Phase equilibria in the ternary systems KBr–MgBr2–H2O and NaBr–MgBr2–H2O at 348.15 K

Abstract

Solid–liquid equilibria in the ternary systems KBr–MgBr2–H2O and NaBr–MgBr2–H2O at 348.15K were determined with the method of isothermal solution saturation. Also determined are the densities of saturated solutions. According to the experimental data, the equilibrium phase diagrams of the two ternary systems were plotted. The phase diagram of first system has two invariant points, three univariant curves and three crystallization fields (which are saturated with respect to MgBr2·6H2O, KBr·MgBr2·6H2O and KBr, respectively, where KBr·MgBr2·6H2O is an incongruent double salt). The phase diagram of the second system has one invariant point, two univariant curves and two crystallization fields (which are saturated with respect to MgBr2·6H2O and NaBr, respectively). The dissolution equilibrium constant of NaBr, KBr, MgBr2·6H2O and KBr·MgBr2·6H2O at 348.15K were fitted with Pitzer equations. A chemical model based on Pitzer equations was constructed to calculate the solubilities of salts in the two systems at 348.15K. The calculated solubilities are in agreement with experimental results.