Morphology and coagulation performance during preparation of poly-silicic-ferric (PSF) coagulant

摘要

A new inorganic polymer, liquid poly-silicic-ferric (PSF) coagulant with various Si/Fe ratios (PSF0.5, PSF1 and PSF3 represent Si/Fe molar ratio of 0.5, 1 and 3, respectively) was prepared using water glass, FeSO4. 7H2O and NaClO3 by co-polymerization. The pH value was measured during the preparation process, the influence of both Si/Fe ratio and reaction time (polymerization or aging time) on the morphology of PSF was explored by transmission electron microscopy (TEM) and turbidity removal by liquid PSF taken from different reaction time was studied by jar test in treating various waters. The solid PSF made from liquid PSF by two different solidification ways was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Coagulation performance by solid PSF was studied compared to that by liquid PSF. The results show that the morphology of PSF by TEM is largely influenced by both reaction time and Si/Fe ratio. The reaction time for optimal species of PSF can be evaluated by measuring the pH value during the polymerization process. The pH value of PSF0.5, PSF1 or PSF3 tends to be stable at reaction time 10, 25 or 55 min, respectively, which is almost coincident with the time reaching the relative stable morphology that is just the optimal species of higher coagulation efficiency. Surface morphology of solid PSF by SEM is greatly influenced by both solidification method and Si/Fe ratio. PSF is found to be a complexation compound of Si, Fe and many other ions, instead of a simple mixture of raw materials. The influence of reaction time on performance efficiency by liquid PSF is more evident than that by solid PSF, and the reaction time needed in preparing solid PSF with excellent coagulation performance is shorter than that in liquid PSF. Solidification process may be not a simple dehydration from liquid coagulant, but a re-preparation process. When settling time with solid PSF as coagulant increases, the reduction of turbidity removal caused by solidification can be retarded, and the removal of dissolved organic matters can be improved.