農作物非食部バイオマスから高純度非晶質シリカの抽出プロセスとコンクリート用混和材としての利活用

摘要

Rice husks, one of the typical agricultural wastes, consist with 70-75 mass% of organics and 15-20 mass% of amorphous silica. Silica can be obtained by combusting rice husks in air. However, silica purity is reduced by metallic impurities contained in rice husks. To extract high-purity amorphous silica from rice husks, the citric acid leaching process was developed to remove the metallic impurities from rice husks. By optimizing the citric acid solution concentration and combustion temperature of rice husks, completely amorphous silica ashes with 99.5 mass% were obtained. To establish the large-scale equipment to produce high purity amorphous rice husk silica, the process parameters in the citric acid leaching and air combustion were optimized. There was no significant difference of silica purity and the impurity contents of rice husk ashes by using between small-scale and large-scale equipment. Citric acid leached rice husk ashes were employed as the reinforcements of concrete materials. Compressive strength in use of high-purity amorphous silica revealed a higher value compared to the use of silica fume and raw rice husk ashes. The effect of citric acid leached rice husk ashes was high pozzolanic reactivity due to high-purity amorphous silica particles and the large surface area due to their porous structures.