Estimation of optimal conditions for crystallization of calcium fluoride for treatment of high-concentration fluorine-containing industrial wastewater

Abstract

This study attempted to utilize fluidized bed reactor for fluoride removal and CaF₂ purity from the industrial wastewater including high concentration of fluoride ion. Effects of HRT, pH, Ca₂⁺ amount and seed height were investigated through lab-scale batch and continuous experiments. Considering fluoride removal efficiently and CaF₂ purity that HRT 5hr, pH6, seed height of 50 cm, [Ca₂⁺]/[F^-](mol/mol) ratio of 0.55 were found to be optimum. Correspondingly, removal fluoride was 82.5%, with a CaF₂ the crystallization rate of 95.1%, respectively. The results of continuous experiment showed that with pellet as CaF₂ , fluoride concentration can be stably reduced to less than 45mg/L in effluent from the influent 300mg/L on average. HR-XRD analysis showed that the crystalline structure of crystals was mainly CaF₂ .