Influence of some essential environmental factors on the reductive precipitation of uranium by sulfate reducing bacteria

• Published in: Chinese journal of geochemistry 2006, Vol.25 (B08), p.102-102
• Main Author: Zhengji YI Kaixuan TAN Aili TAN Zhenxun YU Yanshi XIE
• Format: Article
• Language: English
• Subjects: 地下水; 水文化学; 硫酸盐
• ISSN: 1000-9426; 1993-0364

The rapid kinetics of microbial U （Ⅵ） reduction and low solubility of uraninite make this process a promising strategy for removing uranium from groundwater and preventing its further migration. Nevertheless, some environmental factors that can influence U （Ⅵ） bioreduction, such as pH, the concentration of coexistent anions （sulfate, nitrate） and toxicity of heavy metal cations [Cu（ Ⅱ ）, Zn（ Ⅱ ）, etc], are not well-defined. In this paper, anaerobic batch experiments were performed to evaluate their effects on the enzymatic reduction of U （Ⅵ） by mixed cultures of sulfate reducing bacteria （SRB）. Kinetics investigations under variable pH conditions demonstrated that U （Ⅵ） was mainly reduced during the first 48 h. The yield of this bacterial reduction depended strongly on the pH and increased from 4.3% to 99.4% when the pH was raised from 2.0 to 6.0. No inhibition of U （Ⅵ） bioreduction occurred and the formation of uraninite was concurrent with the precipitation of metal sulfide （ZnS/CuS） at an initial concentration of 20 mg/L Zn （ Ⅱ ） or 10 mg/L Cu （ Ⅱ ）. But addition of 25 mg/L of Zn （ Ⅱ ） or 15 mg/L of Cu （ Ⅱ ） in the bacterial medium stopped U （Ⅵ） reduction due to their toxicities to SRB. Assessment tests for heavy metal toxicity implied that Cu （ Ⅱ ） toxicity probably proceeds by a mechanism different from that of Zn （Ⅱ ） toxicity. The Zn （ Ⅱ ）-induced inhibition of microbial activity can be eliminated, but Cu （ Ⅱ ） toxicity can generate permanent and irreversible damage to SRB. The sulfate concentration as high as 4000 mg/L did not appreciably interfere with U （Ⅵ） reduction, however, the anion level greater than 5000 mg/L significantly slowed the rate of U （Ⅵ） reduction. Moreover, it was found that U （Ⅵ） was not reduced by H2S produced during dissimilatory sulfate reduction.