Thiobacillus uranium

Certain microorganisms (e.g., Thiobacillus ferrooxidans) can facilitate the oxidation of Fe to Fe The Fe ion, in turn, can convert insoluble uranium dioxide to soluble U02 ions by the following reaction ... 

Microbes can control the local geochemical environment of actinides and alfect their solubility and transport. Francis et al. (1991) report that oxidation is the predominant mechanism of dissolution of UO2 from uranium ores. The dominant oxidant is not molecular oxygen but Fe(III) produced by oxidation of Fe(II) in pyrite in the ore by the bacteria Thiobacillus ferroxidans. The Fe(III) oxidizes the UO2 to UOl. The rate of bacterial catalysis is a function of a number of environmental parameters including temperature, pH, TDS, fo2, and other factors important to microbial ecology. The oxidation rate of pyrite may be increased by five to six orders of magnitude due to the catalytic activity of microbes such as Thiobacillus ferroxidans (Abdelouas et al., 1999). 

Rusticyanin is a component in the respiratory chain of the bacterium Thiobacillus ferrooxidans (44-46). This bacterium is capable of growth solely on the energy available from the oxidation of aqua Fe(II) to Fe(III) by O2. It is found in acid mine leachings, and is used commercially in the extraction of copper and uranium (see the review by Ewart and Hughes, this volume). Its ability to take into solution iron pyrites is particularly relevant. It has been suggested that an acid-stable cytochrome mediates electron transfer between rusticyanin and Fe (47, 48). The working pH is —2.0. 

Bacterial leaching with thiobacillus thiooxidans is also an acid leaching process. Sulfidic sulfur, e.g. in pyrites, is oxidized to sulfate and iron(II) is oxidized to iron(lll), which itself oxidizes uranium(IV) to uranium(VI). This process has not yet been operated industrially. 

Tuovinen, O.H. and Kelly, D.P., (1974 (a) (b) (c). Studies on the growth of Thiobacillus ferrooxidans. II. Toxicity of uranium to growing cultures and tolerance conferred by mutation, other metal cations and EDTA. Arch. Mikrobiol., 95 153—164. III. Influence of uranium, other metal ions and 2,4-dinitrophenol on ferrous iron oxidation and carbon dioxide fixation by cell suspensions, ibid, 95 165—180. IV. Influence of monovalent metal cations on ferrous iron oxidation and uranium toxicity in growing cultures, ibid, 98 167—174. 

Magne et al. (1974) made a somewhat similar study, but their emphasis was on the enhancement of the solubility of uranium in granites through the activity of heterotrophic bacteria. In their experiments microbial activity increased the amount of uranium in solution by factors of 2 to 97. Several organisms may have been involved. Bacillus licheniformis being the one species definitely isolated. Species of Thiobacillus were absent, so that the enhancement of solubility observed was probably quite unrelated to leaching processes depending upon the oxidation of pyrite. ... 

Martin PAW, Dugan PR, Tuovinen OH (1983) Uranium resistance of Thiobacillus ferrooxidans. Eur J Appl Microbiol Biotechnol 18 392-395... 

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