Solid-liquid Phase Equilibria of the Quaternary System (NH₄Cl–MgCl₂–SrCl₂–H₂O) at 293.15 and 318.15 K

Solid-liquid phase equilibria and phase diagram of the quaternary system (NH₄Cl–MgCl₂–SrCl₂–H₂O) is very important for the separation of ammonium, magnesium and strontium salts from the salt lake brines. In this paper, the solid-liquid phase equilibria of the quaternary system (NH₄Cl–MgCl₂–SrCl₂–H₂O) at 293.15 and 318.15 K were determined with the method of isothermal dissolution equilibrium. Based on the experimental results, the phase diagrams of the system were plotted. In the phase diagrams of the system there are two invariant points, five univariant curves, and four salt crystal regions. The MgCl₂·6H₂O crystallization region occupies the smallest area, demonstrating that magnesium chloride has a strong desalting effect on the other salts. Comparison of isothermal sections of the quaternary system phase diagram at 293.15 and 318.15 K, it was observed that the crystallization zone of NH₄Cl·MgCl₂·6H₂O and SrCl₂·6H₂O expands with the increasing of temperature, but the crystallization zone of NH₄Cl shrinks, while the area of crystallization zone of MgCl₂·6H₂O was almost constant. It can be concluded that the temperature has a remarkable impact on phase behavior of this quaternary system.