| The enhancement of eutrophication in freshwater bodies has increased blooms of cyanobacteria(blue-green algae)which have brought bad influence on people’s life and production.How to remove the algae effectively and scientifically in water is the key to study.LDHs is a new type inorganic functional material with positive charge.This thesis used Layered Double Hydroxides(LDHs)to remove electronegative algae.In the thesis,the influence law of preparation conditions of LDHs on LDHs’ algae removal performance was studied,the characterization of structural features of LDHs was analyzed,the influence law of water quality factors on the algae removal performance of LDHs was systematically investigated,and the algae removal mechanism of LDHs was discussed.Chemical coprecipitation method was used to prepare LDHs.The influence of preparation conditions of LDHs on the algae removal performance was studied,such as raw materials of different metal combination,the mole ratio of secondary to tertiary valence metal ions(M2+/M3+),the molar ratio of hydroxyl ions to carbonate ions(OH-/CO32-),aging time(H),reaction temperature(Ti),aging temperature(T2)and stirring speed(C).The results showed that the algae removal performance of Zn-Al LDHs is the best in that of the different metal composition.Along with the increase of the mole ratio of Zn2+to Al3+,the removal efficiency of algae by Zn-Al LDHs increased,but it decreased when Zn2+/Al3+exceeded 2.7.The removal efificiency of algae changed irregularly when the mole ratio of OH-to CO32-ranged from 1to 5,and it was high between 2 to 3.The removal efficiency of algae rised slowly with the increase of reaction temperature,and reached maximum at 75 °C.The removal efficiency of algae increased as aging time long from 3 hours to 9hours,but descended after 9hours.The removal efficiency of algae increased with the increase of aging temperature,and reached the higest at 55℃,but after 55℃ it decreased with the increase of aging temperature.The removal efficiency of algae increased with the increase of stirring speed,but it didn’t change after1OOOr/min.The orthogonal test on preparation of Zn-Al LDHs showed that the order of factors affecting the algae removal performance is T2(℃)>OH-/CO32->Zn2+/Al3+>H(h)>T1(℃).The optimum preparation condition of Zn-Al LDHs sample is T2=65℃,OH"/CO32-=2.0:1,Zn2+/Al3+ =2.7:1,H=6h,T1=75℃.Under the optimum preparation conditions,as the water sample whose density of cylindrospermopsis raciborskii is 4.49×108cells/L,the pH value was controlled at 7.04,and the dosage of Zn-Al LDHs is 25mg/L,the removal rate of chlorophyll-a can reach to 94.62%.Zn-Al LDHs was characterized by scanning electron microscopy(SEM),infrared spectrum(FTIR),x-ray diffraction(XRD),specific surface area(BET)and micro electrophoresis.The FTIR and XRD analysis results showed that Zn-Al LDHs contained carbonate ions between the layers,it is multilayer in structure and its layer spacing is 0.758nm.The SEM analysis results showed that the shape of Zn-Al LDHs is inerratic,the diameter of particles is symmetrical,and the surface of particles is rough and has many holes.The BET analysis results showed that the specific surface area of Zn-Al LDHs is 42.81 m2/g,and Its aperture size is 20～60nm.The Zeta potential of Zn-Al LDHs became low with the increase of pH,the isoelectric point of Zn-Al LDHs was 10.45.The thesis studied the effect of Zn-Al LDHs dosage,algal density,pH,turbidity,humic acid,phosphorus and algal species on algae removal by Zn-Al LDHs.The removal efficiency of algae increased along with the increase of the dosage of Zn-Al LDHs.The removal efficiency of algae decreased along with the increase of pH.The removal efficiency of algae increased with the increase of algal density,but it decreased after the density of 6.824×108 cells/L.Due to the competitive adsorption,the removal efficiency of algae by Zn-Al LDHs decreased along with the increase of humic acid and phosphate concentration.The removal efficiency of algae decreased when the water turbidity rised.The dosage of Zn-Al LDHs increased when it was used to remove other algae. |
