Monitoring the effect of hydrothermal treatments on the structure of a natural zeolite through a combined XRD, FTIR, XRF, SEM and N2-porosimetry analysis

A natural zeolite specimen, consisting mainly of heulandite type-II and mordenite, was succumbed to NH4+ and/or H+-exchange followed by one or two calcination steps and further acid leaching. In an attempt to examine the effect of each treatment on the starting material as well as on pre-modified (intermediate) samples, varied calcination temperatures, contact times and solutions concentrations were applied. On the grounds of the properties and expected behavior of pure substances, a combined XRD, FTIR, XRF, SEM and N2-porosimetry analysis enabled the monitoring and comprehension of the phenomena taking place during each treatment, despite the obscurity inherent in each individual analysis when dealing with impure materials. In general, the behavior of the typical counterbalancing ions Na+, K+, Mg2+ and Ca2+, the Fe3+ content, the extraction of Al3+ from the lattice and the removal of amorphous Al-substances were found to be crucial factors concerning the properties of the modified samples.