Review on the Preparation of Cryolite from Industry Waste Containing Fluorine

Rapid development of the fluorine industry has led to mass production of fluorine-containing waste, and direct discharge of this waste will cause serious environmental pollution of water, atmosphere, soil, and so on. Recycling and treatment of fluorine-containing waste are required for environmental protection and to utilize the fluorine resources. Because of decreases in fluorite reserves and inefficient fluorine resource recovery, cryolite has become a potential resource for fluorine recovery. This paper summarizes research on the preparation of cryolite from fluorine-containing substances produced in various industries, mechanisms of contamination under different conditions, and commonly used methods for controlling the product particle size. The results indicate that cryolite prepared in acidic or weakly alkaline solutions with a fluorine–aluminum molar ratio of 5.4–6.6 has high purity. The particle size of the cryolite increases with the addition of a seed during precipitation. This review provides insight for future production of cryolite with regard to purity problems and particle size control.