Adsorption by coniferous leaves of chromium ions from effluent

The chromium adsorption ability of leaves from 34 conifer species were examined. Among them, deciduous conifer species, such as Larix, Ginkgo, Metasequia, and Taxodium, showed high ability to adsorb chromium ions. Factors affecting chromium adsorption were studied using larch (Larix leptolepis) leaves to determine the optimum adsorption conditions. The factors included solution pH, contact time. temperature, and the initial concentration of chromium ions. Maximum adsorption for Cr3+ was ob served at pH 5, and maximum Cr6+ adsorption occurred at PH 3. The amount of Cr6+ adsorbed on the adsorbent increased rapidly during the first 4h, then gradually increased, and finally reached equilibrium in 16h. The adsorption rate of Cr3+ was somewhat slower than that of Cr6+. The adsorption isotherm for Cr6+ adsorption was composed of two straight lines, suggesting that the adsorbent could not practically reduce the concentration of Cr6+ in solution below 1.6mg Cr/l. Column experiments using larch leaf packing suggested that the practical operation could be controlled by monitoring the effluent pH.