Characterization of sulphate sorption on Callovo-Oxfordian argillites by batch, column and through-diffusion experiments

Callovo-Oxfordian argillites are under investigation as a potential host rock for a high-level radioactive waste repository. The purpose of this study was to investigate sulphate sorption on two borehole samples (EST205 K119c and K100c), using three different and complementary laboratory techniques.Batch experiments revealed a fast, weak and reversible sorption of sulphate ions on Callovo-Oxfordian argillites. Quantification was difficult with this method due to uncertainties on low Kd values obtained.Column and through-diffusion experiments confirmed this retention and allowed a better quantification. A clear dependence of sulphate sorption on both mineralogical composition and sulphate content was shown. For the K119c argillite, the sulphate isotherm was fitted with a Langmuir isotherm. Kd values are ranging from 0.15 to 0.37 mL g−1, depending on total sulphate content.