Interlayer Collapse Research Articles

Effect of smectite dehydration on pore water geochemistry in the shallow subduction zone: An experimental approach

The diagenetic smectite to illite transition is widely accepted to cause ubiquitous pore water freshening at convergent margins. However, experimental consolidation tests show that smectite also dehydrates partially with increasing effective stress. To shed light on this process three hydrothermal consolidation tests on a silty smectite‐rich claystone were conducted with stresses (P) up to 70 MPa and at constant temperatures (T) of 20°C, 60°C and 100°C. Fluids expelled during the tests were analyzed for major and trace elements to evaluate dehydration and fluid‐rock interaction with increasing PT conditions. The results document that fluid freshening starts when the effective stress exceeds 1.3 MPa. The smectite interlayer water content decreases from 27 wt‐% to ∼20 wt‐% during the experiments, which is equivalent to an interlayer collapse from 18.5 to ∼15.4 Å. The released interlayer H20 accounts for up to 17% of the total fluid volume released from the consolidating sediment. Major and volatile element geochemistry is influenced by temperature and smectite interlayer collapse. The interlayer collapse is characterized by K and Ca uptake while is B released from smectite. Application of experimental results to the Barbados accretionary margin shows that stress dependent smectite dehydration is an important fluid source mechanism and accounts for substantial fluid freshening. Modeled smectite dehydration suggests a decrease of smectite interlayer water content from 27 wt‐% at the surface down to ∼22 wt‐% at 2 km depth. This leads to chlorinity values as low as 460 mM.

Rehydration of dehydrated-dehydroxylated smectite in a low water vapor environment

Thermal analysis experiments in the environment of an extremely low water vapor concentration provide insight into the first steps of the rehydration mechanism in smectite when completely dehydrated and the interlayer region is collapsed. The relative structural and compositional controls on dehydration and rehydration reactions are compared from a well-characterized suite of samples that vary with respect to chemical composition, octahedral and tetrahedral substitution, octahedral cation site vacancy, and degree of dehydroxylation. Techniques including multi-cycle heating-cooling thermogravimetric analysis and nitrogen gas adsorption on various smectite samples preheated at different temperatures followed by rehydration at ambient conditions were used to characterize the interaction of water molecules with completely dehydrated montmorillonite, beidellite, and nontronite smectite types. Beidellite with high-Al 3+ tetrahedral substitution results in electrostatically undersaturated basal oxygen atoms that exert strong repulsion between the tetrahedral sheets of adjacent 2:1 layers. The interlayer region of dehydrated or dehydroxylated beidellite is capable of being spontaneously rehydrated even in low water vapor environments. In completely dehydrated montmorillonite and nontronite, the external surface area of the crystallites is a primary control on water adsorption at low humidity when the molecules form a shell around the exchangeable cations present on external surfaces. The potential of montmorillonite and nontronite to reopen a collapsed interlayer is significantly lower than beidellite because of their crystal-chemical features that result in 2:1 layer and interlayer cation attraction. With increasing water vapor partial pressure, the hydration potential of interlayer cations provokes a reopening of the interlayer. In a dehydroxylated nontronite, the undersaturated residual oxygen atom strongly bonds the interlayer cation within the ditrigonal ring of the tetrahedral sheet, resulting in a permanent interlayer collapse. The specific surface area calculated from a conventional N 2 gas adsorption measurement using the BET model represents the external surface area of a dehydrated smectite crystallite and can be converted into the mean crystallite thickness. The mean crystallite thickness of a completely dehydrated smectite increases with an increase in preheating temperature.

Study of Interlayer Spacing Collapse During Polymer/Clay Nanocomposite Melt Intercalation

The influence of the chemical structure of alkylammonium organo-modifying montmorillonite clays on the ability to form nanocomposites by melt blending, depending on the processing temperature and the organoclay thermal treatment, has been investigated. On one side chlorinated polyethylene/Cloisite 30B (nano)composite has been prepared by melt intercalation at 175 degrees C and its wide angle X-ray diffraction pattern revealed that the peak characteristic of the interlayer spacing of the organoclay was shifted to lower d-spacing, indicating a collapse of the organoclay structure. On the other side, (nano)composites based on ethylene-vinyl acetate copolymer/Cloisite 30B have been prepared by melt intercalation at 140 degrees C. At this temperature, exfoliation was observed with the as-received organoclay while the same organo-modified clay, simply dried at 180 degrees C for 2 hours, induced again the formation of a composite with a collapsed structure. The effect of the Cloisite 30B thermal treatment on the morphology and mechanical properties of ethylene-vinyl acetate-based (nano)composites was investigated using wide angle X-ray diffraction and tensile tests. In order to shed some light on the origin of this clay interlayer collapse, organoclay modified with various ammonium cations bearing long alkyl chains with different amounts of unsaturations were studied using wide angle X-ray diffraction and X-ray photoelectron spectroscopy before and after thermal treatment at 180 degrees C for 2 hours. Isothermal thermogravimetric analysis of all organoclays was also investigated. The layers collapse effect is discussed depending upon the level of unsatured hydrocarbon present in the organic surfactant.

Use of modified hydroxy-aluminum bentonites for chromium(III) removal from solutions

The retention of chromium(III) from a 2000 ppm chromium basic sulfate and tannery waste solution at pH 4.5 using modified hydroxy-aluminum bentonites (OH-Al bentonites) as adsorbents was studied. OH-Al bentonite was prepared by mixing clay with a hydrolyzed commercial chlorohydroxy Al solution. The modified Al bentonites were obtained by (a) a treatment with 0.5 M sodium chloride and (b) a treatment with a Na-hexametaphosphate solution (HMP) after adding sodium chloride. The effect of heating the adsorbents at 100, 500, 700 and 800 °C on Cr retention as a function of time was also analyzed. Cr retention by modified OH-Al bentonite with HMP increased with time (up to 100 mg Cr/g) where modified OH-Al bentonite was twice that of untreated bentonite. The relatively high uptake of metal from the salt solution by modified OH-Al bentonite treated at 800 °C, in which a complete interlayer collapse occurred, indicated the importance of the contribution of external surface sites to the retention capacity. The maximum Cr uptake from a water waste was 24 mg/g, due to interferences and different chromium species in the industrial solution.

Prediction of Radionuclide Aging in Soils from the Chernobyl and Mediterranean Areas

The aging of soil-pollutant interaction, which may lead to an increase in pollutant fixation, is the main driving force in the natural attenuation of contaminated soils. Here a test was evaluated to predict the aging of radiostrontium and radiocesium in soils from the Chernobyl and Mediterranean areas. After contamination, soils were maintained at various temperatures for up to 12 mo, with or without drying-wetting (DW) cycles. Changes in the quantity of radionuclide reversibly sorbed over time were monitored using an extraction test (1 mol L(-1) NH(4)Cl; 10 mL g(-1); 16 h). The fixed fraction could not be predicted from soil properties controlling the sorption step. Aging was not as relevant for Sr as for Cs. The time elapsed since contamination was the main factor responsible for the slight (up to 1.3-fold) decreases in Sr extraction yields. The additional effect of DW cycles was negligible. Instead, all factors accelerated Cs aging due to the enhancement of Cs trapping by clay interlayer collapse, with up to 20-fold increases in Cs fixation. The DW cycles also caused secondary effects on the Cs-specific sorption pool, which were beneficial or detrimental depending on the soil type. Extraction yields from laboratory aged samples agreed with those from field samples taken a few years after the Chernobyl accident. These results confirm the prediction capacity of the laboratory test and its usefulness in risk assessment exercises and in the design of intervention actions, particularly because neither fixation nor aging were related to the soil properties, such as clay content.

Ammonium Fixation in Sub-grade Decomposed Granite Substrates

Granitic materials represent a common erosive substrate in California and much of the western United States. When granitic rocks weather, they disintegrate into coarse textured, non-cohesive substrates, known generally as decomposed granite (DG). Because of low moisture and N availability, revegetation of these substrates for erosion control is difficult. If nitrate based fertilizers are used, they can be rapidly leached, while NH 4 + fertilizers may be sequestered mineralogically by interlayer fixation. In this study, we focus on the occurrence of NH 4 + fixation on a decomposed granitic substrate and show that the fixation capacities of these sandy saprolites are significant despite analyses indicating that the samples are predominantly quartz, have low clay contents and have low cation exchange capacities (CEC). At field loading rates equivalent to less than 300 kg N ha−1, 36–42% of added NH 4 + may become unavailable to plants due to interlayer collapse and fixation for an unknown period of time. Ammonium fixation did not vary significantly in relation to substrate weathering class in these samples. Oriented X-ray diffraction analysis revealed the presence of vermiculite in particle size fractions from clay to very coarse sands. While other studies have identified silt as the most active fraction, the relative fixation capacity of these granite saprolites was greatest in the fine and very fine sand fractions when considered on a gram for gram basis of each individual particle size. We found that the extractant cation also influenced the measured levels of NH 4 + fixation in these granite saprolites. At loading rates of 0–150 kg NH 4 + ha−1, extraction with KCl resulted in apparent NH 4 + fixation capacities that were twice as great as those found with NaCl extractions when tested at low NH 4 + concentrations and close to 35% greater at higher NH 4 + amendment loading. Estimation of available ammonium in the decomposed granite using conventional KCl extraction methods appears to cause fixation, rather than extraction of at least part of the substrate’s NH 4 + content.

Ammonium–Potassium–Calcium Exchange on Vermiculite and Hydroxy‐aluminum Vermiculite

Binary and ternary cation‐exchange reactions involving NH+4, K+, and Ca2+ on vermiculite and hydroxy‐Al interlayered vermiculite (HIV) were investigated. In the case of vermiculite, NH4‐Ca exchange was nearly indistinguishable from the nonpreference isotherm while HIV exhibited preference for NH+4 The presence of K+ had significant suppressing impact on the apparent NH+4 selectivity in NH4‐Ca exchange in HIV most likely because of retardation of Ca2+ diffusion in the interlayer. For vermiculite, the presence of K+ in the NH4‐Ca system induced apparent high affinity sites for NH+4 most likely because of interlayer collapse. The overall study demonstrated that cation‐exchange selectivity coefficients in vermiculite and HIV are dependent on number and type of cations present.

Ammonium–Potassium–Calcium Exchange on Vermiculite and Hydroxy-aluminum Vermiculite

Binary and ternary cation-exchange reactions involving NH+4, K+, and Ca2+ on vermiculite and hydroxy-Al interlayered vermiculite (HIV) were investigated. In the case of vermiculite, NH4-Ca exchange was nearly indistinguishable from the nonpreference isotherm while HIV exhibited preference for NH+4 The presence of K+ had significant suppressing impact on the apparent NH+4 selectivity in NH4-Ca exchange in HIV most likely because of retardation of Ca2+ diffusion in the interlayer. For vermiculite, the presence of K+ in the NH4-Ca system induced apparent high affinity sites for NH+4 most likely because of interlayer collapse. The overall study demonstrated that cation-exchange selectivity coefficients in vermiculite and HIV are dependent on number and type of cations present.

Effects of Iron Oxidation State and Organic Cations on Dioctahedral Smectite Hydration

AbstractReduction of structural Fe in Na-exchanged dioctahedral smectites decreases swellability in water, but because clay interlayers also collapse in the process the concomitant effect on surface hydration energy is uncertain. This study examined the hydration behavior of oxidized and reduced dioctahedral smectite clays exchanged with polar (Na) and weakly-polar (organic) cations to determine the nature of the surface before and after Fe reduction, and to determine if clay surfaces are hydrophilic or hydrophobic. The H2O content in various dioctahedral smectites decreased if Na was replaced by tetramethylammonium (TMA), trimethylphenylammonium (TMPA), or hexadecyltrimethylammonium (HDTMA). Among the organo-clays, H2O adsorption decreased with increasing complexity of the cation. For oxidized smectites, those exchanged with TMPA retained less H2O than those exchanged with Na at all pressures. The extent of this difference depended on the clay and decreased with increasing applied pressure. Reduction of Fe(III) to Fe(II) in the octahedral sheets decreased the swelling of Na-saturated smectites, apparently causing some previously swelling interlayers to collapse. If the Na interlayer cation was exchanged to alkylammonium after reduction, but prior to swelling-pressure measurements, the swelling increased or remained near constant, suggesting that the organo-cation disrupted the collapse process of the interlayers associated with the reduced smectite layers. Reduced TMPA-saturated smectite surfaces are more strongly hydrated if the octahedral sheet is reduced than if oxidized. Thus, reduction of structural Fe increases the hydration energy of smectite basal surfaces, but swellability could decrease or increase depending on the extent of interlayer collapse occurring with different exchangeable cations.

Effect of the Ionic Status and Drying on Radiocesium Adsorption and Desorption in Organic Soils

Radiocesium (RCs) interaction in organic soils has been studied using adsorption and desorption experiments, and the effects of the ionic status and drying were evaluated. Four organic soils were used: three peaty podzols containing illite and a peat without illitic materials, RCs solid-liquid distribution coefficients (K{sub D}) were determined for each soil in water and in several solutions containing Ca, K, or a mixture of the two. RCs contamination was performed either with a single equilibration or after a three-step preequilibration. Whereas the ionic strength of the solution controlled RCs adsorption in the peat, the level of monovalent species was the most important factor in RCs adsorption in the peaty podzols. Reversibility of RCs adsorbed in the different conditions was assessed in the moist sample and after drying by single and consecutive extractions with either CaCl{sub 2} or CH{sub 3}COONH{sub 4}. RCs adsorption was totally reversible in the peat regardless of the ionic status and the desorption approach used. For the three peaty podzols, due to the presence of specific sites, adsorption reversibility was dependent on the scenario in which this adsorption was performed and on the cation used in desorption. Finally, although NH{sub 4} is known to desorb RCsmore » specifically adsorbed in the soil, it was shown to induce interlayer collapse, and consecutive extractions with CaCl{sub 2} led to higher desorption yields.« less

Pedogenic Formation of High-Charge Beidellite in a Vertisol of Sardinia (Italy)

AbstractThe fine clay (<0.1 μm) fraction of a clayey soil (Vertisol) from Sardinia (Italy) was studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, cation exchange capacity (CEC) and surface area measurements. Smectites were the dominant clay minerals both in the parent material and the soil horizons. The magnitude and location of the smectites’ layer-charges were analyzed using the Hofmann & Kiemen effect (suppression of the octahedral charge following lithium-saturation and heating). The amount of montmorillonite layers was evaluated by measuring the reduction of total surface area and CEC after suppression of octahedral charges and subsequent collapse of montmorillonite interlayers. Reduction of total surface area and CEC after fixation of K and irreversible collapse of interlayers were used to quantify high-charge layers before and after the suppression of octahedral charges. This allowed us to evaluate the amount of tetrahedral high-charge layers. The smectites in the parent material were montmorillonitic-beidellitic mixed layers and exhibited a small proportion of high-charge layers; in particular, layers with a high tetrahedral charge were a very minor component. In the upper soil horizons, the amount of montmorillonitic layers decreased whereas the amount of smectite layers with a high tetrahedral charge increased. FTIR spectroscopy indicated more Fe for Al substitution in the smectites of the soil horizons than in the smectites of the parent material. The results suggested that octahedral charged smectite layers (montmorillonitic) were altered, whereas high-charge beidellitic layers were formed in this soil environment characterized by rather high pH (>8.0).

Atomic-resolution transmission electron microscope evidence for the mechanism by which chlorite weathers to 1:1 semi-regular chlorite-vermiculite

Atomic-resolution transmission electron microscope (TEM) images reveal that IIbb (beta = 97 degrees ) Mg,Al,Fe-chlorite from Koongarra, Australia, transforms to vermiculite via a range of intermediate chemical and structural states. Semi-quantitative analysis of contrast in atomic-resolution images of layer silicates with approximately 1.4 nm basal spacings indicate that the interlayers range from brucite-like to having approximately 0.3-0.6 interlayer cations per formula unit. Octahedral cations (predominantly Mg and Fe) tend to be removed from every second interlayer, leading to semi-regular 1:1 interstratifications of chlorite-vermiculite. Further loss of interlayer cations is accompanied by partial to complete interlayer collapse in the vacuum of the TEM. Resulting intergrowths of chlorite and semi-regular 1:1 chlorite-vermiculite retain the primary chlorite orientation, morphology, and sense of octahedral tilt in 2:1 layers. Although vermiculitization is a continuous process that occurs by a solid-state mechanism, the reaction involves important structural modifications. Atomic-resolution [010] images indicate initial loss of interlayer cations is accompanied by approximately a/3 shifts of 2:1 layers and cations in brucite-like interlayers. Displacements of interlayer cations change the interlayer stacking from IIbb to Iab and shift of the following 2:1 layer converts it from Iab to the Iaa. Displacements are driven by the lower energy of a-type interactions when vacancies occur in sites above tetrahedral cations. Shift of a 2:1 layer alters the subsequent interlayer from IIbb to IIab. Stabilization of every slightly altered second interlayer by introduction of a-type stacking explains development of semi-regular 1:1 chlorite-vermiculite interstratifications. Displacements occur before significant modification of interlayer electron density can be detected in high-resolution images. This observation is consistent with previously reported inhibition of layer shifts by low interlayer charge. Layer displacement may occur by an elastic process (no rupture of bonds within the 2:1 layer) at the tip of the growing vermiculite portion of the intergrowth. Removal of cations from the chlorite-vermiculite junction may be facilitated by rapid diffusion along the vacancy-rich interlayer. Mg is removed in solution, Fe is precipitated locally in aggregates of nanocrystalline Al-, Si-, and P-bearing goethite.

Illite-Smectite Alteration and Accompanying Reactions in a Pennsylvanian Underclay Studied by TEM

AbstractPennsylvanian underclay from Illinois is characterized by well-developed mineral zonation: towards the coal bed, marly limestone gradually evolves into carbonate-free clay, chlorite becomes undetectable and illite/smectite changes from ordered and illite-dominated into random and smectite-dominated, with both types present in the middle of the profile. Transmission electron microscopy (TEM) observations of the bulk material imply that disappearance of calcite is due to dissolution. Movement of SiO2 in the upper part of the profile is evidenced by quartz cementation of clay aggregates; crystallization of kaolinite, by the presence of vermicular aggregates absent from less-altered samples. Illitic material in unaltered (limestone) samples consists of rare, large, Al-rich crystals of mica, interpreted as detrital, and abundant thin crystals of illite/smectite intimately mixed in approximately equal proportions with even thinner crystals of discrete illite. Both are more Mg- and Fe-rich than the large mica crystals and are interpreted as diagenetic, based on their 1Md polytype and the correlation with coal rank. Illitic material of the upper, carbonate-free section of the profile contains the same 3 types of crystals, but in different proportions: illite/smectite crystals dominate and their composition is more smectitic. Two distinct morphologies of the aggregates of crystals with different proportions of the component layers are observed. It explains why 2 different illite/smectites are detectable by X-ray diffraction (XRD) in these samples. The analysis of chemical data suggests that the underclay is a residue after dissolution of all of the calcite and half of the quartz from the original limestone (paleosol and/or telogenetic process). The TEM observations are not decisive regarding the origin of variation within the illitic material. It may result from burial diagenetic illitization of more-smectitic material, similar to the composition preserved in the center of underclay profile, or it may represent telogenetic alteration of illitic clay by acid waters penetrating down from the coal bed. The aggradation model explains the increase in percent K2O, MgO and illite layers in the uppermost part of the profile. Whichever is the direction of reaction, it proceeds on an aggregate-by-aggregate basis and not fundamental particle-by-particle, and cannot be explained by simple opening or collapse of interlayers.

Theoretical evaluation of pillared clay adsorbents: Part II: Differences in porosity between Al-pillared laponite and hectorite

Pillared Clays are proposed as a new class of sorbents with properties which exceed those of zeolites. However, despite of intense research, the materials are still not used as substituents of zeolites. By the present study a better understanding of the potential and limiting factors of pillared clays is achieved by means of geometric models. These models take into account interlayer distance, pillar symmetry, collapse, partial pillaring, layer size and layer stacking. The results are evaluated on microporosity and interpillar distance and compared to experimental data. Because of the important contribution of mesopores to the pore volume of PILCs, a macrostructure in which the experimental mesopore volume has been approximated, is proposed. This paper reports the evaluation of two Al-pillared hectorites, natural and synthetic (laponite), having completely different macrostructures.

Crystal structures and metal uptake capacity of 10Å-manganates: An overview

Marine and synthetic 10Å-manganates and terrestrial todorokites have similar tunnel structures. Each tunnel wall consists of 3 edge-shared [(Mn 4+, Me (2+,3+), Mn 2+)(O 2−, OH −) 6]octahedral strings along the tunnel, where Me (2+,3+) represents transition cations such as Fe 3+, Co 2+, Ni 2+ and Cu 2+. A ceiling or floor is composed of n edge-shared [Mn 4+O 2− 6] octahedral strings along the tunnel. A tunnel is filled mainly by n−2 edge-shared [Me 1+,2+)(OH −, H 2O) 6] octahedral strings, where Me (1+,2+) stands for alkali and alkaline earth cations such as Na +, Ca 2+ and Ba 2+. The n numbers are invariant along the direction normal to the ceilings except where lattice defects occur, but vary randomly along the direction normal to the walls. The interlayer strength of the phases increases with the substitution of Me (2+,3+) for Mn 2+ ions, the oxidation of Mn 2+ to Mn 4+ ions and the concomitant change of their OH − to O 2− ligands in the walls. The ideal lattice of these phases appears to be orthorhombic, but some crystals may be monoclinic mainly because of inhomogeneous cation distributions in the walls and wall distortion. The crystallochemical formulae for the phases can be generalized as Me <(n̄ −2) (1+,2+)(Mn 4+, Me (2+,3+), Mn 2+) 3Mn ñ 4+O 2̃n 2− < (O 2−, OH −) 6 (OH −) 2( n − 3) · 4H 2O where n ̄ denotes the mean of n numbers and is equal to or larger than 3. The upper limit in Me (2+,3+) Mn molar ratios is 3 n ̄ . The presence of Mn 2+ ions or an easy collapse of interlayers upon drying indicates unsaturation with trace cations.

Factors affecting the sorption and fixation of caesium in acid organic soil

SummaryRadioactive caesium deposited on upland Britain following the Chernobyl accident in 1986 remains available for uptake by plants, despite the potential of the contaminated soils to fix Cs. The minimum concentration of Cs+ required to cause Cs+ fixation is 0.60 to 0.75 mm, and this is unlikely to be reached in any contaminated upland soil. It is suggested that the fixation is caused by interlayer collapse of the illitic clay. The observed Cs+ fixation in lowland mineral soils and its absence from acidic upland soils is explained by the action of K+ ions, which can also induce interlayer collapse.Although Cs+ ions are unlikely to be fixed in acid organic soils, they can be strongly sorbed on any unoccupied Cs‐specific sorption sites in the narrow parts of illitic wedge zones. A method for determining the number of such sites is described. For two of the soils studied the number of sites ranged between 8 × 10−8 and 1 × 10−5 mmol kg−1; for two others there appeared to be no unoccupied Cs‐specific sites. Although Cs+ ions sorbed on such sites do not exchange with other ions, they can be desorbed if the concentration of Cs+ in solution is decreased. Thus, radioactive Cs in such soils will remain available for plant uptake, unless interlayer collapse can be induced.

The Interlayer Collapse During Dehydration of Synthetic Na0.7-Beidellite: A 23Na Solid-State Magic-Angle Spinning NMR Study

AbstractThe dehydration and migration of the interlayer cation of the synthetic beidellite Na0.7Al4.7Si7.3O20-(OH)4·nH2O, were studied with solid-state 23Na and 27Al MAS-NMR, heating stage XRD, and thermogravimetric analyses (TGA, DTA). The 23Na MAS-NMR of Na-beidellite at 25°C displays a chemical shift of 0.2 ppm, which indicates a configuration comparable with that of Na+ in solution. Total dehydration proceeds reversibly in two temperature ranges. Four water molecules per Na+ are gradually removed from 25° to 85°C. As a result, the basal spacing decreases from 12.54 Å to 9.98 Å and the Na+ surrounded by the two remaining water molecules is relocated in the hexagonal cavities of the tetrahedral sheet. The chemical shift of 1.5 ppm exhibited after the first dehydration stage illustrates the increased influence of the tetrahedral sheet. The high local symmetry is maintained throughout the entire first dehydration stage. During the second dehydration, which proceeds in a narrow temperature range around 400°C, the remaining two water molecules are removed reversibly without any change of the basal spacing.

Elemental and structural changes in illite/smectite mixed-layer clay minerals during diagenesis in Kimmeridgian- Volgian (- R yazanian) clays in the Central Trough, North Sea and the Norwegian ­Danish Basin

Elemental and structural changes in illite/smectite mixed-layer clay minerals during diagenesis in Kimmeridgian- Volgian (- R yazanian) clays in the Central Trough, North Sea and the Norwegian ­Danish Basin

Luminescence and ESR studies of relationships between O(-)-centres and structural iron in natural and synthetically hydrated kaolinites.

Luminescence, induced by dehydration and by wetting with hydrazine and unsymmetrically substituted hydrazine, and related ESR spectra have been observed from several kaolinites, synthetically hydrated kaolinites, and metahalloysites. The amine-wetting luminescence results suggest that intercalation, not a chemiluminescence reaction, is the luminescence trigger. Correlation between hydration-induced luminescence and g = 2 ESR signals associated with O(-)-centres in several natural halloysites, and concurrent diminution of the intensity of both these signal types as a function of aging in two 8.4 angstroms synthetically hydrated, kaolinites, confirm a previously-reported relationship between the luminescence induced by dehydration and in the presence of O(-)-centres (holes, i.e., electron vacancies) in the tetrahedral sheet. Furthermore, the ESR spectra of the 8.4 angstroms hydrate showed a concurrent change in the line shape of the g = 4 signal from a shape usually associated with structural Fe in an ordered kaolinite, to a simpler one typically observed in more disordered kaolinite, halloysite, and montmorillonite. Either structural Fe centres and the O(-)-centres interact, or both are subject to factors previously associated with degree of order. The results question the long-term stability of the 8.4 angstroms hydrate, although XRD does not indicate interlayer collapse over this period. Complex inter-relationships are shown between intercalation, stored energy, structural Fe, and the degree of hydration which may be reflected in catalytic as well as spectroscopic properties of the clays.

“Chloritized” Vermiculite in a Korean Ultisol Studied by Ultramicrotomy and Transmission Electron Microscopy

Abstract“Chloritized” vermiculite coexisting with kaolin-group minerals, vermiculite, mica, and gibbsite in the 0.2–0.5-µM fraction separated from a Korean Ultisol was studied by ultramicrotomy and high-resolution electron microscopy. The (001) lattice images observed from thin sections showed that the “chloritized” vermiculite was composed of particles which differed in their shape and the stacking of silicate layers. On saturation with K+, the silicate layers had spacings of 14–10 Å, with 14–12-Å layers being dominant. The 8–7-Å layers of a few particles appeared to be segregated close to the basal plane surfaces, but not necessarily close to the edge surfaces. The silicate layers were more or less curved and wavy and were commonly discontinuous. They formed packets (100–500 Å thick) by stacking, which were associated “face-to-face” and/or “edge-to-edge” or stacked parallel or subparallel to form particles of different shapes. The extent of interlayer collapse of the 14-Å layers on heating differed from one particle to the other, but was fairly uniform within a particle. Treatment with hot 1/3 M sodium citrate dissolved the interlayer material and possibly the material present between the packets from the “chloritized” vermiculite and from a few fine plates of kaolin-group minerals. The interlayer material and its chemical composition, therefore, could not be determined.