Aqueous Pb Reduction in Pb-Contaminated Soils by Florida Phosphate Rocks

Lead contamination is of great environmental concern due to its effect on human health. This study investigated the feasibility of using Florida phosphate rocks (PR) to immobilize aqueous Pb from Pb-contaminated soils. Occidental Chemical PR effectively immobilized Pb from 13 Pb-contaminated soils, but its effectiveness was affected by soil pH and extent of Pb contamination, with aqueous Pb reduction ranging from 21.8 to 100%. Longer reaction times improved aqueous Pb reduction. Six out of 7 Florida PR effectively immobilized aqueous Pb from the Burch Loam soil. Phosphate rock from Cargil Fertilizer was ineffective, with aqueous Pb reduction of 4.73%. The relative effectiveness of 6 Florida PR to immobilize aqueous Pb, excluding Cargil Fertilizer PR, was: Occidental Chemical > CF Chemical > Nu Gulf Industries > Agri-Chemical > IMC > Agrico Chemical. Phosphate rock solubility (as estimated by acid extraction and X-ray diffraction) failed to predicate the effectiveness of PR to immobilize aqueous Pb from Pb-contaminated soils, partially due to the complexity and kinetics of reactions between PR and soils. Our results demonstrate that PR has a potential to cost-effectively treat Pb-contaminated soils.