Tetsu K. Tokunaga, Jiamin Wan, Jasquelin Pena, Stephen R. Sutton, and Matt Newville
Contact: Tetsu Tokunaga, 510/486-7176, TKTokunaga@lbl.gov
Research Objectives
Transport of uranium (U) in contaminated soils and sediments is of great concern. Environments affected by U contamination can be very challenging to understand because extreme disequilibrium is likely in such environments, especially during early stages of waste migration, when solutions are still often either highly acidic or highly alkaline. The impact of diffusion is especially important when large fractions of the subsurface have low hydraulic conductivities relative to a small fraction of interconnected preferential flow paths, and where hydraulic gradients are low. In this study, we are concerned with diffusion of U(VI) species, since these are commonly much more soluble and mobile than U(IV) species. Because U(VI) forms a variety of strongly pH-dependent solution complexes and surface complexes, its sorption--and thus its mobility--is strongly pH-dependent. Experiments are being conducted to test various models for predicting transient U(VI) diffusion.
To continue reading more about this project, view the 1-page pdf here.
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 Micro-XANES profiles at day 150, for U(VI) diffusing into Oak Ridge soil from initially acidic (left) and intially alkaline (right) solutions. Neutralizaiton of the alkaline system resulted in strong U(VI) sportion and retardation of the diffusion front. Model calculations are based on measureed porosities, aqueous-phase U(VI) diffusivities, and pH-dependent U(VI) sorption.
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