Measurements and Calculations of Solid-Liquid Equilibria in the Ternary System NaCl-NaBr-H2O at 323 K

The solubilities of salts and densities of saturated solutions in the NaCl-NaBr-H2O system at 323 K were determined with the method of isothermal solution saturation. The equilibrium solid phases in this system are solid solutions [Na(Cl,Br)]. The solid-liquid equilibrium phase diagram of the system has no invariant point. It has only one univariant curve and one crystallization region {saturated with solid solution Na(Cl,Br)}. Based on the above experimental results, the solid solution compositions fit well to a quadratic function of the equilibrium liquid composition. Based on the solubility data in the ternary systems NaCl-NaBr-H2O, the activity product (Q) of the solid solution was formulated with a polynomial of the solid solution composition. The solubilities salts in the ternary system at 323 K were calculated by Pitzer equations with the activity product of the solid solution. The results agree well with the experimental data.