Mobility of zinc in the Callovo-Oxfordian clay-stone

The diffusion of zinc was studied in the Callovo-Oxfordian clay-stone, which is a potential host rock for the retrievable disposal of high-level radioactive wastes. Two in-diffusion laboratory experiments were performed with initial zinc concentrations of 4 10^-5 mol L^-1 and 8 10^-6 mol L^-1 (resp.) for 35 days. The zinc rock profile was acquired using an original technique, the μLIBS, with a high resolution (10 μm), calibrated with the abrasive peeling method. The experimental data, i.e. Zn concentration monitoring in the source reservoir and Zn rock profile, were successfully reproduced using a chemical-transport code. In that code, the sorption of Zn was described by a multi-site ion-exchange model, with only the effective diffusion coefficient value being adjusted (De = 8 10^-11 m² s^-1). This De value, 2 times higher than that of tritiated water, indicates that zinc, like most cations, is also subject to enhanced diffusion in clay rocks. (authors)