Thermodynamic representation of the NaCl + Na2SO4 + H2O system with electrolyte NRTL model

A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H2O binary, the Na2SO4 + H2O binary and the NaCl + Na2SO4 + H2O ternary. The NRTL binary parameters for pairs H2O–(Na+, Cl−) and H2O–(Na+, SO42−), and the aqueous phase infinite dilution heat capacity parameters for ions Cl− and SO42− are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H2O binary and the Na2SO4 + H2O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl(s), NaCl·2H2O(s), Na2SO4(s) and Na2SO4·10H2O(s) are obtained by fitting experimental data on solubilities of NaCl and Na2SO4 in water. The NRTL binary parameters for the (Na+, Cl−)–(Na+, SO42−) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na2SO4 + H2O ternary.

► An electrolyte NRTL thermodynamic model is developed for the NaCl + Na2SO4 + H2O ternary.
► The model requires a minimal number of pure component parameters and binary parameters.
► The model satisfactorily represents various thermodynamic and calorimetric properties.
► The model supports modeling of industrial systems involving brines.