Imaging connected porosity of crystalline rock by contrast agent-aided X-ray microtomography and scanning electron microscopy

J. Kuva, J. Sammaljärvi (Corresponding Author), J. Parkkonen, M. Siitari-Kauppi, M. Lehtonen, T. Turpeinen, J. Timonen, M. Voutilainen

    Research output: Contribution to journalArticleScientificpeer-review

    5 Citations (Scopus)

    Abstract

    We set out to study connected porosity of crystalline rock using X‐ray microtomography and scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM‐EDS) with caesium chloride as a contrast agent. Caesium is an important radionuclide regarding the final deposition of nuclear waste and also forms dense phases that can be readily distinguished by X‐ray microtomography and SEM‐EDS. Six samples from two sites, Olkiluoto (Finland) and Grimsel (Switzerland), where transport properties of crystalline rock are being studied in situ, were investigated using X‐ray microtomography and SEM‐EDS. The samples were imaged with X‐ray microtomography, immersed in a saturated caesium chloride (CsCl) solution for 141, 249 and 365 days and imaged again with X‐ray microtomography. CsCl inside the samples was successfully detected with X‐ray microtomography and it had completely penetrated all six samples. SEM‐EDS elemental mapping was used to study the location of caesium in the samples in detail with quantitative mineral information. Precipitated CsCl was found in the connected pore space in Olkiluoto veined gneiss and in lesser amounts in Grimsel granodiorite. Only a very small amount of precipitated CsCl was observed in the Grimsel granodiorite samples. In Olkiluoto veined gneiss caesium was found in pinitised areas of cordierite grains. In the pinitised areas caesium was found in notable excess compared to chloride, possibly due to the combination of small pore size and negatively charged surfaces. In addition, elevated concentrations of caesium were found in kaolinite and sphalerite phases. The findings concerning the location of CsCl were congruent with X‐ray microtomography.
    Original languageEnglish
    Pages (from-to)98-109
    Number of pages12
    JournalJournal of Microscopy
    Volume270
    Issue number1
    Early online date2017
    DOIs
    Publication statusPublished - 2018
    MoE publication typeA1 Journal article-refereed

    Keywords

    • Connected porosity
    • crystalline rock
    • energy dispersive X-ray spectrometry
    • scanning electron microscopy
    • X-ray microtomography

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