Use of a Unified Model with TBP Dilution for Describing the Extraction of Nitric Acid and Hexavalent Actinide Nitrates in Multicomponent Nitrate Systems

A unified model based on published data and authors’ experimental results was suggested for describing the extraction of An(VI) (An = U, Np, Pu, Am) from HNO3 solutions into TBP solutions of various concentrations. Parallel occurrence of several extraction reactions and of nonstoichiometric physicochemical interaction of the components is assumed. The calculated parameters of the dependence of the concentration equilibrium constants on the total TBP concentration allowed expansion of the range of extractant concentrations described by the model (from 2.7 to 100%) and reduction of the uncertainty in calculation of the HNO3 and An(VI) distribution ratios. The parameter of apparent hydration of nitrate salt cations in the aqueous phase was used for describing the salting-out effect of these salts.