Disentangling competitive adsorption dynamics: engineered Eucalyptus camaldulensis biochar for preferential retention of Pb(II) and Cd(II) in multimetallic systems

) obtained under competitive multicomponent conditions. While the competitive Langmuir model adequately described Pb(II) removal, it poorly fitted Cd(II) adsorption isotherms suggesting that Cd(II) exhibits non-ideal competitive behavior involving heterogeneous site interactions or multi-layer formation, consistent with its softer Lewis acid characteristics and explaining its inferior performance relative to Pb(II) in mixed systems. Thermodynamic analysis confirmed spontaneous, endothermic adsorption processes. Mechanistic studies identified hydrogen bonding, electrostatic attraction, π-π interactions, and inner-sphere surface complexation as primary removal pathways. These findings demonstrate that EC-biochar is a promising eco-friendly adsorbent for the selective retention of Pb(II) and Cd(II) from complex wastewater matrices.