Preparation and characterization of poly-silicic-cation coagulant from industrial wastes

• A low-cost poly-silicic-cation coagulant (PSiC) was prepared from industrial wastes.
• Characteristics of PSiC were analyzed by XRD, FT-IR, UVA and microscopic imaging.
• Coagulation performance of PSiC was evaluated by papermaking wastewater treatment.
• The best Si/(Al + Fe) molar ratio for the structure and morphology of PSiC is 0.8.

A simple and low-cost method was developed to prepare poly-silicic-cation coagulant (PSiC) from industrial wastes. The structure and morphology of the coagulants with different Si/(Al + Fe) molar ratios were characterized by X-ray diffraction (XRD), infrared spectra (IR), ultraviolet/visible absorption (UVA) scanning and microscopic imaging, and the coagulation performances were evaluated by papermaking wastewater treatment. The results show that instead of a simple mixture of the raw materials, new complex compounds are formed in all the PSiCs, and distinctive compounds are found in each PSiC. Furthermore, with the increasing dose of silicon in PSiC, the contents of the ionic polymerized bonds and the high polymers are decreased obviously, and the cross-copolymerization of Fe (III) and Al (III) hydroxyl polymers is weakened. Morphological analysis implies that branch-like PSiC units become smaller with the increase of Si/(Al + Fe) molar ratio, and coagulation experiments indicate that the PSiC with lower Si/(Al + Fe) molar ratio exhibits better coagulation performance in removing turbidity, COD and chroma.