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

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 center dot H2O), double salt (Db, K2SO4 center dot Li2SO4) and arcanite (Ar, K2SO4). The hydrates in this system at both temperatures belong to a hydrate type I, and the double salt (K2SO4 center dot 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. (C) 2015 Elsevier B.V. All rights reserved.