Application Methods Affect Phosphorus-Induced Lead Immobilization from a Contaminated Soil

Phosphate rock (PR) and phosphoric acid (PA) are an effective combination of P sources for immobilizing Pb in contaminated soils. This column experiment examined the effectiveness of different ap-plication methods on Pb immobilization in a contaminated soil. Phos-phate was applied at a P/Pb molar ratio of 4 with half as PR and half PA. While PR was mixed with the soil or placed as a layer, aque-ous PA was applied from the top of the column as one or two ap-plications. After 4 wk of incubation, total and soluble Pb and P, TCLP-Pb (toxicity characteristic leaching procedure) and PBET-Pb (physiologically-based extraction test) in the P-treated soil were de-termined. Phosphate addition effectively reduced leachable Pb to below the EPA drinking water standard of 15mg L21 in all treatments. Mixing both PA and PR with the soil was the most effective method in Pb immobilization, reducing TCLP-Pb by up to 95 % and PBET-P