The electrochemical reduction of hydrogen peroxide on uranium dioxide under intermediate pH to acidic conditions

Keech, Peter G.; Noel, Jamie; Shoesmith, David W.

doi:10.1016/j.electacta.2008.03.008

Cited by 16 publications

(9 citation statements)

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“…In fact, a number of high resolution studies have used identical primary peak shapes and FWHMs to model mixed valence U systems consistently. [5][6][7][8][9][10][11][12]17,36,37,58] There is, however, the question of where to place the background. Most authors tend to tightly wrap the background (usually a Shirley background) around the primary U4f 7/2 peak, ignoring all satellite structures except to help qualitatively identify the U oxidation states present; others attempt to model the entire spectrum including both spin-orbit split peaks and the satellite structure.…”

Section: Mixed Valence Systemsmentioning

confidence: 99%

“…Consequently, and again, it is the relative invariance of ΔE s-p (Fig. 3), even in mixed valence U compounds, [5][6][7][8][9][10][11][12]14,17,36,37,58,61] that strongly constrains the fit and lessens the dependence of interpreting oxidation states on BEs.…”

Section: Mixed Valence Systemsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…For example, it is of great interest to the environmental chemistry community whether U is present in the tetravalent or hexavalent state in the subsurface as oxidation state is a primary control on U solubility and hence its ultimate fate and transport in the environment. However, recent work has provided evidence that U(V) can be a long lived intermediate during fuel corrosion, [5][6][7][8][9][10][11] oxidation of colloidal UO 2 , [12] reduction in Fe(II)-Fe(III) systems, [13][14][15][16] and as an artifact of beam induced reduction of U(VI). [17,18] We reviewed the U XPS literature and abstracted features of interest, where possible, from work that obtained the highest energy resolution with the best estimate of the near-surface representing the bulk.…”

Section: Introductionmentioning

confidence: 99%

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XPS determination of uranium oxidation states

Ilton

Bagus

2011

Surface & Interface Analysis

205

118

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This contribution is both a review of different aspects of X-ray photoelectron spectroscopy that can help one determine U oxidation states and a personal perspective on how to effectively model the X-ray photoelectron spectroscopy of complicated mixed-valence U phases. After a discussion of the valence band, the focus lingers on the U4f region, where the use of binding energies, satellite structures, and peak shapes is discussed in some detail. Binding energies were shown to be very dependent on composition/structure and consequently unreliable guides to oxidation state, particularly where assignment of composition is difficult. Likewise, the spin orbit split 4f 7/2 and 4f 5/2 peak shapes do not carry significant information on oxidation states. In contrast, both satellite-primary peak binding energy separations, as well as intensities to a lesser extent, are relatively insensitive to composition/structure within the oxide-hydroxide-hydrate system and can be used to both identify and help quantify U oxidation states in mixed valence phases. An example of the usefulness of the satellite structure in constraining the interpretation of a complex multivalence U compound is given. Copyright © 2011 John Wiley & Sons, Ltd.Keywords: XPS; uranium; oxidation states IntroductionOne of the great strengths of X-ray photoelectron spectroscopy ( XPS) is its ability to elucidate the valence state of a wide range of elements at the near-surface of materials. Although many features of interest concern bulk properties, it is the surface and the near-surface that has immediate contact with its surroundings and consequently mediates most reactions. With the renewed interest in nuclear energy, characterizing the surface composition and chemical state of actinide-containing materials is important for both industrial applications and understanding the fate and transport of actinides in the environment. This perspective article is focused on uranium as the data set is by far the most comprehensive of all the actinides where an appreciable literature on the XPS of U compounds dates back to the beginnings of the commercialization of XPS in the 1970s. For an early paper on the XPS of a broad range of actinide oxides we refer the reader to Veal et al.[1] A basic understanding of XPS principles is assumed throughout and will not be reviewed.On one level, determining oxidation states with XPS would appear to be a simple exercise of comparing the binding energies (BEs) of core levels to well characterized standards; so why bother? However, interpreting the oxidation states of samples with mixed valence, unknown structures, and complicated or different compositions can pose a challenge, as with any analytical technique. In fact, composition can strongly affect uranium core-level BEs and potentially confuse the determination of oxidation states. For example, perhaps one is working in an oxidizing system and only expects U(VI), yet the U4f 7/2 line has a peak at 382.0 eV and a shoulder at 380.5 eV. Does the shoulder represent a reduced species, po...

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Section: Mixed Valence Systemsmentioning

confidence: 99%

Section: Mixed Valence Systemsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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XPS determination of uranium oxidation states

Ilton

Bagus

2011

Surface & Interface Analysis

205

118

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“…There is a broad literature base to support the reaction of bulk UO 2 and H 2 O 2 in aqueous media proceeding via the following (electrochemically coupled) reaction scheme [17,18,[20][21][22][23][24][25][26][27][28][29]:…”

Section: Introductionmentioning

confidence: 99%

The effect of hydrogen peroxide on uranium oxide films on 316L stainless steel

Wilbraham

Boxall

Goddard

et al. 2015

Journal of Nuclear Materials

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h i g h l i g h t sThe first report of the presence of both UO 2 and polymeric UO 2 2+ in the same electrodeposited U oxide sample.The action of H 2 O 2 on electrodeposited U oxides is described using corrosion based concepts.Electrodeposited U oxide freely dissolves at hydrogen peroxide concentrations <100 lmol dm À3 .At [H 2 O 2 ] > 0.1 mmol dm À3 dissolution is inhibited by formation of a studtite passivation layer. At [H 2 O 2 ] P 1 mol dm À3 studtite formation competes with uranyl-peroxide complex formation. a b s t r a c tFor the first time the effect of hydrogen peroxide on the dissolution of electrodeposited uranium oxide films on 316L stainless steel planchets (acting as simulant uranium-contaminated metal surfaces) has been studied. Analysis of the H 2 O 2 -mediated film dissolution processes via open circuit potentiometry, alpha counting and SEM/EDX imaging has shown that in near-neutral solutions of pH 6.1 and at [H 2 O 2 ] 6 100 lmol dm À3 the electrodeposited uranium oxide layer is freely dissolving, the associated rate of film dissolution being significantly increased over leaching of similar films in pH 6.1 peroxide-free water. At H 2 O 2 concentrations between 1 mmol dm À3 and 0.1 mol dm À3 , formation of an insoluble studtite product layer occurs at the surface of the uranium oxide film. In analogy to corrosion processes on common metal substrates such as steel, the studtite layer effectively passivates the underlying uranium oxide layer against subsequent dissolution. Finally, at [H 2 O 2 ] > 0.1 mol dm À3 the uranium oxide film, again in analogy to common corrosion processes, behaves as if in a transpassive state and begins to dissolve. This transition from passive to transpassive behaviour in the effect of peroxide concentration on UO 2 films has not hitherto been observed or explored, either in terms of corrosion processes or otherwise. Through consideration of thermodynamic solubility product and complex formation constant data, we attribute the transition to the formation of soluble uranyl-peroxide complexes under mildly alkaline, high [H 2 O 2 ] conditions -a conclusion that has implications for the design of both acid minimal, metal ion oxidant-free decontamination strategies with low secondary waste arisings, and single step processes for spent nuclear fuel dissolution such as the Carbonate-based Oxidative Leaching (COL) process.

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