Mineralogy and physico-chemical properties of buffer and backfill

The division performs work relating to bentonite quality, the impact of groundwater chemistry, long-term stability, etc. The division conducts laboratory tests and evaluations as well as theory development and modelling.

Analyses and tests include:

  • Cation exchange capacity (CEC) of clays and soils
  • Determination of original exchangeable cations (EC) in bentonite
  • Aqueous leaching to determine anion, carbon, sulphur, etc contents
  • Rheology on clay gels and dispersions
  • Element analysis, interpretation of ICP-AES, ICP-MS data resulting in smectite structural formulae
  • Quantitative determination of the mineralogical composition of clays using Rietveld refinement of XRD diffractograms
  • Swelling pressure / hydraulic conductivity measurements and how these properties are influenced by e.g. salinity, cation exchange, temperature (below 0 to above 100 °C), etc

The above methods are often used together to provide an integrated understanding / analysis of the studied material, see e.g. the technical report SKB TR-06-30 for further details.

The experimental work has always been strongly supported by theory developed by us. Within a single theoretical framework, we can predict the effect on e.g., swelling pressure due to salinity and temperature changes. The same framework can also be used to predict diffusion through bentonite and has already impacted how experiments are performed. To further enhance the development of theory, we have also state-of the art molecular dynamics expertise, in-house and through collaboration.

Top view of eroding Na-montmorillonite in a 0.1 mm aperture fracture

A long-standing issue for the integrity of a future repository is the threat of glacial water intrusion at repository depth, which can lead to the buffer bentonite eroding due to the onset of colloidal sol formation at the rim of the expanded bentonite. In our laboratory we study and measure the erosion rates and their sensitivity to salinity and to the dominating cation as well as their time development. The experimental work is combined with theoretical analyses emphasising on the principles for describing the different phases of montmorillonite colloids and their transformations.

In 2022 the division will investigate the potential of using synchrotron radiation for studying montmorillonite at various degrees of expansion. This is within the framework of a Vinnova-financed collaboration with Dept. of Theoretical Chemistry at Lund university.


Magnus Hedström

Magnus Hedström

Ph.D. Quantum Chemistry

+46 70 434 55 99