Search Documents

By Patzen Wu, Chao-Ming Tsai, Shaw-Chii Wu, Yuan Lin

INTRODUCTION The development of nuclear industry in Taiwan requires an increasing supply of uranium. Uranium recovery from phosphate ores, becomes an important item of the R & D programs. Many countries have already started such a program. USA has set up an industrial-scale production plant; South Africa, Israel, Morocco and other countries have also engaged in the development of extraction technology of uranium from phosphate ores and started setting up the production plant. In Taiwan, a feasibility study of establishing the production plant was started in 1977. A pilot plant was completed, tested, and operated in 1979. The main source material. - phosphate ores is obtained from China Phosphate Company. The annual yield of the pilot plant has been planned to be one ton of ammonium diuranate (ADU). The Health Physics Division of Institute of Nuclear Energy Research (INER), Atomic Energy Council of Republic of China (ROC AEC), is responsible for the radiation safety control of the plant. The purpose of the radiation safety control is to collect radiation safety information of the plant of this type, to evaluate possible radiation hazards to the personnel, and to analyze the radiation safety of the immediate environment adjacent to the plant. Furthermore, the information and experience obtained are used as the basis for applying radiation safety control to the production plant. The main emphases of the radiation safety control are therefore the arrangement of radiation safety control areas and the collection and evaluation of the health physics data. This report includes the past one and half years' experiences of the radiation safety control of the pilot plant, the planning of the production plant with an annual yield of 10 ton ADU, and considerations given in improving the radiation safety control of the production plant. PILOT PLANT AND ITS OPERATION PROCESS The pilot plant occupies an area of 350 m2 and is a two-story rectangular building. Exits are provided by a front and a rear door. An additional small door at the central right side of the building is connected to the maintenance area located outside the main building. The interior of the building is divided into interconnected offices, laboratories and process area (Figs. 1 and 2). A stairway to the process area of the second floor is located in the central part of the first floor. The second floor offices are accessible by the additional front and rear stairways. The main process area of the first floor is furnished with plastic floor, and the second floor with poriferous iron-grid floor. The building is not furnished with centralized air-conditioning system. Individual air conditioners are, however, available to some laboratories. Because the back door of the building is frequently open, the product storage room is provided with a blower to maintain good ventilation. Natural uranium contents of phosphoric acid solution vary in the range from 0.07 to 0.11 kg/m3. The process consists mainly of the uranium concentration cycle and the purification cycle. A flow diagram of the process is shown in Fig. 3. CONSIDERATIONS GIVEN FOR RADIATION SAFETY CONTROL AND THE ESTABLISHMENT OF RADIATION CONTROLLED AREAS The radiation safety control of the pilot plant is carried out on the basis of the considerations listed below:1,2 1) Since the wet process is adopted, and the flow of the radioactive material is confined to closed pipes and containers, air contamination is therefore not too much of concern. 2) The concentrations of radioactive material of the whole process are mostly less than 10 ppm. An exception is the final ADU product after precipitation and centrifugal separation, which contains up to 50% natural uranium. It is therefore necessary to apply radiation safety control to the process area where

Jan 1, 1981

By Richard L. Breithaupt

INTRODUCTION A shuttle car is a self-propelled rubber-tired haul¬age vehicle designed specifically for underground min¬ing, primarily in coal mines (see Figs. 1 and 2). The drive mechanism is located on the sides of the vehicle, and the load is carried in the center. A chain-and-flight conveyor distributes the load when the car is being loaded by a loading machine or continuous miner and also discharges the load onto a conveyor belt or into a mine car. As the name implies, the shuttle car shuttles back and forth between the working face and the un¬loading point and is not required to turn around. Shuttle cars have served as primary haulage in this country since 1940 and still perform this function in most coal mines today. TYPES OF SHUTTLE CARS Shuttle cars may be battery-powered, diesel-powered, or cable-reel electric powered. Battery-powered cars were used between 1940 and 1950, but are almost out of existence today because of their limited power. Diesel cars have been used in coal mines, but are used mostly in noncoal mines where rules and regulations are not as stringent. Also, objections by organized labor have limited the use of diesel-powered shuttle cars in coal mines. Today, the largest number of shuttle cars are cable-reel cars. Electric power is fed through a cable stored on a cable reel that may have a capacity from 152 to 244 m (500 to 800 ft), depending upon the size of the cable and the cable reel (see Table 1). This, of course, limits the travel of a shuttle car. However, time studies have shown that for the most efficient haulage cycle, the length of haulage should not exceed 91 m (300 ft). As haulage distance increases, the waiting time for the loader or miner becomes longer, and haul¬age efficiency suffers. Cable-reel cars are manufactured in standard hand and opposite standard hand models. A standard car has the operator's control on the left front side and the opposite standard car has the opera¬tor's controls on the right front. Generally a loader or miner operates with two shuttle cars, one of each type. This allows the trailing cable to lie on either side of the entry and prevents the cables from fouling each other. Shuttle cars are designed to operate with either dc or ac power. Cars using dc power are designed for 250-v supply and ac cars are designed for either 440, 550, or 950 v, three-phase voltage. Most coal mines that are relatively level can use dc cars where dynamic brak¬ing is not required. For mines having steep grades (in excess of 15%) ac cars are used because ac traction motors have inherent dynamic braking and are safer when tramming downgrade. A recent innovation in shuttle car design in the last five years has been the introduction of an ac/dc car. This design utilizes ac input power through the cable, and the power is rectified on the car to 250-v do for traction motors. The pump motor and conveyor motor are powered by ac voltage. The main advantage of this design is efficiency-a much smaller cable may be used and the smooth operating characteristics of the dc traction motor is obtained. This prevents shock loading on the traction drive train, which is an undesirable feature of ac traction motors. SHUTTLE CAR FEATURES Elevating Discharge Today, all shuttle cars are equipped with an elevating front conveyor that allows the shuttle car to discharge into a mine car or belt feeder without the use of ramps. Hydraulic Power System Today, all shuttle cars are equipped with an hy¬draulic power system. An hydraulic pump is driven by an electric motor which provides hydraulic power for steering, elevating the front conveyor, and powering the

Jan 1, 1982

By R. W. Bartlett

Aeration curing, over- a long duration in wet- red stockpiles, shows promise as an affordable pretreatment method for oxidizing gold encapsulating sulfide minerals, and possibly organic matter, in low grade refractory ores. Following aeration pretreatment, the ore is reclaimed, neutralized, and cyanide leached by conventional practices. Large tonnages of subeconomic material, including mine stripping waste, may he converted into ore by this new technology. The results presented show that a successful application of this technology will likely require crushing to about -2 cm (-3/4 in.), followed by aeration in a wet stockpile for long periods, up m three years. Natural convection may he inadequate, hut forced air ventilation, at modest pressures and power consumption, is affordable.

Jan 1, 1991

By Donald S. Clarke

The Umuna epithermal precious metal deposit has provided the target for a simulated rock geochemistry exploration program, directed at bedrock exposed in the drainage system of eastern Misima Island. A geochemical halo to the deposit is readily recognised in the mafic meta-volcanic country rock. This halo is defined by anomalous results for both major (K, Na, Ca, Mg) and minor (Au, As, Sb, Cu, Pb, Zn, Ba, Rb, Sr, Cs, Bi, Ga, S) element geochemistry, extending further than 1km from the deposit. Such halos are sufficiently extensive to provide adequate exploration targets in the search for epithermal mineralisation, complementing mineralogic and secondary media geochemical investigations.

Jan 1, 1989

By W. C. Patrick

Introduction The availability of a thorough, simple-to-use roof fall classification system is desirable for several reasons. First, such a system would expedite the reporting of falls for the purposes of estimating material removal costs, analyzing damage levels, and complying with federal regulations to report falls in certain areas of the mine. Second, the classification system would allow the mining engineer to record falls routinely with little time and effort expended. This would encourage him to make observations concerning what type of roof support would work best in a given situation. Third, and probably most important, an adequate roof fall classification system is the first step toward developing a means of predicting the occurrence and extent of future falls. It was with these three reasons in mind that the following classification system was developed. The type of classification chosen reflects the background of the developer and the intended purposes of the system. Hylbert has proposed a geologic-based classification which groups falls as to structural and compositional origin. The need for similar systems is noted by Cox and by Ferm and Melton. Each of these researchers is confronted with a situation requiring a relationship between local geology and roof fall occurrence. Such a relationship would allow the prediction of the relative frequency of falls from a knowledge of local geologic features. The current research is aimed at fulfilling somewhat different requirements, as noted above. Fall geometry has been chosen as the basis of the classification system so fall type can be reported independent of local geological, environmental, and tectonic conditions. This approach parallels that used in the common slope failure classification with groups failures relatively independent of

Jan 1, 1977

By Stefan Lorenz, Robert Galler

"The technical lifetime of underground structures does not only depend on the long-term behavior of individual support elements and material characteristics, but also on various boundary conditions, which influence the entire long-term system behavior of the structure. Thanks to the construction of second tunnel tubes and the corresponding cross passages sampling of support materials such as shotcrete, concrete of the inner lining and rock bolts including sheet membranes is possible. To evaluate the stresses and the supporting effects of the tunnel shells, flat-jack tests and different simulations were performed. With these simulations the percentage of the load bearing behavior of the shotcrete shell can be determined. From the results, conclusions for new design approaches for tunnel construction should be generated. New concepts, in which the outer lining is part of the permanent support elements can be considered. This approach would be applicable for conventional as well as mechanical tunneling. INTRODUCTION Tunnels are an indispensable part of modern transport infrastructure. As multi-generation structures their long-term preservation as well as their technical service life is of central importance. The current state of research in the field of durability of structural elements must be considered separately. In almost all areas a prediction of materials and structural components towards lifetime exists. System-wide investigations were rarely performed, so that there is no technical lifetime consideration of the outer lining in systems included. In this study the mechanical behavior of the interface connection in a double shell lining (DSL) tunnel was investigated in laboratory tests. Objective The target of this work is, at first, to create a large database with the lifetime of different structural elements and materials, which may be the basis of durability considerations of tunnels. Secondly, the goal of these investigations is to optimize tunnel designs and their dimensioning regarding to the technical lifetime. For that matter, it is necessary to analyze the selected approaches of the loss of strength and stiffness of the outer lining."

Jan 1, 2016

By W. Wan

Diesel particulate matter (DPM) emitted from diesel engines is currently considered to be a health problem in underground mines. As a result, attempts have been made to control DPM both by reducing emission rates and by managing the DPM that gets into the mine atmosphere. This paper presents a method for modeling the generation, transfer and distribution of DPM in the mining sections through the use of a convection-based computer model so that controls for emitted DPM can be evaluated. A variety of ventilation strategies and diesel deployment schemes for room-and-pillar development sections were simulated to compare their effects on average DPM concentrations at several fixed and mobile personnel locations in the section. Input data for the model was gathered from actual diesel development sections and derived from experimental study results provided by other researchers. Studied using the model were ventilation schemes using vent tubing and brattice, exhaust location strategies on the vehicles, and the direction of ventilation at the feeder-breaker location. A summary of results from this study will be presented.

Jan 1, 1994

By Y. Q. Zhang, Y. Luo, S. S. Peng

Burrier pillars in underground coal mines could eventually be subjected to a water head due to the build-up of mine water in the old workings. The water head could not only act ns a force to destabilize the pillar, but it could also cause seepage flow through the pillar and its surrounding strata. Excessive seepage flow could induce piping failure that, ill turn, could accelerate the mechanical failure process of the barrier pillars. In this paper, a finite element simulation approach was employed in the evaluation of the barrier pillars. Both the stress distribution and the seepage flow pattern in and around a barrier pillar have been simulated numerically. The effects of ground stress on rock permeability to water seepage has been taken into consideration in these simulations,

Jan 1, 2002

By Peter L. Siems

Humid tropical environments pose many problems for mineral exploration. The problems result from thick lateritic soils, dense vegetation, seasonally heavy rains, deep chemical weathering, few outcrops and thick saprolites. Although geochemical exploration should be potentially a useful technique in these environments, it appears from the scarcity of reports in the literature that insufficient attention has been paid to developing procedures that are specific to the needs of humid tropical areas. For this reason, the authors believe that this account of a geochemical study in a tropical coastal area on the edge of the Brazilian shield is of general interest and importance for potential geochemical exploration surveys in similar areas within the tropics. The objective of the geochemical study was to develop a practical technique of reconnaissance geochemical prospecting for copper deposits in Brazilian tropical coastal lowland areas. In order to achieve this objective, information concerning the secondary dispersion of copper in these areas was required. Consequently, an orientation survey was designed to provide this information. The present account contains details of the geochemical study and the information about the secondary dispersion of copper that was acquired during the course of the orientation survey. Location and Climate The field area is on the Atlantic coastal lowland of Brazil at latitude 13°S. It lies approximately 10 kilometers south of Maragojipe, a city of 15,000 inhabitants; this city is on the western side of the Bay de Todos os Santos about 45 airline kilo¬meters northwest of Salvador. (See Fig. 1) A good gravel road from Sao Felipe to Sao Roque do Paraguay crosses the southern part of the field area. The climate of the area is hot and moist, and is without prolonged dry periods. The mean annual rainfall is about 1600 mm (63 in.) and the greatest precipitation occurs during the winter months of May and June and the summer months of December

Jan 1, 1972

By Yixian Zhao

Although many ultimate pit limit design algorithms have been developed for the past one- quarter century, only the well known Lerchs-Grossmann's (LG) algorithm is capable of producing a truly optimum ultimate pit limit today. This paper presents a graph theory oriented algorithm for optimum ultimate pit limit design. This algorithm produces a true optimal solution and maximizes the total undiscounted net profit for a given 3-D block mine model. The algorithm performs much better than the well known LG algorithm, in terms of the reduction in computation time and computer memory requirements. More importantly the new algorithm is easier to understand and implement than the LG algorithm. Specifically, this paper discusses: 1) the computer representation of arcs and the rules of arc generations which dictate the formation of trees in the graph, 2) the mechanism of joint support and re-allocation, 3) the properties, the general procedures of the algorithm, and the suggested specific steps to implement the algorithm, 4) comparison between the new algorithm with LG algorithm, and 5) some experience in implementation of the algorithm and two case study results.

Jan 1, 1992

By Stanislaw Nawrat, Waclaw Dziurzynski

An increasing concentration of coal production, especially in the circumstances of intensive methane inflow makes the coal mine managing staff apply new techniques of safe mining. It paves also the way for scientists to develop new directions of investigations and implementation of state-of -the- art technical solutions. Simultaneously, it could be noticed that the funds assigned for expansive 'En situ ' investigation are continuously decreasing. Better and better results are reached when applying computer technique in calculations of the parameters of ventilation process. Recent theoretical and experimental investigations of air and gas (methane) flow in longwall areas with caving, combined with the implementation of methane drainage system allowed to create, a mathematical model and consequently to elaborate a computer supported numerical simulation of discussed phenomena. The mathematical model has been modified and the simulation program was prepared in such a way that the software is convenient for a user looking for an optimal solution. The paper presented the methodology of optimal choice of following parameters: - ventilation system - rate of flow through the wall. The procedure takes into consideration keeping a safe level of concentration methane in air flowing through the longwall as well as the criterion of maximum methane concentration within the methane drainage pipe line. Results of variant computer simulation regarding the longwall with caving are shown in graphs and tables.

Jan 1, 1995

By V. Rastogi

Surfactant-based bactericides are able to control acid formation in sulfidic materials such as pyrite and sulfidic ores, thereby helping to abate acid rock drainage. Bactericides are used in the following two ways: as periodic or continuous spray treatments for the prevention of acidification of material actively handled and moved and in controlled-release form for reclamation. Site-specific bactericide treatments are designed for active sites and reclamation. Results from two active coal refuse sites show that acid production can be reduced by 88% or more. Results from reclaimed sites show that bactericide treatment can be more effective than the addition of alkaline materials such as limestone and can reduce acid production from 3,500 to <30 ppm. The controlled-release-pellets treatment outlasts the life of the pellets, as shown by a study of a site now 10 years old A single treatment sets up a change in site microbiology to replace acid-producing Thiobacillus ferrooxidans bacteria with heterotrophic bacteria and creates a stable site without the need for further treatments. A secondary beneficial effect of bactericides is on revegetation, and biomass from treated areas is almost 10 times that from areas not treated with bactericide. Depending on the application, bactericide treatment can be cost effective upfront and certainly long-term, compared to the perpetual water treatment that could be required, even after productive use of the site is completed

Jan 1, 1997

By George S. Austin

Mud is one of the oldest building materials used by man, but it is not only of historic interest. Even today in many parts of the world, particularly lightly forested areas, it is the chief building material. Many authorities believe that at least 30% and perhaps 50% of the world&apos;s present population lives in earthen dwellings (Dethier, 1985, Coffman et al., 1990). Not all of these people are members of primitive societies or live in third world countries. European, African, Asian, and both North and South American countries contain a large number of such structures. In the United States, the American West, and particularly the Southwest, is known for this type of construction. Some of the earliest remains of adobe structures are those discovered in the ruins of Neolithic farming villages in Mesopo¬tamia dating as far back as 7000 BC (Steen, 1972). The word adobe has its roots in Egyptian hieroglyphs denoting brick and evolved to its present form through Arabic and Spanish (Lumpkins, 1977). The Spanish conquest of the New World spread the use of wooden molds to produce a standard adobe brick. Today, the word adobe is used to describe various earth building materials and techniques, usually referring to sun-dried adobe brick now used in the United States, but is also applied to puddled adobe structures, mud-plastered logs or branches (Jacal or waddle-and-daub), pressed-earth blocks, and rammed-earth walls or pisé (Smith and Austin, 1989, Ferm, 1985). Modern mud construction is used in many countries in various parts of the world. In the United States, the states from Texas to California are perhaps best known for this type of construction. Of these states, New Mexico has the dominant reputation for adobe use. Indeed, in New Mexico the Santa Fe style (Fig. 1) has made adobe not only acceptable, but preferred. RAW MATERIALS Adobe soil used by present day adobe producers, and probably past adobe producers as well, is principally sandy loam (50% clay and silt), although clayey silts are used in some areas (Coffman et al., 1990). In New Mexico, the best adobe soils are those developed on stream deposits, particularly Holocene (Recent) terrace deposits and older, loosely compacted geologic formations, such as the Santa Fe Group (Tertiary) located in the Rio Grande Valley. Some modern adobe producers use a mixture of materials from the screened fines of aggregate operations and mud from irrigation ditches in the river valleys combined with varying amounts of sand to produce the proper blend. Mineralogy Bulk Mineralogy: X-ray diffraction analyses of whole rock samples from many parts of the world where adobe is the dominant construction material show the major constituents of adobe are quartz and feldspar, with lesser amounts (in order of abundance) of calcite, clay minerals, and gypsum (Coffman et al., 1990). Adobes from and climates contain considerable calcite; in some cases calcite is second only to quartz in volume. Quartz, feldspar, most of the clay minerals, and some calcite commonly are derived from the mechanical/chemical breakdown of older rocks units. Some of the clay minerals, much of the calcite and perhaps all of the gypsum are precipitated from evaporating water. Clay Mineralogy: Clay-size minerals consist dominantly of clay minerals, but nearly clay-size fractions contain minor amounts of quartz and calcite, and occasionally other nonclay minerals. In earth construction materials from New Mexico, clay-size particles are the most compositionally variable in commercial adobe soils. However, the clay mineral groups in this size fraction consist of about equal parts of expandable clay minerals (smectite and mixed¬layer illite/smectite or I/S) and non-expandable clay minerals (ka¬olinite, illite, and chlorite), with minor quartz, calcite, and feldspar (Smith and Austin, 1989, Austin, 1990). In the and American Southwest, smectite is commonly calcium-rich and the I/S is dis¬organized and randomly interstratified. In a study of 42 New Mex¬ican commercial adobe soils, only two contained chlorite, and vermiculite, sepiolite, and palygorskite were not found. Soils in temperate climates, as are found in the midwestern and northeastern United States, contain an abundance of illite (Potter et al., 1975). The clay minerals in earthen structures of that region and in Europe commonly contain illite with less amounts of kaolinite, smectite, I/S, chlorite, and vermiculite. In contrast, the clay-size fractions of soils of humid tropical areas are typically acid, with kaolinite as the dominant clay mineral and lesser amounts of I/S, illite, smectite, and others (Chamley, 1989).

Jan 1, 1994

By M. J. Howes, C. A. Nixon

INTRODUCTION A safe heat stress control strategy for an underground mine has three elements: Application of an environmental measure which reflects physiological strain with sufficient accuracy for the range of conditions encountered underground. Acceptance of a functional relationship between the environ- mental measure and human performance which is used to optimise the environmental conditions achievable with either ventilation or ventilation and refrigeration. A management control strategy based on the environmental measure which is designed to ensure that work in environments where excessive physiological strain may occur is prevented and corrective action is initiated. The environmental measure that reflects physiological strain is the link between the three elements and, since the turn of the century, the discussion of the merits of various indices has been prolific. One problem in selecting a suitable measure or index is the ease with which it can be physically obtained relative to accurately reflecting the physiological strain. For example, wet bulb temperature is simple to measure and, for a particular mining sys- tem, it may adequately represent physiological strain, however, it would not necessarily provide the same relatively safe measure in a different mining system. The acceptance of a measure which can be universally applied has been confounded by both development and predisposition. That is not to say that there is only one "correct" measure and all others are unsuitable. It is self evident that if the application of a particular index has resulted in adequate control, then that mea- sure is correct for that situation. However, an understanding of the limitations is necessary to ensure that adequate control is maintained as mining conditions change. Almost 100 years after the question of heat stress in mines started to be dealt with in a collective manner, an analysis of the available information is leading towards a general strategy to control this problem. In the paper, the developments in heat stress assessment are briefly examined and followed since the earliest published observations on the effect of heat in mines (Haldane, 1905), efforts to determine a relationship between an environmental measure and human performance are reviewed and summarised and the benefits of control strategies such as acclimatisation and shortened shifts are discussed as they relate to Mount Isa Mines. The results of testing the prototype air cooling power instrument are discussed and a heat stress control strategy outlined. HEAT STRESS AND AIR COOLING POWER The operation of the human engine is analogous to other engines where the conversion of chemical energy from the oxidation of fuel to useful mechanical energy is not 100% efficient. In a diesel engine it is about 33% and in a human engine less than 20% resulting in at least five times as much heat produced by the meta- bolic process as useful work done. Metabolic energy production is related to the rate at which oxygen is consumed and is about 340 W for each litre of oxygen per minute. Using measured oxygen consumption and an average body surface area of 2.0 m2, the approximate metabolic energy production associated with different mining tasks is (Morrison et al. 1968):- • Rest, 50 W/m2 • Light work, 75 to 125 W/m2 (machine, LHD or drill jumbo operators) • Medium work, 125 to 175 W/m2 (airleg drilling, light construction work) • Hard work, 175 to 275 W/m2 (barring down, building bulkheads and timbering) • Very hard work, over 275 W/m2 (shovelling rock) Heat balance is achieved when the rate of producing heat (the metabolic heat production rate) is equal to the rate at which the body can reject heat mainly through radiation, convection and evaporation. Heat exchange between the lungs and the air in- haled and exhaled is normally less than 5% of the total and there- fore usually ignored. Any heat not rejected to the surroundings will cause an increase in body core temperature. Since heat stress is related to the balance between the body and the surrounding thermal environment, the main parameters required to be known when determining acceptable conditions are those associated with the heat production and transfer mechanisms. These can be summarised as follows: Metabolic heat production rates (M - W) Skin surface area (A3) (and effects of clothing) Dry bulb temperature (t[ ]) Radiant temperature (t[ ]) Air velocity (V) Air pressure (P) Air vapour pressure (e [ ]) The rate of heat transfer to or from the environment depends on the equilibrium skin temperature t, and the sweat rate S,. These in turn depend on the response of the body to the imposed heat stress and the effect of thermoregulation (Stewart, 1981). Thermoregulation The body contains temperature sensitive structures which send impulses to the brain at a rate depending on the temperature. Both hot and cold signals can be differentiated and the thermoregulatory response ahivated according to which signal pre- dominates. If "cold" signals are dominant, body heat loss is re-

Jan 1, 1997

By J. B. Hiskey, S. Chander, B. J. Scheiner

The use of selected iron complexing agents in preventing or ameliorating acid mine drainage was investigated. The experiments were conducted in weathering columns using refuse samples from a coal cleaning plant. It was observed that the treatment with iron complexing agents significantly altered the rate of oxidation. Some of the reagents tested reduced the rate of oxidation whereas the others even enhanced it. The results showed that a commercial reagent containing oleyl imidazoline was most effective in retarding the oxidation rate. In addition, a simple treatment with this reagent substantially decreased the rate of oxidation of pyrite in a column that was generating acid at a high rate. The effect of this reagent on the surface properties of pyrite was studied by cyclic voltammetry and zeta potential measurements. The decrease in the rate of oxidation resulted from suppression of both anodic and cathodic reactions at the surface of pyrite.

Jan 1, 1993

By M. C. Williams

The dynamic behavior of batch mill, CSTR mill, and a closed grinding network consisting of a mill, sump, and cyclone was analyzed using the dynamic population balance model (PBM). The dynamic solution of the PBM of a batch, CSTR and a closed grinding network consisting of a mill, sump, and cyclone forms the basis of the dynamic analysis presented here. Two numerical dynamic solution approaches were used. These are: 1) providing additional constraints on breakage selection functions or 2) performing the Arbiter-Bhrany (or other) normalization of the selection functions. Actual experimental anthracite batch grinding data was used to obtain the functionality of the batch dynamic mill selection and breakage functions for a real physical system. The Levenberg-Marquardt algorithm for systems of constrained non-linear equations is used to solve the batch dynamic PBM grinding equations to obtain the grinding selection and breakage rate functions. The mill, sump and hydrocyclone were modeled as a CSTR operating at various retention times. Batch dynamic PBM data was used to provide the mill kinetic and breakage selection function data. Different dynamic solutions were obtained depending on the numerical approach used. Each solution approach to a dynamic PBM with transport, while giving the same prediction for a single batch grinding time, gives different solutions or predictions for mill composition for other grinding times. This fact makes dynamic nodal analysis and control problematic. The fact that the constraint solution approach gives a solution may suggest that normalization for closed networks is not necessary. Differences in solutions to the PBM cannot be excused away by inaccuracies in the data used to model the grinding phenomenon.

Jan 1, 1995

By George P. Demopoulos, Vladimiros G. Papangelakis, Dimitrios Filippou, A. J. Monhemius, G. W. Warren, E. Peters

A new method developed for the estimation of the activity of Ht in mixed sulfate solutions is described and examples of application of this method to the system H2SO4-ZnSO4-FeSO4-Fe2(SO4)3 from 298 to 473 K are offered. The method makes use of an "extended Debye-Hiickel" type of equation that was originally put forth by Das for pure H2SO4 solutions at ambient temperature. The treatment of mixed sulfate solutions was made possible by combining that equation of Das with a speciation algorithm which calculates the abundance of all species formed. The developed method, which also takes into account ionic strength and temperature effects, was used to generate hydrogen ion activity and speciation data for all possible acid/metal sulfate pairs of the system H2SO4-ZnSO4-FeSO4-Fe2(SO4)3. Finally, under the light of the reported data, specific examples of hydrometallurgical reaction systems are analyzed in terms of thermodynamics or kinetics. In particular, the systems discussed are: hydrometallurgical precipitation of hematite, solvent extraction of Fe(III), acid leaching of zinc ferrite, and oxidation of Fe(II) to Fe(III) by O2(aq).

Jan 1, 1993

By S. Bhagwat

Coals capable of emitting 2 lbs SO2/106 Btu heat input must be defined as high sulfur coals. This is because electric utility plants built after 1971 may not emit more than 1.2 lbs SO2, and those built before 1971, and regulated under the State Implementation Plans (SIP), may exceed the 2 lbs S0 limit only under closely defined restrictions concerning ambient air quality and prevention of air quality deterioration. Coals produced in Kentucky, Illinois, West Virginia, Ohio, Pennsylvania, and Indiana account for 77% of SO2 pollution potential and are, therefore, the subject of this investigation. These coals have suffered market share losses in the 10 years from 1974 through 1984. This is due to their sulfur content as well as their lack of price competitiveness with low sulfur western and imported coals. Kentucky and West Virginia have been able to increase their compliance quality coal production substantially, but other states have largely been unable to do so because of nonavailability of low sulfur coal deposits. Assuming that the current relative productivity and cost competitiveness of coal producing states will not change significantly by 1994, this paper makes two projections of coal production in the selected states. In scenario I, the current clean air regulations are assumed to apply until 1994, and coal production in the selected states is projected to in¬crease by about 6% in 1994 compared to 1984. In scenario II, it is assumed that acid rain legislation will be implemented, which will adversely affect the markets for high sulfur coals. Coal production in the selected states under this scenario is projected to decline about 10% between 1984 and 1994, jeopardizing up to 13,000 mining jobs. The author concludes that better coal quality and greater cost competitiveness are both essential to stem the market losses and to regain strength.

Jan 1, 1988

By Chinmoy Sarkar

Mining organizations have been trying to employ best practices at exploration, exploitation and processing level to increase productivity in the supply chain. Traditional techniques of cost control can no longer meet the ambitious target of mine managers. An integrated perspective of Mining Value Chain with enterprise-wide application of information technology (IT) ensures the ability of every mining processes to improve energy, land, capital and labour resource performance while continuing to cut costs and achieve profitability. IT offers enormous potential in mining industry at shaping entirely new opportunities to create value. This paper characterizes important entities of Mining Value Chain and attempts to provide a vision on how IT can transform the mindsets of industry managers addressing the needs of the customers.

Jan 1, 2002

By R. A. Jankowski, R. Gong, R. Bhaskar

The control of respirable coal dust in continuous mining sections involves careful analyses of the generation and transport of the dust, including airflow pattern analyses. Potential dust control devices must be evaluated based on their effect on both local dust transport and potential dust exposure of face personnel. The development of larger and more productive continuous miners increases the need for research on dust control and improvement of visibility in the face area. Two studies relating to underboom dust control are discussed. The first study involved the valuation of potential underboom dust control techniques to reduce operator exposure to dust and determining the relationship between the positioning of exhaust ventilation and the exposure of face personnel as a function of face and operating variables. The study involved full-scale laboratory experiments using a state- of-the-art data acquisition system. The second study related to the use of foam under a continuous miner boom and its effect on silica concentration and respirable dust. The foam study was performed in a coal mine. The laboratory studies involved the fabrication of a full-scale test facility and development of a computer based data acquisition system. This was followed by baseline data collection, smoke trace tests, detailed performance testing of various underboom dust control measures and data analyses. The underground foam test involved the design and installation of the foam generation and delivery system, testing, and data evaluation. The results of the studies are summarized in this paper.

Jan 1, 1991