Removal of Pb(II), Cd(II), Cu(II), and Zn(II) from Aqueous Solutions by Adsorption on Bentonite

Removal of Pb(II), Cd(II), Zn(II), and Cu(II) from aqueous solutions using the adsorption process on bentonite has been investigated. In order to find out the effect of temperature on adsorption, the experiments were conducted at 20, 35, and 50degreesC. For all the metals, maximum adsorption was observed at 20degreesC. The rate of attaining equilibrium of adsorption of metal ions follows the order Zn(II) > Cu(II) > Cd(II) > Pb(II). Equilibrium modeling of the adsorption showed that adsorption of Pb(II), Cd(II), and Cu(II) were fitted to a Langmuir isotherm, while the adsorption of Zn(II) was fitted to a Freundlich isotherm. Dynamic modeling of the adsorption showed that the first order reversible kinetic model was held for the adsorption process. The overall rate constant k', the adsorption rate constant k1, the desorption rate constant k2, and the equilibrium constant Ke for the adsorption process were calculated. From the results of the thermodynamic analysis, standard free energy DeltaG0, standard enthalpy DeltaH0, and standard entropy DeltaS0 of the adsorption process were calculated.