A critical issue in the nuclear fuel cycle is the separation of actinides (An) from lanthanides (Ln) in used nuclear fuel. Minor actinide removal can help reduce long-term toxicity and storage time from thousands of years to just a few hundred years. An(III) and Ln(III) have similar ionic radii and thus their selective separation via solvent extraction presents problems. However, the presence of 5f electrons gives An(III) a somewhat “softer” character relative to Ln(III), and presents a strategy for separation, by using soft binding sites. Herein we present the synthesis and binding properties of amide and thioamide ligand frameworks with soft N-, S- and mixed donor binding sites for selective separation of An from Ln. These ligands are either: i) tripodal pyrazoles containing amide or thioamide groups or ii) dipicolinamide (DPA) and dithiopicolinamide derivatives. Preliminary studies by NMR, UV-VIS, fluorescence spectroscopy, and density functional theory indicate that DPA amide derivatives complex Ln(III) much stronger than their thioamide analogs, and that both thioamide and amide DPA analogs form complexes with UO2+ in the gas phase with 2:1 and 1:1 stoichiometries.

Investigation of Ln(III), An(III), and UO2+ binding properties of soft N- and S- donor site ligands

254th National Meeting (2017)

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