Fluoride-rich wastewater treatment by ballast-assisted precipitation with the selection of precipitants and discarded or recovered materials as ballast

Fluoride is commonly an unwanted by-product in industrial processes becoming highly concentrated at the effluent reaching 1,000 to 50,000 ppm F–. However, most of the defluoridation studies focused on the treatment of low concentrations of fluoride Fe > Al > Zr > Mg). Meanwhile, among the discarded and recovered materials use for ballast CaCO3 demonstrated the highest defluoridation efficiency (CaCO3 > Al2O3 > CaHPO4 > SiO2 > Fe2O3). Calcite did not only act as ballast but also a precipitant by providing additional calcium ions through leaching. The defluoridation by ballasted precipitation could efficiently remove fluoride by 99% and reduced turbidity >90%. Moreover, the parameter correlation could be fitted in a quadratic equation (r2 from 0.8763 to 0.9999). The coefficients were used to estimate the significance of each parameter (showing pH > Ca/2F ratio > ballast dosage).