Utilization of peanut shells as adsorbents for selected metals

Peanut shells of mesh size 10-20 were modified by combinations of treatment s following a 3(2) factorial design. Treatments consisted of either no wash , water wash or base wash followed by no modification or modification with 0.6M citric acid or 0.6M phosphoric acid. The nine samples were evaluated f or their uptake of five metal ions (Cd(II), Cu(II), Ni(II), Pb(II) and Zn(I I)) from solution. The results were compared with metal ion adsorption by t hree commercial cation exchange resins, namely, Amberlite(R) 200, Amberlite (R) IRC 718 and Duolite(R) GT-73. The percent of metal ions adsorbed per gr am of adsorbent was significantly increased by each of the acid treatments, average values ranged from 19 to 34% compared with non-acid treated sample s 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 a cid treatment was not significant for most of the experimental conditions u sed. Acid-treated samples were as effective as Duolite(R) GT-73 in the adso rption of Cd(II) and almost twice as effective in the adsorption of Zn(II) from solutions containing a single metal ion. In solutions containing multi ple metal ions, citric acid samples were found to be most effective and sel ective for Cu(II) compared with Cd(II), Ni(II), and Zn(II). In general, pho sphoric 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 pr omising as metal ion adsorbents. (C) 1999 Society of Chemical Industry.