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Minerals
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Vermiculite: Treatments, Applications, and Structural and Physico-Chemical Characteristics
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Vermiculite: Treatments, Applications, and Structural and Physico-Chemical Characteristics

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (10 December 2021) | Viewed by 9131

Special Issue Editor

Dr. Celia Marcos Pascual

E-Mail Website
Guest Editor
Department of Geology, University of Oviedo, 33003 Oviedo, Spain
Interests: vermiculites; environmental mineralogy; structural and physico-chemical characterization of minerals; characterization techniques (X-ray: diffraction and fluorescence; spectroscopies: Raman, Mössbauer, infrared; electron microscopies: high-resolution transmission and scanning); archeometry

Special Issue Information

Vermiculite, a phyllosilicate with appearance similar to micas at the macroscopic level, has a structure composed of two T-O-T layers joined by an inter-layer. The T-O-T layer is composed of an octahedral (O) sheet of Mg2+, located between two tetrahedral sheets (T) of Si4+. The inter-layer is formed by an octahedral sheet of Mg2+ bound to oxygens or OH- groups. In addition, it contains water. The isomorphic substitutions, especially in the tetrahedral sheets of Si4+ to Al3+, are very common. Due to the presence of water and OH- groups, vermiculite can undergo hydration–dehydration processes that depend on various factors, such as temperature, pressure, particle size, relative humidity, and chemical composition. The chemical formula of vermiculite is: X4(Y2-3)O10(OH)2M·nH2O, where X represents the tetrahedral positions (Si4+ and Al3+), Y the octahedral positions (Mg2+, Fe2+, Fe3+, Cr3+, Ti4+, etc.), and M represents the cations located in the inter-layer space (Mg2+, Ca2+, K+, Na+, etc.) to compensate the charges, as a consequence of the isomorphic substitutions.

In addition to this vermiculite, there are the so-called commercial vermiculites. These vermiculites consist of various interstratified layers of mica/vermiculite, vermiculite with different states of hydration, mixtures of mica and vermiculite, etc. The main characteristic of commercial vermiculites is their exfoliation and expansion capacity when the vermiculite is abruptly heated, and that occurs due to the loss of water molecules located between the silicate sheets.

Vermiculites can be modified by temperature, pressure, chemical treatments, and irradiation. Unmodified and modified vermiculites are characterized by their industrial and technological applications. These applications are a function of the material’s physical and chemical properties and the treatment it has undergone.

The relationship between structural changes of vermiculite and the chemical and physical treatments could contribute to predicting the environmental fate of toxic metals, and developing methods to remove these metals from contaminated waters or soils. In addition, that relationship could give light to ambiguities about their geological origin.

This Special Issue will focus on treatments and applications of vermiculites in a strict sense as well as commercial vermiculites; as well as their structural, physico-chemical characteristics.

Dr. Celia Marcos Pascual
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • vermiculite
  • mixed layers
  • treatments physico-chemical
  • adsorption of heavy metals and organic products
  • structural and physico-chemical properties
  • X-ray techniques (diffraction, fluorescence, etc.)
  • electron microscopy (high-resolution transmission, scanning electron)

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Published Papers (3 papers)

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Research

17 pages, 3592 KiB  
Article
α-Fe2O3 Nanoparticles/Iron-Containing Vermiculite Composites: Structural, Textural, Optical and Photocatalytic Properties
by Marta Valášková, Kamila Kočí, Jana Madejová, Lenka Matějová, Jiří Pavlovský, Beatriz Trindade Barrocas and Kateřina Klemencová
Minerals 2022, 12(5), 607; https://doi.org/10.3390/min12050607 - 11 May 2022
Cited by 9 | Viewed by 2751
Abstract
Vermiculite two-dimensional mixed-layer interstratified structures are a very attractive material for catalysis and photocatalysis. The iron-containing vermiculite from the Palabora region (South Africa) and its samples, which calcined at 500 and 700 °C, were studied in comparison with the α-Fe2O3 [...] Read more.
Vermiculite two-dimensional mixed-layer interstratified structures are a very attractive material for catalysis and photocatalysis. The iron-containing vermiculite from the Palabora region (South Africa) and its samples, which calcined at 500 and 700 °C, were studied in comparison with the α-Fe2O3 nanoparticles/vermiculite composites for the first time as photocatalysts of methanol decomposition, which is an organic pollutant and an efficient source for hydrogen production. The aim of the work was to characterize their structural properties using X-ray fluorescence, X-ray diffraction, infrared spectroscopy, nitrogen physisorption, diffuse reflectance UV-Vis spectroscopy and photoluminescence spectroscopy to explain the photocatalytic effects. The photocatalytic test of the samples was performed in a batch photoreactor under UV radiation of an 8W Hg lamp. The photocatalytic activity of vermiculite–hydrobiotite–mica-like layers at different water hydration states in the interstratified structure and the substitution ratio of Fe(III)/Al in tetrahedra can initiate electrons and h+ holes on the surface that attack the methanol in redox processes. The activity of α-Fe2O3 nanoparticle photocatalysts stems from a larger crystallite size and surface area. The hydrogen production from the methanol–water mixture in the presence of vermiculites and α-Fe2O3 nanoparticles/vermiculite composites was very similar and higher than the yield produced by the commercial TiO2 photocatalyst Evonik P25 (H2 = 1052 µmol/gcat.). The highest yield of hydrogen was obtained in the presence of the Fe/V–700 composite (1303 µmol/gcat after 4 h of irradiation). Full article
(This article belongs to the Special Issue Vermiculite: Treatments, Applications, and Structural and Physico-Chemical Characteristics)
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13 pages, 3806 KiB  
Article
Effect of Water Immersion on Raw and Expanded Ugandan Vermiculite
by Celia Marcos
Minerals 2022, 12(1), 23; https://doi.org/10.3390/min12010023 - 23 Dec 2021
Cited by 6 | Viewed by 2974
Abstract
Effect of water immersion at different times (from 1/2 h to 24 h) on raw and expanded vermiculite from Uganda was investigated. The expansion was carried out by electrical heating at different temperatures and by irradiation with microwaves. After, the expansibility (k) and [...] Read more.
Effect of water immersion at different times (from 1/2 h to 24 h) on raw and expanded vermiculite from Uganda was investigated. The expansion was carried out by electrical heating at different temperatures and by irradiation with microwaves. After, the expansibility (k) and the water absorption content (WA) were obtained and the samples were characterized. The elemental and mineral composition was determined by X-ray fluorescence and X-ray diffraction, respectively; the thermal behavior by thermal gravimetric analyses; and the textural parameters by BET. The expansibility of Ugandan vermiculite is relatively lower than the other commercial vermiculites due basically to its lower K2O content (0.36%) and higher water content (about 20%). The water absorption capacity of samples significantly increased with the increase in heating temperature. The maximum WA content, about 130 mg/g, was obtained at 900 °C for 24 h. The loss of water during the expansion process in the Ugandan vermiculite caused loss of structural order and crystallinity. Moreover, in the samples expanded and subsequently immersed in water, the structural order and crystallinity increased with increasing WA values. Specific surface area and porosity hardly vary with temperature and are practically independent of vermiculite purity. Expanded commercial vermiculites could be a suitable hygroscopic material, given its efficient water absorption. Microwave expanded commercial vermiculites, in this case, would not be recommended. Full article
(This article belongs to the Special Issue Vermiculite: Treatments, Applications, and Structural and Physico-Chemical Characteristics)
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13 pages, 9941 KiB  
Article
Heterogeneous Distribution of Interlayer Cations and Iron as a Plausible Explanation of the Non-Exfoliation of Commercial Vermiculites Post Alcohol Treatment and Microwave Irradiation
by Celia Marcos, Zulema del Río and Alaa Adawy
Minerals 2021, 11(8), 835; https://doi.org/10.3390/min11080835 - 1 Aug 2021
Viewed by 2024
Abstract
Two commercial vermiculites from China and Libby were treated with different alcohols (methanol, ethanol, propanol and butanol) at room temperature for up to one month and afterwards irradiated with microwaves. The exfoliated and non-exfoliated particles were characterized by X-ray diffraction, high-resolution transmission microscopy, [...] Read more.
Two commercial vermiculites from China and Libby were treated with different alcohols (methanol, ethanol, propanol and butanol) at room temperature for up to one month and afterwards irradiated with microwaves. The exfoliated and non-exfoliated particles were characterized by X-ray diffraction, high-resolution transmission microscopy, thermal gravimetric analyses and infrared spectroscopy to explain the inconsistencies in relation to potassium distribution and the exfoliation observed in previous investigations. The percentages of the exfoliated and non-exfoliated particles of the investigated vermiculites greatly varied, with no indication of a relationship between the resultant exfoliation and alcohol treatment. The crystallinity and structural order of the phases composing the particles are independent of the success of their exfoliation. The existence of a mosaic structure, the intra-particle mosaic-like intergrowth of the different mineral phases, in the treated and pristine commercial vermiculites could be attributed to the heterogeneous distribution on the nanoscale of interlayer cations as potassium and iron. Full article
(This article belongs to the Special Issue Vermiculite: Treatments, Applications, and Structural and Physico-Chemical Characteristics)
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