Reductive Immobilization of U(VI) in Fe(III) Oxide-Reducing Subsurface Sediments: Analysis of Coupled Microbial-Geochemcial Processes in Experimental Reactive Transport Systems. Report for November 14, 2002-June 14, 2004.
Roden, E. E. ; Urrutia, M. M. ; Barnett, M. O. ; Lange, C. R.
The overall objective of our research is to address the questions listed above through laboratory-based batch and reactive transport experiments with natural Fe(III) oxide-bearing subsurface materials and a representative pure culture dissimilatory metal-reducing bacteria (DMRB). A unique feature of our research is that we are using levels of total uranium (ca. 10(sup -6) to 10(sup -4) mol per dm(sup 3) bulk volume) and aqueous/solid-phase ratios ((le) ca. 10(sup -3) mol U per kg sediment) which are much closer to those present in contaminated subsurface environments compared to levels employed in previous experimental studies of microbial U(VI) reduction. The goal is to develop a more realistic picture of the dynamics of U(VI) reduction and its interaction with Fe(III) oxide reduction in subsurface sedimentary environments. In doing so, our studies will provide benchmark information on process dynamics that will be useful for scaling up (e.g. through the use of field-scale reactive transport models) to in situ treatment scenarios. In addition, the experimental methodologies and modeling strategies developed for the project may applicable to the evaluation of in situ remediation technologies for other redox-sensitive metal-radionuclide contaminants such as Cr(VI) and Tc(VII). Numerical simulations are being developed hand-in-hand with the experimental work to aid in the interpretation of the observed dynamics of U(VI) behavior, and to contribute to the development of a predictive framework for assessing in situ metal-radionuclide remediation strategies driven by the activity of DMRB.
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