Special Issue "Environmental Applications of Chemically Modified Clay Minerals"

A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (30 August 2020).

Special Issue Editor

Dr. Martin Pentrak
Website
Guest Editor
Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
Interests: smectites; kaolinites; iron; reduction; XRD; XRF; Mössbauer spectroscopy; infrared spectroscopy

Special Issue Information

Dear Colleagues,

On behalf of the Minerals Journal, I would like to invite you to join me in the special issue related to the investigation of clay minerals with a focus on their environmental applications.

Clay minerals are natural materials with unique properties (large specific surface area, cation exchange capacity). Most known clay mineral groups, smectites, and kaolinites are investigated for decades, and their usage has now an extensive range from cosmetics through paper and paints additives to environmental applications. Smectites have a large specific surface area and cation exchange capacity due to the negative layer charge. They are excellent natural adsorbents, but their properties can be enhanced by chemical modification to study their: (1) structural stability under extreme pH conditions (the isolation layers of a toxic waste dumps and spent radioactive fuel storages - acid and alkali activation), (2) redox activity to remediate contaminated waters and soils by industrial or agricultural discharges (chemical and biological redox activation of structural Fe), and (3) reactivity with oversaturated saline solutions (geological clay barriers). These studies are highly recommended for this special issue of the Minerals Journal, but other environmental utilizations of chemically modified clay minerals are welcome, as well.

Finally, the overall goal of this issue is to bring a message about the actual environmental applications of chemically modified clay minerals.

Dr. Martin Pentrak
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 papers will be 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 1600 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

  • smectites
  • kaolinite
  • acid activation
  • redox activation
  • remediation
  • contamination
  • environmental application

Published Papers (3 papers)

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Research

Open AccessArticle
Removal of Salicylic and Ibuprofen by Hexadecyltrimethylammonium-Modified Montmorillonite and Zeolite
Minerals 2020, 10(10), 898; https://doi.org/10.3390/min10100898 - 10 Oct 2020
Abstract
The removal of salicylic acid (SA) and ibuprofen (IB) by sorption onto HDTMA-modified montmorillonite (HM) and zeolite (HZ) was investigated at pH 7. The single sorption data were fitted well by the Freundlich, Langmuir, Dubinin−Radushkevich (DR), and Polanyi−Dubinin−Manes (PDM) models (R2 [...] Read more.
The removal of salicylic acid (SA) and ibuprofen (IB) by sorption onto HDTMA-modified montmorillonite (HM) and zeolite (HZ) was investigated at pH 7. The single sorption data were fitted well by the Freundlich, Langmuir, Dubinin−Radushkevich (DR), and Polanyi−Dubinin−Manes (PDM) models (R2 > 0.94). The sorption affinity of Freundlich and the maximum sorption capacity of Langmuir and PDM models of pharmaceuticals onto HM were consistently higher than that of HZ mainly owing to the higher organic carbon content. In addition, the KF, qmL, and qm values were in the order of IB > SA owing to higher hydrophobicity and molar volume. Since the predominant speciation of SA and IB is anionic at pH 7 (>pKa), sorption onto HM occurs mainly by the two-dimensional surface adsorption onto the pseudo-organic medium in the HM, whereas the interaction of anionic pharmaceuticals with the positively charged “head” of HDTMA is responsible for HZ. Sorption isotherms were fitted well by the PDM model, which indicated that pore-filling was one of the dominating sorption mechanisms. The extended Langmuir model, modified Langmuir competitive model, and ideal adsorbed solution theory employed with Freundlich and Langmuir sorption models were applied to predict binary sorption. The effect of competition between the solutes was clearly evident in the characteristic curves; the maximum sorbed volume (qv.m) was reduced, and the sorbed volume (qv) had a wider distribution toward the sorption potential density. Full article
(This article belongs to the Special Issue Environmental Applications of Chemically Modified Clay Minerals)
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Open AccessArticle
Modified Vermiculite as Adsorbent of Hexavalent Chromium in Aqueous Solution
Minerals 2020, 10(9), 749; https://doi.org/10.3390/min10090749 - 24 Aug 2020
Abstract
The aim of this study was to investigate the efficiency of removing Cr6+ from aqueous solutions using two exfoliated vermiculite: (1) heated abruptly at 1000 °C and (2) irradiated with microwave radiation. The effects investigated were contact time, adsorbate concentration and initial [...] Read more.
The aim of this study was to investigate the efficiency of removing Cr6+ from aqueous solutions using two exfoliated vermiculite: (1) heated abruptly at 1000 °C and (2) irradiated with microwave radiation. The effects investigated were contact time, adsorbate concentration and initial Cr6+ concentration. The adsorption with both exfoliated vermiculites was well described by the DKR isotherm, indicative of a cooperative process and with the pseudo second order kinetic model. The Kd value for the two exfoliated vermiculites was similar, 0.2 ·1010 μg/Kg. The maximum adsorption capacity of Cr6+ with thermo-exfoliated vermiculite, 2.81 mol/g, was much higher than with microwave irradiated vermiculite, 0.001 mol/g; both values were obtained with 0.5 g of vermiculite in contact with distilled water enriched with 1 ppm of Cr6+ for 24 h. Factors such as ion chemistry, the solution pH and ionic strength, influence the values of capacity, adsorption energy and initial adsorption rate values of the exfoliated vermiculite. In addition, these values depended on the exfoliation process, being the adsorption capacity highest with abrupt heating of vermiculite, while the adsorption energy and rate values showed just a slight increase with microwave irradiation. This aspect is important to select the most suitable vermiculite modification treatment to use it as an adsorbent. Full article
(This article belongs to the Special Issue Environmental Applications of Chemically Modified Clay Minerals)
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Open AccessArticle
Relationship between Textural Parameters of Lamellar Products Obtained by Acid Activation of Pure and Commercial Vermiculites and Their Iron and Water Content
Minerals 2020, 10(8), 661; https://doi.org/10.3390/min10080661 - 26 Jul 2020
Abstract
The relationship between textural parameters (specific superficial area (SBET) and porosity (Vp)) of lamellar products obtained from HNO3-activated vermiculites and their iron and water content has been established. Two commercial vermiculites, one thermoexfoliated commercial vermiculite, and one [...] Read more.
The relationship between textural parameters (specific superficial area (SBET) and porosity (Vp)) of lamellar products obtained from HNO3-activated vermiculites and their iron and water content has been established. Two commercial vermiculites, one thermoexfoliated commercial vermiculite, and one pure vermiculite were nitric-acid-treated at 4 and 8 M concentrations for 1, 3, and 7 days. Untreated and treated samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and N2 physisorption analysis. The untreated vermiculites showed a direct relationship between their iron content and the values of SBET, Vp, and pore size; an inverse relationship was observed in the case of the treated samples. The iron content may prevent further leaching of cations but not water loss, therefore forming lamellar products with lower SBET and Vp values. The SBET and Vp values of the studied thermoexfoliated sample were higher than those of the starting sample. The SBET and Vp values of the activated thermoexfoliated sample were lower than those of the activated non-thermoexfoliated sample. Full article
(This article belongs to the Special Issue Environmental Applications of Chemically Modified Clay Minerals)
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