Efficient recovery of highly pure CaF2 from fluorine-containing wastewater using an icy lime solution

Abstract

Developing a feasible and low-cost strategy for the recovery of calcium fluoride efficiently from fluoride-containing wastewater is very essential for the recycle of fluoride resources. Herein, a modified lime precipitation method was employed to recover CaF2 from fluorinated wastewater using a special icy lime solution. Intriguingly, the highest F– removal was greater than 95% under the optimal condition, leaving a fluoride concentration from 200 to 8.64 mg/L, while the lime dosage was much lower than that of industry. Importantly, spherical-shaped CaF2 particles with a 93.47% purity and size smaller than 600 nm were recovered, which has a high potential for the production of hydrofluoric acid. Besides, the precipitation was significantly affected by Ca/F molar ratio, stirring time, temperature, and solution pH. Furthermore, the thermodynamics and kinetics were investigated in detail to reveal the crystallization process. As a result, the defluorination reaction followed the pseudo-second order reaction kinetics model. Also, CO2 in the air adversely influenced the CaF2 purity. Based on this facile method, a high lime utilization efficiency was applied to defluorination, which contributed to protecting the environment and saving costs. This study, therefore, provides a feasible approach for the green recovery of fluorine resources and has significance for related research. HIGHLIGHTS A facile icy lime precipitation method was employed to remove F−.; Highly pure spherical particles with CaF2 of more than 93% were recovered.; Thermodynamics implied that CO2 had an inhibitory effect on the purity of CaF2.; Change in F fitted well with the pseudo-second order reaction kinetics model.; The co-precipitation of CaF2 and CaCO3 occurred.;

Keywords

• calcium fluoride
• fluoride-containing wastewater
• kinetics
• thermodynamics