THERMODYNAMIC MODELING OF CONCENTRATED AQUEOUS-ELECTROLYTE AND NONAQUEOUS SYSTEMS

A new approach to computer simulation of activity coefficients of components in both aqueous and non-aqueous phases is proposed. Only values of standard thermodynamic properties of components are used as initial data. These are: the difference between standard free energy of formation of the pure substance in the solid state and in solution at infinite dilution in the standard state; the heat and temperature of salt melting; the change in heat capacity on fusion; and the average numbers of nearest neighbours of pure components. To describe non-ideality of solutions at high concentrations all kinds of species interactions are taken into account, e.g. free energy of salt-salt, salt-solvent and solvent-solvent interactions. The multicomponent systems are considered to be pseudobinary. An activity coefficient for each salt is estimated by integration of the Gibbs-Duhem equation. The solubility of salts and water activity in some binary and ternary systems are calculated in accordance with experimental data. The form of the equations for activity coefficients in the organic phase is the same as that in the aqueous phase. This method is applied to the calculation of the distribution ratio of caesium nitrate and nitric acid during extraction by an extractant based on a solution of cobalt dicarbolyde in nitrobenzene.