Solubility of ammonium chloride in a MgCl2–NH4Cl–NH3–H2O system at 298 K: Experiments, modeling and prediction

Electrolyte solutions containing ammonia are common in chemistry, biology, process engineering, cosmochemistry and geological processes. MgCl2–NH4Cl–NH3–H2O is related to magnesium-resource utilization, and contains complex chemical equilibria, such as association, salvation and partial ionization. In this work, the solubility of ammonium chloride in the NH4Cl–MgCl2–NH3–H2O system, within a wide range of ammonia from zero to saturated, and initial mass fraction of MgCl2, up to 0.15, were determined experimentally. Meanwhile, a thermodynamic model for prediction was proposed by joining the physical and chemical contributions. We adapted Pitzer’s model with three parameters for the interaction of ion-ammonia to represent the physical contribution; the chemical equilibria of multiple hydrations for NH3 and NH4Cl, multiple ammoniations for Mg2+ and association for NH4Cl–MgCl2–H2O, using six chemical parameters provided the chemical contribution. All parameters were determined by the subsystems of binary and ternary SL equilibrium data. The model and parameters provided predictive results of NH4Cl solubilities in the quaternary of the NH4Cl–MgCl2–NH3–H2O system that agreed well with the experimental results.