Solubilities, Densities, and Refractive Indices in the Quaternary System (Li2B4O7 + Na2B4O7 + Mg2B6O11 + H2O) at 298.15 K

Abstract

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.