Mechano-chemical conversion of rice husk ash and gasifier-derived rice husk ash into porous silicon

Rice husk is an abundant agricultural biomass and a potential source of amorphous silica and porous silicon. To produce high-purity SiO₂ and Si from rice husks, multiple steps of acid leaching to remove impurities and heat treatment to reduce residual carbon are necessary. In this study, a simple mechanochemical (magnesio-milling) experiment was conducted using an attrition mill to convert rice husk ash (RHA) and gasifier-derived rice husk ash (GRHA) into porous Si under various acid leaching (hydrochloric acid and lactic acid) and heat-treatment conditions. Three noteworthy results were obtained. First, eco-friendly lactic acid can be used instead of the harmful acid (hydrochloric acid). Next, the heat-treated GRHA was converted to Si via magnesio-milling without acid leaching. Finally, the carbon content (<0.3 wt%) of RHA and GRHA is a key factor affecting the conversion of SiO2 into Si based on elemental analysis. The purities of the Si samples prepared from RHA and GRHA, analyzed using inductively coupled plasma (ICP) mass spectrometry, were 97.66% and 95.62%, respectively. Furthermore, the porous Si prepared using RHA and GRHA can be utilized as a high value-add material such as an anode material for lithium-ion batteries and nanostructured materials.