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By D. D. Banerjee, S. K. Kawatra, T. C. Eisele

To reduce their sulfur emissions, many coal-fired electric power plants use wet flue-gas scrubbers. These scrubbers convert sulfur oxides into solid sulfate and sulfite sludge, which must then be disposed of. This sludge is a result of reacting limestone with sulfur dioxide to precipitate calcium sulfite and calcium sulfate. The majority of the sludge is simply landfilled, but with increasing landfillimg costs this can cost the plant millions of dollars per year. As a result, this option is rapidly becoming less attractive. Producing marketable materials from the sludge is a far more promising avenue, provided that the products can meet the necessary specifications at a reasonable cost. In this paper, a method is described for using froth flotation and water-only cyclones to remove unreacted limestone from scrubber sludge. The water-only cyclone was found to be very effective for removing the coarser unreacted limestone, grinding ball chips, gravel, and similar coarse impurities. Froth flotation was found to remove fine unreacted limestone, with a minimum of reagent addition.

Jan 1, 1995

By Joseph B. Alberts, David D. DiPonio, Francis B. Manning

From 1996 to 2001, Wayne County and 13 suburban Detroit communities constructed the Downriver Regional Storage and Transport System (DRSTS) to improve area water quality, protect public health and alleviate basement flooding. The project consisted of a 10-mile long storage and transport tunnel, a pump station at the existing wastewater treatment plant, 9 miles of relief sewers (6 in tunnel and 3 in open cut). The work was separated into 10 contracts. Due to hydraulic design requirements and other constraints, the tunnel profile was located generally 65 feet below ground surface within a soft to medium clay strata which skimmed along the top of a very dense glacial till “hardpan” overlaying bedrock. Boulders within the tunnel bore were recognized as a significant, but indeterminate risk. This paper presents a case history of the owner’s contracting strategy for risk assumption and management of the boulder impacts on the project. Actual conditions encountered during construction and contractual adjustments made to address problems are reviewed, and recommendations for future contracts are included.

Jan 1, 2003

By N. B. Aughenbaugh

Compacted, fine-grained soils, often referred to collectively as clays, are used as permeability barriers in many mineral engineering projects such as heap leaching, containment ponds, tailings disposal and earth dams. Source materials for these liners include a variety of sand, silt and clay admixtures. These exhibit dramatically different engineering properties when densified. Therefore, it is imperative to adequately assess and characterize any soils being considered for compacted liners. The permeability and plastic properties of fine-grained soils are reviewed with respect to the state of compaction as the water content varies. Because they are weak in tension, compacted clays are susceptible to cracking when subjected to differential flexural movements. Designs of compacted clay liners also must include an evaluation of their flexibility. That is the ability of a fine-grain soil to bend plastically without cracking. This paper will also discuss the importance of flexibility with respect to soil types, compaction effort, failure mechanism and testing evaluation to the performance of clay liners in preventing seepage of pollutants from a containment site.

Jan 1, 1991

By R. Sivamohan, F. Huang

A mineral processing strategy developed for the finely and complexly interlayered calcite rich wollastonite, microcline, and iron-garnet ore of Jokkmokk, northern Sweden, gives an overall calcite recovery of 89.4% at a grade of 90.7% CaCO3. The wollastonite product assays 53.0% Ca- SiO3 at a recovery of 92.2%. The significant elements of the developed strategy are stepwise grinding, wet high intensity magnetic separation (WHIMS), reverse flotation and starvation flotation. Stepwise grinding avoids the overgrinding of soft calcite. WHIMS removes the colored iron-garnet impurity and thereby increases the whiteness of the product. Reverse flotation enables a simple flotation circuit and starvation `flotation helps to optimize the physicochemical conditions in cleaner flotation by giving rougher products of narrow particle size distributions. Moreover, with the reagent scheme developed in this work only one cleaner stage is necessary for the various rougher flotation products to be upgraded to give the foregoing results. In this paper, the strategy is presented in detail along with appropriate results.

Jan 1, 1990

By I. Nishkov, L. Alexandrova

The kinetics of froth flotation and the three-phase contact (TPC) parameters are studied at temperatures varying from 20°C to 40°C. The material floated consists of glass spheres and a quartz particles with various diameters. Dodecylamine hydrocloride (DDAHCI) is used as a collector. The equilibrium three-phase contact angle is measured with a microscope technique using the modified Mingins-Scheludko method. Using a Wilhelmy method, the temperature effect on the surface tension of the DDAHCI solution is determined. The formation of the thin film on a polished plate of vitreous silica and the expansion of TPC is monitored by means of a metallographic microscope and recorded on a attached camera at different temperatures. The experimental data show an intensification of the flotation kinetics at 30 and 40°C in the case of small particles. Such an intensification is not observed with the larger particles. The cause for intensification of the flotation kinetics is sought for in the dependence of the TPC rate of expansion and induction time on temperature.

Jan 1, 1995

By R. M. Cox

Pneumatic coal loading and conveying systems provide alternative methods for the safe and efficient mining of the thin, high-grade coal seams found in the Southern Appalachians. Pneumatic systems eliminate most of the health and safety hazards associated with the operation of conventional mining and haulage equipment in small low-coal mines by removing powered mobile equipment from the mine. Ventilation is also improved by the coincidental removal of gas and respirable dust from the mine by the operation of the pneumatic loading and conveying system. Other significant advantages of pneumatic coal recovery systems are relative simplicity, operating flexibility, low capital cost, quiet operations, environmental benefits and ease of automation. The design considerations and field evaluations of experimental prototype pneumatic coal loading and conveying systems installed and operated in small thin-seam mines are presented in this paper. In addition, fundamental design criteria and recommendations for the installation and operation of a variety of pneumatic coal loading and conveying systems that offer alternative coal-recovery systems that alleviate the serious health and safety concerns of current small mine operations are proposed.

Jan 1, 2000

By E. Suoninen, K. Laajalehto, L. Kartio

Efficient separation of pyrite from other sulfides is of great importance for the metallurgical performance of flotation processes. In this work Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) were used to study the surface chemistry of pyrite in depression, activation and xanthate adsorption under conditions of controlled potential. Modifications of pyrite surfaces after treatment with depressants (lime, sulfur dioxide, sodium cyanide) and after activation with metal ions (Cu, Pb) were studied. The principal adsorption product identified on pyrite was dixanthogen whose formation started at about +0.15 V and +0.25 V (vs, SHE) in ethyl and amyl xanthate solutions, respectively. Copper xanthate was formed on copper(II) activated pyrite. Activation mechanism of pyrite by copper(II) salts is likely to be electrochemical where copper occurs as copper(I) on the surface of pyrite. Effective depression is achieved by sulfur dioxide and sodium cyanide. Depression at high pH is due to formation of iron(III) hydroxides. Calcium ions do not affect the electrochemistry but adsorb on pyrite and reduce the surface sites for dixanthogen adsorption.

Jan 1, 1995

By B. J. Arnold

A coal's size distribution clay content and moisture content can affect its handling behavior. But the combined effects of these properties and the effects of other properties are not known. Research underway at CQ Inc.'s (formerly EPRI's) Coal Quality Development Center (CQDC) and at Iowa State University (ISU) will answer these questions as part of a four year project to develop a coal handleability index for utilities to use when specifying coals. This paper will present preliminary data from the first year of the project, which focused on obtaining data on the chemical and physical properties of carious coals and their measured handling properties. Additionally, size, ash and moisture analyses and shear test data for several coals used at one power plant will be presented along with correlations between these physical and chemical properties and the measured handling properties. These data lead to the conclusion that while moisture content is the most important variable, the amount of -44 µm (-325 mesh) coal fines is a significant factor in determining coal handling behavior.

Jan 1, 1992

By A. T. Weber, G. T. Adel

Earlier studies on the hydrodynamic interactions between fine particles and air bubbles have shown that fine particle flotation can be improved by using small air bubbles. In the present work, microbubbles ranging in size from 70 to 250 microns have been used in a flotation column for the processing of fine coal. The performance of the microbubble column has been studied as a function of wash water addition rate, aeration rate, feed rate and column length to diameter (L/D) ratio. The information collected from these tests has been used to analyze column behavior and to develop scale-up criteria. The results of this investigation suggest that mixing within the column may not be as significant as bubble size and residence time in determining column performance. Improved recovery can be obtained by decreasing bubble size which increases the flotation rate constant, and also by increasing L/D which increases residence time for a fixed column volume. The increase in residence time with L/D is due to a decrease in the volumetric flow rate of wash water with column diameter.

Jan 1, 1988

By A. T. Sapulek, C. S. Özveren, D. W. Dixon

The prediction of underground methane emission from longwall coal faces has been extensively researched for a number of years and numerous prediction methods have been devised. Many coal mines employ sophisticated environmental monitoring equipment which generates large amounts of data including, methane concentration, air velocity and barometric pressure. Presently this information is mainly used only to indicate alarm and danger levels of the monitored data for management purposes, however, the potential uses of this data are enormous[1]. This information could be used to good effect within a production/methane emission strategy as detailed in a previous paper[2]. The paper presents a practical application of artificial neural networks to underground methane prediction. Data on methane concentration and coal production has been obtained from an underground coal mine. The data is used in a neural network architecture and forecasts of methane concentration have been obtained. The forecasts are examined and there is a discussion of the potential use of the predictions from neural networks in the field of mining production control.

Jan 1, 1995

By S. Mason

Many organizations are realizing that continual improvement in health and safety relies on addressing the potential for various forms of human error. Of these, rule violations are often the most frequent form associated with accidents. These occur when an individual (or individuals) deliberately contravenes established and known safety rules. They have been associated with up to 90% of the accidents and other incidents in some industries, and yet they rarely receive the systematic attention they deserve in the promotion of safety. This paper presents underlying motives that cause violations. These can vary significantly from mine to mine and from job to job. Managers need some measure of the attitudes of the violators to determine the underlying motives behind the violations if they are to determine effective strategies for promoting safe behavior. Questionnaires form the starting point to address attitudes and the motives behind rule violations. The choice of the most suitable questionnaire, how- ever, will vary from organization to organization. Guidelines on the choice of questionnaire are offered.

Jan 1, 2000

By K. Gorazda

The population growth, urban and industry development cause the increased pollution with different substances, which contain phosphorus. It contributes to the increased demand for its compounds, increasing the use of its natural resources, which is considered to be the most accessible source. The forecasts regarding the world natural reserves of phosphorus deposits are saying that more than 50% of resources used currently will be exhausted within next 60-70 years (Steen, 1998). European Union formulated its goals regarding the waste management in 1990. Its main rules include prevention of waste generation, recycling, reuse of waste as the raw materials in technological processes, separate collection and optimization of final removal. The phosphorus recovery from waste is realized currently in many ways: directly from the waste water stream in sewage-treatment plant, from the sewage sludge, from animal waste, industrial waste and other emissions from industry (Przewrocki et al., 2004). According to the rules of cleaner production the waste should be treated as the source of resources for the production of products with full value (Kowalski, 1998).

Jan 1, 2005

By Jianping Sheng, Francis Otuonye

The potential for methane and coal dust explosions in underground coal mining operations has increased in recent years with the introduction of fast coal-cutting machines. Dust explosions usually follow accidental ignition of a methane pocket. The dynamics of the explosion may be strong enough to pick up and disperse coal dust deposited on mine surfaces and ignite the mixture. A self-sustaining dust explosion can then develop and propagate at large distances. Ignition of dusts can result in a fire, and this may also lead to a dust explosion if the burning dust becomes airborne. Entrainment of dust and the resulting dust concentration in the gas stream are some factors which determine the features of the subsequent explosion and flame propagation. A model of coal dust transport in the gas stream due to the initial explosion is presented. In this model, equations for the conservation of mass, momentum and energy are coupled with the convective-diffusive model of dust transport. The system of equations is solved numerically to obtain dust concentration, convective velocity and gas pressure profiles.

Jan 1, 1989

By R. R. Jozefowicz, T. X. Ren, J. S. Edwards

The control of methane emission into underground mine workings is important both for the safety and productivity of the mine. As deeper and gasser coal seams are mined, ventilation methods involving increasing air pressures and quantities across mine workings may not be able to cope consistently with methane emission rates during the production cycle. An accurate prediction of methane emission into mine workings is of great significance in the design of ventilation systems and additional methane control methods if required. Research has been conducted to develop a numerical method for simulating methane flow through strata in which permeability is strongly influenced by mining-induced stress. To achieve this objective, both numerical modelling using Computational Fluid Dynamics (CFD) and laboratory tests on rock samples and granular materials under triaxial stress condition were carried out. Correlation has been established between stress and permeability characteristics of rock-measure rocks and laboratory results are being incorporated into the CFD models. This paper introduces the use of CFD techniques to model methane flow through permeable strata around longwall coal faces currently undertaken at the University of Nottingham.

Jan 1, 1997

By Gordon M. Elliott

Health risk underlies all of today's environmental regulations. Mine Manager's are no strangers to risk, but risk in the context of mine management is not the same as risk in the context of environmental regulation. One of the risks facing the mine manager is whether the mining operations meet environmental compliance standards. These standards are defined in terms of the frequency of occurrence of adverse health effects in an exposed population (i.e., health risk). Demonstration of compliance necessarily involves mathematical modelling and selection of values for input variables. What is not immediately apparent is that the method of estimating the human health risk has a significant influence on remedy selection and the amount of money spent at suspected contaminated sites. Using a hypothetical, mining-related example, this paper illustrates the disassociation between the current deterministic approach to health risk assessment and cost-effective decision making. This paper also illustrates how the probabilistic approach to health risk assessment provides a more realistic characterization of health risk and enables mine managers to identify cost-effective remedial strategies for the site.

Jan 1, 1992

By Leonhard Schmid

INTRODUCTION In the region of Zurich several of the Swiss Interstate Highways meet and have to be linked to form a continuous network. The subalpine glacial topography with hills, ridges and lakes requires the construction of many tunnels (Figure 1). The Milchbuck Tunnel forms part of the inner arterial highway system of the city of Zurich. It passes underneath the ridge separating the Limmat and Glatt valleys. In its final configuration the tunnel will consist of two parallel three-lane tunnels (Figure 2). For the time being only one tunnel is constructed. This tunnel will be operated with two outbound (climbing) lanes and a single inbound (descending) lane (Figure 3). The owner, the Canton of Zurich, awarded the contract for the construction to a joint venture with the following three contractors: Locher & Cie AG (leader), Prader AG, A. Brunner's Erben, all located in Zurich. The actual freezing was performed by subcontractor Philipp Holzmann AG, Mannheim, West Germany. Electrowatt Engineering Services Ltd, Zurich, was design engineer and performed the construction supervision.

Jan 1, 1981

By X. Wu, E. Topuz

Booster fans have been extensively used in underground mines throughout the world. In the United Kingdom, S. Africa, Germany, and other countries, many non-coal and coal mines employ booster fans. These fans help to reduce air leakage, to provide an improved flow distribution and to reduce the overall cost of mine ventilation. Although booster fans have not been used in coal mines in the United States, a recent survey indicated that many coal mines would install booster fans if they were allowed to do so. With the inclusion of coal mines, the use of booster fans in underground mines is expected to increase substantially in order to maintain air quality and quantity requirements. Several techniques are used, with varying degrees of success, in determination of booster fan locations in an underground ventilation network. These techniques include linear programming, critical-path crashing, CPM together with cutset operations, the out-of-kilter method, and simulation techniques. This paper provides a brief comparison of these techniques, and reports on ongoing research for an improved methodology for the determination of booster fan locations.

Jan 1, 1987

By P. Coleman, J. C. Kerkering, S. Iverson

A fatal accident may result when a dozer is driven over a hidden void in a coal surge pile and the dozer falls into the void, burying and suffocating the dozer operator. This type of accident was analyzed by researchers from the Spokane Research Laboratory of the National Institute for Occupational Safely and Health using inexpensive fault-tree programs that had been developed, for use on a personal computer. Fault-tree analysis is a systematic safety-analysis tool that proceeds deductively from the occurrence of an accident event to the identification of the root causes of that event. The analysis identified basic and intermediate events that led to the burial of the dozer and graphically depicted the interrelationship between the basic events as well as the intermediate events leading up to the accident. A sensitivity analysis on assigned probabilities showed which events had the greatest influence on dozer burial in a coal surge pile. Operational guidelines and engineering controls are suggested to decrease the probability of a burial event.

Jan 1, 2002

By A. S. C. Owili-eger

An efficient state-of-the-art dynamic model to simulate and predict the rate of water production in longwall coal mining operations was developed as a tool for mine planning purposes. The model can also provide an estimate of any potential resultant hydrogeological impacts of an operation via an array of element-specific single-valued parameters referred to as the field rating indices. The computational procedure was designed to fully exploit the benefits of hydrogeotechnology and use a combination of conceptual, physical, empirical, and numerical approaches to define, characterize, analyze, and evaluate flow controlling properties of fractured rock systems. The model presented here provides a dynamic prediction method for highly fractured flow; a practical tool in mine and water control planning; and a cost-effective means of assessing, based on the best available technology, the impacts of mining on the water resources within a mining environment to satisfy local and federal regulatory requirements. Unique features include consideration of laminar and non-darcian flow domains in double-porosity-pressure hydrogeological media.

Jan 1, 1990

By P. J. Brown, R. W. Nice

The Thalanga Copper-Lead-Zinc Concentrator in Northern Queensland was commissioned in early 1990. The design of a flotation process for the sequential production of separate copper, lead, and zinc concentrates has always been a most formidable mineral processing challenge. In 1988-1989 during the process design phase, sized fractions of various samples were subjected to quantitative and qualitative mineral analyses. These analytical techniques are collectively known as modal analysis. Modal analysis aided in the selection of key process treatment parameters for the initial laboratory testwork on the Thalanga ore. The work also guided the flowsheet development and quantified the mineralogically imposed limitations on the separation process. This paper describes in general terms how these modal techniques were used to guide the program of laboratory flotation testwork which constituted the flowsheet design phase of this project. During these design studies, the primary grind and regrind requirements were deduced and the basic flowsheet configuration selected. Recent operating plant performance data are to illustrate the value of modal methods in addressing complex metallurgical separation problems.

Jan 1, 1995