Effect of Water and Acid Pre-treatment on the Physicochemical Properties of Rice Husk for Silica Extraction

Abstract

Rice husks are residue materials from rice milling. These materials are mostly discarded after obtaining the rice, however, numerous studies have found out that rice husks are an excellent renewable source of silica. Rice husks are generally turned into rice husk ash in order to extract the silica in the material. Prior to the combustion process, pre-treatment methods are usually done in order to minimize the impurities in the husks. Failure to remove these impurities lead to undesired properties of the extracted silica. As such, we investigate some common pre-treatment methods, namely water and acid (HCl) treatment, and their effects on the surface morphology and elemental composition of the husks after treatment. It was found that H2O was more effective in removing the bromide ions Br−, while HCl becomes less effective at increasing concentration. Also, acid treatment was more effective in removing the sodium and potassium components compared to water treatment. However, efficiency decreases as the acid concentration increases due to interference of silica polymerization. Thus, for the removal of impurities in rice husk, lower concentration of acid pre-treatment is recommended.