Ultrahigh Pb²⁺ ion adsorption by EDTA-modified super-porous silica aerogel derived from rice husk ash

Rice husk (RH), an abundant agricultural residue across Southeast Asia, has drawn increasing interest as a sustainable raw material due to its underutilized potential. In the current study, RH-derived silica aerogel was functionally enhanced by incorporating carboxymethyl cellulose (CMC) as a structural binder and ethylenetriaminepentaacetic acid (EDTA) as a chelating agent, leading to the fabrication of an innovative SA/CMC-EDTA composite designed for efficient Pb²⁺ ion removal from aqueous environments. The fabricated SA/CMC-EDTA was defined employing scanning electron microscopy (SEM), zeta potential analysis, Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). Under fixed conditions, SA/CMC-EDTA exhibited a Pb²⁺ removal efficiency of 95.65 % and a kinetic rate constant of 0.016 g/(mg·min). The uptake followed the Langmuir uptake isotherm and conformed to second-order kinetics, achieving a maximum adsorption amount of 1204.81 mg/g. Compared to Ni²⁺, the material demonstrated a drastically higher selectivity for Pb²⁺ with respective uptake efficiencies of 92.43 and 55.83 %. In addition, the SA/CMC-EDTA material exhibited moderate reusability, showing only a 15.78 % reduction in Pb²⁺ removal efficiency after five consecutive cycles under challenging conditions. When applied to actual wastewater from lead-acid battery recycling, the sorbent achieved a Pb²⁺ elimination rate of 79.14 %. The results confirm the strong Pb²⁺ adsorption capacity of SA/CMC-EDTA and its potential for sustainable and reusable treatment of heavy metal-contaminated wastewater.