PREPARATION OF SILICA FROM RICE HUSKS

Preliminary leaching of rice husks with a solution of hydrochloric aci d before their combustion at 600 degrees C is shown to be required to obtain relatively pure silica (similar to 99,5%) with a high specific surface area (similar to 260 m(2)/g) that is maintained even after hea ting at 800 degrees C, Transmission electron microscopy observations i ndicate that this material has a homogeneous size distribution of nano metric particles. However, if the leaching with HCl is performed on th e white ashes obtained by combustion of the rice husks at 600 degrees C, an amorphous silica with the same purity also is obtained, but its specific surface area decreases to 1 m(2)/g. This behavior is due to a strong interaction between the silica and the potassium contained in the rice husks, which leads to a dramatic decrease of the specific sur face area if KC cations are not removed prior to the heat treatment at 600 degrees C. This finding leads to a better understanding of the ef fect of potassium on the morphology of silica.