Solid–liquid phase equilibria in the systems K2SO4–MSO4–H2O (M = Co, Ni, Cu) from ambient to enhanced temperatures

Reviewing the literature solubility isotherms in the ternary systems K2SO4–MSO4–H2O (M = Co, Ni, Cu, Zn) revealed a lack at ambient temperatures. The solid–liquid phase equilibria have been determined in the systems K2SO4–MSO4–H2O (M = Co, Ni, Cu) at T = 313 K. With increasing bivalent metal sulfate concentration, the solubility of potassium sulfate rises until the two-salt point is reached. Reciprocally, the solubility of the bivalent metal sulfate hydrates (CoSO4·7H2O, α-NiSO4·6H2O, CuSO4·5H2O) increases with rising potassium sulfate concentration. In all three systems the double salts of Tutton's type K2SO4·MSO4·6H2O (M = Co, Ni, Cu) are formed.