bluuebunny/crossref_metadata_2025_split huggingface dataset:
Las bentonitas sedimentarias de la formacion fardes, Granada, España
Authors: Sebastian Pardo E. , Aguayo F. Lopez , Huertas F. , Linares F. 
Published: December 2006

ResumenLa formación Fardes consiste en secuencias alternadas de turbiditas y hemipelagitas. Estos sedimentos han sido silicificados diagenéticamente y se presentan como estratos gruesos de color amarillo, que contienen jarosita y sideronatrita, inicialmente depositados en un medio reductor. Los niveles hemipelagíticos se pueden considerar por su composición quimica y mineralógica como bentonitas, compuestas principalmente de esmectitas, mica y cuarzo. En algunos casos se han encontrado asimismo, calcita, dolomita, halita y yeso. En la fracción <2 µm el mineral más abundante es la esmectita (48%) seguido por la palygorskita y la mica (28% y 32% respectivamente). La composición de la esmectita corresponde a los miembros ricos en Fe de la serie nontronita-beidellita; las micas son verdaderas moscovitas y la paligorskita tiene contenidos anormalmente altos de Fe y Al. Evidencias mineralógicas y geoquimicas indican que estas bentonitas son productos de alteración de rocas volcánicas, posiblemente, andesitas calcoalcalinas.
Re-examination of the kinetics of the thermal dehydroxylation of kaolinite
Authors: Criado J. M. , Ortega A. , Real C. , De Torres E. Torres 
Published: December 2006

AbstractThe results obtained from this study of kaolinite dehydroxylation explain why different investigators have ascribed both first-order kinetics and a diffusion mechanism to this reaction. The fact that activation energies reported by these workers agree well, in spite of the different kinetics assumed when performing the calculations, is also explained. From a comparison of the results obtained by isothermal and non-isothermal methods it is concluded that, for reacted fractions,α, <0·6, kaolinite dehydroxylation is controlled by a diffusion process. A reaction mechanism explaining this behaviour is proposed.
Characterization of X-ray amorphous material in a Scottish soil by selective chemical techniques
Authors: Smith B. F. L. , Mitchell B. D. 
Published: December 2006

AbstractMixed SiO2-Al2O3-Fe2O3 gel systems are a feature of many Scottish soils. They are usually associated with the surface of primary soil particles and consequently when present even in small amounts can have an effect on soil properties incommensurate with the proportion present. Currently, chemical dissolution methods provide the most satisfactory means of assessment. A range of chemical techniques, including dissolution by alkali, dithionite, acid oxalate and pyrophosphate, trimethylsilylation and fluoride exchange, have been used to examine the inorganic gel in a Scottish brown forest soil developed on glacial till derived from epidiorite. The reactivity of the gel, as determined by fluoride exchange, is similar to that reported for Japanese and New Zealand allophanic soils.
The use of combined thermal analysis to study crystallization, pore structure, catalytic activity and deactivation of synthetic zeolites
Authors: Gabelica Z. , Nagy J. B. , Derouane E. G. , Gilson J.-P. 
Published: December 2006

AbstractEmphasis is placed on the advantages of combining simultaneous thermal analysis methods (TG-DTA-DTG) with other complementary physico-chemical techniques for investigating synthesis and various properties of zeolites belonging to the pentasil family. TG and DTA give quantitative information on the dehydration and decomposition of organic guest molecules that interact with intermediate phases obtained during hydrothermal transformation of amorphous aluminosilicate gels into crystalline zeolites. In particular, weight losses (TG) and heat effects (DTA) due to the oxidative decomposition of tetrapropylammonium ions occluded in an intermediate phase have been related to the amount of zeolite ZSM-5 present. As a result, very small particles of this zeolite, amorphous to X-rays, could be detected in the early stages of the crystallization process. Isothermal sorption of small hydrocarbon molecules (n-hexane, 3-methyl-pentane) is used to probe the intracrystalline pore volume of zeolite ZSM-5. The total hydrocarbon uptake (TG) and the shape of the corresponding DTA peak are sensitive to steric modifications of the ZSM-5 channel system by various chemicals, while the sorption rates are better correlated to the extent of zeolite surface poisoning by boron or carbon. TG-DTA data provide an easy means of describing the filling and packing ofn-hexane in ZSM-5 pore structure. Various steps characterizing isothermal competitive sorptions (nitrogen, ethylene, water) or catalytic conversions at high temperature (ethylene, methanol) over H-ZSM-5 are described. Finally, the progressive formation (removal) of carbonaceous residues resulting from these transformations are related to the actual rate of de-activation (re-activation) of a zeolitic material. In this respect, three different synthetic zeolites, namely mordenite, offretite and H-ZSM-5, which differ by their shape-selective properties and structure of their channel network, are investigated by TG.
Magnesia from seawater: a review
Authors: Bhatti A. S. , Dollimore D. , Dyer A. 
Published: December 2006

AbstractThe process developed in the UK to produce magnesium hydroxide from seawater is described, together with the heat treatment that the hydroxide receives to produce the active oxide. Some of the characteristics required of the dolomite used in the process are also discussed. Impurities introduced by the seawater are noted and the means by which they can be reduced explained.
Study of the water-bentonite system by vapour adsorption, immersion calorimetry and X-ray techniques: I. Micropore volumes and internal surface areas, following Dubinin's theory
Authors: Kraehenbuehl F. , Stoeckli H.F. , Brunner F. , Kahr G. , Mueller-Vonmoos M. 
Published: December 2006

AbstractThe adsorption and desorption of water, the layer spacing of the montmorillonite with increasing water content and the heat of immersion with water have been measured for a Na-bentonite and two Ca-bentonites. The bentonite-water system is treated in terms of a micropore-filling process. Uptake of water occurs in discrete stages as the montmorillonite structure expands and the internal surface is calculated from these discrete stages of water adsorption.
L'alteration directe de muscovites et de biotites en halloysite: mise en evidence par microscopie electronique a balayage
Authors: Esteoule-Choux J. , Blanchet C. 
Published: December 2006

ResumeL'altération de biotites et de muscovites en halloysite a été mise en évidence par l'étude en MEB dans l'altération de roches granitiques et de micaschistes. Cette transformation débute par le développement d'un réseau losangique à la surface des feuillets de micas. La croissance par épitaxie de tubes d'halloysite est parfois accompagnée par celle de cristaux de goethite. Le MEB montre que l'halloysite se forme directement à partir du mica et qu'elle apparaît dans les tous premiers stades de l'altération, quelles que soient les conditions.
The dissolution of asbestos fibres in water
Authors: Gronow Janet R. 
Published: December 2006

AbstractThe interaction of chrysotile and crocidolite with water has been investigated in an attempt to identify the factors affecting the rate and the degree of dissolution of asbestos fibres within groundwater systems at landfill sites. Dissolution experiments were used to investigate rate laws and to obtain apparent activation energies for the dissolution of the two minerals. The activation energies related to transport-controlled processes, but as the overall dissolution occurred so slowly it was unlikely to be controlled by processes with such low activation energies. Congruent dissolution of both minerals tended to increase with temperature and time, suggesting that in the long-term environmental situation, congruent dissolution of these two asbestos minerals would occur. However these experiments show that, as the reaction was so slow, there is little likelihood of reduction of the asbestos pollution hazard by the complete dissolution of fibres on prolonged contact with natural waters.
Filtration of clay suspensions through sand
Authors: Ives K. J. 
Published: December 2006

AbstractThe filtration of suspensions containing clay and other particles in water is a common process in drinking water treatment. Such filtration processes are very efficient, producing clear water containing less than 1 mg/l from suspensions with particle concentrations of up to 100 mg/l. This filtration is not straining, but a process of collection of clay particles on the sand surfaces in the pores. The clays may range in size from sub-micron to ∼20 µm, and may be flocculated, and are retained in pores ∼200 µm in size within sand grains ∼500 µm in diameter. The collection process has three principal components (i) transport of clay particles across laminar water streamlines by diffusion, gravity and hydrodynamic forces, (ii) attachment by electrical or van der Waals' forces with hydrodynamic forces intervening, (iii) detachment by fluid shear or instabilities caused by arriving particles. Mathematical and physical models relate suspension concentration, quantity of deposit and permeability to depth in a filter, and time of operation. Fibre-optic endoscopes with CCTV enable video recordings to be made of the behaviour of clay particles in the filter pores, at magnifications up to 500 ×.
Adsorption-desorption of sotalol hydrochloride by Na-montmorillonite
Authors: Sánchez-Camazano M. , Sánchez-Martín M. J. , Vicente M. T. , Dominguez-Gil A. 
Published: December 2006

AbstractThe interaction of montmorillonite with sotalol hydrochloride (4-(1-hydroxy-N-isopropylaminoethyl) methane sulfanilide) was studied by means of adsorption isotherms, XRD and IR spectroscopy. The amount of sotalol adsorbed depended on pH, the maximum amount adsorbed (0·56 mEq g−1) being considerably less than the exchange capacity of the mineral (0·80 mEq g−1). XRD and IR data revealed that the sotalol is adsorbed into the interlayer space, forming a monolayer complex with a d001 spacing of 17·7 Å, and that the mechanisms involved are cation exchange and ion-dipole interactions. Experiments on the in vitro desorption of the drug from the sotalol-montmorillonite complex indicated that desorption is affected by pH, by the salt concentration of the electrolyte, and by the elimination rate of the desorbed organic cations.
Mineralogy of a hydrothermal sequence in a core from the Atlantis II Deep, Red Sea
Authors: Singer A. , Stoffers P. 
Published: December 2006

AbstractThe clay fractions from a 1191-cm long sediment core in the SW Basin of the Atlantis II Deep, Red Sea, were investigated by XRD, electron microscopy and chemical analysis. Talc dominates in the botton portion of the core, near the brine discharge vent. At 1183 cm depth, the clay consists of vermiculite/chlorite and chrysotile. These minerals are of hydrothermal origin and two possible formation pathways are proposed: (i) vermiculite/chlorite and chrysotile formed by the submarine alteration of previously deposited talc; (ii) vermiculite/chlorite and chrysotile authigenically precipitated as a result of changes in the chemical composition of the brine. At 1170 cm depth, a new depositional sequence results from the progressive alteration of swelling 2:1 minerals into vermiculite. At 1025 cm, Mg-rich clay minerals such as chlorite, chrysotile and talc again become prominent. The upper part of the core is characterized by a transition from non-expanding Mg-rich clay minerals to Fe-rich expanding clays, principally nontronite. Periodically, the content of well-crystallized oxides such as hematite in the layers increases. At 1025 cm, some of the Fe-oxides have a morphology similar to that of akaganéite. In the uppermost part of the core, iron oxides appear to consist of a poorly crystalline hydrothermal hematite. An attempt has been made to correlate the various mineralogical assemblages geochemically.
Analysis of illite-smectite interstratification
Authors: Corbató C. E. , Tettenhorst R. T. 
Published: December 2006

AbstractA new approach to understanding illite-smectite interstratification is formulated which incorporates the concepts of interparticle diffraction and elementary illite particles. The analysis shows that nearest-neighbour ordering, non-nearest-neighbour ordering, ordering at the illite end of the composition scale, and the lack of ordering at the smectite end can be explained by expandable interfaces between elementary, i.e. two silicate layers, and larger illite particles. Ordering in I/S clays is significant only when the probability of occurrence of illite is ∼80%. New concepts proposed are an order parameter (ω) and an expansion parameter (β). Interparticle diffraction implies that I/S clays are unusual among all crystalline materials since their XRD size is equal to or larger than the size of their constituent physically separable particles.
Sorption of ethylene glycol monoethyl ether (EGME) on homoionic montmorillonites
Authors: Kellomäki A. , Nieminen P. , Ritamäki L. 
Published: December 2006

AbstractSorption isotherms of ethylene glycol monoethyl ether (EGME) on homoionic Na−, K−, Mg− and Ca-montmorillonites at 25°C were determined. The extent of sorption was found to depend on the exchangeable cations, being larger for the bivalent ionic forms. Uptake of EGME was compared with the retention value obtained by evacuation of the sample wetted with EGME and also interpreted from XRD data. The results indicate that the montmorillonite-EGME complex formed by sorption at the saturation vapour pressure is stable and less ambiguous than after wetting by EGME. Montmorillonites are not suitable reference materials for surface area measurements.
An unusually expandable low-charge vermiculite
Authors: Justo A. , Maqueda C. , Pérez-Rodríguez J. L. , Lagaly G. 
Published: December 2006

AbstractA lamellar macroscopic Mg-vermiculite from Santa Olalla, Spain, which is accompanied by some talc and mica, shows a reversible expansion on glycolation due to the presence of layers with two different charges. The most probable origin of the vermiculite is by low-temperature hydrothermal transformation of phlogopite.
Decarboxylation catalytique de l'acide oxaloacetique en presence de montmorillonite
Authors: Siffert B. , Naidja A. 
Published: December 2006

ResumeLa décarboxylation de l'acide oxaloacétique en acide pyruvique a été étudiée en présence de montmorillonite saturée en cations différents et des mêmes cations à l'état libre (non incorporés). L'action catalytique dépend de la nature du cation, cést-à-dire de sa facilité à former des complexes avec l'acide oxaloacétique. Le réseau argileux intervient dans la catalyse essentiellement par les atomes d'aluminium (ou de fer) situés sur les bords des feuillets argileux. Il joue le rôle d'un métalloenzyme biologique. Le calcul des énergies d'activation pour les différents systèmes met bien en évidence l'activité catalytique de l'argile. En présence du phyllosilicate, la réaction a lieu avec un bon rendement jusqu'à une température de 60°C.
Utilisation de la diffractometrie X pour la determination des constituants amorphes dans les sediments marins (silice biogene et cendres volcaniques)
Authors: Lapaquellerie Y. 
Published: December 2006

ResumeLa détermination des complexes silico-ferriques, hydroxydes métalliques ou autres matériaux amorphes ou pseudocristallins contenus dans les sédiments marins est généralement difficile. La méthode décrite utilise la diffractométrie de RX et permet l'analyse quantitative de quelques-uns de ces matériaux tels que la silice biogène ou les cendres volcaniques. Cette phase amorphe constitue une composante majeure dans certains sédiments marins, d'où la nécessité de pouvoir la quantifier. La méthode reste suffisamment simple, fiable et précise pour permettre aussi la détermination quantitative de la phase cristallisée qui lui est généralement associée.
Analysis of cation distribution in dioctahedral micaceous minerals on the basis of IR spectroscopy data
Authors: Besson G. , Drits V. A. , Daynyak L. G. , Smoliar B. B. 
Published: December 2006

AbstractA method is described for IR spectroscopy whereby combining statistical analysis with the quantitative method described by Slonimskaya et al. (1986) results in more informative spectra. Application of this method to dioctahedral micaceous minerals with vacant trans octahedra has revealed a number of peculiarities in the octahedral cation distribution. This distribution is never completely disordered in the samples studied and shows maximum degree of short-range order in minerals having predominant Al.
Oxidative decarboxylation of isocitric acid in the presence of montmorillonite
Authors: Naidja A. , Siffert B. 
Published: December 2006

AbstractIsocitric acid oxidative decarboxylation was realized in the absence and in the presence of homoionic Na+-, Mn2+-, and Cu2+-montmorillonite. The catalytic activity of the clay depends upon the nature of the interlayer exchangeable cation. Isocitric acid is transformed into α-ketoglutaric acid under the action of the clay mineral saturated with Na+ cations which do not form a complex with the isocitrate anion. Nevertheless, the reaction rate is very much lower than in the presence of the enzymatic system (isocitrate dehydrogenase enzyme and nicotinamide adenine dinucleotide phosphate coenzyme). The reaction mechanism in the presence of clay is given showing the different steps of the transformation.
Surface properties and clay mineralogy of hydrated halloysitic soil clays. I: Existence of interlayer K+specific sites
Authors: Delvaux B. , Herbillon A. J. , Dufey J. E. , Vielvoye L. 
Published: December 2006

AbstractSix deferrated clay (<2 µm) samples from the major B horizons of pedons derived from basaltic pyroclasts (Western Cameroon) were selected. These soil clays, which differ mainly in their contents of halloysite and kaolinite, represent the types of secondary constituents characteristic of different weathering stages in soils derived from such volcanic materials under humid tropical conditions. On these clays, Ca2+-K+exchange equilibria were performed at pH 6 and 0·01nchloride concentration. The amounts of K+specific sites were estimated through a two-site modelling of the exchange isotherm curves. The total and external surface areas of the clays were measured by EGME retention and by the BET treatment of the N2adsorption isotherm, respectively. Relative halloysite content was found to be directly related to all measured surface charge properties,i.e.CEC, amount of K+specific sites, and total and internal surface areas. It was also observed that thermal collapse of halloysitic layers reduced both the CEC and the amount of K+specific sites. All the surface properties observed point to the presence of smectite units intimately associated with halloysite in these clays. The results further suggest that the layer charge of these smectite units differs in different samples.
Formation of synthetic analogues of double metal-hydroxy carbonate minerals under controlled pH conditions: I. The synthesis of pyroaurite and reevesite
Authors: Hansen H. C. B. , Taylor R. M. 
Published: December 2006

AbstractTwo-layered Fe(III)-M(II) hydroxy carbonates (M(II) = Ni or Mg) have been synthesized by induced hydrolysis using controlled air oxidation of an aqueous Fe(II)-M(II) mixture (M(II)/Fe(II) ratio >3) at a pH below which the hydroxide of the M(II) cation precipitates. The crystalline, homogeneous product can be a single phase consisting of very thin circular to hexagonal plates (0·2–0·8 µm diam.). For synthetic reevesite (Ni(II)-Fe(III) hydroxy carbonate), stable spherular aggregates are formed. The well crystallized products have an M(II)/Fe(III) ratio of about two. However, by varying the pH, the initial M(II)-Fe(III) ratio and the oxidation rate, the M(II)/Fe(III) ratio in the product and its crystallinity can be varied. The derived formulae are in reasonable agreement with the known composition of pyroaurite-type compounds. Possible synthesis pathways are discussed. The ability to control some physical and morphological features of the products indicates that the synthesis technique could prove advantageous in the preparation of certain catalyst precursors.
Magnetic ordering in Garfield nontronite under applied magnetic fields
Authors: Murad E. , Cashion J. D. , Brown L. J. 
Published: December 2006

AbstractMössbauer spectra of Garfield nontronite H33a were taken at temperatures between 2·5 and 37 K under longitudinally applied magnetic fields up to 9 T. While no magnetic order was apparent in the absence of an applied field above 7 K, the application of external magnetic fields led to the induction of magnetic hyperfine splitting up to at least 19 K. Variation of the applied fields allowed determination of hyperfine fields of bulk nontronite, and indicated the bulk sample to have a Néel temperature of about 20 K. The non-ideal behaviour of this nontronite, leading to the lack of magnetic order in the absence of applied magnetic fields, is in line with the frustration of antiferromagnetic order in the octahedral sheets due to the presence of about 6% of the iron content in tetrahedral sites, although some influence of magnetic dilution cannot be excluded.
Spectroscopic (ESR, EXAFS) evidence of Cu for (Al-Mg) substitution in octahedral sheets of smectites
Authors: Mosser C. , Mestdagh M. , D'Ecarreau A. , Herbillon A. J. 
Published: December 2006

AbstractESR has been used to obtain information on the octahedral or interlamellar position of Cu(II) in natural smectites from Burkina Faso (West Africa). On the basis of 060 XRD reflections and chemical data, these smectites were found to be Al-rich and dioctahedral. After both Mehra & Jackson, and De Endredy deferrification treatments, the Cu contents remained high (4500 and 22000 p.p.m., respectively). The Cu(II) ESR spectra of these deferrated smectites were compared to those of two reference smectites for which the structural position of Cu(II) was precisely known. The interlayer Cu(II) signal was obtained on a Cu-saturated Camp Berteau montmorillonite, while the octahedral Cu(II) signal was obtained on a synthetic Cu-rich smectite. For this latter reference sample, EXAFS spectroscopy provided evidence that Cu was in six-fold coordination in the octahedral sheet only, and was not exchangeable. In agreement with the experiments by Clementz, Pinnavaia and Mortland, a shift in the g⊥ ESR signal was observed when the air-dried Cu-saturated Camp Berteau montmorillonite (g⊥ = 2·05) was soaked in water for 48 h (g⊥ = 2·13). A small shift in the opposite sense was observed for the synthetic Cu smectite (g⊥ = 2·05 for the air-dried sample, g⊥ = 2·02 for the water-soaked sample). For the two natural smectites a small shift similar to that for the synthetic Cu-smectite was observed. These results indicate that up to 10% of the Cu atoms substitute for Al-Mg-Fe atoms in the octahedral sheets of the smectites studied.
A two-stage model for the formation of clay minerals from tephra-derived volcanic glass
Authors: Hodder A. P. W. , Green B. E. , Lowe D. J. 
Published: December 2006

AbstractThe kinetics of clay formation in buried paleosols developed from late Quaternary rhyolitic tephra layers near Rotorua, New Zealand, can be described in terms of a combination of parabolic and linear kinetics, reflecting the hydration of glass, and the formation of clay minerals, respectively. Such a model is consistent with the formation of clay minerals showing an Arrhenian temperature dependence and suggests, on the basis of calculated activation energies, that the process of formation of Al-rich allophane (imogolite) is diffusion controlled, whereas the rate of formation of Si-rich allophane is controlled by the chemical processes at the site of reaction.