Removal of metallic trace elements (Pb²⁺, Cd²⁺, Cu²⁺, and Ni²⁺) from aqueous solution by adsorption onto cerium oxide...

The equilibrium and kinetic studies of removal of Pb²⁺, Cd²⁺, Ni²⁺, and Cu²⁺ metal ions were carried out using activated carbon prepared from palm kernel shell and doped with CeO₂ (Ce/AC). The obtained material carbon was characterized by XRD which showed some crystalline traces of CeO₂, SEM displaying the porous texture with spherical pores and the determination of pH of point of zero charge (pH_PZC) which was found to be equal to 6. The contact time and adsorbate were thoroughly investigated. The maximum adsorption depends inversely on the hydrated metal radius. This observation was confirmed by calculating the formation energies (ΔH_(M(OH)2)) of M(OH)₂. The metal ionic radii were acting on calculated sorption capacity and that sorption efficiency related to ionic radii of metal was as follows: R_(Ni2+) ≤ R_(Cd2+) < R_(Cu2+) < R_(Pb2+). The texture and morphology of the material after sorption were affected by the metallic ion nature as observed by SEM. The kinetic studies showed that the rate constant (k₂) of pseudo-second-order model decreased with the increase of the hydrated cations radii, while the rate constant of intraparticle diffusion increased with the increase of the ionic radii. The Freundlich isotherm model best fit the experimental sorption data for all the metallic ions.