Tetraphenylborate (TPB)-assisted exchange of Na+ for structural K was explored to establish the extent to which K and radiogenic Ar were removed from mixed-layer illite-smectite (Ilt-Sme) and detrital muscovite in various clay fractions (<1, 1–2 and 2–5 µm) of three Illinois Basin palaeosols and of Ilt-Sme from a K-bentonite (<2 µm) clay. The K–Ar age value of the treated Ilt-Sme was virtually the same as that of the untreated material regardless of TPB exchange duration in the K-bentonite. Interlayer K is extracted quickly but not completely from fine illitic material. Interlayer K is extracted more slowly but more completely from coarser clay-sized muscovite based on changes in X-ray diffraction traces, K contents and K–Ar age values of the palaeosol size fractions upon TPB treatment. One hour of TPB treatment revealed that (1) detrital Ilt-Sme was predominant over diagenetic Ilt-Sme in one palaeosol and (2) relatively more of the K in R0 Ilt-Sme is resistant to TPB treatment than in illite-rich, ordered Ilt-Sme, which indicates that the single illite layers hold K+ against TPB exchange in the fine Ilt-Sme. The age values of all palaeosol size fractions treated for several weeks converged into a narrow range (mean value 247 ± 5 Myr), consistent with the remaining K and Ar being predominantly in illitic interlayers of diagenetic origin. TPB treatment is a promising technique to isolate diagenetic (or pedogenic) illite in clay fractions containing detrital components for K–Ar age determinations.

Claystones and related sedimentary lithologies are considered as potential host rocks for the storage of high-level radioactive waste. The properties of claystones, which govern their barrier performance, can vary significantly between sites and formations. This study summarizes relevant barrier properties, with a particular emphasis on those dependent on burial history and maximum rock temperatures. Given the large number of properties influencing barrier quality, ranking them by relative importance is necessary. The predictable, non-linear behaviour of certain characteristics with geological burial depth allows for a substantial reduction in the number of properties requiring determination. Based on a set of representative repository-relevant rock lithologies, a case study comparison of potential claystone host rocks is presented. Hydraulic conductivity was assumed to be the most critical barrier property, with optimal values in rocks that reached peak diagenesis at burial depths exceeding 2000 m. To further distinguish claystone types and related lithologies in terms of barrier suitability, either cation-exchange capacity, reflecting the content of smectitic layers, or maximum temperature of palaeoburial heating (Tmaxgeo) can be used as an example. Pore-size distribution, correlating with the average particle distance, was particularly suited to estimating maximum burial depth, as it is less affected by thermal anomalies, pore fluid composition or cementation effects. Overall, combining key barrier properties with burial depth-dependent behaviour enables efficient assessment and comparison of claystone formations for deep high-level radioactive waste disposal. A quantitative comparison of various claystones, however, requires establishing a reactive solute transport model that simulates radionuclide release fluxes at specific timescales.

A multi-technique approach has been proposed to characterize weathering phases and their relationships with the primary rhyolitic paragenesis at Piloni di Torniella (Tuscany, Italy) hydrothermal kaolin mine. Analyses were carried out on geological samples and on material extracted from the mine for assessment of the ceramic application of the raw material. A multi-technique protocol was applied, involving both bulk techniques (e.g. X-ray powder diffraction) and microanalytical techniques (e.g. petrographic analysis, scanning electron microscopy with energy-dispersive spectrometry and micro-Raman spectroscopy), including imaging applications. Some secondary phases, such as alunite, halloysite and α-cristobalite, were identified and characterized. Highlighting the presence of such phases is important for the mine license holder and traders, who should manage the specific properties of the final commercial mine products for ceramic applications. Furthermore, a better understanding of the alteration mechanism of biotite at the study site was achieved; in fact, where the alteration process is complete, both kaolinite and halloysite have been identified as intergrown phases in biotite pseudomorphs. This suggests the presence of a lower-temperature fluid (<100°C) percolating in some areas of the mine, probably representing a different alteration stage than that which led to the kaolinization.

Natural zeolites modified with iron(II) ions or iron(III) phases represent two promising approaches for treating hexavalent chromium contamination in water due to their reduction and adsorption capacities, respectively. However, comprehensive comparative analysis of their efficiency remains limited. Fe(II)-modified zeolites can reduce Cr(VI) to the less toxic and insoluble Cr(III) form, while Fe(III)-modified zeolites primarily remove Cr(VI) through surface adsorption. This study evaluates the effectiveness of Fe(II)- and Fe(III)-modified zeolites using synthetic Cr solutions and real contaminated surface water. The materials were characterized via X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray fluorescence spectroscopy to assess their chemical, structural and morphological changes before and after chromium sorption. Batch and column tests determined Cr(VI) removal capacity, while Cr isotopes were used to track reduction reactions. The Fe(II) enrichment via cation exchange was highly effective. The Fe(II)-modified zeolite demonstrated a greater capacity for Cr(VI) removal from contaminated solutions, primarily through a reduction mechanism that converted Cr(VI) to Cr(III), as was confirmed by isotopic analysis. Its performance improved under higher-salinity conditions. However, it required prolonged contact time with the contaminant to achieve optimal efficiency. The Fe(III)-modified zeolite exhibited a heterogeneous distribution of iron oxide/hydroxide phases on its surface. This material showed some favourable characteristics in batch and column tests, including a notably faster Cr removal rate due to direct Cr(VI) sorption. However, it could only perform well when no other competitive ions were present in the solution, severely impacting its application in complex, real matrices.

Engineering muck (EM) is an underutilized construction waste rich in clay minerals. The mechanical properties, composition, microstructures and reaction mechanisms of various EM-based geopolymers produced via acid or alkali activation are comprehensively compared and discussed in this study. The results indicate that EM mainly contains clay minerals (kaolinite, halloysite and dioctahedral mica), feldspar and quartz. The geopolymerization reactivity of EM was improved following crushing and calcination pretreatments, which destroyed the microstructure of the clay minerals and formed a reactive amorphous phase. Acid activation of calcined EM (EM700°C) resulted in greater geopolymerization reactivity than alkali activation. The highest 7 and 28 day compressive strengths of phosphoric acid-activated EM-based geopolymers reached 27.31 and 24.37 MPa, respectively, under a water/binder mass ratio of 0.7 and an Al/P molar ratio of 0.9. Comparatively, the maximum 7 and 28 day compressive strengths of alkali-activated EM-based geopolymers were only 7.82 and 11.66 MPa, respectively, under a water/binder mass ratio of 0.6 and a SiO2/Na2O molar ratio of 1.75. For phosphoric acid activation, reactive Al3+ mainly from calcined clay (e.g. metakaolinite) in EM700°C geopolymerized with PO43– and silica, forming phosphate-containing phases and amorphous silico-aluminophosphate (SAP; Si–O–Al–O–P) gels. In contrast, reactive SiO2 and Al2O3 from EM700°C participated in the geopolymerization process in alkaline solution, forming sodium aluminosilicate hydrate (N–A–S–H) gels and the byproduct faujasite. The geopolymerization reactivity of EM700°C and the resulting composition variations in various solutions contributed to the differences in the compressive strengths of EM-based geopolymers. This study provides a theoretical basis for preparing acid/alkali-activated geopolymers from EM.

Our energy needs must be met by envssironmentally friendly energy sources such as hydrogen energy because fossil fuels are being depleted and are restricted by CO2 emissions. One way to safely store hydrogen is to use porous materials, such as clinoptilolite (CLN), for physical adsorption. In this study, the effect of cation exchange with Ag+ on the hydrogen adsorption properties of Gördes CLN was investigated. The Ag-modified forms were obtained by treating the CLN with 0.01, 0.03, 0.05, 0.15 and 0.30 M AgNO3 solutions at 90°C for 5 h. The mineralogical and textural properties of the raw and Ag-treated CLNs were investigated using X-ray diffraction, X-ray fluorescence and nitrogen gas adsorption analysis. The specific surface area and microporous area values of the Ag-exchanged samples were slightly lower than those of raw CLN. The H2 adsorption capacities of the Ag-modified forms, measured at 77 K, decreased with increasing AgNO3 molarity after reaching an optimal threshold value of 0.01 M. The H2 uptake values ranged between 0.317 and 1.056 mmol g–1. The results of the study are explained as depending on the molarity of the AgNO3 solution used for cation exchange.

The influence of exchangeable alkali cations on glucose uptake, interlayer reorganization and ionic transport was investigated in homoionic Wyoming montmorillonite exchanged with the complete alkali series (Li+, Na+, K+, Rb+ and Cs+). Glucose adsorption was rapid during the initial stage and reached equilibrium after ∼6 h. Under the investigated conditions, the equilibrium uptake was highest for the Li- and Cs-exchanged forms, whereas the Na-exchanged form showed the lowest adsorption amount. X-ray diffraction, differential thermal analysis and Fourier-transform infrared spectroscopy collectively support partial accommodation of glucose within the interlayer region without major disruption of the aluminosilicate framework, although the magnitude of the structural response depended strongly on the exchangeable cation. The largest basal expansion was observed for the Li- and Na-exchanged forms, showing that interlayer opening does not directly parallel adsorption capacity across the alkali series. Broadband impedance spectroscopy further indicates thermally activated ionic transport and a marked cation dependence of both direct current (DC) conductivity and activation energy after glucose loading. In particular, glucose adsorption altered the conduction environment more strongly in the Li- and Na-exchanged systems than in the K-, Rb- and Cs-exchanged forms under the same thermal conditioning. Taken together, the results suggest that glucose uptake, interlayer expansion and ionic transport are governed by coupled effects involving cation hydration, interlayer accessibility and local structural organization rather than by a single cation property alone. This comparative dataset provides a basis for understanding how exchangeable cations regulate saccharide–clay interactions in montmorillonite.

The brick production industry faces increasing environmental pressure due to high energy demands during firing, necessitating the optimization of firing conditions. This study investigates an eco-friendly stepped firing process as a sustainable alternative to conventional direct heat treatment using clayey raw materials from the Ouled Mansour area, north-east Morocco. To evaluate this approach, raw materials were characterized using X-ray diffraction, X-ray fluorescence, infrared spectroscopy, simultaneous thermal analysis, Atterberg limits and particle-size distribution analysis. Brick specimens were then prepared and fired under both conventional and stepped heating processes. Their thermophysical properties (thermal conductivity, thermal diffusivity, porosity, water absorption and density) and compressive strength were assessed. Non-destructive tests (ultrasonic pulse velocity and Schmidt hammer tests) together with mineralogical and microstructural analyses were also performed. The stepped firing process reduces porosity and defects, thereby increasing the ultrasonic pulse velocity from 3197 to 3508 m s–1 and improving compressive strength by up to 21%. Thermal conductivity and density slightly increase, from 0.57 to 0.58 W mK–1 and from 1.60 to 1.62 g cm–3 at 770°C, respectively. The proposed eco-friendly firing process enhances the physico-mechanical performance of bricks while supporting their energy-efficient production, with potential reductions in energy consumption during both manufacturing and the building service life.

In this paper we describe a simple method for determining the aspect ratio (AR) of clay mineral particles by measuring the electrical conductivity of randomly orientated suspensions as a function of volume fraction. The AR of industrial clay mineral products is a key parameter in defining their suitability for a range of applications and in differentiating them from other minerals, but there is no single, well-established technique for measuring it. Most researchers and producers rely on either microscopy or calculations based on particle-size distributions measured by two techniques with different sensitivities to particle dimensions. The effect of particle AR on the electrical conductivity of particle suspensions has been known for over a century and has been used previously to measure an average AR, but this has not become an established method. In this work, the theory of Dukhin and Derjaguin is used to calculate the average particle AR, which is independent of particle size. Using this method, the AR of a range of kaolin, talc and mica samples is measured and compared with values from other techniques. AR measured by the method described is shown to correlate well with the effects of clay minerals on the stiffness of filled polyolefins, as expected from theory.