Diffusivity measurement of heavy ions in Wyoming montmorillonite gels by X-ray computed tomography

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doi: 10.1016/S0169-7722(02)00138-9
Authors:Nakashima, Yoshito
Author Affiliations:Primary:
National Institute of Advanced Industrial Science and Technology, Exploration Geophysics Research Group, Tsukuba, Japan
Volume Title:8th international conference on Chemistry and migration behaviour of actinides and fission products in the geosphere; Migration '01
Volume Authors:Kim, Jae-Il, editor; Geckeis, Horst
Source:Journal of Contaminant Hydrology, 61(1-4), p.147-156; 8th international conference on Chemistry and migration behaviour of actinides and fission products in the geosphere; Migration '01, Bregenz, Austria, Sept. 16-21, 2001, edited by Jae-Il Kim and Horst Geckeis. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0169-7722
Publication Date:2003
Note:In English. 15 refs.; illus., incl. 1 table
Summary:Medical X-ray computed tomography (CT) was applied to the measurement of the diffusion coefficients of heavy ions in an artificial barrier material for the disposal of nuclear wastes. Cs+, Sr2+, I-, and Br- are the heavy ions measured and the barrier used is the water-rich gel of Wyoming montmorillonite (86.5-100 wt.% H2O). X-ray CT yields an inevitable artifact (beam-hardening) in the obtained images. Before the diffusion experiments, the polychromatic primary X-ray spectrum of the CT scanner was measured by a CdZnTe detector, and the effects of the artifact were examined for an aqueous CsCl solution sample. The results show that the beam-hardening artifact derived from the polychromatic photon energy distribution can be suppressed by applying a special image reconstruction method assuming the chemical composition of samples. The transient one-dimensional diffusion of heavy ions in a plastic container filled with the gel was imaged nondestructively by the X-ray CT scanner with an in-plane resolution of 0.31 mm and slice thickness of 2 mm. The results show that diffusivities decrease with increasing clay weight fraction. The degree of the diffusivity decrease was high for cations (Cs+ and Sr2+) and low for anions (I- and Br-). The quantitative decomposition of the contribution of the geometrical tortuosity and of the sorption to the diffusivity was performed by subtracting the diffusivity of nonsorbing I- from the measured diffusivities. The results show that the contribution of the sorption is large for Cs+, Sr2+ and small for Br-. Because X-ray CT allows nondestructive and quick measurements of diffusivities, the technique would be useful particularly for measuring the diffusive migration of harmful radioactive elements. Abstract Copyright (2003) Elsevier, B.V.
Subjects:Alkali metals; Alkaline earth metals; Bromine; Cations; Cesium; Chemical properties; Clastic sediments; Clay; Clay minerals; Computed tomography; Controls; Diffusivity; Disposal barriers; Experimental studies; Halogens; Iodine; Ions; Measurement; Metals; Migration of elements; Mobility; Montmorillonite; Pollution; Radioactive waste; Sediments; Sheet silicates; Silicates; Soils; Sorption; Spectra; Strontium; Tomography; Tortuosity; Waste disposal; X-ray spectra
Record ID:2003043701
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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