Detailed multi-scale characterization of the kaolin quality and the controlling depositional environment is crucial for optimal quality upgrading and for prioritizing potential exploitation areas. In the present work, the quality of El-Tih kaolin, Egypt, was investigated using the chemical/mineralogical characteristics as well as the field observations of the clay. Chemical analysis of major oxides was carried out using energy dispersive X-ray fluorescence (EDS-XRF) spectrometry. Mineralogical analyses were carried out using X-ray diffraction (XRD) and scanning electron microscopy coupled with wavelength-dispersive X-ray spectroscopy (SEM-WDS). Spatial heterogeneity of the quality was evaluated applying kriging geostatistical techniques and potential zones were identified.

Results clarified an upward gradual deterioration of the quality via a decrease in the Al2O3 content and thickness of the clay layers, and an increase in the TiO2 content. According to the kriging maps, areas of high potentiality indices (PI) characterized by high Al2O3 and low SiO2 content and maximum thickness of the kaolin are located to the west and east, and decrease toward the central part of the study area. The high PI zones are dominated by pseudo-hexagonal platy kaolinite, often forming accordion- and book-like aggregates with subordinate quartz and traces of Fe and Ti oxides, yielding minimal TiO2 and Fe2O3 contents. These zones of high PI are considered optimal for exploitation. Kaolinite was formed as a result of intensive weathering of rhyolite/granite and basalt in the source area, and subsequent erosion, transportation and deposition of the weathering mantles in a flood environment with marked depositional energy variations. Results allowed comparison with worldwide kaolin occurrences, and suggested the suitability of the studied kaolins for use in paper coating and filling and in higher-grade ceramics, after removal of free Fe- and Ti-oxide impurities.

Minerals with the general formula Cu4(OH)6A2/nn ± pH2O (A = Cl–, NO3–, SO42–) were synthesized and their behaviour following treatment with chloride, nitrate and sulfate solutions was studied by powder XRD and SEM. Two types of transformation were found: (1) an ion-exchange reaction manifested by preservation of both the precursor's morphology and structural type; (2) a dissolution-crystallization mechanism characterized by changes in the structural type and the morphology.

The results were considered by simultaneous application of the binary presentation of the structures, a bond valence approach and the ion-exchange ability. It was found that the structures of minerals with ion-exchange properties are built from similar layered structural unit of edge-shared and corner-shared Jahn-Teller square frameworks and different interstitial complexes of exchangeable ions, water molecules and cation-water groups. On the basis of their structural features the position of the investigated minerals in mineralogical classifications is also discussed.

This research work deals with chlorite-vermiculite mixed-layer stability under hydrothermal and metamorphic conditions. We used as a case study a clayey flysch unit cropping out in an active geothermal area near to a Recent volcano (Mt. Amiata) in central Italy. The geothermal gradient is higher than the world average and temperatures over 100°C can occur at less than 1 km depth. The mineralogical data, obtained from X-Ray Power Diffraction (XRPD) analysis of clay samples from the same geologic unit, show that the primary anchimetamorphic mineral assemblage (illite, chlorite, illite-smectite mixed layers) is accompanied by secondary phases, such as chlorite-vermiculite mixed-layers and calcite. Reactive flow modelling was used to outline a realistic water-rock (W/R) interaction process able to generate the new minerals. In the numerical simulation, the pristine shale was made to react with a local thermal spring, at an estimated but realistic carbonate reservoir temperature. The simulation predicts that, at a temperature of 120°C, clinochlore dissolves and vermiculite crystallizes, a good proxy of the chlorite-vermiculite crystallization process. Under low water/rock conditions the proportions of the clay minerals (illite, chlorite, smectite and vermiculite) are comparable with the analytical results. The simulation also shows that temperatures higher than 120°C enhance the vermiculite formation. We conclude that the chlorite-vermiculite mixed-layers formed in the recent past due to the upflow of thermal water which permeated the flysch unit. This result indicates that the alteration of the clayey cap-rocks of geothermal reservoirs is enhanced by the interaction with geothermal fluids, and can be used as a prospecting tool.

A detailed survey of the most clay-rich rock units of the Meso-Cenozoic geological section exposed in the Algarve Basin (South Portugal) was performed and data were analysed for the grain-size distribution and mineralogy (whole rock and clay fraction), aimed at a compositional study of the clay-rich sediments and their depositional environment. Granulometry was obtained using wet sieving and laser diffraction by attenuation of X-rays, and the mineralogical study was carried out by X-ray diffraction.

Most clay-rich rock units of the Algarve are classified as silty clays and clayey silts, and only a minority is coarser. The mineralogical study enabled us to define two main types of clays: (1) noncalcareous clays, consisting largely of quartz and clay minerals, with goethite as the typical Fe-rich phase (sediments of Carboniferous, Neogene and Quaternary age and Cretaceous siliciclastic clays); and (2) calcareous clays, which can be calcite-rich clays (Middle and Upper Jurassic) or dolomiterich clays (Triassic and Lower Jurassic), the latter typically containing hematite as an accessory phase. Plagioclase, K-feldspar, and Ti-oxides are often accessory phases, whereas ankerite, anhydrite, gypsum and opal are rare.

In the clay fraction illite generally predominates, resulting probably from weathering of preexisting rocks, as well as the less frequent Fe-chlorite, pointing to incipient chemical alteration under semi-arid climatic conditions. Kaolinite occurs in diverse proportions, being especially abundant in Cretaceous and Cenozoic units; it is mainly related to chemical weathering in continental environments under humid conditions. As the Atlantic Ocean opened during Triassic and the continental environment evolved to a shallow-marine environment with evaporitic conditions, smectite became more expressive, being sometimes accompanied by other Mg-rich phases (chlorite, sepiolite, corrensite and palygorskite). Especially during the Cenozoic the proportion of different phases in the clay mineral association of the sediments reflects the control of tectonic movements and fluctuations in sea level during their deposition.

In this study, adsorption and adsorption kinetics of methyl violet dye from aqueous solutions onto kaolinite were investigated. The effects of adsorbent dosage, pH, ionic strength, contact time, temperature and initial dye concentration were studied. Kinetic and thermodynamic parameters were determined using experimental data. Adsorption capacity decreased with increasing ionic strength. Changes in the initial pH of the dye solution in a range close to the dye's natural pH (i.e. ∼ pH 5.0) values affected adsorption capacity slightly, indicating that adsorption studies could be carried out at the dye's natural pH. The adsorption process followed the Freundlich-type adsorption isotherms and pseudo-second order type adsorption kinetics. However, an intraparticle diffusion process was found to have effects in adsorption processes. Thermodynamic parameters were calculated from the experimental data and enthalpy of the adsorption, ΔH0, was found to be –6.82 kJ mol–1, indicating physisorption nature of the adsorption. Other thermodynamic parameters, ΔS0 and DG0, were also calculated. Negative values of ΔG0 indicated that the adsorption process for methyl violet on kaolinite is spontaneous.

Structural iron in smectites correlates with the cell edge length b and increases the refractive index. The cell edge length b is usually obtained from the position of the (060) reflection, but in this work we show that such b values differ from the values obtained from Rietveld fits because contributions from (hkl) reflections shift the position of the (060) reflection. The correlation between Fe and cell edge length b was significant (r2 > 0.99); the relationship is b [Å] = 8.9977(0.0035) + 0.1117(0.0032) × Fetot. Furthermore, we present for the first time measurements of the refractive index n of Fe-bearing smectites, applying a recently published turbidity method (Weidler & Friedrich, 2007). The refractive index correlates both with structural iron (r2 = 0.64) and with b (r2 = 0.94).

Bentonites are in worldwide use as candidate materials for the encapsulation of high-level radioactive waste (HLRW). To effectively seal waste canisters, bentonite is compacted to bentonite blocks which can be used to build a wall around the canisters. Compaction significantly improves the swelling pressure, which is currently considered as one of the most important parameters for assessing barrier performance. Most of the studies on compressibility of bentonites consider a few different materials only, which does not lead to a general understanding of bentonite performance. In order to identify the actual compressibility differences of different bentonites, a sizeable set of well characterized materials was investigated with respect to the dry densities after compaction.

Different results were obtained for bentonites that had been dried and bentonites that were equilibrated at 70% r.h. (relative humidity) prior to compaction. The dry density of dried bentonites depends on total porosity and particle density. However, the dry density of microporous bentonites depends on the microporosity rather than total porosity because microporosity is not reduced upon compaction. On the other hand, for the samples previously equilibrated at 70% r.h., the water content is most important. However, the water content, i.e. the water uptake capacity at 70% r.h., in turn largely depends on the CEC but also on microporosity. Therefore, under a given load, the 36 bentonites studied showed a significant range of resulting dry densities, depending on water content, CEC and porosity.

In conclusion, for a given bentonite, the dry density after compaction explains some geotechnical parameters such as the swelling pressure. However, for reasons explained in the present study, the dry density cannot be generally used to predict these parameters.

Alkali activation with sodium carbonates is a traditional method to improve bentonite properties for a variety of applications. In some applications, natural sodium-rich bentonites are preferred, and custom regulations require proper declaration of Na-rich bentonites, with respect to activation. Consequently, there is need for a method that can unambiguously distinguish between natural and activated Na-rich bentonites.

The paper deals with the preparation of several alkali-activated sets, specifically (a) anhydrous Na2CO3 with trace amounts of thermonatrite (Na2CO3.H2O) and trona (Na3(CO3)(HCO3).2H2O), hereafter called ASC, (b) mixtures of ASC with CaCO3, and (c) mixtures of ASC with CaCO3 and a Ca2+-rich bentonite at different moisture contents, to distinguish natural and alkali-activated bentonites by simultaneous thermal analysis (STA) linked with a mass spectrometer for the analysis of evolved gases. STA linked with MS revealed alkali activation of bentonites, even in the presence of CaCO3. The moisture content during activation and storage of activated samples, however, has a strong influence on the detection of activated samples by STA-MS. Uncertainties remain with respect to unknown foreign phase contents of technical ASC used for alkali activation in practice and the influence of carbonates like dolomite or siderite, which are often present in natural bentonites.

Biodegradable chitosan/bentonite composites with three different compositions were synthesized by the intercalation method using cetyltrimethylammonium bromide as the cationic surfactant. The composites were characterized using conductivity, density, particle size measurements, FTIR, TGA, XRD and SEM methods. Colloidal stabilities of the suspensions prepared in silicone oil (SO) were observed to increase with decreasing density. The effects of dispersed particle concentration, shear rate, electric field strength, electric field frequency and temperature on the electrorheological (ER) activities of the suspensions were investigated. The electric field viscosities of the suspensions showed typical shear thinning non-Newtonian viscoelastic behaviour. Yield stresses of the suspensions were observed to change in proportion to the square of applied electric field (E). Further, according to creep and creep-recovery analysis, reversible viscoelastic deformations were observed in the suspensions under E ≠ 0 kV mm–1.

Stichtite is a naturally occurring layered double hydroxide (LDH) with the ideal chemical formula Mg6Cr2CO3(OH)16.4H2O. It has received less attention in the literature than other LDHs and is often described as a rare mineral; however, abundant deposits of the mineral do exist. In this article we aim to review a number of significant publications concerning the mineral stichtite, including papers covering the discovery, geological origin, synthesis and characterizsation of stichtite. Characterization techniques reviewed include powder X-ray diffraction (XRD), infrared spectroscopy (IR), near infrared spectroscopy (NIR), Raman spectroscopy (Raman), thermogravimetry (TG) and electron microprobe analysis.