The fine structure of the X-ray absorption spectrum observed on the high energy side of the iron K edge has been recorded with a modified commercial single-crystal X-ray spectrometer. Metallic iron samples exhibited no detectable fine structure, whereas Fe3+ in ferric oxide and Fe2+ in ferrous ammonium sulphate and ferrous sulphate produced significant fine-structure peaks due, presumably, to 1s→4p and 1s→5p electron transitions. The apex of the 1s→4p peak and the minimum between the two peaks were shifted to lower energies by the Fe2+ samples, and the corresponding apices and minima on fine-structure spectra of samples containing Fe3+ and Fe2+ were shifted by an amount which was approximately a linear function of composition. These observations have led to the development of an analytical procedure for the determination of ferric (or ferrous) iron in dry, ground or sedimented clay mineral samples. The lower limit of total iron concentration in the clay sample to which the method is applicable is approximately 1 per cent. The procedure appears promising as an indicator of the oxidation-reduction potential of the geological environment with which the clay mineral may have been in equilibrium, and as a tool of more general geochemical utility.

Stichtite is the layered Mg-Cr(III) hydroxide carbonate of the pyroaurite group. The possibility of describing Cr(III) short range order (SRO) in stichtite by use of ion chromatography of the Cr(III)-hydroxo species following acid dissolution of the compound is described. Two synthetic stichtites of similar composition (average Mg5.73Cr(III)2.27(OH)15.93(O)0.07(CO3)1.10·xH2O) prepared in the absence or presence of hydroxy-bridged Cr(III) dimers and a sample from Dundas, Tasmania, Mg6.29Ni(II)0.02Cr(III)0.90Al0.65Fe(III)0.15(OH)15.26(OH2)0.74(CO3)1.23·xH2O have been examined. Ion chromatography showed the highest degree of SRO for the Dundas stichtite. For the synthetic stichtites the sample synthesized from Cr(III) dimers had the highest SRO. No information on cation ordering could be extracted from powder X-ray diffraction data. Visible spectroscopy indicates that for constant Mg:Cr(III) ratio the crystal field splitting increases with increasing SRO. Two different OH-stretching IR absorption bands (3585 and 3472 cm−1) are assigned to OH coordinated to 3Mg and OH coordinated to 2MgCr or Mg2Cr, respectively.

Hydrotalcite-like compounds (HTlc) were found as secondary products in two corrosion experiments performed with Al plates in highly concentrated solutions (MgCl2-saturated brine) in the presence of metallic and soluble iron at 90ºC under an Ar atmosphere. The durations of the experiments were ∼10 and 13 months, respectively. To investigate the corrosion experiments, solution and gas samples were collected and the main parameters measured. The solid and liquid samples obtained were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ICP-OES. The presence of the hydrotalcite-like phase was confirmed by XRD and SEM. In one experiment HTlc was found only after dialysis. Formation of the hydrotalcite-like phase was observed at lower pH than mentioned in the literature. These results are useful in understanding the long-term behaviour of corrosion products of reactor fuel elements in relation to their possible barrier function and to comprehend the long-term behaviour of this type of waste during its final disposal.

Electron paramagnetic resonance (EPR) spectra of different particle size fractions of four kaolins from diverse sources in North America, Europe and Asia have been investigated in order to characterize their paramagnetic properties and heterogeneity. There were major differences in the sources of the EPR signals from transition metals; V and Mn were structural, Fe was both structural and as associated oxides, and Cu was in the form of an adsorbed ion. The radiation-induced free radical signals commonly known as the A- and B-centres were observed in three of the deposits; however, in addition to the previously reported 27Al hyperfine structure associated with the B-centre, we also observed much smaller 27Al hyperfine structure on the g┴ feature of the A-centre. The other kaolin sample produced four free radical signals that have not previously been reported in kaolins. Each had substantial 1H hyperfine splitting; three are interpreted as corresponding to defect centres associated with Si-OH groups, and the other to a Si hole surrounded by protonated O atoms. The EPR spectra changed progressively with particle size, and measurements on the Asian specimens after grinding showed major differences in the Fe3+ signals from the same particle size fractions separated from the natural samples, thus supporting previous reports that grinding results in major structural changes in the minerals.

Des zéolites de la famille Heulandite-Clinoptilolite se rencontrent dans toute la série cénomanienne littorale péri-armoricaine dans des faciès pétrographiques variés. Souvent présentes à l'étal de traces, leur abondance apparait liée à certaines conditions pétrogénétiques qui peuvent se réaliser localement à diverses périodes mais se généralisent au Cénomanien supérieur provoquant une régionalisation de la ‘paragenèse’: Clinoptilolite, Smectites, Cristobalite.

L'étude au microscope pétrographique et au microscope à balayage des échantillons les plus riches montre que la clinoptilolite se présente en cristaux automorphes dans des pores de dissolution intrasédimentaire. Son origine diagénétique est ici évidente; elle est postérieure à la dissolution des spicules de spongiaires et antérieure à la genèse de certaines sphérules de cristobalite. Ces néoformations se réalisent à partir des solutions interstitielles alimentées, au moins en partie, par l'altération de spicules de spongiaires, feldspaths détritiques, paillettes de mica, glauconie ...

L'origine détritique de la clinoptilolite des sédiments crétacés de la bordure occidentale du bassin de Paris qui avait été envisagée doit donc être écartée; deplús la paragenèse zéolitesmectites-cristobalite ne peut ici être utilisée comme l'indice d'une activité volcanique en cours de dépôt. Une partie des smectites, qui remplit certains pores de dissolution, prend également naissance par diagenèse précoce.

Kaolinite-smectite mixed-layers have been found to have a complex structure with smectite and kaolinite domains within layers. Here we further investigate this structure in samples with 0–80% kaolinite layers, as determined by X-ray diffraction, by means of magic angle spinning nuclear magnetic resonance (MAS NMR) of 29Si and 6Li. The 29Si NMR experiments were carried out on two samples (55 and 80% kaolinite layers), before and after their exchange with Mn2+, a paramagnetic ion that causes NMR signal loss from neighbouring nuclei, in order to investigate the distance between Mn ions and Si atoms in kaolinite sites. The 29Si NMR intensity from such sites (at ~–91 ppm) was reduced upon Mn exchange, indicating that some Mn ions are located near kaolinite Si sites. The position of the 6Li peak changes slightly (–1.3 to –1.8 ppm) but progressively with increasing kaolinite content (0–80% kaolinite layers) of four K-S specimens, suggesting two slightly different chemical environments for interlayer Li, one related to smectite and the other to kaolinite. The two sets of experiments are consistent with a complex structure of kaolinite-smectite, including smectite and kaolinite domains within layers and/or interlayers of varying smectitic and kaolinitic character.

Mica-chlorite mixed-layering was identified by X-ray diffraction (XRD) as a major or subordinate constituent in several slates of the Puncoviscana Formation from Sierra de Mojotoro (Eastern Cordillera, NW Argentina). In order to determine the crystallochemical characteristics of these mixed-layered sequences and interpret their petrological meaning, anchizonal slate P90 was chosen for TEM observations. In this slate, dioctahedral mica and chlorite form interleaved phyllosilicate grains (IPG) or stacks, up to 110 um long, preferentially oriented with (001) planes at a high angle to the slaty cleavage but also oblique to S0.

In agreement with XRD results, the main phyllosilicates identified by transmission electron microscopy (TEM) were dioctahedral mica and random mixed-layer muscovite-chlorite, with chlorite in subordinate amounts and scarce smectite. In the lattice-fringe images of mixed-layer packets, a sequence of irregular stacking that produced apparent 24 Å (10 + 14) layers was observed, but it was frequently possible to distinguish the 10 Å layers from adjacent 14 Å layers. In nearly all packets, 14 Å layers prevail, exhibiting 14 Å:10 Å ratios between 1:1 and 3:1. Some elongated lenticular fissures which are probably a consequence of layer collapse caused by the TEM vacuum were identified in these packets. The straight, continuous appearance of lattice fringes plus the scarce evidence of collapsed layers identified suggest that these packets correspond principally to mixed-layer muscovite-chlorite, which is confirmed by analytical electron microscopy analyses. However, smectite-like layers are probably the third component of some of these mixed-layer sequences, which may account for their high Si and low (Fe + Mg) contents, their low interlayer charge in relation to theoretical interlayer muscovite-chlorite, and for the presence of Ca in the interlayer site.

Textural relationships between chlorite and muscovite packets in IPG along with the observed transformations from 14 Å to 10 Å along the layer, is compatible with a prograde metamorphic replacement of chlorite in stacks by dioctahedral mica layers, probably in the presence of an aqueous fluid.

X-ray analyses of argillaceous rocks from the Skipton anticline show that their average composition is quartz 30%, calcite 27%, feldspar 5%, illite 15%, kaolin 17%. Pyrite and other constituents account for the remaining 6 %. The quartz, calcite and feldspar are considered to be detrital, the variations in their quantity and size reflecting changes in the source of the sediments. The evidence indicates the general predominance of kaolin over illite, which is contrary to other published results on Carboniferous marine shales. A kaolin-rich source is necessary to account for the composition of the sediments. An occurrence of unusually pure and well-crystalline melanterite is recorded from the Draughton Limestone.

Inceptisols are the major forest soils in northern Taiwan. Some chemical, physical and morphological properties have been documented for these soils, yet there is little information on the mineralogy and the charge characteristics of their constituent 2:1 clay minerals. In this study we conducted a detailed characterization of the clay mineralogy of two Inceptisols. Two pedons were sampled at diagnostic horizons and the clay mineralogy was examined by X-ray diffraction. The magnitude of the layer charge of the 2:1 phyllosilicates was estimated using the alkylammonium exchange method (nC = 12). The clay mineralogy of both soils was dominated by vermiculite and mica with small amounts of kaolinite. The surface horizon contained more mica and kaolinite than the lower horizons. The mean layer charge of vermiculite ranged between 0.60 and 0.86 cmolc/(O10(OH)2). The distribution of clay layer charge decreased with increasing soil depth in two pedons. Differences in layer charge between samples are due to differences in weathering processes. The difference in the extent of clay mineral weathering in the A and Bsm horizons could be partly because the mineral surfaces in the Bsm horizon were coated with organo-Fe complexes which protected them from weathering.

Pure samples of the micaceous component of Yorkshire fireclays have been separated. Examination of these by chemical, optical, X-ray, and thermal methods indicates that the material is in all likelihood an intimate mixture (but not an interstratification) of mica and a kaolintype mineral—probably the b/3 disordered kaolinite commonly found in fireclays. The evidence also suggests that this kaolin-type mineral is the end-product of weathering of the mica, and a possible mechanism is suggested.

The sorption properties of iron-modified zeolite (IMZ) and the kinetics of zinc and cadmium uptake by the IMZ were investigated by the batch method. Two kinetic stages were observed, fast uptake up to 240 min, followed by slow uptake up to equilibrium. Kinetic results were fitted to the reaction and diffusion kinetic models, which indicated that intra-particle diffusion was the rate-limiting step. The Vermeulen’s approximation model was used to predict the quantity of Zn and Cd ions removed per gram of IMZ. The results of the successive sorption and desorption of Zn and Cd ions, with different electrolyte solutions, showed the best desorption efficiency with sodium salt solutions. Four successive repetitions of the sorption/desorption cycles showed a small difference between the amount of sorbed and desorbed Zn and Cd ions from the second to the fourth cycle. This indicates excellent sorption/regeneration properties of the IMZ.

La nacrite constitue le plus rare polytype des kaolinites. Traditionnellement, on attribue á ce minéral une genèse hydrothermale (Ross & Kerr, 1931; Hanson et al., 1981 ), cependant Btihmann (1988) décrit sa formation en condition normale de température et de pression dans des milieux de solution et de force ionique élevées. Dans ce travail, la nacrite est mise en évidence dans deux anciens gisements de Pb-Zn situés dans les massifs de Jbel Slata et Garn Halfaya au nord de la Tunisie (Fig.l).

The [MnO|SiO2,Al2O3,FeO,MgO] balanced ratio (i.e. the isometric log-ratio of the MnO concentration relative to the concentration of SiO2, Al2O3, FeO and MgO) of chlorite and of whole-rock composition is an effective discriminant between Mesozoic stratigraphic formations in the Magallanes Basin (Chile). The MnO content in chlorite is only controlled by the host rock chemistry and is dependent on the geological environment. The MnO content in chlorite remains unchanged at low-grade metamorphic conditions. Single-grain chlorite analysis (n = 1042, electron microprobe) and whole-rock analysis (n = 40, X-ray fluorescence) were used to discriminate stratigraphic formations and to decipher differences in the depositional environment in the Magallanes Basin. The samples are from one Upper Jurassic and three Cretaceous sedimentary units that were affected either by low-grade regional metamorphism or by Miocene contact metamorphism. The highest [MnO|SiO2,Al2O3,FeO,MgO] values are recorded in the upper Zapata Formation. The Punta Barrosa, Cerro Toro and Tobífera Formations show slightly lower [MnO|SiO2,Al2O3,FeO,MgO] values. Elevated [MnO|SiO2,Al2O3,FeO,MgO] values at the transition between Zapata and Punta Barrosa Formations record an oxygenated shallow marine environment that can be linked to the closure of the Rocas Verdes Basin and the onset of fold-and-thrust belt formation. Decreasing [MnO|SiO2,Al2O3,FeO,MgO] values from the Punta Barrosa towards the Cerro Toro Formation indicate gradually increasing water depths during the Upper Cretaceous that correlate well with the global sea level.

Kaolin and diatomite are abundant and widely available geological materials that may immobilize or stabilize functional chemical species on their surfaces for various applications. Acid-treated kaolin and diatomite were intercalated with photocatalyst Ag-TiO2 nanoparticles using the sol–gel technique to prepare nanocomposite ceramic materials. The nanocomposites were sintered between 900°C and 1000°C to induce thermal reactions and to enhance nanoparticle–substrate attachment. Chemical and thermal characterizations of the acid-treated materials and intercalated nanocomposites were performed with energy-dispersive X-ray (EDX) analysis and differential scanning calorimetry (DSC), respectively. The Brunauer–Emmett–Teller (BET)-specific surface area and scanning electron microscopy (SEM) were employed for physical and microstructural characterization of the nanocomposites, respectively. Morphological studies revealed a uniform distribution of Ag-TiO2 nanocrystallites in pores and on mineral particle surfaces. The BET analysis showed remarkable surface and grain modification by sintering. Decreases in the BET-specific surface area were observed for the sintered ceramic nanocomposite, Ag-TiO2-kaolin (20.244 to 5.446 m2/g) and Ag-TiO2-diatomite (19.582 to 10.148 m2/g).

Earthquake-induced rock shear through a bentonite-filled deposition hole in a repository for spent nuclear fuel is an important scenario for the safety analysis because it may cause substantial damage to the canister hosting the spent fuel. Appropriate tools to investigate the effects on the buffer and the canister are required.

The study described here explored the laboratory tests conducted to develop a material model of the bentonite buffer to be used in the simulations, the material models that these tests have provided and finite element (FE) simulations of three scale tests of a rock shear for comparison between modelled and measured results. The results were used for validation of the material models and the calculation technique that was used for modelling different rock-shear cases.

The laboratory study consisted of swelling-pressure tests and tests to determine shear strength and stress-strain properties. The material model is elastic-plastic with a nonlinear stress-strain relation which depends on the density of the bentonite buffer and is a function of the strain rate. The three scale tests were modelled using the Abaqus finite element code. Good agreement between modelled and measured results was observed, in spite of the complexity of the models and the difficulties associated with measuring stresses and strains under the very fast shear.

The modelling results thus validate the modelling of the SR-Site. The modelling technique, the element mesh and the material models used in these analyses are well fitted and useful for this type of modelling.

Artificially coloured smectites (smectite pigments) were prepared via the sorption of anionic dyes on smectite saturated with ferric ions (Fe-smectite). Fe-smectite has a surface charge and is capable of decolourizing aqueous solutions containing single-component anionic dyes (Amaranth, Brilliant blue FCF and Tartrazine) or multi-component dyes (dye mixtures). Kinetic and equilibrium models were used to describe the sorption of individual dyes, whereas the decolourization of the multi-component system was studied by monitoring the reduction in the intensity of the absorption bands in the visible light region. The Langmuir–Freundlich dual-site model presented the best fit to the experimental data, and the sorption kinetics followed the pseudo-second order model. The smectite pigments were dispersed in colourless paint (10%, w/w), acting as organic–inorganic hybrid pigments. Colorimetric measurements of the powdered smectite pigments dispersed in colourless real-estate paint showed chemical compatibility without the need for solvents as dispersants. These properties allow the application of coloured smectites as pigments in a sustainable circular economy.

Microcapsules are successfully used in various applications such as self-healing, drug delivery and military camouflage. The shells of the microcapsules based on the traditional surfactant-stabilized emulsion template method are often single organic materials. The surfactants generally have insufficient stability against demulsification during preparation of the microcapsules. In the present study, kaolinite was used as an emulsifier for stabilizing Pickering emulsions and subsequently as an enhancer for forming microcapsules. Kaolinite-armoured polyurea microcapsules were fabricated based on the interfacial polymerization of isophorone diisocyanate at the oil–water interfaces of kaolinite-stabilized Pickering emulsions. The prepared microcapsules with core–shell structure were spherical and exhibited good dispersibility in anhydrous ethanol. The shell thickness (~0.5–1.0 μm) and diameter (~20.0–160.0 μm) of kaolinite-armoured polyurea microcapsules may be tailored by varying the dosages of isophorone diisocyanate and kaolinite and the emulsifying speed of the high-shear homogenizer. Hence, the encapsulation and release performance of microcapsules may be controlled. The kaolinite particles were embedded and armoured in a polyurea matrix. The formed kaolinite-embedded and -armoured polyurea structures might prolong the release of the encapsulated lipophilic Sudan Red (III) from 20 to 45 h. The microcapsules have controllable encapsulation and release characteristics for lipophilic compounds and are cost effective, making them suitable pesticides.

The Gümüşköy kaolin clay deposit, located ~40 km northwest of Kütahya, Turkey, has promising reserves for ceramic production. In order to evaluate the potential use of this region, five representative clay samples were collected and characterized with X-ray diffraction, polarized light optical microscopy, X-ray fluorescence spectrometry, differential thermal analysis and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. According to the Chemical Index of Alteration and Plagioclase Index of Alteration, the kaolin samples were formed by strong chemical alteration of the Tavşanlı volcanites. The clays contain kaolinite, illite, pyrophyllite, montmorillonite and minor halloysite, as well as quartz, plagioclase (andesine), biotite, sanidine, rutile and goethite. The clay samples were used for thermal and physical tests. The plasticity, particle-size distributions firing properties (water absorption, apparent porosity, linear shrinkage, dry bending strength, fired bending strength) and colour parameters of the fired samples were determined. The kaolinitic clay samples from Gümüşköy are suitable for making wall tiles, floor tiles and kiln wares after shaping by dry pressing and extrusion.

The treatment of water containing heavy metals has attracted increasing attention because the ingestion of such water poses risks to human health. Due to their relatively large specific surface areas and surface charges, clay minerals play a significant role in the adsorption of heavy metals in water. However, the major factors that influence the adsorption rates of clay minerals are not well understood, and thus methods to predict the sorption of heavy metals by clay minerals are lacking. A method that can identify the most appropriate clay minerals for removal of a given heavy metal, based on the predicted sorption of the clay minerals, is required. This paper presents a widely applicable deep learning neural network approach that yielded excellent predictions of the influence of the sorption ratio on the adsorption of heavy metals by clay minerals. The neural network model was based on datasets of heavy-metal parameters that are available generally. It yielded highly accurate predictions of the adsorption rate based on training data from the dataset and was able to account for a wide range of input parameters. A Pearson sensitivity analysis was used to determine the contributions of individual input parameters to the adsorption rates predicted by the neural network. This newly developed method can predict the major factors influencing heavy-metal adsorption rates. The model described here could be applied in a wide range of scenarios.