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By Patrick J. Doig

The NS9 Drop Shaft contract formed part of the Waste Pollution Abatement Program (WPAP) conducted by the Milwaukee Metropolitan Sewerage District (MMSD). The contract involved the construction of two shafts, a deaeration chamber and connecting tunnel, and ancillary facilities. Portions of the construction were located in saturated overburden where dewatering was prohibited. Ground freezing was utilized for temporary support of the excavation. This paper concentrates on the freezing system and the excavation of frozen ground, with particular emphasis on the use of mechanical cutting equipment, including a raiseborer and a roadheader.

Jan 1, 1991

By Daniel R. Shawe

Epigenetic ore deposits in Nevada and Utah occur in clusters or belts in a variety of tectonic settings. Many are concentrated in the western half of Nevada in a region containing numerous, relatively large intrusive bodies. Throughout Nevada and Utah, they tend to be clustered in elongate zones or belts. Some of these belts are well defined by the distribution of mineral deposits, patterns of igneous rocks, alinements of faults, and aeromagnetic anomalies, whereas others are equivocal. The Pioche belt in eastern Nevada and western Utah, the Eureka belt in central Nevada, and the Manhattan belt in western Nevada exemplify the general characteristics of these belts, the close relation of some belts to geologic structure, and the lack of a clear correspondence in other belts. Some of these belts are characterized by alined or en echelon faults that disrupt the north-trending Basin ranges, by belts of Cretaceous and Tertiary granitoid and porphyry intrusive rocks near which the ore deposits occur, and by alined magnetic anomalies generally related to the Cretaceous and Tertiary intrusive rocks. All the mineral belts have produced precious and base metals and tungsten; the Manhattan belt in addition has produced magnesite and brucite; and the Pioche belt, uranium, fluorspar, and alunite. The belts in Nevada and Utah may be related to a variety of factors, such as zones of structural weakness in Precambrian rocks, transverse zones of lateral faulting, localized areas of igneous activity, or a combination of these and other factors. Specific types of ore deposits in Nevada and Utah seem related compositionally to the intrusive bodies with which they are associated. Iron deposits, for example, are associated with mafic intrusive rocks such as diorite or gabbro, whereas copper deposits generally and tungsten deposits almost exclusively are associated with granitic intrusive rocks such as quartz monzonltc and granodiorite.

Jan 1, 1976

By F. B. Olender

Idler engineering, operation, and maintenance cannot be covered in depth in a short paper. Therefore, this will be a general look into the subject matter in light or the present-day technology. Depending on the source or reference used, belts for handling bulk material underground came into being between 1900 and 1920, while strip mining appeared in the thirties. The conveyor belt speeds in that era were in the 300 rpm to 500 rpm range. Belt speeds or 600-700 rpm were in vogue in the thirties, and the early sixties saw speeds or 800-900 rpm. Today, speeds or 1000 rpm are not looked at with dismay; in fact, speeds or 2000 rpm are being discussed. Among the driving forces moving the bulk materials handling industry to these greater heights have been the mining operators and engineers. Their appetite to increase output, yield, and reduced per-ton costs has constantly challenged the bulk material handling industry to develop products capable or handling these increased capacities. One or the products affected by this movement is the idler. Apart from the conveyor belt itself, it is one or the most significant parts or a conveyor system because or the sheer numbers needed in an installation.

Jan 1, 1971

By Alessandro Navarra, Aldo Quelopana

Sophisticated models have progressively been developed to address the challenges related to long-term, openpit mine planning under conditions of geological uncertainty. Prior research has acknowledged that strategies for mine planning and the design of mineral concentrators are interdependent; thus, it is highly desirable to optimize them together. However, achieving detailed holistic optimization of the mineral value chain remains unresolved because of the inherent limitations associated with mathematical formulations and computational processing capacity. This paper details a method that contributes to bridging these limitations by employing a novel parallelized variable neighborhood descent approach combined with an embedded mass–balance component using linear programming techniques refined through Dantzig– Wolfe decomposition. This approach is exemplified through a case study of a gold deposit, which illustrates the enhanced performance capabilities of the new algorithm. The findings demonstrate significant improvements in the optimization process for mine planning, providing a stronger link between the mine’s output and processing plant’s capabilities.

Mar 1, 2025

By K. Thomson

The Mule Canyon gold deposit, located 14 miles ESE of Battle Mountain, Nevada, was discovered in 1986 as the result of a GFMC grass-roots exploration program. Drilling to date has identified six discrete orebodies which contain a demonstrated gold reserve of 8.487 million tons at an average grade of 0.136 oz/ton, totaling 1,152,000 ounces. Mineralization is associated with argillic alteration and silicification, localized along NNW trending high-angle faults within Miocene basaltic andesites. Trace element geochemistry at Mule Canyon is typical of upper level hot spring precious metal systems, displaying elevated Ag, As, Sb, Hg, and Se.

Jan 1, 1993

By Cal D. Iles

Decreasing ore grades and increasing labor and material costs have seriously eroded the economic vitality of many mining operations. Coupled with global economic stagnation and recession in the early 1980's, these conditions have forced reevaluation of operating strategies and methodologies with the objective of remaining competitive in a world marketplace. A concept offering large potential benefits is hardrock portable crushing and conveying. Implementation of this system at Duval Corporation's Sierrita open pit copper-molybdenum mine (Figure 1) has significantly reduced mining costs, becoming a major part of Sierrita's cost reduction strategy. Located 48 km south of Tucson, Arizona, the 209 000 t/d property has one portable 60x89 gyratory ore-crusher in operation with tentative plans for two additional units.

Jan 1, 1985

By W. J. Wolfe

Using a combined fire assay-atomic absorption method, gold determinations with a minimum detection limit of 5 ppb were made on 345 samples of Early Precambrian felsic plutonic rocks collected 2 2 from intrusions ranging in size from 4 km to 88 km and in composition from syenite to granodiorite. Gold levels in unmineralized stocks are consistently below the 5 ppb detection limit of the analytical method used. In contrast, analyses of samples from stocks containing gold mines within their borders and in nearby metavolcanic-metasedimentary host rocks show a strongly skewed trace element gold population with a substantial percentage of gold values exceeding 5 ppb and ranging as high as 320 ppb. The data indicate that (1) ore-stage hydrothermal metasomatism has produced widespread Au enrichment in Precambrian intrusions that host epigenetic vein-type gold deposits, and (2) geochemical Au analysis of samples collected from 30 to 50 randomly distributed sites can be used to estimate the gold exploration potential of stock-sized bodies and to outline internal patterns of Au variation which may be useful in directing exploration to particular contacts or portions of a stock. The results do not conclusively indicate unusually high Au content in primary unaltered igneous rocks.

Jan 1, 1975

By S. Chatterjee, S. Bandopadhyay

A spatial modeling technique based on the Bayesian neural network (BNN) is proposed. Incorporation of the Bayesian method for posterior probability of the output parameter helps calculate the uncertainty associated with the estimate. Parameters of the BNN model were selected using a grid search algorithm. The expected value and the variance of block support were calculated by Markov chain Monte Carlo sampling of the posterior distribution at discretized points within the block. The BNN model was validated by applying it to the Walker Lake data set and comparing the results with ordinary kriging results. The comparison revealed that the proposed BNN method performs marginally better than ordinary kriging. The variance map is less smooth than with ordinary kriging, and the proportional effect is less in the BNN-based model than in the ordinary kriging model. The developed BNN model was applied to the Coho block of a placer gold deposit in Nome, AK. Results reveal that the BNN model is globally biased for the Coho block and underestimates the sample mean. The grade volume curve was developed by calculating the block mean and block variance after discretizing the block into a number of points and applying the BNN model to each discretized point.

Jan 1, 2011

By C. E. Schmidt

Homestake crushing and grinding, practice-was completely revised during the period of 1951-1953. During the conversion, both crushing plants at the head frames the Ross and the Yates, were changes at each plant involved replacing the two 8K gyratories with a rebuilt, The flow sheet single thirty inch gyratory for primary crushing to four inch. The gyratory discharges to a seven foot Symons standard cone crusher set at 1-1/8 inch opening. The cone discharge goes to Tyrock screens fed by vibrating feeders. Screen openings, are l/2 inch by 5 inches: at the Ross. Plant, and 3/8 inch by 5; inches at the Yates. Screen oversize goes to a seven foot Symons cone brusher converted to the short head type; the crusher setting is 5/16 inch. Crusher, discharge; is closed circuited with the Tyrock screens, The above crushing installation delivers a minus 5/8 inch rod mill feed to the mill bins. The crushing revision eliminated the-180 heavy South African type stamps, which had previously reduced the 2 inch crushing plant product to a minus 5/8 inch feed for the 10 rod mills, and 8 ball and pebble.; mills, other revisions in the mill flow sheet, resulted in 3 identical units of about 1350 tons per day, capacity per unit, Each unit consists of an open, circuit 6 foot by 12 foot rod mill, fed from two 24 in by 48 inch vibrating feeders of the four feeders available per unit. A gathering belt delivers the ore discharge of the feeders to the Transportoweigher, which in turn discharge s, into the rod; mill feed spout. Rod Mill discharge is the feed for the 9 foot by 11 foot ball mill, The ball mill is closed circuited with a 16 foot by 30 foot Dorr Classifier. The Homestake make amalgamator, for coarse gold recovery in the ball mill circuit, made' necessary a 36 inch spiral conveyor between the classifier rake discharge and, the combination drum and double scoop feeder on the ball mill See Figure l - the flow sheet of the two stage grinding units.

Jan 1, 1958

By Kang-Hyun Lee, In-Mo Lee, Byung-Kyu Kim, Parkm Jinho, Seoung-Won Lee

"In this study, the TBM Resistivity Prediction (TRP) system is developed for predicting the location, thickness, permittivity ratio and electrical conductivity of anomalous zones ahead of tunnel face using the measured resistivity of the ground. The applicability of the developed system was verified by performing field tests at a construction site in which an EPB-shield TBM is used for tunnelling work. In the first field test, it was found that the rock around the tunnel face had the same resistivity and permittivity with the rock ahead of the tunnel face indicating no anomaly ahead of the tunnel face. In the second test, a stronger zone 5-m thick was predicted ahead of the tunnel face based on lower permittivity than that of the rock around the tunnel face. The ground condition assessed by the newly developed TRP system matched well with that either predicted from geophysical exploration or directly obtained from drilling boreholes or from daily observed muck conditions. INTRODUCTION During tunneling work, the emergence of unpredicted zones of relatively weaker or stronger ground can lead to delays in construction work or an increase of construction cost. Predicting anomalous zones ahead of tunnel face in advance can thus prevent time and economic loss. For these reasons, various methods to predict the ground condition ahead of the tunnel face have been studied and developed. Prediction methods using various kinds of equipment include tunnel seismic prediction, ground penetrating radar, electromagnetic surveys based on electronic antennas, and electrical resistivity surveys conducted by analyzing electric currents in the ground ahead of the tunnel face (Ryu et al. 2008). However, most of the prediction methods are only applicable to conventional tunneling job sites, which feature free access to the tunnel face. In mechanized tunneling projects, accessibility to the tunnel face is very limited because the tunnel face is occupied by the TBM."

Jan 1, 2016

By Eduardo Velasco, Paz Navarro, Alfonso Navarro, Claudio Cimiotti, Alejandro Sanz, Nick Karlin

The LA Effluent Outfall tunnel is a 7-mile long, 18' internal diameter, secondary treated effluent discharge tunnel currently under construction by Dragados USA for the Los Angeles County Sanitation District No. 2 (LACSD). The purpose of this tunnel is to add redundancy and increased capacity for discharge of secondary treated effluent from the LACSD’s Joint Water Pollution Control Plant, located in Wilmington, California within Southern Los Angeles County. Current discharge from this facility flows through two existing tunnels of 8' and 12' horseshoe profile, constructed in 1937 and 1958, respectively. When the new tunnel is complete, it will add an additional capacity of 670MGD in peak wet weather flow conditions. Geology of the roughly 7 mile long tunnel was divided into six reaches by the contract documents. Tunnel Reaches (TR) 1 to 3, comprising 19,550' will be excavated in alluvial sands of the San Pedro and Lakewood formations, with cover ranging from 45 to 90 feet. In this reach the tunnel intersects the seismically active Palos Verdes fault Zone. TR 4 is a 1,600' transitional zone between alluvium and the rock formations of the Palos Verdes (PV) Hills, comprised mostly of Malaga Mudstone. TR’s 5 and 6 total 15,591', and are within the rock formations of the PV Hills with overburden ranging from 315' to 475'. The primary constituent of the PV Hills is Altamira

Jun 13, 2021

By P. E. Richardson, N. P. Finkelstein, Z. Chen

The large band gap and insulating properties of sphalerite have limited the application of standard electrochemical techniques for studying its reactions with flotation reagents. This problem has been overcome by developing electrodes that rely on the surface conductance produced when sphalerite is activated with copper or other heavy metals. A brief exposure of the mineral in copper sulfate solutions results in electrodes that exhibit significant electrochemical activity characteristic of copper sulfides. Voltammetry studies conducted on sphalerite activated in 10-4 M CuS04, solutions at pH 4.6 provide information on both the amount and the nature of the activation product(s). It is shown that copper activation is strongly dependent on the electrochemical potential applied during activation. Activation at potentials increasingly negative of the rest potential causes a progressive increase in the amount of copper on the surface; activation at potentials positive of the rest potential decreases the amount of copper on the surface. The results indicate that both the kinetics of copper uptake and, possibly, the chemical composition (stoichiometry) of the activation product are controlled by the electrochemical potential.

Jan 1, 1995

By Peter Amelunxen, Kain Nugent, Brandon Akerstrom, Willem Duyvesteyn, Todd Harvey

In 2024, Capstone Copper Corp commissioned a new sulfide flotation plant at Mantoverde in the Atacama region of Chile to process copper ore at a design rate of 32,000tpd. The pyrite associated with the copper ore body contains cobalt in solid solution, with Co replacing Fe in the pyrite matrix. As per the existing sulfide flotation flowsheet most of the pyrite is depressed and sent to tailings via the cleaner scavenger tail stream. A new project considers the recovery of the pyrite from the cleaner-scavenger tails via froth flotation to produce a cobaltiferous pyrite concentrate, which is then leached via the existing dynamic copper leach pad to oxidize the pyrite and dissolve the cobalt. The cobalt is recovered from the solution by treating a bleed stream of copper SX raffinate through a continuous, counter-current ion exchange (CCIX) facility. This approach to by-production of cobalt confers numerous benefits, including reduced costs compared with alternative cobalt recovery processes, reduced acid consumption in the heap leach, increased copper production, and reduced acid mine drainage potential due to the removal of pyrite from the mill tailings.

Feb 1, 2025

By GRANT COLLIGAN, BROCK O’KELLEY, Corby Anderson

With the world’s ever-expanding push to expand technological capabilities, the need for specialized materials including rare earth elements has exploded. One source found in the USA is bastnaesite, a rare earth bearing fluorocarbonate mineral, currently mined at the Mountain Pass Mine in California. To increase production, it is essential to optimize existing processes and create new ones to better utilize current resources. Therefore, a US Department of Energy Critical Materials Institute sponsored research program was carried out at the Kroll Institute for Extractive Metallurgy to expand the fundamental understanding of the industrial bastnaesite concentrate leaching system. With the help of prior knowledge, thermodynamic calculations and design of experimentation based lab testing, a novel single-stage hydrochloric leach system was created to optimize the rare earth extraction from bastnaesite. Historically, the existing industrial process has utilized a two-stage leach system involving a high-temperature hydrochloric acid leach with liquid solid separations followed by a caustic crack stage of the leach residues. A series of single-stage leach experiments were run by reacting locked cycle flotation concentrates with hydrochloric acid to test common leaching parameters. The results of these patent pending single-stage tests have shown rare earth recoveries significantly higher than reported recoveries of historic two-stage caustic crack processes, all while decreasing the equipment required and the type and amount of reagents needed.

Jan 31, 2022

By Stryker Magnuson

While probe drills are not strictly necessary for all projects, the incorporation and use of probe drills and pre-grouting adds capability and insurance to boring operations. Water ingress and unstable ground can be resolved before becoming a problem and resulting in costly delays through the use of enhanced, 360-degree probe drilling setups. To do this, proper design of the array of drill ports in the shield, matched to the possible ground conditions, is critical. For ground with exceptional water and instabilities expected, additional probing locations are low-cost additions that can lower risk and increase efficiency. In this paper we will look at recent and ongoing projects including the Lower Meramec Tunnel and Jefferson Barracks Phase 2. We will detail the design of those probe drill arrangements, and our overall recommendations for probing/grouting systems that best suit challenging ground conditions and keep projects running smoothly.

Jun 13, 2023

By Kenneth M. Reim

In 1971, United States Borax & Chemical Corporation (U.S.Borax) initiated a mineral exploration program on federal lands in Southeast Alaska, with the commitment that any possible development would be done with great care for the environment. This program resulted in the discovery of a molybdenum deposit and the location of mining claims in 1974, in an area 45 miles east of Ketchikan, now called the Quartz Hill Molybdenum Project (Figure 1). At the time of this mineral discovery, the area was part of the Tongass National Forest, managed by the Forest Service, United States Department of Agriculture, and open to mineral entry and multiple use. In late 1978, the area was designated Misty Fjords National Monument and closed to mineral entry, and in late 1980 the area surrounding Quartz Hill was classified as Wilderness. These new laws and regulations, as well as the special interest environmental groups which oppose resource development, have significantly delayed and increased the costs of developing Quartz Hill.

Jan 1, 1983

By Susan T. Bagley, Kenneth L. Rubow, David H. Carlson, Bruce K. Cantrell, Winthrop F. Watts

Permissible exposure limits (PELs) have been established for gaseous pollutants, carbon monoxide (CO), carbon dioxide (CO2), nitric oxide (NO), nitrogen dioxide (NO2), and some gas-phase hydrocarbons emitted in diesel exhaust. There is, as yet, no PEL recommended for diesel exhaust aerosol (DEA), nor is there a standard method for sampling this aerosol. The University of Minnesota and the U.S. Bureau of Mines have collaborated to develop a personal diesel exhaust aerosol sampler (PDEAS) which utilizes size-selective inertial impaction and gravimetric analysis. During the field tests of this sampler, numerous air quality measurements were made in underground coal mines that use diesel equipment. The mine mean DEA concentrations for the five mines surveyed, determined with the PDEAS in the haulageway, was 0.89 mg/m3 with a standard deviation of 0.44 mg/m3. DEA contributed 52 % of the respirable aerosol at this location. In three of the mines filter samples were collected for DEAassociated polynuclear aromatic hydrocarbons (PAHs) and biological activity determinations. Two of the mines were also monitored for the major gaseous constituents found in diesel exhaust. In general, the PAH and biological activity levels were similar for all three mines, and indicate that up to 25 % of the haulageway concentrations may be contributed by outby diesel vehicles. Measured concentrations of CO, C02, NO, NO2, and SO2, were well below regulated levels. INTRODUCTION Diesel exhaust contains pollutant gases, such as carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, and gas-phase hydrocarbons, as well as DEA. Much of the health-related concern focuses on DEA and associated organic compounds (Watts, 1992a). A wide variety of these PAHs have been identified and some are known carcinogens and/or mutagens. The U.S. Mine Safety and Health Administration (MSHA) has proposed new PELs for these and other contaminants (MSHA, 1989). MSHA has also published an advance notice of proposed rulemaking to establish a separate PEL for diesel particulate (MSHA, 1992). The U.S. Bureau of Mines has collaborated with the University of Minnesota to develop and field test a PDEAS. The PDEAS is a three stage sampler based on the MSA' personal respirable dust sampler. It utilizes a respirable cyclone preclassifier followed by a 0.8 µm cut point impactor and afterfilter operating at a flow rate of 2 L/min. Respirable aerosol greater than 0.8, µm in size is collected by the impactor while DEA, less than 0.8 µm in size, is collected by the afterfilter. Hence, gravimetric analysis of the afterfilter permits measurement of DEA concentrations. This development and laboratory evaluation of the PDEAS were described previously by Cantrell (1990) and Rubow (1990). During field tests of the sampler, numerous air quality measurements were made in continuous miner sections of five underground coal mines that use diesel haulage equipment. These air quality measurements included levels of selected PAH and biological activity associated with DEA collected in the intake and haulageway areas of three of the five underground mines, and CO, CO2, NO, and NO2 in two of the mines. The objectives of this paper are to present the DEA and associated pollutant concentrations measured in these mines and to assess the impact of diesel face-haulage equipment on underground mine air quality. MINE DESCRIPTIONS The mines used for the PDEAS evaluation were designated J, K, L, N, and 0. Mines K, N, and 0 are located in the Western United States, while mines J and L are located in the East. Each mine produces high volatile, bituminous coal with shift production levels varying from 500 to 2000 tons/section. Seam heights varied from 1.5 to 3.0 m. Mines K and N use continuous mining to develop longwall panels. The others are strictly room-and-pillar operations using continuous miners. The number and types of diesel-powered vehicles used at these mines were described by Watts (1992b). Mines J, K, N, and 0 use diesel power to assist in a wide range of activities in addition to coal haulage. These included road maintenance, personnel and materials transport, lubrication, and welding. Mine L used only three diesel-powered shuttle cars to haul coal. SAMPLING AND ANALYSIS METHODS Aerosol Measurements Aerosol samples were collected in the mine portal area, the clean air intake to the continuous miner section, the haulageway one crosscut inby from the feeder breaker and belt, in the return airway, and on selected personnel. The haulageway sampling site was located near the point where the diesel-powered shuttle cars turn around to dump their loads. Additional respirable and DEA samples were collected and have been reported by Haney (1990).

Jan 1, 1993

By A. Benchekroun

The phosphate mining industry is confronted everywhere in the world with financial difficulties and low prices which prohibit further investments and development of new mines even in regions with a comparative cost advantage (North America/ North Africa/ and Middle East). But old mines are being progressively exhausted/ and if no replacement mines come on stream in the near future/ we may soon find ourselves (around the year 2000) with a global annual production capacity of 160 million tonnes of marketable phosphate rock instead of the capacity of 200 million tonnes existing today. Unless prices improve/ phosphate rock/ a non-renewable resource and a vital commodity to world agriculture/ may turn to be in short supply to world fertilizer industry. Whatever the extent of recovery of fertilizer demand/ the expected decline of the production capacity during the 1990 I s is bound to cause the disappearance by the year 2000 of the important surplus characterizing today the supply/demand balance.

Jan 1, 1995

By J. A. Marts, R. C. Gilmore, Jr. Bogin, S. A. Saki, J. F. Brune, J. W. Grubb

"Most, if not all longwall gobs contain explosive gas zones (EGZs), i.e., zones of explosive methane-air mixtures that can cause – and have caused – mine fires and explosions. If the coal is prone to spontaneous combustion, oxygen penetration into the gob must be avoided. This paper summarizes the significant research findings from five years of computational fluid dynamics (CFD) modeling research conducted at the Colorado School of Mines (CSM) under funding from the National Institute for Occupational Safety and Health (NIOSH). CSM Researchers have developed CFD modeling techniques to identify where and under what circumstances EGZs can form in longwall gobs and how EGZ formation and oxygen penetration depend on the ventilation method, face and bleeder ventilation parameters, injection of inert gases and the operation of gob ventilation boreholes. Recognizing these explosion and fire hazards is an important first step in improving the safety of longwall coal mines. CSM modeling research has shown that EGZ formation can be effectively controlled by adjusting ventilation parameters, choosing the proper ventilation pattern and injecting inert gases where necessary. INTRODUCTION In a project sponsored by the NIOSH Office of Mine Safety and Health Research, researchers at the Colorado School of Mines have examined gas compositions and flows in longwall gobs in order to assess explosion and fire hazards. Since gob areas are inaccessible, researchers developed a series of computational fluid dynamics (CFD) numerical modeling tools to characterize these hazards. A variety of CFD models were developed to cover progressively sealed as well as bleeder ventilated gobs for both coal and trona mines. The explosion and fire hazards posed by EGZs in longwall gobs can be summarized as follows.• If the EGZ lies closely behind the longwall face, flames and pressures from an explosion can penetrate the shield supports and reach the active face area, creating blast trauma, burn hazards and toxic, unbreathable atmospheres. • EGZs can be pushed around inside the gob by roof collapses and cave-ins. If they get pushed out into the face area, sudden methane inundations and explosion hazards in face areas can result. • Fresh air flowing into the gob can create an explosion hazard as the gas composition in the gob moves from fuel-rich inert to explosive, creating EGZs. • Ignition sources inside the gob can be frictional ignitions or spontaneous combustion. • Bleeder ventilated gobs are surrounded on all sides by an EGZ that forms along the fringe areas between the fresh-air ventilated bleeder entries and the methane-rich interior of the gob. It is suspected that diffusion flames can propagate rapidly along these EGZ fringes if an ignition occurs"

Jan 1, 2015

Coal fly ash and flue gas desulfurization (FGD) sludges can be returned to mine pits, fills and revegetation zones in Virginia by regulation if (and only if) a positive beneficial use can be shown. Utilization of alkaline fly ash for control of acid drainage from pyritic coal processing waste piles, and use as a soil amendment for revegetation, are the two dominant beneficial uses proposed over time. Both applications must be controlled by the basic chemical properties of the ash proposed for utilization. Currently, public concerns over long-term As and Se leaching from various applications are increasingly driving regulatory options for mine site utilization. Many fly ash materials are relatively low in inherent alkalinity or neutralizing ability, and certain ashes are actually acidic. Failure to add sufficient total alkalinity will result in strong acidification of the ash utilization zones, stripping heavy metals like Mn, Zn and Cu from the fly ash matrix. Similarly, if alkaline ash is loaded into non-acid forming coal wastes at high rates such that leachate pH is > 9.5, significant leaching of As and Se has been documented in large scale laboratory leaching columns. Utilization of fly ash and FGD as a mine soil amendment for revegetation is based upon combined liming and water holding capacity benefits, however, levels of soluble salts (primarily sulfate and borates) limit one-time application rates to 100 Mg/ha or less.

Jan 1, 2006