Geoscientific applications of particle detection and imaging techniques with special focus on the monitoring claymineral reactions

Abstract

The combined use of focused X-ray, electron, and ion beams offers a diverse range of analytical capabilities for characterizing nanoscale mineral reactions that occur in hydrous environments. Improved image and microanalytical techniques (e.g., electron diffraction and energy-dispersive X-ray spectroscopy), in combination with controlled sample environments, are currently leading to new advances in the understanding of fluid-mineral reactions in the Earth Sciences. One group of minerals playing a key role in the containment of radioactive waste and the underground storage of CO2 is the clay minerals: these small, expandable, and highly adsorbent hydrous phyllosilicates form important low-permeable geological barriers by which waste can be safely deposited. In this article we summarize some of the state-of-the-art particle and imaging techniques employed to predict the behavior of both engineered and natural clay mineral seals in proposed storage sites. Particular attention is given to two types of low-permeability geomaterials: engineered bentonite backfill and natural shale in the subsurface. These materials have contrasting swelling properties and degrees of chemical stability that require detailed analytical study for developing suitable disposal or storage solutions.