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.

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.

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.

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.