Producing High-purity Silica And Ultrafine Silica From Rice Husk

Rice husk is the main by-products of rice processing,most people use rice husk as primary fuel, but unprocessed rice husk ash may cause environmental pollution. silica in the rice husk can be used as an ideal raw material of silicon which is a product of fine chemical. Therefore, how to extract silica from rice husk has fine environmental and economic benefits.Silica aerogel,namely precipitate SiO2, is of SiO2 with fine powder or particles.High purity silica is the basic material which was used to produce high purity silicon, polycrystalline silicon and other chip raw material by the semiconductor industry and solar photovoltaic industry. Special structure ultrafine silica with a unique nature demonstrates the property of hydrophilic, reinforcing, thickening, thixotropy, extinction, decentralized nature, insulation, anti-sticking and so on.A method of directly producing high purity silica from rice husk was introduced in this paper.The impact of cycle acid- soaking process conditions on rice husk ash was studied,the removing metallic impurities in rice husk with different substance was studied too.The optimum conditions of the reaction were defined which is the rice husk soaked first for a day,then was refluxed for 3 h with 5% hydrochloric acid, calcining it for 3 h at 550℃.Under these conditions, the whiteness of obtained product was higher than 94, the purity of silica over 99.9%. The specific surface area of the product reached 190.17m2·g-1 by the method of pulse chemisorption, infrared spectra analysis and the X- ray diffraction showed silica product was hydrated silicon dioxide with amorphous structure.At the same time, the method of producing ultrafine silica from rice husk ash was introduced in this paper; The impact on the extraction rate of SiO2 of reacting with calcined alkali method and atmospheric process method was studied; The main factors affecting condition in the process of urltrafine silica was studied, we also discussed the other conditions which can affect the results.Under the optimum conditions conditions, the purity of obtained silica was over 96%, BET 302 m2·g-1.The structure of high purity silica and ultrafine silica were analyzed IR, XRD, SEM, and scanning electron microscope photographs show the basic particle size of the ultrafine silica about 0.2μm.