Thermodynamic evaluation and optimization of the (NaCl + KCl + AlCl 3) system

Abstract

All available phase equilibrium and thermodynamic data for the (NaCl + KCl + AlCl 3) system were collected and critically evaluated. An optimization was performed to obtain the parameters of one set of model equations for each phase (solids, liquid, gas) in order to best reproduce all the data simultaneously. In this way the data are rendered self-consistent, discrepancies among the data are identified, and extrapolations and interpolations can be performed. For the molten phase the Modified Quasichemical Model for short-range ordering was used, with monomeric Al 3+ ions (corresponding to AlCl 4 − complexes in earlier models) predominating in alkali-rich melts, and dimeric aluminum species (corresponding to Al 2Cl 7 − complexes in previous models) predominating in AlCl 3-rich melts. No ternary model parameters were required for the liquid phase; the binary parameters suffice. The models can be used with Gibbs free energy minimization software to calculate phase diagram sections, vapor pressures, and all thermodynamic properties at all compositions and over extended ranges of temperature and pressure.