Heavy metals such as Cd(II) and Pb(II) have received considerable attention. In the first and second studies, sorption behavior of Cd(II) and Pb(II) on zeolite and bentonite were investigated. Bentonite had a higher percent removal of Cd(II) in all chemical conditions compared to zeolite. Both commercial Iranian zeolite and bentonite showed high sorption behavior for removing of Pb(II) from aqueous solutions. Because of high surface area and CEC, zeolite removed more Pb(II) than bentonite in the same chemical condition. We examined sorption reversibility of Cd(II) and Pb(II) on zeolite and bentonite in the third study. The results revealed that the desorption isotherms of Cd(II) and Pb(II) from zeolite significantly deviated from the sorption isotherms indicating irreversible or very slowly reversible sorption. For bentonite sorption/desorption isotherms were similar indicating reversible sorption. Plant availability of Cd(II) and Pb(II) adsorbed on zeolite and bentonite in a pot (sand) culture experiment was investigated in the fourth study. The concentration of Cd(II) and Pb(II) in the corn roots and shoots grown in the enriched bentonite-sand culture system were significantly higher than those planted in the enriched zeolite-sand culture indicating a stronger immobilizing of Cd(II) and Pb(II) by the zeolite. At last, effects of DFOB-siderophore on sorption of Cd(II) and Pb(II) on bentonite was investigated. Siderophore increased sorption of Pb(II) on bentonite while, it decreased Cd(II) sorption on bentonite Keywords Zeolite, Bentonite, Cadmium, Lead, Hysteresis.
