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By J. Sharp, R. Arnold, P. Rusin, T. Young, N. A. Sinclair

Many oxide silver and molybdenum deposits remain undeveloped because chemical extraction yields poor recoveries or is environmentally unacceptable. Bioreductive leaching of such ore samples at MBX resulted in high extractions of silver and molybdenum. When baseline, three-day, cyanide bottle-roll tests were conducted on manganiferous-oxide silver ore, 13.7% of the silver was extracted. In contrast, 86% of the silver was microbially solubilized into the organic growth medium by bioreduction with 99.8% dissolution of manganese. A followup cyanide bottle-roll test yielded an additional 8.5 % silver dissolution, for a total extraction of 94.5%. Baseline, three-day, acid bottle-roll tests of the iron-oxide molybdenum ore Yielded 1.8% molybdenum. However, bioreduction solubilized 93.3% of the molybdenum into the growth medium. An additional 0.3% molybdenum was solubilized during the followup acid bottle-roll test. Microbial treatment of refractory oxide ores with bioreductive bacteria resulted in higher extractions of silver and molybdenum than conventional chemical leaching. The bioleaching process occurred at a near-neutral pH at ambient temperatures. The bacterial solubilization of silver and molybdenum was achieved without the use of cyanide or sulfuric acid.

Jan 1, 1993

By K. Taniguchi, Y. Inada

When underground openings are excavated in rock mass for storage of Liquefied Natural Gas, hereinafter referred to as L.N.G., as its temperature is -162o C, steep temperature gradients and thermal stress occur around the openings. That is, the plastic zone and cracks around openings will expand with time. In this paper, the range of cracks which were obtained by the Crack Analysis Method and the range of the plastic zone which was obtained by the No Tension Analysis Method were investigated and compared.

Jan 1, 1986

By Jean-Michel Rendu

The semivariogram is one of the most important tools available to the geostatistician for the analysis of mineral deposits. To be complete, a semivariogram study must include a minimum of three parts which are highly interdependent. These are: calculation of the semivariogram, mathematical modeling, and geologic interpretation. The known factors and conditions which controlled or influenced the distribution of mineralization within the body being studied should be considered in the analysis .of the semivariogram. The presence and characteristics of successive phases of mineralization, the chemical and physical properties of the host rocks and the mineralization should all be considered. This requires close and continued communication between the geologist and the geostatistician prior to and during the semi-variogram study. Geologic stationarity is needed if meaningful semivariogram results are to be obtained. The first step is, therefore, to determine whether the mineralization can be analyzed as a whole or if different geologically homogeneous sections must be defined and evaluated separately. Different methods can be used to calculate an experimental semivariogram from known sample values. The method chosen will depend not only on the anticipated and actual statistical properties of the deposit, but also on its geologic characteristics.

Jan 1, 1982

By D. J. Cook, R. H. Fan, D. R. Maneval, Y-H. Shen

In this study, two placer mine processing plant effluent waters of significantly different characteristics were tested to determine the applicability of polymers along with other techniques to achieve reduced levels of turbidity. The waters from a Gilmore Creek mine and a Crooked Creek mine were characterized both as to their chemical and physical properties. The inorganic minerals were in large measure identified, and the principal cations were identified. The fine solids were studied as m their mineral identification and the extent of their electrical charges. Test work was done using polyrthylene oxide (PEO) and a liquid cationic polymer along with adjunct additives to determine optimum amounts of these coagulants for minimum consumption and optimum settling efficiency.

Jan 1, 1990

By D. T. Maiers, P. L. Wichlacz, P. A. Pryfogle, J. H. Wolfram

The effects of metal solution concentration, biomass density, length of exposure time, and pH were determined for biosorption of molybdenum (Mo) and chromium (Cr) by three organisms. Results indicate that it is possible to sorb Mo and Cr from dilute solutions. Differences were observed in the abilities of an organism to sorb Mo and Cr as well as among respective abilities of the three microorganisms. This suggests an inherent selectivity of the organism which may afford the means to control a sorption-based process. Results also indicate that the metal sorption abilities of these microorganisms depend on duration of exposure, biomass density, solution pH, and the metal concentration of the solution. Each of these parameters suggests an additional means of controlling the sorption process.

Jan 1, 1989

By A. De Daio, D. W. Fuerstenau, P. C. Kapur

Because of its pronounced tendency to undergo visco-plastic flow, coal ground in the energy- efficient high-pressure roll mill invariably comes out as a briquetted product which must be disintegrated in a conventional type of grinding device such as the ball mill. The aggregates comprise comminuted coal particles that are apparently extensively cracked and weakened during passage of the coal through the high-pressure rolls. Their deaggregation in a ball mill in the second stage is accompanied by further grinding of the coal with a relatively small expenditure of energy. Thus in spite of energy dissipation in briquetting in the roll mill and in disintegrating the briquettes in the ball mill, significant energy savings are possible in the fine grinding of coal in a two-stage serial grinding mode, as compared to ball mill grinding alone. It has been determined that for the best results the energy invested in the two grinding stages must be apportioned in an optimal manner, the energy consumption in the ball milling step is comparable to, even in excess of, the energy spent in the high- pressure roll mill; and 20 to 50 percent energy savings might be possible in grinding coal to minus 200-mesh size by this two-step process, as compared to conventional milling.

Jan 1, 1995

By Steven J. Page, Robert A. Jankowski, John A. Organiscak

Quartz dust is one of the most significant ongoing health concerns in coal mining today. Since initial verification of this health risk in coal mines by the Mine Safety and Health Administration (MSHA) during the early 1980’s, the Bureau of Mines has conducted numerous studies in underground mines to identify the sources of quartz dust and its fundamental characteristics. The most significant underground quartz dust source was found to be the continuous miner excavating rock. The percentage of quartz was also found to be higher in the smaller size fractions of the dust when significant amounts of rock was mined by the continuous miner. Furthermore, the quartz content in the continuous miner return remained fairly consistent at greater distances from the face. Another important factor speculated to affect quartz dust generation and its size characteristics is the morphology of the quartz bearing rock. The quartz content of dust between mines had notable differences with respect to the differences between kaolinite content in the dust. Low kaolinite content was associated with higher quartz content and increased size segregation of quartz into smaller dust particles, indicating that the free silica bonding matrix in the rock is most likely another factor responsible for quartz dust produced through mechanical comminution.

Jan 1, 1991

Coal that meets customer specifications is often stored in silos prior to being loaded into railcars. However, it is often found that, after loading, the coal contained in a particular car does not meet customer specifications. This can occur because of the variability inherent in the coal and because of segregation, mixing and flow inside the silo. Some contracts now require the coal in each car to be within specification. Silo flow models are used to predict quality in such cases. However, developing an accurate silo flow model for each case is difficult and time consuming. This paper examines the viability of using an online analyzer in conjunction with a feedback circuit to optimize the quality of the coal being loaded into trains, so that each car meets the quality specifications.

Jan 1, 2002

By A. G. Journel

Few Earth Scientists realize fully the assumptions they are making, willing or not, when pooling into a same histogram data coming from different locations and considering such histogram as an estimate of a probabilistic distribution. First they need the hypothesis of stationarity in space; second the presence of spatial auto-correlations implies that data be unequally weighted according to their relative locations and the degree of spatial continuity of the underlying phenomenon. The novel technique of indicator kriging allows construction of local or global histogram which can be considered as unbiased estimators of precisely defined probabilistic distributions, full account being given to the underlying continuity. Such estimates of local distributions can be used in mine planning for estimation of local recoverable reserves.

Jan 1, 1982

By J. C. Yingling, J. Sottile

This paper addresses detailed models of the temporal pattern of material flows produced by longwall mining units and procedures for inferring the parameters of these models from field data. First, a model is established that predicts material flows referred to shearer position and cutting element. This model is comprised of trend and fluctuation components. The trend component, which is invariant between repetitions of the cut cycle, accounts for deterministic effects on the flow pattern, such as web depth variation as a function of the cutting operation, systematic tendencies for seam height and cutting speed variations along the face, changes in the relative velocity between the shearer and face conveyor, etc. The fluctuation component models random effects on material flow and employs time series approaches. Subsequently, a method is given for converting the positionally-referenced flows to temporally-referenced flows. The model serves as a basis for generating detailed, accurate computer simulations of material flows from longwall units. As such, it provides a more rigorous foundation for analysis of cutting procedures and outby materials handling systems in longwall mines.

Jan 1, 1994

By S. Lee, F. Campero

"Past heap leach design has evaluated hydrodynamic parameters based on a uniform particle size of heap material, but has ignored the equal importance of the instability of fine migration within heap stack in the beginning stages of the irrigation process. The proposed probabilistic model evaluates internal fine erosion and segregation potential of well-graded crushed ores by considering the entire particle size distribution shape and site compaction degree. Using this model, unsaturated flow model parameters were successfully evaluated based on synthesized soil-water characteristic curve (SWCC). Additionally, one-dimensional unsaturated transient flow modeling with Hydrus 1D® showed that the different recovery efficiencies of heap material under unsaturated flow patterns depending on the particle size distribution and compaction degree of heap material. Agglomeration preprocess employed by most heap leach sites can reduce the potential of fine erosion within heap material significantly, but internal stability of crushed ores and hydrodynamic-based analysis of heap material’s pore structure is equally important in the prescreening stage in order to improve efficiency of the heap leach and avoid a costly agglomeration process. INTRODUCTION Accurate estimation of heap leach recovery is a difficult task due to the variety of design parameters that need to be considered - such as geochemistry, hydro-dynamics, and geotechnical design aspects, most notably particle size distribution through the process of agglomeration. After agglomeration techniques were introduced to heap leach design, the influence of particle size distribution and compaction degree in enhanced heap leach recovery has been neglected. The main purpose of agglomeration is to prevent fine segregation and internal erosion during and after heap stacking for well graded crushed ores, which will eventually diminish heap reach recovery. Recent studies show that agglomerated heap materials that had been consolidated at 10 meters below heap surface can release the fines after contact time with lixiviant to the compacted heap material and produce poor drainage performance (Milczarek et al, 2013). It must be noted that engineers and practitioners should investigate feasibility of agglomeration benefit prior to heap leach design because the agglomeration process can incur up to 20 or 30% of project costs. Internal stability of stacked heap material is mainly governed by the particle size distribution of crushed ores. Depending on this stability, segregation and internal erosion of fines can be mitigated by the application of moderate compaction effort during heap construction. Investigation of segregation and internal erosion potential therefore takes precedence for well graded crushed ore since reaction time and contact area with lixivant are greater in finer ores."

Jan 1, 2016

By S. Chander, A. Briceno

The effect of sample storage in argon and in air on the kinetics of oxidation of pyrite from a coal source was studied using accelerated-weathering tests that were performed in laboratory columns. Prior to the weathering tests, the samples were crushed, ground and stored for various periods of time in either argon or air. The test results showed a dramatic difference in the rate of oxidation of the aged samples. The interpretation of the differences was based on the hypothesis that the aging of pyrite led to the formation of surface coatings that changed with time. "Dry" oxidation produced surface coatings that had properties different from those produced by "wet" oxidation. The significance of these results to pyrite/reagent interactions during flotation and in evaluating the acid-mine-drainage potential of pyritic waste materials is discussed.

Jan 1, 1995

By R. L. Bleifuss, S. Zhong, H. E. Geotzman

Microwave heating of iron ore was investigated as an alternative to conventional reduction processes to solve the problem of slow heat transfer. Microwave heating and reduction tests were run on composite green balls made from coal and magnetite concentrate. Benchscale tests were run on both powdered and pelletized feeds using a 15 kW microwave generator. A significant increase in the reduction rate was obtained. With 20% excess stoichiometric carbon in the mix, more than 90% reduction of the iron ore can be achieved in about 10 min at temperatures of around 1,000°C. The reduction of iron ore with coal by microwave heating produces a pure, dust free, high-Btu flue gas that can be used in related thermal operations. Depending on the purity, the reduced iron product could be fed directly to an electric arc furnace for melting. In some cases, the removal of a slag phase may be required to eliminate excess silica and alumina.

Jan 1, 1997

By M. R. Fletcher

Slags generated by the ferrous metals industry can he used to produce high-value ceramic materials. The properties of these ceramics can be controlled by judicious choices of composition, additives, and processing parameters. Standard methods of materials handling, such as comminution and mixing, are as applicable to slag as to any other mineralogic raw material. In this study, foundry slag was ground, homogenized, melted, and, formed to produce a glass, and then heat treated to crystallize it into a high-strength glass-ceramic. The product shows promise as a low-cost, wear-resistant tile material that (-an he custom cast. This and similar materials made from slags and natural rocks are candidates for use as construction materials, acid-resistant piping, shock-resistant sheathing, rot-proof pilings, and, when foamed, even as pontoons.

Jan 1, 1990

By Graeme Lyall, Oy Leuangthong, Clayton V. Deutsch

There are many variables to consider in the evaluation of nickel laterite deposits including the concentrations of nickel, iron, silica, and magnesia. These variables show complex relationships with each other such as mineralogical constraints, non-linear correlation, and heteroscedasticity. The complex multivariate relationship between the variables cannot be reproduced by conventional Gaussian or indicator geostatistical techniques. We introduce the stepwise conditional transformation method as a pre- and post-processing multivariate transform for the stochastic simulation of a nickel laterite deposit. Transformed data are multiGaussian and independent at h = 0; thus, cosimulation can be avoided after verification that variables are independent at all lag distances. Back transformation restores the features of the input multivariate distribution to the simulated realizations. The complex multivariate correlations are reproduced and sensitivity issues are addressed.

Jan 1, 2002

By William A. Dupree, Mark J. Schultz, William J. Francart

Maintaining intake escapeways clear of contaminants from mine fires has been an issue for many years. Removing fire sources from these entries reduces the risk of contamination greatly. In recent years, concerns have been raised related to contamination of the intake escapeways by leakage when fires occur in adjacent airways. This paper discusses measured leakage rates for multiple stoppings at various pressure drops across stopping lines in a number of actual coal mines. Also addressed are methods for reducing the contamination risks for the intake escapeways, considering the ventilation system employed. The Effects of Air Leakage The effects of air leakage through ventilation controls has been well documented. While normal leakage is expected through stoppings, overcasts and other structures, abnormally high leakage results in an inefficient ventilation system and can increase operational costs for a mine. In addition, excessive leakage results in less control over mine ventilation airsplits. This may compromise the isolation of mine escapeways, and allow adjacent entries to be rapidly contaminated by products of combustion in the event of a mine fire. A study was conducted at ten mines in which air pressure and quantity measurements were taken near the active sections. The method used to construct the ventilation controls to separate airways was also noted. Stopping Construction Table 1 shows the type of stopping construction commonly used in the 10 mines included in this study. Main entry stoppings were normally built with mortared joints (wet stacked) with sealant applied to the high pressure side of the stopping. In most cases the entire face of the stoppings were sealed. In one case only the joints between blocks were sealed but the perimeters were sealed in all cases. Some mines also sealed the low pressure side of the stopping. Solid blocks were normally used for main entry construction and hollow blocks were sometimes used for longwall panel development. [ ]

Jan 1, 1993

By Kenneth J. Leib, Laurie Wirt, M. Alisa Mast

Chemical-constituent loads were determined for an alpine stream in southwestern Colorado that is affected by natural acid drainage from weathering of hydrothermally-altered rock and from acidic metal-rich discharge from abandoned mines. Base-flow loads were compared to storm-related loads using a tracer-dilution approach. A rainstom occurred during the tracer injection, providing the opportunity to measure metal loads before, during, and after storm runoff. Chemical-constituent loads during the storm increased by 1 to 2 orders of magnitude relative to base-flow conditions. The increase in loads was related to two distinct periods; (1) a flush of higher concentrations that occurred soon after rainfall began, and (2) the peak of storm runoff. The initial flush-having no measurable change in discharge--contained the highest loads of trace metals and dissolved iron. The chemical character of peak runoff was distinctly different, as evidenced by the highest loads of total and dissolved major elements and total iron.

Jan 1, 2000

By Roland Froidevaux

The potential use of geostatistics for quantitative ore reserve reporting is shown using a simple gold case study as an example. The need of defining quantitative class limits is stressed, and a possible approach to this problem is suggested.

Jan 1, 1983

By Christoph Schulte-Schrepping, Bou-Young Youn, Rolf Breitenbücher

"The main requirements of two-component grouts are a high workability and sufficient stability against sedimentation with a retention time of more than 72 hours, as well as a rapid strength development im-mediately after grouting. Component A usually consists of OPC, water, bentonite, and retarding agent. Component B, a liquid accelerator, is added to Component A during grouting at the end of the shield tail. Current investigations on different compositions of Component A showed a high workability lasting for at least 72 hours. The workability could be extended with increasing amount of the retarding agent to a certain degree. An increase of the bentonite content improved the stability of the mix, but had a negative impact on the flowability respectively the workability of Component A. High compressive strengths could be rather achieved by an adapted mixing ratio of Component A and B than by increasing the amount of the accelerator. Thereby, the interactions and compatibility of the selected constituents play an essential role. INTRODUCTION In mechanized tunneling with segment linings, the annular gap between segment ring and soil must be filled instantaneously with an adequate grouting mortar. The main functions of the annular gap grouting are to stabilize the tunnel lining and to minimize settlements of the ground surface at the same time. Thereby, two contradictory requirements are demanded on annular gap grouts: On the one hand a high workability and sufficient stability against sedimentation, on the other hand a rapid strength develop-ment immediately after grouting. Besides single-component grouts, which achieve the necessary stiffen-ing by dewatering into the surrounding soil, two-component grouts are used, especially in cohesive soils with a very low permeability. Basically, annular gap grouts are almost exclusively defined on empirical basis. Fundamental studies about the constituents and composition of the grout as well as the related achievable properties are still missing so far. Therefore, it is necessary to investigate the material-specific correlations regarding the relevant parameters of annular gap grouts – workability and flowability, stability of the mix as well as strength development – in comprehensive experiments. Based on the knowledge gained from the investigations, it should also be possible, to perform the grouting material according to a real design concept and thus, to ensure an adequate grouting in prac-tice considering the geological and hydro-geological conditions."

Jan 1, 2016

By P. L. Padgett, J. C. Hower

Five coals blended at a Midwestern United States power station were subjected to detailed analysis of their Hardgrove grindability. The coals, representing four distinct coal beds, are a low-sulfur, high-volatile A bituminous Upper Elkhorn No. 3 coal (Pike County, Kentucky); a medium-sulfur, high-volatile A bituminous Pittsburgh coal (southwestern Pennsylvania); a low-sulfur, subbituminous coal from the northern Powder River Basin (Montana); and two low-sulfur, subbituminous Wyodak coals from two different mines located in the eastern Powder River Basin (Campbell County, Wyoming). All samples that were processed in the Hardgrove grindability tests were also analyzed for their maceral and microlithotype content. The high-vitrinite Pittsburgh coal and the relatively petrographically complex Upper Elkhorn No. 3 coal exhibited different grindability behavior. The petrographic compositions of the Pittsburgh raw feed, the 16 x 30-mesh fraction (HG! test fraction) and the -30-mesh fraction (HGI test reject) are similar, suggesting that the HGI test fraction typifies the whole feed. The eastern Kentucky test sample is not as representative of the whole feed, with the HGI test fraction having lower vitrinite amounts than the rejected -30-mesh fraction. The Powder River Basin coals are high in vitrinite content and show behavior similar to the Pittsburgh coal.

Jan 1, 1998