L'étude porte sur la décomposition du massif de bandes de vibration de valence O-D centré vers 2500 cm−1 que présentent les spectres infrarouge des hydrates à deux couches des vermiculites -Ca et -Mg partiellement deutérées. La détermination des bandes composantes a été effectuée à partir, d'une part de l'étude du dichroïsme des bandes de vibration infrarouge, d'autre part des données structurales disponibles sur les couches interfoliaires de ces minéraux. Ces deux méthodes conduisent—avec un accord satisfaisant—à une décomposition en 4 bandes composantes correspondant à 4 types de liaisons O-D...O. Parmi ces liaisons entre molécules d'eau, certaines sont relativement courtes, ce qui conduit à penser qu'il existe dans la couche interfoliaire de ces hydrates une charpente de molécules d'eau un peu analogue à une charpente anionique.

The chemical, textural and structural transformations of Al13-intercalated montmorillonite, resulting from the depolymerization of the interlamellar Al13 polycations by Na salicylate solutions, were studied. Nitrogen gas adsorption shows a dramatic decrease in specific surface area from 493 to 39 m2g–1, due to the loss of microporosity. Modelling of small-angle X-ray scattering (SAXS) curves shows that the final product contains two phases: a Na-exchanged swelling phase accounting for 40% of the clay, and a fixed interlayer distance (20.8 Å ) phase accounting for 60% of the clay. The Al remaining in the clay galleries (45% of the initial Al) is composed of 13% Al13– and 87% hexacoordinated Al, probably Al(OH)03 and oligomeric Al-salicylate complexes, as shown by 27Al NMR. The instability of Al13-intercalated montmorillonite towards organic ligands is related to the hydration shell of the tridecamer, revealed by SAXS. These results focus on the necessity to take into account the presence of organic ligands in natural media when using materials such as Al13-intercalated clays.

An artificial neural network with back-propagation architecture has been applied to the problem of the quantitative analysis of simulated clay mixtures from synthetic X-ray diffraction (XRD) data. A ‘clay characterization function’ (CCF) has been devised that combines information from two clay XRD peaks into a single peak that simplifies the problem which the neural network must solve. In addition, it eliminates peaks from non-layered minerals. A neural network with 17 neurons in the hidden layer and log-sigmoid transfer functions in each layer is sufficiently successful at predicting the compositions of binary and ternary mixtures of the three model clays to demonstrate the potential of the method. Moreover, training is accomplished in relatively short times using a Levenberg-Marquardt algorithm.

Although the problem ‘solved’ by this neural network is rather simple, the approach has the potential for the much more complex problem of the quantitative phase analysis of mixtures of real clay minerals. In this study, only the CCF peak heights have been used, but the positions and peak widths also contain important information. It may be practical to include as variables not only the concentrations of clay phases, but also compositional information to which XRD is sensitive.

Kaolin deposits >10 m thick overlie unconformably a Mesozoic ophiolite sequence at Jabal Humr, Masirah Island, Oman. The clay's mineralogical and chemical composition, plasticity and moisture content were measured to determine its genesis and suitability for commercial usage. The clay-rich raw material contains 76–94% kaolinite and varying amounts of quartz (micro sheets coating kaolinite) and calcite as well as secondary sulfates. The mode of occurrence, an associated shallow-marine iron oolite/pisolite unit, various secondary minerals which can only form in a gossan environment (oxidation zone of a much older sulfide deposit), and minerals such as gypsum that are highly unstable within a laterite, have led to the conclusion that the Jabal Humr kaolinite deposit cannot have the lateritic origin that has been suggested previously. Rather, it must have formed in a coastal marine environment with a subsequent strong geochemical overprint from the underlying gossan environment, after being enveloped by Tertiary carbonates. A high plasticity and its light colour after firing indicate that this material is suitable for industrial use, especially in pottery. Occasional high contents of up to ∼25% extremely fine-grained quartz (sheet-like, <50 nm thick) reduce the need for quartz addition during the processing for ceramic materials; such natural kaolinite-quartz mixtures already produce a suitable blend of materials. The possible occurrence of spalling during or after firing, caused by the sporadic presence of accessory calcite, can be avoided by by further addition of quartz which leads to the formation of calcium silicate.

This work determines the optimal palygorskite (Plg) content (maximum surfactant adsorption point) to achieve organophilization using the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) at various concentrations. Adsorption assays were carried out in a finite bath after varying the content of Plg and CTAB in solution. In those assays, the effects of time, temperature, pH and thermodynamic characteristics were studied. The results were analysed using the Langmuir, Freundlich, Dubinin–Radushkevich and Tempkin adsorption models. The increase in clay content in the dispersion leads to a decrease in adsorption of surfactant on the clay. It was possible to obtain the optimal Plg content to achieve organophilization at various concentrations of CTAB surfactant. The experimental data fitted well to the Freundlich model. The Dubinin–Radushkevich and Tempkin isotherms confirmed the chemical adsorption of CTAB on Plg clay.

To produce an optimized matrix for the in situ crystallization of zeolite Y, a commercial kaolin chemically treated with NaOH solution at 97°C for 24 h and thermally transformed from 750 to 1100°C was studied. The kaolin calcined at 750°C has 20% more reactive tetrahedral aluminium species for the synthesis of zeolite Y than kaolin calcined at 865°C. The kaolin calcined at 1000°C has amorphous silica zones that may be extracted using caustic solution; this increases the surface area by a factor of 16 and generates mesopores ~5 nm in diameter. These structural changes in the calcined and treated kaolins were combined to prepare microspheres of the mesoporous matrix, upon which well-dispersed crystals of zeolite Y crystallized.

A natural clinoptilolite nanostructure (CNS) along with ultrasonic irradiation was used to remove Cu2+ ions from polluted water. In the first part of this work, natural clinoptilolite was converted to CNS by ball milling. The natural clinoptilolite and prepared CNS samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction, N2 adsorption/desorption and pH at the point of zero charge analyses. The SEM images showed the development of CNS from natural clinoptilolite by ball milling. The N2 adsorption/desorption and FTIR spectroscopy confirmed the greater specific surface area, pore volume and number of surface groups of the CNS compared to the natural clinoptilolite. In addition, the crystalline phase of the CNS was the same as the natural clinoptilolite. In the second part of this work, the ultrasonic-assisted sorption of Cu2+ ions from polluted water by CNS was investigated. These experiments were optimized with response surface methodology based on central composite designs. The effects of initial pH of solution, CNS dosage, sonication time and temperature on Cu2+ ion-removal efficiency were investigated. By using a CNS dosage of 500 mg L−1, an initial pH of 6, a sonication time of 12 min and a sonication temperature of 45°C as optimal conditions, 97% of Cu2+ ions were removed from contaminated water. The initial pH was the most effective variable. Ultrasonic-assisted sorption of Cu2+ was more effective than sorption alone, onto the CNS.

Solid solutions of fluoromicas WMg2Li(Si4−x GexO10)F2 (W = K, Na, Li. 0 ≦ x ≦ 4), which were closely related to taeniolite, were synthesized and the effect of the isomorphic substitution Ge for Si and also the interlayer cations Li, Na and K respectively upon hydration and dehydration were studied by X-ray diffraction, infrared and thermal analysis. The Na- and Li-series exhibit swelling with water, whereas the K-series does not. The increase of tetrahedral germanium substitution reduces hydration and also lowers the dehydration temperature of hydrates in both the Na- and Li-series. The reasons for such tendencies are discussed. Repulsion between interlayer cations and tetrahedral cations seems to play the dominant role. K in opposition to the smaller interlayer cations Li and Na respectively fits in the interlayer sites of the mica structure and lowers repulsion. By increasing the substitution Ge for Si interionic distances become greater and repulsion also decreases.

In liquid-filled batteries, the liquid electrolytes may escape or present a fire hazard and an inert spacer is needed to separate the electrodes. Alternative polymer-based electrolytes are of current technological interest. Solid polymer electrolytes are non-volatile, non-corrosive materials, which can readily be processed into any shape or size. However, despite possessing the required mechanical properties, they have inherently lower conductivity. Gel-based systems are an attempt to strike a balance between the high conductivity of organic liquid electrolytes and the dimensional stability of a solid polymer.

Rectorite was modified with dodecyl benzyl dimethyl ammonium chloride to form organic-modified rectorite (OREC). OREC was used as a filler additive to modify gel polymer electrolytes (GPEs) and prepare composite gel polymer electrolytes (CPEs) which consisted of polymethyl methacrylate (PMMA) used as a polymer matrix, propylene carbonate (PC), used as a plasticizer, and LiClO4, used as a lithium ion producer. A variety of physical and chemical techniques was used to characterize the CPEs. The interlayer d spacing of OREC was much larger than that of the initial rectorite (2.22 nm). OREC also possesses a fine microscopic structure, and has a hydrophobic surface. Molau and XRD analysis of CPEs indicate that OREC has good compatibility with the components of CPEs and can be dispersed well. The effects of temperature and OREC dose on properties were studied. The temperature dependence of ionic conductivity of CPEs is well fitted by the VTF (Vogel-Tamman-Fulcher) relation. OREC doses of 5 phr gave the greatest ionic conductivity. This amount also greatly increased the plasticizer maintenance levels. Due to the occupancy of free volume space in the polymer matrix of CPEs by OREC, the bulk resistance of the CPEs was lowered and the glass transition temperature (Tg) increased. The sheet structure of OREC is thought to improve the decomposition temperature of CPEs.

The explosive ejection of material from a volcanic vent produces pyroclastics. These are stratigraphically important because of their isochronous nature, lateral extent and potential for absolute age determinations. The pyroclastics also provide information on the nature of the volcanic activity, which is possibly the only record because of non-preservation in other areas. The recognition of pyroclastics is therefore important, but often difficult,because the high-temperature igneous material is susceptible to alteration in the diagenetic environment. In Quaternary sediments the composition of glass shards is an important aspect of tephrochronology (Westgate & Briggs, 1980) but in older sediments glass shards are usually altered to clay minerals. Exceptionally, shards are preserved unaltered, as in the case of early carbonate and silica cementation (Francis et al., 1968; Jeans et al., 1977). According to Ross (1928), features that are diagnostic for the recognition of a volcanic clay (bentonite is the term used by Ross) are, in order of apparent reliability: (i) presence of glass relict structure; (ii) presence of minerals and crystal forms characteristic of volcanic rocks, including biotite, feldspar, pyroxenes and hornblende; (iii) absence of minerals that do not have a volcanic origin, including microcline, garnet, muscovite, kyanite and andalusite; (iv) waxy lustre; (v) reaction to water; (vi) optical properties; (vii) chemical properties.

Namacotche gem-bearing pegmatites of Alto Ligonha pegmatite district are heterogeneous, strongly fractionated, and have large Li and Ta and extremely large Cs contents. Clay samples were collected in fracture infillings and dilation cavities with gemstones and were studied using X-ray diffraction (XRD), polarized light microscope, scanning electron microscopy-energy dispersive spectroscopy, high-resolution transmission electron microscopy and chemical analyses. The <2 μm fraction contains cookeite, illite, illite-smectite and suggested irregular mixed-layer cookeite-smectite, beidellite, montmorillonite, kaolinite and goethite.The XRD patterns of chlorite and their d values suggest the presence of ‘di-trioctahedral chlorite’ similar to cookeite-Ia polytype. Cookeite chemical analyses show that Li contents range from 0.82 to 1.08 atoms per half unit cell.

A close relationship has been established between occurrences of gemstones and clay minerals. Some important textures and crystal chemistry are discussed.The main gemstones related to the Namacotche Pegmatite are: morganite (pink cesian beryl), kunzite (spodumene) and elbaite tourmaline. As the mechanisms responsible for the gemstone formation take place at low temperature, the clay minerals paragenesis cookeite ± cookeite-smectite interstratification ± beidellite + montmorillonite ± illite-smectite interstratification, represents a late-stage secondary paragenesis, generated by hydrothermal alteration.

As plots of K-Ar ages vs. percentage of the detrital component of mineral mixtures containing a detrital and a diagenetic illite (or illite-smectite) have different curved shapes, the linear extrapolation method of extracting the end-member ages is not justified. The curvature depends on the difference in K2O contents; thus it can be minimized if the percentage of detrital illite is normalized to the sum of detrital illite plus illitic fraction of diagenetic illite-smectite.

A white-burning, highly-plastic clay from Jamaica, containing mainly disordered kaolinite, was examined recently. It was unusual in that it was practically free from fine mica, and therefore could be purified readily by standard sedimentation techniques.

The cation exchange capacity was abnormally high, and the purified clay mineral, on analysis and calculation of the ionic composition, was found to be deficient in aluminium, but contained magnesium and iron.

The results confirmed the view, previously expressed, that disorder in kaolinites is associated with a high cation exchange capacity and a substituted lattice.

Des phases transitoires ont été préparées par activation thermique de deux montmorillonites, l'une calcique et l'autre sodique, dans le domaine de température 650–950°C, puis étudiées par spectroscopie infrarouge. Le coefficient de désordre à courte distance, défini à partir de l'élargissement et l'intensité de certaines bandes caracteristiques, présente ses valeurs maximales avec les phases transitoires obtenues à 800°C et 820–850°C respectivement pour la couche de silice et la couche d'alumine. Ce résultat a pu être corrélé à plusieurs données expérimentales concernant la cinétique de dissolution de ces phases transitoires dans l'acide fluorhydrique dilué ou dans des solutions saturées d'hydroxyde de calcium. En outre, l'accroissement particulièrement marqué du désordre à courte distance mis en évidence au niveau de la transition V→IV de la coordinance de l'aluminium, confirme l'hypothèses émise antérieurement par d'autres auteurs pour expliquer le troisième effet endothermique de faible intensité observé sur les courbes ATD des montmorillonites entre 800° et 900°C.

L'exploitation des diagrammes de sélectivité de la montmorillonite, en equilibra avec la phase vapeur délivrée par des solutions aqueuses d'éthane 1-2 diol, permet de montrer que la quantité de diol interfoliaire est supérieure a 25 % et qu'elle est directement reliée à la chaleur d'hydratation des cations compensateurs.

Les cinétiques de désorption, réalisées à plusieurs températures, permettent de retrouver les mèmes résultats, à savoir que l'encombrement moléculaire depend du cation compensateur.

Ainsi, la mesure des surfaces totales des minéraux argileux avec l'éthane 1·2 diol n'a de sens que si, d'une part, on opere toujours avec le mème cation (σm = cte) et, d'autre part, on determine la quantité de diol en contact avec la surface à partir de plusieurs cinétiques de désorption réalisées à différentes temperatures.

In order to evaluate the long-term behaviour of the engineered barriers in geological disposal sites for transuranic element-bearing (TRU) waste, an evaluation by numerical analysis is required. Although chemical and hydraulic/mechanical analyses have been conducted independently until now, essentially both type of phenomena occur simultaneously and produce synergistic effects. Therefore, we focused attention on the buffer (bentonite) engineered barrier and conducted a study of which involved incorporating hydraulic/mechanical phenomena into the chemical analysis of bentonite alteration. The simulations employed weakly-coupled chemical and hydraulic/mechanical effects to study the behaviour in one dimension.

The results showed that the dissolution of the montmorillonite is suppressed in the buffer section nearest the cement material. Moreover, in order to achieve a fully coupled analysis in future, the present study also identifies issues that need to be resolved.

Over several decades, a wealth of literature has been devoted to correlations between the chemistries of phyllosilicates and their crystallographic unit-cell parameter values. The c parameter is currently used because of its relation to the layer-to-layer distance, characteristic of the various families of phyllosilicates. The b parameter is also of interest because it allows measurement of the layer lateral dimensions and inherent structural adjustments. This unit-cell distance can be extracted from X-ray diffraction traces from the (06ℓ;33ℓ) diffraction region and by attributing the main diffraction peak observed to a 060 reflection, leading to the relationship b = 6.d(060). The aim of this paper is to revisit the relationships between the b value (or equivalent) of the phyllosilicate (i.e. TO, TOT and TOTO) or hydroxide (i.e. hydroxide, oxyhydroxide and layered double hydroxide) families and the layer chemistry based on a mean ionic radius R of octahedral cations, calculated as $R = \mathop \sum \nolimits_{i = 1}^n ( {r_i.x_i} )$, where ri is the ionic radius of the octahedral cation i and xi is its molar fraction over n types of octahedral cations ($\mathop \sum \nolimits_{i = 1}^n ( {x_i} ) = 1$). The data were collected from the literature and involved both natural and synthetic samples with both dioctahedral and trioctahedral structures of the octahedral sheet. The results showed that b values can be linked strongly to R, leading to suitable linear regressions for all of the studied structures. All correlations were found to be applicable irrespective of the di- or trioctahedral nature of the octahedral sheet, and these are discussed in light of (1) the lateral dimension of the octahedral sheet and (2) the dimensional misfit between the tetrahedral and octahedral sheets. For hydroxide families, all data can be gathered on a single b vs R correlation line, and the dimensional properties of the octahedral sheet can be interpreted simply based on an oxygen–cation–oxygen mean distance. For TO structures, two general b vs R correlation trends were reported, and these were assigned to two adjustment mechanisms corresponding to distinct types of tetrahedral and octahedral distortions. For the mica TOT family, two main trends were also reported, whereas the use of the synthetic mica series allowed us to demonstrate that the obtained scattering of data was mainly driven by the presence of multiple limited solid solutions. Such chemical complexity was also noted for smectites, especially regarding the tetrahedral composition and associated variability in layer charge. This variability made it difficult to propose a general regression correlating b to R values for smectites, although the regression obtained for neutral TOT layers can apply as a first-order relation. Finally, a single general b vs R correlation was obtained for chlorites, and the observed slope of the regression was interpreted according to the role played by the isolated hydroxide sheet on the evolution of the lateral dimension of the structures.

Clay minerals occurring in bituminous and brown coals have been identified by X-rays as illites and kaolinites. On burning coals reactions take place between the clays, lime, ferric oxides and sulphur. The clays set free the sulphur as sulphur dioxide rather than form anhydrite. The influence of clays on slag formation is described. Clays raise the viscosity of slags. In bituminous coal ashes the melting point is raised but in the ashes of brown coals lowered by the presence of clays. Examples in fluxed-ash and cyclone firing are given.

Fixation of K by some West Indian soil clays was proportional to their montmorillonite contents. Reductions in c.e.c. and surface areas occurred after fixation. The reductions in c.e.c. were equivalent to the amounts of K fixed, suggesting that an ion exchange mechanism was operative. Reductions in c.e.c. were proportionately greater than reductions in surface area.

Release of native K from the clays was greater from the < 0-2 μm fractions than those from 0·2−2·0 μm. Appreciable amounts of'recently fixed' K were not released after extraction with 0·03 N NaCl solution. Removal of 'free' iron increased the release of: (i) native K from the 0·2−2·0 μm fractions ; and (ii) 'recently fixed' K from both fractions. The presence of NH4 ions decreased the release of 'recently fixed' K.

The release pattern of the clays indicates that intra-particle diffusion rather than film diffusion or mass action exchange, is the rate-limiting mechanism.

The present study examined the microstructure and mechanical properties of ceramic composites based on a kaolin from Djebel Debbagh, northeast Algeria, composed mainly of kaolinite and halloysite with the addition of various amounts of BaCO3. The composites were prepared by high-energy ball milling and sintered at 1100°C and 1200°C for 3 h. The samples sintered at 1200°C without BaCO3 were composed mainly of mullite, which disappeared with increasing BaCO3 content. X-ray diffraction investigation showed the presence of hexacelsian (BaAl2SiO6 and BaAl2Si2O8), which disappeared at BaCO3 contents >50 wt.% in favour of barium aluminium and barium silicate phases. At 40 wt.% BaCO3 content, the porosity of the composites decreased from 0.7% to 0.1% and the microhardness increased from 7 to 8 GPa, respectively, at 1100°C and 1200°C due to the amorphous phase.