TOWARD AN ACCURATE MODEL OF METAL SORPTION IN SOILS

Radionuclide transport in soils and groundwaters is routinely evaluated in performance assessment (PA) using simplified conceptual models (e.g., K D method) to describe radionuclide sorption. However, the KD approach with linear and reversible sorption of metal cations is rarely observed in the field. This study aims to improve the accuracy of radionuclide migration predictions by developing a mechanistic model of metal sorption processes. Our research investigates the sorption mechanisms and partition coefficients for Ba2+ (analog for 226Ra2+) onto soil minerals, specifically iron oxides and clay phases. We employed a combination of isothermal sorption/desorption measurements, synchrotron spectroscopic analyses, and computer molecular modeling simulations to achieve our objectives. The research goals include evaluating and quantifying the critical mechanisms and geochemical parameters that control the retardation of radionuclides in near-field soils, predicting radionuclide K D values through atomistic simulations, and identifying general trends in metal plume length associated with field sites. Results from this work are anticipated to enhance our understanding and predictive capabilities regarding radionuclide migration at contaminated locations.