title: X-ray absorption spectroscopy studies of reactions of technetium, uranium and neptunium with mackinawite.
abstract: Technetium, uranium and neptunium may all occur in the environment in more than one oxidation state (IV or VII, IV or VI and IV or V respectively). The surface of mackinawite, the first-formed iron sulfide phase in anoxic conditions, can promote redox changes so a series of laboratory experiments were carried out to explore the interactions of Tc, U and Np with this mineral. The products of reaction were characterised using X-ray absorption spectroscopy. Technetium, added as TcO4(-), is reduced to oxidation state IV and forms a TcS(2)-like species. On oxidation of the mackinawite in air to form goethite, Tc remains in oxidation state IV but in an oxide, rather than a sulfide environment. At low concentrations, uranium forms uranyl surface complexes on oxidised regions of the mackinawite surface but at higher concentrations, the uranium promotes surface oxidation and forms a mixed oxidation state oxide phase. Neptunium is reduced to oxidation IV and forms a surface complex with surface sulfide ions. The remainder of the Np coordination sphere is filled with water molecules or hydroxide ions.
authors.affiliation: Centre for Radiochemistry Research, Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. francis.livens@man.ac.uk
authors.forename: Francis R
authors.initials: FR
authors.lastname: Livens
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Jones
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Hynes
authors.forename: John M
authors.initials: JM
authors.lastname: Charnock
authors.forename: J Fred W
authors.initials: JF
authors.lastname: Mosselmans
authors.forename: Christoph
authors.initials: C
authors.lastname: Hennig
authors.forename: Helen
authors.initials: H
authors.lastname: Steele
authors.forename: David
authors.initials: D
authors.lastname: Collison
authors.forename: David J
authors.initials: DJ
authors.lastname: Vaughan
authors.forename: Richard A D
authors.initials: RA
authors.lastname: Pattrick
authors.forename: Wendy A
authors.initials: WA
authors.lastname: Reed
authors.forename: Lesley N
authors.initials: LN
authors.lastname: Moyes
mesh_terms: D004784:Environmental Monitoring; D005296:Ferrous Compounds / Q000737:chemistry*; D009405:Neptunium / Q000032:analysis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D011848:Radioactive Pollutants / Q000032:analysis; D013057:Spectrum Analysis; D013667:Technetium / Q000032:analysis* / Q000737:chemistry*; D014501:Uranium / Q000032:analysis* / Q000737:chemistry*
chemical_list: D005296:Ferrous Compounds; D011848:Radioactive Pollutants; D014501:Uranium; D009405:Neptunium; D013667:Technetium; C022597:ferrous sulfide