bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Problem of Expressing the Specific Surface Areas of Clay Fractions
Authors: Padmanabhan E. , Mermut A. R. 
Published: August 2006

AbstractEstimations of the external specific surface areas (S.S.A.) by the N2-BET method of clay separates that were further fractionated by the high gradient magnetic separation technique revealed that the magnetic fractions had consistently lower S.S.A. compared to non-magnetic fractions. This phenomenon has been attributed, in the past, to the intimate association of Fe-oxides with silicate clays. It is the contention of this study that this reasoning is insufficient due to the following reasons. X-ray diffractograms (XRD) confirmed that heavy minerals were abundant in the magnetic fractions of these clays. Total chemical analyses and energy dispersive X-ray analyses showed that these heavy minerals contained Fe and Ti, which were not completely extracted by the dithionite-citrate bicarbonate (DCB) treatments. Crystallinity and quantity of these oxides in the different fractions did not show any relationships with the S.S.A. Lower S.S.A. were found in the magnetic fractions of both coarse and fine clays in the untreated as well as DCB-treated samples. The average particle density of the magnetic fractions was found to be higher than the non-magnetic fractions, resulting in an underestimation of the S.S.A. This underestimation was further proven when clay-sized illmenite (density = 4.79 Mg m−3) was found to have lower S.S.A. than quartz (density = 2.65 Mg m−3) and well-crystallized Georgia kaolinite (density = 2.61 Mg m−3), even though the illmenite particles were smaller in size compared to the kaolinite particles and similar in size compared to the quartz particles. It is, therefore, proposed that the specific surface areas should be expressed either on a volumetric basis or corrected for differences in density to avoid underestimations when heavy minerals are present in the samples.
Aspects on the Illitization of the Kinnekulle Bentonites
Authors: Pusch Roland , Madsen Fritz T. 
Published: August 2006

AbstractEarlier interpretations of the conversion of the virgin smectite of the Ordovician Kinnekulle K-bentonites into the present mixed-layer illite/smectite imply that it took place through charge increase of the smectite with subsequent uptake and fixation of potassium. Recent analyses show that the layer charge of the smectite component of the I/S is in fact low and they suggest that neoformation of a separate illite phase took place. Pytte's kinetic model gives good agreement with the actual conversion rate for an activation energy of about 25–27 kcal/mole, depending on the adopted rate parameters, temperature history and assumed potassium source. In the Kinnekulle case the rate-controlling factor appears to have been the supply of potassium, which is concluded to have required large-scale, heat-induced groundwater convection.
Rotationally Disordered Illite/Smectite in Paleozoic K-Bentonites
Authors: McCarty Douglas K. , Reynolds R. C. 
Published: August 2006

AbstractThe three-dimensional crystal structure of rotationally disordered illite/smectite (I/S) in K-bentonite samples from the Appalachian basin and neighboring areas is described using the parameters of 1) P0, the proportion of zero-degree layer stacking rotations, such as in the polytype series 1Md-1M; 2) Pcv, the proportion of 2:1 layers with cis-vacant (cv) octahedral sites that are randomly interstratified with trans-vacant (tv) layers; and 3) P60 the proportion of layers with n·60° rotations (as opposed to n·120°) in the rotated layers. These parameters were determined by computer modeling of experimental randomly oriented powder X-ray diffraction patterns.The proportion of cv interstratification in the I/S increases with A1 and decreases with Mg and Fe content. The proportion of n·60° rotations in the rotated layers increases with Mg and Fe content. The cv 120° disordered structure correlates with tetrahedral A1 for Si substitution and increasing tetrahedral charge. The tv n·60° disordered structures correlate with octahedral Mg for A1 substitution. The data indicate that the type of unit cell and nature of rotational disorder in I/S is controlled by the octahedral Mg content. The three-dimensional structures do not show any systematic correlation with Reichweite and percent expandability as determined from diffraction patterns of oriented sample preparations.
Monte Carlo Simulation of Interlayer Molecular Structure in Swelling Clay Minerals. 2. Monolayer Hydrates
Authors: Skipper N. T. , Sposito Garrison , Chang Fang-Ru Chou 
Published: August 2006

AbstractMonte Carlo (MC) simulations of interlayer molecular structure in monolayer hydrates of Na-saturated Wyoming-type montmorillonites and vermiculite were performed. Detailed comparison of the stimulation results with experimental diffraction and thermodynamic data for these clay-water systems indicated good semiquantitative to quantitative agreement. The MC simulations revealed that, in the monolayer hydrate, interlayer water molecules tend to increase their occupation of the midplane as layer charge increases. As the percentage of tetrahedral layer charge increases, water molecules are induced to interact with the siloxane surface O atoms through hydrogen bonding and Na+ counter-ions are induced to form inner-sphere surface complexes. These results suggest the need for careful diffraction experiments on a series of monolayer hydrates of montmorillonite whose layer charge and tetrahedral isomorphic substitution charge vary systematically.
Crystal Chemistry of Hydrous Iron Silicate Scale Deposits at the Salton Sea Geothermal Field
Authors: Manceau A. , Ildefonse Ph. , Hazemann J. -L. , Flank A-M. , Gallup D. 
Published: August 2006

AbstractThe crystal chemistry of Fe-Si scales deposited from geothermal brines at Salton Sea, California, was studied by powder X-ray diffraction and spectroscopic techniques including infrared, 57Fe Mössbauer, 27Al and 29Si nuclear magnetic resonance (NMR), and Fe and Si K-edge extended X-ray absorption fine structure (EXAFS). Scales precipitated at near 250°C from dissolved ferrous iron and silicic acid are composed of hisingerite. This phase is shown to possess the same local structure as nontronite and is a poorly-crystallized precursor of the ferric smectite. A clear distinction can be made at the local scale between hisingerite and 2-line ferrihydrite because, even in their most disordered states, the former possesses a two-dimensional and the latter a three-dimensional anionic framework. At temperature near 100°C Fe-Si scales are a mix of Al-containing opal and hydrous ferrous silicate, whose local structure resembles minnesotaite and greenalite. This hydrous ferrous silicate is very well ordered at the local scale with an average Fe coordination about Fe atoms of 6 ± 1. The difference in crystallinity between the ferrous and ferric silicate scales was related to variations of growth rates of clay particles precipitated from ferrous and ferric salt solutions. The low crystallinity of the ferric smectite suggests that the oxidation of ferrous iron occurs before polymerization with silica.
Tetramethylphosphonium- and Tetramethylammonium-smectites as Adsorbents of Aromatic and Chlorinated Hydrocarbons: Effect of Water on Adsorption Efficiency
Authors: Kukkadapu Ravi K. , Boyd Stephen A. 
Published: August 2006

AbstractTetramethylphosphonium-smectite (TMP-clay) and tetramethylammonium-smectite (TMA-clay), were prepared and characterized as adsorbents for a series of aromatic and chlorinated hydrocarbons. The sorption of benzene, alkylbenzenes, and carbon tetrachloride as vapors and as solutes from water was studied to evaluate the effect of water on adsorption efficiency. Adsorption of organic vapors depended on the N2 BET surface area. TMA-clay was a slightly better adsorbent than TMP-clay, due to its somewhat higher surface area. The Langumir isotherms obtained indicated that adsorption occurred predominantly in the interlayer micropores, apparently on mineral surfaces between onium ions. Adsorption efficiency of both organo-clays decreased, compared to vapor sorptions, in presence of water. Lower sorption was apparently due to shrinkage of the interlayer pore or cavity sizes by hydration of interlayer TMA and TMP cations. Although sorption efficiencies of both organo-clays was reduced in presence of bulk water, the extent of reduction was much less for TMP-clay. Thus, TMP-clay was a better adsorbent than TMA-clay in presence of water, despite its lower surface area, in direct contrast to vapor sorption. The Langumir isotherms indicated interlayer sorption of benzene, alkylbenzenes and carbon tetrachloride from water by TMP-clay. The absence of Langumir isotherms for toluene, ethylbenzene and p-xylene uptake from water by TMA-clay indicated that these bulkier solutes were not adsorbed in the interlayers. These results indicate that hydration of TMA cations causes shrinkage of the interlayer pores to dimensions that exclude these solutes. The lower degree of hydration of TMP cations enables TMP-clay to maintain interlayer pores large enough to accommodate the bulkier alkylbenzenes.
Mechanism of Adsorption and Desorption of Water Vapor by Homoionic Montmorillonites: 2. The Li+, Na+, K+, Rb+ and Cs+-Exchanged Forms
Authors: Bérend Isabelle , Cases Jean-Maurice , François Michèle , Uriot Jean-Pierre , Michot Laurent , Masion Armand , Thomas Fabien 
Published: August 2006

AbstractMethods previously used to distinguish between water adsorbed on external surfaces and in the interlamellar space of Na-montmorillonite during adsorption and desorption of water vapor have been extended to a set of homoionic Li-, Na-, K-, Rb- and Cs-montmorillonite. The textural and structural features have been investigated at different stages of hydration and dehydration using controlled-rate thermal analysis, nitrogen adsorption volumetry, water adsorption gravimetry, immersion microcalorimetry and X-ray powder diffraction under controlled humidity conditions. During hydration, the size of the quasi-crystals decreases from 33 layers to 8 layers for Na-montmorillonite and from 25 layers to 10 layers for K-montmorillonite, but remains stable around 8–11 layers for Cs-montmorillonite. Each homoionic species leads to a one-layer hydrate, which starts forming at specific values of water vapor relative pressure. Li-, Na- and K-montmorillonite can form a two-layer hydrate. By comparing experimental X-ray diffraction patterns with theoretically simulated ones, the evolution of structural characteristics of montmorillonites during hydration or desorption can be described. Using structural and textural data, it is shown that during adsorption: (1) the rate of filling of interlamellar space of the one layer hydrate increases with the relative pressure but decreases with the size of the cations; and (2) the different hydrated states are never homogeneous.
Characterization of Untreated and Alkylammonium Ion Exchanged Illite/Smectite by High Resolution Transmission Electron Microscopy
Authors: Cetin Kenan , Huff Warren D. 
Published: August 2006

AbstractHigh resolution transmission electron microscopy (HRTEM) have been performed on dispersed portions of one R > 1 and two R3 illite/smectite (I/S) samples from Silurian K-bentonites. R > 1 sample was studied by HRTEM before and after alkylammonium ion treatment and R3 samples were studied only after alkylammonium ion treatment. The HRTEM images of the chemically untreated R > 1 sample were predominated by lattice fringe contrast with 20–40 Å periods, interpreted to represent various ordered I/S units. HRTEM images of the three alkylammonium-treated samples displayed very small, dispersed particles composed of illite packets separated by alkylammonium expanded interlayers. In the R > 1 sample, illite packets were mostly 20 Å to 40 Å thick whereas in R3 samples they were predominantly over 40 Å. Although a good degree of dispersion of the bulk samples was achieved, dispersed particles recorded on images were thicker than the fundamental particles postulated by Nadeau and coworkers. Alkylammonium ion-expanded interlayer thicknesses point out a trend toward a higher charge in the expandable interlayers (i.e., illite particle surfaces) with increasing illite content from the R > 1 sample to the R3 samples. In the R3 samples, the interlayer charge is sufficiently high to be vermiculitic.
Adsorption Mechanisms of Imazamethabenz-Methyl on Homoionic Montmorillonite
Authors: Pusino A. , Gelsomino A. , Gessa C. 
Published: August 2006

AbstractThe adsorption of the herbicide imazamethabenz-methyl, a mixture of the two isomers methyl (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H-imidazol-2-yl]-4-methylbenzoate para isomer) and methyl (±)-2-[4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-1 H-imidazol-2-yl]-5-methyl-benzoate (meta isomer), from water onto Al3+, Fe3+-, Ca2+-, K+- and Na+-montmorillonite was studied by analytical (HPLQ methods. The adsorption from an organic solvent was also investigated by spectroscopic (IR) and X-ray diffraction measurements. It was observed that, depending on the acidic properties of the exchangeable cations, two different mechanisms may take place. The first one, acting on Fe3+- and Al3+-clays, involves the protonation of the more basic nitrogen atom of imidazolinone ring of the herbicide because of a proton transfer from the acidic metal-bound water, followed by adsorption on the clay surfaces. In this case, the clay surfaces have greater affinity for the meta than the para isomer, due to the extra-stabilization of the meta protonated form by resonance. The second mechanism, taking place on Ca2+-, K+- and Na+-clays, is hydrogen-bond formation between the ester carbonyl group of the herbicide and hydration water metal ions and is not affected by the structure of the isomers.
Morphology of Kaolinite Crystals Synthesized Under Hydrothermal Conditions
Authors: Fiore Saverio , Huertas F. Javier , Huertas Francisco , Linares José 
Published: August 2006

AbstractScanning electron microscopy has revealed the presence of spherical, lath and platy kaolinite in gels with Si/Al atomic ratio ranging from 1.84 to 0.76 that are hydrothermally treated under different temperature and time conditions. Hemispherical structures and excavated zones, at different stages of evolution, have been observed on the surface of the gel grains, indicating that spherical particles do not precipitate from the solution but are generated from the gels. The quantity of spherical particles depends on temperature, time and the chemical composition of the starting gel. Products from starting material with Si/Al ≈ 1 yield the highest quantity of these particles. Being metastable, sphere dissolution controls the chemistry of the solution and consequently the morphology of the precipitating crystals thus producing more elongated, curved and irregular outlines when gels with Si/Al ≈ 1 are hydrothermally treated.
Preservation of Clay Minerals in the Precambrian (1.1 GA) Nonesuch Formation in the Vicinity of the White Pine Copper Mine, Michigan
Authors: Li Gejing , Mauk Jeffrey L. , Peacor Donald R. 
Published: August 2006

AbstractThe Middle Proterozoic (1.1 Ga) Nonesuch Formation, host of the stratiform copper deposit at White Pine, Michigan, consists of 200 m of principally dark grey clastic sediments which contain detritus obtained dominantly from underlying mafic to intermediate volcanic rocks. Clay minerals from samples collected from the mine area and drill holes up to 100 km away have been studied using SEM, EMPA, TEM and AEM. Two morphologies of phyllosilicates, both including white mica and chlorite, occur in the ‘lower’ Nonesuch Formation: (1) detrital-shaped and (2) matrix. Detrital-shaped phyllosilicate grains are up to 450 microns long with long axes parallel to bedding. Matrix phyllosilicates occur as packets typically <200 Å thick and as pore-filling cement.TEM images of detrital-shaped chlorite generally display 14-Å periodicity, although 24-Å corrensite- like units occur locally. Most detrital-shaped chlorite from the mine area samples have a relatively restricted range of Fe/(Mg+Fe) ratios from 0.52 to 0.58, but the Fe/(Fe+Mg) ratios of detrital-shaped chlorite outside the mine area range from 0.27 to 0.64. TiO2crystals occur within and surrounding the detrital-shaped chlorite. Matrix chlorite has Fe/(Fe+Mg) ratios of 0.47 to 0.63, indicating that it is relatively homogeneous and enriched in Fe compared to detrital-shaped chlorite.Detrital-shaped white mica occurs as a 2Mi polytype and generally has a phengitic composition. Matrix illite-rich I/S occurs as a 1Mdpolytype, is K and Al deficient relative to end-member muscovite and contains significant Fe and Mg.The data are consistent with homogenization of detrital-shaped chlorite in the White Pine mine area by hydrothermal fluids during copper mineralization. The TiO2crystals and corrensite-like units in detrital- shaped chlorite imply that it is at least in part derived from alteration of biotite. The presence of immature 1Mdillite-rich I/S and a one layer chlorite polytype with stacking disorder suggests that the matrix clays are in their original, post-smectite state of formation as consistent with an authigenic origin during early burial diagenesis; i.e., they have not undergone subsequent transformation even though sedimentation and ore deposition occurred prior to 1 Ga.
Hydroxy-Chromium Smectite: Influence of Cr Added
Authors: Volzone C. 
Published: August 2006

AbstractOH-Cr smectites were prepared with different mmol Cr/g smectite: 0.5, 1.5, 3.5, 5, 10 and 20 by treatment with hydroxy-chromium solution prepared at 60°C and one day of hydrolysis with OH/Cr = 2. The samples were characterized by X-ray diffraction (XRD), differential thermal analyses (DTA) and N2 adsorption-desorption isotherms.The d(001) spacings of OH-Cr-smectite were different according to Cr added/g smectite. Larger d(001) spacings: 1.95, 2.05 and 2.07 nm were obtained with 5, 10 and 20 mmol Cr per gram of sample. DTA diagrams of smectite treated with OH-Cr solution showed exothermic peak at 420°C corresponding to Cr203 (confirmed by XRD). N2 adsorption-desorption isotherms of smectite treated with different amounts of Cr preserved the same slit-shaped pores than original sample, but with different micropore volume. This behavior was maintained until treatment temperature of 380°C. The specific area of smectite was increased from 36 to 175 m2/g after treatment with OH-Cr solution. The textural characteristics of OH- Cr smectite heated up to 420°C were changed. The specific area decreased and mesopore volume was produced. The different Cr added modified the structural and textural behavior.
Formation of Mica During Experimental Alteration of K-Feldspar
Authors: Kawano Motoharu , Tomita Katsutoshi 
Published: August 2006

AbstractExperimental alterations of K-feldspar in distilled-deionized water at 150°, 175°, 200°, and 225°C were performed. The alteration products and dissolution mechanism of K-feldspar were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). SEM, TEM, and EDX clearly showed formation of fibrous boehmite less than 1.0 μm in length at the early alteration stages. The boehmite fibers decreased in abundance and rounded platy 1 M mica was produced as alteration proceeded. The mica exhibited initially angular shaped small flakes of 0.69 μm in average size, which developed to rounded platy particles of 1.97 μm. The main chemical reactions occurring in this experimental system can be expressed by: $$\begin{array}{l} \mathop {KAlS{i_3}{O_3}}\limits_{\left[ {K - feldspar} \right]} + 6{H_2}O + {H^ + } \to \mathop {AlO\left( {OH} \right)}\limits_{\left[ {boehmite} \right]} + 3{H_4}Si{O_4} + {K^ + }, \\ \mathop {3KAlS{i_3}{O_8}}\limits_{\left[ {K - feldspar} \right]} + 12{H_2}O \to \mathop {KA{l_3}S{i_3}{O_{10}}{{\left( {OH} \right)}_2}}\limits_{\left[ {mica} \right]} + 2{K^ + } + 6{H_4}Si{O_4} + 22{H^ + }. \\ \end{array}$$ XPS showed no significant changes in intensities of photoelectron lines excited from K, Si, and Al in the K-feldspar surface before and after alteration, however the K/Si molar ratios in the solutions were considerably smaller than that of the original K-feldspar. The results of XPS strongly indicate that no dealkalized layer was produced on the surface, and that dissolution of K-feldspar in aqueous solution proceeded congruently by a surface-reaction mechanism. The discrepancy of mass balance in the solutions may be mainly caused by adsorption of K on the surface of boehmite.
Effects of Iron and Aluminium Oxides on the Colloidal and Surface Properties of Kaolin
Authors: Arias Manuel , Barral M. Teresa , Diaz-Fierros Francisco 
Published: August 2006

AbstractThe association between clay silicates, and iron and aluminium oxides has a major influence on the chemical and physical properties of soils. In this work the interaction of a kaolin substrate with iron and aluminium oxides and/or hydroxides obtained by basification of solutions of the metal ions was compared to that of quartz. Both precipitates were obtained in the presence of the substrates.The aluminium precipitates had higher crystallinity, and thus led to smaller increases in specific surface area than those of iron, and were more effective modifiers of the surface electrical properties of the kaolin-oxide mixtures. At concentrations as low as 0.43% Al (g/100 g of substrate) the point of zero charge (PZC) of the components with variable charge was measurable, while Fe required 2.23% and gave lower PZCs than those of corresponding concentrations of Al. In both cases the PZCs shifted to higher pH as metal concentration was increased, as did the flocculation interval of colloidal suspensions of kaolin, which were close to the PZCs (where these were evaluated).The Al and Fe oxides precipitated on quartz had higher crystallinities. Both metals increased the specific surface area to a similar extent, with an almost linear relationship to metal concentration. Samples containing ca. 6.5% Fe or Al had similar or slightly higher PZCs than corresponding kaolin samples.The results were interpreted by assuming, in the case of kaolin, the union of the metal precipitate with the basal faces of the substrate, so decreasing the negative charge at this surface; and in the case of quartz, the formation of a hydroxide coating that neutralizes the negative charge on the silica surface. The difference between the results obtained for each metal was attributed to the different morphologies of their oxide precipitates.