Measurement and Thermodynamic Modeling Study on the Solid and Liquid Equilibrium of Ternary System NaBr–CaBr2–H2O at 288.15 K

Abstract

The solubilities and refractive indices of the NaBr–CaBr2–H2O system at 288.15 K were determined using the isothermal equilibrium solution method. The phase diagram and refractive index diagram were drawn for this system at 288.15 K. The system belongs to the hydrate II type. The phase diagram is comprised of two invariant solubility points, three univariant solubility curves, and three areas of crystallization: NaBr·2H2O, NaBr and CaBr2·6H2O. Using the temperature-dependent formulas from the literature, the Pitzer parameters and the solubility product constants (ln Ksp) of NaBr·2H2O and NaBr were determined. Applying the Pitzer and Harvie–Weare (HW) model, the solubility product constant of CaBr2·6H2O was fit with the solubilities in this research work, and then, the mean activity coefficients of sodium bromide and calcium bromide and the solubilities for the ternary system at 288.15 K were demonstrated. Comparisons between the calculated and measured solubilities show that the predicted data have good accordance with the experimental results.