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By G. B. Misra

Heat transfer in partially wet mine airways has been the subject of study for quite some time. Of the available models some are quite empirical while some involve highly complicated computation. Models developed by Amano, Mizuta and Hiramatsu and Banerjee and Chernyak as well as that modified by Misra were evaluated for prediction of the rise in temperature and humidity (mixing ratio ) of partially wet mine airways at four different levels in the Mosaboni Mine of Hindustan Copper Ltd. Measurements of barometric pressure, virgin-rock temperature and changes in dry- and wet-bulb temperatures along a certain length of airway were made. The rise in dry-bulb temperature and mixing ratio of air over the sections were calculated using the three models. The study reveals that calculated values of temperature and moisture content agree within possible rage of experimental error with all the three models in case of three levels with low wetness factor, but the agreement was poor for the relatively more wet airway on the 30th level. Errors in the estimation of fw to the tune of 0.025 can lead to fair error up to 0.94 K in the estimated temperature while alternative ways of estimating the heat transfer coefficient [] can introduce errors up to 1.45 K.

Jan 1, 1987

By J. A. Brierley, C. L. Brierley, R. C. II Blake, S. McGinness

A principal long-term goal of this laboratory is to achieve a detailed understanding at the molecular level of the microbial-dependent solubilization of minerals. Three recent advances in this research are summarized. (i) An in situ electrolytic procedure is described whereby large quantities of autotrophic iron-oxidizing organisms may be achieved for fundamental or applied studies. Over 600 grams wet weight of Thiobacillus ferrooxidans were harvested from a single 55-gallon growth vessel. (ii) A basis is presented for classifying some 70 different iron-oxidizing bacteria into one of 4 categories, depending on the type of redox-active electron transport proteins expressed during aerobic respiration on reduced iron. Comparative spectroscopic analyses indicated that different electron transport mechanisms exist in different genera and species of acidophilic bacteria that respire on iron. (iii) A method is introduced to investigate the binding interaction between bacteria and minerals, based on changes in the electrokinetic properties of the two species. Preliminary experiments indicated that the electrophoretic mobilities of pyrite and Thiobacillus ferrooxidans were both altered when the two colloid particles were mixed prior to the actual electrokinetic measurement. The need for more basic information regarding all aspects of the microbial-dependent solubilization of minerals is evident.

Jan 1, 1993

By M. R. Stokes

Over the recent years there has been an increase in the application of retreat mining on longwall faces as mine operators strive for ever greater productivity. The purpose of this paper in then to review current practice as a starting point and then move forward to discuss the future geometry's that a longwall face may take. Single and double production zone three roadway faces are assessed. All possible configurations of three roadway faces are defined. Unsuitable configurations are rejected after analysis of broad ventilation issues. The remaining configurations are then assessed on an operational basis, this includes: limits on retreat synchronisation, structure of centre gate, floor bulging and equipment installation. The remaining viable configurations are then further assessed on ventilation issues, this includes: provision for gas control/gas fringe, face climate and balancing of face flows. Possible face climate is assessed using numerical simulation of the various configurations, the predicted dry/wet bulb temperature and predicted levels of heat stress indices are given and discussed in detail, along with face flow balancing. The necessary conditions required for the successful operation of a double production zone three roadway face system are formulated, together with conclusions as to the possible level of application.

Jan 1, 1997

By Victor Rudenno

Cut-off grade is one of the most critical parameters affecting project cash flow. Its sensitivity is due to the number of other parameters that are correlated with any change in its value. Changes in cut-off grade, average grade and ore tonnage vary and they in turn can affect such parameters as capital and replacement costs, recovery, life of the project and operating costs. Perhaps one of the best definitions of cut-off grade is that of Taylor (1), "... any grade that, for any specific reason, is used to separate two courses of action, e.g. to mine or to leave, to mill or to dump ... . Obviously the most likely specific reason is one governed by economics, involving the return of investment and sufficient profit to motivate development and mining of the deposit. In this paper the cut-off grade is defined as that mining limit which will maximise the economic return for a projected mining venture. The following brief literature survey indicates that when computing the optimum cut-off grade there is a need to be able to directly compute the Discounted Cash Flow Rate of Return (DCFRR) or Net Present Value (NPV), as economically as possible, while allowing for parameter dependencies and variation in project structure.

Jan 1, 1979

By S. P. Banerjee

Injection of inert gases to combat mine fires has been practiced in various parts of the world for a long time. Of late, nitrogen has become the preferred inert gas for control of mine fires and safe salvage of longwall equipment as compared to carbon dioxide or fuel gases produced from burning of fuel. In India, carbon dioxide has been used for fire fighting in a number of mines during the 1960s and 1970s. More recently inert gas produced from burning of fuel oil in surface plants has been used in controlling the atmosphere in fire areas in two mines. In yet other cases, liquid nitrogen has either been poured directly into fire areas in liquid form or injected in gaseous form to keep the fire in check. Nitrogen produced in liquid form in an oxygen plant is more costly than nitrogen produced from PSA (pressure swing adsorption) based plants. A PSA-based plant has been installed in one of the Indian mines in 1986 and more are in the offing. This paper reviews the application of various inert gases in Indian mines and discusses the likely trend of inert gas application in Indian mines in the future.

Jan 1, 1987

By John P. Dunford, Lewis A. Martin

Researchers from the Spokane Research Laboratory, National Institute for Occupational Safety and Health, in cooperation with engineers from the Department of Mining and Geological Engineering, Montana Tech, Butte, MT, conducted tests to evaluate the tensile strength, fiber count, and adhesion of shotcrete applied to panels at the Chief Joseph Mine, a research and training facility operated by Montana Tech. The tests were conducted in the mine ramp 45 m (150 ft) inward from the access portal at a 15.25-m- (50-ft) long test area divided into five 3-m- (10-ft) long sections. The shotcrete was applied with an Aliva 240.5 machine fitted with a predampener. Different amounts of fiber were entrained for each panel. Background data for the tests were obtained from earlier tests in Nevada, where the typical amount of fiber in the shotcrete is 6.54 kg/m3 (11 lb/yd3). All shotcrete was applied to a minimum thickness of 76 mm (3 in). Cylindrical cores were drilled at the wall-rock interface, and adhesion was tested after 28 days of curing. The goal of this research is to reduce the need to install multiple supports at the advancing face by creating a safer mining system that limits the time miners are exposed to unprotected roof.

Jan 1, 2005

By R. D. Schmidt, S. E. Follin

Introduction Mineral recovery from an in situ leaching operation is determined by the often complex interaction of hydrology, mass transport, and chemical kinetics. The operating conditions of many pilot and production scale uranium leaching operations involve heterogeneities in aquifer permeability. Differences in permeability may be naturally occurring, the result of differences in main size or cementation, or they may be induced by leaching activity. Variations in permeability directly affect the fluid flow streamline pattern, fluid flux, and so also leaching geochemistry and uranium recovery. An in situ leaching hydrology model (ISL) and a mass transport-oxidation rate model (ISLGC) have been developed for use in making site specific predictions of the leachability and productive potential of heterogeneous ore deposits, and for the optimal design of leachant injection and recovery operations. The two models are linked by output and input requirements. The ISL hydrology model generates a leachant flow streamline pattern between injection and recovery points in a flow domain incorporating regions of arbitrary permeability. The ISLGC transport model describes the changing solution concentrations of uranium and oxygen and the changing mineral concentrations of uranium and pyrite resulting from convection, longitudinal dispersion, and oxidation reactions. ISL hydrology model Basic equations The differential equation for steady-state two- dimensional flow in an isotropic porous medium is

Jan 1, 1988

By Richard A. Williams

The design, modelling and simulation of solid-liquid mixers remains one of the least advanced aspects of minerals processing, due to difficulties in quantifying complex slurry hydrodynamics from first principles, and in acquiring reliable experimental data for model verification and development. This contribution describes the application of electrical resistance tomography (ERT) for three dimensional imaging of the concentration of mineral particulates in a slurry mixer as a function of key process variables (particle size, impeller type, agitation speed). It is demonstrated how ERT can provide a wealth of detailed data to allow model development, which ultimately will lead to much improved design capabilities and the generation of mixing models which could reside within Particle Process Simulators. This principle is illustrated using descriptions of mixer behaviour based on an empirical approach, although the measurement methodology described is equally suited to development of computational fluid dynamics models, cellular models or design approaches based on artificial intelligence. The experimental data can be built into a visualisation data bank, which acts as a "process toolkit" by allowing a library of process responses to be catalogued. Hence these data can be accessed for the purposes of model development, equipment selection, optimisation of operating conditions or testing on-line control strategies.

Jan 1, 1995

By J. A. Herbst, J. E. Bohrer, Y. C. Lo

A systematic approach has been developed to analyze a phosphate grinding circuit with a view toward determining promising alternatives for increasing mill capacity. This analysis was carried out and capacity increases were predicted in the context of detailed population balance models developed for the plant ball mills and classifier systems. Model development and verification was performed using data obtained in a series of batch tests and two plant test campaigns. The effects of feed rate, percent solids, ball size, and mill material filling, etc., on grinding were investigated in the laboratory and plant. Residence time distribution tests were also performed to determine the transport behavior in the mill. The population balance models were found to provide accurate predictions of full-scale grinding circuit performance. Based on the findings of this study, additional capacity in excess of 25% was predicted for these ball milling circuits by a proper combination of ball size change, mill dilution, and adopting screen classification in place of hydro-cyclones. These predictions have been confirmed by plant tests in which the recommended operating changes have been implemented. Understanding the effects of operating variables on breakage kinetics and the interplay between kinetics, transport, and classification has contributed significantly to increasing the mill capacity.

Jan 1, 1988

By F. C. Schwerer, C. R. McKee, J. C. Seccombe

Production of methane from coal seams requires hydrofracturing, and the length of a hydraulic fracture determines we11 spacing. Since the volume of fluid injected is known, the fracture length is the volume divided by average width and height. If the fracture is contained in the known height of the seam, then fracture width becomes the major factor con- trolling length. Width is proportional to coal compressibility; bulk compressibility is known to be larger than intrinsic compressibility. A method is given here to measure in-situ compressibility (a) from transient pressure testing. Theory linking flow in porous media with rock mechanical properties is reviewed. A consistent derivation of the porous flow equation is given incorporating 3-D deformation and the effective stress parameter "st' linking changes in effective stress and pore pressure. The relations for "st' in terms of a and intrinsic compressibility (ai) are substituted into the field measured porosity-compressibility product (net) and solved for a, the constrained matrix compressibility. In a field example, using 4 wells with an anisotropic analysis, the ratio of major to minor permeability was 17 for the Pratt A seam. a was found to be 6x10-5/psi as opposed to the laboratory value of 1.4x10-6/psi.

Jan 1, 1986

By H. Burger

For mine planning in the hardcoal industry the reliable prediciton of the properties of a deposit-both ahead of the zone to be worked as well as of zones at depths not yet developed - may help improve the production results of workings. With the wide spacing of exploration drillings usual in the coal industry, it is hardly possible to establish adequately reliable plans just by simple kriging methods. During the exploration phase a decision has to be made whether the zone ahead of a face area is economically profitable and, in addition, accessible and safe in order to be included in the production planning. It is, first of all, important to gather global information on certain parts of the planning area it the form of local estimates. Moreover, cut-off problems play a critical role, e.g. if there are set cut-off thicknesses as a criterion for minability or if safety aspects have to be considered. Conditional simulation appears to be a useful geostatistic method in order to localize or predict areas of potential rock burst hazard - based on geological criteria in conjunction with the guidelines by mining authorities - in the zones ahead of a working. It is a means of providing an objective basis for the evaluation and planning of mining activities.

Jan 1, 1986

By S. F. Hillis, J. E. Rourke, K. A. Szalay, O&apos

INTRODUCTION For the past 25 years, tunnel support requirements have frequently been determined, at least in North American practice, by classifying the rock according to the system proposed by Terzaghi (1), using one or more of the 8 Rock Conditions which he defined, the rock load then being selected within the range given for each Condition. However, there is a lack of published data comparing Terzaghi loads with actual measured rock loads, and it would appear that the degree of conservatism, or otherwise, of the Terzaghi approach is very often unknown. Excavation of 4 large diameter tunnels at the Tarbela Dam Project in Pakistan afforded an opportunity to compare Terzaghi and measured loads, through instrumentation of the steel ribs installed for temporary support, and by classification of the geology exposed during the tunnelling operations. In addition, the deformation of the rock surrounding the tunnels was monitored during excavation by means of borehole extensometers installed prior to the start of tunnelling. This paper describes the tunnel instrumentation and the results obtained therefrom, and relates these results to the Terzaghi load coefficients. It also discusses the effects of the methods of excavating the tunnels on the rock loads and rock deformations. PROJECT DESCRIPTION The Tarbela Dam Project is located on the Indus River in

Jan 1, 1974

By Rajiv Hadkar, M. D. McKinley, J. B. Hiskey, B. J. Scheiner, G. W. Warren

Flyash from municipal solid waste incinerators containing roughly 13 to 15% Zn, 2% Pb and 0.2% Cd is an attractive material for simultaneous metal recovery and detoxification. Results have shown that Pb in flyash is present as PbSO4 and PbC12 and that about 70% of the Zn is present in the form of soluble amorphous compounds. Leaching results in a number of acid and basic lixiviants show that acid leaching is clearly more effective than basic leaching which is limited by low solubility of Cd and Zn. Cementation in acid solution with pH < 1 promotes redissolution of the precipitated metal. Successful zinc electrowinning from chloride leaching solutions has also been demonstrated, although Pb2+ and Na+ can be potentially detrimental. The presence of Pb2+ can prevent deposition of metallic Zn, forming zinc oxychloride, ZnC12.4Zn(OH)2, instead. High concentrations of Na+ can also result in precipitation of NaCl. This investigation has shown that hydrometallurgical treatment of MSW flyash through leaching, cementation and electrowinning is a potentially feasible method for simultaneous detoxification and recovery of metal values. Several issues have also been identified which would require further investigation for final process development.

Jan 1, 1993

By C. P. Lazzara, R. W. Pro, A. C. Smith

The U.S. Bureau of Mines conducted a study to evaluate the effectiveness of automatic water sprinkler systems in the extinguishment of incipient conveyor belt fires under ventilated conditions. Large-scale experiments were conducted using a double strand conveyor belt configuration. Standard response, pendent-type sprinklers, with activation temperatures of 100°C, were installed above and between the two strands of belting, in accordance with Federal standards for sprinkler system installations in belt drive areas. Experiments at airflows of 1.1 and 4.6 m/s showed that the sprinklers activated later, the peak heat release rate was larger, and more betting was consumed at the higher airflow. In experiments with 74°C, fast response, directional sprinklers, the sprinklers activated at the same heat release rate for both high and low airflows, but the peak heat release rate and amount of bett consumed was slightly higher at the lower airflow. Experiments were also conducted with 100 °C, standard pendent sprinklers installed above the top belt, in accordance with the National Fire Protection Association (NFPA) Standard 123 for sprinkler system installations in conveyor belt drive areas in underground coal mines. In these experiments, the heat release rate and amount of betting consumed was larger at the higher airflow.

Jan 1, 1995

By Robert Snow, Yingxue Yu, Howard Hanson, Patrick Zhang

One of the major current efforts by the Florida phosphate industry to reduce deep aquifer water consumption is to use 100% recycle water for flotation. This measure alone could save billions of gallons of deep well water annually. However, this also results in higher suspended solids (slimes) in flotation water, causing poor process performance particularly for amine flotation. Polymers could play a major role in allowing the industry to use high-turbidity recycle water for amine flotation without compromising its impact on the Florida economy. The enhancement of rougher flotation by polymers may also have potential. Most importantly, dramatic efficiency improvement may be realized by floating silica first. Adding polymer to flotation feed and/or water is perhaps the most economically viable way of reversing the Crago "double float" process, in order to reduce operating costs and increase phosphate recovery. This paper presents both laboratory and pilot flotation data showing the effect of different polymers on collector dosage and flotation recovery. There appeared to be an optimal range of polymer concentration beyond which the benefits do not offset the drop in phosphate recovery. The effect of poly mer is slime-level dependent. Pilot testing data show that the "Reverse Crago" process (floating silica first followed by phosphate flotation) can outperform the Crago process.

Jan 1, 1999

By H. Polat, B. Mohal, S. Chander

Several nonionic surfactants and one anionic surfactant were tested to enhance the flotation response of a low-rank coal. The nonionic surfactants included an ethoxylated octylphenol and several polypropylene-polyethylene block copolymers, and the anionic surfactant was a dioctyl sulfosuccinate. All of the surfactants improved the yield significantly, but the influence on grade was complex. To elucidate the mechanisms involved, separate studies were conducted to determine the emulsification behavior of the surfactants. For the nonionic water soluble reagents, a correlation between the emulsifying power of the surfactant and the flotation response was observed. An increase in the number of droplets produced was considered to he the main reason for increases in the yield. However, a small amount of surfactant adsorption on coal is essential to promote adhesion of oil droplets. When the surfactant was introduced into the flotation pulp prior to addition of dodecane, the benefits of the surfactant decreased significantly. The decrease was attributed to both a decrease in hydrophobicity of coal through increased surfactant adsorption and a decrease in the surfactant available for emulsification. When a surfactant dispersed in oil was used, the transfer of surfactant to the aqueous phase was minimal, and a considerable increase in yield was observed.

Jan 1, 1995

By Kenneth S. Johnson

High-purity gypsum of Permian age crops out in three major gypsum districts of western Oklahoma. The northwest and southwest districts have important reserves in the Blaine Formation, whereas reserves of the west-central district are in the Cloud Chief Formation. Gypsum beds of the Blaine Formation typically are 10 to 30 feet thick, 95 to 99 percent pure, and interbedded with shales that are 2 to 30 feet thick. The base of the Cloud Chief Formation consists of a massive bed of gypsum that typically is 20 to 100 feet thick and is 92 to 97 percent pure. Anhydrite is present in the sulfate beds, beneath 20 to 100 feet of overburden, at a number of places in all three districts. Total gypsum reserves in the three districts are estimated at 48 billion short tons. These reserves are well suited for open-pit mining or quarrying, because gypsum typically forms hills in the semiarid climate of western Oklahoma, and the gypsum layers are nearly flat lying, without folds or faults. Seven companies currently mine a total of 1.0 to 1.4 million tons of Oklahoma gypsum each year for wallboard, for plaster, as a retarder in portland cement, and as a soil conditioner.

Jan 1, 1978

By C. McLean, S. G. Kolb, A. J. Erickson, S. C. Moore

The Grossschloppen vein-uranium deposit, Bavaria, West Germany, was examined with underground workings during 1980-82 by Esso Erz GmbH, an affiliate of Exxon Minerals Company (EMC). Geologic evaluation entailed dense drilling of a portion of the deposit from workings constructed specifically for the program. Discovered in 1977, the deposit was initially explored by surface diamond drillholes which allowed definition of a 30-60 m wide vein system discontinuously mineralized along a 1000 m strike length and to at least a 450 m depth. The underground program was conceived as a cost-effective procedure to answer questions on vein correlation, grade continuity and variability. A 1200 m decline allowed access for detailed sampling of approximately 10% of the known area of mineralization. Fanned drillholes, logged by gamma probe, were spaced to provide intersections of veins at 10 to 20 m intervals. Six cross-cuts also penetrate the pitchblende and uranophane mineralization which occurs in 0.1 to 2.5 m thick quartz veins. Detailed cross-sections and level plans were constructed for resource estimates of the intensively studied portion of the vein system. The program resulted in the discovery of local, high grade areas and an average grade in the evaluated area nearly double that expected from surface drilling.

Jan 1, 1992

By S. Chander

The use of various electrochemical techniques to study mechanisms of sulfide mineral- flotation reagent interactions is briefly reviewed in this paper. Prior to such studies it is desirable to thermodynamically determine solution conditions favorable for formation of hydrophobic species deemed to be responsible for flotation. The thermodynamic equilibrium involving both the stable and metastable species can be conveniently represented by an Eh-pH diagram. Thermodynamics can also be used to predict conditions where a mineral might not float if depressants are present. Under favorable conditions of flotation there is competition between reactions leading to formation of hydrophobic species with reactions that lead to formation of hydrophilic species. Due to the sluggish nature of the reactions involving sulfide minerals, a knowledge of the kinetic behavior of the system is necessary. Electrochemical methods of investigation are wed in laboratory studies to (1) control the state of oxidation, (2) determine the type and amount of electroactive species present at the mineral surface, and (3) study kinetics of electrode processes. By combining electrochemical techniques and wetting measurements the identification of hydrophobic species that might be present at the mineral surface could be achieved. Both contact angle measurements at mineral electrodes or flotation in a cell equipped with a particulate bed electrode can be used for the wetting measurements.

Jan 1, 1987

By J. Ramirez-Castro

The abstract and text of this chapter were not received in time for printing.

Jan 1, 1982