hide
Free keywords:
-
Abstract:
Ternary ion exchange experiments were performed on the zeolites Na-A, Na/K-X, and Na-Y using Mn2+/Ni2+, Mn2+/Co2+, and Ni2+/Co2+ mixtures as exchange solutions. The different zeolites show distinct preferences for specific transition metal cations, e.g. zeolite A and X prefer Mn2+ over Co2+ and/or Ni2+. The reason for that are the different hydration energies of the cations which have to be applied for the stripping of water molecules from the hydration shell of the cations and changes of the coordination of the cations by the different zeolite frameworks. After repeated ion exchanges, a significant over exchange is observed for all systems, which is especially pronounced at elevated temperatures. That effect is more distinctive for the low silica zeolites A and X but also observed for zeolite Y. The cation exchange conditions have a significant influence on the thermal stability of the zeolites A and X. However, due to the slightly higher pH values of the Mn2+ containing ternary ion exchange solutions, the stability of these zeolites are significant higher compared to those exchanged in ion exchange system containing only Co2+ and/or Ni2+.
