Solid–liquid phase equilibria in the aqueous ternary system Li2SO4 + LiBO2 + H2O at T = 288.15 and 298.15 K

The solubility data and the physicochemical properties including density, pH value and refractive index of the ternary system Li2SO4 + LiBO2 + H2O at T = 288.15 and 298.15 K were determined experimentally with the isothermal dissolution equilibrium method. Based on the experimental results, the phase diagrams and their corresponding physicochemical properties versus composition diagram in the system were plotted. The phase diagrams for the system at T = 288.15 and 298.15 K are all in one invariant point for (Li2SO4·H2O + LiBO2·8H2O), two univariant curves, and two crystallizing regions corresponding to the lithium sulfate monohydrate (Li2SO4·H2O) and lithium metaborate octahydrate (LiBO2·8H2O). The phase diagrams of the ternary system at two temperatures belong to hydrate type I, and neither double salt nor solid solution was found. A comparison of the phase diagrams for the ternary system at 298.15 and 288.15 K shows that the crystallized area of Li2SO4·H2O is increased with the increasing of temperature while that of LiBO2·8H2O is decreased obviously. The physicochemical properties (density, pH value and refractive index) in the ternary system at 288.15 and 298.15 K are changed regularly with the increasing of lithium sulfate concentration in the solution, and singular phenomena for the extreme values are amazedly appeared at the invariant points.