EXAFS spectroscopy was used to study Pb(II) and Hg(II) adsorption complexes on goethite (??-FeOOH) in the presence of Cl-. At pH 7, the dominant Pb(II) species are bonded to edges of FeO6 octahedra and are similar to complexes that occur in the absence of Cl-. At pH ??? 6, Pb(II)-chloro ternary complexes predominate and are bonded to corners of FeO6 octahedra. At pH 6.5, linear Hg(OH)Cl ternary complexes predominate that are bonded to goethite through surface oxygens in a bent Hg-O-Fe geometry. In the absence of Cl-, the Hg(II) surface complexes retain this basic geometry, but an OH group replaces the chloride ion in the first coordination shell.
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XAFS studies of Pb(II)-chloro and Hg(II)-chloro ternary complexes on goethite