Immobilization of Lead in Soil Influenced by Soluble Phosphate and Calcium: Lead Speciation Evidence
- Liping Li *a,
- Kirk G. Scheckelb,
- Lirong Zhengc,
- Guangtao Liua,
- Weiqin Xinga and
- Guoqiang Xianga
- a School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou, Henan 450001, China
b National Risk Management Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH 45224
c Institute of High Energy Physics, the Chinese Academy of Sciences, Beijing 100049, China
We investigated the effect of soluble Ca on the speciation of Pb in phosphate-amended soils. A calcareous soil was amended in sequence with soluble phosphate (0 and 299 mg kg−1 P), calcium nitrate (0, 200, and 400 mg kg−1 Ca), and/or lead nitrate (0 and 1000 mg kg−1 Pb) and incubated for 50 d. Extractable Ca was relatively similar across all samples, with a minor reduction in Ca release for treatments amended with P possibly from the formation of Ca-phosphate minerals. Olsen-P extractability from P-added treatments was highest in the non–Pb-amended soils and was about 40% lower when Pb was added as a result of Pb-phosphate formation. In the absence of P, diethylene triamine pentaacetic acid (DTPA)-Pb extractability increased with increasing Ca amendment; however, in the P-amended treatments, DTPA-Pb decreased with increasing Ca addition. X-ray absorption spectroscopy results of the Pb spiked soils indicate that adsorbed Pb is the primary phase (up to 92%) in non–P-amended soils with minor distribution to hydrocerussite and Pb-phosphate phases. In the P-amended treatments, Pb speciation shifted to Pb-phosphate [chloropyromorphite and Pb3(PO4)2] (42–48%) and adsorbed Pb (44–50%). As Ca concentration increased in the P-amended soils, Pb-phosphate speciation moved from combined chloropyromorphite and Pb3(PO4)2 (0 mg kg−1 Ca) to exclusively chloropyromorphite. The study demonstrates that soluble Ca enhances Pb immobilization with P amendments.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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