Dye wastewater treatment with rice husk-derived silica xerogel: An eco-friendly process

Removal of dye contamination from wastewater is crucial for protecting human health and the environment, and adsorption is considered an effective removal method. In addition, agricultural residues are attractive for use as adsorbents for the adsorption due to their renewability. Therefore, the present work aimed to develop silica xerogel from rice husk (agricultural residue in rice production) into an adsorbent for dye wastewater treatment. In the xerogel synthesis, a non-toxic organic acid (citric acid) was used instead of a toxic inorganic acid for leaching and precipitation steps to lower the environmental impact of the process. It was found that the obtained silica xerogel has physical properties such as a surface area and pore volume, comparable with silica xerogels in other literature. When applying it in the dye (methylene blue) wastewater treatment, the obtained silica xerogel showed better adsorption capacity than unprocessed silica at all studied conditions, i.e. various times, pH and initial concentration. The maximum adsorption capacity of the xerogel and unprocessed silica were 103.45 and 61.78 mg/g, respectively. This indicates the benefit of silica xerogel with low environmental impact when applied in dye wastewater treatment. The adsorption isotherms and kinetic for both types of silica were also conducted. It was found that the adsorption process of methylene blue on the silica fitted the Langmuir adsorption isotherm and followed the pseudo-second-order kinetic model. This provides valuable information for optimizing the operating parameters for best performance in a given situation.