Solid and Liquid Phase Equilibrium in the Quinary System LiCl–Li ₂ SO ₄ –LiBO ₂ –Li ₂ B ₄ O ₇ –H ₂ O at 323.15 K

The phase equilibrium of the quinary system LiCl–Li2SO4–LiBO2–Li2B4O7–H2O at 323.15 K was studied with an isothermal dissolution method. The dry-salt phase diagram of the quinary system consists of one invariant point saturated with LiCl·H2O, Li2B4O7·3H2O, and LiBO2·2H2O, three univariant curves, and three crystallization regions saturated with Li2SO4·H2O corresponding to LiCl·H2O, Li2B4O7·3H2O, and LiBO2·2H2O. The J(H2O), J(Li2SO4), refractive index, and pH value change gradually with the changing concentration. Combining the equilibrium constants for boron-containing species, the pH values, and concentration of total boron, the boron-containing species distributions in the mixed solution in the system were calculated. The concentrations of B3O3(OH)52– and B5O6(OH)4– are very low and can be neglected. The boron-containing species distributions are mainly affected by m(LiCl) in the solution but less by m(Li2SO4). The results of the phase diagram and boron-containing species distribution in the quinary system can provide fundamental thermodynamic data for the extraction of lithium borate from brines.