Kinetic study on the preparation of silica from rice husk under various pretreatments

Abstract

Recovering silica from rice husks by calcination is an economical and attractive method of manufacturing high value-added products. The pretreatment process plays an important role in the preparation of amorphous silica by influencing both the removal of metallic impurities and further decomposition of organic compounds. In this paper, the pyrolysis kinetics of various pretreatment processes, including water soaking, acid leaching and grinding, were investigated using thermogravimetric analysis. The contributions of various pretreatment to the production of silica can be listed as follows: acid leaching > water soaking > grinding. Acid leaching at 120 °C with an acid concentration of 8 mass% and grinding raw material into 100 mesh was most beneficial to the removal of metallic impurities and thermal decomposition of organic compounds. The Flynn–Wall–Ozawa method was employed to derive the kinetic parameters (activation energy and correlation coefficient). The activation energies were calculated to be in the range of 90–156 kJ mol−1 for rice husks with various pretreatments at different conversion fractions. These results provide useful information for the rational design and scaling up of pretreatment reactors.