bluuebunny/crossref_metadata_2025 huggingface dataset:
57Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites
Authors: De Grave E. , da Costa G. M. , Bowen L. H. , Schwertmann U. , Vandenberghe R. E.
Published: August 2006

Seven Al-containing lepidocrocite samples, γ-Fe1−xAlxOOH, prepared from FeCl2/Al(N03)3 solutions with initial Al/(Al + Fe) mole ratios Ci of 0.0025, 0.01, 0.025, 0.05, 0.075, 0.10 and 0.15 mol/mol, were examined by means of Mössbauer spectroscopy at room temperature (RT) and at various temperatures in the range of 8 to 80 K. The spectra at RT and 80°K consist of broadened quadrupole doublets and were analyzed in terms of a single doublet and of a model-independent quadrupole-splitting distribution, the latter yielding the best fit. The observed variations of the quadrupole-splitting parameters with increasing Ci are inconclusive as to whether the Al cations are substituting into the structure. The temperature at which the onset of magnetic ordering is reflected in the spectra, was measured by the thermoscan method with zero source velocity. A gradual shift from 50 K for Ci = 0.0025 mol/mol to 44 K for Ci = 0.10 mol/mol was observed for that temperature. As compared to earlier studies of Al-free γ-FeOOH samples with similar morphological characteristics, the fractional doublet area in the mixed sextet-doublet spectra at 35 K is significantly higher for the present lepidocrocites. This observation is ascribed to the substitution of Al cations into the lepidocrocite structure. A similar conclusion is inferred from the variation with Ci of the maximum-probability hyperfine field derived from the spectra recorded at 8 K and fitted with a model-independent hyperfine-field distribution. The magnetic results suggest that for the sample corresponding to Ci = 0.15 mol/mol, not all of the initially present Al has been incorporated into the structure.
Study of Nanocomposites Obtained by Carbonization of Different Organic Precursors within Taeniolite Matrices
Authors: Bandosz Teresa J. , Putyera Karol , Jagiełło Jacek , Schwarz James A.
Published: August 2006

The lithium form of taeniolite served as the molecular template for carbon nanocomposites. It was intercalated with hydroxy aluminum and hydroxy aluminum-zirconium cations. Aliquots of the inorganic matrices were saturated by furfuryl alcohol followed by its interlayer polymerization. The structures were heated at 973 K in nitrogen to carbonize the polymeric precursor. Additional materials were mixed with polypropylene glycol which was then carbonized within the mineral layers. The surface properties of the nanocomposites were studied by X-ray diffraction (XRD), DTA, SEM and sorption experiments (sorption of nitrogen). The results showed that structural properties of the derived materials depend on the inorganic matrix and organic precursor. The carbon-taeniolite nanocomposites derived from polyfurfuryl alcohol as a precursor were characterized by high carbon content and a high percentage of its surface area in micropores. A broad spectrum of surface characteristics of the final products were found, depending on the history of the sample.
Weathering of Chlorite in a Quartz-Chlorite Schist: I. Mineralogical and Chemical Changes
Authors: Murakami Takashi , Isobe Hiroshi , Sato Tsutomu , Ohnuki Toshihiko
Published: August 2006

The weathering of chlorite, one of the major minerals of the host rock in the uranium ore deposit at Koongarra, Australia, was examined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron microprobe analysis, and transmission electron microscopy (TEM). The conversion sequence of chlorite weathering is: (1) chlorite; (2) chlorite/vermiculite intergrade (showing XRD responses to various treatments intermediate between those of chlorite and vermiculite); (3) interstratified chlorite and vermiculite; (4) vermiculite; and (5) kaolinite. This sequence may be more simply expressed as chlorite ⤒ vermiculite ⤒ kaolinite. The weathering finally changed chlorite into sub-micrometer to micrometer sized Fe minerals and kaolinite. The transformation of chlorite to vermiculite is chemically characterized by an Fe and Mg loss with a slight decrease in the Al/Si ratio. Mg continues to be released throughout the weathering. Fe minerals formed through chlorite weathering are located between chlorite and vermiculite domains (a few μm in size) at first, and then accumulated between grain boundaries, occasionally forming veins. The distribution of Fe minerals is suggestive of preferential pathways of water movement. The time-dependent nature of mineral alteration demonstrated in the present study must be taken into account for the quantitative estimation of radionuclide migration.
Exchange Reactions in the Ca-Mg-Na-Montmorillonite System
Authors: Rytwo Giora , Banin Amos , Nir Shlomo
Published: August 2006

The exchange reactions of Na, Ca and Mg on montmorillonite are revisited employing recently developed analytical and theoretical approaches. The fractional adsorption of the cations has been determined by displacing them from the adsorbed state in one step, using a low concentration of an organic cation of large binding affinity. The analysis of displaced and solution cations employed inductively coupled plasma emission spectrometry. An adsorption model was employed in the analysis of the data. The procedure consists of solving the electrostatic Gouy-Chapman equations and calculating adsorbed amounts of the cations as the sum of the cations residing in the double layer region, and the cations chemically bound to the surface, in a closed system. The model also accounts explicitly for cation complexation in solution. Thus the calculations also considered the adsorption of CaCl+ and MgCl+, which eliminated the apparent increase of the cation exchange capacity (CEC) with divalent cation concentration. The model could explain and yield predictions for our measured adsorbed amounts as well as previously published data, in the binary and ternary systems of Ca/Mg/Na, provided that the fraction of surface sites occupied by calcium did not exceed 0.4. For a larger coverage of surface sites by calcium, a fit of the experimental data required an order of magnitude increase in the binding coefficients of the divalent cations in the binary system Ca/Na and in the ternary system Ca/Mg/Na.
Goethite Dispersibility in Solutions of Variable Ionic Strength and Soluble Organic Matter Content
Authors: Herrera Ramos A. C. , McBride M. B.
Published: August 2006

The degree of flocculation of aqueous suspensions of microcrystalline goethite was measured in salts of monovalent, divalent and trivalent cations at pH 6.0–6.5 over a range of ionic strengths using light scattering measurements at 650 nm. Varying concentrations of soluble humic material as well as the organic ligands, salicylate and citrate, were tested for their effect on flocculation. It was found that KCl and NaCl induced flocculation at lower ionic strength than CaCl2, while AlCl3 favored dispersion at all ionic strengths tested. The simple organic ligands promoted flocculation at low concentration, with citrate having a more pronounced effect than salicylate. At higher concentrations, these ligands reversed their effect, inducing a more dispersed state of the oxide. The organic ligand effect on dispersibility was modified by the particular metal cation present, with Ca2+ being more conducive to flocculation than K+. Soluble humic materials affected goethite flocculation in a qualitatively similar way to that of the simple organic ligands, that is low concentrations favored flocculation while high concentrations induced dispersion. This dispersing effect was partially suppressed by the presence of Ca2+, and completely suppressed by Al3+. Thus, soluble humic substances at relatively high concentrations appear to have a marked dispersing effect on goethite in the absence of polyvalent cations, and a strongly flocculating effect in their presence.

The results can be explained qualitatively by a simple oxide surface charge model, in which chemi-sorption of multivalent cations or organic ligands alters the surface charge. Reactions that increase the magnitude of positive or negative surface charge favor dispersion, while those that reduce the magnitude of charge favor flocculation.
Interrelated Features of Structure and Stacking of Kaolin Mineral Layers
Authors: Zvyagin B. B. , Drits V. A.
Published: August 2006

Layer stackings in the ideal and real kaolinite structures are considered in terms of layer orientations i = 1, 2, … 6, intra- and interlayer displacements of adjacent 0- and T-sheets, si and tk, distortions of these displacements δ1 and δ2, deviations of unit cell parameters ηi = b2i/a2i − 3, εi = γi − π/2, and normal projections cn of the axis vector c on the ab plane.

The ideal monoclinic angle of dickite (cnx = −1/3) and the deviation α - π/2 ≠ 0 for kaolinite are explained by combinations of the δ1 and δ2 values in the sequence of symbols si and tk defining the corresponding structures. Twenty stacking variants in the 3 successive layers of the kaolinite structure are derived, incorporating layer orientations of the same parity, displacements t+, − = [0, ± 1/3] and reflection operations in planes normal to the axis b3. Two deformation mechanisms are proposed for the accommodation of successive layer unit cells adjusting either angular or linear parameters at the agreement of either linear or angular parameters corresponding.
Evolution of Illite/Smectite from Early Diagenesis Through Incipient Metamorphism in Sediments of the Basque-Cantabrian Basin
Authors: Nieto F. , Ortega-Huertas M. , Peacor D. R. , Arostegui J.
Published: August 2006

Prograde evolution of illite/smectite occurring in an unusually-thick (8000 m) sequence of Mesozoic-Cenozoic sediments in the Basque-Cantabrian Basin, Spain, has been studied using XRD and TEM/AEM. The sediments, which are only slightly tilted, cover the range from smectite to illite, and the most deeply buried ones are unique in that they span the range from diagenesis through low-grade metamorphism (anchizone), with no apparent overprinting due to tectonic deformation.

Pelites are absent from the shallow section, but smectite occurs in marls as high-charge, K-dominant and low-charge, K-poor anastomosing arrays of layers. At intermediate depths, authigenic clay is identified largely as R1 I/S, coexisting with packets of R≫3 I/S (nearly pure illite), where illite-like and smectitelike layers can be identified by contrast in TEM images, which is consistent with XRD data. The authigenic clay of the deepest samples consists of illite with no or almost no expandable layers, which occurred as packets with layers largely subparallel to bedding, K-deficient composition in comparison with muscovite, 1Md-like SAED patterns, and 100 Å mean packet thickness. There is no evidence of deformation stress-induced, non-bedding-parallel clays in the deepest samples. Detrital micas with either a phengiterich or a phengite-poor composition range dominate the phyllosilicate fraction of all the samples. Detrital micas show no changes over the diagenesis/metamorphism range and appear to have behaved as if isolated from authigenic clays.

Authigenic clays occur as bedding-subparallel packets that evolved during passive burial metamorphism through dissolution/crystallization of less-evolved clays. Where illite-like and smectite-like layers can be identified, TEM images imply a discontinuous series in which packets of R1 I/S (50% I) transform to packets of nearly-pure illite, that is, an Ostwald-step-rule-like sequence. Such immature illite remains unmodified with further burial, and is apparently the potential predecessor of stress-induced, highly-evolved mica of higher-grade, tectonically-deformed pelites.
Diagenesis of Oligocene Vitric Tuffs to Zeolites, Mexican Volcanic Belt
Authors: de Pablo-Galán Liberto , Chávez-García María de L.
Published: August 2006

Sedimentary zeolites clinoptilolite, mordenite and erionite occur as diagenetic products of ash falls of rhyolitic composition from the Oligocene Chichindaro Formation at the limits of the Mexican Volcanic Belt with the Mexican Highland. These zeolitic tuffs were formed from open hydrologic environments where rhyolitic glass altered to clinoptilolite + opal-C and to clinoptilolite + mordenite + erionite + opal-C. The process of diagenesis was hydrolysis associated with the removal of SiO2, K2O, and Na2O from the rhyolitic precursor and enrichment of Al2O3, MgO, and CaO. The crystallization of clinoptilolite occurs at ratios of SiO2/Al2O3 between 4.91 and 7.14 and (K2O + Na2O)/(MgO + CaO) from 2.19 to 0.79. Formation of clinoptilolite appears to be directly from glass and through a vitreous proto-zeolite intermediate. The zeolitic tuff is in contact with a vitric tuff where ash falls were devitrified to K-feldspar and diagenetically altered to smectite + opal-C.
Clay-Mineral Provenance, Sediment Dispersal Patterns, and Mudrock Diagenesis in the Nankai Accretionary Prism, Southwest Japan
Authors: Underwood Michael B. , Pickering Kevin T.
Published: August 2006

Offscraped strata within the toe of Nankai accretionary prism display an overall facies pattern of thickening and coarsening upward. Detrital clay minerals within the Quaternary trench-wedge facies are dominated by illite; chlorite is the second-most abundant clay mineral, followed by smectite. Relative mineral percentages change only modestly with depth. The hemipelagic clay-mineral population is virtually identical to clays washed from turbidite matrix, and different size fractions (<2 μm and 2–6 μm) show nominal amounts of mineral partitioning. Smectite content increases beneath the trench-wedge deposits, where the upper subunit of the Shikoku Basin stratigraphy (late Pliocene and early Pleistocene) includes abundance of volcanic ash. Syneruptive, subaerial chemical weathering of volcanic source rocks, together with in situ alteration of disseminated glass shards, caused the increase in smectite. Smectite begins a monotonic transformation to illite/smectite (I/S) mixed-layer clay at ~555 mbsf and an estimated temperature of ~65 °C. Ordered (R = 1) I/S interlayering first appears at ~1220 mbsf (<2 μm size fraction) and ~1100 mbsf (<0.2 μm size fraction). The illitization gradient coincides with a reduction in pore-water chlorinity, but depth-related changes in bulk mudstone geochemistry (K2O, Rb) are subtle. The absolute abundances of discrete smectite and I/S appear to be insufficient to account for the magnitude of pore-water dilution via in situ dehydration reactions. Instead, pore water probably was transported to Site 808, either from sources located deeper in the accretionary prism, where bulk mudstone porosities are lower, or from strike-parallel sources where mudstones originally deposited in the Shikoku Basin might contain higher percentages of smectite.
Molecular Structure Effects on Diffusion of Cations in Clays
Authors: Fitch Alanah , Song John , Stein Jenny
Published: August 2006

The roles of molecular structure and charge are examined in the transport of cations within montmorillonite clay films. The series of Ru(NH3)63+, Co(NH3)3+, Co(en)33+, Co(sep)3+ and Co(bpy)33+ are examined in detail via electrochemical and spectrochemical methods. The electrochemical signal is enhanced both in minimizing the time required to develop the signal and in the magnitude of the signal for Ru(NH3)63+. In addition, the potential for the observed reduction peak is shifted negative and the current peak associated with reduction disappears with rinsing of the clay film. These observations are characteristic of a compound that is held by simple electrostatic charge characteristics. In contrast, the compounds Co(NH3)3+, Co(en)33+ and Co(sep)3+, while showing rapid and enhanced signal development, eventually evolve a signal that is diminished with respect to the bare electrode, consistent with a hydrophobic mode of retention. The signal for Co(bpy)33+ is slow to be observed, is diminished with respect to the bare electrode and is shifted positive in potential, all hallmarks of a strong, non-electrostatic mode of binding within the clay.
Effect of Clay Type on the Diffusional Properties of a Clay-Modified Electrode
Authors: Stein Jennifer A. , Fitch Alanah
Published: August 2006

The response of two swelling clays (SWy-1 and SAz-1) and of one non-swelling clay (KGa-1) and of a series of mixtures of these clays to different electrolyte concentrations was examined using clay-modified electrode techniques. A non-interacting probe ion, Fe(CN)63−, was monitored via reduction for its arrival at a Pt electrode coated with thin films of the clay mixtures. The three clays had both different temporal responses and different equilibrium currents. For SWy-1 the currents were developed over time and were dependent upon the electrolyte of the bathing solution, which was consistent with X-ray diffraction data literature for the interlayer dimension. Similar behavior was found for SAz-1, but for KGa-1, currents were instantaneous and were independent of the bathing electrolyte. This suggests that the pores controlling the probe ion transport were between particle or pinhole in nature. When mixtures of the clays were examined, it was found that KGa-1 caused defects within the structures of the mixed clay films. The SWy-1 mixture was not as affected by these disruptions as was the SAz-1 mixture.
Active Components in Clay Condensates and Extracts as Potential Geocatalysts
Authors: Heller-Kallai L. , Goldstein T. P. , Navrotsky A.
Published: August 2006

Conversion of tertiary butylacetate to isobutylene and acetic acid and cracking of n-octane were used as model reactions to monitor the catalytic activity of a condensate and aqueous extract derived from a sample of montmorillonite. The condensate was obtained by condensing the vapor phase evolved on heating the clay and the extract was derived from the clay by prolonged water extraction. Both condensate and extract were colloidal systems, which were separated into solid and liquid fractions by distillation. Reactions carried out in a dynamic system established that the solid components acted as true acid catalysts, whereas the liquid fractions were inactive under the experimental conditions adopted. The catalytic activity per weight of the condensate exceeded that of either the parent clay or the extract.

The present results confirm that colloidal size catalysts of high activity can be generated from clays. Such materials, mobilized and transported alone or with formation fluids, may act as catalysts in places removed in space and time from their source. This finding refutes objections previously raised to the operation of bulk clays as catalysts for reactions with particulate organics and supports the concept that acid catalysts derived from clays may participate in organic geochemical reactions in an aqueous medium.
Origin of Cretaceous and Oligocene Kaolinites from the Iwaizumi Clay Deposit, Iwate, Northeastern Japan
Authors: Mizota C. , Longstaffe F. J.
Published: August 2006

Hydrogen- (δD = −106 to −97‰) and oxygen-(δ18O = +14.0 to +16.6‰) isotope compositions of kaolinite from late Cretaceous and Oligocene deposits at Iwaizumi, northeastern Japan, indicate that these clays formed by weathering of volcanic parent rocks, rather than during hydrothermal (>100 °C) alteration. The Iwaizumi kaolinites also are depleted of D and 18O relative to kaolinite formed during modern, tropical weathering, suggesting that the kaolinite developed under cool or cool-temperate conditions. The oxygen-isotope compositions of the kaolinite increase slightly upward through the deposits, perhaps implying a modest increase in temperature from late Cretaceous to Oligocene time. The δD and δ18O results for kaolinite from the Oligocene deposits closely follow the kaolinite weathering line. However, a small but systematic deviation from this line for the Cretaceous kaolinites is most simply explained by post-formational, hydrogen-isotope exchange between these clays and downward percolating meteoric water.
Effects of Acidity on the Hydrothermal Synthesis of Kaolinite from Silica-Gel and Gibbsite
Authors: Satokawa Shigeo , Miyawaki Ritsuro , Osaki Yasushi , Tomura Shinji , Shibasaki Yasuo
Published: August 2006

A comparative study is reported in which kaolinite has been hydrothermally synthesized at several pH conditions. The syntheses were carried out at 220 °C for 3 to 10 d with distilled water or acidic solutions using a mixture of silica-gel derived from alkoxide and gibbsite with a Si/Al ratio of 1:1 as the starting material. Use of acidic solution for the synthesis promotes the dissolution of the starting materials and leads to kaolinitization at an earlier stage of the reaction. However, the rate of kaolinitization is found to be rather slow, in comparison to the reaction with distilled water. The synthetic kaolinite was characterized by X-ray powder diffraction pattern. Kaolinite synthesized with distilled water was poorly grown for direction of the stacking. For example, crystallite size along the c*-axis = 155 Å, whereas kaolinite synthesized with acidic solution gave a higher crystallite size along the c*-axis, such as 253 Å in the case of the synthesis with 0.1 N HCl. Hinckley index of the synthetic kaolinite was varied from 0.35 to 0.80 by the acidity of the reaction. Different kaolinitization processes are implied by differences observed in the rate of kaolinitization, which has an influence on the nature of the stacking faults of the kaolinite.
Vicinal Faces on Synthetic Goethite Observed by Atomic Force Microscopy
Authors: Weidler P. G. , Schwinn T. , Gaub H. E.
Published: August 2006

In this paper atomic force microscopy-studies are reported suggesting the existence of vicinal faces on the (100) plane of artificially grown goethite. Goethite crystals are commonly regarded to have boundary planes of (100), (010) and (001) faces. In contradiction to these theoretical models TEM and SEM images exhibit (110) and (021) faces to be dominating. These goethite particles consist of many crystallographic coherent domains so that the existence of dislocations on the surfaces has to be assumed. These sites on the surfaces may serve as a nucleation site for the formation of steps. The vicinal faces on the (100) face found with the AFM are (021) faces. They influence the growth velocity of the (100) face to such a degree, that this face vanishes and only (110) faces remain as stable boundary surfaces. The (021) faces are also stable, but have the highest growth rate among the faces considered.
Relation Between Interlayer Composition of Authigenic Smectite, Mineral Assemblages, I/S Reaction Rate and Fluid Composition in Silicic Ash of the Nankai Trough
Authors: Masuda Harue , O'Neil James R. , Jiang Wei-Teh , Peacor Donald R.
Published: August 2006

The compositions, fabrics and structures of authigenic minerals that formed recently from silicic volcanic ash layers from a 1300-meter sediment column obtained at ODP Site 808 of the Nankai Trough were studied using XRD, STEM, AEM and SEM. Smectite and zeolites were first detected as alteration products of volcanic glass with increasing depth, as follows: smectite at 200 m below seafloor (mbsf) (20 °C), clinoptilolite at 640 mbsf (60 °C) and analcime at 810 mbsf (75 °C).

A primitive clay precursor to smectite was observed as a direct alteration product of glass at 366 mbsf (approximately 30 °C). High defect smectite with lattice fringe spacings of 12 to 17 Å and having a cellular texture filling pore space between altering glass shards occurs at 630 mbsf. Packets of smectite become larger and less disordered with increasing depth and temperature. The smectite that forms as a direct alteration product of volcanic glass has K as the dominant interlayer cation.

With increasing depth, smectite becomes depleted in K as the proportion of clinoptilolite increases, and then becomes depleted in Na as the proportion of analcime increases. The composition of the exchangeable interlayer of smectite appears to be controlled by the formation first of K-rich clinoptilolite and then Na-rich analcime, via the pore fluid, giving rise at depth to Ca-rich smectite. Smectite reacted to form illite in the interbedded shales but not in the bentonites. Paucity of K in smectite and pore fluids, due to formation of clinoptilolite under closed system conditions, is believed to have inhibited the reaction relative to shales.
Change in Layer Charge of Smectites and Smectite Layers in Illite/Smectite During Diagenetic Alteration
Authors: Sato Tsutomu , Murakami Takashi , Watanabe Takashi
Published: August 2006

The changes in amount and location of layer charge during diagenetic alteration have been investigated for smectites and smectite layers of illite/smectite interstratified minerals (I/S) by X-ray powder diffraction analysis with various expansion behavior tests: 1) ethylene glycol (EG) solvation (XRD); 2) K-saturation and EG solvation; 3) Li-saturation, heating at 250 °C and glycerol or EG solvation (Greene-Kelly test); and 4) alkylammonium saturation. In the course of low-temperature diagenesis but before the onset of illitization, mean layer charge of smectites continuously increases from approximately 0.56 to 0.73 per O20(OH)4 with increasing depth, and tetrahedral charge also increases continuously from approximately 0.21 to 0.38 per O20(OH)4 (beidellitization). The continuous increase in tetrahedral charge without change in peak intensity and shape suggests that the solid-state Al for Si substitution mechanism appears to predominate within beidellitization. After illitization, the content of the beidellitic layers continuously decreases, while the mean layer charge of expandable layers and the content of illite layers in I/S increase. This suggests that the conversion of a beidellitic layer to an illitic layer preferably occurs during early illitization. Thus, before illitization, beidellite-like layers are formed from precursor smectite, and during the early stage of illitization, the high charged beidellitic layers are probably consumed to form illite layers.
Transition Metals in Llano Vermiculite Samples: An EPR Study
Authors: Schosseler P. M. , Gehring A. U.
Published: August 2006

Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(TV), Fe(III), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 °C. The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 °C.
Size and Shape of Allophane Particles in Dispersed Aqueous Systems
Authors: Karube Jutaro , Nakaishi Katsuya , Sugimoto Hideo , Fujihira Masami
Published: August 2006

Aqueous suspensions of allophane show relatively high viscosity, presumably because of strong particle interaction between the unit particles. To test this hypothesis, we measured the particle weight and particle size of allophane during a dispersion using the light scattering method. The particle weight was more than several hundred times larger than that of the unit particle, and the size was 100–400 nm, whereas the Stokes’ diameter of the particles in the sample was less than 50 nm. Particle weight and size varied with the pH of the sample. Particle sizes were cross-checked by ultrafiltration through membrane filters. The experimental findings show that the unit particles of allophane within dilute dispersions appear to be associated like strings of beads, forming domains (primary floccules) about 100 nm in diameter. When these domains coagulate under certain conditions, they do not grow analogously but form clusters, such as secondary floccules, then precipitate. Formation of secondary flocculation of loose structure accounts for the maximum relative viscosity at the transition pH between dispersion and coagulation.
Tem and X-Ray Diffraction Evidence for Cristobalite and Tridymite Stacking Sequences in Opal
Authors: Elzea Jessica M. , Rice Stephen B.
Published: August 2006

In an attempt to resolve the structure of opal-CT and opal-C more precisely, 24 opal samples from bentonites, Fuller's Earths, zeolite tuffs, biogenic silicas and silicified kaolins have been analyzed by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Results of this examination demonstrate that opal-C and opal-CT are part of a continuous series of intergrowths between end-member cristobalite and tridymite stacking sequences.

These findings are consistent with Flörke's (1955) interpretation of the most intense opal peak at ~4 Å as a combination of the (101) cristobalite and (404) tridymite peaks. The position and width of this peak are controlled by the relative volume of the two stacking types and the mean crystallite size. Direct evidence obtained by HRTEM provides data showing various stacking sequences in opals. Broadening due to crystallite size alone was determined by directly measuring crystallite size by TEM and comparing the measured size to the apparent size calculated using the Scherrer equation. XRD peak broadening is also described in terms of various contributions from structural disorder. The mean opal crystallite size ranges from 120 to 320 Å. For samples at either end of the size range, the crystallite size plays a larger role, relative to stacking disorder, in controlling peak broadening.
Polyvinyl Alcohol-Clay Complexes Formed by Direct Synthesis
Authors: Carrado Kathleen A. , Thiyagarajan P. , Elder Delwin L.
Published: August 2006

Synthetic hectorite clay minerals were hydrothermally crystallized with direct incorporation of a series of five water-soluble polyvinyl alcohols (PVA) of molecular weights from 9000-146,000. The molecular weight of PVA had little effect on the success of hydrothermal hectorite synthesis, d-spacing or the amount of polymer incorporated. The basal spacings range from 19.5 Å to 20.8 Å and the amount of polymer incorporated ranges from 20 wt.% to 23 wt.%. Incorporation of PVA within the clay inter-layers, along with Li(I) ions to compensate the lattice charge, is indicated. Thermal gravimetric analysis and small angle neutron scattering were used to further examine the polymer-clay systems. Small PVA-clay crystallites that are coated with excess PVA are indicated. Removal of the polymer does not alter the extended synthetic clay network, and the nitrogen BET surface area increases from <5 m2/g to >200 m2/g.
Electrodes Modified with Synthetic Clay Minerals: Electrochemistry of Cobalt Smectites
Authors: Xiang Yan , Villemure Gilles
Published: August 2006

Hydrothermal treatment of a mixture of silicic acid, cobalt chloride, sodium dithionite and sodium hydroxide at 250 °C under 500 psi of argon produced a pink solid. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction data showed the product to be a well-crystallized smectite. SEM/EDX analysis gave a unit cell formula of [(Si8.05)(Co5.58)O20(OH)4]Na066. Heating the same mixture at 150 °C without argon gave a less well ordered smectite of composition [(Si7.93)(CO5.92)O20(OH)4]Na0.42. Two peaks were observed in the cyclic voltammograms of electrodes modified with films of these two clays recorded for the blank electrolytes in the absence of any adsorbed electroactive species. The first peak was attributed to the oxidation of a small fraction of the Co2+ sites within the clay lattices to Co3+. The second peak was assigned to further oxidation of these Co3+ to Co4+.
Geologic Control of Severe Expansive Clay Damage to a Subdivision in the Pierre Shale, Southwest Denver Metropolitan Area, Colorado
Authors: Gill J. D. , West M. W. , Noe D. C. , Olsen H. W. , McCarty D. K.
Published: August 2006

Shortly after construction of a subdivision in the southwest Denver metropolitan area in 1986, a portion of the subdivision built directly on steeply-dipping strata of the Pierre Shale began experiencing damaging differential movements, causing house foundations to fail and pavements to warp and crack. This formation is a Late Cretaceous marine clay-shale composed predominantly of fluvial mixed-layer illite/smectite and quartz. During deposition of the shale, periodic and explosive volcanism generated thin beds of bentonite, consisting initially of volcanic ash and subsequently altered to nearly pure smectite. Some of these bentonite beds were exposed in a trench adjacent to the subdivision and perpendicular to the strike of the steeply-dipping strata. The thickest bentonite beds correlated well with linear heave features that these beds parallel the bedrock strike throughout the subdivision were mapped via severely deformed pavements. Mineralogical data show the bentonite bed that correlates with the worst damage within the subdivision consists of about 62% smectite by weight with mixed-layer illite/smectite expandability of 92%. By comparison, a sample of the typical silty claystone, which is fluvial mixed-layer illite/smectite mixed with detrital quartz from the adjacent strata, had about 23% smectite by weight with 70% to 90% illite/smectite expandability. Geotechnical tests for swell potential show that samples of 2 bentonite beds swelled 39% to 43% compared to 2% to 8% for samples of the typical silty claystone. It is proposed that differential swell resulting from stratigraphically-controlled differences in clay mineralogy and grain-size is the primary factor controlling extreme damage for this geologic setting.
Refinement of the Structure of Natural Ferriphlogopite
Authors: Brigatti Maria Franca , Medici Luca , Poppi Luciano
Published: August 2006

Two ferriphlogopite-1M crystals with a composition (K0.99Na0.01)Σ=1.00(Mg2.73Fe2+0.17Fe3+0.08-Ti0.01)Σ=2.299[(Fe3+0.95Si3.05)Σ=4.00O10.17](OH)1.79F0.04 (sample S1) and (K1.02)Σ=1.02(Mg2.68Fe2+0.20Fe3+0.11-Mn0.01)Σ=3.00[(Fe3+0.95Si3.05)Σ=4.00O10.18](OH)1.75F0.07 (sample S2) occur within an alkali-carbonatic complex near Tapira, Belo Horizonte, Minas Gerais, Brazil. Each crystal was studied by single-crystal X-ray diffraction. The least-squares refinements of space group C2/m resulted in R values of 0.031 for S1 and 0.025 for S2. Results showed that Fe3+ substitutes for Si within the tetrahedral sites and that the Fe distribution is fully disordered. The octahedral sites are preferentially occupied by Mg. The presence of Fe3+ within the tetrahedral sheet produces increased cell edge lengths. For sample S1, a = 5.362 Å, b = 9.288 Å, c = 10.321 Å and the monoclinic β angle was: β = 99.99°. For sample S2, a = 5.3649 Å, b = 9.2924 Å, c = 10.3255 Å and the monoclinic β angle was: β = 99.988°. The tetrahedral rotation angle of α = 11.5° is necessary for tetrahedral and octahedral sheet congruency. The enlarged tetrahedral sites are regular, with cations close to their geometric center. Ferriphlogopites have identical mean bond lengths for M1 and M2 sites within standard deviation. The M1-O3 and M2-O3 bond lengths are longer than the mean so that O3 may articulate with the tetrahedra.
Mechanism and Conditions of Clay Formation During Natural Weathering of MSWI Bottom Ash
Authors: Zevenbergen C. , Van Reeuwijk L. P. , Bradley J. P. , Bloemen P. , Comans R. N. J.
Published: August 2006

Municipal solid waste incinerator (MSWI) bottom ash is the slag-like material produced by the incineration of municipal waste and is predominantly composed of glassy constituents, which include inherited manufactured glasses and glasses formed during incineration. Previous results indicate evidence of neoformation of well-ordered clay (illite) from glasses in MSWI bottom ash after 12 y of natural weathering. We investigated the mechanism and conditions of clay formation from glasses during natural weathering using transmission electron microscopy (TEM), experimental leaching experiments and ammonium oxalate extractions. It was concluded that the high surface area and initially high “active” Al and associated Si content predispose the ash to form clay minerals on a relatively short time scale. This work provides evidence that the composition of secondary amorphous aluminosilicate and thus, the type of clay mineral which may form, is determined by the pH of the pore solution rather than by the glass composition. Presumably alternate wetting and drying of the ash during disposal greatly accelerates the formation of well-ordered clays.
Model for Crystalline Swelling of 2:1 Phyllosilicates
Authors: Laird David A.
Published: August 2006

A macroscopic energy balance model for crystalline swelling of 2:1 phyllosilicates is presented. Crystalline swelling for a static system is modeled by a balance among the potential energies of attraction, repulsion and resistance. The potential energy of attraction is due to both the electrostatic interaction between the interlayer cations and the negative surface charge sites and to van der Waals attraction between layers. The potential energy of repulsion is due to the net hydration energy for the interlayer cations, the net hydration energy for the negative surface charge sites and Born repulsion. The potential energy of resistance represents irreversible work needed to overcome the mechanical resistance of the clay water system to both expansion and collapse. The potential energy of resistance is responsible for both hysteresis and the stepwise nature of crystalline swelling.

A numerical solution of the crystalline swelling model is presented and shown to yield reasonable estimates of basal spacings for octahedrally charged clays. Measured and predicted basal spacings are directly compared and are in general agreement (r2 = 0.39). Most of the scatter for the measured vs. predicted basal spacing relationship is attributed to inaccuracies of the assumptions used for the numerical solution. The crystalline swelling model readily accounts for the effects of layer charge and nature of the interlayer cations upon crystalline swelling, but does not account for the effect of charge site location upon crystalline swelling.
Redox Characterization of the Surfaces of Seven Iron-Bearing Minerals: Use of Molecular Probes and UV-Visible Spectroscopy
Authors: Yu Y. Shane , Bailey George W.
Published: August 2006

Redox properties of iron-bearing mineral surfaces may play an important role in controlling the transport and transformation of pollutants into ground waters. Suspensions of seven iron-bearing minerals were reacted with pH and redox indicators under anaerobic conditions at the pH of the natural suspension. The responses of the indicators to the mineral surfaces were monitored by UV-visible spectroscopy using a scattered transmission technique. The Hammett surface acidity function (Hs) and the surface redox potential (Ehs) of these iron-bearing minerals were measured. These measured values were used to calculate Eh values for the seven minerals: goethite = +293 mV; chlorite = +290 mV; hematite = +290 mV; almandite = +282 mV; ferruginous smectite = +275 mV; pyrite = +235 mV; and Na-vermiculite = +223 mV. Calculated surface redox potentials of minerals are different from their potentials measured by platinum electrode in bulk suspensions. UV-visible spectroscopy provides a quick and non-destructive way of monitoring organic probe response at the mineral surface.
Characterization and Origin of 1:1 Phyllosilicates within Peloids of the Recent, Holocene and Miocene Deposits of the Congo Basin
Authors: Wiewióra A. , Lacka B. , Giresse P.
Published: August 2006

The grey-green peloids from the Miocene period to Recent fine-grained deposits on the continental shelf close to Congo-Zaîire River mouth were studied by X-ray transmission diffractometry (XRD), SEM and by EDAX. The peloids have multiphase heterogenous mineral composition. Their most important constituents are detrital minerals like kaolinite, quartz, goethite, 7 Å phases with d(001) ≈ 7.3 Å, and in more maturated grains—nontronite. The d(060) values were used to estimate the general composition of phyllosilicate phases to compare with the composition determined by EDAX. It has been found that d(060) equal to 1.504 Å is common for Fe3+-bearing kaolinite, which is quite abundant for the Recent peloids. The d(060) equal to 1.535 Å and 1.55 Å is characteristic for the di-trioctahedral and trioctahedral 1:l phases, which are abundant within the more evolved Miocene peloids. Nontronite is characterized by d(060) equal to 1.524 Å within concordance with its highly ferrous composition, and partly by its potassic interlayer. It shows cabbage-like nannostructures proving neoformational origin of this mineral in the marine environment.

It has been shown that areas of the low sedimentation rate within the Congo Basin were favorable for the mineral changes and neoformation. For the Holocene vertical profile, we observed levels of slower sedimentation rates. The evolution is expressed by the disappearance of kaolinite at the expense of other 7 Å phases and nontronite. Although more advanced stages of maturation of the studied phases were observed in older peloids (104 to 107 y), one cannot detect a linear relationship of these processes with burial.
Modeling Arsenate Competitive Adsorption on Kaolinite, Montmorillonite and Illite
Authors: Manning Bruce A. , Goldberg S.
Published: August 2006

The adsorption of arsenate (As(V)) on kaolinite, montmorillonite and illite was investigated at varying pH and competing anion concentration while holding As(V) concentration (6.7 × 10−7M), clay suspension density (2.5 g L−1) and ionic strength (0.1 M NaCl) constant. The effects of 2 concentrations of phosphate (P) or molybdate (Mo) (6.7 × 10−7 and 6.7 × 10−6M) on As(V) adsorption envelopes (adsorption vs. pH) gave evidence for direct competitive adsorption (in the case of As(V) + P) and possibly site-specific non-competitive adsorption (As(V) + Mo). Distinct As(V) adsorption maxima occurred at approximately pH 5.0 for kaolinite, 6.0 for montmorillonite and 6.5 for illite, and ranged from 0.15 to 0.22 mmol As(V) kg−1. When both As(V) and P were present at equimolar concentrations (6.7 × 10−7M), As(V) adsorption decreased slightly, whereas As(V) adsorption substantially decreased in binary As(V)/P systems when the P concentration was 6.7 × 10−6M, which was 10 times greater than As(V). The presence of Mo at equimolar (6.7 × 10−7 M) and 10 times greater (6.7 × 10−6M) concentrations than As(V) caused only slight decreases in As(V) adsorption because the Mo adsorption maximum occurred at pH < 4. The constant capacitance surface complexation model was applied to As(V) and P adsorption data and was used to predict As(V) adsorption at varying P concentrations. The model gave reasonable descriptions of As(V) adsorption on the 3 clay minerals at varying pH and in the presence of a competing oxyanion (P), indicating that surface complexation modeling may be useful in predicting As(V) adsorption in soils.
Cation Exchange Capacity of Layer Silicates and Palagonitized Glass in Mafic Volcanic Rocks: A Comparative Study of Bulk Extraction and In Situ Techniques
Authors: Schiffman P. , Southard R. J.
Published: August 2006

The cation exchange capacities (CEC) and extractable cations in smectite, corrensite and palagonitized glass from hydrothermally-altered pillow lavas and hyaloclastite breccias were measured by both bulk wet chemical and in situ microanalytical techniques. Smectite has CEC's between 60 and 120 meq/100 g, palagonitized glass between 30 and 60 meq/100 g, and corrensite approximately 35 meq/100 g as determined by the in situ CsCl-exchange method. These experiments generally verify that Cs exchanges for those cations that are presumed (from the stoichiometry implied by microprobe analyses) to occupy interlayer sites in sheet silicates. Results of conventional CEC determinations are consistent with those determined by the in situ experiments: the individual microanalytical values for smectite and palagonitized glass bracket the bulk CEC values. The in situ experiments imply that Mg is the major extractable cation in smectite, Ca in corrensite, and both Mg and Ca in the palagonitized glass. We speculate that discrepancies between the equivalents of extractable cations predicted from elemental analysis and the equivalents of Cs sorbed may be due to the presence of charge-balancing protons that are not detected by the microprobe analyses. The sum of equivalents of cations extracted by NH4-acetate is about the same as the CEC determined by both the in situ and the bulk methods. Cation proportions indicated by NH4-acetate extractions from bulk samples are also generally consistent with the in situ results for all elements except Mg, which is a minor leachate of the NH4-acetate extractions in all the samples. To explain this discrepancy, we propose that 1) Mg may occupy structural sites within palagonitized glass, which inhibit its extraction by NH4 or Cs, and/or 2) there is a significant quantity of smectite, unsampled by the electron microprobe analyses, which contains insignificant interlayer Mg.
Morphological and Chemical Features of Bioweathered Granitic Biotite Induced by Lichen Activity
Authors: Wierzchos Jacek , Ascaso Carmen
Published: August 2006

To study the physico-chemical activity of lichens on micaceous components of granitic rocks, samples covered by thalli of Parmelia conspersa (Ehrht) Ach. and Aspicilia intermutans (Nyl.) Arn. were collected and examined with Scanning Electron Microscopy (SEM) equipped with a Back Scattered Electron (BSE) detector and an Energy Dispersive Spectroscopy (EDS) microanalytical system. The bio-physical activity of both lichen species leads to a deep alteration of biotite, which results in detachment, separation and exfoliation of biotite plates. Chemically, the bioweathering process of biotite in the lichenmineral contact zone involves considerable depletion of potassium (K) from interlayer positions in biotite and removal of several elements, corresponding to a 9.7% loss in matter. The sequence of the loss of elements is: K+ » Fetot > Ti4+ ≅ Mg2+. There are also some gains in the order: Ca2+ > Na+ » Al3+ > Si4+ attributed to dissolution of co-existing Ca and Na rich minerals. Geochemical mass balance results suggest the transformation of K-rich biotite to scarcely altered biotite interstratified with a biotite-vermiculite intermediate phase in the lichen bioweathered contact zones.
Amorphous Aluminum Hydroxide Formed at the Earliest Weathering Stages of K-Feldspar
Authors: Kawano Motoharu , Tomita Katsutoshi
Published: August 2006

Weathering products formed on the surface of K-feldspar in Yakushima Island, Japan were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). XRD confirmed that the weathering products were composed mainly of gibbsite and halloysite. SEM, TEM and EDX clearly showed formation of amorphous aluminum hydroxide exhibiting 2 distinct habits: 1) curled fibrous or circular forms less than 0.02 μm in diameter; and 2) a spherical habit less than 1.0 μm in diameter. The fibrous aluminum hydroxide exhibited curled fibrous forms or circular forms less than 0.02 μm in diameter and gave a diffuse electron diffraction halo. EDX indicated that the material consisted mainly of Al and very small amounts of Si and Fe. The spherical aluminum hydroxide also gave similar EDX and electron diffraction characteristics to the fibrous material. These fibrous and spherical aluminum hydroxides must be formed as a metastable phase in the earliest weathering stages, and transformed into a stable phase of gibbsite and halloysite as the reaction proceeded.