The interaction of trace levels of cesium with montmorillonitic and illitic clays: Fid-Bau Portal

The interaction of trace levels of cesium with montmorillonitic and illitic clays

Oscarson, D.W / Watson, R.L / Miller, H.G

AbstractThe interaction of Cs⁺ with a montmorillonitic and an illitic clay suspended in solutions of synthetic groundwaters, sodium perchlorate, or sodium acetate was examined over the range of initial Cs⁺ concentrations of 10⁻⁸ to 10⁻⁵ mol/l and at 25° and 80°C. The clays are being considered as possible components of barrier materials in a nuclear fuel waste disposal vault in Canada. Both clays sorb more Cs⁺ at 25° than at 80°C, suggesting an exothermic reaction. Less Cs⁺ is sorbed at pH=5 than at $pH ⋍8.5$ . The lower the K⁺ concentration in the suspending media, the more Cs⁺ is sorbed by the clays. The illitic clay has a greater sorption capacity and affinity for Cs⁺ than does the montmorillonitic clay, even though the montmorillonite has a significantly greater cation exchange capacity and specific surface area. It is likely that a large fraction of Cs⁺ is selectively sorbed and fixed on specific sites in the edge-interlayer region of clays like illite. The montmorillonitic clay, which contains ∼10% illite, fixes some Cs⁺ but less than the illitic clay. The results indicate that, for the disposal of nuclear fuel waste containing ¹³⁵Cs, the illitic clay would be a more effective component of the barrier material than the montmorillonitic clay for slowing the migration of ¹³⁵Cs.