Approaches to surface complexation modeling of Ni(II) on Callovo-Oxfordian clayrock

International audienceCallovo-Oxfordian formation (COX) is as potential host formation for emplacement of long-term nuclear waste repositories in France. The objective of this work is to assess whether a simplified ``bottom-up'' approach may explain the retention of Ni(II) by the COX considering two levels of `upscaling': (i) from clay surfaces to rock clay fraction and (ii) from clay fraction to whole rock samples. To this end, Ni(II) adsorption was investigated by batch equilibrium, XPS, and EXAFS techniques on a representative sample extracted at the location where the storage is supposed to be built (clay content of about 50%) and on the corresponding carbonate-free <2 mu m fractions. The results showed that a simplified ``bottom-up'' approach based on published models available for illite and montmorillonite cannot explain Ni(II) adsorption on the