Removal of heavy metal ions from aqueous solution by modified barks

Abstract Bark, a common waste product in forestry, can be used to selectively remove cations, especially toxic heavy metals from mono or multi saline solutions. Picea, Pinus, Pseudotsuga, Larix, Tectona and Afzelia barks have been used in glass columns, after grinding and treatment with formaldehyde in acid media, to study their ability in binding toxic heavy metal ions such as Pb2+, Zn2+, Cr2+, Fe2+ and Cu2+. The metals are exchanged against protons on the bark substrates that presumably contain carboxyl groups in both pectin and tannin compounds. Removal of these ions depends upon the nature of the bark used, the grain size and the predominant heavy metal ions present in the solutions. The metal ions could be stripped by addition of 0.1 ? HCl, making the substrate regeneration and its reutilization possible.