bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization and Assignment of Far Infrared Absorption Bands of K+ in Muscovite
Authors: Diaz M. , Farmer V. C. , Prost R. 
Published: August 2006

AbstractTo assign far infrared (FIR) absorption bands of K+ in muscovite, dichroic experiments were performed. For a muscovite crystal rotated about a crystallographic axis, c*, a, or b, two bands corresponding to vibration modes of K+ appear, respectively, at 107 and 110 cm−1 (rotation about c*), 107 and 143 cm−1 (rotation about a), and 110 and 143 cm−1 (rotation about b). Two in-plane modes at 107 and 110 cm−1 and one out-of-plane mode at 143 cm−1 are identified for the vibrations of K+ in muscovite. Each of these transition moments are near the crystallographic axes b, a, and c, respectively. These observations match well predictions based on the approximate C3i symmetric environment of K+, although the site symmetry in the space group of muscovite is only C2.
Quantitative Measurement of Paramagnetic Fe3+ in Kaolinite
Authors: Balan Etienne , Allard Thierry , Boizot Bruno , Morin Guillaume , Muller Jean-Pierre 
Published: August 2006

AbstractA method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.
Evolution of Fundamental-Particle Size during Illitization of Smectite and Implications for Reaction Mechanism
Authors: Środoń J. , Eberl D. D. , Drits V. A. 
Published: August 2006

AbstractArea-weighted thickness distributions of fundamental illite particles for samples of illite and illite-smectite from seven locations (including bentonites and hydrothermally altered pyroclastics) were measured by Pt-shadowing technique, by transmission electron microscopy. Most thickness distributions are described by lognormal distributions, which suggest a unique crystallization process. The shapes of lognormal distributions of fundamental illite particles can be calculated from the distribution mean because the shape parameters α and β2 are interrelated: β2= 0.107α − 0.03. This growth process was simulated by the mathematical Law of Proportionate Effect that generates lognormal distributions. Simulations indicated that illite particles grow from 2-nm thick illite nuclei by surface-controlled growth, i.e., the rate of growth is restricted by how rapid crystallization proceeds given a near infinite supply of reactants, and not by the rate of supply of reactants to the crystal surface. Initially formed, 2-nm thick crystals may nucleate and grow within smectite interlayers from material produced by dissolution of single smectite 2:1 layers, thereby transforming the clay from randomly interstratified (Reichweite, R = 0) to ordered (R = 1) illite-smectite after the smectite single layers dissolve. In this initial period of illite nucleation and growth, during which expandable layers range from 100 to 20%, illite crystals grow parallel to [001]* direction, and the dimensions of the (001) plane are confined to the size of the original smectite 2:1 layers. After nucleation ceases, illite crystals may continue to grow by surface-controlled growth, and the expandable-layer content ranges from 20 to 0%. This latter period of illitization is characterized by three-dimensional growth. Other crystal-growth mechanisms, such as Ostwald ripening, supply-controlled growth, and the coalescence of smectite layers, do not produce the observed evolution of α and β2and the observed shapes of crystal thickness distributions.
A New Method for the Prediction of Gibbs Free Energies of Formation of Hydrated Clay Minerals Based on the Electronegativity Scale
Authors: Vieillard Philippe 
Published: August 2006

AbstractA new method for the prediction of Gibbs free energies of formation for hydrated clay minerals is proposed based on the parameter ΔGO= Mz+(clay) characterizing the oxygen affinity of the cation Mz+. The Gibbs free energy of formation from constituent oxides is considered as the sum of the products of the molar fraction of an oxygen atom bound to any two cations multiplied by the electronegativity difference defined by the ΔGO= Mz+(clay) between any two consecutive cations. The ΔGO= Mz+(clay) value, using a weighting scheme involving the electronegativity of a cation in a specific site (interlayer, octahedral, or tetrahedral) is assumed to be constant and can be calculated by minimization of the difference between experimental Gibbs free energies (determined from solubility measurements) and calculated Gibbs free energies of formation from constituent oxides. Results indicate that this prediction method compared to other determinations, gives values within 0.5% of the experimentally estimated values. The relationships between ΔGO= Mz+(clay) corresponding to the electronegativity of a cation in either interlayer or octahedral sites and known ΔGO= Mz+(aq) were determined, thereby allowing the prediction of the electronegativity of transition metal ions and trivalent ions in hydrated interlayer sites and octahedral sites. Prediction of Gibbs free energies of formation of any clay mineral with various ions located in the interlayer and with different cations in octahedral sites is possible. Examples are given for Al-rich montmorillonite from Aberdeen, transition element-exchanged montmorillonite, and Ni-rich stevensite, and the results appear excellent when compared to experimental values.
A Nuclear Magnetic Resonance (NMR) and Fourier-Transform Infrared (FTIR) Study of Glycine Speciation on a Cd-Rich Montmorillonite
Authors: Di Leo Paola 
Published: August 2006

AbstractAs a consequence of treatments with glycine solutions, glycine molecules enter the interlayer of both Ca- and Cd-rich montmorillonite. Measurements of d value suggest that at low glycine concentration (0.01 and 0.1 M glycine solutions) a “flat” arrangement of the glycine molecules occurs in the interlayer. In contrast, intercalation of more than one monolayer of glycine molecules occurs for the montmorillonite treated with a higher concentration of glycine (1 M glycine solution).Interlayer complexation of glycine occurs only for the Cd-rich form of montmorillonite, whereas no complexation is observed for Ca-rich montmorillonite. Both nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) results suggest that the adsorbed glycine, which fully protonates in the interlayer of montmorillonite to give the GlyH2− species, interacts with the interlayer Cd2+ to form the CdGlyx complex mainly through the carboxylate group. The interlayer cadmium, present as both Cd2+ and CdCl−, is complexed by the ligand glycine. In contrast, the cadmium adsorbed on the external surfaces of montmorillonite does not interact with the ligand. Complexation of CdCl+ only occurs for large amounts of adsorption of glycine (e.g., for samples treated with 1 M glycine solution).
Effect of Phosphate on the Formation of Nanophase Lepidocrocite from Fe(II) Sulfate
Authors: Cumplido Jesús , Barrón Vidal , Torrent José 
Published: August 2006

AbstractThe effect of phosphate on the formation of Fe oxides from Fe(II) salts is important because phosphate is a ubiquitous anion in natural environments. For this reason, the products formed by oxidation of phosphate-containing Fe(II)SO4solutions neutralized with bicarbonate were characterized. The rate of oxidation of Fe(II) increased with increasing P/Fe atomic ratio to 0.2 in the initial solution. Goethite (α-FeOOH) or lepidocrocite (γ-FeOOH) or both were produced and identified by powder X-ray diffraction (XRD). The ratio between lepidocrocite and goethite increased with increasing P/Fe. In the 5–8.5 pH range, the formation of goethite predominated at P/Fe < 0.005, but only lepidocrocite was detected by XRD for P/Fe > 0.02. Thus, phosphate favors lepidocrocite formation because lepidocrocite has (1) a layered structure (like its precursor green rust), and (2) a structure less dense than that of goethite, thereby requiring less complete removal of the green-rust interlayer phosphate to form. The lepidocrocite crystals were platy, with prominent {010} faces and the thickness of the plates decreased with increasing P/Fe from >25 nm for P/Fe < 0.005 to <5 nm for P/Fe > 0.1. The solubility of lepidocrocite in acid oxalate was nearly complete for P/Fe > 0.03. The lepidocrocite contained occluded phosphate,i.e., phosphate that could not be desorbed by alkali treatment. The decrease in thebunit-cell length with increasing P/Fe suggests that lepidocrocite may contain structural P.
Formation of Banded Iron-Manganese Structures by Natural Microbial Communities
Authors: Tazaki Kazue 
Published: August 2006

AbstractMicrobial structures in the form of banded zebra patterns have been found as periodic iron-manganese layers in living biomats on the coast of Satsuma-Iwo Jima, a small volcanic island near southern Kyushu, Japan. Electron microscopic observation shows that coccus, fibrous, and bacillus-type bacterial communities construct zebra architecture Fe-Mn layers through biomineralization on and within cells. A living microbial fumarolic ferro-manganese precipitation growing in seawater around an active volcanic island explains one mechanism of banded formation. Biological processes form the elemental zebra pattern, with periodic distribution of bacterial cells with Fe-Mn in each layer of the architecture. Fibrous bacteria are sometimes mineralized with goethite, ferrihydrite, and buserite microcrystals, coated with granular mucoid substances. The biomineralization may then mature to form a recent stratified banded-iron formation. The Satsuma-Iwo Jima zebra architecture is unusual in that it forms under aerobic conditions in a warm shallow-water environment, in contrast to the intermittent oxidizing and reducing conditions in which deep-sea analogues develop.
Structural Chemistry of Fe, Mn, and Ni in Synthetic Hematites as Determined by Extended X-Ray Absorption Fine Structure Spectroscopy
Authors: Singh Balwant , Sherman D. M. , Gilkes R. J. , Wells M. , Mosselmans J. F. W. 
Published: August 2006

AbstractThe incorporation of transition metals into hematite may limit the aqueous concentration and bioavailabity of several important nutrients and toxic heavy metals. Before predicting how hematite controls metal-cation solubility, we must understand the mechanisms by which metal cations are incorporated into hematite. Thus, we have studied the mechanism for Ni2+ and Mn3+ uptake into hematite using extended X-ray absorption fine structures (EXAFS) spectroscopy. EXAFS measurements show that the coordination environment of Ni2+ in hematite corresponds to that resulting from Ni2+ replacing Fe3+. No evidence for NiO or Ni(OH)2 was found. The infrared spectrum of Ni-substituted hematite shows an OH-stretch band at 3168 cm−1 and Fe-OH bending modes at 892 and 796 cm−1. These vibrational bands are similar to those found in goethite. The results suggest that the substitution of Ni2+ for Fe3+ is coupled with the protonation of one of the hematite oxygen atoms to maintain charge balance.The solubility of Mn3+ in hematite is much less extensive than that of Ni2+ because of the strong Jahn-Teller distortion of Mn3+ in six-fold coordination. Structural evidence of Mn3+ substituting for Fe3+ in hematite was found for a composition of 3.3 mole % Mn2O3. However a sample with nominally 6.6 mole % Mn2O3 was found to consist of two phases: hematite and ramsdellite (MnO2). The results indicate that for cations, such as Mn3+ showing a strong Jahn-Teller effect, there is limited substitution in hematite.
Evaluation of the Acidity of Pillared Montmorillonites by Pyridine Adsorption
Authors: Sun Kou M. R. , Mendioroz S. , Muñoz V. 
Published: August 2006

AbstractTwo series of pillared clays were prepared from a purified montmorillonite (95%) from La Serrata of Nijar, Spain, and polycations of Al and Zr using various methods. The effect of both the pillaring cation and the procedure of preparation on the physicochemical characteristics of the resulting materials was studied. Changes in texture were determined by X-ray diffraction (XRD) and N2 adsorption at 76 K and changes in acidity were determined by thermogravimetry following pyridine adsorption at room temperature and further desorption at a constant heating rate of 10 K min−1 in the range of 298–623 K. The relation between the size and charge (n/q) of the pillaring cation, which is dependent on the degree of cation hydrolysis, is the main factor affecting pore size and acidity of the synthesized materials. The pH of the pillaring solution affects the stability of the parent clay and the properties of the pillared clay. Below a pH of 3 and depending on contact time, the montmorillonite may delaminate and partially dissolve to produce products that affect the properties of the resulting materials. Microporosity increases for both Al or Zr-pillared clays. For Zr-pillared clays, microporosity is accompanied by changes in the mesoporosity and macroporosity as a result of clay delamination. Acidity dramatically increases by pillaring, especially strong acidity, and the acid strength distribution depends on starting salt concentration, aging time, and temperature.
Geology and Characterization of Two Hydrothermal Nontronites from Weathered Metamorphic Rocks at the Uley Graphite Mine, South Australia
Authors: Keeling John L. , Raven Mark D. , Gates Will P. 
Published: August 2006

AbstractMining operations during the early 1990s at Uley Graphite Mine near Port Lincoln on southern Eyre Peninsula, South Australia, uncovered abundant nontronite veins in deeply weathered granulite facies schist, gneiss, and amphibolite of Palaeoproterozoic age. Two types of nontronite are present: a bright yellowish-green clay (NAu-1) distributed as veinlets and diffuse alteration zones within kaolinized schist and gneiss, and a massive to earthy, dark-brown clay (NAu-2) infilling fracture networks mainly in amphibolite or basic granulite. The nontronites are the product of low-temperature hydrothermal alteration of primary minerals, biotite, and amphibole. The principal chemical difference between NAu-1 and NAu-2 is a higher alumina content in NAu-1, which was either inherited during hydrothermal alteration of biotite in the host rock or acquired through recrystallization of nontronite during subsequent weathering and associated kaolinization. Sufficient bulk samples of both NAu-1 and NAu-2 were collected to supplement reference nontronite of the Source Clay Repository of The Clay Minerals Society. The clay fraction of the bulk samples is typically >85%. NAu-1 contains minor kaolin and quartz which are easily removed to give a high purity nontronite of composition M+1.05[Si6.98Al1.02][Al0.29Fe3.68Mg0.04]O20(OH)4, similar to that of nontronite from Garfield, Washington. NAu-2 contains fewer total impurities but the presence of trace amounts of submicron carbonate and iron oxyhydroxide requires additional chemical treatment to produce a nontronite of purity comparable to NAu-1. Composition of NAu-2 was calculated as M+0.72[Si7.55Al0.45][Fe3.83Mg0.05]O20(OH)4, although infrared data indicate that at least some Fe is in tetrahedral coordination.
Bleaching Properties of Alumina-Pillared Acid-Activated Montmorillonite
Authors: Falaras Polycarpos , Lezou Fani , Seiragakis Georgios , Petrakis Dimitrios 
Published: August 2006

AbstractThe bleaching of cottonseed oil by alumina-pillared (Al-pillared) acid-activated clays was investigated. Acid activation of a Ca-rich montmorillonite (CMS STx-1) following treatment with 1, 4, and 8 eq/L sulfuric-acid solutions, as well as subsequent pillaring with alumina, produces new materials. These materials have bleaching properties dependent upon the extent of activation of the clay prior to pillaring. The pillared acid-activated montmorillonites possessed higher bleaching efficiency compared to pillared products of the untreated clay. Mild activation of the montmorillonite matrix, pillaring with the Keggin ion [Al13O4(OH)24(H2O)12]7+, and calcination temperatures to 500°C produced materials with the best fractional degree of bleaching. Direct comparison to the performance of a commercial bleaching earth (Tonsil Optimum 214, Sud-Chemie AG. Moosburg, Germany) shows that the efficiency of the Al-pillared acid-activated montmorillonite may be improved. The optimization of the bleaching process is achieved via a judicious utilization of intermediate surface area, relatively high acidity, and enhanced pore volume.
The Effect of Thermal Treatment on Some of the Physicochemical Properties of a Bentonite
Authors: Sarikaya Yüksel , Önal Müşerref , Baran Bülent , Alemdaroğlu Tülay 
Published: August 2006

AbstractA white calcium bentonite (CaB) from the Kütahya region, Turkey, contains 35 wt. % opal-CT and 65 wt. 9c Ca-rich montmorillonite (CaM). Samples were heated at various temperatures between 100–1300°C for 2 h. Thermal gravimetric (TG), derivative thermal gravimetric (DTG), and differential thermal analysis (DTA) curves were determined. Adsorption and desorption of N2 at liquid N2 temperature for each heat-treated sample was determined. X-ray diffraction (XRD) and cation-exchange capacity (CEC) data were obtained. The change in the <d(001) value and the deformation of the crystal structure of CaM depend on temperature. Deformation is defined here as changes of the clay by dehydration, dehydroxylation, recrystallization, shrinkage, fracture, etc. The activation energies related to the dehydration and dehydroxylation of CaB calculated from the thermogravimetric data are 33 and 59 kJ mol−1, respectively. The average deformation enthalpies, in the respective temperature intervals between 200–700°C and 700–900°C, were estimated to be 25 and 205 kJ mol−1 using CEC data and an approach developed in this study. The specific surface area (S) and the specific micropore-mesopore volume (V) calculated from the adsorption and desorption data, respectively, show a “zig zag” variation with increasing temperature to 700°C, but decrease rapidly above this temperature. The S and V values were 43 m2 g−1 and 0.107 cm3 g−1, respectively, for untreated bentonite. They reach a maximum at 500°C and are 89 m2 g−1 and 0.149 cm3 g−1 respectively. The XRD data clearly show that, at 500°C, where the irreversible dehydration is completed without any change in the crystal structure, the porosity of CaM reaches its maximum.
Ion Exchange of Zeolite Na-Pc with Pb2+, Zn2+, and Ni2+ Ions
Authors: Moirou Aggeliki , Vaxevanidou Aikaterini , Christidis Georgios E. , Paspaliaris Ioannis 
Published: August 2006

AbstractThis paper examines the ion-exchange properties of synthetic zeolite Na-Pc, which was produced from perlite-waste fines and has a SiO2:Al2O3 ratio of 4.45:1 and a cation-exchange capacity (CEC) of 3.95 meq g−1. Although equilibrium is attained rapidly for all three metals, exchange is incomplete, with Ac(max) (maximum equilibrium fraction of the metal in the zeolite) being 0.95 for Pb, 0.76 for Zn, and 0.27 for Ni. In both Na → ½Pb and Na → ½Zn exchange, the normalized selectivity coefficient is virtually constant for NAC (normalized equilibrium fraction of the metal in the zeolite) values of ≤0.6, suggesting a pronounced homogeneity of the available exchange sites. The Gibbs standard free energy, ΔG°, of the Na → ½Pb exchange calculated from the normalized selectivity coefficient is −3.11 kJ eq−1 and, for the Na → ½Zn exchange, it is 2.75 kJ eq−1.Examination of the solid exchange products with X-ray diffraction (XRD) revealed a possible decrease in crystallinity of zeolite Pb-Pc as suggested by the significant broadening and disappearance of diffraction lines. This decrease is associated with a reduction of pore opening, as indicated from Fourier-transform infrared analysis (FTIR), which in turn results in a decrease of the amount of zeolitic water. Thermogra-vimetric-differential thermogravimetric (TG-DTG) analysis showed that water loss occurs in three steps, the relative significance of which depends on the type of exchangeable cation and subsequently on the type of complex formed with the cation and/or the zeolite channels. Zeolite Na-Pc might be utilized in environmental applications, such as the treatment of acid-mine drainage and electroplating effluents.
Thermal Decomposition of a Dickite-Hydrazine Intercalation Complex
Authors: Ruiz Cruz María Dolores , Franco Francisco 
Published: August 2006

AbstractThe intercalation complex of a low-defect dickite from Tarifa, Spain, with hydrazine was studied by high-temperature X-ray diffraction (HTXRD) differential thermal analysis (DTA), and ther-mogravimetry (TG). The X-ray diffraction (XRD) pattern obtained at room temperature indicated that the intercalation of hydrazine and H2O into dickite caused an increase of the basal spacing from 7.08 to 10.24 Å, which is slightly lower than the 10.4-Å spacing commonly observed after intercalation into kaolinite. Heating between 25–50°C produced a structural rearrangement of the complex, which decreased the basal spacing from 10.24 to 9.4 Å, and the resulting 9.4-Å complex was stable between 50–90°C. Heating between 90–300°C caused a gradual reduction in spacing, which occurred through a set of intermediate phases. These phases were interpreted to be interstratifications of intercalated and non-intercalated layers. These changes were also observed by DTA and TG. Two main endothermic reactions and two main stages of mass loss, respectively, were indicated in the DTA and the TG curves in the temperature range 25–200°C. This behavior suggests that intercalated molecules, hydrazine and H2O, occupied well-defined sites in the interlayer of the dickite. The intercalated molecules were lost in an ordered fashion as confirmed by the infrared analysis of the decomposition products; H2O was lost in the first stage and ammonia was identified in the second stage. Above 300°C, complete removal of the intercalated molecules restored the basal spacing of the dickite. However, the basal reflections were broadened, the relative intensities were changed, and changes in the dehydroxylation temperature indicated that the intercalation-desorption process induced some stacking disorder in the dickite structure.