Aluminium-substituted goethites are found in many soils and can also be synthesised readily in the laboratory. In recent years, synthetic substituted goethites have been examined by various techniques including XRD, IR, TEM and dissolution kinetics (Thiel, 1963; Jonas & Solymar, 1970; Fey & Dixon, 1981; Fysh & Fredericks, 1983; Schulze & Schwertmann, 1984; Schwertmann, 1984). Transmission electron microscopy (TEM) studies have shown that as Al substitution rises above 10%, the goethite needles become shorter and also thicker in the a direction. Furthermore, crystals which at zero substitution consist of domains parallel to the c axis become less domainic with increasing Al substitution (Schulze & Schwertmann, 1984).

The milling process in the solid-state 2:1 clay minerals, montmorillonite and talc, which have different cation exchange capacities, is reported here. Several instrumental techniques were used to monitor systematically the products formed. The dehydroxylation/amorphization of the montmorillonite and talc structures occurs within 3 and 6 h of milling, respectively. Electron paramagnetic resonance spectra indicated that structural Mn2+ was oxidized more quickly in the montmorillonite structure than in talc, while the paramagnetic defects increased during milling. Nuclear magnetic resonance was also used to monitor the environmental changes for Si and Al during milling.

The present study determined the mineralogy and thermal properties of kaolin from Acoculco (Puebla), at the eastern Trans-Mexican Volcanic Belt and compared it with the nearby deposits of Agua Blanca (Hidalgo) and Huayacocotla (Veracruz). The mineralogy of the kaolins was determined by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. Thermal behaviour was studied by differential thermal analysis, dilatometry and hot-stage microscopy. The Acoculco deposit is composed mainly of kaolinite and SiO2 minerals. In the case of Agua Blanca and Huayacocotla, alunite is abundant in places and minor anatase is also present locally. The Acoculco kaolins are Fe-poor and relatively rich in some potentially toxic elements (Zr, Sb, Pb). They undergo a relatively small amount of shrinkage (∼3–4 vol.%), during firing at 20–1300°C and cooling down to 20°C, except when >10 wt.% alunite is present. These kaolins are a suitable raw material for the ceramics industry. Other applications (pharmaceuticals, cosmetics) would require an enrichment process to eliminate impurities such as Fe oxides.

The Eocene İslambeyli Formation in the Lalapaşa region (NW Thrace, Turkey) consists predominantly of siliciclastic clayey clastics at the bottom and of claystone, tuff and tuffaceous claystone/ sandstone/limestone in the middle and uppermost parts of this formation. Some tuff-tuffaceous beds of the middle–upper parts of the formation are economically viable bentonite depoits. The İslambeyli Formation exhibits vertical variations in the mineralogy, elemental compositions, and smectite-forming processes. Smectite was formed by weathering and diagenetic processes in the fluvial-shore environments in the lower part and by diagenetic alteration in a shallow-marine environment in the middle–upper parts of the formation. Ca-smectite flakes were formed by two processes: direct precipitation; and by means of a dissolution-precipitation mechanism from feldspar and mica. Dissolution-precipitation was most prevalent in the siliciclastic lower part of the formation. The amounts of Al, Fe, Mg and Ca required to form smectite and accessory illite were supplied mainly from the alteration of feldspars, mica and glass shards. The origin of smectite can also be explained by the inferred solution compositions given the parent phases in this formation, and the devitrification of glass shards in pyroclastic-rich middle–upper parts of the formation. In the upper beds, the observed decrease of K and Fe in the smectite structure coincided with both the increase in the amount of smectite and the increase in solution pH suggesting that precipitation of smectite developed over a prolonged period and under arid conditions.

Deuteration (H/D substitution at 200ºC) was performed on powders of two ground talcs of different particle shapes (different basal/lateral surface ratios). Results indicate that the deuteration process is only efficient on lateral talc surfaces, and suggest that the hydrogens located in the hexagonal ring of the talc basal surfaces are not exchanged. The FTIR spectra collected from the two talc samples show that it is possible to discriminate between particles with the same specific surface area but with different basal/lateral surface ratios using the deuteration process.

The exchange of Ca2+ and Na+ by tanthanide ions (Ln3+ = Pr3+, Gd3+, Er3+) in montmorillonite was investigated at two different ionic strengths (0·01 and 0·1 mol/kg). Preferential sorption of Ln3+ was observed and variable selectivity coefficients were found depending upon the lanthanide concentration in the solid, and ionic strength. The highest exchange extent of Ln3+ always occurred for the system Na+/Ln3+, but the exchange selectivities of Ln3+ were generally higher in the exchange system Ca2+/Ln3+. Although the relative affinity of montmorillonite for the three lanthanide ions was similar, distinctive behaviour between Pr3+ and the heavier lanthanides, Gd3+ and Er3+, was noted. The study of Ln3+ adsorption in trace amounts showed specific adsorption of lanthanides at high concentrations of Na+ in the external solution and that the exchange stoichiometries in the interlayer regions were 3 : 1 at equilibrium pH = 4.

Devonian rocks from the Orcadian Basin show an extreme range of organic maturity. Mean vitrinite reflectance ranges from 0·6 to 10·5% and spore colour from yellow-orange to black. Illite/smectite (I/S) is abundant in the clay fraction of lacustrine mudrocks and shows variation in expandability from 30 to <5%. A correlation is observed between expandability and vitrinite reflectance, but the specific relationship is different in the Moray Firth and the Caithness-Orkney areas. Illite ‘crystallinity’ measurements in the Caithness-Orkney area are also correlated with vitrinite reflectance. Geological evidence favours an I/S origin from precursor smectite, and mineral and chemical analyses of lacustrine shales show no evidence for regional differences in composition that might affect illitization rates. The different relationships within each region are believed to result from the different relative response of organic maturity indicators and clay minerals to temperature and reaction time. The lower I/S expandabilities in the Caithness-Orkney region at a given vitrinite reflectance are attributed to relatively longer burial times.

Glutamic acid deamination was realized in the absence and in the presence of montmorillonite saturated with various metallic cations (Na+, Mn2+, Cu2+). The catalytic activity depends upon the interlayer exchangeable cation and the pH of the suspension. A maximum was observed near pH = 5–6. In the presence of the enzyme l-glutamate dehydrogenase and the coenzyme nicotinamide adenine dinucleotide, glutamic acid transforms into α-ketoglutaric acid, but in the presence of montmorillonite, it yields α-hydroxyglutaric acid and traces of butyric acid. However, kinetic and reaction yield are significantly reduced compared to the biological system.

The surface/near-surface chemistry of allophane has been studied by X-ray photoelectron spectroscopy (ESCA) and the bulk material by 27A1 and 29Si solid-state NMR and other techniques. The surface/near-surface Si/Al ratio of allophane is c.1.0, similar to that for kaolinite, zeolite Na-A and sodalite. The core level binding energies for kaolinite and allophane are almost identical, but quite different from those for zeolite Na-A and sodalite, both framework aluminosilicates. The nature and size of these differences is consistent with the differences between the chemistry of sheet and framework silicates. The small variations in the Si(2p) spectra for kaolinite and allophane are discussed in terms of bonding of the tetrahedral units in the two materials.

Genetically homogeneous clay fractions are not always available for K-Ar isotopic dating of authigenic sedimentary material, particularly when dating illitic mixed-layer clay minerals. Three populations of mixed-layer clay minerals have been recognized in Upper Triassic sandstones from the Paris Basin (France), their occurrences being related to the flow of allochthonous fluids across the stratigraphic sections of the basin during Mesozoic times. A method is described for interpreting the K-Ar mixture ages obtained on carefully selected fractions, resulting in constraints being able to be made on the timing of the movements of these fluids.

Intercalation of surfactant and polymer chains between the clay platelets gives rise to molecular ordering that changes both the chain conformation and mobility with respect to the bulk phase. As a local probe, nuclear magnetic resonance is particularly suited for such investigations, and this review reports the main results obtained in the solid state. The properties of the modified clays are studied as a function of the surfactant loading, the nature of the head group, and the length of the hydrocarbon chain(s). The structure and charge of the mineral also influence the behaviour of molecules in the gallery space. Among papers on polymer/clay nanocomposites, those dealing with poly(ethylene oxide) have been studied in particular, using a multinuclear approach. Natural clays often contain paramagnetic species such as Fe(III) that perturb the nuclear magnetic resonance (NMR) relaxation processes and can prevent observation of appropriate NMR data. Accordingly, most organic/clay hybrids are studied with hectorite or synthetic smectites. However, the paramagnetic effect has also been found useful in characterizing clay dispersion within the polymer matrix of the nanocomposites.

Physicochemical properties of representative samples from talc deposits discovered at Pout-Kelle and Memel in Cameroon have been investigated using a variety of techniques. The data allow the study of the mineral crystal-chemistry, chemical and modal compositions, grain size distribution, textures and surface heterogeneity, and morphometric characteristics. As a result, we found that talc (platy or round, Fe-rich) prevails (65–90%) over Cr-chlorite (7–26%), halloysite, chromite, rutile, brucite and magnesite. Chemically, talc ores are made up of SiO2, MgO, Fe2O3 and minor Al2O3. Mode values range from 50 to 55 μm at Memel and from 30 to 90 μm at Pout-Kelle. Specific surface areas measured by BET and t-plot methods range from 1.3 to 2.5 m2/g. The large values of morphometric characteristics are indicative of high crystallinity and platiness. Potential uses of these talc ores in the rubber, plastics and paper industries require beneficiation processes. Interestingly, the Memel deposit and most zones of the Pout-Kelle deposit are free of needle-shaped crystals, an advantage for environmental safety.

The clay deposits in fractures of the metamorphic basement under the Paris Basin sedimentary formations at Sancerre-Couy (France) are composed of trioctahedral species which are exceptionally well crystallized. Three samples were chosen in order to study the chemical composition of 100% expandable saponite, 50% expandable corrensite and 10% expandable chlorite-saponite mixed-layer mineral C90–S10 Two sets of microchemical analyses were performed in order to determine the variations of the composition on large and small numbers of particles. X-ray diffraction (XRD) and Mössbauer spectrometry were performed on purified samples.

The mathematical decomposition of Si, Al and Mg histograms established from microanalyses of a large number of crystals of saponite, corrensite and C90–S10 evidences bimodal populations. The total Fe content of the three species is unimodal whatever the chemical composition of the surrounding rock and the Fe2+/Fe3+ ratio. The structural formulae established from a large number of microanalyses of a few particles show that there are no parental relationships between saponite, corrensite and C90–S10. The expandable layer of corrensite is characterized by a high charge. It is proposed that the tetrahedral sheets adjacent to the brucitic sheet and the exchangeable interlayer in a 2 : 1 unit are identical in corrensite.

Understanding the chemical variability of clay minerals depends on the analytical reliability of the techniques used. Uncertainties in clay mineral compositions were computed for common sources of analytical error such as those that arise from contaminant phases present in clay size-fractions in concentrations below the detection limit of routine XRD screening techniques, and the analytical limits of precision for TEM/AEM analysis. When plotted on standard diagrams used to represent clay mineral compositions, the calculated error envelopes were found to be of significant size, such that analyses of pure illites and pure smectites straddled the field for mixed-layered illite-smectites. In addition, on some diagrams random analytical errors resulted in linear trends identical to those caused by mixtures of two or more clay minerals. It follows that variations in the compositions of clay minerals reported in the literaure do not always necessarily represent the actual chemical variation of the minerals. As a result, current interpretations of clay compositional variations may not be as definitive as hoped.

Se estudia el efecto de la deshidratación sobre la superficie especifica y distribución del tamaño de poro en sepiolita y palygorskita. Se emplean las técnicas de A.T.D., A.T.G., adsorción-desorción de nitrógeno y microscopía electrónica.

La eliminación del agua higroscópico-zeolitica incrementa en los dos minerales la superficie especifica y la proporción de microporos accesibles a las moléculas de nitrógeno.

Con la pérdida del agua de cristalización disminuye, en ambos minerales, la superficie especifica y la proporción de los citados microporos, desapareciendo los de anchura inferior a 7 Å en las próximidades de la eliminación completa de esta clase de agua.

La eliminación del agua de constitución origina neuvos descensos de la superficie especifica en la sepiolita de acuerdo con las alteraciones sufridas, puestas de manifesto en al análisis térmico; más acusadas que en la palygorskita.

Complexes of Cu(lysine)2+2 and Cu(histidine)2+2 have been intercalated between the layers of saponite clays by a simple cation exchange procedure from aqueous solutions of preformed Cu(amino acid)2-complexes. Successful immobilization was obtained with an amino acid: Cu2+ ratio of 5, and a pH of 10 and 7.3 for lysine and histidine, respectively. The synthesized materials were investigated as powders and as thin films by electron spin resonance (ESR), diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). The light blue clays are characterized by an axially symmetric ESR spectrum with A//= 192 G, g//= 2.23 and g⊥ = 2.07, and a d-d absorption band around 600 nm, due to the intercalated planar Cu2+-complexes. Ammonia interacts reversibly with these intercalated complexes, suggesting the presence of a free coordination site. The novel synthesized materials are active in various oxidation reactions with t-butyl hydroperoxide as oxidant.

The choice of kaolinite sample for surface chemical studies is examined. An adsorption apparatus, particularly suited for those studies where the adsorbate acts as a deflocculant, is described. Some preliminary results are given for the adsorption of total phosphate from tetrasodium pyrophosphate solutions and of polyacrylate from sodium polyacrylate solutions. The release of aluminium and silicon from the kaolinite was measured; with tetrasodium pyrophosphate, aluminium-phosphate complexes are formed.

Competitive adsorption measurements suggest that the polyacrylate is adsorbed on the positively charged edges of the kaolinite.

We have investigated the adsorption of D- and L-alanine, and their respective dimers, by three allophanes with different Al/Si ratios. The Kanuma (Al/Si = 1.2) and Kitakami (Al/ Si = 1.5) allophanes were from Japan whereas the Te Kuiti (Al/Si = 1.6) sample came from New Zealand. The three allophanes differed in their capacity for adsorbing alanine but none of the samples showed a clear preference for either the D- or the L-form. In the case of alanyl-alanine both Kanuma and Kitakami allophanes gave a hint of preferring the L- to the D-enantiomer. On the other hand, the allophane sample from Te Kuiti showed a clear preference for L-alanyl-L-alanine. In keeping with this observation, circular dichroic spectrometry indicated that solutions of a racemic mixture of alanyl-alanine, after equilibration with Te Kuiti allophane, became relatively enriched in the Denantiomer. The size, intra-molecular charge separation, and surface orientation, of L-alanyl-Lalanine zwitterions apparently combine to confer ‘structural chirality’ to the complex (adduct) with Te Kuiti allophane. As a result, the mineral-organic complex develops a preference for the L-form of alanyl-alanine. This finding points to a possible role of certain allophanes in the origin of biochirality.

The spatial distribution of the Atterberg limits can be used to distinguish the consistency and behaviour of a soil and its engineering properties, which strongly depends on the water content of the soil and types of silts and clays in the soil. By spatial modeling, and comparing the results of ordinary kriging with the cokriging approach, this study aims to find correlations between the Atterberg limits and the selected physical soil parameters in order to examine how effective they are in generating an understanding of the dynamics of a physical soil system.

In 156 soil samples, the Atterberg limits and soil moisture conditions were determined, and auxiliary functions were selected by application of cokriging using correlation analysis and regression equations obtained by the residual maximum likelihood (REML). These techniques were evaluated by the results of the mean absolute error (MAE) and the mean squared error (MSE). Cokriging analysis was found to be more effective at estimating the liquid limit (WLL) and the plastic limit (WPL) than kriging analysis and with smaller error values. On the other hand, the kriging approach, which had smaller MAE and MSE values, was more effective at estimating the plasticity index (WPI) values than the cokriging method. Unlike the REML regression equations, the field capacity (FC) value was the more suitable parameter for the cokriging estimates. When the necessary labour and time were considered for determining the Atterberg limits, both kriging and cokriging were found to be applicable for estimation of these limits.