BIOPROCESSING OF ACTINOIDS BY USING MICROORGANISMS

摘要

Some attempts were made to remove and recover actinoids (U, Th, Pu) that may be present in nuclear fuel processing effluents and mine tailings, by using microorganisms isolated from uranium deposits. To establish which microorganisms accumulate the most uranium, hundreds of species of microorganisms were screened. Of these species of microorganisms tested, extremely high uranium-accumulating ability was found in some bacteria isolated from North American and Australian uranium deposits. These bacterial strains, Bacillus subtilis and Arthrobacter sp., can accumulate about 615 mg of uranium per gram of microbial cells within one hour, and the uranium-absorbing capacity of these microbial cells exceeds two times that of commercially available chelating resins. These microbial cells can remove uranium from the uranium-refining waste-water with high efficiency. These microbial cells can also accumulate thorium, as well as uranium, with high efficiency. The microbial cells immobilized with polyacrylamide gel have excellent handling characteristics and can be used repeatedly in the adsorption-desorption cycles. In addition, these bacterial strains have an extremely high affinity for plutonium. An almost quantitative recovery of the tetravalent plutonium from a strong acid solution (pH 0/1.5) can be achieved by these bacterial strains. Accordingly, we consider that these new microorganisms isolated from uranium deposits can be used as an adsorbing agent for the removal of the nuclear fuel elements that may be present in nuclear fuel processing effluents, mine tailings and other waste sources.