Treatment of Highly Concentrated Fluoride Wastewater from the Semiconductor Industry by CaCl<sub>2</sub> based on the Adjustment of ζ-Potential
Lilong Zhou, Yadong Zhong, Xuepu Cao, Zhao Hua, Runjing Liu
Abstract
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 CaCl 2 instead of lime as the calcium source precipitant. The effects of Ca 2+ dose and pH on F – removal were investigated. The results show that the F – removal rate is related to the settling properties of CaF 2 . The ζ potential of CaF 2 particles can be lowered by adjusting the solution pH and the agglomeration of CaF 2 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 (Ca 2+ )/ n (F – ) was 0.5 at a pH of 8.5. The CaF 2 sludge with high purity can be obtained to realize resourceful utilization of solid waste.