Selective separation of thorium and uranyl in phases of different polarity using novel benzoxazole-based ligands: A DFT study

Abstract

The separation of thorium and uranium is an important guarantee for the fuel cycle of thorium-based molten salt reactors. Benzoxazole-based ligands have a wide range of applications and are also potential ligands for actinide separation. In this work, density functional theory (DFT) calculations were used to study the intrinsic properties of two ligands, 2,6-bis(benzo[d]oxazole-2-yl)pyridine (ligand a) and 1-(6-(4-acetylbenzo[d]oxazol-2-yl)pyridin-2-yl)ethan-1-one (ligand b), revealing the structural characteristics and complexation behavior of their complexes with Th4+/UO22+. Quantum theory of atoms in molecules (QTAIM) and extended transition state - natural orbitals for chemical valence (ETS-NOCV) analyses show that the ligands form classical coordination bonds with Th4+/UO22+, with M−Noz bonds stronger than M−Npy bonds and partial electron acceptance by carbonyl O. The thermodynamic properties were used to evaluate the separation performance of these ligands for Th4+/UO22+ in four solvents (water, 1-hexanol, n-octanol and n-dodecane), with La more suitable for back extraction process and Lb having stronger binding with Th4+/UO22+. This work provides valuable theoretical insights into Th4+/UO22+ separation based on benzoxazole.