Abstract
The solubilities and relevant physicochemical properties including density and pH values of the aqueous quaternary system (MgCl2 + MgSO4 + MgB6O10 + H2O) at 323.15 K were determined for the first time with the method of isothermal dissolution. According to the experimental results, the dry-salt-phase diagram, water-phase diagram, and physicochemical properties versus composition diagrams were plotted. It was found that there are three three-salt cosaturated invariant points, seven univariant solubility isotherm curves, and five stable crystallization fields corresponding to bischofite (MgCl2·6H2O, Bis), kieserite (MgSO4·H2O, Kie), tetrahydrite (MgSO4·4H2O, Tet), hexahydrite (MgSO4·6H2O, Hex), and mcallisterite (Mg(B6O7)(OH)6·4.5H2O, Mca). Neither solid solution nor double salts were found. On the basis of the extended Harvie–Weare (HW) model and its temperature-dependent equation, single-salt parameters β(0), β(1), β(2), and Cϕ for MgCl2, MgSO4, and Mg(B6O7)(OH)6, mixed ion-interaction parameters θC1,SO4, θC1,B6O7 (OH)6, θSO4,B6O7(OH)6, ΨMg,Cl,SO4, ΨMg,Cl,B6O7(OH)6, and ΨMg,SO4,B6O7(OH)6, and the Debye–Hückel parameter Aϕ at 323.15 K were obtained. In addition, the average equilibrium constants of stable equilibrium solids at 323.15 K were obtained with the method of the activity product constant. The prediction of solubilities of the quaternary system is then demonstrated. A comparison between the calculated and the experimental results shows that the predicted solubilities agree well with experimental data.
Published Version
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