bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long-term weathering of silicates in a sandy soil at Nordmoen, southern Norway
Authors: Teveldal S. , Jørgensen P. , Stuanes A. O. 
Published: December 2006

AbstractWeathering processes have been studied in a podzol profile developed on sand during a postglacial period of 9400 years. Due to disintegration of rock fragments, the particle-size distribution has changed markedly in the upper part of the profile, and minerals have been transferred from sand fractions to silt and clay fractions. The most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctahedral mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite. By using quartz as an internal standard, the annual loss due to weathering was found to be 3·2 g/m2. The release of elements due to silicate weathering was calculated from depletion curves, and the average annual release of Na + K + Mg + Ca for the postglacial period was 19 mEq/m2.
Study of the water-bentonite system by vapour adsorption, immersion calorimetry and X-ray techniques: II. Heats of immersion, swelling pressures and thermodynamic properties
Authors: Kahr G. , Kraehenbuehl F. , Stoeckli H. F. , Müller-Vonmoos M. 
Published: December 2006

AbstractA number of thermodynamic properties were obtained from the determination of adsorption isotherms and enthalpies of immersion for systems with water and Na- and Ca-bentonites. Entropy differences were calculated by combining the enthalpies of immersion and the changes in free energy derived from the adsorption isotherms. The swelling pressures, also calculated from the water adsorption isotherms, are in satisfactory agreement with the experimental data.
Some Comments on the Chemistry and Stability of Interstratified Illite-Smectite and the Role of Ostwald-Type Processes
Authors: Primmer T. J. 
Published: December 2006

AbstractMuch emphasis has been placed recently on the role of Ostwald-type processes (both ripening and the step rule) in the formation of interstratified illite-smectite clay minerals during diagenesis. Closer investigation of the relationships between illite particle thickness (as defined in terms of the fundamental particle theory) and particle chemistry show that simple Ostwald ripening is too simplistic a mechanism to describe observed changes in illite thickness and composition. In addition, available thermodynamic data on clay minerals suggest that the conventional notion of metastability associated with Ostwald's step rule is an inaccurate description of the relationship between illitic clay minerals and their macroscopic 2 : 1 phyllosilicate analogues.
An Unusually Interlayered Clay Mineral from the Eluvial Horizon of a Humus-Iron Podzol
Authors: Bain D. C. , Fraser A. R. 
Published: December 2006

AbstractThe <2 µm fraction from the eluvial horizon of a humus-iron podzol is composed predominantly of a dioctahedral mineral with a basal spacing of 14.7 Å which contracts to 13.7 Å on solvation with glycol, and to 11.4 Å on heating to 300°C. The interlayer region is partially filled with an amorphous organo-Fe-Al complex which is very unstable and is affected by every treatment employed, even homoionic cation saturation. The mineral has a mica-like morphology, contains 3.4% non-exchangeable K2O and is considered to be an interstratified mica-vermiculite formed by the weathering of mica. The contraction of the basal spacing with glycol is probably due to water being removed from the interlayer region of the vermiculite component, leaving only the natural organo-complex in the interlayer; alternatively, the contraction may be more apparent than real, resulting from an interstratification effect. Treatment with H2O2results in partial expansion with glycol.
Comparison of Measured and Calculated Diffusion Coefficients for Iodide in Compacted Clays
Authors: Oscarson D. W. 
Published: December 2006

AbstractAn understanding of the behaviour of contaminants in compacted clays is important in assessing the effectiveness of clay-based barrier materials used in many waste containment strategies. Here the diffusion and sorption behaviour of I−with selected compacted clays is examined (129I is a relatively long-lived radioisotope present in high-level nuclear fuel waste.) Diffusion coefficients,D, and distribution coefficients,Kd, were measured for I−with four clays: bentonite, Lake Agassiz clay (a glacial lake clay composed mainly of smectite, illite, kaolinite, and quartz), interstratified illite-smectite, and kaolinite. For the diffusion experiments the clays were compacted to a dry bulk density, ρ, of ∼1.2 Mg m−3. The mean measuredDvalues,Dm, were as follows: bentonite, 310 µm2s−1; Lake Agassiz clay, 0.62 µm2s−1; illitesmectite, 190µm2s−1; and kaolinite, 74µm2s−1. The measured values were compared with those calculated,Dc, from the following model:D=Doτan/(n+ρKd), whereDois the diffusion coefficient in pure bulk water,τathe apparent tortuosity factor, andnthe solution-filled porosity of the clay. Except for the Lake Agassiz clay, whereDmwas about an order of magnitude lower thanDc, theDmandDcvalues agreed within a factor of about two. The Lake Agassiz clay has a markedly higher organic carbon content than the other three clays, and this could affectτa, which may be overestimated in the model.
The Effect of Thermal Treatment on the Properties of Hydroxy-Al and Hydroxy-Ga Pillared Montmorillonite and Beidellite
Authors: Kloprogge J. T. , Booy E. , Jansen J. B. H. , Geus J. W. 
Published: December 2006

AbstractThe pillaring process of montmorillonite and beidellite with Al and Ga polymers has been studied using XRD, IR,27Al,71Ga, and29Si MAS NMR, TGA, TEM, N2adsorption and chemical analyses. The Al adsorption maximum for montmorillonite is close to 5.5 mEq Al/g clay, whereas the maximum for Ga is higher. Basal spacings of both Ga- and Al-pillared clays vary between 16.7 and 18.8 Å. Freeze-drying of pillared products followed by calcination yielded more regular pillared structures. Pillaring montmorillonite increased the BET surface area from 35 m2/g to 350 m2/g mainly by the creation of micropores <20 Å in diameter. The Al-pillared clays are thermally stable to ∼700°C. Calcination of pillared montmorillonite liberates protons from the pillar, which diffuse into the clay sheet, lowering the thermal stability. In pillared beidellite, mainly silanol groups are formed by breaking Si-O-Al bonds. No reaction is observed between pillars and montmorillonite upon calcination, whereas in pillared beidellite a structural transformation links the pillar to inverted tetrahedra of the tetrahedral sheet. The basal spacing of Ga-pillared montmorillonite collapses to 9.5 Å at 350°C due to the Ga polymer decomposing to Ga3+cations.
Synthesis and Characterization of ‘Epoxyphilic’ Montmorillonites
Authors: Akelah A. , Kelly P. , Qutubuddin S. , Moet A. 
Published: December 2006

Abstract‘Epoxyphilic’ montmorillonites were prepared containing various functional groups which can react with one or both of the components in amine-cured epoxy formulations. The preparation involves the ion exchange of six organic ammonium compounds containing either carboxylic acid, anhydride, phenolic hydroxyl, alcoholic hydroxyl, amide or amine functional groups. X-ray diffraction, elemental analysis and FTIR studies confirm the intercalation of the organic cations to form epoxyphilic montmorillonites. The adsorption behaviour of the modified montmorillonites are compared with the unmodified montmorillonite in an epoxy resin before and after the curing process.
The Competitive Adsorption of Methylene Blue on to Montmorillonite from Binary Solution wih Thioflavin T, Proflavine and Acridine Yellow. Steady-State and Dynamic Studies
Authors: Breen C. , Rock B. 
Published: December 2006

AbstractMethylene blue (MB) has been used as a probe molecule to examine how the uptake dynamics and the equilibria between this dye and the surface of Na+- and H+- montmorillonite were affected by the presence of a second dye. To prevent spectral interference, the yellow dyes thioflavin T, TFT, proflavine, PFH, and acridine yellow, ACY, were chosen to compete with MB for the exchange sites. The MB was initially adsorbed as trimer (MB+)3and then redistributed via collisions between clay particles until equilibrium was reached. At equilibrium in the clay/MB systems, the protonated species (MBH2+) predominated at low loadings (1–5% CEC), whereas at higher loadings the trimer (MB+)3was the major species. The presence of the second, competing dye slowed the approach to equilibrium, significantly reduced the amount of MBH2+formed and provided evidence for the monomeric MB+, dimeric (MB+)2, and trimeric (MB+)3forms of MB. Moreover, the presence of PFH and ACY, which are structurally similar to MB, resulted in more dimeric character in the aggregated form of MB compared to the aggregate formed in the presence of the structurally dissimilar TFT.
Interlayer Adsorption of Macrocyclic Compounds (Crown-Ethers and Cryptands) in 2:1 Phyllosilicates: II. Structural Features
Authors: Casal B. , Aranda P. , Sanz J. , Ruiz-Hitzky E. 
Published: December 2006

AbstractIntercalation of macrocyclic compounds (crown-ethers and cryptands) in 2:1 charged phyllosilicates is a topotactic reaction, the lamellar structure of the pristine material being preserved. X-ray diffraction and spectroscopic (IR, NMR) results provide information on the main structural characteristics of the intercalates. Guest species, which form 1 : 1 or 2 : 1 ligand/cation intracrystalline complexes, lie flat or tilting between the host layers as can be deduced from the increase in the basal space of the silicate and the dichroic effect observed on the CH and NH IR vibration bands of the guest species, after intercalation. The chemical shift observed in 23Na NMR spectra of the solids is associated with the different environment of the cation before and after the intercalation process.
Evidence of a Precursor in the Neoformation of Palygorskite — New Data by Analytical Electron Microscopy
Authors: Suarez M. , Martin Pozas J. M. , Robert M. , Elsass F. 
Published: December 2006

AbstractThe rocks of the palygorskite deposit at Bercimuel (Segovia, Spain) have been studied by transmission electron microscopy and microanalysis. These rocks correspond to the zone of convergence of two alluvial fan systems that have filled the small basin of the River Riaza and would originally have been composed of illite and quartz silts. Among the accumulations of palygorskite it is possible to observe surrounded particles of micromicas that have undergone dissolution and opening thereby giving rise to disordered illite-smectite mixed-layer clays. This process continued up to the individualization of structural relics formed of units of 1–5 layers. At the same time, the chemical composition was modified with a loss of K and Al and a relative increase in Si and Mg, progressively evolving towards the composition of palygorskite. The paleogeographic position of the deposits, and the climatic conditions (arid environment), appear to be the dominant factors in the neoformation of palygorskite by alteration of the original sediments. The basic mineralogical process could be referred to as ‘early diagenesis’ in the formation of calcretes.
Identification of pseudoboehmite in mixtures with phyllosilicates
Authors: Violante A. , Huang P. M. 
Published: December 2006

AbstractThe influence of kaolinite and montmorillonite on the identification of pseudoboehmite was studied by X-ray diffraction (XRD), differential thermal analysis (DTA), infrared absorption (IR), and transmission electron microscopy (TEM). In the randomly oriented samples containing different proportions of the clay minerals and pseudoboehmite, pseudoboehmite was not easily detectable by XRD even in a sample containing 40% of pseudoboehmite. Preheating of the samples at 110-300°C improved the detection limit to 30%. In samples obtained by mixing suitable amounts of the suspensions of the clay minerals (<2μm)and pseudoboehmite, the identification of pseudoboehmite was even more difficult. In oriented samples, pseudoboehmite was detectable only when present in amounts >30%, at low full-scale counts per second (1000-400 cps), on preheated samples in the presence of kaolinite, or on the samples that were Mg-saturated and solvated with ethylene glycol in the presence of montmorillonite. Identification of pseudoboehmite in the presence of kaolinite or montmorillonite by DTA, IR or TEM failed, even in samples containing 50% pseudoboehmite. In the presence of both kaolinite and montmorillonite (1:1 w/w), the identification of pseudoboehmite became much more difficult than in the presence of either mineral alone. The presence of pseudoboehmite in soils may, thus, be undetectable by standard clay mineralogical analyses.
Ammonium illite from anchimetamorphic shales associated with anthracite in the Zemplinicum of the western Carpathians
Authors: Šucha V. , Kraus I. , Madejová J. 
Published: December 2006

AbstractAmmonium-rich illite was identified in shales from the meta-anthracite coalfields of Zemplinicum (the Western Carpathians) together with K-illite and Na-illite using X-ray diffraction (XRD), infrared absorption and chemical analyses. The NH4-abundance in illite was quantified by the position of the 005 XRD reflection and by chemical analysis. Ammonium-bearing illite was probably formed in the temperature interval 200-270°C by illitization of a kaolinite precursor in the presence of ammonium.
Analysis of permeability controls: a new approach
Authors: Cade C. A. , Evans I. J. , Bryant S. L. 
Published: December 2006

AbstractBy modelling a range of rock-forming processes such as compaction and various styles of cementation, a new understanding of how they affect pore-system geometry, and hence permeability, has been gained. For example, almost identical permeability-porosity trends result from progressive compaction or grain overgrowth cementation in a clean sandstone, and these trends are curvilinear on the traditional log-linear plot. The steepening which defines the curve marks the onset of pore-throat blocking. Other cement styles, such as pore-filling carbonates or grain-rimming clays, show different porosity-permeability trends. This new understanding can be used predictively (predicting permeability from predictions of grain size and diagenetic style), or as a tool for identifying the important permeability controls in a set of field data. This latter application is presented and illustrated using data from a variety of sandstone types. This approach has important advantages over commonly used multivariate statistical analysis approaches. It can quickly provide a good understanding of what are (and are not) the important controls on permeability. It also provides a basis for more focused and meaningful statistical analysis to quantify these controls.
Ammonium fixation during illite-smectite diagenesis in Upper Jurassic shale, North Sea
Authors: Lindgreen H. 
Published: December 2006

AbstractClaystones of Kimmeridgian-Volgian-Ryazanian age are the main source rock for oil in the Central Trough, North Sea. During oil generation, illite layers form in illite-smectite (I-S) and the illitesmectites become short-range (IS) ordered and eventually long-range (ISII) ordered. The formation of illite layers involves dehydration and fixation of interlayer cations, K+ and NH4+. The content of soluble NH4 and K in core samples and the content of NH4 and K in I-S were determined, the NH4 by an isotope dilution method. In the Central Trough, soluble K+ decreases with depth, whereas soluble NH4+ increases with depth. From ∼3 km, the ratio NH4/K increases with depth, to an average of ∼0.5 at 4.4 km. In I-S, the ratio NH4/K shows a similar increase with depth. The NH4/K ratio increases significantly in I-S during ordering. It is concluded that NH4 fixation in I-S may be of general importance during burial diagenesis of oil source rocks.
Stable isotopes in illite: the case for meteoric water flushing within the Upper Jurassic Fulmar Formation sandstones, UK North Sea
Authors: Wilkinson M. , Fallick A. E. , Keaney G. M. J. , Haszeldine R. S. , McHardy W. J. 
Published: December 2006

AbstractThe extent to which the diagenesis of sedimentary sequences within the UK North Sea is influenced by the passage of meteoric water is subject of current debate. Petrographic (SEM, TEM, thinsection) observation and stable isotope ratios from authigenic illite separates are used to deduce the pore-fluid evolution of the Fulmar Formation within well 29/10-2 from the Central Graben, with emphasis on the past importance of meteoric water flushing.Petrographic observation shows the illite to have two modes of occurrence (pore-filling and as pseudomorphs after feldspar). These can be equated with two authigenic crystal morphologies (plates and laths) observed by TEM within illite separates prepared for isotopic analysis. The laths are equated with late stage ‘hairy’ pore-filling illite, the plates with illite pseudomorphs after feldspar which are difficult to date petrographically.The δD (−55 to −87‰ SMOW) and δ18O (12.4–14.6‰ SMOW) analyses can be interpreted in terms of a conventional hydrogen-oxygen cross-plot to indicate illite precipitation from pore-waters of meteoric origin at 50–60°C. However, these predicted precipitation temperatures are irreconcilable with the observed petrographic sequence. The hydrogen isotope compositions may have undergone resetting during burial. Consequently, only the δ18O data may be confidently interpreted in terms of the conditions of illite precipitation. This implies illite growth at temperatures above 80°C from waters with δ18O between −2.5 and +6‰ SMOW, leaving the case for meteoric water flushing of the sandstones unproven.
Smectite to illite conversion and K-Ar ages
Authors: Velde B. , Renac C. 
Published: December 2006

AbstractInterpretation of K-Ar determinations of the apparent age of crystallization of diagenetic potassic layer silicates should take into account the current ideas concerning the smectite to illite conversion of clay minerals. These minerals are the major K-bearing neogenic phases in sedimentary rocks and, therefore, it is important to keep in mind their origin and the pathway of their evolution. Another important contributor to K and Ar content are detrital minerals which are not considered in detail in this paper. The radiogenic Ar retained by diagenetic illitic clay minerals (illite and illite-smectite interstratified minerals with a low smectite content) will be a function of: (1) the amount Ar lost through the destruction of mixed-layer and small grained illitic material dissolved to produce new, larger, illite-rich crystals; and (2) the amount of Ar produced and retained in the growing, stable illite mineral grains. Hence the K/Ar ratios in diagenetic illites depend on several variables. In samples where the detrital contribution is small, when the illite growth reaction is rapid, i. e. occurring over a short period of time, the accumulated radiogenic Ar can be used to date the geologic event which caused this crystal growth. However, if the process occurs over a significant period of time, as is usually the case in shales, the age deduced by radiogenic Ar content will indicate the changes in mineralogy and grain-sizes of the different participating phases. These changes will be the result of time and temperature variables of the sedimentation and burial of the samples studied. The radiogenic Ar accumulated will reflect a sequence of mineral changes over a period of time.
The thermal behaviour of an Fe-rich illite
Authors: Murad E. , Wagner U. 
Published: December 2006

AbstractThe phase changes that took place upon heating an Fe-rich illite (OECD #5) to 1300°C in an oxidizing atmosphere were studied by a variety of mineralogical techniques. Infrared spectra, showing the stepwise dehydroxylation of the illite, showed good agreement with variations in sample colour and Mössbauer spectra. Dehydroxylation did not lead to noticeable variations in X-ray powder diffraction patterns until the structural breakdown of illite and formation of new phases at about 900°C Mössbauer spectroscopy proved to be very sensitive to all changes induced by heating, showing the disappearance of Fe2+ at 250°C, the gradual dehydroxylation between about 350 and 900°C, and characteristic features of the products formed at higher temperatures, e.g. the formation of hematite as the illite structure breaks down and the subsequent disappearance of hematite due to the incorporation of Fe in glass above 1200°C. The formation of hematite in clusters large enough to order magnetically at room temperature was first observed in the sample heated to 900°C, whereas at 4.2 K, significant proportions of a magnetically ordered phase could already be identified in the sample heated to 650°C.
Local ordering of chromium(III) in trioctahedral hydroxide sheets of stichtite studied by ion exchange chromatography
Authors: Hansen H. C. B. , Bender Koch C. 
Published: December 2006

AbstractStichtite is the layered Mg-Cr(III) hydroxide carbonate of the pyroaurite group. The possibility of describing Cr(III) short range order (SRO) in stichtite by use of ion chromatography of the Cr(III)-hydroxo species following acid dissolution of the compound is described. Two synthetic stichtites of similar composition (average Mg5.73Cr(III)2.27(OH)15.93(O)0.07(CO3)1.10·xH2O) prepared in the absence or presence of hydroxy-bridged Cr(III) dimers and a sample from Dundas, Tasmania, Mg6.29Ni(II)0.02Cr(III)0.90Al0.65Fe(III)0.15(OH)15.26(OH2)0.74(CO3)1.23·xH2O have been examined. Ion chromatography showed the highest degree of SRO for the Dundas stichtite. For the synthetic stichtites the sample synthesized from Cr(III) dimers had the highest SRO. No information on cation ordering could be extracted from powder X-ray diffraction data. Visible spectroscopy indicates that for constant Mg:Cr(III) ratio the crystal field splitting increases with increasing SRO. Two different OH-stretching IR absorption bands (3585 and 3472 cm−1) are assigned to OH coordinated to 3Mg and OH coordinated to 2MgCr or Mg2Cr, respectively.
Kinetics of phosphate sorption and desorption by synthetic aluminous goethite before and after thermal transformation to hematite
Authors: Ruan H. D. , Gilkes R. J. 
Published: December 2006

AbstractGoethite is an important component of many soils and its transformation to hematite by fire may affect phosphate retention. This study deals with the kinetics of phosphate sorption and desorption by synthetic aluminous goethites and their dehydroxylated products. Phosphate sorption and subsequent desorption were measured for periods up to 128 h. Phosphate sorption increased with equilibrium solution concentration, Al substitution and surface area, and decreased with increasing crystal size. The trend in amount of phosphate sorbed was: partially dehydroxylated goethite > hematite > goethite. Sorption and desorption kinetics are well described by the modified Elovich equation. Desorption of a minor proportion of the sorbed P was rapid and this was sometimes followed by minor resorption. The amount of P desorbed directly reflected the amount that was initially sorbed. Acid dissolution of the Fe oxides with sorbed phosphate suggested that most phosphate was present at the crystal surface and not in relatively poorly accessible micropores.