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 (α-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 pedominate 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.