bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Uranyl Hydrolysis and Multiple Site-Binding Reactions on Adsorption of U(VI) to Montmorillonite
Authors: McKinley James P. , Zachara John M. , Smith Steven C. , Turner Gary D. 
Published: August 2006

AbstractAdsorption of uranyl to SWy-1 montmorillonite was evaluated experimentally and results were modeled to identify likely surface complexation reactions responsible for removal of uranyl from solution. Uranyl was contacted with SWy-1 montmorillonite in a NaCIO4 electrolyte solution at three ionic strengths (I = 0.001, 0.01, 0.1), at pH 4 to 8.5, in a N2(g) atmosphere. At low ionic strength, adsorption decreased from 95% at pH 4 to 75% at pH 6.8. At higher ionic strength, adsorption increased with pH from initial values less than 75%; adsorption edges for all ionic strengths coalesced above a pH of 7. A site-binding model was applied that treated SWy-1 as an aggregate of fixed-charge sites and edge sites analogous to gibbsite and silica. The concentration of fixed-charge sites was estimated as the cation exchange capacity, and non-preference exchange was assumed in calculating the contribution of fixed-charge sites to total uranyl adsorption. The concentration of edge sites was estimated by image analysis of transmission electron photomicrographs. Adsorption constants for uranyl binding to gibbsite and silica were determined by fitting to experimental data, and these adsorption constants were then used to simulate SWy-1 adsorption results. The best simulations were obtained with an ionization model in which AlOH2+ was the dominant aluminol surface species throughout the experimental range in pH. The pH-dependent aqueous speciation of uranyl was an important factor determining the magnitude of uranyl adsorption. At low ionic strength and low pH, adsorption by fixed-charge sites was predominant. The decrease in adsorption with increasing pH was caused by the formation of monovalent aqueous uranyl species, which were weakly bound to fixed-charge sites. At higher ionic strengths, competition with Na+ decreased the adsorption of UO22+ to fixed-charge sites. At higher pH, the most significant adsorption reactions were the binding of UO22+ to AlOH and of (UO2)3(OH)5+ to SiOH edge sites. Near-saturation of AlOH sites by UO22+ allowed significant contributions of SiOH sites to uranyl adsorption.
Iron Substitution in Soil and Synthetic Anatase
Authors: Schwertmann U. , Friedl J. , Pfab G. , Gehring A. U. 
Published: August 2006

AbstractIronIII for TiIV substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. Mössbauer- and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated FeIII in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm−1, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H2O/mol Fe. At 600°C structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiO5, was formed.
Migration of Cu Ions in Cu Montmorillonite Heated with and without Alkali Halides
Authors: Heller-Kallai L. , Mosser C. 
Published: August 2006

AbstractCu montmorillonite heated with or without potassium halide was studied by IR and ESR spectroscopy, supplemented by XRD measurements, microprobe and chemical analyses. It appears that on heating Cu montmorillonite, most of the Cu ions migrate into hexagonal cavities and eventually, when dehydroxylation occurs, into octahedral vacancies. Some Cu ions may penetrate into octahedral vacancies before dehydroxylation. In the presence of potassium halide, deprotonation facilitates penetration of Cu into octahedral vacancies. The presence within the layers of non-exchangeable Cu ions that are inaccessible to water does not necessarily cause the perturbation of OH bending vibrations conventionally attributed to migration of small cations into the structure. Such perturbation was only observed when the basal spacing was reduced to ~9.5Å.
Evolution of Benzylammonium-Vermiculite and Ornithine-Vermiculite Intercalates
Authors: de la Calle C. , Tejedor M. I. , Pons C. H. 
Published: August 2006

AbstractThis report consists of a study of l-ornithine hydrochloride-vermiculite and of benzylammonium hydrochloride-vermiculite complex. The evolution of these organo-vermiculite structures upon heating is studied by X-ray diffraction (XRD) as well as infrared spectroscopy.After heating vermiculite saturated with 1-ornithine cations, it shows condensation of interlayer ornithine molecules (peptide complexes). The stacking mode, opposing ditrigonal cavities, is not modified between aminoacid complex and peptide complex.For vermiculite saturated with benzylammonium cations, the stacking sequence changes through heating by changing benzylammonium to NH4+. This transformation implies a sliding of the layers over each other. The ditrigonal surface cavities become face to face, as in the original mica. There are no random translations as in the starting complex.
Evaluation of Kinetic Models for the Smectite to Illite Transformation
Authors: Elliott W. Crawford , Matisoff Gerald 
Published: August 2006

AbstractThree different models have been reported previously to describe the kinetics of the transformation of smectite to illite (Pytte 1982; Velde and Vasseur 1992; Huang et al. 1993). In order to evaluate the general utility of these models to calculate the timing and extent of this transformation, each model was applied to four different geologic settings (Denver Basin, Gulf Coast, the Salton Sea Geothermal System, and Paris Basin) in which the ages, geothermal gradients and potassium ion activities vary markedly. The model results are compared to the measured percentages of illite in illite/smectite (I/S) and the K/Ar ages of I/S (if available) to test the utility of a given model to a particular basin.Although individual models can be applied to study this transformation within a specific setting, none of these models was successful in simulating the transformation for all four basins. The Salton Sea was simulated best using the model by Huang et al. (1993), which incorporated an increased geothermal gradient during the last 20,000 years. These results indicate that a large fraction of illite formed due to this increased geothermal gradient, and underscores that temperature is a dominant kinetic factor in forming illite. The Denver Basin was simulated well by the models of Velde and Vasseur (1992) and Pytte (1982). The Gulf Coast was simulated very well by the model of Huang et al. (1993) using a term that terminates the transformation at 75% illite. For the Paris Basin, the results are mixed. The models can be refined by comparing the calculated and measured ages of illite such as the K/Ar ages of I/S to understand the thermal history of a particular basin. The calculated ages of illitization derived from these refined models can be used to indicate the time at which source rocks became thermally mature to form oil and gas.
Orientation of Trimethylphenylammonium (TMPA) on Wyoming Montmorillonite: Implications for Sorption of Aromatic Compounds
Authors: Stevens Jeffrey J. , Anderson Sharon J. 
Published: August 2006

AbstractThe orientation of TMPA cations on montmorillonite affects the adsorbate-accessible siloxane surface area and determines whether the TMPA phenyl ring can interact with other aromatic adsorbates by π-π interactions. The purpose of this study was to determine the orientation of TMPA ions in the interlayer of normal-charge and reduced-charge Wyoming montmorillonite. The orientation of TMPA's phenyl group was investigated using infrared dichroism of selected aromatic ring vibrations. X-ray diffraction (XRD) and MacEwan Fourier transforms were used to determine interlayer spacings and to ascertain whether reduced-charge Wyoming montmorillonite is a randomly interstratified mixture of layers with two different d-spacings. For normal-charge montmorillonite, the infrared results showed that the C-N bond axis is neither perpendicular nor parallel to the surface, yet X-ray data suggested that the TMPA phenyl ring is perpendicular or nearly perpendicular to the siloxane surface. In this orientation, the average adsorbate-accessible space between adjacent TMPA ions is 24 Å2, or about 1/3 of the total surface. When the phenyl ring of TMPA is perpendicular to the clay surface, aromatic compounds should be able to interact with TMPA's aromatic ring by π-π interactions, while polar compounds such as water can interact with positively charged nitrogen atom. The reduced-charge montmorillonite used in this study is a randomly interstratified mixture of about 25% collapsed layers with no adsorbed cations and 75% expanded layers that are propped open by TMPA's methyl groups, not by the aromatic ring. The adsorbate-accessible surface area on expanded layers of reduced-charge montmorillonite is 1.5 to 2 times that on normal-charge TMPA-clay, depending on the orientation of TMPA's aromatic ring.
Structural Transformations of Interstratified Illite-Smectites from Dolná Ves Hydrothermal Deposits: Dynamics and Mechanisms
Authors: Drits V. A. , Salyn A. L. , Šucha V. 
Published: August 2006

AbstractStructural transformations of illite-smectite samples of hydrothermal genesis with increasing contents of illite layers were studied by X-ray powder diffraction. The samples were K-saturated and subjected to wetting and drying cycles to increase three-dimensional structural ordering. Diffraction profiles were analyzed with the help of a specially devised computer program based on the approximation of individual diffraction reflections by “bell-shaped” functions, with minimization of the differences between experimental and simulated profiles. The data indicate that the transformations of these illite-smectite samples were accompanied not only by variations in the proportion of illite and smectite layers and in the pattern of their alternation, but also by a change in structure within 2:1 layers.
Sorption Mechanisms of Lanthanum on Oxide Minerals
Authors: Fendorf Scott , Fendorf Mark 
Published: August 2006

AbstractThe retention of hazardous species, including many of the lanthanides, on soils and sediments is vital for maintaining environmental quality. In this study, high-resolution transmission electron microscopy (HRTEM) was used to identify surface precipitates of La and their degree of atomic ordering on oxides of Mn (birnessite), Fe (goethite) and Ti (rutile) over a pH range of 3 to 8. At pH >5.5, the aqueous concentration of La was fully depleted by all three metal-oxides. On birnessite, surface precipitation of La-hydroxide occurred at pH = 5 and appears to be the dominant sorption mechanism on this mineral. Surface precipitation was not observed on rutile or goethite until much higher pH values, 6.5 for rutile and 8.0 for goethite. Precipitation is thus correlated with the points of zero charge (PZC) of the minerals, 6.3 for rutile and 7.8 for goethite, and in each case was observed only at pH values above the PZC. Although La sorption was extensive on all of the minerals at the higher pHs, the depletion of La from solution by rutile and goethite at pH values well below the PZC indicates that the sorption mechanism differs from that on birnessite. While surface precipitation was found to be the dominant sorption mechanism of La on birnessite, surface complexation of monomelic or small multinuclear species appears to predominate in La retention on rutile and goethite at most commonly encountered pH values.
Dissolution of Hectorite in Inorganic Acids
Authors: Komadel P. , Madejová J. , Janek M. , Gates W. P. , Kirkpatrick R. J. , Stucki J. W. 
Published: August 2006

AbstractThe effect of acid type and concentration on the reaction rate and products of dissolution of hectorite in inorganic acids was investigated. The dissolution of hectorite in hydrochloric (HCl), nitric (HNO3) and sulphuric (H2SO4) acids was characterized using quantitative chemical analysis, infrared (IR) and multinuclear MAS NMR spectroscopies. The rate of dissolution increased with acid concentration and decreased in the order HCl ≥ HNO3 = H2SO4 at the same molar concentration. No differences were found in the reaction products of hectorite treated with the three acids. The rate of Li dissolution was slightly greater than that of Mg at lesser acid concentrations (0.25 M), indicating that protons preferentially attack Li octahedra. The gradual changes in the Si-O IR bands reflects the extent of hectorite dissolution. The analysis of 29Si MAS NMR spectra relative peak intensities with dissolution time and acid concentration provided direct dissolution rates for tetrahedral (Q3) Si. After acid dissolution, most Si was bound in a three dimensional framework site (Q4), but a substantial part also occurred in the Si(OSi)3OH (Q31OH) and Si(OSi)2(OH)2 (Q220H) environments. These three sites probably occur in a hydrous amorphous silica phase. Both AlJV and AlVt rapidly disappeared from 27Al MAS NMR spectra of the dissolution products with acid treatment. The changes in IR and MAS NMR spectra of hectorite due to acid dissolution are similar to those of montmorillonite.
Tem Observations of Coherent Stacking Relations in Smectite, I/S and Illite of Shales: Evidence for MacEwan Crystallites and Dominance of 2M1 Polytypism
Authors: Dong Hailiang , Peacor Donald R. 
Published: August 2006

AbstractTEM characterization of stacking relations in I/S of expanded shale samples from the Gulf Coast and Michigan Basin was carried out to address the issues of the degree of coherency and the nature of layer stacking sequences in smectite, I/S and illite. The two-dimensional lattice fringe images obtained from this study show that cross fringes are commonly observed to be continuous over at least 3–4 layers for smectite, 6–7 layers for ordered I/S and 9–10 layers for illite-rich I/S. This demonstrates that such sequences are coherent, or at least semi-coherent (in smectite) units (MacEwan crystallites). The observations demonstrate that so-called fundamental particles are fragments of MacEwan crystallites formed primarily as a result of disaggregation along weakly-bonded smectite interlayers. However, both 0k1 and h01 reflections may coexist in selected area electron diffraction (SAED) patterns. The frequency of occurrence of the coexistence in SAED patterns decreases in the order smectite, I/S and illite for Gulf Coast samples. This is consistent with the presence of turbostratically-related interfaces in packets of all of these materials. Therefore, any given layer sequence in smectite, ordered I/S and illite may have both turbostratic and coherent interfaces. The proportion of coherently-related layers increases with increasing proportion of illite-like layers. The concept of fundamental or elementary particles is not related to layer sequences in non-disaggregated, original rocks. Indeed, it implies relations that are not valid.The lattice fringe images, SAED and optical diffraction patterns demonstrate that where layers are coherently-related, 2M1 is the dominant polytypic sequence in all samples. However, this periodic 2M1 stacking is so frequently interrupted by stacking faults in smectite that it gives rise to apparent lMd polytypism. The degree to which the periodic 2M1 sequences are interrupted by stacking faults decreases with increasing proportion of illite-like layers. The SAED patterns of I/S and illite unmodified since its formation are diffuse parallel to c* and have poorly-defined, non-periodic reflections for indices k ≠ 3N as a measure of local ordering superimposed on poorly-ordered coherent sequences with a turbostratic component. X-ray diffraction (XRD) patterns, as integrated over domains with a range of heterogeneous stacking relations, do not represent simple mixtures of discrete IM and 2M1 polytypes.The observations of this study imply that dissolution-crystallization is a dominant mechanism for the smectite-to-illite transition. The semi-coherent stacking of smectite-like layers in smectite-rich samples implies that either a dissolution-crystallization process took place subsequent to deposition of detrital smectite or that Gulf Coast smectite is an in-situ alteration product of volcanic ash.
Dickite, Nacrite and Possible Dickite/Nacrite Mixed-Layers from the Betic Cordilleras (Spain)
Authors: Ruiz Cruz M. D. 
Published: August 2006

AbstractNacrite, dickite and intermediate dickite-nacrite phases have been identified from the upper Paleozoic sequences of the Maláguide Complex (Betic Cordilleras, Spain). Nacrite developed as euhedral, pseudohexagonal or elongated crystals within sandstones and thin, irregular veins. Dickite developed preferently within extensive zones of fractures as very irregular, compact packets. Intermediate phases occurred in the sandstones and veins similar to the nacrite, or accompanying dickite. The mineral assemblage of the sandstones includes quartz-muscovite-kaolinite-type minerals, with or without albite, carbonates, chlorite and mixed-layers containing chlorite. The metamorphic conditions in which these minerals formed belong to anchizone, as can be deduced from the IC values. Dickite, nacrite and intermediate phases were studied by X-ray diffraction, infrared spectroscopy, differential thermal analysis and micros-copy. The results for dickite indicate a well-ordered mineral and agree with most of the published data. Conversely, IR spectra and DTA curves of nacrite show some differences in relation to the available data for this mineral. Based on the comparison with dickite and nacrite data, intermediate phases can be interpreted either as disordered varieties or as mixed-layered dickite/nacrite.
Angle-Resolved X-Ray Photoelectron Studies of Cleavage in Chlorites
Authors: Evans Stephen , Hiorns Anthony G. 
Published: August 2006

AbstractThe cleavage of two single-crystal chlorites (a clinochlore and a penninite) has been studied using angle-resolved X-ray photoelectron spectroscopy (XPS). Both minerals cleaved in regions not typical of the bulk; the composition of the clinochlore was found to be especially non-uniform. The brucitic interlayer divided evenly between the pair of new surfaces exposed for two cleaves in the clinochlore, but was partitioned unequally in two cleaves in the penninite. The differences in apparent composition between the complementary pairs of surfaces are interpreted to show a marked preference of octahedral Al for the brucitic layer, in agreement with X-ray bulk structure refinements. For both chlorites, the layer charge was reduced in regions of easy cleavage, which also had a higher proportion of Si and less tetrahedral Al than the bulk chlorite. The percentages of tetrahedral aluminium deduced from the XPS surface analyses agreed satisfactorily with the percentages independently determined by consideration of the magnitude of anisotropy in the X-ray photoelectron diffraction (XPD) patterns. The XPD patterns from the clinochlore for rotation about axes parallel and antiparallel to the crystallographic a-axis were identical, showing that tetrahedral ordering was absent.
Potential-Distance Relationships of Clay-Water Systems Considering the Stern Theory
Authors: Sridharan A. , Satyamurty P. V. 
Published: August 2006

AbstractThis paper deals with the use of Stern theory as applied to a clay-water electrolyte system, which is more realistic to understand the force system at micro level than the Gouy-Chapman theory. The influence of the Stern layer on potential-distance relationship has been presented quantitatively for certain specified clay-water systems and the results are compared with the Gouy-Chapman model. A detailed parametric study concerning the number of adsorption spots on the clay platelet, the thickness of the Stern layer, specific adsorption potential and the value of dielectric constant of the pore fluid in the Stern layer, was carried out. This study investigates that the potential obtained at any distance using the Stern theory is higher than that obtained by the Gouy-Chapman theory. The hydrated size of the ion is found to have a significant influence on the potential- distance relationship for a given clay, pore fluid characteristics and valence of the exchangeable ion.
Intercalation of N-Alkyltrimethylammonium into Swelling Fluoro-Mica
Authors: Tamura Kenji , Nakazawa Hiromoto 
Published: August 2006

AbstractTrimethylammonium ions (TMA+) with formula CH3(CH2)n-1N+(CH3)3, with n = 4, 8, 12, 16, 18 and 22 were intercalated into synthetic Li-fluorotaeniolite (Li-FTN) and Li-fluorohectorite (Li-FHT) by cation exchange. The products were analyzed by thermogravimetric (TGA) and X-ray powder diffraction (XRD). XRD patterns exhibited variable (001) spacings of the TMA+/mica complexes depending upon the exchange ratio of TMA+/Li+ and the carbon number of TMA+. Detailed inspection of these XRD patterns clarified the structures of the complexes and also the intercalation mechanism, as follows: The fundamental structure of the complexes is the commonly known intercalation structure where the “paraffin-type bilayers” of TMA+ are in the mica interlayer and their long chains incline at approximately 30° to the silicate sheet. This structure appeared at the final stage of the intercalation reaction. During the intermediate stage of the reaction, units of this structure and those of hydrated mica formed randomly and regularly interstratified structures. Variable (001) spacings in XRD patterns showed the structural change of the complex with an increasing number of TMA+-intercalated units.
Reduction of Structural Fe(III) in Smectite by a Pure Culture of Shewanella Putrefaciens Strain MR-1
Authors: Kostka Joel E. , Stucki Joseph W. , Nealson Kenneth H. , Wu Jun 
Published: August 2006

AbstractShewanella putrefaciens is a species of metal-reducing bacteria with a versatile respiratory metabolism. This study reports that S. putrefaciens strain MR-1 rapidly reduces Fe(III) within smectite clay minerals. Up to 15% of the structural Fe within ferruginous smectite (sample SWa-1, Source Clays Repository of the Clay Minerals Society) was reduced by MR-1 in 4 h, and a range of 25% to 41% of structural Fe was reduced after 6 to 12 d during culture. Conditions for which smectite reduction was optimal, that is, pH 5 to 6, at 25 to 37 °C, are consistent with an enzymatic process and not with simple chemical reduction. Smectite reduction required viable cells, and was coupled to energy generation and carbon metabolism for MR-1 cultures with smectite added as the sole electron acceptor. Iron(III) reduction catalyzed by MR-1 was inhibited under aerobic conditions, and under anaerobic conditions it was inhibited by the addition of nitrate as an alternate electron acceptor or by the metabolic inhibitors tetrachlorosali-cylanilide (TCS) or quinacrine hydrochloride. Genetic mutants of MR-1 deficient in anaerobic respiration reduced significantly less structural Fe than wild-type cells. In a minimal medium with formate or lactate as the electron donor, more than three times the amount of smectite was reduced over no-carbon controls. These data point to at least one mechanism that may be responsible for the microbial reduction of clay minerals within soils, namely, anaerobic respiration, and indicate that pure cultures of MR-1 provide an effective model system for soil scientists and mineralogists interested in clay reduction. Given the ubiquitous distribution and versatile metabolism of MR-1, these studies may have further implications for bioremediation and water quality in soils and sediments.