Adsorption of selected toxic metals by modified peanut shells

The objective of this study was to modify peanut shells to enhance their ad sorptive properties toward the metal ions cadmium (Cd2+), copper (Cu2+), ni ckel (Ni2+), lead (Pb2+) and zinc (Zn2+). Milled peanut shells were initial ly washed with water or 0.1N NaOH or left unwashed. Following these treatme nts or lack of treatment, the shells were either left unmodified or modifie d by a heat treatment in the presence of either 1.0M phosphoric acid or 0.6 M citric acid. Modified peanut shells were evaluated either for adsorption efficiency or for adsorption capacity using the five metal ions listed abov e. Adsorption efficiencies and capacities were compared with efficiencies a nd/or capacities for the commercial chelating or cation exchange resins Amb erlite 200, Amberlite IRC-718, Duolite GT-73, and carboxymethylcellulose. F or the adsorption efficiencies of individual metal ions, modified peanut sh ells met or exceeded the adsorption values for cadmium, copper, nickel or z inc ions compared with the commercial resins Duolite GT-73 and carboxymethy lcellulose. In a solution containing all five metal ions, modified peanut s hells met or exceeded the adsorption efficiencies for cadmium, copper and l ead ions compared with Duolite GT-73, Amberlite IRC-718 and carboxymethylce llulose. Adsorption capacities of modified peanut shells met or exceeded th e adsorption capacity of Duolite GT-73 for lead ions only. Citric or phosph oric acid-modified peanut shells showed a preference for Cu2+ and Pb2+ and appear promising as potentially inexpensive adsorbents for selected metal i ons. (C) 2001 Society of Chemical Industry.