With the rapid development of nuclear energy, the reprocessing of spent nuclear fuels has been attracting major concern owing to their chemical and radioactive toxicities, especially for minor actinides (MAs). It still remains a worldwide challenge to separate trivalent An(III) from Ln(III) due to their similar chemical properties. Therefore, designing efficient extractants at the molecular level is of great importance. Our group has synthesized a series of ligands, N,N'-diethyl-N,N'-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen, Figure 1) through a hard-soft donor combined strategy, which demonstrates excellent group actinide separation ability, the separation factor of Am(III)/Eu(III) with Et-Tol-DAPhen is about 67. Previous studies have reported that the separator factor of Am(III)/Eu(III) with N,N'-diethyl-N,N'-ditolyl-2,2'-bipyridine-6,6'-dicarboxamide (Et-Tol-BPyDA, Lb,) is about 18. In this work, three structurally similar ligands Et-Tol-DAPhen, Et-Tol-BPyDA and N,N'-diethyl-N,N'-ditolyl-pyridine-2,6-dicarboxamide (Et-Tol-BPyDA, Lc, Figure 1) were investigated and compared using relativistic density functional theory. The results reveal that the oxygen atoms of the ligands play a major role in the complexation. In contrast, it can be deduced that the nitrogen atoms of the three ligands play an important role for the An(III)/Ln(III) separation. Moreover, molecular orbital analysis indicates that ligand La is a better electron donor compared to ligands Lb and Lc. In addition, the M-O and M-N (M=Am, Eu) bonds have apparent ionic characters, and the Am-N bonds have more covalent character compared to the Eu-N bonds. Thermodynamic analyses suggest that the complexation reaction [M(NO3)(H2O)6]2+ + L + 2NO3- = [ML(NO3)3] + 6H2O is the most probable for the extraction. This work can provide useful information on achieving efficient actinide separation over the Ln(III) through changing the structural rigidity and hardness or softness of ligands.

Unraveling the nature of the Am(III)/Eu(III) separation with three structurally similar ligands by changing of bridging groups

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.