B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Luke T.
Townsend
,
Samuel
Shaw
,
Naomi E. R.
Ofili
,
Nikolas
Kaltsoyannis
,
Alex S.
Walton
,
J. Frederick W.
Mosselmans
,
Thomas S.
Neil
,
Jonathan R.
Lloyd
,
Sarah
Heath
,
Rosemary
Hibberd
,
Katherine
Morris
Diamond Proposal Number(s):
[13559, 17376, 17243]
Open Access
Abstract: Uranium is a risk-driving radionuclide in both radioactive waste disposal and contaminated land scenarios. In these environments, a range of biogeochemical processes can occur, including sulfate reduction, which can induce sulfidation of iron (oxyhydr)oxide mineral phases. During sulfidation, labile U(VI) is known to reduce to relatively immobile U(IV); however, the detailed mechanisms of the changes in U speciation during these biogeochemical reactions are poorly constrained. Here, we performed highly controlled sulfidation experiments at pH 7 and pH 9.5 on U(VI) adsorbed to ferrihydrite and investigated the system using geochemical analyses, X-ray absorption spectroscopy (XAS), and computational modeling. Analysis of the XAS data indicated the formation of a novel, transient U(VI)–persulfide complex as an intermediate species during the sulfidation reaction, concomitant with the transient release of uranium to the solution. Extended X-ray absorption fine structure (EXAFS) modeling showed that a persulfide ligand was coordinated in the equatorial plane of the uranyl moiety, and formation of this species was supported by computational modeling. The final speciation of U was nanoparticulate U(IV) uraninite, and this phase was evident at 2 days at pH 7 and 1 year at pH 9.5. Our identification of a new, labile U(VI)-persulfide species under environmentally relevant conditions may have implications for U mobility in sulfidic environments pertinent to radioactive waste disposal and contaminated land scenarios.
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Dec 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[15971, 17888]
Abstract: Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root induced physical changes, chemical changes have not been extensively measured in situ on the pore scale.
In this study we couple structural information, previously obtained using synchrotron X‐ray computed tomography (XCT), with synchrotron X‐ray Fluorescence (SR‐XRF) microscopy and X‐ray Absorption Near‐Edge Structure (XANES) to unravel chemical changes induced by plant roots.
Our results suggest that iron (Fe) and sulfur (S) increase notably in the direct vicinity of the root via solubilization and microbial activity. XANES further shows that Fe is slightly reduced, S is increasingly transformed into sulfate (SO42‐) and that phosphorus (P) is increasable adsorbed to humic substances in this enrichment zone. In addition, the ferrihydrite fraction decreases drastically suggesting the preferential dissolution and the formation of more stable Fe‐oxides. Additionally, the increased transformation of organic S to sulfate indicates that the microbial activity in this zone is increased. These changes in soil chemistry correspond to the soil compaction zone as previously measured via X‐ray CT.
The fact that these changes are co‐located near the root and the compaction zone suggests that decreased permeability due to soil structural changes acts as a barrier creating a zone with increased rhizosphere chemical interactions via surface mediated processes, microbial activity and acidification.
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Oct 2019
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B18-Core EXAFS
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Kurt F.
Smith
,
Katherine
Morris
,
Gareth
Law
,
Ellen H.
Winstanley
,
Francis R.
Livens
,
Joshua S.
Weatherill
,
Liam G.
Abrahamsen-mills
,
Nicholas D.
Bryan
,
J. Frederick W.
Mosselmans
,
Giannantonio
Cibin
,
Stephen
Parry
,
Richard
Blackham
,
Kathleen A.
Law
,
Samuel
Shaw
Diamond Proposal Number(s):
[17243]
Abstract: Understanding interactions between iron (oxyhydr)oxide nanoparticles and plutonium is essential to underpin technology to treat radioactive effluents, in clean-up of land contaminated with radionuclides, and to ensure the safe disposal of radioactive wastes. These interactions include a range of adsorption, precipitation and incorporation processes. Here, we explore the mechanisms of plutonium sequestration during ferrihydrite precipitation from an acidic solution. The initial 1 M HNO3 solution with Fe(III)(aq) and 242Pu(IV)(aq) underwent controlled hydrolysis via the addition of NaOH to pH 9. The majority of Fe(III)(aq) and Pu(IV)(aq) was removed from solution between pH 2 and 3 during ferrihydrite formation. Analysis of Pu-ferrihydrite by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy showed that Pu(IV) formed an inner sphere tetradentate complex on the ferrihydrite surface, with minor amounts of PuO2 present. Best fits to the EXAFS data collected from Pu-ferrihydrite samples aged for two- and six- months showed no statistically significant change in the Pu(IV)-Fe oxyhydroxide surface complex despite the ferrihydrite undergoing extensive recrystallisation to hematite. This suggests the Pu remains strongly sorbed to the iron (oxyhydr)oxide surface and could be retained over extended time periods.
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Sep 2019
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B18-Core EXAFS
I14-Hard X-ray Nanoprobe
I18-Microfocus Spectroscopy
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William R.
Bower
,
Katherine
Morris
,
Francis R.
Livens
,
J. Frederick W.
Mosselmans
,
Connaugh M.
Fallon
,
Adam J.
Fuller
,
Louise S.
Natrajan
,
Christopher
Boothman
,
Jonathan R.
Lloyd
,
Satoshi
Utsunomiya
,
Daniel
Grolimund
,
Dario
Ferreira Sanchez
,
Tom
Jilbert
,
Julia E.
Parker
,
Thomas S.
Neill
,
Gareth T. W.
Law
Diamond Proposal Number(s):
[15085, 17270, 13559, 18053]
Abstract: Metaschoepite is commonly found in U contaminated environments and metaschoepite-bearing wastes may be managed via shallow or deep disposal. Understanding metaschoepite dissolution and tracking the fate of any liberated U is thus important. Here, discrete horizons of metaschoepite (UO3●nH2O) particles were emplaced in flowing sediment/groundwater columns representative of the UK Sellafield site. The column systems either remained oxic or became anoxic due to electron donor additions, and the columns were sacrificed after 6- and 12-months for analysis. Solution chemistry, extractions, and bulk and micro-/nano-focus X-ray spectroscopies were used to track changes in U distribution and behavior. In the oxic columns, U migration was extensive, with UO22+ identified in effluents after 6-months of reaction using fluorescence spectroscopy. Unusually, in the electron-donor amended columns, during microbially-mediated sulfate reduction, significant amounts of UO2-like colloids (>60% of the added U) were found in the effluents using TEM. XAS analysis of the U remaining associated with the reduced sediments confirmed the presence of trace U(VI), non-crystalline U(IV), and biogenic UO2, with UO2 becoming more dominant with time. This study highlights the potential for U(IV) colloid production from U(VI) solids under reducing conditions and the complexity of U biogeochemistry in dynamic systems.
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Jul 2019
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I13-1-Coherence
I18-Microfocus Spectroscopy
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Peter G.
Martin
,
Marion
Louvel
,
Silvia
Cipiccia
,
Christopher P.
Jones
,
Darren J.
Batey
,
Keith R.
Hallam
,
Ian A. X.
Yang
,
Yukihiko
Satou
,
Christoph
Rau
,
J. Fred W.
Mosselmans
,
David
Richards
,
Thomas B.
Scott
Diamond Proposal Number(s):
[16701, 16702, 18186]
Open Access
Abstract: Here we report the results of multiple analytical techniques on sub-mm particulate material derived from Unit 1 of the Fukushima Daiichi Nuclear Power Plant to provide a better understanding of the events that occurred and the environmental legacy. Through combined x-ray fluorescence and absorption contrast micro-focused x-ray tomography, entrapped U particulate are observed to exist around the exterior circumference of the highly porous Si-based particle. Further synchrotron radiation analysis of a number of these entrapped particles shows them to exist as UO2—identical to reactor fuel, with confirmation of their nuclear origin shown via mass spectrometry analysis. While unlikely to represent an environmental or health hazard, such assertions would likely change should break-up of the Si-containing bulk particle occur. However, more important to the long-term decommissioning of the reactors at the FDNPP (and environmental clean-upon), is the knowledge that core integrity of reactor Unit 1 was compromised with nuclear material existing outside of the reactors primary containment.
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Jun 2019
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I14-Hard X-ray Nanoprobe
I18-Microfocus Spectroscopy
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Open Access
Abstract: Biological exposures to micro- and nano-scale exogenous metal particles generated as a consequence of in-service degradation of orthopaedic prosthetics can result in severe adverse tissues reactions. However, individual reactions are highly variable and are not easily predicted, due to in part a lack of understanding of the speciation of the metal-stimuli which dictates cellular interactions and toxicity. Investigating the chemistry of implant derived metallic particles in biological tissue samples is complicated by small feature sizes, low concentrations and often a heterogeneous speciation and distribution. These challenges were addressed by developing a multi-scale two-dimensional X-ray absorption spectroscopic (XAS) mapping approach to discriminate sub-micron changes in particulate chemistry within ex-vivo tissues associated with failed CoCrMo total hip replacements (THRs). As a result, in the context of THRs, we demonstrate much greater variation in Cr chemistry within tissues compared with previous reports. Cr compounds including phosphate, hydroxide, oxide, metal and organic complexes were observed and correlated with Co and Mo distributions. This variability may help explain the lack of agreement between biological responses observed in experimental exposure models and clinical outcomes. The multi-scale 2D XAS mapping approach presents an essential tool in discriminating the chemistry in dilute biological systems where speciation heterogeneity is expected.
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Jun 2019
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B18-Core EXAFS
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J.
Sannigrahi
,
D. T.
Adroja
,
C.
Ritter
,
W.
Kockelmann
,
A. D.
Hillier
,
K. S.
Knight
,
A. T.
Boothroyd
,
M.
Wakeshima
,
Y.
Hinatsu
,
J. F. W.
Mosselmans
,
S.
Ramos
Diamond Proposal Number(s):
[63810]
Abstract: Bulk studies have revealed a first-order valence phase transition in
Ba
2
PrRu
1
−
x
Ir
x
O
6
(
0.10
≤
x
≤
0.25
), which is absent in the parent compounds with
x
=
0
(
Pr
3
+
) and
x
=
1
(
Pr
4
+
), which exhibit antiferromagnetic order with transition temperatures
T
N
=
120
and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering, and x-ray absorption measurements to investigate the nature of the Pr ion in
x
=
0.1
. The magnetic susceptibility and heat capacity of
x
=
0.1
show a clear sign of the first-order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that
x
=
0.1
crystallizes in a monoclinic structure with space group
P
2
1
/
n
at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one (
F
m
¯
3
m
) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the
x
=
0.1
compound below 110 K in the neutron diffraction measurements. Meanwhile, the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined high-energy magnetic excitations near 264 meV at temperatures below the valence transition. Low energy INS data show a broad magnetic excitation centered at 50 meV above the valence transition, but four well-defined magnetic excitations at 7 K. The high energy excitations are assigned to the
Pr
4
+
ions in the cubic phase and the low energy excitations to the
Pr
3
+
ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy. The results on the
x
=
0.1
compound are compared with those for
x
=
0
and 1.
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May 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1125, 7453]
Open Access
Abstract: Background: Chemical imaging of the human brain has great potential for diagnostic and monitoring purposes. The heterogeneity of human brain iron distribution, and alterations to this distribution in Alzheimer’s disease, indicate iron as a potential endogenous marker. The influence of iron on certain magnetic resonance imaging (MRI) parameters increases with magnetic field, but is under-explored in human brain tissues above 7 T. New Method: Magnetic resonance microscopy at 9.4 T is used to calculate parametric images of chemically-unfixed post-mortem tissue from Alzheimer’s cases (n = 3) and healthy controls (n = 2). Iron-rich regions including caudate nucleus, putamen, globus pallidus and substantia nigra are analysed prior to imaging of total iron distribution with synchrotron X-ray fluorescence mapping. Iron fluorescence calibration is achieved with adjacent tissue blocks, analysed by inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectroscopy. Results: Correlated MR images and fluorescence maps indicate linear dependence of R2, R2* and R2’ on iron at 9.4 T, for both disease and control, as follows: [R2(s−1) = 0.072[Fe] + 20]; [R2*(s−1) = 0.34[Fe] + 37]; [R2’(s−1) = 0.26[Fe] + 16] for Fe in μg/g tissue (wet weight). Comparison with Existing Methods: This method permits simultaneous non-destructive imaging of most bioavailable elements. Iron is the focus of the present study as it offers strong scope for clinical evaluation; the approach may be used more widely to evaluate the impact of chemical elements on clinical imaging parameters. Conclusion: The results at 9.4 T are in excellent quantitative agreement with predictions from experiments performed at lower magnetic fields.
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Mar 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[9044, 9598]
Abstract: A detailed understanding of the mechanisms and effects of radiation damage in phyllosilicate minerals is a necessary component of the evaluation of the safety case for a deep geological disposal facility (GDF) for radioactive waste. Structural and chemical changes induced by α-particle damage will affect these mineral’s performance as a reactive barrier material (both in the near and far-field) over timescales relevant to GDF integrity. In this study, two examples of chlorite group minerals have been irradiated at α-particle doses comparable to those predicted to be experienced by the clay buffer material surrounding high level radioactive waste canisters. Crystallographic aberrations induced by the focused 4He2+ ion beam are revealed via high-resolution, microfocus X-ray diffraction mapping. Interlayer collapse by up to 0.5 Å is prevalent across both macro- and micro-crystalline samples, with the macro-crystalline specimen displaying a breakdown of the phyllosilicate structure into loosely-connected, multi-oriented crystallites displaying variable lattice parameters. The damaged lattice parameters suggest a localised breakdown and collapse of the OH- rich, ‘brucite-like’ interlayer. Microfocus Fe K-edge X-ray absorption spectroscopy illustrates this defect accumulation, manifest as a severe damping of the X-ray absorption edge. Subtle Fe2+/Fe3+ speciation changes are apparent across the damaged structures. A trend towards Fe reduction is evident at depth in the damaged structures at certain doses (8.76 x 1015 alpha particles/ cm2). Interestingly, this reductive trend does not increase with radiation dose, indeed at the maximum dose (1.26 x 1016 alpha particles/ cm2) administered in this study, there is evidence for a slight increase in Fe binding energy, suggesting the development of a depth-dependant redox gradient concurrent with light ion damage. At the doses examined here, these damaged structures are likely highly reactive, as sorption capacity will, to an extent, be largely enhanced by lattice disruption and an increase in available ‘edge’ sites.
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Feb 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[11412]
Open Access
Abstract: Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron-based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO2+ species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase.
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Feb 2019
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