Mössbauer spectrometry insights into the redox reactivity of Fe-bearing phases in the environment

Charlet, Laurent; Tournassat, Christophe; Grenèche, Jean‐Marc; Wersin, Paul; Géhin, Antoine; Hadi, Jebril

doi:10.1557/s43578-022-00823-8

Cited by 3 publications

(3 citation statements)

References 158 publications

(251 reference statements)

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“…In previous work, it was proposed that iron moves from cis to trans sites during reduction and forms trioctahedral domains and large vacancies in the octahedral sheets. 41 , 45 , 69 , 70 We could not confirm this for the low-red NAu-2 and high-red NAu-2 samples. Either these phenomena are irregular on a small scale and hence difficult to capture by TEM, or our relatively mild CBD treatment did not cause such a reorganization of the octahedral sheets.…”

Section: Resultsmentioning

confidence: 73%

Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions

Qian,

Scheinost,

Grangeon

et al. 2023

ACS Earth Space Chem.

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The redox reaction between natural Fe-containing clay minerals and its sorbates is a fundamental process controlling the cycles of many elements such as carbon, nutrients, redoxsensitive metals, and metalloids (e.g., Co, Mn, As, Se), and inorganic as well as organic pollutants in Earth's critical zone. While the structure of natural clay minerals under oxic conditions is wellknown, less is known about their behavior under anoxic and reducing conditions, thereby impeding a full understanding of the mechanisms of clay-driven reduction and oxidation (redox) reactions especially under reducing conditions. Here we investigate the structure of a ferruginous natural clay smectite, nontronite, under different redox conditions, and compare several methods for the determination of iron redox states. Iron in nontronite was gradually reduced chemically with the citrate-bicarbonate-dithionite (CBD) method. 57 Fe Mossbauer spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy including its pre-edge, extended Xray absorption fine structure (EXAFS) spectroscopy, and mediated electrochemical oxidation and reduction (MEO/MER) provided consistent Fe(II)/Fe(III) ratios. By combining X-ray diffraction (XRD) and transmission electron microscopy (TEM), we show that the long-range structure of nontronite at the highest obtained reduction degree of 44% Fe(II) is not different from that of fully oxidized nontronite except for a slight basal plane dissolution on the external surfaces. The short-range order probed by EXAFS spectroscopy suggests, however, an increasing structural disorder and Fe clustering with increasing reduction of structural Fe.

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Section: Resultsmentioning

confidence: 73%

Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions

Qian,

Scheinost,

Grangeon

et al. 2023

ACS Earth Space Chem.

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“…In particular, this method enables the evaluation of the overall reduction level (Fe(II)/Fe tot ) and distinguishing between different Fe(III) and Fe(II) species in clay materials. [21,25,31] An example of the Mössbauer spectra from the FEBEX sample, which is presented in Figure 4, shows the relative proportions of the main Fe species (structural Fe(III), goethite, haematite and paramagnetic Fe(II)) as a function of the distance from the Fe/clay interface. Thus, at the direct contact point, the average oxidation state of Fe increases because of the accumulation of Fe(III) oxides (mainly goethite), but in parallel paramagnetic Fe(II) (i.e., sorbed Fe(II), ferrous hydroxide or structural Fe(II) from the clay fraction) has also formed.…”

Section: Clay Sidementioning

confidence: 99%

Unravelling the corrosion processes at steel/bentonite interfaces in in situ tests

Wersin

Hadi

Kiczka

et al. 2023

Materials & Corrosion

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Microscopic and spectroscopic analyses were conducted on steel/bentonite interface samples removed from four in situ experiments that were carried out in three underground research laboratories at different temperatures and under different hydraulic and geochemical conditions. The results provide valuable information about the corrosion processes occurring in high‐level radioactive waste repositories. Systematic patterns can be deduced from the results, irrespective of carbon steel grade, type of bentonite and its degree of compaction, geochemical environment or experimental setup. Thus, a clear dependence of the corrosion rates on temperature and exposure period, as well as on the availability of H2O and O2 provided by the surrounding bentonite buffer, is observed. Furthermore, Fe(II) ions released by corrosion interact with the structural Fe in the clay. Recent developments highlight the usefulness of reactive transport modelling in understanding the coupled corrosion and Fe–clay interaction processes.

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“…Further, -OH groups take also part in the charge neutralization, cisand trans-symmetries can be distinguished depending on their mutual symmetry [9]. The distinction between dioctahedral/trioctahedral variants and cis-/trans-OH symmetries with Mössbauer spectroscopy is rather cumbersome [10,11]. Depending on the particular structure and conditions of the formation of sheet silicates, the Fe 3+ /(Fe 2+ + Fe 3+ ) partitioning may significantly vary in them [12].…”

Section: Introduction 1general Overviewmentioning

confidence: 99%

Iron-Bearing Minerals in the Boda Claystone Formation: Correspondences with Stages of Evolution Revealed by Mössbauer Spectroscopy

Lázár,

Máthé,

Németh

et al. 2024

Minerals

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The Boda Claystone Formation (BCF) is an extended sedimentary sequence formed in a shallow-water salt lake under semi-arid to arid climatic conditions during the middle Permian period. The rock was formed predominantly from denuded and altered products of three primary felsic sources, the Mórágy Metagranite Complex, the Baksa Metamorphic Complex and the rhyolitic Gyűrűfű Formation, resulting in the recent dominant sheet silicate components, illite and chlorite. BCF has been considered a potential host rock for high-level nuclear waste, too. Thus, it has been characterized by several powerful methods so far (X-ray diffraction (XRD), transmission electron microscopy (TEM), etc.). 57Fe Mössbauer spectroscopy may provide a unique additional tool to study iron-bearing minerals. Iron is dominantly present in a ferrous form in minerals of the fresh parent rocks (in the biotite group and amphibole), and in a ferric oxide, hematite, in altered Gyűrűfű Formation. During transformations of biotite group minerals and amphibole, the partial release of ferrous iron or its conversion to ferric form takes place with the stabilization of recent illite and chlorite, while the original layered structure is still preserved. Mössbauer spectroscopy revealed the dominant presence of ferrous iron located in cis-M2 octahedral sites both in parent biotite group minerals and in the final illite, as well as chlorite in both stages. The proportion of ferrous iron in biotite group minerals was halved during the stages of evolution by conversion to ferric iron still in sheet silicate illite or by segregation into separate hematite inclusions. The transformation process of biotite group minerals and amphibole of the source rocks is connected only to the iron-bearing smaller fraction of sheet silicates in the BCF clay mineral assemblage. Determination of Fe2+/Fe3+ ratios in sheet silicates was also pertinent in two sections of BCF. Namely, in samples from the Gorica region, Fe3+ was dominant, siting in illite, whereas Fe2+ was also present in significant portions in chlorite in samples from the Western Mecsek Anticline. The interpretation is deduced in correspondence with results of extended XRD, and high-resolution TEM studies.

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Mössbauer spectrometry insights into the redox reactivity of Fe-bearing phases in the environment

Cited by 3 publications

References 158 publications

Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions

Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions

Unravelling the corrosion processes at steel/bentonite interfaces in in situ tests

Iron-Bearing Minerals in the Boda Claystone Formation: Correspondences with Stages of Evolution Revealed by Mössbauer Spectroscopy

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