Physicochemical studies toward the removal of Zn(ii) and Pb(ii) ions through adsorption on montmorillonite-supported zero-valent iron nanoparticles

Abstract

This study reports the adsorption of Zn(II) and Pb(II) on montmorillonite-supported zero-valent iron nanoparticles (nZVI-Mont). The kinetics of Zn(II) and Pb(II) adsorption were evaluated for various contact times. The adsorption of Zn(II) and Pb(II) at different initial concentrations was examined by injecting 0.5 g of adsorbents to achieve equilibrium. The adsorption of Zn(II) and Pb(II) was an exothermic process. The pseudo-second-order kinetic model fits well with the adsorption of Zn(II) and Pb(II) (r² > 0.99 at all temperatures tested). The Zn(II) adsorption process was a simultaneously physical and chemical process, fitting the Freundlich (r² = 0.981), Temkin (r² = 0.983) and the D–R isotherm models (r² = 0.988) well. However, the Pb(II) adsorption only fits the Freundlich isotherm model. The activation energies of the Zn(II) adsorption onto nZVI-Mont were in a range from 11.71 kJ mol⁻¹ to 46.37 kJ mol⁻¹ and the activation energies of the Pb(II) adsorption onto nZVI-Mont were in a range from 0.26 kJ mol⁻¹ to 17.67 kJ mol⁻¹. The negative values for the Gibbs free energy (ΔG^o) and enthalpy of adsorption (ΔH^o) revealed that the adsorption process was spontaneous and exothermic, respectively. In addition, the adsorption mechanisms for Zn(II) and Pb(II) are significantly different.