Direct Determination of Lead Speciation in Contaminated Soils by EXAFS Spectroscopy

Abstract

Direct determination of the chemical form of trace metals in soils still remains a challenge for instrumental analytical techniques. This paper examines the potential of EXAFS spectroscopy to speciate and quantify the form of trace metals in the solid fraction of soil materials using lead as a case study. Three soils contaminated by different sorts of industrial activities, including the synthesis of lead organometallics for gasoline antiknocks, Pb−Zn smelting, and recycling of lead acid battery, were investigated. In soil contaminated by alkyl-tetravalent lead compounds, lead was found to be divalent and complexed to salicylate and catechol-type functional groups of humic substances. Lead sulfate and silica-bound lead are the predominant forms in the vicinity of the battery reclamation area. Near the smelter, lead was found to be divalent and coordinated to O,OH ligands. It is present in several chemical forms, which prevented them from being identified individually. The multiplicity of lead species in soils contaminated by smelting activities is thought to be due to long-term atmospheric emissions and to the variety of lead-containing phases simultaneously, and successively, emitted in the atmosphere. EXAFS can be applied to a wide variety of matrices including sediments, solid and liquid wastes, and fly ash particles.