Conclusions
Acid treatment of RH followed by thermal combustion under controlled conditions gave 22.50% ash of which 90.469% was silica. At optimized conditions, a nanosized, highly purified silica (98.8 mass percentage) was produced with a high surface area, high reactivity, and 99.9% in amorphous form. This nanosilica showed strong and a large number of acidic sites in comparison with commercial silica, making it a good support for catalysts. Considering the availability of RH worldwide, this study shows that economic technology can be used by rice-producing companies to produce highly effective silica and to reduce the environmental impact of the usually uncontrolled burning of the by-products of the industry, namely RH. This is particularly relevant to an agro-based country, which is still importing micro- and nanosilica for some applications.