Green synthesis of silica extracted from rice husk ash

The utilization of waste or by-products of different industries and agricultural sectors has beenof great importance in the scientific, technological, ecological, economical, and social spheresin recent years. Rice husk (RH) is a by-product of rice milling, and its combustion generatesrice husk ash (RHA). RHA contains a huge quantity (۸۵–۹۵%) of amorphous silica and can beregarded 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 silicapowders from RHA, an inexpensive source rich in biocompatible silica. High purity silica hasbeen successfully synthesized from RHA through alkaline extraction using the reflux processfollowed by acidification. RHA was obtained by burning the RH in an electric furnace at ۷۰۰°Cfor ۵ 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 silicatesolution. The final step was to precipitate silica from sodium silicate solution by addinghydrochloric acid to decrease the pH to ۴. Characterizations made in general arethermogravimetric analysis (TGA), X-ray fluorescence (XRF) to investigate the mineralcontents 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.

Keywords:

Rice husk , amorphous silica , agricultural waste