title: Sorption of Am(III) onto 6-line-ferrihydrite and its alteration products: investigations by EXAFS.
abstract: For the long-term performance assessment of nuclear waste repositories, knowledge about the interactions of actinide ions with mineral surfaces such as iron oxides is imperative. The mobility of released radionuclides is strongly dependent on the sorption/desorption processes at these surfaces and on their incorporation into the mineral structure. In this study the interaction of Am(III) with 6-line-ferrihydrite (6LFh) was investigated by EXAFS spectroscopy. At low pH values (pH 5.5), as well at higher pH values (pH 8.0), Am(III) sorbs as a bidentate corner-sharing species onto the surface. Investigations of the interaction of Am(III) with Fh coated silica colloids prove the sorption onto the iron coating and not onto the silica substrate. Hence, the presence of Fh, even as sediment coating, is the dominant sorption surface. Upon heating, Fh is transformed into goethite and hematite as shown by TEM and IR measurements. The results of the fit to the EXAFS data indicate the release of sorbed Am(III) at pH 5.5 during the transformation and likely a partial incorporation of Am into the Fh transformation products at pH 8.0.
authors.affiliation: Institut de Recherches Subatomiques, 23 Rue du Loess, P.O. Box 28, 67037 Strasbourg, France. silvia.stumpf@ires.in2p3.fr
authors.forename: Silvia
authors.initials: S
authors.lastname: Stumpf
authors.forename: Thorsten
authors.initials: T
authors.lastname: Stumpf
authors.forename: Kathy
authors.initials: K
authors.lastname: Dardenne
authors.forename: Christoph
authors.initials: C
authors.lastname: Hennig
authors.forename: Harald
authors.initials: H
authors.lastname: Foerstendorf
authors.forename: Reinhardt
authors.initials: R
authors.lastname: Klenze
authors.forename: Thomas
authors.initials: T
authors.lastname: Fanghänel
mesh_terms: D000576:Americium / Q000032:analysis / Q000737:chemistry*; D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000032:analysis / Q000737:chemistry; D008903:Minerals; D008956:Models, Chemical; D011850:Radioactive Waste / Q000032:analysis; D013055:Spectrophotometry, Infrared / Q000379:methods; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D011850:Radioactive Waste; C094886:goethite; C092844:ferric oxyhydroxide; D000576:Americium