Green Synthesis of Silica Extracted from Rice Husk Ash

There has been a significant rise in the scientific, technological, ecological, economic, and social popularity of applications of by-products or waste materials in various industries including the agricultural sector. A by-product of rice4 milling is Rice Husk (RH), which, when burned, produces Rice Husk Ash (RHA). RHA is considered an economically viable raw material used for developing silica-based products since it contains a significant amount of amorphous silica (between 85 and 95 percent). The current research aims to create a green process for producing silica powders from RHA, an inexpensive source rich in biocompatible silica. High-purity silica was successfully generated from RHA through alkaline extraction using the reflux technique and subsequent acidification. For this purpose, RH was burned in an electric furnace for five hours to create RHA at 700 °C. The obtained ash was washed with hydrochloric acid to eliminate the metallic impurities. The sodium silicate solution was then obtained by refluxing the acid-washed RHA in a NaOH solution. The final step was to precipitate silica from sodium silicate solution by adding hydrochloric acid to decrease the pH by 4. Characterizations made in general are Thermo-Gravimetric Analysis (TGA), X-Ray Fluorescence (XRF) for identifying the mineral contents of RHA, Fourier-Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Simple, efficient, environmentally-friendly, and ideal for mass production are all attributes of the synthetic process.