Synthesis of Amorphous Silica from Rice Husk Ash: Comparing HCl and CH3COOH Acidification Methods and Various Alkaline Concentrations

High purity silica has been successfully synthesized from rice husk ash (RHA) by alkaline extraction using the reflux process followed by acidification. For this study, rice husk was burned in an electric furnace at 700°C for 5 hours to produce RHA. The RHA was refluxed using sodium hydroxide with concentrations of 1.25x10^-3 M (equal to 5% NaOH) and 2.5x10^-3 M (equal to 10% NaOH). The acidification process was performed using hydrochloric acid (HCl) 1 M and acetic acid (CH₃COOH) 1M to produce silica gel. Then, the silica gel was heated to 120°C for 12 hours to produced silica. The characterization of silica was determined using energy-dispersive X-ray analysis, Fourier-transform infrared spectrometry, the Brunauer-Emmet-Teller method, and X-ray diffraction. The results show HCl acidification produced silica of a higher purity than that produced by CH₃COOH acidification. The higher concentration of sodium hydroxide led to higher purity of silica. Based on X-ray diffraction, the silica extracted from RHA was found to be amorphous, and Fourier-transform infrared spectrometry revealed bending and stretching vibrations of Si-O and Si-O-Si. The silica extracted by HCl acidification had a surface area of 236 m²/g, a total pore volume of 0.54 cc/g, and an average pore diameter of 9 nm. The silica extracted by CH₃COOH acidification had a surface area of 204 m²/g, a total pore volume of 0.43 cc/g, and an average pore diameter of 8.4 nm.