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 s...

Direct Determination of Lead Speciation in Contaminated Soils by EXAFS Spectroscopy

Stereochemistry of lead(II) complexes with oxygen donor ligands

This review discusses the coordination number (CN) and the coordination geometry of the first coordination sphere of Pb(II) atoms in crystal structures of 98 lead(II) complexes with O-donor ligands and the stereochemically active lone pair of electrons (LP, E) in the terms of the valence shell electron-pair repulsion (VSEPR) model. The CN of Pb(II) atoms of the first coordination sphere has values falling into the range (3 + E) to (6 + E). The following coordination polyhedra-{psi}-tetrahedron (I), {psi}-trigonal bipyramid (II), {psi}-octahedron (III), {psi}-pentagonal bipyramid with an axial (IV) or equatorial (V) vacant position are formed. For the investigated structures of the Pb(II) complexes, the formula of each compound, the overall CN of the Pb(II) atom considered as the sum of the CN in the first coordination sphere and the number of secondary bonds, the polyhedron shape, the Pb-O bond lengths, and O-Pb-O bond angles in the first coordination sphere, secondary bond lengths, references and REFCODEs are presented in the comprehensive Tables. The quantum chemical investigations performed using density functional theory (DFT) method have confirmed the stereochemical activity of the LP of Pb(II) atoms in the studied structures of lead(II) complexes with O-donor ligands.

Stereochemistry of lead(II) complexes with oxygen donor ligands.

Sorption mechanisms of lead on silicon-rich biochar in aqueous solution: Spectroscopic investigation.

The local atomic environment of lead (Pb) adsorbed to a CH3(CH2)19COOH Langmuir monolayer was investigated in situ using grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy at the Pb LIII edge. Measurements were performed at pH 6.5 of the 10-5 M PbCl2 solution subphase, a condition under which grazing incidence diffraction (GID) revealed a large-area commensurate superstructure underneath the close-packed organic monolayer. The XAFS results indicate covalent binding of the Pb cations to the carboxyl headgroups, and the observed Pb−Pb coordination suggests that the metal is adsorbed as a hydrolysis polymer, rather than as individual Pb2+ ions. The data are consistent with a bidentate chelating mechanism and a one Pb atom to one carboxyl headgroup binding stoichiometry. We discuss how this adsorption model can explain the peculiarities observed with Pb in previous metal−Langmuir monolayer studies. A systematic study of lead perchlorate and lead acetate aqueous solutions is presented and...

J. K. Mohana Rao

Papers

Crystal structure of lead acetate trihydrate