Activated bentonite as a low-cost adsorbent for the removal of Cu(II) and Pb(II) from aqueous solutions: Batch and column studies

In this study, the effects of acid activation with high bentonite contents under mild synthetic conditions on textural and structural properties were explored. The alteration features after activation were fully characterized with the help of X-ray powder diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area, Barrett–Joyner–Halenda (BJH) pore size and volume analyses. The active sites were examined using volumetric titration and confirmed with a pyridine adsorbed FT-IR study. The activated bentonite (ABn) was further utilized for the removal of Cu(II) and Pb(II) ions from aqueous solutions. Batch reactor studies showed that the removal of these toxic metal ions was favored by increases in the pH, initial metal concentrations, contact time, and dose of the adsorbents. The equilibrium data obtained at various initial concentrations reasonably fit well with the Langmuir and Freundlich adsorption isotherms. The adsorption process was fast and the kinetic data fit better to the pseudo-second order kinetic model. The presence of other heavy metal ions, such as Cd(II), Fe(II), and Mn(II), did not significantly suppress the removal of both the Cu(II) and Pb(II); whereas the other cations, such as Na+, K+, Ca2+, and Mg2+ caused a notable decrease in the Pb(II) removal. In addition, the breakthrough data obtained in the column studies fit well with the non-linear Thomas equation, and high loading capacities of Cu(II) and Pb(II) were obtained. Therefore, we demonstrated in this study that the low cost ‘ABn’ solid can be employed as a potential adsorbent for the effective treatment of aqueous waste contaminated with Cu(II) and Pb(II).