Adsorption Kinetic and Equilibrium Studies on Removal of Lead(II) onto Glutamic Acid/Sepiolite

Abstract

In this study, a modified method was used to increase the adsorption of lead ions from aqueous solutions by using modified clay mineral on the laboratory scale. Adsorption experiments have been carried out on the use of both thermal activated sepiolite (TAS) and their glutamate/sepiolite modification (GS) as adsorbents. The experimental data was analyzed using adsorption kinetic models (pseudo first- and second-order equations). The pseudo second-order kinetic model fitted well to the kinetic data (R20.99). Then, the Freundlich and Langmuir models were applied to describe the uptake of Pb(II) on GS and the Langmuir isotherm model agrees well with the equilibrium experimental data (R20.97). The maximum adsorption capacity was observed to be 128.205mg/g by GS according to the Langmuir equation. Desorption efficiency of the GS was studied by the batch method using EDTA, HCl, and HNO3 solutions. Desorption of 69.18, 74.55, and 80% of Pb(II) from GS was achieved with 0.1M EDTA, 0.1M HCl, and 0.1M HNO3 solutions, respectively. FTIR analysis suggests the importance of functional groups such as amino, hydroxyl, and carboxyl during Pb(II) removal. SEM observations demonstrated that an important interaction at the lead-modified sepiolite interface occurred during the adsorption process. In addition, the thermodynamic constants was calculated that the values of the Gibbs free energy (G*), enthalpy (H*), and entropy (S*) of modification were 86.79kJ/mol, -18.91kJ/mol, and -354.70J/mol/K, respectively. The negative value of H* shows exothermic nature of adsorption.