Solid-Liquid Phase Equilibria and Boron Species Distribution in the Brine System Li2SO4-LiBO2-Li2B4O7-H2O at 323.15 K

The solubilities, refractive indices and pH values in the brine system Li2SO4-LiBO2-Li2B4O7-H2O at 323.15 K were obtained by isothermal dissolution method. The dry-salt phase diagram is composed of one invariant point, three univariant curves, and three crystallization regions of Li2SO4 center dot H2O, LiBO2 center dot 2H(2)O and Li2B4O7 center dot 3H(2)O. A comparison of the phase diagrams of this system at 288.15 K, 308.15 K and 323.15 K shows that area of Li2SO4 center dot H2O crystallization zone increases whereas the areas of crystallization zone of lithium metaborate salt and Li2B4O7 center dot 3H(2)O changed intricately with temperature increasing. The refractive indices and pH values in the system change regularly with the lithium metaborate concentration of equilibrium solution changing. The calculated refractive indices with empirical formula are in agreement with the experimental values. Combining the equilibrium constants for different boron species, the distributions of six boron species in the mixed solution in the system were calculated with total boron concentration and pH values. The main boron species in the mixed solution of the quaternary system are B(OH)(3), B(OH)(4)(-), B4O5(OH)(4)(2)- and B3O3(OH)(4)(-). The mole fractions of the four boron species are mainly affected by the concentration of boron concentration.