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By Steven T. Mitchell

The introduction of Vertical Crater Retreat (VCR) Stoping at the Homestake Mine in Lead, SD, constitutes a major advance in Homestake Mining Company's efforts to improve productivity and reduce costs through under- ground mine mechanization. The work to date indicates that Vertical Crater Retreat Stoping is one of the safest methods of underground hardrock mining today, and is competitive with all other forms of stoping in terms of cost and productivity. Homestake anticipates that VCR stoping will account for approximately 35% of the total mine production in 1981.

Jan 1, 1981

By G. M. Swinkels, A. Vizsolyi, E. Peters

A process is described utilizing ferric chloride leaching followed by reduction of the cupric content to cuprous by cement copper, with CuCl obtained thereafter by crystallization. The residual liquor is cemented with sponge iron to produce cement copper and a copper free ferrous chloride solution. The latter is oxidized in an autoclave with oxygen to regenerate ferric chloride and to precipitate excess iron as a granular, filterable hematite. Cuprous chloride crystals are reduced to high purity metal with hydrogen, while sulphur reports almost quantitatively in residues in the elemental form. Pyrite and molybdenite are not leached. This paper describes the important variables in the process, as well as the deportment of minor elements as silver, gold, selenium, tellurium, bismuth, nickel, lead, zinc, magnesium, etc. An elegant method of isolating silver from CuCl crystals is described, as well as recovery of gold from residues by a chloride reagent The process is described as non-polluting and capable of producing refined copper, ore grade iron oxide, elemental sulphur, and yields of minor metals as good or better than obtainable by conventional smelting, without the use of solvent extraction or electrochemistry.

Jan 1, 1981

By Benjamin C. Greene, H. Beecher Charmbury

Water is a most remarkable substance, essential for life of all kinds. As well as needing water to survive, man has always used it for agriculture, transportation, recreation, and many other things. When our country was young and inhabited by few people, the streams, rivers, and lakes were able to provide all the clean water needed by man and take away all the wastes created. However, with our growing population and an ever-increasing demand for goods and services, the public, industry, and government at all levels have become acutely aware of the need to manage the nation's water resources more efficiently. Abundant energy from many sources has helped this nation to become the greatest industrial nation in the world. Coal has contributed a major portion of this energy, generating electricity, running railroads, and maintaining national security during wartime. The result has been the highest standard of living in the world and a time of widespread economic prosperity. The use of water in coal mining is somewhat different from its use in most industries. With the exception of water used in cleaning plants, for underground dust control, and for fire protection, most of the water en- countered in coal mining operations serves no useful purpose. In other words, it is an undesirable element and must be removed, otherwise it will interfere with operations, cause potential water quality problems, and may even stop operations by flooding. In the past, removing water from working areas of most mines was usually a fairly simple matter. Pumps with piping were installed at sumps or low spots in the mine and the water was pumped to the surface or to drainage control facilities constructed for the operation. Ditches were often used to collect and drain the water by gravity to the outside or to main sumps for pump discharge. In either case, the water was allowed to flow into the nearest stream or river. The concept of "water is water" was generally accepted without too much concern for what was in

Jan 1, 1981

By Joseph S. Malesky

The discovery and development of explosives mark one of the most important findings in the history of civilization. Without explosives our vast economic enterprise concerning the mining of coal, copper, iron, aluminum, and various other ores could not function. Explosives are used in all kinds of construction works, in the razing of old buildings, blasting of trenches, driving of tunnels, and in many other instances common to our everyday life. For these reasons explosives are rightfully referred to as the forerunner of progress. An explosive may be defined as a substance (usually a mixture) that, when flame or shock is applied, yields readily to rapid combustion or oxidation, accompanied by the formation of such relatively large quantities of gases as to produce much violence and pressure which, in turn, react against their surroundings and cause what is termed an explosion. By their very nature the action of explosives is destructive and disruptive of adjacent materials. Decomposition of explosives can occur through deflagration, which is rapid burning or combustion, as in the case of black powder, or through detonation, which is an almost instantaneous disruption, as in the case of dynamites and blasting agents. HISTORY OF BLASTING WITH EXPLOSIVES At one time workmen obtained stone blocks for building by grooving the rock with crude picks, driving wooden wedges into niches in the rock, and pouring water on the wedges; the swelling of the wood forced out the blocks. As late as the 17th century, fires were placed against the face of rock to crack it, and water was sometimes dashed on the heated rock to shatter it by sudden cooling. The progress of our country is synonymous with advancement of the improved manufacture and extended use of explosives. Coal had been

Jan 1, 1981

By Ross W. Smith, Mine-Yun Hwang

Many studies have been made of the microflotation of quartz (de Bruyn, 1955; Fuerstenau, 1957; Somasundaran, 1964; Smith, 1973; Fuerstenau, 1976; and Smith and Akhtar, 1976) and alumina (Somasundaran, 1964; Smith and Akhtar, 1976; Fuerstenau and Palmer, 1976; Fuerstenau and Akhtar, 1976; Fuerstenau and Yamada, 1963; Modi and Fuerstenau, 1960) using various anionic and cationic heteropolar hydrocarbon surfactants as collectors. A few studies have been made on these materials using amphoteric hydrocarbon collectors (Wrobel 1969 and 1970; Smith. Haddenham, and Schroeder, 1973; Gupta and Smith, 1975) and only a few studies have been made on the use of fluorocarbon surfactants as flotation collectors Cooke and Talbot, 1955; Somasundaran and Kulkami, 1973). The present investigation compares microflotation response of the two minerals in hydrocarbon and fluorocarbon collector systems of the anionic, cationic, and amphoteric types. An attempt is made to relate flotation response of the minerals to their electrokinetic behavior and the pKa values of the collectors.

Jan 1, 1981

By Waynw P. Myers

Electricity, as normally thought of by a layman's definition, is a man- made force that has no color, no odor, is not visible, cannot be heard, yet man can control it and make it perform his work for him. A person dare not cheat on it, for it then will master him. It has laws, rules, and regulations that must be strictly adhered to if it is to perform in the safest, most reliable, and economical manner. In the early days of coal mining the power source was man himself. Later man employed steam and compressed air to reduce his muscle power requirements needed in the extraction of coal. By the turn of the 20th century, electricity had become the most common source of power for the coal industry. Steam and compressed air are still found in use in isolated cases today for specific applications; however, they are rapidly being replaced by electricity. Electrical laws and regulations are quite extensive and somewhat complex for the proper generation and use of electricity. Man-made laws, rules, and regulations for the care and handling of electricity, designed for man's safety, are rigidly enforced by Mine Safety and Health Ad- ministration (MSHA), as well as the various state departments of mines. BACKGROUND Until recent years most underground coal mines used direct current exclusively for all movable and for some stationary equipment. Exceptions were for permanent pumps, tipple, fan, and outside buildings where alternating current was normally employed. However, over 60 years ago there were mines with dual systems. Alternating current was used for cutting machines, drills, and pumps ; direct current for locomotives. There were no other machines as these were hand-loading mines. Later, during early mechanization in the 1920s, alternating current was also applied to loading machines at some mines. Use of dual electric systems then declined until fairly recently when

Jan 1, 1981

By P. E. Chapman, J. E. Worthington, I. T. Kiff

Increases in the price of gold starting about six years ago, and rapid fluctuations since then, have created a substantial popular interest in the noble metal. Gold prospecting had been at a low ebb since the end of World War II in most of the United States, except for a flurry of activity in Nevada after the Carlin and Cortez discoveries. The last few years, however, have seen a great awakening of interest in gold exploration as well as an opportunity for education for many explorationists in the geology and other vagaries of gold deposits. The writers have participated over the last few years in a search for gold deposits throughout the United States. This search was greatly influenced by the geologic studies of Dr. William Spence at the Haile gold mine in South Carolina, as reported in a companion paper. Spence's studies resulted in definition of a geologic model that has proven useful in a number of other geologic environments in the United States. These programs were all carried out under the auspices of Cyprus Mines Corp. and permission by Cyprus to present these results is gratefully acknowledged. The writers, however, reserve for themselves all responsibility for the results and conclusions. The exploration program to be described began in the southeastern United States. Spence's studies provided a reasonable basis for interpreting and understanding the geology of the Haile deposit, and also provided a means for predicting additional occurrences. This concept was then expanded to other gold occurrences in the Piedmont, and became an effective tool for evaluating other prospects. Finally, it became evident that the concept could be applied in some western gold districts. The following discussion will then include descriptions of other Piedmont examples and a few western districts that also appear to fit the pattern.

Jan 1, 1981

By R. W. Callen, W. A. Hockings

This paper describes a computer program which calculates material balances for complex steady-state material flow circuits encountered in mineral processing. The program determines mass flows in the various process streams of a flowsheet from multicomponent analytical data obtained from samples of the streams. The program, Metallurgical Balance System (MBS), has been used extensively in treating Pilot plant test data, in production evaluation and control, and in plant design. The program performs well even on ill-conditioned data. Input to the program is easily accomplished by unskilled personnel and the output appears in well-formatted tables.

Jan 1, 1981

By Harold L. Bare, Frank R. Barnako

Coal mining historically has been a. hazardous occupation but, in recent years, tremendous progress has been made in reducing accidental coal mine deaths and injuries. The purpose of this chapter is to discuss the basic principles of accident prevention as they are related to coal mining. Accident prevention fundamentals are no different for coal mining than for any other type of work. The fundamentals apply to all industries. Construction workers may be struck by falling tools and materials, and miners may be struck by falling slate and coal. Sailors may be trapped by shipboard fires, and miners may be trapped by mine fires. Railroad brakemen may lose hands and fingers positioning couplers, and miners may lose hands and fingers positioning couplers. Many other examples could be cited, but the point is that accidents that happen in coal mines are basically similar to accidents that happen in other industries. Thus, the basic principles for preventing accidents apply in coal mining as they do in any other type of work. COAL MINE ACCIDENT EXPERIENCE The US Mine Safety and Health Administration (MSHA) is the main source for accident experience data in coal mines. Coal mine operators are required, by law, to forward to MSHA monthly the number of fatal and disabling injuries, man-hours worked, and tons of coal mined. This information is compiled and published quarterly, with annual summaries, by MSHA. Trends in the number of fatalities and fatal injury rates are shown in Fig. 1. Major coal mine disasters, with number of miners killed, and dates of coal mine safety legislation are shown in Table 1. The fatal and disabling injury frequency rates for the coal industry are shown in Fig. 2.

Jan 1, 1981

By Harry L. Washburn, Robert L. Llewellyn, W. J. Halvorsen

Many of the problems that occur in the preparation plant originate from practices in the mine. Impurities in raw coal can be in the seam itself or from extraneous material taken in mining from the roof or bottom. In the case of underground mines, the choice of mining equipment will affect the size consist and the amount of extraneous material included with the coal. Also, governmental regulations concerning the degree of rock dusting, gobbing underground, and cleanup have increased the dirt in raw coal. Sulfur dioxide emission standards, on the other hand, are pressuring the coal industry to clean coal more thoroughly. Coal supplied for coking purposes is nearly all upgraded by washing, while for the largest market, electric power generation, a high proportion is shipped as a raw product with processing, in whole or in part, only necessary when excess impurities are mined with the coal. This chapter will deal primarily with plants that process or wash coal to some extent (Fig. 1) and only incidentally with mines shipping raw run-of-mine coal crushed to a top size of, usually, 51 to 102 mm (2 to 4 in.), with little, if any, other treatment. JUSTIFICATION FOR COAL PREPARATION During the past decade, major changes have occurred affecting the market, profit, and long-range planning of the coal industry. Mining companies have become "partners" with consumers at many new and some old mines, both for steam and metallurgical coals. Coal properties have become "assigned" tonnages at mutually agreed upon conditions and prices. Lower unit-train tariffs have been instrumental in helping coal markets to compete against oil and nuclear energy. Coal prices for power plants are still on a Btu (British thermal unit)

Jan 1, 1981

By James R. Jones

The concern for air pollution goes back centuries as will be seen from this quotation : "Strife and coal, it seems, have a hand-in-hand historical relationship. It was thought by some . . . in the Middle Ages that burning coal filled the air with dangerous poisons. So great was the concern that in 1306 King Edward I of England passed the first and unquestionably the harshest air pollution legislation edict that history will record. His proclamation declared the use of coal an act punishable by death." As related to coal mining, the air pollution problem is primarily that of its customer when using the fuel. Thus the major impact relates to markets for coal rather than the actual mining operation itself. In the vicinity of the coal mine the problem is principally related to fugitive dust from roads, transfer facilities, loading facilities, crushers, etc., and particulate matter (dust or fly ash) from thermal dryers and air cleaning tables. FUGITIVE DUST Most state air pollution regulatory agencies now have rules and regulations requiring control of fugitive dust. Fugitive dust has been defined by the courts as particulate matter other than that emanating from a specific point such as a stack or chimney. A typical air pollution control agency regulation reads as follows : “Fugitive Dust " "No person shall cause, suffer, allow, or permit any material to be handled, transported, or stored; or a building, its appurtenances, or a road to be used, constructed, altered, repaired or demolished without taking reasonable precautions to prevent particulate matter from be- coming airborne. Such reasonable precautions shall include, where applicable, but not be limited to the following:

Jan 1, 1981

By Harry L. Washburn, Robert L. Llewellyn, W. J. Halvorsen

Many of the problems that occur in the preparation plant originate from practices in the mine. Impurities in raw coal can be in the seam itself or from extraneous material taken in mining from the roof or bottom. In the case of underground mines, the choice of mining equipment will affect the size consist and the amount of extraneous material included with the coal. Also, governmental regulations concerning the degree of rock dusting, gobbing underground, and cleanup have increased the dirt in raw coal. Sulfur dioxide emission standards, on the other hand, are pressuring the coal industry to clean coal more thoroughly. Coal supplied for coking purposes is nearly all upgraded by washing, while for the largest market, electric power generation, a high proportion is shipped as a raw product with processing, in whole or in part, only necessary when excess impurities are mined with the coal. This chapter will deal primarily with plants that process or wash coal to some extent (Fig. 1) and only incidentally with mines shipping raw run-of-mine coal crushed to a top size of, usually, 51 to 102 mm (2 to 4 in.), with little, if any, other treatment. JUSTIFICATION FOR COAL PREPARATION During the past decade, major changes have occurred affecting the market, profit, and long-range planning of the coal industry. Mining companies have become "partners" with consumers at many new and some old mines, both for steam and metallurgical coals. Coal properties have become "assigned" tonnages at mutually agreed upon conditions and prices. Lower unit-train tariffs have been instrumental in helping coal markets to compete against oil and nuclear energy. Coal prices for power plants are still on a Btu (British thermal unit)

Jan 1, 1981

By S. C. Libby

Physical degradation of calcined bauxite is related to the presence of goethite in the raw bauxite and to the development of secondary gibbsite. Goethite in the bauxite matrix will shrink and decrepitate during calcining, leaving a friable matrix and allowing disaggregation of the calcined bauxite during transport and handling. A matrix consisting of cryptocrystalline gibbsite alone or mixed with hematite will not shrink during calcination, yielding a calcine with high abrasion resistance. The development of secondary gibbsite between coarse gibbsite crystals also reduces degradation of the calcine by reducing the amount of disruption between grains resulting from differential thermal expansion.

Jan 1, 1981

By Joseph S. Malesky

The discovery and development of explosives mark one of the most important findings in the history of civilization. Without explosives our vast economic enterprise concerning the mining of coal, copper, iron, aluminum, and various other ores could not function. Explosives are used in all kinds of construction works, in the razing of old buildings, blasting of trenches, driving of tunnels, and in many other instances common to our everyday life. For these reasons explosives are rightfully referred to as the forerunner of progress. An explosive may be defined as a substance (usually a mixture) that, when flame or shock is applied, yields readily to rapid combustion or oxidation, accompanied by the formation of such relatively large quantities of gases as to produce much violence and pressure which, in turn, react against their surroundings and cause what is termed an explosion. By their very nature the action of explosives is destructive and disruptive of adjacent materials. Decomposition of explosives can occur through deflagration, which is rapid burning or combustion, as in the case of black powder, or through detonation, which is an almost instantaneous disruption, as in the case of dynamites and blasting agents. HISTORY OF BLASTING WITH EXPLOSIVES At one time workmen obtained stone blocks for building by grooving the rock with crude picks, driving wooden wedges into niches in the rock, and pouring water on the wedges; the swelling of the wood forced out the blocks. As late as the 17th century, fires were placed against the face of rock to crack it, and water was sometimes dashed on the heated rock to shatter it by sudden cooling. The progress of our country is synonymous with advancement of the improved manufacture and extended use of explosives. Coal had been

Jan 1, 1981

By Benjamin C. Greene, H. Beecher Charmbury

Water is a most remarkable substance, essential for life of all kinds. As well as needing water to survive, man has always used it for agriculture, transportation, recreation, and many other things. When our country was young and inhabited by few people, the streams, rivers, and lakes were able to provide all the clean water needed by man and take away all the wastes created. However, with our growing population and an ever-increasing demand for goods and services, the public, industry, and government at all levels have become acutely aware of the need to manage the nation's water resources more efficiently. Abundant energy from many sources has helped this nation to become the greatest industrial nation in the world. Coal has contributed a major portion of this energy, generating electricity, running railroads, and maintaining national security during wartime. The result has been the highest standard of living in the world and a time of widespread economic prosperity. The use of water in coal mining is somewhat different from its use in most industries. With the exception of water used in cleaning plants, for underground dust control, and for fire protection, most of the water en- countered in coal mining operations serves no useful purpose. In other words, it is an undesirable element and must be removed, otherwise it will interfere with operations, cause potential water quality problems, and may even stop operations by flooding. In the past, removing water from working areas of most mines was usually a fairly simple matter. Pumps with piping were installed at sumps or low spots in the mine and the water was pumped to the surface or to drainage control facilities constructed for the operation. Ditches were often used to collect and drain the water by gravity to the outside or to main sumps for pump discharge. In either case, the water was allowed to flow into the nearest stream or river. The concept of "water is water'' was generally accepted without too much concern for what was in

Jan 1, 1981

By Shawn T. Sorrell, Carl Hrovatic

Original by Carl Hrovatic and Shawn T. Sorrell Revised by Carl Hrovatic Land is a precious resource and should be treated as such by all members of our society. The soil covering this earth is only a very thin outer layer, varying in thickness from a few inches to a few feet and covering the rocks and minerals lying beneath the surface. The wise use of this valuable commodity is the responsibility of everyone. Many everyday activities disturb the earth's surface. Examples are highway construction, housing and commercial developments, agriculture, and various types of mining. This chapter discusses the relationships of the environment to land as it applies to surface operations in the coal industry. Mining by surface methods disturbs, for a brief period of time, thousands of acres of land annually. In addition, refuse piles, slurry ponds, abandoned mine structures, unprotected mine openings, and unsightly cleaning plants can also adversely affect land unless properly handled. ACTIVE SURFACE MINING OPERATIONS Mining by surface methods includes rock quarries; sand and gravel pits; huge open pits to extract iron, copper, phosphate, and other ores; and coal mining. Production of coal by surface methods is now approaching 408.2 Mt/a (450 million stpy), amounting to almost 60% of the total coal output. Surface coal mining can be classified into the following five broad categories : Open-pit mining is practiced where coalbeds are extremely thick, as in some western states, or where coalbeds are sharply pitching, as in the anthracite region of the eastern United States. A typical open-pit mine, with coalbeds of 3.05 to 30.5 m (10 to 100 ft) or more thickness and a

Jan 1, 1981

By Stanley M. Moos, Richard Addison

Introduction The Pueblo Viejo gold-silver mine, located in the Dominican Republic, started production in early 1974 processing ores averaging 4 g/t gold and 20 g/t silver at a rate of 7.25 kt/d. The ore milled is a silicified siltstone with average work index of about 8 that occurs as an extensive oxide capping of a primary sulfide ore body. The sulfide ores are refractory to conventional treatment process and extensive research work is now in progress to develop a treatment process for them. The ore deposit has a long history, having been mined by the indigenous Arawak Indians for some time in the early sixteenth century prior to the arrival of the Spanish, and then by the Spaniards. In the early 1950s, Italian engineers attempted to process the sulfide ores. Mining by the Indians and Spanish was abandoned because of low grade and little coarse gold in the oxide ores and by the Italians because of the refractory nature of the sulfide ore. In 1969, Rosario Resources geologists discovered that there existed sufficient reserves of oxide ore for a viable mining operation and the plant was designed, built, and brought into production.

Jan 1, 1981

By P. R. Smith, R. A. Walters

Borates have been mined in the desert areas of California and Nevada for more than 100 years. To about 1890, playa surface mining provided the chief sources of boron minerals. Underground mining of colemanite and later of borax and kernite was predominate until about twenty years ago. Open pit mining of the large deposits of borax and kernite near Boron, California has been most significant for the past twenty years. Mining of colemanite in the Ryan, California area, near Death Valley, began in 1907. Following the discovery of the large deposits in the Boron area (about 1957), mining in the Death Valley area became nearly nonexistent. Only small tonnages were mined for special uses. Little mining was done in the Boraxo area near Ryan. The first claim was made in about 1915. In 1960 the area became the property of the Kern County Land Company, which was acquired by Tenneco Oil Company in 1967. In 1976 the various boiate properties and claims in this region were acquired by American Borate Corporation. The open pit mine is now approximately 122 m (400 ft) deep, 910 m (3000 ft) long and 305 m (1000 ft wide). The borates in the Boraxo pit consist primarily of three minerals. These are about 50% colemanite (CB6011 5H20), about 40% probertite (NaCaB50g 5H20), and 10% ulexite (NaCaBgOg 5H20). The colemanite, along with boric acid and high-grade colemanite ore from Turkey provide the only sodium-free borates for production of textile grade fiberglas. When heated to its decomposition temperature, colemanite decrepitates to a fine powder, which is the basis for the concentration process. The gangue minerals in this deposit are primarily calcite and clays, including bentonite. The ore body has a very low arsenic content, which is a desirable feature. Test work had been done with samples prior to the results discussed herein. This paper will discuss results of test work which were the basis for erection of a plant, and the subsequent plant operations. Laboratory Calcination and Air Tabling Tests Laboratory calcination tests showed that substantial upgrading of the borate could be accomplished by calcining followed by screening of the calcined material. Removal of the + 28 mesh calcine resulted in borate losses of less than 10% with a rejection of 40 weight % or more of the calcine. The minus 65 mesh calcine generally met the requirement of containing 48%, or more, B203. The minus 28 plus 65 mesh material contained an intermediate quantity of borate and would require additional treatment. Testing demonstrated that ore would not have to be reduced to a size finer than 19 mm (3/4 in.) prior to calcination. A temperature range from 400 to 455OC (750 to 850°F) was apparently satisfactory. Calcination at a temperature of 48Z°C (900°F), or higher, was unsatisfactory due to fusion. All laboratory calcination tests were static tests conducted by placing small covered charges in a laboratory furnace for 40 min. In all tests vapor issues from the furnace for 5 to 7 min. Following this period the ore could be heard "popping," due to decrepitation of the colemanite. The reaction generally continued for approximately one-half hour. Various size fractions of the calcination products from laboratory tests were subjected to laboratory air tabling tests, usually after removing the plus 28 mesh material. Laboratory air tabling tests were conducted employing a Whippet V-80 model air table manufactured by Sutton, Steele and Steele Co. now known as Tripple S Dynamics. Variables include both end and side-tilt, speed of vibration, and quantity of air rising through the deck. In addition to the variables in the machine itself, the feed rate is also a rather critical variable. Testing demonstrated that all - 28 mesh size fractions of the calcine could be successfully concentrated to 48% F2O3 or greater. For the finer material recoveries into the concentrate were between 85 and 90% of the borate. With the coarser material a substantial amount of middling was produced which required cleaner tabling. Laboratory calcination and air tabling tests indicated a process whereby the borate could be concentrated to about 50% B203 with borate recoveries approaching 90%. Moreover, the iron content of the concentrate was well below the required specification of 0.3% Fe2O3. Pilot Plant Calcination Following the laboratory test work described above, pilot plant testing was conducted to prove the process, provide data for engineering studies, and provide product for a prospective purchaser. The kiln used was 0.9 m-diam (3 ft) by 9.0 m (30 ft) long and had a belly section 1.2 m-diam (4 ft) by 2.74 m (9 ft) long near the discharge end. The kiln was operated at a speed of 0.7 rpm. Gas was fired into the kiln at an average rate of 27.1 m3/hr (958.4 cu ft per hr). The air to gas ratio used was 10:1. The ore was fed to the kiln countercurrent to the flame and discharged through a hopper into a screw conveyor which discharged to a 1.2 m (48 in.) Sweco separator. The separator had 28, 65, and 150 mesh screen cloths, with the plus 28 mesh fraction being discarded. The minus 28 mesh fractions were later subjected to air tabling. The exit gases, containing some calcine dust, were swept through two cyclones to recover the dust. The gases then were scrubbed in a Ducon scrubber; very little dust reported past the first cyclone. The dust from the first cyclone was also saved in drums. In addition to the gas rate, the flue gas velocity, after

Jan 1, 1981

By Edmund J. Korber, Donald E. Raab, Frank A. Burns

During the early 1960s, the advent of self- advancing longwall roof supports triggered serious consideration by Bethlehem management to introduce the technique of longwall mining at one of our central Pennsylvania coal mines. Although longwall mining was initially justified as a means to cope with the severe roof conditions at our Mine 32 (Watson, B., 1971), the result of the endeavor has been a consistent and reliable level of coal production, first from Mine 32 and then later from Mine 33, over a period of fifteen years. Longwall production from the Cambria Division has been the mainstay of the low volatile coal required by Bethlehem Steel for steel production. Let us review the events that led to this accomplishment, as well as where we stand today.

Jan 1, 1981

By Paul E. Rosten

Introduction This papers describes some of the latest improvements that have been incorporated or planned by the Cleveland-Cliffs Iron Co. to reduce operating costs and improve pellet quality. The Cleveland-Cliffs Iron Co. operates and manages mining, beneficiation, and pelletizing operations in Michigan, Canada, and western Australia. This paper deals with the grate-kiln pelletizing operations at Republic, Humboldt, Tilden, Empire, and Pioneer in Michigan, and the Adams and Sherman in Ontario, Canada. Table I characterizes each operation in regard to location, ore type, pellet capacity and date that pellets were first produced. All of the operations with the exception of Pioneer and Tilden, utilize downdraft-two-pass grate cycles of drying followed by preheating. Pioneer utilizes an all-downdraft, three-pass grate cycle which consists of three drying zones followed by the preheat zone. The Pioneer and Tilden cycles have been described previously (Lindroos and Koski, 1966; Villar and Dawe, 1975; Koski, 1977). Tilden utilizes a three-pass grate cycle with a stage of updraft drying, followed by two downdraft drying stages. Recuperation systems which supply hot gases to a drying zone from second stage cooling were designed and fur¬nished for Tilden I. Tilden II will be identical. Empire IV will also be furnished with a recuperation system. The Adams grate¬kiln system was retrofitted with a recuperation system. This paper will summarize some of the efforts that are in effect or planned for grate-kiln pelletizing systems to: (1) reduce operating and maintenance costs, (2) reduce energy requirements, (3) improve product quality, and (4) meet environmental standards.

Jan 1, 1981