Preparation of anhydrous aluminum fluoride

Because direct roasting of aluminum fluoride hydrate will hydrolysis, resulting in higher alumina content in aluminum fluoride products. To solve this problem, a two-step process for the preparation of anhydrous AlF3 from AlF3·3H2O and NH4HF is described in this paper. First, AlF3·3H2O was dried at 220 ℃ for 9–12 h, and then NH4HF (the mass ratio of AlF3·3H2O to NH4HF was 1:20) was added, and the mixture was roasted from room temperature to 650 ℃. The results showed that the hydrolysis of aluminum fluoride can be avoided effectively by the two-step roasting method with NH4HF, the purity of the anhydrous AlF3 was 99.8 wt%, and the concentration of alumina, the main impurity, was less than 0.1 wt%.