An isotope exchange investigation was made of diffusion in type-A synthetic zeolite possessing a structure comprising SiO4 and AlO4 tetrahedra. The exchange processes could be explained by assuming that 2 different processes with differing diffusion rates were occurring at the same time (table 8), and could be described by:

slow:     D(cm2/s) = 3 x 10-7exp[-6.5(kcal/mol)/RT]

fast:     D(cm2/s) = 6 x 10-5exp[-6.2(kcal/mol)/RT]

This was because the exchangeable ions in the structure had structurally unequal positions. The Rb isotope exchange proceeded so quickly that no accurate diffusion data could be derived. The exchange processes were similar to those found for Cs.

Isotope Exchange Investigations in Silicate Ion Exchangers. Kinetics of the Self-Diffusion of Alkali Metal Ions in Type-A Synthetic Zeolite. E.Hoinkis, H.W.Levi: Zeitschrift für Naturforschung, 1967, 22a[2], 226-32