Sorption kinetics of uranium-238 and neptunium-237 on a glacial sediment

Studies of uptake of radionuclides by natural materials have shown that sor ption may occur via fast equilibrium exchange and/or slow kinetic processes , which can be described using a series of box models. This paper describes the use of such models to evaluate the solid-solution partitioning of U-23 8 and Np-237 On a clay rich sediment. Experimental data are obtained using the batch sorption technique, which are then analysed using 1, 2, and 3 box kinetic models. Uptake of U-238 in initially rapid, with approximately 90% sorbed within the first 30 minutes. Sorption continues, but at a slower ra te. Uptake of Np-237 is initially slower than U, with approximately 30% sor bed within the first 30 minutes. Sorption again continues, at a slower rate . Analysis of the experimental data indicates that sorption can be describe d using 2 and 3 box kinetic models. The results demonstrate that sorption o f uranium and neptunium on clay rich sediments occurs via equilibrium and k inetically controlled pathways, with neptunium being controlled by kinetics to a greater extent than uranium. The 2 or 3 box model can describe sorpti on of neptunium, uranium requires the 3 box model.