Peanut Shell Activated Carbon: Adsorption Capacities for Copper(II),Zinc(II),Nickel(II) and Chromium(VI) Ions from Aqueous Solutions

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.