Solid and Liquid Phase Equilibrium in the Quinary System LiCl–Li2SO4–LiBO2–Li2B4O7–H2O 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)₅^2– 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.