Effect of temperature on the extraction of nitric acid and plutonium(IV) nitrate with 30 vol% tributyl phosphate (TBP)

The author's own and published data were evaluated for characterizing the effect of temperature on the distribution of nitric acid and plutonium(IV). The solutes were distributed between 30 vol% TBP in an aliphatic diluent and aqueous solutions containing nitric acid and zero to macro amounts of plutonium(IV) and uranyl nitrates. The temperature dependence of the distribution ratios is described with empirical model equations and examples of the dependence in the absence and presence of uranium(VI) are given. Taking infinite dilution of all solutes of the system as a standard state, the enthalpy change of the extraction reaction could be estimated as -17 kJ/mol for nitric acid, but no numerical estimate was possible for plutonium(IV)