Solid–liquid phase equilibria in the system K2SO4–MgSO4–H2O at 318 K

The polythermal solubility diagram of the system K2SO4–MgSO4–H2O presents the formation of three double salts, picromerite, leonite, langbeinite appearing in this order with increasing temperature. In the temperature range between 314.15 K and 320.65 K, picromerite and leonite ought to coexist. The search in the literature revealed a lack of isothermal phase equilibrium data within this temperature range. Therefore, the solubility in the system K2SO4–MgSO4–H2O was determined in the whole concentration range at 318 K. The solid phases, epsomite, leonite, picromerite and arcanite occur with increasing potassium sulfate concentration. A two-salt point of leonite and picromerite is established at 0.618 molal K2SO4 and 3.030 molal MgSO4 at the temperature of investigation.