Study On Preparation Of Modified Polysilicate Composite Flocculants And Its Properties

Nowadays,the water resource pollution situation was serious all over the world.The main sources of drinking water such as rivers and lakes were contaminated by large amounts of industrial and urban wastewater.Therefore,effective treatment of sewage was imminent.The flocculation method was the most widely used in water treatment technology.With the development of modern technology,more green environmental protection and excellent performance flocculants were needed.In this paper,flocculants were prepared by modifying polysilicate metal salts,which were applied to the flocculation treatment of raw drinking water.On this basis,two flocculants were prepared: boron-modified polyaluminum titanium silicate flocculant(B-PSATi)and polyaluminum silicate-cationic starch composite flocculant(PSAS-CS).B-PSATi was prepared with sodium silicate,aluminium sulfate,titanium sulfate and sodium tetraborate as raw materials.The morphology and structure of the flocculant were characterized by XRD,SEM and EDS.The optimum preparation conditions were determined by single factor experiments: pH=2.5,n(Al+Ti)/n(Si)=0.6,n(Al)/n(Ti)=8:2,n(B)/n(Si)=0.05.Taking kaolin-sodium humate solution as simulated water samples,the turbidity and color removal rates could reach 97.56% and 98.08% at the flocculant dosage of 0.5 mL/L and the simulated water pH of 7-9.The polyaluminum titanium silicate flocculant modified by sodium tetraborate significantly improved the flocculation performance and the stability of the polysilicate metal salt,which provided the possibility for large-scale industrial production.PSAS-CS composite flocculant was prepared with sodium silicate,aluminium sulfate,starch and cationic etherifying agent as raw materials.The morphology and structure of the flocculant were characterized by SEM,FTIR and XRD.The flocculation mechanism of PSAS-CS composite flocculant was analyzed based on Zeta potential.The optimum preparation conditions were determined by single factor experiments: pH=3,n(Al)/n(Si)=0.9,m(CS)/m(Si)=0.25.Taking kaolin-sodium humate solution as simulated water samples,the turbidity and color removal rates could reach 97.79% and 98.07% at the flocculant dosage of 1.5 mL/L and the simulated water pH of 5-9.The flocculation performance of polysilicate metal salt was obviously improved due to the modification of cationic starch and polysilicate aluminum salt.The PSAS-CS composite flocculant possessed the advantages of both organic and inorganic flocculants,and reduced the possibility of secondary pollution.