An advanced mineralogical study of the clay mineral fraction of the Boom Clay

Abstract

In Belgium, the Boom Clay is studied aso ne of the potential host rocks for the geological disposal of radioactive waste. The clay minerals within the Boom Clay contribute significantly to the retardation of the release of radionuclides from the potential repository to the geosphere and biosphere due to their sorption capacity. The major processes responsible for this behaviour are cation exchange in the interlayer of (mostly) swelling clays like smectites, and surface complexation on the broken edges of clay platelets (Baeyens and Bradbury, 1997; Bradbury and Baeyens, 1997; 2000). Due to these processes, clay minerals also dictate to a high extent the pore water chemistry of argillaceous rocks (Bradbury and Baeyens, 1998). Besides a high sorption capacity, clay minerals may equally possess substantial reduction-oxidation potential, depending on their nature and Fe content (Neumann et al., 2011). Several naturally-occurring mechanisms have already been identified which are able to alter the Fe(II)/Fe(III) content of clay minerals (Schaefer et al., 2011), thereby changing both their redox behaviour as well as their layer charge and as such their total adsorptive capacity (Gorski et al., 2013). Novel electrochemical methods were developed to probe the total electron-accepting and electron-donating capacity of clay minerals, based on kinetic probes (Neumann et al., 2008; Gorski et al., 2011). The detailed study of the clay mineral characteristics is therefore fundamental in our understanding of the Boom Clay composition and geochemical processes, and forms the base for further experimental work and modelling. The objectives of this PhD are to study the clay mineral characteristics of various Boom Clay samples, both qualitatively and quantitatively, and to couple this information to geochemical parameters and processes. This coupling would allow to gain a better insight into the retention properties of Boom Clay towards radionuclide dispersion starting from baseline mineralogical information.status: publishe