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Silica Extraction from Rice Husk by Warm Water Pretreatment

Rice husk (RH) has high content of silica. In this study, the extraction of silica from rice husk while maintaining the organics was carried out by warm water pre-treatment followed by alkaline hydrolysis. RH powder was treated with water at 50oC and 100oC prior to treatment with 1 M of sodium hydroxide (NaOH) aqueous solution at 50oC. The filtrate from the alkaline hydrolysis was then further reacted with 1 M of hydrochloric acid (HCl) for silica extraction. The samples obtained after each stage of the treatments were carefully characterized and their chemical compositions were determined. The morphology of the untreated and treated RH powder was analyzed by Scanning Electron Microscopy (SEM). Estimation on the silica content was made by Energy Dispersive X-ray (EDX). The functional group present in untreated and treated RH were determined by Fourier Transform Infrared Spectroscopy (FTIR). The percentage of silica extracted from ΔH2O/NaOH-RH filtrate was higher (18.9%) than from H2O/NaOH-RH filtrate (12.6%). FTIR spectroscopy data indicated the disappearance of siloxane group when RH was treated with hot water and warm water followed by alkaline hydrolysis. The selected extraction method has successfully recovered silica at high yield but at the same time maintaining the organic compounds in the rice husk.