Production method of cryolite

There are many preparation methods for cryolite, which can be divided into fluorite method, phosphate fertilizer by-product method, and fluorine-containing waste method according to the source of fluorine.

Cryolite is sodium fluoroaluminate, and its molecular formula is Na3AlF6. With excellent performance, cryolite is not only an indispensable co-solvent in the aluminum smelting industry, but also widely used in other industries, such as opalizing agent in the enamel industry, wear-resistant filler in the rubber and grinding wheel industry, and sunscreen in the glass industry.

Using smelting fluorine-containing non-acid as raw material, cryolite is prepared by processes such as neutralization and impurity removal, synthesis reaction, washing and drying. Under the optimal conditions of neutralization and impurity removal pH of 7.5, reaction pH of 8.0, feed ratio Na:Al:F of 4:1:6, reaction temperature of 80°C, and reaction time of 60min, the fluorine recovery rate can reach 98.9%, the residual fluoride ion concentration can be reduced to 200mg·L-1; the quality of the obtained cryolite product meets the requirements of GB/T4291-2017, and the ratio of sodium to aluminum substances is 2.5, which belongs to the middle molecular ratio cryolite.

The process is simple in operation and low in cost. About 30kg of cryolite can be obtained by treating 1m³ of smelting fluorine-containing waste acid. The resource utilization of smelting fluorine-containing waste acid is realized, the difficulty of subsequent treatment of waste acid is reduced, and the environmental pollution of smelting waste acid is reduced.