Comparison of the Effectiveness of the Coprecipitation Method for SiO₂ Extraction from Natural Pahae Zeolite and Palm Oil Boiler Ash

Abstract

This study explores the effectiveness of coprecipitation for extracting high-purity SiO₂ from natural Pahae zeolite and palm oil boiler ash (POBA). Coprecipitation is advantageous in silica synthesis, as it enhances product purity and homogeneity. In this work, natural Pahae zeolite and POBA were calcined, treated with HCl and NaOH, and subsequently titrated to form silica gel, which was dried and ground for analysis. The Fourier transform infrared (FTIR) analysis verified the presence of functional groups of silica. X-ray diffraction (XRD) confirmed that the extracted silica was amorphous, with a broad peak at 2θ = 22°. Particle size analysis (PSA) indicated a median particle size (D50) of 0.687 µm for SiO₂ from Pahae zeolite and 0.316 µm for POBA, with mean particle sizes of 0.944 µm and 0.323 µm, respectively. Furthermore, the X-ray fluorescence (XRF) analysis showed that the silica extraction reached 92.18%, while the differential scanning calorimetry (DSC) test indicated excellent stability of the extracted SiO2. In addition, scanning electron microscopy (SEM) images revealed a granular morphology, with smoother particles from Pahae zeolite than from POBA. Energy dispersive X-ray (EDX) results showed that silica content was approximately 31.5% in POBA and 34.7% in Pahae zeolite. Additionally, Brunauer–Emmett–Teller (BET) analysis confirmed the mesoporous nature of the extracted SiO₂, with a type IV nitrogen adsorption-desorption isotherm and a hysteresis loop, characteristic of mesoporous materials. The BET surface area of 189.20 m²/g, pore volume of 0.7310 cm³/g, and pore diameter of 8.41 nm indicate a well-developed porous structure.