Phosphate addition to uranium-contaminated subsurface environments is a promising approach for in situ remediation that promotes the formation of sparingly soluble uranyl-phosphate solids. In the presence of calcium at concentrations commonly observed in groundwater, the solid calcium autunite [Ca(UO2)2(PO4)2] might form, and this solid is less soluble than chernikovite [H3OUO2PO4�3H2O] or uranyl orthophosphate [(UO2)3(PO4)2�4H2O]. However, calcium phosphate solids can also precipitate under specific conditions, and dissolved uranium concentrations may then be controlled by uranium adsorption to these solids. At pH 7.5, some form of amorphous calcium phosphate precipitated while calcium autunite-like solids precipitated at pH 4 and 6. An integrated approach combining aqueous phase analysis (ICP-MS, TOC), solids characterization (XRD, SEM-EDS, EXAFS, LIFS), and equilibrium modeling was used to identify the dominant mode of uranium uptake and to distinguish the exact contributions of adsorption versus precipitation. The results can aid in the design of effective in-situ remediation strategies.

Integrated approach to study phosphate-based uranium immobilization from contaminated subsurface environments in the presence of calcium

245th National Meeting (2013)

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