Highly efficient separation of Np(IV) with three Benzene-centered tripodal diglycolamides: solvent extraction and supported liquid membrane transport studies

The separation of neptunium from high level liquid waste (HLLW) is a challenging task. The variable oxidation state of neptunium and the autocatalytic generation of nitrous acid complicate its extraction into the PUREX (Plutonium Uranium Redox Extraction) solvent. Here, three benzene centered multiple diglycolamide (DGA) ligands were explored for the liquid-liquid extraction and transport study of Np(IV) across a PTFE flat sheet supported liquid membrane. The ligands were dissolved in a 5 % isodecanol-95 % n-dodecane mixture. The transport studies were carried out keeping ²³⁹Np tracer in the feed phase (usually 3 M HNO₃) and the strip phase containing 0.5 M HNO₃ + 0.5 M oxalic acid mixture, while extraction studies were usually performed from 3 M HNO₃. Both the studies suggest that ligand L_I, in which the three DGA arms are connected to the 1,3,5-positions of the benzene ring via ethylene spacers, containing ethyl groups at the other positions, showed the highest extraction and transport of Np(IV). Ligand L_III, with a propyloxy ether between the ring and the DGA unit, displayed the lowest, while ligand L_II, having an amido ethylene linkage between the DGA moiety and the benzene ring, showed intermediate extraction and transport behavior. The transport data suggest a highly efficient transport of Np(IV) (about 85–95 %, 5 h) with all the ligands. The permeability coefficient, diffusion coefficients and stability were also determined.