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Abstract
In this work, the chemical structural characterization of the erionite-type zeolite from Agua Prieta, Sonora, México, was performed on both pristine and Na, Ca, and Mg exchanged samples in order to identify the various modifications due to cation exchange. The samples investigated were those that showed the best behaviour of CO2 and CH4 adsorption at zero coverage levels and the higher values of surface area reported in our previous studies. According to the crystal-chemical formula (Na3.44K1.96Mg0.63Ca0.62)[Al8.21Si27.79O71.85]·29.63H2O, the pristine sample has been classified as erionite-Na. Morphological FE-SEM investigation performed on both pristine (ERIN) and Na-exchanged samples (ERINa3) showed a similar range of fiber diameters (27–37 nm). The chemical analyses of the ion-exchanged samples evidenced the upload of Ca and Mg following ion exchange with Na. Rietveld analysis results allowed the identification of the chemical structural modification caused by the ion exchange process, occurring mainly at the Ca1 site.
Highlights
There are more than 240 zeolite frameworks reported, which are subdivided into 232 synthetic zeolites and 67 mineral species of natural zeolites [1,2]
High Resolution Scanning Electron Microscopy (HR-SEM) images of the pristine and Na-exchanged erionite zeolites are shown in Figure 2, in which a morphology of compacted elongated prisms is observed
The morphology and chemical composition are different from that reported for the zeolitic material from Tierra Blanca de Abajo, Mexico [8], which is characterized by isolated fibers with diameters ranging from 200 to 500 nm and clinoptilolite as an accessory phase
Summary
There are more than 240 zeolite frameworks reported, which are subdivided into 232 synthetic zeolites and 67 mineral species of natural zeolites [1,2]. Natural zeolites have a mainly volcanic origin. They can occur both in crystallized forms found in igneous and metamorphic rocks, as well as in grains of smaller diameters agglomerated in sedimentary rocks [3,4]. Various zeolite species may form by hydrothermal activity associated with different types of igneous rocks. This type of deposit mainly includes alteration in active geothermal fields and alteration associated with ore deposition. Regardless of the formation mechanism, the zeolite deposits are characterized as “sedimentary deposits”
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