In the last 60?years, the study and characterization of zeolites has been an important factor for industrial progress, given their catalytic properties, their high adsorption or desiccant capabilities, permitting oil refining, industrial gasses treatments, industrial ovens, and industrial waste treatments. Another application is water remediation [1], consisting of the removal of cationic pollutants like ammonium. Although the use of the surfactant requires extensive study, its desorption has been identified as a potential problem due to limited information on its toxicity and effects on environmental microorganisms. In the same way, the synthesis of the pharmaceutical penicillin G produces wastewater with a concentration of this drug. Its elimination by biological treatment of the pharmaceutical tailwater is incomplete; but great results can be obtained via treatment with cerium-loaded natural zeolites [2].
The enhancement of concrete physical properties has been determined by using natural zeolites [3], due to interconnected reticule cavities or pores that can be used to adsorb molecules, like a molecular sieve, as well as ion exchange, as a heavy atom trap [4].
The study of minerals for water treatment, especially natural zeolites, has been performed due to the capacity of adsorption, ion exchange, or chemical reaction with different elements. In our studies, we propose an alternative synthesis method of natural zeolite-type material obtained through volcanic ash coming from Nevado del Ruiz volcano in Colombia [5] and compare it with natural zeolite natrolite type subgroup coming from Germany (Hammerunterwiesenthal city). The structure of both zeolites is based on the disorder of the silicon-aluminum in the framework, allowing the ion exchange of K+ cations, that present a similar tubular or fibrous morphology.
The volcanic ash, which is a combination of tiny fractured rocks, was subjected to hydrothermal processes coupled with annealing at around 673?K for several periods. Its characteristic behavior was directly observed as a natural zeolite with metastable properties with the environment [6]. Crystallite sizes are influenced by crystal-chemical changes, caused by dehydration, heat treatment, and pressure conditions during the characterization.
The natural zeolite-type material from volcanic ash is characterized by the presence of gismondine, hydrated calcium aluminosilicate, litosite, clinoplitolite-Na, and phillipsite-K, whists the natural zeolite from Germany have gonnardite and mesolite zeolite types. The gonnardite zeolite ((Na5.84Ca1.6) (Al9Si11O40) (H2O)9.87) presents a tetragonal structure, identified through XRD measurements where (Si, Al) occupancy disordered in tetrahedral position and H2O occupied polyhedral position [7]. In the case of mesolite ((Na4.96Ca4.96) (Al16Si24O80) (H2O)23.36), this zeolite presents an orthorhombic structure and the same position of (Si, Al) and H2O.
The micrograph in the image on the cover shows the zeolite morphological structure from volcanic solid rock, characterized by the self-organization of hexagonal columnar forms. This characteristic is typical of volcanic sediments subjected to high temperatures and long periods of relaxation time. This condition allows energy for a sedimentary rock formation that is part of the structure, giving rise to predominant formations such as those shown.
The morphological properties of the mesolite zeolite are characterized by a fibrous and white structure with radial groupings. Due to the presence of gonnardite zeolite, the structure is often made with fine individual fibrous or tubular crystals protruding. The gonnardite has this morphology due to the effects of basaltic lavas and a hydrothermal alteration in zones with high calcite and water presence. This environmental condition is very important for zeolite fabrication from volcanic ash. The volcanic ash from pyroclastic clouds has a high concentration of aluminosilicates, like labradorite precursors, that can be used to obtain zeolites. The morphological characterization of the natural zeolite-type from volcanic ash has agglomerates or granules (size around 5?μm) with tubular or flake-type structures in different zones [5].
Acknowledgements
This work was supported by Universidad Nacional de Colombia. The authors acknowledge the geo-scientist Tania Caterinne Martínez Cárdenas for the supply of samples from Germany.
Further reading
[1]P.J. Reeve, H.J. Fallowfield
J. Environ. Manage., 205 (2018), pp. 253-261
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[2]J. Zhang, et al. Chem. Eng. J., in press.
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[3]Y.T. Tran, et al.
Composites Part B, 165 (2019), pp. 354-364
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[4]T.P. Belova
Heliyon, 5 (2019)
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[5]Jorge A. Calderón, et al.
Solid State Phenom., 257 (2016), pp. 233-236
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[6]Heiddy P. Quiroz, et al.
Momento, 48E (2014), pp. 1-13
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[7]Yu.V. Seryotkin, S.N. Dementev, A.I. Ancharov
J. Struct. Chem., 57 (2016), pp. 1386-1391
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