bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intercalation of Al13-Polyethyleneoxide Complexes into Montmorillonite Clay
Authors: Montarges Emmanuelle , Michot Laurent J. , Lhote François , Fabien Thomas , Villieras Frédéric 
Published: August 2006

AbstractNovel promising modified clays adsorbents were synthesized by intercalating hydroxy-Al polymer associated with poly(ethyleneoxide) in the interlayer of montmorillonite. Two different PEOs of low molecular weight (600) and high molecular weight (100,000) were used. In both cases, the resulting materials are hydrolytically stable and display a slightly better crystallinity than the materials prepared in the absence of PEO. Thermal analysis and infrared spectroscopy indicate changes in the PEO molecular conformation after intercalation revealing interactions between the polycations and the organic molecules. The chain length of the polymer has a strong influence on the surface area of the pillared materials obtained after calcination at 500°C. The use of the high molecular weight polymer leads to products with a higher specific surface area (about 400 m2/g) whereas the lower molecular weight compound does not modify significantly the surface areas. This behavior can be explained by the different nature of the species intercalated in the interlayer. PEO(600) leads to isolated organometallic species whereas PEO(100,000) seems to lead to a network of complexed polycations linked by ethylene oxide units. In the case of the PEO(100,000), high amounts of polymer in the pillaring solution provoke a partial dissolution of the octahedral layer of the clay.
Decarbonation Behavior of Mg-Al-CO3 Hydrotalcite-like Compounds during Heat Treatment
Authors: Hibino Toshiyuki , Yamashita Yasumasa , Kosuge Katsunori , Tsunashima Atsumu 
Published: August 2006

AbstractHistorically, the decarbonation of Mg-Al-CO3 hydrotalcite-like compounds (HTlc) has been thought to occur between 400° and 500°C. The present work demonstrates that when HTlcs having the maximum Al content, Al/(Al + Mg) = 0.33, are heated to 500°C, 20–30% of the carbonates remain. The evolution of the remaining carbonates was observed as two maxima, at 600 and 900°C At these temperatures, Al ions go into MgO, and spinel (MgAl2O4) forms. Therefore, the carbonates are released as the Al ions migrate.At a lower Al content, Al/(Al + Mg) = 0.25, CO2 evolution is almost complete at 500°C. This HTlc has no maximum of CO2 evolution above 500°C. Lower charge densities, due to lower Al contents, lead to lower amounts of remaining carbonate anions.
Effects of Exchangeable Cations on Hydraulic Conductivity of a Marine Clay
Authors: Rao S. Narasimha , Mathew Paul K. 
Published: August 2006

AbstractA laboratory study of the hydraulic conductivity (HC) of a marine clay with monovalent, divalent and trivalent cations revealed large differences in HC. The exchangeable cations employed in this study are Na, K, NH4, Mg, Ca and Al in order of increasing valency. An interpretation of the results derived from consolidation tests suggests that HC is significantly affected by the valency and size of the adsorbed cations. An increase in the valency of the adsorbed cations leads to quicker rates of consolidation and higher HC, while, for a constant valency an increase in the hydrated radius of the adsorbed cations results in a lower rate of consolidation and HC. The reduction in HC was related to the dispersion and deflocculation of clay. Lower valency and higher hydrated radii of the exchangeable cations enable the double layer repulsive forces to predominate, thereby increase dispersion and deflocculation.
Nature of Structural Disorder in Natural Kaolinites: A New Model Based on Computer Simulation of Powder Diffraction Data and Electrostatic Energy Calculation
Authors: Artioli G. , Bellotto M. , Gualtieri A. , Pavese A. 
Published: August 2006

AbstractA new model for the description of the structural disorder in natural kaolinite materials is proposed, based on the stacking of two 1:1 layers and their enantiomorphs, and encompassing previously proposed models. The layers, where randomly stacked along the c axis (using probabilistic functions nested in recursive algorithms), correctly describe the observed powder diffraction patterns of natural kaolinites with any density of structural faults. The proposed model was evaluated using electrostatic energy calculations against earlier models of disorder based on layer shift, layer rotation, statistical occupancy of the Al octahedra, or enantiomorphic layers. The present 4-layer model has a minimum of potential energy with respect to the previous models. As expected, the fully ordered triclinic structure of kaolinite possesses the absolute minimum of potential energy.
A (1:1) 7-Å Fe Phase and its Transformation in Recent Sediments: An HRTEM and AEM Study
Authors: Amouric Marc , Parron Claude , Casalini Lionel , Giresse Pierre 
Published: August 2006

AbstractYoung marine green grains, from Fe-rich sediments, were studied by using HRTEM systematically combined with punctual microchemical EDX analyses. Experimental results demonstrated these grains were made of a mixture of very small phases (mainly 1:1 and 2:1 silicates layer phases) with a dominant 7-Å Fe specie. All the main crystallochemically characterized phases appeared intimately related in the same evolutionary process. Each of them experienced different and well described conversion mechanisms. So first, a starting original Fe-rich kaolinite recrystallized via solution into another particular 7-Å Fe-rich phase, the composition of which varies from a di-tri to a pure trioctahedral (Mg + Fe) end member.This Fe-rich 1:1 mineral is effectively not a classical one. Then crystallization of a 10Å, rather dioctahedral K-rich phase occurs at the expense of it, through 1:½:1 interstratified structures. Such an evolution takes place through a solid state mechanism in which one 10-Å layer replaces one 7-Å layer. Another part of mica-like structures may also directly develop after dissolution of original kaolinites. The development of 10-Å K-rich phases could be significative of the beginning of the glauconitization process in these grains.
Magnesium-Rich Clays of the Meerschaum Mines in the Amboseli Basin, Tanzania and Kenya
Authors: Hay R. L. , Hughes R. E. , Kyser T. K. , Glass H. D. , Liu J. 
Published: August 2006

AbstractThe Sinya Beds of the Amboseli Basin in Tanzania and Kenya consist largely of carbonate rocks and Mg-rich clays that are intensely deformed where exposed in and near former meerschaum mines. The carbonate rocks consist of limestone and dolomite in Tanzania, but only dolomite has been identified in Kenya. Sepiolite and mixed-layered kerolite/stevensite (Ke/St) are subordinate constituents of the carbonate rocks. The carbonate rocks and overlying bedded sepiolite were deposited in a semiarid lake basin at the foot of the large volcano Kilimanjaro. Calcite and dolomite of the carbonate rocks have δ18O values 4–6‰ lower than calcite and dolomite of the late Pleistocene Amboseli Clays, suggesting that the Sinya Beds were deposited in the middle or early Pleistocene under a different climatic regime when meteoric water had lower δ18O values than at present.Mg-rich clay minerals form veins and fill cavities in the Sinya Beds. The principal clay minerals are sepiolite and Ke/St, some of which contains substantial Al and Fe (Al-Ke/St). NEWMOD® modeling and other X-ray diffraction (XRD) data suggest that most of the Ke/St contains 25–50 percent kerolite layers, but minor amounts of kerolite-rich Ke/St are present in some samples. Illite with an inferred high content of Fe or Mg is a minor constituent of the samples with Al-Ke/St. The cavity-filling clays were chemically precipitated, as shown by field relationships and SEM study. The early-deposited clays of veins and cavities are principally Ke/St with minor sepiolite, and the latest clay is sepiolite (meerschaum), generally with minor Ke/St.The δ18O values of cavity-filling Ke/St range from 22.5–25.6‰ and correlate with mineral composition, with the highest values associated with the highest content of stevensite and the lowest values with the highest content of kerolite. This relation suggests that high salinities favored stevensite and low salinities favored kerolite. δ18O values of sepiolite (meerschaum) fall in the middle of the range for Ke/St, suggesting that salinity was not the main control on sepiolite precipitation. High values of aSiO2/aMg2+ may have been a major factor in sepiolite precipitation.Different mixtures of dilute ground water and saline, alkaline lake water in pore fluids may largely account for the differences in clay mineralogy of cavity-filling clays. Sepiolite is the dominant clay mineral in lacustrine sediments of the Amboseli Basin, and the cavity-filling sepiolite may reflect a high proportion of lake water. The low-Al Ke/St may have formed from fluids with a higher proportion of ground water. Detrital clay was very likely a factor in forming the Al-Ke/St, for which δ18O values suggest a saline environment.
Some Evidence Supporting the Existence of Polar Layers in Mixed-Layer Illite/Smectite
Authors: Cuadros J. , Linares J. 
Published: August 2006

AbstractThe fraction <20 μm of a bentonitic material was selected to study the transformation of smectite into illite under hydrothermal conditions. Powder XRD showed that the studied material was composed of 97% dioctahedral smectite and 3% of quartz, cristobalite and plagioclase. The XRD analysis of the oriented, glycolated sample showed that the smectitic phase was actually a randomly interstratified illite/smectite with 11% illite. The chemical analysis of the sample yielded the structural formula: K0.25Na0.25Ca0.12Mg0.13(Al2.76Fe0.33Mg1.03)(Si7.66Al0.34)O20(OH)4. The reaction conditions of the hydrothermal experiments were: KCl concentrations 0.025, 0.05, 0.1, 0.3, 0.5, 1 M; temperature 60, 120, 175, 200°C; run time 1, 5, 15, 30, 90, 180 days; solid: solution ratio 1:5. XRD of run products showed an important transformation of smectite into illite, in contrast with all other techniques (DTA, IR, NMR), which did not detect any transformation of the original material. This suggests that illite quantification in I/S by means of XRD patterns after hydrothermal experiences can be much affected by other variables. The original material and the run products were analysed by means of DTA. The starting material displayed two dehydroxylation peaks, one at 560°C corresponding to illite, and the other at 650°C corresponding to smectite. Quantification of the two dehydroxylation peaks also yielded a content of 11% illite. The run products displayed DTA diagrams in which the smectitic peak remained unaltered, but the illitic one was reduced or eliminated by the presence of exchangeable K in the interlayer. When exchangeable K was removed the illitic dehydroxylation peak appeared again. The coherence of XRD and DTA in quantifying the proportion of illite layers and the effect of exchangeable K on dehydroxylation of illite layers in mixed-layer illite/smectite seem to be positive proofs of the existence of polar layers.
The Hydrophilicity and Hydrophobicity of Clay Minerals
Authors: van Oss C. J. , Giese R. F. 
Published: August 2006

AbstractThe terms “hydrophobic” and “hydrophilic” are typically used in a non-specific sense and, as such, they have a limited utility. Surface thermodynamic theory, as described here, allows a natural and potentially powerful definition of these terms. The boundary between hydrophobicity and hydrophilicity occurs when the difference between the apolar attraction and the polar repulsion between molecules or particles of material (1) immersed in water (w) is equal to the cohesive polar attraction between the water molecules. Under these conditions, the interfacial free energy of interaction between particles of 1, immersed in water (ignoring electrostatic interactions), exactly zero. When is positive, the interaction of the material with water dominates and the surface of the material is hydrophilic; when is negative, the polar cohesive attraction between the water molecules dominates and the material is hydrophobic. Thus, the sign of defines the nature of the surface and the magnitude of may be used as the natural quantitative measure of the surface hydrophobicity or hydrophilicity.
Instability of SiO2 Colloids and Sorption of Ca2+ Ions
Authors: Chan Sook Peng , Fraser David S. , Cheng Stephen Y. S. , Xu Yingnian , Koga Yoshikata 
Published: August 2006

AbstractSiO2 sols were made unstable by addition of Ca2+ ions. The resulting states of instability were classified as gelation, flocculation, and precipitation by means of observation, by checking the Tyndall effects on the supernatant or suspending solution, as appropriate, and by measuring the apparent densities of flocculated mass. The concentrations of free Ca2+ ions left in solution were measured by means of a Ca2+ ion selective electrode. The amounts sorbed onto SiO2 particles were then calculated by material balance. It was found that while the amount sorbed dictates the limit of stability, the SiO2 concentration in the mixture is an important factor deciding the state of instability. Depending on the SiO2 concentration, there were two distinct flocs with the apparent floc density of 6 ± 1 and 12 ± 1 mg SiO2/ml.
Hydrothermal Synthesis (250°C) of Copper-Substituted Kaolinites
Authors: Petit Sabine , Decarreau Alain , Mosser Christine , Ehret Gabrielle , Grauby Olivier 
Published: August 2006

AbstractTo obtain Cu-kaolinites with a controlled range of chemical compositions, syntheses were performed by hydrothermally ageing gels with kaolinite stoichiometric compositions. Gels were prepared with sodium metasilicate and nitrates of octahedral cations. Temperature of synthesis was 250°C with a corresponding equilibrium water pressure of 38 bars.Three samples with copper contents ranging from 0.1 to 7% and another one with the chemical composition of the Cu end-member were synthesized. While this fourth sample led to tenorite after the hydrothermal treatment, the three others crystallized well into kaolinite.Up to almost 1% CuO was measured by TEM in some isolated ‘clean’ and hexagonal kaolinite particles. EPR and XPS spectroscopies were consistent with an octahedral position of Cu2+. In IR spectra, vAl-OH-Cu absorption bands were not observed, but vAl2OH bands appeared more and more blurred when Cu content of samples increased. Weak bands situated at 868 cm−1 and 840 cm−1 are tentatively attributed to δAlCuOH. By differential thermal analysis, a downward shift of 20°C in temperature of the endothermic peak from the less Cu-rich sample to the most Cu-rich one, argued for the existence of some Al-OH-Cu bonds, whose binding energies are presumed to be less than the Al-OH-Al ones.In view of these results, Cu2+ appears incorporated in the octahedral sheet of kaolinite. Moreover, this incorporation is made without major perturbation of the kaolinite structure.
Lead-210 Derived Sedimentation Rates from a North Louisiana Paper-Mill Effluent Reservoir
Authors: Pizzolato William N. , De Hon René A. 
Published: August 2006

AbstractLower Wham Brake is a cypress, rim-swamp artificially enclosed in 1950 as a 22 km2 industrial reservoir by the International Paper Company (IPC)-Bastrop Mill, for regulating downstream water quality. Sediment cores were examined by XRD to differentiate paper-mill effluent deposition from the underlying detrital sediments and by 210Pb decay spectroscopy to determine sediment accretion rates.Anatase and kaolin from the IPC paper-mill effluent delineated a well-defined, anthropic, silty-clay, A horizon above a clay, 2Ag horizon. Anatase concentrations were no greater than 1.7% in the A horizon and was absent in the underlying 2Agl horizon. Kaolin deposition was significantly correlated to the A horizon by an average increase of 84% above the kaolinite detrital background. Pyrite was detected in the A horizon as a transformation mineral following sulfur reduction of the paper-mill effluent.Five of the six sediment cores showed an inflection in the excess 210Pb activity profile consistent with a present-day reduction in sediment supply. The average modern sedimentation rate was 0.05 cm yr−1. Average sedimentation observed during historic accretion was 0.22 cm yr−1, about 4.4 times greater than the modern rate of accretion. Reduction in sediment accretion can be attributed to upstream levees completed in 1934 and loss of organic accumulation following the 1950 reservoir impoundment. However, radiometric dating could not precisely correlate the geochronology of kaolin/anatase introduction due to complex oxidation/reduction cycles concurrent with the modern accretion regime.
Beidellite in E Horizons of Northern Idaho Spodosols Formed in Volcanic Ash
Authors: McDaniel P. A. , Falen A. L. , Tice K. R. , Graham R. C. , Fendorf S. E. 
Published: August 2006

AbstractWhile soils formed in tephra are typically dominated by poorly crystalline clay minerals, the occurrence of smectite in E horizons of podzolized soils (Spodosols) has been well-documented. We have observed a well-crystallized smectite mineral dominating the clay fraction of E horizons in tephra-derived soils of northern Idaho. This study was initiated to examine properties and distribution of this mineral along a developmental sequence of high-elevation, forested Spodosols formed in 6800-yr-old Mazama tephra. Three soils exhibiting strong, moderate, and weak E horizon development were sampled along an elevational and climatic gradient. The smectite mineral was identified as beidellite based on expansion and layer charge characteristics. Heated, Li-saturated samples from the most strongly developed E horizon exhibited relatively complete expansion to 1.8 nm with glycerol solvation and mean layer charge was calculated to be 0.44 molc/formula unit using sorption characteristics of alkylammonium ions. Apparent crystallinity and relative abundance of the beidellite in clay fractions decrease with decreasing E horizon development. The more poorly crystalline beidellite is associated with a non-expansive 1.4-nm mineral with considerable Al-hydroxy interlayering. Beidellite was not detected in underlying glacial drift or in a thin layer of 200-yr-old ash that mantles these soils, suggesting it is not inherited from these materials. Rather, our results indicate that beidellite forms in these soils in an environment characterized by low pH and a large flux of organic metal-complexing agents.
Flocculation and Coagulation of Ca- and Mg-Saturated Montmorillonite in the Presence of a Neutral Polysaccharide
Authors: Fuller L. G. , Goh Tee Boon , Oscarson D. W. , Biliaderis C. G. 
Published: August 2006

AbstractThe objective of this study was to observe flocculation of montmorillonite in the presence of a glucose polymer (dextran) and to observe the effect of saturating cation and coagulant addition on the flocculation process. Flocculation of montmorillonite was dependent on polymer molecular weight, polymer/clay ratio (w/w), nature of exchangeable cation, and ionic strength of the suspension to which the polymer was added. The T500 dextran (molecular weight = 5 × 105) caused enhanced sedimentation of Ca-montmorillonite suspension at a polymer/clay ratio of ≤0.01. Increasing the polymer concentration above this level stabilized the suspension such that sedimentation was less than or equal to that of the control. The T2000 dextran (molecular weight = 2 × 106) caused a similar increase in the sedimentation of Ca-montmorillonite at polymer/clay ratios of <0.1. The ability of the T2000 polymer to cause flocculation at greater polymer/clay ratios as compared to the T500 polymer was attributed to the lower osmotic pressure between clay particles for equal concentrations of the two polymers. Flocculation of Ca-montmorillonite by dextran was enhanced when the clay had initially been coagulated by the addition of salt. Reduction of the diffuse double layer upon addition of salt permitted the polymer to extend beyond the electrostatic barrier of the clays. Dextran was not able to flocculate Mg-montmorillonite suspensions with or without the presence of coagulant. The displacement of water molecules at the clay surface rather than within the hydration shell of the more highly polarizing Mg cations by polymer segments resulted in a greater polymer collapse on the clay surface leaving fewer and shorter polymer loops and tails available for contacting adjacent clay particles.
Clay Mineral Thermometry—A Critical Perspective
Authors: Essene E. J. , Peacor D. R. 
Published: August 2006

AbstractDiagenetic clay minerals usually occur as heterogeneous assemblages of submicroscopic layers consisting of different structure types such as illite, smectite and chlorite, with variable composition within a given structure type, and with highly variable concentrations of imperfections. The dimensions of mixed-layering, the semi-coherent to coherent nature of the structures across the layering, and compositional heterogeneity occur at a scale well below that of an individual thermodynamic phase. These relations imply that most clays are not distinct minerals or phases, and that assemblages of clays in shales and mudstones are incompatible with the phase rule. Such relations are better evaluated in terms of the formation of metastable materials with each small unit having unique chemical properties, rather than as a small number of stable homogeneous phases. Consequently, treatment of most clay minerals in terms of equilibrium stability with either a thermodynamic or experimental approach is subject to error.Chemical reactions involving most clay minerals are best understood with kinetic models. These involve a great variety of parameters such as time, fluid/rock ratio, deformation history, nature of starting materials and transformation mechanisms, as well as the variables, such as temperature, pressure and composition, that are commonly used to define equilibrium. Solubility experiments on the stabilities of clay minerals are unlikely to attain equilibrium at low temperatures. Moreover, the activity of soluble species may be controlled by surface equilibria, or by absorbed or exchangeable cations. Interpretations of available experiments on the solubility of illite vs. other mineral assemblages are in violation of Schreinemakers’ rules and indicate lack of equilibrium.Predictable sequences of clay minerals as a function of temperature are best understood through the Ostwald step rule, in which clay mineral assemblages undergo reactions in response to kinetic factors that represent reaction progress rather than an approach to equilibrium. Currently used clay mineral thermometers (illite crystallinity, smectite/illite reaction, chlorite composition) are not based on equilibrium reactions. Such systems are not accurate thermometers and therefore have questionable utility.