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Colloid diffusion in compacted bentonite; microstructural constraints

Michael Holmboe, Susanna Wold and Mats Jonsson
Colloid diffusion in compacted bentonite; microstructural constraints
Clays and Clay Minerals (August 2010) 58 (4): 532-541

Abstract

In Sweden and in many other countries, a bentonite barrier will be used in the repository for spent nuclear fuel. In the event of canister failure, colloidal diffusion is a potential, but scarcely studied mechanism of radionuclide migration through the bentonite barrier. Column and in situ experiments are vital in understanding colloid diffusion and in providing information about the microstructure of compacted bentonite and identifying cut-off limits for colloid filtration. This study examined diffusion of negatively charged 2-, 5-, and 15-nm gold colloids in 4-month diffusion experiments using MX-80 Wyoming bentonite compacted to dry densities of 0.6-2.0 g/cm (super 3) . Breakthrough of gold colloids was not observed in any of the three diffusion experiments. In a gold-concentration profile analysis, colloid diffusion was only observed for the smallest gold colloids at the lowest dry density used (estimated apparent diffusivity D (sub a) nearly equal 5X10 (super -13) m (super 2) /s). The results from a microstructure investigation using low-angle X-ray diffraction suggest that at the lowest dry density used, interlayer transport of the smallest colloids cannot be ruled out as a potential diffusion pathway, in addition to the expected interparticle transport. In all other cases, with either greater dry densities or larger gold colloids, compacted bentonite will effectively prevent diffusion of negatively charged colloids due to filtration.


ISSN: 0009-8604
EISSN: 1552-8367
Coden: CLCMAB
Serial Title: Clays and Clay Minerals
Serial Volume: 58
Serial Issue: 4
Title: Colloid diffusion in compacted bentonite; microstructural constraints
Affiliation: Royal Institute of Technology, KTH School of Chemical Science and Engineering Nuclear Chemistry, Stockholm, Sweden
Pages: 532-541
Published: 201008
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 30
Accession Number: 2010-095233
Categories: Environmental geologySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, Copyright, Clay Minerals Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201050
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