Sorption properties of chemically-activated carbons 1. Sorption of cadmium(II) ions

Chemically-activated carbons were prepared by reacting corn-stalks with concentrated sulphuric acid at 180-220degreesC and by activation with zinc chloride at 600degreesC. Sulphuric acid-activated carbons measure surface areas in the order of 20 m(2)/g, while those activated with zinc chloride measure surface areas of about 700-900 m(2)/g. The concentrations of carbon-oxygen functional groups, on sulphuric acid-activated carbons are higher than those on zinc chloride-activated ones. Sorption of Cd(II) depends on the chemistry of the surface of activated carbon rather than on its surface area. Light metals ions such as Na+ decreased the Cd(II) ion sorption onto activated carbons, high concentration of Na+ may stop sorption of Cd(II) onto activated carbons. Chemically-activated carbons can be used for a number of cycles after regeneration with a slight decrease in sorption capacity after each cycle. The sorption of Cd(II) onto chemically-activated carbons is associated with a release of protons indicating that the sorption of this heavy metal ion and probably of other metal ions takes place via ion exchange mechanism. The sorption of Cd(II) ions is controlled at least partially by pore diffusion. Cadmium(II) sorption on chemically-activated carbons depends on the concentration of the metal ions indicating first-order mechanism. (C) 2004 Elsevier B.V. All rights reserved.