Immobilization of lead by application of zeolite: Leaching column and rhizobox incubation studies

Application of zeolite can reduce lead (Pb) mobility in soil. Leaching columns and rhizobox incubation experiments were carried out to investigate the leaching processes and rhizosphere behavior of Pb in a Pb-contaminated soil amended with zeolite. Zeolite addition reduced Pb release from the contaminated soil as well as increasing leachate pH and decreasing the bioavailable Pb concentration. Leachate pH was not significantly different among different zeolite dose treatments at the same measurement time. Leaching of Pb from the treated soil was lower than that from the untreated soil for the first nine weeks but the trend was reversed for the final weeks of the study. The Pb concentration in the leachate did not appear to be sensitive to changes in pH. It was concluded that when a relatively low amount of zeolite was added (<20 mg kg(-1)), the cation exchange capacity was the dominant factor for regulating Pb leaching behavior. The DTPA extractable Pb in the rhizosphere was similar to 15% higher than that in the close-root and bulk soil. In addition, the amounts of DTPA extractable Pb in the rhizosphere soil not treated with zeolite were 10% and 16% higher than in the rhizosphere soil with 10 and 20 g kg-1 zeolite addition, respectively. It could be concluded that zeolite addition inhibits uptake of Pb by affecting rhizospheric behavior.