bluuebunny/crossref_metadata_2025 huggingface dataset:
Refinement of the Crystal Structure of Cronstedtite-2H2
Authors: Hybler Jiří , Petříček Václav , Fábry Jan , Ďurovič Slavomil
Published: February 2003

The crystal structure of cronstedtite-2H2 was refined in a hexagonal cell, space group P63, Z = 2, using two acicular crystals from Wheal Maudlin, Cornwall, England, and from Pribram, Czech Republic. The Wheal Maudlin sample has the chemical composition <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">(Fe2.2912+Fe0.7093+)(Si1.298Fe0.7073+Al0.004)O5(OH)4 and the Příbram sample has the composition <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">(Fe2.2692+Fe0.7313+)(Si1.271Fe0.7243+Al0.005)O5(OH)4. The results of refinements are as follows: a = 5.500(1), c = 14.163(2) Å, V = 371.08(8) Å3, R = 3.83%, from 381 independent reflections, and a = 5.4927(1), c = 14.1481(2) Å, V = 369.70(4) Å3, R = 4.77%, from 1088 independent reflections for the Wheal Maudlin and Příbram samples, respectively. The best Fovs.Fc agreement was achieved when the structure was interpreted as merohedral twin; several possible twinning laws are discussed. The cronstedtite layer consists of one tetrahedral sheet and one octahedral sheet. There is one octahedral (M1) position, occupied by Fe only, and two tetrahedral (T1, T2) positions in the structure. Refinement of occupancy of tetrahedral sites led to values Si:Fe = 0.45:0.55(1) (Wheal Maudlin) and 0.432:0.568(8) (Příbram) in T1, and Si: Fe = 0.99:0.01(1) (Wheal Maudlin) and 0.888:0.112(7) (Příbram) in 72. Whereas the size of T1 is reasonable (average dT1-O = 1.693 Å (Wheal Maudlin), 1.691 Å (Příbram)), T2 is unusually large: (dT2-O= 1.740 Å (Wheal Maudlin), 1.737 Å (Příbram)) with respect to the small or almost zero Fe content. As an explanation, an alternative structure model comprising a certain amount of vacancies in T2 is presented. The tetrahedral rotation angle α is highly positive (+12.1° and +12.5° for the Wheal Maudlin and Příbram samples, respectively), and the layer belongs to the Franzini type A. Distortion parameters of octahedra and tetrahedra are given for both samples. One hydrogen atom engaged in the hydrogen bond was located in the Wheal Maudlin sample.
Effect of Acid and Alkali Treatments on Surface-Charge Properties of Selected Minerals
Authors: Jozefaciuk Grzegorz
Published: February 2003

Bentonite, biotite, illite, kaolin, vermiculite and zeolite were treated with 0.1, 1.0 and 5.0 mol. dm−3 HCl or NaOH. Suspensions of Na homoionic forms of the initial and the treated minerals were back titrated with 0.1 mol. dm−3 NaOH. From back-titration data variable surface charge, QV, vs. pH dependencies and apparent surface dissociation constant distribution functions were estimated. Variable charge vs. pH curves were scaled against cation exchange capacity at pH 7.2 to obtain actual charge, QA, vs. pH plots. In general both treatments led to an increase of QV, while the QA value increased and decreased depending on the mineral and the treatment. Products of 5 mol dm−3 NaOH action on zeolite and of 1 and 5 mol. dm−3 NaOH on kaolin apparently developed a positive surface charge below pH ∼3.7 and below ∼4.3, respectively.

The heterogeneity of charge-generating surface groups was observed in natural minerals. During acid treatment, the number of weakly-acidic surface functional groups increased while the number of groups of stronger acidic character decreased. The opposite was found for alkaline treatment: the number of surface groups of intermediate acidity increased and that of low acidity decreased.
Stability of Magadiite Between 20 and 100°C
Authors: Dietzel Martin , Letofsky-Papst Ilse
Published: February 2003

New experimental data with respect to the solubility of natural and synthesized magadiite at elevated temperatures and in alkaline solutions are presented. The results show that the solubility of magadiite increases according to the expression ln(Kmag) = −8146·T(K)−1 − 5.71 from 20 to 100°C (<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">(ΔGR0(Kmag)=19.6±0.3 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">ΔHR0(Kmag)=16.2±0.4kcalmol−1). The experimental results and the related data from the literature suggest that the formation of magadiite may be favored by a decrease of temperature and pH (pH >9) as well by large amounts of Na+ ions and low ionic strength. These effects are related to the value of <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">ΔHR0(Kmag), the distribution of dissolved silica species, the stoichiometry of magadiite, and the occurrence of negatively-charged species, respectively.
Preparation and Porous Properties of Materials Prepared by Selective Leaching of Phlogopite
Authors: Okada Kiyoshi , Nakazawa Noriyuki , Kameshima Yoshikazu , Yasumori Atsuo , Temuujin Jadambaa , MacKenzie Kenneth J. D. , Smith Mark E.
Published: February 2003

Porous silica products obtained by selective leaching of phlogopite using an acid solution were investigated by XRD, MAS NMR, SEM, TEM, DTA/TG, and N2 and Ar gas adsorptions. The phlogopite powder was leached by a nitric acid solution at various concentrations (0.01–10 M) at 5–150°C for 10 min–480 h. Selective leaching of the phlogopite powder became extensive when the concentration of nitric acid was >1 M. Only SiO2 remained after the treatment, the other components (MgO, Al2O3, K2O and Fe2O3) being selectively leached from the product. At higher leaching temperatures, the leaching rate became faster and the resulting maximum specific surface area of the porous silica product became larger at each leaching temperature. The porous silica products were found by SEM and TEM, to maintain their original platy particle shape even after the selective leaching. The 29Si MAS NMR spectra of the products, however, revealed that the linkage structure of SiO4 tetrahedra converted to a framework type from a layered type in the original phlogopite. The porous silica product with the maximum specific surface area (532 m2/g) was obtained by leaching in a nitric acid solution with concentration of 5 M at 90°C for 15 min. The pore-size distribution of the porous silica product was bimodal with micropores of ∼0.7 nm and mesopores of ∼4 nm. The pore size of the products changed from 0.7 nm to 4 nm and further to 6 nm with increased leaching time. The present results are discussed in relation to those reported for phlogopite by other workers.
Vibrational Analysis of Palygorskite and Sepiolite
Authors: McKeown David A. , Post Jeffrey E. , Etz Edgar S.
Published: February 2003

Lattice dynamic calculations for the sepiolite and palygorskite structures using polarized Raman and FTIR spectra provide a fundamental basis for interpreting spectral features by assigning vibrational modes. The Si-O stretch and O-Si-O bond bending force constants determined for palygorskite are similar to equivalent values calculated previously for other phyllosilicates. The Mg-O bond stretch values, on the other hand, are about half of those determined for the equivalent Al-O and Mg-O bond stretch environments in other phyllosilicates, suggesting that the bonding within the octahedral ribbons in palygorskite and sepiolite is weaker than that in the continuous octahedral sheets in micas. The weaker bonding allows more flexible octahedral environments in palygorskite and sepiolite, giving rise to higher probabilities for cation substitutions and vacancies relative to the micas. Above ∼700 cm−1 in the IR and 750 cm−1 in the Raman spectra, the eigenmodes are dominated by atomic displacements within the silicate sheets. Below 700 cm−1 the eigenmodes become mixed with motions among the Mg octahedra and the silicate sheets; the eigenmodes assigned to the most prominent peaks in the Raman spectra (near 700 cm−1) belong to this group. As mode frequencies decrease, the corresponding eigenmodes evolve from more localized Mg-O stretch, O-Mg-O bend and O-Si-O bend motions to longer-range motions such as silicate sheet deformations caused by silicate tetrahedra rotation and silicate sheet shearing around the Mg-octahedral sheets.
Hydrothermal Synthesis of Zn-Smectites
Authors: Higashi Shoji , Miki Kazuhiko , Komarneni Sridhar
Published: February 2003

Two varieties of Zn-smectite were synthesized hydrothermally: sauconite, with an ideal composition of Na0.4Zn3(Si3.6Al0.4)O10(OH)2·nH2O; and a Zn equivalent of hectorite, with an ideal composition of Na0.4 (Li0.4Zn2.6)Si4O10(OH)2·nH2O (referred to here as Zn-hectorite). For comparison, hydrothermal synthesis of the related trioctahedral smectites of hectorite, Na0.4(Li0.4Mg2.6)Si4O10(OH)2·nH2O and hectorites containing Cu, Co or Ni in the octahedral sheets instead of Mg were also attempted. The results showed that sauconite, Zn-hectorite and hectorite could be synthesized in the temperature range 100–125°C but hectorites containing Cu, Co or Ni in the octahedral sheet, under the same conditions or even at a temperature of 150°C, could not.
Infrared Evidence of Dioctahedral-Trioctahedral Site Occupancy in Palygorskite
Authors: Chahi A. , Petit S. , Decarreau A.
Published: February 2003

A Mg-rich palygorskite sample from phosphorite deposits of Ganntour (Morocco) with the structural formula <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">Si8(Mg2.6Al1.19Fe0.33III□0.88)Ca0.056Na0.024K0.104O20(OH)2(OH2)4⋅4H2O, was studied by FTIR spectroscopy. In both OH-stretching and OH-bending regions, there is evidence of dioctahedral Al2□OH, AlFe□OH and trioctahedral Mg3OH features, leading to a di-trioctahedral crystallochemical model of octahedral site occupancies in ribbons of Ganntour palygorskite.

This model, established through the IR spectroscopy study of a Mg-rich palygorskite, seems to be appropriate for many other palygorskites with lower Mg content in the octahedral sheet.
In Situ Characterization and Differentiation of Kaolinites in Lateritic Weathering Profiles Using Infrared Microspectroscopy
Authors: Beauvais Anicet , Bertaux Jacques
Published: February 2003

Lateritic weathering kaolinites have been characterized in situ and differentiated for the first time by means of infrared microspectroscopy (IRMS). Four classical OH-stretching bands have been observed in the Fourier transform infrared (FTIR) spectra, at 3695, 3668, 3650 and 3620 cm−1, denoted ν1, ν2, ν3 and ν4, respectively, plus a band at 3595 cm−1 associated with the octahedral substitution of Fe3+ for Al3+. Infrared microspectroscopy of thin-sections of lateritic weathering profiles provides useful information on the types of kaolinite present in different horizons of the profile. The spectra obtained from large well-ordered kaolinite crystals look like those obtained by diffuse reflectance in that, compared with the KBr disk spectra of <2 µm powders, bands at 3668 and 3650 cm−1 are enhanced, and the strong absorption of KBr disks at 3695 cm−1 is replaced by a broad weaker band from 3700–3680 cm−1. In laterites, these large well-ordered kaolinites often exhibit a band at 3595 cm−1 indicative of significant Fe3+ substitution for Al3+ in the structure. The IR microspectra obtained from regions of small, more poorly-ordered kaolinites do not differ so markedly from that of KBr disks. All show enhanced absorption around 3650 cm−1 compared with well-ordered kaolinites, indicating that the disorder is due, at least in part, to domains of dickite-like and/or nacrite-like stacking in their structure. The 3595 cm−1 band is always weaker than that of the well-ordered kaolinite in the same profile. The IRMS data from well-characterized reference kaolinites show that the ratio Aν2/Aν3 is a pertinent IR order index for kaolinites. The larger this index, the larger is the area of the 3595 cm−1 band, and the larger and the more ordered is the kaolinite sample. It is suggested that the diversity of FTIR spectra observed reflects intergrowths of kaolinite-dickite polymorphs, or at least mixtures of high- and low-defect kaolinites which are frequently encountered in the lateritic geosphere rather than pure kaolinitic phases. The largest kaolinites having secondary crystallized in voids are the most ordered and the most ferruginous and have been considered as useful mineralogical tracers of the recent evolution of old lateritic terrains.
Intercalation of Benzamide into Expanded Kaolinite Under Ambient Environmental Conditions
Authors: Kelleher B. P. , O'Dwyer T. F.
Published: February 2003

Waste kaolinite from a fertilizer industry was intercalated with n-methylformamide (NMF) under ambient conditions. The complex was washed, characterized and then reacted with benzamide (dissolved in ethanol) under similar conditions. Using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis (DTA), clear evidence of benzamide intercalation was observed after a reaction time of 48 h. The FTIR and DTA analysis also confirmed that the ethanol was not involved in the intercalation and that both NMF and benzamide are present in the interlayer region.
Effects of Oxyanions on the Edta-Promoted Dissolution of Goethite
Authors: Campbell Jillian L. , Eick Matthew J.
Published: February 2003

Organic ligands, such as EDTA, accelerate the dissolution of silicate and oxide minerals. In natural systems, oxyanions can compete with organic ligands for mineral surface sites thereby affecting ligand-promoted dissolution rates, either enhancing or inhibiting dissolution, depending upon pH. The influence of selenite, molybdate and phosphate on the EDTA-promoted dissolution of goethite has been examined and a mechanism proposed for the observed differences in dissolution rates over a pH range of 4–8. We propose that the surface complex formed by EDTA is the controlling factor for the observed dissolution rate, with mononuclear complexes accelerating dissolution compared to bi- or multinuclear complexes. Dissolution results from our experiments suggest that EDTA forms multinuclear complexes at pH values ⩾6 and mononuclear complexes at pH values <6. Dissolution results show that when the oxyanion and the EDTA are present in the system at concentrations nearly equalling the surface sites available for adsorption, the oxyanion reduces the adsorption of EDTA and inhibits dissolution. However, if the oxyanion is present at lower concentrations at pH values ⩾6, EDTA is adsorbed but the number of carboxylic groups that can bind to the surface is reduced causing the formation of mononuclear complexes. This shift to a weaker surface complex enhances the EDTA-promoted dissolution of goethite in the presence of the oxyanions compared to EDTA-promoted dissolution in their absence.
Influence of Silicate- and Magnesium-Specific Adsorption and Particle Shape on the Rheological Behavior of Mixed Serpentine-Goethite Suspensions
Authors: Tartaj P. , Cerpa A. , García-González M. T. , Serna C. J.
Published: February 2003

The influence of dissolved species and particle morphology on the electrokinetic behavior and the initial yield stress values of Cuban lateritic aqueous suspensions was studied. The lateritic samples were mixtures of serpentine and goethite in different relative proportions. The addition of silicate and Mg ionic species, which are normally found in natural waters used in industrial processes, affected the electrokinetic and flow behavior of the lateritic suspensions. Specific adsorption of these species on particle surfaces was shown by a shift of the isoelectric point and the maximum of the initial yield stress to more acidic pH (Si ionic species adsorption) and more basic pH (Mg ionic species adsorption), when compared to suspensions containing only non-adsorbing electrolytes. The initial yield-stress values determined in samples consisting entirely of goethite varied from sample to sample. A detailed crystallochemical characterization revealed that these changes were associated with the axial ratio (i.e. ratio of particle length to width) of the mineral particles. Goethite samples with larger particle size (smaller number of particles for a given solid concentration) and greater axial ratios presented initial yield-stress values greater than those goethites with smaller particle size and lower axial ratio.
A New Method for the Prediction of Gibbs Free Energies of Formation of Phyllosilicates (10 Å and 14 Å) Based on the Electronegativity Scale
Authors: Vieillard Philippe
Published: February 2003

The method for prediction of Gibbs free energies of formation, based on the parameter ΔGO=Mz+(clay) characterizing the oxygen affinity of the cation Mz+, on the smectites, considered as hydrated clay minerals, has been used for micas and brittle micas, and yielded underestimated values. This method of prediction can be improved by a new set of parameters ΔGO=Mz+(clay), characterizing the electronegativity of a cation in a specific site (interlayer, octahedral, tetrahedral in the 10 Å minerals), determined by minimizing the difference between experimental Gibbs free energies and calculated Gibbs free energies of formation from constituent oxides. By considering the crystal structure of 10 Å and 14 Å minerals, and assuming the same electronegativity of cations, ΔGO=Mz+(o), in the octahedral sheets, an attempt is made to determine the electronegativity of cations in the brucitic sheet, ΔGO=Mz+(b). The results indicate that this prediction method compared to other determinations, gives values within 0.25% of the experimentally-estim ated values. The relationships between ΔGO=Mz+(clay) corresponding to the electronegativity of a cation in the interlayer, octahedral, tetrahedral or brucitic sites and known ΔGO=Mz+(aq) were thus determined, allowing the determination of the electronegativity of transition metal ions and trivalent ions in each of the four sites and consequently contribute to the prediction of Gibbs free energies of formation of different micas and chlorites. Examples are given for low-Fe clinochlore whose solubility is measured experimentally and the results appear excellent when compared with experimental values.
Biogenic Saponite From an Active Submarine Hot Spring, Iceland
Authors: Geptner A. , Kristmannsdóttir H. , Kristjansson J. , Marteinsson V.
Published: February 2003

A study of the mineralogy, chemical composition and structure of poorly-crystalline saponite precipitated from a submarine hot spring in Eyjafjordur, northern Iceland is reported. Special emphasis was placed on the microstructures of the minerals and a possible connection with biological activity during their precipitation. The microstructures of the minerals were found to be very similar to specific clay minerals precipitated from geothermal vents in oceanic rift zones. The composition of the minerals was, however, found to be similar to magnesium silicate scales formed in geothermal installations in Iceland where geothermal waters were mixed with cold fresh waters. High contents of organic substances were found in the clay mineral samples as compared to geothermal precipitates from other localities. Microstructural features of the layer silicates in one of the samples suggest that a gelatinous substance was a precursor of the saponite clay. The organic matter content appears to be greater when the precipitates are more crystalline.
Site Occupancies by Iron in Nontronites
Authors: Gates W. P. , Slade P. G. , Manceau A. , Lanson B.
Published: February 2003

Twelve nontronites and two ferruginous smectites have been characterized with respect to Fe3+ occupancy of tetrahedral sites. The techniques used were near infrared, Fe-K X-ray absorption near-edge and X-ray absorption fine-structure spectroscopies, along with two X-ray diffraction techniques. The results show that calculations of the structural formulae of many nontronites should be adjusted to include Fe3+ in tetrahedral sites. The nontronite from Spokane County, Washington, (∼44% Fe2O3) is essentially an end-member with its non-siliceous tetrahedral sites occupied by Fe3+. Samples with chemical compositions similar to Garfield nontronite (∼36.5% Fe2O3) may have small amounts (<5% of total Fe3+) of tetrahedral Fe3+. Tetrahedral Fe3+ is unlikely to be present in samples containing less than ∼34% Fe2O3.
Solid-State Nuclear Magnetic Resonance Study of Sepiolite and Partially Dehydrated Sepiolite
Authors: Weir Mark R. , Kuang Wenxing , Facey Glenn A. , Detellier Christian
Published: February 2003

The assignment of the 29Si CP/MAS-NMR spectrum of naturally-occurring sepiolite clay was re-examined using 29Si COSY and 1H-29Si HETCOR pulse sequences. Each of the three main resonances at −92.1, −94.6 and −98.4 ppm has been attributed to one of the three pairs of equivalent Si nuclei in the basal plane, and the resonance at −85 ppm to Q2(Si-OH) Si nuclei. On the basis of the COSY experiment, the resonance at −92.1 ppm is unambiguously assigned to the intermediate, near-edge Si sites. The HETCOR experiment revealed that the resonance at −94.6 ppm cross-polarizes almost entirely from the Mg-OH protons, and therefore is assigned to the central Si position. The remaining resonance at −98.4 ppm correlates strongly to the protons of the structural water molecules and therefore is assigned to the edge Si sites. Nearly complete rehydration was achieved at room temperature by exposing sepiolite samples that had been partially dehydrated at 120°C to water vapor or to D2O vapor. The rehydration results support the 29Si NMR peak assignments that were made on the basis of the COSY and HETCOR experiments.

The 29Si CP/MAS-NMR spectrum corresponding to the folded sepiolite structure in which approximately one half of the structural water has been removed by heating to 350°C is reported for the first time. The chemical shift values and relative intensities are significantly different compared to the resonances that are observed in the corresponding spectrum of the true sepiolite anhydride. These observations support the earlier claim that sepiolite heated to ∼350°C exists as a distinct phase to be differentiated from that of the completely dehydrated state.
A Microwave-Assisted Method for the Rapid Removal of K From Phlogopite
Authors: Stout Stephen A. , Komarneni Sridhar
Published: February 2003

The ability to remove K rapidly with a solution containing sodium tetraphenylborate (NaTPB) from the interlayers of naturally-occurring phlogopite using a microwave-assisted technique has been examined. Samples were equilibrated with a 1.0 N sodium chloride (NaCl) – 0.2 N NaTPB – 0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at 60, 80 and 100°C under both conventional and microwave-assisted heating methods and for periods of time ranging from 1 to 3 h. The samples also underwent treatments of either continuous time periods or for successive treatments of 1 h with a washing step between each treatment.

Following sample treatment, the expansion of the c-axis value (d001) from 10.0 to 12.2 Å indicated the presence of hydrated Na ions in the phlogopite structure. Under most treatment conditions the 10.0 Å peak remained even after treatment due to incomplete K removal. Chemical analysis and X-ray diffraction (XRD) revealed that samples heated using microwave radiation exchanged their interlayer K for Na much more rapidly than under conventional heating for all treatment times and temperatures. The successive treatments also degraded the mica more rapidly than the continuous treatments. The greatest amount of K (95%) was removed when the mica was treated three times for 1 h at 60°C. The results suggest that successive treatments of phlogopite mica heated under microwave radiation will rapidly remove K from the mica. Decreasing the amount of time required to prepare K-depleted phlogopite micas will make these materials more appealing as ion exchangers for separation of Cs from nuclear wastes.
Local Order of the Transition Metals for the Substitution (Co1−yCuy)2Al(OH)6Cl·nH2O (0 ⩽ y ⩽ 1) in a Copper-Aluminum-Layered Double Hydroxide-Like Phase
Authors: Leroux Fabrice , Moujahid El Mostafa , Roussel Hervé , Flank Anne-Marie , Briois Valérie , Besse Jean-Pierre
Published: February 2003

The substitution in layered double hydroxide-like phases (LDH) of composition <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">(Co1−y2+Cuy2+)2Al3+(OH)6Cl−⋅nH2O(0⩽y⩽1) was studied by X-ray diffraction and X-ray absorption spectroscopy. It was found that the lamellar character is maintained over the entire range of the substitution. The local order for the composition {Co2Al} is typical of brucite-like sheets, whereas segregation into small domains may explain the results obtained when the percentage of Cu atoms is increased. The {Cu2Al} end-member material presents a local order around the Cu atoms closely related to the botallackite structure as present in basic layered Cu salts, with the presence of two distinct Cu-Cu distances.
Adsorption of Olefins on Aluminum- and Aluminum/Tetramethylammonium-Exchanged Bentonites
Authors: Moronta Alexander , Taylor Scott , Breen Christopher
Published: February 2003

One montmorillonite, STx-1 (Texas, USA), was activated with different amounts of Al and tetramethylammonium (TMA+) cations to obtain materials with a combined Al3+ and TMA+ content equal to its cation exchange capacity. The adsorption capacity of these samples was studied saturating them with hept-1-ene at room temperature. The samples were heated and the evolved gases analyzed by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. Hept-1-ene reacted with the clays via proton transfer and resulted in the formation of a variety of reaction products (>60 hydrocarbons). In general, the presence of TMA+ cations significantly reduced the population of protons to selectively produce isomerization and hydration products.
Dehydroxylation and Transformations of the 2:1 Phyllosilicate Pyrophyllite at Elevated Temperatures: An Infrared Spectroscopic Study
Authors: Wang Ling , Zhang Ming , Redfern Simon A. T. , Zhang Zhenyu
Published: February 2003

The thermally-induced dehydroxylation and transformations of the 2:1 phyllosilicate pyrophyllite have been studied using infrared spectroscopy in the frequency range 350–11000 cm−1 and the temperature range 200–1500°C. The dehydroxylation of pyrophyllite to pyrophyllite dehydroxylate occurs between 500 and 900°C. It is characterized by a decrease in the intensity of the OH signals and phonon bands of pyrophyllite and the eventual disappearance of these features as well as the appearance of extra signals related to pyrophyllite dehydroxylate and an intermediate phase. Our results are consistent with previous observations that the SiO4 tetrahedral sheet structure still exists in pyrophyllite dehydroxylate, that the Si-O-Al linkages and 2:1 structure remain in the pyrophyllite dehydroxylate, and that AlO5 trigonal bipyramids form.

Two extra OH bands at 3690 and 3702 cm−1 and their overtones at 7208 and 7234 cm−1 are observed, for the first time, in samples annealed at the temperature range 550–900°C. Our results suggest that the formation and dehydroxylation of the extra OH species can be strongly affected by kinetic effects. The experimental evidence shows that the dehydroxylation of pyrophyllite is a two-stage process. The appearance of these additional OH bands is interpreted in terms of an unknown intermediate phase, and may be related to the second endothermic peak observed at high temperatures in DTA experiments. Pyrophyllite dehydroylate decomposes into a Si-rich amorphous phase and mullite in the temperature range 950–1100°C. Cristobalite is observed in the temperature range 1150–1500°C.
Crystal-Size Distributions of Clays During Episodic Diagenesis: The Salton Sea Geothermal System
Authors: Kim Jin-wook , Peacor Donald R.
Published: February 2003

Crystal-size distributions (CSDs) for clay minerals with depth were measured from the Salton Sea Geothermal Field (SSGF) as a test for the presence and meaning of theoretical crystal-size distributions in a natural system. The SSGF is a classic open hydrothermal system, and crystals are forming directly without apparent modification of early-formed crystals, over a wide range of temperature. Thus, the measured CSDs are the actual distributions for a single episode in which all crystals grew at the same time from solution at different temperatures and depths, rather than through modifications of shallower samples.

Some TEM images of ion-milled samples from a range of depths were used to measure the crystal thicknesses of illite, chlorite and biotite. Grain-size histograms flatten, broaden and shift to larger sizes with increasing depth. Values of α and β were calculated and used to verify that the measured distributions are log normal. Reduced grain-size distributions for illite in SSGF samples obey steady-state constraints.

The observations appear to be consistent with evolution of illite with increasing depth in the SSGF system by growth in an open system giving rise to log-normal distributions, followed by supply-controlled growth in an open system. Because crystals at different depths grew simultaneously under different temperature and fluid conditions as a function of depth, they do not represent different stages of a single evolving system. The relations imply that isochemical and isothermal systems which permit an evolving system to be sampled are rare or non-existent. The data for distributions for a given depth in the SSGF are consistent with growth in an open system. The collective relations therefore imply that caution should be used in interpreting conditions of crystal growth in natural systems even where CSDs give results which are necessary for, but not sufficient to prove, a given modeled mechanism.
A New Extraction Procedure for Simultaneous Quantitative Determination of Water-Soluble Metals in Reaction Products of Clays and Inorganic Salts
Authors: Colina Fernando G. , Esplugas Santiago , Costa Jose
Published: February 2003

Kaolin, a possible source of Al, may be reacted with inorganic acids or salts to form different Al salts that can be further processed to prepare metallic Al. Although the reaction of kaolin and acid in aqueous solution can be monitored by chemical analysis of Al, the Al salts must be extracted from any unreacted kaolinite. Also, the lixiviation of Ti or Fe species present in kaolin should be monitored. A simple extraction procedure is reported to determine, quickly and quantitatively, water-soluble Al, Ti and Fe metals present in products of reaction of kaolin (85 wt.% kaolinite, 12 wt.% mica, 2 wt.% feldspar, 1 wt.% quartz) with inorganic salts, such as sodium hydrogensulfate, using conventional glassware for the glass reaction tubes. Optimum results are obtained with 250 mL glass reaction tubes. The best operating conditions found for this piece of equipment are: (1) sample weight of 0.05 g, (2) lixiviation time of 1 h, and (3) lixiviating agent, 50 mL of an aqueous solution of pH = 1 H2SO4 at its boiling point. Comparisons are made with soxhlet extraction and beaker and magnetic stirring methods.
Diffusion of H2O and I− in Expandable Mica and Montmorillonite Gels: Contribution of Bound H2O
Authors: Nakashima Yoshito
Published: February 2003

Self-diffusion coefficients of H2O molecules in water-rich gels of Na-rich expandable mica synthesized using natural talc were measured by pulsed-gradient spin-echo 1H nuclear magnetic resonance (NMR), and the dependence on mica fraction (0.00–43.8 wt.%) and temperature (30.0–60.9°C) was examined. On the basis of the NMR results, the self-diffusion coefficient of H2O, Dwater, in the gel can be expressed by ln(Dwater/D0water) = 1.64[exp( −0.0588w) - 1], where D0water is the self-diffusivity of bulk water at temperature and w is the weight fraction of the mica (wt.%). The activation energy of H2O diffusivity in mica gel is nearly equal to that in bulk water. These findings indicate that the normalized diffusivity, Dwater/D0water, is independent of temperature. The diffusivity of I−, Diodine, in the gels was examined by X-ray computed tomography (CT) at 22°C, and the influence of the mica fraction (0.00–24.8 wt.%) was studied to determine the contribution of bound H2O. The X-ray CT results show that the normalized I− diffusivity, Diodine/D0iodine, obeys the above-mentioned phenomenological curve where D0iodine is the I− diffusivity in bulk water. I− is non-sorbing, and thus its diffusion is restricted only by the geometrical complexity of the pore structure of gels. Therefore, the effect of bound H2O molecules on average H2O diffusivity is negligible for w <24.8 wt.%. Diffusivity is governed by free or unbound H2O molecules diffusing in the geometrically complex and tortuous pore structure of mica-mineral grains. This is a result of the large population of unbound H2O far from the grain surface compared to the small population of bound H2O near the grain surface. The diffusion of I− ions in montmorillonite gels was examined by X-ray CT for w <16.7 wt.% montmorillonite. The normalized iodine diffusivity, (Diodine/D0iodine) obtained is in reasonably close agreement with the literature data for the normalized diffusivity of H2O and is similar to the master curve of expandable mica. Therefore, bound H2O molecules near negatively charged clay surfaces do not play a major role in the H2O diffusivity for water-rich montmorillonite gels.
Monolayer to Bilayer Transitional Arrangements of Hexadecyltrimethylammonium Cations on Na-Montmorillonite
Authors: Bonczek James L. , Harris W. G. , Nkedi-Kizza Peter
Published: February 2003

A low-charge Na-montmorillonite (SWy-2) was exchanged with hexadecyltrimethyl-ammonium (HDTMA) at levels equal to 20, 40, 60, 70, 80, 90, 100, 150 and 200% of the cation exchange capacity (819 mmol(+)/kg) to determine the nature of adsorption and the ionic composition of the clay interlayers. In contrast with earlier work with smaller aliphatic cations, which suggested random interstratification of interlayers occupied by either organic or metallic cations, there was no evidence of cation segregation into homogeneous interlayers. Instead, X-ray analysis indicated that the organic cations assumed two dominant configurations which were roughly equivalent in prevalence at ∼70% coverage of the CEC. Below 70% exchange the organocations existed predominantly in heterogeneous monolayers with Na+, attaining basal spacings of between 1.41 and 1.44 nm which were sensitive to changes in relative humidity. Relative humidity effects indicated that Na+ and HDTMA occupied functionally discrete domains within the interlayer as shown by the free interaction of water and a neutral organic solute, naphthalene, with Na+ and HDTMA, respectively. At greater levels of HDTMA exchange (up to 100% of the CEC), the organocations assumed a predominantly bilayer configuration. Transition to a fully-developed bilayer indicated by a 1.77 nm d-spacing at 100% coverage was gradual, suggesting some interstratification of the monolayers and bilayer configurations between 70 and 100% exchange. Sorption of naphthalene to the organoclays within this range of coverage was well correlated with clay organic carbon content, consistent with relatively unimpeded interlayer access of neutral organic molecules.
Smectite Quasicrystals in Aqueous Solutions as a Function of Cationic Surfactant Concentration
Authors: Kuwaharada Satoru , Tateyama Hiroshi , Nishimura Satoshi , Hirosue Hideharu
Published: February 2003

Quasicrystals of synthetic fluoromagnesian smectite (FMS) in dodecyltrimethylammonium chloride (DTAC) solutions were investigated as a function of the DTAC concentration by wet type X-ray diffraction (XRD) ζ potential measurements, and dispersion and coagulation (DC) tests. The FMS had an electronegative potential and it was dispersed randomly in an aqueous suspension without DTAC. When the DTAC concentration was 0.002 mol/dm3, FMS tactoids started to develop a structure in which the layer thickness was 1.85 nm. At the isoelectric point, the DTAC concentration was 0.012 mol/dm3 and the FMS tactoid formed a regular stacked structure with a 2.25 nm layer thickness. As the ζ potential of FMS changed from negative to positive, the DC test and XRD measurement showed that the FMS association gradually changed from coagulation to dispersion, which indicates that the formation of the bilayer of surfactants on the surface of FMS produces a repulsion between DTA+ adsorbed on the silicate layer of the FMS surfaces. When the equilibrium concentration of DTAC in solution exceeded the critical micelle concentration (CMC), the ζ potential of FMS became greater than the previous values. The XRD analysis of this suspension showed that there were two kinds of rational FMS stackings; one has a layer thickness of 3.20 nm, and the other has a layer thickness of 5.45 nm due to an interstratified structure composed of 3.20 and 2.25 nm layers. The interstratified structure was confirmed by the calculated XRD profiles.
Hydroxyl-Stretching Bands in Polarized Micro-Raman Spectra of Oriented Single-Crystal Keokuk Kaolinite
Authors: Shoval S. , Yariv S. , Michaelian K. H. , Boudeulle M. , Panczer G.
Published: February 2003

Polarized micro-Raman spectra of a single large crystal of Keokuk kaolinite were recorded in the OH-stretching region with the laser beam directed along the different crystal axes. The Raman spectra are characterized by five OH-stretching bands at 3694, 3683, 3668, 3650 and 3620 cm−1 labeled A, Z, B, C and D, respectively. The relative intensities of these five bands depend on the orientation of the crystal and the scattering geometry. The spectra agree with the assertion that bands A and Z arise from out-of-plane vibrations, whereas band D corresponds to an in-plane vibration. The area ratios of the various bands were calculated from fitted curves of spectra recorded with the electric vector of the laser beam parallel to different crystallographic planes. The increments in the relative areas of bands B and C were parallel to those of bands A and Z and it appears that out-of-plane vibrations made considerable contributions to these bands also. From the change of area ratios with the change in the direction of the electric vector of the laser beam, bands A and Z were attributed to LO and TO frequencies of one inner-surface hydroxyl vibration. Bands A + Z, B, C and D were attributed to the vibrations of the hydroxyls assigned by Bish (1993) as OH(3), OH(4), OH(2) and OH(1), respectively. These observations were supported by photoacoustic and transmission IR spectra.
Syntheses and Characterization of Birnessite by Oxidizing Pyrochroite in Alkaline Conditions
Authors: Yang Deng S. , Wang Ming K.
Published: February 2003

Birnessite can be used as a precursor in the preparation of manganese oxides. Synthesis of pure birnessite is difficult because of a side reaction, which yields hausmannite. This study aimed to develop a modified oxidation-deprotonation reaction (ODPR) method to eliminate the formation of hausmannite, and to investigate the influence of alkalinity on the synthetic products. In contrast to the conventional synthesis of birnessite through oxygen or permanganate oxidation, the ODPR method can produce birnessite without any impurities, within 5 h, and in a reproducible fashion. The distinctive feature of the ODPR method is the bubbling of N2 gas into NaOH and Mn2+ solutions before mixing the NaOH with Mn2+, in order to keep oxygen away from each solution. As soon as white pyrochroite was formed, oxygen gas was forced in as an oxidant to initiate the oxidation reaction. A black suspension with a blue tint appeared after 5 h of reaction. These precipitates were collected and examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR) and Raman spectroscopy. The average oxidation state of the Mn oxides was also determined. The results showed that pure birnessite with good crystallinity was formed. Oxidation of 1 M NaOH mixed with Mn2+ solution formed random-stacked birnessite. However, the oxidation of 4 M NaOH mixed with Mn2+ formed birnessite. Random-stacked birnessite can be transformed into birnessite by ageing suspensions at 313 to 373 K.
Activity Diagrams of Zeolites: Implications for the Occurrences of Zeolites in Turkey and of Erionite Worldwide
Authors: Birsoy Rezan
Published: February 2003

Sedimentary zeolite occurrences are widespread in Central and Western Anatolia, Turkey. Erionite occurrences in Central Anatolia have significant health implications for inhabitants of the region. The widespread occurrences of zeolites are generally associated with volcano-sedimentary rocks and consist of low-temperature forms. The aim of the work was to define specifically the formation mechanism and chemical characteristics of these volcano-sedimentary deposits, and particularly, the stability conditions for erionite. The first step was to construct chemical potential diagrams and calculate thermodynamic data for erionite and Ca-saponite. Then, equilibrium activity diagrams were calculated for the zeolites and related minerals in the system of Ca-Na-K-Mg-Fe-Al-Si and H2O. Stability diagrams for log [aCa2+/(aH+)2] — log [aNa+/aH+] and log [aCa2+/(aH+)2] — log [aK+/aH+] for various saturation phase activities of Al3+ and SiO2 (aq) were plotted for sedimentary conditions. The coexisting phases and chemical characteristics of the each deposit were evaluated by examination of the activity diagrams. Deposits which do not include some of the common sedimentary zeolites, possibly have high Al3+ activity (equal to or greater than gibbsite saturation) or low SiO(aq) activity (less than quartz saturation) during formation. In addition, erionite was found to be very sensitive to the alkalinity of the system and is stable in only a limited range of thermochemical conditions.
Weathering of Chlorite: I. Reactions and Products in Microsystems Controlled by the Primary Mineral
Authors: Aspandiar Mehrooz F. , Eggleton Richard A.
Published: February 2003

The weathering of chlorite in hydrothermally-altered basalt was studied with XRD, TEM and electron microprobe to determine the type and orientation of secondary minerals. Optical examination indicated chlorite assemblages to have altered in two distinct microsites: one microsite near micro-fissures traversing the regolith units, and the other away from the continuous passages. In this paper, weathering mechanisms and products of chlorite present in microsites distant from the micro-fissures are reported. In all the regolith units the original chlorite grain remained intact and was pseudomorphed by secondary products. In the saprock, chlorite altered to corrensite with possible random interstratifications of chlorite and corrensite and corrensite and vermiculite. In the saprolite, corrensite altered to vermiculite. Parallelism of two axes of the products with the host indicated topotactic alteration. In the fine saprolite, vermiculite was found to alter to kaolinite via a randomly interstratified kaolinite-vermiculite stage with a high proportion of kaolinite. Goethite crystallized in between packets of kaolinite, vermiculite and kaolinite-vermiculite. Though the disruption of the crystal structure of vermiculite is necessary in its alteration to kaolinite, the reaction was such as to maintain parallelism of the c axis. The alteration of chlorite to vermiculite was characterized by the loss of Mg and Fe and minor Al, all ions considered to be lost from the brucite-like sheet of chlorite. The Fe released during the alteration of vermiculite to kaolinite is likely to have migrated to micropores to form goethite. The presence of interstratifications of the end-members of layer silicates involved in the reaction sequence suggests that interstratifications are common during layer silicate weathering in environments where space is limited and consequently solution and ionic transport passages are restrictive.
Zeolitization of a Phonolitic Ash Flow by Groundwater in the Laach Volcanic Area, Eifel, Germany
Authors: Bernhard Franz , Barth-Wirsching Ulrike
Published: February 2003

Field and experimental studies were performed to understand the formation conditions of the Nettetal zeolite deposit, Laach volcanic area, Germany. This deposit shows pronounced small- (cm) and large-scale (tens of meters) variations of zeolitization, despite the same phonolitic precursor glass throughout the occurrence. Zeolitization of the pyroclastic ash flow is restricted to three distinct layers that are 0.15 to 10 m thick and separated by fresh ash. The glassy matrix is altered to chabazite, phillipsite, analcime and K-feldspar in various combinations, whereas the pumice clasts are altered predominantly to chabazite. Mass changes during zeolite formation appear to be small, and Ca enrichment in chabazite and phillipsite may have occurred after their formation by cation exchange.

The zeolites and zeolite assemblages observed in the Nettetal deposit were experimentally reproduced by reacting the phonolitic glass at 100–200°C with distilled water and 0.01 M alkaline solutions as well as with varying solid/liquid ratios and grain-sizes. Chabazite and phillipsite represented metastable transition phases with respect to analcime and K-feldspar. A high solid/liquid ratio accelerated the conversion of glass to zeolites.

None of the classic models of zeolite formation is fully applicable to the Nettetal deposit. The most probable environment for zeolitization in this deposit is the stagnant fringe water zone immediately above the groundwater table. In this zone, representing a relatively closed system, favorable solution compositions for zeolite formation could have been developed rather quickly by glass-water interaction, which is not possible within the more thoroughly flushed deeper parts of the groundwater system. The three distinct zeolite layers are probably the result of temporarily changing groundwater levels.