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

Abstract Electrolyte solutions containing ammonia are common in chemistry, biology, process engineering, cosmochemistry and geological processes. MgCl 2 –NH 4 Cl–NH 3 –H 2 O 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 NH 4 Cl–MgCl 2 –NH 3 –H 2 O system, within a wide range of ammonia from zero to saturated, and initial mass fraction of MgCl 2 , 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 NH 3 and NH 4 Cl, multiple ammoniations for Mg 2+ and association for NH 4 Cl–MgCl 2 –H 2 O, 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 NH 4 Cl solubilities in the quaternary of the NH 4 Cl–MgCl 2 –NH 3 –H 2 O system that agreed well with the experimental results.