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Immobilization of Soil Pb by Different Amendments

In situ immobilization of heavy metals in polluted soil with immobilizing agents is a fast and effective approach to alleviating the environmental and healthy pressure resulted from soil pollution. Here we evaluated the effectiveness of three metal-immobilizers, namely potassium dihydrogen phosphate(KH2PO4), calcium carbonate(Ca CO3)and sodium silicate(Na2Si O3), on soil Pb immobilization. After amendment of these immobilizing agents, soil p H, bioavailable Pb, and Pb fractions were measured, and the crystal structure of soil was also studied by X-ray diffraction technique. Chemicals KH2PO4, Ca CO3 and Na2Si O3 performed the best in immobilization of Pb-polluted soil at a mass addition rate of 5%, 5% and 2%, respectively. Soil exchangeable Pb was decreased while residual Pb increased by three amendments.Lead precipitates Pb3(PO4)2, Pb CO3, and Pb Si O3 occurred in soil after adding immobilizers, resulting in the immobilization of Pb in soil.Compared with the control, the addition of KH2PO4 reduced bioavailable Pb and exchangeable Pb by 95.7% and 96.1%, respectively, but increased residual Pb by 4.7 times, showing that KH2PO4 possessed the best Pb-immobilizing performance among all three amendments.