Vapor pressure measurements for metal chloride systems by the Knudsen effusion method

Thermodynamic knowledge of metal chlorides, such as vapor pressure and activity in salt/slag, are of remarkable industrial interest, particularly in fields related to the recovery/recycle/reuse of metal materials. In this study, a new apparatus for measuring the vapor pressure of metal chlorides from molten salt/slag was designed and tested with reference compounds. The results are in a good agreement with the available literature data. Using the developed apparatus, vapor pressure measurements for a KCl-NaCl-CaCl₂ system have been performed. Using the measured data the activities of components were obtained. Simultaneously, the activities of components were calculated using a thermodynamic code, Factsage 5.2 wherein the Modified Quasi-chemical Model was employed to obtain the necessary thermodynamic parameters. The both data agree reasonably well with each other. The results suggested that the KCl-NaCl system exhibits similar behavior with ideal solution; while in the KCl-CaCl ₂ and NaCl-CaCl₂ systems there are possible interactions between CaCl₂ and KCl/NaCl. For the ternary system KCl-NaCl-CaCl ₂, in some concentration range (mole fraction of NaCl 0.25-0.50) NaCl behaves as in an ideal solution, suggesting a larger affinity between KCl and CaCl₂ than that between NaCl and CaCl₂.