Utilizing Ionic Liquids as Bifunctional Reagents for the Ionothermal Synthesis of Uranyl Compounds

The extraction of actinides, specifically uranyl and other actinyl ions, from fission products is a critical aspect of spent nuclear fuel reprocessing. In this study, ionothermal syntheses were conducted to control the formation of uranyl (UO₂)²⁺ salt complexes generated by exposure to a selection of ionic liquids (ILs). The high-thermal stability and ligation potential of ILs were exploited in a multifaceted approach toward uranyl salt complexation by enabling ligation of the IL anionic component while simultaneously providing polar reaction media to promote speciation. Furthermore, an evaluation of uranyl complex templating by the IL cation revealed that small, heterocyclic cationic molecules resulted in more densely packed anionic clusters. The uranium source was also varied to determine the oxidizing effect of nitrate on the ILs and the propensity for nitrate and acetate byproduct formation. Uranyl triflate was found to be the optimal uranium source for the production of pure uranyl complexes. The degree to which nitrate oxidizes the ILs was investigated to determine what oxidation products form and subsequently coordinate to the uranyl ion. Finally, it was shown that a uranyl succinate framework can be synthesized in high yield from an IL that contains succinate as the anion.