Research

Jump to: Review

14 pages, 5951 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Melting Behaviour under Pressure of Kaolinite Clay: A Nanoscale Study

by Brahim Khalil Benazzouz and Ali Zaoui

Minerals 2023, 13(5), 679; https://doi.org/10.3390/min13050679 - 16 May 2023

Cited by 2 | Viewed by 1105

In this study, the curves of variation of melting temperature as a function of pressure were determined for pressures up to 20 GPa using molecular dynamics (MD) calculations. The CLAYFF force field is used for the simulated PT curve of the clay kaolinite [...] Read more.

In this study, the curves of variation of melting temperature as a function of pressure were determined for pressures up to 20 GPa using molecular dynamics (MD) calculations. The CLAYFF force field is used for the simulated PT curve of the clay kaolinite structure. For this purpose, we have adopted the Z-method to determine the melting point (Tm) and superheat limit temperature (TLS) for different densities in kaolinite clay. In addition, various quantities, such as the radial distribution function (RDF), the mean square displacement (MSD), and the diffusion coefficient were evaluated in order to ensure the solid behaviour at the superheat limit temperature and the liquid behaviour at the melting point for the equilibrated structure of kaolinite. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Figure 1

22 pages, 15876 KiB

Open AccessFeature PaperArticle

Numerical Study of Gas Breakthrough in Preferential Rocks for Underground Nuclear Waste Repositories

by Xiang Zhang, Hang Yin, Wenjie Yu, Zhen Lei and Juntong Qu

Minerals 2023, 13(3), 393; https://doi.org/10.3390/min13030393 - 11 Mar 2023

Viewed by 1225

Abstract

During the long-term storage of radioactive waste, the continuous generation of gas in the disposal area may influence the integrity of host rock. Thus, the investigation of gas migration and breakthrough in low-permeability rock is indispensable for the stability assessment. In this work, [...] Read more.

During the long-term storage of radioactive waste, the continuous generation of gas in the disposal area may influence the integrity of host rock. Thus, the investigation of gas migration and breakthrough in low-permeability rock is indispensable for the stability assessment. In this work, the pore space models of four potential host rocks (Boom clay, COx argillite, Opalinus clay, and Beishan granite) were generated via the binarization of the Gaussian random field. This method provides a randomly formed pore network that does rely on an initial definition of pore shape. The constructed models were analyzed and validated by using the mathematical morphology. A numerical calculation scenario of gas breakthrough on the basis of the Young–Laplace equation was proposed and applied. Results show that the gas breakthrough pressures are 2.62–4.11 MPa in Boom clay and 3.72–4.27 MPa in COx argillite. It enhances the idea that the capillary-induced gas breakthrough is possible at pressures lower than the fracture threshold. For Opalinus clay and Beishan granite, no connected pathway exists, and the breakthrough is more likely to occur through pathway dilation or fractures. The presented method has the advantage of experimental reproducibility and brings a new idea for the investigation of fluid migration in low-permeability rocks. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Figure 1

12 pages, 1777 KiB

Open AccessArticle

Vermiculite Modified with Fe³⁺ Polyhydroxy Cations Is a Low-Cost and Highly Available Adsorbent for the Removal of Phosphate Ions

by Fernando H. do Nascimento and Jorge C. Masini

Minerals 2022, 12(8), 1033; https://doi.org/10.3390/min12081033 - 17 Aug 2022

Cited by 2 | Viewed by 1730

Abstract

This paper demonstrates that intercalating Na⁺ homoionic vermiculite with Fe³⁺ polyhydroxy cations (1:1 molar ratio OH⁻ to Fe³⁺) significantly improved the affinity of the clay mineral-based sorbent toward phosphate. Kinetic experiments revealed that adsorption is fast, approaching an [...] Read more.

This paper demonstrates that intercalating Na⁺ homoionic vermiculite with Fe³⁺ polyhydroxy cations (1:1 molar ratio OH⁻ to Fe³⁺) significantly improved the affinity of the clay mineral-based sorbent toward phosphate. Kinetic experiments revealed that adsorption is fast, approaching an equilibrium within about 200 min of contact time, and that the rate-limiting step is the intraparticle diffusion. Adsorption isotherms fitted to the Freundlich equation and a two-site Langmuir model, consistent with the heterogeneity of adsorption sites. The separation factor derived from the Langmuir constant revealed that the adsorption was favorable and even irreversible for high-affinity minor adsorption sites. The adsorption capacity was 299 ± 63 μmol g⁻¹ (9.3 ± 2.1 mg P g⁻¹), a value similar to several other clay-based phosphate adsorbents. Application to reservoir water spiked with 10 mg L⁻¹ in P removed about 71% of the available phosphate. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Figure 1

17 pages, 3188 KiB

Open AccessEditor’s ChoiceArticle

Molecular Dynamics Simulation and Cryo-Electron Microscopy Investigation of AOT Surfactant Structure at the Hydrated Mica Surface

by Daniel M. Long, Jeffery A. Greathouse, Guangping Xu and Katherine L. Jungjohann

Minerals 2022, 12(4), 479; https://doi.org/10.3390/min12040479 - 14 Apr 2022

Cited by 2 | Viewed by 2616

Abstract

Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity [...] Read more.

Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity experiments that revealed the binding of anionic surfactant to the negatively charged surface via adsorbed cations. At low loading, cylindrical micelles formed on the surface, with sulfate head groups bound to the surface by water molecules or adsorbed cations. Cation bridging was observed in the presence of weakly hydrating monovalent cations, while sulfate groups interacted with strongly hydrating divalent cations through water bridges. The adsorbed micelle structure was confirmed experimentally with cryogenic electronic microscopy, which revealed micelles approximately 2 nm in diameter at the basal surface. At higher AOT loading, the simulations reveal adsorbed bilayers with similar surface binding mechanisms. Adsorbed micelles were slightly thicker (2.2–3.0 nm) than the corresponding bilayers (2.0–2.4 nm). Upon heating the low loading systems from 300 K to 350 K, the adsorbed micelles transformed to a more planar configuration resembling bilayers. The driving force for this transition is an increase in the number of sulfate head groups interacting directly with adsorbed cations. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Graphical abstract

16 pages, 1416 KiB

Open AccessEditor’s ChoiceArticle

Effect of Structural Fe Reduction on Water Sorption by Swelling and Non-Swelling Clay Minerals

by Christos Vasilopanagos, Cédric Carteret, Stephen Hillier, Anke Neumann, Harry J. L. Brooksbank and Hugh Christopher Greenwell

Minerals 2022, 12(4), 453; https://doi.org/10.3390/min12040453 - 07 Apr 2022

Cited by 3 | Viewed by 2248

Abstract

Ferruginous clay minerals in saturated soils and within hydrocarbon deposits often exist in a reduced state. Upon introduction of dissolved oxygen, or other oxidants, the clay minerals oxidise and changes in mineral surface charge and sorption capacity occur, resulting in changes in hydration [...] Read more.

Ferruginous clay minerals in saturated soils and within hydrocarbon deposits often exist in a reduced state. Upon introduction of dissolved oxygen, or other oxidants, the clay minerals oxidise and changes in mineral surface charge and sorption capacity occur, resulting in changes in hydration as well as flux of intercalated species. Here we examine the sorption of water to the Fe-containing clay minerals nontronite NAu-2 (23 wt% Fe) and illite IMt-2 (7 wt% Fe) as a function of Fe oxidation state and exchangeable cations by means of water vapour volumetry and N₂ surface area analysis. The clay minerals were chemically reduced using sodium dithionite. Sorption isotherms of water vapour and nitrogen, controlled relative humidity diffractograms, and chemical analyses were recorded. The results show that, after reduction using sodium dithionite, increased amounts of water vapour and nitrogen were adsorbed to the high Fe content nontronite, despite decreased interlayer separation. Little change was observed for the non-swelling and low Fe content illite. Sodium from the reducing agent was found to exchange with calcium present in the starting clay minerals, and sodium balanced the additional mineral charge generated during reduction. The findings presented in this study deliver improved understanding of sorption at the surface of the reduced clay minerals, which aid constrain the role of clay mineral interfaces in subsurface environments. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Figure 1

15 pages, 4490 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Hydrotalcite-like Copper Hydroxyl Salts as a Photocatalyst and Adsorbent for Hexavalent Chromium Removal

by Chitiphon Chuaicham, Karthikeyan Sekar, Vellaichamy Balakumar, Li Zhang, Jirawat Trakulmututa, Siwaporn Meejoo Smith and Keiko Sasaki

Minerals 2022, 12(2), 182; https://doi.org/10.3390/min12020182 - 30 Jan 2022

Cited by 5 | Viewed by 2903

Abstract

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu₂(OH)₃NO₃. From XRD and UV-DRS [...] Read more.

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu₂(OH)₃NO₃. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Graphical abstract

18 pages, 7294 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) in Montmorillonite/TiO₂ Composite for Photocatalytic Degradation of Phenol

by Li Zhang, Chitiphon Chuaicham, Vellaichamy Balakumar, Bunsho Ohtani and Keiko Sasaki

Minerals 2021, 11(12), 1381; https://doi.org/10.3390/min11121381 - 08 Dec 2021

Cited by 7 | Viewed by 3447

Abstract

The Fe(III)-doped montmorillonite (Mt)/TiO₂ composites were fabricated by adding Fe(III) during or after the aging of TiO₂/Ti(OH)₄ sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO₂ and Fe/Mt/TiO₂, respectively. In the xFe-Mt/(1 − x [...] Read more.

The Fe(III)-doped montmorillonite (Mt)/TiO₂ composites were fabricated by adding Fe(III) during or after the aging of TiO₂/Ti(OH)₄ sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO₂ and Fe/Mt/TiO₂, respectively. In the xFe-Mt/(1 − x)Fe-TiO₂, Fe(III) cations were expected to be located in the structure of TiO₂, in the Mt, and in the interface between them, while Fe(III) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO₂. The narrower energy bandgap (

E g

) lower photo-luminescence intensity were observed for the composites compared with TiO₂. Better photocatalytic performance for phenol degradation was observed in the Fe/Mt/TiO₂. The 94.6% phenol degradation was due to greater charge generation and migration capacity, which was confirmed by photocurrent measurements and electrochemical impedance spectroscopy (EIS). The results of the energy-resolved distribution of electron traps (ERDT) suggested that the Fe/Mt/TiO₂ possessed a larger amorphous rutile phase content in direct contact with crystal anatase than that of the xFe-Mt/(1 − x)Fe-TiO₂. This component is the fraction that is mainly responsible for the photocatalytic phenol degradation by the composites. As for the xFe-Mt/(1 − x)Fe-TiO₂, the active rutile phase was followed by isolated amorphous phases which had larger (

E g

) and which did not act as a photocatalyst. Thus, the physically adsorbed Fe(III) enhanced light adsorption and avoided charge recombination, resulting in improved photocatalytic performance. The mechanism of the photocatalytic reaction with the Fe(III)-doped Mt/TiO₂ composite was proposed. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Graphical abstract

19 pages, 5597 KiB

Open AccessArticle

Mineralogical and Physico-Chemical Characterization of the Oraşu-Nou (Romania) Bentonite Resources

by Gheorghe Damian, Floarea Damian, Zsolt Szakács, Gheorghe Iepure and Dan Aştefanei

Minerals 2021, 11(9), 938; https://doi.org/10.3390/min11090938 - 29 Aug 2021

Cited by 13 | Viewed by 3285

Abstract

The objective of this study is to describe the mineralogical composition and chemical properties of the Oraşu Nou bentonite, from northwestern Romania. For mineralogical determinations, the following were used: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FR-IR), thermogravimetric analysis, scanning electron microscopy coupled [...] Read more.

The objective of this study is to describe the mineralogical composition and chemical properties of the Oraşu Nou bentonite, from northwestern Romania. For mineralogical determinations, the following were used: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FR-IR), thermogravimetric analysis, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The chemical compositions and physical properties of the bentonites and bentonitized rocks were also determined. Calcium type montmorillonite is the predominant mineral in this deposit. Its average mass fraction is between 35% and 75%, reaching up to 95%. A small amount of halloysite and very fine cristobalite were also identified in the fine fraction. Quartz, feldspar, and kaolinite were identified as impurities. The average pH of natural bentonite is 6.2. Its cation exchange capacity (CEC) is in the lower-middle range for smectites at 45.89 cmol/kg, absorption capacity 43.58 mL/g, swelling degree 9.41%. Because of the high amounts and purity of montmorillonite, the valuable component mineral, the way is open to an easy refinement of this important resource. This way very high-quality colloidal suspensions can be obtained which can be used in the most modern applications of micro- and nanostructured materials. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Figure 1

Review

Jump to: Research

23 pages, 4378 KiB

Open AccessFeature PaperReview

Nanoclay-Reinforced Nanocomposite Nanofibers—Fundamentals and State-of-the-Art Developments

by Ayesha Kausar, Ishaq Ahmad, O. Aldaghri, Khalid H. Ibnaouf and M. H. Eisa

Minerals 2023, 13(6), 817; https://doi.org/10.3390/min13060817 - 15 Jun 2023

Viewed by 1777

Abstract

Nanoclays are layered mineral silicates, i.e., layered silicate nanosheets. Nanoclays such as montmorillonite, bentonite, kaolinite, etc., have been used as reinforcements in the nanofibers. Numerous polymers have been used to fabricate the nanofibers, including poly(vinylidene fluoride), poly(vinyl alcohol), polycaprolactone, nylon, polyurethane, poly(ethylene oxide), [...] Read more.

Nanoclays are layered mineral silicates, i.e., layered silicate nanosheets. Nanoclays such as montmorillonite, bentonite, kaolinite, etc., have been used as reinforcements in the nanofibers. Numerous polymers have been used to fabricate the nanofibers, including poly(vinylidene fluoride), poly(vinyl alcohol), polycaprolactone, nylon, polyurethane, poly(ethylene oxide), and others. To develop better compatibility with polymers, nanoclays have been organo-modified prior to reinforcement in the nanofiber matrices. This state-of-the-art review highlights the fundamentals, design, fabrication, and characteristics of the polymer/nanoclay nanofibers. The nanoclay filled nanocomposite nanofibers have been fabricated using electrospinning and other fiber processing techniques. The electrospinning technique has been preferred to form the nanoclay-filled nanofibers, owing to the better control of processing parameters and resulting nanofiber properties. The electrospun polymer/nanoclay nanofibers usually have fine nanoparticle dispersions, microstructures, smooth textures, and narrow diameters. The physical properties of the designed nanofibers depend upon the processing technology used, solvent, solution/melt concentration, flow rate, spinning speed, voltage, and other process parameters. Hence, this review attempts to assess a literature-driven consequence of embedding nanoclays in the polymeric nanofibers in a broad context of the application of these fibrous materials. Conclusively, to design the polymer/nanoclay nanofibers, montmorillonite nanoclay has been observed as a nanofiller in most of the studies, and, similarly, the electrospinning technique was preferred as a fabrication technique. Almost all the physical properties of the nanofibers studied revealed dependences upon the choice of the polymer matrix for nanofiber formation as well as the nanoclay contents, modification, and dispersion state. Accordingly, the nylon/nanoclay nanofibers have been investigated for nanofiller dispersion, mechanical properties, and thermal profiles. The antibacterial properties were among the prominent features of the poly(vinyl alcohol)/nanoclay nanofibers. The poly(vinylidene fluoride)/nanoclay systems were explored for the microstructure, crystallinity, and piezoelectric properties. The polycaprolactone/nanoclay nanofibers having fine microstructure were capable of forming tissue engineering scaffolds. The drug delivery and sound absorption properties were noticeable for the polyurethane/nanoclay nanofiber systems. Moreover, the poly(lactic acid)/nanoclay nanofibers were found to have prominent biodegradability and low gas permeability features. The resulting polymer/nanoclay nanocomposite nanofiber systems found potential for the technical applications of sensors, packaging, tissue engineering, and wound healing. However, thorough research efforts have been found to be desirable to find the worth of polymer/nanoclay nanofibers in several concealed technological sectors of energy, electronics, aerospace, automotives, and biomedical fields. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Graphical abstract

20 pages, 1727 KiB

Open AccessFeature PaperReview

The Stability of Anthocyanins and Their Derivatives through Clay Minerals: Revising the Current Literature

by Robson Cunha, Pollyana Trigueiro, María del Mar Orta Cuevas, Santiago Medina-Carrasco, Thiago M. Duarte, Luzia M. de C. Honório, Dihêgo H. L. Damacena, Maria Gardennia Fonseca, Edson C. da Silva-Filho and Josy A. Osajima

Minerals 2023, 13(2), 268; https://doi.org/10.3390/min13020268 - 14 Feb 2023

Cited by 6 | Viewed by 4047

Abstract

In recent years, anthocyanins, natural dyes, have promoted great scientific and technological interest. Their intrinsic antioxidant properties and health benefits make them ideal representatives of natural dyes as replacements for synthetic dyes. However, their instability can limit their use. A promising strategy to [...] Read more.

In recent years, anthocyanins, natural dyes, have promoted great scientific and technological interest. Their intrinsic antioxidant properties and health benefits make them ideal representatives of natural dyes as replacements for synthetic dyes. However, their instability can limit their use. A promising strategy to increase the color stability of anthocyanins is their interaction with clay minerals structures. Clay minerals have characteristics favorable to the stabilization of natural dyes, such as adsorption capacity, good surface chemistry, ion exchange capacity, abundance, non-toxicity, and environmental compatibility. This review summarizes relevant works that present different clays or clay minerals as robust inorganic matrices for incorporation, improved stability, and increased resistance against the thermal- and photodegradation of anthocyanins. In addition, several authors propose different applications for the formed anthocyanin-based hybrids. Full article

(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Feature Papers in Clays and Engineered Mineral Materials

Share This Special Issue

Special Issue Editor

Special Issue Information

Published Papers (10 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI