Diffusion of organic anions in clay-rich mediaeffect of porosity exclusion on retardation

International audience; The transport of emerging organic contaminants through the geosphere is often an environmental issue. The sorption of organic compounds slows their transport in soils and porous rocks and retardation is often assessed by extrapolation of batch experiments. However, transport experiments are preferable to strengthen migration data and modelling. In this context, we evaluated the adsorption of various organic acids by means of through-diffusion experiments in a sedimentary clay-rich rock (Callovo-Oxfordian, East of Paris Basin, France). A low diffusivity of organic anions was quantified with effective diffusion coefficients, De, ranged between 0.5 and 7 10$^{−12}$ m$^2$ s$^{−1}$. These values indicated an organic anion exclusion. As for chloride, the porosity accessible to organic anions was lower than that of water: $\varepsilon _a$(organic anions)