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By V. B. Menon, L. D. Michaels, M. E. Mullins

Introduction The cleaning of coal to remove sulfur and inorganic impurities has, in recent years, become an essential operation in any coal utilization process. US coals, on average, contain about 3% total sulfur, of which more than 60% is generally inorganic or pyritic sulfur. Existing technologies such as heavy media cycloning, selective agglomeration, and electrostatic separation have the potential for removing about 80% of the pyrite from coal (Khoury, 1981). In view of the large volumes of coal being used today, there exists a need for the development of new processes to further improve the separation of pyrite from coal. Colloidal particles in suspension possess surface charges that are related to the chemical composition of the particles. In aqueous suspensions, the surface charge is a function of pH. For coal-pyrite mixtures, it is possible, by an adjustment of the pH (also a function of polar molecules), to reach a state where the charge on coal is very close to zero, but the charge on pyrite is still substantial. The introduction of collector particles with a charge opposite that of the pyrite should then result in the selective flocculation of pyrite and collec¬tor. These flocculates should settle out much faster than coal and could be removed from the bottom of the settling column. This note discusses our preliminary observations of the effect of clay-based collector particles, especially bentonite, on the settling behavior of coal and pyrite. These experiments were conducted with a view to developing a new electrokinetic flocculation process for separation of coal-pyrite mixtures. Experimental The objective of the experiments was to determine the effects of clay-based additives on the settling rates of clean coal, pyrite, and coal-pyrite mixtures. Illinois Colchester (No. 2) coal was obtained after processing in an existing coal cleaning facility. This coal was reported to contain less than 0.3% pyritic sulfur, which was in the form of a fine powder with an average particle size of 5µm. Pyrite (of average particle size 5 µm) was also obtained from the same facility and reportedly contained less than 0.1% coal. The zeta potentials of coal and pyrite in water were measured as a function of pH using a zetameter. The pH was adjusted by adding sodium hydroxide or hydrochloric acid to the suspensions. Sedimentation experiments were conducted in 50-mL glass cylinders, and settling rates were measured by noting the height of clear liquid above the settling front as a function of time. Settling behavior was also charted by periodically taking photographs of the system. The following systems were investigated: •a slurry consisting of 2.5 g of clean Illinois Colchester coal in 50 mL of water of pH 6.0, with and without the addition of 0.5 g of bentonite (Fisher, purified grade) ; • a slurry consisting of 2.5 g of pyrite in 50 mL water of pH 6.0, with and without the addition of 0.5 g of bentonite ; and • a slurry consisting of a mixture of 1.25 g clean coal and 1.25 g pyrite in 50 mL water of pH 6.0, with and without the addition of 0.5 g of bentonite. In addition, experiments were conducted with kaolinite (Bath, South Carolina) and alumina (Fisher, purified grade) as collector materials to verify the observed effects. Results and discussion Figure 1 shows the zeta potential values for the Illinois coal and pyrite as a function of pH. The zeta potentials of coal and pyrite decrease with increasing pH, changing from an initially positive value at low pH to a negative value at high pH. The point of zero charge (PZC) for the coal is at a pH of 6.2, while the PZC for pyrite occurs at a pH of 10.3.

Jan 1, 1988

By Jamal Rostami

Continuous miners (CM) are the most popular underground mining machinery in soft rock mining, playing a dominant role in the production of minerals ranging from coal to evaporites while finding increasing use in salt and potash mines. Along with the ongoing technological advancements in the mining industry and the underground equipment, new generation of CMs offer several new features that are designed to enhance their operational capabilities and production rate. In addition to new bits and bit holders, one of the areas of improvement is the cutterhead design through computer modeling and simulation based on the full scale cutting tests. This paper discusses the state-of the-art CM technology and development of the computer models for design analysis and performance estimation of CMs. The general approach used in the modeling, along with the results of field trials for several projects will be presented.

Jan 1, 1998

By Y. T. Auck, M. E. Kukura, L. G. Stevens

At its Technical Development Center in Tucson, Arizona, the UOP Mineral Sciences Division operates a completely integrated pilot plant testing a proprietary process for the extraction of nickel from limonite/saprolite ores. The process is based on the reductive roast- ammonia leach procedure now employed in several plants around the world. The process improvements are such that nickel extractions well above that experienced in these processes are possible, particularly on the more garnieritic/saprolitic ores. This paper will describe the process and the results of process development studies. The data show that pilot plant results confirm those obtained on the smaller laboratory and bench scales of experimentation.

Jan 1, 1979

By R. K. Mehta

Conventional triboelectrification based dry coal beneficiation methods require ground coal as a prerequisite feed material, energy intensive static-in-line mixer or cyclonic tribocharger configuration, and transport and/or improvement in the design of free-fall separators to improve the separation efficiency of [me pyrite/mineral matter from coal. The proposed paper illustrates the two concepts. First, the use of ceramic media in a polyurethane lined attitor in achieving simultaneous grinding and differential charging. Second, the use of an electrocentrifuge to selectively separate coal from mineral matter present in the triboelectrified mixture. It is of interest to note that some ceramic media can satisfy the requirements of both desired density and work function to achieve grinding and differential charging.

Jan 1, 1996

By Tomb. T. F., R. A. Haney

During the past several years, the Mine Safety and Health Administration (MSHA) has conducted studies in underground mining operations to obtain information on occupational exposures to diesel particulate (DP), mine environmental DP levels and on the effectiveness of methodologies used to control DP. The studies conducted were representative of four coal mines and 10 metal mines. The metal mines included two lead-zinc mines, one limestone mine, two potash mines, one zinc mine and four salt mines. Three of the four coal mines were using disposable diesel exhaust filters to remove particulate from the exhaust and one was using a reusable wire mesh filter. Results of these studies indicate that average DP levels in coal mines not using exhaust filters range from 0.9 to 2.1 mg/m3, The use of exhaust filtration devices reduced these levels by about 50% to 90%. Studies conducted in metal and nonmetal mines showed average DP levels ranging from 0.3 to 1.6 mg/m3.

Jan 1, 1996

By W. K. Collins, C. L. Dahlin, D. C. Dahlin, W. K. O’Connor, G. E. Rush

Direct mineral carbonation was investigated as a process to convert gaseous CO2, into a geologically stable final form. The process utilizes a slurry of water, with bicarbonate and salt additions, mixed with a mineral reactant, such as olivine (Mg2SiO4) or serpentine [Mg3Si2O5(OH)4]. Carbon dioxide is dissolved into this slurry, resulting in dissolution of the mineral and precipitation of magnesium carbonate (MgCO3). Optimum results were achieved using heat-pretreated serpentine feed material and a high partial pressure of CO2 (Pc02). Specific conditions include 155°C, PC02 = 185 atm and 15% solids. Under these conditions, a 78% conversion of the silicate to the carbonate was achieved in 30 minutes. Process mineralogy was utilized to investigate the appropriate feed characteristics, identify the process products and interpret the mineral dissolution and carbonate precipitation reaction paths. Key words: Mineral carbonation, Carbon dioxide sequestration, Carbonates

Jan 1, 2003

By A. H. Summers

The La Choya mine is located 55 km south of Sonoyta in northwestern Sonora, Mexico. Mineralization is controlled by a 40 meter thick thrust fault zone which created a permeable host for the metal-bearing hydrothermal solutions. The ore body is mined by open pit using wheel loaders and truck haulage. Gold and silver are recovered from low grade ore by heap leaching followed by carbon adsorption.

Jan 1, 1997

By Robert Mermelstein, Robert W. Kilpper

In a long term toxicology study SPF, F-344 rats were exposed 6 hours/day, 5 days/week for up to 24-months to a special test toner at 0, 1 (low), 4 (medium), and 16 (high) mg/m3, or Ti02 at 5 mg/m3, or Si02 at 1 mg/m3 by the inhalation route. The test toner was composed of about 90% random, high molecular weight acrylic copolymer and 10% high purity, medium color, furnace type, carbon black. It was enriched in fine particles such that the respirable aerosol concentrations (ACGIH) were to 0, 0.35, 1.4 and 5.6 mg/m3. There were no effects of exposure on survival, causes of death, body weight, food consumption or clinical chemistry and hematology parameters. There was no evidence for systemic or upper respiratory system toxicity as all of the changes were restricted to the lungs and associated lymph nodes. The lung tumor frequencies in the control (air and Ti02) and toner exposed groups were comparable. There were no changes at the low exposure level, which is the most relevant in regard to potential human exposures. The lung changes at the high exposure level consisted of decreased alveolar clearance, increased toner retention, increased lung weight, chronic inflammation, decreased pulmonary function and a moderate degree of focal fibrosis in all animals. The changes in the middle exposure level were smaller in magnitude than at the high level, and a very slight degree of fibrosis was found in 20% of the animals. In a follow-up investigation, female F-344 rats were exposed to one of three toner concentrations; control, low (10 mg/m3) or high (40 mg/m3) for 13 weeks followed by five, 13 week observation intervals. At the low exposure level, slight clearance retardation and modest inflammatory changes were observed at the end of exposure. They returned to normal values within six months post-exposure. In contrast, at the high exposure level, increased lung weight, decreased alveolar clearance and a disproportionate increase in toner retention, as well as an inflammatory response, were noted, which persisted throughout the post-exposure interval. While no significant histopathological changes were noted at the end of exposure, a very slight degree of fibrosis was observed in all of the animals in the high exposure group, after 65 weeks of observation. All of the above alterations are ascribable to "lung overloading", a generic response to excessive amounts of any dust retained in the lungs for a prolonged time interval. Published accounts in the toxicology literature document that long-term inhalation of large quantities of even innocuous particles such as Ti02, carbon black, petroleum coke, toner, and other polymeric and insoluble materials has resulted in a spectrum of generically similar pulmonary changes. Scaling of the rat-data, using 1 mg dust/g of lung as a threshold for "lung overloading", normal ventilatory parameters and 300-500 day human retention halftimes project "lung overloading" upon long-term exposure to insoluble respirable dust above 0.2-0.33 mg/m3. Other types of information are consistent with an exposure limit in the range of 0.4-1.0 mg/m3 for respirable dust. The absence of definitive toxicology data in support of the current OSHA respirable nuisance dust limit, coupled with the lack of sound epidemiology data, indicate the need to reexamine the validity of the current nuisance dust health standard.

Jan 1, 1991

By Pierre Ollivier, Dominique Morin, Pr. Ivo Toromanoff

Refractory gold ores have been processed by bio-hydrometallurgical process at B.R.G.M. (Bureau de Recherches Géologiques et Minières), Research Centre ,Orleans,France. The liberation of gold has been studied and the following steps for gold recovery improved. The overall process flowsheet has been established comprising different ways of treatment before the final discharge of the effluent. Iron and arsenic are successfully precipitated under well controlled Eh-pH conditions. Long term stability tests have been conducted and the research programme is to be continued with the crystallo graphic studies of the precipitates. Economical studies have been performed on the base of data obtained on parameters studies.

Jan 1, 1990

By D. Leppert

Large deposits of natural zeolites may provide cost-effective alternatives for treatment of soil and water contaminated ) with heavy metals and radionuclides. Research on the Bikini atoll demonstrated that addition of clinoptilolite to the soil significantly reduces cesium uptake by plants. Re- search on the potential use of zeolites in soils at Bunker Hill, ID indicated only minor benefits at very high contamination levels vs. US Bureau of Mines (USBM) work on the use of zeolites for treatment of mine waste waters emphasized problems with natural waters that previous studies have not addressed. High levels of competing calcium in natural waters significantly decrease the effectiveness of zeolites for heavy metal sorption and may limit the usefulness in these applications.

Jan 1, 1991

By W. D. Presley, T. R. Harrell

This paper will be a case history of the shaft and tunnel concrete lining techniques used at the Rocky Mountain Pumped Storage Project located in northwest Georgia. Emphasis will be placed on the shaft lining techniques with only a brief description of the tunnel concrete lining techniques. The 10.67 meter (35 foot) diameter shaft and tunnel concrete linings are 0.61 meter (2 foot) nominal thickness with a single row of reinforcing bars. The tunnel was placed in 18.29 meter (60 foot) lengths with bulkheaded end sections. The 172.72 meter (566.68 foot) vertical shaft was placed in 3.05 meter (10 foot) high sections using jump forming techniques.

Jan 1, 1985

By S. I. Nozhko, V. N. Guliy, A. A. Zolotarev, L. M. Luyshnia

The study of the apatite deposits of the Aldan Shield shows wide spread of the Precambrian apatite-carbonate ores and possibilities of using them for extraction of apatite. Dependency of flotation on ore minerals was studied according to the following scheme: preparation of the monomineralic samples of anhydrite, gypsum, chlorite, serpentine, phlogopite, apatite; mixing them in apatite ore of the average composition; followed by flotation. Another series of the experiments was conducted to ascertain a dependence of flotation activity of the different minerals on the different flotation reagents, which were used as collectors. It has been shown that apatite from silicate-carbonate ores is most extractable because it has the biggest size of grains and is the most free of inclusions. Beneficiation of the sulphate-containing apatite-carbonate rocks is possible when flotol - 7.9 is used as a collector. Meanwhile, the use of the tallaktam leads to an increase in the sulphate recovery. The estimation of individual technological features of the layered Mghydrosilicates and their influence on the process of beneficiation has been examined using samples of apatite-dolomite ore (P205-8%) with the addition of the phlogopite, serpentine and chlorite. The results show that there is little influence of the chlorite presence on the flotation while the serpentine presence leads to a decrease of the flotation, because of its high specific surface area.

Jan 1, 1993

By John Frostiak

The Campbell gold operation of Placer Dome Inc. produces an arsenopyrite-sulfide concentrate that must be treated by roasting, biooxidation or pressure oxidation to obtain high gold recoveries. Pressure oxidation is a proven process that also meets Ontario's stringent environmental regulations. A comparison of biooxidation and pressure oxidation was completed early in 1990. Placer Dome selected pressure oxidation as the preferred process to replace the roaster. The commercial plant design was based on technology supplied by Sherritt Gordon. In July of 1991, the existing roaster operation was shut down and a new pressure oxidation plant was commissioned. The Campbell Red Lake Mine, in Balmertown in northwestern Ontario, is the first plant in Canada to use Sherritt Gordon's pressure oxidation technology to recover gold from a refractory ore body. A similar process has been used at Sao Bento in Brazil since 1986. The Porgera complex in Papua New Guinea also uses Sherritt's technology. At the Campbell Mine, gold occurs as either free gold or is encapsulated with sulfide minerals, mainly arsenopyrite, pyrite and pyrrhotite. These sulfide species are recovered from the ore by crushing and grinding to 80% -75. µm (200 mesh), followed by flotation. About 40% of the gold in the ore is recovered by gravity separation. The remainder reports to the ground slurry feed to flotation. The flotation concentrate averages about 55 to 60 t/d (60 to 66 stpd). A typical analysis is shown in Table 1. Before the installation of the pressure oxidation plant, the flotation concentrate was treated in a two-stage, fluid bed roasting circuit. Roaster off-gases passed through two parallel sets of cyclones, followed by electrostatic precipitators. Arsenic trioxide was captured in a four-chamber baghouse before the gas was discharged to a stack. The arsenic trioxide was sold or conveyed to an underground storage vault. The roasted calcine was fed to a gravity separation circuit and then subjected to cyanide leaching. Gold was recovered from the filtered leach solution in a Merrill-Crowe zinc precipitation circuit.

Jan 1, 1992

By Gregory A. Hope, Kym Watling, Matthew I. Jeffrey, Ronald Woods

Surface enhanced Raman Spectroscopy carried out in real time has been applied to identify surface species formed during gold leaching in chloride and thiosulfate media. Chloride ion is adsorbed prior to the gold dissolution potential, but its coverage is significantly diminished at the beginning of leaching. A gold chloride band is again observed when dissolution is rapid, together with bands characteristic of AuC14- ions in solution. With thiosulfate, a thin gold sulfide layer is formed slowly in the potential region where leaching occurs. At higher potentials, thiosulfate is oxidized to sulfur and sulfate, both products being identified by Raman spectroscopy.

Jan 1, 2005

By K. S. E. Forssberg, M. I. Hallin

In many cases, the reuse of process water in flotation plants is desirable both for plant operating reasons and for environmental protection. The main advantages are better housekeeping of fresh water and process chemicals together with the reduction of polluting species to the environment. There are however a number of problems involved in the use of recycled process water. The main problem is that recycling sometimes has a deterious effect on the process and can occur months after the start of water recycling. The Division of Mineral Processing of Luleå University of Technology has been conducting experiments on recycling of process water at various sulphide plants in Sweden for over ten years. The experiments have been carried out in pilot- and full industial scale, in collaboration with the mining companies operating the plants. Until 1988 investigations were carried out in four different sulphide plants. The objectives of the experiments were: first to document differences in the composition of the process water during recycling; secondly to investigate any changes in the pulp chemistry of the flotation circuits wich may be due to the influence of recycled water; and lastly to establish critical levels, if any. of the parameters measured. While conducting experiments of this kind several things have to be kept in mind. Normally, recycling is done by using tailings pond water as process water. This means that time effects are important, because of the time lag between water input in the tailings pond and the reclaim of that water back to the plant. As will be shown, the

Jan 1, 1989

By L. W. Stanger, Erich U. Petersen, William J. Tafuri, Donald M. Hausen, Douglas N. Halbe

Gold mineralization at the Mercur Mine was controlled primarily by structure and secondarily by lithology in Mississippian-age sedimentary rocks. Gold was localized where Sevier-age high angle northeast-striking faults are intersected by younger northwest-striking fault zones. The Lulu Graben is a northeast- striking fault zone composed of a south-dipping master fault coupled with subsidiary or antithetic faults. The Twist Fault zone, a sinuous, low-displacement , north-striking zone of fracturing, bisects the graben. Large- tonnage disseminated ore bodies formed east of the Twist Fault zone within silty, thin-bedded, bioclastic carbonates. West of the Twist Fault zone, gold was restricted to rock near peripheral faults surrounding a subvertical collapsed pipe developed within the graben. An overlying thick carbonaceous shale capped the ore zone. Presence of abundant limited- displacement faulting and of hydrothermal jasperoid is associated with cartonate-hosted disseminated gold. Conversely, increased fault displacement and widespread brecciation are associated with reduced dissemination of gold into normally receptive carbonates.

Jan 1, 1990

By Alan M. Ritchie, Paul Miskelly

The 2-D code FIDHELM has been used to simulate conditions in piles of pyritic material with vertical dimensions of 20 to 70 m and a horizontal dimension of 500m. Those properties of the pile and its external environment (wind, temperature) important in determining the time and space dependence of sulfide oxidation, have been identified. A prescription to evaluate the overall sulfide oxidation rate in a pile of known volume but variable geometry has been developed.

Jan 1, 2000

By M. K. Han, K. N. Han, P. B. Queneau, W. J. Dawson

The development and scale up of hydrothermal synthesis processes for manufacture of high performance materials is discussed. Traditional hydrometallurgical processes are reviewed, leading into a discussion of process development concerns for manufacture of modern materials. Three case studies are presented, including a piezoelectric ceramic, barium titanate for multiyear capacitors, and high purity chromium metal. Factors for selection of reactor design are presented, as well as results of scale-up studies on the three products.

Jan 1, 1993

By Robert A. Jankowski, Fred N. Kissell

Recent allegations about tampering of coal mine dust samples have led to suggestions that the coal industry needs a respirable dust compliance sampling method that is less subject to tampering. The sampler designs under consideration include fixed location monitors that could be mounted on a mining machine or located at a stationary location in the mine, and samplers that are worn, like the existing samplers. Fixed-point samplers have a design advantage, since samplers worn on the body will have size and weight limitations. On the other hand, in some cases there are respirable dust concentration gradients, which will dictate careful placement of a fixed-point sampler inlet to determine the exposure of workers. This study examined dust concentration-gradient data obtained by the Bureau of Mines and others over the last decade. As an example of spatial gradients at continuous miners, a fixed-point monitor located in front of the operators cab shows a higher dust concentration than a sampler located on the operator and reduced exposure when the sampling location is behind the operator cab. It may be necessary to use a sampling tube with a machine mounted monitor, to sample in the operators breathing zone in the cab to provide a more representative sample of the miners exposure. For face workers on longwalls or on continuous miner sections using remote control, the study shows significant dust level gradients and gradient variations between typical operator positions and mining machine locations. In addition, if fixed-point monitoring is used to monitor an area, vs the exposure of specific workers, dust control technologies currently employed to ensure reduced dust exposure such as the diversion of dust laden air away from the workers, or through the use of remote control of mining machinery may not indicate the same dust reduction obtained with current sampling techniques.

Jan 1, 1993

By Lynn B. Hales, Randy Ynchausti, Jeffrey D. Mckay

Many consider rougher flotation control to be more of an art than a science. Some have even thought it impossible to make process control decisions and changes without human interaction. Controlling flotation bank pulp levels to maintain consistent pulling rates in the face of changing feed slurry flow rates, varying mineral types, and inconsistent reagent additions can be daunting. However, an advanced supervisory control strategy was installed on the plant floor to control an industrial rougher flotation circuit with little or no operator interaction. Plant staff monitored the flotation circuit under supervisory control and reported benefits of up to 4% improvement in copper recovery above that achieved with an older supervisory control strategy. To accomplish this work, a novel use of instrumentation to solve a flotation bank pulp level control problem was employed, a new implementation approach was used to correct some flaws in the older approach, and careful attention was paid to a few key process control principles. This paper discusses important aspects of these activities.

Jan 1, 2000