Electrokinetic control of the growth of gypsum aggregates in compacted montmorillonite

Mineral precipitation and its impact on the barrier functions of clayey materials have attracted attention in the geological disposal of radioactive wastes. In this study, the growth of gypsum aggregates in compacted montmorillonite was investigated using the electrokinetic method. The results demonstrated that the morphology of aggregates can be partially controlled by adjusting the initial concentration of Ca in Na/Ca mixed montmorillonite. In particular, a lower initial Ca concentration maintained for long periods of time engendered the growth of gypsum as a layer of large aggregates up to 700 mu m. The layer of gypsum aggregates was made for a short duration (1 day) without excess salt remaining around the layer. The short duration and the absence of excess salt represent the main advantage of the electrokinetic method compared to a counter diffusion method to form artificial precipitates in clayey materials. Techniques to enhance and control aggregates are useful to prepare altered bentonite, which can be used to evaluate the impact of precipitates and their morphologies on the diffusivity and permeability of compacted bentonite.