Redox front formation in an uplifting sedimentary rock sequence: An analogue for redox-controlling processes in the geosphere around deep geological repositories for radioactive waste

Yoshida, Hidekazu; Metcalfe, Richard; Yamamoto, Koshi; Murakami, Yuki; Hoshii, Daiki; Kanekiyo, Atsuko; Naganuma, Takeshi; Hayashi, Toru

doi:10.1016/j.apgeochem.2008.03.015

Cited by 14 publications

(4 citation statements)

References 49 publications

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“…Especially in deep geological repositories, Fe-bearing clay minerals play an important role in controlling and immobilizing the radionuclides in radioactive waste by reducing them to a lower and less soluble valence state. A thorough comprehension of these redox processes can significantly contribute to the safety assessment. , Such a complete picture of the nontronite structure, reduction, and Fe redox state identification builds up a strong basis for studies on Fe-bearing clay minerals and serves as a bench mark test for Fe redox state measurements in other clays.…”

Section: Discussionmentioning

confidence: 99%

“…A thorough comprehension of these redox processes can significantly contribute to the safety assessment. 78 , 84 Such a complete picture of the nontronite structure, reduction, and Fe redox state identification builds up a strong basis for studies on Fe-bearing clay minerals and serves as a bench mark test for Fe redox state measurements in other clays.…”

Section: Discussionmentioning

confidence: 99%

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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: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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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“…For these reasons, a number of scientific investigations at different locations worldwide have been conducted to examine the subsurface microbiota and the biogeochemical processes they catalyze at the specific locations including the Äspö Hard Rock Laboratory in Sweden (Pederson, 1997), Olkiluoto, Finland ; Yucca mountain, Nevada Horn et al, 2004), and the Waste Isolation Pilot Plant in New Mexico (Vreeland et al, 1998). Microbial processes that can impact the fate and transport of waste components include oxidation-reduction reactions, complexation with organic ligands and biopolymers (i.e., EPS), corrosion/weathering of waste forms and storage vessels, and transport properties of surrounding sediments/rock (Pedersen, 1996;Haveman and Pedersen, 2002;Wilkins et al, 2007;Yoshida et al, 2008;Perdrial et al, 2009;Anderson et al, 2011;Holyoake et al, 2011).…”

Section: Waste Repositoriesmentioning

confidence: 99%

Earth as a Microbial Habitat

Ehrlich¹,

Newman²,

Kappler³

2015

Ehrlich's Geomicrobiology

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“…Long-lived radionuclides from spent nuclear fuels require isolation for up to 100 000 years and, thus, are of great concern. In several countries (e.g., Sweden, Finland, and Japan), such radioactive waste is intended to be stored permanently in metal canisters embedded in crystalline bedrock at depths of 400–500 m. , The presence of dissolved O 2 will enhance canister corrosion and increase the risk of canister failure. , Oxidizing conditions will also enhance the solubility/mobility of redox-sensitive radionuclides (e.g., Pu, Np, Tc, and U) ,− and, thus, increase the risk of radioactive exposure to the surface environment. Thus, the safety of the repository relies on sustained reducing conditions throughout the repository lifetime.…”

Section: Introductionmentioning

confidence: 99%

A Combined X-ray Absorption and Mössbauer Spectroscopy Study on Fe Valence and Secondary Mineralogy in Granitoid Fracture Networks: Implications for Geological Disposal of Spent Nuclear Fuels

Drake

Dideriksen

et al. 2020

Environ. Sci. Technol.

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Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.

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Redox front formation in an uplifting sedimentary rock sequence: An analogue for redox-controlling processes in the geosphere around deep geological repositories for radioactive waste

Cited by 14 publications

References 49 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

Earth as a Microbial Habitat

A Combined X-ray Absorption and Mössbauer Spectroscopy Study on Fe Valence and Secondary Mineralogy in Granitoid Fracture Networks: Implications for Geological Disposal of Spent Nuclear Fuels

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