The small angle X-ray scattering data obtained in an earlier investigation of a series of Na-montmorillonite clay samples containing varying concentrations of sodium metaphosphate have been used to calculate the potential energy φ(x) of the interaction between two isolated parallel clay platelets separated by a distance x. All φ(x) curves have the form expected for Na-montmorillonite. In each curve there is a potential well for a platelet separation approximately equal to the most probable separation distance determined in the earlier study. Because the depth of the potential well is of the order of 0·01 eV for all samples, the attractive forces are relatively weak. While the calculated φ(x) functions are not highly accurate, in future investigations precautions can be taken to increase the reliability of the computed potential energy functions. This preliminary study suggests that determination of φ(x) from small angle X-ray scattering data can be a useful method for quantitative study of interparticle forces in Na-montmorillonite clays.

Anthropogenic activity releases hazardous contaminants and pollutants that are not removed fully by water treatments. Among such pollutants, bisphenol-A (BPA) and bisphenol-S (BPS) are included in a series of Endocrine Disruptive Compounds, which may cause disruption due to hormone blockage or mimicking. Thus, even though those pollutants are not considered lethal, they are hazardous to health due to their similarity to 17β-estradiol, and they have been shown to cause developmental malformation in Zebrafish and breast and prostate tumors in rodents. Both BPA and BPS have been found in water sources at concentrations >30 μg L–1 and since water treatment plants are ineffective at removing them, their concentration is constantly increasing. The purpose of the present study, using a collection of experiments performed by B.Sc. and M.Sc. students, was to apply clay-based materials to the removal of such health hazards from water. Specifically adapted modified clays as neutral organoclays can optimize the interaction between pollutants and the matrix to achieve efficient adsorption. Such an approach is very effective for relatively insoluble pollutants such as BPA, but less so for the more soluble BPS. On the other hand, BPS can be photodegraded catalytically using raw clay or TiO2-impregnated clay. At low catalyst concentration, the modified clay was as effective as a commercial TiO2 catalyst, whereas combining it with H2O2 yielded considerably better results. In summary, clay minerals offer solutions for the removal of health-hazardous pollutants from water, based on different procedures and mechanisms. The versality of clay minerals allows 'tailoring' specifically adapted materials that might improve their efficiency based on such very specific pollutant-matrix interactions.

An infrared method has been developed for estimating kaolinite in sediments. Hydroxyl stretching bands of kaolinite in sediments can be recorded by using a differential technique which eliminates the overlapping owing to other mineralic constituents present. By adding known amounts of an appropriate standard to the sample and by measuring intensities of the OH bands before and after the addition it is possible to calculate the proportion of kaolinite in the test sample. The choice of the added standard is made from characteristic features of the hydroxyl stretching bands.

An electro-optic birefringence technique was employed to study the orientation mechanism of montmorillonite in an electric field. The instantaneous reversal of the field polarity produced evidence of a low voltage permanent dipole and a high voltage induced dipole. This technique was used to study theeffect ofelectrolyte concentration on the rotational diffusion coefficient, a measure of the rate at which the particles rotate or relax, within the solution, from a preferred orientation. Thus, a measure of the immediate environment of the particles was obtained that is not an average effect for the whole system, yet allows for the full development of the clay-cation-water interactions under the experimental conditions. It was found that particle rotation could be accounted for using the measured particle size and normal water viscosity only when the double layer was fully developed, with no free ions or other perturbations. As soon as perturbations were applied, either by adding salts or applying an electric field, the measured particle size and normal viscosity would not account for the data. Either the rotating moiety has to be larger, that is, be a particle plus a water hull, or the viscosity greater, or in some cases both.

Fourier-transform infrared (FTIR) spectroscopic studies were carried out on 1,6-hexanediamine hydrochloride (HDA)-treated synthetic fluorhectorite to determine the orientation of functional groups within the structure. Oriented crystal layers were prepared by flocculating the smectite slurry with glass fibers to obtain a 100-µm-thick paper. Orientations were determined by measuring integrated IR band intensities at various incident beam angles (≤60°), inasmuch as absorption occurred only if the oscillating dipole of the functional group interacted with the electric vector of the incident radiation. The H-N-H plane in amine groups was aligned parallel to the lamellar plane. The H-O-H plane of the small amount of sorbed water was inclined 45° or more to the interlamellar layer, and the OH groups were inclined 45° to this layer.

Even with the incorporation of HDA in the interlamellar structure, at high humidity, additional water sorbed. The sorbed water competed with and displaced amine groups from the surface, resulting in randomly oriented amine groups. Many of the amine groups were ionized, whereas the additional sorbed water showed little orientation.

This study demonstrated that the orientation of intercalated amines in fluorhectorite can be determined by following the intensity changes in infrared-active bands as a function of the incident beam angle. With intercalated HDA, the orientations were influenced by the presence of interlayer water.

The influence of pressure on the electrical resistivity of clay-water systems was investigated and found to reflect the abnormal nature of adsorbed water. The resistivity of montmorillonite—water systems varied with pressure in a manner similar to a dilute salt solution at pressures above 7000 psi. At pressures below this, abnormal pressure-resistivity relations resulted which were attributed to the presence of abnormal water associated with clay mineral surfaces. The pressure-induced breakdown of the abnormal water associated with montmorillonites was found to occur in abrupt stages as indicated by anomalies in the pressure—resistivity curves.

The anomalies indicated that layers of adsorbed water have differing degrees of structural bonding by which variations of the water-orientating ability of clay minerals may be compared. In general calcium montmorillonite was found to allow the most rigid bonding of the adsorbed water while sodium montmorillonite gave rise to the most extensive development of the abnormal water.

The abnormal water was found to re-form with some hysteresis effects when the pressure was released. An increase in temperature was found to decrease both the amount and the relative strength of the abnormal water.

A detailed explanation of the most important properties of natural and synthetic silica and silica gels is given. Specific reference is made to the differences between the formation of synthetic silica gels and of quartz and cristobalite. The effect exerted by the synthetic products is explained and the importance of their amorphous condition on their reactivity is also referred to. On the basis of ultra- and electron-microscopic studies it is demonstrated that these synthetic products are not crystalline, but amorphous aggregates, and it is also shown how their reactivity can be increased by appropriate dispersion before use.

The colloidal properties of silicone resins are then pointed out and their production explained. Their advantages over purely organic matter and the reasons for this difference are also referred to.

Finally, reasons are given why more attention must be paid to colloid science in any field where silica or silicones are studied or put to use.

K-Ar isotopic dating has been applied to alkali-rich nanometer-sized illite separates of bentonites since the late 1990s. In the present study, K-Ar and Rb-Sr isotopic analyses were based on mineralogical determinations and morphological observations of similarly nm-sized separates (<0.02, 0.02–0.05, and 0.05–0.1 μm) depleted in alkalis and recovered from Santonian (85.8–83.5 Ma) bentonites of the Campos Basin located offshore the southeastern Atlantic coast (Rio de Janeiro State, Brazil). On the basis of XRD analyses and geochemical/mineralogical simulations, the size fractions consist essentially of the smectite-rich end-member of the smectite-to-illite trend with no more than 9% authigenic illite layers. High K-Ar values from 42.6 ± 3.2 to 70.2 ± 2.1 Ma confirm the occurrence of detrital illite in one sample at least, the age data being meaningless. A second group of K-Ar values ranges from 15.5 ± 10.7 to 41.3 ± 10.8 Ma, while the smallest (<0.02 and 0.02–0.05 μm) fractions with <0.42% K2O lack detectable radiogenic 40Ar and yield analytically 0 Ma ages. Two samples including that with the detrital illite were leached with dilute acid and the Rb-Sr method was applied to the untreated, leachate, and residual fractions of the different separates. The combined isotopic data suggest that illitization started at ~44 ± 4 Ma when the bentonites were subjected to a temperature of ~60°C. The leachable Sr yielded 87Sr/86Sr ratios of 0.7106–0.7108, which is greater than those of seawater either during deposition or recently, and of the initial ashes. They do not correspond to the chemical signature of pore fluids, but more likely to removals from fragile edges of the illite-smectite layers probably impacted by the rough initial chemical treatment applied to empty the smectite interlayers. Illitization was either a side effect of a major contemporaneous smectitization or an independent process that occurred later, in the progressively buried bentonite beds. Of variable duration, it was probably dependent on burial-induced temperature increase in the bentonites, which monitored the fixation of K in the smectite layering with or without a changing fluid chemistry. On the basis of the combined K-Ar and Rb-Sr isotopic data, illitization lasted either until ~15 Ma or even 0 Ma for some of the finest size fractions.

Injured bone tissues can be healed with bone grafts, but this procedure may cause intense pain to the patient. A slow and localized delivery of nonsteroidal anti-inflammatory drugs (NSAIDs) could help to reduce the pain without affecting bone regeneration. The objective of the present study was to use [Mg-Al]-layered double hydroxide (LDH) as a matrix for controlled release of sodium naproxen (NAP). This system could be applied in biomaterial formulations (such as bone grafts) to achieve a local delivery of naproxen. [Mg-Al]-LDH successfully incorporated up to 80% (w/w) of naproxen by the structural reconstruction route, with the [Mg-Al]-LDH interlayer space increasing by 0.55 nm, corresponding to the drug molecule size. The evaluation of the naproxen release kinetics showed that 40% of the drug was delivered over 48 h in aqueous medium (pH 7.4 ± 0.1), indicating the potential of [Mg-Al]-LDH/NAP for local release of naproxen at adequate concentrations. Kinetic modeling showed that the naproxen release process was closely related to the Higuchi model, which considers the drug release as a diffusional process based on Fick’s law. The chemical stability of NAP after the release tests was verified by 1H NMR. The [Mg-Al]-LDH/NAP also exhibited low cytotoxicity toward fibroblast cells (L929 cell line), without modifications in their morphology and adhesion capacity. These results describe a suitable approach for preparing efficient systems for local delivery of nonsteroidal anti-inflammatory drugs for biomedical applications.

The Crystal Packer module in the Cerius2 modeling environment has been used to study the structure of montmorillonite intercalated with Al(OH)3-fragment (gibbsite-like) polymers. Basal spacings in gibbsite-like polymers arranged in 2 layers in the interlayer of montmorillonite varied in the range 19.54–20.13 Å, depending on the type and arrangement of Al(OH)3 fragments. The inhomogeneous distribution of intercalating species in the interlayer and, consequently, the turbostratic stacking of layers has been found for gibbsite-like polymers as well as in the case of Keggin cations (Čapková et al. 1998). The dominating contribution to the total sublimation energy comes from electrostatic interactions for both intercalating species, gibbsite-like polymers and Keggin cations.

Ludox SiO2 sols with a reasonably uniform size of 12 nm and in the high concentration of 10 to 40 wt% were transformed to gels by lowering the pH. The process from sol to gel, followed by light scattering, did not show a sign of fractal growth within the length scale of observation (>0 nm). Rather, a density fluctuation due to a dynamic (non-equilibrium) disorder was apparent. Together with the results of viscosity measurements, it was concluded that the process consists of 3 stages: 1) A dynamic (non-equilibrium) density fluctuation grows rapidly. 2) Such density fluctuation acquires some order. 3) The entire bulk loses fluidity and becomes a macroscopic gel.

A model describing the electric double layers in clay-electrolyte systems containing particles with different surface charge densities was developed and used to calculate the film thickness of water present in a clay paste. The average water film thicknesses (~18 Å) calculated by considering the clay to contain 9 groups of particles of different charge densities did not differ from those calculated by assuming one average charge density; provided the minimum potential between particles remained constant. These values, however, were higher than those obtained from gravimetric water determinations by about 30%. The overestimation of the average thickness of the water films by the theoretical model is most likely due to the assumption of a complete parallel arrangement of particles in the paste and the validity of the Gouy theory for double layers on clays.

This paper describes in detail phosphate minerals occurring in refractory clays of Missouri and their effect on the refractory degree of the clays. The minerals identified include carbonate-fluorapatite (francolite), crandallite, goyazite, wavellite, variscite and strengite. It is emphasized that these phosphates occur only in local isolated concentrations, and not generally in Missouri refractory clays.

The Missouri fireclay region comprises 2 districts, northern and southern, separated by the Missouri River. In this region, clay constitutes a major part of the Lower Pennsylvanian Cheltenham Formation. The original Cheltenham mud was an argillic residue derived from leaching and dissolution of pre-Pennsylvanian carbonates. The mud accumulated on a karstic erosion surface truncating the pre-Cheltenham rocks. Fireclays of the northern district consist mainly of poorly ordered kaolinite, with variable but minor amounts of illite, chlorite and fine-grained detrital quartz. Clays of the southern district were subjected to extreme leaching that produced well-ordered kaolinite flint clays. Local desilication formed pockets of diaspore, or more commonly, kaolinite, with oolite-like nubs or burls of diaspore (“burley” clay).

The phosphate-bearing materials have been studied by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectral analysis (SEM-EDS) and chemical analysis. Calcian goyazite was identified in a sample of diaspore, and francolite in a sample of flint clay. A veinlet of wavellite occurs in flint clay at one locality, and a veinlet of variscite-strengite at another locality.

The Missouri flint-clay-hosted francolite could not have formed in the same manner as marine francolite. The evidence suggests that the Cheltenham francolite precipitated from ion complexes in pore water, nearly simultaneously with crystallization of kaolinite flint clay from an alumina-silica gel. Calcian goyazite is an early diagenetic addition to its diaspore host. The wavellite and variscite-strengite veinlets are secondary, precipitated from ion complexes in ground water percolating along cracks in the flint clay. The flint clay host of the variscite-strengite veinlet contains strontian crandallite. All of the phosphates contain significant amounts of strontium. The source of P, Ca and Sr was the marine carbonates. Dissolution of these carbonates produced the argillic residue that became the primordial Cheltenham paludal mud, which ultimately altered to fireclay.

Preliminary firing tests show that the presence of phosphates lowers fusion temperature. However, it is not clear whether poor refractoriness is due to the presence of phosphates, per se, or to Ca, Sr and other alkaline elements present in the phosphates.

Mixtures of kaolinite clay and quartz sand were packed in columns and leached with NaCl-CaCl2 solutions of different concentrations (ranging from 0.5 M to distilled water) having sodium adsorption ratios (SAR) of 5, 10 and 20. Sodium hexametaphosphate (NaHMP) (10 g/m3) was added to each solution. Changes in the hydraulic conductivity (HC) and clay concentration in the effluent were measured, and the dispersion of the clay was evaluated. In the absence of NaHMP, using distilled water instead of 0.01 M solutions caused some reduction in the HC; the reduction became more severe as the SAR increased. At SAR 20 the HC dropped to 73% of that obtained when the 0.5 M salt solution was used. This reduction in HC was related to increases in the pH of the effluent and partial dispersion of the clay. On adding the NaHMP to the leaching solutions, a marked decrease in the HC and severe clay dispersion were observed at all SAR levels, if the kaolinite-sand mixtures were leached with dilute solutions and distilled water. The HC dropped to 40% of that obtained when leaching with 0.5 M salt solution, and dispersed clay in the effluent peaked at about 1% in the SAR 20 treatment following leaching with distilled water. The observed reduction in the HC of the kaolinite-sand mixture when NaHMP was added to the leaching solutions was due to the dispersive effect of NaHMP and sodium on the kaolinite. The polyanion NaHMP reduced the edge-to-face particle interactions, thereby enabling the dimise double-layer repulsion forces to predominate. Following addition of the polyphosphate, the response of kaolinite to sodium and electrolyte concentration was similar to that reported in the literature for smectite.

Clay minerals undergo significant changes when exposed to weathering agents. Some of these changes were revealed by studying a sequence of samples collected from weathering profiles developed on shales. Illite and chlorite are modified by the development of expandable layers within the illite and chlorite structures. The suggested mechanism of alteration of chlorite is the oxidation and removal of octahedral iron. Chemical analyses indicate that interlayer potassium is removed from illites. Removal of potassium may be accomplished by an exchange reaction between potassium ions and hydronium ions in the environment.

The origin of underclays is controversial. In an attempt to shed some light on this subject, three shale-underelay profiles were studied. The changes in clay minerals from shales to underelays are very similar to those in weathered shale profiles. This similarity lends support to the theory that some underelays are products of weathering.

A random-layer disordered kaolinite from Conception de Buenos Aires, Jalisco, Mexico, gives an X-ray diffraction pattern resembling that of halloysite but has a kaolinite morphology. The mineral was located in a lignite deposit and, apparently was formed by alteration of volcanic rocks from the Cenozoic, with rapid cooling and sedimentation in lacustrine deposits. It is associated with plagioclase, quartz, cristobalite, montmorillonite, goethite and organic material. The analysis of purified material (44.84 per cent SiO2, 40.36 per cent Al2O3, 0.30 per cent Fe2O3, 0.31 per cent CaO, and 13.99 per cent ignition loss) corresponds to the formula (Si3·88 Al0·11 Fe0·01) (Al3·99 Fe0·01)O10 (OH)8. X-ray diffraction indicated a d001 of 7.56 Å, an intense 020, and displaced and nonsymmetrical reflections corresponding to a bi- and tridimensional diffracting system closer to halloysite than to kaolinite. Computed cell edges were a = 5.18 Å, b = 8.97 Å, and c = 7.45 Å. Electron micrographs showed anhedral rounded particles averaging 0.22 µ in size, while infrared absorption indicated some displacement in the absorption bands. The relationships of the mineral to kaolinite, halloysite and disordered kaolinites are discussed in terms of the 7°38′ twist of the tetrahedra, the intensities of the reflections, and the calculated AlIV substitution.