Field assessment of lead immobilization in a contaminated soil after phosphate application.
A pilot-scale field demonstration was conducted at a Pb-contaminated site to assess the effectiveness of Pb immobilization using P amendments. The test site was contaminated by past battery recycling activities, with average soil Pb concentration of 1.16%. Phosphate amendments were applied at a 4.0 molar ratio of P/Pb with three treatments: T1, 100% P from H(3)PO(4); T2, 50% from H(3)PO(4)+50% from Ca(H(2)PO(4))(2); and T3, 50% from H(3)PO(4)+5% phosphate rock. Soil samples were collected and characterized 220 days after P application. Surface soil pH was reduced from 6.45 to 5.05 in T1, to 5.22 in T2, and to 5.71 in T3. Phosphate treatments effectively transformed up to 60% of total soil Pb from the non-residual fraction (sum of water soluble and exchangeable, carbonate, Fe-Mn oxide, and organic fractions) to the residual fraction relative to the control. In addition, P treatments reduced Toxicity Characteristic Leaching Procedure (TCLP) Pb from 82 mg l(-1) to below EPA's regulatory level of 5 mg l(-1) in the surface soil. Scanning electron microscopy-energy dispersive X-ray elemental analysis and X-ray diffraction analysis indicated formation of insoluble chloropyromorphite [Pb(5)(PO(4))(3)Cl] mineral in the P-treated soils. Although H(3)PO(4) is necessary to dissolve meta-stable Pb in soil for further lead immobilization, it should be used with caution due to its potential secondary contamination. A mixture of H(3)PO(4) and Ca(H(2)PO(4))(2) or phosphate rock was effective in immobilizing Pb with minimum adverse impacts associated with pH reduction.
Melamed
Ricardo
R
Center for Mineral Technology, Ministry of Science and Technology, Av. Ipê 900, Ilha da Cidade Universitaria, 21941-590, Rio de Janeiro, Brazil.
Cao
Xinde
X
Chen
Ming
M
Ma
Lena Q
LQ
D000327:Adsorption; D003247:Conservation of Natural Resources; D004736:Energy-Generating Resources; D004787:Environmental Pollution / Q000517:prevention & control*; D007854:Lead / Q000032:analysis* / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D012037:Refuse Disposal; D012989:Soil Pollutants / Q000032:analysis*
D010710:Phosphates; D012989:Soil Pollutants; D007854:Lead