Influence of Mass Transfer on Bioavailability and Kinetic Rate of Uranium(VI) Biotransformation
In contaminated subsurface sediments, U(VI) resides in both interparticle (where active water flow occurs) and intraparticle domains (where static water resides). Dissimilatory metal reducing bacteria (DMRB) can reduce aqueous (interparticle) U(VI) to U(IV) under anoxic conditions yielding an insoluble precipitate [U(IV)O{sub 2}]. Intraparticle U(VI) can only be reduced by DMRB if it dissolves and diffuses to the interparticle domain populated by microbiota, or if the DMRB release, or dispose of electron to soluble compounds that can diffuse to, and react with intraparticle U(VI) precipitates. At DOE Hanford site, recent characterization of U(VI) speciation and physical location in 30-year contaminated sediments demonstrated that U(VI) resides as a U(VI)-silicate microprecipitates in small fractures and cleavages within sediment particle grains exhibiting pore sizes of a few microns or less. The U(VI) microprecipitates dissolved slowly into undersaturated pore water, but the dissolution kinetics and diffusive rate of U(VI) transport from intraparticle regions was slow when compared to the reduction rate of aqueous U(VI) by DMRB. These results indicated that: (1) a majority of the sorbed U(VI) pool was not physically accessible to DMRB due to size restrictions of the grain porosity, and (2) the bioavailability and overall rates of microbial U(VI) reduction in the sediments could be limited by the mass transfer rates of U(VI) from intraparticle regions. This research is focused on the bioavailability and kinetic rates of microbial reduction of U(VI) associated with intraparticle regions. The understanding of the influence of mass transfer on microbial reduction of U(VI) is needed not only at the Hanford site, but also at Oak Ridge FRC, where a critical issue is the long term diffusion of U(VI) from fine-grained saprolite matrix that is physically inaccessible to DMRB. The objectives are: (1) Develop approaches to characterize microscopic properties of mass transfer processes. (2) Identify and characterize biogeochemical strategies for accessing intraparticle U(VI) by representative dissimilatory metal reducing bacteria. (3) Evaluate the influence of mass transfer on U(VI) bioavailability, microbiologic reduction rate and location. (4) Develop coupled kinetic models of the U(VI) dissolution, mass transfer processes, and microbially mediated U(VI) reduction.
- Research Organization:
- Pacific Northwest National Laboratory, Richland, WA
- Sponsoring Organization:
- USDOE Office of Science (SC)
- OSTI ID:
- 895387
- Report Number(s):
- CONF-NABIR2004-34; TRN: US0700454
- Resource Relation:
- Conference: Annual NABIR PI Meeting, March 15-17, 2004, Warrenton, VA
- Country of Publication:
- United States
- Language:
- English
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