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By L. W. Berger, and R. I. Jaffee, D. N. Williams

The effects of hydrogen on the properties of binary Ti-A1 alloys containing 2.5, 5, and 7 pct aluminum and ternary alloys of the same compositions with added interstitial elements oxygen, nihrogen, and carbon were stzdied. Aluminum increases the apparent hydrogen solubility of the a-phase, resulting in a marked increase in resistance to impact embrittlement. In the Ti-5Al and Ti-7Al alloys, for example, the addition of 180 and 305 ppm hydrogen, respectively, did not cause embrittlement, while unalloyed titanium was embrittled by as little as 75 ppm. The role of aluminum in increasing hydrogen solubility of the a-phase probably accounts for the excellent hydrogen tolerance of a-ß alloys containing considerable amounts of aluminum. There is some evidence that aluminum retards the rate of hydride precipitation. If so, these alloys may be susceptible to slow-strain embrittlement. UNALLOYED a-titanium is extremely sensitive to small amounts of added hydrogen in that there is a marked decrease in notch properties. For example, as little as 100 ppm hydrogen is sufficient to lower the room-temperature notch-impact strength from over 100 to less than 20 in.-lb.' This loss of impact Strength has been associated with the Presence of hydride phase in the microstructure. Hydrogen in the amounts encountered in commercial practice

Jan 1, 1959

By John Chipman, Wayne L. Worrell

Using recent thermodynamic data for the carbides and oxides of tantalum, columbium, and vanadium, the stable solid phases aboue 1300°K and at 1 atm CO(g) pressure in each M-C-O system have been determined. Pourbaix-Ellingham diagrams have been constructed and are used to estimate the minimum temperatures necessary to obtain these metals by carbothermic reduction under reduced pressures. TANTALUM, columbium, and vanadium react with carbon to form the M,C and MC carbide phases. The M,C carbides have narrow homogeneity ranges, but the MC phases possess considerable ranges of homogeneity.' The free energies of formation of the MC carbides were recently measured, and those of MC and M2Ccarbides have been estimated., (The notations MC and MC denote, respectively, the carbide compositions at the carbon-rich and at the metal-rich boundaries of the homogeneous MC phase.) In this paper, these carbide data are combined with thermodynamic data for the oxides to predict the stable phases in the Ta-C-O, Cb-C-O, and V-C-O systems at specified temperatures and oxygen pressures. M-C-O PHASE DIAGRAMS The solid phases in equilibrium above 1300°K for each M-C-0 system are shown in Figs. 1, 2, and 3. Above 1300°K, the vapor would consist entirely of carbon monoxide; and these phase diagrams were obtained by specifying the vapor pressure of CO(g) to be 1 atm. The temperature at which any two solid phases become unstable is specified along the two-phase equilibrium lines in each diagram. To simplify the diagrams, all solid phases in the Ta-C-O and Cb-C-O systems are represented as stoichiometric compounds. However, the homogeneity ranges of VO and VC are indicated, because they form a complete series of solid solutions.3 It also should be noted that the homogeneity range of

Jan 1, 1964

Jan 1, 1967

By L. W. Berger, R. I. Jaffee, D. N. Williams

The effects of hydrogen on the properties of binary Ti-A1 alloys containing 2.5, 5, and 7 pct aluminum and ternary alloys of the same compositions with added interstitial elements oxygen, nihrogen, and carbon were studied. Aluminum increases the apparent hydrogen solubility of the a-phase, resulting in a marked increase in resistance to impact embrittlement. In the Ti-5Al and Ti-7Al alloys, for example, the addition of 180 and 305 ppm hydrogen, respectively, did not cause embrittlement, while unalloyed titanium was embrittled by as little as 75 ppm. The role of aluminum in increasing hydrogen solubility of the a-phase probably accounts for the excellent hydrogen tolerance of a-ß alloys containing considerable amounts of aluminum. There is some evidence that aluminum retards the rate of hydride precipitation. If so, these alloys may be susceptible to slow-strain embrittlement. UNALLOYED a-titanium is extremely sensitive to small amounts of added hydrogen in that there is a marked decrease in notch properties. For example, as little as 100 ppm hydrogen is sufficient to lower the room-temperature notch-impact strength from over 100 to less than 20 in.-lb.' This loss of impact Strength has been associated with the Presence of hydride phase in the microstructure. Hydrogen in the amounts encountered in commercial practice

Jan 1, 1959

By Frederic Benard

PRIOR to 1936, the Ontario Refining Co. received all incoming blister copper from The International Nickel Company's smelter in the usual form of 460-lb. cakes, or slabs. These were received in open cars in lots of 250 pieces. At the refinery the cakes were unloaded onto narrow-gauge cars, for convenient handling and pickup by charging cranes. In March 1936, an investigation was started on the feasibility of transferring converter copper in the molten state from the smelter to the refinery anode furnaces, a distance of 1 ¼ miles. Although common in steel practice, the transportation of blister copper in this form had not previously been attempted and a preliminary study of the various factors involved was therefore necessary. For this purpose, a series of experiments was made in which molten copper, removed at different stages during the furnace cycle, was held in a small portable holding furnace. This vessel was essentially a refractory-lined steel cylinder provided with ports for filling and emptying, heated by an oil burner. Dimensions of the steel shell were 3 ft. 10 in. diameter by 7 ft. 3 in. long, and thickness of refractories depended on the design and combination used for the particular experiment. The vessel was filled with approximately 2 ½ tons of copper at a predetermined temperature, the lining having been preheated to a definite point by means of an oil burner. All openings were well luted and temperature readings were made every 15 min. by means of an immersion-type thermocouple. In this manner the rate of heat loss resulting with different refractory design could be developed. The ratio of exterior surface to weight of metal was taken into consideration in comparing the experimental results with what might be expected for a full-sized unit, and observations were also made on type and degree of slag accretion. It was not possible to get as much information on this latter point as desirable, but all evidence showed that the problem would be control of slag build-up rather than attack on refractories. From the information derived, and in consultation with the engineering staff of the supplying company, an order was placed for the first

Jan 1, 1938

By Carl Henrich

Jan 1, 1893

By F. W. Bowdish

Analysis of data on the equilibrium exchange of sodium ions from salt solutions for calcium ions, from various fractions of an oxidized calcareous iron ore from Lorraine, France, strongly suggests that the calcium may be attached to the solid by only one of its bonds. Nearly equal values were found for the equilibrium expression from data covering concentration ranges of 1000 fold for the salt and 235 fold for the ion-exchangeable calcium. Differences indicated between the exchangeable calcium contents of the slime and the sandy portions of the ore, as well as the equilibrium relationship itself, are of importance in the flotation of the ore. During an experimental program on the flotation of oxidized calcareous iron ores from Lorraine, France, ion-exchangeable calcium was found in the ore. Because this source of calcium ions, if not controlled, could thwart all efforts at flotation, an extensive study was made of the phenomenon. The part of that study reported here was to obtain data on the equilibrium established between ore solids and solutions of sodium chloride, and to analyze the data to try to understand better the physical chemistry of the exchange. The ore contains oolites of goethite and quartz grains embedded in a matrix consisting of calcite and a brown cement believed to be the residue from oxidation of the silicate minerals found in fresh unoxidized ore. When ground, a substantial fraction of the ore becomes a fine slime in which is concentrated more than half of the alumina content of the ore. It is believed that the alumina occurs as unidentified clay minerals with which most of the ion-exchange capacity of the ore is associated. A preliminary experiment on the exchange of ions from the ore for sodium ions from solutions of NaCl showed that calcium was about ten times as abundant as magnesium in the exchange solutions. Thus calcium was the predominant ion in causing difficulties with flotation, and it was the only one for which data was obtained in this study. It is believed that the omission of magnesium ion exchange from consideration does not invalidate the results. It is possible, however, that inclusion of magnesium in the analyses and calculations or its prior elimination from the samples would have improved the consistency of the results. EXPERIMENTAL Data about the equilibrium exchange of sodium from solutions for calcium from the solids were obtained using two different samples of material. The solids

Jan 1, 1963

By Hubert E. Risser

Although, for about a half-century the percentage of coal production provided through strip mining has steadily increased, recent trends indicate that a peak in percentage (not tonnage) is being approached, principally because of the decline in economic adrantage enjoyed by strip mining compared to underground mining. Factors contributing to the decline are the decrease in the margin of advantage in manpower requirements held by strip mining; an increase in depth and volume of overhurden, requiring larger equipment and capital investment; increasing lack of reserve land blocks large enough to support extensive strip mining operations; more stringent legislation for reclamation of stripped land, with increasingly higher costs of such reclamation; and the increasing costs of land surface rights for strip mining. Already there has been a peak and suhsequent decline in relative importance of strip mining insome major Eastern coal-producing states; trends indicate that a peaking for the whole Eastern region is on the way. Although, in the West the pressures are less severe, they will, nevertheless, reduce to an increasing degree the advantage that strip mining has possessed. For about half a century, strip mining has been providing an ever-increasing share of total coal output in the United States, and in the past 30 years this share has grown from less than 8% to 33.7%, as shown in Fig. 1. Fig. 1 also shows that strip mining is gaining faster in the West than in the East. From 1961 to 1967, output from strip mines grew 63.6 million toqs, or 52.2%. Certainly there is nothing in such performance to indicate any peaking in the level of strip coal-mine production. But the fact is that, if not in actual tonnage, strip mining appears to be reaching its peak in relative importance, at least east of the Mississippi River. And the area east of the Mississippi provides 90.0% of the strip and 94.9% of the total coal production of the nation. The relative economic advantage which spurred strip mining's growth for a third of a century has been diminishing markedly in recent years. Fig. 2 shows evidence of this decline. From 1947 until 1961, strip tonnage output remained fairly stable, at the end of the period showing only a 12.5% decline. Meanwhile, underground coal production fell 44.5%. As the result of the greater decline in underground coal, strip coal in 1961 furnished 30.3% of the total coal produced, compared to only 22.1% in 1947. In the succeeding six years, however, underground coal output increased by 76.5 million tons, while strip output increased only 63.6 million. Further evidence of the strengthening of underground coal's relative position — or if you will, the weakening of strip coal's position — can be found in the major coal stripping states: Illinois, West Kentucky, Ohio, Pennsylvania, Indiana, and West Virginia, which in 1966 provided 80% of the nation's strip coal. Fig. 3 shows what has been happening in three states lying in the Appalachian field and in the total output of these three states. In the figure, the column height represents the output of coal mined by all methods. The number at the base of each column is the percentage mined by stripping. In Pennsylvania and Ohio, the percentage of strip mining increased between 1956 and 1961, but by 1966 had declined from the 1961 level. In West Virginia, a decline occurred during the first five years but was followed by a rise. In January 1968, Coal Age published an article listing the locations and capacities of new large mines in the planning and construction stages that would be operating by 1968-1971. The plans for West Virginia and Pennsylvania indicated all the new mines would be underground. Except to the extent they might replace existing under-

Jan 1, 1970

By J. Douglas, W. T. Ford, G. E. Henderson, I. F. Roebuck

An implicit numerical method is presented for simulating the differential and algebraic relations governing one-dimensional three-phase flow in porous media. The method is based upon compositional representation of the hydrocarbon system. Variable physical properties and water-oil capillary forces are included in the formulation; however, the effect of gravity is ignored. The effects of changing composition and mass transfer are considered through the use of known phase behavior concepts and correlations. The differential and algebraic equations and the numeric approximations to these equations are presented, and the computing algorithm is discussed in detail. This method is used to simulate a single-phase, two hydrocarbon-component gas displacement laboratory experiment. The method is also applied in simulating a solution gas drive and a gas injection problem using a reservoir oil represented as a nine-component mixture. For comparative purposes, the latter two problems also are examined with a one-dimensional volumetric model. The results of the simulation of the laboratory experiment demonstrate the relevance of this method to problems wherein the effects of mass transfer significantly enter the displacement process. The comparison of the results of the volumetric and compositional methods applied to a reservoir system illustrates not only the advantages and benefits derived from examining the hydrocarbon system composition, but also the necessity of this approach in application to a general reservoir problem. INTRODUCTION The advent of large memory, high-speed digital computers enabled reservoir engineers and mathematicians to pool their knowledge in the development of sophisticated techniques for the prediction of oil and gas reservoir performance. These techniques have progressed from volumetric and trend analysis calculations to the development of "mathematical models", or reservoir simulators. These latter models, in general, utilize finite difference approximations to the rather complex partial differential equations that mathematically describe the physics and thermodynamics of fluid flow in porous media. Many forms of this "model" type are available today, and much of the recent literature has been devoted to either improving known methods or developing new techniques for use in these prediction methods. The more advanced techniques in use at this time consist of the solution of differential and algebraic relations that describe a reservoir geometry in one, two or three dimensions and that incorporate reservoir hydrocarbon and water fluid systems that obey specified physical laws, having properties that might easily be measured in the laboratory. This type of model utilizes formation volume factors and other volumetric data, expressed directly as functions of pressure, to represent the reservoir fluid system. Experience gained with this type of simulator, commonly known as a "beta-factor model", has indicated that the approach has many outstanding defects, most of them due to the assumption that those properties measured in the laboratory completely describe the behavior of the fluid system throughout the life of the project under study. The effects of varying hydrocarbon composition and mass transfer between the phases of this hydrocarbon system must, by definition, be ignored. These defects, which may often be ignored in

Jan 1, 1970

By O. M. McRae

The Courtland-Gleeson area is in Cochise County about 15 miles east of Tombstone in southeastern Arizona. Rocks exposed in the area range in age from Pre-cambrian to Quaternary. The Precambrian is repre-sented by the Pinal schist. Paleozoic rocks include the Cambrian Bolsa quartzite and Abrigo limestone, Mississippian Escabrosa limestone, and the Permo-Carboniferous Naco Group limestones. Rocks believed to be of Triassic and/or Jurassic age include the Copper Belle monzonite porphyry, Turquoise granite, and Gleeson quartz monzonite. The Cretaceous is represented by andesitic volcanics and various sedimentary rocks. Tertiary rocks include the intrusive and extrusive Sugarloaf quartz latite porphyry and numerous dikes of various rock types. Quaternary conglomerates cover the northern and eastern part of the area. The geologic structure is extremely complex. All rocks as old as early Tertiary have been involved in either tilting, normal faulting, high angle reverse faulting, imbricate thrusting or folding and overfold-ing. Major deformation was initiated during the first half of the Tertiary. Northeast-southwest compres-sional forces caused thrust plates containing lower Paleozoic rocks to override Cretaceous rocks. Subsequently, two large slide blocks of lower Paleozoic rocks, acting under the influence of gravity, moved eastward. The imbricate structure and the gravity slide blocks were then broken by late Tertiary normal faults. INTRODUCTION The Courtland-Gleeson area, or Turquoise Mining District, has long been recognized as an area of extreme structural complexity. Gilluly 2 referred to the entire district as a "gigantic thrust breccia". In 1962, Bear Creek Mining Company completed a two year program of detailed geologic mapping supported by exploration drilling. The purpose of this paper is to present some of the results of this investigation and to provide a structural interpretation based on these results. The geologic map that accompanies this report is generalized and shows only the major and significant features. The area was initially mapped on aerial photographs on a scale of 1 in. equals approximately 500 ft. These data were transferred to a planimetric base using a vertical sketch master. LOCATION The Courtland-Gleeson area is in central Cochise County, about fifteen miles east of Tombstone, and about twenty-two miles northeast of Bisbee in southeastern Arizona (Fig. 1). The area is readily accessible over graded gravel roads from both Tombstone and Elfrida. GENERAL GEOLOGY Rocks exposed in the area range in age from Pre-cambrian to Quaternary. wilson3 and Gilluly2 have published very detailed descriptions of the principal rock units exposed in the area. Only a summary description is provided in Table I. A great number of previously unmapped narrow Tertiary dikes and small irregular masses of hornblende andesite porphyry, lamprophyre, and aplite intrude the Gleeson quartz monzonite in the western part of the map area. The scale of the map prohibits showing them. The aplite dikes are related to, and bear the same structural relationships as, the Sugarloaf quartz latite dikes found in this area. For that reason, and because both the hornblende andesite porphyry and the lamprophyre are post-mineral and post-thrusting, their omission from the map is not considered significant. Because so many of the contacts in the district are fault contacts, because bedding faults appear to be prevalent but are difficult to recognize and map, and because igneous intrusions are so common throughout the sedimentary section, it is virtually impossible to measure an exact total thickness of any of the sedimentary rock units. Nevertheless, neither the field mapping program nor the diamond drilling provided any basis for suspecting that the thicknesses of the sedimentary units are significantly greater or less than what might be inferred from surrounding districts.

Jan 1, 1967

By Chung Yu, Wang

CHINA can he roughly divided into three metallogenetic province: North China, the Yangtze Valley, and South China. In North China the old Pre-Cambrian schists and gneisses are represented by the abundance of quartz mines in which sporadic occurrences of copper, lead, zinc, gold, and silver are sometimes found in subordinate quantities. Along the Yangtze Valley and in Central China, extending eastward as far as Shantung, are found here and there intrusions of dioritic rocks, in which occur the famous contact deposits of iron ore, besides which minor quantities of copper. lead, and zinc are also found. In South China the igneous intrunsions are of granitoid type in which, or in the vicinity of which, occur in certain regions immense deposits of antimony, tungsten, tin, and mercury. Broadly speaking. most of the famous coal mines are now situated in regions north of the Yangtze River, in which occur also the sedimentary deposits of iron in contradistinction to the contact deposits of iron along the Yangtze Valley.

Jan 1, 1943

By Jasper L. Stuckey

PYROPHYLLITE, first identified as soapstone,1 later as agalmatolite,2 and finally as pyrophyllite,3 has been known to occur in North Carolina for more than 130 years and has been produced intermittently in commercial amounts for the past 100 years. Pyrophyllite mining, however, has become a major industry in North Carolina only during the past 25 years. North Carolina and California are the chief producing states. Current annual production averages 125,000 tons, of which slightly more than 90 pct comes from North Carolina. Distribution and Geologic Setting: All known pyrophyllite deposits in North Carolina are associated with rocks of the Carolina Slate Belt,4 which is composed of a vast series of metamorphosed volcanic and sedimentary materials, occurring as two zones extending in a northeast-southwest direction across the state. The larger of these zones, lying in the central Piedmont region, varies from 8 to 50 miles wide. The smaller zone lies along the eastern edge of the Piedmont region and is partly covered by coastal plain sediments.

Jan 1, 1958

By A. T. Yu

On March 18, 1964, the 52,000 dwt ore carrier M/S Houn Maru called at the port of Coquimbo, Chile, on its maiden voyage to take iron ore to Japan. This marked the first time a vessel of this size ever arrived at Coquimbo, and the event promises to drastically accelerate henceforth iron ore exports from Coquimbo province. This was made possible by the use of a versatile shiploading system recently installed by Cia. Minera Santa Fe. Coquimbo has no mechanized loading facilities other than six conventional 5-ton cargo cranes. Limited space on shore further complicates the stocking problems. To make the best of what is available, a meticulously organized semi-hand-loading system has been developed through the years.

Jan 5, 1964

By R. W. Raymond

THE sudden death of Dr. Drown, on Nov. 17, 1904, brought to multitudes the pang of personal loss. Of all those who, as students at Lafayette College, the Massachusetts Institute of Technology and Lehigh University, were brought under his influence, not one can have forgotten him, and all will now acknowledge, with an unfading gratitude, what they owe in professional equipment to his wise, clear, skillful guidance, and in character to his sympathetic, stimulating personality. Outside of this wide circle, the experts of both hemispheres will lament the departure of one who, in his department of scientific inves¬tigation, both knew what work was needed, and how to do it so that it needed not to be done again. The older members of the American Institute of Mining Engineers will remember with gratitude the part he took, as Secretary from 1873 to 1884, in promoting the interest of that organization, and in shaping the plan and policy which it has followed with such noteworthy success. And, in addition to all these (though partly included among them), there are a host of friends; who can scarcely think of the public loss by reason of their own. Thomas Messenger Drown was born March 19, 1842, at Phil¬adelphia, Pa. His parents were natives of New England; and. he was the youngest of their three sons. He received his preliminary education in the public schools and the High School of Philadelphia, from which he was graduated in 1859. Be-

Jul 1, 1905

By L. W. Bahney

MANY methods for the determination of gold or silver, or both, in cyanide solutions have been published, which with care in manipulation, and modification in some cases, will give results that are satisfactory. It is possible to classify or group these methods as follows: 1. Evaporating the solution in a porcelain or agate-ware dish containing litharge,1 or in a "boat" made of lead foil. 2. Forming a lead sponge containing the precious metals by means of zinc shavings,2 zinc dust,3 or a piece of aluminum.4 3. Decomposing the cyanide solution with an acid and precipitating the precious metals by the use of one or a combination of some of the following: Copper sulphate,5 sodium sulphite,6 hydrogen sulphide,7 cement copper.8 4. Precipitating the silver by zinc dust held in a Hooch crucible and determination with a standard solution of sulphocyanate.9 5. Electrolysis.10 6. Colorimetry.11

Jan 2, 1915

[Pumps: oil-well: plunger: essential parts, G26, 130; 74, 828 improved type, 74, 846 leakage, 74, 837 operating cycle, 74, 833 Uren design, G26, 145 sucker-rod failures, G26, 136 sucker-rod stress, 74, 835 sucker rods, 74, 830, 832 tubing, 74, 833 tubing difficulties, G25, 138; 74, 836 Olivite, 73, 337 valve and seats, 74, 832 Punching: Monel metal, 78, 86 nickel, 78, 86 Punjab. See Indian Empire. PUPIN, M. L biography, M26, 113 John Fritz medalist, 1931, M81, 499 recipient of Washington Award, M28, 155 PURDY, R.: Discussions: on Relative Efficiencies of Domestic Fuels in Relation to Their Costs and Their Advantages 108, 353 on Uses on Coal in the Ceramic Industry, 108,389,398]

Jan 1, 1936

By Peter F. Weiss, H. Riedler, I. M. Moschitz, A. Olsacher, G. B. Fettweis

CONTENTS : 1. NATURAL FACTORS Geology Petrography and Rock Mechanics Mining System Orientation Rock Bolting System Movability of the Ore Grain Size Distribution Permeability Contamination Value of the Ore Hydrology 2. TECHNICAL FACTORS Height Length and Width Drawing Areas Time Factor Water Predrainage Surf ace Draining Underground Draining Advancing Slitting Sequence of Development Initiation of the Caving Process Drawing Rate 3. SPECIFIC MINING RULES Advancing Development Drawing Rate Interruption of Drawing (Water Distribution, Concentration of Mud, Dilution) Blasting 4. CONTROLS Safety Controls for Operation Computerised Drawing Control Structure of the Computer Program Hard Ware Print Outs 5. SUMMARY 6. ACKNOWLEDGEMENTS 7. REFERENCES Under the heading "Development System for Block Caving under Severe Conditions" a report was presented to this congress regarding a magnesite mine using block caving for several years. On account of the experience gathered in this mine and the results of far reaching exchange of experience, as well as under due consideration of the international literature it is tried to systematically list and briefly discuss the following factors that have to be considered for development and draw control of block caving. 1. NATURAL FACTORS It is self evident that this implies all those circumstances given by nature and which cannot be altered by man. Any mining activity is subjected to those and the success is depending on how far technology can be adjusted to those conditions. Geology Deposits of considerable thickness with rather steeply inclined flat-faced contacts are optimal for block caving. While vertically there is practically no limitation- for the deposit, theoretically, the smallest horizontal basis apt for operating block caving is the minimum area necessary to get the rock to completely cave in by undercutting and drawing. Practically, only consider- ably bigger main dimensions are found, mainly because of technical factors (machinery and equipment) and economic factors (cost ratio of exploration vs. development, danger of contamination).

Jan 1, 1981

By Ernst M. Cohn

The demonstrations of the "Silent Sentry" by Union Carbide Corp. in 1957 and of a special tractor-plow by Allis-Chalmers in 1959 ushered in the technology era of fuel cells. The idea for direct conversion of chemical to electrical energy, first published in 1801 by Davy in England and Ritter in Germany, has been kept alive by a few people through 150 years: Grove built the first hydrogen-oxygen fuel cell in 1839; Mond and Langer made electrolyte contributions around 1890 that are still used today; Baur worked on coal-based cells from 1900; Bacon started his work in the '30's, which resulted in the first multi-kilowatt unit in the '50's; Davtyan studied molten-salt electrolytes in the '40's, followed by Ketelaar in the '50's; and Justi developed highly active electrodes in the '50's, to name only some of the pioneers. Despite the tremendous increase in research and development of fuel cells, these direct energy converters are still in their infancy. They will find their functional application in space, where power density must be maximized and product water utilized. These early systems will provide valuable experience in system engineering and reliability.

Jan 9, 1964

By W. C. McClain

The amount of vertical subsidence occurring over a longwall operation is a function of the thickness of material removed, the quantity and quality of any fill material, the width of the extraction, and the depth. The relationship between these variables is empirically determined, and subsidence can be predicted using only a few easily established constants which are subject to local conditions, such as the angle of draw. Associated with the vertical subsidence are both tensional and compressional horizontal strains. The component of strain in the direction of face advance is temporary, while the component perpendicular to the direction of working is permanently retained by the ground. It is these horizontal strains and the vertical strain (tilt) which result in damage to surface structures. It is possible to ameliorate the consequences of mining subsidence by utilizing the well-proved techniques described in this paper in the underground operations and on the surface. INTRODUCTION In the past, American mining practice in stratified deposits has been mostly restricted to production by the room-and-pillar system where a sizable percentage of the salable product is left in place as pillars. These pillars are usually regularly spaced and provide a permanent support for the roof of the mine and the surface above. The longwall system employs an advancing face which may be as much as several hundred yards long and some sort of breaking and loading machine which moves back and forth along the length of the face. The roof is supported behind the face only to a distance required to provide working space for the production machine. The supports are then withdrawn and the roof is allowed to cave. The longwall system therefore possesses the various advantages of complete extraction, thus effectively increasing reserves, while at the same time eliminating the necessity and cost of installing artificial supports such as roof bolts and heavy steel girders over large areas. Longwall mining has long been practiced in Europe, where it has undergone an involved development, culminating in the recent perfection of powered-loading machines and automatic self-propelled supports, offering high productivity. With ever-in creasing

Jan 1, 1967

By Robert M. Funk, James E. Lawver

The development of a laboratory and pilot-scale high-tension electrostatic flowsheet for the production of iron-ore super concentrates having silica contents in the range of 0.1% is presented, A variety of hematite and magnetite ores were tested with this flowsheet, and the pertinent metallurgical data are given. The applications and limitations of this process are brought out in terms of both practical and theoretical considerations. There have been many new developments in the past few years that have required mineral beneficiation engineers to consider new techniques for iron-ore concentration. Developments in iron powder metallurgy, and particularly the making of sheet metal directly from high-purity iron-ore concentrates, and the concept of using metallized pellets as a substitute for scrap in electric-furnace steelmaking have created demands for what is commonly referred to as iron-ore superconcen-trates. In most cases, specifications for superconcentrates are that they contain less than 0.1% total gangue, with some applications requiring less than 0.05% gangue. To produce these concentrates, new and modified processes are being developed, and the three methods receiving attention as the primary concentrating methods are: 1) Magnetic separation in which dry rotor-type equipment is used for magnetite and the high-intensity magnets are used for hematite. 2) Amine flotation. 3) "High-tension" electrostatic separation (or, elec-trodynamic concentration). This paper examines the high-tension electrostatic process in terms of its limitations and abilities for the production of iron-ore superconcentrates. A technically effective and simple flowsheet was developed through laboratory and 5 and 100-ton pilot-plant studies for the production of concentrates containing from 0.02 to 0.20% SiO, with iron recoveries between 85 and 90%. The process is also shown to be economically feasible. Laboratory Test Program Separation Characteristics: The suitability of the electrostatic high-tension method for iron-ore supercon-centration stems from the fundamental mechanism governing the process, i.e., particles are separated on the basis of differences in electrical conductivities. This conductivity is a characteristic property of minerals, and if the difference between the conductivities of two min- erals is great enough, then their separation can be performed by a high-tension machine. As shown in Figs. 1 and 2, the critical factor is the time necessary for the particle charge density, which is established by a corona discharge field, to decay to a level such that the centrifugal force acting on the particle exceeds its electrostatic, or image, force. At this point, the particle can leave the rotor at some trajectory and fall into an appropriate product receptacle. This decay time is directly proportional to electrical conductivity, and the process variables, such as feed rate, rotor speed, electrode configuration, and rotor composition, are selected to optimize the ability of the separator to resolve different conductivities. Table 1 lists the measured conductivities for some of the iron and gangue minerals used in developing the flowsheet. These results were obtained by using the conductivity cell described by Lawver and Wright.' The discharge curve of most minerals that lend themselves to super concentration by high-tension is so fast that the

Jan 1, 1971