Solid–liquid metastable phase equilibria for the ternary system (Li2SO4 + K2SO4 + H2O) at 288.15 and 323.15 K, p = 0.1 MPa

• Metastable solubility in the ternary system at 288.15 and 308.15 K was determined.
• Physicochemical property of the metastable equilibria was measured.
• The congruent and incongruent double salt of K2SO4·Li2SO4 were found.
• Calculated values of density and refractive index agree well with experimental results.

Metastable solubilities and physicochemical properties including density and refractive index of the aqueous ternary system (Li2SO4 + K2SO4 + H2O) at 288.15 and 323.15 K and p = 0.1 MPa were determined with the isothermal evaporation method. On the basis of experimental data, the metastable phase diagrams and the diagram of physicochemical properties versus composition in the ternary system at 288.15 and 323.15 K were plotted. In the metastable phase diagrams of this ternary system at 288.15 and 323.15 K, in all there are two invariant points, three univariant solubility curves, and three metastable crystallization regions, corresponding to lithium sulfate monohydrate (Ls, Li2SO4·H2O), double salt (Db, K2SO4·Li2SO4) and arcanite (Ar, K2SO4). The hydrates in this system at both temperatures belong to a hydrate type I, and the double salt (K2SO4·Li2SO4) belongs to incongruent at 288.15 K and congruent double salt at 308.15 K, respectively. A comparison of the metastable phase diagrams at 288.15 and 323.15 K shows that the area of Ar is decreased obviously whereas the areas of Db and Ls are increased with the increasing of temperature, and no solid solutions were found. The density and refractive index in the metastable ternary system at 288.15 and 323.15 K change regularly with the mass fraction of potassium sulfate concentration and reach the extreme values at the invariant points. The densities and refractive indices were correlated with empirical equations, and the calculated values at two temperatures agree well with the experimental results.

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