Measurements and Predictions of Phase Equilibria of the Quinary System LiCl–NaCl–MgCl2–SrCl2–H2O and Its Quaternary Subsystem LiCl–MgCl2–SrCl2–H2O at 298.2 K

The underground brines in the Sichuan Basin of China are abundant in lithium, potassium, and strontium resources. In this work, measurements and predictions of phase equilibria on the LiCl–NaCl–MgCl2–SrCl2–H2O system and its subsystem LiCl–MgCl2–SrCl2–H2O at 298.2 K are presented to better utilize these liquid mineral resources. The solubility of salts in the saturated liquid phase of the two systems was measured by a chemical analysis. X-ray diffraction was used to identify the corresponding equilibrium solid phases for both systems. The results indicate that the simplified dry-base diagrams of this quinary system with the saturation of LiCl·H2O and MgCl2·6H2O both consist of one quinary invariant point, three isothermal solubility univariate curves, and three equilibrium solid phase crystallization zones. However, the dry-base diagram with the saturation of NaCl contains two quinary invariant points, six solubility univariate curves, and five solid phase crystallization zones. The phase diagram of quaternary system LiCl–MgCl2–SrCl2–H2O contains five crystalline regions, six solubility univariate curves, and two quaternary invariant points. Furthermore, using the Pitzer ion-interaction model, the solubility data of the two systems at 298.2 K are predicted based on reported ionic parameters. By comparing the experimental and calculated phase diagrams, it is found that the theoretical calculations are generally consistent with the experiments. This suggests that the calculations are reliable and accurate.