The present work describes the removal of Direct Red 81, Methyl Orange, Methylene Blue and Crystal Violet from aqueous solution using halloysite nanotubes. The clay mineral was physicochemically characterized using various methods. The influences of pH, interaction time, initial dye concentration, adsorbent amount and temperature on adsorption were monitored and interpreted. Although previous work has shown that acidic pH conditions favour the adsorption of pollutants from aqueous systems by clay materials, in this study maximum removal was possible over a wide range of pH conditions (pH ≥2–12). Adsorption was very rapid, and equilibrium was attained within 30 min. For all four dyes studied, chemical reaction seemed significant in the rate-controlling step, and the pseudo-second-order chemical reaction kinetics provided the best correlation of the experimental data. Thermodynamically, the process was spontaneous, with Gibbs energy decreasing with increasing temperature. Halloysite would be suitable for removing dyes from aqueous solution. This was further tested by using the halloysite nanotubes for the removal of complex dyes from printing and ink industry effluents.

A series of weathered Paleozoic slates was studied in an area southwest of the Montes de Toledo mountain range where the weathered slates are overlain by a raña formation and show three weathering levels. The fresh slate (at 30 m depth) is composed of ferrous chlorite, mica, quartz and feldspars. In the lowest part of the weathering profile the ferrous chlorite begins to evolve to smectite, and in the intermediate level, all the chlorite has been transformed into smectite. In the upper level (in contact with the raña formation), the smectites evolve to kaolinite, and the micas, which are unaffected at greater depths, begin to evolve to vermiculite, and there has been segregation of the free iron oxyhydroxides producing red, ochre and white zones. Two principal weathering processes, separated in time but superimposed, have been identified.

Clay mineral assemblages in both shales and sandstones of Miocene age have been studied in a well from the Ulleung Basin, a back-arc basin in the East Sea. Samples were examined from burial depths of ~800 to 3000 m. At the shallowest depths the shales contain assemblages dominated by R0 mixed-layer illite-smectite (I-S) together with illite, kaolinite and minor chlorite. The sandstones also contain I-S, but are dominated by large amounts of authigenic kaolinite. In both shales and sandstones I-S becomes R1 ordered at ~ 1000 m depth and at 2000 m depth, and deeper, I-S expandabilities are <20%. At ~ 2400 m depth, kaolinite in the sandstones is replaced by abundant Li-tosudite, indicating that clay mineral diagenesis has been affected by a hydrothermal episode. Furthermore, organic maturity data indicate that much of the succession has experienced considerably higher temperatures in the past. Vitrinite reflectance data are best modelled by a short lived (0.1–0.01 Ma) heating event in the Pliocene. This suggests that the shallow depths over which the smectite to illite reaction is completed and the extensive kaolinitization of the Miocene sandstones may also be related to the hydrothermal event.

This study focuses on the mineralogical and chemical analysis of sediments overlying basaltic basement through which seawater circulates (ODP Leg 168, flank of the Juan de Fuca Ridge). A SEM and TEM-EDX study of the authigenic clays and zeolites allowed the characterization of the hydrothermal phases and the determination of their mechanism of formation. Silicate authigenesis related to hydrothermal alteration of sediment was observed in the sediment layer just above basement at sites located >30 km from the ridge axis. This sediment alteration is particularly intense at Site 1031 where authigenic formation of Fe-Mg- rich smectites (montmorillonite and saponite) and zeolites occur, linked to the dissolution of biogenic calcite. Vertical advection of basement fluid through the sediment column is required to produce this alteration. This process is still active at Site 1031, based on systematic variations in porewater profiles and temperatures obtained from stable isotopic data on calcium carbonates, and the nature of authigenic minerals.

Mössbauer spectra of Garfield nontronite H33a were taken at temperatures between 2·5 and 37 K under longitudinally applied magnetic fields up to 9 T. While no magnetic order was apparent in the absence of an applied field above 7 K, the application of external magnetic fields led to the induction of magnetic hyperfine splitting up to at least 19 K. Variation of the applied fields allowed determination of hyperfine fields of bulk nontronite, and indicated the bulk sample to have a Néel temperature of about 20 K. The non-ideal behaviour of this nontronite, leading to the lack of magnetic order in the absence of applied magnetic fields, is in line with the frustration of antiferromagnetic order in the octahedral sheets due to the presence of about 6% of the iron content in tetrahedral sites, although some influence of magnetic dilution cannot be excluded.

Asulam (p-aminobenzenesulphonylmethylcarbamate) is adsorbed by alkaline and alkaline-earth cation saturated montmorillonites at room temperature either by protonation or by physical forces. On heating it decomposes to different products depending on the polarizing power of the exchange cation. On Mg–clay, sulphanilic and carbamic acid are obtained; the latter decomposes after equilibration at 100% relative humidity. In Ba– and Ca–systems, sulphanilamide and sulphanilic acid are produced with minor amounts of p–aminobenzenesulphonylcarbamate anion. Sulphanilamide is the main decomposition product in Na–, K–and Cs–systems. On Li–clay, decomposition of the Asulam results in the formation of p–aminobenzenesulphonylcarbamate anion and p–aminobenzenesulphonylcarbamic acid, probably as a consequence of the intermediate polarizing power of this cation.

The Yaylayolu kaolin deposit is situated in the vicinity of Tavşanlı, Kütahya, western Turkey. Mineral identification and characterization studies were conducted using powder X-ray diffraction (XRD), differential thermal analyses (DTA), scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM-EDX), X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR) techniques. The degree of crystallinity, Hinckley's index (HI) and the Stoch index (SI) values were determined for kaolinite from the deposit.

Five representative samples from the kaolin deposit were used for ceramic technological tests. Particle size distribution, pH value, loss on ignition, A12O3, Fe2O3 and TiO2 contents were determined, drying shrinkage, firing shrinkage, dry bend strength, fired bend strength, water absorption, pfefferkorn plasticity index, whiteness of the fired and unfired samples (L* value) and bulk density were measured. The kaolin was found to be suitable for making white cement and wall tiles, floor tiles, and tableware items which are shaped by dry pressing and extrusion.

Kaolinite-rich rocks are widespread in Chinese coal-bearing strata. Three main types of deposits are recognized. Those deposits identified as flint clays are several metres thick and show lateral variations in bed composition. The kaolinite is thought to have formed mainly on the adjacent landmass, but some crystallization of gels within the basin is not ruled out. Tonsteins, which formed from the in situ alteration of airfall volcanic ashes, are very common in the coal measures and are up to 0.5 m thick. Finally, kaolinite deposits are described where the development of kaolin is related to weathering of coals either close to or at the present land surface.

In Moroccan calcareous mountains, red soils are distinguishable from brown soils, not only by their colour but also by their microaggregated structure. Clay mineral dispersion studies of these soils were carried out by increasing pH, after different treatments. The formation of the pseudo-particles appears to be dependent on the fixation of amorphous Fe on clay and on the chemical binding of those clays by amorphous Al-hydroxy-polycations. This can be explained by the high isoelectric point of ferric compounds such as ferrihydrite which are soluble in ammonium oxalate. Based on these results and using techniques of granulometric analysis, red clays aggregated in pseudo-particles were separated from less rubified clays. Hematite was identified in pseudoparticles from red soils and an increase of amorphous Fe has been shown in aggregated clays. These microstructural conditions characterizing rubification could also favour it, by creating microsites where water activity decreases and allows the crystallization of hematite by dehydration of ferrihydrite.

The soils examined are from alluvial sheet deposits in a high valley where they are subjected to alternate wetting and drying, leading to desiccation. They are principally derived from shale and limestone bedrock in the surrounding mountains which are rapidly eroded and transported down valley mainly when the snow melts. The soils have engineering properties of fairly low density, high permeability, high plasticity with the plasticity index above the A line (CH range). These properties are correlated with the size grading and the clay mineralogical composition – about 30% calcite, 45-50 % clay minerals, dominated by Fe3+ and Mg-smectites and fine-grained muscovite. The clay mineralogy is explained in terms of Millot's zone of smectitization affecting biotite from detrital shale fragments, the muscovite remaining substantially unaltered. Calcite solution and redeposition account for the chalky texture and strong bond.

This study focuses on the characterization, thermal behaviour and firing properties of clays from Cap Bon Basin, Tunisia. Chemical (inductively coupled plasma atomic emission spectroscopy) and mineralogical (X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy) characterization of the clays was carried out. Physical properties were identified using particle-size distribution and Atterberg limits tests. Differential thermal analysis/thermogravimetry, dilatometry, XRD and FTIR analyses were conducted to assess the thermal behaviour, transformations and crystalline phase development during firing. The clays studied show large proportions of silt and clay fractions. They are rich in SiO2, Al2O3 and Fe2O3 and mostly consist of illite, kaolinite, smectite and minor mixed-layer illite-smectite. Associated minerals are mainly quartz, calcite and feldspar. To monitor the firing properties, three clay mixtures referred to as M1, M2 and M3 were prepared according to the physicochemical and mineralogical characteristics of the raw clays. These were sintered at 900°C, 1000°C and 1100°C and tested for firing shrinkage, flexural strength and water absorption. As a result, various mineralogical transformations occurred at 900–1100°C associated with the crystallization of new phases. The main transformations identified at >1000°C resulted in the formation of anorthite and mullite, causing significant densification of the fired ceramic materials. Sintering at 1100°C increased the densification and thus improved the flexural strength. At this temperature, the sintered ceramic tiles exhibited excellent properties, namely water absorption of 2–3% and flexural strength of 30–41 MPa, indicating that these studied clays might be used as raw materials for the production of stoneware tile ceramics.

The interactions between glycine and two Na-, Ca- and Cu-exchanged smectites with different layer-charge location were studied. The sorption of glycine depends on the nature of the interlayer cations (Ca < Na < Cu), and on the type of smectite. Sequential extraction procedures were carried out in order to test the possibility of removing metals and/or glycine from the smectite interlayer. By the end of the treatments, the release of the amino acid from the substrates, with the exception of Cu-rich smectite, was virtually complete. The thermal curves of glycine-smectites confirm the stronger bonding of the amino acid with Cu-exchanged samples, and FTIR spectra indicate that glycine is mainly sorbed in the zwitterionic form. The data obtained suggest that in investigations into mechanisms of the binding of metals by minerals and their subsequent mobilization, amino acids merit close attention.

The bentonite deposits in Başören Kütahya, W Anatolia, Turkey were formed by alteration of Pliocene perlite and pyroclastic rocks. Two types of bentonites are distinguished in this area on the basis of their physical properties, chemistry and occurrence. Bentonites were examined to determine their mineralogical, chemical and physical properties. Analytical methods include X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis and measurement of cation exchange capacity (CEC), swelling volume, water adsorption, bleaching capacity, and firing shrinkage. Bentonites consist mainly of dioctahedral smectite. They also contain zeolite, opal-CT, cristobalite, quartz, feldspar, dolomite and calcite. The ‘Type 2’ bentonites had greater CEC, swelling volume, water adsorption and bleaching capacity than ‘Type 1’. The variation in the physical properties of the two bentonites is attributed to the differences in the non-clay mineralogy and to the chemical composition and nature of interlayer cation.

In the oil fields in the Central Graben of the North Sea, Maastrichtian chalk is an important hydrocarbon reservoir, but oil may also be found in the Danian chalk, consisting of white chalk interbedded with clay layers. Within the chalk section, discrete intervals appear like chalk but contain large amounts of quartz (up to 100%). The aim of the present investigation is to reveal the mechanism for formation of the quartz in these intervals and to discuss their regional distribution and importance for the reservoir properties. Samples of chalk, including quartz-rich intervals, and clay layers from three wells SA-1, Rigs-1 and Rigs-2 in the South Arne Field have been investigated. Calcite-free residues obtained using a buffered dissolution of calcite were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The main silica phase in the Upper Cretaceous–Danian chalk in the three wells is a nano-size α-quartz. This has probably formed from Si dissolved from radiolarians in the free-water phase. The 600 Å diameter α-quartz spheres precipitated in the free-water phase with subsequent flocculation of the spheres and sedimentation of the flocs. Variations in the proportion of quartz in the chalk are attributed to variations in the amount of radiolarians in combination with variations in CO2 concentrations in the water; increased CO2 causes dissolution of coccoliths and thus a relative enrichment in quartz. This formation mechanism is regional and makes it probable that the layers rich in nano-quartz may be found over large areas provided that the chalk is authigenic. Quartz-rich layers are generally of low permeability and in areas with authigenic chalk these layers may act as internal seals in chalk reservoirs.

Electron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.

Three-component interstratification of layer silicate minerals in the clay fractions of soils and sediments is probably more common than is generally realized. However, interpretation of the proportion and arrangement of the various components from experimentally recorded X-ray diffraction curves is difficult and in this paper a series of calculated diffraction patterns are presented which illustrate the types of diffraction patterns obtained from interstratified mica-vermiculite-montmorillonite systems.

The Dalradian meta-limestones of the Banffshire coast have been investigated as part of a study of the mineralogy of Scottish sedimentary and metamorphic rocks, the main purpose of which is to assess the extent to which soil minerals are inherited from such parent rocks. Saponite was found to be a common constituent of the non-carbonate fraction. Thin sections of the limestones were examined microscopically and the textural relationships between the saponite and the other minerals, particularly those of undoubted metamorphic origin, suggest that the saponite was formed during the metamorphism. Recent reports of the hydrothermal synthesis of saponite at elevated temperatures and pressures support this hypothesis.

La fixation du potassium par la montmorillonite sous l'effet des cycles d'humectation et de dessiccation est un phénomène bien connu. On ne peut cependant considérer ce dernier comme responsable de la rétrogradation du K dans les sols que si cette fixation peut se produire même en présence d'autres cations. Chaussidon (1963) avait étudié dans ce but l'évolution de la montmorillonite de Camp-Berteaux K-Ca soumise à des cycles d'humectation et de dessiccation, et avait observé aussi, dans ce cas, une fixation du K. Depuis, les auteurs de la présente communication ont pu proposer un mécanisme de fixation du K par la montmorillonite. A la lumière de ces résultats (aussi les résultats de Glaeser & Mering (1954)) l'étude de l'évolution de la montmorillonite biionique K-Ca sous l'effet des cycles d'humectation-dessiccation a pu être reprise et interprétée. Les résultats de Chaussidon sur la montmorillonite de Camp-Berteaux et ceux qui ont été obtenus sur celle du Wyoming permettent d'établir une comparaison entre les deux minéraux. Le mécanisme de fixation du K est identique et une interprétation des différences observées est proposée.