Oxalic Acid-assisted Sol–gel Synthesis of High-purity Amorphous Silica from Geothermal Waste

Abstract

This study focuses on the synthesis of amorphous silica from geothermal waste using the sol-gel method with oxalic acid, exploring the impact of pH variation (8 to 13) and the role of microwave heating. Optimal conditions were achieved at pH 8, yielding the highest silica purity of 96.275% and a recovery of 51.16%. Fourier transform infrared analysis confirmed the silica structure, while XRD results verified its amorphous nature with minimal crystalline impurities. Microwave heating significantly enhanced process efficiency by reducing typical carbon residues from gelation. Consistent with previous research, this microwave-assisted approach provides a quantitative improvement, being 30–48 times faster and using 4–50 times fewer reagents while producing nanoparticles as pure, stable, and monodisperse as conventional methods. Field-emission scanning electron microscopy analysis revealed uniform spherical particles under optimal pH, with an average size below 70 nm, whereas extreme pH levels resulted in irregular morphologies. This research contributes to the sustainable utilization of geothermal waste and provides valuable insights for optimizing silica synthesis in various industrial applications.