Abstract
Four naturally occurring zeolites were examined to verify their assignments as chabazites AZLB-Ca and AZLB-Na (Bowie, Arizona) and clinoptilolites NM-Ca (Winston, New Mexico) and NV-Na (Ash Meadows, Nevada). Based on powder X-ray diffraction, NM-Ca was discovered to be mostly quartz with some clinoptilolite residues. Treatment with concentrated HCl (12.1 M) acid resulted in AZLB-Ca and AZLB-Na, the chabazite-like species, becoming amorphous, as confirmed by powder X-ray diffraction. In contrast, NM-Ca and NV-Na, which are clinoptilolite-like species, withstood boiling in concentrated HCl acid. This treatment removes calcium, magnesium, sodium, potassium, aluminum, and iron atoms or ions from the framework while leaving the silicon framework intact as confirmed via X-ray fluorescence and diffraction. SEM images on calcined and HCl treated NV-Na were obtained. BET surface area analysis confirmed an increase in surface area for the two zeolites after treatment, NM-Ca 20.0(1) to 111(4) m2/g and NV-Na 19.0(4) to 158(7) m2/g. 29Si and 27Al MAS NMR were performed on the natural and treated NV-Na zeolite, and the data for the natural NV-Na zeolite suggested a Si:Al ratio of 4.33 similar to that determined by X-ray fluorescence of 4.55. Removal of lead ions from solution decreased from the native NM-Ca, 0.27(14), NV-Na, 1.50(17) meq/g compared to the modified zeolites, 30 min HCl treated NM-Ca 0.06(9) and NV-Na, 0.41(23) meq/g, and also decreased upon K+ ion pretreatment in the HCl modified zeolites.
Highlights
The spectra obtained for AZLB-Ca, Figure 1, and AZLB-Na, Figure 2, suggests the presence of chabazite if one compares the patterns to that obtained from simulations [45]
No phases indicative of clinoptilolite, heulandite, or alpha quartz were observed in either sample AZLB-Ca or AZLB-Na, Figure 1 and Figure 2, respectively
The assignment of four natural zeolites, labeled AZLB-Ca, AZLB-Na, NV-Na, and NM-Ca, as containing chabazite and clinoptilolite forms were examined by X-ray powder diffraction
Summary
Published: 17 July 2021Natural zeolites, which are composed of hydrated aluminosilicates containing groupI and II metals [1], are an abundant resource [2], with desirable chemical properties for many different applications, such as in construction [3], slow release of fertilizer [4,5,6,7,8,9,10], cosmetics [11], reduction of lactate or ammonia in mammalian blood [12], removal of Fe and Mn from water [13], catalysis and ion exchange [14], and in environmental protection [15]. Zeolites have a crystalline structure with small voids, commonly called pores, that act as a site for the zeolite to capture or stabilize different cations or molecules. These compounds have been utilized to remove salinity/sodicity [16], copper [17], Cr6+ [18], Mn2+ [19], heavy metals [20], ammonia [21], phosphorus [22], purify urine [23], zinc [24]. Zeolites contain cations to stabilize the negative charge in their structure, with Na+ , K+ , Ca2+ , and Mg2+ being the four most common with others possible [26]. During the ion exchange process, zeolites adsorb toxic metal ions dissolved in solutions into their pores while releasing the other cations present in the structure into the Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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