Iron leaching from sludge incineration ash for preparation of polymeric ferric chloride

Sludge incineration ash (SIA), a by-product of sludge incineration, is a powdery material riches in Fe₂O₃, SiO₂, CaO, Al₂O₃, MgO and P₂O₅. Extraction of Fe from SIA by acid leaching to prepare polymeric ferric chloride flocculant for water purification is a green and sustainable method to recycle SIA. In this study, the optimal synthesis conditions of SPFC were explored, and its microscopic characterizations showed that Fe exists in an amorphous state, with the main valence state in the trivalent state, and Fe combines with Si and other non-metallic elements with different chemical bonds. The SEM showed that SPFC exhibits a rough porous reticulated structure. By applying SPFC in real domestic wastewater, the removal rates of turbidity, SS, and COD could reach 97.73%, 99.10%, and 78.17%, respectively; by applying SPFC in real river wastewater, the removal rates of turbidity, SS, and COD could reach 93.80% and 91.59%, respectively. In addition, compared with commercially available flocculants, the flocculation performance of SPFC was significantly better than that of traditional commercially available PFC.