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

• A composite coagulant polymeric ferric zinc sulfate (PFZS) was prepared.
• PFZS's preparation was optimized by using response surface method (RSM).
• The characterization of PFZS shows more bars structure.
• PFZS presents more efficient coagulation–flocculation performance in municipal sewage treatment than PFS.

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 °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.

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