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By J. E. Clennell

It is a common observation that the improvements introduced in practice since the first announcement of the cyanide process have been almost entirely mechanical. Although .a good deal of study land research has been devoted to the chemical problems [involved, the results obtained appear trifling in comparison. Few of the suggested modifications in the chemical treatment have come into practical use and those only in limited fields. Nevertheless, if we study the recent history of the cyanogen compounds from a somewhat broader standpoint, we shall find that considerable additions have been made, not only to our knowledge of their chemical properties, but also to their applications for industrial purposes. The present review of these advances naturally falls into two divisions: (1) processes involved in the treatment of ores; (2) manufacture of cyanides and other related compounds. Part I. Advances in the Chemistry of Ore Treatment by Cyanide In the attempt to extend the scope of the process, various ores have been encountered which contain gold and silver in such forms that they will not yield satisfactorily to ordinary methods of cyanide treatment. In some cases the difficulty is due to the excessive action on the solution of base metals present in the ore; in others, to the occurrence of minerals such as dyscrasite (the native alloy of antimony and silver), or a supposed oxidized manganese compound containing silver, which are either altogether insoluble in or very slightly attacked by cyanide. A particularly troublesome case is that of the so-called "graphitic" ores, containing carbon in some form which has the property of precipitating gold and silver already dissolved. Other efforts have been directed to improving extraction by electrolysis of working solutions, and by addition of various chemicals with or without electrolysis; to the diminution of cyanide consumption by "re-

Jan 1, 1916

By L. A. Tarshis, H. E. Cline

A stability criterion for a lamellar eutectic interface was derived previously1 assuming that the wavelength, A,. of the perturbation which grows most rapidly is much larger than the lamellar spacing. A. This assumption was required to permit averaging of both the interface temperature and composition over the complicated geometry of a lamellae. If this assumption is invalid, as has been suggested.2,3 then the problem becomes too complicated to solve completely. The first of these analyses1 did not calculate the wavelength. A,. of the initially unstable perturbation. whereas the more recent analysis.' which led to a contradiction of this assumption. did not include one of the key factors for determining this wavelength. To rigorously determine the wavelength, the effect of the curvature of the perturbed interface (not considered by either of the above treatments) must be included. By omitting this term, one would be led to an incorrect conclusion regarding the magnitude of A,. but to an accurate criterion for stability as evidenced by the excellent agreement with experimental observations.' In the case of single-phase alloys. the critical wavelength. A,. for instability can be calculated from the Mullins and Sekerka4 (M.S.) analysis which includes the effects of capillarity. In the following discussion, the M.S. analysis is applied to lamellar eutectics and the critical wavelengths calculated for reasonable growth conditions in Pb-Sn eutectic alloys. In order to apply the M.S. analysis to eutectics. one may substitute i) the effective liquidus slope.1 m*. for the single-phase liquidus slope and ii) the ratio of the bulk alloy composition. C,. to the average interface composition in the liquid (Ci = CE where CE is the equilibrium eutectic composition) for the distribution coefficient to give:

Jan 1, 1970

By John C. Smock

The ten years, 1879 to 1888, inclusive, have been notable in the history of iron-making for the great rise during the latter part of 1879 and the earlier half of 1880; for the maximum of production in 1882 ; for the gradual decline and the reduced product through 1883,1884 and nearly to the end of 1885; then, for the recovery through- 1886 and 1887; and the extraordinary outputs of our iron furnaces during the last three years. The price of pig-iron might be taken as an index to the condition of the iron-mining industry, and if represented graphically, they would shorn approximately parallel curves. The mining industry cannot always respond quickly to a rise in price and an increased demand for ore; nor can its production drop simultaneously with sudden falls in price of iron and of ore. Hence, the irregularities of the one are not reflected in the other. The statistics of the iron mines collected by the United States census, for the year ending June 30, 1880, exhibit admirably their condition at that time. The reports received from mine owners and managers, of the production for the year 1888, furnish the basis for a comparison and supply data for some notes on the changes in the iron-mining industry in New York which have taken place in this period of time. The iron-ores of New York may be grouped in the following districts: I. The Highlands of the Hudson (magnetites). II. The Lake Champlain and Adirondack Region (magnetites). III. St. Lawrence and Jefferson Counties (red hematites). IV. Clinton and Wayne Counties (fossil-ores of the Clinton Group). V. Dutchess and Colnmbia Counties (limonites). VI. The Hudson River (carbonates). VII. Staten Island (limonites). The ores of the first and second districts, as enumerated, are almost exclusively magnetites; those of the third and fourth are hematites;

Jan 1, 1889

By Theodore Holt

Outline of the Process THE Mines Operating Co.'s plant at Park City, Utah, was designed to treat the low-grade fillings in the old stopes of the Ontario mine. These fillings carry 6 to 14 oz. of silver, 1 to 2 lb. copper, 0.01 to 0.015 oz. of gold, and a small percentage of lead and zinc. The treatment consists in mixing the crushed ore with coal dust and salt and then roasting in a new type of furnace y combustion of the contained fuel. The roasted ore is leached with an acid salt solution to dissolve the silver, gold, copper, and lead. At present these metals are precipitated together on scrap iron and the product sold to a refinery. The only new feature of importance in this scheme of treatment is the roasting process, which makes possible the chloridizing of ores without any loss of the valuable metals, and at a very low cost. History of the Development of the Process The roasting process had its beginning in connection with research work at the Utah State School of Mines. N. C. Christensen, Jr., who held one of the School of Mines' fellowships, was engaged in some experimental work on blast roasting. At the same time I was doing some work on the insoluble gold in Mercur base ores. Mr. Christensen roasted some of this base gold ore in his pot furnace, and found that when he mixed a sufficiently low percentage of fuel with the ore, it did not sinter but roasted to a leachable product. We considered this a new application of blast roasting, and proceeded to test out a large number of ores in several different types of small roasters which we constructed. This experimental work continued well into the summer of 1911.

Jan 7, 1914

By C. A. Stetefeldt

The purpose of this paper is to convince the managers of silvermills that their customary reports in regard to the percentage of silver saved are far from the truth. It may be unpleasant for them to have the proofs of this fact brought before the public, and for this rezson the author refrains from giving the names of the mines and mills from which the statistics here recorded were obtained. It may be asked: What is gained by informing the stockholders of our silver-mines that they receive incorrect reports? Will this increase their dividends or lessen their assessments? In the first place, it is always better to publish honest facts than fiction. In the second place, many superintendents believe in the correctness of their reports, and have no idea how much they deceive themselves. Finally, the knowledge that hitherto unexpected losses of silver take place may lead to the adoption of methods by which these losses are greatly reduced. These remarks refer also to smelting-works. The present paper, however, is concerned exclusively with amalgamation and lixiviation. The first and most important error is found in the inaccuracy of the commercial assay; the second in the incorrect sampling of tailings in amalgamation. Further, mills not doing custom-work, but reducing exclusively ores from mines to which the mills belong, are in the habit of weighing the ore only approximately and without making moisture-tests. Thus, a correct basis for calculating the actual percentage of silver extracted is lacking. The superintendent, then, finds it convenient to report the apparent extraction, i.e., the extraction indicated by comparing the value of the roasted ore, minus soluble salts, with the value of the tailings. How many errors are thereby committed it is not necessary to point out.

Jan 1, 1895

By T. Sterry Hunt

THE geognostical relations of the metals and their ores present many problems of great interest, alike for the geologist, the chemist, and the mining engineer. The association with certain rock-formations of characteristic mineral species may help to guide the geologist in the identification of geological horizons, and throw light on the chemical activities which have been especially manifested in certain periods; while it is clear that such relations, if established, must be of great utility to the miner, and especially to the explorer of new regions. In inquiries of this kind, however, it is only by careful observations over wide areas, and by the collocation of a great number of facts, that anything like a safe basis for induction can be attained. The effects of hasty and imperfect generalizations in this field have already in many instances been felt to the prejudice of scientific progress. I come before you to-night, therefore, not to lay down any laws or general principles, but to call your attention to certain facts, many of them doubtless known to you, which have forced themselves on my attention, with regard to the associations of various metallic ores and other useful minerals with different series of stratified rocks, and to ask you to aid the progress of this branch of geognostical inquiry. Your observations in the various regions to which you may be called by your professional duties will enable you to determine how far these associations are mere coincidences, and how far they are chemical and geological constants. The associations here to be noticed concern only those mineral species which occur, either distributed through the strata in such a manner as to show that they are contemporaneous deposits, or occupy rifts or gash-veins in these strata, and may be supposed to have been

Jan 1, 1873

By T. Sterry Hunt

THE geognostical relations of the metals and their ores present many problems of great interest, alike for the geologist, the chemist, and the mining engineer. The association with certain rock-formations of characteristic mineral species may help to guide the geologist in the identification of geological horizons, and throw light on the chemical activities which have been especially manifested in certain periods; while it is clear that such relations, if established, must be of great utility to the miner, and especially to the explorer of new regions. In inquiries of this kind, however, it is only by careful observations over wide areas, and by the collocation of a great number of facts, that anything like a safe basis for induction can be attained. The effects of hasty and imperfect generalizations in this field have already in many instances been felt to the prejudice of scientific progress. I come before you to-night, therefore, not to lay down any laws or general principles, but to call your attention to certain facts, many of them doubtless known to you, which have forced themselves on my attention, with regard to the associations of various metallic ores and other useful minerals with different series of stratified rocks, and to ask you to aid the progress of this branch of geognostical inquiry. Your observations in the various regions to which you may be called by your professional duties will enable you to determine how far these associations are mere coincidences, and how far they are chemical and geological constants. The associations here to be noticed concern only those mineral species which occur, either distributed through the strata in such a manner as to show that they are contemporaneous deposits, or occupy rifts or gash-veins in these strata, and may be supposed to have been

By George F. Becker

Complexity of Rock-Fractures. - The strains to which rocks have been subjected are manifestly very complex, and it is entirely safe to presume that every possible node of deformation and rupture is exemplified. The most superficial inspection of any ordinary mountain region is sufficient to assure the observer that the rocks have been pressed, stretched, bent, buckled, twisted, and shorn. The study of torsional rupture cannot fail, therefore, to throw light on geological phenomena. The question is, how areas which have been broken in this manner are to be distinguished from those which have yielded to other systems of forces. Phenomena of Joints. - It is well known that a large part of the more homogeneous rocks and some very heterogeneous rocks are intersected by partings, often called joints. These partings are frequently flat surfaces, even when seen in very large exposures, but are sometimes surfaces of moderate single or double curvature. Joints usually occur in groups, in each of which the several partings are parallel to one another, and several such groups often intersect the same rock-mass. In such cases the different systems make large angles with one another. Nearly all students of the subject of jointing have reached the conclusion that joints are faulted surfaces, the dislocations usually being of small amplitude; and this conclusion receives abundant support from the study of thin sections under the microscope. It has thus been shown that much even of what would be regarded in I hand-specimens as mere slaty cleavage consists, in reality, of innumerable microscopic faults. For this reason, Mr. Daubrée rejects the term "joint," as failing to imply the existence of relative motion, and has introduced the terms “diaclase” and “paraclase” as substitutes.1

Jan 1, 1913

By Eugene Coste

ALTHOUGH some of the observers who first paid especial attention to the occurrences of oil and gas in the strata (such as Hunt in 1859, Andrews in 1861, Winchell in 1865, Mendelejeff in 1876, Höfer in 1876, Minshall in 1881, and I. C. White in 1883) seem to have been impressed with the fact that oil and gas deposits were connected with the disturbances in the rocks caused by their upheaval,1 yet, with the exception of Mendelejeff, and possibly Andrews, these observers do not appear to have understood what is really the one essential factor in the occurrence of oil and gas in the strata: viz., the faulting, uplifting, fracturing, fissuring, and jointing always accompanying even slight rock disturbances, and in certain districts (petroliferous provinces)2 allowing solfataric hydrocarbon emanations to force their way up from the interior and to reach and impregnate the porous portions of sediments subjected to the disturbances. Instead of this simple explanation to account for the observed connection between petroleum deposits and rock disturbances, most of the observers mentioned above, and many others who have followed them on the name lines since, have entirely reversed the problem. To them, instead of the dissemination of gases from fissures into the sediments, it presented the accumulation and concentration, according to anticlinal or other geologic structures, of oil and gas originally present throughout the whole mass of the strata where they were produced by the decomposition or distillation of organic remains. Whether this important problem involves accumulation from sources within the oil-bearing strata themselves, or infiltration and dissemination from outside sources, may be easily determined if all preconceived ideas are put aside and the established facts only are considered.

Jan 9, 1914

By P. H. Royster

SOMETHING of a mystery has attached itself to the production of ferromanganese in the blast furnace. This alloy has been produced on the Continent almost continuously since 1876 and in very considerable tonnages, but little definite information concerning the practice is to he found in technical literature, and almost nothing in the way of a theory of the manganese furnace. In this country prior to 1904, bit one company had attempted its production in a serious way, and none of the operating data or other information from this company has been, or is, available to the public. In the last 5 years, as a result of the restriction of imports, a number of furnaces have been blown in on this alloy, with the result that in 1918 as many, as 18 furnaces were in blast. The majority of the men in charge of these furnaces had had little previous experience in such operations. Realizing the advantages both to the country and to the industry from a pooling of operating data and experiences, the Bureau of Mines, in the summer of 1918, undertook the collection of data from ferromanganese furnaces. Although the results of this investigation have already been reported to the companies cooperating, they may he of permanent metallurgical interest, so this paper attempts to give, briefly, the more important points brought out in the investigations. OPERATING DATA IN FERROMANGANESE PRACTICE Operating data were collected by the Bureau from 11 ferromanganese furnaces, which will be referred to throughout this paper as furnaces A, B, C, F, G, I, J, K, L, M, and P. The dimensions, of seven of the furnaces are given in Table 1. The companies from whom this infor-

Jan 2, 1919

By W. M. Bertholf

To establish the minimum or break-even efficiency of a preparation plant it is necessary to determine the ratio of production costs per ton of run-of-mine coal to sale price per ton of clean coal. This ratio is then divided by the percentage of plant recovery. Assume, for example, that washability data indicate that 80 pct of the run-of-mine coal may be recovered as clean coal selling for $5.50 per ton. If the same plant incurs $4.00 per ton mining costs and $0.25 per ton preparation costs, the cost to sale price ratio would be 4.25/5.50, or 77.3 pct. Since the plant is capable of recovering 80 pct of the run-of-mine coal the minimum plant efficiency would be 77.3/80, or 96.6 pct. If the plant efficiency were increased to 100 pct the limit on preparation costs would be increased to $0.40. Therefore, the washing operation must be accomplished at a cost of $0.25 to $0.40 per ton and the efficiency must be 96.6 pct or higher. By plotting a curve of efficiency vs preparation costs and taking into consideration the plant cost, feed rate, operating costs, and yields of the various flowsheets it is possible to select a financially sound process. Table I classifies preparation processes according to their nature of separation. It must be remembered that what is thought to be ideal does not always prove practical under actual operation. An outstanding example is the work done on the plunger-type jig. It was determined by the law of equivalence that this unit could treat satisfactorily only sizes differing by no more than a ratio of 2. Yet these same plunger-type jigs are successfully treating sizes considerably greater than this ratio.

Jan 12, 1957

By Juhani Pulkkinen, Pekka Lappalainen

Preplaced cable bolts - fully grouted old hoisting cables or stress relieved steel strands - have been used succesfully to pre- reinforce ore contact zones and pillars in sublevel stoping at Outo- kumpu Oy mines for ten years. The purpose is to make open stoping methods possible even in "poor'' conditions and to decrease waste rock dilution. Since 1971 more than 120 km cable bolting has been done, and plans for this year in five mines amount to 33 km. In order to understand the function of cable bolt, pull-out tests have been done both in the laboratory and in situ. Bond strength between cable and cement is highly dependent on cable structure and cable surface dirtiness. Steel cables with steel core and rough surface structure have highest bond strength ( 6 MP~). A cable bolt is a friction bolt. After losing its peak bond strength - after starting to move - a cable bolt still has a high loading capacity due to the friction caused by the uneven surface of the cable. Cable bolting is done before actual stoping from existing drifts, sublevel drifts, e.g. or from special bolting drifts. In general stress relieved steel strands are used; 2 x 15.2 mm dia per hole. FEM or BEM calculation is utilized in cable bolting design. Bolts 2 are in fan shape, 10 m ... 50 m long and are spaced 1/20 m ... 1/50 m2 at stope walls. Pretensioning of cable is not needed, when bolting is done before rock deformations. Bolting costs vary between 0.3 USD ... 1.0 USD/ore ton. In the beginning only manual cable installing technique bras used. Now bolting can be done as fully mechanized with the developed cable bolting machine; i.e. drilling of the hole, installing and cutting of cables and grouting of hole.

Jan 1, 1983

By Thomas D. West

The fact that iron expands when heated, until fusion takes place, and that molten iron is consequently less dense than solid iron of the same grade, is now universally admitted. It was proved by the extensive experiments of Mr. Thomas Wrightson, reported in the Jownal of the Iron and Steel Institute (1890, No. 1, p. 72, and 1891, No. 1, pp. 75, log), and, in a manner, is illustrated in heavy founding by the shrinkage 'of the molten metal, which must be " fed " in order to obtain solid castings. This decrease in volume requiring " feeding" while the metal is still liquid I call " shrinkage," applying the term " contraction" to the decrease in volume which takes place after solidification, while the iron is cooling to atmospheric temperature. The light-work founder, not having the opportunity to make heavy castings, in which shrinkage can be observed, is apt to confound the two; but they are in fact distinct, and are separated by an act of expanion, which takes place at the moment of solidification. The fact of this expansion was first practically demonstrated by Mr. John R. Whitney, of Philadelphia, Pa., whose experiments are recorded in the National Car and Locomotive Builder of May, 1889. Experiments recently made by the writer indicate that there is a constant relation between this expansion and the preceding shrinkage and forcibly demonstrate the necessity of " feeding " a casting to make its interior solid. This is a matter with which all makers and users of castings have experienced difficulty. The founder being heretofore unable to define correctly the principles involving the urgent necessity of " feeding " has failed to impress the moulder with its importance in making sound castings.

Jan 1, 1897

George W. Maynard, New York, N. Y.:—It is well known that there are many magnetite-mines of which the ore is too low-grade for direct use in the blast-furnace. For carrying out the sintering process, the preliminary step, in the case of magnetites, is the separation of the ore from the gangue by magnetic concentration. The resulting fine-grain product is very objectionable in the blast-furnace, and when used must be a very small percentage of the charge. The sintering process has saved the situation by furnishing a product which is absolutely ideal on account of its cellular structure. (In reply to questions by W. J. Tudor, and Joseph W. Richards, the following additional information was given by Dr. Maynard.) The percentage of iron in the product is determined entirely by the degree of concentration of the raw material and is practically not increased by the sintering operation. The magnetic concentrates at Port Henry and at the Benson and one or two other mines contain from 65 to 67 per cent. of metallic iron. The cost of sintering is from 39 to 41 cents per ton of product, including superintendence, depreciation, and repairs. The itemized figures are about as follows : Mixing (including labor), 24; power, 9; ignition, 5; repairs, 3; total, 41 cents. Prof. J. W. Richards, South Bethlehem, Pa.:—From a metallurgical standpoint I question the accuracy of the statement on p. 374: " C.—An increased reducibility of the iron so treated. (This has been conservatively estimated as 5 per cent. better than the best available ore.)" It seems to me that when a material is' sintered in this way, the constituents present, as lime, silica, and alumina, have a chance to form a compound with the iron oxide; that such a compound, if formed before the material goes into the blast-

Jan 1, 1913

W. ROWLAND Cox,* New York, N. Y. (written discussion?).-The process described by Mr. Malcolmson undoubtedly represents a great stride toward conservation of our natural resources. Without discussing the subject from an economic standpoint, I wish further to emphasize the fundamental principles of the Smith process in order that its economic value may be fully appreciated. The process is essentially a means of producing an ideal fuel, as regards its combustion qualities, by the removal of the so-called volatile matter from the coal, in the form of byproducts, which have value for other purposes far in excess of their fuel value. In other words, coals which contain. large amounts of gas, tar, and ammonia, and are not suitable for domestic or industrial fuel, or for treatment in byproduct coke ovens or gas retorts; because they possess poor coking qualities, can he prepared for commercial use by the. Smith process with a very high degree of efficiency. Much work has been done along this line, both in this country and in Europe, in developing a means of preparing coal, as the economic advantages have long been recognized. To the best of my knowledge, the Smith process is the only one that has proved its commercial adaptability. Distillation of coal at 900° to 1000° F. (480° to 540° C.) yields a large amount of tar and oils. The residue of the distillation, however, is a very friable semi-coke, wholly unsuitable for use as a fuel, unless it can be charged directly into a byproduct gas producer. The problem which confronted the inventor was then to convert this carbon residue into a commercial product, and it is in this step that the Smith process has overcome the obstacles which prevented a number of other methods from becoming commercially practicable.

Jan 10, 1918

By Frank Firmstone

In the summer of 1842 my father, William Firmstone, was engaged by Charles Jackson, Jr., of Boston, to examine the conditions in the Lehigh valley as a site for blast-furnaces using anthracite for fuel. In consequence of his report, he was further engaged by Mr. Jackson to build a furnace for him and his partners on the Lehigh canal, 2 miles above the mouth of the river at Easton. Work was begun in the fall of 1842, and the first furnace blown-in in 1844. The history of the works, therefore, from 1844 to 1887, when my own connection with them ceased, covers only four years less than the whole period of the rise, culmination, and commencement of the decline in the smelting of iron with anthracite in America, the beginning of which, in a commercial sense, may be put in 1839.' Although this paper, as the title indicates, is concerned almost exclusively with the furnaces at Glendon, still what was done there was more or less influenced by current opinion in the district, and even reflects, to some extent, the changes in opinion and practice with mineral fuel the world over. No. 1 Furnace was built of red brick, on four piers, had three tuyeres and fore-hearth and tymp, as was universal with furnaces using mineral fuel until the introduction of Lurmann's cinder-tuyere. The dimensions and profile are shown in Figs. 1 and 2. The first hearth (Fig. 1) was of sandstone; all after were of fire-brick (Fig. 2). The profile was no doubt derived directly from Gibbons's furnace,2 for it appears from W. Firmstone's note-books that in October, 1840, he visited " Gibbons' new furnaces building at Corbyn Hall," and I have an old drawing,

Jan 1, 1910

By Courtenay de Kalb

The Exposed Treasure gold-mine has, for the past four years, been one of the largest producing mines of Southern California, its annual output havirig con~tituted I per cent. of the total gold and silver production of the entire State. At the present moment the property is idle, owing to the large quantity of water encountered on the lower levels, which will require the installation of a powerful pumping-plant before operations call be recommenced. Moreover, a prompt change in the character of the ore has occurred at water-level, which makes imperative an extensive campaign of development in the region of the un-oxidized ores before a plant adapted to their treatment call be definitely decided upon. The character of the changes encountered in these deeper ores makes the geology of this deposit a matter of importance, riot only for the immediate district, but for the desert region of Southern California in general, where many mines exist having in the oxidized belt conditions that, in many respects, resemble those in the Exposed Treasure mine. The deposit is situated in an apparently isolated butte about 2.5 miles south from the town of Mojave, on the Mojave desert. The butte, though apparently isolated, is in Fact geologicallg part of an extinct volcano, known as Soledad butte, which rises out of the plain 1.5 miles SW. of' the mine, to an altitude of 4,650 ft. above sea-level. Other buttes also rise from the desert plain toward the south and east, and again to the westward, all being closely related geologically to Soledad butte,—the whole constituting a single system as to origin and time. Since the end of the period of active volcanism in this region, there has been extensive denudation, the ancient plateau having been dissected during an epoch of apparently exces-

Jan 1, 1908

By John W. Chang

Introduction Automatic control of primary ball mill circuits has received much attention over the past decade, primarily because its advantages ultimately can be translated into economic terms. Apart from such obvious benefits as improved product quality, increased throughput, and more stable operation, less direct benefits such as easier operation, more orderly maintenance scheduling, and timely management reports all can be realized with the application of modern automatic process control equipment and techniques. Software configurable digital computer-based control systems offer ease of change in control strategies. Occasional control strategy changes are necessary whenever control objectives change or circuit modifications occur. The dependency of control strategies on control objectives and circuit equipment to effect optimal circuit operation is an important, but often neglected issue. Because of the potential for even better control, research and development work continues. [See (Ulsoy & Sastry, 1981) and (Hulbert & Braae, 1981).] Some of the possibilities are discussed later in this presentation. A few preliminary remarks may be in order concerning the relationships among control objectives, control strategies, and circuit equipment. Generally accepted control objectives for primary ball mill circuits include: 1. Maintaining a desired percent solids in the mill. 2. Maintaining a desired measure of particle size distribution at the cyclone overflow. 3. Maximizing throughput. Control Objective I is a requirement for proper operation of the ball mill, especially if it is a grate mill. It concerns smooth movement of material through the mill. Control Objective 2 is a product specification - one of the requirements for proper flotation operation. Control Objective 3, an expression of the desire to get the most out of the circuit, is the easiest to evaluate in economic terms. It assumes that the processes downstream

Jan 1, 1982

By Foster Fraas

MOST commercial electrostatic separators utilize the electrical property of conductivity, but although based on the same principles, they are constructed in a variety of forms, a common one being the simple roll type. Some information obtained during an investigation of that type of separator, and which indirectly is applicable to other types, is presented here. NUMERICAL RELATIONSHIP In Fig. I material discharged from hopper 6 is fed onto grounded rotating roll 2. Electrode 3 is at a high electrical potential with respect to roll 2, and any conductive particle in contact with roll 2 therefore acquires an electrical charge of such polarity that, when present in the electrical field, the force on it is in the direction of electrode 3. A detailed description of the charging by conductance as utilized in electrostatic separators may be found in a previous publication.1 As a result of this force, the path of the projected particle is changed in increasing amounts in the direction toward region C as the magnitude of the charge is increased. With the dividing edge 4 the projected particles may be divided into two fractions -those in region C designated as "deflected" or " deflectant " and those in region B designated as "residue." [ ] When material is passed over the roll only once, a complete separation is seldom obtained, therefore most commercial separators contain several roll-separator units in series, and some practical machines use as many as 12. In this paper a "pass" means the passage of material over a single-roll unit. The procedure is to repass either residue B with a low potential on electrode 3 or deflectant C with a high potential on 3. Most electrostatic separations follow a flowsheet of roughing and cleaning either the concentrate or the tailing, on both. In a specific instance, a dry, heated mixture of wet cleaned chromite and garnet from an

Jan 1, 1942

By R. P. Marshall, L. P. Costas

The solid solubility of lithium in aluminum was determined by two independent techniques, electrical resistivity and microhardness, and the results are in close agreement. The solubility limits X-ray diffraction studies of the intermetallic compound LiAl indicate that its composition is nearly independent of temperature when in equilibrium with the terminal solid solution of aluminum. THE investigation of the aluminum-rich portion of the aluminum-lithium system at the Savannah River Laboratory was prompted by the observation that over-aged alloys consistently differed from the equilibrium states predicted by the latest published diagrams. Chemical analyses of these alloys showed their impurity contents to be quite low; therefore, the results obtained should have very nearly coincided with true equilibrium. A survey of the literature disclosed that previous studies had been made with metallographicig or electrical resistivity methods,4'5 but that agreement between results and technique was poor as evidenced in Fig. 1, which also includes the present results for comparison. The discrepancies have been attributed to impurities,3 and this is undoubtedly true in the early work.1'4'5 The latest Studies,''~ conducted with starting materials of higher purity, employed metallographic analysis, a technique that is quite sensitive to local homogeneity and depends strongly on subjective interpretation. In the present work the problem of defining solubility limits was approached in two ways. The first measured a physical property, electrical resistivity, at the equilibrium temperature. The second, a micro-hardness characterization of a diffusion zone, is a room temperature evaluation of a mechanical property under conditions removed from equilibrium. A close correlation between two such basically different approaches would strongly justify confidence in the results. I) MEASUREMENT OF SOLUBILITY OF LITHIUM IN ALUMINUM BY ELECTRICAL RESISTIVITY Experimental Procedure. Alloys for electrical resistivity measurements were made by melting and

Jan 1, 1962