Red clay is considered to be of significant value to the economy in Morocco, particularly in the Safi region, because of its abundance. This raw material has long been known for its quality in the manufacture of clay materials, but its use was limited to traditional ceramics. The red clay raw material was the subject of the current study with the objective of opening new industrial applications that will give added value to the Safi red clay. The physicochemical, mineralogical, and thermal properties of the Moroccan red clay were determined by X-ray fluorescence (XRF), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis, X-ray diffraction (XRD), oriented aggregate, and particle-size analyses, powder density by helium pycnometry, carbonate content using the Bernard method, differential thermal analysis (TG–DTA), and the BET surface area. The compacted dry powder particles were calcined at three sintering temperatures: 900, 1000, and 1100°C for 2 h. The effect of sintering temperature on ceramic properties, such as apparent porosity, water adsorption, bulk density, and mechanical strength, was examined. Dense ceramics with lower porosity and greater mechanical resistance (~300%) were produced by increasing the sintering temperature from 900 to 1100°C. The conclusion was that the evolution of physicochemical and thermal properties is related to mineralogical changes, which show that anorthite is the major phase at higher temperatures.

The levels of CO2 emissions generated by the cement industry and the growth in demand for its products have led to a search for ways to reduce these emissions. The use of supplementary cementitious materials has become one of the solutions proposed for this problem. Illite, which is found all over the world, is a possible supplementary cementitious material. Before illite can be used, it must be milled and treated thermally in order to activate it, so that the alkalis (Na+ and K+) are free and available to react. Alkalis in cement participate in deleterious reactions (alkali-silica reaction) or have a beneficial effect (alkaline activation). The alkalis present in the rocks can play an active role in these phenomena, however. In addition, the material could be influenced by the alkaline environment produced by the cement. The current study was aimed at analyzing whether an alkali release occurs and if so, how it is affected when a milled and thermally treated illitic rock is in contact with water or an alkaline solution. The material was characterized by X-ray fluorescence, polarizing microscopy, and X-ray diffraction (XRD). The sample was treated thermally at 300, 600, and 900°C, and the thermal activation was evaluated through XRD, density, and Atterberg limits. The evolution of alkali release was studied by determining the sodium and potassium concentration of contact water obtained by mixing the samples with different pH solutions for various lengths of time. In addition, the calcium concentration was determined. The concentrations of sodium and potassium in the contact water were determined by flame photometry, and of calcium by EDTA (ethylenediaminetetraacetic acid) titration. The results showed that with increasing age, increasing solution pH, and higher treatment temperatures, alkali release occurred and increased, whereas Ca2+ concentration decreased.

The Bursa-Orhaneli and Keles-Harmanalan coal deposits were developed in swampy and fluvial-lacustrine environments in western Anatolia under the E–W-trending graben zone during the Neogene. The present study aimed to determine the mineralogical and geochemical properties of clays interlayering the coal seams to define the origin of clay minerals, in particular, smectite. These deposits, comprising argillaceous sediment, marl, coal seam, mudstone, organic-rich shale, and sandstone, were deposited in a lacustrine environment accompanied by volcanogenic materials. The characteristics of sediments and their parent rocks were examined using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, palynology, and chemical analyses. The association of abundant smectite with quartz, amphibole, accessory chlorite, and a decrease in feldspar in fluvial-lacustrine sediments compared to those in the smectite accompanied by feldspar and volcanic glass and the absence of quartz and amphibole in the pyroclastic units suggest that smectite had detrital and authigenic origins. Flaky smectite shows either detrital, irregularly outlined coating and filling pores of terrigenous sediments or in situ precipitation edging resorbed feldspar and devitrified volcanic glass. Chemical analyses of the smectite-rich fraction show montmorillonite compositions with an average structural formula of: (Ca0.42Na0.25K0.08)(Al2.76Fe0.47Mg0.59Ti0.07Mn0.002)(Si7.65Al0.35)O20(OH)4.

The positive correlation of Al2O3 vs. TiO2 and K2O vs. Rb may be related to the abundant detrital input. Feldspar and biotite were replaced by illite during diagenesis.

An increase in the Ni/Co and V/(V + Ni) ratios in the altered units also suggest oxic, suboxic to anoxic conditions, under the control of a dry, warm to subtropical climate in fresh water and lakes during the Late Eocene to Middle Miocene. The slight enrichment of light rare earth elements (LREE) compared to heavy rare earth elements (HREE) with positive Eu and positive/negative Ce anomalies reflect fractional crystallization of feldspar. The δ18O and δD values of smectite and illite fractions and the wide range of δ34S isotope values (–1.5 to 15‰) for pyrite and chalcopyrite associated with coal indicate a signature of both diagenetic and partial hydrothermal origin.

Researchers have long been committed to developing alternative, low-cost nanomaterials that have comparable capacity to carbon nanotubes. Halloysite nanotubes (HNTs) are naturally hollow, multi-walled, tubular structures that have high porosity, enlarged volumes and surface areas, and hydroxyl groups ready for modification. In addition, HNTs are non-toxic, biocompatible, inexpensive, abundant in nature, and easy to obtain. Magnetic nanocomposites have aroused widespread attention for their diverse potential applications in analytical fields and so magnetic halloysite nanotubes (MHNTs) have emerged as outstanding magnetic nano-adsorbent materials. Owing to their superparamagnetism, selective adsorption ability, and easy separation and surface modification, these captivating nanomaterials excel at extracting and enriching various analytes from environmental, biological, and food samples. The current review article gives an insight into recent advances in the design, functionalization, characterization, and application of MHNTs as magnetic, solid-phase extraction sorbents for separation of antibiotics, pesticides, proteins, carcinogens such as polycyclic aromatic hydrocarbons (PAHs), dyes, radioactive ions, and heavy-metal ions in complex matrices.

The state of iron in coal gangue minerals is an important factor in determining the potential for value-added utilization of this solid waste; this is especially true for the coal gangue coming from the Pingshuo open-pit mine in China. The objective of the present study was to characterize the petrological, mineralogical, and chemical states of Fe in the coal gangue from the Carboniferous Taiyuan Formation. Methods used included polarizing microscopy, X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS), X-ray fluorescence, micro-Fourier-transform infrared (micro-FTIR) spectroscopy, and Mössbauer spectroscopy. The coal gangues are mudstones, silty mudstones, and pelitic siltstones, which are composed primarily of kaolinite, quartz, feldspar, pyrite, illite, and magnesite. In coal gangue, the Fe was found to occur in ferruginous minerals, in crystal-lattice substitutions, or in a colloidal state. The ferruginous minerals in the coal gangue are pyrite and marcasite, and the pyrite morphologies are framboidal, euhedral octahedral crystals, subhedral granular crystals, and irregular crystals. The results of SEM–EDS and micro-FTIR confirmed that the lattice substitution of Fe in the coal gangue minerals occurred mainly in kaolinite, resulting in two types of kaolinite: iron-containing and iron-free kaolinite. The former may be transformed from volcanic biotite and the latter from volcanic feldspar. The Mössbauer spectra of kaolinite showed intense doublets with isomer shift and quadrupole splitting values consistent with tetrahedrally coordinated Fe3+ and ocahedrally coordinated Fe2+, suggesting the presence of two types of substitution sites: (1) Fe2+ replacing Al3+ in the octahedral sheet; and (2) Fe3+ replacing Si4+ in the tetrahedral sheet. This study has important theoretical significance for the high-value utilization of coal gangue.

The supply of Corumbataí Formation rocks, which occur widely in the State of São Paulo, Brazil, and are used by Santa Gertrudes Ceramic Cluster, is dwindling and prospecting for new deposits is essential. The current study aimed to map and characterize new reserves of ceramic raw materials which would guarantee mineral and economic sustainability of the important concentration of ceramic-processing capability in that area, and thereby contribute to improving and diversifying the range of products manufactured and to promoting a greater presence in the international market. To achieve the proposed objectives, 16 profiles were sampled and the samples were submitted to granulometric analysis by laser diffraction, and the major elements by inductively coupled plasma-mass spectrometry, and the mineralogical compositions of clay samples were determined by X-ray diffraction and ceramic properties. Six lithofacies were identified and grouped into two facies associations: a lower shoreface association comprising massive siltstone (Sm) and laminated siltstone (Sl); lithofacies, and an upper shoreface association comprising heterolithic sandstone (Sh), lenticular sandstone (Sle), intercalated sandstone/siltstone (Si), and altered siltstone (Sa) lithofacies. The lithofacies of the lower shoreface association were more clayey, flux with a significant presence of illite and microcline, and a more uniform granulometry distribution, which made its classification possible, technologically, as stoneware and semi stoneware. The main application of this material is in the production of coatings through the wet milling process. The lithofacies of the upper shoreface association was sandier, had a refractory presence with kaolinite and montmorillonite, and had a less uniform granulometric distribution; technologically, it can be characterized as porous and semi-porous. The main application of this material is in the production of coatings by the dry milling process. The results obtained by facies analysis combined with the geochemical and ceramic properties of the Corumbataí Formation rocks revealed both vertical and lateral variations of the lithofacies, which influence their properties, behavior, and application as ceramic raw materials.

Smectites are effective binders of aflatoxin in aqueous solutions. Unfortunately, their efficacy is reduced in guts because of interference by biomolecules and essential nutrients within the gut. Tunnel structures in palygorskite and sepiolite may function as molecular sieves and may, therefore, serve as alternatives or complements to smectites in binding aflatoxins but not larger biological compounds. The objective of the current work was to determine the effect of heat treatment on aflatoxin B1 (AfB1) adsorption and selectivity for biomolecules by two palygorskites (Plg_PK and Plg_CN), sepiolite (Sep), and a palygorskite-smectite mixture (Plg-Sm) in comparison with a smectite (Sm-37GR). The clays were heated at 250, 400, 500, and 600°C while phase and structural changes were characterized by X-ray diffraction and infrared spectroscopy. Comparative AfB1 adsorption was determined in aqueous and in simulated gastric fluids. The clay structures collapsed irreversibly in Sm-37GR and folded in fibrous clays with heating at 400°C or more. Sm-37GR adsorbed more AfB1 than all of the other clays; the estimated adsorption capacity followed the trend Sm-37GR (44 g kg–1) > Plg_PK (18.12 g kg–1) > Sep (12.7 g kg–1) > Plg_CN (11.4 g kg–1) > Plg-Sm (9.0 g kg–1). This trend appeared to be correlated with the abundance of smectite in the clays. Sepiolite had greater binding strength for AfB1 than the other clays. With intact clay structures, heating induced a negligible effect on AfB1 adsorption by the fibrous clays while in Sm-37GR and Plg-Sm, adsorption increased with heating at 250°C. Tunnel folding and structural collapse that had occurred at 400°C caused an abrupt decline in AfB1 adsorption irrespective of the clay type. The sepiolite clay adsorbed the least pepsin (370 g kg–1) while smectite adsorbed the most (1430 g kg–1). Consequently, in the simulated gastric fluid, adsorption declined by 25–30% in sepiolite, 52–60% in smectite, and remained unaffected in the palygorskites. Aflatoxin B1 adsorption probably occurred through H-bonding at the surface with the silanol group in palygorskite and sepiolite. No evidence that AfB1 molecules occupied the tunnels of the natural or heated palygorskite or sepiolite was observed in the present study. Palygorskite and sepiolite had a much smaller adsorption capacity for AfB1 than the smectite but also adsorbed less pepsin; therefore, both may be effective aflatoxin binders in gastrointestinal systems.

Hydrothermal solutions related to magmatic intrusions that occurred during the Oligo-Miocene resulted in advanced multi-stage alterations and, to varying degrees, kaolinization over a wide area of the Biga Peninsula. The most important formations in these kaolin deposits occurred along the NE–SW-trending Çan-Etili-Bayramiç fault zone. The Bahadırlı, Duman, and Çaltıkara quarries are well preserved kaolin deposits throughout these fault zones located within the Çan Volcanics. Mineralogical, geochemical, and isotopic analyses were performed to identify the environments of formation of kaolins and the origin of the hydrothermal solution that led to the formation of these deposits.

The mineralogical assemblages of each of the quarries differ from each other. The Bahadırlı kaolin quarry comprises kaolinite + alunite ± quartz ± smectite ± plagioclase ± K-feldspar. The Çaltıkara kaolin deposits consist of kaolinite + quartz + alunite ± iron-oxide and ore minerals. The Duman kaolin quarry was considered in two different slopes as a hanging wall block and a footwall block, and the blocks contain kaolinite + quartz + plagioclase ± smectite and kaolinite ± alunite ± smectite ± quartz ± plagioclase ± K-Feldspar ± gypsum, respectively. During petrographic investigations, it was observed that kaolinization occurred generally in K-feldspar and plagioclase phenocrysts and partially in the matrix. Mineralogical and micromorphological investigations revealed that the kaolin group includes the dioctahedral minerals kaolinite and halloysite. According to the trace element contents of the kaolinites, the Çaltıkara and Bahadırlı deposits had a hypogene origin, while the Duman deposit had a supergene origin. δ18O isotopic values of kaolinites ranged from +10.3 to +18.3‰. δ34S isotopic values ranged from –17.2 to +20.2‰ of alunite, galena, and pyrite minerals, which indicate different formation environments for the kaolin quarries. 40Ar/39Ar dating of alunite revealed that the timing of acid-sulfate alteration was compatible with the magmatic intrusions. All these data revealed the mineralogical, chemical, and isotopic differences caused by the effect of different hydrothermal processes in three kaolin deposits located on the same fault zone, close to each other and similar in age.

Clays are abundant materials in the Amazon region and have been used historically by ancient Amazonian people to produce ceramic and cosmetics products. The current study aimed to evaluate the potential of four clays from the metropolitan area of Manaus, each with a different color, for cosmetics applications. Two clays were collected in the Ponta Negra region (red and gray in color) in Manaus, one in Careiro (white), and one in Itacoatiara (black). After drying in an oven for 24 h at 105°C, the four clays were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetry (TGA), differential thermal analysis (DTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle-size analysis, and detection of microorganisms. The amounts of Al, Si, Cl, K, Ca, Ti, Cr, Fe, Zn, P, and S in all samples were below the limits for use in cosmetics. The main phases identified were kaolinite 1A, quartz, gibbsite, and the rare kaolinite 2M. Approximately 40 wt.% of each sample was in the < 20 μm particle-size range. Analyses by SEM revealed pseudo-hexagonal kaolinite structures with nano-islands and nanocrystallites. The low toxicity, mineralogic compositions, and particle-size findings suggest that Amazonian clays are promising for cosmetics applications.

Many kaolinites are known to exhibit limited intercalation capacity which affects their usage. Some reports have linked this lack of reactivity to particular structural features or to slow kinetics; others recommended increasing intercalation temperature as a remedy. The purpose of the current study was to investigate systematically the N-methylformamide (NMF) intercalation capacity of three kaolinites differing in layer stacking order (KGa-1b, KGa-2, and Imerys Hywite Alum) in the 5–150°C temperature range. Near-infrared spectroscopy (NIR) was employed to record the full kinetics of intercalation in closed systems with excess NMF. Increasing intercalation temperature accelerated the reaction, but the NMF uptake decreased and eventually vanished. Complementary thermogravimetric analysis (TGA) confirmed this unexpected trend. All kaolinites exhibited the same behavior, but the amount of inert material was in the order of their stacking-fault concentration at all temperatures: KGa-2 > Hywite > KGa-1b. Subjecting the samples to stepwise temperature changes showed that, once intercalated, the NMF could not deintercalate and was removed from equilibrium with the surrounding fluid. Thus, intercalation capacity was not a unique feature of the material because it depended on thermal history. As stacking order and thermal history had no detectable effect on the NMF-hosting environment, the unusual temperature dependence was attributed tentatively to the adverse effect of temperature on the adsorption of NMF on the edges of the crystallites, which is a prerequisite for intercalation.