Experiments and Prediction of Solid–Liquid Phase Equilibria in the Quinary System NaBr–KBr–MgBr2–SrBr2–H2O and Its Quaternary Subsystem NaBr–MgBr2–SrBr2–H2O at 308.2 K

To efficiently exploit and utilize bromine-rich brine resources of China, solid–liquid phase equilibria of the quinary system NaBr–KBr–MgBr2–SrBr2–H2O (saturated with KBr) and the quaternary system NaBr–MgBr2–SrBr2–H2O at 308.2 K were studied in detail by the isothermal dissolution equilibrium method. The dry salt phase diagram of the quinary system NaBr–KBr–MgBr2–SrBr2–H2O (saturated with KBr) includes one invariant point, three isothermal dissolution curves, and three crystallization regions (NaBr·2H2O, KBr·MgBr2·6H2O, and SrBr2·6H2O) under the condition of KBr saturation. And the crystallization region of KBr·MgBr2·6H2O is the smallest, so KBr·MgBr2·6H2O is difficult to crystallize and precipitate. Similarly, The dry salt phase diagram of the quaternary system NaBr–MgBr2–SrBr2–H2O is composed of two invariant points, five isothermal solubility curves, and four crystallization fields, which are hydrate salts NaBr·2H2O, MgBr2·6H2O, and SrBr2·6H2O and anhydrous simple salt NaBr. The crystallization region of MgBr2·6H2O is the smallest, the solubility of magnesium bromide is the largest, and it is difficult to crystallize and precipitate in this saturated solution. Furthermore, the mixing ion-interaction parameter ΨNa, Sr, Br of Pitzer’s model is fitted, which can be used for the subsequent prediction of phase equilibria containing strontium system. In addition, the solubilities of salts in the quinary system and the quaternary subsystem were theoretically predicted, and the experimental value was compared with the calculated value. The calculated value was in good agreement with the experimental value.