Selective separation of Am(III)/Eu(III) by effectively adjusting the aliphatic ring in bis-1,2,4-triazine ligands: A theoretical study

In recent years, bis-1,2,4-triazine ligands have been widely used in actinide separation processes for their good separation ability and stability in high acidity. However, the hard stripping of BTP, kinetics sluggish of BTBP, and inexhaustive separation of BTPhen are still issues to be improved. Here, we evaluated the effects of bis-1,2,4-triazine ligands containing 6-membered aliphatic rings L1-3 and bis-1,2,4-triazine ligands containing 5-membered aliphatic rings L4-6 on selective separation of Am(III)/Eu(III) to understand the structure-effect relationship of ligands (skeleton of pyridine L-1,L-4, bipyridine L-2,L-5, and phenanthroline L-3,L-6). Six bis-1,2,4-triazine ligand structures are optimized based on density function theory(DFT). Herein, complexations of L-2, L-3 L-5 L-6 with Am/Eu ions were investigated. The results show that all BTPs ligands preferentially bind to Am(III). The electronic structures of the [M(L)(2)(NO3)](2+) (M = Am, Eu) complex and the bonding properties between metal and ligand were investigated. The results suggest that phenanthroline containing six-membered aliphatic rings L-3 shows the best affinity for Am(III) and phenanthroline containing five-membered aliphatic rings L-6 show faster dynamics. The calculated thermodynamic and separation factors indicate that L-6 has the best selective separation of Am(III)/Eu(III). In conclusion, the skeleton of phenanthroline has the best extraction effect on Am(III), while the kinetics and separation effect can be improved by adjusting aliphatic rings.