Model associations of layer silicates (kaolinite and montmorillonite) and iron oxyhydroxides were obtained by precipitating hydrous iron oxide in clay suspensions at different loading. The porosity of these clay-hydrous iron oxide associations was studied in the macro- and mesopore range by mercury intrusion porosimetry (MIP) and in the micropore region by nitrogen adsorption isotherms, being the fractal geometry applied to the approaches used in porosity studies. Results of nitrogen adsorption isotherms showed that surface area and microporosity of kaolinite and montmorillonite increased upon Fe precipitation, especially for montmorillonite. This process is accompanied by an increase in the surface fractal dimension Ds(N2) by the presence of hydrous iron oxide coating the clay particles. Results of MIP also showed a decrease in the pore volume by Fe precipitation on montmorillonite due to a decrease in the number of large pores and a development of new medium-size pores. An increase of the fractal dimension Ds(Hg) was also observed.

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.

Goethite is an important component of many soils and its transformation to hematite by fire may affect phosphate retention. This study deals with the kinetics of phosphate sorption and desorption by synthetic aluminous goethites and their dehydroxylated products. Phosphate sorption and subsequent desorption were measured for periods up to 128 h. Phosphate sorption increased with equilibrium solution concentration, Al substitution and surface area, and decreased with increasing crystal size. The trend in amount of phosphate sorbed was: partially dehydroxylated goethite > hematite > goethite. Sorption and desorption kinetics are well described by the modified Elovich equation. Desorption of a minor proportion of the sorbed P was rapid and this was sometimes followed by minor resorption. The amount of P desorbed directly reflected the amount that was initially sorbed. Acid dissolution of the Fe oxides with sorbed phosphate suggested that most phosphate was present at the crystal surface and not in relatively poorly accessible micropores.

Spötl et al. (1996) have re-examined studies published by us on clay materials of sandstones in the Paris Basin. They refute the XRD characterization, K-Ar dating and formation temperature of one of the interstratified illite-smectite phases identified and have provided an alternative explanation of the published results. However, the authors ignored some basic data provided in the publications under discussion, and they have not been able to explain readily why some of the data were discarded. Furthermore, part of their disagreement is unsubstantiated. We maintain that, on the basis of coherency and consistency of all the data obtained, as well as on independent published results, the most satisfactory interpretation for the thermal evolution of the Paris Basin is the one that we suggested in our publications.

A quantification technique useful in analysis of clay-rich deposits containing sepiolite and/or palygorskite has been developed by combining diffractometric and chemical data and represents a considerable improvement on classic quantification based on X-ray diffraction. The required data are: intensity ratios between certain diffraction peaks of calcite-dolomite and sepiolite-palygorskite-smectites, and also the CaO, MgO, K2O, Al2O3 and SiO2 contents. The validity of this method was tested by analysis of artificial mixtures of pure phases of the minerals found in such deposits.

A parallel reaction model is developed for describing the conversion of smectite to illite. Each reaction represents a group of similar smectite layers that require the same activation energy and have the same illitization rate. The model considers that the rate-determining reactant is smectite itself which follows first-order Arrhenius kinetics. By modelling the data from hydrothermal illitization experiments and from a Gulf Coast well, the activation energies are found to be distributed in the range of 11–24 kcal/mol with a maximum reaction at 18 kcal/mol, which involves 65% of reactive smectite. A frequency factor in the order of 10−3–10−4/s, obtained from the data fitting, appears to be adequate for modelling natural diagenesis in sedimentary basins. The distribution pattern of activation energies is considered to be controlled by the degree of heterogeneity of the initial smectite and the degree of electrostatic interactions between smectite layers and the newly formed illite layers during reaction.

The preparation and characterization of Ti-pillared acid-activated clays (designated Ti PAACs) and conventional Ti-pillared clays (designated Ti PILCs) are described. Preliminary catalytic results show that these materials possess remarkably enhanced abilities to catalyse the dehydration of pentanol compared with their Al counterparts (in excess of 200% in the case of the PILCs and up to 82% for the PAACs). These activities approach those previously reported for non-pillared acid-activated clays.

Nitrogen adsorption and desorption isotherms were obtained for microcrystalline, platy crystals of synthetic Al-substituted goethites synthesized from the ferrous system and heated to 260°C. Specific surface area, cumulative pore area and frequency of mesopore wall-separations of 2–15 nm in size increased as Al substitution increased. Nanometre-size micropores developed at heating temperatures between 200 and 240°C and decreased during the growth of hematite crystals between 240 and 260°C. Aluminium substitution had little effect on micropore development and a moderate effect on mesopore development. The increases in micropore volume and specific surface area due to heating are much smaller than is reported in the literature for large, lath-like crystals of goethite that develop abundant slit-shaped micropores.

The interaction between interlamellar Lu(III) cations and the layered silicate structure has been studied by means of MAS-NMR, XRD and EDX. Irreversible fixation of exchangeable Lu(III) cations upon hydrothermal treatment at 300°C of Lu-saturated montmorillonite is reported, through the formation of the crystalline phase Lu2Si2O7. It is shown that the lowest temperature previously described for this reaction, 400°C, does not indicate a thermodynamic boundary. This basic solid-state finding is relevant for some clay applications such as those related to the safety of nuclear waste repositories with engineering barriers.

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.

The chemical and structural stability of a Spanish sepiolite from Vallecas, Spain, was studied in 0.04 n NaOH (pH = 12.6), a saturated solution of Ca(OH)2 (pH = 12.6) and deionized/distilled water (pH = 7). The chemical stability was evaluated by determining the concentrations of Mg, Si and Ca in the solid residues during the kinetic test. The structural stability was studied by determining the changes in specific surface area and ‘crystallite’ size. The specific surface was determined by the BET method and the ‘crystallite’ size by the profile of the X-ray diffraction line. The main conclusion was that sepiolite is a material with high chemical stability in neutral and alkaline media, with no significant structural changes. However, in alkaline media, greater dissolution of silica was observed than in neutral media, the silica being derived from the most external tetrahedra attached to the OH− groups.

Aqueous suspensions of sepiolite, tagged with fluorescent dyes, have been studied using electro-fluorescence polarization spectroscopy. The binding modes of some 37 fluorescent dyes and optical brightening agents to the rod-like sepiolite particles have been determined. Many of the dyes are found to bind with a degree of order to the clay particle's major axis. The binding geometries of the cationic dye molecules tested were found to be dependent upon molecular size. This supports the view that these cationic dye molecules are constrained within the channels which are characteristic of the mineral sepiolite. Results for uncharged and anionic dye molecules are also presented; no dependence of binding geometry upon molecular size was found. The anionic molecules are most likely to associate with the exterior cationic magnesium surface. The results indicate that some of the anionic dyes are too large to fit in the channels. Some of the uncharged molecules adopt a number of orientations upon binding which gives rise to an average geometry being observed for these dyes.

Les substrats argile-alkylammonium sont utilisés dans ce travail comme des modèles de sol, dans le but d'étudier les interactions entre un pesticide neutre peu soluble dans l'eau, le dinoseb, et des substrats dont les surfaces ont été rendues hydrophobes. Les spectrométries infrarouge (IR), Raman et de réflexion diffuse dans l'UV-visible sont utilisées de façon complémentaire aux isothermes d'adsorption pour préciser la localisation et l'état des molécules pesticide retenues sur les substrats. Dans le cas de la vermiculite-décylammonium, la fixation du dinoseb est observée à la fois sur les surfaces externes et dans les espaces interfoliaires, les molécules de pesticide sont directement en interaction avec les atomes d'oxygène de la surface des feuillets et avec les cations ammonium, par liaisons hydrogène. Le taux de molécules de dinoseb retenues sur l'hectorite-décylammonium est beaucoup plus faible. Les molécules fixées ont alors une structure voisine de celle des molécules libres. Ces analyses montrent que le caractère hydrophobe de la surface des complexes organominéraux est une condition nécessaire, mais non suffisante, pour la fixation de molécules peu solubles dans l'eau. Notre étude souligne l'importance des interactions spécifiques par liaison hydrogène entre le pesticide et le feuillet de vermiculite dans le processus de rétention.

The major and trace element contents and mineralogical composition of Cenozoic bentonites from the southern Apennines (Italy) have been determined, for the whole-rocks and the <2 µm size-fractions, in order to constrain parental affinities. The main mineralogical and chemical differences have been recognized in eleven samples allowing them to be grouped into two distinct subsets. The differences are based on smectite abundance, occurrence or lack of detrital clay phases, different contents of Ti, Fe, Mn, K, P, Rb, Sc, V, Cr and Ni and differences in the Eu/Eu* and Ti/Al elemental ratios. These ratios indicate an affinity for felsic volcanics for the subset showing high smectite contents. The low smectite subset shows, instead, an affinity for Cretaceous-Oligocene southern Apennine shales. A similar result is obtained using the La-Th-Sc and Th-Sc-Zr/10 diagrams. We suggest that during the deposition of the southern Apennine shales, episodic volcanic events took place. These were associated with the suture stage of the Tethyan ocean that promoted accumulation of felsic ash in the related basin and the diagenetic alteration of these materials produced bentonitic layers interbedded with shales.

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has been used to determine the nature of acid sites present in Na+-, Ni2+- and Al3+-exchanged montmorillonite using the diagnostic base, pyridine. The pyridine additions were performed in situ at 25°C in the presence of liquid benzene or deuterated 1,4-dioxan to ascertain whether the acidity profile was influenced by the presence of either the non-polar or oxygenated solvent. Pyridine treated Ni2+-montmorillonite exhibited absorption bands characteristic of Lewis bound base in both benzene and deuterated 1,4-dioxan indicating that the Lewis acid sites were present at low temperature and were accessible in both solvents. The presence of a strong 1537 cm−1 band in pyridine-saturated Al3+-montmorillonite confirmed that this clay acted as a Brønsted acid in benzene. However, this diagnostic band was significantly reduced in the presence of deuterated 1,4-dioxan.

A series of reduced-charge montmorillonites (RCMs) was prepared from Li-montmorillonite from Jelšový Potok (Slovakia) by heating at various temperatures (105–210°C for 24 h. The amount of fixed Li, 0.09–0.67 per O20(OH)4, increased with increasing temperature, confirming preparation of a set of samples of variable layer charge from the same parent Li-montmorillonite by varying only the preparation temperature. Infrared spectroscopy revealed that Li was trapped in the hexagonal cavities of the tetrahedral sheet at all temperatures. Partial deprotonation of the samples, reflected in the decrease of the intensities of the OH-bending bands, was observed after treatments above 120°C. Analysis of the OH-stretching region showed Li in the previously vacant octahedra in the samples heated above 150°C. Weak inflections near 660 and 720 cm−1 confirmed development of local trioctahedral character of octahedral cations coordinated with OH groups in the sample heated at 210°C. Gradual decrease of the layer charge due to Li fixation led to a shift of the Si-O stretching band to higher frequencies and to the appearance of new, pyrophyllite-like bands at 1120 and 419 cm−1.

Palygorskite has been identified as a major constituent of the clay fraction in mid-Cretaceous deposits of the Meseta, the Middle Atlas, and the Rif in central and northern Morocco. Two types of palygorskite are differentiated, based on the morphology of crystallites, bio- and lithofacies associations of the containing sediments. Type 1 occurs in sections of the Meseta and the Middle Atlas, where the mineral displays bundles of long fibres under the electron microscope and is associated with shallow marine carbonate and evaporite facies. Type 2 was found in the Rif, where palygorskite occurs mostly as bundles of shorter fibres in turbiditic sediments of a supposed deep-marine environment. Associated microfossils indicate reworking of the palygorskite-bearing sediment from shallower parts of the basin. Palygorskite apparently grew authigenically in the chemically restricted environments of the Meseta and the Middle Atlas, whereas it is of a detrital origin in the Rif section. We consider that sediments containing authigenically formed palygorskite (type 1) could be the source of detrital palygorskite (type 2). Type 1 deposits on the North African shelf were probably partly reworked and responsible for the supply of palygorskite to mid-Cretaceous Atlantic basins, where the mineral is well known from several DSDP sites. As in the case of various Recent deep-sea palygorskite occurrences, aeolian transport may have significantly contributed to palygorskite supply to the ocean basins.

Mudrocks and sandstones from the Palaeocene of the central North Sea have been studied to assess the petrology, diagenesis and extent of any chemical interaction between the two lithologies. Authigenic and detrital minerals have been distinguished using a variety of electron microscope techniques. Small but significant quantities of authigenic minerals, which would not be detected by conventional petrographic tools, have been detected through the use of high-resolution electron beam techniques. Sandstone mineralogy has been quantified by point counting, and mudrock mineralogy semi-quantified by XRD. The detrital and authigenic mineralogy in the sandstone is almost identical to that found in the mudrock. The principal difference is in the relative proportions. Qualitative mass balance suggests that cross-formational flow has not been significant in either clay or quartz diagenesis.

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.

One-dimensional swelling tests and hydraulic conductivity tests have been performed at vertical effective stresses up to 450 kPa on Na-bentonite powder and compacted sand/Na-bentonite mixtures (5, 10 and 20% bentonite by weight) to investigate the use of bentonite-improved soils for waste containment. It was found that bentonite powder swells to reach a final state described by a single straight line on a plot of void ratio against the logarithm of vertical effective stress, regardless of preparation technique. Swelling of sand/bentonite mixtures expressed in terms of the clay void ratio show a deviation from bentonite behaviour above a stress which depends on the bentonite content. Hydraulic conductivity data for bentonite and sand/bentonite mixtures indicate an approximately linear relationship between logarithm of hydraulic conductivity and logarithm of void ratio. A design model based on the clay void ratio, and the sand porosity and tortuosity is presented enabling the hydraulic conductivity of a mixture to be estimated.