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

摘要

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) (r(2) > 0.99 at all temperatures tested). The Zn(II) adsorption process was a simultaneously physical and chemical process, fitting the Freundlich (r(2) = 0.981), Temkin (r(2) = 0.983) and the D-R isotherm models (r(2) = 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 (Delta G(o)) and enthalpy of adsorption (Delta H-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.