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By N. Ohmura, H. Saiki, T. Nagaoka

A microbiological flotation system that facilitates the removal of pyritic sulfurfrom coal is reported. The chemoautotrophic bacterium Thiobacillus ferrooxidans is utilized as a pyrite-selective biological surfactant that augments the flotation-mediated rejection of pyritic sulfur. The bacteria were produced by continuous cultivation in 50-L tanks, where it was possible to produce 3.8 x 1012 cells/day when the dilution rate was optimal and the pH was 1.6, a condition that prevented ferric precipitation. Prior to flotation, the bacteria were mixed with coal, which allowed cells to selectively adhere to the pyrite. The adherence of bacteria made the pyrite surfaces more hydrophilic, which facilitated separation by increasing the tendency of pyrite to sink, while the hydrophobic coal floated. When a synthetic coal/pyrite mixture (10.1 % sulfur) was subjected to microbial flotation, the level of sulfur rejection was stable during the entire period of operation (i.e., one hour). In the absence of bacteria, flotation reduced the sulfur content of a coal/pyrite mixture to within the range of 6.7% to 7.4%, with the combustible recoveries ranging from 93.9% to 99.0%. In the presence of bacteria, the sulfur content of cleaned coal was in the range of 1.3% to 1.4%, with the combustible recoveries ranging from 80.8% to 86.3%. Bacterial activity accounted for 57% of the total sulfur rejected through flotation. The desulfurization capacity of the system was further confirmed by testing it with run-of-mine coal. The pyritic sulfur content was reduced from 2.9% in the feed coal to around 1.2% in the froth product, while 80% of the combustible recovery was retained. Microbial flotation removed 60% of the pyritic sulfur from the feed. These findings demonstrated that micro¬bial flotation could be utilized for the removal of pyritic sulfur from coal in a semicontinuous system.

Jan 1, 2000

By Michael J. Rinker, P. A. Tibble, M. Wiseman, R. V. Nicholson

Tailings, from an active copper-zinc operation, containing about 10% sulphur were investigated to assess the onset of acid production and potential lime requirements for treatment of drainage. Oxygen consumption rates were measured over two years to verify spatial and seasonal variations in sulphide oxidation rates. Shallow cores were collected to assess the quality of tailings porewater and to characterize solids that had been subjected to oxidation and depletion of neutralization potential (NP) for several years. Oxygen consumption data were used to quantify rates of NP depletion and onset of acid drainage from the near- surface tailings. Based on measured oxygen consumption rates and identification of NP remaining in the tailings, future lime use in the treatment plant was expected to rise significantly without mitigation. Geochemical modeling calculations were calibrated with observed oxygen consumption rates and the model results agreed well with actual lime use in the waste water treatment plant during operations. The modeling also demonstrated the benefits of lower lime demands and treatment costs after closure as a result of construction a soil cover on the acid generating tailings.

Jan 1, 2000

By G. E. Jones, G. K. Hoffman

Through the USGS National Coal Availability pro-gram, two San Juan Basin studies have been completed. The study areas are in the northwest Bisti field, Fruitland Formation and in the eastern Standing Rock field, Menefee Formation. Original resources are 4.66 Gt and 3.46 Gt (5.14 billion stand 3.82 billion st), respectively, in the Bisti and Standing Rock areas. Bisti coal resources are greatly reduced by the Bisti-De-Na-Zin wilderness area (1.13 Gt (1.25 billion st)). Technological restrictions remove 31% from Standing Rock original resource. Available resources are 60% (2.79 Gt(3.07 billion st)) of the Bisti original resource and66% (2.26 Gt (2.49 billion st)) of the original Standing Rock resource.

Jan 1, 2000

By Kim A. Lapakko, William W. III White

The ASTM standard method D 5744-96 was developed to provide a well-defined kinetic test protocol, conducted under controlled reaction conditions, with the intent of generating reproducible results. A preliminary indication of the repeatability of a simplified alternative method (MN DNR method) was assessed and results from the MN DNR method were compared to those from the ASTM method. To provide an indication of repeatability, six samples from three different rock types were subjected to dissolution testing for periods of 20 to 68 weeks. Drainage pH values at the end of the tests were within 0.5 units in all cases and within 0.05 units in four cases. The percent difference from the mean for overall sulfate rates from paired cells ranged from 0.04 to 1756, with a median of 6.3%. Nine samples from four rock types were subjected to both MN DNR and ASTM tests for periods of 20 to 132 weeks. The difference in final drainage pH values forsix of the samples was less than 0.1 unit, and these values were less than pH 3.65 or greater than pH 8.0. The final drainage pH difference for the last three samples ranged from 0.15 to 0.4, and these values were ill the pH range of 6.2 to 7.2. The sulfate release rates for the periods of record for the MN DNR method were 70 to 150% of those for the ASTM method, with a median value of 110%. Sulfate and calcium release from the two methods was not substantially different. The MN DNR method typically produced higher magnesium release.

Jan 1, 2000

By R. Codell, D. L. Hughson

While benchmarking the integrated finite-volume code MULTIFLO against the analytical solution of Philip et al. (1989) for cylindrical underground openings, we found numerical simulation of dripping threshold flux consistently higher than the analytical solution for both rectangular and unstructured grids. The magnitude of error is proportional to the alpha parameter characterizing capillarity. This may bias estimates of repository performance towards non-conservatism.

Jan 1, 2000

By M. Canty

This paper presents results from pilot-scale and field testing of an innovative technology that uses sulfate-reducing bacteria (SRB) to treat and control acid mine drainage (AMD). Sulfate-reducing bacteria, a common group of anaerobic bacteria, produce hydrogen sulfide and bicarbonate when supplied with sources of carbon and sulfate. Hydrogen sulfide reacts with metal ions in AMD, precipitating them as metal sulfides. The bicarbonate produced serves to help neutralize the drainage. Pilot-scale metal-removal efficiencies reached 99% for zinc, 99% for aluminum, 96% for manganese, 98% for cadmium and 96% for copper. However, the iron and arsenic removals were not as effective as the aforementioned metals. This was largely attributed to high levels of iron and arsenic that contaminating the organic substrate. There was evidence that both adsorption and sulfate reduction were occurring within the reactors. The SRB field demonstration involved using the flooded subsurface mine workings of the Lilly/Orphan Boy Mine near Elliston, MT, as an "in situ biological reactor." In the mine, high removal efficiencies were observed for aluminum, cadmium, copper and zinc (70% to near 100%) during the four years of monitoring. However, for reasons similar to the pilot scale testing, low removal efficiencies were observed for arsenic and iron. Sulfate reduction was evident by measured decreases in sulfate and the detection of soluble sulfide within the mine water.

Jan 1, 2000

By Y. T. John Kwong

Modified after procedures for assessing acid-generating potential of coal spoils, most acid-base-accounting (ABA) analyses inadequately characterize highly varied metal deposits. Although mineralogy critically controls acid generation and metal leaching, acquisition of appropriate data and their interpretation are poorly developed. Metal loading rates are commonly determined by kinetic testing, which rarely duplicate actual field samples and conditions. Accurate predictions and reduced assessment costs can conceivably be achieved by (i) use of geochemical analyses to define surrogate indicators; (ii) intelligent acquisition and use of mineralogical data; and, (iii) compilation of geo-environmental ore-deposit models to validate inference based on detailed geology.

Jan 1, 2000

By J. H. Kempton, D. Atkins, W. Locke

The scrutiny given to model predictions of pit-lake water quality has focused attention on the uncertainty associated with long-term predictions. Although comparison of probabilistic predictive modeling of water quality in existing pit lakes suggest that short-term predictions can bracket most parameters, un¬certainties in wall-rock reactions and the stability of groundwater composition and climate remain unquantified This overview of the uncertainties associated with longer-term predictions is presented as support for those considering policy decisions that must be made in the absence of reliable estimates of future conditions.

Jan 1, 2000

By R. C. Ford

The advent of solvent extraction-electrowinning (SX-EW) technology for recovery of copper from low grade oxide ores has extended the operational lives of many historic mines in the western United States, and made many other orebodies economically viable worldwide. Many of these operations are mature and face closure within the next decade, depending on market conditions. Closure of a large copper heap leach operation has not been undertaken, and differs in some important chemical respects from closure of gold leach pads. Challenges for closure include prediction of solution chemistry and draindown characteristics, determining the benefit of cover placement in semi-arid climates and evaluation of solution management strategies once the economics of copper recovery are no longer favorable. This paper discusses issues pertinent to copper heap closure in semi-arid and arid climates, and strategies for their management.

Jan 1, 2000

The ever-increasing power (and decreasing cost) of computers has opened up substantial oppor¬tunities for 'Vision'-based systems in both on-line and off-line control. This paper reviews image analysis applications in use at the Julius Kruttschnitt Mineral Research Centre (JKMRC) for: •blast and mill feed size monitoring; •AG/SAG mill model-based control; •mineral liberation; and •froth flotation control. The SPLIT™ image analysis system is being used to estimate muck pile and ROM feed sizings. AG/SAG mill feed sizing is being used in a dynamic model for mill control. A new generation mineral liberation analyzer has been developed with Philips Electron Optics. The Philips-JKMRC mineral liberation analyzer offers a substantial improvement in resolution and speed over previous developments. While on-line liberation control continues to be something of a pipe dream, measuring liberation "one shift behind" is now feasible. A robust instrument has been developed to measure flotation froth bubble size and velocity. The instrument also derives a parameter that allows different froth textures to be distinguished. The instrument has been used for on-line control in coal and sulfide flotation. For coal froth, an online ash estimate has been achieved at one site and is being tested at other sites. Overall, image analysis is finding many applications in mineral processing and control.

Jan 1, 2000

By S. Veeramasuneni, C. D. Dunbar

The rate of hydration influences many important physical properties of gypsum. Previous research examined the rate of gypsum hydration and related this to compressive strength and microstructure development using BET specific surface area analysis. The analysis of gypsum porosity in combination with BET surface area and rate of hydration remains to be done. In the present study, mesoporosity is analyzed using the numerical method of Barrett, Joyner and Halenda (BJH) to gain a greater understanding of gypsum hydration and microstructure development. The rate of hydration has a significant effect on mesoporosity of the gypsum matrix. The results reveal the effect of mesoporosity and hydration rate on some macro physical properties of gypsum.

Jan 1, 2000

By P. R. Desam, J. D. Miller, A. Datta

The flow behavior of bubble-particle aggregates in separation tanks is important for many flotation systems, particularly for wastewater treatment. These aggregates can be considered as the dispersed phase in a continuous liquid phase of water and the flow characteristics determine the efficiency of the bubble separation process. In this work, a general methodology for the computational fluid dynamics (CFD) simulation of a bubble separation tank is described. This system is analyzed by Eulerian-Lagrangian approach. The momentum transfer from the dispersed phase to the continuous phase is quantified using the Particle-Source-In Cell (PSI-Cell) method. With CFD simulations, the effectiveness of different tank design parameters are evaluated in terms of the extent of bubble separation.

Jan 1, 2000

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 S. S. Peng, C. T. Holland

Mountain Top Removal (MTR) mining started in West Virginia nearly thirty years ago. This surface mining method can extract multiple coal seams as thin as a few inches thick with total recovery and minimum rock dilution in very steep mountainous terrain. It is highly efficient even if coal seams are in close proximity and small in aerial extent. Consequently, MTR has been widely used in the Central Appalachian Coalfield (mainly Kentucky, Tennessee, Virginia and West Virginia) for the past thirty years with great success. In that respect, there has been no demand for research and little scientific research has been performed to investigate its impacts on the surroundings in the history of MTR mining. However, in the past two years the debate over the MTR mining has grown quickly and in times become very intensely. This paper describes chronologically the issues raised by various parties, legal actions, its impacts on mining permit application and research projects developed to address the issues.

Jan 1, 2000

By M. L. Free, L. Anthian

Electrochemical, chemical, and image analysis techniques were utilized together with statistical analysis methods to determine the effect of various anode impurities on copper electrorefining performance. Results indicate that arsenic is a beneficial anode impurity. Anode lead and sulfur are shown to decrease electrorefining performance. Specific emphasis is given to the influence of individual elements on current efficiency, slime particle generation, and cell voltage parameters.

Jan 1, 2000

By Robert R. McDougal, Anne E. McCafferty, Bruce D. Smith

Magnetic, electromagnetic, and radiometric airborne survey data have been used in regional and local (drainage basin) scales. In a regional geoenvironmental assessment of the state of Montana, magnetic and radiometric data compiled from airborne surveys were used along with other digital geologic and geochemical data to prioritize mining districts for potential acid water generation. Probability ratio mapping was done in order to integrate the interpretation of many different digital data sets. On a more local scale, the Animas (CO) and Boulder Basin (MT) watersheds have been studied using helicopter geophysical surveys. The airborne geophysical surveys show many more structural features than the geologic maps. Combined interpretation of the geophysical data sets using the probability ratio method has resulted in identification of areas of alteration. Airborne radiometric data in the Boulder Basin area suggests that rocks with high potassium and thorium also have a high acid water buffering capacity.

Jan 1, 2000

By C. G. Buttleman, W. C. Brice

In Minnesota, reclamation of active aggregate mining sites is primarily regulated through local permits issued at the county, township, or municipality. However, for abandoned or depleted aggregate mining sites, a responsible party for reclamation is often no longer available. Since 1995, the Minnesota Department of Natural Resources has reclaimed several abandoned aggregate sites using innovative public/private partnerships and emphasizing native plant materials. The purpose of these projects is to demonstrate cost effective reclamation methods that can be utilized by both aggregate operators and local government and to promote mine planning and resource identification as it relates to reclamation.

Jan 1, 2000

By Kostas Fytas, Pierre Bousquet, Bill Evanelou

Acid mine drainage (AMD) is a serious environmental problem that preoccupies the Canadian Mining Industry. Considerable amounts of money are spent every year in an effort to prevent or reduce the acid mine drainage phenomenon. AMD occurs when sulphide minerals (ex. pyrite) contained in rock are exposed to air and water and subsequently oxidise to produce low pH water. This acid effluent has the potential to mobilise any heavy metals contained in the rock. Coating the sulphide minerals with silicates is a new promising technology to reduce AMD. Pynte is treated with a solution containing H2O2, sodium silicate and a buffering agent. H2O2 oxidises a small part of pyrite producing ferric iron (Fe3+) ions. These ions subsequently react with the silicate ions to produce ferric hydroxide-silica that precipitates on the pyrite surface producing a passive coating. This silicate coating can protect the grains of pyrite from oxidation. This paper presents a series of experiments that confirm that silicate coating can considerably reduce AMD.

Jan 1, 2000

By JoAnn Silverstein, Eric A. Marchand

Competition between Thiobacillus ferrooxidans and non-iron-oxidizing heterotrophic bacteria was induced by the addition of glucose to a co-culture of T. ferrooxidans and A. acidophilum in an oxygen-limited environment. Iron oxidation was inhibited as dissolved oxygen was used preferentially for glucose metabolism. Furthermore, as the water became anoxic, glucose was consumed along with the oxidized iron species (Fe3+) during iron respiration resulting in a pH increase from 2.0 to 4.0. Results suggest that biologically mediated acidification of drainage water can be reversed by dispersion of an easy to degrade, soluble, and inexpensive carbon source such as glucose into the subsurface.

Jan 1, 2000

By R. L. Grayson

Conventional mine safety wisdom states that "the most efficient mines are also the safest." Since the 1980s, small mines (and contractors) have been targeted as the most dangerous because of their fatality records. However, statistical analysis of West Virginia safety and production data from 1993 indicated that, when considering the correlation between accident severity and tons mined per employee-hour worked, the most efficient mines were, with the exception of very small mines, not the safest operations. This paper presents the results of an extended analysis of West Virginia mine safety using 1993 and 1996 data and concludes with the method used to suggest current priorities for focusing interventions.

Jan 1, 2000