Adsorption of lead(II) ions using surface-modified chitins

To establish the feasibility of the removal of lead using chitin, adsorption characteristics were investigated at various temperatures and concentrations. The adsorption characteristics of chitin were analyzed by determining its adsorption equilibrium, kinetics, and thermodynamic properties. The data gathered favor the Langmuir over the Freundlich model. The adsorption capacity of the surface-modified natural chitin for Pb(II) removal increased significantly when the adsorbent was treated using the xanthation method. The homogeneous surface diffusion model described the adsorption kinetic data well and can be used to predict the chitin performances; therefore, it could be helpful for design considerations. Under the steady-state reaction conditions, the change in Gibbs free energy (Delta G(o)) ranged from -19.03 to -21.50 kJ/mol, and the enthalpy (Delta H-o) and entropy (Delta S-o) changes were 16.54 kJ/mol and 0.124 kJ/mol/K, respectively; i.e., a higher temperature favors a spontaneous Pb(II) adsorption by chitin when using the xanthation method. Thermodynamic calculations indicate that the adsorption of lead on the adsorbents was spontaneous and endothermic. Application of the chitin modified with the xanthation method to the removal of Pb(II) metals from wastewater is expected to be economical and effective.