Removal of selected metal ions from aqueous solution using modified corncobs

The objective of this study was to convert corncobs to metal ion adsorbents for wastewater treatment. Ground corncobs were modified with either 0.6 M citric acid (CA) or 1.0 M phosphoric acid (PA) to help improve their natura l adsorption capacity. The effect of a combination of wash and modification treatment was tested for corncob adsorption efficiency with five different metal ions (cadmium, copper, lead, nickel, zinc) individually or in a mixe d solution containing each metal at a 20 mM concentration. Results were com pared to those of commercial resins Amberlite IRC-718, Amberlite 200, Duoli te GT-73 and carboxymethylcellulose (CMC). Modified corncobs showed the sam e adsorption efficiency as Duolite GT-73 for cadmium, copper, nickel and zi nc ions and had greater adsorption than CMC for nickel and zinc ions. For m ixed metals, the modified corncobs exhibited the same adsorption efficiency as Duolite GT-73 for cadmium and copper ions and the same or higher adsorp tion than Amberlite IRC-718 for lead ions. Adsorption capacities of modifie d samples were compared to those of Amberlite IRC-718, Amberlite 200 and Du olite GT-73. Commercial resins generally had higher adsorption capacities t han modified corncobs. However, the adsorption capacity of modified corncob s for copper and lead ions was equivalent to Duolite GT-73, but was lower t han for Amberlite IRC-718 or Amberlite 200. Depending on the specific metal ion and the presence or absence of other metal ions, chemically modified c orncobs were at least equivalent in adsorption properties to all of the com mercial cation exchange resins examined in this study. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.