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  • Title: X-ray absorption spectroscopy studies of reactions of technetium, uranium and neptunium with mackinawite.
    Author: Livens FR, Jones MJ, Hynes AJ, Charnock JM, Mosselmans JF, Hennig C, Steele H, Collison D, Vaughan DJ, Pattrick RA, Reed WA, Moyes LN.
    Journal: J Environ Radioact; 2004; 74(1-3):211-9. PubMed ID: 15063549.
    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.
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