Chestnut shell as heavy metal adsorbent: optimization study of lead, copper and zinc cations removal

The influence of initial cation concentration, temperature and pH was investigated to optimize Pb(2+), Cu(2+) and Zn(2+) removal from aqueous solutions using acid formaldehyde pre-treated chestnut shell as adsorbent. Experiments were planned according to an incomplete 3(3) factorial experimental design. Under the optimal conditions selected, the metal ion adsorption equilibrium was satisfactorily described by the Langmuir isotherm model. The maximum pre-treated chestnut shell adsorption capacity was obtained for Pb(2+) ions, 8.5 mg g(-1), and the order of cation affinity was Pb(2+)>Cu(2+)>Zn(2+). A model that considered the effect of axial dispersion was successfully used to describe the fixed-bed adsorption behaviour of Pb(2+), Cu(2+) and Zn(2+) ions at the flow rates essayed. Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies showed that the functional groups involved in metal ions binding included carboxyl, hydroxyl, ether, alcoholic and amino groups.