Zeolites for nuclear waste treatment: Co, Ni and Zn uptake into synthetic faujasite X - Part II. Effect of the presence of large cations on the leaching of Co, Ni and Zn radioisotopes

Pellets of the synthetic zeolite X were loaded with the radioisotopes Co-60, Ni-63 and Zn-65. The pellets were then calcined. A secondary ion-exchange step introduced a large cation, barium, into the zeolites with a view to blocking the release of the radioisotopes under leaching conditions. Leaching was carried out over 84 days with synthetic sea and ground waters as well as deionised water. Leach tests were evaluated in terms of cumulative fraction of isotopes released and as diffusion coefficients derived from leaching profiles. Cobalt containing samples were cement encapsulated and further leach studies carried out. Some minor reduction in isotopes release was observed in the presence of barium but this was not consistent.