Treatment of Highly Concentrated Fluoride Wastewater from the Semiconductor Industry by CaCl2 based on the Adjustment of ζ-Potential

The semiconductor production process generates a large amount of highly concentrated, acidic, fluorinated wastewater. In this work, wastewater with an initial F– concentration of 1800 mg L–1 from the semiconductor industry was treated using CaCl2 instead of lime as the calcium source precipitant. The effects of Ca2+ dose and pH on F– removal were investigated. The results show that the F– removal rate is related to the settling properties of CaF2. The ζ potential of CaF2 particles can be lowered by adjusting the solution pH and the agglomeration of CaF2 particles can be enlarged, resulting in the increase of defluorination efficiency. The defluorination rate for the actual industrial process reached 99.49%, and a discharge standard of industrial wastewater of 10 mg L–1 was achieved when the n(Ca2+)/n(F–) was 0.5 at a pH of 8.5. The CaF2 sludge with high purity can be obtained to realize resourceful utilization of solid waste.