Mobility and plant-availability of Cd(II) and Pb(II) adsorbed on zeolite and bentonite

The objective of this work was to study the desorption behaviour and plant-availability of Cd(II) and Pb(II) adsorbed on zeolite and bentonite in a batch and a pot (sand) culture experiment. In a sequential desorption experiment Cd(II) and Pb(II) desorption from the zeolite (at 50, 75 and 100% of maximum adsorption capacity, SCmax) equilibrated with 0.01 M Ca(NO3)2 was lower as compared to bentonite at all the metal ion loading rates. Amounts of 3, 14 and 31% of the initially adsorbed Pb(II) were desorbed from the bentonite but only 1, 3 and 5% from the zeolite. The corresponding desorbed quantities of Cd(II) were 53, 65 and 71% for bentonite and 41, 33 and 21% for zeolite. In the pot (sand) culture experiments in a greenhouse, corn seedlings were planted in pots filled with quartz sand mixed with zeolite or bentonite enriched with Cd(II) or Pb(II). The concentration of Cd(II) and Pb(II) in the corn roots and shoots grown in the enriched bentonite–sand culture system was significantly higher than those planted in the enriched zeolite–sand culture indicating a stronger immobilizing of Cd(II) and Pb(II) by the zeolite.