Application of Design Experiments in Optimizing Silica Extraction from Coal Fly Ash and the Product Characterization

Abstract

Mesoporous silica was successfully extracted from coal fly ash using the sol-gel method at optimum temperature and stirring speed. To optimize conditions for silica extraction the temperature response and stirring speed were analyzed using Design-Expert software with a central composite design under response surface methodology. The study yielded optimal conditions at 80 °C and 260 rpm. The ideal response under these circumstances yielded 7.8% coal fly ash silica (SCFA). Fourier transform infrared spectroscopy analysis results showed that the SCFA had a wavelength of specific silica compounds at 1013 cm⁻¹, which is the result of intermittent strain vibrations caused by Si–O–Si. Surface analysis by scanning electron microscope - energy dispersive X-ray spectroscopy reveals that the SCFA material has a relatively rough, porous surface, dominated by silicon and aluminum. The SCFA is a mesoporous material with a large surface area of 223 m²/g , a total pore volume of 0.45 cm³/g and an average pore diameter of 7.8–8.1 nm. Overall, the characterization results indicate that SCFA has a large surface area, a stable mesoporous structure and a chemical composition dominated by SiO₂ (93.35%). These characteristics make the material a promising candidate for use as a metal adsorbent, catalyst media and functional material in field environments and industries.