Water Activity and Solubility of the System MgCl2–RbCl–H2O at 323.15 K

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The water activities of the MgCl2–RbCl–H2O ternary system and its sub-binary systems have been measured with the isopiestic method at 323.15 K. The measured water activities for the MgCl2–H2O and RbCl–H2O sub-binary systems agree well with the results reported in literature. The measured equal water activity lines of the MgCl2–RbCl–H2O ternary system are not straight lines, which means the mixing behavior of the solutions do not obey Zdanovskii’s rule. The solubility of the MgCl2–RbCl–H2O ternary system has been determined with the Flow-Cloud-Point method at 323.15 K, and the measured results are roughly consistent with values reported in the literature. The Pitzer model was selected to correlate the water activity and solubility data measured in this work. The predicted water activities and solubility isotherm for the MgCl2–RbCl–H2O ternary system at 323.15 K, with binary solution parameters only, both deviated from the experiment values. The ternary solution Pitzer model parameters were obtained by fitting the measured water activities in the ternary system. The water activities and solubility isotherms of the MgCl2–RbCl–H2O ternary system at 323.15 K were calculated including both binary and ternary solution parameters. The calculated water activities are consistent with the experimental values. The calculated solubility isotherms are roughly consistent with experiment values, except they deviate somewhat in the RbCl crystallization region.