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By J. A. Herbst, Z. Rogovin

In order to develop more accurate procedures for scale-up and design of semi-autogenous grinding mills through detailed mathematical models, a better understanding of the charge motion and rocklball segregation is needed. To achieve this a 0.61 m (2.0 ft) diam by 0.305m (1 .0ft) length plexiglas mill was constructed as a scale model of a commercial SAG mill. Rock motion in the rotating mill was simulated using various sizes of ceramic balls. Quantitative measurements of dynamic angle of repose, water and slurry motion, holdup and size segregation of the charge were taken. In addition, a video presentation (available to the public) was prepared to elucidate charge and water motion at various mill speeds, charge volumes, rocksize distribution, and flow rates.

Jan 1, 1990

By Robert L. (Original by) Llewellyn

Many of the problems that occur in the preparation plant originate from practices in the mine. Impurities in raw coal can be in the seam itself or from extraneous material taken in mining from the roof or bottom. In the case of underground mines, the choice of mining equipment will affect the size consist and the amount of extraneous material included with the coal. Also, governmental regulations concerning the degree of rock dusting, gobbing underground, and cleanup have increased the dirt in raw coal. Sulfur dioxide emission standards, on the other hand, are pressuring the coal industry to clean coal more thoroughly. Coal supplied for coking purposes is nearly all upgraded by washing, while for the largest market, electric power generation, a high proportion is shipped as a raw product with processing, in whole or in part, only necessary when excess impurities are mined with the coal. This chapter will deal primarily with plants that process or wash coal to some extent (Fig. 1) and only incidentally with mines shipping raw run-of-mine coal crushed to a top size of, usually, 51 to 102 mm (2 to 4 in.), with little, if any, other treatment.

Jan 1, 1981

By J. Girard-Dwyer, J. Johnson, J. Whyatt

The choice of fragmentation method is one of the most fundamental aspects of mine design, and often has a major impact on the safety and economic viability of an operation. Almost exclusively, underground mining operations rely on either mechanical excavation or drill and blast techniques to extract rock. Each of these fragmentation methods has distinct advantages and disadvantages, and each is appropriate, and economic, for different mining conditions. However, the choice of fragmentation method can have a pronounced effect on the amount of damage created in the rock mass surrounding the opening. This paper reviews a number of case studies where both mechanical excavation and traditional drill and blast were used in underground mines. Ground support requirements in the mechanically excavated areas are compared to the support requirements in the blasted sections in order to demonstrate the potential safety and cost benefits of the various fragmentation methods.

Jan 1, 2003

By Mark W. Springett

The examination of relatively well behaved distributions subject to truncation by a cutoff grade in the mine clearly demonstrates that a bias is inevitably introduced when the selection is based on the results of samples which are subject to even the most idealised error distribution. The idealised error used in this paper is assumed to be normally distributed with a mean of zero and is thus unbiased. The bias introduced can be minimised but it cannot be eradicated. A better understanding of the bias can lead to improved procedures for mine sampling, sample preparation, assaying and estimation of selection units which will not only reduce the discrepancy but more significantly will increase the efficiency of mining selection and hence profitability.

Jan 1, 1989

By R. D. Begley, A. W. Khair

This paper presents an assessment of modeling techniques in predicting subsidence over longwall areas. Extensive instrumentation has been made, both at the surface and subsurface, at three longwall mines in northern West Virginia. Ground movements were monitored during a three- year period until subsidence ceased in these areas. A comparative analysis of empirical subsidence prediction techniques including graphical (NCB), profile function, influence functions (USBM, Bals', Knothe's, and zone area) will he presented. A brief geologic and topographic description of each site, along with the instrumentation and monitoring program, will also he presented.

Jan 1, 1990

By Kevin Lofftus

The rest potentials of molybdenite electrodes are measured as a function of pH in absence and presence of flotation reagents. The chemicals used include sodium ethyl xanthate, kerosene, dextrin,sodium hydrosulfide, hydrated sodium molybdate, sodium sulfate, and hydrated sodium thiosulfate. The effect of dissolved oxygen is also noted. The obtained data are correlated with the results of micro-flotation tests obtained under similar chemical conditions.

Jan 1, 1984

By E. L. Mann, Robert L. Virta

Asbestos is a generic name given to six fibrous minerals that have been used widely in commercial products. The six types of asbestos are chrysotile, crocidolite, amosite, anthophyllite asbestos, tremolite asbestos, and actinolite asbestos (Table 1). Chrysotile is the asbestiform variety of serpentine. Crocidolite, amosite, antho-phyllite asbestos, tremolite asbestos, and actinolite asbestos are the asbestiform analogues of riebeckite, cummingtonite-grunerite, anthophyllite, tremolite, and actinolite, respectively. Although amosite is an acronym for the Asbestos Mines of South Africa (AMOSITE) and does not specify a mineral type, it generally is composed of cummingtonite-grunerite asbestos so the terms are assumed to be synonymous.

Jan 1, 1994

The estimation of local recoveries, such as the local recovered tonnage of ore and its corresponding grade at a given cutoff grade, is an important problem in a selective mining operation. Multigaussian kriging provides a simple solution to this specific problem. The solution is also complete in the sense that local recoveries are estimated together with their estimation variances. It is thus possible to assess confidence limit intervals on the estimated recoveries. Multigaussian kriging has been applied to the Jerritt Canyon deposit in a most realistic situation. The various steps of the estimation procedure are presented in detail and the potential of the method is demonstrated in view of the results. The obtained results show that the estimated recoveries are in good agreement with the actual recoveries and the actual estimation errors are correctly predicted by the estimation variances. Multigaussian kriging thus appears as a useful and fully operationable tool for the mining industry.

Jan 1, 1986

By Erie F. Wolstenholme

The purpose of this paper is to describe work undertaken, within the System Dynamics Research Group at Bradford Management Centre, into the development and application of a System Dynamics model of an international mineral industry; aimed at providing a basis for analysis of the interrelationship of supply, consumption and price over time, under different production and stocking policies. A review is presented of some of the major characteristics and problems associated with such industries. This is followed by an outline description of the model and the way it has been applied to examine various supply responses, in the light of changing consumption patterns. Demonstration results deal with model validation and with analysis of international buffer stocks and conflicting supply policies on the historic situation in the copper industry.

Jan 1, 1979

Because of its many advantages, roof bolting has been widely used in hard-rock underground mines. In this paper, the applicability of roof bolts to mine openings in frozen ground, and the affects of bolts on the stability of the openings are presented. A comprehensive finite-element program, ABAQUS, was used to analyze the temperature distribution, the stress field and the displacement, field around a mine opening. Openings that were supported by roof bolts and openings that were unsupported were both analyzed. The thermal and mechanical processes were treated as a quasi-coupled problem, with the thermal analyses being conducted first, followed by the mechanical analyses in each case. For the opening under consideration, i.e., a roof area of 15 m2, five to seven roof bolts are appropriate. When the number of bolts is less than five, the displacement within the ground can be improved only locally.

Jan 1, 1997

By J. E. Murphy, L. A. Walters, F. H. Nehl, G. B. Atkinson

The US Bureau of Mines investigated the selective electrowinning of Ag and Au from cyanide solutions contaminated with Cu with the goal of decreasing the amount of Cu codeposited. Decreasing Cu codeposited will reduce refinery costs. Direct current was applied to the cell in pulsed and square wave voltages at 0.7 A h/150 mL of solution. Times tested for each cycle ranged from 1 to 10,000 msecs. Graphite, lead and stainless steel were evaluated as electrode materials. Square wave electrowinning at 70°C (158° F) gave the best separation of Ag and Au from Cu. Applying 2.5 V during the duty cycle, 0.0 V the rest of the period, a duty cycle of 10% to 30%, and a period of 100 msecs to 1000 msecs gave the following results: Ag concentrations decreased from 34 µg/mL to 0.1 µg/mL. Au concentrations decreased from 54 µg/mL to 0.2 µg/mL and Cu concentrations remained almost constant at 560 µg/mL.

Jan 1, 1995

By Angus Campbell, Michael J. Gobla

Numerous techniques for treating, controlling, and preventing acid rock drainage have been applied at the Summitville Mine Superfund Site. Challenging aspects of the remote mine site include the wide-spread occurrence of acid-generating soils and rocks, extensive surface and underground mine workings, and a cold and wet climate. Water treatment was an immediate necessity when the Government took control of the abandoned site in December of 1992. Subsequent reclamation activities have emphasized prevention and control of ARD to minimize future water treatment requirements. A combination of conventional, innovative, and experimental methods are being applied to successfully mitigate ARD at Summitville.

Jan 1, 2000

By F. M. Benavides

The mining complex being analyzed consists of four mines and two processing plants located in an area where there are several existing modes of transportation. Figure 1 shows a map of the general layout of the four proposed mines and the two existing processing plants. The mines are identified by the numerals "I" through "IV" and the plants by the letters "A" and "B". A proposed overland conveyor would collect the product from all four mines and convey it to Processing Plant A. Alternate transportation systems are as follows: Railroad transport from Mines I and II to Plant B; Highway trucking from Mines I and II to Plant A; Off-the-road truck haulage from Mine III to Plant B and from Mine IV to Plant A. River transportation from the mines to the processing plants was not considered in this study under the assumption that the high capital investments for the loading and unloading facilities, in addition to difficult traffic problems, would make this mode of transportation unattractive.

Jan 1, 1980

By Bruce B. Hanshaw

The Tertiary carbonate aquifer of central Florida is composed of about 2/3 calcite and 1/3 dolomite with minor amounts of quartz and apatite. The Mg content of the calcite is lower in the recharge areas than in the deeper confined parts of the aquifer system. Various geochemical lines of evidence indicate that much of the dolomite is of penecontemporaneous origin but that some may have been formed much later, possibly by ground water. Theoretical studies indicate that the Mg/Ca ratio in solutions is about unity for the three-phase equilibrium, calcite-dolomite-water. Solutions, such as ocean water and some subsurface brines, have Mg/Ca ratios higher than one and should represent dolomitizing solutions. In the areas of principal recharge to the Floridan aquifer, ground water is undersaturated with respect to both calcite and dolomite, and the Mg/Ca ratiois as low as 0.05. As the water moves downgradient, the Mg/Ca ratio systematically increases and approaches unity; saturation of the solution with respect to both calcite and dolomite also increases with length of travel in the system. Thus, in the zone of active potable-water circulation, the chemical process is one of dissolution of minerals until saturation is reached or exceeded. However, in the deeper brackish-water zones that underlie peninsular Florida, dolomite may be forming where the Mg/Ca ratio is greater than one. The necessary Mg may be derived from ocean water or brines recycled through the system as the hydrologic regimen is changed. The driving force may be simple mixing, relative fluctuations of sea level, or a combination of mechanisms.

Jan 1, 1972

By Dell H. Adams

Coal exploration may be defined as the acquisition of data necessary to define and acquire a block of coal which can be mined at a profit. Unlike ore minerals, coal resources are widespread and relatively abundant with supply exceeding demand in almost every case. Thus simple discovery of coal is generally not enough. The chemical and physical variability of individual coal seams, the capital intensive nature of coal mine development, and the changing patterns of utilization require that a multiphase, three-dimensional evaluation be made of each potential reserve. Factors which must be investigated include not only the quantity and quality of the coal but also the geologic, hydrologic, and engineering characteristics of the seam and its surrounding strata. Acquisition of property to provide a secure base for exploration and mine development is equal in importance to the geologic and engineering programs. The successful development of a coal reserve requires that control of coal and, in the case of a strip mine, the surface be in the form of contiguous blocks of sufficient size to support mining.

Jan 1, 1981

By H. Fayed

Two-phase (water and air) flow in a self-aspirated WEMCO flotation machine has been investigated using computational fluid dynamics (CFD). The geometric model is a replica of a 300 m3 cell. A 72-degree sector containing two blades of the ten-blade rotor has been modeled and periodic boundary conditions are applied in the circumferential direction. Simulation of a sector of the machine allows acceptable resolution of the mean flow field using 4x106 grid points. The flow is modeled by Euler-Euler approach, and transport equations are solved using a commercial software ANSYS-CFX5 [1]. Unsteady simulations have been performed. In a self-aspirated machine, airflow rate is not known a prior; it is an output from the CFD simulation. Uniform mean bubble diameter of 0.7 mm has been specified as an input for the simulation. Air flow rate and power consumption have been monitored with time, and results indicate a stable operation. Air volume fraction contours and velocity field in different regions of the machine are presented and discussed.

Feb 27, 2013

By Charles T. Holland

The tonnage produced on mechanized automated retreating longwall faces in the United States is growing rapidly. This time last year some 14 faces were operating, and in addition to that, three were known to be down looking towards revision or repairs before being placed back in service. These, it is believed, are now in service. It is estimated at the present time, therefore, that somewhere between 20 and 25 faces are being operated in the country. A survey made last year by the School of Mines, West Virginia University, indicated that longwall mining in general has been beset with a great many problems, some more serious than others. The problems that we propose to discuss here are those pertaining to roof and floor trouble in the tailgates. Longwalls are operating in this country at the present time under an overburden ranging from 200 feet to nearly 3000 feet. Main and tailgate entries are operating in panels of up to five each, with the width of the pillars between these entries varying from 20 to 50 feet. Face lengths are running from 270 feet to 670; actually a face 800 feet long should be possible. The most economical face is often spoken of as being around 450 feet.

Jan 1, 1969

In 1993, the United States' economy grew at a rate of about 3%. The Gross Domestic Product rose to $6.4 trillion. With more than 258 million people - 599,000 in mining including petroleum - the United States has more than 100 million dwelling units and more than 190 million licensed motor vehicles. New private housing starts rose 7% to 1.3 million units, new car production fell 3% to 5.5 million units and truck and bus production rose 21 % to 4.9 million units. The rate of inflation was under 3% and the prime rate of interest 6%. The Producer Price Index (1982 = 100) was unchanged from 1992 for fuels and re¬lated products and power at 80 and met¬als and metal products at 119, while chemicals and allied products rose 2% to 128 and non-metallic mineral prod¬ucts rose 2% to 120. The merchandise trade deficit rose 27% to $116 billion.

Jan 1, 1994

The concept of classification in wet, closed circuit ball milling is expanded beyond the performance of the classifying equipment to include all aspects of the fines removal system of the grinding circuit. Design and operating parameters that effect fines removal are identified and discussed, and a quantitative index for circuit classification effectiveness is presented.

Jan 1, 1987

By J. W. Merks

Spreadsheet software is an effective tool for simulating dynamic stochastic systems such as mineral processing plants. The two-product formula is used to show how to set up a Monte Carlo simulation in a spreadsheet template and how to calculate variances of dependent variables. The key to a reliable and realistic simulation model is to obtain unbiased estimates for all independent variables and variances in the set that defines the stochastic system. Monte Carlo simulation is also a powerful tool for optimizing sampling procedures, for applying sensitivity analysis and for designing and evaluating experiments.

Jan 1, 2000