Solubility measurement and thermodynamic modeling of solid-liquid equilibria in quaternary system NaCl–CaCl2–SrCl2–H2O at 323.15 K

Highlights: • The phase diagrams in systems NaCl–SrCl₂–H₂O and NaCl–CaCl₂–SrCl₂–H₂O were presented. • The Pitzer thermodynamic model of the two systems was constructed. • The calculated solubility data agree well with the experimental values. -- Abstract: The solid-liquid phase equilibria in the systems NaCl–SrCl₂–H₂O and NaCl–CaCl₂–SrCl₂–H₂O at 323.15 K were studied with the isothermal dissolution method. The solid-liquid equilibrium phase diagrams were constructed with the experimental results. A comparison of the diagrams of system NaCl–SrCl₂–H₂O from 288.15 to 373.15 K shows that area of strontium chloride salt region decreased obviously whereas the areas of NaCl almost invariant. The dry-salt diagram of the NaCl–CaCl₂–SrCl₂–H₂O system consists of four single-salt crystallization regions for NaCl, SrCl₂·6H₂O, SrCl₂·2H₂O and CaCl₂·2H₂O, five univariant solubility curves and two invariant points. Combining Pitzer binary parameters obtained in the literatures, the Pitzer mixing parameters θ_Na,Ca, θ_Na,Sr, θ_Ca,Sr, Ψ_Na,Ca,Cl, Ψ_Na,Sr,Cl and Ψ_Ca,Sr,Cl were fitted with the solubility data in this study and literatures. The model was then used for predicting the solubilities of the two systems. The experimental data are in accordance with the predicted results.