Special Issue "Special Clays and Their Applications"

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Clays and Engineered Mineral Materials".

Deadline for manuscript submissions: closed (30 June 2020) | Viewed by 8062

Special Issue Editor

Prof. Dr. Alberto Lopez Galindo
E-Mail Website
Guest Editor
Instituto Andaluz de Ciencias de la Tierra, CSIC-University of Granada, Avda. de las Palmeras, 4, 18100 Armilla, Granada, Spain
Interests: special clays; clays and health; geology of clays

Special Issue Information

Dear Colleague,

Unlike common commercial clays, widely found in most countries and used in applications requiring low-value materials such as brick-making, pottery or engineering, special clays are much scarcer. Highly pure clay minerals are only found in a small number of countries in a few deposits that vary in size but are usually small, and the industrial use of these minerals gives them high commercial value. Examples of these minerals are natural products such as kaolin and other kaolin-bearing clays (ball clay, fire clay, flint or hard clay, and halloysite), bentonites, fibrous clays and Fuller’s earth, but other treated, modified or synthetic clays are also included. The specific properties of these special clays (inertness and stability in some cases, reactivity and catalytic activity in others) are directly related to their colloidal size and crystal structure, resulting in highly specific surface, optimum rheological properties and/or excellent sorptive capacity, which makes them very useful in a wide variety of industrial applications.

This Special Issue summarizes the most recent advances made in the application of special clays in fields as varied as the oil industry, water treatment, environmental remediation, green chemistry, colloids, bio- and nanocomposites, degradation and stabilization of polymers, health care etc.

Prof. Dr. Alberto Lopez Galindo
Guest Editor

Manuscript Submission Information

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Keywords

  • kaolin
  • bentonite
  • fibrous clays
  • hectorite
  • halloysite
  • healing clays
  • sorption–desorption of contaminants
  • acid-activated and organophyllic bentonite
  • clay minerals-based advanced materials
  • clay/polymer nanocomposites

Published Papers (5 papers)

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Research

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Article
Physico-Chemical, Mineralogical, and Chemical Characterisation of Cretaceous–Paleogene/Neogene Kaolins within Eastern Dahomey and Niger Delta Basins from Nigeria: Possible Industrial Applications
Minerals 2020, 10(8), 670; https://doi.org/10.3390/min10080670 - 28 Jul 2020
Cited by 5 | Viewed by 992
Abstract
The demand for kaolinitic clays for various industrial applications is increasing globally. The present study evaluated the potential industrial applications of kaolins from the Eastern Dahomey and Niger Delta Basins, Nigeria. The colour, pH, electrical conductivity (EC), particle size distribution (PSD), plastic limits [...] Read more.
The demand for kaolinitic clays for various industrial applications is increasing globally. The present study evaluated the potential industrial applications of kaolins from the Eastern Dahomey and Niger Delta Basins, Nigeria. The colour, pH, electrical conductivity (EC), particle size distribution (PSD), plastic limits and liquid limits of the kaolins were determined. Mineralogical properties were assessed using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA). The chemical compositions of the kaolins were determined using X-ray fluorescence spectrometry (XRF). The kaolins were generally acidic, with pH less than 7 with low EC. The moderate plasticity indices (PI ≥ 10%) for the kaolins suggested their potential use in the manufacturing of structural clay products without extrusion. Kaolinite was the only kaolin mineral present with anhedral–subhedral–euhedral crystals. The platy morphology of the kaolinites in the Cretaceous kaolins are very important in paper production. Other minerals present in the kaolins were quartz, muscovite, anatase and goethite. The major oxide contents of the kaolins were dominated by SiO2, Al2O3, Fe2O3 and TiO2. Based on chemical specifications, the raw kaolins are not suitable for most industrial applications except for the Cretaceous Lakiri kaolins in the paper and ceramic industries (except for TiO2 and K2O content). The study concluded that the kaolin deposits would require beneficiation for large-scale industrial applications. Full article
(This article belongs to the Special Issue Special Clays and Their Applications)
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Article
Flow and Tableting Behaviors of Some Egyptian Kaolin Powders as Potential Pharmaceutical Excipients
Minerals 2020, 10(1), 23; https://doi.org/10.3390/min10010023 - 26 Dec 2019
Cited by 10 | Viewed by 1802
Abstract
The present work aimed at assessing the pharmaceutical tableting properties of some Egyptian kaolin samples belong to the Abu Zenima kaolin deposits (estimated at 120 million tons). Four representative samples were selected based on kaolinite richness and their structural order-disorder degree, and after [...] Read more.
The present work aimed at assessing the pharmaceutical tableting properties of some Egyptian kaolin samples belong to the Abu Zenima kaolin deposits (estimated at 120 million tons). Four representative samples were selected based on kaolinite richness and their structural order-disorder degree, and after purification, they were dried at 70 °C and heated from room temperature up to 400 °C (10 °C/min). Mineralogy, micromorphology, microtexture, granulometry, porosimetry, moisture content, bulk and tapped density, direct and indirect flowability, and tableting characteristics are studied. Results indicated that purified kaolin samples were made up of 95–99% kaolinite, <3% illite, 1% quartz and 1% anatase. The powder showed mesoporous character (pore diameters from 2 to 38 nm and total pore volume from 0.064 to 0.136 cm3/g) with dominance of fine nanosized particles (<1 μm–10 nm). The powder flow characteristics of both the ordered (Hinckley Index HI > 0.7, crystallite size D001 > 30 nm) and disordered (HI < 0.7, D001 < 30 nm) kaolinite-rich samples have been improved (Hausner ratio between 1.24 and 1.09) as their densities were influenced by thermal treatment (with some observed changes in the kaolinite XRD reflection profiles) and by moisture content (variable between 2.98% and 5.82%). The obtained tablets exhibited hardness between 33 and 44 N only from the dehydrated powders at 400 °C, with elastic recovery (ER) between 21.74% and 25.61%, ejection stress (ES) between 7.85 and 11.45 MPa and tensile fracture stress (TFS) between 1.85 and 2.32 MPa, which are strongly correlated with crystallinity (HI) and flowability (HR) parameters. These findings on quality indicators showed the promising pharmaceutical tabletability of the studied Egyptian kaolin powders and the optimization factors for their manufacturability and compactability. Full article
(This article belongs to the Special Issue Special Clays and Their Applications)
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Article
Colloidal and Thermal Behaviors of Some Venezuelan Kaolin Pastes for Therapeutic Applications
Minerals 2019, 9(12), 756; https://doi.org/10.3390/min9120756 - 04 Dec 2019
Cited by 3 | Viewed by 1152
Abstract
This work contributes to the knowledge of colloidal and thermal properties of some important primary-originated kaolin deposits from Bolivar State, Venezuela, and their possible use as semisolid formulations in medicinal muds for topical applications. Eight selected high purity kaolin samples were characterized. Rheological [...] Read more.
This work contributes to the knowledge of colloidal and thermal properties of some important primary-originated kaolin deposits from Bolivar State, Venezuela, and their possible use as semisolid formulations in medicinal muds for topical applications. Eight selected high purity kaolin samples were characterized. Rheological and thermal properties were correlated to physico-chemical characteristics of the clay suspensions (pH, Ca2+, and Mg2+ cation desorption and surface charge). Most of the studied kaolin pastes showed adequate viscosities, acceptable skin safe pH, and good thermal properties for pelotherapeutic uses. Three of the studied samples, in particular, showed very high kaolinite purities (>92% kaolinite), elevated viscosities (>1 Pa·s), and good thermal and pH performances for topical application. Full article
(This article belongs to the Special Issue Special Clays and Their Applications)
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Article
Evaluation of the Sorption Potential of Mineral Materials Using Tetracycline as a Model Pollutant
Minerals 2019, 9(7), 453; https://doi.org/10.3390/min9070453 - 21 Jul 2019
Cited by 6 | Viewed by 2214
Abstract
Tetracycline (TC) is among the most used antibiotics in animal feedstock in the EU. Antibiotics’ persistence as emerging pollutants in the environment is evidenced by their long half-life in residual organic-mineral sediments and waters. The risk associated with this persistence favours antibiotic-resistant microbiota, [...] Read more.
Tetracycline (TC) is among the most used antibiotics in animal feedstock in the EU. Antibiotics’ persistence as emerging pollutants in the environment is evidenced by their long half-life in residual organic-mineral sediments and waters. The risk associated with this persistence favours antibiotic-resistant microbiota, affecting human health and ecosystems. The purpose of the present work is to assess the adsorption of TC into natural clay minerals, synthetic iron hydroxides and calcined sewage sludge. TC adsorption isotherms were performed in three replicated batch tests at three different pH values (4, 6, 8) and TC concentrations (33–1176 mg·L−1). X-Ray diffraction (XRD) mineralogy, cation exchange capacity (CEC), Brunauer, Emmett and Teller specific surface area (BET-SSA) and point of zero charge salt effect (PZSE) were determined for the characterization of materials. Sorption was analysed by means of fitting Langmuir and Freundlich adsorption models, which showed good fitting parameters for the studied materials. Low-charge montmorillonite (LC Mnt) is displays the best sorption capacity for TC at maximum TC concentration (350–300 mgTC·g−1) in the whole range of pH (4–8). Sepiolite and smectites adsorbed 200–250 mgTC·g−1, while illite, calcined sludge or iron hydroxides present the lowest adsorption capacity (<100 mgTC·g−1). Nevertheless, illite, sepiolite and ferrihydrite display high adsorption intensities at low to medium TC concentrations (<300 mg·L−1), even at pH 8, as is expected in wastewater environmental conditions. Full article
(This article belongs to the Special Issue Special Clays and Their Applications)
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Review

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Review
Spanish Bentonites: A Review and New Data on Their Geology, Mineralogy, and Crystal Chemistry
Minerals 2019, 9(11), 696; https://doi.org/10.3390/min9110696 - 11 Nov 2019
Cited by 11 | Viewed by 1423
Abstract
A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They [...] Read more.
A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites. Full article
(This article belongs to the Special Issue Special Clays and Their Applications)
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