X-ray absorption spectroscopy studies of reactions of technetium, uranium and neptunium with mackinawite.
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.
Livens
Francis R
FR
Centre for Radiochemistry Research, Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. francis.livens@man.ac.uk
Jones
Mark J
MJ
Hynes
Amanda J
AJ
Charnock
John M
JM
Mosselmans
J Fred W
JF
Hennig
Christoph
C
Steele
Helen
H
Collison
David
D
Vaughan
David J
DJ
Pattrick
Richard A D
RA
Reed
Wendy A
WA
Moyes
Lesley N
LN
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*
D005296:Ferrous Compounds; D011848:Radioactive Pollutants; D014501:Uranium; D009405:Neptunium; D013667:Technetium; C022597:ferrous sulfide