Measurements and Predictions of the Solubilities in the Ternary System MgBr2 + SrBr2 + H2O at 288 and 308 K

The stable phase equilibria of the ternary system MgBr2 + SrBr2 + H2O at 288 and 308 K were studied with the isothermal dissolution equilibrium method. The compositions of solutions and solid phases have been determined and the equilibrium solid phases at the invariant points were identified with the aid of the X-ray diffraction method. The phase diagrams of this system at 288 and 308 K were both constructed in terms of experimental results. Two stable phase diagrams show that this system is hydrate type I at two temperatures without formation of a solid solution or complex salt. Both the phase diagrams are composed of one invariant point, two univariate curves, and two crystallization regions (SrBr2·6H2O and MgBr2·6H2O). The equilibrium solid phases of the invariant point at 288 and 308 K are both SrBr2·6H2O and MgBr2·6H2O, respectively. Combining the Pitzer single-salt parameters of MgBr2 and SrBr2 reported in the literatures, the unreported mixing ion-interaction parameters θMg,Sr and ΨMg,Sr,Br at 288 and 308 K were fitted with the measured values in this study using the Pitzer equations. The agreement between the experimental values and calculated results in the ternary system MgBr2 + SrBr2 + H2O at 288 and 308 K shows that the parameters fitted with solubilities are reliable.