Separation of neptunium and plutonium with neutral phosphorus ligands: A theoretical perspective

Abstract

Effective treatment of the transuranic neptunium and plutonium from nuclear waste is of great importance and remains a challenge for developing advanced nuclear fuel cycles. Currently, novel ligands for efficient separation of actinides need to be designed urgently. Neutral extractants containing phosphorus have shown great potential for actinides separation. In this paper, we systematically explored the extraction and separation performances of neptunium(IV,V,VI) and plutonium(IV) by three phosphorus derivatives, di(1-methyl-heptyl) methyl phosphonate (P350), tri-iso-amyl phosphate (TiAP), and tributyl phosphate (TBP) by density functional theory (DFT). The outcomes showed that these neutral phosphorus reagents act as monodentate ligands through the PO group for all the extraction complexes. According to bonding nature analysis, the P350 ligand has the strongest complexing ability to the studied actinide cations. In addition, these ligands show a preference to coordination with Pu4+ and NpO22+ over Np4+ and NpO2+, respectively. As expected, the thermodynamic analysis demonstrated the potential application of these neutral extractants in Np and Pu separation, among which the P350 ligand is more promising than TBP and TiAP in acid solution system. This work can help to further understand the separation mechanism of Np/Pu with neutral phosphorus reagents and provide insight into the development of highly efficient extractants in recovery of Np and Pu.