Solubility of aluminum in cryolite-alumina electrolytes

The complex influence that additives of aluminum, calcium, lithium, and potassium fluorides have on the total solubility of aluminum in the cryolite-alumina melt is studied. The investigations were performed at a constant overheating of the melt saturated by alumina (15°C relative to the liquidus temperature). The aluminum solubility was determined via the prolonged holding of metal in the melt at a specified temperature with the subsequent sampling of the specimen, which was rapidly frozen, and the metal content in it was determined by a gas-volumetric analysis. It was seen that, as the cryolite ratio (CR) decreases from 2.5 to 2.2, the aluminum solubility in the electrolyte drops by a factor of 1.7, while the further decrease in CR to 2.1 does not cause its substantial variation. The introduction of 3 wt % LiF and 5 wt % KF into the melt with a constant overheating of the melt substantially decreases the metal solubility, namely, by a factor of 2.9 and 1.5, respectively.