Metastable phase equilibria for the ternary aqueous system of lithium sulfate and potassium sulfate at T = 308.15 K: Experimental data and prediction using Pitzer model

Abstract

The metastable solubilities and the physicochemical properties including density, refractive index, pH and conductivity in the ternary system (Li2SO4 + K2SO4 + H2O) at T = 308.15 K were determined experimentally using the isothermal evaporation method, and the metastable phase diagram and the physicochemical properties versus composition diagram were plotted. In the metastable phase diagram, there are two invariant points, three univariant curves and three crystallization regions corresponding to lithium sulfate monohydrate (Li2SO4 · H2O), double salt (K2SO4 · Li2SO4) and arcanite (K2SO4). It was found that the double salt of K2SO4·Li2SO4 belongs to the incongruent double salt, and the hydrate of Li2SO4 · H2O belongs to hydrate type I. On the basis of Pitzer model of the electrolyte solution theory, the mixing-ion parameter of θLi,K, \({\Psi _{Li,K,S{O_4}}}\) and the metastable equilibrium constants of the solid phases K2SO4, Li2SO4 · K2SO4 and Li2-SO4 · H2O at 308.15 K were obtained for the first time. The calculated metastable solubility data for this ternary system at 308.15 K agree well with the experimental values, and this result indicates that the mixing-ion parameters and the metastable equilibrium constants obtained in this work are reliable.