In ion adsorption rare earth element (REE) deposits, REE are adsorbed onto clay minerals. Previous experimental studies indicate that adsorption depends on the chemical and physical properties of the clay and on the pH and salinity of the solution. This work presents adsorption experiments using two natural, purified kaolins with contrasting particle sizes exposed to different ligands at low and high ionic strengths (I) and at different pH levels to assess their influence on the adsorption of REE onto kaolinite. The results reveal that: (1) REE adsorption is rapid; (2) water/dilute nitric acid experiments gave optimum adsorption; (3) high-I NaCl, Na2SO4 and NaHCO3 demonstrated the least adsorption; (4) REE and yttrium are more adsorbed onto kaolinite in water/dilute nitric acid at lower pH, but adsorption is higher at higher pH when NaCl is present; (5) high I allowed less adsorption; and (6) scandium and thorium are more effectively adsorbed than REE and yttrium. The data suggest inhibition of adsorption by complex ion formation in solution at high I, and in the presence of strongly binding ligands (Cl–, SO42–, CO32–). Adsorption induces no REE fraction for low-I solutions in nitric acid, whereas enhanced chloride complex formation for light REE results in the preferential adsorption of heavy REE. sulphate inhibits adsorption, and carbonate at low I inhibits light REE adsorption relative to heavy REE, whereas at high I kaolinite may dissolve. Low-crystallinity, weathering-derived kaolinite demonstrates an order of magnitude more adsorption than processed, hydrothermal kaolin as a result of its increased surface area and adsorption sites.

The precise characterization of the mesoporous mineral matrix of a geopolymer is greatly complicated by its amorphous nature. No conventional characterization technique allows for its direct investigation. We propose here the use of alternative current impedance spectroscopy (AC-IS; generally called ‘complex impedance spectroscopy’) as an indirect method for probing geopolymers via their ionic conduction properties. Our study of ∼50 K-geopolymer pellets using AC-IS has made it possible to better describe the mesoporosity of alkali-activated materials. The latter were prepared by partial substitution of metakaolin by argillite, and these were then subjected to heat treatment up to 900°C and exposed for a long time to high or low relative humidity. The metakaolin substitution rate along with post-synthesis temperature and storage conditions were the variables that allowed us to track the phenomenon of charge transport via mesoporosity. Refining the impedance spectra over a range of temperatures, using simple and robust models, provided a set of values for the activation energies and diffusion coefficients. The results confirmed the open and ‘through-hole’ nature of the porosity, the localization of K+ cations in the interstitial liquid and their diffusion through the amorphous ceramic matrix during heat treatment, as well as the possible resumption of long-term alkaline activation for poorly reactive aluminosilicate sources.

Kaolinite, a widely distributed clay mineral, is extensively applied in construction, industry and agriculture due to its physical, chemical and mechanical properties. This study employed quantum mechanics-based first-principles calculations to investigate the crystal structure, electronic properties and mechanical properties of kaolinite at various temperatures from a microscopic perspective. The main conclusions are as follows: structurally, lattice parameters (a, b, c) and volume increased with temperature, with c showing the largest such increase. The interlayer spacing between silicate tetrahedral and alumina octahedral layers slightly decreased from 0.3733 to 0.3702 Å, indicating that temperature exerts a stronger influence on the interlayer hydrogen bonds than on the covalent bonds within the layers. Electronically, in the 0–750 K range, kaolinite’s band gap narrowed from 5.13 to 5.06 eV; s orbital electrons of Al atoms jumped from the valence to the conduction band, reducing insulation. Mechanically, the elastic constants C11, C22, C33, C44 and C66 decreased while C55 increased with temperature. The bulk modulus declined continuously, whereas the shear modulus and Young’s modulus first increased then decreased. The universal anisotropy index decreased markedly, reducing elastic anisotropy. Temperature (0–750 K) significantly affects kaolinite’s properties. This study provides a reliable theoretical basis for optimizing the physicochemical and mechanical properties of kaolinite-based materials.

Hydrogenation of CO2 into high-value carbon-containing compounds can effectively reduce greenhouse gas emissions. These plasma-catalysed systems offer convenient reactions under mild conditions, and, combined with their widely distributed, low-cost clay minerals, they can effectively reduce reaction costs and promote their further industrial application. However, research on their synergistic applications remains limited at present. In this work, we propose a model for synergistic catalytic CO2 conversion by coupling clay minerals and dielectric barrier discharge (DBD) plasma. The synergistic effects of eight typical clay minerals on CO2 conversion and CO selectivity catalysed by DBD and their influencing factors were explored through a combination of performance tests and characterization using X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy. Based on the performance and characterization results, minerals exhibiting a two-dimensional tubular structure, increased surface hydroxyl groups, appropriate transition metal active components and low water contents demonstrate greater CO2 conversion rates and CO selectivity. This work demonstrates that clay minerals can be used as effective DBD catalysts and represent low-cost green catalysts for the DBD catalytic system. This is of great significance for the rapid screening of clay minerals that are favourable for CO2 catalytic reactions and their further modification and application.

The circular recovery and reuse of nutrients from wastewater is vital for achieving sustainability goals and the European Green Deal objectives. This study investigates the selective recovery of ammonium (NH4+) using a zeolitic tuff rich in chabazite zeolite. We focused on targeting its applicability for farm-scale applications from different anaerobic digestates undergoing various pre-treatments (screw compression, microfiltration and centrifugation). The results were compared with a zeolitic tuff rich in phillipsite and chabazite from a previous study. The tested wastewaters included swine, cattle and municipal solid waste digestates. Adsorption isotherms and kinetics were evaluated, considering key factors such as initial NH4+ concentration, contact time, competing ions (e.g. K+), total solids content and pre-treatment strategies. The adsorption process followed the Freundlich model, indicating heterogeneous multilayer sorption, whereas the kinetic data aligned with pseudo-first-order and intraparticle diffusion models. NH4+ removal efficiency was inversely correlated with K+ levels and solids content, with livestock-derived digestates enabling the greatest nitrogen recovery per gram of zeolitic tuff due to their favourable composition and kinetics. Among the tested pre-treatments, centrifugation proved most effective, improving active site accessibility. A preliminary field-scale trial using microfiltered swine digestate at a 3% solid-to-liquid ratio demonstrated the feasibility of batch operation, with an estimated nitrogen recovery of 715 kg N year–1. This work lays the foundation for future comparisons with other zeolitic tuffs, such as those rich in clinoptilolite, and it supports the principle of nutrient circularity in agriculture by reducing reliance on synthetic fertilizers.

The clayey sludge resulting from aggregate washing in quarries of the Marrakech region generates significant environmental impacts and adds an economic burden to the industry. This study aims to characterize these clayey sludges in order to explore their potential for ceramic applications. Fifteen samples were collected from various quarries along the major waterways of the Marrakech region. The physical properties of the clayey materials were analysed according to particle-size distribution and plasticity limits. The mineralogical composition was determined using X-ray diffraction and Fourier-transform infrared spectroscopy. The chemical composition was determined using X-ray fluorescence spectroscopy. The carbonate and volatile contents were determined by calcimetry and loss on ignition at 500°C and 950°C, respectively. SiO2 and Al2O3 are main constituents, while quartz, feldspars and clay minerals are the main phases, along with minor calcite and hematite. Illite is the dominant clay mineral, followed by kaolinite and chlorite. The clayey material exhibits low to medium plasticity and variable particle-size distributions. The chemical composition of these sludges confirms their potential for red ceramic applications. However, their low plasticity, variable particle-size distribution and mineralogical composition, characterized by a low clay mineral content, limit their direct applicability. To improve their suitability for ceramic production, adding clay-rich tempers is essential to enhancing their mineralogical composition, granulometry and plasticity. Furthermore, the results provide a valuable guide for selecting local materials for Marrakech pottery and can serve as a model for other regions.

Clay minerals in the Yishu fault zone, as typical products of hydrothermal activity, carry critical information regarding subsurface geothermal processes. To clarify their hyperspectral remote sensing characteristics and their guiding value for geothermal resource exploration, this study takes the Yishu fault zone and three key subareas (Tangtou, Tongjing and Fangzi) as the research objects. Based on ZY1-02D hyperspectral remote sensing data, combined with principal component analysis and the Crósta method, we analysed the spectral features of typical clay minerals (illite, montmorillonite and chlorite) and extracted their spatial distribution patterns. In addition, ZY1-02E thermal infrared data were used to invert the land surface temperature so as to explore the spatial correlation between clay mineral distribution and geothermal anomalies. The results show that the spatial distribution of clay minerals is closely associated with fault structures, being mainly concentrated along the four major fault belts of the Yishu fault zone and their surrounding areas. High-intensity hydrothermal alteration zones dominated by clay minerals exhibit significant spatial overlap with surface temperature anomalies. The consistent distribution of clay minerals and known geothermal fields further confirms that the hyperspectral characteristics of clay minerals can effectively indicate the upwelling channels and accumulation zones of geothermal fluids. This study provides a rapid and accurate technical method for geothermal resource prospecting in the Yishu fault zone and other tectonically similar regions.