ADSORPTION OF HEAVY-METAL IONS BY HARDWOOD BARKS

Forty five species of hardwood barks were examined to evaluate their abilities to remove toxic heavy ions from aqueous solution. The barks considerably varied in the adsorption ability to each metal ion. Of the barks tested, high adsorption abilities for Cd2+, Cu2+ and Zn2+ were found in Fraxinus mandshutica var. japonica, Magnolia kobus var. borealis, Magnolia obovata, Morus bombycis, Populus maximowiczii, Populus sieboldii, Styrax japonica and tree species of walnut family (Juglandaceae). However, most of the barks were inefficient in removing of Ag+, Co2+, Mn2+ and Ni2+. Batch experiments using Cd(NO3)2 solutions and Populus maximowiczii bark indicated that the adsorption of heavy metal ion by bark adsorbent was markedly affected by the pH of solution and the initial concentration of heavy metal ion in the solution. Almost quantitative removal of Cd2+ from 1 mM Cd(NO3)2 solution was achieved by a column packed with Populus maximowiczii bark. Before the column broke through, the packing had retained 10.7 - 20.4 mg Cd2+ g adsorbent.