Integrated Nonlinear Equilibrium and Kinetic Modeling, Thermodynamic Evaluation, and Desorption Analysis of Cd(II) Adsorption Onto Vine Rod-Derived Biochar

This study investigates Cd(II) adsorption from aqueous solutions onto biochar derived from vine rods (BC-VR) through physicochemical characterization, nonlinear kinetic and equilibrium modeling, thermodynamic evaluation, and desorption studies. BC-VR exhi-bited a highly porous structure, a specific surface area of 363 m2/g, and a predominance of micropores. The effects of pH, contact time, initial Cd(II) concentration, temperature, and coexisting ions were investigated. A maximum Cd(II) removal efficiency of 99.7% was obtained at pH 3.4 using an adsorbent dosage of 3 g/L at 298 K and a contact time of 24 h. Kinetic and possible rate-controlling contributions were evaluated using several nonlinear adsorption models. Equilibrium data were also analyzed using nonlinear isotherm equations. Model selection was based on multiple statistical criteria, including the corrected Akaike information criterion and Akaike weights. The pseudo-second-order model provided the best overall description of the kinetic data, whereas the Langmuir model best represented the adsorption equilibrium, with a maximum capacity of 65.36 mg/g at 303 K. Thermodynamic analysis indicated spontaneous and endothermic adsorption, with ΔG° values from −37.17 to −38.98 kJ/mol and ΔH° of 15.74 kJ/mol. Desorption under acidic conditions demonstrated the feasibility of Cd(II) recovery. These findings support the potential application of BC-VR for Cd(II) removal.