Solid–Liquid and Vapor–Liquid Equilibria, Volume Properties in Water–Calcium (Magnesium) Methanesulfonate: Experimental Data and Modeling with Pitzer and Pitzer–Simonson–Clegg Formalism

Water vapor pressure was determined by a static method at 298.15 K and a dew point method at 323.15 K in the Ca(CH3SO3)2–H2O and Mg(CH3SO3)2–H2O systems. Equilibrium isothermal solubility for Ca(CH3SO3)2–H2O was determined from 250.15 to 353.15 K, and from 250.15 to 318.15 K for Mg(CH3SO3)2–H2O. A new hydrate was revealed in the system, Ca(CH3SO3)2·4H2O. It melts incongruently at 282.4 K. Additional data for ice liquidus obtained using DSC in both systems are in good agreement with literature. Based on vapor–liquid (VLE) and solid–liquid (SLE) equilibria data, parameters of the Pitzer–Simonson–Clegg and Pitzer models were obtained. Stability parameters of Mg(CH3SO3)2·12H2O, Ca(CH3SO3)2·4H2O and Ca(CH3SO3)2 were estimated. Binary phase diagram fragments were calculated. The eutectic point in Mg(CH3SO3)2–H2O was estimated using the Tamman method and from phase diagram calculations is in good agreement. The eutectic point in Ca(CH3SO3)2–H2O was not estimated by the Tamman method due to supercooling. Both metastable and stable phase diagrams were calculated. Pitzer and PSC models were extended with a pressure dependence used to predict the volume properties of the solutions. Densities of the solutions were measured in both binary systems at 288.15, 298.15, and 308.15 K.