Studies of the paragenesis of authigenic illite in arkosic sandstones of various regions and ages have revealed that the illitization of kaolinite is an important reaction accounting for the formation of authigenic illite in sandstones during burial diagenesis. The illitization of kaolinite takes place at an intermediate burial depth of 3–4 km, where pressure can reach values of 100 MPa (≈ 1000 bars). The purpose of the present study was to analyze the effect of pressure on the rate of kaolinite illitization in alkaline conditions. Hydrothermal reactions were conducted on KGa-1b kaolinite in KOH solution at 300°C and under pressures of 500, 1000, and 3000 bars for 1 to 24 h. The visual examination of the X-ray diffraction (XRD) patterns indicated a notable influence of pressure on the reaction rate. Molar percentages of muscovite/illite formed at each time interval were calculated from the analysis of two diagnostic XRD peaks, representing the 060 reflections of kaolinite and muscovite/illite. The data were modeled to obtain the initial rate of conversion at each pressure. The results indicated that the initial rate of kaolinite to muscovite/illite conversion is one order of magnitude greater at 3000 bars than at 500 or 1000 bars. Comparison of these data with those in the literature show a faster conversion rate (several orders of magnitude) in an initially high-alkaline solution than in a near-neutral solution.

Theoretical models of the mechanical properties of hydrated smectites, saturated with a variety of cations, are of much value in determining the potential for their use in various applications, including clay-polymer nanocomposites, but the development of such models is still in its infancy. The purpose of this study was to calculate the effects of divalent cations on the structural and mechanical elasticity of montmorillonite under different degrees of hydration. A theoretical study of the swelling and hydration behavior of montmorillonite was, therefore, undertaken using density functional theory (DFT) to investigate the basal spacing behavior of the homoionic montmorillonite with varying amounts of water in the interlayer space. The effect of the degree of the hydration of divalent interlayer cations (Mg2+/Ca2+/ Sr2+/Ba2+) on the structure expansion of the interlayer space was analyzed. In addition, the results obtained were compared to calculations performed on the montmorillonite model with a monovalent cation (Na+). The basal spacing (d001) is governed by the size and the degree of hydration of the countercations. The structures containing divalent cations are more compact than structures with monovalent cations. Ba-exchanged montmorillonite was found to have the largest d001 value for any degree of hydration (‘dry,’ one water layer, or two layers). The basal spacings of ‘dry’ montmorillonite exchanged with small cations, Mg2+ and Ca2+, are very similar. In hydrated models, the d001 expansion correlates with the ionic radius of the interlayer cation. The dependence of the total electronic energy on the volume expansion was calculated. From the energetic curves, bulk modulus (B0) was obtained by fitting in order to show how the compliance of the material depends on the type of interlayer cation and on the degree of hydration. With increasing water content in the interlayer space, the bulk modulus decreased, suggesting that the c-axial compression becomes easier with increasing hydration of the clay mineral. The values of the bulk modulus in hydrated systems are less sensitive to the type of the interlayer cation.

The current study demonstrates how co-existing zeolite and clay minerals formed by the alteration of tephra in a closed-basin lacustrine and lake-margin environment can retain the overall composition of the original bulk tephra for many elements, even when diagenetic conditions and resulting authigenic mineral assemblages change. Zeolite and clay minerals co-exist in the closed-basin, saline-alkaline lacustrine altered tephra of Pleistocene Olduvai Gorge, Tanzania, and their diagenetic histories can be reconstructed using variations in their textures and compositions. The authigenic minerals in the altered tephra of the Olduvai paleolake form a classic ‘bull’s-eye’ pattern, with clay-dominated tephra in the distal lake margin, chabazite and phillipsite in the proximal margin, and phillipsite ± K-feldspar in the intermittently dry lake and lake center. Fifteen representative samples of altered volcanic ash lapilli (designated Tuff IF) were analyzed by X-ray diffraction (XRD), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and scanning electron microscopy (SEM) to determine their authigenic mineral assemblages and bulk compositions, and to texturally and compositionally compare their clay mineral and zeolite components.

Textural observations indicate that clay minerals formed first, followed by zeolites and finally feldspars. Clay minerals, however, persist even in the most altered samples. The overall composition of Tuff IF shows only limited change in Fe, Si, Al, and Na between fresh, clay-altered, and zeolite-dominated diagenetic environments, despite significant differences in authigenic assemblage. Where zeolites dominate the assemblage, the remaining clay minerals are rich in Mg, Fe, and Ti, elements that are not readily incorporated in zeolite structures. Where clay minerals dominate, they are more Al-rich. A ‘mixing model’ combining clay-mineral and zeolite compositions yields a close approximation of the original volcanic glass for most elements (exceptions including Mg, Ca, and K). This initial composition was preserved in part by the redistribution of elements between co-existing clay minerals and zeolites.

NEWMOD was developed by R.C. Reynolds, Jr., for the study of two-component interstratifications of clay minerals. One-dimensional X-ray diffraction (XRD) profiles of an interstratified system of two clay minerals can be simulated using NEWMOD, given a set of parameters that describes instrumental factors, the chemical composition of the system (e.g. the concentration of Fe and interlayer cations), and structural parameters (e.g. proportions of the two components, the nature of ordering, and crystallite size distribution). NEWMOD has served as the standard method for quantitatively evaluating interstratified clay minerals for >20 y. However, the efficiency and accuracy of quantitative analysis using NEWMOD have been limited by the graphical user interface (GUI), by the lack of quantitative measures of the goodness-of-fit between the experimental and simulated XRD patterns, and by inaccuracies in some structure models used in NEWMOD. To overcome these difficulties, NEWMOD+ was coded in Visual C++ using the NEWMOD architecture, incorporating recent progress in the structures of clay minerals into a more user-friendly GUI, greatly facilitating efficient and accurate fitting. Quantitative fitting parameters (unweighted R-factor, Rp, weighted R-factor, Rwp, expected R-factor, Rexp, and chisquare, χ2) are included, along with numerous other features such as a powerful series generator, which greatly simplifies the generation of multiple simulations and makes NEWMOD+ particularly valuable for teaching.

The Antalya Unit, one of the allochthonous units of the Tauride belt, is of critical, regional tectonic importance because of the presence of rifting remnants related to the break-up of the northern margin of Gondwana during Triassic time. Paleozoic — Mesozoic sedimentary rocks of the Antalya Unit consist mainly of calcite, dolomite, quartz, feldspar, and phyllosilicate (illite-smectite, smectite, kaolinite, chlorite, illite, chlorite-smectite, and chlorite-vermiculite) minerals. Illite-smectite (I-S) was found in all of the sequences from Cambrian to Cretaceous, but smectite was only identified in Late Triassic-Cretaceous sediments. R0 I-S occurs exclusively in early-diagenetic Triassic—Cretaceous units of the Alakırçay Nappe (rift sediments), whereas R3 I-S is present in late-diagenetic to low-anchimetamorphic Cambrian—Early Triassic units of the Tahtalıdağ Nappe (pre-rift sediments). Kübler Index (KI) values and the illite content of I-S reflect increasing diagenetic grades along with increasing depth. Major-element, trace-element, rare-earth-element (REE), and stable-isotope (O and H) compositions were investigated in dioctahedral and trioctahedral smectites and I-S samples from the pre-rift and rift-related formations. Both total layer charge and interlayer K increase, whereas tetrahedral Si and interlayer Ca decrease from smectite to R3 I-S. Trace-element and REE concentrations of the I-S are greater in pre-rift sediments than in rift sediments, except for P, Eu, Ni, Cu, Zn, and Bi. On the basis of North American Shale Composite (NASC)-normalized values, the REE patterns of I-S in the pre-rift and rift sediments are clearly separate and distinct. Oxygen (δ18O) and hydrogen (δD) values relative to SMOW (Standard Mean Oceanic Water) of smectite and I-S reflect supergene conditions, with decreasing δ18O but increasing δD values with increasing diagenetic grade. Lower dD values for these I-S samples are characteristic of rift sediments, and pre-rift sediments have greater values. On the basis of isotopic data from these I-S samples, the diagenesis of the Antalya Unit possibly occurred under a high geothermal gradient (>35ºC/km), perhaps originating under typical extensional-basin conditions with high heat flow. The geochemical findings from I-S and smectites were controlled by diagenetic grade and can be used as an additional tool for understanding the basin maturity along with mineralogical data.

Vibrational spectra of two kaolinite-dimethylsulfoxide intercalates, obtained using inelastic neutron scattering (INS), were analyzed with a view to understanding the dynamics of the hydrogen atoms in the structure. The main focus was on the spectral region 0–1700 cm−1, which is difficult to analyze using optical spectroscopy. The experimental vibrational spectra of kaolinite:dimethylsulfoxide and kaolinite:d6-dimethylsulfoxide collected using two different spectrometers were interpreted by means of the solid-state DFT calculations. Calculated spectra were obtained by both normal-mode analysis and molecular dynamics going beyond the harmonic approximation. The Al-O-H bending modes were found to be spread over the large interval 100−1200 cm−1, with the dominant contributions located between 800 and 1200 cm−1. The shape of the individual hydrogen spectrum depends on whether or not the respective hydrogen atom is involved in an O-H⋯O hydrogen bond and on its strength. The modes corresponding to the in-plane movements of the inner-surface hydrogen atoms are well defined and always appear at the top of the intervals of energy transfer. In contrast, the modes generated by the out-of-plane movements of the hydrogen atoms are spread over large energy intervals extending down to the region of external (lattice) modes. The C-H modes are concentrated mainly in the three regions 1200–1450 cm−1, 800–1100 cm−1, and 0–400 cm−1. While the first two regions are typical of the various deformational modes of methyl groups, the low-energy region is populated by the modes corresponding to the movements of the whole dimethylsulfoxide molecule.

In cases where the provenance of raw materials used in the manufacture of local archeological ceramics is of interest, a detailed study of thermal transformations of minerals may be useful. The purpose of this study was to measure mineralogical transformations of different types of clays obtained during experimental firing runs, carried out at different temperatures, with the main goal of establishing Algarve reference groups based on the composition of raw material and high-temperature mineralogy, which may be compared with ceramics in studies of provenance. Eleven samples of clay-rich raw materials from the Algarve Basin (southern Portugal) were fired to temperatures ranging from 300 to 1100°C in increments of 100°C under oxidizing conditions. These were chosen to have variable chemical and mineralogical compositions, representing the main compositional range of the clay deposits from the region. Mineralogical and geochemical characterizations of the original clays were carried out by X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. Mineral transformations on the fired products were also studied by XRD.

Three groups of clays were distinguished according to the type of neoformed high-temperature minerals: (1) non-calcareous clays; (2) clays containing calcite as the only carbonate; and (3) clays with dolomite or dolomite + calcite. Firing of non-calcareous clays produced mullite at 1100–1200°C. Gehlenite and wollastonite formed by firing calcite-rich clays above 900°C, accompanied by anorthite or larnite in samples with small or large calcite contents, respectively. Firing of dolomite-rich clays at temperatures >900°C yielded a member of the gehlenite-åkermanite group and diopside. Anorthite, enstatite, periclase, forsterite, and monticellite may also form in the firing products.

The characterization of poorly crystalline minerals formed by weathering is difficult using conventional techniques. The objective of this study was to use cutting-edge spectroscopic techniques to characterize secondary Fe mineralogy in young soils formed in basaltic cinders in a cool, arid environment. The mineralogy of a chronosequence of soils formed on 2, 6, and 15 thousand year old basaltic cinders at Craters of the Moon National Monument (COM) was examined using synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy in combination with selective extractions. Fe K-edge XAFS is useful for determining speciation in poorly crystalline materials such as young weathering products. Over 86% of Fe in the soil clay fractions was contained in poorly crystalline materials, mostly in the form of ferrihydrite, with the remainder in a poorly crystalline Fe-bearing smectite. The XAFS spectra suggest that ferrihydrite in the 15 ka soil clay is more resistant to ammonium oxalate (AOD) extraction than is ferrihydrite in the younger materials. Fe in the poorly crystalline smectite is subject to dissolution during citrate-bicarbonate- dithionite (CBD) extraction. The results indicate that relatively few mineralogical changes occur in these soils within the millennial time frame and under the environmental conditions associated with this study. Although the secondary mineral suite remains similar in the soils of different ages, ferrihydrite crystallinity appears to increase with increasing soil age.

The contamination of aquatic environments by toxic metals such as radionuclides is of great concern because of the tendency of those metals to accumulate in the vital organs of humans and animals, causing severe health problems. The objective of this study was to investigate the use of natural and modified magadiite clay as an adsorbent to remove Th(IV), U(VI), and Eu(III) from aqueous solutions. Magadiite from the Amazon region, Brazil, was modified chemically with 5-mercapto-1-methyltetrazole (MTTZ) using a multi-step or heterogeneous synthesis pathway. The natural and modified materials were characterized using 29Si and 13C nuclear magnetic resonance, scanning electron microscopy, nitrogen gas adsorption, and elemental analysis. The physical-chemical properties of the chemically modified magadiite sample were modified, e.g. the specific surface area changed from 35.0 to 678.9 m2 g−1. The ability of the magadiite to remove Th(IV), U(VI), and Eu(III) from aqueous solution was then tested by a series of adsorption isotherms adjusted to a Sips equation. The effects of properties such as pH, contact time, and metal concentration on the adsorption capacity were studied. The adsorption maxima were determined to be 7.5 × 10−3, 9.8 × 10−3, and 12.9 × 10−3 mmol g−1 for Th(IV), U(VI), and Eu(III), respectively. From calorimetric determinations, the quantitative thermal effects for all these cations/basic center interactions gave exothermic enthalpy, negative Gibbs free energy, and positive entropy, confirming the energetically favorable conditions of such interactions at the solid/liquid interface for all systems.

Many environmental applications in the inorganic remediation field are based on the swelling and ion-exchange capacities of smectites, even though these can be affected by hydrothermal treatment in water and acidic media. Here a systematic study of the properties of layered silicates that could affect their hydrothermal stability at different pH is described: type of layers, octahedral occupancy, layer charge, and origin of the layer charge. The silicates studied were selected on the basis of their different characteristics associated with these properties. Kanemite (1:0 phyllosilicate), kaolinite (1:1 phyllosilicate), and pyrophyllite and talc (2:1 phyllosilicates with no-layer charge) were examined in order to determine the effect of layer structure, whereas the hydrothermal reactivity of silicates with different layer charge was analyzed by comparing the talc-hectorite-Laponite® and talc-saponite-trioctahedral vermiculite series. Samples were treated hydrothermally at 300ºC for 48 h in pure water and in a 0.01 M HNO3 solution and the final products were analyzed by X-ray diffraction, scanning electronic microscopy, and solid-state nuclear magnetic resonance spectroscopy. All layered silicates, except for kanemite, were found to remain intact after hydrothermal treatment in water and acidic media, with only minimal short-range structural changes observed. The extent of the structural changes depended on the octahedral sheet occupancy (greater extent) and the number of isomorphic substitutions (lesser extent), both of which weaken the structure.

Although structural disorder in kaolinite has been investigated extensively, it is still not understood properly. To investigate the problem, a kaolinite specimen of sedimentary origin from Capim, Brazil, was examined, mainly by transmission electron microscopy (TEM). Selected-area electron diffraction (SAED) along the Xi ([100], [110], and []) directions shows various features, from completely discrete patterns to heavily streaked ones along the c* direction, suggesting that the degree of stacking disorder is variable among individual grains. High-resolution TEM images indicate that stacking faults are mainly caused by disorder of alternating t1 (~ −a/3) and t2 (−a/3 +b/3) layer displacements. Furthermore, stacking faults have been observed (1) as isolated stacking faults (e.g. insertion of an isolated t2 `fault' in an ordered sequence with t1 layer displacement) and (2) as interstratification of two kinds of multilayer blocks having regular t1 and t2 layer displacements. A mixture of grains with various degrees and modes of disorder with alternating t1 and t2 layer displacements may explain the experimental profile of the 02, 11 X-ray diffraction band.

Faults related to displacement of the octahedral vacancy and/or to layer rotation were also observed in HRTEM images. The SAED patterns along the Yi ([010], [310], and []) directions occasionally have extra spots and/or streaks, suggesting the presence of stacking sequences with (±60°, 180°) mutual layer rotation and/or with (0, ±b/3) layer displacements. The local dickite or nacrite-like fragments formed by these faults are in qualitative agreement with recent low-temperature FTIR results from this sample, where distinct ν(OH) absorption bands reflect multiple interlayer O-H⋯O environments that are possibly ascribed to dickite and nacrite.

Disposal facilities in deep geological formations are considered to be a possible solution for long-term management of high-level nuclear waste (HLW). The design of the repository generally consists of a multiple-barrier system including Fe-based canisters and a clay backfill material. The Fe-clay system will undergo a thermal gradient in time and space, the heat source being the HLW inside the canisters. In the present paper, the effect of a thermal gradient in space on Fe-smectite interactions was investigated. For this purpose, a tube-in-tube experimental device was developed and an 80–300ºC thermal gradient was applied to a mixture of MX80 bentonite, metallic Fe (powder and plate), magnetite, and fluid over periods of 1 to 10 months. Transformed and newly formed clay minerals were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy. The main mineralogical transformations were similar to those described for batch experiments: smectite was destabilized into an Fe-enriched trioctahedral smectite and Fe-serpentine or chlorite as a function of the experimental conditions. Newly formed clay was observed all along the walls of the gold tube. Their crystal chemistry was clearly different from the clays observed in the hot and cold part of the tubes. The thermal diffusion of elements was also observed, especially that of Mg, which migrated toward the hottest parts of the tubes. In the end, the thermal gradient affected the redox equilibria; more reduced conditions were observed in the hotter parts of the tubes.

The morphology of hydrotalcites determines their use in catalysis, biomedicine, or adsorption as they may work as anion exchangers or as drug deliverers. In catalysis, reagents need access to as much surface area as possible; in biomedicine, drugs have to be encapsulated. However, the parameters and the mechanisms which direct the synthesis towards a certain morphology are not well understood. Precipitating agents or crystallization conditions are expected to play a crucial role. In the present study, hydrotalcites were synthesized in the presence of two precipitating agents (NaOH or NH4OH) under three different crystallization conditions (conventional, microwave, or ultrasound irradiation) which determined the morphology of the final product, layered or vesicular. The features are explained through the template effect of the liberated gases on the co-precipitation and crystallization processes and consequently on the final structure/morphology of the synthesized solids. Indeed, the nodular particles crystallize using the effluent gases as templates. Fractal dimension and particle-size distributions, determined by small-angle X-ray scattering (SAXS) and gas adsorption are compared and correlated to the presence of ammonium. Although the materials obtained are heterogeneous, it is possible to propose a microscopic geode model.

The origins of dolocrete and associated palygorskite in the Çanakkale region of Turkey have been little studied, but are of fundamental importance for a more complete understanding of the mineralogy of this region. The present study was undertaken in order to narrow this gap. Siliciclastic red mudstones within alluvial-fan deposits of the Middle Miocene Sariyer Formation locally contain dolocretes in various forms (powdery, nodular, and fracture-filling) and scarce matte-brown, authigenic clay lenses. The mineralogical characteristics of dolocrete and authigenic clay lenses were examined using polarized-light microscopy, X-ray diffraction, differential thermal analysis and thermal gravimetry, scanning-electron microscopy, and infrared spectroscopy, as well as by chemical and isotopic methods. These analyses indicate that the dolocretes are indeed predominantly dolomite, coexisting with variable amounts of palygorskite. The authigenic clay lenses are composed mainly of palygorskite. Dolomite appears as euhedral crystals, whereas palygorskite developed authigenically as interwoven fibers on and between resorbed dolomite crystals, rimming euhedral crystals, and as fiber bundles (where dolomite ± magnesite is absent). The stable-isotope values and some petrographic features, such as alveolar texture and dolomite needles, support a pedogenic origin for the dolocretes. In the initial stage, dolomite formed by replacement of siliciclastic red mudstones and/or by precipitation from percolating soil-derived water in a near-surface setting. Subsequently, palygorskite either precipitated on the dolomite crystals from relatively more evaporative water, replaced the host-rock mudstone in the presence of Al + Fe, or formed directly from solution where the Ca/Mg ratio decreased and the Al + Fe increased. In view of the large Cr and Ni contents of the bulk-rock samples, the elements required for the crystallization of dolomite and palygorskite (namely Mg, Ca, Si, Al, and Fe) may have been supplied by weathering of ophiolitic rocks that crop out in the area.

Differentiating clay minerals that formed in a supergene environment during deep chemical weathering from those that formed during hydrothermal alteration at higher temperatures associated with a mineralizing event is important in the exploration for epithermal Au deposits. The purpose of this study was to further elucidate this topic by comparing morphological and chemical properties of clay minerals in saprolite overlying epithermally altered bedrock at the Vera Au deposit, Queensland, Australia, with those of clay minerals in saprolite overlying bedrock adjacent to the epithermal alteration zone. X-ray diffraction (XRD) and analytical transmission electron microscopy (ATEM) investigations identified kaolinite, illite, and interstratified illite-smectite, together with quartz, Fe and Ti oxide minerals, and the sulfate minerals jarosite, gypsum, alunite, and natroalunite. Kaolinite crystals within the weathered argillic alteration zone proximal to the epithermal quartz vein are generally larger (up to 3 μm in diameter) and better formed (subhedral to euhedral) than crystals in saprolite distal to the hydrothermal alteration zone, in which smaller (mostly <1 μm), subhedral to anhedral crystals dominate. Energy-dispersive spectrometry (EDS) analysis of single crystals indicated that kaolinite within the alteration zone has an Al/Si ratio indistinguishable from reference kaolinite and has small Fe concentrations, whereas distal saprolitic kaolinite has smaller Al/Si and greater Fe/Si ratios, consistent with the formation of low-Fe kaolinite during hydrothermal alteration and higher-Fe kaolinite during weathering. Illite and interstratified illitesmectite (I-S) were distinguished from kaolinite by their morphology and greater K/Si and smaller Al/Si ratios. The Illite and I-S morphology ranged from thin irregular masses through lath-like crystals in hydrothermal samples to larger, irregularly shaped crystals. The Ca/Si and K/Si ratios of single crystals in Ca-saturated clay minerals were consistent with the I-S interstratification parameters determined from XRD patterns.

LongYan kaolin has a large Fe content which affects the coloring. Bioleaching treatments to remove Fe impurities were conducted here using indigenous dissimilatory Fe(III)-reducing bacteria. The factors that affect bioleaching efficiency include bioleaching time, carbon source, pH, temperature, pulp density, and inoculum density and these were examined. Environmental scanning electron microscopy and X-ray diffraction were used to examine any textural or mineralogical changes at the surface of the kaolin that may have occurred during the bioleaching. Iron impurities in the kaolin were reduced from 0.88% to 0.48% with an increase in the natural whiteness index from 60.8% to 81.5% after 7 days of bioleaching treatment. A granulometric analysis of dispersed kaolin demonstrated that the bioleaching resulted in a decrease in particle size. The results demonstrated that the bioleaching was very effective at improving the quality of the kaolin, where insoluble Fe(III), either adsorbed to the kaolin surfaces or admixed as amorphous forms, was leached out by micro-organisms as water-soluble Fe(II).

The occurrence of halloysite and/or kaolinite in clay-rich, vein-like zones in saprolites in Hong Kong has provided the opportunity to examine the conditions determining the formation of one kaolin mineral or the other and also the nature of their particles. Clay-rich zones within tuffaceous or granitic saprolites from six different hillside sites have been examined in replicate samples by optical and scanning electron microscopy, X-ray diffraction, and thermal analysis. Kaolin minerals, sometimes together with Mn oxides and Fe oxides/oxyhydroxides, have formed within discontinuities within the altered host rocks. The fabrics of kaolin infills generally indicated several generations of kaolin formation and that shear and deformation have commonly occurred within the infills. The infills were either light or dark in color. Light-colored infills often comprised pure, or nearly pure, halloysite or kaolinite. Dark Mn- and Fe-rich infills all contained kaolinite, while including some halloysite. The very halloysitic, light-colored infills occurred in saprolites in both granite and tuff as long tubular shapes in parallel bunches. The light-colored, very kaolinitic infills occurred in tuff only, in large platy or near-platy shapes within vermiform packets. In dark-colored infills, early kaolin mineral crystallization was limited by impurities from the breakdown of primary minerals leaving dissolved and re-precipitated compounds of Mn and Fe within the infill. Kaolin minerals in infill at all the sites except one are considered to have formed as a result of weathering. The exception comprises white infills in tuff that are composed of extremely small, closely packed particles, suggesting formation by hydrothermal action. Generally, the kaolin minerals have formed by neogenesis out of solution in the discontinuities. Drying, with the formation of Mn and/or Fe oxides/oxyhydroxides, had occurred several times, indicating enhanced drainage. Where drying had occurred, kaolinite had formed. Where indications of drying in infills were absent, halloysite was predominant.

Chemically modified bentonites are being developed with the aim of preserving low hydraulic conductivity in the presence of potentially aggressive permeants in pollutant-containment applications. ‘Multiswellable’ bentonite (MSB) has been obtained by treating standard sodium bentonite with propylene carbonate. Research on the engineering properties of MSB has focused mainly on permeability and chemical compatibility. Solute diffusion and membrane behavior in MSB have not yet been investigated. A combined chemico-osmotic/diffusion test was performed on a MSB specimen using a 5 mM CaCl2 solution. Permeability with distilled water and with the 5 mM CaCl2 solution was measured prior to and after the chemico-osmotic/diffusion tests. The material exhibited time-dependent membrane behavior with a peak osmotic efficiency value (ω) of 0.172 that gradually shifted to zero upon breakthrough of calcium ions. Effective diffusion coefficients of calcium and chloride ions were in the range commonly described for untreated bentonite at similar porosities. After the chemico-osmotic/diffusion stage and permeation with 5 mM CaCl2, the hydraulic conductivity of MSB increased from 1.1 × 10−11 m/s to 7.0 × 10−11 m/s. The MSB was apparently converted into a calcium-exchanged bentonite at the end of the test. Prehydration and subsequent permeation might have contributed to elution of the organic additive from the clay. Further investigation is recommended to clarify the effect of prehydration on the hydraulic performance of MSB in the presence of potentially aggressive permeants.

The effects of surfactants on bentonites have been of great scientific interest for many years. Even though quaternary alkylammonium salts (QAS) have been studied, very few data are available on the comparative performance of different chain-length QAS for the modification of the surface properties and adsorption properties of bentonites. The objective of this study was to investigate the effect of chain length on the adsorption of cationic surfactants onto bentonite. The surface and adsorption properties of different chain-length QAS, i.e. hexadecyltrimethylammonium bromide (HTAB, C16), tetradecyltrimethylammonium bromide (TTAB, C14), and dodecyltrimethylammonium bromide (DTAB, C12), to produce organo- bentonites (OB) were studied. The concentrations of QAS were selected based on the cation exchange capacity (CEC) of the clay mineral. Zeta potential, swelling, and viscosity measurements and scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) analyses were used to explain the changes in surface properties. The results indicated that the best modification of bentonite was obtained using a 16-carbon chain length QAS (HTAB) in a 1:1 ratio of QAS to CEC. The basal spacing at this concentration was measured to be 22.19 Å, which also corresponded to the maximum adsorption density. The OB produced at this concentration showed the best hydrophobic character based on the swelling tests in toluene. The extent of hydrophobicity and adsorption density was correlated with the CEC and alkyl chain of the QAS. All these properties were used to elucidate the mechanism of modification governing the bentonite/QAS system.

High-resolution transmission electron microscopy (HRTEM) images of two dioctahedral micas, celadonite and cis-vacant (cv) illite, were examined in detail to understand the effects of electron radiation on their structures during image acquisition. Celadonite, a dioctahedral mica with Fe and Mg as major octahedral cations, originally has a trans-vacant (tv) octahedral sheet but the contrast in the highresolution transmission electron microscopy (HRTEM) images indicates a different cation distribution in the sheet. Furthermore, the β angle for the 1M polytype derived from the HRTEM images is ~98.5º, which is considerably smaller than that (~100.5º) reported for celadonite. In previous works, cation migration from the tv to cv-like configurations and a decrease in the β angle after dehydroxylation of celadonite/ glauconite by heating were reported. The same phenomenon, dehydroxylation and subsequent cation migration, probably occurs by electron radiation in TEM. However, the new cation-distribution models derived from HRTEM images along the [100] and [110] directions are not in agreement. On the other hand, the contrast in a number of HRTEM images from an illite specimen in which cv-illite is dominant is the same as that for the tv-dioctahedral layer. This result is also interpreted as cation migration accompanied by dehydroxylation in TEM, as reported in heated cv-illite. The increased β angle (~102.5º) from that in the natural state (101.5º) estimated from the HRTEM images also supports this interpretation. This phenomenon is a large obstacle to the investigation of phyllosilicates containing Al-rich cv and Mg,Fe-rich tv 2:1 layers, using HRTEM.