Evaluating ion exchange resin efficiency and oxidative capacity for the separation of uranium(IV) and uranium(VI)

Under oxic conditions, recovery of U(VI) from three exchange resins (Bio-Rad AG？ 1x8 Poly-Prep？ prefilled columns, Bio-Rad AG？ 1x8 powder, and Dowex？ 1x8 powder) ranged from 72% to 100% depending on the dosed mass, eluent volume, and resin selected. Dowex？ 1x8 resin was the only resin found to provide 100% recovery of U(VI) with fewer than 5 bed volumes of eluent. Under anoxic conditions, all three resins oxidized U(IV) in aqueous solutions with relatively low U(IV) concentrations (<3x10-6 M). Resin-induced oxidation was observed visually using a leuco dye, safranin-o. Oxidants associated with the resin were irreversibly reduced by the addition of Ti(III). After anoxic resin pre-treatment, a series of U(IV)/U(VI) mixtures at micro-molar levels were prepared and separated using the Dowex？ 1x8 resin with 100% recovery of both U(IV) and U(VI) with no resin-induced changes in oxidation state.Currently available anion exchange resins with apparently identical physical properties were found to have significantly different recoveries for hexavalent uranium at micro-molar concentrations. A novel qualitative technique was developed to visually assess oxidative capacities of anion exchange resins under acidic anoxic conditions. A protocol was developed for pre-treatment and use of currently available anion exchange resins to achieve quantitative separation of U(IV) and U(VI) in aqueous solutions with low U(IV) concentrations. This method can be applied to future work to quantitatively assess dissolved U(IV) and U(VI) concentrations in both laboratory and field samples.Uranium exists naturally in the environment within host rocks, soils, groundwaters, and surface waters. Mobilization of naturally occurring uranium can lead to groundwater concentrations in excess of the drinking water standard of 1.3×10-7 M or 30 ppb [1,2]. More commonly, mining and processing of uranium ore, as well as nuclear weapons development, has resulted in the development of persistent groundwater plume