Optimization of coagulation-flocculation treatment of wastewater containing Zn(II) and Cr(VI)

Abstract

In this study, polymeric ferric sulfate (PFS) was employed as a coagulant to treat the wastewater containing Zn(II) and Cr(VI). Based on the mechanism of redox reaction, Cr(VI) was firstly transferred to Cr(III) with the help of (NH4)2Fe(SO4)2) (FAS) as the reductant. Afterwards, the influence of variable factors including FAS dosage, PFS dosage, pH value and settling time on the coagulation-flocculation treatment of the two heavy metals was estimated. The results show that the optimum removal efficiency of Zn(II) was obtained at a PFS dosage of 100 mg/L, pH 7-8 and settling time of 30 minutes. Meanwhile, the removal efficiency of Cr(VI) reached the highest value when the FAS dosage was 1.2 times of theoretical requirement, with the PFS dosage of 20 mg/L, pH 7-8 and settling time of about 30 minutes.