Stable phase equilibrium of the quaternary system NaCl-MgCl2-NH4Cl-H2O at 348.15 K and its application in industry

Abstract Based on the requirement of the new technology to achieve comprehensive utilization of sodium and magnesium resources by using the mother solution from the preparation of potassium salt as raw material, the phase equilibrium data of the quaternary system NH4Cl-MgCl2-NaCl-H2O as well as its ternary subsystems MgCl2-NH4Cl-H2O and NaCl-NH4Cl-H2O were investigated by an isothermal equilibrium method under atmospheric pressure at 348.15 K, and the dry-salt phase diagram and water-phase diagram were drawn. Two invariant points and four crystallization fields including two single salts NH4Cl and NaCl, one hydrate salt MgCl2·6H2O, and one double salt MgCl2·NH4Cl·6H2O were determined in this quaternary system. Combining our results with available experimental data in the literature, an optimized process to produce ammonium carnallite and NaCl was proposed. Using the Pitzer electrolyte solution model, the experimental results were regressed and calculated. The calculated values agree well with the experimental values.