Clay minerals are known for their high specific surface area and high site density, which make them ideal adsorbents for heavy metals. Bentonite, a commercially available clay (primarily composed of montmorillonite), has been proposed as buffer for long-term remediation of radioactive spent nuclear fuels (SNFs) in deep underground repositories. High specific surface area and high sorption density of montmorillonite combined with its high chemical stability make it an ideal buffer for confinement of radioactive wastes. Uranium is a major radioactive element generally found in SNFs and hence, studying uranium-montmorillonite interactions is important in understanding the fate and transport of uranium in these repositories. A range of studies on interaction of U(VI) with various clay minerals are available. However, under anoxic conditions that would initially prevail in the repository environment, U(IV) would be the most abundant species. Our understanding of adsorption behavior of U(IV) aqueous species onto natural minerals is very limited and, to the best of my knowledge, no study on interaction of aqueous U(IV) species with montmorillonite exists. Moreover, kaolinite (a 1:1 phyllosilicate) and palygorskite (with a structure different from usual layered structure of phyllosilicates) will also be important to consider as adsorbents in order to understand the role of different clay structures in adsorbing uranium. Adsorption of U(IV) onto pretreated montmorillonite, kaolinite and palygorskite is being studied under anoxic condition for a pH range of 2 to 7. Preliminary experiments with untreated clays indicate higher extents of adsorption for montmorillonite and palygorskite as compared to those for kaolinite for pH range 2 to 5. Various total U(IV) loadings will be employed to understand the effect of sorbate-sorbent ratio on the extent of adsorption. Due to the presence of basal ion exchange sites in clay minerals, adsorption trends U(IV) will also be controlled by concentration of competing Na<sup>+</sup> ions in system. Hence, adsorption of U(IV) will also be examined for multiple Na<sup>+</sup> loadings.

Trends of uranium (IV) adsorption onto clay minerals

2019 Spring National Meeting

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