Supersaturation Phase Regions of the Ternary Systems KCl–CaCl2–H2O and KCl–MgCl2–H2O at 273.2 K during Isothermal Evaporation

Abstract This article presents minor improvements to the traditional experimental method used for obtaining the metastable phase diagram of a ternary water–salt system during isothermal evaporation. Using two ternary systems—namely KCl–CaCl2–H2O and KCl–MgCl2–H2O at 273.2 K—as examples, experiments were conducted with the improved method. The results showed that because the liquid phase was supersaturated, the two-salt cosaturation point in the stable phase equilibrium diagram became a two-salt cosaturation curve in the supersaturation phase diagram when using the improved method. By combining the stable phase diagram with the supersaturation phase diagram obtained using the improved method, the phase-correlation diagram was constructed and the isothermal evaporation–induced supersaturation phase regions of the two ternary systems were obtained. Thus, the supersaturation limit of the isothermal evaporation process was determined. Comparative experiments using the traditional metastable phase diagram method demonstrated that the randomly obtained metastable solubility curve lies within the supersaturation phase region determined using the improved method. In addition, the density and refractive index of each supersaturated liquid-phase point obtained using the improved method in the two ternary systems were determined. The characteristic coefficients of the corresponding empirical formulas used to calculate the density and refractive index were fitted. The calculated values agreed with the measured values.