High-Grade Biosilica Isolated from Diluted Acids Leached Rice Husk

Rice husk which consists of ~20% silica seems to be quite promising to be the biosilica resources. As one of the most abundant agricultural wastes derived from paddy milling sites, rice husks have been generally directly burn on sites causing air pollution and environmental problems. Rice husk silica is amorphous in nature which is quite reactive and has a great potential to be used as a raw material for various silica based products. The aim of this experiment was to study the efficacy of diluted acids such as HCl and citric acid in order to obtain high-grade silica. The characterisation of silica ashes included the analysis of composition and structure using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), X-ray Fluorescence (XRF). The specific surface area of silica was determined using Brunauer, Emmet, Teller-Surface Area Analyzer (BET-SAA). Silica produced from these experiments had an amorphous form. The highest silica purity with Si content of 96.2% was obtained from rice husk treated using diluted HCl. However, the highest specific surface area of ~253 m2/g was derived from diluted citric acid treated rice husks. Diluted acids seemed to be quite effective in removing metallic impurities enabling to produce high grade biosilica.