bluuebunny/crossref_metadata_2025 huggingface dataset:
Clay Diagenesis in the Sandstone Reservoir of the Ellon Field (Alwyn, North Sea)
Authors: Hassouta Lhoussain , Buatier Martine D. , Potdevin Jean-Luc , Liewig Nicole
Published: August 2006

The nature, composition, and relative abundance of clay minerals in the sandstones of the Brent Group reservoir were studied between 3200–3300 m in a well of the Ellon Field (Alwyn area, North Sea). The sandstones have a heterogeneous calcite cement which occurred during early-diagenesis. Clay diagenesis of the cemented and uncemented sandstones was investigated using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction analyses (XRD), and infrared spectroscopy (IR). The influence of cementation on clay neoformation is demonstrated in this study. Detrital illite and authigenic kaolinite are present in both the calcite-cemented and uncemented sandstones suggesting that kaolinite precipitated before calcite cementation. In the uncemented sandstones, blocky dickite replaces vermiform kaolinite with increasing depth. At 3205 m, authigenic illite begins to replace kaolinite and shows progressive morphological changes (fibrous to lath-shape transition). At 3260 m, all sandstones are not cemented by calcite. Illite is the only clay mineral and shows a platelet morphology.

In the cemented samples, vermiform kaolinite is preserved at all depths, suggesting that dickite transformation was inhibited by the presence of the calcite cement. This observation suggests that calcite cement would prevent fluid circulation and dissolution-precipitation reactions.
Effect of Phosphate on the Crystallization of Hematite, Goethite, and Lepidocrocite from Ferrihydrite
Authors: Gálvez Natividad , Barrón Vidal , Torrent José
Published: August 2006

We investigated the crystallization of ferrihydrite prepared by hydrolysis of Fe(NO3)3 solutions containing phosphate. Crystallization was studied at different pH (3–9), temperatures (298, 323, and 373 K), and initial P/Fe atomic ratios for periods to 730 d. Generally, crystallization was inhibited or only poorly crystallized lepidocrocite was formed at P/Fe > 2.5%. Phosphate favored the formation of hematite over goethite at all temperatures for most of the pH and P/Fe ranges investigated. This result is consistent with a model in which phosphate acts as a template for hematite formation, in analogy with other anions, such as oxalate. However, goethite was preferentially formed at alkaline pH and P/Fe > 1%, probably because high phosphate concentration resulted in a large increase in the negative charge of the ferrihydrite particles. This resulted in turn in less aggregation, a process that is known to precede dehydration to hematite. Phosphate greatly influenced the morphology of hematite and goethite. Hematite was often ellipsoidal or spindle-shaped. Twinned goethite crystals with a hematite core were formed at alkaline pH at P/Fe > 1%. Both hematite and goethite particles incorporated phosphate in an occluded form not desorbable by repeated alkali treatments.
Structural Study of Monomethylammonium and Dimethylammonium-Exchanged Vermiculites
Authors: Vahedi-Faridi A. , Guggenheim Stephen
Published: August 2006

Vermiculite crystals from Santa Olalla, Spain, were first Na exchanged and then intercalated with monomethylammonium (= NH3(CH3)+, MMA) and dimethylammonium (= NH2(CH3)2+, DMA) molecules, respectively, by immersion in 1 M ammonium-chloride solutions at 65°C for 2–3 wk. MMA-and DMA-exchange with vermiculite resulted in crystals with near perfect three-dimensional stacking, suitable for single crystal X-ray diffraction analysis. Unit cell parameters are: a = 5.353(2) Å, b = 9.273(3) Å, c = 11.950(6) Å, and ß = 98.45(4)° for MMA-exchanged vermiculite and a = 5.351(2) Å, b = 9.268(4) Å, c = 12.423(8) Å, and ß = 98.33(5)° for DMA-exchanged vermiculite. Refinement results are R = 0.059 and wR = 0.073 (MMA-exchanged vermiculite) and R = 0.059 and wR = 0.064 (DMA-exchanged vermiculite). The results are based on structures which show substitutional disorder, and thus the presented models are derived from average structures.

There are two distinct sites for the MMA molecule in MMA-exchanged vermiculite. One crystallo-graphically unique MMA is oriented such that the N-C axis of the molecule is perpendicular to the basal oxygen plane, with the N ion offset from the center of the interlayer by 1.04 Å. The other MMA is located such that the N ion is at the center of the interlayer between adjacent 2:1 layers, presumably with the N-C axis of the molecule oriented parallel to the basal oxygen plane. This represents the first known occurrence of an organic molecule located exactly between the two adjacent 2:1 layers. Both sites are located between hexagonal cavities of adjacent layers. DMA molecules in DMA-exchanged vermiculite are located such that the N ion is offset from the central plane in the interlayer by 0.95 A. A static model is proposed with two orientations of DMA to produce a DMA “zigzag” orientation of molecules parallel to the (001) plane. The plane defined by the C-N-C atoms in the molecule is perpendicular to the (001) plane. An alternate model is more dynamic, and it involves the rotation of DMA molecules about one C-N axis.

Identical starting material was used in previous studies on tetramethylammonium (TMA)-exchanged vermiculite and tetramethylphosphonium (TMP)-exchanged vermiculite. The effect of onium-ion substitutions on the 2:1 layer shows that the tetrahedral rotation angle, α, is significantly smaller for MMA-and DMA-exchanged vermiculite vs. TMA and TMP-exchanged vermiculite. Tetrahedral and octahedral bond distances of the 2:1 layer of the TMA, TMP, MMA, and DMA-exchanged structures may be explained by the location of the organic cation relative to the basal oxygen atom plane and by the differences in the geometries of the organic molecule. Thus, the 2:1 layer is affected by the interlayer molecule, and the 2:1 layer is not a rigid substrate, but interacts significantly with the onium ions.
Hydrothermal Conversion of Trachytic Glass to Zeolite. 3. Monocationic Model Glasses
Authors: De’ Gennaro Maurizio , Langella Alessio , Cappelletti Piergiulio , Colella Carmine
Published: August 2006

Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/Al molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tuffs. The products of the hydrothermal treatment at 100, 150, and 200°C of single glasses or glass mixtures with deionized H2O or monosaline solutions (NaCl, KCl, CaCl2) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.
Sorption of Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) Compounds by Hectorite Clays Exchanged with Aromatic Organic Cations
Authors: Jaynes W. F. , Vance G. F.
Published: August 2006

Adsorptive-type organoclays, where hydrocarbons adsorb directly to the siloxane surfaces, were studied to find new organic cations and to determine the parameters that produce effective sorbents. Organoclays were prepared from hectorite by cation exchange with small, aromatic organic cation salt solutions. Trimefhylphenylammonium (TMPA) chloride was obtained and iodide salts of commercially-unavailable aromatic cations were synthesized and used to prepare organoclays. An aqueous mixture of benzene, toluene, ethylbenzene, and xylenes (BTEX) consistent with the composition of unleaded gasoline was used in sorption isotherms to compare the sorptive properties of the organoclays. Only the TMPA, methylphenylpyridinium (MPPyr), and trimethylammonium indan (Indan) organoclays were effective BTEX sorbents. Organoclays prepared from methylpyridinium (MPyr), trimethylammonium biphenyl (Biphenyl), and trimethylammonium fluorene (Fluorene) were poor sorbents. The MPPyr and TMPA organoclays preferentially sorbed ethylbenzene, whereas the Indan organoclay preferentially sorbed benzene and toluene. Langmuir-type sorption isotherms for the TMPA, MPPyr, and Indan organoclays implied surface adsorption, whereas linear isotherms suggested that partitioning was the sorptive mechanism for the MPyr, Biphenyl, and Fluorene organoclays. Water hydrating the small MPyr cation and the larger bulk of the Biphenyl and Fluorene cations may have blocked BTEX access to the interlayer siloxane surfaces. Although the rather bulky MPPyr and Indan cations produced effective organoclays, compact size and low hydration are organic cation properties that typically yield effective adsorptive-type organoclays.
Modeling of Organic and Inorganic Cation Sorption by Illite
Authors: Polubesova Tamara , Nir Shlomo
Published: August 2006

Sorption of several organic and inorganic cations on illite (Clay Minerals Society Source Clay Imt-2) was determined experimentally and results compared to model calculations. The cations studied were crystal violet (CV+), benzyltrimethylammonium (BTMA+), benzyltriethylammonium (BTEA+), Ca2+, Mg2+, K+, Na+, Cs+, and Li+. The adsorption-model calculations involved a solution of the electrostatic Gouy-Chapman equations. The model considered specific adsorption and sorption/exclusion in the double-layer region in a closed system. Model calculations considered the simultaneous presence of four to six cations in the system. The adsorption of CV included formation of neutral and charged complexes. The adsorption attained 0.37 mol kg−1 or 150% of the cation exchange capacity (CEC) of illite in aqueous suspension. The adsorption of BTMA and BTEA did not exceed the CEC and was reduced with an increase in ionic strength. The sorption of CV below the CEC was rather insensitive to the ionic strength because of the large binding coefficients and was only slightly reduced in NaCl, CsCl, or Na2SO4 solutions. When added in amounts exceeding the CEC in high ionic strength, 0.667 M NaNO3, NaCl, or CsCl solutions, the adsorbed quantities of CV increased to three times the CEC. At high sulphate concentrations (0.333 M Na2SO4), the adsorption was below the CEC. Model calculations yielded satisfactory simulations for the adsorption, particularly for cations added in amounts approaching or exceeding the CEC. The binding coefficients for formation of neutral complexes followed the sequence: CV > Ca > BTMA > BTEA > Cs > Mg > K > Na > Li. Model calculations also suggested that sites were present which bound exchangeable cations, particularly K+, Na+, and Mg2+, very tightly.
Preparation and Properties of Hematite with Structural Phosphorus
Authors: Gálvez Natividad , Barrón Vidal , Torrent José
Published: August 2006

Synthetic hematites prepared in the presence of phosphate can incorporate phosphorus (P) in forms other than phosphate adsorbed by ligand-exchange on the crystal surface. To investigate the nature of such occluded P, which is also found in some natural specimens, we prepared 13 hematites by aging ferrihydrite precipitated from Fe(NO3)3-KH2PO4 solutions. The P/Fe atomic ratio of the resulting hematites ranged from 0 to 3% and all incorporated significant amounts of OH. As P content is raised, particle morphology changes from rhombohedral to spindle or ellipsoid-shaped. Despite the grainy appearance in transmission electron microscope images, X-ray diffraction data indicate that the particles are single crystals. Specific surface area ranged from 66 to 91 m2g−1, partly in micropores. The intensity of the absorption bands due to Fe3+ ligand field transition in the visible region, as measured by the second derivative of the Kubelka-Munk function, suggests that both OH and P contribute to an Fe deficiency in the structure. Such a deficiency is also apparent from the 104/113 peak intensity ratio in the X-ray diffraction patterns. The c unit-cell length increases with increasing P content. The infrared spectra exhibit four bands in the P-OH stretching region (viz., at 936, 971, 1005, and 1037 cm−1) which suggest that occluded PO4 possesses a low symmetry. Congruent dissolution of P and Fe was observed on acid treatment of the hematites, the dissolution rate being negatively correlated with the P content. All observations are consistent with the occluded P in the hematites being structural. A model is proposed where P occupies tetrahedral sites in the hematite structure, thus resulting in an Fe deficiency and facilitating proton incorporation.
Smectites in Iron-Rich Calcareous Soil and Black Soils of Taiwan
Authors: Pai Chuang-Wen , Wang Ming-Kuang , Wang Wei-Min , Houng Kun-Huang
Published: August 2006

The iron-rich calcareous soil (Typic Rhodustalf) from the Penghu island group represents a volcanic area. The black soils (Typic Haplustert, Vertic Endoaquoll, Typic Hapludolls) are typical of eastern Taiwan. Four A horizons and a pedon from the iron-rich calcareous soil and four pedons from the black soils were studied to analyze soil properties and clay compositions. The objective was to compare the properties of smectites developed from different parent materials. The materials were studied by using conventional X-ray diffraction (XRD) of K- and Mg-saturated clays and involved the alkylam-monium (C = 12) method and the Greene-Kelly test. The mean-layer charge of smectites (0.48–0.52 cmol(c)/O10(OH)2) in the iron-rich calcareous soil was found to be higher than the black soils (0.43–0.48 cmol(c)/O10(OH)2). A smectite of higher charge developed from the basalts. This smectite is enriched in Fe and Mg, and lacks Si, thereby forming beidellite and/or nontronite. In contrast, under high precipitation, elevated temperature, base saturation (e.g., Na, K, Ca, Mg), and about equal wet and dry cycles per year in the black soil environments, smectites developed from the complicated geologic site of eastern Taiwan. These smectites transformed to smectite-kaolinite mixed-layer clay and thus, resulted in lower-charge smectites. The K fixation capacity of the iron-rich calcareous soil was higher than the black soils.
The Structure of U6+ Sorption Complexes on Vermiculite and Hydrobiotite
Authors: Hudson Eric A. , Terminello Louis J. , Viani Brian E. , Denecke Melissa , Reich Tobias , Allen Patrick G. , Bucher Jerome J. , Shuh David K. , Edelstein Norman M.
Published: August 2006

The sorption of the uranyl oxo-cation (UO22+)at different types of binding sites on layer silicate mineral surfaces was investigated. Well-characterized samples of vermiculite and hydrobiotite were exposed to aqueous uranyl under conditions designed to promote surface sorption either at fixed charge ionexchange sites or at amphoteric surface hydroxyl sites. The local structure of uranium in the sorption samples was directly measured using uranium L3-edge extended X-ray absorption fine structure (EXAFS). Polarized L1- and L3-edge X-ray absorption near-edge structure (XANES) measurements were used to characterize the orientation of uranyl groups in layered samples. X-ray diffraction (XRD) measurements of interlayer spacings were used to assess the effects of ion-exchange and dehydration upon the mineral structure. The most significant findings are: (1) Under conditions which greatly favor ion-exchange sorption mechanisms, uranyl retains a symmetric local structure suggestive of an outer-sphere complex, with a preferred orientation of the uranyl axis parallel to the mineral layers; (2) Upon dehydration, the ionexchange complexes adopt a less symmetric structure, consistent with an inner-sphere complex, with less pronounced orientation of the uranyl axis; and (3) For conditions which favor sorption at surface hydroxyl sites, uranyl has a highly distorted equatorial shell, indicative of stronger equatorial ligation, and the detection of a neighboring U atom suggests the formation of surface precipitates and/or oligomeric complexes.
Quantification and Characterization of Maghemite in Soils Derived from Volcanic Rocks in Southern Brazil
Authors: da Costa Antonio Carlos S. , Bigham Jerry M. , Rhoton Fred E. , Traina Samuel J.
Published: August 2006

Many soils developed from volcanic rocks in southern Brazil exhibit spontaneous magnetization caused by the presence of fine-grained maghemite (γ-Fe2O3), but few attempts were made to quantify or characterize this important soil component. To that end, clays were separated from freely drained soils derived from acid (≥63% SiO2), intermediate (54–62% SiO2), and basic (≤53% SiO2) igneous rocks produced by the Paraná flood volcanism. The sample set included soils with a wide range of pedogenic development on different landscape positions. The Fe oxide mineralogy of these samples was examined by using a combination of selective dissolution, magnetic susceptibility, and X-ray diffraction (XRD) techniques. Hematite and maghemite were the primary Fe oxides in mature soils (Oxisols, Ultisols, and Alfisols) developed from basic rocks; whereas goethite was dominant in all other soils, especially those formed from acid-intermediate rocks. The association of maghemite with basic rock materials suggests that it was primarily formed by oxidation of lithogenic magnetite. A strong, positive correlation (R2 = 0.89) was obtained between mass specific magnetic susceptibility (χ) of the clay fractions and maghemite contents estimated by XRD. Either method could be used for quantitative analyses, but χ was more sensitive than XRD at low maghemite concentrations (<2 wt. %). The clay-sized maghem-ites were superparamagnetic with an estimated value for the mass specific magnetic susceptibility (χlf) value of 91,000 × 10−8 m3 kg−1 and frequency dependent variations of 10–15%. The maghemites also had low unit cell constants, which, if attributed entirely to replacement of Fe by Al, would correlate with Al substitutions in the range of 5–16 mole %. Selective dissolution of the soil maghemites was achieved by treatment of Fe oxide concentrates with 1.8 M H2SO4 at 75°C for 2 h.
Spectroscopy Study of Arsenite [As(III)] Oxidation on Mn-Substituted Goethite
Authors: Sun Xiaohua , Doner Harvey E. , Zavarin Mavrik
Published: August 2006

Mn-substituted goethite was synthesized and the interaction between arsenite (As(III)) and Mn-substituted goethite was investigated by both solution chemistry and X-ray adsorption near edge structure (XANES) spectroscopy. Results indicate that the oxidation of As(III) is favored by Mn-substituted goethite. This reaction was more sensitive to temperature than to pH. Different reaction mechanisms may account for As(III) oxidation. Since As(III) is more mobile and toxic than As(V), the oxidation reaction of As(III) with Mn-substituted goethite may decrease arsenic toxicity under some conditions.
Refinement of the Kaolinite Structure From Single-Crystal Synchrotron Data
Authors: Neder R. B. , Burghammer M. , Grasl TH. , Schulz H. , Bram A. , Fiedler S.
Published: August 2006

The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRF, Grenoble, France (λ = 0.6883, T = room temperature). The volume of the crystals was 8 and 0.8 μm3, respectively. Unit-cell parameters are: a = 5.154(9) Å, b = 8.942(4) Å, c = 7.401(10) Å, α = 91.69(9)°, β = 104.61(5)°, γ = 89.82(4)°. Space group Cl is consistent with the observed data. All non-hydrogen atoms were independently refined with anisotropic displacement parameters. The positions and isotropic displacement parameters for the three interlayer H atoms were refined also. The position of the intralayer H was found by difference-Fourier methods, although refinement was not possible. Difference-Fourier maps suggested large anisotropic displacement vectors of this intralayer H, however, no evidence for a second maximum was found. The diffraction patterns show diffuse scattering in streaks parallel to [001]* through hkl reflections with hk ≠ 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.
Determination of Illite-Smectite Structures using Multispecimen X-Ray Diffraction Profile Fitting
Authors: Sakharov Boris A. , Lindgreen Holger , Salyn Alfred , Drits Victor A.
Published: August 2006

A procedure for structural investigations by X-ray diffraction of mixed-layer structures incorporating swelling layers has been developed. For each sample, specimens saturated with different cations (Na, Mg, and Ca), are analyzed both as air-dried and as glycolated. One structural model fitting all the observed patterns then provides the structure of the sample. Samples tested include: Mite-smectite (I-S) minerals from Kazachstan (a rectorite), Dolna Ves in Slovakia, Kinnekulle in Sweden, the North Sea, and Scania in Sweden. The fitting of the patterns of the Kazachstan rectorite demonstrated that the instrumental parameters applied in the modeling were correct. For the I-S minerals from Slovakia and Kinnekulle the observed patterns were fitted with one two-component I-S model. However, the Ca-saturated and air-dried specimen of the Kinnekulle bentonites had two types of swelling interlayers. For the Slovakian I-S with Reichweite = 2, an alternative two-phase I-S plus I–V (V = vermiculite) model fitted the experimental X-ray diffraction patterns equally well. The I-S mineral from Scania is in fact a three-component I-T-S (T = tobelite) and the North Sea sample is a four-component I-S-V-V, one type of the swelling layers having swelling characteristics intermediately between smectite and vermiculite. In addition to layer types and distribution, interlayer compositions, such as the amount of interlayer glycol and water and of fixed and exchangeable cations, were determined.
Dehydroxylation Behavior of Heat-Treated and Steam-Treated Homoionic cis-Vacant Montmorillonites
Authors: Emmerich Katja , Madsen Fritz Thule , Kahr Guenter
Published: August 2006

Li+, Na+, Ca2+, Sr2+, Cu2+, or Zn2+-saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200–700°C. Half of each heated sample was subsequently autoelaved under steam at 200°C (∼1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer.

Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li+, Cu2+, and Zn2+ ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu2+ and Zn2+-rich samples release 16–23 meq/100 g of Mg2+ from the structure. No Mg2+ release is observed for the Li+-rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu2+, Zn2+, and Li+-rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu2+ and Zn2+-rich smectites show a peak doublet between 480–700°C. For the Li+, Na+, Ca2+, and Sr2+-rich montmorillonites, the second peak disappeared and a third peak at ∼760°C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.
Layer Charge Influences on the Hydration of Expandable 2:1 Phyllosilicates
Authors: Laird David A.
Published: August 2006

The objective of this study was to investigate the influence of layer charge on the hydration of Mg-saturated expandable 2:1 phyllosilicates. Water retained by 12 Mg-saturated clays at 54% relative humidity was quantified gravimetrically. X-ray diffraction and total chemical analysis were used to determine the hydratable surface area (447–759 m2g−1) and layer charge [0.327–0.754 electrons per formula unit (e f.u.−1)] of each sample. Water retained by the clays increased with both hydratable surface area and layer charge of the clays. However, the increase in H2O content with layer charge occurred only on external surfaces of the clays. This result suggests that the H2O on external surfaces is localized around the cation/charge sites rather than forming multi-layers as was suggested previously. A model is proposed for the hydration of expandable 2:1 phyllosilicates. The model assumes that interlayer volume controls interlayer hydration and that the number of cation/charge sites on external surfaces controls hydration of external surfaces.
Swelling of Formamide-Montmorillonite Complexes in Polar Liquids
Authors: Onikata Masanobu , Kondo Mitsuji , Yamanaka Shoji
Published: August 2006

A new osmotic-swelling system for montmorillonite with formamide (FA) is described. Water and a variety of polar organic liquids were used to swell FA-montmorillonite complexes. The post-swelling behavior of the complex is interpreted in terms of the bi-functionality of FA as an electron donor/acceptor and the magnitude of the donor number (DN) of the polar liquid relative to that of FA. The FA-montmorillonite complex shows limited swelling of d(001) <2.3 nm for polar liquids with DNs larger than that of FA. In contrast, the FA-montmorillonite complex shows osmotic swelling when the DN of the polar liquid is smaller than that of FA.
Direct Imaging of Zirconia Pillars in Montmorillonite by Analytical Electron Microscopy
Authors: Crozier P. A. , Pan M. , Bateman C. , Alcaraz J. J. , Holmgren J. S.
Published: August 2006

Analytical electron microscopy was used to confirm the location of pillars of zirconia in pillared montmorillonite. Data show that the pillared clay is of “high” quality, with surface areas ranging from 200 to 250 m2/g and (001) spacings in the 17–18 Å range. The zirconia-rich pillars were observed using bright-field imaging, annular dark-field imaging, and energy-filtered imaging. The composition of the pillars was confirmed by performing nano-analysis using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy. The pillars apparently have an irregular shape <50 Å in size. The shape and relatively large size of the pillars suggest that zirconia dispersion is not ideally distributed in this sample. This study is apparently the first report of electron microscopy observation of pillaring material in clays.
Effect of Illite Particle Shape on Cesium Sorption
Authors: Rajec Pavol , Šucha Vladimír , Eberl Dennis D. , Środoń Jan , Elsass Françoise
Published: August 2006

Samples containing illite and illite-smectite, having different crystal shapes (plates, “barrels”, and filaments), were selected for sorption experiments with cesium. There is a positive correlation between total surface area and Cs-sorption capacity, but no correlation between total surface area and the distribution coefficient, Kd. Generally Kd increases with the edge surface area, although “hairy” (filamentous) illite does not fit this pattern, possibly because elongation of crystals along one axis reduces the number of specific sorption sites.
Nuclear Magnetic Resonance (NMR) Study of Cd2+ Sorption on Montmorillonite
Authors: Di Leo Paola , O'Brien Paul
Published: August 2006

113Cd solid-state nuclear magnetic resonance (NMR) was used to identify possible Cd2+ adsorption sites in montmorillonite. The montmorillonite was treated with 0.1 and 1 M CdCl2 aqueous solutions and samples with 13 and 8-µm particle size were used. The data are consistent with a two-site model for sorption of Cd2+ on montmorillonite. Cd2+ is localized in the montmorillonite in two different sites: 1) in the interlayers as hydrated Cd2+ and 2) on the external surface, probably with few H2O molecules hydrating to it. Cadmium is also adsorbed as CdCl+ in the interlayer. Treatment with a 0.1 M CdCl2 solution produces adsorption of free Cd2+ in the interlayer whereas treatment with 1 M CdCl2 resulted in adsorption of Cd2+ in both the interlayer and on surface sites and the adsorption of CdCl+ in the interlayer. A larger particle size favors Cd2+ adsorption on the external surface whereas a smaller particle size favors Cd2+ adsorption in the interlayer.
First Occurrence of a Stacking Sequence Including (±60°, 180°) Rotations in Mg-Rich Annite
Authors: Kogure Toshihiro , Nespolo Massimo
Published: August 2006

Transmission electron microscopy (TEM) observation shows narrow regions in a Ti-containing Mg-rich annite of composition (K0.90Na0.02)(Mg0.72Fe2+1.78Mn0.03Ti0.27Al0.05)(Si2.77Al1.23)O10(OH,F)2from a granitic rock, where the ±60° and 180° stacking angles occur extensively. These regions are a few hundreds of nanometers thick along the [001]* direction and are within 1Mor 2M1annite. The stacking sequence in one of these regions was determined by two atomic-resolution images recorded along [1̄10] and [010] of the same crystal. Stacking sequences with ± 120° or 180° rotations are dominant, although those with ±60° rotations occur also. Locally 2Oand more complex sequences exist. Compositional analysis by TEM indicated no difference in the chemical compositions between these regions and the adjacent ones with regular 1Mor 2M1stacking sequence. The origin of these unusual stacking sequences in annite is discussed.
Preparation of Kaolinite-Amino Acid Intercalates Derived from Hydrated Kaolinite
Authors: Sato Makoto
Published: August 2006

Intercalation of amino acids into 10.0-Å hydrated kaolinite was studied by powder X-ray diffraction (XRD), differential thermal analysis-thermal gravimetry (DTA-TG), and infrared (IR) spectroscopy. Intercalation was found to be dependent on the chain-length, pH, and the concentration of the amino acid zwitterion. Near the isoelectric point, fully intercalated phases were obtained in solutions of concentration >0.5–1 M for glycine (Gly), 2–3 M for β-alanine (β-Ala), and 12 M for both γ-aminobutyric acid (γ-Aba) and δ-aminovaleric acid (δ-Ava). ∊-aminocaproic acid (∊-Aca) with a long chain (C = 6) was only partially intercalated. Intercalated amino acid formed a mono-molecular arrangement with the alkyl chain tilting toward the layer at an angle related to H2O content. The compositions of the intercalates of the Gly and β-Ala are Al2Si2O5(OH)4·(Gly)0.67·0.24H2O and Al2Si2O5(OH)4·(β-Ala)0.63·0.25H2O, respectively, based on TG data. From IR data, Gly and β-Ala molecules are found intercalated as zwitterions and these molecules form hydrogen bonds with both the Al-OH and Si-O surfaces of kaolinite. Washing the intercalate with water produced a hydrated kaolinite, which may form a second amino-acid intercalate of high order. Thus, hydrated kaolinite intercalates or deintercalates amino acids depending on concentration and conditions.
Infrared Study of the Intercalation of Potassium Halides in Kaolinite
Authors: Yariv S. , Lapides I. , Nasser A. , Lahav N. , Brodsky I. , Michaelian K. H.
Published: August 2006

KCl-, KBr-, and KI-kaolinite intercalation complexes were synthesized by gradually heating potassium-halide discs of the dimethylsulfoxide (DMSO)-kaolinite intermediate at temperatures to 330°C. Two types of complexes were identified by infrared spectroscopy: almost non-hydrous, obtained during thermal treatment of the DMSO complex; and hydrated, produced by regrinding the disc in air. The former showed basal spacings with integral series of 00l reflections indicating ordered stacking of parallel 1:1 layers. Grinding resulted in delamination and formation of a disordered “card-house” type structure. The frequencies of the kaolinite OH bands show that the strength of the hydrogen bond between the intercalated halide and the inner-surface hydroxyl group decreases as Cl > Br > I. The positions of the H2O bands imply that halide-H2O interaction decreases in the same order. Consequently, the strength of the hydrogen bond between H2O and the oxygen atom plane increases in the opposite sequence.

In the non-hydrous KCl-kaolinite complex the inner hydroxyl band of kaolinite at 3620 cm-1 is replaced by a new feature at 3562 cm-1, indicating that these OH groups are perturbed. It is suggested that Cl ions penetrate through the ditrigonal hole and form hydrogen bonds with the inner OH groups. In contrast, Br and I ions are too large to pass into the ditrigonal holes and do not form hydrogen bonds with the inner hydroxyls.
Polarity Effect on Dichlorobenzene Sorption by Hexadecyltrimethylammonium-Exchanged Clays
Authors: Sheng Guangyao , Boyd Stephen A.
Published: August 2006

Sorptive properties of organoclays may be greatly influenced by the physicochemical properties of organic sorbates. Hexadecyltrimethylammonium(HDTMA) clays were prepared using a high-charge smectite (HDTMA-SAz-1), a low-charge smectite (HDTMA-SWy-2), and an illite (HDTMA-ILL). The resultant organoclays were used to sorb aqueous phase 1,2-dichlorobenzene (o-DCB), 1,3-dichlorobenzene (m-DCB), and 1,4-dichlorobenzene (p-DCB). Sorptive characteristics of these compounds were determined by their molecular polarities (o-DCB >m-DCB >p-DCB) and the HDTMA-clay interlayer distance. HDTMA-ILL was used for comparison to HDTMA-SAz-1 and HDTMA-SWy-2. All dichlorobenzene isomers were directly intercalated in the interlayers of HDTMA-SAz-1, causing interlayer expansion.o-DCB andm-DCB were not intercalated in the interlayers of HDTMA-SWy-2 at low concentrations, but intercalation occurred at higher concentrations, which caused interlayer expansion. The concentration needed to produce interlayer expansion depended on the solute molecular polarity, hence a higher concentration ofm-DCB thano-DCB was required.p-DCB was sorbed primarily by the HDTMA phase on the external surfaces of HDTMA-SWy-2. In the presence of chlorobenzene (CB),p-DCB sorption by HDTMA-SWy-2 is greatly enhanced, owing to the interlayer expansion by CB and a cosolvent effect. Sorption ofo-DCB resulted from both direct solvation-type interactions with HDTMA and partitioning into HDTMA. Such sorption results in double-sigmoid isotherms.m-DCB weakly solvates the HDTMA and partitions into the HDTMA, displaying either a double-sigmoid or a type-III isotherm depending on clay type.p-DCB lacks ability to solvate HDTMA and partitions into HDTMA as its sole mechanism, producing type-III isotherms. HDTMA-clays are potentially effective for treating dichlorobenzene-contaminated wastewater.
Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite
Authors: Janney Dawn E. , Cowley John M. , Buseck Peter R.
Published: August 2006

High-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), annular dark-field scanning transmission electron microscope (STEM) images, and electron nano-diffraction were used to examine structures of synthetic 2- and 6-line ferrihydrite specimens. HRTEM images of 2-line ferrihydrite (2LFh) show scattered small (~1-3 nm) areas with lattice fringes surrounded by areas free of fringes. All SAED patterns show two bright rings corresponding to d-values of ~0.15 and 0.25 nm; each ring has a conspicuous shoulder on each side. Faint rings corresponding to d-values of 0.08, 0.095, 0.100, 0.106-0.114 (very broad ring), and 0.122 nm are visible in strongly exposed SAED patterns. Nanodiffraction patterns show conspicuous streaks and a lack of superlattice formation.

HRTEM images of 6-line ferrihydrite (6LFh) display larger crystallites (typically ~5-6 nm) with lattice fringes visible in many thin areas. SAED patterns show rings corresponding to d-values of 0.148, 0.156, 0.176, 0.202, 0.227, and 0.25-0.26 nm and a shoulder extending between d-values of ~0.25 and 0.32 nm. Faint rings corresponding to d-values of 0.086, 0.093, 0.107, 0.112, 0.119, 0.125, and 0.135 nm are visible in strongly exposed SAED patterns. Small quantities of hematite, magnetite or maghemite, and an acicular material tentatively identified as goethite were observed in the 6-line ferrihydrite, but these quantities do not contribute significantly to the overall diffracted intensity from the sample.
Influence of Organic and Inorganic Salts on the Coagulation of Montmorillonite Dispersions
Authors: Penner D. , Lagaly G.
Published: August 2006

The colloidal state (stable, coagulated, or gel-like) and the rheological properties of Na-rich montmorillonite (Wyoming) dispersions are strongly influenced by organic cations. This effect is shown for homologous organic cations: alkyl trimethylammonium ions, paraquat, diquat, alkyl bispyridinium ions, and the triphenylmethane dyes crystal violet, methyl green, and tris (tri-methylammonium phenyl) methane chloride. The critical coagulation concentrations, cK, are small (often < 1 mmol/L) because the cations are enriched in the Stern layer and influence the solvent structure near the surface. The strong adsorption of the counterions at the clay-mineral surface causes cK values to increase with the solid content. Charge reversal (recharging) of the particles was observed with the longer chain alkyl trimethyl-ammonium ions, dodecyl bispyridinium ions, and crystal violet. Other cations reduced the electrophoretic mobility to zero but positive particle charges were not observed.

The plastic viscosity increased sharply at the critical coagulation concentration and showed a minimum slightly below cK, which was caused by the electroviscous effect. Yield values were developed at concentrations above cK. In most cases, yield values reached a plateau where the amount of organic cations was ∼0.5 mmol/g, i.e., about half of the cation-exchange capacity. The cK values decreased with increasing hydrophobicity of homologous compounds, but the yield value showed maxima at intermediate chain lengths. The yield value of several 0.5% dispersions was high, e.g., dodecyl trimethylammonium ions, 71 Pa; paraquat, 100 Pa; diquat, 42 Pa; hexyl bispyridinium ions, 53 Pa (vs. Ca2+, 0.2 Pa; Al3+, 0.7 Pa). The storage modulus as a function of the number of organic cations changed in a similar way as the yield value, and high values were observed (e.g., dodecyl trimethylammonium ions, hexyl bispyridinium ions: 1000 Pa, paraquat: >4000 Pa). Thus, dispersions with high viscosity, yield value, and pronounced viscoelasticity are obtained by coagulating Na-rich montmorillonite dispersions with organic cations.
Chlorite, Corrensite, and Chlorite-Mica in Late Jurassic Fluvio-Lacustrine Sediments of the Cameros Basin of Northeastern Spain
Authors: Barrenechea José F. , Rodas Magdalena , Frey Martin , Alonso-Azcárate Jacinto , Mas José Ramón
Published: August 2006

The distribution and crystal-chemical characteristics of chlorite, corrensite, and mica in samples from a stratigraphic profile in the Cameros basin are controlled by changes in the sedimentary facies. The lacustrine marls and limestones from the base and the top of the profile contain quartz + calcite + illite ± dolomite ± chlorite ± albite ± paragonite ± Na, K-rich mica. Chlorite is rich in Mg, with Fe/(Fe + Mg) ratios ranging between 0.18–0.37. A formation mechanism involving reaction between Mg-rich carbonate and dioctahedral phyllosilicates is proposed for these Mg-rich chlorites, on the basis of the mutually exclusive relationship found between Mg-rich chlorite and dolomite, together with the relative increase in the proportion of calcite in samples containing chlorite.

The mudrocks from the middle part of the profile are composed of quartz + albite + illite + corrensite (with a mean coefficient of variability of 0.60%) ± chlorite. Corrensite and chlorite are richer in Fe2+ than those from the base or top of the profile, with mean Fe/(Fe + Mg) ratios of 0.51 and 0.56, respectively. Textural and compositional features suggest a formation mechanism for the corrensite, chlorite, and chlorite-mica crystals through replacement of detrital igneous biotite. Whether or not corrensite occurs with chlorite appears to be related to redox conditions. The presence of corrensite alone is apparently favored by oxidizing conditions, whereas the occurrence of corrensite + chlorite is related to more reducing conditions. Corrensite shows higher Si and Na + K + Ca contents, and slightly lower Fe/(Fe + Mg) ratios than chlorite. The presence of corrensite and the lack of random chlorite-smectite interlayering is discussed in terms of the fluid/rock ratio; the occurrence is related to the hydrothermal character of metamorphism in the Cameros basin.
Effects of Iron Oxidation State and Organic Cations on Dioctahedral Smectite Hydration
Authors: Stucki Joseph W. , Wu Jun , Gan Huamin , Komadel Peter , Banin Amos
Published: August 2006

Reduction of structural Fe in Na-exchanged dioctahedral smectites decreases swellability in water, but because clay interlayers also collapse in the process the concomitant effect on surface hydration energy is uncertain. This study examined the hydration behavior of oxidized and reduced dioctahedral smectite clays exchanged with polar (Na) and weakly-polar (organic) cations to determine the nature of the surface before and after Fe reduction, and to determine if clay surfaces are hydrophilic or hydrophobic. The H2O content in various dioctahedral smectites decreased if Na was replaced by tetramethylammonium (TMA), trimethylphenylammonium (TMPA), or hexadecyltrimethylammonium (HDTMA). Among the organo-clays, H2O adsorption decreased with increasing complexity of the cation. For oxidized smectites, those exchanged with TMPA retained less H2O than those exchanged with Na at all pressures. The extent of this difference depended on the clay and decreased with increasing applied pressure. Reduction of Fe(III) to Fe(II) in the octahedral sheets decreased the swelling of Na-saturated smectites, apparently causing some previously swelling interlayers to collapse. If the Na interlayer cation was exchanged to alkylammonium after reduction, but prior to swelling-pressure measurements, the swelling increased or remained near constant, suggesting that the organo-cation disrupted the collapse process of the interlayers associated with the reduced smectite layers. Reduced TMPA-saturated smectite surfaces are more strongly hydrated if the octahedral sheet is reduced than if oxidized. Thus, reduction of structural Fe increases the hydration energy of smectite basal surfaces, but swellability could decrease or increase depending on the extent of interlayer collapse occurring with different exchangeable cations.
Transmission Electron Microscopy Study of Illitization in Pelites from the Iberian Range, Spain: Layer-by-Layer Replacement?
Authors: Bauluz Blanca , Peacor Donald R. , Gonzalez Lopez Jose Manuel
Published: August 2006

A sequence of interstratified illite-smectite (I-S) and illite in Paleozoic pelites and metapelites from the Iberian Range, Spain, was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The fine-grained matrix of diagenetic pelites is composed of I-S with sequences of illite- and smectite-like layers in a given sample. The Reichweite (R) values as determined by XRD and averaged over heterogenous I-S layer sequences increase with increasing grade, apparently continuously, in sharp contrast with TEM observations of other published sequences. Changes in I-S sequences along layers are rarely observed. In the higher-grade diagenetic pelites, I-S coexists with illite. Each I-S phase has a composition similar to that of illite, implying unique Al-Si distributions in contrast to smectite and muscovite. Selected area electron diffraction (SAED) patterns of I-S and illite are diagnostic of 1Md polytypism. Anchizonal metapelites consist of larger packets of well-crystallized muscovite, with SAED patterns corresponding to a two-layer polytype.

The continuous sequence of changes studied by TEM in I-S sequences and lateral transitions among these units is consistent with illitization by layer-by-layer replacement, although other processes are possible also. Replacement of individual layers probably occurs via fluids at reaction interfaces, in contrast to solid-state reactions, sensu strictu. The transition from the diagenetic to anchizonal rocks (transition in textures and formation of muscovite-2M1) occurred via dissolution/crystallization, however, presumably by tectonic stress. XRD and TEM data imply a consistent prograde trend in the sequence, the XRD data denning the average, long-range Reichweite ordering sequence, whereas the TEM data define the short-range layer sequences.
Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce and La
Authors: Valverde J. L. , Cañizares P. , Sun Kou M. R. , Molina C. B.
Published: August 2006

A commercial bentonite (primarily smectite) from Fischer Scientific Company (F bentonite) and a natural bentonite from Peru (P bentonite) were used in the preparation of pillared clays with polyoxymetal cations of Al that were subsequently modified with Ce and La. Several Al/metal ratios (5 and 9) were used to investigate the effects on the thermal and hydrothermal stability of these synthetic clays. The structure of these materials was studied by X-ray diffraction. Isotherms were determined by N2 adsorption. Thermal stability was determined using thermogravimetric (TG) measurements and ara-monia-TPD (temperature programmed desorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 Å, with surface areas from 239 to 347 m2g−1, with microporosity contributing from 50 to 80% of the total surface area. Pillared clays prepared from F bentonite generally showed larger basal spacings and surface areas than those prepared from P bentonite. Pillared clays modified with Ce or La did not show any apparent structural changes relative to the Al-pillared clays. Pillared clays modified with Ce and La had similar acid properties as Al-pillared clays. In contrast, the thermal and hydrothermal stabilities of these materials were greater than Al-pillared clays. However, Ce-pillared clay appears to be more effective than La-pillared clay in delaying the dehydroxylation of pillared clays with increasing temperature. The intercalation of Ce and La into Al-pillared clays improved the thermal stability, which may increase the utility of these materials as catalysts.
Multiple Episodes of Clay Alteration at the Precambrian/Paleozoic Unconformity, Appalachian Basin: Isotopic Evidence for Long-Distance and Local Fluid Migrations
Authors: Ziegler Karen , Longstaffe Fred J.
Published: August 2006

Chlorite and illite are commonly associated with ubiquitous secondary K-rich feldspar in the rocks located immediately above and below the Precambrian-Paleozoic unconformity in southwestern Ontario, and elsewhere in the mid-continent of North America. This alteration assemblage is attributed to long-distance migration of hot brines driven westward by orogenic processes originating along the eastern seaboard of North America. The δD and δ18O values of chlorite and illite, plus K-Ar dates for secondary K-rich feldspar and illite, were used to determine the nature, origin, and timing of the fluids that altered Precambrian granites and their overlying rocks in southwestern Ontario. The δ18O values of the chlorite-forming fluids are best explained by initial hot brines (≥50°C) evolved mostly from seawater. Secondary K-rich feldspar formation followed shortly thereafter, as the fluids cooled and perhaps mixed with meteoric water. Regional migration of the brines was induced by Taconic orogenic events to the east. The hydrogen and oxygen isotopic compositions for the secondary illite of the early to mid-Carboniferous indicate its crystallization from local meteoric water at low temperatures (40–55°C). Infiltration of local meteoric water into the Paleozoic and uppermost altered Precambrian rocks occurred during uplift, erosion, and subaerial exposure of local arches in southern Ontario. The local basement reactivation and associated secondary illite formation in this portion of the North American hinterland was likely a distal expression of east-coast Acadian and Alleghanian orogenic activity.