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By I. H. Clark

In some mining situations, backfills are not only required to be free-standing but are also expected to provide hangingwall support. It may therefore be specified that the backfill withstand a certain calculated stress within a given time. Given the materials available, the choice of backfill composition is not always straightforward, and an approach to the evaluation of cemented tailings backfill is therefore proposed. The general use of such a method will greatly assist in both the scientific analysis of the material properties for industry-wide purposes of comparison and decision-making as regards the choice of fill.

Jan 1, 1988

By Van Rensburg C S J

The options that are open to engineers for cooling mines are limited and are primarily dependent upon the thermophysical properties of coolants. These properties are carefully analysed in the context of cooling mines and a comparison is drawn among Ammonia (R717), Monochlorodifluoromethane' (R22), Dichlorodifluoromethane (R12) and Water (R718). From this comparison the extent of Ammonia's superiority as refrigerant is Evident.

Jan 1, 1988

By J. Lorosch

Improvement of current leaching technology was found necessary when processing ores which are more difficult to leach because they generate highly viscous, air-rejective pulps. Cyanidation of these pulps has to run at low oxygen concentrations if the conventional aeration technique with compressed air is used. Since the dissolution rate of precious metals mainly depends on the concentration of dissolved oxygen in the pulp [1, 4, 5], the kinetics of the gold extraction become slow in such cases, which in turn often leads to a significant decrease in the overall gold output within the conventional leaching time of up to 48 hours.

Jan 1, 1988

By C. M. Rastle

Resource Technology Associates (RTA) has developed a flocculation-flotation process that increases phosphate recoveries from current operating plants. A major advantage of the process is the ability to float the phosphate from the matrix without a preliminary separation to remove the slimes. A majority of the material that is now discarded in the slime fraction will be recovered in the new process. The process can also be used to recover phosphate material from current slime ponds either as a separate feed or mixed with matrix material. Flotation tails from the process demonstrate improved dewatering characteristics then those seen from conventional float tails.

Jan 1, 1988

By Kuster D

Under humid conditions geochemical exploration for rare-metals is, at the reconnaissance level,usually carried out by stream sediment and soil sampling. As the secondary dispersion patterns are distinctly different in arid environ- ments, other exploration methods have to be applied (MATHEIS & KOSTER, 1985).

Jan 1, 1988

By E. F. Divers

In response to a request from the Mine Safety and Health Administration, the Bureau of Mines has recently completed a respirable dust survey of 18 U.S. coal preparation plants. Of these, three were essentially free of dust problems. Respirable dust exposure of workers in the remaining plants depended on the time spent in the dusty areas. In five of the plants surveyed, Bureau tests showed that in some areas worker exposures could exceed Federal dust limits in less than 2 hours.

Jan 1, 1988

In Europe there are many regions, where coal or lignite is mined with surface methods. In most of these regions coal/ lignite is mined below groundwater table and mining opera- tions require pumping big volumes of water. Drawdown of groundwater table has influence on surface water and ground- water on adjacent areas. Mine drainage requires purification and its discharge changes flow in existing streams. Some of mine water is used by mining companies themselves, some is used by other industries, some for communal purposes and some for irrigation. However, majority of mine water is dis- charged to rivers without use. The above issues are discus- sed on the background of general, technical and water charac- teristics of such regions in B European countries. Conclu- sions and prospects for future complete the paper.

Jan 1, 1988

By Woodcock J. T, Sparrow G. J

Activated carbon particles obtained from a number of Australian CIP operations were examined with an optical and a scanning electron micro- scope and an electron microprobe. External surfaces, and polished sec- tions through individual particles, were examined with special reference to materials on the surface and to calcium and gold distributions. Photographs are presented of surface contamination of the particles by salts precipitated from the pulp such as calcium carbonate (calcite), calcium sulphate (gypsum), and a magnesium salt; ore minerals such as quartz, hematite, pyrite, arsenopyrite, pentlandite, and various alumino- silicates; and other substances such as grinding media and a fungus. Calcite was very abundant but the other materials were less common. Contamination in the interior of carbon particles was almost exclu- sively calcium carbonate, and extensive contamination extended to the centre of some particles. A possible mechanism for the formation of cal- cium carbonate inside the carbon particles is noted. Gold X-ray dot maps of sections through carbon particles indicated that gold was distributed throughout coconut shell carbons and that although gold was more concentrated near the outer surfaces of extruded peat carbon particles, it was also present to depths of at least 500 ¦m. The gold distribution throughout the carbon particles was similar to that rf alrit~

Jan 1, 1988

By C. J. Van Niekerk

When gold plant residues are cycloned for producing a coarse product for backfilling the gold and uranium values are upgraded in the backfill product. Gravity concentration, wet high intensity magnetic separation and froth flotation were investigated as first-stage recovery processes to recover these economic values from backfill prior to placement underground. This paper addresses the recovery of values from flotation concentrates and also details the economic feasibility of a treatment route including flotation, followed by roasting of flotation concentrate to liberate gold entrapped in pyrite and reverse gold leaching of the calcine so produced.

Jan 1, 1988

By J. G. Groppo, A. E. Bland, B. K. Parekh, W. F. Stotts

Many coal preparation plants discard fine coal (generally minus 100 mesh) because it is difficult to beneficiate economically. At the Kentucky Energy Cabinet Laboratory (KECL), the waste streams from several Kentucky preparation plants were evaluated for cleaning with counter-current column flotation. A series of performance evaluations were conducted using a 0.05 m (2 in.) internal diameter (I.D.) 7.9 m (26 ft.) high laboratory column. The objectives of these tests were to assess the performance in terms of recovery and percent ash in clean coal and to optimize the operating parameters relative to combustible recovery and grade. Refuse streams containing 30-50 percent ash were upgraded to 2-8 percent ash with Btu recoveries of nearly 90 percent. A pilot scale column flotation cell was installed at the Bell County Coal preparation plant. This pilot plant utilized a 5.79 m (19 ft.) high and 0.15 m (6 in.) I.D. column to verify the performance data of the 0.05 m (2 in.) I.D. column for two different waste streams. Performance evaluation and pilot plant testing results related to scale-up are discussed.

Jan 1, 1988

By W. E. Wallace, P. S. Mike, C. A. Hill, V. Vallyathan, M. J. Keane

Respirable quartz duet and a kaolin clay dust have been found to be of comparable cytotoxic potential in vitro on a specific surface area basis (Wallace, et a1,1985), despite the distinctly different potentials of quartz and clay for causing pneumoconiosis or pulmonary fibrosis (Sheers, 1984). A respired particle depositing in a respiratory bronchiole or alveolus will contact a pulmonary surfactant hypophase, of which a primary component is diacyl glycerophosphorylcholine, or diacyl lecithin (DPL) (Clements, et al, 1970). Several studies have found that adsorption of such surfactant suppresses in vitro cytotoxic effects of quartz dust (Marks, 1957). Subsequent phagocytosis and digestion by a macrophage may remove the coating, restoring cytotoxic potential and initiating disease processes (Iles, 1979). Adsorption of dipalmitoyl lecithin (DPL) from emulsion in physiologic saline by respirable sized quartz dust and kaolin dusts, and consequent diminution of the dusts' hemolytic and macrophage cytotoxic potential have been reported (Wallace, et al, 1985). This report presents additional data on the cell-free in vitro phospholipase A2 enzymatic digestion of dipalmitoyl lecithin adsorbed on a quartz and a kaolin respirable sized dust (Wallace, et al, 1988) to investigate mineral specific differences in the rates of digestion and of consequent restoration of dust membranolytic potential. Respirable crystalline alpha quarts used was eighty percent smaller than 5 micorometer aerodynamic diameter with a nitrogen adsorption specific surface area of 3.97 m2/g. Respirable kaolin dust was ninety percent smaller than 5 micrometer diameter and had a specific surface area of 13.25 m2/g.

Jan 1, 1988

This session comprises six papers: One paper is specifically on advances in drilling techniques, a paper presents a classification for water inrush rich with corresponding guidelines for protection, two papers are concerned with mining impacts in integrated catchment management - one from the quality viewpoint and the other from the quality viewpoint, and the final two papers are case studies of mine dewatering - one for an underground mine threatened by a karst limestone aquifer and the other of an open-cut mine threatened by interbedded sand aquifers. The paper entitled, Practical mine dewatering by means of surface drilled wells by Sides is innovative in presenting the case for wells as cost effective and appropriate for a number of purposes including exploration, re-opening old mines, dewatering, grout emplacement and monitoring.

Jan 1, 1988

By R. Tunold, Y. J. Zhang

"The cathodic kinetics of aluminum deposition from aluminum chloridealkali chloride melts was studied by use of electro-cnemical transient techniques at 700 °C. Aluminum deposited as an insoluble product on a glassy carbon electrode and as a partly soluble product on a tungsten electrode. The deposition was found to be a simple diffusion controlled process involving the exchange of three electrons. The diffusion coefficient of aluminum chloride was calculated - 4.sx10-s cm2 ·S-I in AlCl3 -NaCl-LiCl melts and 2.6x10-s cm2 ·S-' in AlCl3 -NaCl-KCl melts. For AlCl3 -NaCl-CsCl system the diffusion coefficient exhibited some uncertainty due to nucleation. The determined rate constant of aluminum deposition reaction was on the order of 10-' -10-2 cm'S:' Constant potential electrolysis was carried out. TiB2 was well wetted by aluminum. The species of melts penetrated into graphite and glassy carbon but not into tungsten. The diffusion coefficient of species in glassy carbon was evaluated.IntroductionAluminum chloride electrolysis is attractive for its power saving of 30%. Different process to circumvent the conventional chlorization to obtain aluminum chloride economically, such as directly chlorizating mixture of Al~03 and C in a cell with A-shaped laminated bipolar electrodes by rising chlorine (1), or by use of a composite anode (2), will promote the electrolysis technology to be realized industrially. With the appearance of the Alcoa process periodically there are studies on the kinetics of aluminum deposition. Some discrepancies seem to exist on the mechanism of aluminum deposition. Borne studies (3,4,5) showed that the deposition of aluminum was hindered by diffusion process in the melts. M.Gabco et a1. (6) claimed a preceding dissociation of a complex being the rate controlled step. This paper presents our results on the mechanism of aluminum deposition from the study by use of transient techniques and some results from constant potential electrolysis."

Jan 1, 1988

By P. J. How, T. O. Hagan, M. F. Handley

Inelastic deformation of highly stressed rock in deep mines needs to be quantified in both time and space. Since most deformation occurs by shear, continuous monitoring of discontinuities in the rock from boreholes holds promise. The casing. Al interpretations of shear movements are based on a simple relation between shear displacement and the resulting change in tilt of the sensor. A prototype has been constructed and has undergone laboratory trials with satisfactory results. Underground trials will commence shortly. The instrument as designed has the potential for other applications, both in the civil-engineering and mining industries. paper describes an instrument that is both cheap and reliable, and capable of monitoring such shear movements continuously. The principle of operation is based on two capacitive gravity sensors mounted orthogonaly to each other in a sealed aluminum

Jan 1, 1988

By J. Dille

Metallic cobalt exist in two allotropic forms : the hexagonal compact a which is stable at low temperature ( ( 420') and the cubic form 0 stable at higher temperature. This latest form is the only one which is ductile. During the electrode position of Co, in moderate acidic conditions, we noticed a code position of both a and B forms. The influence of several parameters on the B/a ratio in the deposit was investigated. High acidity and the presence of Fe increased its ratio; on the opposite, high temperature promote the a phase. No significant influence on the material were noticed. The differentiation of a and B forms of Co is rather difficult and the method of J. Scoyer was improved quite successfully.

Jan 1, 1988

By Robert D. Pehlke

"Current continuous casting processes are going through a rapid evolution of advances and new developments. At the same time, intense efforts are being directed to the development of radical new technologies such as continuous casting of thin slabs and strip steel.Traditionally, the casting processes for steel have been anticipated by the development and implementation of processes in the non-ferrous industry. This trend is reviewed and what it may portend for steel is described.IntroductionThe continuous casting of steel has been a widely adopted process in the production of steel. The concepts for this processing go back into the early and mid 1800's; however, commerical development was delayed for a variety of reasons until the mid twentieth century.Beginning in the early 1960's, adoption of continuous casting was initiated and continues at this point in time to be accelerated. In Japan, more than 90% of the steel produced is continuously cast (1). More than 50% of the steel produced in the United States is continuously cast and this fraction continues to rise (2). Numerous examples can be cited of installations costing well over $200,000,000 which have provided a payoff in less than a year and a half. As this process has continued to be applied and its technology to increase, computer control systems have been installed. In particular, in the larger plants producing slabs, sophisticated computer systems involving the integration and networking of mini-computers, micro-computers, and mainframe including back-up systems at all levels are being utilized. Pehlke (3), and Harabuchi and Pehlke (4) have described the structure of these systems."

Jan 1, 1988

By S. J. Hogan, T. William

"By the year 2000, the steel industry, not only in the United States but in the rest of the world, will undergo significant changes. On the other hand, there will be a number of areas in which change will be minimal.The current capacity of the industry worldwide is approximately 800-810 million metric tons. This may grow to some extent, as Third World countries install capacity. However, much of it will be neutralized as the industrialized countries shrink their current capacities.There will be several breakthroughs in terms of technology, some of which deal with the production of iron outside of the blast furnace. However, these processes will not be far enough advanced by that time to replace the blast furnace, rather they will supplement it.In terms of steelmaking and the subsequent rolling process, there should be a number of basic improvements. The strip mills will roll sheets with a very slight variance in gauge, which will give the customers a better product for automatic stamping machines. Ordinary carbon steel, in a number of instances, will be replaced by high-strength, low-alloy steel, which will reduce the tonnage necessary for present-day applications, such as construction.The corporate organization will be significantly changed as joint ventures and mergers will reduce the number of companies, as well as facilities in operation. This will enable the industry to reduce its capital investment and improve operating costs, so that it will be able more effectively to compete with other materials, such as plastics, cement, aluminum, etc."

Jan 1, 1988

By A. Van den Steen

In the early fifties Professor Breckpot of the Louvain University in Belgium in collaboration with the Research Laboratory of Metallurgie Hoboken, discovered the possibility to separate nickel from cobalt sulfate solutions by a nickel sulfide depolarized cementation. This reaction, completed later with a zinc precipitation, was developed into purification processes for the Shituru and Luilu Gécamines cobalt plants in Zaíre. Due to increasing demand for higher quality products and the necessity of lowering the production costs, more laboratory and pilot plant investigations concerning the key parameters for the nickel and zinc sulfides precipitation were under- taken. Especially the relative stabilities of cobalt, nickel and zinc sulfides, precipitated with elemental sulfur or sodium hydrosulfide, were examined in relatlon with the pH and with the redox potential. These investigations have led to better plant practice and new development possibilities. The valorisation of the precipitated sulfides has also been considered.

Jan 1, 1988

By L. G. Austin, R. S. C. Rogers

INTRODUCTION Coal is geologically a sedimentary rock with distinct bedding planes containing a mixture of petrographic constituents. Yet. because of its chemical nature, it also has some of the characteristics of a polymeric material. In addition, it is extensively precracked to give a macropore structure and also has a substantial internal volume of microporosity. Add to this the mineral constituents dispersed in the coal in a variety of forms and sizes. and it can be readily appreciated that coal is a complex and heterogeneous material. It has to date not been possible to predict the particle size distributions produced by breakage of coals from a priori application of the principles of fracture mechanics. However, there is a substantial body of data resulting from empirical observation of size distributions produced under various conditions, primarily from grinding mills. It is the function of this review to outline how this empirical information can be used to predict product size distributions for those systems which have been studied systematically, and to suggest future avenues of research using similar methodology. FRACTURE THEORY APPLIED TO COAL It is, of course, possible to devise experiments for slow crack propagation in a coal. However, the evidence is that coal breaks by brittle fracture in the mills and mining machines of industrial importance and therefore the theory of brittle fracture is sufficient to illustrate the important features of the fracture of coal. In order to produce size reduction a solid must be stressed by the application of force. The force can be a tensile (stretching), compressive, or shear force, and the three dimensional stress pattern in the solid represents the tensile, compressive, and shear forces per unit area acting in any direction through any point in the solid. As an illustration consider the case of a simple one-dimensional tensile stress: then stress is defined as a=F/A where F is the force. A is the cross-sectional area of the solid normal to F and strain. E, is defined as the fractional change in the length of the solid. so that E= x/L where x is the extension of an original length of L. Coal behaves as an elastic material over short times (although viscoelastic creep can occur if the stress is maintained over long times) and if it is not stretched too far the coal returns to its original shape when the stress is removed; otherwise catastrophic failure occurs and the coal fractures at a stress termed the tensile strength. The failure under stress of an elastic material is termed brittle fracture. Elastic material fails at small stain and the stress-stain relation to where brittle fracture occurs is the empirical Hooke's law. a= YE, where Y is Young's modulus. The work done on the solid to take the solid from zero external stress to a stressed state by slowly increasing F up to a final stress u is the integral of the stress times the strain. This reversible strain energy is stored in the solid and. using Hooke's law. is u /2Y per unit volume of solid. If the solid is immediately loaded to u the work done is [EAuL] which Is a2 /Y per unit volume, that is, twice the reversible work.

Jan 1, 1988

By J. Siege1, R. S. Popielak

A computer model was used to simulate the effect of leakage through confining beds on a hypothetical in situ leach operation in an aquifer with a thin mineralized section. The simulations were used to assess economic and potential environmental implications of leakage on an in situ leach operation. Four scenarios were modeled - three representing cases with different degrees of confinement, and the fourth representing a stratified ore zone under a low degree of confinement. The model simulated the travel path and travel time of lixiviant given the hydraulic conditions prescribed in each scenario. The results show that the travel path and travel times vary by about 10% for confinement ranging from nearly impermeable (essentially no leakage) to an extremely low level (thin confinement with a permeability about equal to that of the aquifer) for isotropic aquifer conditions. The aquifer thickness contacted by the lixiviant varied from 85% to 90%. Horizontally, 55% to 60% of the aquifer was contacted. The flow paths in the stratified aquifer were reduced in the vertical direction and expanded horizontally. Forty- five percent of the aquifer thickness was contacted vertically with 88% contacted horizontally. Break- through time for lixiviant traveling at mid-depth of the aquifer increased two times when the leakage was increased from nearly zero to a value representative of thin and highly permeable confinement. Leakage affects the economics of in situ mining by (1) increasing the time required to leach out the ore, and (2) increasing the thickness of the ore zone aquifer to be restored. The potential for environmental impacts appears to be minor. In all four simulations, the lixiviant did not contact the confining strata. Restoration would be limited to cleanup of the ore zone aquifer within the thickness contacted by lixiviant and within the radius of the lixiviant that traveled farthest away from the production cell.

Jan 1, 1988