Screening of Uranium Absorbing Organisms and U-Bioprocessing

近年来，利用各种微生物从水体系中回收铀、钍等核燃料元素已成为湿法冶金技术的研究热点。我们从多个角度对各种微生物和生物物质对核燃料元件的生物积累进行了研究。在铀矿床中，可以假定在矿山土壤和水系统中可能存在一些对铀具有高富集能力的微生物，以及具有从矿石中浸出铀能力的不同种类的微生物。因此，寻找具有增强从铀矿床中积累铀的能力的进一步微生物将是有用的。为了筛选从北美和日本的铀矿床和特殊自然环境中分离的微生物，以最大限度地富集铀，对数百种微生物进行了检测。有些微生物每克微生物细胞可在1小时内积累约600毫克（5毫当量）的铀。细胞的铀积累能力是市售螯合剂（2-3mEq/g吸附剂）的两倍。利用聚丙烯酰胺固定化新型微生物从铀精炼废水中回收铀。因此，这些固定化细胞可以高效地从铀废水中回收微量铀。这些菌株对钍的积累能力也很高。因此，这些从铀矿床和特殊自然环境中分离出来的新微生物可用作吸附剂，用于去除可能存在于冶金废水、矿山尾矿和其他废物来源中的核元素。

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.