Abstract
Understanding interactions between radionuclides and mineral phases underpins site environmental cleanup and waste management in the nuclear industry. The transport and fate of radionuclides in many subsurface environments are controlled by adsorption, redox, and mineral incorporation processes. Interactions of iron (oxyhydr)oxides with uranium have been extensively studied because of the abundance of uranium as an environmental contaminant and the ubiquity of iron (oxyhydr)oxides in engineered and natural environments. Despite this, detailed mechanistic information regarding the incorporation of uranium into Fe(II)-bearing magnetite and green rust is sparse. Here, we present a co-precipitation study in which U(VI) was reacted with environmentally relevant iron(II/III) (oxyhydr)oxide mineral phases. On the basis of diffraction, microscopic, dissolution, and spectroscopic evidence, we show the reduction of U(VI) to U(V) and stabilization of the U(V) by incorporation within the near surface and bulk of the ...
Highlights
Uranium is a problematic contaminant at nuclear sites and is the dominant radionuclide by mass in radioactive wastes destined for geological disposal
During biological and abiotic reduction of U(VI), U(V) reportedly forms as a transient species.[5−7] Recent work has suggested that U(V) can be stabilized at mineral surfaces[8−12] and via incorporation into environmentally relevant ironoxide phases such as goethite (α-FeOOH) and magnetite (FeIIFeIII2O4).[13−21] establishing the extent of U(V) stability upon interaction with Feoxides is essential in underpinning predictive models for U behavior in environmental systems that currently do not recognize the presence of U(V)
U speciation needs to be determined at a molecular scale, which is a key step in defining the significance of U(V) in environmental systems and in developing realistic models for predicting the environmental fate of uranium
Summary
Uranium is a problematic contaminant at nuclear sites and is the dominant radionuclide by mass in radioactive wastes destined for geological disposal. Uraniumbearing magnetite and green rust were synthesized using a direct co-precipitation method in experiments performed at room temperature in an anaerobic chamber.[32] In brief, solutions of 0.1 M FeCl2, 0.2 M FeCl3, 0.3 M HCl, and 0.0126 M U(VI)Cl6 were mixed for 24 h before mineral precipitation was induced by introduction of the Fe(II)/Fe(III) solution into a N2-sparged 28−30% (w/v) NH4OH solution (pH 11) that was being continuously stirred over 15 min to a final pH of 9. This led to the instantaneous co-precipitation of the uranium-doped minerals. Analysis of the EXAFS spectra was performed in Artemis and Athena with details given in the Supporting Information.[36−40] U M4 edge HERFDXANES spectra were recorded at European Synchrotron Radiation Facility, beamline ID26,41 through the use of an Xray emission spectrometer[42,43] and analyzed using iterative transformation factor analysis[12,44] to determine the proportion of U(IV), U(V), and U(VI) in the samples
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