Uranium, a legacy contaminant at US DOE sites such as the ORIFC, can be mobile in the subsurface. The pore-scale response of uranium to pH and selected ligands in heterogeneous soil and mineral matrices was investigated through column experiments employing advective chemical gradients. The pH or concentrations of phosphate, bicarbonate, and acetate flowing through dedicated columns were increased while influent uranium (VI) concentration was held constant over time. Porewaters were analyzed from multilevel ports. Increased phosphate and pH reduced uranium transport while bicarbonate and acetate enhanced uranium release and decreased its accumulation in the matrix compared to a control column. X-ray fluorescence microprobe mapping and X-ray absorption spectroscopy characterized the uranium retained in the matrix phases. U(VI) occurred in all columns while U(IV) was also present in the phosphate, bicarbonate and pH columns. These findings will help us predict dissolved uranium attenuation in response to pH and ligand concentration gradients.

Investigation of uranium attenuation and release at column and pore scales in response to advective geochemical gradients

243rd National Meeting (2012)

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