Influence of Inherent Silicon and Metals in Rice Husk on the Char Properties and Associated Silica Structure

To obtain high-purity amorphous silica from rice husk char through heat treatment, the distribution of silica and other metallic species in this char and their effects on char combustion reactivity were investigated. The pore properties, crystal structures, and particle sizes of rice husk chars and ashes were analyzed. It was observed that an embedded structure mixing amorphous silica and carbon existed, and its size may be 1–10 nm. This structure may protect the amorphous property of silica during heat treatment. The inherent metallic species were also distributed in the pore size range of 1–10 nm; furthermore, these species accelerated the burnout rate and the crystallization of amorphous silica above 1000 °C.