bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Simulations of Montmorillonite Intercalated with Aluminum Complex Cations. Part I: Intercalation with [Al13O4(OH)24+x(H2O)12−x](7−x)+
Authors: Čapková P. , Driessen R. A. J. , Numan M. , Schenk H. , Weiss Z. , Klika Z.
Published: August 2006

The structure of montmorillonite intercalated with [Al13O4(OH)24+x(H2O)12−x](7−x)+ cations ( for short), where x = 0, 2 and 4, has been studied using the Cerius2 modeling environment. The Crystal Packer module used in the present study takes into account only the nonbonded interactions between the silicate layer and the Keggin cations. Minimization of the total sublimation energy led to the following conclusions: the structure of the interlayer (that is, the orientation of Keggin cations and the basal spacing) depends on the charge of cations (that is, on the degree of hydrolysis, x). The values of basal spacings in the range 19.38–20.27 Å have been obtained, depending on the charge and arrangement of cations in the interlayer. The dominating contribution to the total sublimation energy comes from the electrostatic interactions. Translations of cations along the 2:1 layers give only small fluctuations of the total sublimation energy and basal spacings. No preference for the position of cations in the interlayer of montmorillonite was found during translation along the 2:1 layers. This result confirmed the inhomogeneous distribution of cations in the interlayer and turbostratic stacking of layers.
Interstratification in Expandable Mica Produced by Cation-Exchange Treatment
Authors: Tateyama Hiroshi , Noma Hiroaki , Nishimura Satoshi , Adachi Yoshio , Ooi Masaru , Urabe Kazuo
Published: August 2006

A unique interstratified expandable mica was obtained by cation exchange treatments using an expandable mica synthesized from talc. The 23Na magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectrum of the expandable mica used as a starting material showed that it had 2 kinds of Na+: one was exchangeable and the other was not exchangeable. Half of the Na+ per unit cell of the expandable mica was replaced with Mg2+ by cation exchange treatments. The X-ray powder diffraction (XRD) analysis of the Mg2+-exchanged expandable mica, after heating at 73°C, indicated that Na+ in the interlayer sheets was exchanged with Mg2+ in every second layer and that it had an interstratified structure with a 12.5-Å layer thickness and a 9.6-Å layer thickness. The structure of the Mg2+-exchanged expandable mica was changed into a unique interstratified structure by the calcination at 600°C; one component had a stacking sequence of talc and a small amount of OH−, but the other had a different stacking sequence from talc and no structural OH—.
Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study
Authors: Turner David R. , Pabalan Roberto T. , Bertetti F. Paul
Published: August 2006

Batch sorption experiments at fixed initial Np(V) concentration (∼1 × 10−6M237Np), M/V ratio (4 g L−1), and ionic strength (0.1 molal NaNO3) were conducted to determine the effects of varying pH and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:c="http://cambridge.org/core/content" xmlns:core="http://cambridge.org/core" xmlns:m="http://cambridge.org/core/metadata" xmlns:cup="http://contentservices.cambridge.org" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest">PCO2 on Np(V) sorption on SAz-1 montmorillonite. The results show that Np(V) sorption on montmorillonite is strongly influenced by pH and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:c="http://cambridge.org/core/content" xmlns:core="http://cambridge.org/core" xmlns:m="http://cambridge.org/core/metadata" xmlns:cup="http://contentservices.cambridge.org" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest">PCO2. In the absence of CO2, Np(V) sorption increases over the entire pH range examined (∼3 to ∼10), with measured sorption coefficients (KD) of about 10 mL g−1 at pH < 6 to KD ∼ 1000 mL g−1 at a pH of 10.5. However, for experiments open to atmospheric CO2 (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:c="http://cambridge.org/core/content" xmlns:core="http://cambridge.org/core" xmlns:m="http://cambridge.org/core/metadata" xmlns:cup="http://contentservices.cambridge.org" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest">PCO2=10−3.5atm), Np(V) sorption peaks at KD ∼ 100 mL g−1 at pH of 8 to 8.5 and decreases at higher or lower pH. A comparison of the pH-dependence of Np(V) sorption with that of Np(V) aqueous speciation indicates a close correlation between Np(V) sorption and the stability field of the Np(V)-hydroxy complex NpO2OH0 (aq). In the presence of CO2 and aqueous carbonate, sorption is inhibited at pH > 8 due to formation of aqueous Np(V)-carbonate complexes. A relatively simple 2-site Diffuse-Layer Model (DLM) with a single Np(V) surface complexation reaction per site effectively simulates the complex sorption behavior observed in the Np(V)-H2O-CO2-montmorillonite system. The good agreement between measured and DLM-predicted sorption values suggests that surface complexation models based on parameters derived from a limited set of data could be useful in extrapolating radionuclide sorption over a range of geochemical conditions. Such an approach could be used to support transport modeling and could provide a better alternative to the current use of constant KD values in performance assessment transport calculations.
Formation of Vermicular Kaolinite from Halloysite Aggregates in the Weathering of Plagioclase
Authors: Jeong Gi Young
Published: August 2006

Halloysite and kaolinite coexist in anorthosite weathering profiles in the Sancheong district, Korea. X-ray diffraction (XRD) analysis on a transect of partially weathered anorthosites reveals an increasing amount of kaolinite development with weathering age. Microtextures were examined by scanning electron microscopy (SEM) of thin sections and raw samples in an attempt to resolve the genetic relation between halloysite and kaolinite. In the earliest stage of weathering, halloysite ellipsoids and short tubes form on the plagioclase surfaces. The successive formation of new grains from the early grains results in globular aggregates where halloysite grains are partially interconnected. With the further progress of weathering, the halloysite grains coalesce from the inner part of the aggregate outward, and convert into stacked kaolinite plates. Continuous addition of halloysite grains on existing plates and their subsequent conversion into plates form long vermicular kaolinite. Solid-state transformation is suggested as a major conversion mechanism. Concurrently with its successive transformation into kaolinite, halloysite also continuously precipitates, giving rise to overgrowths on vermicular kaolinite. Halloysite forms as a kinetically favored metastable precursor and is subsequently transformed into thermodynamically stable kaolinite. Halloysite and kaolinite coexist temporarily in the weathering profile far from equilibrium.
Hydroxyl Deformation in Kaolins
Authors: Frost Ray L.
Published: August 2006

The hydroxyl deformation modes of kaolins have been studied by Fourier transform (FT) Raman spectroscopy. Kaolinites showed well-resolved bands at 959, 938 and 915 cm−1 and an additional band at 923 cm−1. For dickites, well-resolved bands were observed at 955, 936.5, 915 and 903 cm−1. Halloysites showed less-resolved Raman bands at 950, 938, 923, 913 and 895 cm−1. The first 3 bands were assigned to the librational modes of the 3 inner-surface hydroxyl groups, and the 915-cm−1 band was assigned to the libration of the inner hydroxyl group. The band in the 905 to 895 cm−1 range was attributed to “free― or non-hydrogen-bonded inner-surface hydroxyl groups. The 915-cm−1 band contributed ~65% of the total spectral profile and was a sharp band with a bandwidth of 11.8 cm−1 for dickite, 14.0 cm−1 for kaolinites and 17.6 cm−1 for halloysites. Such small bandwidths suggest that the rotation of the inner hydroxyl group is severely restricted. For the inner-surface hydroxyl groups, it is proposed that the hydroxyl deformation modes are not coupled and that the 3 inner-surface deformation modes are attributable to the three OH2-4 hydroxyls of the kaolinite structure. For intercalates of kaolinite and halloysite with urea, a new intense band at ~903 cm−1 was observed with concomitant loss in intensity of the bands at 959, 938 and 923 cm−1 bands. This band was assigned to the non-hydrogen-bonded hydroxyl libration of the kaolinite-urea intercalate. Infrared reflectance (IR) spectroscopy confirms these band assignments.
Reactivity of Basal Surfaces, Steps and Edges of Muscovite: An AFM Study
Authors: Zhang Z. Z. , Bailey G. W.
Published: August 2006

The reactivity of basal surfaces, steps and edges of muscovite was studied by imaging surface precipitates of PbCl2 using atomic force microscopy (AFM). We reacted PbCl2 solution with freshly cleaved muscovite surfaces and found that PbCl2 precipitates were formed on the basal surfaces, steps and edges. It was observed that PbCl2 precipitated preferentially along the steps compared to the basal surfaces and that PbCl2 precipitates at multiple-layer edges were needle-shaped and oriented in different directions. One of the muscovite samples we cleaved had muscovite fragments sitting on the freshly cleaved surfaces. These fragments resulted from previously formed cracks. Thus, we were able to compare the reactivity of the weathered surfaces with that of freshly cleaved surfaces. It was found that PbCl2 was not precipitated along the edges of previously cracked muscovite fragments. These results clearly demonstrated that the edges of freshly cleaved muscovite are the most reactive surface sites, whereas the edges of weathered muscovite are not as reactive. We believe that the surface reactivity of the edges of freshly cleaved muscovite is likely due to terminal or Al-OH1/2− groups on these crystalline surfaces, which favor adsorption of Pb2+ ions and the subsequent nucleation and precipitation reactions. We also investigated the effect of drying rate on the morphology of the surface precipitates. Fast drying resulted in a nearly complete covered surface with a leaflike morphology, whereas slow drying resulted in more isolated surface clusters.
Analytical Electron Microscopy in Clays and Other Phyllosilicates: Loss of Elements from a 90-nm Stationary Beam of 300-keV Electrons
Authors: Ma Chi , FitzGerald John D. , Eggleton Richard A. , Llewellyn David J.
Published: August 2006

Diffusion of alkali and low-atomic-number elements during the microbeam analysis of some silicates by analytical electron microscopy (AEM) has been known for some time. Our repeated analyses at 300 kV of kaolinite, halloysite, smectite, biotite, muscovite and pyrophyllite, however, showed differential loss (relative to Si) of not only alkali elements (such as K, Na, Mg) and low-atomic-number elements (such as Al) but also higher-atomic-number elements (such as Fe, Ti). For AEM of these phyllosilicates, a Philips EM430/EDAX facility with a tungsten filament was used to provide a current of 0.3 nA in a stationary beam of nominal diameter 90 nm. The loss of Al in kaolin minerals during analysis is particularly severe. Kaolin crystals can be damaged by the electron irradiation over several seconds, making it the most sensitive clay to the electron beam; in general, relative phyllosilicate stabilities are kaolin < smectite < pyrophyllite < mica. A clear dependence of element loss on crystallographic orientation has been observed for layer silicates in our study; a greater element loss occurred when the plane of the specimen foil was perpendicular to the basal planes of the phyllosilicate crystals than when the foil was parallel to the basal planes. Lower beam current, larger beam diameter and thicker specimens all reduce the loss of elements. The initial stage of irradiation produces highest rates of element loss and the rate of loss can be fitted by an exponential decay law. The analyses at low temperature of phyllosilicates showed that element loss remains serious in our analytical conditions. Since the element loss appears to be instrument- and method-dependent, one should use closely related, well-characterized phyllosilicates as compositional standards to calibrate any AEM instrument that is to be used to analyze unknown phyllosilicates, and the standards and unknowns should be analyzed under identical conditions.
Stirring Effects on Properties of Al Goethite Formed From Ferrihydrite
Authors: Schwertmann U. , Stanjek H.
Published: August 2006

Minerals in surface environments form in both turbulent and non-turbulent systems. This study compares the properties of Al goethite formed from ferrihydrite at 60°C in 0.3 M KOH with and without mechanical stirring. Compared to the static system, stirring increased crystal order and needle thickness, decreased unit cell edge length a, but not b and c, reduced the separation between the 2 OH-bending vibrations, increased Al substitution and promoted hematite formation.
Water Retention by Colloidal Allophane and Imogolite with Different Charges
Authors: Karube Jutaro , Abe Yukihiro
Published: August 2006

Water retention curves of colloidal allophane and imogolite with different charges and different pretreatments were measured using a tension plate and a pressure plate apparatus. An irreversible effect of air-drying was found for the water retention of colloidal allophane even for particles of less than 50 nm in Stokes’ diameter collected from air-dried soil. This was attributed to the irreversible submicroscopic aggregation of allophane. Fresh allophane colloids with a low absolute net charge retained more water above −100 J Kg−1 than did highly charged ones due to the formation of a microporous structure. Allophane did not swell under ordinary conditions, but the relatively highly charged allophane recovered water retention above −100 J kg−1 during the wetting process. Imogolite retained 1.5 times more water than Na-montmorillonite at about −650 J kg−1 due to micropores formed by intertwining fibrous particles.
Adsorption of Monovalent Organic Cations on Sepiolite: Experimental Results and Model Calculations
Authors: Rytwo Giora , Nir Shlomo , Margulies Leon , Casal Blanca , Merino Jesus , Ruiz-Hitzky Eduardo , Serratosa Jose Maria
Published: August 2006

Adsorption of neutral organic molecules and the monovalent organic cations methylene blue (MB) and crystal violet (CV) to sepiolite was determined experimentally and investigated by an adsorption model. The largest amounts of MB and CV adsorbed were about 4-fold of the cation exchange capacity (CEC) of sepiolite. Consequently, it was proposed that most of the above described adsorption was to neutral sites of the clay. The adsorption model considered combines the Gouy-Chapman solution and specific binding in a closed system. The model was extended by allowing cation adsorption to neutral sites of the clay, in addition to adsorption to negatively charged sites and adsorption to neutral complexes formed from 1 cation adsorbed to a negative surface site. The amount of available neutral sites was determined from the adsorption of the neutral molecule Triton-X 100 (TX100). The model could adequately simulate the adsorption of the neutral molecules TX100 and crown ether 15-crown-5 (15C5) as well as the organic cations. Due to aggregation of MB molecules in solution, their adsorption was somewhat less than that of CV at the larger added concentrations. A consideration of the molecular dimensions of TX100, MB and CV suggested that their adsorption was mostly to external sites of the clay and that their entry to the sepiolite channels was largely excluded. This interpretation is supported by infrared spectroscopy (IR) measurements, which show large perturbations of the peak corresponding to vibrations of external Si-OH groups of the clay and confirm complete occupancy of external sites by MB and CV.
Oxygen Isotope Compositions of Mixed-Layer Serpentine-Chlorite and Illite-Smectite in the Tuscaloosa Formation (U.S. Gulf Coast): Implications for Pore Fluids and Mineralogic Reactions
Authors: Ryan P. C. , Conrad M. E. , Brown K. , Chamberlain C. P. , Reynolds R. C.
Published: August 2006

Oxygen isotopic compositions were determined for coexisting mixed-layer serpentine-chlorite (Sp-Ch) and illite-smectite (I-S) from 5 Tuscaloosa Formation sandstone cores sampled between 1937 and 5470 m burial depth. High gradient magnetic separation (HGMS) was used to concentrate Sp-Ch and I-S from the <0.5 μm fraction of each core sample into fractions with a range in the Sp-Ch: I-S ratio, and end-member δ18O compositions were determined by extrapolation. The Sp-Ch δ18O values range from + 10.4 to 13.7% and increase with burial between 3509 and 5470 m. The only exception is Sp-Ch from 1937 m, which has an anomalously high δ18O value of +12.6‰ The I-S δ18O values range from +16.1 to 17.3% and do not change significantly between 3509 and 5470 m burial depth.

Pore water δ18O compositions calculated from Sp-Ch and I-S values and measured borehole temperatures range from −2.6 to +10.3‰ The isotopically light values indicate that Sp-Ch formed at shallow burial depths in the presence of brackish to marine water and/or meteoric water. The depth-related increase in δ18O of Sp-Ch is attributed to oxygen exchange between mineral and pore water during diagenetic mineral reactions. Increasing δ18O values, in conjunction with XRD and SEM data, indicate that transformation of serpentine layers to chlorite layers and Ibb polytype layers to Iaa polytype layers occurred on a layer-by-layer basis when individual layers dissolved and recrystallized within the confines of coherent crystals. Possible explanations for the variation in I-S δ18O values include depth-related differences in pore water δ18O values present at the time of I-S crystallization, contamination by detrital 2M, mica and 1M polytype rotations that facilitated oxygen exchange.
Iron Oxides in a Soil Developed from Basalt
Authors: Goulart A. T. , Fabris J. D. , de Jesus Filho M. F. , Coey J. M. D. , da Costa G. M. , de Grave E.
Published: August 2006

A dusky red Oxisol forming on a tholeiitic basalt is found to contain varying proportion of aluminous hematite (Hm) and titanoaluminous maghemite (Mh) in the different size fractions. Maghemite is the main iron oxide in the sand and silt fractions whereas Hm is dominant in the clay fraction, together with gibbsite (Gb), kaolinite (Ka), rutile (Rt) (and probably anatase, An) and Mh. Maghemite is also the major oxide mineral in the magnetic separates of soil fractions (sand, about 65% of the relative Mössbauer spectral area; silt, 60%). Hematite (sand, 30%; silt, 15%) and ilmenite (Im) (sand, 5%; silt, 16%) are also significantly present in the magnetic extract. Accessory minerals are Rt and An. No magnetite (Mt) was detected in any soil fraction. Sand- and silt-size Mh have similar nature (a0= 0.8319 ± 0.0005 nm; about 8 mol% of Al substitution; saturation magnetization of 49 J T−1 kg−1), and certainly a common origin. Lattice parameters of clay-Mh are more difficult to deduce, as magnetic separation was ineffective in removing nonmagnetic phases. Al content in Hm varies from 14 mol% (clay and silt) to 20 mol% (sand). The proposed cation distribution on the spinel sites of the sand-size Mh is:
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:c="http://cambridge.org/core/content" xmlns:core="http://cambridge.org/core" xmlns:m="http://cambridge.org/core/metadata" xmlns:cup="http://contentservices.cambridge.org" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest">[Fe0.92Al0.08] {Fe1.43Ti0.18 □0.39}O4

(◻ = vacancy, [ ] = tetrahedral sites and { } = octahedral sites), with a corresponding molar mass of 208.8 g mol−1. The predicted magnetization based on this formula is σ ≅ 68 J T−1 kg−1, assuming collinear spin arrangement. The large discrepancy with the experimentally determined magnetization is discussed.
Hisingerite: A Ferric Kaolin Mineral with Curved Morphology
Authors: Eggleton Richard A. , Tilley David B.
Published: August 2006

Hisingerite, first described in 1810, has been variously regarded as noncrystalline, as a septechlorite, as ferric allophane, as ferric halloysite and as poorly crystalline nontronite. Hisingerite from the original localities of Gillinge and Riddarhyttan in Sweden has a composition close to Fe2O3·2SiO22H2O. X-ray diffraction (XRD) analysis of Riddarhyttan hisingerite yields very broad maxima at 7.7, 4.44, 3.57, 2.56, 2.26, 1.69 and 1.54 Å, and that from Gillinge is similar. Cation exchange capacities are 2.2 meq/100 g (Riddarhyttan) and zero (Gillinge). Transmission electron microscopy (TEM) shows a fabric of concentric spheres and part spheres, with diameters of about 140 Å and walls up to six 7-Å layers thick. High-resolution images of the sphere walls reveal a 2-layer structure similar to that of kaolinite. A calculated diffraction pattern based on a model of 4 concentric shells of ferric kaolinite structure matches the observed pattern quite closely. Some other hisingerites, notably that from Bellevue King Mine, Idaho, show 10-Å layers as well as 7-Å layers, and this hisingerite has a CEC of 32 meq/100 g and a weak 15.5-Å X-ray reflection in addition to a pattern similar to Riddarhyttan hisingerite. It is concluded that hisingerite is a curved ferric 7-Å 1:1 layer silicate analogous to halloysite, and that many of the hisingerites reported in the literature contain admixed nontronite.
The Role of Sepiolite-Palygorskite in the Decay of Ancient Egyptian Limestone Sculptures
Authors: Rodriguez-Navarro Carlos , Sebastian Eduardo , Doehne Eric , Ginell William S.
Published: August 2006

An ancient Egyptian limestone sculpture was found to be undergoing major structural decay when stored in a museum environment. Mineralogical and petrographic analysis of the limestone showed a high proportion of clay (≥ 10% by weight) that was concentrated along bedding planes. The clay fraction consisted mostly of sepiolite (>90%) and palygorskite (<10%). Minor quantities (≤l%) of soluble salts (NaCl and NaNO3) were also found. Wetting/drying with distilled water and relative humidity cycling resulted in the same delamination cracking damage as that observed in the museum environment. Thermomechanical analyses (TMA) confirmed that the damage was due to expansion (>4.5%) parallel to bedding planes when the limestone was immersed in water. The expansion due to swelling of the clays was directly observed at high magnification in an environmental scanning electron microscope (ESEM) when wetting/drying cycles were performed. X-ray diffraction (XRD) analysis showed that crystalline swelling of sepiolite occurred. This was determined by a shift of (110) reflection (from 12.07 to 12.20 Å) and a decrease of (060) reflection (4.47 Å, to 4.44 and 4.41 Å), when in contact with ethylene glycol (EG) and dimethyl sulfoxide (DMSO), respectively. Swelling also occurred due to hydration of the clay surfaces and to electrostatic forces between clay particles, which, it was assumed, was promoted by the presence of Na counterions in water solution. Possible treatments for the conservation of these artistic objects are proposed and discussed.
Effects of Secondary Iron Phases on Kaolinite 27Al MAS NMR Spectra
Authors: Schroeder Paul A. , Pruett Robert J. , Hurst Vernon J.
Published: August 2006

Eight kaolinite and 2 halloysite samples were analyzed using 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, chemical analysis and magnetic susceptibility to understand the effect of isomorphously substituted Fe3+ and secondary Fe phases on the NMR signal. Known additions of goethite and hematite were made to determine the response of kaolinite 27Al MAS NMR spectra and sample magnetic susceptibilities.

Results from high field (11.7 T) NMR studies show positive correlations between 1) Fe content, 2) magnetic susceptibility and 3) relative intensity of the spinning side band (SSB) to central band (CB) ratio. No correlation is observed between the mass-corrected NMR spectral intensity and Fe content. Comparative high/low field (11.7 T/8.46 T) NMR studies show a decrease in the relative ratio of line broadening with increasing Fe content. Projected trends of known additions of hematite and goethite versus magnetic susceptibility extrapolate back to zero y intercepts that have Fe concentrations higher than actually measured.

Absolute intensity observations have negative implications for the use of 27Al MAS NMR spectroscopy in assessing Fe-ordering in kaolinites. First, high-energy, short (1/6 of π/2 solutions) pulse sequences do not produce reliable quantitative data needed to assess paramagnetic line-broadening affects caused by different Fe-ordering clustering scenarios. The lack of perfect correlation between SSB/CB, Fe content and magnetic susceptibility indicates that differences exist with respect to 1) the amount of isomorphously substituted Fe, 2) the ordering of the Fe within kaolinite, 3) the concentration of secondary Fe phases and 4) magnetic susceptibility of the secondary Fe assemblage. Variability of line-width ratios at different field strengths indicates an increasing second-order quadrupole effect (SOQE) with increasing Fe. Finally, the difference between the observed Fe content and that predicted from magnetic susceptibility measurements suggest that magnetic domain properties of secondary Fe phases behave differently from Fe domains bound in kaolinite.
Diagenetic Transformation of Magnesite Pebbles and Cobbles to Sepiolite (Meerschaum) in the Miocene Eskişehir Lacustrine Basin, Turkey
Authors: Işik Ece Ö.
Published: August 2006

Magnesite pebbles in Miocene lacustrine conglomerates in northwest Turkey have been partially to totally replaced by sepiolite. Only 5% of the magnesite pebbles have been converted to essentially pure sepiolite; the rest represent mixtures of magnesite and sepiolite. This process of sepiolitization is documented by X-ray diffraction (XRD), chemical, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques. These techniques show that the sepiolitization proceeds from the rim towards the core of the pebbles. The conglomerates, with pebbles of magnesite and ultramafic rocks, were deposited in a near-shore environment on the margin of a large Miocene lake with an ophiolitic substratum. The diagenetic transformation of magnesite to sepiolite is believed to have been caused by the interaction of mixed meteoric and lacustrine waters, which were undersaturated with respect to magnesite. The sepiolitization occurred during the highstands of the lake, when the near-shore conglomerates were flooded by the silica-rich lake waters. The pH of the water during the sepiolitization was probably on the order of 10.5–11.5. The sedimentary magnesite beds in the center of the Miocene basin show no sepiolitization, which is explained by the presence of pore water saturated with respect to magnesite.

The magnesite-sepiolite replacement process is chemically modeled as a 4-stage process from dimerization to polymerization.
Mineralogical Transformation of Bioweathered Granitic Biotite, Studied by HRTEM: Evidence for a New Pathway in Lichen Activity
Authors: Wierzchos Jacek , Ascaso Carmen
Published: August 2006

The question of whether clay minerals can be biogenically transformed as a result of lichen activity at the lichen-rock interface remains unresolved. We applied several microscopical and analytical techniques—scanning electron microscopy-back-scattered electron (SEM-BSE), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM)—in an attempt to address this issue. Unaffected granitic biotite and bioweathered material from the granitic biotite and Parmelia conspersa lichen thalli interface were examined using HRTEM after ultrathin sectioning. The n-alkylammonium treatment of ultrathin sections was carried out in order to study the biogenous mineralogical transformation of the biotite. Microsamples proceeding from unaffected biotite zones demonstrated homogenous 10-Å d(001)-value biotite phase. HRTEM images of lattice fringes of samples taken from the lichen-biotite contact zone reveal large areas of both unexpanded (10-A) and randomly and R = 3 distributed expanded (from 14- to 30-Å) layers of phyllosilicates identified as interstratified biotite-vermiculite. Results of artificial biotite weathering (replacement of K by Ca ion) also revealed the biotite-vermiculite phase formation, indicating that K release in biotite is one of the mechanisms responsible for interstratified mineral phase formation. Two parallel processes, physical exfoliation of biotite and inter-layer ionic exchange of K and subsequent vermiculite formation, are the mechanisms for biotite bioweathering induced by lichens.
Effect of Al and Organic Acids on the Surface Chemistry of Kaolinite
Authors: Ward David B. , Brady Patrick V.
Published: August 2006

The cause of pH and ionic strength-dependent proton and hydroxyl adsorption onto kaolinite is specific binding at edge Al and Si sites, and it can be modeled as a function of temperature with a triple layer model (TLM) of the mineral-solution interface. Exchange of Al for protons and hydroxyls is observed at low pH, with a stoichiometry approaching 1:3 (Al:H+). Adsorption of organic acids from dilute solutions depends on: 1) solution pH; 2) the functionality of the acid; and, to a lesser extent, 3) temperature. Such adsorption may occur primarily at Al sites exposed on kaolinite edges, as indicated by sorption experiments on the constituent oxides, where negligible sorption was observed on SiO2 (quartz), but was significant on Al2O3 (corundum) surfaces. Under similar conditions, oxalate adsorbs more strongly than acetate or formate to aluminol sites.
Combination Bands in the Infrared Spectroscopy of Kaolins—A Drift Spectroscopic Study
Authors: Frost Ray L. , Johansson Ursula
Published: August 2006

Kaolinites with varying degrees of defect structures have been studied by both mid-infrared (IR) and near-IR diffuse reflectance spectroscopy (DRIFT). Difference bands were observed in the 2650- to 2750-cm−1 region. This region coincides with the kaolinite-deuterated hydroxyl stretching region. Summation bands were observed in the near-IR spectra in the 4500- to 4650-cm−1 and in the 7050- to 7250- cm−1 region. Each of the spectral regions of the summation and difference bands is both kaolin polytype and sample dependent. It is proposed that each of these sets of bands arises from the combination of the hydroxyl stretching frequencies and the hydroxyl deformation frequencies and, to a lesser extent, the silicon-oxygen symmetric stretching vibration of the siloxane layer. Additional difference bands of very low intensity were also observed at 2930 and 2856 cm−1. Combination bands were observed in all kaolinites at 2137 and 2227 cm−1. Each of the 3 major combination spectral regions was composed of 5 component bands corresponding to the 4 IR active and the 1 Raman active kaolinite hydroxyl stretching frequencies. Combination bands were also observed at ~1932 and 1821 cm−1.
Iron Influence in the Aluminosilicate Zeolites Synthesis
Authors: Basaldella E. I. , Torres Sánchez R. M. , Tara J. C.
Published: August 2006

The level of Fe impurities in 2 well-crystallized kaolinites was modified (by addition or chemical removal treatment) to analyze the Fe influence in the aluminosilicate zeolite synthesis.

The original and modified clays were heat-treated in order to change their reactivity for zeolite A synthesis, and their thermal transformations were studied by X-ray diffraction (XRD), determination of point of zero charge (PZC) and infrared (IR) techniques. It was established that many structural changes took place, regardless of the Fe clay content. Furthermore, the presence of Fe species in alkaline solution or in the solid phase did not seem to greatly influence the zeolite crystallization, because only small differences in the conversion values among samples with different Fe contents were registered. The crystallization process seemed to be related mainly to AI coordination changes produced by the thermal and Fe removal treatments used.
Swelling and Texture of Iron-Bearing Smectites Reduced by Bacteria
Authors: Gates Will P. , Jaunet Anne-Marie , Tessier Daniel , Cole Michael A. , Wilkinson Henry T. , Stucki Joseph W.
Published: August 2006

Microbial reduction of clay mineral structural Fe(III) decreases the swelling of nontronite gels, most importantly at intermediate oxidation states (40 to 80 cmol Fe(II) kg−1 clay). The purpose of this study was to establish whether microbial reduction of structural Fe(III) decreased the swelling of other Fe-bearing smectites and to discern the influence that organic compounds of microbial origin (bacterial cells, cell fragments and/or exudates) may have on clay swelling and texture. Structural Fe(III) was reduced by incubating smectite suspensions with either a combination of Pseudomonas bacteria or a mixture of anaerobic bacteria. The influence of organics on clay swelling was estimated on smectites suspended in either organic or inorganic media in the absence of bacteria. The gravimetric water content of the reduced clay gels equilibrated at various applied pressures was recorded as a function of Fe oxidation state. Transmission electron microscopy (TEM) was employed to determine the influence of bacteria and type of media on the texture of reduced smectite gels. Reduction of structural Fe(III) by bacteria decreased the swelling pressure of all Fe-bearing smectites. Increased clay swelling, due to the presence of organics (organic medium, exudates or cell fragments), was correlated to the total Fe content, the extent of structural Fe reduction, as well as the initial swelling characteristics of the Fe-bearing smectites. High structural Fe(II) contents (>50 cmol Fe(II) kg−1) resulted in increased attractive forces between clay platelets that decreased clay swelling, even in organic medium suspensions. Microbial reduction resulted in increased face-face association of individual clay layers, forming larger and more distinct crystallite subunits than in nonreduced clay gels. But, perhaps more importantly, microbial reduction of structural Fe(III) resulted in an increased association between crystallite subunits and, thus, an overall larger particle size and pore size distribution, due to the interaction of bacteria ceils, cell fragments and organic exudates.
Evaluation of Gas Transport Properties of Backfill Materials for Waste Disposal: H2 Migration Experiments in Compacted Fo-Ca Clay
Authors: Gallé C. , Tanai K.
Published: August 2006

Swelling clays may play a major role in the underground disposal of high-level nuclear waste (HLW) in deep geological formations. A multibarrier concept including a waste container, a steel overpack, an engineered barrier consisting of compacted clay (buffer) and the host rock is a potential technique for such HLW disposal. It is anticipated that H2 will be the main gas generated, mainly by anaerobic metal corrosion during disposal lifetime. After complete resaturation, the clay barrier will have a very low permeability and H2 may accumulate in the space between the overpack and the clay barrier. This could result in pressures exceeding the resistance of the clay and damage to the entire engineered barrier system (EBS).

The French Atomic Energy Commission (CEA) has performed an experimental program on H2 gas migration in a French clay referenced Fo-Ca. The tests were conducted with a specific odometer-type cell developed by the Power Reactor and Nuclear Fuel Corporation (PNC) in Japan. Permeability tests on compacted Fo-Ca clay samples of specific dry densities between 1.6 and 1.9 and for water saturation degrees between 70 and 100% provided significant H2 permeability data (ranging from 10−15 to 10−21 m2). Gas migration experiments were also performed to study the behavior of Fo-Ca clay under high gas pressure. Two kinds of gas transport threshold pressures were detected in unsaturated compacted clay. The first one, called “critical pressure”, is the pressure over which a gas outflow migrates into the clay. This pressure probably exceeds the capillary pressure of the largest pores within the clay. The second one, called “breakthrough pressure”, is detected with increasing gas injection pressure. A sudden rise of gas outflow is subsequently observed. The occurrence of the gas breakthrough is associated with the aperture and propagation of preferential gas transport pathways in the clay. This is apparently linked to the hydromechanical properties and stress state of the clay. When clay samples are not fully watersaturated, the critical pressure is always lower than the breakthrough pressure. However, when the clay is saturated, the 2 pressures appear to be very close. Finally, this study showed that breakthrough pressure—a key parameter for the long-term stability of the clay buffer—varies considerably with the gas injection increments and with the size of the sample. The results of these experiments are consistent with those reported previously by other investigators.
Transformation Mechanisms and Interstratification in Conversion of Smectite to Kaolinite: An HRTEM Study
Authors: Amouric Marc , Olives Juan
Published: August 2006

The transformation of smectite into kaolinite and kaolinite-smectite interstratification were studied in samples belonging to the Argiles Plastiques formation of the Paris basin, by high-resolution transmission electron microscopy (HRTEM). Two original smectite phases, 1) beidellite with 1-nm-thick layers, and 2) beidellite-montmorillonite with 1.25-nm-thick layers, are progressively transformed into kaolinite-smectite mixed-layer minerals, and into kaolinite. As the percentage of kaolinite layers increases in the interlayered minerals, the kaolinite-smectite layer sequences, initially disordered, become locally more ordered, with the presence of KS and KKS units repeated 2 to 4 times (K = kaolinite layer, S = smectite layer). Two solid-state mechanisms seem to be responsible for the formation of kaolinite: 1) the transformation of 1 smectite layer into 1 kaolinite layer, denoted S → K, by stripping of a tetrahedral sheet and the adjacent interlayer region; 2) the intercalation of 1 kaolinite layer into smectite, denoted 0 (zero)→K. Structural and chemical incidences of these mechanisms are discussed.
Use and Limitations of Second-Derivative Diffuse Reflectance Spectroscopy in the Visible to Near-Infrared Range to Identify and Quantify Fe Oxide Minerals in Soils
Authors: Scheinost A. C. , Chavernas A. , Barrón V. , Torrent J.
Published: August 2006

We measured the visible to near-infrared (IR) spectra of 176 synthetic and natural samples of Fe oxides, oxyhydroxides and an oxyhydroxysulfate (here collectively called “Fe oxides”), and of 56 soil samples ranging widely in goethite/hematite and goethite/lepidocrocite ratios. The positions of the second-derivative minima, corresponding to crystal-field bands, varied substantially within each group of the Fe oxide minerals. Because of overlapping band positions, goethite, maghemite and schwertmannite could not be discriminated. Using the positions of the 4T1←6A1, 4T2←6A1, (4E;4A1)←6A1 and the electron pair transition (4T1+4T1)←(6A1+6A1), at least 80% of the pure akaganeite, feroxyhite, ferrihydrite, hematite and lepidocrocite samples could be correctly classified by discriminant functions. In soils containing mixtures of Fe oxides, however, only hematite and magnetite could be unequivocally discriminated from other Fe oxides. The characteristic features of hematite are the lower wavelengths of the 4T1 transition (848–906 nm) and the higher wavelengths of the electron pair transition (521–565 nm) as compared to the other Fe oxides (909–1022 nm and 479–499 nm, resp.). Magnetite could be identified by a unique band at 1500 nm due to Fe(II) to Fe(III) intervalence charge transfer. As the bands of goethite and hematite are well separated, the goethite/hematite ratio of soils not containing other Fe oxides could be reasonably predicted from the amplitude of the second-derivative bands. The detection limit of these 2 minerals in soils was below 5 g kg−1, which is about 1 order of magnitude lower than the detection limit for routine X-ray diffraction (XRD) analysis. This low detection limit, and the little time and effort involved in the measurements, make second-derivative diffuse reflectance spectroscopy a practical means of routinely determining goethite and hematite contents in soils. The identification of other accessory Fe oxide minerals in soils is, however, very restricted.
Coprecipitates of Cd, Cu, Pb and Zn in Iron Oxides: Solid Phase Transformation and Metal Solubility after Aging and Thermal Treatment
Authors: Martínez Carmen Enid , McBride Murray B.
Published: August 2006

Solid phase transformation and metal solubility were monitored after coprecipitation of Cd2+, Cu2+, Pb2+ and Zn2+ with Fe3+ to form ferrihydrite by titration to pH 6. The (co)precipitates were aged at room temperature for up to 200 d and subsequently heated for 60 d at 70 °C. The mode of (co)precipitate formation, rapid and slow titration, was also investigated. Metal solubility was measured by anodic stripping voltammetry. Surface area, Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis were used to follow the transformation of ferrihydrite after initial (co)precipitation. Electron microprobe analysis (EMPA) was used to show the distribution of metals within ferrihydrite aggregates. Thermal treatment produced a reduction in soluble Cd2+ and Zn2+, whereas Pb2+ appeared to be expelled from the solid phase. The more stable coprecipitate (formed by slow titration) maintained a constant Cu2+ solubility after thermal treatment. Characterization of the solid phase by XRD indicated that the presence of low levels of metals did not affect the initial or final transformation products, although metals present during the slow titration seemed to stabilize a higher surface area material. The rapid titration resulted in a less ordered (1-line) ferrihydrite than the slow titration (9-line). Furthermore, FTIR analysis indicated that the presence of metals promoted the formation of mixed (microcrystalline) end-products. The initial coprecipitation products seem to determine the final thermal transformation products. These transformation products include ferrihydrite, hematite (Hm), and goethite (Gt)- and lepidocrocite-like microcrystalline structures. Although experimental conditions were favorable for the homogeneous distribution of metals throughout the coprecipitate, EMPA suggests that Cu and Zn segregation within aggregates of Fe oxides occurs.
Hydroxy-Interlayers in Expansible Layer Silicates and Their Relation to Potassium Fixation
Authors: Saha Uttam K. , Inoue Katsuhiro
Published: August 2006

Hydroxyaluminosilicate (HAS) and hydroxyaluminum (HyA) ionic solutions having final Al concentrations ranging from 3.74 to 4.00 mM; NaOH/Al molar ratios of 1.0, 2.0 and 2.5; and Si/Al molar ratios of 0.00, 0.27–0.30, 0.51–0.56 and 0.95–1.01 were prepared through the interaction of AlCl3, or-thosilicic acid and NaOH solutions. When these solutions reacted with <2 µm sized vermiculite (Vt) and montmorillonite (Mt), varying amounts of Al and Si were fixed on Vt and Mt clays. Potassium fixation and exchange capacities of HyA/HAS (OH/Al = 1.0, 2.0 and 2.5)-Vt and HyA/HAS (OH/AI = 2.0)-Mt complexes were compared with those of untreated Vt and Mt at added K levels ranging from 21 to 319 cmolc kg−1. The untreated Vt clay showed K fixation as high as 94 cmolc kg−1, in contrast to only 16 cmolc kg−1 exchangeable K. The untreated Mt fixed a maximum of 9 cmolc K kg−1 out of a total K adsorption capacity of 67 creole kg−1. In the HyA/HAS-Vt complexes, K fixation reduced drastically in comparison to untreated Vt, and ranged from 9 to 24 cmolc kg−1 out of their total K adsorption capacities of 61 to 81 cmolc kg−1. In the HyA/HAS-Mt complexes, too, the amount of K fixed reduced to a great extent in comparison to Mt and ranged from 1.48 to 1.84 cmolc kg−1. Potassium became more exchangeable due to the presence of hydroxy-interlayers in the clays. The reduction in CEC and the well-known propping effects of hydroxy-cations’ islands in the interlayers might have hindered K fixation by the complexes. The relationships of maximum K fixing capacities of the HyA/HAS-Vt complexes with the amounts of Al, Si and Al + Si fixed on Vt were all exponential and negative. However, the amount of Al + Si or only Al fixed on Vt appeared to be the best indicator of K fixation capacities of hydroxyinterlayered Vt clay.
131I− Sorption by Thermally Treated Hydrotalcites
Authors: Olguín María Teresa , Bosch Pedro , Acosta Dwight , Bulbulian Silvia
Published: August 2006

The sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for 131I− sorption from water solution and it was determined as a function of the calcining temperature. The radionuclide content was determined by γ-spectrometry. Solids were characterized by thermal analysis, X-ray diffraction (XRD), electron microscopy and Brunauer-Emmett-Teller (BET) analysis. For 0.1 M Na I solution, labeled with 131I−, sorption capacity was found to be 0.24 meq g−1 (7.2% of the anion exchange capacity, AEC). But, if the sample was previously calcined at 773 K and the HT structure destroyed, the sorption of I− increased considerably, up to 2.08 meq g−1 (63% of the AEC) and the HT structure was reconstructed. The 131I− sorption at very low concentrations (10−14M) was 0.04 × 10−14 meq of 131I− g−1 in the noncalcined HT, but for calcined samples at 773 K, the sorption increased to circa 0.97 × 10−14 meq g−1. Calcination temperature determines the surface area of the resulting mixed oxides, and that property seems to be the most important factor controlling the I− sorption. If the calcination temperature was increased to 873 K, the specific surface area of the oxide mixture increased and I− sorption increased as well, whereas calcination of HT at 973–1073 K resulted in a low surface area and a low I− retention.
Surface Microtopography of Lath-Shaped Hydrothermal Illite by Tapping-Mode™ and Contact-Mode AFM
Authors: Kuwahara Yoshihiro , Uehara Seiichiro , Aoki Yoshikazu
Published: August 2006

Lath-shaped hydrothermal illite particles in Izumiyama pottery stone were examined by contact-mode atomic force microscopy (CMAFM) and tapping-mode AFM (TMAFM) in air. With CMAFM, the lath-shaped particles showed interlacing patterns on the (001) surface in deflection images, while in height images such patterns were unclear. Also, evidence of artifacts caused by frictional forces between the surface and tip and/or edge effects were found in the CMAFM height images of the particle and Si substrate surfaces. In contrast, TMAFM showed interlacing patterns clearly in both amplitude and height images, and artifacts were barely evident. The TMAFM height images permitted the accurate measurement of 1.0- or 2.0-nm height steps corresponding to single or double mica layers, as well.

Many lath-shaped particles in the Izumiyama hydrothermal illite exhibit interlacing patterns on their (001) surface, as shown by these AFM observations. The interlacing patterns are characterized by polygonal spirals with comparatively wide spacings and steps having a height of 1.0 or 2.0 nm. Generally a single lath-shaped particle has a single spiral center on the (001) surface, and 2 mica layers rotated 120° originate from the dislocation point. These support the view that lath-shaped illites belong to the 2M1 polytype. It is likely that these illite particles were formed by a uniform process of development that is characterized by very slow growth, spiral mechanisms in that growth and low supersaturation conditions.