Uranium is widely used as nuclear fuel for power generation throughout the world. Spent nuclear fuel, primarily composed of U(IV) oxide, is generated as waste in nuclear fission process. Storage of spent nuclear fuel in deep underground repositories under anoxic condition is a potential long-term management strategy. Montmorillonite, because of its low hydraulic conductivity, self-swelling capacity and generally high ion adsorption capacity, is being considered as a buffer material for packing between the canisters bearing spent nuclear fuel and the host rock in such repositories. While U(VI) adsorption to montmorillonite has been studied over a range of conditions, our understanding of U(IV) adsorption to montmorillonite is very limited.  At the conditions of many geologic repositories, U(IV) will be the dominant form of uranium that would interact with a montmorillonite barrier. In this study we focused on the mechanisms of U(IV) adsorption to montmorillonite as a function of pH and background sodium concentration. Montmorillonite is composed of two types of adsorption sites: (1) edge sites and (2) fixed charge basal sites.  The affinity of metal binding to edge sites is pH dependent, while the availability of binding to basal sites is affected by the ionic strength of the solution. We examined the extents of U(IV) adsorption for total U(IV) concentration of 15 to 25 nM, a montmorillonite loading of 1 g/L and sodium chloride concentrations of 10 or 100 mM. The montmorillonite was preequilibrated with anoxic deionized water to ensure removal of an interlayer trace amount of oxygen. A non-electrostatic surface complexation model was developed to interpret the adsorption results obtained under these conditions.

U(IV) adsorption onto montmorillonite in an anoxic environment

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.