SOLVENT EXTRACTION OF THORIUM NITRATE WITH TRI-n-BUTYL PHOSPHATE. A CHEMICAL MODEL

ABSTRACT

The chemical model presented is founded on the prediction of all chemical reactions taking place in a solvent extraction system. Starting from equilibrium constant expressions of these chemical reactions the corresponding mathematical formulae for calculation of the concentrations of distributing species are derived. If the required chemical reactions in the organic phase are involved, the model fits the experimental data and enables the calculation of the concentrations of distributing species in the organic phase within the concentration range in which the distribution of reacting species was measured.

The model is used to describe the extraction of thorium nitrate with tri-n-butyl phosphate (TBP). It characterises the distribution data by formation of disolvate and trisolvate of thorium nitrate with TBP, in addition to the dimerization of TBP. The diluent induced variations of the extraction constants values have been correlated by means of the empirical solvent polarity parameter, E_T. The activity coefficients of TBP, not included in solvation of thorium nitrate, are also calculated.