Attenuation of Pb and Sb in shooting range soils by Fe amendments

Abstract

Lead (Pb) and antimony (Sb) contamination pose a major environmental risk at firing ranges and threaten land sustainability. Methods for the stabilization of metal (loid) contaminants are necessary to prevent off-site migration of metals in surface and ground water or from soil erosion. In the present study, two remediation treatments (ferric chloride/calcium carbonate and nanoscale zero-valent iron (nZVI)) were applied to flow-through soil columns containing four types of soils (sand, sandy loam, loamy sand, and silty loam) to study Pb and Sb behavior. Water runoff was continuously monitored for three months prior to amendment addition and for the following ten months. Soils were characterized before and after reaction. We found Sb was more mobile than Pb in all soil systems and was primarily present in the dissolved fraction whereas Pb was associated with both soil organic matter (SOM) and Fe colloids. Dominant Pb solid phase species were comprised of Pb0, PbO, PbCO3, and Pb sorbed to Fe(III) oxides while Sb was present as fully oxidized Sb(V) in soil and soil solution. The nZVI addition had minimal impact on Pb and Sb immobilization compared to control soil. The FeCl2 and CaCO3 amendment decreased pore water Sb concentrations by >80% for all soil types and >96% reduction in the fine- and coarse-grained soil types (silt loam and sand). Lead was initially mobilized coinciding with a decrease in pH from the hydrolysis of Fe(II) in solution. Additional soil treatments have the potential to be effective for system-wide immobilization with adequate additions of CaCO3 buffer. Though this study focused on bullet fragment weathering as a source of Pb and Sb the results have application to environmental monitoring and remediation efforts at mining or industrial runoff sites.