A new view on iron-claystone interactions under hydrothermal conditions (90 °C) by monitoring in situ pH evolution and H2 generation

Many countries are considering the geological disposal of high-level radioactive waste combining natural clayey and engineered barriers (e.g. steel canister, bentonite, clay host rock, concrete). This configuration can lead to metallic iron-claystone interactions. Although a lot of experimental data on iron/clay interactions already exists, none of it allows the understanding and quantifying of the close interactions between the mineralogical transformations and the iron corrosion process. To fill this gap, a parametric kinetic investigation of iron/claystone interactions at 90 degrees C in a water saturated-anoxic medium was carried out. A new approach is adopted to monitor a series of original experiments with various Fe-0/claystone mass ratios. The continuous in situ monitoring of H-2 production and of pH time-evolution allows to precisely follow the reaction rate and the chemical changes induced by the mineralogical transformations. In addition, gas composition and solid run products were characterized. We highlight that the Callovo-Oxfordian claystone of the Paris Basin (France) investigated here, in contact with metallic iron, drives the iron corrosion process, by controlling some medium parameters (like pH) and by acting as a Fe-consumer incorporating the released iron into neoformed Fe-rich clays minerals.