Experimental and theoretical study of lanthanides extraction by diglycolamides with branched chains

The PUREX process recovers most of the U and Pu, generating a large amount of high-level liquid waste (HLLW) that still contains many valuable elements. Liquid-liquid extraction is an important and efficient technology for treating HLLW from spent fuel reprocessing. Diglycolamides exhibit good selectivity for An(III) and Ln(III) and are a key focus in research on treating HLLW for available nuclides. In this study, two asymmetric diglycolamides with branched chains were synthesized: N,N′-dimethyl-N,N′-di(1-ethylhexyl) diglycolamide (DMDEHDGA, LI) and N,N′-dimethyl-N,N′-di(2-ethylhexyl) diglycolamide (DMD2EHDGA, LII). The extraction performance of Ln(III) was tested using these two ligands in 40/60 (v/v)% octanol/kerosene system. The structure-activity relationship of the ligands were analyzed by density functional theory (DFT). The structures of the ligands and the complexes of the ligands with Ln(III) were firstly optimised, and subsequently the differences between the two ligands were analysed using hard and soft acid-base (HSAB) theories and bond level analysis. The results show that the extraction performance of ligand LI with alkyl branch closer to the coordination center is better, and the complexes formed with Ln(III) are more stable.