Phase equilibrium of the quaternary system K2SO4–MgSO4–(NH4)2SO4–H2O at 25 °C

The solubilities of the ternary system MgSO4–(NH4)2SO4–H2O and the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 0 °C were measured, and the phase diagrams of these two systems were plotted. On the basis of the phase diagrams obtained, we analyzed each saturation point and crystalline region. It indicated that ammonium sulfate as the salting-out agent can form double salt MgSO4·(NH4)2SO4·6H2O with magnesium sulfate, realizing better separation of sodium sulfate and magnesium sulfate. On the basis of the Pitzer model of electrolyte solution theory, the ionic strength function was introduced to express the interaction parameters between two kinds of electrolyte at 0 °C. The interaction parameters were regressed from the experimental data of the ternary systems, and the solubilities of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 0 °C were calculated. The results showed that the calculated values were well consistent with experimental results.