Attenuation of Soluble Radionuclide Contaminants in Subsurface By Soil Fe-Minerals.

The U.S. Department of Energy (DOE) faces the challenge of cleaning up groundwater plumes contaminated by radioactive metals, e.g., uranium and technetium. The mobility of these metals in contaminated aquifers is governed, in part, by redox state of Fe minerals and microbial dynamics of subsurface. Therefore, there is a particular interest in understanding the reactivity of abiotic/biotic Fe(II) with  contaminants to sparingly soluble phases, e.g., Tc(IV)-oxides/sulfides and U(IV)-oxides, and long-term stability of the (bio)reduced contaminants and Fe(II) phases. Insights into these processes, hence, is essential to model movement of contaminants in subsurface. To comprehend the role of soil Fe-minerals, we investigated reactivity’s of (a) (bio)transformed  Fe-oxides and reference clays, which are ubiquitous in soils, and (b) anoxic sediments from  DOE sites, with contaminants under various (bio)geochemical conditions. In this talk, insights gained from these studies will be presented. Particular emphasis will be on the importance of application of ⁵⁷Fe-Mössbauer spectroscopy to identify and characterize Fe mineral phases in soil samples.