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Abstract

Yang, J. and Xi Tang. 2009. Leaching characteristics of phosphate-stabilized lead in contaminated urban soil and mill waste. JEMREST 6:00-00

10.4029/2009jemrest6no18

Soil lead (Pb) contamination resulting from smelting and mining activities is a known threat to human health and ecosystem. In situ immobilization using phosphate-based amendments is being proposed as a potential cost-effective and environmental-sound remedial alternative for stabilizing soil Pb and reducing the associated human exposure and ecological risks through an induced transformation of labile Pb species to the insoluble lead phosphates. In an effort to assess the long-term stability and leachability of phosphate-immobilized Pb in soil, urban soil and mill waste containing about 4000 ppm Pb were treated with soluble phosphate and then packed into the PVC 30-cm long, 4-cm diameter columns 10 years post treatment. The soil columns were subjected to leaching tests using the USEPA standard Toxicity Characteristic Leaching Procedure (TCLP) and Simulated Precipitation Leaching Procedures (SPLP) under the conditions with or without the presence of plant growth. The phosphate soil treatment was found to effectively immobilize soil Pb and significantly reduce leachable Pb regardless of the leaching procedure, soil type, and plant presence. The reduction of soil Pb leachability was more effective in urban soil, and the amount of leachable Pb by TCLP was slightly higher with a delayed leaching breakthrough. In all case, the soil treatment resulted in aqueous Pb levels below the EPA water quality criteria. The presence of plant growth had no adverse impact on stimulating Pb leachability in the soils, but actually minimized the potential risk of enhanced phosphate leaching by the treatment. This study demonstrated that the Pb-phosphates formed after treatment are stable under the surface soil conditions and the treatment effects are sustainable in long-term. The phosphate treatment could be potentially used as an alternative to reduce the Pb-associated risks of soil and safeguard humans and water quality from the contamination.