Adsorption of some heavy metal ions on sulfate- and phosphate-modified kaolin

Kaolin (bright white lumps) from Ubulu-Ukwu in Delta State of Nigeria was modified with 200 mu g mL(-1) of phosphate and sulphate anions to give phosphate- and sulfate-modified adsorbents, respectively. The adsorption of four metal ions (Pb2+, Cd2+ Zn2+, and Cu2+) was studied as a function of metal ions concentration. The metal ions showed stronger affinity for the phosphate-modified adsorbent with Pb2+, Cu2+, Zn2+, and Cd2+ giving an average of 93.28%, 80.94%, 68.99%, and 61.44% uptake capacity. The order of preference for the various adsorbents shown by the metal ions was as follows: Pb2+> Cu2+> Zn2+> Cd2+ Desorption studies showed that the phosphate-modified adsobent had the highest affinity for the metal ions, followed by the sulfate-modified clay while the unmodified clay had the least affinity. The experimental data were fitted by both the Langmuir and Freundlich models. (c) 2004 Published by Elsevier B.V.