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By Ripu Daman Lama

The size of coal pillars in mines until recently has been determined by experience without being based upon scientific investigations. As a consequence, the size of pillars had invariably been larger than could be accounted for because of the number of unknown factors involved which influence the strength, dictating the use of large safety factors. With the mining going deeper, the size of the pillars greatly increases and sometimes a considerable portion of the mineral property are blocked in the mine pillars required to support the superincumbent strata. With the advances in the field of Rock Mechanics, attention of mine planning engineers has been focused upon the design of mine pillars for safe and efficient working as well as decrease losses of coal. The problem involves the study of three factors: (1) Presence of stresses in the area and their distribution on pillars in the course of extraction. (2) The influence of external factors on the strength of coal. (3) The inherent mechanical properties of coal. These aspects have been studied by a large number of investigators, the first by in-situ stress measurements and photoelastic studies and the second and third aspect by studies conducted in the laboratory on small size specimens (Bunting, 1911; Evens & Pomeroy, 1961; Gaddy, 1956; Greenland et al, 1941; Steart 1954). The size of the specimens tested in the laboratory has been limited to a few inches and the results obtained have been extrapolated by large factors, sometimes several hundred times the largest specimen tested. In these tests much consideration has not been given to

Jan 1, 1971

By N. J. Myers, S. J. Nemeth

POWER in the mill at Appalachian Sulphides Inc. is provided by 86 electrical motors ranging from 1 to 200 hp and totaling 1200 hp. After a careful study of different types of support for these cables an expanded metal trough was chosen as the most suitable. One hundred and twenty feet of trough were installed in 18-in. width and 150 ft in 6-in. width. This trough carries all the power as well as the control circuits. Now that the electrical distribution system is complete it is clear that this type of cable supporting system offers many advantages. To handle the same amount of cable in conduit, for example, would have required such a jungle that wiring all the different motors and controls would have been very difficult, even for the original hook-up. In the Appalachian Sulphides operation it has been necessary to make changes from time to time in the wiring of the different motors. These changes are readily made with the present cable supporting system because the trough leaves the wires accessible for rerouting as needed.

Jan 1, 1958

By C. Richard Tinsley

INTRODUCTION Project financing has been defined by various authors in this book. It is founded on reliance upon the project's own future cash flows and secondarily on the collateral value of the asset base developed. It is chiefly provided by the banking community who, after an assessment of the risks involved (See Chapter 9) analyse the company's presentation (See Chapter 10) in order to structure a financing package often at a leverage of up to 80% debt. This paper describes the various support and structuring techniques used to delimit and abate the risk components perceived from the banks' experience on project development especially for the period before cash flow is generated (pre completion). ADVANTAGES The advantages of project financing extend beyond the offloading of risks to banks. Among the advantages are the following: 1. Longer loan maturity than conventional, unsecured financing; 2. Loan disbursement and repayment tailored to specific mine; 3. Ability of a joint venture without a "track record" to raise financing; 4. Obtain financing where further direct borrowing (corporate credit) limited by existing indentures; 5. Possibility of arranging finance off-balance sheets; 6. Leverage return on equity; 7. Obtain tax savings with certain project financing structures; and 8. Obtain flexible loan repayment conditions. It can also be said that from the point of view of the company, project financing has certain disadvantages which can be summarised as follows: 1. Perceived higher cost (risk premium) compared with straight corporate credit; 2. More documentation; and 3. Need to negotiate risk-sharing aspects. The main attraction of project financing is the ability to pass certain risks on to the lenders within a flexibly funded transaction. (For a more detailed description of the specific risks see the author's paper at the beginning of Chapter 9. The same risk system is followed here.) The typical project financing has corporate support prior to completion and will usually carefully control the resultant cashflow after completion to ensure the bank does not unnecessarily assume further risks of an equity nature. WITHIN THE COMPANY'S CONTROL Operating Risk This is broken into three interrelated segments for ease of description. Technical Component: This must be specifically addressed if new technology or unproven adaptations are to be used. The banks will have scrutinized the sampling and bulk testing work, perhaps grilling the geological, mineral processing, metallurgical, and mining engineering staff or consultants directly. A number of supports are available such as: TECHNOLOGY GUARANTEE: Either the company itself or the process developer will guarantee that the technology will work for a period of, say, six months to two years after startup. If not, then financial penalties will apply although these are rarely sufficient to repay the loan. Many process developers are weak financially and may have little substance to back such a guarantee.

Jan 1, 1985

By Arthur V. Abbott

TO rightly use materials, two kinds of knowledge are essential: first, the actual strength of the substance; and secondly, the forces to which, in the structure, it may be subjected. Nearly all of the data which we have at the present time have been obtained from the experiments made on the materials used in Europe, and by foreign investigators. The materials commonly used in this country, es-

Jan 1, 1884

By A. B. Kinzel

Precise knowledge regarding the effect of heat treatment on the properties of steel has made possible the detailed specifications and instructions covering optimum heat-treating temperatures and practices that are in current use. A distinct contrast is presented by the metallurgical treatment of steel adjacent to a fusion weld, as such steel is subjected to each temperature from room temperature to fusion temperature, and cooled at a rate that is not generally controllable but is predetermined by the nature of the assembly to be welded, the kind of welding used, and the surrounding conditions. This is true regardless of the type of fusion welding: oxyacetylene, electric arc, thermit or flash resistance. Therefore it seemed desirable to investigate the effect of this metallurgical treatment on the characteristics of carbon steels commonly used for welding, by a detailed study of metal subjected to each temperature range; i.e., each heat-affected zone. Oxyacetylene welding was chosen for the investigation because of the experimental facility of accurately segregating and studying each temperature zone. The nature of the zones produced by other types of welding is the same. The difference is primarily a matter of dimensions of each of the temperature zones involved. The advantages and disadvantages of the extent of the zone are of prime moment, and are discussed after the presentation of the detailed zone study. No mention is made of the fused metal proper, as this has been the subject of much published research and the nature of the solidified metal is fairly .ell known. General Method The scheme of procedure in the work herein reported involved the testing of the metal of each temperature zone adjacent to the weld in so

Jan 1, 1935

By A. B. Kinzel

Precise knowledge regarding the effect of heat treatment on the properties of steel has made possible the detailed specifications and instructions covering optimum heat-treating temperatures and practices that are in current use. A distinct contrast is presented by the metallurgical treatment of steel adjacent to a fusion weld, as such steel is subjected to each temperature from room temperature to fusion temperature, and cooled at a rate that is not generally controllable but is predetermined by the nature of the assembly to be welded, the kind of welding used, and the surrounding conditions. This is true regardless of the type of fusion welding: oxyacetylene, electric arc, thermit or flash resistance. Therefore it seemed desirable to investigate the effect of this metallurgical treatment on the characteristics of carbon steels commonly used for welding, by a detailed study of metal subjected to each temperature range; i.e., each heat-affected zone. Oxyacetylene welding was chosen for the investigation because of the experimental facility of accurately segregating and studying each temperature zone. The nature of the zones produced by other types of welding is the same. The difference is primarily a matter of dimensions of each of the temperature zones involved. The advantages and disadvantages of the extent of the zone are of prime moment, and are discussed after the presentation of the detailed zone study. No mention is made of the fused metal proper, as this has been the subject of much published research and the nature of the solidified metal is fairly .ell known. General Method The scheme of procedure in the work herein reported involved the testing of the metal of each temperature zone adjacent to the weld in so

Jan 1, 1935

By M. W. Bartley, Hugh M. Roberts

SUBSTANTIAL deposits of Bessemer hematite have been found recently by drilling beneath Steep Rock Lake, Ontario, which is situated in the northern part of the Lake Superior Region. It will be practicable to divert the waters flowing into this lake and develop open pits on the upper part of two large ore bodies by damming off and pumping out the water in the part of the lake in which they occur. Ultimately, the bulk of the ore will be mined by underground methods. Owing to the generally massive nature of the rocks in the area, no underground flows of major consequence are anticipated after diversion of the lake. The Steep Rock deposits are attributed in origin to hydrothermal replacement. They were formed, for the most part, along an unconformable, brecciated contact between the Steep Rock limestone and an overlying younger volcanic series. The replacing solutions came in as igneous after-effects, following upon the intrusion of basic igneous rocks that invaded the hanging-wall volcanics. It is believed that this took place in a geological period roughly equivalent to late Middle Huronian, which was the period when the most extensive iron-bearing rocks of the Lake Superior Region were formed. Comparison is made with other deep-seated iron-ore bodies in the Lake Superior Region, the origins of which are ascribed in the discussion to hydrothermal replacement.

Jan 1, 1943

By Ralph A. Sherman, J. M. Pilcher

BY surface treatment of coal is meant the application of a material, either solid or liquid, to the surface of pieces of coal. The purposes of surface treatment are varied. They may be to identify or "trade- mark" the coal, to modify the burning characteristics, the coking tendencies, or the behavior of the ash, to prevent the freezing of wet coal, or to control the dust. The control of dust is the usual purpose of surface treatment. TRADE-MARKING COAL The application of color to the surface of coal for the purpose of identification and registration of the trade-mark has been practiced to some extent. In 1928, the Glen Alden Coal Co. began to color its coal and adopted the trade-mark, "Blue Coal." The Old Ben Coal Co. later followed a similar practice with "Green Coal." A commoner means of identification of coal has been the stenciling of designs or pasting labels on large lumps or in the distribution of small cardboard tags through the smaller sizes. The details of the method used to color coal have not been revealed. Usually all of the coal is not treated, because of the expense. Only enough pieces are colored to show clearly when distributed through the coal. The patent literature gives information on some of the methods proposed. Esselen and Weiss have patented the deposition of a coloring material in the valleys of the surface of the coal. Sperr covers the quenching of coke with water containing a pigment or dye that will deposit on the coke. He also suggests electroplating with copper or nickel. Glinsmann subjects the freshly fractured coal surface to the action of an alkali or alkali earth ferricyanide and a ferric salt. Barsky and Hanson specify a method for the application of the same chemicals covered by Glinsmann. COATINGS FOR IMPROVEMENT OF APPEARANCE As a purchaser often judges coal by its appearance, modification of the surface has been attempted from time to time, particularly of the surface of outcrop or stored coal, which has become covered with a brown film of iron oxides, but information is lacking as to the extent or success of the

Jan 1, 1950

By Kenneth Seaver

It is rather gratifying that in the field of the manufacture of refractories, in which, as a whole, foreign practice has surpassed us, the United States stands pre-eminent in the making of silica brick. In some instances European manufacturers have refused point-blank to credit the possibility of making to such specifications as are Common with us, until the actual completed shapes were shipped for inspection. But both the manufacturer and consumer in foreign lands are now frankly learning from us, and benefiting by our advanced practice in this field, as is evidenced by the orders placed here and the efforts put forth abroad to come up to the standard of American-made material. In no metallurgical operation has the employment of silica brick spread with such leaps and bounds as in the building of plants for the carbonization of coal, particularly in the byproduct coke oven. Today, in practically all types of oven, the structure above the floor level (except the facings) is of silica, while in the recuperative and in some regenerative types, its use is extended to that portion of the oven below the floor as well. By reason of the fact that there are a number of classes of refractories of higher silica content than the usual so-called fire-clay brick, there is sometimes a misunderstanding as to the class of material referred to as "silica" brick. We here refer only to a brick having a silica content of 94 per cent. or more and made usually from quartzite rock with a small percentage of lime as a binder. The term "silica" brick is sometimes rather loosely applied to brick from highly siliceous clays, or to a quartzite refractory of mingled fire-clay and quartz rock; but such products are not considered in this discussion. : Materials The rock from which practically all high-grade silica brick are made is a true quartzite or metamorphosed sandstone, variously known as

Jan 1, 1916

By Howard Smith

OF late considerable experimental and, theoretical interest has been shown in the rates of transformation from a single phase, usually a supercooled solid solution, into one or more phases. Such reactions may involve both diffusion and transformation of the major constituent, as in iron alloys, or it may simply involve diffusion, as in superstructure forma-tion and in age-hardening systems. Most of the work has been confined to ferrous alloys1-9t although two investigations have been made on copper alloys10,11. That such work may be of considerable, practical importance has been demonstrated by Bain12, by the workers at the Kaiser Wilhelm Institut fur Eisen-forschung13,14, and by the everyday use of precipitation and age-harden-inn principles15. Experiments in this country have generally followed Davenport and Bain's technique of rapid supercooling followed by isothermal treatment. In Germany16,17 the work has been extended to the study of the influence of accurately controlled and measured rates of cooling. The work on steel indicates that there are two subcritical temperature ranges where reaction starts sooner after quenching and proceeds at a more rapid rate than at other temperatures. At subcritical temperatures above Ar" where reaction is dependent upon atomic migration there is a period of time of which the length depends upon the alloy content and the temperature, before which no reaction has been detected. Daven-port and Bain1 find that different sorts of atoms in solid solution in gamma iron affect the length of this "prereaction" period differently, manganese

Jan 1, 1935

By S. R. Zimmerley, John Gross

A survey of the status of ore dressing in 19231 placed particular stress on the need of research in the crushing and grinding of ore, especially on the need for a method of measuring the surface of the products obtained in crushing and grinding and for fundamental data on the law of crushing, in order that intelligent conclusions may be drawn from actual crushing or grinding experiments. There has been no satisfactory means of determining the surface of crushed products. The results have been judged entirely by the amount of the various sizes produced, based on sieve sizing for particles above 74 microns in size and on microscopic measurement or elutriation for particles below 74 microns, a method which could give only a general idea of what had been accomplished. The fact that the long controversy between the followers of Kick and of Rittinger has resulted in no accepted conclusion is evidence of the need for fundamental data on the crushing law. Some Methods of Measuring Surface of Particles A dissolution method was used by Wolff to measure surfaces of glass powder. A mixture of sodium carbonate and sodium hydroxide was the solvent and the amount of glass dissolved in two hours from the powder was compared with that dissolved from a glass plate.2 Lately Herbert F. Kriege has used the dissolution method in determining surface of calcite and limestone.3 Dr. Geoffrey Martin and his coworkers in England have also used a dissolution method to determine surface on quartz. They compared the amount of quartz dissolved from the sample in one hour by a hydrofluoric acid solution with the amount dissolved from a measured quartz

Jan 1, 1930

By F. J. Norton

THE object of this investigation was to make a comprehensive study of the degassing of molybdenum in order to determine how rigorous a treatment was necessary to completely remove sorbed gases from molybdenum electrodes in vacuum tubes. Some work has also been done with tungsten, nickel and carbon. As a logical development of this work it has been shown that the gas is present throughout the body of the metal and a study has been made of the solubility of nitrogen in molybdenum and tungsten and the rate of diffusion of nitrogen through molybdenum has been calculated. Tests were made on molybdenum from all the commercial sources and no difference was discovered in the nature of the gases present, the amounts or the ease of removal. The reason for this was apparent when a study was made of the manner in which gases are absorbed by gas-free molybdenum. It is necessary to heat molybdenum to 1760° C. in a vacuum of the order of 0.001 micron for a time which varies lineally with the thickness, in order to obtain a condition in which no further gas is evolved by the sample. A sample so degassed can be handled and subsequently assembled in a tube and then degassed readily. The gases obtained from molybdenum are carbon monoxide and nitrogen, the nitrogen being the more difficult to remove.

Jan 1, 1932

By Archer Wheeler

THE copper industry in the Province of Katanga, in the Belgian Congo, which is now controlled and operated by the Union Minere du Haut Katanga, had its inception many years ago in the vision of a Scotsman, Robert Williams, now Sir Robert Williams, Baronet. He it was who personally negotiated the mineral concession with King Leopold of Belgium, sent in the prospecting parties who located most of the present mines of the company, later arranged for the Belgian participation from which the present company was formed, and has been its active mentor ever since. The idea back of his efforts was the establishment of an industry on the Congo-Zambezi divide, of sufficient importance to draw up to it the head of the Cape to Cairo Railroad, the dream of Sir Cecil Rhodes, and the consummation of which he had left as a legacy to Mr. Williams, his successor. The reports of the prospecting expeditions showed that copper in profitable quantity was there, but many difficulties lay in the way of the establishment of the infant industry. The isolated location of the mines, various tribal wars, the Boer War, and many other factors contributed to making progress very slow. However, in spite of these difficulties the railroad was finally built and a blast-furnace plant erected at Lubumbashi, near Elisabethville, the capital of the Province. Operations of this plant were started in 1911, treating high-grade oxidized ores and producing pig copper by a reducing smelting. Production has been continuous since that time and the company has grown so that at present it ranks as the largest individual copper producer in the industry. It is a fitting monument to the foresight, optimism and driving force of its founder, and the progressive policies of his Belgian colleagues. In January, 1914, the Union Miniere du Haut Katanga engaged as its consulting engineer, Archer E. Wheeler, metallurgical engineer, at that time general superintendent of the Great Falls plant of the Anaconda Copper Mining Co. Mr. Wheeler was commissioned by the Board of Directors to proceed into Katanga, and make all necessary investigations to enable him to report on a comprehensive development program, and to recommend a scheme of treatment particularly for their low grade

Jan 1, 1932

By G. K. Manning, C. H. Lorig

TWO metallurgical tools have acquired wide use within the past several years as a means of studying the transformation characteristics of steel. One is a technique used first by Bain and Davenport for determining the transformation characteristics of a steel at constant temperature; the second is the end-quench hardenability test. Constant-temperature transformation curves like those of Bain and Davenport have done much to rationalize the metallography of steel; however, in commercial practices, constant-temperature transformation is seldom encountered, therefore only rarely can such curves be directly applied. The real reason for the determination of such curves lies in the fact that they provide a way of thinking about transformation that is both convenient and productive. The end-quench hardenability test is a more practical means of studying transformation, for, by correlating positions on the hardenability bar with shapes of different masses, an almost direct application of the results can be made. Unfortunately, the end-quench test, though practical, can do very little toward improving the metallurgists' way of thinking about transformation. These two metallurgical tools, dealing with precisely the same phenomenon, should be very closely associated in metallurgists' minds. Actually, they are frequently pushed into separate mental corners and considered as being more or less distinct and unrelated. The reason for this is that no strong connecting link between them has been developed. An attempt is sometimes made to relate these two tools by projecting the critical cooling rate on the isothermal transformation plot as illustrated in Fig. I. The critical cooling rate is considered as a constant rate-though in practical applications, cooling rates are never constant—and this constant cooling rate is given uniform significance from the Ae temperature down to the temperature of initial transformation. A little thought indicates the errors of such a procedure. Certainly the time interval spent just below point A of Fig. I cannot be as effective in promoting nucleation as is the time interval spent just above point B. Yet the procedure represented in Fig. I considers all the time spent between temperatures A and B to be just as effective in promoting nucleation as though all the time were spent at temperature B. Furthermore, change the shape of the isothermal curve between points B and C in any way desired, and the required critical cooling rate is not changed one iota. This cannot possibly be true. Such a way of thinking about critical cooling rates not only is incapable of giving any results that are quantitatively satisfactory but is likely to give very misleading qualitative results.

Jan 1, 1947

By G. K. Manning, C. H. Lorig

TWO metallurgical tools have acquired wide use within the past several years as a means of studying the transformation characteristics of steel. One is a technique used first by Bain and Davenport for determining the transformation characteristics of a steel at constant temperature; the second is the end-quench hardenability test. Constant-temperature transformation curves like those of Bain and Davenport have done much to rationalize the metallography of steel; however, in commercial practices, constant-temperature transformation is seldom encountered, therefore only rarely can such curves be directly applied. The real reason for the determination of such curves lies in the fact that they provide a way of thinking about transformation that is both convenient and productive. The end-quench hardenability test is a more practical means of studying transformation, for, by correlating positions on the hardenability bar with shapes of different masses, an almost direct application of the results can be made. Unfortunately, the end-quench test, though practical, can do very little toward improving the metallurgists' way of thinking about transformation. These two metallurgical tools, dealing with precisely the same phenomenon, should be very closely associated in metallurgists' minds. Actually, they are frequently pushed into separate mental corners and considered as being more or less distinct and unrelated. The reason for this is that no strong connecting link between them has been developed. An attempt is sometimes made to relate these two tools by projecting the critical cooling rate on the isothermal transformation plot as illustrated in Fig. I. The critical cooling rate is considered as a constant rate-though in practical applications, cooling rates are never constant—and this constant cooling rate is given uniform significance from the Ae temperature down to the temperature of initial transformation. A little thought indicates the errors of such a procedure. Certainly the time interval spent just below point A of Fig. I cannot be as effective in promoting nucleation as is the time interval spent just above point B. Yet the procedure represented in Fig. I considers all the time spent between temperatures A and B to be just as effective in promoting nucleation as though all the time were spent at temperature B. Furthermore, change the shape of the isothermal curve between points B and C in any way desired, and the required critical cooling rate is not changed one iota. This cannot possibly be true. Such a way of thinking about critical cooling rates not only is incapable of giving any results that are quantitatively satisfactory but is likely to give very misleading qualitative results.

Jan 1, 1947

By John Mark Patek

Knowledge of the relative floatability of silicate minerals is increasing in importance as flotation is being applied to the concentration of nonsulfides. Many silicates are in themselves commercial products amenable to concentration by flotation. Moreover, the selective flotation of other nonsulfide minerals, such as cassiterite, depends largely upon the floatability of associated gangue silicates. Differences in floatability existing between the various silicates have not- been sufficiently appreciated; for example, the feldspars that differ greatly in floatability have generally been merely treated as "feldspar." It was the purpose of the work described in this paper to determine by experiment the differences in floatability between silicates; to investigate the causes for such differences, and to discover a means of predetermining approximate floatability without the necessity of experimentation. Determining Floatability The relative floatability of 20 silicates so selected as to represent all of the more common silicate types1 was obtained by flotation tests enumerated in Table 1. The mineral to be floated was crushed dry on a steel plate, and screened repeatedly during crushing through an 80-mesh screen in order to produce a sand with all grains as close to 80 mesh as possible. The sand was placed in dilute (6N) hydrochloric acid until free of soluble foreign material, and then washed with tap water about ten times in order to remove both acid and fines. The resultant product, which averaged 82 per cent plus 200 mesh, was floated in 50-gram charges in a 50-gram Denver celluloid flotation machine with 0.008 gram of terpineol, and from 0.01 to 0.05 gram of oleic acid in a solution acidified with sulfuric acid. The degree of separation of one mineral from another was determined by counting under a nlicroscope the grains of each mineral, both in the concentrate and in the tailings, and comparing their relative abundance in each. Unless the comparison showed a decided difference in amount,

Jan 1, 1935

Mounting pressures to increase efficiency and yield, conserve energy, or minimize pollution have all taken their toll on the minerals industry. As management and technical personnel take a harder look at their operations for ways to shave cents off operating costs or to squeeze a bit more productivity out of existing equipment, instrumentation often comes up as the most effective answer. When Amax Lead installed an automatic grind control system in its Buick mill, ore throughput increased by 3 to 5%. Mill operators calculate that the initial investment is returned to them several times annually.

Jan 2, 1978

By Douglas W. Fuerstenau, Kalanadh V. S. Sastry

A mathematical model is developed for flotation in a countercur-rent column where continuously generated air bubbles rise through a downward flowing pulp. The model is based on the assumption of axially dispressed plug flow of both the liquid and air-bubble phases. An appropriate flotation-rate expression, which takes into account the changing concentration of solid particles on the bubble surface, is formulated and applied to the column flotation process. Although a complete solution of the resulting equations is not possible for the general case, solutions for specific limiting cases have been obtained. From these, it is possible to predict theoretically the dependence of the column performance on certain variables. Specifically, concentration profiles as a function of height in the column have been calculated for various values of the characteristic dimensionless parameters. The effect of axial dispersion on the perforance of the equipment is pointed out. In recent years, there has been considerable progress in delineating the fundamental physicochemical principles underlying the unit operation of flotation and in advancing methods for kinetic analysis and process modeling of flotation.' In general, nearly all such process research has been concerned with the analysis of conventional flotation equipment and circuits. From these investigations, the possibility of developing and designing flotation apparatus for more efficient separation appears limited with conventional equipment. How- ever, recently there has been an attempt to apply coun-tercurrent flow techniques to flotation in the context of a flotation column.- some of the results from pilot-plant studies2 indicate possibilities for success of this process at least in obtaining higher-grade concentrates though not higher recoveries. A flotation column operates on countercurrent principle in which bubbles continuously generated at the bottom of the column rise through the downward flowing slurry. A schematic diagram of the flotation column is shown in Fig. 1. The physicochemical principles of bubble-mineral attachment, using this flotation column, are essentially the same as those which prevail in conventional equipment, the only differences being in the flow patterns of the various phases. The salient operating feature of the column as compared to those of a conventional cell is that neither mechanical nor turbulent pneumatic agitation is employed. The column is

Jan 1, 1971

By Simon D. Strauss

COPPER In terms of mining activity, copper is the leading nonferrous metal. It is true that in recent years the volume of aluminum consumption in the non-Communist world has exceeded the volume of copper consumption, but virtually the entire primary aluminum supply is derived from bauxite. On the average, only four tons of bauxite need be mined to produce a ton of aluminum. By contrast, the highest-grade, large-scale copper mines now in operation (those in the Congo) must mine at least 20 tons of ore to produce a ton of copper. In the United States an average of 150 tons of ore must be mined to produce a ton of copper. This does not take into account the huge amounts of waste overburden that must be stripped from the open-pit mines to account for their steadily rising share of the world's copper output. Copper epitomizes the economic problems of the mining industry in many ways. Its price is highly volatile, considering its great economic importance. It has been a tool of mankind longer than any other of the base metals-the dawn of history has been classified as "The Bronze Age." World Copper Production Although copper is mined in many countries, in recent years 70% of the non-Communist world production has come from six countries. Two of these are industrialized countries and are large consumers-United States and Canada. The other four are developing countries with very small domestic requirements-Chile, Zambia, Zaire, and Peru. Heavily dependent on copper exports to sustain their domestic economies, these countries find themselves oscillating between prosperity and depression with the changing levels of copper prices. In an effort to control their own destiny, in 1968 they formed an organization of copper exporting countries (CIPEC) which was designed to study copper markets and possibly to intervene actively in these markets. (When this chapter was being prepared, no actual steps along such lines had been taken.) Many of the leading industrialized nations are wholly dependent on imports for their primary copper supplies. These include West Germany, the United Kingdom, France, Italy, and many others. Japan, now the non-Communist world's second largest copper consumer, produces only 10 to 15% of its requirements from domestic mines. Although the bulk of the copper output is smelted in the country where it is mined, there is a limited international trade in copper concentrates. Canada, the Philippines, Australia, and Papua-New Guinea are significant exporters of copper concentrates; Japan, Germany, the United States, and Sweden are importers. However, this trade accounted for only about 10% of the non-Communist world production of copper during the decade of the 1960s.

Jan 1, 1976

By Edwin S. Smith

Current research in the phenomenon of liquefaction has indicated some of the in situ material properties which should be considered in the planning of waste deposits. Practical experience in tailings disposal, however, must be combined with the results of theoretical and laboratory studies to develop the most economical and safe techniques against liquefaction failure. One of the many responsibilities of mining engineers and mill superintendents is providing for the safe and economic disposal of wastes (or tailings) that remain after a mineral has been extracted from an ore. The cost of disposal of these tailings exerts a considerable influence on the minimum grade of ore extracted from the mine. It varies to a great extent with each project and is dependent on many diverse factors, such as the local topographical, meteorological and seismological conditions together with the applicable water pollution laws of the area. The process used to extract a mineral from an ore determines the physical characteristics of the tailings and, thus, is one of the more important factors to be considered in the planning of disposal facilities. Today's trends in ore-processing operations complicate the problems of waste disposal: recently developed extraction methods result in the production of finer tailings, the use of lower grade ores produces greater volumes of wastes, and the enhanced land values in the vicinity of industrial plants preclude the former practice of spreading wastes laterally and force the expansion of waste deposits upwards to greater heights. The frequent occurrence of stability problems in waste deposits indicates that many mining organizations may not be employing current soil mechanics concepts and practices. One of the most spectacular, and often most disastrous, types of tailings dike failure is that resulting from liquefaction of the fine particles combined with a breach of the main retaining dike. TAILINGS DISPOSAL Since the many variations in site conditions, ore bodies and extraction processes dictate the general disposal procedures and mill superintendents incorporate special facilities to provide the most economical disposal method consistent with accepted safety standards, it is only natural that there are almost as many different disposal techniques as there are disposal areas. Methods used in the construction of retaining dikes include: (1) transporting granular material from an adjacent borrow pit and (2) mechanically segregating the total effluent and allowing the coarse fraction to form a retaining dike by hydraulic deposition. The location of a plant and the surrounding topography exert the greatest influence on the layout of tailings disposal facilities. Most of the above-ground waste deposits can be classified as side-hill, (Fig. 1,) cross-valley, (Fig. 2,) or stockpile deposits. Side-hill disposal areas are probably the most common type of layout because of the natural advantage of gravity flow, without the disadvantage of river diversion usually needed for tailings ponds formed behind cross-valley dikes. Stockpiles, which are placed on relatively level ground, require four retaining dikes and the effluent generally has to be pumped up into the disposal area. Changing production techniques or developments adjacent to disposal areas have produced variations or partial combinations of these three categories. In a series of articles, Lenhart describes many of the problems encountered in the disposal of tailings and certain innovations used to overcome them. He discusses weaknesses in design and layout and shows that disposal techniques are often learned the

Jan 1, 1970