The Modification And Applied Research On Silicia

Silica, which is widely used in rubber, coating, fuel, plastic and papermaking industry, is considered as the most important chemical raw materials. There is a large market demand, however, in nowadays, the majority of products are dependent on import. On the other hand, there are a great number of fly ash in emissions which don't get enough utilization.In this paper, two processes including acid method and concentrated alkali fusion method were investigated. In these two methods, fly ash was used as raw material, with the phase diagram analysis, and combined with screening of different activators to extract SiO2. Finally, the best process operation process conditions were obtained. For the acid method, the optimum process condition was figured out as follows:acid concentration was 3.5mol/L, bath temperature was 80℃, reaction time was 30min, stirring speed was 180 r/min. The dissolution rate of 81.3% and the purity of 98.5% for SiO2 were obtained under the best process. For the concentrated alkali fusion, the optimum technology was found as follows:the mass ratio of soliumhydroxide to ash fly was 3.5 to 5, the best aging time was three days using wet mixing method. Under the optimum process, the dissolution rate of 95.5% and the purity of 98.6% for SiO2 were achieved.The experiments of modification of fly ash obtained from above mentioned process were also conducted. Some conclusions were obtained as follows:the temperature of pre-treatment was 80℃; the pretreatment time was fixed at 60 min; the temperature of modification was 120℃, the modification time was 90 min. In this work, the KH550 was selected as a modifier, and the best dosage was 30%(vol%). Under this condition, the surfacehydroxyl number of obtained powder was 0.3312/nm2 with lipophile value of 35.1% and DBP value of 2.4mL/g. All targets were met or exceeded the national standard requirements.The modified SiO2 can be used in new materials and synthesizing of five-coordinated silicon compounds which can synthesis epoxy silicon compounds (siliane binder) at lower temperature. The obtained siliane binder can replace the silane cupling agent. The tensile strength of diaphragm materials increased more than 7% though the addition of modified SiO2.This research can give grounds to make high-value use of ash fly. It has great significances for improving the present situation of dependence on silicia's imports.