Marine clay mineral authigenesis, referred to as reverse (silicate) weathering, is one of the first-order controls on seawater pH through the generation of acidity and thus plays a significant role in controlling carbon cycling between marine sediments, oceans and the atmosphere over geological timescales. Reverse weathering is mainly regulated by the rates of silicate and carbonate weathering on the continents, the reactivity of detritus supplied to the oceans and the rates of seafloor weathering. These processes provide essential dissolved components (e.g. K+, Mg2+, Ca2+, Si(OH)4, Al3+, Fe2+/3+) to the marine porewater inventory that cause authigenic clay minerals, such as odinite, glauconite, celadonite and greenalite, to form close to the sediment–seawater interface. Such clay mineral reactions impact the sedimentary cycling versus sequestration of chemical elements, importantly Si, Fe, Mg and K, and consequently contribute to the fluctuations in climate and seawater composition recorded in marine archives over geological time. This review explores the links between reverse silicate weathering and the climate system across geological timescales and provides estimates of the elemental uptake fluxes associated with modern-day clay mineral authigenesis. Novel isotope proxies (e.g. δ41K and δ30Si) and promising new dating techniques (e.g. in situ Rb/Sr geochronology) provide improved constraints on the timing, kinetics and environmental significance of clay mineral reactions on the ocean floor. We also consider recent geoengineering developments linked to reverse weathering reactions, such as ongoing attempts to reduce atmospheric CO2 concentrations via marine alkalinity enhancement and the application of marine clay mineral-based slow-release fertilizers to soils to optimize nutrient availability.

The present study documents coastal processes of movement and subsidence that affect the clayey sediments of the exposed mudflats (‘mudflat sediments’) on the receding western shore of the Deep Dead Sea (‘western Dead Sea shore’) and the formation of subsidence features: subsidence strips and clustered sinkholes. The properties of the clayey sediments that promote movement and subsidence and the development of the subsidence features in the exposed mudflats are the unconsolidated fine-particle texture composed of clay and carbonate minerals, their being dry near the surface and wet at the subsurface, their soaking with saline water and brine and the abundance of smectitic clays saturated with sodium and magnesium. Field observations indicate that narrow subsidence strips with/without clustered sinkholes were developed by movement and subsidence in mudflat sediments via lateral spreading. Wide subsidence strips with clustered sinkholes were developed via increased subsidence in mudflat sediments due to the progress of dissolution within a subsurface rock–salt unit. The emergence of sinkholes occurs via subsidence of mudflat sediments into subsurface cavities resulting from dissolution within a subsidence rock–salt unit. The coastal processes on the receding Dead Sea shore and the formation of the subsidence features are part of the adjustment of the Dead Sea periphery to the lowering of the base level. A contribution of slow mass movement seaward to the coastal processes on the receding Dead Sea shore is indicated.

This study investigates two clayey facies from the Bomkoul area in the littoral region of Cameroon for their suitability as fired clay building products. The field study consisted of a geological survey and a geotechnical mission (G0). Assessment of the raw clayey materials included their mineralogy, particle size, determination of Atterberg limits, density and shear stress. Firing properties (shrinkage, water absorption and flexural strength) at 900−1100°C were also determined. The two main facies observed in the field are the mottled red/yellow grey clays from surface ‘A’ with a thickness of 2.0–2.5 m and the deep blackish fossiliferous schisteous grey clays ‘B’ with a thickness of 8−10 m. Estimation based on boreholes revealed a minimum of 1,400,000 tons of clayey materials. These reserves will supply a small brick-manufacturing unit for a minimum period of 25 years at an extraction rate of 50,000 tons per year. The main clay minerals of both samples are kaolinite (35% and 49%) and illite (1–11%). Both samples contain quartz (47% and 49%) as non-clay minerals, associated with a small amount of anatase (0.5–2.6%) and trace hematite (<1%). The major oxides are SiO2 (71–76%) and Al2O3 (14%). The raw clayey material ‘A’ was finer and more plastic than the ‘B’ facies. The technological properties of the fired bricks obtained from the ‘A’ facies showed greater potential than the ‘B’ facies in terms of sonority and flexural strength. A mixture made of 40% ‘A’ and 60% ‘B’ yielded satisfactory brick properties at 1050°C.

This study aims to synthesize nano-metakaolin (NMK) through mechanical activation and to investigate the physical, chemical and microstructural changes that occur to the initial raw material. The efficiency of the activation process is affected by various process parameters as well as the mineralogy of the original material. Two different kaolin qualities were subjected to mechanical activation through high-energy ball-milling (HEBM) under various conditions. The parameters investigated were the milling speed and time. The final properties of the NMK samples produced were examined using X-ray diffraction, Fourier-transform infrared spectroscopy, laser dynamic light scattering, thermogravimetry/differential thermal analysis, Brunauer–Emmett–Teller and scanning electron microscopy analysis. Additionally, the pozzolanic activity of the fully activated samples was evaluated using the Chapelle test. The percentage of impurities contained in the initial kaolin affected the transformation into metakaolin. The milling parameters also affected the activation, contributing mainly to the particle size of the final material. Finally, concerning the metakaolin microstructure, the material showed a tendency to form stacks and agglomerates of plates due to the development of powerful static forces.

Laterite could play a crucial role in soil stabilization and environmental remediation, but its internal particle interaction mechanism remains unclear. This study, based on molecular dynamics simulations, used umbrella sampling methods to measure the interaction strength between amorphous alumina and montmorillonite particles in laterite. The mechanisms were explored using differential charge density analysis and bond energy analysis. The results show that the interaction process between alumina and montmorillonite exhibited initial repulsion, then attraction, followed again by repulsion. Calcium ion-induced polarization, the negative charge on the alumina surface and the bonding strength during adsorption played key roles in this interaction. Notably, the bond energy measurement results in this study are consistent with data from other related research, validating the data’s accuracy. These findings improve our understanding of the microscopic mechanisms of laterite particle interactions, providing a scientific basis for its application in soil stabilization and environmental remediation.

Swelling soils, particularly those rich in smectite, present significant challenges to civil engineering due to their shrinking–swelling behaviour. Lime stabilization is a commonly used practice to address this, but the reactivity of smectite minerals in an alkaline limestone environment differs widely. This study investigates the reactivity of two Moroccan smectite-rich clays – montmorillonite-dominated bentonite and stevensite/saponite-rich bentonite – when treated with aerial lime. Through mineralogical, microstructural and mechanical analyses, this study highlights the distinct behaviour of montmorillonite, which reacts with lime to form calcium silicate hydrate gels, compared to the inert response of stevensite/saponite. Despite its low pozzolanic activity, stevensite-bentonite demonstrates greater mechanical strength, reaching 2.5 MPa in the S3 mixture (90% stevensite-bentonite and 10% lime). This strength is attributed to the formation of calcite through the de-dolomitization of dolomite. The findings reveal different stabilization mechanisms between dioctahedral and trioctahedral smectites, offering new insights for soil stabilization strategies involving these smectite types.

Tri-octahedral clay minerals have the potential to be used as CO2 sorbents at intermediate temperatures (200–400°C) owing to their thermal stability in this temperature range. In this study, Laponite RD®, a commercially synthesized hectorite (with Na+ as the exchangeable cation) was used to investigate its capacity of CO2 adsorption at 200°C and ambient pressure. Various cations such as Co2+, Ni2+, Mg2+ and Ca2+ were employed to exchange Na+, with the aim being to study their effects on the capacity for adsorbing CO2. The commercial sample showed an adsorption capacity of 144 µmolCO2 g–1. Most of the other exchanged samples displayed a lower quantity of CO2 adsorbed. An exception was the Ca2+-saturated sample, which exhibited a better performance (163 µmolCO2 g–1) compared with Laponite RD®. Thus, with its greater affinity towards CO2, such a sample could be a good candidate for CO2 capture. For all of the samples, most of the CO2 was desorbed, and the formation of carbonate bonds was not observed using Fourier-transform infrared spectroscopy, suggesting that the CO2 was mainly physisorbed.

Peloids are natural therapeutic muds or clays used in balneotherapy and other health treatments. The aim of this study is to prepare and qualify three artificial peloids by maturation for 360 days of some Tunisian smectitic clays with a naturally chlorinated sodic mineral water from a spring in Korbous, Tunisia. This was done to improve our understanding of the behaviour of these clays and the physicochemical changes that affect the clays during maturation, with the purpose of providing suitable raw materials as a solid phase for peloid preparation. The results showed that parameters such as mineralogy, geochemistry, granulometry, cation-exchange capacity, consistency parameters (Atterberg limits and plasticity index), specific surface area, cooling kinetics and pH are all affected by the geochemistry of the thermal water used during maturation. Mineralogical modifications mostly concern the clay minerals’ contents, particularly smectite, and subordinately the dissolution of gypsum and the neoformation of halite. The observed improvements to the plasticity index and cooling kinetics can be explained by the ability of water molecules, and especially cations, to diffuse into the clay particles. The main exchangeable cations are Na+ and Ca2+, along with Mg2+ and K+, which promote swelling and increase water retention and consequently retention of heat in thermal spa treatments. The chemical composition of the major elements is closely linked to the mineralogical compositions of the clays, and also to the chemical composition of the thermal water used in their maturation. The safety profiles of the peloids obtained at different maturation times were evaluated, particularly regarding their content of potentially toxic elements such as arsenic.

A clay from Weslatiya that is widely used in Tunisian ceramic production has abundant reserves but generates significant waste, posing environmental concerns if not handled appropriately. This study explores the valorization of this local clay by incorporating ceramic waste (chamotte) and quartz sand to produce eco-friendly materials, in line with sustainability and circular economy principles. X-ray diffraction and scanning electron microscopy analyses reveal that incorporating chamotte at levels exceeding 15% by weight improves the material’s properties. The Young’s modulus of the composite increases to 80 GPa, more than 2.5 times that of the basic clay. Chamotte can replace up to 30% of quartz sand without significantly affecting densification or porosity while preserving structural integrity. This approach offers flexibility in terms of material composition, enhancing performance and promoting sustainability by reusing waste materials for high-performance ceramics in industrial applications.

Calcined clay minerals were examined as adsorbents for the removal of heavy metals from aqueous solutions. Five clay minerals (kaolinite, dickite, pyrophyllite, hydrobiotite and montmorillonite) were thermally treated at 100–1000°C and were characterized according to cation-exchange capacity (CEC), Brunauer–Emmett–Teller (BET) specific surface area and X-ray diffraction. The CEC and BET specific surface area decreased at high temperature. Kaolinite, dickite and montmorillonite had the lowest crystal order at 800°C. The adsorption capacity of the clay minerals except hydrobiotite decreased with calcination. Hydrobiotite showed a high adsorption capacity of heavy metals regardless of heat treatment. The adsorption capacity of kaolinite and dickite for heavy metals and Cs increased at 1000°C, and that of Cs on hydrobiotite decreased at 800°C. The adsorption sequence of the metals on kaolinite, dickite, pyrophyllite and montmorillonite was Pb > Cs > Co, Ni, Cd for temperatures up to 800°C, and the order for the adsorption on the clay minerals depended on the temperature, according to the adsorption capacity and the distribution coefficient.

This study focuses on the synthesis of poly(3,4-dihydro-2H-pyran-alt-maleic anhydride) and poly(3,4-dihydro-2H-pyran-co-maleic anhydride-co-vinyl acetate) and their nanocomposites modified with organoammonium salts. The goal was to investigate the structural, dynamic mechanical and thermal properties of the polymers and nanocomposites, with a particular focus on the role of organoclay modification. In this study, bentonite was modified using alkyl ammonium salts with varying chain lengths (C14, C16 and C18). Ion-exchange processes led to the transformation of the character of bentonite from hydrophilic to hydrophobic, facilitating the formation of hybrid structures. Dynamic mechanical analysis, differential thermal analysis, differential scanning calorimetry and thermogravimetric analysis were used to characterize the viscoelastic and thermal properties of the polymers and their nanocomposites. The results showed that the incorporation of organoclay structures, particularly those modified with C18 alkyl groups, significantly improved the viscoelastic properties, with the greatest storage modulus being observed in the nanocomposites. The thermal analysis revealed that the nanocomposites exhibited a distinct three-step degradation process, unlike the copolymer, which underwent two-step degradation. Despite this difference, no significant improvement in thermal stability was observed in the nanocomposites compared to the copolymers. The study concludes that the incorporation of long-chain alkyl ammonium salts into bentonite and their use in copolymerization significantly impact the thermal and dynamic mechanical properties of the resulting nanocomposites. The modification of bentonite with C18 alkyl groups led to the most stable and dynamic mechanically robust nanocomposites, providing valuable insights into the role of organoclay modification in improving the performance of polymer-based nanocomposites.

A celadonitic clay deposit is located ∼40 km north-west of Yazlıca-Kütahya (Türkiye) and has promising reserves for ceramic production. To evaluate the potential use of this region, 10 representative clay samples were collected and characterized using X-ray diffraction (XRD), polarized-light microscopy (PM), X-ray fluorescence (XRF), differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). According to the Chemical Index of Alteration and Chemical Index of Weathering, the celadonitic clay samples were formed by strong chemical alteration of the Kızıltepe volcanic rocks occurring in the study area. Based on XRD data, SEM-EDS data and chemical and thermal analysis results, the primary minerals present were celadonite-Al, montmorillonite and nontronite in the clay samples formed by the weathering of basaltic rocks. The clay samples were used in thermal and physical tests. Firing properties, including water absorption, dry shrinkage, firing shrinkage, total shrinkage and glaze adhesion, were determined. The white clay specimens are suitable for more decorative and less load-bearing applications, having high porosity and low strength. The green clay samples, however, are ideal for technical and industrial ceramics, having an extremely compact structure and high strength. The properties of these two clays are beneficial for application in different areas in terms of their mechanical and ceramic performance. Additionally, the representative green celadonitic clay samples were used in recipes for opaque, transparent and matte glazes, creating artistic glaze effects for pigments. Hence, the green clay samples could be used as a ceramic pigment.

The dissolution kinetics occurring on clay minerals are influenced by various factors, including pH, temperature and mineral lattice structure. However, the influence of the surfactant is rarely studied. In the present work, cationic surfactants were investigated in terms of the dissolution of clay minerals in acidic environments. Kaolinite was selected as the representative clay mineral. The cationic surfactant inhibited the dissolution of clay minerals because it limited the attack of H+ on the kaolinite surface and then inhibited the dissolution of kaolinite by modifying the hydrophilicity of the kaolinite surface towards hydrophobicity. The inhibition ability of the surfactant might be related to its molecular structure and the type of acid used in dissolution experiments.

This article addresses the subject of treating clayey soils to reduce the swelling in this type of soil. The study used a calcium-rich solution and examined the influence of this solution on the <2 μm clay fraction, on the non-clay fraction and on clay soil swelling. The dissolution of clay-fraction minerals during this treatment was also examined. A mineralogical and free-swelling analysis was carried out on three natural clay soils from three different locations in Algeria. The solution rich in Ca ions had a significant influence on clay mineralogy, as all the clay minerals nearly disappeared and only traces of smectite, illite, chlorite and kaolinite remained. The almost complete disappearance of minerals after contact with the Ca solution may be linked to the high pH of the porewater, because an increase in pH accelerates the alteration of these minerals. The pH of the solution induced significant modifications in the samples, revealing the high reactivity of the minerals during this treatment. Furthermore, the treatment allowed for a nearly total reduction of the sensitivity of these soils to water (i.e. swelling).