Solubilities, Densities, and Refractive Indices in the Quaternary System (Li 2 B 4 O 7 + Na 2 B 4 O 7 + Mg 2 B 6 O 11 + H 2 O) at 298.15 K

Solubilities, densities, and refractive indices in the quaternary system (Li2B4O7 + Na2B4O7 + Mg2B6O11 + H2O) at T = 298.15 K and p = 0.1 MPa were investigated experimentally with the method of isothermal dissolution equilibrium. According to the experimental data, the phase diagrams and the diagrams of densities and refractive indices versus lithium tetraborate composition in the solution were plotted, respectively. In the phase diagrams of the quaternary system at 298.15 K, there are one invariant point, three univariant isotherm dissolution curves, and three crystallization regions corresponding to Li2B4O7 · 3H2O, Na2B4O7 · 10H2O and Mg2B6O11 · 15H2O, respectively. The size of crystallization areas of salt is in the order Mg2B6O11 · 15H2O > Na2B4O7 · 10H2O > Li2B4O7 · 3H2O, which demonstrates Mg2B6O11 · 15H2O can be more easily separated from solution in this quaternary system. The solution density and refractive index of the quaternary system at 298.15 K change regularly with the increasing of Li2B4O7 concentration. The calculated values of density and refractive index using empirical equations of the quaternary system are in good agreement with the experimental values.