Study On The Mian Influencing Factors Of Nano-TiO₂Removal By Coagulation With Aluminium Sulphate

With the rapid development of nanotechnology, more and more syntheticnano-materials have been produced. The widespread use and application in daily lifefor nano-materials will inevitably lead to gross release of such materials into theenvironment. There is a great deal of research shows that nano-materials will inducephysislogical toxicity to organism, and once these materials enter into body ofhuman, which will give possible health risks to human. Water is the source of thelives, and its safety is essential to everybody. However, the removal of nanoparticleshave so far receive only scant attention in water treatment process, and there is nolimited to concentrations of nanoparticles in water quality standard.To investigate the effect of water quality on coagualtion for removalingnanoparticles and the nanoparticles residues after water treatment process,nano-TiO₂was selected as the targeted pollutant. A series of jar tests were conductedfor the coagulation of nan-TiO₂with aluminium at different coagulation conditions,concentration of humic acid and surfactant. The first objective of this study was toevaluate the elimination capacity of nan-TiO₂by inorganic aluminum salt, andexamined the mechanism of the factors affecting the coagulation process. Theseresult could provide a basis to practical application in the future.Experimental investigation showed that high intensity of the mixed-phasestirring speed benefitted formation and growth of micro flocs in raw water, and thestirring time could not be too long. While the flocculation phase of stirring speedwas the major factor in turbidity removal, over high G and over low G would lead toturbidity increase. Aluminium sulphate had great charge neutralization to nano-TiO₂,and it was demonstrated here that nan-TiO₂can be effectively removed duringaluminium coagualtion with an appropriate coagulant dose. The removal rate ofnano-TiO₂in40mg/L aluminium sulphate can be up to95.8%.The pH and alkalinity of raw water could change the specise distribution ofhydrolyzed aluminum and surface charge status of nao-TiO₂, which had a greatinfluence on coagulation. The optimum pH of coagulation was6.7to9.0. Theflocculation mechanism of aluminium included charge neutralization and furl withinoptimum pH ranges. The effects of coexisting anions (H₂PO_4-、SiO₃^2-、 SO₄^2-andNO^3-) on removal of nano-TiO₂were varied widely, representing restraining effect,accelerating effect and no remarkable effect, respectively. However, coexistingcations (Na⁺、NH₄⁺、Ca²⁺and Mg²⁺) on coagulation had a little impact, Ca²⁺andMg²⁺could compress double electricity layers to reduce the surface potential ofnano-TiO₂, and promoted the removal rate. NH₄⁺had the lagerly inhibition on coagulation.In raw water, the removal rate of nan-TiO₂was decreased with lowconcentration of humic acid, and increased in adding high concentration of humicacid. Sodium dodecyl benzene sulfonate （SDBS） and cetyl trimethyl ammoniumbromide （CTAB） had a disadvantage for nao-TiO₂removal, and SDBS had moresignificant inhibition than CTAB. The effect of SDBS on coagulation representedrestraining effect in the first and then accelerating effect, at last restraining effect.Humic acid and CTAB could adsorb on the surface and changed the surfacepotential of nano-TiO₂. Mastersize2000result showed that humic acid and SDBShad a great effect to the growth of flocs. FT-IR result stated that humic acid andSDBS could decrease the specise distribution of hydrolyzed aluminum. XRD resultillustrated that the flocs had amorphous state, and the crystal structure of nano-TiO₂was not destroyed after coagulation.