Screening of Uranium Absorbing Organisms and U-Bioprocessing

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In recent years, the recovery of nuclear fuel elements such as uranium and thorium from aqueous systems using various microorganisms has become the center of hydrometallurgical process.We have been working on the bioaccumulation of nuclear fuel elements by various microorganisms and biosubstances from several angles.In a uranium deposit, it can be presumed that some micro-organisms having a high accumulating ability for uranium, and different species of microorganisms having an ability to leach uranium from ore may exist in mine soil and aqueous systems. It would, therefore, be useful to find further microorganisms having an enhanced ability to accumulate uranium from uranium deposits.To screen microorganisms isolated from uranium deposits and peculiar natural environments in North America and Japan for maximal accumulation of uranium, handreds of microorganisms were examined. Some microorganisms can accumulate about 600 mg (5 mEq) of uranium per gram of microbial cells within 1h. The uranium accumulating capacity of the cells is twice greater than that of commercially available chelating agents (2-3mEq/g adsorbent).We attempted to recover uranium form uranium refining waste water by using new microorganisms immobilized in polyacrylamide. As a result, these immobilized cells can recover trace amounts of uranium from uranium waste water with high efficiency. These strains have also a high accumulating ability for thorium. Thus, these new microorganisms isolated from uranium deposits and peculiar natural environments can be used as an adsorbing agent for the removal of nuclear elements that may be present in metallurgical effluents, mine tailings and other waste sources.