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By W. S. Landis

WHEN dealing with a new reagent, one is concerned with three principal factors: available supply, cost, and results. The atmosphere contains an inexhaustible supply of oxygen mechanically mixed with nitrogen (omitting rare gases and minor impurities) in the proportions of one volume of oxygen to four volumes of nitrogen. (All figures are based on slide-rule precision and minor impurities are neglected.) Expressed in terms of weight, 1 ton of oxygen represents a volume of 22,500 cu. ft. and is contained in a volume of 112,000 cu. ft. of air. Water, also an inexhaustible supply, is a chemical compound containing 89 per cent. oxygen and, 11 per cent. hydrogen. Of the hundreds of schemes proposed for the enriching of air or separation of oxygen, nothing of value has yet appeared. From the standpoint of mechanical separation, liquefaction followed by rectification is the only process that has been developed to a really commercial stage. Theoretically, it should be a .simple matter to separate the mechanical mixture of nitrogen and oxygen; but fractionation can be performed only by converting to the liquid phase and this phase can be obtained only at lower than critical temperatures. The problem, therefore, is not so simple and the cost of the actual operation bears no relationship to the theoretical simplicity of the process. The largest single unit of the required apparatus so far placed in commercial use will handle only 60,000 cu. ft. of air per hour through a compressor which operates at a little over 250 lb. per sq. in. After this apparatus has operated continuously for 14 to 18 days it must be shut down for 6 to 8 hr. to be thawed out, have accumulated impurities removed and again cooled down for production. The cost of such a unit erected in batteries, with necessary spares for maintaining production, and including prime movers, hoisting and all auxiliary equipment, will be about $125,000. To produce one ton of oxygen per hour requires two operating machines of this size; and if the production is to be absolutely continuous a spare unit must be provided. To operate a plant of two units requires 10 or 11 men, excluding boiler attendants, if steam is generated in the plant.

Jan 11, 1924

By Colin C. Harris, Nathaniel Arbiter

The flotation operation can be analyzed in terms of three groups of variables. The first, largely independent of control by the operator, embraces the fixed physical and chemical properties of the ore minerals. The second includes all chemical and physical effects imposed on an ore after mining that influence its floatability. These can be either purposefully or accidentally applied. The third embodies the flotation-machine characteristics which realize the potential floatability of selected ore minerals in terms of grade and recovery levels. The machine effectiveness thus depends not only on its own contribution, but on the prior influence of all other variables on floatability. HISTORICAL DEVELOPMENT From the earliest days, flotation mills used many types of machines. Hoover 20 in 1914 mentioned as then important the Potter-Delprat tank for gas generation by acid, the DeBavay cones for skin flotation, the Elmore mixer and separation chamber for vacuum flotation, and his own modification of the Mineral Separation cell for the agitation froth process. Less important at the time were the MacQuisten tube and the Hyde cell. By 19274~ scores of machines had been developed and dozens had found their way into mills. From then on, however, under the scrutiny of competitive tests, many fell into disuse. Taggart in 19454~ classified processes broadly as skin flotation and froth flotation, dividing machines for the latter into the three categories: bubble column, pulp body, and combination.* Under 'bubble column' he listed all pneumatic, cascade, and subaeration cells; and under 'pulp body' those cells in which gas was generated by boiling, chemical action, and pressure reduction, as well as the agitation-froth type. At that writing skin flotation, the cascade machines, and all pulp body and combination machines were said to be extinct, leaving pneumatic and subaeration types dominant (u. S. practice). The process of elimination has continued to the present, with almost all pneumatic cells succumbing to the pressure of competition from subaeration machines. The only new machines to appear in recent years have been double-impeller types f and these have met with only limited acceptance.

Jan 1, 1962

By C. P. Sandberg

C. P. Sandberg, London, Eng. 1 think we should all be grateful to the Pennsylvania Railroad Company, and to their chemist, Dr. Dudley, for spending so much time and money in order to solve an important question; nor are me less indebted to the public spirit which leads them to impart tlie experience thus gained. In Europe nothing similar has hitherto been done, either by a company or by any private individual. In England the great railway companies employ their engineers in other ways, and do not keep a chemist or specialist to study rails; bat even if they did they would probably not publish the results. The chief professional engineers are so occupied with their private practice of railroad construction generally, that they cannot be expected to devote their time and energies to so special a question. The German Railway Union has, in my opinion, missed the real object of its elaborate researches by falling into the error of specifying costly, impracticable tests for rails—tests at the same time which do not infallibly expose the impurities that may be in the rails under examination. There has, therefore, been nothing done on this side of the Atlantic in the way of exhaustive study to determine the best composition for steel rails. America should consequently have full credit for the enlightened example which she has set. I wish, however, to make a few remarks on Dr. Dudley's second paper,—& paper which follows very much upan the same lines of argument as the first red three years ago, upon which I have previously touched in my pabr on the same subject read at the meeting in August last. If Dr. Dudley had discovered a new metal he could hardly, I think, have taken wore pains to prove that he was correct in his first formula for the best chemical colnposition of steel rails. But I hare seen so much done in the way of proof by experiment that I am inclined to think that almost anything can be proved by experiments and by satnples. If Dr. Dudley would only give up his formula, which would not suit any country—not even America—

Jan 1, 1881

C. P. Sandberg, London, Eng. 1 think we should all be grateful to the Pennsylvania Railroad Company, and to their chemist, Dr. Dudley, for spending so much time and money in order to solve an important question; nor are me less indebted to the public spirit which leads them to impart tlie experience thus gained. In Europe nothing similar has hitherto been done, either by a company or by any private individual. In England the great railway companies employ their engineers in other ways, and do not keep a chemist or specialist to study rails; bat even if they did they would probably not publish the results. The chief professional engineers are so occupied with their private practice of railroad construction generally, that they cannot be expected to devote their time and energies to so special a question. The German Railway Union has, in my opinion, missed the real object of its elaborate researches by falling into the error of specifying costly, impracticable tests for rails—tests at the same time which do not infallibly expose the impurities that may be in the rails under examination. There has, therefore, been nothing done on this side of the Atlantic in the way of exhaustive study to determine the best composition for steel rails. America should consequently have full credit for the enlightened example which she has set. I wish, however, to make a few remarks on Dr. Dudley's second paper,—& paper which follows very much upan the same lines of argument as the first red three years ago, upon which I have previously touched in my pabr on the same subject read at the meeting in August last. If Dr. Dudley had discovered a new metal he could hardly, I think, have taken wore pains to prove that he was correct in his first formula for the best chemical colnposition of steel rails. But I hare seen so much done in the way of proof by experiment that I am inclined to think that almost anything can be proved by experiments and by satnples. If Dr. Dudley would only give up his formula, which would not suit any country—not even America—

Jan 1, 1881

Discussion of the paper of E.. C. LEE, presented at the St. Louis meeting, October, 1917, and printed in Bulletin-No. 130, October, 1917, pp. 1825 to 1832. H. M. WILSON, Pittsburgh, Pa.-The statement ill the paper of T. T. Read, "Increasing Dividends Through Personnel Work;" that the offering of substantial money rewards for avoidance of accidents is much more effective than mere propaganda or education respecting accident prevention, is a, point fully substantiated in the experience of insurance inspection under workmen's compensation acts. The first year under the Workmen's Compensation Law in Pennsylvania, during which over 2000 mines were tinder the observation and protection of the inspectors of the insurance companies, has resulted in several inspections of each mine, a splendid cooperation .between the operators, the State mine inspectors and the insurance inspectors, and an average reduction in premium rate for insurance from $3.83 to $2.77, a reduction of more than $1 per $100 of payroll, on an average payroll of nearly $100,000,000, In other words, the insurance companies have

Jan 1, 1918

By Everett Carpenter

THE average daily production of crude oil-in Kansas a1 the beginning of the year was about 71,000 1 bbl. and, at its close, 82,000 bbl.-an increase of 11,000 bbl. per day. The total production for the state during the year was about 28,250,000 bbl., or an average of practically 77,500 bbl. per day for the year. This increase in the production was the result of the discovery of several new pools of high-grade oil. COWLEY AND SUMNER COUNTIES One of the principal factors in bringing the production of the. state back to its former level was the newly discovered pools in western Cowley County. During December, 1923, the Waite Phillips Co. completed its Johnson No. 1 in Sec. 20, T. 33 S., R. 3 E., which opened up the Rainbow pool about 12 miles southwest of Winfield. In this pool, the production comes from the Burbank sand, locally called the "Rainbow," found at a depth of 3200 ft. The sand varies in thickness from 25 to 40 ft. in the seventeen wells completed during the year, and the initial productions ranged from 300 to 3000 bbl. per day of 40° Be. oil. The Rainbow pool is purely a wildcat discovery, for no. rocks suitable for the use of the geologist are present. To determine the geologic conditions, the larger companies core-drilled the Rainbow area immediately after the discovery. The Marland Refining, Co., drilling on the Graham farm in Sec. 9, T. 33, R. 3, failed to find the Burbank sand and continued to the Siliceous lime, often erroneously called the Wilcox, at 3505 ft., where a well with an initial production of 900 bbl. of 40 Be. oil was obtained. In the development following this discovery, 4 additional wells were completed, 3 of which encountered pay sand at 2500 ft., the initial productions each being about 200 barrels. Judging by the sands already proved and the area indicated as probably oil bearing by the development to date, these pools have a very promising outlook for the future. It is not unlikely that a field second only to El Dorado may have been opened.

Jan 3, 1925

By Carle Hayward

IN reheating quenched steel to remove part of the hardness, the softening effect has generally been considered to be a function of temperature and time. The temperature effect is well known, and long before pyrometers were heard of the blacksmith was able to do a good job of tempering, by rule-of-thumb methods and experience in judging temperatures. Modern conditions, which demand steel that will withstand the severest tests, require that the heat treatment he carried out with every possible precaution to secure the best results obtainable. Pyrometers and heat-treatment furnaces of many types are on the market and improvements are continually being made so that it is now possible to regulate the temperature in heat treatment very accurately. There is -still a question regarding the time that the steel should be subjected to treatment. It is customary with all operators to insure the desired tem-pressure throughout the specimen and it is generally supposed that a longer treatment of a hardened steel produces a further softening but there are few published figures showing the exact effect of time of treat-ment at constant temperature. A search of the literature disclosed several brief statements that the tempering effect was a function of both time and temperature, but in no case were any figures given. The opinion is very generally held that the well-known tempering colors are accurate indicators of the degree of tempering. This is disputed by Brearley (The Heat Treatment of Tool Steel, page 102) who states: It has been said that the result would be the same in respect to both hardness and other properties whether the colors were obtained by a shorter heating at a higher temperature or a longer heating at a lower one. This, to say the least, is a very doubtful conclusion, and is certainly not borne out by mechanical tests on oil-hardened and tempered motor car steels, which, after tempering for periods varying from 15 min to 2 hr., show no very great differences. The present investigation had for its object the obtaining of some definite data regarding the effect of time, which might serve as a guide to those engaged in the heat treatment of steel. The Rhode Island Tool Co. cooperated by furnishing the steel and machining the test specimens.

Jan 2, 1917

By R. G. Robins, O. J. Kwok

The application of chemical thermodynamic theory to high temperature aqueous systems is discussed as a basis for the explanation of thermal precipitation. The derivation of high temperature potential/ pH diagrams is briefly outlined in order to show a temperature/pH relationship for hydrolytic precipitation, which is an effect that is caused simply by heating an aqueous solution. Various examples of thermal precipitation are given, with particular reference to separation of metal values from leach solutions. Metal sulphate solutions are shown to precipitate basic sulphates, hydrated sulphates , oxides, hydroxides, and oxydroxides of the metal depending largely on the pH, the concentration of metal ion, and the concentration of sulphate or bisulphate. The CuS04-H2S04-H20 system is treated in some detail, and the separation of copper from other metal ions is investigated. Other separations involving Fe, Ni, Zn, Cd, and Cr are considered. Other advantages of thermal precipitation, such as the formation of high purity, large particle size and easily filterable materials, are presented. The kinetics of thermal precipitation are also briefly examined.

Jan 1, 1973

By Frank C. Roe

Two cogent and ubiquitous facts have supported a constant search by the ore processing industry for better wear resistant materials in equipment. First, designs and types of equipment change or improve continually to meet the economic and physical demands of different and/or leaner ores. Second, practically all equipment is subject to impact and abrasion conditions that probably are more severe and extensive than in any other industry. Development and testing by operators and equipment manufacturers alike, has produced an extensive variety of longer lasting metal alloys, rubber, plastics, ceramics and other materials to improve equipment performance under different specific conditions. The need for diversified materials becomes obvious upon the simple realization that no two beneficiation operations are identical. Among the variables in the handling of ore are: 1. Size and weight of ore particles. 2. Hardness and sharpness of ore particles. 3. Concentration of ore particles in liquid or gas suspension. 4. Velocity and direction of particle impact toward equipment surface. 5. Coefficient of friction between ore particles and equipment surface. 6. Temperature of operation. 7. Chemical environment of operation.

Jan 12, 1967

By Zay Jeffries

THE object of the present paper is to enlarge somewhat on the general principles advanced in my discussion 1 of Mathewson and Phillips' article on. The Recrystallization of Cold-Worked Alpha Brass on Annealing.2 It will also serve as an acknowledgment of Prof. Howe's3 most important remarks on my contribution. In this paper the writer has adopted Prof. Howe's suggestion to substitute the term "germinative temperature" for "critical temperature for grain growth." Instead of being an exact or certain temperature it should be considered that the germinative temperature phenomenon exists throughout a small temperature range. Factors Influencing Fast Growth Phenomena The development of grains of macroscopic size at the germinative temperature should be considered the extreme condition of a general rule. When considered in this light it is not strange that the development of these large grains should be the exception and not the rule. The principal factors influencing the operation of the laws of fast growth temperature are as follows: 1. Rate of heating.

Jan 10, 1916

By D. W. Fuerstenau

Locked-cycle grinding experiments on mineral mixtures provide a means to study circuit performance in simulated continuous grinding systems. Such experiments with calcite/quartz mixtures revealed that approximately twenty-five 2-minute cycles are required before the composition of the circuit product and the recycle material attain steady state. The circulating load, after steadily increasing during the first 15 cycles, continued to fluctuate over a narrow range. Previous batch ball mill grinding of mineral mixtures has shown that breakage rate functions of minerals are time- independent but composition-dependent. In the closed-circuit grinding of ores with constituents having different grindabilities, the grinding rate parameters for the components also would therefore change during the transient period. With fluctuations in feed composition occurring randomly every half to one hour in processing plants, it is quite likely that the grinding circuit can be in unsteady state perpetually. The significance of these observations is discussed in this paper in the con- text of the models used in control schemes for the grinding circuits

Jan 1, 1984

By G. Sandoz

A simple diffusion-couple experiment was carried out for the purpose of determining whether chromium in sufficient amounts would cause the cementite phase in cast irons to become thermodynamically stable with respect to graphite and austenite at 1750°F. The implications of the results to some current theories on graphitization mechanisms are discussed. The literature abounds with evidence that chromium retards the decomposition of cementite to graphite and austenite or ferrite, for example during first-stage and second-stage graphitization in malleabilizing white cast irons and the subcritical graphitization of steels. Efforts to explain this retarding action of chromium have been conjectural, however, because the mechanisms controlling graphitization kinetics in the absence of chromium have never been clearly established. Concerning rate control, there are basically two schools of thought: 1) that graphitization rates are limited by diffusion potential (the stability of cementite relative to graphite, and 2) that graphitization rates are limited by diffusivity of Fe, C, Si, vacancies, and so forth.5'10 Chromium then, is thought either to increase the stability of cementite or to retard some critical diffusion process.

Jan 1, 1960

By Kendall E. Born

Production of crude oil in Tennessee during 1937 was slightly over 37,000 bbl., an 85 per cent increase over the preceding year and the highest since 1928. Closer cooperation between the operators and the State Division of Geology has resulted in more accurate data than have been possible for the past few years. Such cooperation is most desirable, especially in this state, which has no law requiring the filling of drilling permits, logs, and production figures. The increased production for the year has resulted from discoveries of four small pools in the shallow district of Clay and near-by counties. The most promising of these began production late in 1937 and consequently has had little effect on the 1937 total. These discoveries, along with renewed activities in some of the older areas, have increased the production for Clay and adjoining counties from less than 5000 bbl. during 1936 to over 21,000 bbl. in 1937. The Mississippi lime production in Scott and Morgan Counties declined from 16,335 bbl. in 1936 to 14,644 bbl. during 1937. While the decline curve on this production has been gradual, some of the wells are over 20 years old, and it becomes necessary to look for other favorable structures in this general region if increased production is to be obtained or past production maintained. The only natural gas marketed off the lease in Tennessee during 1937 was in Morgan County, where a small amount was furnished for the town of Sunbright and its immediate vicinity. The gas occurs with the oil in the Boone Camp field and small amounts were put on the line from the near-by Coon Hollow and Seabolt pools. Development There were 59 wells spudded in during 1937, of which 18 were drilling or only temporarily shut down on Dec. 31, 1937. Of the 41 completions, 17 produced oil, 5 were gas wells of undetermined quantity, and 19 were dry or near-dry holes. The flush production on the new wells totaled about 1300 bbl. per day. The more important wildcats are listed in

Jan 1, 1938

By Walter Miller

Advancement in engineering in the refining industry during 1933 might be likened to the jagged flame of a poor wick-test kerosene—a few outstanding high spots, but not broadly spectacular. Economic conditions were unsatisfactory for the first six or eight months, but the improvement in the latter part of the year had some immediate effect in stimulating new designing and building. The national legislative program involving the industry drew the attention of executives away from petroleum technology to some extent. The National Recovery Act, and its offspring, the Petroleum Code, demanded deep and continued study to put the machinery into smooth motion. From a purely technical engineering stand, therefore, the emergency measures might be considered a temporary brake on progress. The ultimate effect, if the whole industry can get back "out of the red," may well be a more than expected advance. Of course, petroleum technologists and engineers, including both those engaged within and those busy in designing and building for the industry, continued their efforts, and much of the results of their work will undoubtedly see the light of day under the improved economic conditions, which bid fair to stay with us. There was little improvement during 1933 in atmospheric distillation, sweetening processes, or furnace design, but experimentation during the year on these subjects may materialize into distinct advances. The trend toward compact distilling and fractionating equipment, especially in the Appalachian district, deserves noting. A number of refineries in that district replaced obsolete shell still units with up-to-date tube stills and efficient fractionating towers, both for the better separation of lubricating fractions from the crude and for improving the boiling range of the gasoline. A number of small skimming and topping plants in flush fields, such as East Texas, which felt the pinch of production control, were forced to shut down, but the stronger among them are consolidating their positions by installing cracking equipment and in some cases more modern crude-distillation units. Motor Fuel For the first time in many years a reviewer is able to point to at least a temporary cessation in the competitive race in the manufacturing

Jan 1, 1934

By Arthur Zentner

The electrolytic zinc plant of today is foreshadowed in the patents issued to Léon Létrange of Paris in 1881 and 1883l. He proposed roasting zinc blende to make the zinc soluble in water or sulphuric acid, thus obtaining a sulphate solution. His purification was apparently that used in the lithopone work of the day. For electrolyzing he proposed anodes of carbon or lead, for cathodes zinc, copper or brass. Numerous patents by other workers were taken out in the first 10 years, most of which dealt with sulphate solutions. It is easy to presume that the formation of chlorine gas in zinc chloride electrolysis caused early emphasis on sulphate work. Lack of success with this invited further work with chloride solutions. Efficient and cheaper oxidizing agents for use in the chloride processes were more generally available. Carbon anodes could be used instead of lead anodes, which were blamed for much of the early electrolyzing troubles and remained in disfavor for many years. Carl Hoepfner received his first zinc patents in 18902. He was the most persistent of those who worked with chloride solutions and met with the largest measure of success. Hc built three plants, only one of which remained in operation. This was built in 1896 at the plant of Brunner, Mond & Co., Winnington, England, now part of Imperial Chemical Industries Ltd. It leached with by-product calcium chloride from the company's Solvay alkali plant and returned to it the chlorine formed in electrolyzing. The zinc plant had a capacity of 5 long tons of zinc, said to have been doubled later, and remained in operation until 1924. No commercial plant using chloride solutions has operated since then. E. A. Ashcroft experimented in the middle nineties with chloride, alkaline and sulphate solutions on materials from Broken Hill, Australia. He built a plant with a rated capacity of 10 long tons of zinc per day, at Cockle Creek, New South Wales, in 1898. This figure was never approached nor was cyclical operation achieved. The work in the plant appears to have been largely with sulphate solutions. The plant suffered from a multitude of troubles: poor roasting, gclatinous silica, liberal use of live steam in solutions to combat the gclatinous silica with considerable

Jan 1, 1937

By H. E. Elliott, R. S. Busk, A. T. Peters

ONE of the problems of the fabricator of metals and alloys is the propensity of some composition ranges toward abnormal grain growth during certain stages of fabrication. In this respect magnesium alloys are no exception among alloys. Fortunately, convenient foundry control methods have been developed by which the abnormal grain growth possible in certain magnesium-alloy castings can be suppressed. An unusual characteristic of magnesium alloys, however, is that castings of some composition ranges are subject to local grain growth during heat-treatment without the necessity of intentional mechanical stressing of the part prior to heat-treatment. This effect occurs only under certain critical casting conditions, and only in certain alloys of greater than about 8.5 per cent aluminum content, such as C alloy (Mg, o per cent Al, 2 per cent Zn, 0.2 per cent Mn) and G alloy (Mg, i0 per cent Al, 0.2 per cent Mn). The first observation of this phenomenon in cast magnesium alloys occasioned much surprise, since it is not observed in other metals. Jeffries and Archer' have stated that "the grain size of cast metals, provided they have not been plastically deformed, cannot be changed by heating below the melting point." The study of the conditions leading to abnormal grain growth in cast magnesium alloys, and of the mechanism of this phenomenon, has led to some very interesting observations. Perhaps the most significant of these was the observation that stresses originating from cooling contraction in magnesium-alloy castings are the only stresses necessary, under certain conditions, to cause local recrystallization and subsequent grain growth in the casting during heat-treatment. of abnormal local grain growth was a definite problem in the production foundry on C alloy sand castings. Illustrated (Fig. r) is a picture of a casting scrapped because of this defect. A mottled effect is produced in coarse-grained areas by suitable etching solutions. The properties of metal in the affected area are much impaired by such grain coarsening. Ultimate tensile strengths of half the normal value have been measured in metal of this nature. In this paper are described the techniques that have been developed by The Dow Chemical Co. for studying, and in large measure solving, this production problem. Also discussed are studies of the mechanism by which excessive grain coarsening occurs, and the fundamental conditions that produce this effect. The abnormal grain growth discussed in this paper will be referred to as "germination," since this term has been defined' as any process leading to an abnormally coarse grain size. This paper deals only with abnormal local grain growth that may occur during the solution heat-treatment of certain magnesium-alloy castings, as dis-

Jan 1, 1945

Canadian owned Lake are carriers will be used again this year in an attempt to make up the deficit caused by the two months steel-strike. Buffalo mills need between 5 million and 6 million tons of ore before the Lakes navigation season ends. Mutual Security Program aid will help reactivate Austria's largest iron ore mine. The Erzberg development is one of the moat important in Europe. MSA announced approval of $500,000 in supplemental financing of equipment. Following the war, the Russians stripped the Erzberg and Radmar deposits of equipment. The he Carborundum Corp. is going to build a $2.44 million plant at Akron, NO.. TOP near Niagara Falls for production of rare metals used by the Atomic Energy Commission. A subsidiary, the Carborundum Metals Co., Inc.,, will produce zirconium, hafnium sponge metals. The pyrochlore rich Sukulu Hills in Eastern Uganda will be mined under a pool arrangement including Tinto Mines, Monsanto Chemicals and Frobisher Mines. The combine will be known as the Uganda Development Corp., Pyrochlore is used in the manufacture of heat-resisting. alloys for Jet engines.

Jan 1, 1952

By John P. Cosgro

The increasing use of internal furnace-boilers for power-plants at mines (doubtless due to the facility with which they may be installed by reason of their portability; the fact that they require no masonry setting, cast-iron fronts, buck-stays, etc., and practically no foundation; and the successful maintenance of their claim to equal and even superior economy, as compared with boilers of other types1) warrants this description of a method of remedying an injury which may occur, to such a furnace, even though it satisfies the requirements of the formula adopted by the U. S. Board of Supervising Inspectors of Steam Vessels.2 I refer to the sagging and deformation which may result from overloading the boilers for a considerable period—say, several days. This is sometimes unavoidable under the exacting conditions of continuous day-and-night service, and (in spite of all rules and precautions) the occasional careless or unskillful work of attendants. Such a trouble is by no means unknown on shipboard, where this type of boiler is so largely employed.

Jan 1, 1906

By C. O. Brawner

Simple, specific rules for achieving slope stability in open-pit mines are impossible to devise. Each pit has a different mining program and a different set of environmental conditions, and its final slope design must be based on an individual evaluation of the actual site. The overall philosophy of pit stability, however, is tending towards a limit design concept. Since slope angle has a great influence on the economics of most open-pit mines, efforts are being made to reduce the theoretical factor of safety for slope stability to very near 1.0. (Factor of safety is here defined as shear strength/shear stress on the most probable plane of failure.) Actually, where detailed, statistically significant testing has been done and a comprehensive ground control program is being instituted to warn of movement at an early stage, safety factors as low as 1.1 or 1.2 may be justified. The cost of the necessary procedures, however, is high. There are many factors that influence stability, but this article will be confined to three-rock structure, groundwater, and blasting.

Jan 8, 1969

By T. C. King

AT the new Graham-Central Mill of Eagle-Picher, near Galena, Ill., material is simultaneously dewatered and introduced into the ball-mill scoop boxes by the use of variable-speed, 24-in. spiral classifiers. This arrangement has proved satisfactory in that the moisture content of the wet feed is reduced, thus allowing maintenance of density within the mills, and a constant feed at any desired rate to the mills is provided. In this mill the primary feed is wet crushed to minus ½ in. and preconcentrated by jigs to produce a bulk lead-zinc-iron concentrate and a waste tailing. The jig concentrate is then dewatered by a conventional dewatering classifier and stored in, bins ahead of the ball mills. Even though this material is well dewatered, the discharge at the bin bottom is sloppy because of the gradual drainage of the water from the surface of the particles. Conventional belt feeders with vertical cutoff gates are unsatisfactory because of the flushing characteristic of the wet sand.

Jan 1, 1950