Researches Of The Images And Structures, Coagulating Properties And Mechanism Of Polysilicate-containing Composite Inorganic Polymer Flocculants

A series of polysilicate-containing composite inorganic polymer flocculants , such as polysilicate-aluminum chloride , polysilicate-ferric sulfate, polysilicate-aluminum-ferric, polysilicate-aluminum chloride containing boron etc, which have different Al/Fe/Si/B molar ratio, are prepared by prepolymerization, using AlCl3 , Fe2(SO4)3, industrial water glass, sulphuric acid and borax as raw materials. The flocculants are studied roundly by using many modern techniques. The interactions between polysilicic acid, boron, aluminum ion, ferric ion and the hydrolysate of aluminum and iron are examined by IR and XRD measurements. The images of flocculants are investigated by an electron microscope. The electrical properties of flocculants were measured by a Microprocessor EC Meter. The coagulating properties were tested by jar tests. Finally, the coagulating mechanism is discussed. The experiment results show that: the images of the flocculants are ramificate and have fractal characteristics, but are different with Al/Fe/Si/B molar ratio; There are interaction between Al3+, Fe3+, B , the polynuclear hydroxy complexes of Al3+, Fe3+and polysilicic acid, which can affect the polymerization process of polysilicic acid and hydrolysis-polymerization process of aluminum and ferric in solution, and mainly affected by Al/Fe/Si/B molar ratio; the electrical conductivity of solutions as a function of aging time also confirm that there are interaction among all parts; compared with inorganic polymer flocculants, polysilicate-containing composite inorganic polymer flocculants are characterized by having higher turbidity removal, color removal, better coagulating efficiency by jar test, which affected by Al/Fe/Si/B molar ratio, pH value and the dosage. In fact, the coagulating mechanism is surface chelating and surface sedimentation. It is said that adsorption is before hydrolysis, then the hydrolysis and sedimentation reaction of the polynuclear hydroxy complexes take place on the adsorption surface, as the same time they counteract the electric charge of the colloids and suspended substances then adsorb and bridge the floccules.