“Super moiety”-phosphoramidate in task-specific ionic liquids for effcient thorium separation through hybrid interaction

Abstract

Replacing conventional solvents by ionic liquids is a promising route to greener nuclear fuel cycles. Here, we report a unique multi-functional task-specific ionic liquid (TSIL) for the extraction and separation of trace thorium (Th). The phosphoramidate substituted butyl groups to imidazolium ionic liquid (PN-TSIL) shows superior extraction ability and selectivity (distribution rations of Th ~ 8302 and separation factor of Th to uranium (U) ~ 793 at 2 mol/L HNO3). For industial application purpose, an extraction chromatographic resin perpared by PN-TSIL (called PN-TSIL Resin) was made to develop a rapid, highly specific separation technique for simulative 229Th/233U separation process. Moreover, combination of spectroscopic investigations, quantum-mechanical calculations and thermodynamic parameters mearsurment, an unprecedented resolution picture of extraction process was delineated. The extraction ability and selectivity of thorium could be explained by the multiple binding sites though hybrid interactions (coordination and hydrogen bond) between thorium and PN-TSIL, leading to an entropy-driven extraction process. The understanding of solvent extraction mechanism in molecular scale will inspire new ways for TSIL design for nuclear fuel cycles.