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Gel formation at the front of expanding calcium bentonites

Daniels, Katherine A. ORCID:, Harrington, Jon F., Milodowski, Antoni E., Kemp, Simon J., Mounteney, Ian and Sellin, Patrik 2021. Gel formation at the front of expanding calcium bentonites. Minerals 11 (2) , 215. 10.3390/min11020215

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The removal of potentially harmful radioactive waste from the anthroposphere will require disposal in geological repositories, the designs of which often favour the inclusion of a clay backfill or engineered barrier around the waste. Bentonite is often proposed as this engineered barrier and understanding its long-term performance and behaviour is vital in establishing the safety case for its usage. There are many different compositions of bentonite that exist and much research has focussed on the properties and behaviour of both sodium (Na) and calcium (Ca) bentonites. This study focusses on the results of a swelling test on Bulgarian Ca bentonite that showed an unusual gel formation at the expanding front, unobserved in previous tests of this type using the sodium bentonite MX80. The Bulgarian Ca bentonite was able to swell to completely fill an internal void space over the duration of the test, with a thin gel layer present on one end of the sample. The properties of the gel, along with the rest of the bulk sample, have been investigated using ESEM, EXDA and XRD analyses and the formation mechanism has been attributed to the migration of nanoparticulate smectite through a more silica-rich matrix of the bentonite substrate. The migration of smectite clay out of the bulk of the sample has important implications for bentonite erosion where this engineered barrier interacts with flowing groundwater in repository host rocks.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Publisher: MDPI
ISSN: 2075-163X
Date of First Compliant Deposit: 1 June 2023
Date of Acceptance: 8 February 2021
Last Modified: 03 Jun 2023 10:19

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