Synergistic adsorption of Pb2+ and CrO42- on an engineered biochar highlighted by statistical physical modeling

Statistical physics-based adsorption models were used to provide a deep analysis of the single and binary adsorption of Pb2+ and CrO42- on an engineered biochar. New physical interpretations of the adsorption mechanisms of these pollutants were reported. Results showed that the adsorption capacities in binary systems were higher than those obtained in single systems at 298 K. The adsorption capacities at saturation were 606 and 346 mg/g for Pb2+ and CrO42- in mono-component systems, while they were 1420 and 488 mg/g for these pollutants in binary solutions at 298 K. Model parameters confirmed the presence of a synergistic adsorption effect between both ions (Pb2+ and CrO42-) on the same functional group of the biochar. Modeling results allowed to sketch the adsorption orientation of metallic adsorbates on the adsorbent surface and to estimate the corresponding adsorption energies. These calculations indicated an endothermic adsorption due to the presence of both physical and chemical interactions in the single and binary adsorption systems. Overall, both steric and energetic factors affect the adsorption mechanisms of Pb2+ and CrO42- on this novel biochar. (C) 2020 Elsevier B.V. All rights reserved.