Fe(II) Uptake on Natural Montmorillonites. I. Macroscopic and Spectroscopic Characterization

Soltermann, Daniela; Fernandes, Maria Marques; Baeyens, Bart; Dähn, Rainer; Joshi, Prachi; Scheinost, Andreas C.; Gorski, Christopher A.

doi:10.1021/es501887q

Cited by 41 publications

(96 citation statements)

References 54 publications

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“…The best agreement ("Fit 1") could be obtained for weighted spectra containing of Fe 2+ (30-40%) and Fe 3+ (60-70%). Iron was found to be preferentially in ferric form in both Milos-and Wyoming-montmorillonite that agreed with the assumption of earlier studies 9,53,58 . The differences in the quality of the fits between the Milos-and Wyoming-montmorillonite can be explained by the different distribution of the Fe atoms in the structure.…”

Section: Exafs Spectrasupporting

confidence: 89%

“…An important step towards is the better understanding of the iron uptake mechanism in the determination of relevant edge surfaces of montmorillonite. Such information will be essential for understanding the mechanism of the probable oxidative uptake of iron (Fe 2+ aq -> Fe 3+ surf) by clay minerals 9 . In the best case, the comparison of the ab initio based XAFS calculations and the measurements will result in the determination of the oxidation state of Fe in the bulk and at the surface.…”

Section: Implication Of the Theoretical Study In The Interpretation Omentioning

confidence: 99%

“…(1) X-ray adsorption fine structure (XAFS) and Mössbauer-spectroscopy are the two most widely applied tools for the spectroscopic identification of structural Fe incorporation in clay minerals 3,9,20,21,22 . The data analysis is often based on reference spectra for Fe 2+ and Fe 3+ endmembers, which, however, may represent Fe in a mixed structural state.…”

Section: Introductionmentioning

confidence: 99%

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Combined XAFS Spectroscopy and Ab Initio Study on the Characterization of Iron Incorporation by Montmorillonite

Kéri

Dähn

Krack

et al. 2017

Environ. Sci. Technol.

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Iron occurs in clay minerals in both ferric and ferrous forms. Depending on its oxidation state and the environmental conditions, it can participate in redox reactions and influence the sorption processes at surfaces of clay minerals. Knowing the oxidation state and the preferential structural position of Fe and Fe is essential for the detailed understanding of the mechanism and kinetics of such processes. In this study, molecular dynamics (MD) calculations based on density functional theory (DFT+U) were applied to simulate the incorporated Fe in bulk montmorillonite and to explain the measured Fe K-edge X-ray absorption fine structure (XAFS) spectra. The analysis of the experimental data and simulation results suggested that iron in montmorillonite is preferentially incorporated as Fe into the octahedral layer. The simulations showed that there is no preferential occupation of cis- or trans-sites by Fe and Fe in bulk montmorillonite. A very good agreement between the ab initio simulated and the measured XAFS spectra demonstrate the robustness of the employed simulation approach.

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Section: Exafs Spectrasupporting

confidence: 89%

Section: Implication Of the Theoretical Study In The Interpretation Omentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Combined XAFS Spectroscopy and Ab Initio Study on the Characterization of Iron Incorporation by Montmorillonite

Kéri

Dähn

Krack

et al. 2017

Environ. Sci. Technol.

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“…Another hypothesis for sorption irreversibility could be related to Fe(II) adsorption-induced interfacial ET reactions, from highly reactive surface-bound Fe(II) to clay structural Fe(III). 42,44,45,83 We suggested previously that Fe(II) initially adsorbs to clay edge sites, a removal from solution as indicated in Figure 1,f.…”

Section: Identification Of Reactive Mineral Phases For Tc(vii) and Crmentioning

confidence: 66%

Tc(VII) and Cr(VI) Interaction with Naturally Reduced Ferruginous Smectite from a Redox Transition Zone

Qafoku

Pearce

Neumann

et al. 2017

Environ. Sci. Technol.

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Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as important sources of electron equivalents limiting the transport of redox-active contaminants. While most laboratory reactivity studies are based on reduced model clays, the reactivity of naturally reduced field samples remains poorly explored. Characterization of the clay size fraction of a fine-grained unit from the RTZ interface at the Hanford site, Washington, including mineralogy, crystal chemistry, and Fe(II)/(III) content, indicates that ferruginous montmorillonite is the dominant mineralogical component. Oxic and anoxic fractions differ significantly in Fe(II) natural content, but Fe remains constant, demonstrating no Fe loss during its reduction-oxidation cyclings. At native pH of 8.6, the anoxic fraction, despite its significant Fe(II), ∼23% of Fe, exhibits minimal reactivity with TcO and CrO and much slower reaction kinetics than those measured in studies with biologically/chemically reduced model clays. Reduction capacity is enhanced by added/sorbed Fe(II) (if Fe(II) > 8% clay Fe(II)); however, the kinetics of this conceptually surface-mediated reaction remain sluggish. Surface-sensitive Fe L-edge X-ray absorption spectroscopy shows that Fe(II) and the resulting reducing equivalents are not available in the outermost few nanometers of clay surfaces. Slow kinetics thus appear related to diffusion-limited access to electron equivalents retained within the clay mineral structure.

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“…This Fe is considered to be immobile but can undergo reversible redox reactions with the diffusing Fe 2+ , through the reduction by Fe 2+ sorbed on the Fig. 11 Proposed Fe diffusion mechanism at the steel-bentonite interface edges (Schaefer et al 2011;Soltermann et al 2013Soltermann et al , 2014, and also on basal surfaces (Komadel et al 2006;Latta et al 2017). Moreover, sorption of diffusing Fe 2+ on pre-existing Fe 3+ bearing oxides (e.g.…”

Section: A Phenomenological Description Of the Fe Diffusion Mechanismmentioning

confidence: 99%

Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland

Hadi

Wersin

Serneels

et al. 2019

Clays and clay miner.

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Corrosion of steel canisters containing buried high-level radioactive waste is a relevant issue for the long-term integrity of repositories. The purpose of the present study was to evaluate this issue by examining two differently corroded blocks originating from a full-scale in situ test of the FEBEX bentonite site in Switzerland. The FEBEX experiment was designed initially as a feasibility test of an engineered clay barrier system and was recently dismantled after 18 years of activity. Samples were studied by Fspatially resolved`and Fbulk`experimental methods, including Scanning Electron Microscopy, Elemental Energy Dispersive Spectroscopy (SEM-EDX), μ-Raman spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and 57 Fe Mössbauer spectrometry, with a focus on Fe-bearing phases. In one of the blocks, corrosion of the steel liner led to diffusion of Fe into the bentonite, resulting in the formation of large (width > 140 mm) red, orange, and blue colored halos. Goethite was identified as the main corrosion product in the red and orange zones while no excess Fe 2+ (compared to the unaffected bentonite) was observed there. Excess Fe 2+ was found to have diffused further into the clay (in the blue zones) but its speciation could not be unambiguously clarified. The results indicate the occurrence of newly formed octahedral Fe 2+ either as Fe 2+ sorbed on the clay or as structural Fe 2+ inside the clay (following electron transfer from sorbed Fe 2+). No other indications of clay transformation or newly formed clay phases were found. The overall pattern indicates that diffusion of Fe was initiated when oxidizing conditions were still prevailing inside the bentonite block, resulting in the accumulation of Fe 3+ close to the interface (up to three times the original Fe content), and continued when reducing conditions were reached, allowing deeper diffusion of Fe 2+ into the clay (inducing an increase of 10-12% of the Fe content).

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Fe(II) Uptake on Natural Montmorillonites. I. Macroscopic and Spectroscopic Characterization

Cited by 41 publications

References 54 publications

Combined XAFS Spectroscopy and Ab Initio Study on the Characterization of Iron Incorporation by Montmorillonite

Combined XAFS Spectroscopy and Ab Initio Study on the Characterization of Iron Incorporation by Montmorillonite

Tc(VII) and Cr(VI) Interaction with Naturally Reduced Ferruginous Smectite from a Redox Transition Zone

Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland

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