Plutonium(VI) / Pyrazolone / Synergism / Thermodynamics / DPSO / TBP / TOPO SummarySynergistic 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 (AG, AH, AS) evaluated by performing the experiments at various fixed temperatures (288 Κ 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. entropy changes counteracted the reaction. The negative entropy changes suggested the adduct formation reaction to be of addition type and not of substitution. It was considered worthwhile to evaluate these thermodynamic parameters by using different monodentate neutral donors of varying basicities with an objective of comparing the previously obtained data for Pu(VI) with HPMBP and various bidentate neutral donors. A comparison of the entropy changes in the two systems (monodentate and bidentate neutral donors) was considered to be important from the point of view of our earlier interpretation of the bidentates behaving as monodentates. Further, it was thought interesting to compare the behaviour of Pu(VI) vs. that of U(VI) with HPMBP and monodentate neutral donors reported earlier from our laboratory [7].

SummaryExtraction of Th(IV) and U(VI) using PEG-2000/(NH

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Synergism / Am(ni) / HTTA / DHDECMP / TBP / ThermodynamicsSuininary Synergistic extraction of Ani(in) was studied with HTTA in combination with bifunctional (DHDECMP) and mono-functional (TBP) neutral donors in benzene medium at various fixed temperatures. The equilibrium constant (log K^) for the organic phase synergistic reaction with DHDECMP was found to be higher by about two Orders of magnitude as compared to that with TBP, in spite of their comparable basicities. This indicated the bi-functional behaviour of DHDECMP in contrast to the previous studies reported for Pu(VI) where DHDECMP was observed to behave as a mono-fiinctional donor. Thermodynamic Parameter viz. high + ve AS with DHDECMP compared to that with TBP supported this conclusion. However, the Ai/ values were comparable in the two cases and this was attributed to the expenditure of more energy for the release of larger number of water molecules by DHDECMP in comparison to that by TBP.

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Synergistic extraction of hexavalent plutonium was studied with HPMBP in combination with DBDECMP, DHDECMP or CMPO in benzene medium at various fixed temperatures. The equilibrium constants for the organic phase addition reaction (log Ks) were found to follow the trend in basicity of the neutral donors. Thermodynamic parameters were evaluated and these indicated that organic phase reaction is an addition and not a substitution reaction. Further, the bidentate donors act as monodentates.

Synergistic extraction of hexavalent uranium was studied using acidic extractants HTTA/HPMBP with two different bifunctional neutral donors, DHDECMP and CMPO, from HNO 3 medium at various fixed temperatures. The equilibrium constants for the organic phase addition reaction (log K s ) were correlated with the basicity (K h ) of the neutral donors. The data reported earlier for monofuctional neutral donors (DPSO, TBP, TOPO) were used for the comparison. A linear correlation between log K s and log K h was observed for U(VI)/HTTA/S (S = neutral donor) system. However, in U(VI)/HPMBP/S system, the observed log K s values for bifunctional neutral donors were much lower than those expected from linear correlation. This was attributed to the different mechanisms operative in the synergistic extraction i.e. substitution in the former vs. addition in the latter. These conclusions are also supported by the thermodynamic data obtained in the present studies. Nevertheless, it is seen that bifunctional neutral donors act only as monofunctional with both HTTA and HPMBP.