The effects of thermal decomposition on the surface properties and the chemical activity of rice husk ash were investigated by XRD, XRF, BET, chemical analysis, and electrical conductivity method. The results show that with simple hydrochloric acid pretreatment of rice husks, white rice husk ash comprising of pure amorphous silica with high specific surface area (145-311 m2·g-1) was obtained from the heating rice husks at the temperature 550-900°C. The metallic impurities in rice husk ash were substantially reduced, and decrease of impurities resulted in difficult formation of crystalline phase from amorphous silica in rice husk ash. The crystalline phase of distorted quartz structure was formed above 1000°C. The surface properties and the chemical activity of silica in rice husk ash strongly depended on the soaking temperature and were slightly affected by the soaking time at a given temperature.
