GEOCHEMICAL MODELING OF URANIUM IN-SITU RECOVERY (ISR) POST-MINING SITE CONDITIONS

In-situ recovery (ISR) uranium mine restoration is generally based upon a return of the site to pre-mining baseline conditions. Uranium ISR sites typically exhibit varying degrees of natural attenuation potential that may influence the degree of restoration required. Surface complexation modeling provides useful insight into the geochemical restoration potential of a mined aquifer, providing stakeholders with a better understanding of potential restoration requirements and challenges for specific pre- and post-mining geochemical conditions. This presentation will summarize findings from our 1-D uranium transport surface complexation modelling efforts for an existing ISR mine. Batch adsorption isotherm experiments were conducted using post-mining/pre-reclamation, and post-mining/post-reclamation soil core samples, site upgradient groundwater water, and completed using varying pH and uranium concentrations. Isotherm filtrates were analyzed by ICP-OES, and results used to determine soil attenuation capacity using a combination of PHREEQC for geochemical and transport calculations, and PEST for parameter fitting. A general composite, site-specific mineral assemblage approach was used the surface complexation estimates. Forward model runs were completed to predict the transport of uranium plumes during various mine restoration geochemical conditions.