green synthesis of silica extracted from rice husk ash

The utilization of waste or by-products of different industries and agricultural sectors has been of great importance in the scientific, technological, ecological, economical, and social spheres in recent years. rice husk (rh) is a by-product of rice milling, and its combustion generates rice husk ash (rha). rha contains a huge quantity (85–95%) of amorphous silica and can be regarded as an economically viable raw material in the production of silica-based products. the objective of the present work is to develop a green procedure for the preparation of silica powders from rha, an inexpensive source rich in biocompatible silica. high purity silica has been successfully synthesized from rha through alkaline extraction using the reflux process followed by acidification. rha was obtained by burning the rh in an electric furnace at 700°c for 5 hours. the ash was washed with hydrochloric acid to eliminate the metallic impurities. then the acid-washed rha was refluxed using sodium hydroxide to get the sodium silicate solution. the final step was to precipitate silica from sodium silicate solution by adding hydrochloric acid to decrease the ph to 4. characterizations made in general are thermogravimetric analysis (tga), x-ray fluorescence (xrf) to investigate the mineral contents of rha, fourier-transform infrared spectroscopy (ftir), x-ray diffraction (xrd), and scanning electron microscopy (sem). the synthetic procedure is straightforward, inexpensive, environment-friendly, and suitable for large-scale production.