Thermodynamic description of the ternary systems of the core sulphate system Na2SO4–K2SO4–MgSO4–CaSO4

The ternary subsystems of the quaternary sulphate system Na2SO4–K2SO4–MgSO4–CaSO4 were thermodynamically assessed using the available experimental information on phase equilibria. The dataset containing all binary sub-systems, published earlier, was extended to describe phase equilibria of the four sub-ternary systems. Furthermore, a first dataset covering the entire quaternary system has been generated. In the absence of the experimental information on the high order systems the proposed dataset can be used for interpolative and predictive thermodynamic calculations. Ternary interaction parameters were embedded in the framework of the modified associate species model for the description of the liquid phase. The solubility between langbeinite compounds (K2Me2(SO4)3 with Me = Ca, Mg) was treated with a multi-sublattice model. The resulting new databank being compatible with the general oxide database is used for the representation of phase equilibria in the ternary subsystems. To validate the thermodynamic dataset, the calculated values of phase transition temperatures are compared with the experimental results of the selected compositions of the ternary systems obtained by differential thermal analysis (DTA). •Four ternary alkali-alkaline earth sulphate systems were thermodynamically assessed.•The langbeinite phase was introduced using a sub-lattice model.•Phase transition temperatures of the selected compositions were verified using DTA.•The Gibbs energy dataset was validated by comparing with our experiments and used for predictive calculations.•Calculated phase equilibria are in good agreement with the own experimental data and from the literature.