XAFS studies of Pb(II)-chloro and Hg(II)-chloro ternary complexes on goethite

EXAFS spectroscopy was used to study Pb(II) and Hg(II) adsorption complexes on goethite (alpha-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 less than or equal to 6, Pb(II)-chloro ternary complexes predominate and are bonded to corners of FeO6 octahedra. At pH 6.5, linear HO(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.