Environmental problems caused by human intervention in nature are some of the most critical challenges facing human societies. It is essential to use suitable adsorbents to remove pollutants. The abundance, natural abundance and low cost of fine soil have made it a good candidate for removing environmental pollutants. In this research, removal of safranin dye by natural and acidic-organic-treated fine soil with sulfuric acid and ethanolamine was studied. The characteristics of natural and acidic-organic-treated fine soil were confirmed using X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller and scanning electron microscopy techniques. The adsorbents were placed in contact with different concentrations of safranin dye solution separately. After that, the effects of adsorbent amount (0.4–3.2 g L−1), contact time (0–60 min), adsorbate concentration (5–20 ppm) and pH (3–11) were evaluated regarding the optimum safranin adsorption process. The greatest adsorption capacity of fine soil was calculated as 1250 mg g–1. The experimental results were evaluated using thermodynamic and kinetic models. The data showed that the process follows the Langmuir isotherm model and pseudo-second-order kinetic model. The intraparticle diffusion model estimated the possible mechanism of dye adsorption. Overall, it can be deduced that natural fine soil is an efficient remover of human pollutants.

The antibacterial, antifungal and antioxidant effects of halloysite nanoclay, Cloisite 10A (C10A) and Cloisite 15A (C15A) organonanoclays were examined in this study. The antimicrobial action was assessed using the agar-well method and the disc diffusion method. The free radical-scavenging effects of the clays were determined using the 2,2-diphenyl-1-picrylhydrazyl method. Halloysite showed antimicrobial activity against Pseudomonas aeruginosa, Enterococcus faecalis and Staphylococcus aureus. C10A was effective against both Gram-positive bacteria (S. aureus, Listeria monocytogenes, Bacillus subtilis and E. faecalis) and Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae and P. aeruginosa). Additionally, only C10A was found to have an antimicrobial effect on Candida glabrata of 18 mm amongst the tested clays. C15A showed an antimicrobial effect on S. aureus and K. pneumoniae. It was determined that the antifungal properties of organoclays were higher than those of halloysite. The most effective clay type was determined to be C10A. The positively charged inner surface of the halloysite nanoclay can provide a large area to which negatively charged free radicals can attach. The modified C15A used in this study has two long-chain alkyl groups attached, whereas the modified C10A has a single long-chain alkyl group and a benzyl group attached. It is proposed that the differences in these antimicrobial effects are due to the structures of the molecules. According to these results, organoclays as green source materials could be used as additives and coatings in food processing, biomedical devices, filters and paints due to their antimicrobial and antioxidant properties.

The interface performance between clay–sand mixtures and concrete structures is governed by the mixture's composition and its physical properties. Moisture content and particle-size distribution play important roles in deciding the mixture's arrangement of soil particles, porosity, hydraulic conductivity and behaviour under various mechanical loadings. Application of a polymer interfacial coating can improve the bond performance between soils and concrete mainly via interfacial friction/mechanical interlocking. The present work analyses the development of interfacial strength between clay–sand mixtures and a polymer coating with changes in particle gradation. The multi-scale mechanisms at the interface are investigated, giving primary attention to soil porosity. A 50:50 clay–sand mixture exhibited a greater interfacial adhesive performance compared to other soil mixtures. In addition, the moisture-controlled pores and gradation-controlled pores demonstrated differences in macroscale interfacial strength. Both mercury intrusion porosimetry (MIP) and 129Xe nuclear magnetic resonance (NMR) were utilized to detect the pore structure of the mixtures. 129Xe-NMR revealed the pore distribution of the mixtures as ranging from macropores to nanopores, and MIP complemented the pore information by determining the critical pore entry diameter in the macropore regime. Mesopores dominated with increasing fine sand content until a threshold value was reached; thereafter, merging of pores occurred and macropores dominated.

This study examines the effects of the chemical composition of the clay fraction of various soil horizons on radiation shielding parameters. X-ray fluorescence (XRF) analysis did not reveal significant differences in the concentration of the most abundant oxides (Al2O3, SiO2, Fe2O3) among the various horizons. Consequently, the mass attenuation coefficient did not vary among the horizons in terms of the photon energies studied (15 keV–10 MeV). The mean free path (MFP), half-value layer (HVL) and tenth-value layer (TVL) did not differ for energies up to 100 keV. However, at higher energies, these parameters were mainly influenced by the differences in the densities of the soil horizons. The effective atomic number did not differ across the horizons for the various photon energies, nor did the mass attenuation coefficient. It is shown that slight differences in the chemical composition of the clay fraction of soil horizons do not affect radiation shielding parameters (MFL, HVL, TVL) for low photon energies (<500 keV). Density is more important for radiation shielding than the chemical composition of the various horizons of the same soil type for higher energies (>100 keV); hence, compacting the clay fraction might be more efficient for radiation shielding purposes at higher energies.

Toxic pharmaceutical pollutants, such as nicotine, represent a significant threat to natural water sources due to their continuous discharge. To address this issue, clay minerals and their composites have demonstrated exceptional adsorptive and remedial capabilities for wastewater purification. This research focused on developing green clay-polymeric adsorbents for the efficient removal of pharmaceutical pollutants from industrial wastewater. The synthesis involves creating halloysite nanotube–polythiophene nanocomposites through a green and cost-effective method using vapour polymerization and a solvent-free, ball-milled technique for the adsorptive removal of nicotine from wastewater. The investigation evaluates the impacts of preparation, modification and environmental conditions on the adsorptive performance of these clay-based nanocomposites compared to pure polythiophene. The polymerization process was evaluated by varying the vapour polymerization holding time for a fixed amount of oxidant (FeCl3) and halloysite nanotube (HNT) to investigate the impacts of monomer vapour exposure time on the polymerization of nanocomposites. Following the characterization of the synthesized adsorbents using various methods, the study investigated the impacts of various parameters (e.g. adsorbent dosage, pH and contact time) on the adsorption capabilities of the materials on a laboratory scale. The results revealed that the incorporation of HNT improved the adsorbing performance of nanocomposites. The pH, absorbent concentration and contact time directly affect nicotine adsorption. Significantly, halloysite–polythiophene 3 with a 2 h polymerization duration demonstrated the maximum adsorption efficacy of 78.94% at pH 10 after a 24 h contact time. The environmentally friendly halloysite-based nanocomposite shows promising potential as an effective adsorbent for pharmaceutical pollutant (nicotine) removal from aquatic environments.

The formation of iron-rich phyllosilicates can occur at different natural or engineered settings. In this study, the influence of pH in the hydrothermal synthesis of iron-rich phyllosilicates was investigated in the pH range 8.50–12.10 after the ageing of the precursor. The synthesized samples were characterized by powder X-ray diffraction, Raman and Mössbauer spectroscopies and transmission electron microscopy. Three domains of pH were identified, and these correlated with silica availability and its speciation in the solution. The formation of 1:1-type FeIII/FeII phyllosilicate was observed between pH 9.67 and 10.75. Above pH 10.75, two types of phyllosilicate-like mineral phases were observed. In addition to 1:1-type FeIII/FeII phyllosilicate, 2:1-type FeIII/FeII phyllosilicate was observed. Below pH 9.67, mainly amorphous silica and iron oxides were observed. The findings show that pH governed the crystallinity and nature of the obtained phyllosilicate-like phases.

Montmorillonite (Mnt), belonging to the smectite group and representing a 2:1-type clay mineral with good cation-exchange and swelling capacities, is a common clay component of soils. It was observed that some Mnt preparations exhibit peroxidase-like (P-L) activity using N,N-diethyl-p-phenylenediamine sulfate salt as a substrate. Both native (non-swelling) and swelling Mnt exhibited similar P-L activity. Modification of Mnt with copper and iron influenced both P-L activity and phenol polymerization. Both free and textile-bound Cu-Mnt (Sigma-Aldrich) enabled phenol removal. Soil Mnt P-L activity is probably involved in lignin breakdown and decontamination of soils polluted with phenol-containing molecules.

Lightweight expanded clay aggregates (LWAs) are porous materials with low density and high strength (EN-13055-1), and they are important in sustainable construction through their lightweight nature and ability to provide thermal or acoustic insulation. The objective of this work was therefore to evaluate the preparation of LWAs using a smectite clay (M1 formulation), whose application in common ceramic production is difficult. An alternative approach was proposed for the valorization of phosphate sludge and a palygorskite-rich sediment by mixing them with expanded clay (M2 formulation) for LWA production. This could result in economically cost-effective products with significant environmental benefits. Pellets were prepared and fired at various temperatures (1100°C, 1125°C and 1150°C), and relevant properties such as bloating index, density, water absorption and compressive strength were determined. Additionally, the microstructure, mineralogical transformations and phase compositions under various sintering temperatures were investigated. Increasing the temperature from 1000°C to 1150°C significantly improved the expansion properties of LWAs, and 1150°C seemed to be the optimal firing temperature at which the best expansion properties were achieved. In addition, the incorporation of the selected waste improved the properties of the final products, leading to lower density, greater strength and greater bloating with the development of the internal pore structure as compared to the LWAs without this addition. Because of their low density (0.6 g cm–3) and sufficient compressive strength (0.86 MPa), the manufactured LWAs can be used in construction (as insulating panels or in lightweight concrete) and in green roofs.

This work aims to characterize and study the properties of an Algerian diatomaceous earth (Sig-Mascara) as a catalyst carrier. A commercial product of diatomite was characterized by granulometric analysis, X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis/differential scanning calorimetry and scanning electron microscopy/energy-dispersive X-ray spectroscopy methods. To purify the diatomite and remove the impurities (iron oxides, clay minerals, quartz and organic matters), the <63 μm fraction of the diatomite was separated out. The 15Ni/Ds-700 catalyst has lower SiO2, Al2O3 and CaO contents compared with the original diatomite. The NiO content of the catalyst is 15 wt.%, indicating successful impregnation. According to the nitrogen sorption–desorption results, the specific surface area of the purified diatomite particles (<63 μm) increased from 26.47 to 46.33 m2 g–1 compared to crude diatomite. The 15Ni/Ds-700 catalyst was applied in the dry reforming of methane to obtain synthesis gas (CO and H2). The results showed that the catalyst was relatively stable during catalytic measurements for 6 h, although the conversion rate value was low (12%).

The zeolitic rocks of Akrotiri, on Santorini Island (Aegean Sea, Greece), can be grouped according to the zeolite minerals present. The first group includes zeolitic rocks that contain only clinoptilolite, the second group contains clinoptilolite and mordenite and the third group contains only mordenite. Clinoptilolite accounts for up to 56 wt.% and mordenite for up to 69 wt.% of the rocks. All samples contain feldspars (8–36 wt.%), clay minerals (6–8 wt.%), quartz (3–6 wt.%), opal-CT (2 wt.%), amphibole (2–4 wt.%) and amorphous materials (4–7 wt.%). The studied samples were classified chemically as andesites or dacites. The ammonium-exchange capacity of the studied samples was 104–158 meq 100 g–1. According to Commission Implementing Regulation (EU) No. 651/2013, zeolitic rocks that contain ≥80 wt.% clinoptilolite, ≤20 wt.% clay minerals and are free of fibrous minerals and quartz can be used as feed additives in animal husbandry. Zeolites with fibrous habit (mordenite, erionite, secondarily roggianite and mazzite) and SiO2 minerals such as quartz, cristobalite and tridymite can be dangerous to both humans and animals. The mineralogical study showed that, due to their low clinoptilolite content and the presence of both quartz and fibrous mordenite, the studied zeolitic rocks do not conform with European Regulation No. 651/2013. As a result, their use as feed additives and nutrition supplements is prohibited.

Clay minerals are effective adsorbents for the remediation of pesticides in wastewater due to their large superficial areas and excellent cation-exchange capabilities. However, this adsorption effect can be reduced by the accumulation of adsorbents on clay minerals, amongst other problems. Therefore, in this study, montmorillonite (Mnt) modified by layered double hydroxide (LDH) with different loading amounts was successfully prepared using an in situ method. The results from X-ray diffraction, Fourier-transform infrared spectrometry, Brunauer–Emmet–Teller (BET) and scanning electron microscopy analyses revealed that LDH structures were successfully combined with the Mnt layer and formed a porous structure. However, excess LDH still caused the aggregation and accumulation of layers. The adsorption performance of LDH@Mnt for atrazine (ATZ) and paraquat (PQ) was investigated, and the removal efficiency of the LDH@Mnt composite was higher than those of Mnt and LDH alone. The kinetic study revealed that the adsorption process fitted the pseudo-second-order model and internal diffusion model, and 3-LDH@Mnt had the greatest absorbability efficiency for both ATZ and PQ, indicating the adsorption process was controlled by the number of active sites of the adsorbent. The generalized Langmuir model accurately characterized the adsorption process of ATZ and PQ elimination in the adsorption isotherm investigation, indicating that the adsorption energies of the active sites on the adsorbents were different. 3-LDH@Mnt had better absorbability performance for ATZ/PQ, and the sorption capacities were 7.03 and 91.9 mg g–1, respectively. According to site energy distribution theory, the amount of sorption sites of the composite adsorbent was large and the average adsorption energy was high, both of which being beneficial for the adsorption of ATZ and PQ. The effects of pH, coexisting anions and reuse experiments were also tested, indicating that the LDH@Mnt composite possessed high adsorption stability. This excellent removal performance represents a promising strategy for the remediation and elimination of pesticide contaminations from the environment.

In the present study, a comparison of the thermal-insulation and mechanical performances of cement and heat-stabilized compressed earthen blocks (CEBs) was carried out to determine the factors which influence those properties. The raw clays used consist mainly of kaolinite, orthoclase and quartz. The mechanical strength increased with increase in both the amount of cement added and the firing temperature. However, the responses are better for cement-stabilized CEBs. The thermal insulation of fired bricks is greater than that of cement-stabilized bricks. This difference was related to the decrease in porosity and the formation of continuous-surface. The decrease in thermal insulation is mainly related to the formation of continuous-surface in cement-stabilized CEBs, whereas in the fired CEBs, it is due to the modification of pore volume. The mineralogy of the raw clays is statistically correlated to porosity and continuous-surface development that were confirmed as the main factors in the modification of both the mechanical strength and the thermal insulation. In cement-stabilization, the decrease in insulation is due to the development of continuous surface, while for heat-stabilization, mineral transformations during the sintering reduced continuous-surface formation and the insulation was controlled by both radiation and reduced surface conduction. The influence of the mineralogy of the raw material shows that clay content favours the insulation in fired bricks obtained at T ≤ 1000°C, while sand contents favour densification. In contrast, clay contents reduce the mechanical response of cement-stabilized material due to limited cement–clay interactions. In general, the mechanical response is more favourable in cement stabilization, while thermal insulation is better in fired bricks.

The rheological properties of three Na-activated, trioctahedral Mg-bentonites (hectorite clay from the CMS Source Clay Project repository, saponite clay from Spain and stevensite clay from Rhassoul, Morocco) and a sepiolite clay from Greece were examined after dynamic ageing at temperatures up to 230°C. The 5% w/v suspensions were prepared by dispersing the clay mineral samples in distilled water. The suspensions underwent dynamic, thermal ageing for 16 h before determination of the viscosity, filtration loss, filter cake thickness and pH and the concentration of dissolved Na+ and Mg2+. Thermal ageing contributed to the dispersion of clay particles, with a direct effect on plastic and apparent viscosity, introducing pseudoplastic behaviour. With the exception of the stevensite clay at 230°C that displayed limited dissolution at 230°C and partial conversion to kerolite, the clays were stable at high temperatures. The Na-activation of all clays except for stevensite was not adversely affected by thermal ageing. Thermal ageing of stevensite at 230°C facilitated Na exchange and yielded suspension with high viscosity and low filtrate loss. Only the suspensions of hectorite and those of stevensite aged at 230°C met with American Petroleum Institute specifications. The thermal behaviour and rheological properties of the clays might be interpreted according to the intrinsic properties of the clay minerals, such as layer charge and charge distribution.

In this study, the effects of two different ammonium-exchange methods to improve the ammonia (NH3) gas adsorption of raw clinoptilolite (CLN) from Gördes (Türkiye) was investigated. The first method involved direct modification of CLN by 0.5 or 1.0 M NH4NO3 solutions at 80°C for 4 and 8 h followed by calcination. In the second method, CLN was converted to the Na+ form prior to modification with ammonium nitrate and calcination under the same conditions. Both methods yielded H+ forms of CLN through the removal of exchangeable cations without damaging the crystal structure. Ammonia adsorption isotherms were determined at 298 K for a total of eight different H+ forms synthetized using both methods. The Na-1.0-8h CLN sample with the highest NH3 adsorption capacity obtained using the second method was selected as the parent CLN. In addition, to determine the effects of doping different cations into the structure on the NH3 adsorption properties of the selected parent CLN sample, cation-exchange processes were carried out using 0.5 and 1.0 M NaNO3, KNO3, Ca(NO3)2 and Mg(NO3)2 solutions at 80°C for 4 h. The raw and modified CLNs were characterized using X-ray diffraction, X-ray fluorescence, scanning electron microscopy and N2 adsorption analyses. Cation-exchanged samples with a wide range of NH3 adsorption capacities (3.61–4.93 mmol g–1) were compared with other zeolites from the literature.

This study examines the origin and distribution of clay minerals of the pedological horizons of Kori Ouallam watershed (south-western Niger). It is based on field sampling campaigns and a series of laboratory analyses. A total of 49 samples were analysed, 28 from surface horizons (0–10 cm depth) and 21 from pedological profiles (0–1 m depth). The samples were analysed by X-ray diffraction on bulk and clay (<2 μm) fractions, X-ray fluorescence spectrometry, laser granulometry, organic matter and calcium carbonate content, macroscopic observations (binocular loupe) and scanning electron microscopy equipped with an energy-dispersive spectrometry system. The pedological horizons are characterized by low organic matter contents (<1%) and no calcium carbonate. The particle-size distribution shows net textural differentiation, with a predominance of sandy loam to sandy clay loam textures in the upper horizons and clay loam to clay in the deep horizons. The main major oxides were SiO2 (46.3–89.0%), Al2O3 (5.0–24.2%) and Fe2O3 (1.0–27.9%). Kaolinite (64–98%) is the predominant clay mineral at all horizons, associated with low to moderate proportions of illite (1–34%) and traces of chlorite. Kaolinite is essentially inherited from the parent rock, whereas illite results from chemical alteration by bisialitization of the primary minerals initially rich in potassium feldspar contained in the parent rock. However, soil texture and organic matter vary independently with clay mineralogy. An extended study of all of the pedological facies that make up south-western Niger, combined with supplementary analyses, would further improve our understanding of clay mineralogy in the Sahelian zone.

Natural sepiolite has great potential for application in wound healing, haemostasis and medicines. This paper introduces a versatile solid-state sintering technique for preparing sepiolite-based nanocomposites with enhanced antibacterial properties, and the physical, structural, rheological and antibacterial properties of which were determined to be enhanced. The incorporation of nanosized Ag and metal oxides into sepiolite composites results in a notable improvement in their antibacterial efficacy against Escherichia coli and Staphylococcus aureus in comparison to the unmodified sepiolite. With a low silver content of just 5%, the sepiolite–Ag composite achieves an antibacterial rate of ~100%. Furthermore, the rheological properties exhibited by the sepiolite composites are noteworthy, suggesting their suitability for use in wound-dressing applications due to their exceptional workability. The methodology employed in this research has the potential to offer a viable substitute for the production of economical and effective natural antibacterial nanocomposites.

The objective of this research was to study the cellulose addition effect on the geopolymerization of heated clay. The clay, composed of illite, plagioclase and kaolinite, was heated at 700°C for 2 h and mixed with cellulose (up to 10 mass%). The mixtures were NaOH-activated, and shaped samples were aged at 83°C for 30 days. The cured samples were investigated by using X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. The influence of the cellulose addition on the mechanical/physical properties was also evaluated. The results showed that zeolite ZK-14, hydrosodalite, sodium carbonate and a geopolymer composed of poly(sialate) units were formed in all cured samples. The relative amounts of zeolite and metakaolin evolved antagonistically, whereas that of illite slightly decreased with increasing cellulose content. Metakaolin and illite were involved in the geopolymerization process. Cellulose addition led to the improvement of the flexural strength of the samples and to porosity reduction. By contrast, water absorption was increased. The positive effect of cellulose on sample performance is explained on the basis of hydrogen bonding between the functional moieties of cellulose and the active sites of sample constituents, namely zeolites, metakaolin, illite and the geopolymer. As a filler, zeolite probably contributed to sample strengthening, and the detrimental impact of Na-carbonate was insignificant. Based on the results obtained, the composites could be used as binders for brick manufacturing or as lightweight mortars.

Polymer-based composites modified with organoclay are economically beneficial candidates for a variety of applications. Different types of impurities accompany montmorillonite phases in various bentonites, which impact the quality and cost of organoclays and final composites. To obtain organoclays for clay composite applications, eight Iranian raw bentonites from different geographical locations were selected as the candidates and characterized by X-ray diffraction (XRD). Sample IB was chosen due to its high purity and lower cristobalite content than the other samples. It was purified by centrifugation or sedimentation methods using a sodium hexametaphosphate (NaHMP) dispersant. The cation-exchange capacity (CEC) was measured for bentonite before and after purification by sedimentation, and it showed a significant increase from 6.944 to 12.128 eq g–1, confirming successful purification. Organoclays were prepared using purified bentonite (sedimentation method) with two surfactants (cetyltrimethylammonium bromide and octadecylamine), and the amount of octadecylamine was optimized. Purified bentonite and organoclay were characterized by XRD, scanning electron microscopy (SEM) and X-ray fluorescence. The results indicate that most of the impurities were removed after purification, and the interlayer space of organoclays increased to 35 Å in the optimized sample prepared with an amount of octadecylamine that was twice the CEC in purified bentonite. The prepared organoclay was used to improve low-density polyethylene (LDPE) polymer properties. The clay–polymer composite properties were studied by field emission SEM, thermogravimetric analysis and tensile strength tests. The organoclay was fully dispersed in the LDPE matrix and in the sample with 5 wt.% of organoclay, where Ti (the temperature at which 10% of the sample is decomposed) and T50% (the midpoint of degradation) were 17°C and 13°C greater than those of polyethylene, respectively. Additionally, the sample residue with 5 wt.% of organoclay at 600°C was 43.4%. The tensile strength of polyethylene increased from 8.67 to 9.03 MPa in the sample with 4 wt.% of organoclay.

In sediments, clay minerals are mainly detrital. Formed by continental weathering, they are carried by surface transport predominantly by rivers, glaciers and, to a lesser extent, winds to the adjacent sedimentary basins and then are redistributed by oceanic currents. In a sedimentary core, the variability in the clay mineral assemblages reflects either variable physical and chemical weathering conditions in the watershed, typically with a significant link to climatic conditions, or changes in the mineral source, the latter being associated with various transport agents. When different sources are involved, a combination of mineralogical and geochemical proxies allows us to trace the detrital provenance, but they also indirectly provide valuable information on transport pathways and palaeocurrents. This manuscript reviews several examples from the literature and ongoing research on clay mineral variability in marine or lacustrine sedimentary records and interprets them in terms of: (1) climate control at different timescales, from the Neogene to the Quaternary; and (2) transport paths. Examples are selected to review the various clay-derived proxies in existence.