Synthesis of Silica from Rice Husk by One-step Combustion, Fluidized Bed Combustion, and Alkaline Extraction

Abstract

The objective of this research was to synthesize silica (SiO₂) from rice husk by three techniques: one-step combustion, fluidized bed combustion and alkaline extraction. First, the rice husk was treated with 1 M of HCL for 3 hours. Then it was combusted in a box furnace under flowing of oxygen at varied temperature of 500, 600, 700, and 800ºC for 45 or 60 min. After determining the purity and specific area of obtained products, it was concluded that the optimum condition for the one-step combustion was firing at 700 ºC for 60 min. The obtained product was amorphous having 99.9% (wt.0) SiO₂ and specific surface area of 315± 5 m²/g. The rice husk was also pyrolyzed in a fluidized bed burmer at 550 ºC for 15 min under flowing of nitrogen and then fired at 600 ºC for 3 hours under flowing of air. The obtained silica was also amorphous having the purity of 99.8% and the specific surface area of 331 ± 6 m²/g. For the last method, the rice husk ash was extracted by 1 M NaOH. This technique yielded 96.6% SiO₂ having the highest specific surface area of 404± 5 m²/g.