Experimental Investigation and Thermodynamic Modeling of Solid–Liquid Equilibria in the Ternary System KCl–CsCl–H2O to High Concentrations from 273.15 to 348.15 K

The solubilities in the ternary system KCl–CsCl–H2O at 348.15 K were studied with the isothermal dissolution equilibrium method. The phase diagram of the system at 348.15 K is composed of one invariant point, two unvariant curves, and two single-salt crystallizations for KCl and CsCl. A comparison of the diagrams of the system KCl–CsCl–H2O from 298.15 to 348.15 K shows that the solid solution forms at 298.15 K and disappears at 323.15 and 348.15 K. Combining Pitzer binary parameters of KCl and CsCl obtained from the literature and solubility data in the system CsCl–H2O, the temperature dependence equations for Pitzer mixing parameters (θK,Cs and φK,Cs,Cl) and dissolution equilibrium constants of CsCl were built on the basis of the Pitzer model. The model for the mixed system provides reasonable mineral solubility from 273.15 to 348.15 K. The assumption of no solid solution existence in the ternary system can be applied in parameter fitting and solubility calculation. The results on the phase diagrams and thermodynamic model of the system KCl–CsCl–H2O can supply basic thermodynamic data and theoretical references for CsCl separation from the brine containing KCl.