[Analysis of reaction process between Si and Fe in poly-silicic-ferric sulfate (PSF) coagulant]

A new inorganic polymer coagulant, poly-silic-ferric sulfate (PSF) with various Si/Fe ratios (PSF0.5, PSF1 and PSF denote Si/Fe molar ratios of 0.5, 1 and 3, respectively), was prepared using water glass, ferrous sulfate and sodium chlorate by co-polymerization, and pH value was measured during the preparation process. The influence of both Si/Fe ratio and reaction time (polymerization time) on the complexation process (bonding mode) between Si and Fe was explored with many analytical methods (such as X-ray diffraction (XRD), ultraviolet/visible absorption (UVA) scanning, transmission electron microscope (TEM), photon correlation spectra (PCS) and infrared spectrum (IR) using PSF samples taken from different reaction time at different Si/Fe ratios. The results show that the characteristics of PSF are largely influenced by both reaction time and Si/Fe ratios. PSF is found to be a complexation compound of Si, Fe and many other ions, instead of a simple mixture of raw materials. The complexation process between Si and Fe may be different from various Si/Fe ratios, namely, the bonding rate, bonding mode and the stability of the bond between Si and Fe are different from various Si/Fe ratios: the polymer based on Si-O-Fe-O-Fe-O-Si bond may be formed at low Si/Fe ratio, in comparison with that based on Si-O-Fe-O-Si-O-Si bond at high Si/Fe ratio; the formation rate of Fe-O-Fe bond is rapid and there may be a mutual acceleration between Fe-O-Fe bond and Si-O-Fe bond, while the formation rate of Si-O-Si is slow and maybe there is a mutual retardation between Si-O-Fe bond and Si-O-Si bond; the stability of Fe-O-Fe bond is weaker than that of Si-O-Fe or Si-O-Si bond.