bluuebunny/crossref_metadata_2025_split huggingface dataset:
Layer Charge-Cation-Exchange Capacity Relationships in Montmorillonite
Authors: Maes André , Stul M. S. , Cremers Adrien 
Published: August 2006

AbstractThe charge density distribution among different classes of a series of reduced charge mont-morillonites is heterogeneous as in the parent Camp Berteau clay. In addition, charge reduction proceeds inhomogeneously. Up to 20% differences in charge density can be accounted for by aikyl chains extending at the edges of the clay particle. A realistic charge density-cation-exchange capacity relationship for hec-torite, Otay montmorillonite, and a series of reduced charge montmorillonites of Camp Berteau is obtained by accounting for the influence of particle radius and for the extent of alkyl chains lying outside the clay layers in the charge density calculations.
Ca-K Exchange Reaction and Interstratification in Montmorillonite
Authors: Inoue Atsuyuki , Minato Hideo 
Published: August 2006

AbstractCation-exchange equilibrium for Ca-K-montmorillonite was studied at 35°, 50°, and 90°C and at three total normalities of the equilibrium solution (0.1, 0.05, and 0.01 N). Changes of the standard free energy for the exchange from K-montmorillonite to Ca-montmorillonite were determined to be −53, −270, and −393 cal/eq at 35°, 50°, and 90°C, respectively. Changes of the standard enthalpy and entropy were 1.7 kcal/eq and 5.6 cal/eq/degree at 35°C, respectively. The sign of the change of the standard free energy was found to be determined mainly by the entropy change, in particular, by the hydration entropy of the cations.The calculation of the excess functions indicates that the mixing model of Ca-K-montmorillonite approximates that of a regular solution. Montmorillonite having potassium equivalent ion fraction of 0.1 to 0.7 consists of a random interstratification of Ca-montmorillonite (15.6 Å) and K-montmorillonite (12.6 Å).
Influence of Organic Anions on the Crystallization of Ferrihydrite
Authors: Cornell R. M. , Schwertmann U. 
Published: August 2006

AbstractHydroxy-carboxylic acids inhibit the crystallization of ferrihydrite in the pH range 9–11 in the ordercitric > meso tartaric > L-tartaric ≫ lacticand favor hematite formation relative to goethite in the orderL-tartaric > citric > meso tartaric > lactic.The crystal shape of hematite can change from hexagonal plates to acicular in the presence of these acids. The influence of the acids on the crystallization rises with increasing concentration and with falling pH.The effectiveness in suppressing crystallization depends on whether and how strongly the acid adsorbs on ferrihydrite and how strongly it complexes with Fe3+ in solution. Inhibition of crystallization of hematite is believed to be due to the di- and tricarboxylic acid linking ferrihydrite particles in an immobile network. Goethite formation is suppressed by the acid complexing with Fe in solution and hindering nucleation; strongly adsorbing acids also adsorb on the nuclei and hinder further growth. Certain acids can induce hematite formation because they contain a group which acts as a template for nucleation of hematite.
Effect of Ionic Strength and Ion Pair Formation on the Adsorption of Nickel by Kaolinite
Authors: Mattigod Shas V. , Gibali A. S. , Page A. L. 
Published: August 2006

AbstractAdsorption of Ni(II) by Ca- and Na-saturated kaolinites was studied in equilibrating solutions with total Ni concentrations ranging from 118 to 946 μg/liter. Background electrolytes used in these experiments were 0.005,0.01,0.025, and 0.5 M Ca(N03)2,0.002 and 0.005 M CaSO4, 0.01 and 0.1 M NaNO3, and 0.005 and 0.05 M Na2SO4, Ion speciation in equilibrium solutions was calculated by the computer program GEOCHEM. Computed Ni2+ concentrations and activities at equilibrium were correlated with total Ni adsorbed by kaolinite. Increasing ionic strength resulted in decreasing Ni adsorption. Adsorption of Ni was greater from solutions when NO3 was the dominant anion. Based on adsorption data in SO4 medium, the standard free energy of adsorption of Ni2+ ion on kaolinite was computed to be —27 kJ/mole.
An Interpretation of Cation Selectivity Variations in M+−M+ Exchange on Clays
Authors: McBride Murray B. 
Published: August 2006

AbstractThe decreasing preference of montmorillonite for K+ relative to Na+ as the clay adsorbs increasing amounts of K+ is shown to be the general rule for the exchange of strongly hydrating ions by weakly hydrating ions. Variability in the mass-action selectivity coefficient is interpreted in terms of a composition-dependent surface entropy, which is a function of the chemical properties of the exchanging ion as well as the nature of the adsorption sites. The generally used mass-action form of exchange equation may only be applicable to exchange systems in which both ions have solution-like mobility at the exchanger surface. It is suggested that experimental variables such as ionic strength can greatly influence the degree of fit of data to a given ion-exchange equation.
Formation of Polymeric Species in the Interlayer of Bentonite
Authors: Bart J. C. , Cariati F. , Erre L. , Gessa C. , Micera G. , Piu P. 
Published: August 2006

AbstractInfrared spectroscopic, X-ray powder diffraction, diffuse reflectance, and electron-spin resonance examination of homoionic bentonite from Sardinia treated with diazomethane indicates that poly-methylene was formed in the interlayer position. Polymerization can be attributed to the acidic properties of the residual water in the interlamellar space, depending on the nature of the exchanged ion. The presence of an interlayer polymer causes the clay to assume strong hydrophobic properties.
Clay Deposits of Las Aguilas Formation, Barker, Buenos Aires Province, Argentina
Authors: Zalba Patricia E. 
Published: August 2006

AbstractMineralogical, chemical, and geological aspects of four types of clay deposits in Las Aguilas Formation northwest of Barker in Buenos Aires Province, Argentina, indicate that these products of lateritic alteration of Precambrian granite are predominantly kaolinitic with minor amounts of halloysite, illite, and chlorite. Minor amounts of quartz, feldspars, and ferric oxides are also present. Of the four types, one is suitable for high quality refractories, another can be used for wall tiles and china, and a third, the most abundant, can be used for red ceramics; the fourth has no special use. The abundance of the clays is calculated to exceed eleven million metric tons.
Weathering of Enstatite to Talc Through a Sequence of Transitional Phases
Authors: Eggleton Richard A. , Boland J. N. 
Published: August 2006

AbstractOrthopyroxene (En85) weathers initially by vacancy diffusion, and through this process hydration occurs and a sequence of biopyriboles develops, culminating in a talc-like layer silicate whose structure joins coherently to the orthopyroxene structure. Oxidation of Fe2+ to Fe3+ colors the altering pyroxene yellow. The ‘talc’ does not remain in structural coherence with the pyroxene after it has exceeded a few tens of nanometers in size; it is replaced by a mixture of talc and smectite. In some areas the mixture has an epitactic relation to the pyroxene, but commonly it fills faceted solution holes without crystallographic relation to the parent structure. Continued weathering extends the yellow zone at the periphery of the orthopyroxene, and the alteration product increases in smectite and decreases in 'talc’ During this stage of the reaction, MgO and SiO2 are released to form colorless true talc around the altering pyroxene. Eventually, the yellow alteration may become a smectite pseudomorph after orthopyroxene or it may be changed entirely to a mixture of vein talc and iron oxides. The complete conversion of orthopyroxene to talc plus oxides thus takes place through three sequential mineral reactions without the development of a noncrystalline phase.
Cu2+-Adsorption Characteristics of Aluminum Hydroxide and Oxyhydroxides
Authors: McBride M. B. 
Published: August 2006

AbstractThe nature of Cu2+ adsorption by boehmite, gibbsite, and noncrystalline alumina was studied over a range of equilibrium pH (4.5–7.5) and Cu2+ concentration (10−3–10−8 M) by electron spin resonance (ESR). Available chemisorption sites at pH 4.5 were the most numerous for noncrystalline alumina (~1 mmole/100 g), less for boehmite, and least for gibbsite as indicated by the relative strength of the rigid-limit ESR signal attributed to Cu2+ adsorbed at discrete sites. The chemisorption process involved immobilization of Cu2+ by displacement of one or more H2O ligands by hydroxyl or surface oxygen ions, with the formation of at least one Cu-O-Al bond. As the pH was raised from 4.5 to 6.0, essentially all of the solution Cu2+ appeared to be adsorbed by the solids. However, the noncrystalline alumina and boehmite chemisorbed much of the total adsorbed Cu2+ (10 mmole/100 g), whereas precipitation or nucleation of Cu(OH)2 in the gibbsite system was indicated. Precipitated Cu2+ was more readily redissolved by exposure to NH3 vapor than chemisorbed Cu2+.
Free Energies of Formation of Illite Solid Solutions and Their Compositional Dependence
Authors: Merino Enrique , Ransom Barbara 
Published: August 2006

AbstractElectron probe analyses of diagenetic illites in Eocene sandstones from Kettleman North Dome, California, along with analyses of coexisting interstitial waters were used to calculate apparent molal free energies of formation of the illites at the in situ conditions of 100°C and 150 bars. Various triangular and rectangular compositional plots, once contoured for free energy, crudely indicate that the free energy decreases as the potassium content increases, decreases as the Al-for-Si substitution increases, and appears to be a minimum along a narrow composition valley having ~3% Fe2O3 of octahedral cations. Qualitatively, the shape of the free energy surface suggests only small departures from ideality.The illites and water samples used in the calculations were chosen as close to each other as possible and are in equilibrium. The waters contain mainly Cl−, SO42−, Na+, and Ca2+ and have a total salinity of ~10,000 ppm. The illites, which coexist in the sandstones with diagenetic quartz, albite, and K-feldspar, are phen-gitic and contain 5–9% K2O, 1–3% total FeO, 1% MgO, and minor Na2O, MnO, and TiO2. The Fe2O3/FeO ratio has been set arbitrarily to 7 by comparison with published analyses.Log K (100°C) was first calculated for the equilibrium illite ⇄ ions from the ionic activities obtained through speciation calculations for each water sample. The apparent free energies of formation of illites at 100°C were then calculated. The effect of instrumental uncertainty on the values of ΔGf was assessed by accepting a 2.5 or 3.5% error in the probe analyses and by using a Monte Carlo method of error propagation. The free energies of formation obtained (on the basis of O10(OH2)) range from -1280 to -1320 kcal/mole at 100°C and 150 bars, and their Monte-Carlo uncertainties are less than ±2 kcal/mole. Combining the compositions of natural, coexisting aqueous solutions and mineral solid solutions through thermodynamic equations constitutes a fast method to determine, at least crudely, the free energy-composition surface for the solid solution. This is in contrast to experimental methods such as calorimetry or hydrothermal equilibrium, which are very time-consuming and difficult.
Influence of Exchangeable Cation Composition on the Size and Shape of Montmorillonite Particles in Dilute Suspension
Authors: Schramm Laurier L. , Kwak Jan C. T. 
Published: August 2006

AbstractViscosity and light-transmission measurements of dilute suspensions of montmorillonites having different exchangeable cations were used to calculate relative particle sizes as a function of cation composition, where particle size is expressed as the number of clay plates per tactoid relative to the number of plates per tactoid for Li-montmorillonite, after exchange of Li, Na, K, Cs, and Mg by Ca. Tactoid sizes increased in the order Li < Na < K < Mg < Ca, with the number of plates per tactoid relative to Li-montmorillonite varying from 1.5 for Na- to 6.1 for Ca-montmorillonite. The results for tactoid sizes derived from light transmission and those derived from viscosity data are in reasonable agreement with each other and with literature data for similar systems. Upon exchange of Ca-counterions for Li-, Na-, or K-coun-terions, a sharp initial decrease in tactoid size was observed over approximately the first 30% of cation exchange. Upon further exchange, tactoid sizes changed only slightly, but when Ca was exchanged for Cs or Mg, a much more gradual decrease in particle size was observed.
Electrical Potential Between Dissimilar Clay Double Layers
Authors: Helmy A. K. , Natale I. M. , Mandolesi M. E. 
Published: August 2006

AbstractA model describing the electric double layers in clay-electrolyte systems containing particles with different surface charge densities was developed and used to calculate the film thickness of water present in a clay paste. The average water film thicknesses (~18 Å) calculated by considering the clay to contain 9 groups of particles of different charge densities did not differ from those calculated by assuming one average charge density; provided the minimum potential between particles remained constant. These values, however, were higher than those obtained from gravimetric water determinations by about 30%. The overestimation of the average thickness of the water films by the theoretical model is most likely due to the assumption of a complete parallel arrangement of particles in the paste and the validity of the Gouy theory for double layers on clays.
Electrical Conductivity of Na/Ca-Montmorillonite Gels
Authors: Shainberg I. , Oster J. D. , Wood J. D. 
Published: August 2006

AbstractThe specific conductivity, κg, of Na/Ca montmorillonite gels (0.02 and 0.04 g clay/cm3) as a function of the specific conductivity of the interclay solution, κw, was measured. For low values of κw (<3 mmho/cm) the conductivity curves were convex with respect to xw; at higher values they were linear. The κw at which deviation from linearity began increased with increasing sodium content from 0.7 mmho/cm for the Ca-montmorillonite gel to 2.6 mmho/cm for Na-montmorillonite gel. The intercept of the linear portion of the conductivity curve increased and its slope decreased with increasing exchangeable sodium. The experimental results were described by a conductance model comprised of two elements connected in parallel: an element consisting of the solid and solution phases connected in series, and another consisting of the solution phase. At low electrolyte concentrations, the first element accounts for the curvature of the κg-κw curve, whereas at high electrolyte concentrations, the second element dominates, and the curve is linear with a slope determined by a formation factor and an intercept determined by exchangeable cation mobility.An adjustable parameter in the conductivity term for the first element, which accounts for the thickness of the clay particles, increased with exchangeable Na, and its numerical value indicated that the solid phase also includes the diffuse double layer. The mobility of the exchangeable cation relative to that in water increased from 4% for Ca to 41% for Na with the largest increase occurring between 20 and 40% exchangeable Na. Similar effects of exchangeable Na were evident on the axial ratio of the clay particles calculated from the slopes of the linear lines. These observations are consistent with an exchangeable-ion demixing model where the initial exchangeable Na is adsorbed on the external surfaces of the Ca-montmorillonite tactoids without affecting exchangeable ion mobility or tactoid size. Further additions of exchangeable Na result in Na adsorption on the internal surfaces of the tactoid and tactoid breakdown with a subsequent increase in both exchangeable ion mobility and the axial ratio of the clay particles.
Characterization of Adsorbed Iron in Montmorillonite by Mössbauer Spectroscopy
Authors: Diamant A. , Pasternak M. , Banin A. 
Published: August 2006

AbstractThe Mössbauer effect of Fe57 was used to probe and characterize iron ions adsorbed on the interlayer surfaces of montmorillonite. Measurements were performed with Fe- and Ca-saturated mont-morillonites. At 210°K the intensity of the Fe2+ line was greatly reduced, apparently due to the melting of interlayer water. Neither the structural Fe2+ in Ca-montmorillonite nor the adsorbed Fe3+ in Fe-mont-morillonite were affected by the melting process. From the temperature dependence of the absorption intensity, the effective Debye temperature of all the iron species appears to be approximately the same (θD = 189 ± 5°K). This result allowed for an accurate determination of the population of Fe2+/Fe3+ in various samples.
Methane Solubilities in Clay Slurries
Authors: Stoessell Ronald K. , Byrne Patricia A. 
Published: August 2006

AbstractMethane solubilities at 25°C were measured at 350, 550, and 750 psia in dilute (< 11 wt. %) clay slurries of Na-montmorillonites and argillaceous sediment. Methane solubilities were not significantly affected by the presence of clay. Water hydrated onto the external clay surfaces did not appear to exclude methane. In addition there was no detectable sorption of methane onto the clays. The measured solubilities are consistent with an open structure of the water hydrated onto the clay surface for which the partial molal volume is larger than that of normal water. The results imply that aqueous methane solubilities measured in the laboratory can be used to determine degrees of methane saturation in interstitial solutions in unconsolidated sediments.
Geochemistry of Hydrothermal Chlorite Replacing Igneous Biotite
Authors: Parry W. T. , Downey L. M. 
Published: August 2006

AbstractHydrothermal chlorite replaces igneous biotite in the Gold Hill, Utah, quartz monzonite. Chemical compositions of coexisting biotite and chlorite determined by electron microprobe and wet chemical methods were used to evaluate chemical mass transfer during the alteration process. The mole ratio Mg/(Mg + Fe) varies from 0.52 to 0.65 in the chlorite and from 0.51 to 0.60 in the parent biotite. The Mg content of the chlorite decreases systematically with increase in the volume percent replacement of biotite. Homogenization temperatures of fluid inclusions in nearby quartz microveinlets indicate that the chloritic alteration took place at approximately 200°C.Textural relationships suggest that the alteration of biotite to chlorite is isovolumetric, but a comparison of mineral compositions and mineral assemblages with phase diagrams in which Al or volume are conserved among solid phases suggests that the chlorite compositions are best explained as a function of reaction progress in an Al-conservative system. The chlorite composition changes in response to changes in solution composition produced by the dissolution of successive small amounts of biotite. Representative mass balance for the alteration of all of the biotite to chlorite in 1 m3 of rock containing 336 moles of biotite indicates that 74 moles of Mg, 35 moles of Fe3+, 420 moles of H+, and 2 moles of Mn are added to the rock and that 311 moles of K, 54 moles of Fe2+, 76 moles of Ti, 53 moles of F, and 6 moles of Cl are lost to solution. The mass transfer for partially altered biotite is 11 to 188 moles of K, 2 to 46 moles of Ti, 2 to 44 moles of F, and 0.3 to 6 moles of Cl removed per cubic meter of rock and 1 to 26 moles of Fe3+ and 20 to 347 moles of H+ added. The mass transfer of Mg varies from 12 moles added to 32 moles removed per cubic meter of rock depending on mineral composition and extent of replacement.
Adsorption of Stearic Acid by Chrysotile
Authors: Berkheiser Vaughn E. 
Published: August 2006

AbstractStearic acid adsorption by chrysotile asbestos in hexane was shown to occur by the formation of a Mg-stearate complex on the mineral surface. Infrared spectroscopy showed no evidence of physically adsorbed stearic acid over the range of concentration employed. Absorption bands at 1560 and 1410 cm−1 in the spectrum of the chrysotile-stearic acid complex correspond with band positions in the spectrum of a synthesized Mg-stearate complex. No evidence of the acid form, which produces a band at 1713 cm−1, was present in the spectrum of the chrysotile complexes. At an equilibrium concentration of 0.8 mg stearic acid/ml, the mineral adsorbed 42 mg stearic acid/g. By heating the mineral in molten stearic acid, additional stearic acid beyond that observed by adsorption from solution was adsorbed in the carboxylate form. Calculations based on the molecular dimensions of stearic acid and the crystal structure of chrysotile indicate that the limiting factor in possible surface occupancy is the molecular size of stearic acid rather than the surface density of Mg-OH adsorption sites.
Effects of Temperature on the Sorption of Lanthanides by Montmorillonite
Authors: Miller Steven E. , Heath G. Ross , Gonzalez Richard D. 
Published: August 2006

AbstractThe diffusion of exchanged Yb, Ho, and Eu from interlayer positions in montmorillonite was studied using infrared spectroscopy (IR), X-ray powder diffraction, and cation-exchange measurements. Dehydration of exchanged montmorillonite between 100° and 280°C caused the ions to diffuse into the hexagonal rings of surface oxygens. Subsequent migration into vacant octahedral sites was small regardless of the radius of the cation. Considerable ion fixation in excess of the cation-exchange capacity of the clay was observed at 20°C in both water and a 1:1 water:95% ethanol mixture. Evidence for hydrolysis as a possible mechanism for cation fixation was obtained by observing frequency shifts for deuterated hydroxyl groups using IR spectroscopy. A major IR band centered at 2680 cm−1 was observed for all three lanthanide-exchanged montmorillonites studied and assigned to the OH-stretching frequency of a lanthanide hydroxide. This band intensified on heating at 300°C for 1 hr. An IR band between 690 and 710 cm−1 also was observed for all three lanthanide-exchanged montmorillonites and was assigned to a lanthanide-hydroxyl deformation mode. No hydrolysis was observed for Na-montmorillonite, as expected from the very low hydration energy of Na+.
Effects of Substitution of Germanium for Silicon in Imogolite
Authors: Wada Shin-ichiro , Wada Koji 
Published: August 2006

AbstractImogolites in which a part or all of Si was substituted with Ge were synthesized from solutions containing aluminum ion and silicic and/or germanic acid. The products were similar to natural imogolite in their tubular morphology, electron diffraction patterns, and differential thermal analysis curves. However, the external diameter of the tube increased with increasing Ge substitution up to about 33 Å, and associated changes appeared in the X-ray powder diffraction patterns, suggesting that the substitution of Ge for Si caused a decrease in the curvature of the gibbsite sheet with which SiO- or GeO-tetrahedra are associated. Infrared absorption bands at 995 and 930 cm−1 in imogolite disappeared and new bands appeared at 910 and 810 cm−1 on substitution of Ge for Si, whereas those in the region between 700 and 300 cm−1 remained unchanged or changed little. The former two bands were assigned to Si-O vibrations and the latter bands to Al-O vibrations.