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.

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.

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.

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.

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.