Stabilizing lead bullets in shooting range soil by phosphate-based surface coating

Abstract

Soil lead (Pb) is well known as a threat to human health and ecosystem. Although relatively insoluble, lead bullets in shooting range soil can be readily released into soluble forms through natural weathering processes and thus pose significant human and environmental risks. In this study, laboratory experiments were conducted to investigate if the Pb bullets in shooting range soil can be stabilized through surface coating of phosphate-based materials. Results indicated that FePO 4 or AlPO 4 coatings, insoluble metal phosphates, have been successfully formed on the surface of the Pb bullets. The EPA Toxicity Characteristic Leaching Procedure (TCLP) test showed that FePO 4 or AlPO 4 surface coating would effectively reduce the Pb solubility or leachability of the bullets. The surface coating under pH of 4 coating and 77–98% by AlPO 4 coating as compared with the non-coating. Leachable Pb concentration in the contaminated shooting range soil was reduced by 85–98% or 77–98% as a result of the FePO 4 or AlPO 4 solution treatment. This study demonstrated that the FePO 4 or AlPO 4 –based surface coating on lead bullets can effectively inhibit the Pb weathering and significantly reduce the Pb release from soil through in situ chemical stabilization, which could be potentially applicable as a cost-effective and environmental-sound technology for the remediation of Pb-contaminated shooting range soil.