| During coagulation process, addition of a coagulant aid, sometimes can strengthenthe coagulation effect. Activated silica, as an inorganic polymeric coagulant aid, isinexpensive, and non-toxic material. However, its property is not stable, and it’sdifficult to preserve. This would limit its application in water treatment. Therefore,research on the characterization of activated silica to improve its performance is ofimportance.In order to examine the effects of initial pH and mass concentration of SiO2to theactivated silicic acid, the size and zeta potential of dispersion of the flocculant wereexamined during the activation process. The results show that the appropriate conditionsare pH=10, the mass concentration of SiO2is1%, and the activation time is48h. Inorder to improve the properties of activated silica, TiCl4was used as an additive toprepare a polysilicate-titanium coagulant aid under base conditions. The influence ofdosing order of TiCl4and concentrated sulfuric acid, and the dosage of TiCl4wasinvestigated. The results show that, in the sequence of first addition of concentratedsulfuric acid and then TiCl4to the sodium silicate solution with1%mass concentrationof SiO2, and under the condition of initial pH=10, Si/Ti=20, and activation time of48hours, a relatively stable polysilicate-titanium polymer was formed. Compared withactivated silicic acid, the new flocculant has a larger particle size in water and higherzeta potential when it is dispersed in water. The IR spectra show that titanium wasinvolved in the polymerization reactions: a new bond of Ti-O-Si was formed. Using scanning electron microscopy and fluorescence microscopy, the results show that themorphology of solid polysilicate-titanium is sheet-like aggregated, and it has along-chain in liquid, compared with the activation silica’s spherical distribution, it canplay a better role in bridging adsorption.Using Al2(SO4)3as a coagulant and the prepared polysilicate-titanium as coagulantaid, the effects of its coagulant-flocculation on removal of turbidity and humic acidwere studied, which was also compared with activated silica. The results show thataddition of polysilicate-titanium as coagulant aid can significantly improve the turbidityremoval and it also can broaden the application of coagulation pH range (it shows goodeffect when pH=6～8). When pH=7, dosage of Al2(SO4)3is10mg/L, addition of theflocculant at the ratio of Si/Al=2, the water turbidity after treatment can reach as low as1.05NTU, or a turbidity removal rate is98.3%; its coagulation-flocculation effect isbetter than activated silica. When addition of polysilicate-titanium in coagulation is usedto remove the humic acid in water, UV254and DOC of the water after treatment weremeasured. The results show that the addition of polysilicate-titanium has improved theoverall coagulant effect than that of activated silica. It can broaden the effective range ofpH in UV254removal, at the same time it can also significantly increase the effect ofDOC removal. When the dosage of Al2(SO4)3is80mg/L, Si/Al=2, in the range ofpH=6～8, the rate of UV254removal is higher than98%; and when pH=6, DOC in thewater after treatment can reach as low as1.817mg/L. or a DOC removal of74.0%. |
PDF Full Text Request