Investigation of individual and competitive adsorption of Cu(II), Cd(II), and Pb(II) on montmorillonite in terms of surface complexation and kinetic properties of Cu(II) adsorption

Abstract

In this study, individual and competitive Cu(II), Cd(II), and Pb(II) adsorptions on montmorillonite were searched by considering surface acidic functional groups of adsorbent. pH dependency of adsorptions and kinetic properties of Cu(II) adsorption was investigated. Cu(II) adsorption on montmorillonite fits pseudo-first-order reaction with the 0.008k value. Individual and competitive heavy metal adsorptions were modeled using Langmuir, Freundlich, Temkin, and Dubinin-Astakhov isotherms. Adsorption capacities were calculated using equations of related linearized models. The adsorption capacities of individual metal adsorption, obtained from linearized models, are higher than the yielded capacities from competitive adsorption experiments. All adsorption energies calculated from linearized Dubinin-Astakhov model varied between 7 and 16kJ/mol. The values of adsorption energies gained for metal adsorption in competition did not significantly differ from those of individual adsorption. Since montmorillonite surface behaves as a weak acid and has a strong buffer effect at pH values between 2 and 3, the pH dependency of adsorption was explained by taking into account the surface acidic properties of adsorbent and introduced preferred surface sites beyond adsorption with increasing pH. Cu(II), Cd(II), and Pb(II) existence on loaded montmorillonite was proved by the aid of SEM-EDX results.