Thermodynamics of synergistic extraction of hexavalent plutonium with HPMBP and neutral donors: Monodentate versus bidentate

Synergistic extraction of hexavalent plutonium was studied from HNO3 medium (0.05 M) with 1-phenyl, 3-methyl, 4-benzoyl, pyrazolone-5 (HPMBP) and different monodentate neutral donors viz. diphenyl sulphoxide (DPSO), tri-n-butyl phosphate (TBP) and tri-n-octyl phosphine oxide (TOPO) using benzene as a diluent. Thermodynamic parameters (Delta G, Delta H, Delta S) evaluated by performing the experiments at various fixed temperatures (288 K to 318 K) were compared with those reported previously for the bidentate neutral donors (DBDECMP, DHDECMP and CMPO). The net enthalpy changes were negative and comparable. The monodentate neutral donors, however, showed a larger decrease in the entropy values. Further, the negative values of enthalpy and entropy changes indicated that the organic adduct formation is an addition reaction as reported earlier for the bidentate donors.