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

摘要

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 center dot H2O), double salt (K2SO4 center dot Li2SO4) and arcanite (K2SO4). It was found that the double salt of K2SO4 center dot Li2SO4 belongs to the incongruent double salt, and the hydrate of Li2SO4 center dot H2O belongs to hydrate type I. On the basis of Pitzer model of the electrolyte solution theory, the mixing-ion parameter of theta(Li,K), Psi(Li,K,SO4) and the metastable equilibrium constants of the solid phases K2SO4, Li2SO4 center dot K2SO4 and Li2SO4 center dot 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.