The phase diagrams of the systems MgCl2 + MgB6O10 + H2O and MgSO4 + MgB6O10 + H2O at 323.15 K and Pitzer model

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The solubilities and the relevant physicochemical properties of the systems MgCl2 + MgB6O10 + H2O and MgSO4 + MgB6O10 + H2O at 323.15 K were determined by the method of isothermal dissolution, and the phase diagrams and the diagrams of physicochemical properties versus composition were plotted. Both of the systems belong to a simple eutectic type, and neither double salts nor solid solution were found. Based on the extended Harvie-Weare (HW) model and its temperature-dependent equations, the value of the singlesalt Pitzer parameters β(0), β(1), β(2), and CO for MgCl2, MgSO4, and Mg(B6O7)(OH)6, the mixed ion-interaction parameters \(\theta _{Cl, B_6 O_{10} }\), \(\theta _{SO_4 , B_6 O_{10} }\), \(\Psi _{Mg, Cl, B_6 O_{10} }\), \(\Psi _{Mg, SO_4 , B_6 O_{10} }\), the average equilibrium constants (lnKaver) of solids in the systems and the Debye-Huckel parameter AO were fitted. Using the Pitzer parameters and the average equilibrium constants of solids at equilibrium, the solubilities of the two systems at 323.15 K have been calculated. Comparisons between the calculated and experimental results show that the predicted solubilities agree well with experimental data.