Thermodynamic evaluation and optimization of the (Na2SO4 + K2SO4 + Na2S2O7 + K2S2O7) system

A complete, critical evaluation of all phase diagram and thermodynamic data was performed for all phases of the (Na2SO4 + K2SO4 + Na2S2O7 + K2S2O7) system and optimized model parameters were obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for modelling the liquid phase. The model evaluates first- and second-nearest-neighbour short-range ordering, where the cations (Na+ and K+) are assumed to mix on a cationic sublattice, while anions (SO42-,S2O72-) were assumed to mix on an anionic sublattice. The Compound Energy Formalism was used for modelling the solid solutions of (Na,K)2SO4 and (Na,K)2S2O7. The models can be used to predict the thermodynamic properties and phase equilibria in multicomponent heterogeneous systems. The experimental data from the literature were reproduced within experimental error limits.