Synthesis of high purity calcium fluoride from fluoride-containing wastewater

The present reports a new process for recovering high purity calcium fluoride from wastewater. A column reactor system with calcium sulfate dihydrate as reaction medium was used. It was found that spherical calcium fluoride with the purity of beyond 99 % was successfully obtained, and meanwhile the concentration of fluoride in wastewater was reduced to less than 10 mg/L. The present process realized the effective removal of fluoride while recovering high-purity calcium fluoride. Parameters including initial fluoride concentration, the influent flow rate, wastewater pH and time had a great effect on the fluoride removal efficiency. The fluoride recovery process included dissolution of calcium sulfate dihydrate and formation of calcium fluoride by the reaction of Ca2+ ion and F- ion. When the initial concentration of fluoride in wastewater was 1000 mg/L, the fluoride removal efficiency of the two column reactors in series was more than 99 %. This work provides an effective strategy which can be adopted in resource utilization and standard discharge of fluorine-containing wastewater.