Coagulation performance and mechanism of polyaluminum ferric chloride (PAFC) coagulant synthesized using blast furnace dust

• Optimal parameters of PAFC synthesis from blast furnace dust were obtained.
• Self-made PAFC outperformed commercial PAC in turbidity and color removal.
• Coagulation mechanism of PAFC for turbidity and color removal were compared.

The research focused on the synthesis and coagulation performance of polyaluminum ferric chloride (PAFC) coagulant in order to explore a comprehensive utilization for blast furnace dust. The optimal conditions for PAFC synthesis were: fifty grams of blast furnace dust reacted with 150 mL hydrochloric acid diluted solution for 3 h at 90 °C and 10 g of aluminum dross reacted with 150 mL hydrochloric acid diluted solution for 2.5 h under room temperature; In co-polymerization stage, the Al/Fe molar ratio = 7:3, basicity B = 1.8, polymerization temperature 60–70 °C, and reaction time (pre-polymerization time of aluminum + copolymerization time of aluminum and iron) 1.0 h + 3.0 h. The main results are as follows: (1) The coagulation tests indicated that self-made PAFC outperformed commercial PAC in turbidity and color removal. (2) Self-made PAFC and flocs generated in water treating process were measured by Scanning Electron Microscopy. Surface charge characteristics of PAFC were measured by Zetasizer 3000HS. Charge neutralization was a very important coagulation mechanism of PAFC in turbidity removal process. And there were other coagulation mechanisms besides charge neutralization such as bridge connection and sweep flocculation, playing significant roles in decolorization process.