Unfolding the extraction and coordination behavior of actinides by cyclohexyl phosphonate derivatives

The effect of branching in the carbon chain of phosphonate-based extractants on the selective extraction of actinides from fission products of spent nuclear fuel has been investigated experimentally and through quantum chemical calculations. Although phosphonate-based extractants have been known for a long time, only a few studies have reported the extraction of actinides using cyclohexyl phosphonates. In this study, two dialkylcyclohexyl phosphonate-based extractants, namely di- iso -butyl-cyclohexyl phosphonate (DiBCyHeP) and di- sec -butyl-cyclohexyl phosphonate (DsBCyHeP), were evaluated for the extraction of actinides. The difference in actinide extraction arising from variations in the alkyl chain substituents of the extractant molecules were further examined using density functional theory (DFT) computations to investigate the electronic structure and complexation behavior of the ligands with actinides such as U(VI) and Pu(IV). The extraction performance of DiBCyHeP and DsBCyHeP for actinides and fission products was compared with that of the commercially used PUREX solvent (1.1 M TBP/ n -DD) under identical conditions. The experimentally measured distribution ratios for actinides showed good agreement with the computed binding affinities of the corresponding metal-ligand complexes.