Theoretical insights into the separation of Am(III) and Eu(III) using N,O-hybrid ligands based on difuran skeletons

Abstract

The separation of minor actinides and lanthanides is a challenging step in high-level nuclear waste disposal. Designing ligands with An(III)/Ln(III) efficient separation performance remains an important task for the treatment of accumulated radioactive waste and the recovery of minor actinides. In this article, we introduce eight symmetrical N,O-hybrid ligands formed from furan and N heterocycles, and systematically study the properties of these ligands and the coordination structures, bonding properties and thermodynamic behaviors of their Am(III)/Eu(III) complexes. All analyses of the geometric structure, Wiberg bond index, QTAIM, and NBO of the complexes indicate that the chemical bonds formed between Am(III) and the ligand have more covalent characteristics and are stronger than the bond between Eu(III) and the ligand. The thermodynamic results show that the eight extractants have good extraction ability and separation performance for Am(III) and Eu(III). This study shows that ligand rigidity and side-chain nitrogen atoms significantly influence bonding strength and separation efficiency for Am(III) and Eu(III), and that the ligand L¹ formed by non-rigid skeleton and pyridine side chain have the strongest extraction ability and the best separation performance. This study provides some theoretical support for the design of N,O-hybrid extractants for the effective separation of lanthanides and actinides.