Solid-Liquid Phase Equilibria of the Aqueous Ternary System (MgSO4 + Mg2B6O11 + H2O) at (288.15, 298.15, and 308.15) K

Solubilities, densities, refractive indices, and pH values for the ternary system (MgSO4 + Mg2B6O11 + H2O) at (288.15, 298.15, and 308.15) K and 0.1 MPa, obtained using the method of isothermal dissolution equilibrium, are reported for the first time. On the basis of the experimental data, the phase diagrams and the physicochemical properties of density, refractive index, and pH versus concentration of magnesium sulfate were plotted. It was found that there are one invariant point, two univariant curves, and two crystallization regions corresponding to inderite (Mg2B6O11 center dot 15H(2)O, Inde) and epsomite (MgSO4 center dot 7H(2)O, Eps). The crystallized area of inderite is larger than that of epsomite at three temperatures, indicating that the solubility of inderite is lower than that of epsomite. Comparison of the phase diagrams at (288.15, 298.15, and 308.15) K shows that the areas of Inde and Eps increase with increasing temperature. There are no solid solutions and double salts at these three temperatures in this system. The density and refractive index of this ternary system at the three temperatures change regularly with the changing concentration of magnesium sulfate. Empirical equations for the density and refractive index were further used to correlate the data, and the calculated results agree well with the experimental values at the three temperatures.