WP1: Diffusion measurements, surface-complexation and macro-scale diffusion modeling

Understanding the response of clay materials to geoelectrical methods requires information about the distribution of ions between surface and solution as well as their mobility within the different parts of the electric double layer. The clay material will be geochemically characterized and the surface chemistry will be determined. Based on this data a Surface Complexation Model will be created to calculate the electrostatic environment as well as surface and solution chemistry for clay mineral grains in nanoconfined environments, including electrostatic spillover effects between edges and basal surfaces as well as the interactions of overlapping EDLs from adjacent surfaces. Diffusion experiments will give insight into ion surface mobility and its impact on the diffusion coefficient. The data obtained from the diffusion experiments can later be used for diffusion modelling to obtain diffusion coefficients, effective porosities, and sorption coefficients. The models created in WP1 will be validated and improved using the experimental data obtained by the experimental parts of WP1 and the other work packages.

So far, a two-dimensional Charge Regulation Surface Complexation Model, called CRESCENDO, for general surface and solution chemistry has been created and validated for simple test cases (Manuscript in review). Further development is already underway, with the final goal to apply the model to clay surfaces and particle arrangements. Experimental geochemical characterization as well as diffusion experiments employing Na-exchanged Montmorillonite clay are foreseen and will serve as calibration data for the developed model.