Adsorption Characteristics of Trivalent Rare Earths and Chemical Stability of a Silica-Based Macroporous TODGA Adsorbent in HNO3 Solution

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In order to separate trivalent minor actinides (Am and Cm) from high-level liquid waste generated in a nuclear fuel reprocessing process, a silica-based macroporous TODGA (N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide) adsorbent (TODGA/SiO2-P) was prepared. In this study, the adsorption characteristics of some trivalent rare earths (Y, Nd, and Eu), whose separation behaviors were similar to those of the minor actinides from HNO3 solution with the TODGA/SiO2-P adsorbent, and the chemical stability of the adsorbent against the HNO3 solution were evaluated experimentally. It was found that the adsorbent exhibited a quite strong adsorption especially for Y(III). The standard enthalpy change for the Y(III) adsorption was determined to be −2.5 kJ·mol−1 using the van’t Hoff equation, which indicates that the adsorption was an exothermic reaction. The results of chemical stability experiments showed that the adsorbent had relatively excellent properties in long-time contact with the HNO3 solution.