Characterization and coagulation performance of solid poly-silicic–ferric (PSF) coagulant

An inorganic polymer, liquid poly-silicic–ferric (PSF) coagulant, with different Si/Fe molar ratios was prepared using water glass, FeSO4 · 7H2O and NaClO3 by co-polymerization. The solid PSF made from liquid PSF by two different solidification approaches was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. A comparison of coagulation behavior between PSF and polyferric sulfate (PFS) was explored. The results indicate that PSF is a complexation compound of Si, Fe and other ions, instead of a simple mixture of raw materials. The surface morphology of solid PSF is a function of the solidification method and the Si/Fe ratio. The reaction time needed in preparing solid PSF with excellent coagulation performance is shorter than that in liquid PSF. The solidification process is not a simple dehydration from liquid coagulant, but a re-preparation process. The optimal dose by PSF is 7.5 mg/L according to residual turbidity, in comparison with 10.5 mg/L by PFS. PSF has higher UV254 removal than PFS, with a difference from 10% to 60% at given dose range. When settling time with solid PSF as coagulant increases, the slight reduction of turbidity removal caused by solidification can be retarded, and the removal of dissolved organic matters can be improved.