Influence of acid leaching on biosilica particles derived from palm oil fuel ash (POFA) for cationic dye removal

Abstract

Palm oil fuel ash (POFA) is an agricultural waste residue rich in silica, which constitutes up to 60% of its chemical composition. This study investigates the extraction of biosilica particles from POFA using a hydrochloric acid (HCl) leaching pretreatment, with a focus on the effect of a relatively low acid concentration on the product yield. Biosilica particles treated with 1 M HCl (nS-1MHCl) exhibited 11% higher yield compared to untreated POFA (nS-0MHCl). The physicochemical characteristics of the extracted biosilica particles were examined using Fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). FESEM micrographs revealed spherical silica particles with relatively uniform sizes and the presence of surface pore cavities. In batch adsorption experiments, the leached nS-1MHCl sample achieved a maximum methylene blue (MB) removal efficiency of 94% over an initial MB concentration range of 10–50 ppm. Collectively, these findings demonstrate that extracting biosilica particles from POFA for MB removal represents a viable strategy for valorizing agricultural waste ash into high-value products.