. Keeney

The utilization of hydro-electriic power in electro-metallurgical industries, aside from purely mechanical operations, may be of two kinds. The electric energy may be used to supply the heat necessary for the performance of the chemical reactions of a metallurgical process, or the electrolytic action of a direct current may be employed for extraction of metals, either in a reduction process or a refining process. In discussing this subject, it is well to distinguish between established industries, which are producing metals and alloys at a, profit by use of the electric current, and the many processes which are either still in the experimental stage or have not even passed the paper stage of development of a patent. That is, we consider electro-metallurgical industries as commercial operations which are now consuming large blocks of electric energy, while processes which are not in commercial operation are only prospective consumers. Also, owing to the difliculty and risk of any attempt to foresee the effect of the European war upon electro-metallurgical industries, we have felt obliged to disregard the war entirely, and state our opinions regardless of its existence. Application of Electric Energy to Metallurgy Disregarding electrolytic refining processes, the applications of electric energy to metallurgy, when considered from a commercial viewpoint, may be classified as follows: Industries Experimental Processes Manufacture of aluminum Electric-furnace smelting of: Electric-furnace manufacture of: Ferro-alloys Copper ore Pig iron Zinc ore Steel In this paper only the above industries and experimental processes will be considered as possible consumers of hydro-electric power in large quan-

Jan 1, 1916

(There are 70 Student Chapters in the United States, 2 in Canada) University of Alabama-University, Alabama, Mining and Metallurgical Society, Win L Mason University of Alaska-College, Alaska, Mining Society of the University of Alaska, E H Beistline University of Arizona-Tucson, Arizona, Miners Society Birmingham-Southern College-Birmingham, Alabama, Pick and Hammer Club, Daniel D Arden University of British Columbia-Vancouver, British Columbia, G M Dawson Club, H C Gunning University of California-Berkeley, California, Mineral Technology Association, W H Somerton Carnegie Institute of Teehnology-Pittsburgh, Pennsylvania, The Metals Club, Gerhard Derge Case Institute of -Technology-Cleveland, Ohio, Case Metallurgical Engineering Society, Robert F Hehemann

Jan 1, 1956

By Hans Lundberg

By electrical prospecting, orebodies that do not otherwise manifest themselves at the surface may be located. Conditions favorable to success with the methods are: Favorable geological conditions, such a proportion of minerals of good electrical conductivity in the orebody as will render the latter materially a better conductor than the enclosing rock, situation of the orebody within the range of influence of the electrical currents used and in proportion to this range a sufficient area of horizontal cross section of the orebody. The result is to permit of spotting drill holes accurately and to save the expense of drilling barren ground. THE art of prospecting, like other branches of mining, has developed rapidly during the last ten years, mainly because of the advancement of mining geology, but also because of the development of "geophysical methods," which are based on the different physical characters of minerals and rocks, e. g., specific gravity, elasticity, and magnetic and electric properties. These methods have proved of great value, especially in countries where the rock is covered by soil and direct geologic investigation is out of the question. In prospecting for orebodies, the methods based on studying differences in electrical conductivity have proved most successful; for which reason, the methods of electrical prospecting have been subject to the most energetic and systematic work, especially in Sweden. This paper gives a brief description of the methods of electrical prospecting now in use, especially the new electromagnetic methods, which have not been described before. The great differences in the electrical properties, especially in conductivity, between ore minerals and rock minerals are fundamental to all methods of electrical prospecting, for which reason, the electrical conductivity of ore minerals and rock minerals has been carefully studied in connection with and previous to the development of the various methods of prospecting with electricity. Ore minerals with a metallic luster, such as chalcopyrite, iron pyrite, galena, specular iron, magnetite, etc., also graphite and a number of cows, have considerably higher conductivity than the surrounding rock and soil (see Table 1). The figures of the table denote the specific resistance W, expressed in ohms for a cube with an edge of 1 centimeter.

Jan 7, 1925

New York Meets first Wednesday after first Tuesday of each month. DAVID' H. BROWNE, Chairman. JOHN H. JANE WAY, Vice-Chairman. F. E. PIERCE, Secretary, 35 Nassau St., New York, N. Y. P. A. MOSMAN, Treasurer. LEWIS W. FRANCIS. BENJAMIN B. LAWRENCE. Boston Meets first Monday of each winter month. HENRY L. SMYTH, Chairman. ALFRED C. LANE, Vice-Chairman. HENRY A. WENTWORTH, Secretary-Treasurer, 60 India St., Boston, Mass. A. H. EUSTIS, F. G. STANTIAL. Columbia Holds four sessions during year. Annual meeting in September or October. STANLY A. EASTON. Chairman. FREDERIC KEFFER, Vice-Chairman. LYNDON K. ARMSTRONG, Secretary-Treasurer, P. O. Drawer 2154, Spokane, Wash.

Jan 3, 1916

By E. H. Dix

All commercial aluminum contains small percentages of copper, iron, and silicon as unavoidable impurities. The purest metal obtainable commercially, special grade high purity ingot, contains a maximum of 0.50 per cent. impurities of which the usual minimum amount of copper is 0.01 per cent.; silicon, 0.12 per cent.; and iron, 0.20 per cent. This grade is too costly for most purposes. The two standard grades, Nos. 1 and 2, containing a minimum of 99.0 and 98.0 per cent. aluminum, respectively, are more generally used. Other grades of secondary aluminum often contain as high as 3 or 4 per cent. of impurities, which include 1 per cent., or more, of zinc. Specifications for high-grade aluminum-casting alloys generally allow a maximum of 1.7 per cent. for total impurities. The S. A. E. Specification No. 33, which is intended to cover alloys made from secondary aluminum ingot, gives the iron maximum as 1.5 per cent. and the maximum for silicon (including manganese and tin) as 0.75 per cent. The effect of even relatively small amounts of impurities on the physical properties of ingot aluminum is shown by the following cornparison of two lots of aluminum, which may be taken as representative of special grade and grade No. 2 ingot, respectively. AnalysEs Special Grade, Gbade No. 2, Per Cent. PeR CBnt. Copper................................. 0.01 0.32 Silicon................................. 0.12 0.32 Iron................................... 0.42 0.82 Aluminum.............................. 99.45 98.54

Jan 1, 1923

By E. H. Dix

All commercial aluminum contains small percentages of copper, iron, and silicon as unavoidable impurities. The purest metal obtainable commercially, special grade high purity ingot, contains a maximum of 0.50 per cent. impurities of which the usual minimum amount of copper is 0.01 per cent.; silicon, 0.12 per cent.; and iron, 0.20 per cent. This grade is too costly for most purposes. The two standard grades, Nos. 1 and 2, containing a minimum of 99.0 and 98.0 per cent. aluminum, respectively, are more generally used. Other grades of secondary aluminum often contain as high as 3 or 4 per cent. of impurities, which include 1 per cent., or more, of zinc. Specifications for high-grade aluminum-casting alloys generally allow a maximum of 1.7 per cent. for total impurities. The S. A. E. Specification No. 33, which is intended to cover alloys made from secondary aluminum ingot, gives the iron maximum as 1.5 per cent. and the maximum for silicon (including manganese and tin) as 0.75 per cent. The effect of even relatively small amounts of impurities on the physical properties of ingot aluminum is shown by the following cornparison of two lots of aluminum, which may be taken as representative of special grade and grade No. 2 ingot, respectively. AnalysEs Special Grade, Gbade No. 2, Per Cent. PeR CBnt. Copper................................. 0.01 0.32 Silicon................................. 0.12 0.32 Iron................................... 0.42 0.82 Aluminum.............................. 99.45 98.54

Jan 1, 1923

By N. F. Dyson, T. R. Scott

The iilzfluence of catalytic agents on the oxidation of ZnS has been studied under pressure leaching conditions, using a chemically prepared sample of ZnS which was substantially unreactive on heating at 113°C with dilute sulfuric acid and 250 psi oxygen. Nurnerous prospective catalysts were added at the ratio of 0.024 mole per mole ZnS in the above reaction but pvonounced catalytic activity was confined to copper, bismuth, rutheniuwl, molybdenum, and iron in order of. decreasing effectiveness. In the absence of acid, where sulfate was the sole product of oxidation, catalysis was exhibited by copper and ruthenium only. Parameters affecting the oxidation rate were catalyst concentration, temperature, time, oxygen pressure, and a7riount of acid, the first two being most important. The main product of oxidation in the acid reaction was sulfur, with trinor amounts of sulfate. An electrochemical (galvanic) mechanism has been suggested for the sulfuv-forming reaction, whereby the relatively inert ZnS is "activated" by incorporation of catalyst ions in the lattice and the same catalysts subsequently accelerate the reduction of dissolved oxygen at cathodic sites on the ZnS surface. Insufficient data was obtained to Provide a detailed mechanism for sulfate fornzation, which is favored at low acidities and probably proceeds th'rough intermediate transient species not identified in the preseni work. THE oxidation of zinc sulfide at elevated temperatures and pressures takes place according to the following simplified reactions: ZnS + io2 + H2SO4 — ZnSO4 + SG + HsO [i] ZnS + 20,-ZSO [21 In dilute acid both reactions occur but Reaction [I] is usually predominant, whereas in the absence of acid only Reaction [2] can be observed. Both proceed very slowly with chemically pure zinc sulfide but can be greatly accelerated by the addition of suitable catalysts, as suggested by jorling' in 1954. Nevertheless, an initial success in the pressure leaching of zinc concentrates was achieved by Forward and veltman2 without any deliberate addition of catalytic agents and it was only later that the catalytic role of iron, present in concentrates both as (ZnFe)S and as impurities, was recognized and eventually patented.3 It is now apparent that another catalyst, uiz., copper, may have also played a part in the successful extraction of zinc, since copper sulfate is almost universally used as an activator in the flotation of sphalerite and can be adsorbed on the mineral surface in sufficient amount The importance of catalysis in oxidation-reduction reactions such as those cited above has been emphasized by various writers and Halpern4 sums up the situation when he writes that "there is good reason to believe that such ions (e.g., Cu) may exert an important catalytic influence on the various homogeneous and heterogeneous reactions which occur during leaching, particularly of sulfides, thus affecting not only the leaching rates but also the nature of the final products." Nevertheless relatively little work has appeared on this topic, one of the main reasons being that sufficiently pure samples of sulfide minerals are difficult to prepare or obtain. When it is realized that 1 part Cu in 2000 parts of ZnS is sufficient to exert a pronounced catalytic effect, the magnitude of the purity problem is evident. An incentive to undertake the present work was that an adequate supply of "pure" zinc sulfide became available. When preliminary tests established that the material, despite its large surface area, was substantially unreactive under pressure leaching conditions, the inference was made that it was sufficiently free from catalytic impurities to be suitable for studies in which known amounts of potential catalytic agents could be added. The first objective in the following work was to identify those ions or compounds which accelerate the reaction rate and, for practical reasons, to determine the effects of parameters such as amgunt of catalyst, temperature, time, acid concentration, and oxygen pressure. The second and ultimately the more important objective was to make use of the experimental results to further our knowledge of the reaction mechanisms occurring under pressure leaching conditions. The fact that catalysts can dramatically increase the reaction rate suggests that physical factors such as absorption of gaseous oxygen, transport of reactants and products, and so forth, are not of major importance under the experimental conditions employed and an opportunity is thereby provided to concentrate on the heterogeneous reaction on the surface of the sulfide particles. As will appear in the sequel, the first of these objectives has been achieved in a semiquantitative fashion but a great deal still remains to be clarified in the field of reaction mechanisms. EXPERIMENTAL a) Materials. The white zinc sulfide used was a chemically prepared "Laboratory Reagent" material (B.D.H.) and X-ray diffraction tests showed it to contain both sphalerite and wurtzite. The specific surface area, measured by argon absorption at 77"K, varied between 3.9 and 4.6 sq m per g. Analysis gave 65.0 pct Zn (67.1 pct theory) and 31.9 pct S (32.9 pct theory). Other metallic sulfides (CdS, FeS, and so forth) used in the experiments were also chemical preparations of "Laboratory Reagent" grade. Samples of mar ma-

Jan 1, 1969

By A. N. Mitinsky

Discussion of the paper of A. N. MITINSKY, presented at the San Francisco meeting, September, 1915, and printed in Bulletin No. 104, August, 1915, pp. 1697 to 1705. LAWFORD H. FRY, Burnham, Pa. (communication to the Secretary*). -The author assumes that the proportional limit and the elastic limit are coincident or very nearly so, and then further assumes that the stress corresponding to these two points is the least stress which if repeated will cause failure. The point is extremely interesting and it is to be regretted that the author did not quote experimental data to show the relation between the limit of repeated stress and the other properties of the material. The author's suggestion that a steel of poor quality may have a normal value for the yield point and tensile strength (see Fig. 2) and an abnormally low elastic limit, and that this will correspond to a low resistance to repeated stress, may account for a number of failures of axles in which the tensile tests show normal physical properties. If so and if a determination of the proportional limit would have eliminated the material before it was put into service, this determination will merit most earnest attention. It appears, however, that considerable further research is necessary before any definite conclusion as to the quality of a steel can be drawn from its proportional limit. Mr. Mitinsky's paper is extremely interesting and if it stimulates thought and work along the lines indicated, it may prove of considerable practical benefit. H. V. WILLE, Philadelphia, Pa.-The paper discusses the difference between the proportional limit, or elastic limit, and the yield point, and refers to the fact that much harm results from confusion of the terms yield point and elastic limit. Similar confusion has arisen in this country; the American-Society for Testing Materials does not even consider the elastic limit and proportional limit to be identical and recently adopted the following definitions:

Jan 12, 1915

By Nathaniel Arbiter, Norman L. Weiss

Factors now accelerating the trend to larger concentrators and larger equipment units are reviewed. After almost 40 years of stability with unit sizes less than 100 cu ft, 200 and 300-cu-ft flotation-cell units are now operating and a 500-cu-ft machine is being built. The design of these cells is considered, as is the design and operation of flotation circuits against the background of the need to achieve greater process efficiency while holding down operating and investment costs. Particular attention is paid to the scale-up problem. With the newer cells having five to ten times higher unit capacities, the advantages resulting from this in sampling, mill operation nnd control, testing and plant layout are indicated, as well as the broad direction for changes in the overall design of 50,000 to 100,000-tpd concentrators. A comparison is given of the available larger cells of U.S. manufacture with analysis of differences and similarities. After almost 60 years of application in this country, froth flotation is still by far the most important process for concentrating metallic ores as well as a number of nonmetallic ores including fluorspar, phosphate rock, and potash. Its use on iron ores and coal is increasing. In the metals groups, the largest plants and the greatest progress are found in copper and molybdenum mills, and the section of this paper that deals with applications will be found most pertinent to that field. During its long reign, the flotation process has passed through several phases of evolution and has achieved progress in economy, efficiency. and simplicity of operation. Much of today's success in the flotation of low-grade ores can be attributed to that progress. Even more important to us than our ability to cope with today's conditions are tomorrow's problems, which we can contemplate with some prescience and confidence. Our annual production of copper, lead, zinc, and molybdenum—to mention only the most important metals occurring in the U.S. as sulfides- must be held at a high level in the face of a declining grade of ore. It is probable that the tonnage of such ores mined and processed will double in this country before the turn of the century. Not only will many of the existing flotation mills be enlarged again and again, but larger mills will be built here and abroad to meet our needs. At this moment, in fact, there are at least three proposed new foreign mills or expansions that envision 100,000-tpd milling rate on copper ores. Table 1' shows the trend in copper ore grades in U.S. in recent years. Table 2' shows the projected annual growth rate of consumption 1966-1985. A study by one of the authors 25 years ago showed that of 32 copper mills in North America with more than 100-tpd capacity, only eight had capacities exceeding 10,000 tpd. The average for these eight was 25,000 tpd. These included the three giants of that day, Magna, Arthur, and Morenci; the other five averaged a little over 10,000 tpd. Today instead of the eight mills with capacities exceeding 10,000-tpd capacity we have 25, and the mill with less than 1000-tpd capacity is fast becoming extinct. Much less range is found in lead and zinc mills, which are still generally small except for the few with over 1000-tpd capacity in Missouri, Utah, and Idaho, and a few zinc ore mills in the same size category. Molybdenum and potash operations are the fastest growers in North America today, but when one considers the projected increase in consumption of copper together with the projected decrease in grade of ore (3% annually), he can foresee that copper ore milling will soon lead the list. Technological improvements to meet the challenge of lower-grade ores have taken the wholly predictable path toward bigger equipment. In mining, shovels, draglines, scrapers, and trucks have led the way; in ore processing, we have seen a rapid increase in size of grinding mills, flotation cells, and pumps. Twenty-five years ago, for example, the 10-ft-diam ball mills treating 2000 tpd at Morenci were considered the giants, but today some grinding mills in similar service have five times that capacity. The specific matters to be dealt with in this paper are 1) the underlying principles that affect flotation-machine design, and the conditions required to produce

Jan 1, 1971