Solid–Liquid Phase Equilibria and Boron Species Distribution in the Quaternary System LiCl–LiBO2–Li2B4O7–H2O at T = 323.15 K and P = 0.1 MPa

The solubilities of salts, refractive indices, and pH values of the equilibrium liquid phases in the quaternary system LiCl–LiBO2–Li2B4O7–H2O at 323.15 K were investigated by the isothermal dissolution method for the first time. The dry-salt diagram of the quaternary system consisted of one invariant point, three univariant curves and three crystallization fields corresponding to LiCl·H2O, LiBO2·2H2O, and Li2B4O7·3H2O. The solution refractive indices and pH values change regularly with the changing of concentration. Combining the equilibrium constants for different boron species, the distributions of six boron species in the mixed solution in the systems LiCl–LiBO2–H2O, LiBO2–Li2B4O7–H2O, and LiCl–Li2B4O7–LiBO2–H2O were calculated with the total boron concentration and pH values. The main boron species in the mixed solution of the quaternary system are B3O3(OH)4–, B4O5(OH)42–, B(OH)3, and B5O6(OH)4–. The boron species distributions are mainly affected by the pH values and the concentration of total boron and LiCl in the solution. The results of phase diagram and boron species distribution in the quaternary system can supply foundation data for separating lithium borate from brines.