Study on the Mechanism and Process of Preparing Calcium Fluoride from Regenerated Cryolite.

The solid waste generated during the process of aluminum electrolysis served as a valuable secondary source of fluorine. Within this category, regenerated cryolite stood as an intermediate product obtained from the anode carbon slag of aluminum electrolysis, which underwent treatment through flotation or baking. Regenerated cryolite could be transformed into more valuable products such as aluminum and calcium fluorides. This paper used regenerated cryolite as the raw material and calcium carbonate as the reagent, and the effects of baking temperature, insulation time, and reagent-to-cryolite mass ratio on the degree of cryolite transformation were discussed. The transformation degree of cryolite was characterized by baking loss rate, leaching loss rate, reaction rate, and fluoride ion concentration. Optimal transformation conditions were baking temperature of 850–900°C, insulation time of 2.0–3.0 h, and a mass ratio of calcium carbonate to regenerated cryolite of 0.7–0.8:1. The orthogonal experimental results showed that temperature had a significant effect, followed by the reagent, with time being a weaker factor. At a baking temperature of 900°C, a mass ratio of 0.8:1, and an insulation time of 2.0 h, the conversion rate of regenerated cryolite was 66.82%, and the purity of the direct calcium fluoride was 73.3%. By suitable acid leaching, the resultant calcium fluoride can be increased obviously. [ABSTRACT FROM AUTHOR]