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Peanut shells of mesh size 10±20 were modi®ed by combinations of treatments following a 3 2 factorial design. Treatments consisted of either no wash, water wash or base wash followed by no modi®cation or modi®cation with 0.6 M citric acid or 0.6 M phosphoric acid. The nine samples were evaluated for their uptake of ®ve metal ions (Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II)) from solution. The results were compared with metal ion adsorption by three commercial cation exchange resins, namely, Amberlite 1 200, Amberlite 1 IRC 718 and Duolite 1 GT-73. The percent of metal ions adsorbed per gram of adsorbent was signi®cantly increased by each of the acid treatments, average values ranged from 19 to 34% compared with non-acid treated samples at 5.7%. The percent of metal ions adsorbed for base-washed samples were higher than water-washed or unwashed shells. Interaction between wash and acid treatment was not signi®cant for most of the experimental conditions used. Acid-treated samples were as effective as Duolite 1 GT-73 in the adsorption of Cd(II) and almost twice as effective in the adsorption of Zn(II) from solutions containing a single metal ion. In solutions containing multiple metal ions, citric acid samples were found to be most effective and selective for Cu(II) compared with Cd(II), Ni(II), and Zn(II). In general, phosphoric acid-modi®ed shells removed the most metals from solution for the experimental samples and were more effective in removing Cd(II) and Zn(II) than two of the three commercial resins. Acid-modi®ed peanut shells are promising as metal ion adsorbents.

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Peanut shells of mesh size 10–20 were modified by combinations of treatments following a 32 factorial design. Treatments consisted of either no wash, water wash or base wash followed by no modification or modification with 0.6 M citric acid or 0.6 M phosphoric acid. The nine samples were evaluated for their uptake of five metal ions (Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II)) from solution. The results were compared with metal ion adsorption by three commercial cation exchange resins, namely, Amberlite® 200, Amberlite® IRC 718 and Duolite® GT‐73. The percent of metal ions adsorbed per gram of adsorbent was significantly increased by each of the acid treatments, average values ranged from 19 to 34% compared with non‐acid treated samples at 5.7%. The percent of metal ions adsorbed for base‐washed samples were higher than water‐washed or unwashed shells. Interaction between wash and acid treatment was not significant for most of the experimental conditions used. Acid‐treated samples were as effective as Duolite® GT‐73 in the adsorption of Cd(II) and almost twice as effective in the adsorption of Zn(II) from solutions containing a single metal ion. In solutions containing multiple metal ions, citric acid samples were found to be most effective and selective for Cu(II) compared with Cd(II), Ni(II), and Zn(II). In general, phosphoric acid‐modified shells removed the most metals from solution for the experimental samples and were more effective in removing Cd(II) and Zn(II) than two of the three commercial resins. Acid‐modified peanut shells are promising as metal ion adsorbents. © 1999 Society of Chemical Industry

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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.