ABSTRACT:The adsorption of copper(II), zinc(II), nickel(II) and chromium(VI) ions from aqueous solutions onto an activated carbon produced from peanut shell was studied as a function of the concentration of the ions and the pH value. The amounts of Cu(II), Zn(II) and Ni(II) ions adsorbed increased with increasing equilibrium pH of the solution, while the uptake of Cr(VI) ions decreased. For Cr(VI) ions, maximum uptakes were found at a pH below the point of zero charge of the adsorbent (pH pzc ). The amount of metal cation adsorbed at a given equilibrium concentration increased in the order Ni(II) < Zn(II) < Cu(II). This metal ion uptake order may be explained from a consideration of the combined effects of the electronegativity of the metal ion and the first stability constant of the corresponding metal hydroxide. The activated carbon produced from peanut shell was an effective and economic adsorbent for the removal of metal cations at pH ≥ pH pzc and anions at pH ≤ pH pzc .

Activated carbon with a high adsorption capacity for the removal of organic compounds from aqueous solutions was made from phosphoric acidactivated peanut shells. Adsorption isotherms for the uptake of phenol, iodine, Methylene Blue and tannic acid were obtained at 22 C. Freundlich, Langmuir and previously developed equation models all explained the experimental data satisfactorily. Further analysis using the Dubinin-Radushkevich equation showed that the maximum micropore volume accessible to the adsorbate decreased as the molecular size increased, suggesting a molecular sieve or gate effect. A comparison was made with the micropore volume as determined by nitrogen adsorption at 196 C. The results presented indicate that peanut shell residues provide a suitable option for the preparation of activated carbon with good surface properties and the ability to remove organic compounds from aqueous solutions.

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