Precipitate flotation of fluoride-containing wastewater from a semiconductor manufacturer

Precipitate-flotation of fluoride-containing wastewater from a semiconductor manufacturer was investigated. The process involves the addition of calcium chloride to generate precipitate and the subsequent removal of calcium fluoride (CaF2). Results from dispersed air flotation (DiAF) experiments indicate that through the adjustment of molar ratio of calcium and fluoride ([Ca2+]/[F−]) and pH values, the residual fluoride concentration of lower than 10 mg/L in the effluent could be obtained. The concentration of sodium dodecyl sulfate (SDS) significantly affected the removal efficiency of CaF2. Flotation reaction was not affected by pH. Flotation efficiency decreased with increasing ionic strength and in the presence of sulfate. However, the depressed flotation could be improved by increasing SDS concentration.