Solubility determination and thermodynamic modeling in the quaternary system Li2SO4 – LiBO2 – Li2B4O7 – H2O at T = 308.15 K and p = 0.1 MPa

Abstract

The solubilities, refractive indices and pH values in the systems LiBO2 – Li2B4O7 – H2O and Li2SO4 – LiBO2 – Li2B4O7 – H2O at 308.15 K were studied by isothermal dissolution equilibrium method. The phase diagram of the ternary system has two single salt crystallization regions of LiBO2·8H2O and Li2B4O7·3H2O, one invariant point and two univariant solubility curves. The dry-salt diagram of the quaternary system is composed of three single salt crystallization regions for Li2SO4·H2O, LiBO2·8H2O and Li2B4O7·3H2O, three univariant solubility curves and one invariant point. The physicochemical properties in the two systems change regularly with the concentration of lithium metaborate of equilibrium solution changing. Combining Pitzer binary parameters obtained in the literatures, the lacking Pitzer mixing parameters in the quaternary system were fitted with the solubilities. The deviation between the calculated solubilities and experimental data in the quaternary system shows that the assumption of only two boron species in the solution is not very accurate, but the calculated results with the assumption can still describe the experimental values.