Alumina Solubility and Dissolution Rate in NaF-KF-AlF3-LiF-CaF2 Low-Temperature Electrolyte

The NaF-KF-AlF3-based electrolyte is a promising low-temperature electrolyte for aluminum reduction. The solubility and dissolution rate of alumina in NaF-KF-AlF3-LiF-CaF2 melt with a cryolite ratio (CR) ranging from 1.5 to 1.8 were investigated by the rotating corundum disk method at 1073 K to 1153 K. The effect of the composition and temperature of the melt on the solubility and dissolution rate of alumina were discussed. The results show that the solubility and dissolution rate of alumina in the melt decrease with the increase of LiF and CaF2 content, and the effect of LiF on the alumina solubility is greater than that of CaF2. The decrease of the CR and temperature lead to a marked reduction of the alumina solubility and alumina dissolution rate. The dissolution rate of alumina depends on the dissolution rate in the first 5 minutes. The alumina dissolution is a zero-order reaction in the first 5 minutes, and a first-order reaction in the next 30 minutes.