A CHEMICAL-MODEL OF THE SOLVENT-EXTRACTION SYSTEM - NITRIC-ACID URANYL-NITRATE WATER TRI-N-BUTYL PHOSPHATE (TBP)-DILUENT

A mathematical model founded on the equilibrium constants expressions has been developed for the simultaneous extraction of nitric acid and uranyl nitrate with TBP in alkane diluents. The model uses chemical ac tivities of nitric acid and uranyl nitrate in the aqueous phase and th e stoichiometric concentrations of their TBP solvates in the organic p hase. The apparent formation constants of the species (TBP)(2), (TBP)( 2) . HNO3, TBP . HNO3 and UO2(NO)(3) . 2TBP, present in the organic ph ase, have been established. The model fits well the distribution resul ts over the whole concentration range of the extraction isotherms, and extractant concentrations 5-100% TBP. The starting data are the chemi cal activities of nitric acid and uranyl nitrate in the aqueous phase and their stoichiometric concentrations in the organic phase.