Thermodynamic representation of the NaCl + Na 2SO 4 + H 2O system with electrolyte NRTL model

Abstract

A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H 2O binary, the Na 2SO 4 + H 2O binary and the NaCl + Na 2SO 4 + H 2O ternary. The NRTL binary parameters for pairs H 2O–(Na +, Cl −) and H 2O–(Na +, SO 4 2−), and the aqueous phase infinite dilution heat capacity parameters for ions Cl − and SO 4 2− are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H 2O binary and the Na 2SO 4 + H 2O 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·2H 2O (s), Na 2SO 4(s) and Na 2SO 4·10H 2O (s) are obtained by fitting experimental data on solubilities of NaCl and Na 2SO 4 in water. The NRTL binary parameters for the (Na +, Cl −)–(Na +, SO 4 2−) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na 2SO 4 + H 2O ternary.