The self-diffusion of various cations in hydrated natural mordenite was studied. From the variation of the self-diffusion coefficient with temperature (table 26), the energy of activation and the pre-exponential factor for the self-diffusion process were calculated from the Arrhenius equations:

Ba2+:     D(cm2/s) = 9.72 x 10-9exp[-10.14(kcal/mol)/RT]

Ca2+:     D(cm2/s) = 3.65 x 10-10exp[-10.45(kcal/mol)/RT]

Cs+:     D(cm2/s) = 9.72 x 10-12exp[-4.31(kcal/mol)/RT]

K+:     D(cm2/s) = 2.11 x 10-8exp[-7.14(kcal/mol)/RT]

Na+:     D(cm2/s) = 4.89 x 10-7exp[-8.74(kcal/mol)/RT]

Rb+:     D(cm2/s) = 8.51 x 101exp[-20.26(kcal/mol)/RT]

Sr2+:     D(cm2/s) = 3.86 x 10-5exp[-15.97(kcal/mol)/RT]

The values were found to exhibit peculiarities which were not so evident in studies of analcite and chabazite; zeolites having simpler channel structures. Only limited exchange of the divalent ions, Ca2+, Sr2+ and Ba2+, with the sodium form of the exchanger could be achieved. These divalent-ion self-diffusion studies exhibited unusual features and the interpretation of the results was complicated by the unknown effect of the sodium ions present in the lattice. These studies showed, however, that much insight into the motion of ions in these zeolite channels could be obtained from kinetic measurements.

Self-Diffusion of Various Cations in Natural Mordenite. L.V.C.Rees, A.Rao: Transactions of the Faraday Society, 1966, 62, 2103-10