[en] Accumulations of microorganisms in the in situ leaching environment are believed responsible for plugging of the orebody and thus decreasing uranium extraction. To assess the contribution of microbial growth to this problem, packed columns of ore and core specimens were leached in the laboratory. Samples collected at four in situ uranium mining operations revealed pseudomonads, Xanthomonads, Bacillus sp. and Micrococcus sp. These microorganisms, inoculated into simulated leaching conditions, decreased permeability in two uranium ores by one order of magnitude in 20 days. Hydrogen peroxide alleviated microbial plugging in the laboratory. Periodic injection of hydrogen peroxide through the production well into the orebody may reduce microbial plugging problems in the field

[en] Waste water from uranium mines in the Ambrosia Lake district near Grants, New Mexico, USA, contains uranium, selenium, radium and molybdenum. The Kerr-McGee Corporation has a novel treatment process for waters from two mines to reduce the concentrations of the trace contaminants. Particulates are settled by ponding, and the waters are passed through an ion exchange resin to remove uranium; barium chloride is added to precipitate sulfate and radium from the mine waters. The mine waters are subsequently passed through three consecutive algae ponds prior to discharge. Water, sediment and biological samples were collected over a 4-year period and analyzed to assess the role of biological agents in removal of inorganic trace contaminants from the mine waters. Some of the conclusions derived from this study are: (1) The concentrations of soluble uranium, selenium and molybdenum were not diminished in the mine waters by passage through the series of impoundments which constituted the mine water treatment facility. Uranium concentrations were reduced but this was due to passage of the water through an ion exchange column. (2) The particulate concentrations of the mine water were reduced at least ten-fold by passage of the waters through the impoundments. (3) The sediments were anoxic and enriched in uranium, molybdenum and selenium. The deposition of particulates and the formation of insoluble compounds were proposed as mechanisms for sediment enrichment. (4) The predominant algae of the treatment ponds were the filamentous Spirogyra and Oscillatoria, and the benthic alga, Chara. (5) Adsorptive processes resulted in the accumulation of metals in the algae cells. (6) Stimulation of sulfate reduction by the bacteria resulted in retention of molybdenum, selenium, and uranium in sediments. 1 figure, 16 tables

[en] Microorganisms were evaluated for use in recovery of uranium under conditions of in-situ solution mining. The cultures tested were Thiobacillus ferrooxidans, the faculative-thermophilic TH3 strain, and two Sulfolobus species. Growth of the organisms occurred in the presence of 0.34 to 5.0 mM uranyl ion with higher concentrations being inhibitory. Uranium ore from the Anaconda Minerals Co. Jackpile mine was not readily leachable by microorganisms. To support bacterial activity the ore was supplemented with pyrite or ferrous iron. The ore possessed some toxic properties. T. ferrooxidans was able to assist in leaching of uranium from the ore at a hydrostatic pressure of 10.3 MPa

[en] The theme of the International Biohydrometallurgy Symposium (IBS) held in Jackson Hole, Wyoming, August 22--25, 1993, is ''Biohydrometallurgy: An Industry Matures''. This is a developing technology which made important contributions to the minerals industry. The IBS-93 is focused on recent advances achieved in fundamental and applied aspects of research and development of biotechnologies applied to mineral domains. The papers presented at the Symposium are grouped together in two volumes, which are the following: this volume contains papers selected for publication which are predominantly dealing with subjects related to laboratory and industrial scale bioleaching of base and precious metals, biocorrosion phenomena, diverse bioreduction processes and electrochemical reactions. Individual papers have been processed separately for inclusion in the appropriate data bases

[en] The extraction of some metal values, e.g., uranium or copper, may be accomplished by using solutions to remove metals from ore bodies without practicing conventional mining. This process is referred to as in situ leaching and has been used industrially to recover uranium. The growth of microbial populations during in situ leaching is believed to be one of the causes of flow path plugging in the ore body, which results in decreased uranium production. Leach solution and solid samples from well casings and submersible pumps were collected from an in situ mining operation experiencing plugging problems. Bacillus sp., Micrococcus sp., pseudomonads, and xanthomonads were isolated from these samples on concentrations of 10⁵ colony-forming units per milliliter. A mixed culture of these organisms was inoculated into a uranium core specimen in the laboratory to assess the role of microbes in the plugging problem. A one-third decrease in permeability was effected in 16 days. Hydrogen peroxide killed the microorganisms in the core and alleviated the plugging problems. Periodically injecting hydrogen peroxide into the ore body through the production wells may reduce microbial plugging problems

[en] Waste water from uranium mines in the Grants, New Mexico region must be treated to remove trace elements before discharge. During the treatment process waters are retained in three consecutive algae ponds. The system was found to be effective in lowering the concentrations of uranium, selenium and molybdenum. The uranium had the greatest apparent depletion, present in the mine's effluents at 4.6 and 5.8 ppm and reduced to 0.8 ppm in the final discharge. The mechanism of depletion has not yet been defined but settling of particulates and biological accumulation are considered to be the active processes. Large populations of microorganisms were found in the waters pumped from the uranium mines and passing through the pond system. Of particular interest was the presence of sulphate-reducing bacteria, believed to be Desulfovibrio and/or Desulfotomaculum