In the framework of an underground radioactive waste disposal, 129I constitutes for the argillaceous media one of the most penalizing elements owing to its very long life and its very low affinity. The objective of this work is to characterize the iodide transfer through the Tournemire argillite (Aveyron, France), in order to study thoroughly the iodide diffusive behaviour through an argillaceous matrix. An experimental methodology, which was based on a multi experimental method approach (batch, radial diffusion and through diffusion experiments), was applied for three different tracers: iodide, bromide, HTO. In the first part of this work, we show that the comparison between the HTO diffusion parameters and the anionic species highlights the existence of an anionic exclusion phenomenon which restricts the access of the anionic species to an accessible porosity inferior to the total rock porosity. In the second part of this work, we demonstrate that our retention and diffusion experiments indicate the existence of a significant affinity between 125I and the Tournemire argillite. The 125I retention appears to be irreversible, or with a kinetically very slow desorption within the duration of our experiments. Moreover, this retention intensity seems to be dependent on different experimental parameters such as the initial concentration of iodide or the ionic strength of the synthetic pore-water solution.