Preparation Of High Value-added Silica From Biomass Fly Ash

With the development of renewable energy in the country,the potential of biomass resource fuel utilization has been stimulated.The waste of biomass resources is avoided,and huge social and economic benefits are produced at the same time.The scale and quantity of national biomass power plants continue to expand,and the biomass ash produced has also increased,causing more and more serious pollution to the ecological environment and increasing environmental pressure.It is urgent to explore its large-scale,resource-based,and green treatment and disposal Way.Biomass fly ash has the characteristics of high Si O₂ content and low heavy metal content,and is an ideal silicon source for preparing silica.This paper proposes a process for preparing high value-added silica by chemical precipitation using biomass fly ash as raw material.The acid leaching and purification technology of biomass fly ash,the process conditions for preparing water glass from biomass fly ash and the process for preparing silica from water glass were studied.The specific process is as follows:According to the elemental composition characteristics of biomass fly ash,the biggest factors affecting the acid leaching experiment are determined as reaction temperature,reaction time,concentration of sulfuric acid leaching solution,and reaction solution-solid ratio.The more efficient process conditions for acid leaching and purification of biomass fly ash were obtained:the reaction temperature was 100°C,the reaction time was 180 min,the sulfuric acid concentration was 20%,the liquid-solid ratio was 6:1,and the ball mill speed was 500 r/min.The Si O₂ content in biomass fly ash was increased to 95.2%.Using the biomass fly ash after acid leaching to remove impurities as the raw material,the water glass solution is prepared by reacting with sodium hydroxide lye.The effects of ash-to-liquid ratio,reaction time,lye concentration and reaction temperature in the reaction system on the preparation of water glass by dissolving Si O₂ in biomass fly ash were experimentally studied.The experimental results show that the best experimental conditions for preparing water glass are:the ratio of liquid to ash is 6:1,the reaction time is 2 h,the concentration of lye solution is 3 mol/L,and the reaction temperature is 105℃.Using the water glass prepared by the above method as a raw material,high value-added silica is prepared by adopting a chemical precipitation method.The effects of reaction sulfuric acid concentration,reaction temperature,p H at the end of the experiment,ultrasonic frequency,and aging time on the oil absorption value of silica were studied.The experimental high-efficiency preparation conditions were determined:the concentration of sulfuric acid was 10%,the reaction temperature was 60°C,the endpoint p H was 7,the ultrasonic frequency was 20 k Hz,and the aging time was 120 min.A preliminary modification experiment was carried out on the prepared silica samples.In the modification,bis-[γ-（triethoxysilyl）propyl]tetrasulfide was used as the modifier.Influence on the dispersibility of silica samples.It is determined that the optimum addition amount is 6%,which improves the dispersibility of silica.By XRD phase analysis,TEM dispersion analysis,SEM micromorphological analysis,BET specific surface area analysis and physical and chemical properties analysis of the silica samples,the results show that the silica samples have a specific surface area of 316.81 m²/g and an oil absorption value of 3.4.cm³/g,and various properties are better than those of commercially available silica products.The initial 20 times magnification experiment was carried out,and the fluctuation of product quality was not large,which met the requirements of the"HG/T3061-2009"standard.The process of preparing silica from biomass fly ash is not only conducive to realizing large-scale treatment of biomass fly ash in power plants,but also realizing its resource utilization.The acidic solution in the purification process can be further recycled,avoiding environmental pollution,and a very small portion of the remaining alkaline residual ash after the reaction is left for further dissolution treatment,thereby reducing waste of resources.Finally,products such as alumina are prepared by treating the generated acid leaching solution.This process is a sustainable development technology with high resource recycling rate,considerable economic added value and environmental friendliness.