Benefits of applying X-ray computed tomography in bentonite based material research focussed on geological disposal of r
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CLAY AND MODIFIED CLAYS IN REMEDIATING ENVIRONMENTAL POLLUTANTS
Benefits of applying X-ray computed tomography in bentonite based material research focussed on geological disposal of radioactive waste Heini Maria Reijonen 1 & Jukka Kuva 1 & Pasi Heikkilä 1 Received: 12 November 2019 / Accepted: 19 February 2020 # The Author(s) 2020
Abstract Bentonite-based geomaterials are included in the designs of geological repository planning in most countries, especially in high-level radioactive waste disposal. Physical integrity of the bentonite sealant is key in assuring its hydraulic and retention properties, which affect the long-term performance of the repositories. Examination of the internal textures and structures of bentonite has been challenging until recently. Here, X-ray computed tomography (XCT) is applied to improve the textural and structural characterization of natural and man-made bentonite samples. Based on these initial analyses, clear benefits have been identified compared with conventional bentonite research methods. First, applying XCT prior to destructive analytical methods provides means to distinguish secondary features or in situ textures. It allows to eliminate false interpretations due to sample deformation and guides subsampling. Second, XCT images add the third dimension to analyses, allowing larger spatial coverage in less time. Overall, findings support the application of XCT for reducing uncertainties related to physical characterization of bentonite samples, both natural and industrial. They also show that XCT has potential to be developed to support quality assurance processes for bentonite sealant manufacturing. Keywords X-ray computed tomography (XCT) . Bentonite . Geological disposal . Radioactive waste . Natural analogue . Geomaterial
Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-020-08151-2) contains supplementary material, which is available to authorized users.
forms. Depending on the repository design, bentonite can be used as dried and ground, or further modified (e.g. via cation exchange). In addition, in some designs, mixtures of bentonite, sand and/or aggregates are considered. In order to assess longterm performance of these materials, geological formations of bentonite have been studied in the past (often referred to as natural analogues, NA, see e.g. Reijonen and Alexander 2015), but no detailed large-scale textural analyses have been produced to date. Here, the X-ray computed tomography (XCT) method is applied to bentonites, providing a new, structurally more profound way to interpret the results of physical and chemical analyses of samples. The study is a compilation of three phases: 1) initial assessment of the method supported by experimental data (Alexander et al. 2017), 2) applying the method in the initial phase for new NA investigations and 3) applying the method on engineered samples to enable comparison.
* Heini Maria Reijonen [email protected]
Background
Utilizing clay materials in the g
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