Clays from the Saïss basin (northern Morocco) used traditionally in the ceramic industry in the Fez area were studied using mineralogical and physicochemical techniques to evaluate their potential suitability as raw materials for ceramics manufacture. X-ray diffraction was used to determine their mineralogical composition. The physical properties determined were particle-size distribution and consistency limits. The chemical composition was determined using X-ray fluorescence analysis and Fourier-transform infrared spectrometry. The structural changes of the mineral phases in the raw materials during firing were studied over a temperature range of 500–1000°C. In the pottery site from Fez, generally potters use a mixture of 25% fine clay (ARFS) from the upper part of the Miocene marls and 75% sandy clay (ARFR) from the lower part of the Miocene marls. The ARFS clay yielded very rigid specimens after firing that artisan potters would find difficult to handle so as to produce desired shapes and sizes. However, the specimens obtained from ARFR clay show signs of faltering. The mixture of these two clayey materials from this pottery site is therefore necessary to obtain the optimal paste for ceramics purposes. The chemical compositions indicated that SiO2, Al2O3, CaO and Fe2O3 are the major minerals, with trace amounts of K2O and MgO. Quartz, feldspars and clay minerals prevail in all samples. Kaolinite, illite and smectite are the dominant clay mineral phases, with traces of chlorite and interstratified illite–smectite. The classification of these samples using appropriate ternary diagrams showed that the proportions used in the mixture produce a new material with adequate characteristics for the production of traditional ceramics.

Clay minerals are used widely in health products both as cosmetic and pharmaceutical ingredients. To optimize use, natural compounds are mixed with clay powder. The aim of the present study was to synthesize new, coloured hybrids based on purified Tunisian clay and powders of natural flowers: Malva sylvestris, Chrysanthemum coronarium, Silene dioica, Anagallis monellin and Pelargonium × hortorum. The floral pigments in Tunisian flowers were studied. The chlorophylls (a and b), total flavonoids (TF), total phenolic compounds (TPC), and carotenoids were analyzed using UV-Vis spectrophotometry and high-performance liquid chromatography (HPLC-DAD). In addition, the antioxidant capacity was determined using the oxygenated radical absorption capacity assay (ORAC) and the antioxidant capacity to reduce ferric ion assay (FRAP). The properties of the studied clay were evaluated by means of pharmaceutical and microbiological tests. The coloured hybrids were prepared by solid–solid reaction and analyzed using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Chlorophyll a is present in large quantities in the Malva flower which presents the smallest antioxidant capacity. Chlorophyll b and the TPC are more abundant in the Pelargonium × hortorum. The TF appears in large quantities in the Anagallis flower. The carotenoids are present in the largest amounts in the Chrysanthemum. The results of the clay characterization justify its use as a pharmaceutical and cosmetic agent. The mixture of dried flowers and purified clay is used in the synthesis of new and biocoloured hybrids; these can be used as biocosmetic products without negative side effects on human health or the environment.

Artificially coloured smectites (smectite pigments) were prepared via the sorption of anionic dyes on smectite saturated with ferric ions (Fe-smectite). Fe-smectite has a surface charge and is capable of decolourizing aqueous solutions containing single-component anionic dyes (Amaranth, Brilliant blue FCF and Tartrazine) or multi-component dyes (dye mixtures). Kinetic and equilibrium models were used to describe the sorption of individual dyes, whereas the decolourization of the multi-component system was studied by monitoring the reduction in the intensity of the absorption bands in the visible light region. The Langmuir–Freundlich dual-site model presented the best fit to the experimental data, and the sorption kinetics followed the pseudo-second order model. The smectite pigments were dispersed in colourless paint (10%, w/w), acting as organic–inorganic hybrid pigments. Colorimetric measurements of the powdered smectite pigments dispersed in colourless real-estate paint showed chemical compatibility without the need for solvents as dispersants. These properties allow the application of coloured smectites as pigments in a sustainable circular economy.

Bentonite-based tablets offer multiple advantages over other types of formulated tablets, including being biocompatible and cost-effective, and they can be used to develop gel-like matrices that have potential for use in sustained-release formulations. Developing a high-load sustained-release formulation has been reported to be challenging; therefore, the aim of this study was to develop systematically bentonite-based sustained-release tablets for a high-load active agent (ibuprofen) and investigate their release kinetics. Ibuprofen-loaded tablets (800 mg) were prepared using wet and dry granulation followed by enteric coating of the tablets. Fourier-transform infrared spectroscopy, differential scanning calorimetry and X-ray powder diffraction were used to evaluate the compatibility of ibuprofen with bentonite. The results show that these tablets comply with compendial requirements. In addition, the release profile of the formulations reveals that the drug follows a non-Fickian release model. The present formulation demonstrates a new use of bentonite as a safe and cost-effective excipient with adequate binding and compaction for preparing sustained-release tablets.

High-whiteness kaolinite mining reserves are scarce. In some locations, it is necessary to remove material to access them (adding to the cost). Therefore, processes have been developed to eliminate contaminants, such as iron, and provide alternatives to the used contaminated materials that, after being treated, meet quality criteria. In our previous research, we developed an electrochemical process for kaolin whitening at the laboratory level and bench scale, demonstrating the reaction mechanisms that occur during the removal of iron from kaolin. However, the geometry used at the laboratory level does not present the most suitable position for the electrodes. Therefore, in the present study, we focused on the geometry and the function of the electrodes. This is necessary during the escalation process to reach the pilot-scale level. The study was carried out using computer-aided engineering in the COMSOL Multiphysics computer program and by analysing the distribution of the electric potential and the electric current of the geometries considered while performing the scaling. The results indicated that the change in the anode position from perpendicular to parallel to the discs improved the distribution of electric current density on the cathode surface and so increased the elimination of iron through electrochemical deposition. Similarly, to reduce the amount of material used in the construction of the reactor, the anode-size effect was analysed, revealing that relatively small anodes improved the distribution of electric current density over the entire surface of the electrode and not only at the edges.

Clay-swelling inhibitors are often used to prevent the hydration of clay minerals, which can reduce the risk of wellbore instability and reservoir damage. The molecular behaviour of clay-swelling inhibitors at the montmorillonite–water interface is crucial for revealing their inhibition mechanisms and for evaluating and designing inhibitor molecules. N1,N1'-(ethane-1,2-diyl)bis(N1-(2-aminoethyl)ethane-1,2-diamine) (NETS), a low-molecular-weight clay-swelling inhibitor, is used widely to prevent clay swelling. Herein, the adsorption mechanism of NETS on the surface of montmorillonite (Mnt) was investigated using molecular dynamics (MD) simulations. In particular, the effects of molecular conformation and temperature on adsorption ability were investigated. The results show that the adsorption ability of NETS on the Mnt surface was affected significantly by the molecular conformation. Specifically, the dihedral angle of NETS adsorbed on the surface of Mnt decreases by ~20° and tends to adsorb on the surface of Mnt in a plane state. In addition, the adsorption stability of NETS on the Mnt surface decreased with increasing temperature, as was found using MD simulations. Detailed analysis shows that increasing temperature can lead to more frequent conformational changes, which weaken the interaction between NETS and Mnt, thus reducing adsorption stability. These molecular insights into the interaction mechanism between NETS and Mnt are beneficial for the evaluation of inhibitory effects and for the selection and molecular design of new clay-swelling inhibitors for use in drilling fluids.

The search for sufficiently high-quality clays for use in the tile industry represents a significant challenge. This study aimed to prepare Muttalip green clay tiles with flexural strengths adhering to the TS EN 1304:2016 standard. Muttalip green clay was subjected to sieving, vacuum pressed, dried and then baked to obtain galette tiles. The tiles were analysed subsequently using optical techniques, including X-ray diffraction, X-ray fluorescence spectrometry and field-emission scanning electron microscopy. The influence of various firing temperatures (900, 950 and 1000°C) on the flexural strength of the tiles was also investigated. The tiles obtained at 950°C exhibited a maximum flexural strength of 153.91 kg cm–2. Fourier-transform infrared spectroscopy revealed that the tiles reflect ultraviolet A radiation and absorb infrared radiation. Muttalip green clay is a suitable material for preparing tiles for roofing applications.

High-performance electrodes with outstanding catalysts play a vital role in the commercial application of direct ethanol fuel cells. In the present study, a supported catalyst with controllable Pd loading, prepared using a facile impregnation method with sepiolite as a carrier, was synthesized and tested for electrocatalytic oxidation of ethanol. Physical characterization revealed the pore structure and large specific surface area of the sepiolite, which provided excellent conditions for the loading of nanometal clusters. The Pd-sepiolite had greater electrocatalytic ethanol activity and anti-intermediate product poisoning performance than a metallic Pd disc electrode under alkaline conditions. Under these experimental conditions, the electrochemical activity in terms of ethanol oxidation increased significantly with increasing Pd loading. Considering both the activity and stability of the electrodes, 23 wt.% Pd loading on sepiolite was selected with a coating amount of 140 μg cm–2 on glassy carbon. Factors such as ethanol/potassium hydroxide concentration, scanning rate and temperature had direct impacts on peak current densities as well as on reaction kinetics as depicted by Tafel plots. The electrochemical impedance test showed that Pd intercalation could improve significantly the conductivity of sepiolite and reduce the electron-transfer resistance in the electrocatalytic process. Thus, Pd-loaded sepiolite is a simple and effective catalyst for direct ethanol fuel cells.

Allophane-related aluminium silicates with various chemical compositions were synthesized using a hydrothermal reaction with inorganic reagents as starting solutions. The X-ray diffraction traces of the synthesized allophanes showed broad reflections centred at 0.34 and 0.23 nm, which were attributed to the imogolite-like structure of the allophanes. Energy-dispersive X-ray measurements confirmed that the Al-rich materials were synthesized as targeted. The specific surface area of the synthesized allophanes was 313–500 m2 g–1, which is greater than that of a natural allophane (248 m2 g–1). The amount of nitrate adsorbed on the synthesized allophanes tended to increase as the Al content increased. The maximum amount of nitrate adsorbed was 2.07 mmol g–1 at pH ~2, which was comparable to that of a common anion-exchange material. A possible adsorption mechanism for nitrate at lower pH levels is the weak NO3– interaction of the positively charged surface of Al-OH2+ sites.

This work elucidated the performance and mechanisms of Pb2+ adsorption by kaolinite, montmorillonite, goethite and ferrihydrite using batch experiments. The contributions of various adsorption mechanisms were quantified using a stepwise extraction method. Several characterizations (scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, point of zero charge analysis and X-ray fluorescence) were utilized to analyse the physicochemical properties and the potential adsorption mechanisms. The results indicated that the adsorption processes of montmorillonite and goethite approached equilibrium within 20 min, while 60 min were required for the adsorption processes of kaolinite and ferrihydrite. The adsorption processes of Pb2+ by the four minerals best fit the pseudo-second order model. The adsorption capacities of the four minerals for Pb2+ followed the order: montmorillonite > goethite > ferrihydrite > kaolinite, and the maximum adsorption capacities were 69.20, 46.95, 34.32 and 18.62 mg g–1, respectively. The stepwise extraction test showed that the adsorption mechanism of Pb2+ was dominated by ion exchange for montmorillonite, precipitation and complexation for goethite and complexation for kaolinite and ferrihydrite.

This paper presents systematic molecular dynamics modelling of Na-montmorillonite subjected to uniaxial compression and unidirectional shearing. An initial 3D model of a single-cell Na-montmorillonite structure is established using the Build Crystal module. The space group is C2/m, and COMPASS force fields are applied. Hydration analysis of Na-montmorillonite has been performed to validate the simulation procedures, where the number of absorbed water molecules varied with respect to the various lattice parameters. A series of uniaxial compression stress σzz and unidirectional shear stress τxy values are applied to the Na-montmorillonite structure. It is shown that the lattice parameter and hydration degree exhibit significant influence on the stress–strain relationship of Na-montmorillonite. The ultimate strain increases with increases in the lattice parameter but decreases in the number of water molecules. For saturated Na-montmorillonite, more water molecules result in a stiffer clay mineral under uniaxial compression and unidirectional shearing.

Clays have been used widely as sorbents of potentially toxic elements, especially Pb. However, their adsorption efficiency has been studied mostly under static experimental conditions, which are labour-intensive. In this study, dynamic adsorption experiments were established using micro-columns to assess the adsorption behaviour of natural Fe-Mg-rich clays for Pb ions by varying the inlet solution pH, Pb concentration and flow rate. The clays, consisting of varying amounts of palygorskite and Fe-smectite, were diluted with quartz (Qz) sand to enhance their permeability. Greater adsorption capacity was observed for the mixed palygorskite/Fe-smectite-rich clay beds (45.2 ± 0.01 mg g–1) followed by the Fe-smectite-rich (35.7 ± 0.07 mg g–1) and palygorskite-rich (20.0 ± 0.03 mg g–1) clay beds. The results indicated that the greater adsorption efficiency of palygorskite/Fe-smectite-rich clays could be attributed to synergistic effects due to the coexistence of palygorskite and Fe-smectite clay phases, which have distinct physicochemical characteristics. Moreover, the results obtained showed good agreement with the static experiments, implying that the use of micro-columns could describe adsorption adequately over shorter experimental times.

The environmental conditions in Maritime Antarctica are more favorable to soil development than in continental areas, which is reflected in the content and type of clay minerals present. In this context, soil clay minerals of Fildes Peninsula, South Shetland Islands were studied with the aim of relating them to periglacial and paraglacial processes as possible indicators of initial pedogenic processes. In this work, textural, mineralogical and crystallochemical characterization of clay minerals as well as chemical and physical soil analyses were carried out. The soil samples represented various surface cover types present on Fildes Peninsula. All samples were composed mainly of clay minerals, plagioclase, quartz and minor zeolites and pyroxene. The clay mineral content was very variable and reached up to 63% w/w. The clay minerals present are mainly smectite, vermiculite, chlorite and minor kaolinite, mica, corrensite and interstratified illite–smectite, with smectite and vermiculite dominating in almost all of the samples. The primary minerals display chemical alteration, and smectite formed by alteration of plagioclase. The clay mineral types were related to the parent material, which was affected by low-grade metamorphism and hydrothermal alteration that transformed biotite and chlorite into vermiculite via interstratified chlorite–vermiculite. Furthermore, this process and/or ongoing surface weathering transformed vermiculite into smectite. The genetic relationship observed between vermiculite and smectite suggests progressive alteration and transformation into a phase with intermediate composition between vermiculite and smectite. Therefore, vermiculite could be at least in part the smectite precursor. Samples closer to the current Collins Glacier front are composed mainly of vermiculite, with the greatest chemical variation occurring where the soils were developed from a mixture of initially glacially transported volcanic rocks through periglacial and fluvial processes. The clay minerals from the centre and south of Fildes Peninsula are mixtures of montmorillonite and vermiculite, as well as of chlorite and corrensite in various proportions. The clay minerals in soils developed on the west coast are a mixture of Fe-rich montmorillonite and vermiculite.

The rare earth element (REE) content of the Tunisian Permian–Neogene shales have been studied to determine the origins of the clay minerals in these shales. The Permian–Neogene series overlies the Palaeozoic basement that has been studied via oil-drilling cores. This study of REEs was performed in various palaeogeographical domains of Tunisia, from the ‘Saharan Platform’ in the south to the ‘Nappes Zone’ in the north. In this work, those levels rich in illite (Palaeozoic, Triassic and Jurassic), smectite (Campanian–Maastrichtian) and palygorskite (continental Eocene) as well as some Miocene levels rich in halloysite are examined. The distribution of REEs in the Tunisian margin sediments is generally homogeneous, except for the Miocene levels containing halloysites. The normalization curves of REEs vs North American shale composite characterize the inherited clays regardless of the dominant minerals, except for a few cases of neoformation. The flat REE curves indicate a detrital origin of the studied clay levels.