bluuebunny/crossref_metadata_2025 huggingface dataset:
The Genesis of a Mordenite Deposit by Hydrothermal Alteration of Pyroclastics on Polyegos Island, Greece
Authors: Kitsopoulos Konstantinos P.
Published: August 2006

The vitric component of the silicic pyroclastic flows and surge deposits (Prassa ignimbrite unit), from the northwestern exposures of the pyroclastics formation of Polyegos Island, South Aegean Sea Volcanic Arc in Greece, is replaced by authigenic zeolite and clay minerals. Mordenite dominates, and clinoptilolite (heulandite type 3), illite and illite-smectite (I-S) are subordinate. Opal-CT, quartz, feldspar, biotite and halite complete the mineralogical suite. In the southwestern part of the pyroclastics formation (Myrsini pyroclastics unit), kaolinite, halloysite, alunite and amorphous silica are the major mineralogical constituents as a result of a strong hydrothermal alteration by solutions enriched in SO42-. Scanning electron microscope (SEM) examination proved that the 1st type of zeolites formed within the area were heulandite minerals, following the formation of smectite, as a result of the activity of pore fluids within the volcaniclastic pile. There was no substantial evidence to support a hypothesis that mordenite was formed with the heulandite minerals after the initial stages of glass dissolution, other than some very minor mordenite that was formed from a gel-like type of material. The majority of mordenite present is most often draped over and formed from the crystals of heulandite minerals. Heulandite minerals often show advanced dissolution effects. The mineral dissolution was due to the emplacement of rhyolite lava domes and flows and the associated temperature rise and circulation of hydrothermal fluids, which had also mixed with seawater. The volcanic activity raised the temperature and changed the pore fluid chemistry, and the more unstable members of the heulandite minerals group were transformed to mordenite. Clinoptilolite (heulandite type 3), which was found within a few samples, was thermally more stable than any heulandite type 1 or 2 phases initially present. Therefore, clinoptilolite was either transformed more slowly or within a very few cases, it has not been affected at all. A heulandite-minerals-derived material acted as the major precursor for the formation of mordenite. The temperature increase within the area and the later hydrothermal alteration effect are also indicated by the illitization of the smectite. Mordenite is also found to have formed from I-S clays. Overall, mordenite formed as a result of elevated temperature and high Na+ concentration.
Infrared Reflectance Study of Thermally Treated Li- and Cs-Montmorillonites
Authors: Karakassides M. A. , Petridis D. , Gournis D.
Published: August 2006

The structure of Li- and Cs-montmorillonites was studied using infrared (IR) reflectance spectroscopy. The spectra of heat-treated clays between 80 and 220 °C were analyzed by Kramers-Krönig inversion in order to obtain the optical and dielectric properties of the clays. The analysis revealed the transverse-optic (TO) and longitudinal-optic (LO) components of the asymmetric stretching vibration of Si-O-Si bridges. Major differences, in particular the systematic development of new bands, were found in the Li-montmorillonite LO and TO spectra with increasing temperature. These changes were attributed to the migration of the Li-cations into the layer structure.
Application of Inverse Gas Chromatography to the Study of the Surface Properties of Slates
Authors: Rodriguez M. A. , Rubio J. , Rubio F. , Liso M. J. , Oteo J. L.
Published: August 2006

Inverse gas chromatography (IGC) at zero surface coverage was used for determining the surface characteristics of a slate sample. Previously this sample had been characterized by means of X-ray diffraction (XRD), chemical analysis, infrared (IR) spectroscopy and nitrogen adsorption. Quartz, muscovite and chlorite were the minerals foming the slate. A well-defined mesoporous structure with pores of 15 Å of interlayer distance was observed. Chemical analysis and IR spectroscopy corroborated the X-ray results. The surface characteristics of the slate were defined in relation to nonspecific and specific interactions with organic molecules. In accordance with the nonspecific interactions, the London component (γSD) of the surface free energy gave an estimation of the surface energy of the slate sample. The obtained values for γSD were 140.0, 124.8, 108.2 and 96.8 mN m-1 at 100, 110, 120 and 130 °C, respectively. These values were characteristic of an inorganic sample of high surface energy. The values of the thermodynamic variables—differential heat of adsorption, free energy and entropy of adsorption—were in accordance with these results. At the same time, specific interactions were characterized by the ηπ parameter and the acid-base (KA, KB) indices. The positive value of ηπ (0.09 kJ mol-1) indicated the presence of Lewis acidic sites on the slate surface. The value of KA (acid index) of 1.17 was higher than the value of KB (base index) of 0.37; this result confirmed the acidic nature of the studied slate's surface.
Relationship Between Cation Exchange Selectivity and Crystalline Swelling in Expanding 2:1 Phyllosilicates
Authors: Laird David A. , Shang Chao
Published: August 2006

A theoretical model describing the interaction between crystalline swelling and cation exchange selectivity is proposed for expanding 2:1 phyllosilicates. The model is based on the assumption that changes in basal spacing of a clay are phase changes, and that each phase of a clay has a different selectivity constant for a particular cation exchange reaction. Energy barriers stabilize the various phases over a limited range of interlayer ionic composition. These energy barriers cause hysteresis in crystalline swelling, which in turn causes hysteresis in cation exchange. Results are presented for an experiment involving Ba-Mg exchange on a synthetic fiuoro-hectorite. The results demonstrate key aspects of the proposed model, including a correlation between measured selectivity coefficients and basal spacings (R2 = 0.85), an abrupt change in basal spacing that corresponds with an abrupt change in selectivity and corresponding hysteresis in crystalline swelling and cation exchange selectivity. The results also demonstrate increased selectivity for the preferred cation (Ba) at high solution mole fraction of the preferred cation. This trend is opposite of that observed for heterogeneous natural smectites but consistent with predictions of the model for a homogeneous smectite.
Characterization of the Solids Obtained by Pillaring of Griffithite (High Iron Content Saponite) with Al-Oligomers
Authors: Vicente Miguel Angel , Suarez Mercedes , Bañares-Muñoz Miguel Angel , Martin-Pozas Jose
Published: August 2006

Griffithite, a high Fe content saponite (Griffith Park, California) was pillared with Al polymeric solutions, using different Al/clay ratios. The cation exchange began when Al-polycation solutions were added, being completed during the dialysis of the samples. Pillared solids were obtained by calcination of intercalated precursors at 500 °C. The content of A12O3 increased from 7.35% in the natural griffithite to about 14% in the pillared samples, equivalent to the fixation of about 1.4 mmol Al per g of clay. The surface areas of the pillared griffithite were between 230–300 m2 g-1. The intercalation and pillaring of griffithite were easier than that of a less-crystalline nonferrous saponite.
Calorimetric Measurement of the Enthalpy of Hydration of Clinoptilolite
Authors: Carey J. William , Bish David L.
Published: August 2006

The 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

The 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

The 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

A 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

X-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

The 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

Interactions 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

Smectite 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

The 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

In 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

Progressive 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

Adsorption-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

The 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

We 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

The 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.
Stability of n-Butylammonium Vermiculite in Powder and Flake Forms
Authors: Jiménez de Haro María C. , Ruiz-Conde Antonio , Pérez-Rodríguez José L.
Published: August 2006

Interaction between n-butylammonium (BA) chloride and vermiculite from Santa Olalla (Spain) has been studied in large flake (5 × 5 × 0.1 mm) or ground powder (≤80 µm) samples. The differences in adsorption and decomposition of BA ions in both particle sizes have been established. In the interlamellar space, the BA ion remains unaltered in powder samples, but is degraded in flakes. The experimental results suggest decomposition of the BA in the interlamellar space of vermiculite flakes by breaking of the C-N bond. The degradation of BA takes place over a short period. The variety with BA in the interlamellar space is transformed into a new one, due to the degradation of alkylammonium. The transformation occurs through an interstratified phase formed between BA-vermiculite and NH4-vermiculite, and finally a phase appears in which only ammonium is present in the interlamellar space. Due to the many industrial applications of alkylammonium-clays, determination of the stability of alkylammonium in the interlamellar space of clay minerals is of great importance.
Randomly Interstratified Kaolinite-Smectite from Galicia (NW Spain): A New Procedure for Determination
Authors: Corti Giuseppe , Fernández Sanjurjo Maria Jose , Ugolini Fiorenzo Cesare
Published: August 2006

A new protocol was developed to examine an assemblage of kaolinite-smectite in a buried horizon of a paleosol developed on gabbro parent material. The new extraction procedure appears suitable for removing kaolinite and for ascertaining the nature of the smectite interstratified with kaolinite. Smectite was identified by X-ray diffraction (XRD) and infrared (IR) patterns, cation exchange capacity (CEC) and chemical analyses.

The results obtained provide for increased understanding of the process of transformation of smectite into kaolinite.
Properties of Water in Calcium- and Hexadecyltrimethylammonium-Exchanged Bentonite
Authors: Anderson Michael A. , Trouw Frans R. , Tam Cheok N.
Published: August 2006

Dynamical and thermodynamic properties of water at room temperature in Ca- and hexade-cyltrimethylammonium- (HDTMA) exchanged bentonite were determined for 4 different water contents (~0.03–0.55 g water g-1 clay). Incoherent quasi-elastic neutron scattering (QENS) was used to measure the translational and rotational mobility of water in the clays, while chilled mirror dewpoint psychrometry measured water activity of the samples, differential scanning calorimetry (DSC) provided information about the temperature of dehydration and X-ray diffraction (XRD) quantified layer spacings for the clays. The neutron scattering data were fit to a jump diffusion model that yielded mean jump lengths, jump diffusion residence times and rotational relaxation times for water in the clays. Mean jump lengths were quite similar for the 2 different cation saturations at equivalent water contents, and decreased with increasing water content. The fitted jump lengths ranged from 0.27–0.5 nm and were 2–4 times larger than that found for bulk water (0.13 nm). Jump diffusion residence times were 3–30 times longer than that for bulk water (1.2 ps) and also decreased with increasing water content. The residence times were somewhat shorter for HDTMA-clay as compared with Ca-clay at equivalent water contents. Rotational motion was less strongly influenced than translational motion by the presence of the clay surface. The energy state of water in the 2 cation saturations were quite different; dehydration temperatures for the HDTMA-clay were approximately 30 °C lower than the Ca-clay at equal water contents, while water activities, as P/P0, were up to 0.6 units higher. A linear relationship was found between water activity and the translational diffusion coefficient, although at the highest water content, the diffusion coefficient of water for the HDTMA-clay was approximately 30% higher than that measured for bulk water.
Five-Coordinate Aluminum in Allophane
Authors: Childs Cyril W. , Hayashi Shigenobu , Newman Roger H.
Published: August 2006

Samples of Silica Springs allophane from Tongariro National Park, New Zealand, having Al/Si atomic ratios in the range 1.1-1.9, were studied by 27Al nuclear magnetic resonance (NMR) spectroscopy with high field strength (9.4 and 11.7 T) and fast magic-angle spinning (MAS) (9-13 kHz). Spectra for all samples show peaks for 6- and 4-coordinate Al and also for 5-coordinate Al. For 1 sample, the peak for 5-coordinate Al is dominant. Use of 2 instruments and 2 field strengths allowed the integrity of the spectra and the assignment of 5-coordinate Al to be verified. The “true” chemical shift (after a small correction for quadrupolar shift) observed for 5-coordinate Al in Silica Springs allophane is 36 ± 1 ppm, which is consistent with shifts reported for 5-coordination in well-characterized crystalline structures. We suggest that 5-coordination in Silica Springs allophane is associated with the edges of fragments of incomplete octahedral sheets that are bonded to disordered, though more complete, curved tetrahedral sheets in the primary particles of this allophane. Other allophanes with Al/Si < 2, and which are poor in octahedra relative to tetrahedra, may also have significant Al in 5-coordinate sites.
Characterization of Octahedral Substitutions in Kaolinites Using Near Infrared Spectroscopy
Authors: Petit S. , Madejová J. , Decarreau A. , Martin F.
Published: August 2006

Fourier transform infrared (FTIR) spectroscopy investigations in the near infrared (N1R) region of synthetic and natural kaolinites with various octahedral substitutions have been carried out in order to elucidate the relationships between the substituted cations and specific features of the NIR spectra. The combination modes of the OH stretching and bending vibrations characterizing Fe(III), Ga(III) and Cr(III) octahedral substitutions are identified in the NIR region at 4466, 4498 and 4474 cm-1, respectively, and the first overtones of the OH stretching vibrations at 7018, 7018 and 6986 cm-1, respectively. As far as we know, the bands of kaolinites containing Ga(III) or Cr(III) have not been reported yet. For both Ga(III) and Cr(III), the NIR observations explain why the bending vibration bands of AlGaOH and AlCrOH groups are not observed in the middle infrared (MIR) region.
Application of an Internal Standard Technique by Transmission X-Ray Diffraction to Assess Layer Charge of a Montmorillonite by Using the Alkylammonium Method
Authors: Janek M. , Smrčok L’.
Published: August 2006

Transmission X-ray diffraction (XRD) of C6–16alkylammonium ion-exchanged montmorillonite SAz-1 with Ag-behenate as an internal standard provided accurate estimates ofd(001) values of the alkylammonium ion-exchanged montmorillonite. Inspection ofd(001) values were made to assess the possible formation of gauche conformers (alternate arrangements of the molecules) in the interlayer and to determine the critical carbon chain length,nC. Using conventional constraints fornC(I′) andnC(II) equal to 1.36 and 1.77 nm, respectively, provided ambiguousnC(I′) andnC(II) values. The dependence of full-width at half-maximum values onnCallowed better estimates ofnC(I′) andnC(II) because “integral” and “non-integral” peak characteristics relating to interstratification could be included in the assessment.

The effect of inaccurate estimates ofnC(I′) andnC(II) values on calculated interlayer cation exchange capacity (Ci) using two conventional concepts of calculation were compared. It was found that a procedure based on the summation of fractions of the layer charge gave relative errors ofCi<2%, even where the number of carbon atoms corresponding to bothnC(I′) andnC(II) differed by ± 1nCfrom the correct values. This method of calculation ofCiis recommended when reliable values ofCiare needed.
Diffuse Reflectance Spectra of Al Substituted Goethite: A Ligand Field Approach
Authors: Scheinost Andreas C. , Schulze Darrell G. , Schwertmann Udo
Published: August 2006

Previous investigations of goethite revealed a substantial variation of color and diffuse reflectance spectra (DRS) in the extended visible range (350–2200 nm). To better understand the causes of this variability and to assess the potential of DRS as a mineralogical tool, we investigated the DRS of pure and Al-substituted goethite, α-Fe1−xAlxOOH with x from 0 to 0.33, and mean crystal lengths (MCL) from 170 to 1800 nm. The strongly overlapping ligand field bands were extracted by fitting the single-electron transitions 6A1 → 4T1, 6A1 → 4T2, 6A1 → (4E; 4A1), and 6A1 → 4E(4D) as functions of the ligand field splitting energy, 10 Dq, and the interelectronic repulsion parameters, Racah-B and -C. With x increasing from 0 to 0.33, 6A1 → 4T1 decreased from 10,590 to 10,150 cm−1 (944 to 958 nm), and 6A1 → 4T2 decreased from 15,310 to 14,880 cm−1 (653 to 672 nm), while 10 Dq increased from 15,770 to 16,220 cm−1. From the change of 10 Dq we calculated a decrease of the Fe-(O,OH) distances from 202.0 to 200.9 pm (−0.5%). This decrease is smaller than the average decrease of all (Al,Fe)-(O,OH) distances (−1.8%) calculated from the change of the unit-cell lengths (UCL). That is, there remains a substantial difference in size between the larger Fe- and the smaller Al-occupied octahedra in the solid solution which may indicate the existence of diaspore clusters within the goethite structure. The increasing strain in the crystal structure due to the size mismatch and limited contractibility of the oxygen cage around Fe may be the primary reason for Al substitution being restricted to x < 0.33. The bands 6A1 → (4E; 4A1) and 6A1 → 4E(4D) did not shift, indicating a constant covalency of the Fe-(O,OH) bonds with B = 628 cm−1 and C = 5.5B. Whereas variation of band energies could be explained in terms of the Fe-(O,OH) ligand field, the variation of color and band intensities was mainly determined by crystal size. Although our study confirmed the potential of DRS for mineralogical investigations, there is still a gap between the fundamental theory and the explanation of some spectral features.
Fe3+-Rich Montmorillonite-Beidellite Series in Ayvacik Bentonite Deposit, Biga Peninsula, Northwest Turkey
Authors: Çoban Fazli , Işik Ece Ö.
Published: August 2006

The Ayvacık bentonites, products of Miocene calc-alkaline volcanic rocks, are composed of smectite of the montmorillonite-beidellite series. Fault-related hydrothermal solutions have altered andesitic rocks to dioctahedral smectites. Differences in the micro-morphology of the two end-members are distinguished by scanning electron microscopy (SEM) studies. The beidellite particles are of delicate ribbons and rosette habits, whereas montmorillonite particles are very thin, curled sheets and flakes. Clay size (<2 µm) fractions contain (in wt. %) 54.90–56.80 SiO2, 19.65–28.54 Al2O3, 0.45–6.28 Fe2O3, 0.10–1.72 CaO, 0.80–4.15 MgO, 0.55–1.88 K2O, and 0.08–1.15 Na2O, which confirm that the beidellites are Fe-rich (5.06–6.28 wt. %), except for one sample (0.45 wt. % Fe2O3). The Greene-Kelly test (Li-saturation and heating) gave very good results for the measurement of the d(001) of the two end-members. Nickel, Ti, and Cr enrichment in smectite is related to the chemical composition of hydrothermal solutions that passed through the ophiolite complex.
Surface Layer Types of Kaolinite: A High-Resolution Transmission Electron Microscope Study
Authors: Ma Chi , Eggleton Richard A.
Published: August 2006

High-resolution transmission electron microscopy (HRTEM) examinations have indicated that three types of surface layers may exist in natural kaolinite crystals. Type 1 has the expected 7-Å surface layer as terminations. Type 2 has one 10-Å pyrophyllite-like (or low-charge beidellite-like) layer as the surface layer on one side of a kaolinite particle (i.e., the layer sequence is TOTOTO … TOTOTOT, where T stands for tetrahedral sheet, O for octahedral sheet). Some industrial-grade highly-ordered kaolinites have such a 10-Å 2:1 surface layer on one side of the crystal. The spacing between the 10-Å layer and the adjacent 7-Å layer is not expandable. Type 3 kaolinite has one or several 10-Å collapsed smectite-like layers at one or both sides of a stack, i.e., (TOT)TOTO … TOTOTOT(TOT), forming a special kind of kaolinite-smectite interstratification. This type has only been recognized in some poorly-ordered kaolinites. The surface smectite layer(s) contribute to higher cation exchange capacity (CEC) values. These 10-Å surface layers were not detectable by X-ray diffraction (XRD). HRTEM and electron diffraction examination also revealed the structural features of individual kaolinite crystals. All kaolinites (from various origins and sources) studied show C-face-centering Of non-hydrogen atoms. Defects within the layer structure are common in both well-ordered kaolinite and poorly-ordered kaolinite.
Structural Study of Tetramethylphosphonium-Exchanged Vermiculite
Authors: Vahedi-Faridi A. , Guggenheim Stephen
Published: August 2006

Vermiculite from Santa Olalla, Spain, was intercalated with tetramethylphosphonium [P(CH3)4+ = TMP], using a TMP-bromide solution at 70°C for three weeks. The resulting TMP-exchanged vermiculite, which contained a small (<5% of a site) amount of residual interlayer Ca, showed near perfect three-dimensional stacking. Cell parameters are a = 5.3492(8) Å, b = 9.266(2) Å, c = 14.505(6) Å, β = 97.08(2)°, space group is C2/m, and polytype is lM. Single-crystal X-ray refinement (R = 0.052, wR = 0.061) located two crystallographically unique sites for the phosphorus atoms (TMP molecule). The phosphorus atoms are occupied partially [P1 = 0.146(6), P2 = 0.098(5)] and are offset from the central plane of the interlayer by 1.23 Å to form two P-rich planes in the interlayer. Electrostatic interactions between the P cations and basal oxygen atoms essentially balance the negative charge associated with Al for Si substitutions in the tetrahedral sites. In addition, the orientations of the TMP molecules are probably different owing to packing constraints. The H2O site is located in the center of the interlayer, at the center of the silicate ring, and ∼3.09 Å from the Ca, which is also located on the central plane of the interlayer. Other H2O molecules are present in the interlayer, but could not be located by the diffraction experiment because they are randomly positioned in the interlayer. The tetrahedral rotation angle, α, is affected by the intercalation of TMP relative to tetramethylammonium (TMA), thus indicating that 2:1 layers are not simply rigid substrates, and that dynamic interactions occur during reactions involving adsorption and exchange.
Comparison of Adsorption of Phosphate, Tartrate, and Oxalate on Hydroxy Aluminum Montmorillonite Complexes
Authors: He J. Z. , De Cristofaro A. , Violante A.
Published: August 2006

Competitive adsorption between phosphate, tartrate and oxalate was studied on two hydroxy aluminum montmorillonite complexes (AlMt1.6 and AlMt6), which were prepared by adding a base to pH 5.5 to samples containing 1.6 and 6.0 mol Al per kg clay. The quantities of phosphate, tartrate and oxalate adsorbed were more closely related to the amount of OH-Al species coatings on the montmorillonite than to the surface area of the complexes. The adsorption capacity of phosphate was much greater than that of tartrate or oxalate for both samples. Adding molar amounts of oxalate and tartrate resulted in an oxalate/tartrate adsorption ratio (Rf) of ∼1. However, in the presence of phosphate, Rf values were <1.0, and the Rf values decreased with increasing amounts of added phosphate, indicating that tartrate competed with phosphate more effectively than oxalate. The presence of tartrate also reduced phosphate adsorption by the complexes. The efficiency of tartrate in reducing phosphate adsorption increased by increasing the initial tartrate/phosphate molar ratio and by adding tartrate 2 h before phosphate addition. Tartrate and oxalate added as a mixture in equimolar quantities were much more effective in inhibiting phosphate sorption than tartrate alone under the same organic ligand concentrations, probably because more sites with high affinity for both the organic ligands were occupied by tartrate and oxalate than by tartrate alone. The efficiency of tartrate alone, or combined with oxalate, in preventing phosphate adsorption was greater for the complex containing a lesser amount of OH-Al species coating the montmorillonite surfaces. This result may be attributable to a greater proportion of sites specific for organic ligands present on AlMt1.6 compared to AlMt6 complex.