HYDROTHERMAL DAMAGE OF ION-EXCHANGED A-TYPE ZEOLITE CATION-DIRECTED MECHANISMS OF PHASE-TRANSFORMATION

Zeolite A with approximately 60% of Na exchange for the cations Li, K, Mg, Ca, Sr, Cd, Zn, Co, Ni, and Mn has been subjected to hydrothermal treatments at various temperatures. The extent of hydrothermal damage has been assessed by use of the molybdate method and by water-sorption capacity. X-ray methods have been used to characterize the final products. Consideration of the results suggests several reasons for the observed stabilities, and these are discussed in relationship to the solubilities and formation energies of the appropriate metal hydroxide as well as to the creation of new phases. In some cases, identification of crystalline products may be possible. The relevance of the results to gas drying and natural gas desulfurization on an industrial scale is commented on.