bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Humic Acid on the Crystallization of Aluminum Hydroxides
Authors: Singer A. , Huang P. M.
Published: August 2006

The effects of humic acid (HA) on the crystallization of precipitation products of Al under mildly acidic to alkaline conditions were investigated. The extent of Al precipitation substantially decreased with increasing HA concentration (0 to 75 µg/ml) in the pH range 6 to 10 during the 80-day aging period. The X-ray powder diffraction (XRD) data show that, at pH 6.0, the amount of pseudoboehmite formed in the systems decreased with the increasing concentration of HA present. The proportion of Al hydroxide polymorphs (gibbsite and bayerite) was greatly influenced by the amounts of HA present in the systems. At pH 6.0 and HA concentration of 37.5 µg/ml, all the precipitation products of Al were noncrystalline. At pH 8.0 and a HA concentration of 12.5 µg/ml, the formation of gibbsite and bayerite was completely inhibited and only pseudoboehmite was evident in the XRD patterns. Further increase in HA concentration (25–75 µg/ml HA) at pH 8.0 resulted in no precipitation of Al, and only a broad peak at ∼3.3 Å, characteristic of HA, was observed. The XRD patterns of the precipitates of Al formed in the absence of HA at pH 10.0 showed the characteristic peaks of bayerite. At pH 10.0, the precipitation products of Al formed even at the HA concentration of 2.5 µg/ml yielded no XRD peaks. Infrared absorption spectra and transmission electron micrographs of the precipitation products of Al formed in the systems studied substantiate the findings obtained by XRD. The data obtained in this study indicate that HA affects the formation of Al hydroxide polymorphs, pseudoboehmites and short-range ordered mineral colloids.
Structural Fluorine in Sepiolite
Authors: Santaren Julio , Sanz Jesus , Ruiz-Hitzky Eduardo
Published: August 2006

Sepiolite from Vallecas-Vicálvaro, Spain, contains 1.3% fluorine. Laser microprobe mass spectrometry of this sepiolite suggests the presence of fragments of (SiO2)nOMgF and (SiO2)nOMgOH, which are typical of the sepiolite structure. During thermal dehydroxylation, the fluorine in this sepiolite is removed simultaneously with OH groups at about 750°C. Nuclear magnetic resonance spectroscopy (NMR) of 19F indicates that the fluorine is located in the interior of the sepiolite structure, probably substituting for OH groups, and is homogeneously distributed. In the Vallecas-Vicálvaro sepiolite, about one of every four OH groups bound to Mg2+ is substituted by fluorine. The kinetics of extraction of Mg2+ and F- ions by acid treatment (1 N HCl) shows a more rapid extraction of Mg2+, with a monotonous decrease of the Mg/F ratio as the extent of extraction increases. These results support the internal location of the fluorine, as suggested by the NMR data.
Analytical Transmission Electron Microscope Studies of Plagioclase, Muscovite, and K-Feldspar Weathering
Authors: Banfield Jillian F. , Eggleton Richard A.
Published: August 2006

Analytical and high-resolution transmission electron microscopy of weathered plagioclase and K-feldspar provided microtextural and chemical data that suggest a sequential formation of weathering products. An alteration layer < 1 µm thick on feldspar surfaces had short-range order and was termed protocrystalline. Relative to the parent feldspars the protocrystalline layer was depleted in Ca, Na, K, and Si and significantly enriched in Fe. On plagioclase, the protocrystalline material was replaced by Ca-Fe-K-smectite, another protocrystalline material, and spherical halloysite. Abundant tubular halloysite on the corroded surface apparently formed by reprecipitation of components released by plagioclase dissolution. The K-feldspar was markedly more resistant to weathering than the plagioclase.

Recrystallization of the patchily developed protocrystalline rind produced Fe-bearing, aluminous smecrite, which was ultimately replaced by spherical halloysite and laths of kaolinite. Muscovite laths within plagioclase crystals were converted initially to illite by loss of K, then to randomly interstratified illite/smectite, and then to smectite that contained Mg, little K and Fe, and was more aluminous and contained less Ca than the smectite that originally replaced the plagioclase. Smectite was replaced epitactically by kaolinite. Kaolinite was the stable weathering product of the feldspars and muscovite in the profiles. It probably formed in equilibrium with a solution whose composition was no longer controlled by the microenvironment within the feldspar, but approached that of meteoric water.
Influence of Hydrazine on the Vibrational Modes of Kaolinite
Authors: Johnston C. T. , Stone D. A.
Published: August 2006

Raman and Fourier-transform-infrared (FTIR) spectroscopic methods and X-ray powder diffraction (XRD) techniques have been used to study the influence of hydrazine on the vibrational modes of kaolinite. Strong vibrational perturbations of the OH-stretching and -deformation bands were observed in the Raman and FTIR spectra on intercalation. The intensities of the Raman- and IR-active OH-stretching bands decreased significantly upon intercalation; the intensities of the Raman bands were reduced to a greater extent than the IR bands. The deformation bands were also strongly perturbed by the presence of hydrazine in the interlamellar region. Upon evacuation of the intercalate, two new bands at 3628 and 912 cm−1 were noted, indicating the presence of a different structural conformation of the complex under vacuum. Similar results were obtained using XRD, on evacuation of the kaolinite-hy-drazine (KH) complex the d(001) value decreased from 10.4 to 9.6 Å. Partial collapse of the intercalate from 10.4 to 9.6 Å was probably due to keying of the -NH2 moiety of hydrazine into the siloxane ditrigonal cavity, as indicated by a blue-shift of the inner-OH band from 3620 to 3628 cm-1. Structural OH vibrational modes may therefore be useful probes of amine interactions with clay mineral surfaces.
Preparation of a Kaolinite-Polyacrylamide Intercalation Compound
Authors: Sugahara Yoshiyuki , Satokawa Shigeo , Kuroda Kazuyuki , Kato Chuzo
Published: August 2006

Acrylamide has been polymerized between the layers of kaolinite by heat treatment. Acrylamide monomer was first intercalated by the displacement reaction between a kaolinite-N-methylformamide (NMF) intercalation compound and a 10% acrylamide aqueous solution. The resulting intercalation compound showed a basal spacing of 11.3 Å. Infrared (IR) spectroscopy and 13C nuclear magnetic resonance spectroscopy with cross polarization and magic angle spinning (13C CP/MAS-NMR) indicated the replacement of NMF by acrylamide. IR spectroscopy also showed the formation of hydrogen bonds with the hydroxyls of kaolinite. When the kaolinite-acrylamide intercalation compound was heated at 300°C for 1 hr, the basal spacing increased to 11.4 Å, and IR and 13C CP/MAS-NMR showed the disappearance of C=C bonds, indicating the polymerization of acrylamide. The heat-treated kaolinite-acrylamide intercalation compound was resistant to 30 min-washing with water, whereas the untreated kaolinite-acrylamide intercalation compound collapsed after the same treatment, an observation consistent with acrylamide polymerization between the layers of kaolinite. IR spectroscopy revealed that polyacrylamide was hydrogen bonded to kaolinite, but in a manner different from the hydrogen bonding of acrylamide.
Influence of Clay on Water Movement in Coarse-Textured Soils
Authors: Gal Menachem , Whittig Lynn D. , Faber Ben A.
Published: August 2006

Effects of clay content on saturated hydraulic conductivities (k) of two coarse textured soils, Vista (mixed thermic Typic Xerochrepts) and Hanford (mixed nonacid Typic Xerorthents), and a medium textured soil, Wyo (thermic Mollic Haploxeralfs) series, were investigated. The clay and combined sand + silt fraction extracted from each of the soils were mixed with the respective soils to yield mixtures ranging from 0% clay to clay levels exceeding those in the natural soils. Rates of water movement through prepared columns of the mixtures were compared to rates through unfractionated soils.

Hydraulic conductivities for unfractionated soil and prepared mixtures were high for the Vista (maximum k = 100) compared with the Hanford (maximum k = 30) and Wyo (maximum k = 20) samples. These conductivities suggest that the relatively even distribution of particles among fractions of sand, silt, and clay gave rise to a greater proportion of larger conducting pores in the Vista sample, whereas the preponderance of particles in the fine sand and very fine sand and coarse silt fractions of the Hanford soil and in the medium silt or fine silt and clay fractions of the Wyo soil limited the proportions of larger conducting pores. Marked differences in k were measured for mixed-fraction systems for all soils. The largest k values for the Hanford soil were from systems containing proportions of the different size fractions similar to that of the natural soil. The highest k values for the Vista soil were from systems containing a clay content slightly less than or greater than that of the natural soil. Additions of clay to Wyo soil increased k values.
Ordered and Disordered Organic Intercalates of 8.4-Å, Synthetically Hydrated Kaolinite
Authors: Costanzo P. M. , Giese R. F.
Published: August 2006

Stable, three-dimensionally ordered complexes were formed from synthetically hydrated, highly ordered kaolinite (d(001) = 8.4 Å) and several organic compounds. Removal of the intercalated organic compound by drying or by water washing recovered the 8.4-Å hydrate with its ordered layer stacking essentially unchanged. Some of the complexes were stable for less than a day, whereas others appeared to be stable indefinitely. The compounds that formed ordered complexes were dimethylsulfoxide, formamide, hydrazine-hydrate, 1,1-dimethylhydrazine, ethylene glycol, glycerol, and pyridine. Clay-organic complexes that were prepared from methanol, ethanol, 1- and 2-propanol, acetone, acetic acid, propionic acid, acetaldehyde, N-methylformamide, methylethyl ketone, tetrahydrofuran, and K-acetate were stable only if they were immersed in the intercalating medium and had little or no stacking order.

Many of the organic compounds intercalated by the 8.4-Å hydrate are not known to be intercalated by non-hydrated kaolinite either directly or indirectly. Isolated water molecules appear to be keyed into the ditrigonal holes formed by the basal oxygen of the silicate tetrahedra of the 8.4-Å hydrate. These water molecules, referred to as “hole water,” and fluorine ions that had replaced ~20% of the inner-surface hydroxyls of the 8.4-Å phase sufficiently altered the interlayer bonding to allow an expansion of the inner-layer spaces by a variety of guest molecules. The presence of these guest molecules between the clay layers not only changed the basal spacing and perturbed the infrared (IR) bands arising from the inner-surface hydroxyls, it also shifted the position of the IR band arising from the inner hydroxyl.
Li-Bearing Stevensite from Moldova Nouǎ, Romania
Authors: Ianovici Virgil , Neacşu Gheorghe , Neacşu Vasilica
Published: August 2006

Li-bearing smectite minerals occurring as hydrothermal alteration products of magnesium silicate minerals in skarns associated with the Moldova Nouǎ, Romania, porphyry copper deposit were examined by X-ray powder diffraction, infrared spectroscopy, and thermal and chemical analyses. Li-bearing smectite containing 0.45–0.50 Li/unit cell is common, whereas smectite containing 0.21–0.33 Li/unit cell is less common. Both materials coexist with talc and kerolite. The Li-bearing smectite minerals (b = 9.111 Å) contains semi-ordered or ordered stacking and is highly crystalline, similar to saponite. After 3-yr storage under laboratory conditions in an air-dried state (RH = 50%) or after heating for 2 hr at 100°, 200°, 300°, or 400°C, the Li-bearing smectite minerals showed charactenstics of a regular 1:1 interstratification of anhydrous and dihydrate layers. Some segregation of the anhydrous, monohydrate, and dihydrate layers was noted.

The amount of Li-for-Mg substitution was found to be close to that in hectorite, and the number of octahedral vacancies was similar to that in stevensite. This Li-bearing smectite apparently formed directly from colloidal suspensions at atmospheric temperature and pressure.
Treatment of Microanalyses of Intimately Mixed Products of Mica Weathering
Authors: Fordham A. W.
Published: August 2006

Weathering of minerals often produces intimate mixtures of reactants and products in a smaller volume than that explored by an electron microprobe. As a result, many microanalyses are difficult to decipher because they are composite analyses of mixtures. A procedure to resolve such microanalyses into their component parts was applied here to data obtained in a study of the weathering of muscovite and biotite in granite gneiss and associated soils. A key element oxide content (K2O, in the examples demonstrated) was plotted against Si/Al ratio for all data. This achieved a spread of points having an external shape depending on the compositions of the pure phases present in the various mixtures analyzed. In all probability, some of the microanalyses consisted of only a single phase, or almost so, and these points were located at or near extremities of the body of data. The aim of subsequent treatment was to encompass the data within boundary curves, each of which corresponded to mixtures of any two of the pure phases present. The chemical compositions of some phases, for example, kaolinite and muscovite, are known, and boundary curves for such mixtures were calculated directly. The compositions of unknown or suspected phases, however, were estimated from the graph of K2O content against Si/Al ratio, in conjunction with graphs of the other element oxide contents plotted against Si/Al ratio. The unknown compositions were subsequently refined by successive approximations. Data in the vicinity of the boundary curves were adjusted for the presence of free iron oxides containing structural Al. Once a satisfactory set of intersecting boundary curves was developed to encompass the data, the compositions of the major phases in each system were obtained, and the diagram of boundary curves was used to estimate the relative proportions of these phases at each point analyzed by the microprobe.
Reduction and Reoxidation of Nontronite: Extent of Reduction and Reaction Rates
Authors: Komadel Peter , Lear Paul R. , Stucki Joseph W.
Published: August 2006

The reduction and reoxidation of three nontronite samples, GAN (API H-33a, Garfield, Washington), SWa-1 (ferruginous Washington smectite), and NG-1 (Hohen Hagen, Federal Republic of Germany) were studied with visible absorption and Mössbauer spectroscopy. The intensity of the intervalence electron transfer (IT) band at 730 nm in these nontronites was monitored during reduction and reoxidation at 277, 294, and 348 K. The results showed that the intensity of the band followed the number of Fe(II)-O-Fe(III) groups in the clay crystal, increasing to a maximum at about Fe(II): total Fe = 0.4; upon complete reduction, the band decreased to about the intensity of the unaltered, oxidized sample. With reoxidation of the sample with O2, the intensity of the band increased sharply, followed by a gradual decay back to the original, oxidized intensity. The ultimate level of Fe reduction achieved was at least 92%. Concomitantly, the color changed from yellow through green, blue-green, dark blue, light blue, and light gray as the Fe(II) content increased. The GAN nontronite was more difficult to reduce than the SWa-1 or NG-1 samples. The rate and level of reduction increased with the amount of reducing agent added.
Formation of Polyethylene Glycol on Montmorillonite by Sterilization with Ethylene Oxide
Authors: Pusino A. , Gennari M. , Premoli A. , Gessa C.
Published: August 2006

The effect of ethylene oxide-sterilization on homoionic (Na+, K+, Ca2+, Cu2+, Al3+, and Fe3+) montmorillonite samples was examined. The results indicate that ethylene oxide polymerized to polyethylene glycol in the interlayer of Cu2+-, Al3+-, and Fe3+-saturated clays, as substantiated by the increase in the d(001) values, as well as by the decrease in the cation-exchange capacity after reaction. On the contrary, ethylene oxide failed to react in the presence of the Na+-, K+-, and Ca2+-clays, likely due to the lower acidity of the exchange cations.
Use of Competitive Ion Exchange for Intercalation of Montmorillonite with Hydroxy-Aluminum Species
Authors: Figueras F. , Klapyta Z. , Massiani P. , Mountassir Z. , Tichit D. , Fajula F. , Gueguen C. , Bousquet J. , Auroux A.
Published: August 2006

Three montmorillonite samples, from Wyoming (particle size <0.2 µm, 4.6 wt. % Fe2O3), Greece (<14 µm, 6.5 wt. % Fe2O3), and Poland (0.5 wt. % Fe2O3, two fractions <2 µm and 2–10 µm) were intercalated with hydroxy-Al species. The amount of hydroxy-Al cations exchanged by the clays depended on the particle size: it decreased from 31 wt. % Al2O3 for 0.2 µm in size to 22.6 wt. % for >2 µm. The X-ray powder diffraction (XRD) pattern showed that most of the material was not intercalated after refluxing at 80°C for 2 hr; several redispersions of the pillared clay in hot water were required to obtain a single sharp XRD line at 18.6 Å. The diffusion of the Al cations therefore limited the cation-exchange process. The addition of NH4+ to the pillaring solution decreased the amount of Al fixed by the clay from 31 (no NH4+ to 26 wt. % (NH4+/Al = 10), but increased slightly the microporous volume of the resulting pillared material from 0.13 to 0.14 ml/g. The competition between NH4+ and Al-hydroxy cations for ion-exchange sites forced the Al species into the interlayer space and increased the homogeneity of the resulting pillared material. The influence of particle size on the amount of Al exchanged was then reduced. After calcination in air at 700°C the pillared Wyoming clay retained a microporous volume of 0.09 ml/g if no NH4+ was added, compared with 0.11 ml/g for a NH4+/Al ratio of 10. The Fe content of the clay affected the thermal stability of pillared clays at 800°C: for two samples prepared by competitive ion exchange (NH4+/Al = 10) the microporous volume increased from 0.06 ml/g for 6.4 wt. % Fe2O3 to 0.08 ml/g for 0.5 wt. % Fe2O3. The acidity of the pillared clay was determined by calorimetric adsorption of ammonia at 150°C, on samples calcined at 500°C. Pillared montmorillonite prepared using noncompetitive intercalation showed a weak acid strength: most sites adsorbed ammonia with an enthalpy of 65 kJ/mole. The intercalation of the same original clay using competitive ion exchange yielded a solid that possessed both weak (heat = 60 kJ/mole) and strong (120 kJ/mole) acid sties. Competitive ion exchange appears to be a simple means of preparation of large quantities of pillared clays of reasonable thermal stability and higher acidity than those obtained by conventional methods.
Mineralogy, Geochemistry, and Origin of the Underclays of the Central Coal Basin, Asturias, Spain
Authors: Alonso Olga Elvira , Brime Covadonga
Published: August 2006

Samples of underclays corresponding to nine different coal beds of the María Luisa coal seam in the Aller valley (Asturias, Spain) were collected to determine whether their mineralogy and geochemistry could be used for correlation. The underclays are dominated by illite, with an average abundance of 46%, and contain smaller amounts of chlorite, kaolinite (chlorite always more abundant), paragonite, pyrophyllite, mixed-layer illite/smectite (I/S), and mixed-layer muscovite/paragonite. This mineralogical association along with the illite “crystallinity” values (mean values of “crystallinity” in air-dried and ethylene glycol-solvated illite are 0.48° and 0.35°2θ, respectively) suggest that the samples have undergone very low-grade metamorphism. No consistent variation in the mineral components with increasing depth below the coal was noted. The presence of chlorite and K-feldspar precludes the development of the underclays by extensive leaching by acid swamp waters and thereby suggests that their mineral composition was determined largely by provenance.

Thirty-seven mineralogical and geochemical variables were treated by stepwise discriminant analysis. The variables that best served as discriminators between the underclays were: illite + I/S contents of both the whole rock and clay fraction, illite “crystallinity” of the clay fraction in both air-dried and glycolated patterns, pH of the samples, and the elements (in order of atomic number) Na, Al, K, Ca, Ti, V, Sr, Zr, Nb, Ba. The Molino underclay is clearly distinct from the other eight underclays, suggesting its potential use in regional correlation.
Use of Inorgano-Organo-Clays in the Removal of Priority Pollutants from Industrial Wastewaters: Structural Aspects
Authors: Srinivasan Keeran R. , Fogler H. Scott
Published: August 2006

Novel modified clay adsorbents were prepared by blocking cation-exchange sites of an expandable clay, such as montmorillonite, with polymeric or polyvalent inorganic ions and by using cationic surfactants as sources of surface organic carbon. Electrokinetic measurements demonstrated that the adsorbed polycations were essentially nonexchangeable. Adsorption and desorption experiments revealed that about 90% of the cationic surfactant was apparently irreversibly bound to the surface. Flocculation and peptization studies were performed to establish that the adsorbed surfactant moiety was oriented with its hydrocarbon tail towards the surface. Such a configuration of simultaneously adsorbed polycations and cationic surfactants was designated as an inorgano-organo-clay (IOC). As shown in an accompanying paper, these IOCs bind priority pollutants as strongly as granulated activated carbon.
Use of Inorgano-Organo-Clays in the Removal of Priority Pollutants from Industrial Wastewaters: Adsorption of Benzo(a)Pyrene and Chlorophenols from Aqueous Solutions
Authors: Srinivasan Keeran R. , Fogler H. Scott
Published: August 2006

Benzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.
Infrared Vibrations of Hematite Formed from Aqueous- and Dry-Thermal Incubation of Si-Containing Ferrihydrite
Authors: Vempati R. K. , Loeppert R. H. , Sittertz-Bhatkar H. , Burghardt R. C.
Published: August 2006

Ferrihydrite samples having Si/Fe molar ratios ranging from 0 to 1 were synthesized by the reaction of Fe2(SO4)3 and Na2SiO3 with NaOH to an equilibrium pH of 8.2. Hematite formed by incubating the ferrihydrite (Si/Fe molar ratios ≤0.05) at pH 12.5 and 91°C for 36 hr had a globular morphology. Hematite formed from Si-free ferrihydrite gave infrared (IR) bands at 548, 471, 397, and 337 cm−1, whereas, hematite formed from Si-containing ferrihydrite having 0.001 to 0.05 Si/Fe molar ratios gave broad IR bands at about 550, 450, and 330 cm−1. Ferrihydrite having Si/Fe molar ratios ≥0.10 did not transform to hematite following the aqueous-thermal treatment.

The ferrihydrite samples were thermally treated for 2 hr at consecutive 100°C intervals from 100° to 800°C. The Si-free ferrihydrite transformed at 300°C to poorly crystalline hematite. Transmission electron microscopic analyses indicated that the hematite consisted of aggregates of spheroidal particles of 20–80 Å cross sections. Broad IR bands were observed at 529 and 452 cm−1; however, after heating the sample to 800°C, the particle cross sections increased to about 150–600 Å, and additional IR bands were present at 378 and 325 cm−1. The differences in the IR patterns of hematite formed from ferrihydrite at 300° and 800°C were probably due to increases in particle size and aggregation and improved crystallinity of the hematite particles following the higher temperature treatment. The hematite formed by the thermal transformation of the ferrihydrite having a 0.01 Si/Fe molar ratio was also spheroidal, and IR vibrations were present at about 528 and 443 cm−1. An increase in the temperature of the thermal treatment, however, did not result in additional IR bands.

Differences in the IR vibrations of hematite formed during aqueous- and dry-thermal treatments of the ferrihydrite samples were probably due to differences in the particle size and morphology of the product. The Si content, due to its effect on particle size of the precursor and the prevention of sintering and particle growth of hematite, influenced the IR pattern of the product. Particle morphology and IR spectroscopy may therefore be useful indicators of the precursor of hematite and the conditions of hematite formation in soil.
Structural Variations in Chlorite and Illite in a Diagenetic Sequence from the Imperial Valley, California
Authors: Walker Jeffrey R. , Thompson Graham R.
Published: August 2006

Samples of cuttings from the Borchard A-2 well, Imperial Valley, California, were collected over a measured borehole temperature interval 135° to 275°C. The <0.5-µm (e.s.d.) fraction was separated using high-gradient magnetic separation (HGMS) to create a nonmagnetic fraction rich in illite and a magnetic fraction rich in chlorite. Chlorite was less easily separated from illite in lower temperature samples (<200°C), presumably due to the presence of polymineralic grains of chlorite and illite. Grains in higher temperature samples were more nearly monomineralic and more easily separated.

The chlorite is the IIb polytype. The thickness of coherent scattering domains of chlorite increased until 220°C and then remained constant. The amount of 7-Å interstratified material increased downhole until 195°C and then decreased. Over the same temperature interval, the illite polytypes varied systematically from 1Md (135° to 175°C) to 1M + 2M1 (230° to 275°C) and coherent scattering domains in the mineral became thicker to about 200°C and then remained constant in thickness. The percentage of illite in mixed-layer illite/smectite (I/S) increased from 40% at 135°C to 100% at temperature >205°C; ordering in the I/S changes from R0 to R1 between 135° and 155°C, and from R1 to R ≥ 3 at temperatures >155°C.

The concurrent structural changes in chlorite and illite indicate a general improvement in the overall structural order of the clay minerals with increasing temperature. Differences between chlorite and illite suggest that the minerals may have reacted differently to changing conditions or that they may have formed by different mechanisms. The exclusive occurrence of IIb chlorite at temperatures as low as 135°C extends the limit of IIb chlorite stability to temperatures lower than previous estimates.
A Novel Differential Thermal Analysis Method for Quantifying the Sorption Capacity of Smectite Clay
Authors: O'Brien Paul , Williamson Colin J.
Published: August 2006

The enthalpy of freezing of methyl salicylate sorbed by four commercial montmorillonite clays was used to estimate the absorption/adsorption capacity of the clay. Differential thermal analysis was therefore employed to give a quantitative estimate of the sorption capacity of the clay for methyl salicylate. The absorption capacity of the clay depended on the state of hydration and ranged from 30.4% for an 8% water content to 9.7% for a montmorillonite containing 24% water.
Molecular-Scale Imaging of Clay Mineral Surfaces with the Atomic Force Microscope
Authors: Hartman H. , Sposito Garrison , Yang Andrew , Manne S. , Gould S. A. C. , Hansma P. K.
Published: August 2006

Specimen samples of Crook County montmorillonite and Silver Hill illite, purified and prepared in the Na-form, were imaged under 80% relative humidity using an atomic force microscope. The direct images showed clearly the hexagonal array of hexagonal rings of oxygen ions expected for the basal planes of 2:1 phyllosilicates. Fourier transformation of the digital information obtained by the microscope scanning tip led to an estimate of 5.1 ± 0.3 Å for the nearest-neighbor separation, in agreement with the ideal nearest-neighbor spacing of 5.4 Å for hexagonal rings as derived from X-ray powder diffraction data. The atomic force microscope should prove to be a useful tool for the molecular-scale resolution of clay mineral surfaces that contain adsorbed macromolecules.
Study of Some Physicochemical Properties of Pillared Montmorillonites: Acid-Base Potentiometric Titrations and Electrophoretic Measurements
Authors: Avena Marcelo J. , Cabrol Raúl , De Pauli Carlos P.
Published: August 2006

The surface charges and the zeta potential of a Na-montmorillonite (Na-mont) and two pillared montmorillonite (MP1 and MP2) samples with different aluminum contents were determined by Potentiometric titrations and electrophoretic measurements. At pH >9 the two pillared montmorillonite samples showed zeta potentials similar to those of Na-mont, but at pH <8, the negative zeta potential shifted to lower negative values as the aluminum content increased. Sample MP1, which had a greater Al content, showed an isoelectric point (IEP) of 5.0–5.5. Titration curves obtained by acid-base Potentiometrie titration for sample MP1 showed a well-defined cross-over point at pH = 5.0, whereas this point was not observed for sample MP2 in the pH range studied. The results indicate, in principle, that both techniques can be used to characterize surface charges in this type of material. An attempt was also made to relate the data obtained from electrophoretic mobility and Potentiometrie titrations.
Direct High-Resolution Transmission Electron Microscopic Measurement Of Expandability Of Mixed-Layer Illite/Smectite In Bentonite Rock
Authors: Środoń Jan , Andreoli Cristina , Elsass Françoise , Robert Michel
Published: August 2006

Samples of mixed-layer illite/smectite were investigated from a single bentonite bed zoned with respect to expandability from 90 to 30%. Chips of natural rocks were embedded in a resin, using a procedure designed to preserve the original fabric, cut with an ultramicrotome, and observed by high-resolution transmission electron microscopy (HRTEM). These observations confirmed the X-ray powder diffraction (XRD) model of mixed-layer clays, i.e., that illite/smectite grains in natural rocks are built of mixed-layer crystals, from 1 to as many as 15 silicate layers thick (4–6 interlayers per crystal on average). These crystals are present either as individual particles (loose crystals) or, typically, they form nearly parallel face-to-face groupings called here quasi-crystals. Free fundamental smectite and illite particles as defined by Nadeau and coworkers were essentially absent.

Illite and smectite interlayer spacings were 10 and 13.5 Å, respectively. Crystal thickness and number of interlayers were measured for 35–100 mixed-layer crystals per sample. Illite/smectite expandabilities were calculated from these data in two ways: either neglecting the crystal edges or accounting for them. The former determinations agree well with XRD estimates of expandability and the latter, with expandabilities calculated from the distributions of fundamental particle thickness measured by a shadowing technique in the TEM. This result explains the systematic discrepancy between XRD and TEM measurements of illite/smectite expandability.
Cross-Linked Hydroxy-Al-Montmorillonite as a Stationary Phase in Liquid Chromatography
Authors: Tsvetkov Faina , Mingelgrin U. , Lahav N.
Published: August 2006

Quasi-spherical particles (7-µm mean diameter) were prepared from cross-linked hydroxy-Al-montmorillonite (basal spacing =15.3 and 18.6 Å) by spray-drying. These particles (SP-CLM) were used as a packing material for columns in high-pressure liquid chromatography (HPLC). Aromatic phosphate esters, chlorosubstituted phenyl-ureas, monosubstituted benzenes, and the o-, m-, and p-isomers of disubstituted benzenes were separated on the columns, using isopropanol and hexane. Alkyl and alkoxy groups in the solute molecules sterically hindered the interaction of these molecules with the solid phase. The retention of the isomers of disubstituted benzenes that possess one electronegative (or dipolar) and one nonpolar substituent increased in the order: o- < m- < p-. In contrast, for all investigated disubstituted benzenes containing two electronegative (or dipolar) substituents, the o-isomer was retained on the 18.6-Å SP-CLM more strongly than the m- and p-isomers. The chromatographic data suggest that the strength of the interaction of phenolic groups with the solid phase increased with the acidity of these groups. The o-isomers of phenols that contained an additional electronegative (or dipolar) substituent displayed an exceptionally strong adsorption. The capacity of the o-isomers of disubstituted benzenes containing two electronegative (or dipolar) substituents to form chelates with Al probably was responsible for the strong retention of such o-isomers compared with the retention of the corresponding m- and p-isomers.

Cross-linked hydroxy-Al-montmorillonite acted as a strong and selective adsorbent for many families of organic compounds. It was used successfully as the solid phase in HPLC separations with eluents ranging from nonpolar (e.g., hexane) to highly polar (e.g., water).
Diagenesis of Oligocene-Miocene Vitric Tuffs to Montmorillonite and K-Feldspar Deposits, Durango, Mexico
Authors: de Pablo-Galan Llberto
Published: August 2006

Montmorillonite and K-feldspar deposits of potential economic interest occur in the Late Oligocene-Miocene tuffs of the Vizcarra Formation in the state of Durango, Mexico. The two minerals were formed separately from rhyodacitic to rhyolitic pyroclastic deposits in a closed hydrologie system and diagenetically altered following two different patterns. In material deposited on dry land the glass was completely replaced by K-feldspar, and the interstices between the replaced glass bubbles and shards were filled with chalcedony, quartz, and albite. Pyroclastic material deposited in an alkaline lacustrine environment were diagenetically altered to montmorillonite, which formed the bentonitic tuffs widely exposed beneath the K-feldspar-rich tuff. These bentonitic tuffs contain as much as 85% montmorillonite plus authigenic chalcedony and quartz. Pyrogenic sanidine, quartz, and oxybiotite, coarse glass shards, and clastic grains make up about 8% of the clay-rich tuffs. The composition of the montmorillonite corresponds to the formula (Si3.88Al0.12)(Al1.41Mg0.59)O10(OH)2(Ca0.07Mg0.11,Na0.28K0.06). The montmorillonite is dioctahedral, the surface acidity is of the Lewis type, and the clay swells to one- and two-layer complexes. The cation-exchange capacity is 64 meq/100g; base exchange is Ca2+, 15; Mg2+, 20; Na+, 4.1; and K+, 1.0 meq/100 g. Its interlamellar charge is 18.6 microcoulombs/cm2. Dacitic pyroclastics were deposited later at higher elevations along the margins of the basin. Percolating solutions apparently removed a siliceous leachate from the dacitic glass and partially altered it to clinoptilolite.
Determination of Surface Areas of Mineral Powders by Adsorption Calorimetry
Authors: Ticknor Kenneth V. , Saluja Preet P. S.
Published: August 2006

Adsorption calorimetry was used to develop a method for determining the surface area of low-surface-area materials (<1 m2/g), which required no pretreatment of the surface, such as outgassing at elevated temperatures. The method involved flowing heptane through a small amount of sample (0.15 to 1.0 g) in the flow cell of a commercial microcalorimeter. When thermal equilibrium was reached at the powder-heptane interface, pure heptane was replaced with a heptane carrier-solution containing 0.6 volume % n-butanol (n-BuOH) as the preferential adsorbate. The integral enthalpy of preferential saturation adsorption, ΔHsat, of n-BuOH on the surface was found to be a function of the BET surface area of the sample. An empirical relationship between ΔHsat and BET surface area was determined over a surface area range of about three orders of magnitude (0.095 to 81 m2/g) by performing adsorption experiments on five α-alumina standard reference powders. The technique was applied to the determination of surface areas of untreated rock and mineral powders.
Transmission and Analytical Electron Microscopic Study of Mixed-Layer Illite/Smectite Formed as an Apparent Replacement Product of Diagenetic Illite
Authors: Jiang Wei-Teh , Peacor Donald R. , Merriman R. J. , Roberts B.
Published: August 2006

Ordered illite/smectite (I/S) and illite in a pelitic rock from a prograde metamorphic sequence in North Wales were observed by transmission electron microscopy. The dominant phyllosilicate noted was diagenetic-metamorphic illite, occurring as subparallel packets of layers, each about a few hundred Ångstroms thick. It exhibited two-layer polytypism (presumably 2M1) and numerous strain features and had a composition of (K1.21Na0.12)(Al3.36Fe0.31Mg0.33)(Si6.28Al1.72)O20(OH)4.

I/S occurred as thick packets of wavy layers having 10-Å subperiodicity and sharp differences in contrast in successive lattice fringes. All stages in a replacement series were noted, from one or two layers of smectite within illite, through thin packets of I/S, to thick packets that contained inherited deformation textures of diagenetic-metamorphic illite. Deformed illite was replaced by I/S more commonly than was undeformed illite. The I/S replacing undeformed original illite had significantly greater order, primarily of R1 type (ISISIS…), than that replacing deformed illite. R> 1 I/S occurred as small crystallites and contained relatively less smectite than the ordered I/S, Single smectite layers were spaced within several illite layers, forming curved packets of layers. IISIIS… (R2) and IIISIIIS… (R3) ordering were present locally, as was discrete smectite. Analytical electron microscopic analyses indicated that the I/S, (K0.46Na0.43)(Al3.75Fe0.06Mg0.19)(Si6.26Al1.74)O20(OH)4, was rectorite-like in composition and had smaller (Mg + Fe) contents and greater Al/Si ratios than the coexisting illite, which was also anomalous in terms of general crystal-chemical relationships between coexisting illite and I/S in burial diagenesis environments. The I/S appears to have formed by replacement of diagenetic-metamorphic illite, presumably at very low temperatures under hydrous conditions via dissolution and crystallization.
Transformation of Akaganéite Into Goethite and Hematite in Alkaline Media
Authors: Cornell R. M. , Giovanoli R.
Published: August 2006

The conversion of akaganéite to goethite and/or hematite in alkaline media has been followed by X-ray powder diffraction and transmission electron microscopy (TEM). The rate of transformation fell and the amount of hematite in the product increased as the [OH−] decreased to < 1 M. Kinetic studies and TEM indicated that the transformation involved dissolution of akaganéite followed by reprecipitation of goethite and/or hematite. The rate-determining step was the dissolution of akaganéite.

Silicate species retarded the formation of goethite + hematite principally by inhibiting dissolution of akaganéite; to a lesser extent, they interfered with the nucleation of goethite. Silicate modified the morphology of goethite, but not hematite.

Comparison of the transformation behavior of akaganéite with that previously observed for ferrihydrite indicated that the composition of the reaction product depended strongly on the transformation conditions, i.e., pH and the presence of foreign species. The nature of the solid precursor was important insofar as its degree of crystallinity governed the dissolution kinetics and its surface properties influenced interaction with any foreign species in the system.
Adsorption of Hydroxy-Al Polycations and Destabilization of Illite and Montmorillonite Suspensions
Authors: Gu Baohua , Doner H. E.
Published: August 2006

Water-infiltration characteristics of soil can be improved by preventing clay dispersion. The present study determined the adsorption properties of hydroxy-Al polycations (Al-p) and their relation to the destabilization of clay suspensions. Al-p was synthesized and fractionated into nominal molecular weights between 104 and 5 × 104. The reactions of Al-p with Na-illite and Na-montmorillonite indicated a very strong affinity of Al-p to the clay surfaces. The maximum adsorptions of Al-p by Na-illite and Na-montmorillonite were found to be 0.37 and 1.7 mmole Al/g, and very close to the cation-exchange capacity of the two clays, suggesting that the adsorption was chiefly controlled by the mechanism of charge screening. Adsorption of Al-p increased the points of zero charge (PZCs) and the apparent points of zero salt effect (PZSEs) of illite and montmorillonite. PZSEs for both clays were 4.7 at their maximum Al-p adsorption, and PZCs ranged from 5.3 to 6.4, depending on solution ionic strength and the individual clay minerals. The differences in PZCs were probably due to outer-sphere complex formation between Al-p-treated illite and montmorillonite and the swamping electrolyte. Critical flocculation concentrations (CFCs) of Al-p for Na-illite and Na-montmorillonite were at 0.28 and 1.0 mmole Al/g, whereas zero electrophoretic mobilities were at about 0.36 and 1.67 mmole Al/g Al-p additions. Excessive addition of Al-p reversed this surface charge of clay colloids and restabilized the illite but not montmorillonite suspensions. This difference was probably due to the stronger and more extensive interparticle bridging of montmorillonite particles by Al-p than those of illite. The CFCs for the two clays were also found to be dependent on sodium adsorption ratio (SAR), pH, and ionic strength. Increases in SAR and pH significantly increased the CFC, whereas an increase in ionic strength decreased the CFC.
Orientation of Hexanediamine in Synthetic Fluorhectorite
Authors: Hertl William , Bartholomew Roger F.
Published: August 2006

Fourier-transform infrared (FTIR) spectroscopic studies were carried out on 1,6-hexanediamine hydrochloride (HDA)-treated synthetic fluorhectorite to determine the orientation of functional groups within the structure. Oriented crystal layers were prepared by flocculating the smectite slurry with glass fibers to obtain a 100-µm-thick paper. Orientations were determined by measuring integrated IR band intensities at various incident beam angles (≤60°), inasmuch as absorption occurred only if the oscillating dipole of the functional group interacted with the electric vector of the incident radiation. The H-N-H plane in amine groups was aligned parallel to the lamellar plane. The H-O-H plane of the small amount of sorbed water was inclined 45° or more to the interlamellar layer, and the OH groups were inclined 45° to this layer.

Even with the incorporation of HDA in the interlamellar structure, at high humidity, additional water sorbed. The sorbed water competed with and displaced amine groups from the surface, resulting in randomly oriented amine groups. Many of the amine groups were ionized, whereas the additional sorbed water showed little orientation.

This study demonstrated that the orientation of intercalated amines in fluorhectorite can be determined by following the intensity changes in infrared-active bands as a function of the incident beam angle. With intercalated HDA, the orientations were influenced by the presence of interlayer water.
The Nature of Cation-Substitution Sites in Phyllosilicates
Authors: Bleam William F.
Published: August 2006

A fundamental property of electrostatic potentials is their additivity. This study demonstrates that the electrostatic potential of a negatively charged, cation-substituted phyllosilicate layer can be represented as the sum of two potentials. Viewing cation substitution as a defect, one potential is derived from the atoms in a charge-neutral, unsubstituted layer such as pyrophyllite or talc. The “neutral-layer” potential rapidly decays to zero with distance from the layer and is determined primarily by the atoms in the first two atomic planes parallel to the (001) surface, i.e., the basal oxygens and tetrahedral cations. The second component, characterized as a “defect” potential, is a long-range potential derived from cation-substitution. The model used to compute the electrostatic potentials, a two-dimensional Ewald lattice sum, represents the atoms of a single phyllosilicate layer as point charges.
Polarized Single-Crystal Fourier-Transform Infrared Microscopy of Ouray Dickite and Keokuk Kaolinite
Authors: Johnston C. T. , Agnew S. F. , Bish D. L.
Published: August 2006

Single-crystal Fourier-transform infrared (FTIR) spectra of Keokuk kaolinite and Ouray dickite were obtained with an FTIR microscope. Although numerous IR, FTIR, and Raman spectra of polycrystalline kaolinite and dickite can be found in the literature, the present data represent the first reported single-crystal vibrational spectra for these clay minerals. The orientation of the crystallographic axes of dickite was determined using a cross-polarizing optical microscope fitted with an 550-nm optical retardation plate. Assignment of the inner hydroxyl group OH1 to the 3623-cm-1 band was confirmed, and the angle of this OH group to the b-axis was determined to be 47° based upon the measured dichroic ratio. The 3702-3710-cm−1 absorption feature appeared to consist of two closely spaced bands having slightly different polarization behavior. The inner-surface hydroxyl group OH3 was assigned to the absorption bands at 3710 cm−1. The calculated angle of the OH3 groups to the b-axis was found to be 22°, which agrees well with the angles determined by X-ray powder diffraction and neutron diffraction. The remaining hydroxyl groups, OH2 and OH4, were assigned to the 3656 cm-1 band; the angle of the OH2 and OH4 groups to the b-axis was measured at 45°. The polarization behavior of the OH-deformation bands of dickite at 911, 937, and 952 cm−1 was found to be similar to that observed in the OH-stretching region. Single-crystal FTIR spectra of Keokuk kaolinite showed that rotation of the electric vector around the c/z axis in the ab plane of kaolinite resulted in a behavior distinct from that of dickite. The OH-stretching bands of kaolinite were found to be considerably more polarized than the corresponding bands of dickite. This is related directly to the fact that dickite possesses a glide plane (space group Cc) compared with kaolinite, which does not (space group C1).