A comparative analysis of natural zeolites from various Cuban and Mexican deposits: structure, composition, thermal properties and hierarchical porosity

Cuban and Mexican zeolites are of particular interest from economic outlook because of their exceptional properties and abundance. Here, we present the results of the comparative study of the elemental, structural, morphological, thermal and textural properties of natural zeolites: clinoptilolite, mordenite and erionite from various deposits. Despite a complex phase and element compositions of the studied materials, some general features were detected. The observed dehydration steps are related to water desorption from porosity of different size ranges: mesopores, main and small zeolite voids. This dehydration pattern interferes with the exchangeable cation composition that also affects the general trends. Thermochemical properties of samples are influenced by the geographical location of the deposits. Depending on the origin of the sample, the dehydration enthalpy varies in quite a wide range, which is a function of both zeolite framework structure and exchangeable cation composition. The study of meso- and macropore systems reveals that all the samples exhibit multimodal pore size distribution and possess significant amounts of mesoporosity and even macroporosity. Among the studied samples, the mordenite from Palmarito de Cauto, the clinoptilolite from Etla and the erionite from Agua Prieta (Sonora) have a significant number of pores with average size of about 3 nm. All the samples, except erionite from Agua Prieta, show macroporosity with rather well-defined pore size between 0.3 and 2 μm. The porosity over mass does not change noticeably from one sample to other and varies from 0.32 to 0.65 cm3 g−1.