bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calorimetric Measurement of the Enthalpy of Hydration of Clinoptilolite
Authors: Carey J. William , Bish David L. 
Published: August 2006

AbstractThe enthalpy of hydration of natural clinoptilolite was determined by isothermal immersion calorimetry on Ca-, Na- and K-exchanged clinoptilolite (Fish Creek Mountains, Nevada). Heats of immersion of clinoptilolite were determined at initial H2O contents ranging from θ = 0.02 to 0.85 (where θ is the ratio [H2O content]/[maximum H2O content]). The heat of immersion (liquid H2O reference state) of Ca-clinoptilolite ranged from -7.5 (θ = 0.87) to -25.7 kJ/mol-H2O (θ = 0.19); values for Na-clinoptilolite ranged from -6.3 (θ = 0.85) to -21.8 kJ/mol-H2O (θ = 0.11); and values for K-clinoptilolite ranged from -7.7 (θ = 0.80) to -24.6 kJ/mol-H2O (θ = 0.02). Linear regression of the calorimetric data provided the following values for the complete heat of immersion (from θ = 0): Ca-clinoptilolite, -30.3 ± 2.0; Na-clinoptilolite, -23.4 ± 0.6; and K-clinoptilolite, -22.4 ± 0.8 kJ/mol-H2O.The heat of immersion measurements were compared with the enthalpy of hydration results of Carey and Bish (1996) determined in a thermogravimetric study of the same samples. The heat of immersion data are similar but of smaller magnitude than the values of enthalpy of hydration and are believed to be more accurate because they represent direct measurements of this thermodynamic property.The effect of dehydration of clinoptilolite on the thermal evolution of the potential high-level radioactive waste repository at Yucca Mountain was considered by comparing the amount of energy consumed by clinoptilolite dehydration with the amount of energy necessary to heat rocks lacking hydrous minerals. The extra energy consumed on heating clinoptilolite from 25 to 200 °C ranges between 70 and 80% in excess of that required for nondehydrating materials (that is, clinoptilolite acts as a heat sink). These results indicate that accurate thermohydrologic modeling of rock units at Yucca Mountain should consider the thermal effect of dehydration/hydration processes in clinoptilolite and other hydrous minerals, in addition to the water produced/adsorbed during heating/cooling.
Adsorption of Benzyltrimethylammonium and Benzyltriethylammonium on Montmorillonite: Experimental Studies and Model Calculations
Authors: Polubesova Tamara , Rytwo Giora , Nir Shlomo , Serban Carina , Margulies Leon 
Published: August 2006

AbstractThe adsorption of the monovalent organic cations benzyltrimethylammonium (BTMA) and benzyltriethylammonium (BTEA) to montmorillonite was studied as a function of their concentrations and ionic strength. At low ionic strength the adsorbed amounts of BTMA and BTEA reached values of the cation exchange capacity (CEC) of the clay. An increase in the ionic strength resulted in reduction in the adsorbed amounts of the organic cations, unlike the pattern observed previously with organic monovalent cationic dyes. The reduction in adsorbed amounts of BTMA and BTEA depended on the inorganic cations according to the sequence Cs+ > Na+ > Li+, which follows the sequence of binding coefficients of these inorganic cations added. The type of the anion (that is, Cl−, ClO4−, SO42-) had no effect on the adsorbed amounts. An adsorption model which considers the electrostatic Gouy-Chapman equations, specific binding and closeness of the system could adequately simulate the adsorbed amounts of BTMA and BTEA and yield predictions for the effect of the ionic strength and concentration of electrolytes. The binding coefficient employed was K = 5000 M−1 for the formation of neutral complexes of BTMA and BTEA. This value is larger than those found for the inorganic cations but is several orders of magnitude below those found for the monovalent dyes. The binding coefficients for the formation of charged complexes of BTMA and BTEA were 20 and 5 M−1, respectively. The basal spacing of the clay did not change significantly with the adsorbed amounts of both BTMA and BTEA up to the CEC.
Effects of Exchanged Cation and Layer Charge on the Sorption of Water and Egme Vapors on Montmorillonite Clays
Authors: Chiou Cary T. , Rutherford David W. 
Published: August 2006

AbstractThe effects of exchanged cation and layer charge on the sorption of water and ethylene glycol monoethyl ether (EGME) vapors on montmorillonite have been studied on SAz-1 and SWy-1 source clays, each exchanged respectively with Ca, Na, K, Cs and tetramethylammonium (TMA) cations. The corresponding lattice expansions were also determined, and the corresponding N2 adsorption data were provided for comparison. For clays exchanged with cations of low hydrating powers (such as K, Cs and TMA), water shows a notably lower uptake than does N2 at low relative pressures (P/P0). By contrast, EGME shows higher uptakes than N2 on all exchanged clays at all P/P0. The anomaly for water is attributed to its relatively low attraction for siloxane surfaces of montmorillonite because of its high cohesive energy density. In addition to solvating cations and expanding interlayers, water and EGME vapors condense into small clay pores and interlayer voids created by interlayer expansion. The initial (dry) interlayer separation varies more significantly with cation type than with layer charge; the water-saturated interlayer separation varies more with cation type than the EGME-saturated interlayer separation. Because of the differences in surface adsorption and interlayer expansion for water and EGME, no general correspondence is found between the isotherms of water and EGME on exchanged clays, nor is a simple relation observed between the overall uptake of either vapor and the cation solvating power. The excess interlayer capacities of water and of EGME that result from lattice expansion of the exchanged clays are estimated by correcting for amounts of vapor adsorption on planar clay surfaces and of vapor condensation into intrinsic clay pores. The resulting data follow more closely the relative solvating powers of the exchanged cations.
Improvements to the Quantitative Assay of Nonrefractory Minerals for Fe(II) and Total Fe Using 1,10-Phenanthroline
Authors: Amonette James E. , Charles Templeton J. 
Published: August 2006

AbstractA method using 1,10-phenanthroline (phen) to quantify Fe(II) and total Fe in nonrefractory minerals was modified to improve the accuracy and precision and to eliminate the inconvenience of performing much of the analysis under darkroom conditions. Reagents were combined to minimize solution-handling errors, volumes of the reagent additions were determined gravimetrically and the acid-matrix solution was preheated to near-boiling before sample contact. The darkness requirement, which stems from the photoreduction of Fe(III) to Fe(II) in the presence of phen, was eliminated by the use of opaque amber-colored high-density-polyethylene bottles during the digestion step and for storage of the digestate and subsequent dilutions before Fe(II) analysis. Reduction of Fe(III) for total-Fe analysis was accomplished either by exposure to light from a Hg-vapor lamp or by reaction with hydroxylamine, NH2OH. Although the minimum periods required for adequate reduction ranged from 1.5 to 4 h, the optimum reduction periods were between 6 and 10 h. When standard samples containing Fe(II) and MnCl2 were digested and analyzed for total-Fe using the light treatment (with incidental heating to 35–45 °C), significant decreases and in some instances, oscillations, in absorptivity were obtained. Similar experiments with NH2OH, or with CrCl3 showed no effect. The absorptivity of most digestates stored in opaque bottles was stable for at least 2 weeks, although digestates with Mn concentrations above 3 µg mL−1 showed proportional decreases in absorptivity. Analysis of 8 geochemical reference materials by the modified method (using NH2OH) yielded excellent agreement with published values and a mean relative standard deviation of 0.6%. Total-Fe results obtained using the light treatment, however, were generally lower (∼2% relative) than the NH2OH values, although this difference decreased with longer irradiation periods. Use of NH2OH was deemed preferable because it was simpler, faster, minimized interferences from Mn and eliminated the need for specialized apparatus. Lastly, MICA Fe was shown to be unreliable as a primary reference material for Fe(II) determinations.
Characterization of Intercalated Smectites Using XRD Profile Analysis in the Low-Angle Region
Authors: Janeba Daniel , Čapková Pavla , Weiss Zdeněk , Schenk Henk 
Published: August 2006

AbstractX-ray diffraction (XRD) characterization of natural and intercalated smectites is usually limited to the apparentd-value estimated from the peak maxima in the raw data. This can lead to the misinterpretation of the measured data. In the case of XRD, the interference function is modulated by instrumental factors (Lorentz-polarization factor, diffraction geometry) and physical factors (structure factor, surface roughness effect). These effects lead to diffraction profile distortions, depending on the diffraction angle and peak full width at half maximum (FWHM). As a result, the diffraction profiles for structures with large line broadening (FWHM > 1°) exhibit a significant peak shift (Δd∼ 1.5 Å), especially at low angles (2θ ≤ 10°). The present work deals with the detailed analysis of all these effects, their corrections and their consequences for the interpretation of diffraction patterns (including possible errors in determining lattice parameters or the structure model). The investigated materials were montmorillonites (MMT) intercalated with hydroxy-Al polymers. Diffraction profile analysis revealed the correctedd-values and showed that the intercalated sample is not a mixed-layered structure. As a result a structural model of the interlayer is presented.
Measurement of Fundamental Illite Particle Thicknesses by X-Ray Diffraction Using PVP-10 Intercalation
Authors: Eberl D. D. , Nüesch R. , Sucha V. , Tsipursky S. 
Published: August 2006

AbstractThe thicknesses of fundamental illite particles that compose mixed-layer illite-smectite (I-S) crystals can be measured by X-ray diffraction (XRD) peak broadening techniques (Bertaut-Warren-Averbach [BWA] method and integral peak-width method) if the effects of swelling and XRD background noise are eliminated from XRD patterns of the clays. Swelling is eliminated by intercalating Na-saturated I-S with polyvinylpyrrolidone having a molecular weight of 10,000 (PVP-10). Background is minimized by using polished metallic silicon wafers cut perpendicular to (100) as a substrate for XRD specimens, and by using a single-crystal monochromator. XRD measurements of PVP-intercalated diagenetic, hydrothermal and low-grade metamorphic I-S indicate that there are at least 2 types of crystallite thickness distribution shapes for illite fundamental particles, lognormal and asymptotic; that measurements of mean fundamental illite particle thicknesses made by various techniques (Bertant-Warren-Averbach, integral peak width, fixed cation content, and transmission electron microscopy [TEM]) give comparable results; and that strain (small differences in layer thicknesses) generally has a Gaussian distribution in the log-normal-type illites, but is often absent in the asymptotic-type illites.
Dehydration, Diffusion and Entrapment of Zinc in Bentonite
Authors: Ma Y. B. , Uren N. C. 
Published: August 2006

AbstractInteractions with bentonite are important in the chemical speciation and fate of heavy metals in soils and other ecosystems. The interactions of Zn with bentonite were studied using X-ray diffraction (XRD), dehydration, kinetic and sequential extraction procedures. The species and activity of Zn retained by bentonite were affected markedly by pH. The Zn(OH)+ was retained by bentonite prepared at pH ≥ 6.9. The extent of dehydration of Zn(OH)+-bentonite was higher than that for Zn-bentonite. At a relative humidity of 55.5%, the basal spacing of the Zn(OH)+-bentonite was from 1.21 to 1.26 nm with 1 water sheet and that of the Zn-bentonite was 1.51 nm with 2 water sheets. The greater affinity of Zn(OH)+ for bentonite than Zn was associated with a lower degree of hydration. When an aqueous suspension of Ca-bentonite was incubated with soluble Zn, the concentration of Zn retained by the Ca-bentonite was linearly related to the square root of time. The rate of the interaction was controlled probably by the interlayer diffusion and subsequently by the diffusion into the ditrigonal cavities in bentonite. The Zn retained by bentonite was dehydrated in situ so as to increase the bonding of Zn with surfaces of bentonite. With hydrothermal treatment the retained Zn could diffuse easily into the cavities and transform increasingly to the residual forms that are associated with the entrapped form.
Hydrothermal Origin of Smectite in Volcanic Ash
Authors: Mizota Chitoshi , Faure Kevin 
Published: August 2006

AbstractSmectite and fine-grained quartz were separated from 6 volcanic ash samples collected in Japan from Shinmoe-dake Volcano, southern Kyushu, and Mt. Usu Volcano, southern Hokkaido. Oxygen isotope ratios of smectite in the volcanic ash range from +6.9 to +12.9 per mill (‰), which are comparable to the values of smectite (δ18O = +6.5 and +9.4‰) from currently active geothermal fields. Evaluation of the oxygen isotope data from smectite (δ18O = +6.9 and +8.4‰) and quartz (δ18O = +6.6 to +11.2‰) in volcanic ash erupted from Shinmoe-dake in 1959 indicates a hydrothermal origin at elevated temperatures (150 to 270 °C) from waters that have calculated 8180 values (8180 = -3 to +5%o) that are enriched relative to local meteoric water (δ18O = -7 to -8‰). This precludes an authigenic formation of the smectites under ambient temperatures in crater lakes and/or somma-atrios which had been previously proposed as a plausible mechanism. A peculiar clay flow was extruded on the somma-atrio of Mt. Usu Volcano. The isotopic composition of the clay (<0.5 μm, δ18O = + 12.2‰) and evidence from geophysical exploration over volcanic vents of Shinmoe-dake support the concept that extensive hydrothermal alteration is taking place within volcanic vents.
Molecular Simulations of Montmorillonite Intercalated with Aluminum Complex Cations. Part II: Intercalation with Al(OH)3-Fragment Polymers
Authors: Čapková P. , Driessen R. A. J. , Numan M. , Schenk H. , Weiss Z. , Klika Z. 
Published: August 2006

AbstractThe Crystal Packer module in the Cerius2 modeling environment has been used to study the structure of montmorillonite intercalated with Al(OH)3-fragment (gibbsite-like) polymers. Basal spacings in gibbsite-like polymers arranged in 2 layers in the interlayer of montmorillonite varied in the range 19.54–20.13 Å, depending on the type and arrangement of Al(OH)3 fragments. The inhomogeneous distribution of intercalating species in the interlayer and, consequently, the turbostratic stacking of layers has been found for gibbsite-like polymers as well as in the case of Keggin cations (Čapková et al. 1998). The dominating contribution to the total sublimation energy comes from electrostatic interactions for both intercalating species, gibbsite-like polymers and Keggin cations.
Electron Microscopy and X-Ray Analysis of Lacustrine Clays from the Charo Canyon, State of Michoacán, Mexico
Authors: de la Torre G. Carbajal , Alcántara I. Israde , Rodríguez J. Serrato , Reyes-Gasga J. 
Published: August 2006

AbstractIn this paper we analyzed by electron microscopy and X-ray diffraction (XRD) the exposed lacustrine clay in a stratigraphic column at Charo Canyon, State of Michoacán, Mexico. Smectite, cris-tobalite, albite and quartz are the main mineral species in the sediments. Smectite is the most abundant and has a nanometric twinned small particle habit. The low crystallinity of the smectite detected in some of the samples seems to be associated with instability of the paleohydrological regime in which clayey material was deposited. Iron from underlying volcanic ash is apparently responsible for the iron concentration detected in the smectite structure.
Comparative Study of the Mobility of Major and Trace Elements During Alteration of an Andesite and a Rhyolite to Bentonite, in the Islands of Milos and Kimolos, Aegean, Greece
Authors: Christidis George E. 
Published: August 2006

AbstractProgressive alteration by seawater of an andesite in the Aegean Island of Milos and an ignimbrite in the Aegean Island of Kimolos, Greece, formed bentonites with or without zeolites. Both profiles are dominated by migration of alkalis and uptake of Mg, Fe and H2O, while Al and Ti are immobile. The relative removal of alkalis controls the formation of either smectite or zeolites. The behavior of Ca and Si depends on the chemistry of the parent rock. In the rhyolitic profile, alteration is controlled by gain of Mg, Fe2+ and Ca and loss of Na, K and Si, while in the andesitic profile by gain of Mg and Fe2+ and loss of Na, K and Ca. In both profiles, significant uptake of SO4- was not observed. Moreover Zr, Nb, V and Ni are immobile and have been enriched residually, while Sr, Rb and Y are lost in both profiles. Thorium is immobile in the rhyolitic profile but is leached in the andesitic profile. Also, the rare earth elements (REE) display fractionation in both profiles; the degree of fractionation increases with the degree of alteration to bentonite. Fractionation of the REE in both profiles and mobility of Th in the andesitic profile are related to the existence of monazite (rhyolitic profile) and apatite (andesite profile). The REE and Th appear to partition into phosphates rather than smectite.The mobility of Y coupled with the immobility of Nb increases the Nb: Y ratio with advancing alteration, rendering discrimination diagrams that use this ratio to determine the nature of the protoliths misleading. Mass balance calculations showed that in the smectite-rich zones the water: rock (WR) ratio might be as high as 13:1 in both profiles, while in the zeolite-bearing zones it is about 5.5:1. Such WR ratios explain the observed extensive mass transfer and suggest that the pore fluid chemistry might overprint the chemical characteristics of the parent rocks controlling smectite and bentonite chemistry.
Modeling Adsorption-Desorption Processes of Cd on Montmorillonite
Authors: Undabeytia T. , Nir S. , Rytwo G. , Morillo E. , Maqueda C. 
Published: August 2006

AbstractAdsorption-desorption of Cd to Ca montmorillonite (SAz-1) was studied at concentrations ranging from 44.5 to 266.8 μM. An adsorption model was employed in the analysis of the data. The procedure consists of solving the electrostatic Gouy-Chapman equations and calculating adsorbed amounts of the cations as the sum of the cations residing in the double-layer region, and the cations chemically bound to the surface, in a closed system. The model also accounts explicitly for cation complexation in solution. The model yields good predictions for the adsorbed amounts of Cd, Ca and Mg, by employing binding coefficients from previous studies for the divalent cations and for Na, K and CdCl+. The model calculations also yield good predictions for the apparent hysteresis observed in the adsorbed amounts of Cd after each of 3 cycles of desorption. The apparent hysteresis is explained by the reduction in the total concentrations of Ca and Mg in desorption cycles, and the corresponding increase in the magnitude of the surface potential. Our estimates indicate that adsorption of Cd is mostly to planar, rather than edge sites of the clay mineral.
Vermicular Kaolinite Epitactic on Primary Phyllosilicates in the Weathering Profiles of Anorthosite
Authors: Jeong Gi Young 
Published: August 2006

AbstractThe microtextural changes in the kaolinization of primary phyllosilicates including biotite, sericite, clinochlore and muscovite were investigated by scanning electron microscopy (SEM) and microchemical analysis of thin sections of weathered anorthosite. Kaolinization began at grain edges and propagated toward the interior. Grains were highly fanned out from the edges and exfoliated into several flakes along the basal cleavages, producing lenticular voids. Finally, long vermicular kaolinite pseudomorphs were formed after primary phyllosilicates. Statistical analysis showed a ninefold increase in volume during the kaolinization of biotite, suggesting that most AI in the kaolinite was imported from ambient weathering solution. Weathering primary phyllosilicates supplied templates suitable for the thick epitactic overgrowth of kaolinite to form long vermicular pseudomorphs. AI was sufficiently available due to the intense weathering of soluble anorthosite. Although present in small amounts, primary phyllosilicates gave high volumetric and mineralogical contributions to the weathering profiles by facilitating kaolinite precipitation.
Hard and Soft Acid-Base Model Applied to Bivalent Cation Selectivity on a 2:1 Clay Mineral
Authors: Auboiroux M. , Melou F. , Bergaya F. , Touray J. C. 
Published: August 2006

AbstractWe applied the hard and soft acid-base (HSAB) model (Xu and Harsh 1990a, 1990b) to bivalent cation exchange on a purified Ca-montmorillonite. As a result, a satisfactory model is proposed to describe the gradual selectivity of exchange with Ca for 4 of the 6 metals studied (Cd, Cu, Pb, Zn). The selectivity is predicted as a function of the differences of electronegativity and softness of the metals. The deviation of Ni and Co data from the predicting model is interpreted in terms of hydration (Ni and Co being the most strongly hydrated ions). The fitting parameters of the model, α and β, are related to the electronegativity and softness characteristics of the surface, respectively. Their ratio gives information on the nature of bonding. Results suggest that covalent bonding modifies electrostatic interactions, which in turn affect selectivity, with an increasing influence of covalent bondings in the order: Pb < Cd < Zn < Cu.To balance the lack of representativity of the model for the small molar fraction (NM), we propose to associate to the HSAB model an equation describing the variation of the Vanselow selectivity coefficient as a function of the molar fraction of metal on clay.
The Interlayer Structure of La-Vermiculite
Authors: Slade Phillip G. , Self Peter G. , Quirk James P. 
Published: August 2006

AbstractThe structure of the interlayer cation-water system in La-vermiculite with a unit cell of a = 5.33(5), b = 9.18(6), c = 15.13(9) Å and β = 96.82(7)° has been determined in space group C2/m. Under ambient conditions, the interlayer La cations are distributed on a 3a × b superlattice which disappears on dehydration but returns on rehydration. The basal spacing does not change during the dehydration/rehydration process. The character of the superlattice spots indicate that the cation-water system, at ambient conditions, is ordered over relatively large domains. The La cations are surrounded by 8 neighboring water molecules in a distorted cubic arrangement. The spaces between the La-water clusters are occupied by triads of water molecules that are relatively mobile.