Influence of environmental factors on reductive bioprecipitation of uranium by sulfate reducing bacteria |
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Authors: | Zheng-Ji Yi Kai-Xuan Tan Ai-Li Tan Zhen-Xun Yu Shi-Qiang Wang |
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Institution: | aState Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;bSchool of Nuclear Resources and Safety Engineering, University of South China, Hengyang, Hunan 421001, China;cGraduate School of the Chinese Academy of Sciences, Beijing 100039, China |
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Abstract: | Microbial reduction of soluble uranyl U (VI)] to insoluble uraninite by sulfate reducing bacteria (SRB) is a promising remediation strategy for uranium-contaminated groundwater. Effects of environmental factors, including pH and coexisting ions, on U (VI) bioreduction processes (UBP) remain unknown. Anaerobic batch experiments were performed to evaluate impact on UBP. Kinetic investigations with varied pH demonstrated that U (VI) was reduced mostly within 48 h. The bioprecipitation yields depended strongly on pH, increasing from 12.9% to 99.4% at pH 2.0 and 6.0, respectively. Sulfate concentration 4000 mg l−1 did not affect UBP; however, sulfate concentration 5000 mg l−1 significantly slowed UBP. Biogenic H2S produced during sulfate reduction was not directly involved in UBP. At 20 mg l−1 Zn or 10 mg l−1 Cu, no UBP inhibition was observed and uraninite was detected in metal sulfide precipitate. However, 25 mg l−1 Zn or 15 mg l−1 Cu stopped UBP completely. Cu toxicity mechanism probably differed from Zn. The ability to reduce U (VI) was lost permanently with exposure to 15 mg l−1 Cu, but not for Zn 25 mg l−1. No uraninite could be detected before nitrate removal, suggesting nitrate strongly inhibited UBP, which may possibly be related to denitrification intermediates controlling the solution redox potential. |
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Keywords: | Sulfate reducing bacteria (SRB) U (VI) bioreduction process (UBP) pH Oxyanion Heavy metal |
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