Maximising E-waste leachate adsorption: multi-component isotherm models and mechanisms with scalable mesoporous sugarcane bagasse-derived biochar

Heavy metal contamination is a primary environmental and health concern contributing to organ damage, neurological disorders and developmental issues. Adsorption is an efficient, cost-effective method for removing heavy metals from contaminated water. In this study, the adsorption of five metals (Cu²⁺, Ni²⁺, Pb²⁺, Ag⁺ and Mn²⁺) into mesoporous sugarcane bagasse-derived biochar (surface area: 1061.77 m² g⁻¹) was investigated using multi-component isotherm models, including Extended Langmuir (EL), Extended Freundlich (EF), Modified Competitive Langmuir (MCL) and Extended Sips (ES). The biochar was synthesised via KOH activation (1, 1 w/w) followed by pyrolysis at 800 °C. The ES model was found to best describe the competitive adsorption behaviour. Among the tested metals, Pb²⁺ exhibited the highest adsorption capacity (605.45 mg/g), followed by Cu²⁺ (501.77 mg/g). Kinetic analysis using pseudo-first-order and pseudo-second-order models confirmed chemisorption superiority, specifically for Cu²⁺, Mn²⁺, and Pb²⁺. The rate-limiting step was temperature-dependent; intraparticle diffusion dominated at 25 °C, while chemisorption prevailed at 55 °C. The thermodynamic analysis (ΔH > 0, ΔG < 0) confirmed that the adsorption process is endothermic and spontaneous under the tested conditions. After three regeneration cycles, the biochar structure stability is confirmed with evidence of full adsorbate removal.