Complex formation enhances the sorption of various diamines from aqueous solutions by montmorillonite in the presence of copper and vice versa. A distinct difference was observed between chelating and nonchelating diamines. The effects were measured quantitatively, and the resulting structures were investigated by X-ray diffraction tedhniques. No direct correlation was observed between cell height and the configuration of the interlayer complexions; ‘keying’ of organic and organometallic cations into the oxygen surfaces is inferred.

An investigation of bulk-rock and clay-fraction compositions of two sedimentary cores from southern Chile was performed to evaluate the record of temporal climatic changes during the late Quaternary (11 ky and 30 ky BP). The bulk mineralogy shows an abundance of feldspars, mica and quartz, with lesser chlorite, amphibole and pyroxene, and variable amounts of carbonates. The clay fraction consists of illite, chlorite and scarce smectite. Smectite shows platy morphology, an Al-Fe beidellite chemical composition, and is detrital. Smectite, together with biogenic carbonate, increases in levels diagnostic of warmer phases. Increases in smectite are attributed either to the beginning of chemical weathering, allowed by the glacial retreat, or to ice extension and sea-level variations. Warmer climates also favoured the increase of carbonate productivity. Levels diagnostic of colder phases show a large decrease in carbonate, small amounts of smectite and large amounts of chlorite and mica, as the abundance of glaciers reduced the productivity and prevented chemical weathering.

Two cryptokarstic (covered karsts) halloysitic deposits were compared: the Entre Sambre et Meuse in Belgium and the Périgord in France. Both belong to a continental margin subject to marine transgression and regression cycles which enhance the karstic activity. This geodynamic context appears to be very favourable to the formation of halloysite. The similarity of the geodynamic context of both sites leads to a genetic convergence linked to specific properties of the cryptokarstic system, especially, the ability to collect the percolating waters and to juxtapose the conditions of precipitation, accumulation and maturation of the halloysite silico-aluminous gel precursors. However, each site also displays pronounced specificities relevant to: the nature of the host rock of the halloysite (a partly silicified limestone in the first, a smectite-kaolinite argilite in the second); the aluminium source (allochtonous in the first, relatively autochtonous in the second); and the halloysite content of the deposits (of ∼ 100% in the first, and 40% maximum in the second).

The phase behaviour of aqueous suspensions of NAu1 nontronite was studied on size-selected particles by combining osmotic pressure measurements, visual observations under polarized light, rheological experiments and Small Angle X-ray Scattering (SAXS). NAu1 suspensions display a liquid crystalline behaviour as they exhibit a Isotropic/Nematic (I/N) transition that occurs before the sol/gel transition for ionic strengths below 10–3 M/L. This I/N transition shifts towards lower volume fractions for increasing particle anisotropy and its position in the phase diagram agrees well with the theoretical predictions for platelets. SAXS measurements reveal the presence of characteristic interparticular distances in the isotropic, nematic and gel phases. In the gel phase a local lamellar order is observed which shows that the “house of cards” model is not appropriate for describing the gel structure in swelling clay materials at low ionic strength. Furthermore, by combining results from osmotic pressure measurements and X-ray scattering, it appears that the pressure of the system can be well described using a simple Poisson-Boltzmann treatment based on the repulsion between charged infinite parallel planes. In terms of rheological properties, even if the thermodynamical status of the sol/gel transition remains partially unclear, the yield stress and elasticity of the gels can be easily renormalized for all particle sizes on the basis of the volume of the particles. Furthermore, rheological modelling of the flow curves shows that for all the particles an approach based on excluded volume effects captures most features of nontronite suspensions.

Cambrian and Ordovician pelites and greywakes from the Iberian Range were studied using XRD, EMPA and AEM/TEM techniques, lllite and chlorite are the main phases in Cambrian <2 µm fractions. Illites show crystallinities (IC) from 0.28 to 0.23°2θ the 2M1 is almost the only polytype; they do not have expandable layers, and they are heterogeneous in composition. Chlorites show two compositional types, both containing variable proportions of smectite-like layers. Clinochtores growing over bedding surfaces are also present. An evolutionary trend from anchizone to near the anchizone-epizone limit has been proposed for Cambrian samples.

In the Ordovician <2 µm fractions, illites are associated with minor chlorites and kaolinites. The ICs range from 0.68-0.28°2θ the 2M1 polytype dominates over 1M, and it is associated with illitesmectite mixed-layering (R3 ordering). An evolutionary trend from diagenesis to low grade anchizone has been inferred.

Chemical analyses of coarser detrital micas indicate muscovite and phengite compositions. The compositional heterogeneity exhibited by authigenic and detrital phases suggests that chemical equilibrium was not attained.

X-ray photoelectron diffraction data from single crystals of a biotite containing ∼1% Ti show that although this element is located entirely in octahedral sites, the Ti sites are not precisely equivalent to those of Mg and Fe. Comparisons of Ti 2p X-ray photoelectron spectra from two biotites and from two titaniferous phlogopites (∼0·3–·5% Ti) with those from Ti(II), Ti(III) and Ti(IV) oxides indicate that this element is present as Ti(III) rather than Ti(IV) in all four micas.

TiO2/stevensite nanocomposite photocatalysts were synthesized by a solvothermal method using TiCl3/HCl as reactants and the stevensite clay mineral extract as support. The prepared photocatalyst samples were then characterized using various techniques such as X-ray diffraction (XRD), Infrared spectroscopy (IR) and Transmission Electron Microscopy (TEM). The Points of Zero Charge (PZC) of the various samples were evaluated by titration of the non-modified and the Ti-modified clay aqueous dispersions, with cationic surfactant solutions. The photocatalytic activity of the resulting nanocomposites samples were evaluated for the removal of Orange G (OG) from aqueous solution as a model dye pollutant. The data indicate that the formation of Na+-stevensite by the TiO2 particles leads to TiO2/stevensite nanocomposites having higher specific surface areas and mesopore volumes, and lower PZC values. Further, the photocatalytic activity was greater for the TiO2/stevensite nanocomposites having the greatest Ti amount, as compared to a pure TiO2 sample, and increased with the increase of the TiO2 content in the TiO2/stevensite nanocomposites.

Two suggestions as to the structure of sorbed water on clays have received considerable attention. Macey (1942), arguing from the similarity between the structure of ice and of the oxygen atoms exposed at a sheet surface, has suggested that the first layers of such water might have a structure similar to that of ice. Hendricks and Jefferson (1938), on the other hand, suggested the well-known “hexagonal-net” structure, a concept which was later extended to montmorillonite (Hendricks, Nelson and Alexander, 1940), and which has recently been used increasingly in the interpretation of the properties of clays (Grim and Cuthbert, 1945; Grim, 1942; Mering, 1946).

Some difficulties in the application of these theories to montmorillonite have already been pointed out by Williamson (1947-48), but some other aspects of the problem appear to merit further consideration. For example, there is an obvious space problem which is influenced by the position of the exchangeable cations and their frequency of distribution in the space available for water.

The supposed analogy between hydrogen montmorillonite and a weak organic acid has encouraged several investigators, notably Berger and Deuel, to attempt to esterify the exchange positions using standard organo-chemical methods.

In our opinion the experimental evidence so far presented to establish the course and extent of the esterification reaction is inconclusive. Thus Berger determined the methoxyl content of the product obtained by treating dry hydrogen montmorillonite with diazomethane in ether without showing that sorbed methyl alcohol was absent. This omission is particularly relevant when Berger states that he dried his starting material at 150°C. Data on the dehydration of hydrogen montmorillonite has shown that under these conditions Berger's sample probably contained more than 2% sorbed water. Taking into account the difficulty of washing montmorillonite free of methyl alcohol, this amount of water would be sufficient to hydrolyse enough diazomethane to account for the observed methoxyl contents.

Dacitic andesitic calc-alkaline lavas and their pyroclastic rocks of Upper Cretaceous age are widespread in the Ordu area, eastern Black Sea Coast of Turkey. Ca-bentonite and Ca/Nabentonite deposits with significant economic potential formed in the broader region. The mineralogy and geochemistry of these deposits were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analyses. The parent rocks (PR) and bentonite samples were analysed for the major and trace element contents, including rare-earth elements, to understand the effect of differential alterations on element mobility. The bentonites contain mainly di-octahedral Ca-montmorillonite with minor amounts of illite, quartz, calcite, dolomite and feldspar. Primary K-feldspar and plagioclase phenocrysts were altered in the bentonite horizons, and were completely leached at greater depth. For this reason, the higher quality bentonites are found at deeper zones. Bentonite horizons are characterized by relatively high loss on ignition (LOI: 9.8–20.8%) and MgO content (3–5%) and low K2O (<0.5%) and Na2O (<2%) contents compared with the least altered parent rocks. Silicon, Ca, Mg, Mn and P are markedly enriched whereas Fe, Na, K and Ti are depleted in the bentonite samples. The chondrite-normalized rare earth element (REE) patterns show identical trends characterized by strong light rare earth element (LREE) enrichment in both the PR and bentonite samples. The LREE contents are higher than those of their heavy counterparts (HREE) in the samples. Alteration of the PR to bentonite is associated with intense chemical leaching and subsequent removal of K and Na in open-system conditions.

Potassium-bentonites have been found in the Courceyan Lower Limestone Shales near Burrington Combe and Oakhill, Somerset, consisting of thin, greenish yellow, plastic clays interbedded within a mudrock and limestone sequence. Mineralogically, the clay fraction is composed of virtually monomineralic interstratified illite-smectite containing 7–10% smectite layers. The clay fraction of the surrounding mudrocks, however, consists of an illite-chlorite dominated assemblage. Their mineral composition, trace element content, and the relative abundance of zircon crystals suggest an origin from burial of montmorillonite originally formed from volcanic ash. The presence of anomalously high trace element contents with both euhedral and rounded zircon grains in the Oakhill K-bentonites suggests a secondary or reworked origin for these samples. In contrast, the presence of a non-anomalous trace element content and large (>100 μm) euhedral zircon grains suggests that the Burrington K-bentonite is primary in origin. Modelling of whole-rock rare-earth element (REE) patterns shows that the Oakhill REE pattern can be derived from the Burrington pattern by the addition of small contributions from zircon and monazite, two major heavy minerals present. These K-bentonites probably represent the oldest Carboniferous K-bentonites so far recorded in the British Isles.

A range of allophane samples (atomic AI/Si bulk ratios 1.1-1.9) from Silica Springs, New Zealand, has been characterized by X-ray photoelectron spectroscopy (XPS). Binding energies of Si 2s, Si 2p, Al 2p, O 1s, C 1s, and N 1s electrons, together with the kinetic energies of Al KL23L23 Auger electrons, at or near the surface of allophane aggregates, have been derived. The values for Al, Si and O electrons are similar to those for kaolinite but also to those for some framework silicates (feldspars) having 4-coordinate Al. Values for N electrons suggest that N occurs in organic structures. Comparison of XPS and bulk Al/Si ratios shows an enrichment of Al at or near the surface of allophane aggregates. The same is true for C and N. Extraction with citrate-dithionite-bicarbonate (CDB) reagent leaves the surfaces depleted in Al. The CDB extracts have higher Al/Si ratios than the bulk allophanes. Similarly, CDB treatment reduces the degree of surface enrichment of C and N. Small increases in the binding energies of Si electrons following CDB treatment suggest partial dissolution of the bulk structure though a concomitant removal of a separate phase or species cannot be ruled out. The results may be accounted for in terms of the structure previously suggested for the primary spherules of Silica Springs allophane (Childs et al., 1990) though the composition of the spherules at or near the surface of the allophane aggregates is different from those of the bulk.

Marine clays of SE Norway lifted above sea-level have been subjected to weathering for 8500 years. As a result of this weathering a major part of the quartz, K-feldspar and plagioclase disappeared in the 0·2–0·6 µm fraction. Trioctahedral illite passed through the sequence: illite → mixed-layer illite-vermiculite → vermiculite → dissolution. This transformation started at a depth of 3 m, and the 2:1 layers dissolved in the upper part of the profile. Chlorite was broken down by weathering into finer particles. As a result, chlorite was first removed from the coarser fractions. Dioctahedral illite in the clay fractions passed through the following transformations in the upper part of the profile: illite → mixed-layer illite-vermiculite → vermiculite → chloritized vermiculite. Weathering models for the size fractions 0·2–0·6 and 0·2–2 µm showed that total amounts of dissolved material from these fractions in the upper part of the profile could be calculated as 55 and 38%, respectively. Dioctahedral 2:1 layers were most resistant to weathering, resulting in 75% dioctahedral phyllosilicates in the 0·2–0·6 µm fraction in the uppermost part of the profile, in contrast to 30% dioctahedral illite in the unweathered sample. This study illustrates the importance of investigating different fractions and not only material finer than 2 µm.

Dans le cadre de l'étude de l'interaction eau-kaolinite, des mesures de conductivité (pertes diélectriques) et de permittivités réelles ont été entreprises à fréquence variable (103–107 Hz) et en fonction de la température (27–80°C). La conductivité croît avec la fréquence et la température de mesures. L'utilisation d'un modèle de conduction par déplacement de protons par sauts discrets entre sites localisés est applicable. La loi σ′(ω) ∼ Aωs est vérifiée. L'évolution du paramètre s en fonction de la pression de vapeur d'eau permet de déterminer le mécanisme d'établissement de la monocouche d'eau sur le solide. La permittivité réelle décroît avec la fréquence. C'est une fonction croissante de la pression de vapeur d'eau. Un calcul simple permet de retrouver la loi expérimentale relative à la permittivité ɛ′ ∼ exp(K√P).

The adsorption of the Asulam herbicide (4-aminobenzensulphonyl-methyl-carbamate) by Al- and H-montmorillonite has been studied by IR spectroscopy, thin layer chromatography and chemical analysis. This compound is adsorbed from CCl4 solution at room temperature through protonation of the NH2 functional group by the ‘acidic’ water coordinated to the interlayer cation of the clay. After heating the complex at 75°C for 20 h, a hydrogen-bond between the C=O group of the Asulam and the water is established and the organic molecule decomposes to sulphanilic and carbamic acids. If the complex is equilibrated at 100% relative humidity, the carbamic acid becomes unstable, and the IR spectrum shows only the bands typical of the acidic montmorillonite-sulphanilic acid complex. The catalytic properties of the clay surface are demonstrated by comparison with the transformations occuring in the organic molecule on heating in concentrated mineral acids.

Iron cations in the octahedral sheet are a disadvantage to the industrial application of palygorskite clays. In this study, a palygorskite sample from eastern China (Mayaoshan deposit, Jiangsu Province) is shown to have an Fe content that is much greater than usual. The structural formula of the Fe-rich palygorskite sample was established as (Si7.48Al0.52) (Al1.24Fe0.94Mg1.77Ti0.03⁏1.02)O20(OH)2(OH2)4. The palygorskite is seen to be dioctahedral according to the structural formula, consistent with Fourier transform infrared data. Occurrences of AlFe3+ɏOH and Fe3+Fe3+ɏOH vibrations in the OH-stretching and -bending regions show that Fe atoms occupy inner sites of octahedral sheets. A Mössbauer spectrum confirmed that Fe ions occupy inner octahedral sites as trivalent Fe cations (Fe3+).

Sodium montmorillonite and pyridine form a regular complex of spacing 23·3 kX in the presence of traces of moisture. The minimum interlamellar composition necessary for the formation of the complex is approximately Na+ (C5H5N)4 (H2O)2. The intensities of the 00l reflections are considered incompatible with the complex having a five layer structure and an alternative arrangement is proposed.

The exchange capacities, surface areas (both external and total), and heats of immersion in water were measured on a selection of clay minerals and a fine-grained muscovite. The charge density (expressed as 103 X m-eq/m2) of muscovite was 3·6. This was, as expected, much higher than those of clay minerals which tended to group together, the average values being: kaolinites, 2·0; hydrous micas, 1·7; halloysites and montmorillonites, 1.4. The heats of immersion (expressed as J/m2) were, in contrast, more widely spread: muscovite, 0·63; halloysites and kaolinites, 0·49; hydrous micas, 0·28; montmorillonites, 0·14. The explanation advanced for the differences is that they reflect changes in surface energy and cohesion of the silicate layers.