Geomicrobiological in-situ containment of uranium in subsurface and its long-term stability

Uranium is a redox-sensitive element. While U （Ⅵ）, the oxidized form of uranium, is soluble and thus mobile in groundwater, U （Ⅳ） readily forms UO2（s） and is precipitated. Recent geomicrobiological researches demonstrated that dissimilatory metal reducing bacteria can effectively remove uranium fi＇om contaminated groundwater by reducing soluble U （Ⅵ） to relatively insoluble U （Ⅳ）. This novel form of microbial reduction of U （Ⅵ） is reported to be much faster than abiological reduction. The objective of this work was to investigate U （Ⅵ） reduction by indigenous bacteria in uranium-bearing black shale sediment and to determine whether microbially-precipitated uranium has long-term stability in subsurface. Through this study, fundamental information on the effects of microorganisms on the fate of redox-sensitive elements in natural settings will be provided. Soil and sediment samples were collected from uranium-bearing black shale in the Dukpyung area in Korea. Microbial inoculum was prepared from soil and sediment slurry supernatant. The reactors were purged with N2 ： CO2 gas （80 ; 20） to maintain anaerobic condition. Glucose, acetate or lactate was added as an electron donor at a final concentration of 5 mM.

Geomicrobiological in-situ containment of uranium in subsurface and its long-term stability