No abstract

The objective of this study was to modify peanut shells to enhance their adsorptive properties toward the metal ions cadmium (Cd 2 ), copper (Cu 2 ), nickel (Ni 2 ), lead (Pb 2 ) and zinc (Zn 2 ). Milled peanut shells were initially washed with water or 0.1 N NaOH or left unwashed. Following these treatments or lack of treatment, the shells were either left unmodi®ed or modi®ed by a heat treatment in the presence of either 1.0 M phosphoric acid or 0.6 M citric acid. Modi®ed peanut shells were evaluated either for adsorption ef®ciency or for adsorption capacity using the ®ve metal ions listed above. Adsorption ef®ciencies and capacities were compared with ef®ciencies and/or capacities for the commercial chelating or cation exchange resins Amberlite 200, Amberlite IRC-718, Duolite GT-73, and carboxymethylcellulose. For the adsorption ef®ciencies of individual metal ions, modi®ed peanut shells met or exceeded the adsorption values for cadmium, copper, nickel or zinc ions compared with the commercial resins Duolite GT-73 and carboxymethylcellulose. In a solution containing all ®ve metal ions, modi®ed peanut shells met or exceeded the adsorption ef®ciencies for cadmium, copper and lead ions compared with Duolite GT-73, Amberlite IRC-718 and carboxymethylcellulose. Adsorption capacities of modi®ed peanut shells met or exceeded the adsorption capacity of Duolite GT-73 for lead ions only. Citric or phosphoric acid-modi®ed peanut shells showed a preference for Cu 2 and Pb 2 and appear promising as potentially inexpensive adsorbents for selected metal ions.