Modeling of the solubility of alumina in the NaF-AlF3 system at 1300 K

Abstract: The experimentally well-known alumina solubility in the range of acidic to neutral cryolite-base melts has been modeled thermodynamically in terms of several oxyfluoride solutes. For an acidic melt, cryolite ratio r=1.5, the dominant solute is monoxygen Na₂Al₂OF₆. In a less acidic regime, dioxygen Na₂Al₂O₂F₄ is dominant, whereas for neutral compositions (r=3), Na₄Al₂O₂F₆ starts to gain importance. The fit of the model to the experimental solubility data is virtually perfect. The values of the equilibrium constants for the formation of the individual solutes are reported. The formation and conversion of these oxyfluoride complexes serve as an effective buffer opposing change in the melt basicity.