Abstract 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.

Abstract To date, published studies have proven that the reactions at the iron/bentonite interface are complex and only partly understood. In the present study, mixtures of bentonite powder and iron powder were prepared, which allowed for varying individual parameters. The results confirmed some controversial previously reported conclusions and revealed new findings. More specifically, Na-exchanged samples showed a reduced extent of corrosion compared to Ca/Mg-exchanged ones, and the addition of reactive silica increased the extent of corrosion, which has not been reported to date. The negative temperature effect (less corrosion at higher temperatures), which was reported previously, could only be confirmed for Ca/Mg-bentonites. One Na-bentonite showed the opposite effect, but this sample also contained reactive silica in contrast to the others. The present study proves for the first time that the type of exchangeable cation can affect the type of corrosion product, which could be an explanation for why the 7 Å corrosion product was not reported in all corrosion tests (sometimes only magnetite was reported). In addition, experiments that ran for 36 months showed that the corrosion progress of six different bentonites was different. Three bentonite/iron mixtures did not show progress in corrosion after 12 months, whereas the other three showed ongoing corrosion. Using the former three bentonite/iron mixtures would significantly increase high-level radioactive waste canister lifetime, but future work should be devoted to the identification of the reason for this differing long-term performance, differing thermal behaviour and differing corrosion products resulting from different types of exchangeable cation.

Abstract Magnetite-enriched mining tailings are a cost-effective and abundant catalytic material with inherent magnetic recyclability. Yet their practical application in catalysis is often constrained by their limited surface area and sluggish reaction kinetics. To address these issues, we developed a facile one-step co-precipitation method to synthesize a magnetic nano-Fe 3 O 4 (MNP) catalyst that exhibits enhanced surface reactivity for efficient activation of H 2 O 2 towards tetracycline (TC) degradation. The system achieved complete (100%) removal of TC at an initial concentration of 20 mg L –1 within 90 min and demonstrated robust catalytic performance across weakly acidic to neutral pH conditions. Mechanistic investigations confirmed that ⋅OH is the primary reactive oxygen species involved, with ⋅O 2 ⁻ and 1 O 2 providing supplementary contributions to the degradation. Remarkably, the intrinsic magnetic properties ensured efficient MNP catalyst recovery. This work provides a sustainable and scalable wastewater treatment strategy, leveraging mining tailings as a cost-effective resource to treat wastewater while also providing economic and environmental benefits.

Abstract Iron mining waste is produced from the iron ore mining operations of El Ouenza Mine (north-east Algeria), and it is not currently recycled to preserve the environment. The current study aims at developing sustainable clay bricks by mixing clay with different proportions of iron mining waste (ranging from 10 to 50 wt.%) and fired at 850°C and 950°C. Addition of 30 wt.% Iron mining waste had a positive effect on the physical and mechanical properties of the fired clay bricks. Linear shrinkage, water absorption and porosity were reduced, while compressive and flexural strengths were increased. Furthermore, up to 30 wt.% of iron mining waste addition to the mixtures improved compressive and flexural strengths to 59.17 and 10.06 MPa, respectively, when the bricks were fired at 950°C. According to their thermal conductivity, the bricks with 10–50 wt.% iron mining waste are considered as thermal insulators, with thermal conductivity values ranging from 0.45 to 0.56 W m –1 K –1 . Adding 30 wt.% of iron mining waste can lead to the production of eco-friendly bricks with high mechanical and thermal properties, generating economic and environmental benefits.

Abstract Serra de Tramuntana of Mallorca is a mountain range built of a stack of thrust sheets composed mostly of Mesozoic platform carbonates, and it formed in the Oligocene and Miocene during the Alpine orogeny. Volcanic rocks, intruding the Triassic sediments, and known mostly from the bottom of the lowest thrust sheet, offer an opportunity for dating the post-sedimentary thermal history of this mountain range and for evaluating the maximum palaeotemperatures by studying the mineralogy and K–Ar dating of authigenic illite. Such a study was conducted on 16 samples from two outcrops, employing X-ray diffraction (XRD), optical microscopy, electron probe microanalysis and K–Ar dating of separated clay fractions. Illite was found in 10 samples, but only one sample was identified as pure volcanic rock, not contaminated by older detrital material. This sample yielded a K–Ar age of 133–140 Ma, which is within the experimental error for three grain-size fractions. This was confirmed by extrapolating the ages of a contaminated sample, and it is interpreted as representing the age of the maximum palaeotemperatures. These palaeotemperatures were estimated using several illite characteristics, including the Kübler Index applied to shales as below but close to the diagenesis/anchimetamorphism boundary (180–200°C). The dated pre-tectonic early Cretaceous thermal event is interpreted as recording the extremely high geothermal gradient at the end of the Mesozoic extensional phase. The maximum palaeotemperatures during the Oligocene–Miocene tectonic burial of Mallorca were not high enough to reset the Mesozoic K–Ar age of illite, thus being lower than ∼250°C, and, based on the preserved Cretaceous illite XRD characteristics, lower than 180–200°C.

Abstract This study investigates the influence of interlayer cations on the thermodynamics and sorption mechanisms of water in a reference Wyoming montmorillonite. The behaviour of the montmorillonite exchanged with monovalent cations (Li+, Na+, K+, Rb+, Cs+) or divalent cations (Mg2+, Ca2+, Ba2+) is compared. The analysis combines X-ray diffraction (XRD), water sorption isotherms at various temperatures and mid-infrared spectroscopy. Li+, Mg2+ and Ca2+ promote greater water uptake and swelling, whereas K+, Rb+ and Cs+ significantly limit these processes. The behaviour of Na+ and Ba2+ stands out, demonstrating intermediate water uptake and high swelling. Mid-infrared spectral analysis supports these observations. It is shown that a cation’s effect on water uptake and swelling correlates best with the product of its elementary charge and ionic radius rather than with other properties such as the electrostatic potential, solvation enthalpy or chemical hardness. However, differences in isotherm shapes, hysteresis between adsorption and desorption and the variation of isosteric heat with water content suggest the presence of two distinct sorption mechanisms: one involving Li+, Cs+, Mg2+, Ca2+ and Ba2+, and another involving Na+, K+ and Rb+. These findings indicate that isotherm shape and swelling alone do not directly reflect water uptake capacity. These findings thus outline that the chaotropic (structure-breaking) or kosmotropic (structure-making) nature of the cations, along with the complex interplay between cation hydration and TOT layer attraction, may explain the complex observed differences.