Fluoride removal by induced crystallization using fluorapatite/calcite seed crystals
Affiliation of Author(s):
环境与市政工程学院
Journal:
Chemical Engineering Journal
Key Words:
中文关键字:诱导结晶;氟去除;氟磷酸钙;方解石;晶种,英文关键字:Induced crystallization; Fluoride removal; Fluorap
Abstract:
The removal of fluoride from water by induced crystallization using fluorapatite (FAP)/calcite seed crystals was investigated. Batch experiments were conducted to determine optimal operating parameters.
The effect of FAP/calcite mass ratio of the seed crystals, initial seed crystal concentration, molar ratios
of Ca2+:PO4 3:F and contact time were examined. FAP/calcite with any mass ratio reduced fluoride concentrations from 9.5 mg/L (0.5 mM) to less than 1 mg/L. The use of FAP alone and calcite alone was not
effective. Use of initial seed crystal concentrations greater than 4.0 g/L were correlated to residual fluoride concentrations less than 1.0 mg/L. The optimal parameters for fluoride removal were an initial seed
crystal concentration of 6 g/L (FAP 4.8 g/L, calcite 1.2 g/L), Ca/P/F molar ratio of 8:4:1, and contact time of
1 h. The final pH was always close to neutral. The presence of natural organic matter (NOM) in the raw
water was found to not affect fluoride removal. SEM–EDS and XRD analysis showed that fluoride removal
was due to crystallization of Ca5(PO4)3F on the surface of FAP. Phosphate, but not fluoride, accumulated
on calcite by adsorption. The seed crystal could be regenerated easily, and used repeatedly, and used seed
crystals could also be used as resources in phosphorus fertilizer production. Induced crystallization using
FAP/calcite as a seed crystal is an economically and environmentally friendly process, and has the potential to remove fluoride from groundwater.