Extraction of Silica from Rice Straw Using Alkaline Hydrolysis Pretreatment

Abstract

Rice straw is an abundant resource in Asian countries, for instance, Malaysia and India. Rice straw is a major agricultural waste product, which caused disposal issue in areas. Residue burning crops was adopted for the farmers to dispose of rice straw after harvest in order to prepare seedbed preparation for next season. An alarming air pollution report impacted by open burning of rice straw contributes to global warming. Commercialization of silica is an alternative method to dispose of agro-waste residues. The main objective of this research is to extract silica from rice straw. The amorphous silica was derived by first digesting rice straw with Soda AQ solution by varying NaOH concentration from 5 wt% - 25 wt% and 0.1 wt% anthraquinone (AQ) to dissolve silica content and acid precipitation at pH 7 to obtain silica gel. Other parameters such as the effect of digestion temperature (60 °C to 90 °C), digestion time (1 hour to 3 hours), and Soda AQ to rice straw impregnation phase ratio (150:5 to 500:5). The optimum effects of parameter had yielded 74.11 % of silica and it was demonstrated by Soda AQ with NaOH concentration 20 wt% and 0.1 wt% AQ, temperature of 75 °C, digestion time of 3 hours and the ratio 200:5 of Soda AQ to rice straw. Characterization of rice straw was performed by using Fourier Transforms Infrared Spectroscopy (FTIR). The commercialization of silica had the potential to be utilized as construction materials and silica gel that aids to absorb moisture.