Procedia Earth and Planetary Science
The WRI-15 – 15th Water-Rock Interaction International Symposium was held in Évora in Portugal, a UNESCO World Heritage City, from 16 to 21 October 2016. Chaired by José Manuel Marques from CERENA / IST, under the auspices of the Water-Rock Interaction Working Group (WRI-WG) of the International Association of Geochemistry (IAGC). The Symposium covered the most important top topics in the field of Water-rock Interaction, including 8 Keynotes and a Special Session dedicated to the late Mike Edmonds. 319 Delegates from 33 countries were registered for the Symposium. The volume summarizes the extended abstracts of the invited, oral, and poster presentations at the Symposium.
The Callovo-Oxfordian clay formation (COx) is the potential host rock for long term nuclear waste repository in France. The clayey component of COx consists mostly of illite, smectite and interstratified illite/smectite (I/S) clay minerals. We performed a series of molecular dynamics (MD) computer simulations in order to quantify the molecular scale mechanisms responsible for the adsorption and transport of ions at the hydrated surfaces of illite, smectite, and I/S clays. New structural models of illite, smectite, and I/S allowed us to identify several structurally different adsorption sites at the basal surfaces of all three clay substrates. Adsorption free energy profiles above each individual adsorption site on each clay surface for a wide range of metal cations were then calculated and the metal sorption properties for the three clay surfaces are compared in terms of the preferable sorption sites and their surface distributions, most stable adsorption distances, and free energies of adsorption. The resulting equilibrium constants for surface adsorption and ion exchange were calculated and found in general agreement with available literature data. The observed discrepancies between the exchange energies obtained in the current MD simulations and the values obtained through the interpretation of recent X-ray reflectivity measurements can be attributed to the differences in the description of the exchange reaction equilibria between the experimental conditions and the simplified conditions of our simulations.