Characterization and coagulation-flocculation behavior of an inorganic polymer coagulant - poly-ferric-zinc-sulfate

Recent studies on improving the behavior of the coagulation-flocculation process have attracted a widespread interest. Iron-based composite coagulant has been demonstrated to enhance the performance of the coagulation-flocculation in previous research. In this research, a type of coagulant, poly-ferric-zinc sulfate (PFZS) was prepared by co-polymerization. The preparation process was optimized by using response surface method (RSM). The structure and morphology of PFZS were investigated by FTIR, XRD and SEM. In addition, parameters affecting coagulation-flocculation behavior such as coagulant dosage, initial pH in wastewater and settling time were also studied. The results show that the optimum temperature, Zn/Fe molar ratios and aging time for preparation of PFZS are 70 degrees C, 1.0 and 3.0 h, respectively; FTIR and XRD results demonstrate that PFZS is a complex compound with mainly ferric-zinc polymeric species rather than a simple mixture of raw materials. In the coagulation-flocculation process of municipal sewage treatment, PFZS exhibits a better coagulation performance compared with poly-ferric-sulfate (PFS). At optimal pH value in the range of 7-9, PFZS can reach the best turbidity removal rate 93.42% at a dosage of 12 mg/L, whereas PFS can only reach 90.36% at the best coagulant dosage of 16 mg/L. (C) 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.