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An indigenous iron-reducing microbial community from MX80 bentonite - A study in the framework of nuclear waste disposal

Lookup NU author(s): Katie Gilmour, Dr Colin Davie, Professor Neil GrayORCiD

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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).


Abstract

Highly compacted MX80 bentonite has been selected as the engineered buffer and backfill material in severalproposed concepts for long-term deep geological storage of nuclear waste. Iron-reducing bacteria reduce Fe (III)to Fe (II) and some are adapted to high temperatures and desiccated environments, in keeping with periods ofless habitable conditions within the repository. In one potential UK repository concept, iron from carbon steelcanisters may contribute to an iron-rich environment at the clay-canister interface. This could lead to changes inthe mineralogy and iron-content of MX80 bentonite due to variation of the redox state and solubility, which inturn could alter the geomechanical properties of the clay. To investigate the potential role of iron-reducingbacteria in this process enrichments were carried out with both commercially available MX80 bentonite powderand compacted MX80 bentonite to identify the presence of an indigenous iron-interacting community in theclay. Throughout these enrichments Fe (II) soluble, Fe (II) total, and pH were measured, and the enrichmentswere subjected to 16S rRNA community analysis. Concentrations of Fe (II) total peaked at day 28 in all enrichments;however, the concentration was overall higher when accompanied by bacterial growth. Fe (II) solubleremained low throughout. 16S rRNA gene sequencing revealed the presence of several putative iron-interactingbacteria, as well as thermotolerant and spore-forming species. The indigenous community was largely comprisedof firmicutes, including iron-reducers and spore-forming bacteria such as Desulfosporosinus. Therefore, MX80bentonite inherently carries a viable microbial community which could potentially interact with structural ironpresent within MX80 bentonite or other mineral components, such as a carbon steel waste canister. Variousresearch has shown that microbial activity is unlikely within the bulk bentonite provided high compaction ismaintained. The importance of this high compaction is highlighted by the finding here of a viable, robust andfunctionally diverse community within the clay and activity may be possible anyway at edge sites and interfaceswhere, locally, swelling pressures might not fully develop.


Publication metadata

Author(s): Gilmour KA, Davie CT, Gray N

Publication type: Article

Publication status: Published

Journal: Applied Clay Science

Year: 2021

Volume: 205

Print publication date: 01/05/2021

Online publication date: 06/03/2021

Acceptance date: 22/02/2021

Date deposited: 16/05/2021

ISSN (print): 0169-1317

ISSN (electronic): 1872-9053

Publisher: Elsevier BV

URL: https://doi.org/10.1016/j.clay.2021.106039

DOI: 10.1016/j.clay.2021.106039


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