Preparation And Coagulation Properties Of SiO₂ @ Al₁₃ Core-shell Composites

Al₁₃(Al₁₃O₄(OH)₂₄(H₂O)₁₂⁷⁺) with a Keggin structure is the formation of aluminum in the process of forced hydrolysis of Al3+. Due to the highly charge, it is beneficial for adsorpting and charge neutralizatiing of particles in water. And then, the particles off-steadied, aggregated, settled, so as to achieve the purpose of water purification. The quality of inorganic polymer flocculants polyaluminum chloride(PAC) is used to be evaluated by the content of Al₁₃.In this paper, we prepare different basic PAC through micro-drops of alkali method and purify Al₁₃ by SO₄^2-/Ba²⁺ precipitation replacement method. Meantime, we verify coagulation performances of PAC and Al₁₃ in the kaolin wastewater. Uniform SiO₂ spherical particles distributing in sub-micron particle sizes are prepared by St(o|¨)ber method. Then, SiO₂@Al₁₃ core-shell structure composite material is prepared by electrostatic self-assembly. We discuss the different reacted conditions exerting the effect on the preparation of composite material. Its coagulation performances is tested for playing particle size effect to increase its applicability.The study includes the following parts.(1) Preparation and coagulation performances of PAC and Al₁₃PAC of different basic are prepared by the micro-drops of alkali method and Al₁₃ are purified by SO42-/Ba2+ precipitation replacement method. We discuss different basicity producing effect on the Al morphology distribution. Studies have shown that, for PAC, the content of Alb are less than 50% when the basic(B) in ranging from 0.5 to 1.5;as with the increasing of basic up to rang from 2.0 to 2.5,the content of Alb reaches more than 60%. Alb levels reached more than 90% in purified Al₁₃.Because of the formation of Al₁₃-aggregates which reduce the Ferron activity,the content Alb reduced to 60%. Coagulation tests show that, highly basic PAC have the stronger capacity of electric-natrual, so it show up better turbidity removal efficiency.While for Al₁₃ with the increase in basic, the capacity of electric-natrual of Al₁₃-aggregates are relatively reducing.(2) Preparation and Characterization of mono-dispersed silica dioxide Uniform size distribution of sub-micron silicon dioxide is prepared with St(o|¨)ber method. Research shows that, with the increasing concentration of water, average particle sizes of silicon dioxide range from 170nm to 200nm mainly effected by the number of unstable nuclei during the initial reaction; average particle sizes also similarly increase with the increasing concentration of ammonia mainly effected by the hydrolysis reaction rate; because of increasing TEOS concentration, the number of three-dimensional network of chains also contributes to the increase in average particles size of silica dioxide. Optimizing the variety of factors, we can prepare the required size of uniform SiO₂ spherical particles. Mesoporous distributes on the spherical surface and the surface possesses negative charge in pH=4⁹.(3) Preparation and coagulation properties of SiO₂@Al₁₃ core-shell structure materialSiO₂@Al₁₃ core-shell structure materials are prepared through electrostatic self-assembly method. Researches show that, with the ratio of Al/Si increasing, the content of Al₁₃ loading on silica surface increase; when the ratio up to more than 1:1,Al₁₃ coating on the surface have little change. With reaction temperature increasing, the amount of Al decreases, so high temperature have a negative effect on the coating of Al₁₃ on the spherical surface. The increasing basic, because of the information of Al₁₃-aggregates connecting by OH-, the steric effect is not beneficial for the loading. The analysis show that, the roles on the silica surface are physical effects. Coagulation experiments show that, relativing to the pure Al₁₃, SiO₂@Al₁₃ composite materials form large particle size and the turbidity removal effect is better for the particle size effect.