This study examines the effect of German camomile (Matricaria camomilla L.) cultivation on the weathering of minerals present in the clay fraction of five different soil series modified or not unmodified (control) with cattle manure. A factorial experiment was performed in a randomized complete block design (RCBD) with three replications. At harvest time the rhizosphere soil was separated from bulk soil and the mineralogy was examined by X-ray diffraction (XRD). Trioctahedral chlorite transformed to hydroxy-interlayer vermiculite (HIV), while kaolinite disappeared. The presence of HIV was identified by an increase in the intensity ratio of the 1.0 and 1.4 nm peaks after Na-citrate pretreatment and K-saturation. It is suggested that Al3+ is released during dissolution of kaolinite and subsequently enters into the interlayer sheet of chlorite, and consequently the brucite layer disappears. This was verified by a significant Mg2+ increase in the soil solution in three out of five experiments at harvest time compared to pre-planting. The pots amended with manure showed the same changes as the pots without manure. The results of this study may explain the presence of unexpected clay minerals in regions with unsuitable conditions for their formation.

La fixation du toluène et sa polymérisation dans les espaces interfoliaires d'une montmorillonite-Cu(II) au cours de cycles de déshydratation, adsorption, désorption de l'excès de réactif et réhydratation, ont été étudiées. Elles ont été suivies au moyen de diverses méthodes d'analyse (thermogravimétrie, radiocristallographie et spectrophotométrie d'absorption infrarouge). Les résultats rappellent ceux obtenus lors de l'étude du système montmorillonite-Cu(II)-benzène. Ainsi, la fixation du toluène s'effectue selon deux réactions, correspondant l'une à l'adsorption d'une molécule de toluène, l-autre à celle de trois molécules de toluène par ion Cu2+. Toutefois, l'affinité du toluène pour la montmorillonite est supérieure à celle du benzène.

Aung et al. (2014, 2015) described the activation of kaolin samples to remove coloured pigments from rice-bran oil, the effects of various treatments on their decolourization capacity, and the characterization of these kaolin samples by physical methods. This research used a kaolin sample from Ranong in southern Thailand, and investigated the effects of grinding and heat treatment prior to acid activation of the mineral. The various activated mineral phases were then characterized by a combination of X-ray diffraction, Fourier-Transform infrared spectroscopy and X-ray fluorescence. This work represented an extension of research reported previously by Worasith et al. (2011a), in which various samples of the same Ranong kaolin were characterized after grinding and acid activation, and their capacities to decolourize rice-bran oil evaluated (Worasith et al., 2011b). However, despite the similarities in the experiments, there are some important differences in the results presented in these two sets of publications, which raise questions concerning the conduct of this type of research and the generality of any conclusions derived.

Silicification and illitization due to diagenesis result in the modification of porosity and permeability in many North Sea reservoirs, including Greater Alwyn. A good estimation of the mineral composition is required as input/output data for geochemical modelling modes intended to reproduce these effects. Using sedimentological studies to determine laterally equivalent facies, three facies were chosen. ‘Initial states’ for modelling were thus defined as the present-day composition of less-evolved laterally-equivalent facies, ‘final states’ as the present-day composition in the most evolved part of the basin. Precise actual mineral compositions were calculated using a reconciliation program, DATREC. Average compositions calculated for each facies in each field provided data useful in constraining input/output values used in modelling, and gave insights into depositional variation. Arithmetic tests assuming isochemical transformations, constraining the chemical compositions of ‘initial states’ to fit actual mineralogical compositions of ‘final states’, were run using this software. They show that, from an arithmetical point of view, if the assumption of equivalent facies holds, isochemical reactions can occur in some, but not in all facies, thereby demonstrating the importance of checking equivalence of facies and diagenesis hypotheses by quantitative calculations.

Experimental studies of reactions between water and kaolinite, kaolinite + quartz, kaolinite + quartz + muscovite and natural kaolinitic mudstones (Jurassic Draupne Formation; Norwegian North Sea; Rhaetic Westbury Formation, SW England; Tertiary ball clay, SW England) at 50 MPa and 150°C or 200°C have demonstrated that quartz saturation can be achieved readily at 200°C At 150°C quartz saturation is achieved for natural mudstones, but not for mineral mixtures because of slow reaction kinetics. Geochemical solution modelling demonstrates coincidence between observed fluid compositions and those expected for the solid mineral assemblage. In addition to inorganic solutes, organic acid anions including citrate are reported as products in experiments with natural mudstones (especially the Draupne Formation). Fluids supersaturated with respect to quartz are unlikely to be developed from mudstones which lack smectites or amorphous silica.

The search for sufficiently high-quality clays for use in the tile industry represents a significant challenge. This study aimed to prepare Muttalip green clay tiles with flexural strengths adhering to the TS EN 1304:2016 standard. Muttalip green clay was subjected to sieving, vacuum pressed, dried and then baked to obtain galette tiles. The tiles were analysed subsequently using optical techniques, including X-ray diffraction, X-ray fluorescence spectrometry and field-emission scanning electron microscopy. The influence of various firing temperatures (900, 950 and 1000°C) on the flexural strength of the tiles was also investigated. The tiles obtained at 950°C exhibited a maximum flexural strength of 153.91 kg cm–2. Fourier-transform infrared spectroscopy revealed that the tiles reflect ultraviolet A radiation and absorb infrared radiation. Muttalip green clay is a suitable material for preparing tiles for roofing applications.

This work presents the synthesis of minerals with a layered structure in supercritical water/ethanol mixtures to decrease the critical coordinates of the solvent regarding water. Depending on the water/ethanol ratio of the solvent, we obtained three different minerals adopting an octahedral brucitic sheet: (1) without a Si-tetrahedral sheet (O); (2) associated with one Si-tetrahedral sheet (T-O); or (3) intercalated between two Si-tetrahedral sheets (T-O-T). We have thus shown that ethanol in a supercritical water/ethanol mixture changes the solubility of silicon with a direct consequence on the formation of the tetrahedral silicon sheets and thus makes it possible to control the structure of the synthesized layered material.

The objective of the DOPAS international project is to design a sealing-plug system for deep geological repository (DGR) use, to provide detailed plans for the design of such plugs, to test the characteristics of the materials to be used and the construction technology and to install four experimental in situ plugs. The Czech experimental pressure and sealing-plug (EPSP) experiment is being conducted in a rock environment consisting of granitoids at the Josef Regional Underground Research Centre. The concept of the experiment is based primarily on the use of materials and technology available in the Czech Republic and the principal aim is to demonstrate the technical viability and functioning of a pressure-resistant plug located in a future DGR. The completion of the EPSP experiment will contribute towards both the demonstration of how sealing-plug systems behave under real underground conditions and the long-term safety of a future DGR in the Czech Republic.

Bentonite clay is often included as a buffer, backfill and/or sealing material in designs for deep geological repositories for radioactive wastes. It is expected that bentonite materials may undergo some mineralogical alteration as they interact with in situ groundwaters over long timescales on the order of thousands to millions of years. Long-term modelling of these materials is therefore important in order to demonstrate confidence that the engineered designs will continue to perform as required over their intended lifetimes (required assessment timescales can be up to 1 million years). The key geochemical processes that must be considered in such modelling are mineral dissolution and precipitation and cation exchange. These processes are expected to occur simultaneously and so modelling of their coupled effects and their rates (kinetics) is necessary. Illustrative reactive-transport models of the geochemical alteration of montmorillonite (the primary mineral in bentonite exhibiting cation exchange) are presented which demonstrate that one possible approach to fully coupling cation exchange and clay mineral dissolution kinetics, referred to here as the ‘all-component coupling’ approach, may lead to unrealistic behaviour due to feedback that may occur in the formulation. This feedback can be avoided if a ‘common-component’ conceptual model for the dissolution of exchanger end members is adopted, where only the saturation of the exchanger ‘structural unit’ is considered when evaluating the potential for dissolution of the mineral. Such considerations have been proposed historically in stability analyses for montmorillonite, but have not been explored widely in the modelling literature.

In this study, the adsorption of NH3 gas on a bentonite from Ünye (Turkey) in its natural state and after acid treatments, was investigated experimentally at 298 K and up to 100 kPa. Bentonite was treated with HCl solutions of various concentrations (0.5–2.5 M) at 75°C for 4 h. X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption and thermogravimetric/differential thermal analysis (TG/DTA) were used to characterize the bentonite before and after acid treatment. The quantitative XRD analysis demonstrated that the bentonite sample was composed predominantly of smectite (75%), with abundant feldspar (20%) and minor opal-CT, analcime and quartz (5%). Increasing gas adsorption values of acid-treated bentonites were analysed depending on the structural changes of the clay. The NH3-adsorption capacities of the bentonite samples (3.801–5.068 mmol g–1) were also compared with previously studied clay-based materials (0.828–4.000 mmol g–1) in terms of their textural and structural differences.

Uniaxial and isothermal compression tests of kaolinite were carried out using molecular dynamics simulations. Five different temperatures (300, 400, 500, 600 and 700 K) and pressures ranging from 0.0001 to 50 GPa were selected to study the temperature and pressure effects on the mechanical properties of kaolinite. As kaolinite may undergo a phase transition at ~1572 K, a highest temperature of 700 K was chosen to avoid such structural change. The Young's modulus, strength and elastic constants of kaolinite under various temperatures were calculated, and the relative change of the elastic constant C33 with temperature was found to be almost 12 times greater than the relative change of the interlayer constant C11. The microstructures under various compressive strains were tracked and they exhibited various failure modes in three directions. The temperature and pressure effects on the mechanical properties of three crystal directions were analysed. The results showed that the Young's modulus of the z-direction is the most affected by temperature; however, the influence of temperature on the strengths of the three crystal directions was the same. In addition, the structure of the z-direction was the most sensitive to temperature under the same hydrostatic pressure due to the weak interactions between layers.

Several generations of chamosite, including a red variety, occur in the Ordovician hydrothermalized oolitic ironstone from Saint-Aubin-des-Châteaux (Armorican Massif, France). Their chemical re-examination indicates a low Mg content (0.925 < Fe/(Fe + Mg) < 0.954), but a significant variation in IVAl. Minor vanadium is present at up to 1.1 wt.% oxide. Variations in IVAl, the vanadium content and the colour of chamosite are related to the hydrothermal reworking of the ironstone. Taking into account other published data, the ideal composition of chamosite is (Fe5–xAl1+x)(Si3–xAl1+x)O10(OH)8, with 0.2 < x < 0.8 (0.2: equilibrium with quartz; 0.8: SiO2 deficit). The red chamosite (IIb polytype) has a mean composition of (Fe3.87Mg0.23Mn0.01□0.07Al1.74V0.07)(Si2.33Al1.67)O10(OH)8. This chamosite is strongly pleochroic, from pale yellow (E || (001)) to deep orange red (E ⊥ (001)). Visible–near-infrared absorbance spectra show a specific absorption band centred at ~550 nm for E ⊥ (001), due to a proposed new variety of Fe/V intervalence charge-transfer mechanism in the octahedral sheet, possibly Fe2+ – V4+ → Fe3+ – V3+. While the formation of green chamosite varieties is controlled by reducing conditions due to the presence of organic matter as a buffer, that of red chamosite would indicate locally a weak increase of fO2 related to oxidizing hydrothermal solutions.

The flat-layer method of X-ray diffraction and conditions for focusing are discussed.

The kinetics of structural change of a highly ordered kaolinite intercalated with potassium acetate have been studied through both intercalation and deintercalation. Deintercalation of the intercalated kaolinite, brought about by washing for different time intervals was followed by both X-ray diffraction and Raman microscopy. X-ray diffraction shows the kaolinite to be highly ordered with a Hinekley index of 1.42 and intercalated to ~90%. X-ray diffraction also showed that the intercalated kaolinite was deintercalated by 80% in the first minute of washing. An additional Raman band, attributed to the inner surface hydroxyl groups, strongly hydrogen bound to the acetate, is observed at 3605 cm-1 for the potassium acetate intercalate with the concomitant loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm-1. Upon deintercalation, the intensity of the 3605 cm-1 band decreased as the 3695 cm-1 band increased. The Raman spectral changes brought about upon deintercalation mirrored the changes observed by X-ray diffraction. Deintercalation of kaolinite caused disordering of the kaolinite.

In the course of hydrothermal experiments with a saponitic clay, evidence for the dissolution of the accessory sepiolite and the formation of smectite has been detected above 120°C Hydrothermal reactions with a clay to water ratio of 1:3 were performed at temperatures of 60, 90, 120, 175 and 200°C with time intervals of one month to one year.

The BET surface area and cation exchange capacity (CEC) are correlated with the sepiolite and the smectite content determined from XRD data. These relations have been used to recalculate the time dependence of the mineral contents in the time/temperature conditions of the experiments. The Ea values obtained for sepiolite dissolution (7-18 kcal/mol) or smectite formation (4.8-5 kcal/mol) indicate that sepiolite dissolution controls the rate of the process. Both results fit an apparent firstorder reaction and the system seems to evolve to a stable mineral composition in a short time period, ranging from one to 10 years as temperature decreases.