Exploring novel functionality for efficient extraction of UO22+ and Th4+in ionic liquid: Mechanism, speciation, selectivity, stability and stripping

Abstract

Novel ligand functionality, 5-bromo-N1, N3-bis(4,6-dimethylpyridin-2-yl)isophthalamide, was explored for highly efficient and selective separation of UO22+ and Th4+ in pyridinium based ionic liquid. The comprehensive investigation revealed that, both in ionic liquid as well as in molecular diluents the extraction predominantly proceeded via ‘solvation’ mechanism. However, the species involved in extraction were UO2(NO3)2, L and Th(NO3)4, L in ionic liquid, while UO2(NO3)2, 2 L and Th(NO3)4, 3 L in molecular diluent. The highly viscous ionic liquid resulted the mass transfer slower during extraction. In ionic liquid based system, the extraction processes were endothermic, spontaneous and entropy driven. Ionic liquid based solvent systems exhibited high radiation stability, which was attributed to the formation of resonance-stabilized aromatic cation as well as the restricted movement of radicals in viscous ionic liquid. The aqueous solution of sodium carbonate was found to be effective for the stripping of UO22+, while oxalic acid solution was found to be effective for Th4+. The solvent systems were used for processing of simulated high level waste solutions of a Research Reactor (RR) and Fast Breeder Reactor (FBR) origin.