Preparation Of Silica Aerogel From High-Alumina Fly Ash: An Experimental Study

Fly ash is mainly produced through coal combustion in coal-fired power plant. It is oneof the most industrial wastes all over the world.The raw materials used in this research came from coal-fired power plant in innerMongolia. The SiO₂ and Al₂O₃ contents of the fly ash TF-04 is over 85%. The fly ash consistsof mainly mullite and silicate glass phases, with minor amount of α-Al₂O₃. The mixtures ofthe fly ash and Na2CO3 were calcinated at 870℃ for 90min, and fly ash/ sodium carbonate(in quality) was 1.00∶0.8. The powder sintered leaded to thermal decomposition reaction ofmullite and vitreous glass balls, and changed to the nepheline soluble in acidic solution, andthe mullite' diffraction was disappeared in the XRD pattern. The dissociation proportion ofthe fly ash mixture is up to 94.6%. The activiation energy of the sintering reaction in the flyash-Sodium carbonate system is 129.86kJ/mol from the dynamical experiments.The white carbon black and silica aerogel were prepared by sol-gel and chemicalprecipitation methods. The first was that nepheline was leached from hydrochloric acid witha concentration of 2.5-5mol/L. After filtering and removing impurity, such as α-Al₂O₃ andCaTiO3, and the solution was changed from sol to gel. The silica particles were growed andaggregated and through filtrating, and Al₂O₃ and SiO₂ was separated. The content of Al₂O₃ inthe silica precipitant prepared was around 1%, and the silica extraction efficiency was up to93.44%. The white carbon black was prepared from silica gel through filtering and drying.The silica aerogel AG1 was prepared from distilled water soaking and filtering and drying.The SiO₂ content of the products is over 99.45%, and satisfying the standard of silica areogelTMS-100P, and specific surface area is 775.12m2/g.The second method was immited surfactant PEG from silica sol. The surfactant has theeffect of room space hinder and package particles that the particles are dispersed, and theeffect of joining the particles. Thus it could adjust the hole's structure and particle distruction.In the experiments, azeotropic distillation method was used to prevent the particlesaggregation. The silica areogel AG2 was producted by reaction temperature at 45℃, PEGmolecular weight 8000, and concentration 0.5%, additive amount 50 mL.The SiO₂ content ofthe as-prepared products is over 99.35%, and specific surface area is 773.1m2/g, with anaverage pore size around 4.09nm.The silica aerogels prepared using the above method weremesopore materials by the pore size.The technique, used to prepare the white carbon black and silica aerogel from the fly ashin this research, is high efficiency in saving energy, with environment-kindness.Simultaneously it could consume a large amount of fly ash discharged by the electrical plant,which is propitious to reduce the industrial solid wastes and to improve the localenvironment.