Field demonstration of in situ immobilization of soil Pb using P amendments |
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Authors: | Ming Chen Lena Q MaSatya P Singh Rocky X CaoRicardo Melamed |
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Institution: | a Everglades Research and Education Center, University of Florida, Belle Glade, FL 33430, USA b Soil and Water Science Department, University of Florida, Gainesville, FL 32611-0290, USA c Center for Mineral Technology, Ministry of Science and Technology, Av. Ipê 900, Ilha da Cidade Universitaria, Rio de Janeiro, 21941-590 Brazil |
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Abstract: | A long-term field-scale demonstration project on the feasibility of using P to immobilize Pb in a Pb-contaminated urban soil was conducted. Phosphate was applied at an average rate of 3040 mg P/kg soil based on a P/Pb molar ration of 4.0, with four treatments: T0, no P application; T1, H3PO4 only; T2, 1/2 H3PO4+1/2 CaH2PO4; and T3, 1/2 H3PO4+1/2 phosphate rock. Soil samples were collected and analyzed 220 days after the P applications. For all P treatments, toxicity characteristic leaching procedure (TCLP) extractable Pb levels in surface soils (0-10 cm) were reduced to below 5.0 mg Pb/l, with T2 also effective in reducing the TCLP Pb level in subsurface soils (10-30 cm, <4.63 mg/l). Sequential extraction analysis indicates that P was effective in transforming soil Pb from non-residual fractions to a residual fraction. Such a transformation was mainly through dissolution of Pb associated with carbonate fraction and precipitation of pyromorphite-like minerals, which were confirmed using X-ray diffraction (XRD). Among these three treatments, T3 was the most effective in reducing Pb mobility and minimizing P and Pb leaching in the soil. Our research clearly demonstrates that P amendments were effective in immobilizing Pb in contaminated soil. |
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Keywords: | Pb contamination In situ immobilization P amendment Urban soil Sequential extraction Toxicity characteristic leaching procedure (TCLP) |
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