Influence of dynamical conditions on the reduction of U(VI) at the magnetite-solution interface.
The heterogeneous reduction of U(VI) to U(IV) by ferrous iron is believed to be a key process influencing the fate and transport of U in the environment. The reactivity of both sorbed and structural Fe(II) has been studied for numerous substrates, including magnetite. Published results from U(VI)-magnetite experiments have been variable, ranging from no reduction to clear evidence for the formation of U(IV). In this contribution, we used XAS and high resolution (+/-cryogenic) XPS to study the interaction of U(VI) with nanoparticulate magnetite. The results indicated that U(VI) was partially reduced to U(V) with no evidence of U(IV). However, thermodynamic calculations indicated that U phases with average oxidation states below (V) should have been stable, indicating that the system was not in redox equilibrium. A reaction pathway that involves incorporation and stabilization of U(V) and U(VI) into secondary phases is invoked to explain the observations. The results suggest an important and previously unappreciated role of U(V) in the fate and transport of uranium in the environment.
Ilton
Eugene S
ES
Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, USA. Eugene.Ilton@PNL.gov
Boily
Jean-François
JF
Buck
Edgar C
EC
Skomurski
Frances N
FN
Rosso
Kevin M
KM
Cahill
Christopher L
CL
Bargar
John R
JR
Felmy
Andrew R
AR
D052203:Ferrosoferric Oxide / Q000737:chemistry*; D005583:Fourier Analysis; D008906:Mining; D010084:Oxidation-Reduction; D012996:Solutions; D013816:Thermodynamics; D014501:Uranium / Q000737:chemistry*
D012996:Solutions; D014501:Uranium; D052203:Ferrosoferric Oxide