Thermodynamic modeling of aqueous Na+–K+–Mg2+–SO42− quaternary system

A comprehensive thermodynamic model based on the electrolyte non-random two-liquid (eNRTL) theory is developed for aqueous Na+–K+–Mg2+–SO42− quaternary system. The model accounts for the liquid phase nonideality by two binary interaction parameters per water-electrolyte and electrolyte–electrolyte pair. The temperature dependence of the binary interaction parameters is further correlated with three temperature coefficients associated with a Gibbs Helmholtz type expression. We obtain the binary interaction parameters for the H2O:(Mg2+ SO42−) pair, the (Na+ SO42−):(Mg2+ SO42−) pair and the (K+ SO42−):(Mg2+ SO42−) pair by regressing appropriate thermodynamic data. Integrated with other eNRTL binary interaction parameters in the literature, the eNRTL model accurately represents various thermodynamic properties of aqueous Na+–K+–Mg2+–SO42− quaternary system and its subsystems with temperatures up to 473.15 K and electrolyte concentrations up to saturation.