Comparative study on batch adsorption of Pb2+, Cd2+ and Ni2+ onto corn cob charcoal and activated silica: Kinetic and characterization studies

Heavy metal contamination of water poses serious environmental and health risks. Therefore, this study aims to evaluate the efficiency of charcoal and activated silica as low-cost adsorbents for the removal of Pb(II), Cd(II), and Ni(II) ions from aqueous solutions. The effects of pH, temperature, and contact time on adsorption were systematically evaluated. For silica, the maximum adsorption capacities were 7.50 mg/g for Pb(II), 7.50 mg/g for Cd(II), and 7.50 mg/g for Ni(II), while for charcoal, the corresponding capacities were 7.50 mg/g, 7.50 mg/g, and 7.51 mg/g, respectively. Optimal adsorption occurred at pH 4 for Pb(II) and pH 6 for Cd(II) and Ni(II), with maximum removal efficiencies of 86.44%, 80.34%, and 71.56% for silica and 96.34%, 90.49%, and 92.75% for charcoal. Adsorption kinetics were evaluated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, with the pseudo-second-order model providing the best fit (R² = 1.000), indicating chemisorption-dominated processes. Intraparticle diffusion analysis suggested that adsorption was particle-diffusion controlled, with boundary layer thickness (Xᵢ) ranging from 7.46 to 7.47 mg/g. The results demonstrate that both adsorbents, particularly charcoal, are highly effective for the removal of Pb(II), Cd(II), and Ni(II) ions and hold potential for the treatment of industrial wastewater.