bluuebunny/crossref_metadata_2025 huggingface dataset:
Deintercalation of Hydrazine-Intercalated Low-Defect Kaolinite
Authors: Frost Ray L. , Kloprogge J. Theo , Kristof Janos , Horvath Erzsebet
Published: August 2006

The deintercalation of a low-defect kaolinite intercalated with hydrazine was studied by X-ray diffraction, diffuse reflectance infrared spectroscopy (DRIFT), and Raman microscopy over 30 d. X-ray diffraction showed that the kaolinite was fully intercalated. More than 120 h were required for the hydrazine-intercalate to decompose. The Raman spectra of the hydrazine intercalate showed only a single band at 3620 cm−1, which was attributed to the innerhydroxyl group. Upon deintercalation, additional Raman bands were observed at 3626 and 3613 cm−1. These bands decreased in intensity with further deintercalation. As deintercalation proceeded, the bands assigned to the inner-surface hydroxyl groups at 3695, 3682, 3670, and 3650 cm−1 occurred and increased in intensity. DRIFT spectra showed two bands at 3620 and 3626 cm−1 for the fully intercalated kaolinite only. Upon deintercalation, an additional band assigned to intercalated water was observed at 3599 cm−1 and increased in intensity at the expense of the 3626-cm−1 band. Bands attributed to the innersurface hydroxyl groups increased in intensity with deintercalation. Both the Raman and DRIFT spectra showed complexity in the NH-stretching region with two sets of NH-symmetric and antisymmetric stretching bands. Deintercalation was followed by the loss of intensity of these bands. Significant changes were also observed in the hydroxyl deformation and water-bending modes as a result of deintercalation. A model of hydrazine intercalation of kaolinite based on the insertion of a hydrazine-water unit is proposed. The hydrated end of the hydrazine molecule hydrogen bonds with the innersurface hydroxyl groups resulting in the formation of a band at 3626 cm−1 in the DRIFT spectra.
Determination of Mean Crystallite Dimensions from X-Ray Diffraction Peak Profiles: A Comparative Analysis of Synthetic Hematites
Authors: Crosa Mario , Boero Valter , Franchini-Angela Marinella
Published: August 2006

X-ray diffraction (XRD) profile analysis of eight synthetic hematite samples was performed to identify the best parameters for determining the apparent mean crystallite dimension (D) and, consequently, surface area, The samples are comparable to soil hematite with respect to crystallinity. The procedure included: a) deconvolution of the XRD peaks to Gauss and Cauchy components and subtraction of the instrumental profile, b) determination of D from full-width at half-maximum, integral breadth, and integral breadth measurements of the Cauchy component, and c) comparison of deduced surface areas with those obtained by the N2-BET adsorption method. As expected, D values are strongly influenced by the broadening parameters. An appropriate selection of peaks is required to obtain size values along the crystallographic axes a (hkl: 110,300) and c (hkl: 104, 116) and to calculate reliable surface areas. Using the Cauchy component of the above peaks, the calculated surface areas compared well with those measured by the N2-BET adsorption method.
Formation of Goethite and Hematite from Neodymium-Containing Ferrihydrite Suspensions
Authors: Nagano Tetsushi , Mitamura Hisayoshi , Nakayama Shinichi , Nakashima Satoru
Published: August 2006

The effects of neodymium (Nd) on the transformation of ferrihydrite to iron oxides was studied. The possible isomorphous substitution of Nd3+ for Fe3+ in iron oxides was examined also. Nd was used as an inactive substitute of trivalent radioactive actinide elements. Hydrolysis of ferric nitrate solution containing 0–30 mole % of Nd formed Nd, Fe-rich ferrihydrite as initial precipitates, which were poorly crystalline. Aging of the Nd-containing ferrihydrite in 0.3 M OH− at 40°C and at pH 9.2 at 70°C formed Nd-free goethite and Nd-substituted hematite. The abundance of these crystalline phases was related to Nd in the parent solutions. Phase abundance, unit-cell parameters, and peak width were estimated by use of the Rietveld method.
Experimental Alteration of Volcanic Tuff: Smectite Formation and Effect on 18O Isotope Composition
Authors: Cuadros Javier , Caballero Emilia , Huertas F. Javier , Jiménez de Cisneros Concepción , Huertas Francisco , Linares José
Published: August 2006

Three samples of volcanic tuff were hydrothermally altered at ∼82°C in a soxhlet apparatus for periods from 745 to 2706 h. The samples correspond to partially altered specimens of volcanic tuff with 6 wt. % (T3a) and 9 wt. % (T3b) smectite and to the calcination product of the latter (T3c). The calcination treatment melted the smectite in the sample. Untreated samples and alteration products were studied by X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, and oxygen isotope analysis. DTA-TG of the <2-µm size fractions showed that there was a small increase of smectite relative to glass after alteration for samples T3a and T3b, with the amount of smectite increasing exponentially with time. No smectite formed in sample T3c. These results suggest that smectite acts as a nucleation site for the precipitation of new smectite. The amount of glass in the <2-µm size fraction increased, although slightly decreased relative to smectite. SEM-EDX analysis showed smectite with the approximate structural formula of Na0.22K0.08Mg0.12Ca0.03VI(Al1.47Fe0.05Mg0.48)IV(Si3.97Al0.03)O10(OH)2.

Oxygen isotope composition of the <2-µm size fraction became enriched in 18O by alteration, the >2-µm size fraction of T3b did not vary, and that of T3c was depleted in 18O. Our results are consistent with three processes during alteration: 1) oxygen isotope exchange between volcanic glass and water, 2) neoformation of smectite, and 3) hydration and consequent hydroxylation of the calcined glass.
Glyphosate-Hydrotalcite Interaction as Influenced by pH
Authors: Sanchez Martín M. Jesús , Villa María V. , Sánchez-Camazano María
Published: August 2006

Adsorption and the mechanism of adsorption of the herbicide glyphosate [N-(phosphonomethyl) glycine] by hydrotalcite (HT) and by hydrotalcite calcined at 500°C (HT500) was studied. The values of the Freundlich K constant of the adsorption isotherms and the distribution coefficients, Kd, depend on the pH of the adsorption system and vary between 55.54–9603 (K) and 36.82–6252 (Kd) for HT and between 10,106–23,242 (K) and 17,801–26,558 (Kd) for HT500. X-ray diffraction and infrared spectroscopy studies showed that glyphosate is not adsorbed into the interlayer of HT. The adsorption mechanisms are (1) electrostatic attraction between the surface of HT, charged positively below pH 12 according to its point of zero charge and the glyphosate anion, and (2) ligand exchange between the P-OH and/or C=O groups of the herbicide and the Al and Mg atoms of the HT surface. The occurrence of one or both mechanisms depends on the pH of the adsorption system. These adsorption mechanisms and the amphoteric nature of glyphosate account for the variation in K and Kd values with respect to pH. Previous studies on adsorption of different organic anions by HT have only considered the mechanism of anion exchange as important.
Compositional Gap in Dioctahedral-Trioctahedral Smectite System: Beidellite-Saponite Pseudo-Binary Join
Authors: Yamada Hirohisa , Yoshioka Katsuaki , Tamura Kenji , Fujii Kazuko , Nakazawa Hiromoto
Published: August 2006

A series of hydrothermal experiments were performed to determine the phase relations on the beidellite-saponite pseudo-binary join. Quenched glasses with stoichiometric dehydrated compositions of an Na-rich smectite on the join were heated at 250–500°C for durations of 1–151 d at 100 MPa. Time-temperature diagrams showed that immiscibility occurs between dioctahedral smectite (beidellite) and trioctahedral smectite (saponite) below 400°C. Thus, smectite with intermediate chemical composition was considered as metastable in this system. Above 400°C the assemblage of regularly interstratified saponite-chlorite, quartz, and feldspar was recognized in the intermediate chemical compositional region of this join. On the beidellite side of this join, beidellite and mixed-layer phases of smectite and a regular interstratification of montmorillonite-beidellite, are possible phases that occur at <300°C. They readily reacted to form a mixture of dioctahedral rectorite plus quartz at 300°C. This assemblage then reacted to a dioctahedral “mica”, which can expand with glycol and quartz. On the saponite side of this join, a single phase, saponite, existed at <400°C, and transformed to saponite plus trioctahedral rectorite with aging and increasing temperature of synthesis. The alteration was affected strongly by the chemical composition of the binary system.
Hydrogen-Isotope Exchange in Halloysite: Insight from Room-Temperature Experiments
Authors: Hsieh Jean C. C. , Yapp Crayton J.
Published: August 2006

Halloysite is a common pedogenic clay mineral, often found in young soils developed on volcanic deposits (Dixon, 1989), It is a member of the kaolin group of clays with the same ideal stoichiometric composition as kaolinite [Al2Si2O5(OH)4]. Halloysite, however, often contains water of hydration (i,e., Al2Si2O5(OH)4·nH2O), and is commonly found with a tubular morphology, This “rolling” of halloysite has received a great deal of study because there is no generally agreed upon mechanism for the process and there is no corresponding phenomenon in natural kaolinite (e.g. , Bates et al., 1950; Bailey, 1989; Singh, 1996; Singh and Mackinnon, 1996). The crystal structure of halloysite often shows stacking disorder. This property, combined with a rolled morphology, makes identification by X-ray diffraction (XRD) difficult. The XRD peaks at 7.5, 4.4, and 3.6 Å are often asymmetric with a large width at half peak height (Bailey, 1989).
Structural Model of Al13-Pillared Montmorillonite
Authors: Dimov Virgil I. , Ilieva Albena V. , Khaltakova Nelly G. , Filizova Liudmila D.
Published: August 2006

Alumina-pillared montmorillonite is prepared by intercalation of polyoxyhydroxy aluminum cations (Al137+) of a natural montmorillonite from Dimitrovgrad, Bulgaria. Transmission electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and surface area (BET) methods are used to study the untreated and pillared forms of the montmorillonite. A structural model involving deformed Al13 pillars is proposed. Four pillar types are derived and these pillars are uniformly distributed over the interlayer-cation positions of montmorillonite. Calculated electron diffraction patterns were simulated using the multi-slice method. The structural model explains the increased ordering along the c axis of the pillared form compared with the untreated montmorillonite. The model explains the structure of a pillared montmorillonite with different distributions of the pillars in the interlayer. The proposed model is consistent with the observed data.
Adsorption and Degradation of Triasulfuron on Homoionic Montmorillonites
Authors: Pusino Alba , Braschi Ilaria , Gessa Carlo
Published: August 2006

The adsorption and degradation of the herbicide triasulfuron [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide] (CMMT) on homoionic Fe3+-, Al3+-, Ca2+-, or Na+-exchanged montmorillonite in aqueous medium were studied. Ca- and Na-exchanged montmorillonite were ineffective in the adsorption and degradation of triasulfuron. The adsorption on Fe-and Al-exchanged montmorillonite was rapid, and equilibrium was attained after 5 min. Degradation of the herbicide was slow and the type of the degradation products depended on the nature of the exchangeable cations. In the presence of Fe3+-rich montmorillonite, the metabolites 2-(2-chloro-ethoxy)benzenesulfonamide (CBSA), 2-(2-chloroethoxy)-N-[[(4-hydroxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide (CHMT), and l-[2-(2-chloroethoxy)benzene-l-sulfonyl]-7-acetyl-triuret (CBAT) were the only identified products, whereas 2-amino-4-methoxy-6-methyltriazine (AMMT), CBSA, CHMT, and CBAT were the primary metabolites for the Al3+-rich montmorillonite. A Fourier transform infrared (FT-IR) study of montmorillonite samples after the interaction with triasulfuron in organic solution suggests that the hydrolysis mechanism involves the adsorption of the herbicide on the 2:1 layers.
Smectite Diagenesis in Neogene Marine Sandstone and Mudstone of the Niigata Basin, Japan
Authors: Niu Ben , Yoshimura Takahisa , Hirai Akio
Published: August 2006

Illitization of smectite during progressive burial diagenesis occurs differently in sandstone and mudstone, which are interbedded in the sedimentary sequence of the Niigata basin. Reaction progress of illitization of smectite via mixed-layer illite-smectite (I-S) in the mudstone is more complete than in the sandstone. In sandstone, smectite converts to (Reichweit, R ≥ 3) I-S and illite via random (R = 0) I-S to ordered (R = 1) I-S, and authigenic chlorite and quartz form as products of the illitization of smectite.

The original composition of detrital smectite and the occurrence of Na+, K+, Ca2+, Mg2+, and Fe2+ in pore fluids partly control both illitization of smectite and the resulting authigenic mineral products in the diagenetic process. In mudstone, detrital smectite is K- and Si-rich in composition, and the illitization of smectite indicates that the original composition is mostly inherited. Excess silica owing to illitization is released to produce authigenic quartz. In sandstone, smectite forms primarily by precipitation. The evolving compositions produced by early illitization form smectite, then random (R = 0) I-S, and then ordered (R = 1) I-S. These transitions are related to compositions of pore fluid. Changes in K/(K + Ca + Na) vs. K + Ca + Na imply that the increase of interlayer cations occurs by absorption and smectite transforms to random (R = 0) I-S, followed by the exchange of interlayer cations to ordered (R = 1) I-S with increasing diagenetic grade. Late illitization from (R = 1) I-S to R ≥ 3 suggests decomposition of smectite and early I-S with an increase in the number of illite layers. Dissolution experiments of host rocks with pure water and 0.01 M HCl solution reflect the differences in chemistry of the original pore fluid and authigenic carbonate in the process of diagenesis of clastic rocks. These results explain how chemical composition produces large variations in transformation temperature of smectite to illite in the diagenetic process.
Inhibition of Sintering by Si During the Conversion of Si-Rich Ferrihydrite to Hematite
Authors: Glasauer Susan M. , Hug Paul , Weidler Peter G. , Gehring Andreas U.
Published: August 2006

The distribution and chemical state of Si in a synthetic 2-line ferrihydrite with a Si/(Si + Fe) molar ratio of 0.11 was studied. Heat treatment under oxidizing conditions shows that Si-rich ferrihydrite is stable to 400°C. The transformation to hematite and the formation of a polymerized amorphous-silica phase occur at 850°C. At this temperature, the specific surface area decreases greatly and the average pore diameter increases, which is indicative of sintering. Heating under severe reducing conditions causes a segregation of Si from Fe and results in a mixture of elemental Fe and SiO2. Surface and structural data suggest that Si is located near the particle surface where it limits the rearrangement of Fe octahedra to form hematite.
Phase Analysis of Clays Using an Expert System and Calculation Programs for X-Ray Diffraction by Two- and Three-Component Mixed-Layer Minerals
Authors: Plançon A. , Drits V. A.
Published: August 2006

X-ray phase analysis of clays is difficult because these materials generally consist of a mixture of different phases, i.e., mixed-layer minerals, individual clay minerals (non mixed-layer), and associated minerals, such as calcite and quartz. The analysis requires knowledge that presently is incorporated in a computer-based expert system. This expert system is capable of a) identification of associated minerals; b) identification of individual clay minerals; c) identification of the nature of the mixed-layer minerals; d) approximate structural characterization of the mixed-layer minerals; and e) precise structural determination of the mixed-layer minerals by comparison of experimental X-ray diffraction (XRD) patterns with calculated patterns for different models. Accuracy of the conclusions drawn by the expert system has been verified with literature data. Programs for the structural characterization of mixed-layer minerals must allow a) modification of the structural characteristics, abundances, and order-disorder distribution of the layers; b) modification of the distribution of the sizes of coherent scattering domains; and c) consideration of mixed-layer clays with more than two components. Two programs were written to calculate the XRD patterns of two- and three-component mixed-layer minerals consisting of any layer type and without any limitation in the order-disorder relationships.
Thermal Behavior of the Kaolinite-Hydrazine Intercalation Complex
Authors: Ruiz Cruz María Dolores , Franco Francisco
Published: August 2006

The intercalation complex of a low-defect (“well-crystallized”) kaolinite from Cornwall, England, with hydrazine was studied by high-temperature X-ray diffraction (HTXRD), differential thermal analysis (DTA), and thermogravimetry (TG). The X-ray pattern at room temperature indicated that intercalation of hydrazine into kaolinite causes an increase of the basal spacing from 7.14 to 10.4 Å, as previously reported. Heating between 25-200°C produces a structural rearrangement of the complex, which initially causes a contraction of the basal spacing from 10.4 to 9.6 Å. In a second stage, the basal spacing reduces to 8.5 Å. Finally, in a third stage, a reduction in spacing occurs through a set of intermediate phases, interpreted as interstratifications of intercalated and non-intercalated 1:1 layers. Evidence for these changes was observed by DTA, where three endothermic reactions are observed at low temperature. This behavior suggests that intercalated molecules occupy several well-defined sites in the interlayer of the kaolinite complex. The intercalated molecules deintercalate in an ordered fashion, which explains the successive and discontinuous contraction of the basal spacing of the complex. Heating between 200-400°C caused a limited increase in stacking order of the kaolinite structure, whereas dehydroxylation of kaolinite and the disappearance of its X-ray reflections occurred between 450-640°C.
Mössbauer and Infrared Study of Heat-Treated Nontronite
Authors: Karakassides Michalis A. , Gournis Dimitris , Simopoulos Thanassis , Petridis Dimitris
Published: August 2006

The Mössbauer and infrared spectra of Li- and Rb-saturated nontronites from Washington, USA (SWa-1), heat treated at different temperatures, were measured. The Mössbauer results show that diffusion of Li+ into the 2:1 layer by heat treatment at 250-300°C does not affect the magnetic hyperfine interactions of the octahedral iron centers. In contrast, significant changes were observed by calcination at temperatures >300°C for Li-saturated nontronites. The main features of the Mössbauer spectra recorded at different temperatures reveal superparamagnetic behavior with a blocking temperature of ~5 K. The superparamagnetic behavior is related to small magnetic domains created by partially broken Fe-O-Fe bonds upon heat treatment. The infrared spectra of Li-rich nontronite, heat treated at 300°C, show changes attributed to Li migration into the hexagonal cavities. Heating to higher temperatures, produced changes in the spectra of the Li- and Rb-saturated nontronites owing to the dehydroxylation of the layer structure. The dehydroxylation process begins with the loss of OH groups in the FeOHFe bridges and is completed with the disruption of the Al-O bonds at >600°C.
Dielectric-Relaxation Spectroscopy of Kaolinite, Montmorillonite, Allophane, and Imogolite under Moist Conditions
Authors: Ishida Tomoyuki , Marino Tomoyuki , Wang Changjun
Published: August 2006

The dielectric behavior of kaolinite, montmorillonite, allophane, and imogolite samples adjusted to a water potential of 33 kPa was examined using a time-domain reflectometry method over a wide frequency range of 103-1010 Hz. A dielectric relaxation peak owing to bound H2O was observed. The observation of this peak required the precise determination of the contributions of dc conductivity. The peak is located at 10 MHz, indicating that the relaxation time of the bound H2O is approximately ten times longer than the relaxation time of bound H2O with organic polymers, such as an aqueous globular-protein solution. The structure of bound H2O differs between phyllosilicates and amorphous phases, based on differences in relaxation strength and the pattern of distribution of the relaxation times. The dielectric process involving rotation of bulk H2O molecules was also observed at 20 GHz. The relaxation strength of bulk H2O increased with an increase in the water content. The interfacial polarization in the diffuse double layer occurred only in montmorillonite and kaolinite, indicating that mechanisms involving the Maxwell-Wagner and surface-polarization effects cannot be extended to include allophane and imogolite. Although these results suggest that additional work is required, a tentative conclusion is that a tangential migration of counter-ions along clay surfaces may be important.
Effect of Kaolinite and Sulfate on the Formation of Hydroxy-Aluminum Compounds
Authors: Garcia-Gonzalez M. Teresa , Vizcayno Carmen , Cortabitarte Javier
Published: August 2006

OH-A1 solutions were prepared by adding appropriate amounts of NaOH to A1C13 to obtain OH/Al mole ratios of 2.0, 2.5, 2.7, 3.0, and 3.3 in the final suspension. Solid Na2SO4 and Georgia kaolinite (KGa-2) were added individually and jointly to the OH-Al solutions. All samples were aged for 30, 70, and 180 d. X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectrometry were used to characterize precipitates. Bayerite, gibbsite, and nordstrandite crystallized at mole ratios of 3.0 and 3.3, with bayerite being the most abundant. A morphology of clusters of triangular pyramids is described for bayerite. Despite the aging duration, only noncrystalline Al compounds were obtained in mole ratios of 2.0, 2.5, or 2.7. The addition of sulfate to OH-A1 solutions in mole ratios of 2.0 and 2.5 produced crystalline basic aluminum sulfates of variable morphology, but with similar chemical compositions. These phases lost crystallinity with aging. The product from a 2.7 OH-Al solution was X-ray amorphous hydroxysulfate. In contrast, products obtained at mole ratios of 3.0 and 3.3 contained no sulfate ion, which restricted the formation of gibbsite, bayerite, and nordstrandite. The addition of kaolinite to the solutions in OH/A1 mole ratios of 3.0 and 3.3 favored the formation of nordstrandite. The simultaneous addition of sulfate and kaolinite to the OH-A1 solutions in mole ratios of 2.0 and 2.5 produced prevalent sulfate over kaolinite, whereas the opposite occurred at mole ratios 3.0 and 3.3.
Mineralogical and Rb-Sr Isotope Studies of Low-Temperature Diagenesis of Lower Cambrian Clays of the Baltic Paleobasin of north Estonia
Authors: Kirsimäe Kalle , Jørgensen Per
Published: August 2006

X-ray diffraction (XRD), Rb-Sr isotope analysis, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FTIR) methods were used to study diagenetic illite and illite-smectite (I-S) in Lower Cambrian unlithified clays of shallow depth of burial in the northern part of the intercratonic Baltic paleosedimentary basin of the East-European Platform. The studies focused on the <0.06-µm size fraction of the clay. This fraction consists of a highly illitic illite-smectite (I-S) and a poorly crystalline illite (PCI), with some traces of Fe-rich chlorite also present. Rb-Sr isotopic data for the <0.06-µm size fractions suggest that the illitic I-S and PCI have different formation ages. No precise isotopic ages were derived directly owing to the composite illite mineralogy and retention of radiogenic Sr. This retention occurred because of imperfect isotopic homog-enization at low water/rock ratios. The age of burial diagenesis is proposed to coincide with the time of maximum burial depth, which was achieved during the Middle to Late Devonian and continued until Permian-Triassic erosion. Because of the shallow depth of burial (<2 km), diagenesis was probably a low-temperature (<50°C) transformation process. The resident time of 100–150 million years at maximum burial had a major influence in the process.
Composition of Clinoptilolite Formed from Volcanic Glass During Burial Diagenesis
Authors: Ogihara Shigenori
Published: August 2006

The composition of clinoptilolite formed from volcanic glass was investigated from cuttings collected from the offshore MITI-Somaoki borehole, 52 km east of Soma City, Japan. Unaltered volcanic glass and clinoptilolite-replaced glass were found coexisting in the same silicic tuff at 1000 m depth, but unaltered volcanic glass and clinoptilolite did not coexist in individual glass shards, and each material analyzed in this study was pure. The SiO2 and Al2O3 contents of the pure clinoptilolite and the pure, unaltered glass were 69.32 and 13.05 wt. %, and 70.03 and 11.54 wt. %, respectively. The SiO2 content was almost the same and the Al2O3 content was greater in the clinoptilolite-replaced glass compared with the unaltered volcanic glass. As a result, the SiO2/Al2O3 ratio in the clinoptilolite-replaced glass (SiO2/ A12O3 = 5.31) was slightly lower than that of the unaltered volcanic glass (SiO2/Al2O3 = 6.07). The extra-framework cation composition of the clinoptilolite-replaced glass was three times richer in K (K2O = 7.84 wt. %) than the unaltered volcanic glass (K2O = 2.59 wt. %). The cation selectivity of clinoptilolite, which shows a preference for K to Ca and Na, played an important role in the concentration of K in clinoptilolite during clinoptilolite formation from volcanic glass, although the initial pore waters and the volcanic glass were not especially relative K.

Clinoptilolite-replaced glass in the calcite-cemented tuff at 1100 m depth was not enriched in Ca, suggesting that the exchangable-cation composition of clinoptilolite did not change by exposure to Ca-rich solutions at this depth. Apparently, the exchangable-cation composition of clinoptilolite, once formed, is relatively stable and difficult to change, even under conditions in which calcite is precipitating on clinoptilolite crystals.
Infrared Study of Water Sorption on Na-, Li-, Ca-, and Mg-Exchanged (SWy-1 and SAz-1) Montmorillonite
Authors: Xu Weizong , Johnston Cliff T. , Parker Paul , Agnew Stephen F.
Published: August 2006

An environmental infrared microbalance (EIRM) cell was used to study H2O sorption on two montmorillonite samples as a function of water content and type of exchangeable cation. The vibrational spectra showed that H2O sorbed to the clay at low-water content was strongly influenced by the exchangeable cation and by the close proximity to the clay surface. At water contents <6 H20 molecules per exchangeable cation, the H-O-H bending mode of H2O (v2 mode) shifts to a lower frequency and is characterized by an increase in molar absorptivity. In contrast, the positions of the asymmetric and symmetric OH-stretching modes of sorbed water (v1 and v3 modes) shift to higher energies. These observations indicate that H2O molecules sorbed to the clay surface at low-water content are less hydrogen bonded than in bulk H2O. In addition, the vibrational-stretching and bending bands of the structural OH groups of the 2:1 layer are also strongly influenced by H2O content and type of exchangeable cation. By using the EIRM cell, the molar absorptivities of the structural OH-bending vibrations were measured as a function of H2O content. The position and molar absorptivity of the structural OH-bending bands at 920, 883, and 840 cm-1 are strongly influenced by H2O content and type of exchangeable cation. The molar absorptivity of the 920-cm-1 band, which is assigned to the AlAlOH group, decreased strongly at low-H2O content. This reduction in intensity is assigned to a dehydration-induced change in orientation of the structural OH groups resulting from the penetration of H2O molecules into siloxane ditrigonal cavities that are not associated with a net negative charge from isomorphous substitutions.
Adsorption Kinetics of Pentachloroethane by Iron-Bearing Smectites
Authors: Cervini-Silva Javiera , Wu Jun , Stucki Joseph W. , Larson Richard A.
Published: August 2006

The oxidation state of structural Fe greatly alters surface chemistry, which may have a large influence on clay-organic interactions. The effect of structural-iron oxidation state on chlorinated hydrocarbons at the clay-water interface was examined. Pentachloroethane (5CA) was reacted with oxidized, reduced, and reoxidized forms of three different smectites: montmorillonite, ferruginous smectite, and nontronite in aqueous suspension under controlled-atmosphere conditions. Pentachloroethane was found to adsorb at different rates for the three smectites. A series of 5CA-adsorption rate constants in the presence of these clays showed a strong correlation with the Fe(II) content of the clay (r2 = 0.98). The clay surface behaves as a Brønsted base and promotes 5CA dehydrochlorination. The adsorption kinetics at the clay-water interface were described by the formation of a precursor complex prior to 5CA dehydrochlorination.
Ti-Bearing Phases in the Huber Formation, an East Georgia Kaolin Deposit
Authors: Schroeder Paul A. , Shiflet Jason
Published: August 2006

Six kaolin samples from the Lower Tertiary Huber Formation near Wrens, Georgia were analyzed using transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), chemical analysis, and magnetic susceptibility to characterize the Ti-bearing phases. Selected samples were treated with 5 M NaOH to remove kaolinite and concentrate the Ti-bearing phases for additional analysis. TiO2 content in the bulk fraction ranges from 1.2 to 5.4 wt. %. There are at least three Ti-bearing phases, including anatase, rutile, and a poorly defined nanocrystalline form. Anatase is most abundant and is commonly found with {010} faces in association with kaolinite edge and basal faces. The nanocrystalline form occurs at 0–1 wt. %, and rutile occurs in trace amounts. Bulk XRD analysis correlates well with the bulk TiO2 chemical measurements. Average anatase unit-cell parameters are a = 0.37908 ± 0.0002 nm and c = 0.951 ± 0.001 nm. These parameters indicate an approximate chemical formula of Fe3+0.05Ti4+0.95O1.95(OH)0.05.

The distribution of TiO2 content as a function of depth may be useful to obtain original grain-size variations associated with relative sea-level changes responsible for the deposition of the Huber Formation. Evidence for original depositional sediment properties can be seen in the occurrence of pseudomorphic replacement of micas and fecal pellets by kaolinite. Additional evidence for post-depositional changes includes the sub-micrometer euhedral character and low Fe content of the anatase (relative to soil-derived anatase). These observations for the Huber Formation are consistent with a previously published theory for kaolin genesis that includes biomineralization of originally coarser-grained aluminosilicates into a kaolinite-rich ore body.
The Effect of Al on Fe Oxides. XIX. Formation of Al-Substituted Hematite from Ferrihydrite at 25°C and pH 4 to 7
Authors: Schwertmann Udo , Friedl Josef , Stanjek Helge , Schulze Darrell G.
Published: August 2006

Iron oxides in surface environments generally form at temperatures of 25 ± 10°C, but synthesis experiments are usually done at higher temperatures to increase the rate of crystallization. To more closely simulate natural environments, the transformation of 2-line ferrihydrite to hematite and goethite at 25°C in the presence of different Al concentrations and at pH values from 4 to 7 was studied in a long-term (16–20 y) experiment. Aluminum affects the hydrolysis and charging behavior of 2-line ferrihydrite and retards crystallization. Al also promotes the formation of hematite over goethite and leads to multidomainic discoidal and framboidal crystals instead of rhombohedral crystals. The strong hematite-promoting effect of Al appears to be the result of a lower solubility of the Al-containing ferrihydrite precursor relative to pure ferrihydrite. Hematite incorporates Al into its structure, as is shown by a decrease in the a and c-cell lengths and a decrease in magnetic hyperfine fields (Mössbauer spectroscopy). With hematite formed at low-temperature, these decreases were, however, smaller for the cell length and greater for the magnetic field than for hematite produced at higher temperatures. Both phenomena are removed by heating the hematite at 200°C. They are attributed to structural OH and/or structural defects. The relative content of Al in the structure is lower for hematite formed at 25°C than for hematites synthesized at higher temperatures (80 and 500°C). The maximum possible substitution of one sixth of the Fe positions was not achieved, similar to soil hematites. These results show that properties of widely distributed soil Al-containing hematites can reflect formation environment.
Influence of Synthesis pH on Kaolinite “Crystallinity” and Surface Properties
Authors: Fialips Claire-Isabelle , Petit Sabine , Decarreau Alain , Beaufort Daniel
Published: August 2006

Hydrothermal syntheses were performed at various pH values and temperatures to induce variability in kaolinite defect density. Temperature of synthesis ranged from 200 to 240°C, for 21 d. Initial pH at room temperature ranged from 0.5 to 14. The starting material was a hydrothermally treated gel, with an atomic Si/Al ratio of 0.93, partly transformed into kaolinite.

Kaolinite was obtained for a wide range of pH. Although no influence of temperature on “crystallinity” (i.e., defect density) was observed, the effect of pH was important. A continuous series was obtained from a low-defect kaolinite, with high thermal stability and a hexagonal morphology for the most acidic final pH, to a high-defect kaolinite, with low thermal stability and lath shape for the most basic final pH. These variations of kaolinite properties appear related to the pH dependence of kaolinite surface speciation. Increasing pH value results in increased cation adsorption on the kaolinite external surfaces and increases in the elongation of particles.
A Model for the Mechanism of Fe3+ to Fe2+ Reduction in Dioctahedral Smectites
Authors: Drits V. A. , Manceau A.
Published: August 2006

A model to compensate the 2:1 layer having excess negative charge owing to the reduction of Fe3+ to Fe2+ by sodium dithionite buffered with citrate-bicarbonate in nontronite, beidellite, and montmorillonite is proposed. This model is based on reassessing published experimental data for Fe-containing smectites and on a recently published structural model for reduced Garfield nontronite. In the reduced state, Fe2+ cations remain six-fold coordinated, and increases of negative charge in the 2:1 layer are compensated by the sorption of Na+ and H+ from solution. Some of the incorporated protons react with structural OH groups to cause dehydroxylation. Also, some protons bond with undersaturated oxygen atoms of the octahedral sheet. The amount of Na+ (p) and H+ (ni) cations incorporated in the structure as a function of the amount of Fe reduction can be described quantitatively by two equations: p = m/(1 + K0mrel) and ni = K0mrel/(1 + K0mrel); with K0 = CEC (9.32 − 1.06mtot + 0.02mtot2), where mtot is the total Fe content in the smectite, m is the Fe2+ content, mrel is the reduction level (m/mtot), CEC is the cation-exchange capacity, and K0 is a constant specific to the smectite. The model can predict, from the chemical composition of a smectite, the modifications of its properties as a function of reduction level. Based on this model, the structural mechanism of Fe3+ reduction in montmorillonite differs from that determined in nontronite and beidellite owing to differences in the distribution of cations over trans- and cis-octahedral sites.
The Dependence of Localized Crystallization of Halloysite and Kaolinite on Primary Minerals in the Weathering Profile of Granite
Authors: Jeong Gi Young
Published: August 2006

The formation of kaolin-group minerals in the weathering profile of granite, under the humid, temperate climate as found in Korea, was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron microprobe analysis (EMA). The granite was gradually weathered to saprolite. K-rich feldspar was not weathered in the profile, but plagioclase partially weathered to halloysite septa (i.e., wall-like masses). At the bottom of the profile, biotite had weathered to regularly interstratified biotite-vermiculite (B-V), and subsequently to kaolinite, with a considerable increase in grain volume. In the upper part of the profile, loose aggregates of transported clays, including halloysite and kaolinite, coated the preformed halloysite septa in the weathered plagioclase. Halloysite had precipitated as a metastable phase in the microfissures of partially weathered plagioclase. Kaolinite had precipitated heavily in the weathered biotite, where surfaces supply abundant templates facilitating the nucleation of kaolinite. The localized crystallization of halloysite and kaolinite, depending on the distribution of primary minerals, strongly influenced the kaolin mineralogy of the granite weathering profile.
Characteristics of Clay Minerals in Gouges of the Dongrae Fault, Southeastern Korea, and Implications for Fault Activity
Authors: Choo Chang Oh , Chang Tae Woo
Published: August 2006

The Dongrae fault within the Yangsan fault system is considered one of the major faults in the southeastern part of Korea, extending over 150 km. The results of K-Ar radiogenic dating of fault gouges collected from six localities show a relatively wide range in age from 57.5 million years ago (Ma) to 40.3 Ma. Fault gouges are composed of newly formed minerals, including smectite, illite, zeolite, kaolinite, K-rich feldspar, apatite, and pyrite. The occurrence of abundant smectite and illite-lMd with lesser quantities of zeolite suggests that the fault gouges experienced hydrothermal alteration at low temperatures. Smectite is probably unstable relative to other clay minerals, such as illite and zeolite. Considering that filiform mordenite is replacing the smectite, we suggest that mordenite formed by recrystallization involving a solid-state transformation. Under high fluid/rock ratios, smectite seems to have formed in the early stage of alteration. In contrast, zeolite minerals and authigenic K-rich feldspar progressively appeared with time as the fluid/rock ratio decreased with the changing chemistry of the hydrothermal fluids. The composition of clay minerals in the gouge materials probably was controlled by the chemistry and the amount of circulating fluids derived from adjacent granitic rocks.
Transmission Electron Microscopy Study of Very Low-Grade Metamorphic Rocks in Cambrian Sandstones and Shales, Ossa-Morena Zone, Southwest Spain
Authors: López-Munguira A. , Nieto F.
Published: August 2006

This study examines the evolution of the texture, structure, and chemical composition of rocks derived from clastic materials of the Ossa-Morena Zone (Hesperian Massif, Spain). Previous studies of phyllosilicates in these rocks (by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, and electron microprobe) indicated a temperature decrease from bottom (epizone conditions) to top (diagenetic conditions) of the rock section.

At the nanometer scale, phyllosilicate packets form large angles where grains intersect with no preferred orientation. With metamorphic grade, packets are wide and defect free, compared to packets at lower grade. These packets are ∼ 15 layers under diagenetic conditions to >80 layers in the epizone. Dioctahedral K-rich micas (muscovite, phengite, and illite) have coexisting 1Md, 1M, and 2M polytypes. Long-period polytypes of 4, 5, and 6 layers are reported for the first time in dioctahedral K-rich micas. The chemical compositions of the micas are nearly identical in the anchizone and the diagenetic zone, comprising an illitic (0.8 atoms per formula unit, a.f.u., of K) and a phengitic component (0.15 a.f.u, of Mg and 0.13 a.f.u, of Fe). Fe may correspond to a ferrimuscovitic substitution. Epizone samples have a high phengitic content (Mg = 0.24 a.f.u.) and almost no illite component. One diagenetic sample has coexisting berthierine, trioctahedral chlorite, sudoite, and corrensite. Berthierine and chlorite are identical in composition. Because of the clastic nature of the system, the composition of corrensite is not typical of other corrensites, with higher Al content, Fe/Mg ratio at ∼1, and K as the exchangeable cation.

Textural differences between the diagenetic zone and the anchizone are the progressive increase in the size of dioctahedral K-rich mica grains, which involves an increasing illite crystallinity based on the Kübler index. The chemical compositions of these micas are illite (diagenesis and anchizone) and phengite in the epizone. There are no intermediate phases, suggesting a compositional gap between illite and phengite. The coexistence of different polytypes of dioctahedral K-rich micas and the absence of chemical homogeneity indicate disequilibrium in the Cambrian pelitic rocks studied.
One-Step Synthesis of Alkyltrimethylammonium-Intercalated Magadiite
Authors: Pastore Heloise O. , Munsignatti Marcelo , Mascarenhas Artur J. S.
Published: August 2006

Cetyltrimethylammonium- and tetradecyltrimethylammonium-intercalated magadiites were prepared by direct syntheses, starting from sodium metasilicate (Na2O/SiO2 = 1.0) and nitric acid. Total substitution of sodium by cetyltrimethylammonium or tetradecyltrimethylammonium cations was not achieved in the range of surfactant: silicon molar ratios used in this study. When a phosphoniun-based surfactant replaces the ammonium surfactants in the same procedure, the result of the synthesis is a mixture of quartz and unmodified surfactant. If dodecylammonium bromide is used, an MCM-41 molecular sieve is obtained. The substitution of the silicon source by tetramethylammonium silicate or of nitric acid by hydrochloric, hydrofluoric, or acetic acids also yields MCM-41 molecular sieves, indicating that the formation of magadiite is greatly dependent on the presence of sodium cations and nitrate anions.
Low-Temperature Acid Weathering in Newhaven, Sussex, United Kingdom, and Its Application to Theoretical Modeling in Radioactive Waste-Disposal Sites
Authors: De Putter Thierry , Bernard Alain , Perruchot Alain , Nicaise Dominique , Dupuis Christian
Published: August 2006

Tertiary weathered sediments located immediately to the west of the harbor at Newhaven, Sussex, UK, were investigated by examination of major and trace elements by scanning electron microscope (SEM), microprobe, and inductively coupled plasma mass spectrometer (ICP-MS), and the mineralogy was studied by optical petrography, X-ray diffraction (XRD), transmission electron microscope (TEM), selective leaching, and thermodynamic modeling. Studied outcrops experienced acid leaching by sulfuric acid percolating downward through Tertiary sediments overlying Cretaceous chalk. The progressive neutralization of the percolating acid fluids resulted in “sequentially” layered neoformation of minerals: jarosite, iron oxides, aluminous minerals (sulfates, oxyhydroxides), gypsum, and Fe-Mn oxides. Substantial agreement was found between field observations and mineral assemblages obtained by modeling with the program CHILLER. These results suggest that the initial assumptions on the weathering process and mechanisms are correct. The relevance and implications of this study in the modeling of future denudation and weathering processes of radioactive waste-disposal sites (both deeply buried sites for high-leveI waste and surface sites for low-level waste) are discussed. Neoformed phases, such as jarosite, aluminous minerals, and silico-aluminous gels may play a significant role in the efficient trapping of mobilized pollutant radionuclides.
Incorporation of Radioactive Contaminants into Pyroaurite-Like Phases by Electrochemical Synthesis
Authors: Roh Y. , Lee S. Y. , Elless M. P. , Foss J. E.
Published: August 2006

During electrochemical remediation of radionuclide, 235U, 238U, and 99Tc-contaminated aqueous solutions, pyroaurite-like phases, ideally [M(II)M(III)(OH)16CO3·4H2O] where M = Fe, were synthesized following coprecipitation with iron from metal iron electrodes. The effect of radionuclides on the transformation of amorphous precipitates to crystalline pyroaurite-like phases was investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray analysis, Fourier-transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. The synthetic iron carbonate hydroxide phases showed primary XRD peaks at 0.7 and 0.35 nm and FTIR spectra that indicated the presence of a brucite-like sheet structure with carbonate anions occupying the interlayer. Divalent and trivalent iron, eroded from the electrode, occupies the octahedral sites of the brucite-like sheets. The carbonate anions in the interlayer balance the excess positive charge from isomorphous substitution of the Fe2+ or Fe3+ by reduced uranium (U4+) and technetium (Tc4+). Because of the lower solubility associated with crystalline phases than amorphous phases, incorporation of radioactive contaminants into pyroaurite-like phases by electrochemical syntheses represents a more effective approach for removing U and Tc from contaminated aqueous solutions than traditional technologies.
Reduction and Sorption of Chromium by Fe(II)-Bearing Phyllosilicates: Chemical Treatments and X-Ray Absorption Spectroscopy (XAS) Studies
Authors: Brigatti Maria Franca , Lugli Cristina , Cibin Giannantonio , Marcelli Augusto , Giuli Gabriele , Paris Eleonora , Mottana Annibale , Wu Ziyu
Published: August 2006

The reduction of hexavalent chromium species in aqueous solutions by interaction with Fe(II)-bearing solid surfaces was studied using a 0.96 × l0−3 M Cr(VI) solution and iron-rich clays with different Fe(II)/Fe(III) ratios, layer charge, and exchange properties, i.e., chlorite, corrensite, and montmorillonite. Experimental studies demonstrated that Fe(II)-bearing phyllosilicates reduce aqueous Cr(VI) ions at acidic pH. Chlorite and corrensite, owing to the high Fe(II)/Fe(III) ratio, are electrochemically reactive, as rapid Cr(VI) reduction indicated. In contrast, montmorillonite showed minimum to nil reactivity towards Cr(VI). Furthermore, corrensite, which is high in both Fe(II)/Fe(III) ratio and exchange capacity, adsorbs the greatest amount of chromium.

X-ray absorption spectroscopy at Al, Mg, Fe, and Cr K-edges was used to investigate the adsorbed chromium species. The montmorillonite sample, unaffected by treatment with Cr(VI) solution, displays no change at any investigated edge. Edge shape and energy also do not change for the Mg and Al spectra in corrensite, and changes are minor in chlorite. By contrast, the Fe K-edge changes both in chlorite and corrensite, and indicates an increase of Fe(III) in treated samples at the expense of pre-existing Fe(II). Cr K-edge spectra show that chlorite and corrensite sorb Cr(III), which implies its reduction from Cr(VI) in the interacting solution.