Metastable Phase Equilibrium in the Aqueous Quaternary System LiCl + Li2SO4 + Li2B4O7 + H2O at 273 K

Abstract

The metastable phase equilibrium in the quaternary system LiCl + Li2SO4 + Li2B4O7 + H2O was studied at T = 273 K using an isothermal evaporation method. The solubilities, densities, and pH values were determined experimentally. The crystalloid forms of the solid phase were determined using chemical analysis and an X-ray diffraction method. On the basis of the experimental data, the metastable phase diagram, water diagram, pH value diagram, and density diagram were plotted. The experimental results show that this system is of a simple eutectic type; no double salt or solid solution formed at the investigated temperature. The phase diagram consists of one invariant point, three univariant curves, and three crystallization regions. The three crystallization regions correspond to salts LiCl·H2O, Li2SO4·H2O, and LiBO2·8H2O. The salt LiBO2·8H2O has the largest crystallization field, whereas the salt LiCl·H2O has the smallest crystallization field. The salt LiCl has a strong salting-out effect on the salt Li2SO4·H2O. Comparisons between the metastable and stable phase diagrams at different temperatures show that the crystallization form of lithium borate has changed. In the stable phase diagrams at T = (298 and 288) K, the crystallization form of lithium borate is Li2B4O7·3H2O, while in the metastable phase diagram at T = 273 K, the crystallization form of lithium borate is LiBO2·8H2O.