Probing the Biogeochemical Behavior of Technetium Using a Novel Nuclear Imaging Approach

Lear, Gavin; McBeth, Joyce; Boothman, Christopher; Gunning, Darren J.; Ellis, B. L.; Lawson, Richard; Morris, Katherine; Burke, Ian T.; Bryan, Nicholas; Brown, Andy; Livens, Francis R.; Lloyd, Jonathan R.

doi:10.1021/es802885r

Cited by 45 publications

(56 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…; Burke et al, 2010;Lear et al, 2010) and with Tc(IV) colloids, Tc(IV)-carbonate complexes and Tc(IV)-organic complexes all reported to enhance the solubility of Tc(IV) above 10 À8 mol l À1 under certain conditions (Alloit et al, 2009;Gu et al, 2011;Plymale et al, 2011). Further, bioreduction (where indigenous sediment microorganisms are stimulated to produce reducing conditions by the addition of an electron donor) has been shown to be an effective means of removing Tc(VII) from solution in microcosm (Burke et al, 2005;Begg et al, 2007;Law et al, 2010a), column (Michalsen et al, 2006;Lear et al, 2010) and field studies (Istok et al, 2004) over a wide range of conditions.…”

mentioning

confidence: 99%

“…Further, bioreduction (where indigenous sediment microorganisms are stimulated to produce reducing conditions by the addition of an electron donor) has been shown to be an effective means of removing Tc(VII) from solution in microcosm (Burke et al, 2005;Begg et al, 2007;Law et al, 2010a), column (Michalsen et al, 2006;Lear et al, 2010) and field studies (Istok et al, 2004) over a wide range of conditions. A typical feature in these bioreduction experiments is that the removal of Tc(VII) is associated with the development of microbially-mediated Fe(III) reduction in the sediments (Burke et al, 2005;Fredrickson et al, 2004;Li and Krumholz, 2008;Michalsen et al, 2006;Wildung et al, 2004).…”

mentioning

confidence: 99%

“…Furthermore, removal is thought to be dominated by abiotic electron transfer from sediment associated biogenic Fe(II) to Tc(VII) in all but Fe-poor environments (Lloyd et al, 2000;Begg et al, 2007;Fredrickson et al, 2004;Plymale et al, 2011;Law et al, 2010a;Zachara et al, 2007). Indeed, in experiments using different sediment types, Tc has been found to be associated primarily with Fe-rich (Lear et al, 2010, Fredrickson et al, 2004 or Fe(II)-rich nano particles. However, the details of which Fe(II)-bearing minerals mediate Tc(VII)-reduction in heterogeneous sediments are poorly constrained.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Redox interactions of technetium with iron-bearing minerals

et al. 2011

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

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Redox interactions of technetium with iron-bearing minerals

et al. 2011

View full text Add to dashboard Cite

show abstract

“…For example (see Fig. 17 the association and speciation of the fission product, technetium-99, found in radioactive wastes, was examined under reducing conditions over a range of concentrations in estuarine sediments Lear et al 2010). Anoxic incubation experiments were conducted with direct (transmission electron microscopy and gamma camera imaging) and indirect (incubation experiments and chemical extractions) experimental techniques employed.…”

Section: Use Of (S)tem To Assess Transport and Retardation Mechanismsmentioning

confidence: 99%

Analytical Transmission Electron Microscopy

Brydson

Brown

Benning

et al. 2014

Reviews in Mineralogy and Geochemistry

View full text Add to dashboard Cite

“…For example (see Fig. 17 the association and speciation of the ission product, technetium-99, found in radioactive wastes, was examined under reducing conditions over a range of concentrations in estuarine sediments Lear et al 2010). Anoxic incubation experiments were conducted with direct (transmission electron microscopy and gamma camera imaging) and indirect (incubation experiments and chemical extractions) experimental techniques employed.…”

Section: Use Of (S)tem To Assess Transport and Retardation Mechanismsmentioning

confidence: 99%

6. Analytical Transmission Electron Microscopy

Brydson¹,

Brown²,

Benning³

et al. 2014

Spectroscopic Methods in Mineralogy and Material Sciences

View full text Add to dashboard Cite

INTRODUCTIONAnalytical transmission electron microscopy (TEM) is used to reveal sub-micrometer, internal ine structure (the microstructure or ultrastructure) and chemistry in minerals. The amount and scale of the information which can be extracted by TEM depends critically on four parameters; the resolving power of the microscope (usually smaller than 0.3 nm); the energy spread of the electron beam (of the order of an electron volt, eV); the thickness of the specimen (almost always signiicantly less than 1 mm), and the composition and stability of the specimen. An introductory text on all types of electron microscopy is provided by Goodhew et al. (2001), while more detailed information on transmission electron microscopy may be found in the comprehensive text of Williams and Carter (2009). INTRODUCTION TO ANALYTICAL TRANSMISSION ELECTRON MICROSCOPY (TEM) Basic design of transmission electron microscopes (TEM)The two available modes of TEM-CTEM and STEM-differ principally in the way they address the specimen. Conventional TEM (CTEM) is a wide-beam technique, in which a close-to-parallel electron beam loods the whole area of interest and the image (or diffraction pattern), formed by an imaging (objective) lens after the thin specimen from perhaps 10 6 -10 7 pixels on a digital camera, is collected in parallel. Scanning TEM (STEM) deploys a ine focused beam, formed by a probe-forming lens before the thin specimen, to address each pixel (here, a dwell point) in series and form a sequential image as the probe is scanned across the specimen. Figures 1 and 2 summarize these different instrument designs; here it should be noted that many modern TEM instruments are capable of operating in both modes, rather than being instruments dedicated to one mode of operation.In both types of instrument analytical information from a small region is usually collected using a focused beam. The smallest region from which an analysis can be collected is deined by the diameter of this beam and hence the corresponding through-thickness volume in the Brydson, Brown, Benning, Livi specimen within which various elastic and inelastic scattering (energy-loss) processes take place.In both CTEM and STEM, electrons are produced from an electron emitter, focused and collimated into a beam and inally accelerated to a given beam energy. Key instrumental components, which affect the microscope resolution and analytical performance, are:• the electron emitter which can operate via either a thermionic or ield emission mechanism or a combination of the two; ield emission provides the brightest, most monochromatic and coherent source of electrons.• the accelerating voltage (E o , typically in the range 60-300 kV) and hence incident electron energy; the higher the accelerating voltage the higher the resolution and the larger the sample penetration (although, in certain cases depending on the elements present and their chemical bonding, sample damage via sputtering may be an issue above a certain threshold energy).In the CTEM (Fig. 1), two or more electro...

show abstract

Probing the Biogeochemical Behavior of Technetium Using a Novel Nuclear Imaging Approach

Cited by 45 publications

References 54 publications

Redox interactions of technetium with iron-bearing minerals

Redox interactions of technetium with iron-bearing minerals

Analytical Transmission Electron Microscopy

6. Analytical Transmission Electron Microscopy

Contact Info

Product

Resources

About