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By William J. Robinson

What is the cummulative rate of recovery of copper from a sulfide leach dump? This is one of the most frequently asked questions today. We, in the industry, ask it of each other when we meet; however, the technical answers may vary from "I don't know" to 'quite good" from people within the same company. Management also poses this question because it plays a vital role in our planning for future production. The answer is difficult because of the many variables between different operations such as physical construction of the dump, topography of the original site, characteristics of dump material, mineralization, water application, etc. Each has a bearing on the rate of recovery. OPERATIONAL DATA Our method of water distribution is unique in that each dump is drilled to allow physical injection of water into the dump. The in¬jection holes are drilled vertically, on 251 centers, from the surface of the dump. Normally, the holes are drilled 40' deep and cased with 4" PVC perforated pipe.. The pipe is perforated at one-foot intervals with four V diameter holes at 901 spacing on the pipe circumference. We formerly alternated shallow holes (20'-40') with deep holes (80'-l80') in an effort to cover the entire dump and hasten oxidation. The shallow hole depth varied according to the compaction thickness. The deep hole depth varied according to the height of the dump and the original ground profile, We prefer to have the deep holes end 20'-30' above the original ground level. This generally allows us to penetrate the coarse material at the bottom of the dump. We had to discontinue the deep holes_ in order to cover more dump area in a shorter period of time to meet increased production requirements.

Jan 1, 1972

By R. K. Agarwal

In this paper a simple three-layered medium is considered. A circular hole is centrally located in the intermediate layer. The layered sheet is loaded uniaxially perpendicular to the stratification. The Young's modulus of the intermediate layer is lower than that of the outer layers. The stress distribution around the circular hole in a stratified medium is significantly different when compared to the case of a continuous homogeneous medium. The distribution depends upon the ratio of the height of [the] intermediate layer and [the] hole diameter. A comparison of stress the distribution and procedures for preparation and testing of [the] model are given. The potential of the technique is outlined.

Jan 1, 1968

By Wayne R. Hopkins

Southern Arizona has one of the world's principal concentrations of copper ore bodies. Twenty miles south of Tucson, close to the Mexican border at Sahuarita in Pima County, is the Twin Buttes mine. In mid-1973, the Anaconda Company and American Metals Climax Incorporated (AMAX) established a 50-50 partnership to operate and expand the Twin Buttes property. Anamax Mining Company was established as the operating company for this joint venture. The production from the Twin Buttes mine is shared between the two partners who market independently. A major expansion of the Twin Buttes operation has included an accelerated stripping programrne for the pit, an expansion of the sulphide concentrator, the construction of an oxide leach plant and a 57 MW diesel generating power station. Part of this major expansion, the large tonnage oxide processing plant was brought on stream in 1975 and is now close to design capacity. The "mine to market gap" has been closed by producing high-purity copper cathodes at the mine site from oxide ore reserves. By using a hydrometallurgical process route, copper production is possible with negligible effects on the environment.

Jan 1, 1976

By Michael E. Stickney

"Soft technology" computers and computer programs-brings to mind a room full of machines, tape drives, disks, plotters, and printers spitting out financial reports. Computers now have a much broader scope of applications because of reductions in equipment size and cost. For example, people now interact directly with computers to control events. Such computers and associated equipment-called interactive control systems-are often small, relatively inexpensive, and can be designed to increase productivity at mining operations. This is accomplished by improving communications between individuals; giving employees the information needed to make decisions in real time, as events are happening; and giving individuals the background needed to perform more effectively. This paper will describe a procedure for determining the return on investment for interactive control systems, and describe four such systems. The analysis process is general in nature and can be applied to any type of mining operation or production process.

Jan 4, 1981

By David M. Shaw, John C. Franklin

A 32-channel warning system for high working level, fan operation, and airlock-doors has been constructed. The working level monitors have a microcomputer for accumulating the pulses, converting to working level, and triggering an alarm at a variable set point and at one working level. The system also detects when underground fans lose power or air doors are open. The system can detect changes in air velocity which indicate surface fan failures or changes in the ventilation system. Using this alarm system, the ventilation engineer will be alerted prior to excessive levels of radon daughters being reached so corrective action can be taken.

Jan 1, 1981

By F. C. Nicolli, J. P. Barbosa, P. S. M. Soares, A. V. Estevez

INTRODUCTION Spent household dry cell batteries are frequently disposed of with metropolitan wastestream (MSW) in landfills where they can leak due to handling or aging. Frequent rain and sun cycles, especially in tropical environments, coupled to the action of leachate, dissolve their metal constituents which will eventually reach rivers, lakes and underground water. It is well known that some of these metals are fundamental to sustain life and that is why living organisms concentrate them through their metabolism, but it has been also recognized that beyond specific limits they can definitely be deleterious to the environment. In other words, high concentration of heavy metals are proven to cause chronic or acute diseases and toxic reactions, by acting on mammals' kidneys, liver and nervous system. In addition, some metals frequently used in household batteries, as mercury and cadmium, are said to be carcinogenic (Landis et al. 1995, Silva et al. 1988). Occasionally, plants to treat MSW are coupled to compost production. Household batteries present in MSW can be dragged into these plants, contaminating their products and eventually reaching vegetables making them not proper to consume by people and animals. Alternatively, batteries are also conveyed to incinerators and burned, throwing into the atmosphere volatile species. These can either act as contaminants as toxic vapor species or be delivered by winds and scavenged by rains contaminating soils and water far away from their source. In conclusion, despite the treatment applied to MSW, one can say that battery residues are potentially environmentally hazardous. The careful assessment of the environmental impact caused by residues of household batteries it is not an easy task and it can be referred as a multivariable problem. First, many different household batteries are produced by industry and the potential environmental hazard associated to their disposal depends primarily on the type of battery and manufacturer's technology. These characteristics will dictate how resistant the battery case is to handling and the

Jan 1, 1998

By K. Adam

Uncontrolled disposal of pyrite wastes and concentrates comprise a major source of acid drainage in active and abandoned sulphide mines. In this paper, the state?of-the-art mitigation measures implemented for the final reclamation and closure of a pyrite concentrate stockpile at Platia Karra, Stratoni mines, Greece, are presented.

Jan 1, 2002

By J. D. Patsey, G. T. Lineberry

Introduction A computer program was developed for analyzing drum-type hoists before modifying an existing system or designing a new one. Its use permits the preliminary evaluation of a system before seeking technical assistance from mine hoist designers and manufacturers. The user-friendly program accepts a variety of data and analyzes hoisting systems for any balance state. The program can be used to calculate skip capacity to yield a desired production rate, solve for drum face width, select a permissible wire rope, estimate total horsepower of the hoist plant, and estimate annual power cost. Whether required for a large mining complex or for a relatively small operation, a hoisting system must be carefully designed to ensure the efficient, reliable, and safe flow of material. Because shaft sinking and hoist installation can total between 2.5% and 3% of the cost of opening a deep mine, proper hoist selection is critical. Today's mining engineer has at his disposal the most powerful design and analytical aid ever, the micro- computer. There is, unfortunately, limited software for the study of hoisting systems, unlike that for other materials handling equipment (Manula and Albert, 1980; Prelaz et al., 1964; Bucklen, 1969; Thompson, 1985). HOIST reduces a time-consuming set of calculations to a concise package of interrelated subprograms. A literature review revealed no common-user pro- grams to analyze hoisting systems, although at least four major hoist designers/manufacturers/installers have their own in-house programs. To provide a tool with which the mining engineer could preliminarily analyze a materials hoisting system or could check the calculations of a hoist contractor, a computer program was developed. HOIST was written in BASIC for the IBM-PC for ease of program adaptation and to en- courage field use on compatible systems. Details of program development are omitted, since the basic principles of hoisting analyses are relatively straightforward, simple, and readily accepted (Har- mon, 1973; Nordberg, n.d.; Adler, 1957). Program features, intended usage, and benefits of the com- puterized solution are emphasized over theory development and mathematical rigor. Background The mine hoist system that is selected and installed at a mine is the "lifeline" of that mine, with installations lasting 20 years or more. Thorough study is warranted to ensure that productivity demands are met at a minimum cost per ton. The increased cost of a large, powerful, high-speed hoist must be offset by increased production to justify its selection. To optimize this tradeoff, an extensive hoisting analysis should be performed. The analyses to properly size the skip (or cage ) , the drum, and the hoist drive are conducive to computerization, permitting rapid evaluation of changeable operating and design parameters, such as velocity, acceleration, state of balance, and productivity demand. The program is particularly useful in conducting sensitivity trials, such as investigation into the effect of change of productivity on skip capacity and on horsepower of the hoist drive. HOIST is currently limited to the study of drum-type hoists with cylindrical drum(s). However, only minor changes to the program would permit analysis of friction hoists and conical drum configurations. Model development and testing The program is based on accepted equations and physical relationships. Examples of manual calculations formed the basis for decision points and program branching. Data is input in the order that it would be needed if the problems were solved manually. The choices are arranged likewise. HOIST was developed in sections, with manual solutions performed to check program logic. The testing became more rigorous as sections were completed. Output from one section becomes input for following sections, as appropriate. The simplified flow diagram of HOIST is given in Fig. 1.

Jan 1, 1988

By Richard Dunmore

Most coal seams in the United Kingdom contain firedamp, some of which is released into the ventilating airways as the strata around a working relax. The close sequence of seams in carboniferous strata is usually such that seams in adjacent roof and floor strata are also disturbed and potentially large quantities of firedamp can enter the workings from these sources. Since emission depends on the disturbance rate of the seams, higher coal production rates associated with increased mechanisation in the colliery accentuate the problem. Firedamp concentrations in UK underground workings are subject to statutory regulations1. To enable production to continue uninterrupted and in safety the problem is tackled by ventilation engineers by the provision of adequate ventilation in the airway and by the technique of firedamp drainage. In the UK the latter usually takes the form of cross-measure boreholes in roof strata, and increasingly also in floor strata, drilled from the gateroads, especially from return airways. In this way firedamp emitted from disturbed seams in adjacent strata can be extracted directly to the surface or to some safe position outbye, and the airways of the working district are not contaminated. Despite the use of firedamp drainage, considerable quantities of firedamp enter the ventilation air- stream and the concentration levels may be seen to be related to the coal production activites in the district. Figure 1 shows a typical recording of methane concentration obtained by a BM1 methanometer at a position outbye in a return gate where firedamp drainage was operating. The general rise in level throughout the working week may be seen, together with peaks occurring during production shifts and the gradual decay of emission over the weekend. In view of the fact that ventilation and firedamp drainage contribute a considerable proportion to the operating costs of the colliery, it is essential that the ventilation and firedamp drainage requirements be calculated as accurately as possible at the planning stage of the working. In the past the ventilation engineer has had to rely heavily on experience in neighbouring workings but with the development of mines in previously unworked areas there is clearly a need for a methodical approach to meet the requirements of planning. The work described in this paper represents such an approach and it is hoped that successful development and application of the method of prediction will lead to the widespread adoption of a routine procedure. The current development of a method of prediction of firedamp emission into longwall workings is based on the theoretical treatment of gas emission from coal seams proposed by Airey2 in 1971, which was based on his study of gas emission from broken coal 3 which was published in 1968. In common with other experimental methods of prediction, the method enables a calculation to be made of the total make of gas emitted from all sources of gas in the strata per tonne of mined coal.

Jan 1, 1980

By Diane Germain, Normand Tassé, Claude Dufour

At the East Sullivan site, pore-waters underlying a wood waste cover that prevents sulfide oxidation are characterized by an anoxic environment, abundance of dissolved organic substrates, and near neutral pHs. Such conditions favor sulfate reduction and base metals precipitation as sulfides, as well as carbonate-metal precipitation. Pore-water composition from 1992 to 1998 shows a significant Fe2+ decrease. Therefore, the restoration strategy of that site capitalizes on these alkaline and reductive properties. Since 1998, a novel treatment of acid effluents, based on the recirculation of water discharged around the impoundment through the organic cover, is tested on the site. Available data gathered in 1998 and 1999 shows that the pH of recirculated water flowing within the wood waste cover increases by 2 to 4 units and that Fe,, concentrations decrease by a factor greater than 6.

Jan 1, 2000

By Naomi H. Harley, Daryl E. Bohning, Isabel M. Fisenne

INTRODUCTION Underground mines in many parts of the world have elevated levels of short-lived 222Rn daughters. Lung cancer implicating exposure to short-lived daughters is documented in the U.S., Czechoslovakia, Canada, Sweden, the U.K., France and Newfoundland. An elevated lung cancer mortality (in excess of that expected) has been observed when cumulative exposure to alpha emitting short-lived 222Rn daughters (218Po, 214pb 214Bi 214Po) is greater than about 60 working level months (WLM) [1]/ (Hewett, D. 1979). This is equal to an absorbed alpha dose of about 30 rads to shallow basal cells in bronchial epithelium. Long-lived alpha emitters are also present in underground mines, and especially uranium mines because of airborne particulates containing uranium. The 238U parent of this primordial series supports other long-lived emitters 234U 230Th, 226Ra, Pb(210Po) which are in some degree of radioactive equilibrium with the parent 238U. Airborne particulates can be present due to drilling on the face of the ore body as well as in all parts of the mine through resuspension from the mine floor. Particles from 1 µm to about 5 µm penetrate the nose with reasonable efficiency and deposit primarily in the tracheobronchial tree. They are removed by ciliary motion (the bronchial escalator) but deliver an alpha dose to basal cells in bronchial epithelium during clearance in the same manner as short-lived 222Rn daughters. It is the purpose of this work to indicate the alpha dose to basal cells in bronchial epithelium delivered by the long-lived emitters 234, 238U. The dose calculations reported here based upon a few measured values of these isotopes in air in uranium mines in New Mexico and Colorado. MEASURED 234, 238U IN URANIUM MINE ATMOSPHERES In 1979, the U.S. Bureau of Mines undertook a study to evaluate personal monitors to be worn by miners to measure short-lived 222Rn daughters. One of these devices sampled air at 100 cm3/min through a 13 mm glass fiber filter, with a small pump worn on the belt. Alpha particles emitted by 222Rn daughters on the filter were measured continuously by a thermoluminescent dosimeter (TLD) chip. Each monitor was worn by a miner for a 170 hour working month and approximately one cubic meter of air was sampled during this period. Six different mines were selected for the test in New Mexico and Colorado. The mines used either wet or dry drilling methods. Miners in each location were equipped with the personal monitors. Subsequent to their use in evaluating the shortlived daughters, Dr. Robert Droullard of the Bureau generously gave us these filter samples along with a few blank glass fiber filters from the same box of filters used in the study so that long-lived emitters present in these mine atmospheres could be determined radiochemically. Four of the samples have been run for 234, 238U. The radiochemical procedure for uranium is adapted from USDOE, Environmental Measurements Laboratory Manual (Harley, J.H., 1976). Briefly, the samples were placed in platinum crucibles, spiked with 232U tracer and pretreated with nitric and hydrofluoric acid. The residue was fused with potassium fluoride to transpose to pyrosulfate. The fused cake was dissolved in 7 [N] hydrochloric acid and the solution passed through an anion exchange column to isolate uranium. Iron was removed using mercury cathode electrolysis. Uranium was electrodeposited onto platinum dies and counted using solid-state alpha spectrometry. The samples from each type of mine (wet and dry) were analyzed. The samples in the "wet" mine in New Mexico were selected on the basis of the original TLD measurement because they were near the maximum occupational standard for radon daughters. These samples should also represent upper limits to longlived activity encountered, since they were obtained at drilling operations on the face of the ore body. Samples collected in the "dry" mine in Colorado were pot associated with a particular location in the mine and should be representative of a month long overall exposure in many locations and operations. The values are shown in Table 1. The two uranium isotopes are in equilibrium and their alpha activity

Jan 1, 1981

By J. W. Lowry

After years of processing copper porphry ores, the Ray concentrator of Kennecott Minerals Company installed a concentrate regrind mill in its flotation circuit. The first cleaner concentrate is reground rather than the usual rougher concentrate. An additional cleaning of the reground product yields an increase in copper content of the final concentrate and a significantly lower insol content. The desired goal of decreasing the energy requirements for smelting the concentrate has been achieved.

Jan 1, 1980

By Carrie Pourvahidi

The California High Speed Rail Authority (Authority) was created by the State of California through legislation in 1996. The purpose of the Authority is to plan, construct, finance and operate a statewide intercity high speed passenger rail system. In 2004 the Authority prepared a programmatic level environmental document in compliance with the California Environmental Quality and National Environmental Protection Acts (CEQA and NEPA).The Authority and Federal Railroad Administration (FRA) were the lead agencies overseeing the development of the environmental documentation. The resulting document includes two volumes and 64 supplemental technical reports analyzing the transportation needs for California and the selection of an approach to meeting the project transportation needs. The Programmatic Environmental Impact Report and Environmental Impact Statement (EIR/EIS) identified High Speed Rail as the most environ-mentally protective, sustainable and economical approach to meeting the state?s projected transportation needs.

Jan 1, 2008

By B. P. Boisen

INTRODUCTION The rapidity of onset, rate of increase, and magni¬tude of loads in an underground support system can be measured using load cells or pressure cells, whichever is appropriate to the type of support. These instruments should be installed at the various instrumented station locations immediately after excavation. If the loading of a member is of interest, the load should be measured, whereas if the deflection or strain of a member is of interest, the strain should be mea¬sured. It makes as little sense to use a load cell to allow computation of strain as it does to measure the strain and then back calculate the load. Tunnel steel set de¬signers today invariably rely on the early work of Karl Terzaghi, the basis for which is load, so load measure¬ment should be the main concern. The current trend of using strain gages on steel sup¬port systems stems from the inability by some to eval¬uate unusual loading conditions caused by uneven block¬ing. In fact, uneven blocking will obscure almost any attempt (whether with load cells or strain gages) to properly evaluate support performance. The load curve in Fig. I shows the development of a characteristic early peak load sometimes called the "rear abutment load" seen in many underground open¬ings. It is thought that the peak reflects the coupling of the rock and the support system, and that the magnitude will increase until some yielding, or minor failure, of the support system occurs. At that time, the slight deforma¬tion of the support system promotes the formation of minute shears in the opening walls, and these shears tend to distribute stress between the support system and the adjacent rock in proportion to the relative rigidity of the support elements and the rock. In normal rock, as a result of this stress redistribu¬tion, subsequent load magnitudes generally do not reach the magnitude of the early peak load. In physically unstable (squeezing) or chemically un¬stable (swelling) rock, however, the loads experienced after passage of the early peak load may in fact show a slow, continuous increase. One of the very important purposes of load instrumentation is to provide the means for recognizing such long-term adverse trends, thus enabling the proper remedial steps to be taken. Another purpose of load instrumentation is to pro¬vide a comparison between the magnitudes of the early peak load and the subsequent stable load. The ratio of these two loads is analogous to a safety factor, and may be used to evaluate the efficiency and economy of the support system design. Aside from considerations of economy, it may be well to design support systems which do not have excessively high ratios of early peak load to subsequent stable load. Should these ratios be exces¬sively high, the support system may be so rigid that the yield or failure associated with stress redistribution may occur with explosive violence. Load cells for use in mines, tunnels, and on con¬struction projects come in many forms. Almost all, however, employ the same procedures for installation, readout, etc. Therefore the following comments are almost universal in application. LOAD CELL INSTALLATION Load cells should be installed with bases parallel to the surfaces against which they bear. Care must be taken to orient the cells so that their signal cables are protected from accidental damage as a result of con¬struction, maintenance, or cleanup activities. Most electronic load cells are compensated for tem¬perature variations likely to be encountered during nor¬mal operations. However, if a large difference is an¬ticipated between the calibration temperature [21°C (70°F)] and the average operating temperature, the cells should be conditioned to the operating temperature for at least 8 hr prior to installation. This is to insure that the initial reading, made under no-load conditions prior to installation, provides a stable value to which subse¬quent measurements can be referred. Hydraulic load cells tend to be temperature sensitive and should be used with that in mind. Also, hydraulic load cells tend to be soft compared to electronic types and will sometimes allow movement to take place in a system intended to be semirigid. Furthermore, hydrau¬lic load cells tend to be difficult to read remotely. Care must be taken to use bearing plates on both sides of load cells which are sufficiently rigid and of high enough bearing capacity to prevent bending and crush¬ing under load. This is very important with tieback load cells (basically a ring of steel) which can easily dig into bearing plates. MAINTENANCE AND TROUBLESHOOTING Except for a direct hit by a miner's axe or flyrock from a blast, most hydraulic load cells are nearly in¬destructible and require little, if any, maintenance. Hy¬draulic oil on the bearing plates is a good indication of a leak and the need for corrective action. Field maintenance of electronic load cells involves protecting the instrument and signal cable from mechani¬cal damage and from unnecessary exposure to dirt and moisture, and recognizing and correcting damage and the effects of normal wear and tear.

Jan 1, 1982

By Bernard J. Scheiner, R. J. Wesely, Cy E. Jordan, A. D. Zunkel, Gary M. Wilemon

The U.S. Bureau of Mines has investigated leaching of off-grade western United States phosphate deposits using sulfuric acid (H2SO4) in the presence of methanol. A combination of ore grinding followed by sulfuric acid in methanol leaching extracted over 80 pct of the phosphate. This leaching technique significantly limited the dissolution of iron, aluminum, and magnesium impurities and produced a phosphoric acid that was well within the desired limits for these impurities. The dissolution rate of phosphate rock in the sulfuric acid methanol system was significantly slower than the conventional aqueous sulfuric acid dissolution. Initially dissolution of the phosphate particle was controlled by the amount of surface area available to the sulfuric acid reactant. After about an hour of leaching, phosphate dissolution was slowed almost to a stop, limited by the rate of ion diffusion through the calcium sulfate barrier layer surrounding the unreacted phosphate particle. Consequently, the ore was ground below 38-pm to increase the particle surface area available and improve the overall dissolution kinetics and extraction. In addition, the sulfuric acid was slowly metered into the reactor to prevent any excess heat from the mixing of acid with the methanol from simulating the formation of methyl sulfates. The formation of methyl sulfate ultimately lowered the overall phosphate extraction by exhausting the supply of available sulfate ions for the dissolution reaction. Subsequent evaporation of the methanol from the product acid decomposed the methyl sulfates leaving undesirable sulfate ions in the product acid. Slow acid addition to the reactor provided high phosphate extraction and limited the amount of sulfate in the final product acid.

Jan 1, 1993

By Regina N. Tempel, Laurie S. Balistrieri, Lisa L. Stillings, Lisa A. Shevenell, Maggy F. Lengke

Dexter pit lake, within the townsite of Tuscarora, Nevada, has been in existence since 1990 and provides a natural laboratory for the study of cycles of trace elements associated with ore deposits (e.g. As, Cu, Pb, and Se). Our goal in this study is to develop and calibrate methods of geochemical modeling that may be applied to estimating the concentrations and fluxes of trace elements in pit lake systems. Our initial modeling work considers limnology, hydrology, wall rock mineralogy and geochemistry, benthic fluxes, and colloid composition. Results from our work may be useful in evaluating water quality in the arid West.

Jan 1, 2000

By R. F. Davis

The evaluation and selection of coals for producing metallurgical coke is indeed a com- plex process simply because coal is a complex and variable substance which is sensitive to how it is treated from the time it is mined until it is transformed into coke. A review of the the more common evaluation tests made on coal and how the test results are applied in commercial practice. Parameters used to select coal blends for wet and preheated charges should also be of interest.

Jan 1, 1980

By Jacques B. Wertz

Recurring movements remotely connected with the Murray fracture zone and the San Andreas fault complex, together with the slow northwestward drift affecting the Baja California peninsula, could progressively have accentuated the tensional situation already connected with the anticlinorium in southern Arizona. From the fragmentary data gathered on the Texas lineament, it appears that a very mild curvature, concave to the northeast, may be present along this belt throughout Arizona. Those localities where the successive changes in direc¬tion of the strands of the lineament belt seem to occur do generally coincide with intersections of both north-northwestern and northeastern breaks. It is along the outward, southern fringe of the belt (at such structural centers like Bisbee, Baboquivari, Ajo) that the greatest impact of regional movements could be expected to have occurred through tangential-torsional stresses. Although it si accepted that the north-northwestern and more particu¬larly the northeastern fractures in Southeast Arizona are propitious to or partially responsible for mineralization, it seems undeniable that the Texas lineament belt must have greatly increased the potentialities for ore throughout the Arizona copper province. While intrusive bodies occur near major intersections, with the Texas lineament belt as a common denominator, it seems, the ore deposits are to be found close to one of the intrusive stocks, varying in distance from contiguity (Bisbee) to one or two miles away (Silver Bell orebodies).

Jan 1, 1970

By R. E. Ray

As coal reserves at shallow depths continue to be exhausted, a number of US coal companies are developing seams previously considered too deep to mine economically. Because of increased cover load, mines operating in deeper seams face unique ground control problems. In addition, the volume of methane gas in coal beds increases with depth, and ventilation requirements are much more stringent for deep mines than for shallower mines. When the longwall mining method is wed at great depths, ventilation, ground control, and operational considerations all influence the design of longwall panels. This paper examines these influences, particularly ventilation and operational considerations, on the feasibility of two-, three-, and four-entry longwall development panels in Jim Walter Resources' four deep mines.

Jan 1, 1988

By Broderick E. Davis

Each year, about 45 Mt (50 million st) of flotation tailings are discarded in Florida phosphate operations. These tailings only contain about 4% of the phosphate in the ore. However, more than half of the phosphate in the tailings is concentrated in the +600 µm (+28 mesh) size fraction at grades of up to 20% P205. Many phosphate producers have attempted to solve this problem by floating the +425 µm (+35 mesh) flotation feed separately. However, phosphate recoveries in these circuits are typically only 60%. For seven sampled phosphate operations, the phosphate content of the +600 µm (+28 mesh) fatty acid tailings ranged from 15% to 25% P205. In every case, the +600 µm (+28 mesh) fatty acid tailings was higher in grade than the overall flotation feed. Attempts to efficiently recover this coarse phosphate have apparently been unsuccessful at these seven phosphate operations. Recovery of this coarse phosphate would provide an additional 900 kt to 2.5 Mt (I to 2.7 million st) of phosphate annually and add an additional year to the reserves of these important deposits. A typical central Florida phosphate matrix is composed of three different mixtures of minerals. The +1.18 mm (+ 16 mesh) portion is chiefly phosphate pebbles and is beneficiated by sizing. The -106 µm (-150 mesh) portion contains virtually all of the clay minerals and is discarded in the hydrocyclone overflow. The -l mm +106 µm (-16 +150 mesh) material is a mixture of quartz and phosphate minerals.

Jan 1, 1993