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By V. Rastogi

Acid rock drainage is the result of exposure of sulfidic materials, such as pyrites and sulfidic ores, to air and water. The oxidation of these sulfides is catalyzed by more than a million times by the bacteria Thiobacillus jerrooxidans and close families. Inhibition of these bacteria can mitigate 98% or more of the acid loading generated. This can be achieved by the use of certain surfactants that are selectively bactericidal to the lithotropic acidophilic bacteria. Bactericides are used in two ways. As periodic or continuous treatments for prevention of acidification of material actively handled and moved, and in controlled release form for reclamation where treatment sets up a change in site microbiology to replace Thiobacillus jerrooxidans with heterotrophic bacteria and creates a stable site without need for further treatments. Use of bactericides begins with laboratory testing of the site material to qualify the site for bactericide treatment and dosage determination. Site specific treatments are designed for active sites and reclamation. Once acid production is controlled, solubilization of metals is correspondingly reduced. Results and economics of use from active and reclamation sites are presented.

Jan 1, 1995

By Paul D. Kovscek, Charles D. Taylor, Edward D. Thimons

When blowing ventilation is used on a mining section, a machine-mounted scrubber is often required to maintain face dust levels below 2 mg/m3. Operation of the scrubber also affects airflow patterns at the face and the dilution of liberated methane. Reductions in scrubber flow can result in increased methane concentrations. During mining, loading of the scrubber filter with dust is likely to reduce airflow. Detecting changes in scrubber flow is difficult, especially with extended cutting, because the machine must be operated from a remote location. Tests were conducted to demonstrate how scrubber airflow could be continuously monitored at a remote location. Three variables, static pressure at the fan inlet, differential pressure across the scrubber filter, and scrubber fan motor current, were continuously monitored while the scrubber filter was incrementally loaded to reduce air flow. The results show that monitoring each variable provided a way for estimating scrubber flow.

Jan 1, 1995

By J. P. Barbosa, R. V. V. Araújo, R. B. E. Trindade

Bromide stabilizes the auric or aurous ion by forming a stable complex in acidic aqueous solution. The oxidizing agent normally used for the process is bromine, which is a corrosive liquid with high vapour pressure. This is, in fact, the main reason why it has not found acceptance yet as an industrial oxidant for gold. Ferric ion with hydrogen peroxide and/or sodium hypochlorite have already proved to be effective oxidants for the dissolution of gold from a rotating disc in a bromide-containing aqueous solution. In the present work, preliminary tests with four selected ore samples were tested to evaluate the dissolution of gold with the same system already tested with the rotating disc (Br-/Fe3+/H2o2/NaCIO). Compared to the conventional cyanidation, results were superior in one instance only. The major obstacle seems to be the maintenance of a suitable potential to allow the complex formation. However, the studied system may be interesting, is in some situations it may yield better results than conventional cyanidation; therefore, further investigation seems to be worth doing.

Jan 1, 1995

By Julius Rubinstein, Victor Badenicov

The development of column flotation is the most significant achievement in the area of mineral processing in the last few decades. The high efficiency of column flotation allows a reduction in process time, a decrease in the number of cleaner stages and in the volume of the circulating load in the flotation circuit, and, as a result of this, an increase in consistency and reliability of operations. Unique multisectional column flotation apparatuses were developed. Such designs have a number of essential advantages as compared to monocells. A change from monocells to multisectional column allows to provide favourable conditions for separation of particles of various floatability. To attain that aim particular hydrodynamics and aeration regime is established in each section of the column, operational variables being adjusted according to the floatability of the material. Therefore in multisectional column machines the material-apparatus feedback can be established, process variables optimized depending on the characteristics of the floated materials. This concept forms the basis of column designs we have developed. For the first time column cell with alternating slurry Rows (combination of co- and counter-current flows) were developed and commercialized . Successful operation was reported of the new generation of columns with cell volumes of 10 to 80 m3 and the height of 4-6 m in copper, molybdenum, antimony, tungsten and nickel ores and coal slurry processing at different plants. Operation experience of these cells showed their considerable design and operational advantages and verified the proposed options and relationships. The new apparatus is provided with a pneumohydraulic aerator allowing to control bubble size distribution, the service life of the aerator is not less than two years. A multilevel flotation model was developed and used to work out a technique of column design and process parameters calculation. A method of the apparatus design parameters calculation based on laboratory test results (scaling up) was worked out. The method is based on flotation macro and micro-hydrodynamics simulation.

Jan 1, 1995

By M. R. Peterson

The U.S. Bureau of Mines (USBM) is investigating alternative methods to strip metal-loaded solvent extractants. Hydrolytic, precipitation, and hydrogen pressure stripping all recover metal or metal salts directly from the organic solvent extractant. Pure metals, metallic oxides, or metal salts can be formed, allowing direct production of value-added products. Aspects affecting commercial application are emphasized, including metal recovery from actual ore leach solutions, particle size control, organic modifier and diluent effects on stripping and metal recovery efficiencies, metal grade, seed addition, mixing intensity, recycling efficiency, and reactor plating. Metal separations from copper ore leach solutions and complex waste leach solutions were examined.

Jan 1, 1995

By Fred L. Stanley, Ricky Q. Honaker, Michael J. Mankosa

Spiral concentration has gained a great deal of popularity as a cheap, effective method for recovering fine coal (8x100 mesh). Typically, 6-turn, wide-profile spirals are used in either a single pass, open- circuit configuration or in combination with a middlings retreat circuit. Recent work conducted at Carpco, however, has indicated that a split feed scenario and/or hydraulic classification in advance of spiral concentration offers significant advantages in both capacity and metallurgical performance. In addition, it has also been shown that the apparent density separation which naturally occurs in a hydraulic classifier provides significant up-grading in terms of pyrite and ash rejection. The results from this study will be presented in comparison with those obtained from open-circuit spiral testing.

Jan 1, 1995

By W. P. Blacutt

A financial-economic model incorporating physical, market and policy variables has been developed for mining investment in Bolivia. Additional risk criteria emanating from political instability, new mining legislation, recent environmental regulations and a new minerals taxation system are accounted for and are integrated into the investment decision model. Results of the model indicate that geologic and market variables have the dominant effect on the investment-worth function. Among policy variables, exchange rate and taxation policies have the most significant influence. Depreciation allowance for infrastructure development has negligible weight in the investment-worth function. The business structure of the firm considering investing in the Bolivian Polymetallic Project, is found to be an instrumental factor in the investment-worth outcome.

Jan 1, 1995

By S. Hartwig, K. Wohiwend, J. Forsberg, G. Bergling

New, larger cutters requiring higher operating loads and thus increased cutterhead thrust, higher cut¬terhead speeds and more pronounced demands of maintaining high penetration rates also in mixed ground, constantly augment the loads on TBM main bearings. At the same time, the demand of a single TBM model covering a wide diameter range limits the available space for the main bearing at the smaller end. Innovative concepts and advanced methods of calculating bearing loads and lifetimes are needed to meet the demands which TBM suppliers and their customers face. This paper reviews different design approaches and covers the influence of lubrication on bearing life and condition monitoring as well.

Jan 1, 1995

All coal preparation unit operations in which fine coal is handled depend to some extent on wettability of coal surface by water. The wetting results from interactions between the coal surface and water molecules that are determined by the composition of coal matrix (interrelated with coal rank) and heterogeneous constituents such as oxygen functional groups, mineral impurities and pores. The contact angle of water on an unoxidized, homogeneous coal hydrocarbon matrix is calculated to be 100o, and much lower values measured on real coal specimens result from contributions from the heterogeneous constituents. While the effect of wettability is critical in flotation and oil agglomeration, suppression of respirable dust, and coal water fuels, it has been shown to play a significant role also in coal flocculation with semi-hydrophobic and totally hydrophobic flocculants.

Jan 1, 1995

By Michael G. Nelson, Dot J. Helm, Edmond C. Jr. Packee

Under a Section 319 Water Quality grant from the U. S. Environmental Protection Agency, a working group of government agencies, mining industry representatives, and University of Alaska researchers undertook reclamation of an abandoned mine site on Birch Creek, near mile 101 of the Steese Highway. Stream hydrology, water quality, and the extent and nature of natural revegetation, were measured before the site was then recontoured to decrease the bedload deposition and bank erosion of the streams. Methods for stabilization of streams and rivers appear to have much in common with those for locations further south, but are subject to complications unique to the North, such as the formation of aufeiss, and to a lack of accurate climatological data. Natural revegetation appears to be possible for most northern placer mine sites. However, it may take place more slowly than required by public perception. Preliminary data indicate a surprising lack of nutrients in the floodplains of mined areas. Natural revegetation may be enhanced by selective planting of grasses and willows, which will contribute variously to soil quality, bank stabilization, and short-term appearance. Monitoring of hydrologic and water quality data, and of natural and artificially placed vegetation will continue at the .Birch Creek site through the summer of 1995,

Jan 1, 1995

By J. W. Wilson

In the ultrafine coal cleaning process, small coal particles (-400 mesh) are produced during the pulverizing operation. After the coal cleaning process, these ultrafine particles are very difficult to dewater, and create problems in coal transportation, storage and handling at utility plants. Research work on ultrafine coal dewatering and briquetting has resulted in the development of a single stage operation that is potentially more effective and economic than conventional thermal drying and briquetting processes. The final coal product have a moisture content of less than 15% and possess high strength and water resistance that satisfies coal transportation, storage and handling requirements.

Jan 1, 1995

By James P. Morris, William H. Hansmire

The U. S. Department of Energy's (DOE) Yucca Mountain Project (YMP) is a scientific endeavor to determine the suitability of Yucca Mountain for the first long term, high level nuclear waste repository in the United States. The status of this long-term project from the construction perspective is described. A key element is construction of the Exploratory Studies Facility (ESF), which is being excavated with a 7.6 m (25 ft) diameter tunnel boring machine (TBM). Development of the ESF may include the excavation of over 15 km (9.3 mi) of tunnel varying in size from 3 to 7.6 m (10 to 25 ft). Prior to construction, extensive constructibility reviews were an interactive part of the final design. The intent was to establish a constructible design that met the long-term stability requirements for radiological safety of a future repository while maintaining flexibility for the scientific investigations and acceptable tunneling productivity.

Jan 1, 1995

By D. C. Martin

Construction of the Cerro Colorado on-off leach pad in northern Chile required placement of approximately 3,000,000m3 of fill over a P1an area of approximately 600,000m in irregular terrain with relief of up to 40m. Earthwork construction was completed in approximately six months using mine waste which was placed in 4 to 6m lifts using mine haul trucks. The lift thickness was reduced and the compactive effort increased in the upper 10m to enable development of a mat and additional resistance to possible differential settlements under dynamic (earthquake) conditions. A single 80 mil (2mm) HOPE liner was used below the leach pads and this was protected from the loading and unloading equipment using an engineered liner system consisting of screened sand, gravel and silt from local sources as the bedding and cover layers, and a heel of screened gravel and primary crushed low grade ore. Settlement monitoring, field testing and subsequent assessments of liner performance have indicated an adequate design was achieved and the project proceeded with considerable savings in time and construction costs.

Jan 1, 1995

By Y. Q. Lu

Efficient flotation of fine phosphate minerals from a deslimed waste phosphate stream (-74 microns) has been achieved by both bench-scale flotation and by flotation with a 2-inch air-sparged hydrocyclone (ASH) unit. A sample was collected from the waste phosphate slime stream at the SF Phosphate Limited Operations near Vernal, Utah, for flotation experiments at University of Utah laboratories. The collector used was a mixture of fatty acid, petroleum sulfonate and kerosene. Bench-scale flotation test results show that the minus 15-micron particles have a significant adverse effect on phosphate flotation. When the minus 15-micron material was removed by a classifying hydrocyclone, improved flotation recovery and concentrate grade were realized. A bench-scale flotation recovery of 86 % with a concentrate grade of 16% P2O5 was obtained from classified waste slime (74 x 15 microns) feed material containing 11.3% P2O5 In contrast, a 90% P2O5 recovery was achieved with a concentrate grade of 16-18% P2O5 by single-stage ASH flotation. With a second stage of ASH flotation, a concentrate containing 23% P2O5 was realized at an overall recovery of 75%. These results indicate that the industrial application of ASH flotation technology for phosphate recovery from waste slimes is promising.

Jan 1, 1995

By W. H. Jang

Although surface chemistry fundamentals of semi-soluble minerals have been studied by many researchers, detailed understanding of these systems is still incomplete. In-situ FT-IR/IRS techniques have recently been used to successfully describe the adsorption of carboxylates at semi-soluble mineral surfaces. However, the wetting characteristics of these adsorbed films require further consideration. In this regard, the hydrophobicity and stability of transferred Langmuir-Blodgett (LB) monolayers of fatty acids at fluorite and calcite surfaces has been studied by contact angle measurements with polar and apolar liquids. Generally, it was found that the transferred LB monolayers of fatty acids at a calcite surface are unstable whereas such monolayers transferred at a fluorite surface are stable, as revealed from advancing and receding contact angle measurements. These results are believed to be due to the incomplete reaction of fatty acid monolayer at the calcite surface. In addition it was found that a closely packed well-ordered stearate monolayer with good hydrophobicity, equivalent to that of a transferred LB monolayer, can be formed at fluorite surfaces by spontaneous adsorption and self-assembly from aqueous solutions.

Jan 1, 1995

By A. D. Shuloyakov, V. A. Zukerman, G. A. Finkelstein, V. I. Kurets

Possibilities of electric pulse disintegration are discussed with emphasis on high selectivity of the process as compared to mechanical comminution methods especially when applied to polymineral ores. Physical explanation of this phenomenon is suggested. The authors present results of some experimental tests illustrating regularity of this phenomenon irrespective of origin of ores or dissemination pattern of valuable minerals including both dissipated and accessory minerals. Some operating plants applying this principle are described the plants used either for mineral research purposes or for obtaining pure monomineral fractions or for treatment of gems to be faceted. Obstacles for implementation of this technology are mentioned.

Jan 1, 1995

By S. R. S. Sastri

By using the data of E.A. Hersam and F.C. Bond's equation for energy consumption in comminution, a method was developed to analyze the performance of industrial jaw crushers. The study showed that industrial jaw crushers are generally operated below capacity. The study also showed that industrial jaw crushers generally have sufficient installed power to operate at, full capacity. The method presented can be used to estimate the capacities and power requirements of jaw crushers.

Jan 1, 1995

By Shuji Owada, Keisuke Yasukawa

Electrostatic and/or high tension separation has been used for the separation of rare metal bearing minerals, foods, industrial wastes and so on. Since the separation is achieved by the difference mainly in surface conductivity of particles, the efficiency in humid circumstances is very low, and then, the applicability is considerably limited. We applied the following two-stage pretreatment technique to the separation process, which involves (1) adjustment of surface wettability by adsorbing surfactant on the particle surface and (2) control of the surface conductivity by spraying with electrolyte aqueous solution. The addition of this pretreatment technique has been found to have a great advantage over conventional methods. Separation efficiency is achieved even in humid circumstances and selectivity can also be obtained between insulator minerals. The selectivity is very similar to that of flotation in wet process. This separation technique will be applied not only to mineral processing but the processing of industrial waste such as electric and electronic waste materials.

Jan 1, 1995

By R. K. Singhal

A sizable surface mining industry exists in Western Canada. There are the surface coal mines in the provinces of Alberta, British Columbia, and Saskatchewan producing the bulk of Canadian Coal. The two oil sands plants in Fort McMurray, Alberta producing synthetic crude oil are surface mining operations. Much of the metalliferous mining in British Columbia is carried out by open pit methods. This paper discusses the current surface mining methods in both of these industries with particular reference to Alberta. Issues relating to environmental impact assessment, mine reclamation and mine site closure have been dealt with.

Jan 1, 1995

By C. L. Schneider, R. P. King

The ability to predict the liberation spectra that will be produced by a closed-continuous grinding circuit is of fundamental importance for the design, optimization and control of most operations in an ore dressing plant. The only known approach through which such a calculation can be performed is the population-balance-model equation. The latest, and certainly most significant, advance made in this area is the solution proposed by King (1990), which requires one textural parameter measured directly from the ore being studied. The main advantage of King's solution is that, unlike the conventional solutions, it does not require the estimation of hundreds of arbitrary parameters that cannot be independently measured. However, King's solution relies heavily on a knowledge of the detailed internal structure of the Andrews-Mika diagram (Andrews and Mika, 1975), which has never been measured for any ore. The characterization of the internal structure if the Andrews-Mika diagram requires the measurement of the liberation spectra at several progeny sizes produced by the breakage of monosize-monograde particles at several different grades. In this paper, a procedure based on magnetic fluid fractionation for generating seven narrow-size, narrow-grade samples is presented. Each of these samples was then broken into six progeny size classes in an ultrasonic mill. The one- dimensional liberation spectra of each of the 42 progeny and seven parent particle samples were then measured by image analysis. The measured linear-grade distributions are presented in this paper. The calculation of the correspondent volumetric-grade distributions is discussed.

Jan 1, 1995