An heterogeneous isotope exchange technique was used to study the diffusion of 133Ba and 85Sr in type-X zeolite. The diffusion process was found to be non-uniform. Some 80% of the exchangeable Ba ions and 65% of the Sr ions diffused with a high diffusion coefficient, and the remainder with a low one. The two coefficients differed by 4 to 5 orders of magnitude at room temperature (table 49). At 0 to 120C, the activation enthalpy for the slow process was about twice as high as that for the fast process.

Kinetics of the Self-Diffusion of Ba and Sr Ions in Synthetic Zeolite X. Isotope Exchange Studies of Silicate Ion Exchangers. H.Hoinkis, H.W.Levi: Zeitschrift für Naturforschung A, 1969, 24[11], 1784-90

Table 49

Tracer Diffusion Parameters for Type-X Zeolite