Valorization of Sarawak Rice Husk: Synthesis and Characterization of Enhanced Purity Amorphous Silica via Hydrochloric Acid Leaching

Abstract

Rice husk (RH) is a global agricultural byproduct that poses environmental challenges due to disposal via open burning. This study contributes new findings on the RH valorization from Roban, Sarawak, establishing a highly effective hydrochloric acid (HCl) leaching protocol that yields amorphous silica with enhanced purity. The scientific significance lies in the successful optimization of treatment parameters to achieve superior silica oxide (SiO₂) purity of 97.26 wt%, and significantly enhanced whiteness index (WI) (74.4), demonstrating the efficiency of this protocol for regional variants. Furthermore, the structural analysis demonstrates the isolation of a predominantly amorphous phase, providing a critical baseline for utilizing Sarawak-specific agricultural waste in high-performance industrial applications. Energy dispersive X-ray (EDX) spectroscopy analysis confirmed the successful elimination of metallic impurities (P, K, Ca, and Fe), resulting in a reduced mass yield from 43.18% to 36.64%. Furthermore, HCl treatment narrowed the particle size distribution (SPAN: 1.66) and slightly reduced the mean diameter to 33.0 µm. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses confirmed that both samples retained a stable amorphous structure. These results demonstrate that RH from this region is a viable, low-cost precursor for high-quality silica production, offering a sustainable alternative for agricultural waste management.