Effect of high ionic strengths on U(VI) retention in montmorillonite

Argillaceous rock and clay minerals have properties that make them very valuable for nuclear waste storage. They are practically insoluble and have high sorption capacities. North German clay deposits feature pore waters of particularly high ionic strengths. In the depths that are relevant for nuclear waste repositories, the ionic strength of the pore water ranges from 1.8 mol/l to 3.3 mol/l. To be able to make an informed decision about the long term safety of nuclear waste disposal, the effect of high ionic strengths on radionuclide retention needs to be taken into account.
This work focuses on the uranium retention on montmorillonite in sodium and calcium chloride solutions of high ionic strengths. Montmorillonite serves as a model clay. It is the main component of some North German clay formations that conform to the criteria for deep-level nuclear waste disposals. Furthermore, it is a component of the backfill material that will be used in nuclear waste repositories. Sodium and calcium chloride are the main constituents of the pore waters found in North German argillaceous rock. The sorption experiments presented here were conducted in presence and absence of carbon dioxide.