Statistical physics interpretation of the adsorption mechanism of Pb2+, Cd2+ and Ni2+ on chicken feathers

The mechanism of adsorption of Pb2+, Cd2+ and Ni2+ on chicken feathers was studied via statistical physics theory. A detailed theoretical analysis was performed using three models that assumed the adsorption of these metal ions via one, two or three types of surface functionalities from chicken feathers. These surface functionalities corresponded to carboxylic, disulfide and amino groups. The monolayer adsorption model with two types of functional groups was selected to analyze the steric and energetic factors involved in the removal of these heavy metals. Results of the statistical physics modeling showed that this adsorption system was multi-ionic with the presence of both endothermic and exothermic adsorption stages depending on solution temperature. Calculated adsorption energies were associated to physical adsorption forces where the carboxylic and disulfide functional groups were responsible of metal binding on chicken feathers. Thermodynamic calculations of configuration entropy, free enthalpy and internal energy indicated that the adsorption of Pb2+, Cd2+ and Ni2+ on chicken feathers was a spontaneous and feasible process. These findings contribute to understand and characterize the thermodynamic nature of the adsorption of heavy metal ions on natural adsorbents like chicken feathers. (C) 2020 Elsevier B.V. All rights reserved.