LEAD(II) AND CADMIUM(II) REMOVAL FROM AQUEOUS SOLUTIONS USING HAZELNUT AND ALMOND SHELLS SORBENT MATERIALS

Removal of toxic metal ions from natural and waste waters is of great importance for the health of living organisms and for environmental protection. Alternatively to the conventional chemical treatments, such as precipitation, reverse osmosis, etc, biosorption shows a growing interest for toxic metal ions removal from contaminated aqueous solutions. The sorption ability of every type of biomass towards metal ions depends on many variables that characterize the solution. Among these, the ionic strength (I) is one of the most important and cannot be neglected during an accurate adsorption study. For this reason and with the aim of quantitatively define the influence of I, here are reported the results of kinetic and thermodynamic studies on the sorption capacity of Hazelnut (HS) and Almond (AS) shells toward Pb(II) and Cd(II) in NaCl aqueous solution in a wide I range (0.05 <I (mol L-1) < 0.5) at room temperature. The formation of chloride complexes have been always considered. To avoid the hydrolysis of the metal ions the pH value of solutions was kept at 5. HS and AS have been grinded, washed and sieved before using. The materials were characterized by FT-IR and SEMEDX analysis. The FT-IR spectra showed the presence of numerous Odonor sites indicating that sorption process occurs by chemical interaction of metal ions with these binding groups. The residual metal concentration in aqueous solutions during the kinetic and equilibrium experiments was measured by Differential Pulse Anodic Stripping Voltammetry (DP-ASV). Several kinetic and isotherm equations were used to fit the experimental data. The pseudo second order equation was the best in terms of fit for all the systems investigated. Although all the isotherm models fitted properly the equilibrium data, the Langmuir model was the best one for the Pb(II)- HS/AS systems, whereas Sips model showed the best results for the Cd(II)- HS/AS systems