Extraction of tetravalent actinides and zirconium from nitric acid solutions with tributyl phosphate in diluent in the presence of uranyl nitrate and its mathematical description within the framework of the new approach

Abstract

To extend the previously suggested “chemical” model of the extraction of uranyl nitrate, nitric acid, and water, equations are suggested for describing the distribution of tetravalent actinides and zirconium between their aqueous nitric acid solutions and tributyl phosphate in diluent, including the systems containing uranyl nitrate. The aqueous phase equilibria taken into account include the hydrolysis of the cations, their complexation with nitrate ions to form triple-charged cations, which are the basic species of the elements in aqueous solutions, and dimerization of the cations with an increase in their concentration. In the presence of uranyl nitrate, it is also necessary to take into account so-called cation-cation interactions reflecting, most probably, the formation of oxo complexes or nitrate ion pairs.