The unusual extraction behavior of americium(III) and dioxouranium(VI) from picric acid medium using neutral oxodonors II. A thermodynamic study

The role of temperature on the distribution of Am³⁺ and UO₂ ²⁺ was investigated in the extraction systems involving TBP and DOSO as the neutral oxodonors and picrate as the organophilic counter anion. The inner-sphere water molecules and their substitution by the oxodonor molecules appeared to influence the extraction constants of these metal ions. The conditional extraction constants for Am³⁺ were found to be larger (about 3 order of magnitude) than those for UO₂ ²⁺. From the thermodynamics data it appeared that both TBP as well as DOSO bind Am³⁺ ion through outer-sphere coordination. In presence of 1M NaCl, though the interaction with TBP remains unaltered DOSO tend to form an inner-sphere complex. On the other hand, UO₂ ²⁺ forms inner-sphere complexes with DOSO and outer-sphere complex with TBP in the absence of salt. In the presence of 1M NaCl, both TBP and DOSO form inner-sphere complexes. The effect of ionic strength on metal ion extraction was also investigated. For Part I see Ref. 9.