Determining uranium speciation in Fernald soils by molecular spectroscopic methods. FY 1993 progress report

Abstract

This progress report describes new experimental results and interpretations for data collected from October 1,1992, through September 30,1993, as part of the Characterization Task of the Uranium in Soils Integrated Demonstration of the Office of Technology Development, Office of Environmental Restoration and Waste Management of the US Department of Energy. X-ray absorption, optical luminescence, and Raman vibrational spectroscopies were used to determine uranium speciation in contaminated soils from the US Department of Energy's former uranium production facility at Fernald, Ohio (18 mi northwest of Cincinnati). These analyses were carried out both before and after application of one of the various decontamination technologies being developed within die Integrated Demonstration. The treatment technologies included soil washes with carbonate, citrate, Tiron, and Tiron/dithionite mixtures. This year the program focused on characterization of the uranium speciation remaining in the soils after decontamination treatment. X-ray absorption and optical luminescence spectroscopic data were collected for approximately 40 Fernald soil samples, which were treated by one or more of the decontamination technologies. Results for the A-series soils from the Incinerator Area suggest that the treated soils can be divided into three sets. The first set comprises control samples that are little changed from the untreated soils. The second set encompasses most of the A-series samples. The uranium remaining in these soils appears to have a slightly higher ratio of tetravalent to hexavalent uranium than the untreated soils. Determining Uranium Specfatkxi in Femald Soils have. The third set consists of only All soils that were treated by Tiron, carbonate, o? both, but with no reducing agent. This set appears to have the highest ratio of tetravalent to hexavalent uranium remaining in the soil for any sample examined thus far. Observation of different x-ray absorption spectra in the second and thud sets suggests that there are several uranium species-rather than a single intransigent species-left in the soils following treatment and that the treatment chemistry may be dictating the difference in the remnant species. The treated B-series soils from the Plant 1/Storage Pad Area are less easily categorized. However, from the usual x-ray absorption criteria, it appears that they retain primarily hexavalent uranium following the treatments. The optical luminescence data demonstrate that there is a decrease in size (and probably quantity) of the particulate hexavalent uranium that gives rise to the green emission. Thus, all treatment technologies do seem to lead to a more dispersed, finer grained contamination. Some instances of particulate green emission still exist in these samples, and the spectral band structure suggests that this is attributable to a schoepite phase. An orange emissive phase, also seen in many samples, is probably attributable to a hexavalent uranium species, but its identity has not been confirmed. New Raman and luminesc...

The geochemical behaviour of Tc, Np and Pu in spent nuclear fuel in an oxidizing environment

“…The major U-bearing phases found in soils at the former U-processing site at Fernald in Ohio, USA, were Ca-metaautunite, U-Ca-oxide, uraninite, and uranium (IV) meta-phosphate (U3PO4) ). Bertsch et al (1994 and Allen et al (1994) used XAS to determine the oxidation state of U in bulk soil samples. The position of the U-LnI edge indicated that 80% of the U was hexavalent.…”

Analytical electron microscopy characterization of Fernald soils. Annual report, October 1993--September 1994

“…Lee and Marsh [3] used X-ray diffraction (XRD) to identify the major non-uraniumbearing phases in the soils as quartz, clays, calcite, and dolomite. Bertsch et al [5] and Allen et al [6] have used X-ray absorption spectroscopy (XAS) to determine the oxidation state of uranium in bulk soil samples from Fernald. The shift to higher energies of the X-ray absorption uranium L H!…”

“…Allen et al [6] have determined U-0 bond lengths by using XAS data to calculate radial distribution functions (RDF); however, as the data have not been corrected for phase shifts, the bond lergths may be in error.…”

“…Allen et al [6] have suggested that schoepite (uranyl oxide hydrate) is an important phase in Fernald soils, although they present no evidence for its existence. There are two types of schoepite, hydrated and dehydrated, which have characteristic XRD reflections (7.37 A and 3.59 A for hydrated schoepite, 5.11 A and 3.43 A for dehydrated schoepite).…”

“…Table 1 lists the various techniques used to characterize Fernald soils and the type of information they can provide. The luminescence and Raman spectroscopic methods used by Allen et al [6] are unreliable techniques for performing this type of analysis, although once the phases have been established by using AEM, these methods might be used to estimate the relative amounts of phases in bulk soil. (These methods will still be subject to errors due to the large size of some uranium phases and interference from other phases in the soils.)…”