HR: 08:00h
AN: B21C-01    [Abstracts]
TI: Elucidating Geochemical and Biogeochemical U(VI) Reduction Via Soil Sterilization at Oak Ridge, Tennessee
AU: * Bank, T L
EM: banktl@ornl.gov
AF: Environmental Sciences Division, Oak Ridge National Lab PO Box 2008 , Oak Ridge, TN 37831-6038
AU: Jardine, P M
B21C-01 AF: Environmental Sciences Division, Oak Ridge National Lab PO Box 2008 , Oak Ridge, TN 37831-6038
AU: Phelps, T J
B21C-01 AF: Environmental Sciences Division, Oak Ridge National Lab PO Box 2008 , Oak Ridge, TN 37831-6038
AU: Ginder-Vogel, M A
B21C-01 AF: Dept. of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
AU: Fendorf, S E
B21C-01 AF: Dept. of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
AU: Baldwin, M E
B21C-01 AF: 3Nuclear Science and Technology Division, Oak Ridge National Lab PO Box 2008 , Oak Ridge, TN 37831-6227
AB: The adsorption and reduction of U(VI) onto sterilized and nonsterilized soil from the Oak Ridge Reservation was studied to distinguish biogeochemical versus geochemical effects on metal reduction. The Oak Ridge soil under investigation is a saprolite sequence of interbedded weathered shale and limestone obtained at the capillary fringe with a pH near 7.6. Experiments were conducted on unaltered soils as well as subsamples of the soil that were pre-treated to remove free oxides and/or organic matter. Soils were sterilized by either steam sterilization at 121⁰C or by γ-irradiation using a Cobalt-60 source with a γ-ray dosage of 20kGy. Sterile and nonsterile U(VI) batch experiments were completed aerobically over a reaction time of 400 hours. The reactions were buffered using 25mM HEPES and NaHCO₃. Initial U(VI) concentrations ranged from 0.5 to 10 ppm. The effects of sterilization on bacterial population, soil mineralogy, pH, ζ-potential, cation exchange capacity, redox potential, and soil organic matter (SOM) were identified. Sterilization by irradiation was >99.99% efficient and steam sterilization was approximately 99% efficient. Major mineralogy, soil pH, and clay mineral ζ-potential were unaffected by the sterilization techniques. The cation exchange capacity of the irradiated soils decreased from 40 to 30 cmol_c/kg. Sterilization by irradiation caused some degradation of the SOM, as determined by UV-VIS, however the results were practically insignificant due to the small quantity of SOM in the Oak Ridge soil (<0.1%). The redox potential of the soil before and after sterilization is being tested. Results indicate that the removal of U(VI) from solution onto untreated soils was significantly increased in soil sterilized by γ-irradiation compared to nonsterilized soil and suggests that geochemical processes, rather than biogeochemical processes, controlled U(VI) sorption/reduction in these soils. Results of experiments completed using soils pre-treated with H₂O₂ to remove soil organic matter (SOM) indicate that SOM was not a major sorbent of U(VI). Batch experiments completed on soils that contained no free oxide minerals indicate that Fe and Mn oxides were an important control of U(VI) transformations in the studied soil. Future experiments will quantify the effects of Fe, SOM, and indigenous microorganisms on U(VI) sorption and reduction at Oak Ridge.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0418 Bioremediation
SC: Biogeosciences [B]
MN: Fall Meeting 2005