The Solubility of Aluminum in Cryolite Melts

Abstract

The solubility of Al in cryolite melts saturated with Al₂O₃ has been determined by titration with electrolytically generated O₂. The results may be expressed by

$$\begin{gathered} wt\;pct\;Al=-0.2877+0.0268\left( {NaF/Al{{F}_{3}}\;wt\;ratio} \right) \hfill \\ \quad \quad \quad \quad \;\;\;+2.992\times {{10}^{{-4}}}\left( {temp\;^{\circ}C} \right)-0.00192\left( {\%\;Ca{{F}_{2}}} \right) \hfill \\ \quad \quad \quad \quad \;\;\;-0.00174\left( {\%L{{i}_{3}}Al{{F}_{6}}} \right)-0.00288\%\left( {\%\;NaCl} \right) \hfill \\ \end{gathered}$$

with a standard deviation of ± 0.017. Ranges covered were ratio 0.8 – 2.3, temperature 969 – 1054°C, CaF₂ ≤ 14%, Li₃AlF₆ ≤ 20%, and NaCl ≤ 10%. There was no significant effect of adding 0 – 38% K₃AlF₆ or 0 – 10% MgF₂. It was found that solubility was approximately proportional to activity of Al when Al - Cu alloys were used.

Possible mechanisms of solution are discussed.