Wan Jiamin, Tokunaga Tetsu K, Brodie Eoin, Wang Zheming, Zheng Zuoping, Herman Don, Hazen Terry C, Firestone Mary K, Sutton Stephen R
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Environ Sci Technol. 2005 Aug 15;39(16):6162-9. doi: 10.1021/es048236g.
Nuclear weapons and fuel production have left many soils and sediments contaminated with toxic levels of uranium (U). Although previous short-term experiments on microbially mediated U(VI) reduction have supported the prospect of immobilizing the toxic metal through formation of insoluble U(IV) minerals, our longer-term (17 months) laboratory study showed that microbial reduction of U can be transient, even under sustained reducing conditions. Uranium was reduced during the first 80 days, but later (100-500 days) reoxidized and solubilized, even though a microbial community capable of reducing U(VI) was sustained. Microbial respiration caused increases in (bi)-carbonate concentrations and formation of very stable uranyl carbonate complexes, thereby increasing the thermodynamic favorability of U(IV) oxidation. We propose that kinetic limitations including restricted mass transfer allowed Fe-(III) and possibly Mn(IV) to persist as terminal electron acceptors (TEAs) for U reoxidation. These results show that in-situ U remediation by organic carbon-based reductive precipitation can be problematic in sediments and groundwaters with neutral to alkaline pH, where uranyl carbonates are most stable.
核武器及燃料生产致使许多土壤和沉积物被铀（U）污染，其含量达到有毒水平。尽管先前关于微生物介导的U(VI)还原的短期实验支持了通过形成不溶性U(IV)矿物来固定这种有毒金属的前景，但我们为期更长（17个月）的实验室研究表明，即使在持续的还原条件下，微生物对U的还原也可能是短暂的。在最初的80天内U被还原，但之后（100 - 500天）又重新氧化并溶解，即便能够还原U(VI)的微生物群落持续存在。微生物呼吸作用导致（生物）碳酸盐浓度增加，并形成非常稳定的碳酸铀酰络合物，从而增加了U(IV)氧化的热力学有利性。我们认为，包括传质受限在内的动力学限制使得Fe-(III)以及可能的Mn(IV)持续作为U再氧化的终端电子受体（TEA）。这些结果表明，在pH值为中性至碱性、碳酸铀酰最为稳定的沉积物和地下水中，通过基于有机碳的还原沉淀进行原位U修复可能会存在问题。
