REMOVAL OF HEAVY-METAL IONS FROM AQUEOUS-SOLUTION BY MODIFIED BARKS

Bark, a common waste product in forestry, can be used to selectively r emove cations, especially toxic heavy metals from mono or multi saline solutions. Picea, Pinus, Pseudotsuga, Larix, Tectona and Afzelia bark s have been used in glass columns, after grinding and treatment with f ormaldehyde in acid media, to study their ability in binding toxic hea vy metal ions such as Pb2+, Zn2+, Cr2+, Fe2+ and Cu2+. The metals are exchanged against protons on the bark substrates that presumably conta in carboxyl groups in both pectin and tannin compounds. Removal of the se ions depends upon the nature of the bark used, the grain size and t he predominant heavy metal ions present in the solutions. The metal io ns could be stripped by addition of 0.1 N HCl, making the substrate re generation and its reutilization possible.