The electron back-scattered diffraction (EBSD) technique has been applied to fine-grained kaolin minerals to determine the polytypes (kaolinite, dickite and nacrite) of individual grains and their crystallographic orientations in a scanning electron microscope (SEM). Because kaolin minerals are prone to radiation damage by the intense electron beam necessary to obtain EBSD patterns, the beam has to be rastered across the specimens during pattern acquisition. Kaolinite-dickite and nacrite are easily distinguished by their trigonal or hexagonal symmetry about the [001]* direction, respectively, of the Kikuchi bands with k = 3n. Dickite can be differentiated from kaolinite by mirror symmetry parallel to the a-c plane, and by the characteristic contrast of HOLZ rings.

As EBSD analysis is performed using a SEM, morphological characters can be correlated with polytypes. Dickite fragments could be discerned as oriented overgrowths on nacrite plates. Dickite was observed to always adopt euhedral shapes in a diagenetic mixture of kaolinite and dickite. Lath-shaped dickite is elongated along the a axis direction. Rhombohedral dickite consists of crystals with {1̄11} indexed to the side facets.

The behavior of fine-grained mineral systems is dependent on pore-fluid characteristics. The systematic analysis of previously published studies supports the development of a fabric map in the pH and ionic concentration space as a working hypothesis. This conceptual study is complemented with an extensive battery of tests where surface charge and particle interactions are controlled through pore-fluid characteristics. The macro-scale tests include sedimentation, viscosity and liquid limit, and involve a wide range of solid volume fractions (suspension to sediment) and strain levels. Experimental results permit the development of an updated fabric map on the pH-ionic concentration space which takes into consideration all experimental results. The fabric map is structured around a critical pH level and a threshold ionic concentration beyond which van der Waals attraction prevails.

Transmission electron microscopy (TEM) has been used to demonstrate the biological formation of a hollow spherical halloysite-like mineral in freshwater systems. The interaction between clays and microbes was investigated in microbial films from laboratory cultures derived from natural sediments. Optical and electron microscopic observations of cultured microbes revealed that thin clay films covered areas of the bacterial cell wall. X-ray diffraction of the thin films after 2 y of ageing showed a 7.13 Å d spacing, consistent with a 7 Å halloysite-like phase [Al2Si2O5(OH)4 H2O]. Fourier transform infrared analysis of the thin film exhibited the characteristic adsorption bands for O−H (3651 cm−1), C−H and C−N (2925, 1454 and 1420 cm−1, respectively), suggesting that the phase was closely associated with adhesive organics. Observation by TEM of the thin films revealed that spherical, hollow, halloysite-like material formed on both coccus- and bacillus-type bacterial cells. Electron diffraction analysis of this material showed 2.9, 2.5, 2.2 and 1.5 Å d spacings. The present investigation strongly suggests that the thin film wall of the spherical halloysite-like material was associated with bacteria as a bio-organic product. This material, referred to hereafter as bio-halloysite, is further evidence for the microbially-mediated formation of clay minerals. The identity of the bacteria responsible for bio-halloysite formation is unknown, but is tentatively assigned to sulfate-reducing bacteria on the basis of morphology and the presence of reducing conditions in the microcosm at the end of the experiments.

The common observation that smaller particle-size fractions of sedimentary rocks yield younger K-Ar apparent ages than the larger particle-size fractions of the same stratigraphic age was analyzed with the aid of the 40Ar/40K ratio from 14 stratigraphically and regionally different sections. Estimation of the loss of radiogenic 40Ar from varied clay-rich size fractions was based on two models: a relationship between particle size and the 40Ar/40K ratio, and a theoretical diffusional loss from spherical particles. The differences between the two models and reconciliation of their results are discussed. For the smallest fractions (up to <0.5 μm), percent-wise losses of 40Ar from the spherical particles model increase from Upper Carboniferous and Permian (38±10%), to Late Triassic (47±10%), and to Miocene and Late Neogene (65±8%). This trend suggests that escape of 40Ar from the smaller particles in older sediments decreased or even stopped after deposition of the sedimentary sections.

The large 40Ar losses derived from small 40Ar/40K ratios in the younger Tertiary sediments, indicate that addition of K to the small fractions is, at least in part, responsible for the young K-Ar apparent ages in geologically different settings. In several 102–103 m thick sections, authigenic illite in the <0.1 to <2 μm fractions yields young K-Ar apparent ages resulting from simultaneous 40Ar production and release during clay authigenesis. In a production and loss model, a first-order escape-rate parameter (e) was estimated at 0.2 × 10−8 to 4 × 10−8 y−1, depending on the K-Ar apparent age of the size fractions and the stratigraphic age of the section. The limitations and uncertainties of the methods of evaluating diagenetic 40Ar losses from fine clay particles are discussed.

The Gourougou volcanic massif (northeastern Morocco) is actively prospected for bentonite deposits. Five bentonites originating from different environments were selected for the present study: hydrothermal alteration of obsidian perlite glass inside the volcanoes themselves (Providencia and Tribia deposits); alteration of pyroclastic flows in a marine shallow water to lagoonal lacustrine environment (Ibourhardayn deposit); ash falls in marine or lacustrine systems (Moulay Rachid and Melg el Ouidan (formerly Camp Berteau) deposits). All of these bentonites were probably formed from volcanic glass originating from a rhyolitic magma at different stages of differentiation as shown by slight variations of REE and incompatible element abundances. The crystal-chemical characteristics of the smectite vary according to alteration conditions: beidellite predominates in hydrothermal systems, whereas montmorillonite predominates in lagoonal and lacustrine environments, and mixed-layer beidellite-montmorillonite in the sea-water-altered pyroclastic flows. All these dioctahedral smectites exhibit a heterogeneous distribution of charge as shown by the presence of partially expandable (1 EG) or non- expandable (0 EG) layers in the K-saturation state. The proportion of the collapsed or partially expandable layers is not related to the average layer charge or to the cation exchange capacity. This militates for an overall heterogeneous charge distribution. Compared to other natural or experimental alteration systems of similar rhyolitic glass, the formation of beidellite or montmorillonite appears to be controlled by the amounts of Mg in the system.

The extremely toxic protein, ricin, is derived from castor beans and is a potential terrorist weapon. Adsorption to clays might minimize the environmental persistence and toxic effects of this toxin. Ricin adsorption to clay minerals was measured using batch adsorption isotherms. Enzyme-linked immunoassay methods were used to quantify aqueous ricin concentrations. Montmorillonite, sepiolite and palygorskite effectively adsorbed ricin from aqueous solutions and yielded mostly Langmuir-type isotherms. The monolayer adsorption capacity from a Langmuir equation fit at pH 7 was 444 g ricin/kg for montmorillonite (SWy-2), but was only 5.6 g ricin/kg for kaolinite (KGa-1b). Monolayer capacities for sepiolite (SepSp-1) and palygorskite (PFl-1) at pH 7 were 59.2 and 58.1 g ricin/kg. The high-charge montmorillonite (SAz-1) effectively adsorbed ricin at pH 7, but yielded a linear isotherm with K = 5530 L/kg. At pH 5, both montmorillonites (SWy-2 and SAz-1) yielded Langmuir-type isotherms with monolayer capacities of 694 and 641 g ricin/kg. Clay samples with higher cation exchange capacities generally adsorbed more ricin, but adsorption also followed specific surface area. X-ray diffraction of <2 μm SWy-2 treated with 470 g ricin/kg indicated expansion up to 34.6 Å at buffered pHs of 4 and 7, but not at pH 10. Furthermore, ricin adsorption was greatest at pH 4 and 7, but minimal at pH 10. Treatment with 1.41 kg of purified ricin/kg clay at pH 5 yielded a 35.3 Å peak and adsorption of ~1.2 kg ricin/kg. Similar treatment with lower-purity ricin yielded less expansion and lower adsorption. The 35.3 Å peak interpreted either as a d002 or d001 reflection indicates a 70.6 Å or a 35.3 Å ricin/SWy-2 complex. This implies that adsorption and air drying have compressed interlayer ricin molecules by 18 to 65%. Effective ricin adsorption by montmorillonite suggests that it could be used to minimize the toxic effects of dispersed ricin.

We report a combined experimental and theoretical study of uranyl complexes that form on the interlayer siloxane surfaces of montmorillonite. We also consider the effect of isomorphic substitution on surface complexation since our montmorillonite sample contains charge sites in both the octahedral and tetrahedral sheets. Results are given for the two-layer hydrate with a layer spacing of 14.58 Å. Polarized-dependent X-ray absorption fine structure spectra are nearly invariant with the incident angle, indicating that the uranyl ions are oriented neither perpendicular nor parallel to the basal plane of montmorillonite. The equilibrated geometry from Monte Carlo simulations suggests that uranyl ions form outer-sphere surface complexes with the [O=U=O]2+ axis tilted at an angle of ~45° to the surface normal.

The thermal stability of surfactant-modified clays plays a key role in the synthesis and processing of organoclay-based nanocomposites. Differential thermal analysis (DTA), thermogravimetric measurement and differential scanning calorimetry (DSC) were used in this study to characterize the thermal stability of hexadecyltrimethylammonium bromide-modified montmorillonites prepared at different surfactant concentrations. Analysis by DSC shows that the molecular environment of the surfactant within the montmorillonite galleries is different from that in the bulk state. The endothermic peak at 70–100°C in the DTA curves of the modified montmorillonites is attributed to both the surfactant phase transformation and the loss of free and interlayer water. With an increase of surfactant-packing density, the amount of water residing in the modified montmorillonite decreases gradually, reflecting the improvement of the hydrophobic property for the organoclay. However, the increase in the surfactant packing density within the galleries leads to a decrease in the thermal stability of the organoclays.

With an increase of initial surfactant concentration for the preparation of organoclays, the surfactant- packing density increases gradually to a ‘saturated’ state. It was found that the cationic surfactant was introduced into the montmorillonite interlayer not only by cation exchange but also by physical adsorption.

Reaction of a Mg-Al carbonate layered double hydroxide (LDH) with boric acid leads to a borate-pillared LDH with the stoichiometry [Mg0.65Al0.35(OH)2][B3O5]0.35.0.65H2O and an interlayer spacing of 1.07 nm. Infrared and 11B magic angle spinning nuclear magnetic resonance data are consistent with the presence of polymeric triborate anions of the type [B3O4(OH)2]nn- in the interlayer galleries so that the material can be formulated as [Mg0.65Al0.35(OH)2][B3O4(OH)2]0.35.0.30H2O. The flame-retardant properties of the borate-pillared material and the carbonate precursor in composites with ethylene vinyl acetate copolymer were compared. Introduction of the borate anion leads to a significant enhancement in smoke suppression during combustion without compromising the flammability of the material. This is related to the synergistic effect between the host layers of the LDH and the borate anions uniformly distributed in the interlayer region.

In this study a robust design method is developed for extracting Li from boron (B) clays with the aim of minimizing cost and maximizing productivity. Lithium is commercially extracted from brines and certain minerals. Its extraction from clays has previously been found to be expensive, a major part of the extraction cost being attributed to the raw materials used. In this study, raw materials from lower-cost resources are used without applying any standardization to them and this might increase variation in the results. To minimize the variation, and achieve high extraction levels, robust design, statistical design and analysis of experiments, and response surface methodologies are utilized. As a result, consistently higher extraction levels have been achieved compared to previous studies. The experiments were conducted using the Bigadiç boron clay fields in Turkey. However, the method is generally applicable to other cases also.