Mineralogic Residence and Desorption Rates of Sorbed 90Sr in Contaminated Subsurface Sediments: Implications to Future Behavior and In-Ground Stability

90Sr desorption process will be quantified in coarse-textured Hanford sediments contaminated by different waste types and a reaction-based reactive transport model developed to forecast 90Sr concentration dynamics in Hanford's 100-N plume. Previous research has addressed 137Cs desorption from HLW-contaminated sediment providing results critical for HLW tank farm closure decisions. This renewal focuses on 90Sr with the objective of providing fundamental knowledge to predict future in-ground behavior as required for sound remedial decisions. Preliminary observations that suggest that 10-y sorbed 90Sr in coarse-textured sediment resides in the interiors of basaltic lithic fragments. This intraparticle retention defines a new conceptual model for 90Sr retardation that is tentatively attributed to internal domains of phyllosilicates formed from the weathering of basaltic glass. Research will characterize the spatial locations, composition, and reactivity of these intragrain phyllosilicate domains using spectroscopic, microscopic, and wet chemical methods. Intragrain porosity, diffusivity, and tortuosity will be estimated using emersion experiments coupled with particle imaging (using electron, X-ray, and NMR techniques). Desorption rates and extent will be measured from contaminated Hanford sediments of different waste impact in electrolytes that promote isotopic exchange, ion exchange, and/or dissolution. Desorption results will be interpreted with a geochemical-physical model that incorporates aqueous speciation, mass transfer, and other important factors. Batch and column experiments will be performed with sediments from Hanfords 100-N plume to quantify factors controlling long-term release rates and river stage effects. Newfound understanding and geochemical parameters will be incorporated into the FLOTRAN reactive transport code for simulation of 100-N plume dynamics