Thermodynamic evaluation and optimization of the (NaNO3 + KNO3 + Na2SO4 + K2SO4) system

•Thermodynamic model for the (NaNO3 + KNO3 + Na2SO4 + K2SO4) system.•The Modified Quasichemical Model was used for the molten salt phase.•The Compound Energy Formalism was used for the solid solutions.

A complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the (NaNO3 + KNO3 + Na2SO4 + K2SO4) ternary reciprocal system, and optimised model parameters have been found. The model parameters obtained for the four binary common-ion subsystems (i.e. (NaNO3 + Na2SO4), (KNO3 + K2SO4), (NaNO3 + KNO3) and (Na2SO4 + K2SO4)) are used to predict thermodynamic properties and phase equilibria for the entire system. The Modified Quasichemical Model in the Quadruplet Approximation for short-range ordering was used for the molten salt phase, and the Compound Energy Formalism was used for the various solid solutions.