bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intercalation of Benzamide into Expanded Kaolinite Under Ambient Environmental Conditions
Authors: Kelleher B. P. , O'Dwyer T. F. 
Published: February 2003

AbstractWaste kaolinite from a fertilizer industry was intercalated with n-methylformamide (NMF) under ambient conditions. The complex was washed, characterized and then reacted with benzamide (dissolved in ethanol) under similar conditions. Using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis (DTA), clear evidence of benzamide intercalation was observed after a reaction time of 48 h. The FTIR and DTA analysis also confirmed that the ethanol was not involved in the intercalation and that both NMF and benzamide are present in the interlayer region.
Effects of Oxyanions on the Edta-Promoted Dissolution of Goethite
Authors: Campbell Jillian L. , Eick Matthew J. 
Published: February 2003

AbstractOrganic ligands, such as EDTA, accelerate the dissolution of silicate and oxide minerals. In natural systems, oxyanions can compete with organic ligands for mineral surface sites thereby affecting ligand-promoted dissolution rates, either enhancing or inhibiting dissolution, depending upon pH. The influence of selenite, molybdate and phosphate on the EDTA-promoted dissolution of goethite has been examined and a mechanism proposed for the observed differences in dissolution rates over a pH range of 4–8. We propose that the surface complex formed by EDTA is the controlling factor for the observed dissolution rate, with mononuclear complexes accelerating dissolution compared to bi- or multinuclear complexes. Dissolution results from our experiments suggest that EDTA forms multinuclear complexes at pH values ⩾6 and mononuclear complexes at pH values <6. Dissolution results show that when the oxyanion and the EDTA are present in the system at concentrations nearly equalling the surface sites available for adsorption, the oxyanion reduces the adsorption of EDTA and inhibits dissolution. However, if the oxyanion is present at lower concentrations at pH values ⩾6, EDTA is adsorbed but the number of carboxylic groups that can bind to the surface is reduced causing the formation of mononuclear complexes. This shift to a weaker surface complex enhances the EDTA-promoted dissolution of goethite in the presence of the oxyanions compared to EDTA-promoted dissolution in their absence.
Influence of Silicate- and Magnesium-Specific Adsorption and Particle Shape on the Rheological Behavior of Mixed Serpentine-Goethite Suspensions
Authors: Tartaj P. , Cerpa A. , García-González M. T. , Serna C. J. 
Published: February 2003

AbstractThe influence of dissolved species and particle morphology on the electrokinetic behavior and the initial yield stress values of Cuban lateritic aqueous suspensions was studied. The lateritic samples were mixtures of serpentine and goethite in different relative proportions. The addition of silicate and Mg ionic species, which are normally found in natural waters used in industrial processes, affected the electrokinetic and flow behavior of the lateritic suspensions. Specific adsorption of these species on particle surfaces was shown by a shift of the isoelectric point and the maximum of the initial yield stress to more acidic pH (Si ionic species adsorption) and more basic pH (Mg ionic species adsorption), when compared to suspensions containing only non-adsorbing electrolytes. The initial yield-stress values determined in samples consisting entirely of goethite varied from sample to sample. A detailed crystallochemical characterization revealed that these changes were associated with the axial ratio (i.e. ratio of particle length to width) of the mineral particles. Goethite samples with larger particle size (smaller number of particles for a given solid concentration) and greater axial ratios presented initial yield-stress values greater than those goethites with smaller particle size and lower axial ratio.
A New Method for the Prediction of Gibbs Free Energies of Formation of Phyllosilicates (10 Å and 14 Å) Based on the Electronegativity Scale
Authors: Vieillard Philippe 
Published: February 2003

AbstractThe method for prediction of Gibbs free energies of formation, based on the parameter ΔGO=Mz+(clay) characterizing the oxygen affinity of the cation Mz+, on the smectites, considered as hydrated clay minerals, has been used for micas and brittle micas, and yielded underestimated values. This method of prediction can be improved by a new set of parameters ΔGO=Mz+(clay), characterizing the electronegativity of a cation in a specific site (interlayer, octahedral, tetrahedral in the 10 Å minerals), determined by minimizing the difference between experimental Gibbs free energies and calculated Gibbs free energies of formation from constituent oxides. By considering the crystal structure of 10 Å and 14 Å minerals, and assuming the same electronegativity of cations, ΔGO=Mz+(o), in the octahedral sheets, an attempt is made to determine the electronegativity of cations in the brucitic sheet, ΔGO=Mz+(b). The results indicate that this prediction method compared to other determinations, gives values within 0.25% of the experimentally-estim ated values. The relationships between ΔGO=Mz+(clay) corresponding to the electronegativity of a cation in the interlayer, octahedral, tetrahedral or brucitic sites and known ΔGO=Mz+(aq) were thus determined, allowing the determination of the electronegativity of transition metal ions and trivalent ions in each of the four sites and consequently contribute to the prediction of Gibbs free energies of formation of different micas and chlorites. Examples are given for low-Fe clinochlore whose solubility is measured experimentally and the results appear excellent when compared with experimental values.
Biogenic Saponite From an Active Submarine Hot Spring, Iceland
Authors: Geptner A. , Kristmannsdóttir H. , Kristjansson J. , Marteinsson V. 
Published: February 2003

AbstractA study of the mineralogy, chemical composition and structure of poorly-crystalline saponite precipitated from a submarine hot spring in Eyjafjordur, northern Iceland is reported. Special emphasis was placed on the microstructures of the minerals and a possible connection with biological activity during their precipitation. The microstructures of the minerals were found to be very similar to specific clay minerals precipitated from geothermal vents in oceanic rift zones. The composition of the minerals was, however, found to be similar to magnesium silicate scales formed in geothermal installations in Iceland where geothermal waters were mixed with cold fresh waters. High contents of organic substances were found in the clay mineral samples as compared to geothermal precipitates from other localities. Microstructural features of the layer silicates in one of the samples suggest that a gelatinous substance was a precursor of the saponite clay. The organic matter content appears to be greater when the precipitates are more crystalline.
Site Occupancies by Iron in Nontronites
Authors: Gates W. P. , Slade P. G. , Manceau A. , Lanson B. 
Published: February 2003

AbstractTwelve nontronites and two ferruginous smectites have been characterized with respect to Fe3+ occupancy of tetrahedral sites. The techniques used were near infrared, Fe-K X-ray absorption near-edge and X-ray absorption fine-structure spectroscopies, along with two X-ray diffraction techniques. The results show that calculations of the structural formulae of many nontronites should be adjusted to include Fe3+ in tetrahedral sites. The nontronite from Spokane County, Washington, (∼44% Fe2O3) is essentially an end-member with its non-siliceous tetrahedral sites occupied by Fe3+. Samples with chemical compositions similar to Garfield nontronite (∼36.5% Fe2O3) may have small amounts (<5% of total Fe3+) of tetrahedral Fe3+. Tetrahedral Fe3+ is unlikely to be present in samples containing less than ∼34% Fe2O3.
Solid-State Nuclear Magnetic Resonance Study of Sepiolite and Partially Dehydrated Sepiolite
Authors: Weir Mark R. , Kuang Wenxing , Facey Glenn A. , Detellier Christian 
Published: February 2003

AbstractThe assignment of the 29Si CP/MAS-NMR spectrum of naturally-occurring sepiolite clay was re-examined using 29Si COSY and 1H-29Si HETCOR pulse sequences. Each of the three main resonances at −92.1, −94.6 and −98.4 ppm has been attributed to one of the three pairs of equivalent Si nuclei in the basal plane, and the resonance at −85 ppm to Q2(Si-OH) Si nuclei. On the basis of the COSY experiment, the resonance at −92.1 ppm is unambiguously assigned to the intermediate, near-edge Si sites. The HETCOR experiment revealed that the resonance at −94.6 ppm cross-polarizes almost entirely from the Mg-OH protons, and therefore is assigned to the central Si position. The remaining resonance at −98.4 ppm correlates strongly to the protons of the structural water molecules and therefore is assigned to the edge Si sites. Nearly complete rehydration was achieved at room temperature by exposing sepiolite samples that had been partially dehydrated at 120°C to water vapor or to D2O vapor. The rehydration results support the 29Si NMR peak assignments that were made on the basis of the COSY and HETCOR experiments.The 29Si CP/MAS-NMR spectrum corresponding to the folded sepiolite structure in which approximately one half of the structural water has been removed by heating to 350°C is reported for the first time. The chemical shift values and relative intensities are significantly different compared to the resonances that are observed in the corresponding spectrum of the true sepiolite anhydride. These observations support the earlier claim that sepiolite heated to ∼350°C exists as a distinct phase to be differentiated from that of the completely dehydrated state.
A Microwave-Assisted Method for the Rapid Removal of K From Phlogopite
Authors: Stout Stephen A. , Komarneni Sridhar 
Published: February 2003

AbstractThe ability to remove K rapidly with a solution containing sodium tetraphenylborate (NaTPB) from the interlayers of naturally-occurring phlogopite using a microwave-assisted technique has been examined. Samples were equilibrated with a 1.0 N sodium chloride (NaCl) – 0.2 N NaTPB – 0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at 60, 80 and 100°C under both conventional and microwave-assisted heating methods and for periods of time ranging from 1 to 3 h. The samples also underwent treatments of either continuous time periods or for successive treatments of 1 h with a washing step between each treatment.Following sample treatment, the expansion of the c-axis value (d001) from 10.0 to 12.2 Å indicated the presence of hydrated Na ions in the phlogopite structure. Under most treatment conditions the 10.0 Å peak remained even after treatment due to incomplete K removal. Chemical analysis and X-ray diffraction (XRD) revealed that samples heated using microwave radiation exchanged their interlayer K for Na much more rapidly than under conventional heating for all treatment times and temperatures. The successive treatments also degraded the mica more rapidly than the continuous treatments. The greatest amount of K (95%) was removed when the mica was treated three times for 1 h at 60°C. The results suggest that successive treatments of phlogopite mica heated under microwave radiation will rapidly remove K from the mica. Decreasing the amount of time required to prepare K-depleted phlogopite micas will make these materials more appealing as ion exchangers for separation of Cs from nuclear wastes.
Local Order of the Transition Metals for the Substitution (Co1−yCuy)2Al(OH)6Cl·nH2O (0 ⩽ y ⩽ 1) in a Copper-Aluminum-Layered Double Hydroxide-Like Phase
Authors: Leroux Fabrice , Moujahid El Mostafa , Roussel Hervé , Flank Anne-Marie , Briois Valérie , Besse Jean-Pierre 
Published: February 2003

AbstractThe substitution in layered double hydroxide-like phases (LDH) of composition (Co1−y2+Cuy2+)2Al3+(OH)6Cl−⋅nH2O(0⩽y⩽1) was studied by X-ray diffraction and X-ray absorption spectroscopy. It was found that the lamellar character is maintained over the entire range of the substitution. The local order for the composition {Co2Al} is typical of brucite-like sheets, whereas segregation into small domains may explain the results obtained when the percentage of Cu atoms is increased. The {Cu2Al} end-member material presents a local order around the Cu atoms closely related to the botallackite structure as present in basic layered Cu salts, with the presence of two distinct Cu-Cu distances.
Adsorption of Olefins on Aluminum- and Aluminum/Tetramethylammonium-Exchanged Bentonites
Authors: Moronta Alexander , Taylor Scott , Breen Christopher 
Published: February 2003

AbstractOne montmorillonite, STx-1 (Texas, USA), was activated with different amounts of Al and tetramethylammonium (TMA+) cations to obtain materials with a combined Al3+ and TMA+ content equal to its cation exchange capacity. The adsorption capacity of these samples was studied saturating them with hept-1-ene at room temperature. The samples were heated and the evolved gases analyzed by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. Hept-1-ene reacted with the clays via proton transfer and resulted in the formation of a variety of reaction products (>60 hydrocarbons). In general, the presence of TMA+ cations significantly reduced the population of protons to selectively produce isomerization and hydration products.
Dehydroxylation and Transformations of the 2:1 Phyllosilicate Pyrophyllite at Elevated Temperatures: An Infrared Spectroscopic Study
Authors: Wang Ling , Zhang Ming , Redfern Simon A. T. , Zhang Zhenyu 
Published: February 2003

AbstractThe thermally-induced dehydroxylation and transformations of the 2:1 phyllosilicate pyrophyllite have been studied using infrared spectroscopy in the frequency range 350–11000 cm−1 and the temperature range 200–1500°C. The dehydroxylation of pyrophyllite to pyrophyllite dehydroxylate occurs between 500 and 900°C. It is characterized by a decrease in the intensity of the OH signals and phonon bands of pyrophyllite and the eventual disappearance of these features as well as the appearance of extra signals related to pyrophyllite dehydroxylate and an intermediate phase. Our results are consistent with previous observations that the SiO4 tetrahedral sheet structure still exists in pyrophyllite dehydroxylate, that the Si-O-Al linkages and 2:1 structure remain in the pyrophyllite dehydroxylate, and that AlO5 trigonal bipyramids form.Two extra OH bands at 3690 and 3702 cm−1 and their overtones at 7208 and 7234 cm−1 are observed, for the first time, in samples annealed at the temperature range 550–900°C. Our results suggest that the formation and dehydroxylation of the extra OH species can be strongly affected by kinetic effects. The experimental evidence shows that the dehydroxylation of pyrophyllite is a two-stage process. The appearance of these additional OH bands is interpreted in terms of an unknown intermediate phase, and may be related to the second endothermic peak observed at high temperatures in DTA experiments. Pyrophyllite dehydroylate decomposes into a Si-rich amorphous phase and mullite in the temperature range 950–1100°C. Cristobalite is observed in the temperature range 1150–1500°C.
Crystal-Size Distributions of Clays During Episodic Diagenesis: The Salton Sea Geothermal System
Authors: Kim Jin-wook , Peacor Donald R. 
Published: February 2003

AbstractCrystal-size distributions (CSDs) for clay minerals with depth were measured from the Salton Sea Geothermal Field (SSGF) as a test for the presence and meaning of theoretical crystal-size distributions in a natural system. The SSGF is a classic open hydrothermal system, and crystals are forming directly without apparent modification of early-formed crystals, over a wide range of temperature. Thus, the measured CSDs are the actual distributions for a single episode in which all crystals grew at the same time from solution at different temperatures and depths, rather than through modifications of shallower samples.Some TEM images of ion-milled samples from a range of depths were used to measure the crystal thicknesses of illite, chlorite and biotite. Grain-size histograms flatten, broaden and shift to larger sizes with increasing depth. Values of α and β were calculated and used to verify that the measured distributions are log normal. Reduced grain-size distributions for illite in SSGF samples obey steady-state constraints.The observations appear to be consistent with evolution of illite with increasing depth in the SSGF system by growth in an open system giving rise to log-normal distributions, followed by supply-controlled growth in an open system. Because crystals at different depths grew simultaneously under different temperature and fluid conditions as a function of depth, they do not represent different stages of a single evolving system. The relations imply that isochemical and isothermal systems which permit an evolving system to be sampled are rare or non-existent. The data for distributions for a given depth in the SSGF are consistent with growth in an open system. The collective relations therefore imply that caution should be used in interpreting conditions of crystal growth in natural systems even where CSDs give results which are necessary for, but not sufficient to prove, a given modeled mechanism.
A New Extraction Procedure for Simultaneous Quantitative Determination of Water-Soluble Metals in Reaction Products of Clays and Inorganic Salts
Authors: Colina Fernando G. , Esplugas Santiago , Costa Jose 
Published: February 2003

AbstractKaolin, a possible source of Al, may be reacted with inorganic acids or salts to form different Al salts that can be further processed to prepare metallic Al. Although the reaction of kaolin and acid in aqueous solution can be monitored by chemical analysis of Al, the Al salts must be extracted from any unreacted kaolinite. Also, the lixiviation of Ti or Fe species present in kaolin should be monitored. A simple extraction procedure is reported to determine, quickly and quantitatively, water-soluble Al, Ti and Fe metals present in products of reaction of kaolin (85 wt.% kaolinite, 12 wt.% mica, 2 wt.% feldspar, 1 wt.% quartz) with inorganic salts, such as sodium hydrogensulfate, using conventional glassware for the glass reaction tubes. Optimum results are obtained with 250 mL glass reaction tubes. The best operating conditions found for this piece of equipment are: (1) sample weight of 0.05 g, (2) lixiviation time of 1 h, and (3) lixiviating agent, 50 mL of an aqueous solution of pH = 1 H2SO4 at its boiling point. Comparisons are made with soxhlet extraction and beaker and magnetic stirring methods.
Diffusion of H2O and I− in Expandable Mica and Montmorillonite Gels: Contribution of Bound H2O
Authors: Nakashima Yoshito 
Published: February 2003

AbstractSelf-diffusion coefficients of H2O molecules in water-rich gels of Na-rich expandable mica synthesized using natural talc were measured by pulsed-gradient spin-echo 1H nuclear magnetic resonance (NMR), and the dependence on mica fraction (0.00–43.8 wt.%) and temperature (30.0–60.9°C) was examined. On the basis of the NMR results, the self-diffusion coefficient of H2O, Dwater, in the gel can be expressed by ln(Dwater/D0water) = 1.64[exp( −0.0588w) - 1], where D0water is the self-diffusivity of bulk water at temperature and w is the weight fraction of the mica (wt.%). The activation energy of H2O diffusivity in mica gel is nearly equal to that in bulk water. These findings indicate that the normalized diffusivity, Dwater/D0water, is independent of temperature. The diffusivity of I−, Diodine, in the gels was examined by X-ray computed tomography (CT) at 22°C, and the influence of the mica fraction (0.00–24.8 wt.%) was studied to determine the contribution of bound H2O. The X-ray CT results show that the normalized I− diffusivity, Diodine/D0iodine, obeys the above-mentioned phenomenological curve where D0iodine is the I− diffusivity in bulk water. I− is non-sorbing, and thus its diffusion is restricted only by the geometrical complexity of the pore structure of gels. Therefore, the effect of bound H2O molecules on average H2O diffusivity is negligible for w <24.8 wt.%. Diffusivity is governed by free or unbound H2O molecules diffusing in the geometrically complex and tortuous pore structure of mica-mineral grains. This is a result of the large population of unbound H2O far from the grain surface compared to the small population of bound H2O near the grain surface. The diffusion of I− ions in montmorillonite gels was examined by X-ray CT for w <16.7 wt.% montmorillonite. The normalized iodine diffusivity, (Diodine/D0iodine) obtained is in reasonably close agreement with the literature data for the normalized diffusivity of H2O and is similar to the master curve of expandable mica. Therefore, bound H2O molecules near negatively charged clay surfaces do not play a major role in the H2O diffusivity for water-rich montmorillonite gels.
Monolayer to Bilayer Transitional Arrangements of Hexadecyltrimethylammonium Cations on Na-Montmorillonite
Authors: Bonczek James L. , Harris W. G. , Nkedi-Kizza Peter 
Published: February 2003

AbstractA low-charge Na-montmorillonite (SWy-2) was exchanged with hexadecyltrimethyl-ammonium (HDTMA) at levels equal to 20, 40, 60, 70, 80, 90, 100, 150 and 200% of the cation exchange capacity (819 mmol(+)/kg) to determine the nature of adsorption and the ionic composition of the clay interlayers. In contrast with earlier work with smaller aliphatic cations, which suggested random interstratification of interlayers occupied by either organic or metallic cations, there was no evidence of cation segregation into homogeneous interlayers. Instead, X-ray analysis indicated that the organic cations assumed two dominant configurations which were roughly equivalent in prevalence at ∼70% coverage of the CEC. Below 70% exchange the organocations existed predominantly in heterogeneous monolayers with Na+, attaining basal spacings of between 1.41 and 1.44 nm which were sensitive to changes in relative humidity. Relative humidity effects indicated that Na+ and HDTMA occupied functionally discrete domains within the interlayer as shown by the free interaction of water and a neutral organic solute, naphthalene, with Na+ and HDTMA, respectively. At greater levels of HDTMA exchange (up to 100% of the CEC), the organocations assumed a predominantly bilayer configuration. Transition to a fully-developed bilayer indicated by a 1.77 nm d-spacing at 100% coverage was gradual, suggesting some interstratification of the monolayers and bilayer configurations between 70 and 100% exchange. Sorption of naphthalene to the organoclays within this range of coverage was well correlated with clay organic carbon content, consistent with relatively unimpeded interlayer access of neutral organic molecules.