The 14 elements from La to Lu (except the unstable Pm) form a group with similar chemical characteristics provided by their electronic configurations. Widespread, albeit in low abundance (hence their original description as ‘rare’), they were soon viewed as an opportunity to trace rock origins and geological processes. In addition to this scientific use, their technological applications have increased over the decades, which have multiplied in the present electronic age. Their exponential growth in demand and limited abundance have transformed them into strategic resources. Characteristic of clay minerals, which take centre stage in so many industrial applications and scientific issues, they have been discovered to be involved in this story as important commercial rare earth element (REE) deposits. This review describes how phyllosilicates bind REE, how environmental conditions modify REE contents in phyllosilicates and how such interactions can be used to trace both original rocks and the nature of modifying geological processes. Phyllosilicates bind REE strongly and concentrate them as adsorbed species in inner and outer poly-coordination complexes. This mode of binding controls the capacity for REE retention by phyllosilicates in conjunction with the physicochemical conditions of environmental fluids (salinity, pH, temperature, ligands, Eh) and fluid:rock ratios to determine the contribution of clay minerals to bulk REE signatures and their modifications in geological processes (soil formation, clay mineral precipitation from fluids, alteration, diagenesis, ore formation, transport).

Oil-based drilling fluids (OBDFs) are widely used in high-temperature ultra-deep wells, high-inclination wells, horizontal wells and various complex wellbores due to their excellent lubricity, high temperature stability, salt tolerance and contamination resistance. However, the intrusion of drill cuttings during drilling destabilizes water-in-oil (W/O) emulsion drilling fluids. Therefore, bentonite – a common component of drill cuttings – was selected to study the factors influencing its dispersion stability in W/O emulsions. The macroscopic stability of the system was evaluated via static observation, and the dispersion state was characterized using optical microscopy. Additionally, the viscosity, the contact angle of bentonite after adsorption of various surfactants, the interfacial tension and the charge of the bentonite particles were measured. The results indicate that various surfactants affect dispersion stability through distinct mechanisms. The system stabilized by a non-ionic surfactant exhibited low interfacial tension and the greatest stability. Furthermore, dispersion stability increased with surfactant concentration. Finally, binary surfactant systems were formulated with Span80. Calcium stearate demonstrated a significant synergistic effect with Span80, improving the stability of the bentonite dispersed in the emulsion, with an optimal ratio of 1:1. The mechanism of the stable dispersion of bentonite in oil was analysed, providing theoretical guidance for improving the stability of W/O emulsion drilling fluids during drilling operations.

The reduction of volatile organic compounds (VOCs), especially the oxidation of highly toxic and chemically resistant toluene, remains a challenge in environmental catalysis. In this research, a porous TiO2/SiO2 support was initially fabricated through titanium pillaring of montmorillonite and then calcined and acid-leached as an efficient platform for Pt nanoparticle immobilization to yield Pt–TiO2/SiO2. The experimental data showed that the catalyst loaded with 0.37 wt.% Pt (0.37Pt–TiO2/SiO2) exhibits superior toluene oxidation performance, reaching a T90 of 190°C. Moreover, the catalyst exhibited remarkable water resistance, maintaining high efficiency even in the presence of 10% water vapour and outstanding long-term stability, with no substantial deactivation after 48 h of continuous operation. The performance improvement is explained by the high dispersion of Pt nanoparticles on the support and the metal–support interaction between Pt and TiO2, characterized by electron transfer from TiO2 to Pt. This interaction facilitates the adsorption and activation of reactant molecules. In situ diffuse reflectance Fourier-transform infrared spectroscopy explained the catalytic mechanism: toluene is sequentially transformed into benzyl alcohol, benzaldehyde and benzoate intermediates, which are subsequently converted to maleic anhydride by opening the ring and eventually mineralized into CO2 and H2O. This work developed a high-performance, durable catalyst using cost-effective and abundant natural minerals, offering promising prospects for practical abatement of industrial VOCs.

The accurate identification of clay minerals and associated phases remains challenging, particularly in fine-grained samples with complex assemblages. To assist in their identification, this study introduces MinMatch, a database and automated search program containing over 500 oxide compositions of clay minerals and their associated phases from soils, sediments and rocks. The program compares normalized oxide data with reference entries and ranks potential matches using Pearson correlation coefficients, supported by SiO2:Al2O3 ratios and additional statistical and graphical parameters. Its performance is demonstrated using mineral oxide datasets from well-characterized samples of the 12th Reynolds Cup competition, derived from coarse- and fine-grained separates analysed using energy-dispersive X-ray spectroscopy combined with scanning and transmission electron microscopy. The results show that MinMatch consistently ranks compositionally equivalent minerals among the top matches and successfully discriminates between closely related varieties. The approach provides a rapid, quantitative and reproducible tool for clay mineral studies, complementing X-ray diffraction and other analytical methods.

This work studies the hydrothermal synthesis of zeolitic materials from three types of industrial waste (granite cutting sludge; slate cutting sludge and aggregate washing sludge), which are regarded as low-cost materials. The synthesis was carried out through acid pretreatment with aqua regia to minimize iron content, followed by alkaline melting at 600°C followed by a hydrothermal crystallization stage at 180°C for 12 h. Characterization of the three synthesized zeolite materials by X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed that the methodology used induced the formation of LOS (Losod) zeolite (Na12Al12Si12O48·xH2O) as the predominant phase in all products, regardless of the waste used as the raw material. The end-products have a significant amorphous fraction (33–43 wt.%) and a zeolitic crystalline fraction (51–66 wt.%) and are enriched in Na and Al, and they have Si/Al and Na/Al ratios ranging from 1.27 to 1.39 and from 0.58 to 1.05, respectively, characteristic of low-silica zeolites. The synthetic zeolites showed reduced CO2 adsorption capacities at room temperature (0.50–0.55 mmol g–1) compared to commercial zeolites such as 13X (3.45 mmol g–1).

Santa Maria Island (Azores, Portugal) hosts diverse clayey materials derived from the intense weathering of basaltic–andesitic volcanic units, volcaniclastic deposits and localized Miocene marine sediments. This study provides a preliminary characterization of 20 clay samples to assess their suitability for ceramics. Textural analyses revealed a clay fraction often of >70%, indicating advanced alteration, and a particle-size distribution favourable for ceramic processing. The clayey materials are dominated by total phyllosilicates, with kaolinite prevailing, along with minor quartz, Fe- and Ti-oxides and scarce feldspars as accessory phases. The materials are characterized by high Al2O3 and Fe2O3 contents and low CaO–Na2O contents, with Chemical Index of Alteration values of 88–98%, consistent with intense leaching under humid weathering conditions. Technological tests revealed low to moderate cation-exchange capacities in kaolinite-rich samples and greater values in smectitic and palygorskitic clays. Abrasivity is variable, controlled by the quartz content, microstructure and grain angularity, while density remained within expected ranges. According to their consistency, most samples are projected within the medium- to high-plasticity field, compatible with requirements for structural ceramics, with plastic index/liquid limit ratios comparable to successful red ceramic formulations. Rheological measurements showed predominantly shear-thinning behaviour, ranging from nearly Newtonian kaolinitic suspensions to highly pseudoplastic smectitic gels, suggesting that blending strategies may be necessary. The SiO2–Al2O3–total flux ternary diagram indicated that most samples fall within compositional domains comparable to those of widely used ceramic clay bodies, with a subset shifted towards greater total flux contents. The Santa Maria Island clays constitute a robust and versatile clay resource base suitable for red structural ceramics and, in specific cases, showing technological compatibility with healing clay/peloid-type applications.

This study investigates the potential of six illite-rich clay samples from the Lower Cretaceous outcrops of Zemlet El Beidha (southern Tunisia) as precursors for geopolymer synthesis. Τhe raw materials are predominantly illitic, although kaolinite remains a main reactive phase. Samples BHG2 and BHG5 were specifically selected for further investigation due to their relatively high kaolinite content compared to the remaining samples and due to their distinct secondary mineralogy, with BHG2 being rich in hematite and BHG5 being rich in calcite. This selection allowed for a comparative analysis of how different impurities affect geopolymerization. The samples were calcined at 550°C, 750°C and 950°C to determine the optimal dehydroxylation temperature. Alkali activation was systematically performed using 10, 12 and 14 M NaOH solutions to assess the influence of alkalinity on the polycondensation process. The 12 M NaOH was most effective for the dissolution of aluminosilicate phases without the detrimental effects of excess sodium. Structural characterization (X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy) confirmed that the greatest compressive strength (∼8 MPa) was achieved with BHG5 calcined at 750°C. Although this strength is lower than that of kaolinite-based geopolymers, it meets the requirements for non-structural applications, such as thermal insulation or lightweight masonry units. This research demonstrates a viable pathway for valorizing abundant illitic-kaolinitic Tunisian clays into sustainable construction materials.