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By Joel K. Witt, Jackson G. Jenkins, Wendy M. Gort, Brent A. Whitman

A major concern for operators of leaching/SX-EW plants is a phenomenon known as gunk or crud. The build up of gunk is typically the result of fine particulates which are transported via the leach operation to the solvent extraction plant. The particulates develop into a solid layer that concentrates at the aqueous/organic interface. This can cause phase separation problems which can result in entrainment and other deleterious operating conditions. Most operations physically remove the gunk from the SX settlers and process it via a centrifuge or coalescer to remove valuable organic. While both methods have served for many years, Magma is currently evaluating the use of a chemical surfactant which induces a definitive separation of particulates from organic.

Jan 1, 1994

By W. M. Hart, Q. H. Shen, J. S. Chen, S. S. Peng

The automatic data-acquisition systems that are now available can continuously monitor and record changes in leg pressure and changes in advancing ram stroke in every shield. These systems can record shearer position at any moment during a mining operation. The data obtained can be used to improve production and maintenance management and can be used to provide better roof control at the longwall face. Research now being conducted jointly by West Virginia University and Cyprus Amax Coal Co. is aimed at developing a longwall-management system (LMS) for mine operators. The LMS software package, which works in the Microsoft Windows NT environment, performs data interpretation and analysis, production management, maintenance management and ground-control management for longwall mining.

Jan 1, 1997

By Thomas H. Koenning, James R. Boulton

The coal mined by Cyprus at the Shoshone mine near Hanna, WY is highly susceptible to spontaneous combustion. Spontaneous heatings have occurred in the gob of several of the longwall panels and, in some cases, following roof falls. Prevention and detection methods have evolved over the years as more has been learned about the occurrences. Seal design and construction have progressed to reduce air leakage into the gob. Pressure balancing has been successful as a supplement to good workmanship in reducing leakage. Early heating detection has improved as knowledge has been gained. Prior methods of detection relied upon thermocouples detecting a temperature change. Later a gas chromatograph was used to analyze gob gas samples. Initially the products of combustion (POC) were relied upon for detection. Most recently, lack of oxygen depletion in the gob has been used as an early warning of problems. Examples are presented to illustrate the evolution of spontaneous combustion control at the Cyprus Shoshone coal mine. Methods have been developed which minimize the oxygen concentration in the gob and reduce the potential for spontaneous combustion.

Jan 1, 1997

By Donald G. Wieland, James H. Meinholz

INTRODUCTION The Milwaukee, Wisconsin Metropolitan Area provides an ideal opportunity to review the advancement of the art and science of mixed face tunneling in the past 65 years. Although there were earlier tunnel projects in the Milwaukee area, by other agencies, the majority of those driven in the Twentieth Century have been done under contract with the Milwaukee Metropolitan Sewerage District through the agency of the Sewerage Commission of the City of Milwaukee and the Metropolitan Sewerage Commission of the County of Milwaukee. Legal Description of District The Milwaukee Metropolitan Sewerage District was created by the Wisconsin Legislature in 1921 together with the Metropolitan Sewerage Commission of the County of Milwaukee. This concept of subregional wastewater control was an outgrowth of an investigation and report from a commission appointed by the Common Council of the City of Milwaukee in 1909 to study final sewage disposal for the City. In 1911 that Commission, comprised of J. W. Alvord, George C. Whipple and Harrison P. Eddy, recommended that the City construct a water filtration plant, construct a Menomonee River flushing works, expand the intercepting sewer system and, after a thorough study of the then existing and developing methods of sewage treatment, construct a sewage treatment plant. In response to those recommendations, the Wisconsin Legislature, in Chapter 608 of the Laws of 1913, created the Sewerage Commission of the City of Milwaukee. Recognizing that the improvement of surface water quality would require action on a watershed basis, the Legislature, in Chapters 554 and 590. of the Laws of 1921, created the

Jan 1, 1979

By P. J. Suardini, S. K. Kawatra

A number of on-stream coal slurry analyzers are presently being developed and commercialized for measuring ash and solids in coal process streams, particularly around flotation circuits. The eventual goal of these efforts is to develop on-line quality control systems for flotation circuits and other fine-coal cleaning operations. As part of this on-line monitoring and control effort, it is important to gain a better understanding of the response of industrial flotation circuits to changing operating conditions. This paper summarizes the results from a detailed sampling program performed at an industrial coal flotation circuit in western Pennsylvania. The testing focused on evaluating the response of the circuit to changes in reagent dosages, operating conditions and feed compositions. The testing indicated that it is desirable to maintain high collector-to-frother ratios to enhance coarse particle flotation. The recovery of fine impurity particles was also proportional to water recovery, due to hydraulic entrainment. Key words: Industrial, Coal, Flotation, Circuit, Reagent, Response.

Jan 1, 1995

Successful longwall gate entry design requires control of vertical and horizontal stresses. Vertical, or overburden, stresses are most severe in the tailgate where they are concentrated by longwall panel extraction. Horizontal stresses can also be highly destructive but they are less well understood. This paper discusses measurements of in situ horizontal stress fields in the eastern United States, experience with horizontal stress in longwall mines and methods for predicting and controlling horizontal stresses. The information presented was collected through site investigations at 45 US longwalls and an international literature review.

Jan 1, 1992

By V. Roze, M. E. A. Robertson, C. J. Sharland

Current Techniques - Fire Assay Fire assay of gold has been used for several thousand years and is a well known technique to the traditional assayer. Very few assayers wish to use the method but to date there has been no viable alternative. Fire assay is expensive in labour, time, capital and running costs. Workers can be exposed to hazards and uncomfortable working conditions such as lead fumes, heat stress, dust and eye strain. The high capital cost of putting up the building and equipping it, together with running costs which increase annually at a prohibitive rate makes the technique less attractive each year. The main requirement in most assay laboratories is to maximise throughput economically. This is difficult with fire assay as it is impossible to automate. Each sample for analysis is handled by at least 12 people and each person represents a potential source of error. Record keeping and report generation has to be done manually which is both slow and prone to errors. Replacement of staff requires a considerable training period and with a large turnover of personnel this presents yet another problem. The presence of silver and dross in the gold sample affects the accuracy at low gold values. X-ray fluorescent analysis Two methods of XRF instrumentation have been used with limited success. The first type is a laboratory instrument employing L X-rays. Small samples of a few grams, which are not representative,

Jan 1, 1988

By Hill McDonald

Sand and gravel deposits may be explored by many different methods. The methods used by The Standard Slag Company are primarily two in nature. One is using an auger which is limited in depth by various soil conditions. The other is a heavy wall dry sampler and a heavy wall wet sampler. The heavy wall dry sampler takes continuous uncontaminated samples up to seven inches in diameter. The heavy wall wet sampler takes continuous uncontaminated samples up to six inches in diameter. For us, the maximum depth of the heavy wall samplers has been two hundred fifty feet of which one hundred feet was above the water table and one hundred fifty feet was below the water table.

Jan 1, 1972

By Anthony Peach, Lok Home

Introduction Raise boring is the most accepted form of mechanized hard rock boring in the mining industry. It appeared logical to take this mechanization one step further by introducing computers. Atlas Copco Jarva has produced a series of raise boring models that use an integrated computer. The company decided to use electronics and computerization, not for marketing purposes, but to make its equipment more cost-effective. Basis of Cost-Effective Design From the manufacturer's standpoint, it is possible for the equipment owner to reduce the cost of putting in raises by: • Replacing existing components with less expensive components that produce the same results; • Replacing existing components with more expensive components that make the equipment more productive; • Mechanizing equipment to reduce associated labor costs; and • Combining the above. Analysis of a standard raise boring machine (RBM) system showed that little could be done with less expensive components. It appeared, however, that the RBM could be more productive by transmitting more horsepower through the expensive drill string, while being precisely controlled by computers. An RBM system includes a basic machine, drill pipe, accessories, reamer, and cutters. The approximate percentage cost of various components on a standard system capable of boring 300 m (985 ft) long and 3-m-diam (10-ft-diam) aises in medium to hard rock is shown in Table 1. Also shown is the increased cost above standard of the Jarva computerized machine, and the productivity of both. Increased Productivity Penetration is important during the reaming cycle for more productive raise boring. This is possible by increasing the cutter load with constant rpm or increasing the rpm with constant cutter load. To increase thrust and maintain rpm requires increased capacity in the cylinders, drive train, main thrust bearings, drill string, electrical motors, and power units. To increase rpm and maintain cutter load requires only increased capacity in the electrical motors and power units. This is possible because the torque requirement remains constant for a constant thrust load. Only the horsepower increases, proportional to rpm. Since cutter costs are a big factor in raise boring, changes in machine performance must be analyzed to assess the effect on cutter performance. With a standard or typical carbide cutter, as used on raise boring machines, the effects of increased thrust or rpm are shown in Table 2. The assumption is made that the base data is the current rpm and thrust range where the cutters are now operated. It is also assumed one variable is held constant while the other increases. The result of this comparison, approximately, is that a 50% penetration increase can be achieved with little or no increase in cutter cost if rpm is increased 50% and cutter load is maintained constant. A similar 50% penetration increase can be achieved with a 45% increase in cutter cost, if the cutter load is increased by 20% and maintained constant. From an equipment standpoint, it is significantly less expensive to increase rpm 50% than it is to in-

Jan 7, 1984

By J. A. Finch

The use of pneumatic methods for measuring interface level in flotation columns is analysed. It is shown that errors can vary over a wide range (e.g. 40 cm. in one industrial application) depending on bubble size, particle size, bubble loading, liquid hold-up and bulk slurry density. Accurate measurements (+ 5 cm) can be obtained by measuring intensive properties of the froth near the interface. Methods based on the measurement of temperature and conductivity are described and analysed. Control of the interface level using these measurements subject to various disturbances is demonstrated.

Jan 1, 1988

By Friedrich Steinhäusler

RADON SOURCES AND CONTROL MEASURES IN THE MINING ENVIRONMENT Most of the contamination of the mine atmosphere by radon 222 is due to radon emanating from solid or fractured ore surfaces of walls, roof and floor. Also radon gas emanates from broken ore either from storage in backfilled mined-out areas as applied in e.g. shrinkage stopping methods or from ore spillage along intake airways mainly due to the use of trackless haulage. To a lesser extent water itself can represent an additional source of radon, which emanates into air from open drainage ditches or seepages along intake airways. The contribution from water can be controlled effectively by isolating the water from the primary intake air system, e.g. by diverting the water through pipes and/or sealing of seepages by grouting. However, control of radon emanating from rock surfaces creates a major technical problem with significant impact on the economic aspects of mining operations, if adequate radiological conditions must be maintained. Basically this can be achieved by suppressing the emanation process itself, confining already emanated radon or by removal of radon from the mine atmosphere. Extensive research has been carried out on the rate of radon emanation as a function of barometric pressure changes (Pohl-Rüling and Pohl, 1969). It could be shown that the radon supply consists of a permanent and variable component. The former results from the surface of the rock and depends mainly on the emanating fraction of its radium 226 content; the latter originates from within the rocks and is a function of the suction effect of decreasing barometric pressure, rock porosity and fissures. The practical application of this barometric pump effect for depressing the rate of radon emanation, e.g. by pressurizing the mine atmosphere, is limited due to high costs for providing a sink for absorption of radon and air as well as lack of permeability in most uranium ore bodies (Schroeder et al., 1966). Mine air cleaning by removal of radon can be achieved with the use of cryogenic methods, chemical removal, adsorption into charcoal beds, use of a gas centrifuge or general ventilation techniques. Technical problems have so far prevented the application of any of these methods other than ventilation. It is common practice to use the age-of-air concept, i.e. fresh air is delivered to the worker as directly as possible and removed quickly afterwards thereby maintaining the air "young". Engineering principles for quantity distribution of air through underground working areas are straightforward for general mining situations where radon constitutes an environmental contamination problem. However, in cases of high uranium ore content this concept may result in high costs with regard to installation and energy requirements for effecting both frequent air changes as well as sufficient heating of the air in cold seasons. Taking into account that the investment in ventilation systems is a major cofactor for the overall ore production costs this can be a limiting and decisive component in the assessment of the economic feasibility of specific mining operations and mineral reserves in general. Effective control of the radon flux from the rock surface prevents the initial contamination of the mine air with radon directly at the source. A radon diffusion barrier for practical application in mining requirements should fulfill the following requirements: - reduction of radon emanation rate by at least an order of magnitude - high mechanical strength - ease of sealant application onto surface to be coated - water resistant - low fire hazard - resistant to temperature changes encountered in mines - high cost efficiency in relation to exposure reduction achieved (direct and indirect costs) - low degree of maintenance. In the past several materials have been tested as sealants for controlling the emanation of radon from surfaces of rock and building materials. Epoxy paints reduce radon emanation rate only by a factor of 2 to 6 (Auxier et al., 1974; Eichholz et al., 1980; Keith Consulting Engineers, 1980). Although it is possible to prevent the escape of more than 99 % of the radon to the environment with gel seals over 80 mm thick (Bedrosian et al., 1974), practical applicability is very limited. Multilayer coatings of epoxy resins with various additives require meticulous preparation and flawless application of seamless four-layer coatings in four days to impede radon diffusion (Culot et al., 1976), otherwise results from this method have not been totally satisfactory (Leung, 1978). Aluminium foil laminated with polyethylene and paper on each side is under test as radon barrier but results are not available yet (Ericson, 1980). However, this method has the inherent disadvantage that possible malfunctioning electrical installations can cause fire or electrical shock through the sealant. Polyurethane foam coatings have been used on stoppings as very effective sealants. It does, however, represent a potential danger of spontaneous ignition and it is expensive (Rock, 1975). Thus, there is still need for a material which has similar properties as outlined above. In the following results are reported from investigations on the suitability of various materials as radon diffusion barriers.

Jan 1, 1981

By Alden B. Carpenter

The Dead Sea is the only relatively large body of surface water having bromide concentrations comparable to those in the brines of the Smackover Formation in Arkansas. The Dead Sea, like the Smackover brines, contains a great deal of calcium and is very low in sulfate and iodide. The relationships between potassium, divalent cations, and chloride indicate that over 20 percent of the bromide in the Dead Sea is derived from some source other than by the evaporation of sea water. A similar type of study of the Smackover brines in Arkansas indicates that approximately 60 percent of the bromide has been derived from some source other than sea water. Both the Dead Sea and Smackover brines are very low in iodide suggesting that the excess bromide has not been derived from organic matter. The origin of the excess bromide is probably the same for both of these brines, but the source of this bromide remains unknown.

Jan 1, 1978

By R. Simon

Strain-burst phenomena are generally characterised by sudden releases of energy in a volume of highly stressed rock. Strain bursts are encountered in situations such as crown pillar bursts during cut-and-fill mining, face bursts at development headings cord floor bursts in deep shaft sinking. This paper describes a simple two-dimensional linear elastic FE modeling approach that leads to the calculation of the energy-release rate (ERR) and the total energy storage rate (TESR) in the rock-mass around the openings. The merits of using such energy parameters in the analysis of strain-burst problems for identifying areas of high energy release/storage are discussed through a case stud v. However, much site-specific back analyses are needed to better understand how strain bursts and energy parameters are interrelated.

Jan 1, 1999

By Peter K. Weissenborn, Robert J. Pugh

The contrasting behaviour of electrolytes in inhibiting coalescence of bubbles was explained by the positive and negative distribution of anions and cations at the gadwater interface. Further, the efficiency of electrolytes which do inhibit coalescence of gas bubbles can be linked to a counter ion hydration mechanism and the effect of electrolyte concentration on gas solubility. A correlation was found between the transition concentration of electrolyte needed to prevent the coalescence of bubbles and the reduction in gas solubility. Hence, the inhibition of bubble coalescence in electrolyte solutions appears to be linked with the utilization of water molecules in the hydration of cations and a consequent reduction of water available for gas solubility.

Jan 1, 1995

By D. Tao, B. K. Parekh

Fine coal particles are difficult to separate effectively from liquids or other solids. Ultrasonic energy may be used to enhance the efficiency of the conventional fine-particle separation processes widely used in the coal and mineral industries. Flotation, settling and dewatering tests were conducted using several fine coal samples to study the effects of ultrasonic treatment on these processes. Process variables such as particle size, ultrasonic treatment time and solids concentration were investigated for their impacts on ultrasonic treatment effectiveness. The results obtained from this study showed that ultrasonic treatment is an effective approach for enhancing solid/solid separation in flotation and solid/liquid separation in sedimentation and dewatering of fine coal. SEM microphotographs demonstrate that ultrasonics cleaned particle surfaces, which is, in part, responsible for the observed improvement in fine coal separation processes.

Jan 1, 2000

By L. John Minnick

Current developments in using lime and limestone slurries to remove sulfur oxide gases from the stacks of coal- and oil-burning furnaces have established an important need for treatment systems which include adequate disposal of resulting waste materials. The paper briefly outlines the classes of scrubbers which are using lime and limestone and describes the characteristics of the by-product material being produced. Some discussion is also included relating to methods of disposal of the scrubber underflow. Since coal-burning plants also produce fly ash as a waste material, one system developed by the author's company combines this material with the sulfur oxide by-products. The mixture is processed in a manner which converts the waste products into usable materials with acceptable structural and environmental properties. Recent interest in protection of ground waters from heavy-metal leachates has made the fly ash-sulfur oxide system an acceptable means of disposal, because the conversion products have very low permeability and adequately encapsulate soluble salts within the hardened mass. Although only limited information is available on the types and chemical requirements of limestone used in these processes, a few guidelines are presented to indicate the range of materials that can be used with good results.

Jan 1, 1974

By Joseph M. Denk, Gary J. Wirth

This paper summarizes a three phase face ventilation study which was conducted from September 1989 through March 1990 to determine face area methane liberation patterns on two extended longwall sections. The coal seam being mined was considered gassy and the mine liberated an average of 14.4 million cubic feet per day (cfd) or 0.41 million cubic meters per day (cmd) of methane through the mine fans. The mine also used an extensive underground degasification program to recover up to 13.4 million cfd (0.38 million cmd) of methane. Data was collected while the longwall sections were mining from the beginning, middle and end of panel extraction to determine the relationship between the methane liberation and extent of longwall retreat. As expected, methane concentrations did increase from the headgate (intake) to the tailgate (return) side of the longwall face and peak concentrations were detected above the shearer as it passed a methanometer location during mining. There were significant differences in the methane liberations due to the location of the active face within the longwall panel. Results from this study could be used to determine a minimum design face air quantity for an extended longwall section operating under similar conditions.

Jan 1, 1991

By Christopher J. Hall

It has been known for a long time that summing pressure drops and rises due to friction, shock, fans and natural ventilation is incorrect. In fact, lost works and works should be summed. In spite of this, the traditional method of finding a fan/system operating position has been the H/Q Curve. This paper presents (lost) work/m curves, progressing from a single fan moved around the system to include natural ventilation work, and fans in a series, parallel and series/parallel. The solutions obtained graphically are substantiated by dry air thermodynamic solutions, and the traditional solutions are shown to be in error. This method of solving problems is particularly useful when moving fans around the system, and essential in series/parallel and series situations with substantially different fan densities. The dry air analysis is employed because of its simplicity. Real air, with evaporation and condensation, will react somewhat differently, and one should use real densities (i.e.[l + w +w]/va ) when using this method. One source of error when applying this method to real air, although probably not major, will be investigated in a subsequent paper. Friction and shock losses are proportional to the square of the mass rate of flow, leading to the typical parabolic system curve. However, the unbalanced water stuff potential energy term, on a unit mass basis, is substantially independent of the mass rate of flow. It is possible that this could be handled as a negative natural ventilation work.

Jan 1, 1987

By D. A. Stanley, B. J. Scheiner

The U.S. Bureau of Mines has thoroughly investigated the flocculation of phosphatic clay waste with polyethylene oxide (PEO). The studies included both theoretical and applied aspects of the flocculation sequence. The screen dewatering technique developed by the Bureau was field tested at four different Florida phosphate mines. The results of these field studies are presented. Also, to determine the mechanisms of the interaction of PEO with montmorillonite clays common to the phosphatic clay waste, a number of theoretical studies were conducted. An empirical equation was developed to describe the amount of PEO needed for flocculation. Infrared, ion exchange, and rheology techniques were used to study the interaction of PEO with Florida clays. The results of these studies are also presented.

Jan 1, 1993

By M. C. Fuerstenau

With increased emphasis on controlled blasting, which is the first and least-costly stage of comminution, ore grindability and plant throughput can be increased by 5% to 10%, and energy savings of up to 10% appear possible. Crushing and grinding efficiencies are presented for ore blasted under regular and adjusted field conditions. An economic analysis of drilling and blasting through crushing and grinding is presented, suggesting that cost savings approaching 10% may be achieved

Jan 1, 1997