Research On Preparation And Property Of Silica From Rice Husk Ash Using Precipitation Method

China’s annual output of about 0.4 tons of rice husk (RH), with the silicon content of about 90% of the complete combustion. At present the majority of discarded as waste, utilization rate is low, and the rice husk ash (RHA) can not be timely treatment. On the basis of rational utilization of resources and improve the economic value added and protect the environment, the silica was prepared from power RHA using Na2CO3 solution by precipitation method, to further comprehensive recovery and utilization of RH resources. Firstly, the dissolution process parameters of silica from RHA were optimized, the key parameters of reaction temperature, the ratio of material to liquid, the concentration of Na2CO3 solution and the reaction time were discussed, and the effects of the filtrate recycling use by adjusting the washing liquid concentration were also explored. Then focus on the modification of silica end product and filter cake stage by KH coupling agent or PEG 6000, to solve the aggregation problem of precipitation silica and improve the dispersity、hydrophobicity index and DBP absorption value of products. The main research contents and conclutions are as follows:The silica was extraction from rice husk ash by precipitation method.Through the single factor experiment and response surface method, the extraction technology was optimized. The results showed that:when the reaction temperature was 100℃, the ratio of RHA to Na2CO3 solution was 15 g:300 mL, the concentration of Na2CO3 solution was 20 wt.%, the reaction time was 3 h, the yield of silica from RHA could reached 92.39%. Effects of Na2CO3 filtrate recycling, will be found when the washing liquid was adjusted to 10 wt.% Na2CO3 solution as compensation in the loss of process, other conditions remain unchanged, the yield of silica from RHA could remain above 90%, indicating that the filtrate can be recycled, and the washing liquid and cooling water recyclable utilization, not only save the cost but also solve the problems of filtrate reclaim. FT-IR spectra showed that the existence of large number of hydroxyl groups and adsorbed water on silica surface can easy to make particles reunion. XRD results showed that the silica is amorphous structure model. SEM picture showed that the product had a serious agglomeration phenomenon, and the distribution of particles was uneven, the individual particles were not easy to distinguish.The results modified silica by KH570 showed that 5 g silica was dispersed with 90 mL deionized water (pH4-5), and then 5 mL modifier were added into the solution and reacted for 70min at the temperature of 90℃, the obtained modified samples hydrophobicity index can reached 100%, the DBP absorption value decreased from 1.97 mL/g to 1.15 mL/g. It indicated that the aggregation state of product decreased, and the uniformity of dispersed particles increased.The particle size analysis shows that the modified particle size by KH570 little overall change, but the aggregate more easily disperse. FT-IR detection shows that the KH570 hydrolysis products were successfully reacted with particle surface -OH. BJH pore size distribution showed that the silica finish modified with KH570, make the original product with large holes and large specific area were destroyed, and the growth of aggregate will be dissociated, but the organic solvent dispersion and hydrophobic will be improved. SEM showed that the phenomenon of particle agglomeration was weakened, the particle was more compact and the pore distribution was more uniform.Using PEG 6000 modified silica in the stage of filter cake, the optimum process conditions are as follows:The filter cake with 80 mL water dispersion, add the amount of 15 wt.% PEG 6000 modified 2 h under the temperature 70℃, the DBP absorption value of modified silica was about 3.00 mL/g. FT-IR analysis showed that the surface modification with PEG 6000 in the filter cake stage was feasible, the PEG 6000 can winding grafted on the surface of the product effectively. Particle size analysis showed that PEG 6000 adsorption on the silica surface, not only can promotion particles coacervation, but also can prevent the agglomeration of particles continue to grow, and make particle size distribution more uniform. Besides, it can effectively increase the porosity, specific surface area and dispersion of the products. SEM showed that the aggregates were released, the distribution of the particles was more uniform, and the overall dispersion was improved. At the same time, the filter cake stage modification, easier to removal impurity ions wrapped in the filter cake, but also makes the product easier to dry caking, products are looser and easily broken, overcomes the problems easily caking in drying process.