Interaction of corroding iron with bentonite in the ABM1 experiment at Äspö, Sweden: A microscopic approach

Wersin, Paul; Jenni, Andreas; Mäder, Urs (2015). Interaction of corroding iron with bentonite in the ABM1 experiment at Äspö, Sweden: A microscopic approach. Clays and clay minerals, 63(1), pp. 51-68. Clay Minerals Society 10.1346/ccmn.2015.0630105

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Bentonite and iron metals are common materials proposed for use in deep-seated geological repositories for radioactive waste. The inevitable corrosion of iron leads to interaction processes with the clay which may affect the sealing properties of the bentonite backfill. The objective of the present study was to improve our understanding of this process by studying the interface between iron and compacted bentonite in a geological repository-type setting. Samples of MX-80 bentonite samples which had been exposed to an iron source and elevated temperatures (up to 115ºC) for 2.5 y in an in situ experiment (termed ABM1) at the Äspö Hard Rock Laboratory, Sweden, were investigated by microscopic means, including scanning electron microscopy, μ-Raman spectroscopy, spatially resolved X-ray diffraction, and X-ray fluorescence. The corrosion process led to the formation of a ~100 mm thick corrosion layer containing siderite, magnetite, some goethite, and lepidocrocite mixed with the montmorillonitic clay. Most of the corroded Fe occurred within a 10 mm-thick clay layer adjacent to the corrosion layer. An average corrosion depth of the steel of 22–35 μm and an average Fe2+ diffusivity of 1–26×10–13 m2/s were estimated based on the properties of the Fe-enriched clay layer. In that layer, the corrosion-derived Fe occurred predominantly in the clay matrix. The nature of this Fe could not be identified. No indications of clay transformation or newly formed clay phases were found. A slight enrichment of Mg close to the Fe–clay contact was observed. The formation of anhydrite and gypsum, and the dissolution of some SiO<inf>2</inf> resulting from the temperature gradient in the in situ test, were also identified. © 2014, Clay Minerals Society. All right reserved.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Rock-Water Interaction

UniBE Contributor:

Wersin, Paul; Jenni, Andreas and Mäder, Urs

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0009-8604

Publisher:

Clay Minerals Society

Language:

English

Submitter:

Andreas Jenni

Date Deposited:

19 Oct 2015 11:46

Last Modified:

25 Jul 2016 14:48

Publisher DOI:

10.1346/ccmn.2015.0630105

Uncontrolled Keywords:

Bentonite, In situ experiment, Interface, Iron

URI:

https://boris.unibe.ch/id/eprint/72223

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