A Density Model for Multicomponent Liquids Based on the Modified Quasichemical Model: Application to the NaCl-KCl-MgCl₂-CaCl₂ System

A theoretical model based on the modified quasichemical model is presented for the density of multicomponent inorganic liquids such as molten salts. By introducing in the Gibbs energy of the liquid phase temperature-dependent molar volume expressions for the pure components and pressure-dependent excess parameters for the binary (and, if necessary, higher-order) interactions, it is possible to reproduce and eventually predict the molar volume and the density of the multicomponent liquid phase using standard interpolation methods. The model is applied to the NaCl-KCl-MgCl₂-CaCl₂ liquid solutions. No ternary pressure-dependent model parameters were required; the binary pressure-dependent parameters suffice to reproduce satisfactorily the experimental density data available for the NaCl-KCl-MgCl₂, NaCl-KCl-CaCl₂, NaCl-MgCl₂-CaCl₂, KCl-MgCl₂-CaCl₂, and NaCl-KCl-MgCl₂-CaCl₂ liquids. This is the first of two articles on the density model. In a subsequent article, the model is applied to the NaF-AlF₃-CaF₂-Al₂O₃ base electrolyte used for the electroreduction of alumina in Hall–Héroult cells.