An X-ray absorption study of the fate of technetium in reduced and reoxidised sediments and mineral phases

Morris, Katherine; Livens, Francis R.; Charnock, John; Burke, Ian T.; McBeth, Joyce; Begg, James D.; Boothman, Christopher; Lloyd, Jonathan R.

doi:10.1016/j.apgeochem.2007.10.014

Cited by 59 publications

(65 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Normalized Tc X-ray absorption near edge structure (XANES) spectra for the mineral phases are shown in Fig. 3 was no evidence for the pre-edge feature that is characteristic of the forbidden 1s?4d transition seen in TcO 4 À species (Maes et al, 2004); indeed all the spectra were typical of a Tc(IV)-like valence (Fredrickson et al, 2004;Plymale et al, 2011;Morris et al, 2008). Thus, low concentration tracer experiments coupled with higher concentration XANES experiments show that the different Fe(II)-bearing mineral phases have different reactivity to Tc(VII) but that abiotically mediated reductive scavenging of TcO 4 À to Tc(IV) is the dominant retention mechanism for Tc in these systems.…”

Section: Low-concentration Tracer Experimentsmentioning

confidence: 99%

“…Interestingly, in sediment microcosm experiments where Tc(IV)-labelled sediments have been reoxidized, some samples have been shown to contain both Tc(VII) and Tc(IV) using XAS techniques (Burke et al, 2006;Morris et al, 2008;Fredrickson et al, 2009). In a study using sediments from the Oak Ridge Field Research Center (Fredrickson et al, 2009), both Tc(IV) and Tc(VII) were observed on the wet sediment paste using XANES and repeated washing with water removed the sediment associated Tc(VII).…”

Section: Low-concentration Tracer Experimentsmentioning

confidence: 99%

“…Reoxidation of immobilized radionuclides in contaminated aquifers could occur via transport of oxygenated waters through the sediments, water table fluctuations, or disturbance of the geosphere by construction or erosion (Burke et al, 2006;Wu et al, 2007). Furthermore, reoxidation caused by nitrate, a common pollutant found at nuclear facilities, is also a potential route to radionuclide reoxidation via, for example, biologically mediated Fe(II)-oxidation coupled to NO 3 À reduction (Burke et al, 2006;Geissler et al, 2011;Morris et al, 2008;Senko et al, 2005;Wu et al, 2010;Law et al, 2010b;Law et al, 2011). Recent experimental work on sediments suggests that Tc associated with Fe(II)-bearing sediments is recalcitrant to reoxidation even though significant reoxidation of Fe(II) to Fe(III) occurs during both air and nitrate reoxidation (Burke et al, 2006;Fredrickson et al, 2009;Geissler et al, in press;Jaisi et al, 2009 .…”

mentioning

confidence: 99%

See 2 more Smart Citations

Redox interactions of technetium with iron-bearing minerals

et al. 2011

Self Cite

View full text Add to dashboard Cite

AbstractIron minerals influence the environmental redox behaviour and mobility of metals including the long-lived radionuclide technetium. Technetium is highly mobile in its oxidized form pertechnetate (Tc(VII)O4–), however, when it is reduced to Tc(IV) it immobilizes readily via precipitation or sorption. In low concentration tracer experiments, and in higher concentration XAS experiments, pertechnetate was added to samples of biogenic and abiotically synthesized Fe(II)-bearing minerals (bio-magnetite, bio-vivianite, bio-siderite and an abiotically precipitated Fe(II) gel). Each mineral scavenged different quantities of Tc(VII) from solution with essentially complete removal in Fe(II)-gel and bio-magnetite systems and with 84±4% removal onto bio-siderite and 68±5% removal onto bio-vivianite over 45 days. In select, higher concentration, Tc XAS experiments, XANES spectra showed reductive precipitation to Tc(IV) in all samples. Furthermore, EXAFS spectra for bio-siderite, bio-vivianite and Fe(II)-gel showed that Tc(IV) was present as short range ordered hydrous Tc(IV)O2-like phases in the minerals and for some systems suggested possible incorporation in an octahedral coordination environment. Low concentration reoxidation experiments with air-, and in the case of the Fe(II) gel, nitrate-oxidation of the Tc(IV)-labelled samples resulted in only partial remobilization of Tc. Upon exposure to air, the Tc bound to the Fe-minerals was resistant to oxidative remobilization with a maximum of ∼15% Tc remobilized in the bio-vivianite system after 45 days of air exposure. Nitrate mediated oxidation of Fe(II)-gel inoculated with a stable consortium of nitrate-reducing, Fe(II)-oxidizing bacteria showed only 3.8±0.4% remobilization of reduced Tc(IV), again highlighting the recalcitrance of Tc(IV) to oxidative remobilization in Fe-bearing systems. The resultant XANES spectra of the reoxidized minerals showed Tc(IV)-like spectra in the reoxidized Fe-phases. Overall, this study highlights the role that Fe-bearing biogenic mineral phases have in controlling reductive scavenging of Tc(VII) to hydrous TcO2-like phases onto a range of Fe(II)-bearing minerals. In addition, it suggests that on reoxidation of these phases, Fe-bound Tc(IV) may be octahedrally coordinated and is largely recalcitrant to reoxidation over medium-term timescales. This has implications when considering remediation approaches and in predictions of the long-term fate of Tc in the nuclear legacy.

show abstract

Section: Low-concentration Tracer Experimentsmentioning

confidence: 99%

Section: Low-concentration Tracer Experimentsmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Redox interactions of technetium with iron-bearing minerals

et al. 2011

Self Cite

View full text Add to dashboard Cite

show abstract

“…A number of experiments that examined the reduction and retention of 99 Tc in natural sediments whose oxidation states have been artificially altered (Burke et al 2006, Burke et al 2005, Fredrickson et al 2004, Morris et al 2008, Zachara et al 2007) yielded some interesting and useful results for secondary 99 Tc sequestration. Reduction of Tc(VII) to Tc(IV) by ferrous iron (Fe(II)) in solution is sluggish (homogeneous kinetics), even though the reaction…”

Section: Goethitementioning

confidence: 99%

“…The atomic structure of goethite, recently determined by Yang et al (2006), is shown in Figure 2.5. On the other hand, examining the reduced run products with X-ray absorption spectroscopy (XAS) methods (briefly described in Appendix A) has revealed that the 99 Tc-bearing phase is a separate, reduced Tc(IV) oxide phase and may not be substituting for Fe(III)-O in the host ferric oxyhydroxide phase (Burke et al 2006, Fredrickson et al 2004, Fredrickson et al 2009, Morris et al 2008, Peretyazhko et al 2008a, Watson et al 2001, Wharton et al 2000, Zachara et al 2007). In the most detailed study, Fredrickson and coworkers (Fredrickson et al 2009) found that Tc(IV)O 2 -like compounds could exist in a number of states, including physically separate phases or those that are inter-grown with Fe(III)-O compounds.…”

mentioning

confidence: 99%

Review of Potential Candidate Stabilization Technologies for Liquid and Solid Secondary Waste Streams

Pierce¹,

Mattigod²,

Westsik³

et al. 2010

View full text Add to dashboard Cite

Executive SummaryPacific Northwest National Laboratory has initiated a waste-form testing program to support the longterm durability evaluation of a waste form for secondary wastes generated from the treatment and immobilization of Hanford radioactive tank wastes. The purpose of the work discussed in this report is to identify candidate stabilization technologies and getters that have the potential to successfully treat the secondary waste stream liquid effluent, mainly from off-gas scrubbers and spent solids, produced by the Hanford Tank Waste Treatment and Immobilization Plant (WTP). Down-selection to the most promising stabilization processes/waste forms is needed to support the design of a solidification treatment unit (STU) to be added to the Effluent Treatment Facility (ETF). To support key decision processes, an initial screening of the secondary liquid waste forms must be completed by February 2010. Later, more comprehensive and longer term performance testing will be conducted, following the guidance provided by the secondary waste-form selection, development, and performance evaluation roadmap. The resulting waste form will be compliant to regulations and performance criteria and will lead to cost-effective disposal of the secondary wastes.This report starts with a brief review of some of the most commonly used solidification formulations that would be candidates for secondary liquid waste streams. In this review, the available data on performance are discussed, and some preliminary recommendations are provided for materials that should undergo additional screening testing. We also 1) discuss options for disposal of WTP secondary solid waste streams, 2) provide a brief overview of standard regulatory test methods used for measuring contaminant leachability and waste-form physical strength (with emphasis on the U.S. Environmental Protection Agency's [EPA's] new methods as a screening tool for comparing waste solidification materials of interest), and 3) provide an overview of factors that must be considered in long-term performance testing, including state-of-the-art characterization tools that can provide the data needed to technically defend predictive modeling simulations of long-term material behavior. The long-term wasteform testing and solid and leachate characterization must be robust enough to effectively predict material performance in the Integrated Disposal Facility over the 10,000-year period of performance for the engineered system. The solidification technologies for liquid waste streams include cement/grout, containerized Cast Stone, phosphate-bonded ceramics, alkali-aluminosilicate geopolymers, hydroceramics, L-TEM, and fluidized-bed steam reforming (FBSR). In addition to these, other mature technologies and two compounds, namely goethite and sodalite (that are still being developed), that show considerable promise as waste forms or getters are also discussed. It is our recommendation, based upon the available literature, that Cast Stone, chemically bonded phosphate ceramics (Ceramicrete...

show abstract