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The Bentonite Barrier - Swelling Properties, Redox Chemistry and Mineral Evolution


  • Daniel Svensson

Summary, in English

Bentonite is planned for use as a buffer material in high-level radioactive waste repositories, where safety

assessment is performed for very long periods (100-1000 ka). This thesis focuses on the swelling of smectites in liquid

water, and analysis of bentonite from field experiments at Äspö Hard Rock Laboratory, Sweden. Four field experiments

were analyzed (Alternative Buffer Material experiment, ABM1, ABM2; Temperature Buffer Test, TBT; and Prototype)

with focus on Fe- redox chemistry and formation of trioctahedral smectite. The techniques used were mainly synchrotron

X-ray diffraction and X-ray absorption spectroscopy. In ABM1 and Prototype the Fe(II)/Fe-total ratio had increased. In

TBT no significant increase in Fe(II) was found; instead the corrosion products were dominated by Fe(III). Formation of

trioctahedral clays was found in the iron-bentonite experiments (ABM1, ABM2, TBT), but not in Prototype where the

heater instead was of copper. In swelling experiments, Ca-Wyoming montmorillonite was shown to expand and partly

form a four-water-layer hydrate at lower temperatures in water. This was studied in more detail, and the influence of

divalent interlayer cation, temperature, layer charge, salt and irradiation was investigated. Among the investigated

smectites, decreased temperature increased the crystalline swelling until ice was formed. Lower smectite layer charge

increased the crystalline swelling. Increasing the Gibbs hydration energy of the divalent interlayer cation increased the

crystalline swelling. Introduction of salt in the water partly dehydrated the montmorillonite at 20°C, but minimized the

dehydration of montmorillonite upon ice formation at low temperatures (-50, -100°C), especially with CaCl2. It was

found that in a gradient of ethylene glycol and water a 21 Å basal distance was formed in the montmorillonite, which was

higher than in the pure liquids.

Publishing year




Document type



Centre for Analysis and Synthesis


  • Chemical Sciences


  • montmorillonite
  • bentonite
  • smectite
  • freezing
  • thawing
  • hydration
  • intercalation
  • four-water-layer
  • ethylene glycol
  • X-ray diffraction
  • time-resolved
  • spatial-resolution
  • Fe
  • redox
  • iron
  • ABM
  • TBT
  • Äspö





  • ISBN: 978-91-7422-385-9

Defence date

9 March 2015

Defence time


Defence place

Lecture hall C, Kemicentrum, Lund University, Faculty of Engineering (LTH), Getingevägen 60, Lund


  • Jon Otto Fossum (Professor)