Sorption of radionuclides by Tertiary clays

The sorption capacity of different clay types for some metals (Co, Cs, Sr and Zn), occuring as common radionuclides in radioactive waste deposits, had been analysed by a static (batch technique) and a dynamic method (percolation tests, in which the driving force is a hydraulic gradient). Sorption capacity generally increased with an increasing pH of solution. A decrease of sorption capacity had been observed in the order Zn > Cs > Co > Sr for the batch and Cs > Zn > Sr > Co for the percolation tests. Clay marls showed a distinctly higher sorption respectively retention capacity as pure clays. Sorption capacity depends on solution parameters like type and concentration of radionuclide, pH, salt concentration, etc., and on rock parameters like mineral content (e.g. swelling clay minerals and carbonates), organic material, rock pH, microfabric, etc. A third parameter of great influence is the contact time between clay and solution. The adsorption isotherms reflect two different adsorption mechanisms : a very rapid adsorption (a few minutes) on the external surfaces of clay minerals and a slow adsorption process (weeks and longer), due to the diffusion of metal ions into the interlayer space of clay minerals.Wagner Jean-Frank, Czurda Kurt.A. Sorption of radionuclides by Tertiary clays. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol III : Geochemistry of clays. Nuclear waste disposal. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 149-158. (Sciences Géologiques. Mémoire, 87