Optimization And Performance Analysis Of Preparation Of Silica From Rice Husk And Rice Straw Biochar

All over the world,China is the country with the largest rice planting area producing a large amount of rice by-products,such as rice husks and rice straw,each year.Since the content of SiO₂in rice husk biochar reaches more than 80%,it can be used as a raw material for the preparation of silica;the content of SiO₂in rice straw biochar is about 50%,but there are few studies on the preparation of silica from rice straw biochar,in order to take advantage of the high silicon content of rice straw biochar and explore new ways for the resource utilization of rice straw,In this study,rice husk and rice straw biochar were used as raw materials,and rice husk biochar was used as a reference object to explore the effect and feasibility of preparing silica from rice straw biochar.Using the method of alkali-soluble acid precipitation,the intermediate product sodium silicate of silica was first extracted by rice husk and rice straw biochar,and a single-factor test was conducted with sodium silicate modulus and SiO₂dissolution rate as research indexes,the effects of the concentration of Na OH solution,liquid-solid ratio,reaction temperature and reaction time on sodium silicate modulus and SiO₂dissolution rate were studied.the optimal reaction conditions for the preparation of sodium silicate from rice husk and rice straw biochar were analyzed by central combined design response surface method;The effects of aging time,reaction temperature,concentration of sulfuric acid solution and reaction endpoint p H on the purity of silica prepared from rice husk-based sodium silicate and rice straw-based sodium silicate were further investigated using sodium silicate as the raw material and the optimum preparation conditions and properties of silica were analyzed by response surface method.It provides theoretical basis and technical support for the preparation of silica from rice straw biochar,and is intended to open up a new way for the resource utilization of rice straw.The research uses rice husk and rice straw biochar as raw materials to prepare sodium silicate solution.Through response surface optimization,the optimal conditions for preparing sodium silicate from rice husk biochar and rice straw biochar are as follows that the concentration of Na OH solution was 2mol/L,and the ratio of liquid-solid ratio was 7m L/g,the reaction temperature was 90℃,and the reaction time was 4h.Under these conditions,the modulus of sodium silicate prepared from rice husk biochar was 1.65,and the dissolution rate of SiO₂was 78.6%;the modulus of sodium silicate prepared from rice straw biochar was 0.69,the dissolution rate of SiO₂was61.3%.Through the central combination design response surface method,the optimal conditions for preparing silica from rice husk-based sodium silicate and straw-based sodium silicate were obtained as follows that the reaction temperature was 80℃,concentration of sulfuric acid solution was 11%,reaction endpoint p H was 9,and aging time was 2h.Under the optimized conditions,the purity of silica prepared by rice husk biochar was 98.76%,and the purity of silica prepared by rice straw biochar was 94.68%.The characterization of the silica samples prepared in this study revealed that the silica particles prepared in this experiment all had a spherical structure,the particle size was between20～30nm;the silica prepared from both materials is in amorphous amorphous form;the silica prepared by rice husk and rice straw biochar was compared with the national standard HG/T3061-2009.It was found that the indexes of the silica prepared under the optimized conditions in this study met the national standard.This experiment can realize the preparation of standardized silica from rice straw biochar,which has positive significance for the resource utilization of rice straw.