Contamination of aquatic systems is a serious environmental problem given the pollution of natural waters by heavy metal ions. Mercury is one of the most toxic heavy metals since it is not biodegradable and causes a lot of toxic effects in the human body. Its presence is due to a combination of natural processes (volcanic action, erosion of mercury–containing sediments) and anthropogenic activities (mining operations, tanneries, metal plating facilities) as well. Adsorption is considered to be one of the most effective and economical treatment methods for mercury removal of effluents. In order to focus on the kinetics and thermodynamics of the mercury(II) adsorption, two main adsorbents were selected: magnetic chitosan and magnetic graphene oxide. Chitosan is a multifunctional polymer that has primary and secondary hydroxyl groups, as well as highly reactive amino groups. It has been regarded as a useful starting support for adsorption purposes. Numerous investigations on chemical activation of chitosan have been carried out to increase its adsorption capacity for metals. In the past, magnetic chitosan has emerged as a new generation of materials for environmental decontamination, since magnetic separation simply involves applying an external magnetic field to extract the adsorbents. Graphene oxide produced from graphite after chemical oxidation, is one of the most important derivatives of graphene. It is characterized by a layered structure with oxygen functional groups bearing on the basal planes and edges. In the present study, a full thermodynamic analysis was realised for the adsorption of mercury(II) onto both magnetic graphene oxide and magnetic chitosan. The parameters determined were the change of Gibbs free energy (ΔG0, kJ/mol), change of enthalpy (ΔH0, kJ/mol) and entropy change (ΔS0, kJ/mol K). A deep kinetic study was realized in order to examine the adsorption dynamics of the process. The experimental results were fitted to the pseudo–first, -second order and Elovich equations.

Thermodynamics, Kinetics, Mercury(II), Modeling, Magnetic chitosan, Magnetic graphene oxide