Microscopic mass transfer and its influence on microbial reduction of U(VI)
In contaminated subsurface sediments, U(VI) resides in both intergrain (where active water flow occurs) and intragrain domains (where static water resides). Dissimilatory metal reducing bacteria (DMRB) can reduce aqueous (intergrain) U(VI) to U(IV) under anoxic conditions yielding an insoluble precipitate [U(IV)O{sub 2}]. Intragrain U(VI) becomes bioavailable if it dissolves and diffuses to the intergrain domain, or if the DMRB release soluble reductants that can diffuse to, and react with intraparticle U(VI) precipitates. Microscopic and spectroscopic analyses of uranium-contaminated sediments from Hanford have revealed that U(VI) often exists as a precipitate within intragrain domains of sediment clasts. Intragrain U(VI) dissolves slowly into undersaturated pore water with kinetics limited by the mass transfer from intragrain domains to bulk solution. This research investigated the microscopic mass transfer process and its effects on the microbial reduction of intragrain U(VI). The research has used Hanford sediments, but the resulting understanding and models are relevant to the Oak Ridge FRC, where a critical issue is the long term diffusion of U(VI) from a fine-grained saprolite matrix that is physically inaccessible to DMRB. The objectives are: (1) characterize and develop numerical models to describe the microscopic mass transfer process in intragrain domains of Hanford sediment; (2) identify and characterize biogeochemical strategies used by DMRB to access intragrain U(VI) by representative dissimilatory reducing bacteria; and (3) evaluate the coupling of dissolution kinetics, uranyl speciation, mass transfer, and microbial activities in the microbial reduction of intragrain U(VI) precipitates.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA; Yonsei University, Kongwon-Do, Korea; Argonne National Laboratory (ANL), Argonne, IL
- Sponsoring Organization:
- USDOE - Office of Science (SC)
- OSTI ID:
- 894569
- Report Number(s):
- CONF-ERSP2006-32
- Country of Publication:
- United States
- Language:
- English
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