Showing papers in "Clays and Clay Minerals in 2015"

Modified mineral phases during clay ceramic firing

Abstract: Ceramic clays are among the most complicated of ceramic systems because of the very intricate relationship between the behavior of minerals during ceramic processing and their modifications during heating. A major challenge is to predict the phase changes in clay ceramics. The aims of this study were to establish reference data of ceramic products that can be formed based on the mineralogical compositions of the local raw materials. These data, in turn, can be compared with archeological ceramics in order to study their origins. The mineralogical compositions and modifications during firing (550–1100°C under oxidizing conditions) of seven clayey materials sampled from the main clay deposits of northern Morocco were evaluated by X-ray powder diffraction. Two groups of clays were distinguished according to the type of neoformed high-temperature minerals: non-calcareous clays and calcareous clays. For the non-calcareous raw materials, spinel was produced at 950°C. Cristobalite and mullite were formed at temperatures in excess of 1000°C from clays that contain illite, kaolinite, and chlorite. In clays containing vermiculite and large amounts of chlorite, hematite was formed at temperatures in excess of 950°C. Firing of calcareous clays at temperatures >950°C yielded Ca-silicates (diopside, gehlenite and wollastonite), spinel, cristobalite, hematite, and feldspars. Mullite may also form in the calcareous clay products when the carbonate content exceeds 10%.

Revisiting the Infrared Spectrum of the Water-Smectite Interface

Abstract: An overlap of bands produced by the O−H stretching vibrations of H2O (O–Hw) and structural OH (O−Hs) in smectite hampers the study by infrared spectroscopy (IR) of both their layer and interlayer structure. The present study re-evaluated the D2O saturation of smectite as a tool to enable separation of the overlapping bands at ambient conditions. Real-time monitoring by Attenuated Total Reflectance infrared spectroscopy (ATR-IR) was employed during in situ sample drying and H2O or D2O saturation at ambient temperature. Six dioctahedral and one trioctahedral pure smectites in Ca2+-, Na+-, and Cs+-cationic forms were studied to explore variability in total layer charge, charge location, and interlayer cation. The IR data showed the interlayer O−Dw signature at 2700–2200 cm−1 as a proxy for the O−Hw signature in the 3700–3000 cm−1 region. In addition to the expected liquid-like bands of D2O in the interlayer, these O−Dw spectra exhibited an additional sharp stretching feature in the 2695–2680 cm−1 range. No significant cation dependence of the sharp band position was observed between pairs of Ca- and Na-smectites for relative humidity (RH) between 60 and 80%, despite the large difference in the ionic potential between these interlayer cations. The intensity of the sharp band was found to be almost insensitive to changes in water content within the range 60–80% RH. The sharp band frequency decreased linearly with increasing total charge of the 2:1 layer (and can be used as a proxy for it), but no effect of charge location could be discerned. In agreement with early studies, this band was attributed to D2O located on the surface of the interlayer, pointing one O−D group toward the siloxane surface. Based on its high frequency, this band was indicative of free O−D oscillators, with very little or no involvement in hydrogen bonding (“dangling OD”). By analogy to the spectra of D2O-smectites, the spectrum of H2O-smectites also involves a sharp O−Hw analog at ~3630 cm−1 overlapping with typical OHs bands (e.g. Al2OH). As a result of this overlap, the sharp 3630 cm−1 O−Hw contribution was often missed or attributed solely to O−Hs.

Methylene blue adsorption on the basal surfaces of kaolinite: structure and thermodynamics from quantum and classical molecular simulation

Abstract: Organic dyes such as methylene blue (MB) are often used in the characterization of clays and related minerals, but details of the adsorption mechanisms of such dyes are only partially understood from spectroscopic data, which indicate the presence of monomers, dimers, and higher aggregates for varying mineral surfaces. A combination of quantum (density functional theory) and classical molecular simulation methods was used to provide molecular detail of such adsorption processes, specifically the adsorption of MB onto kaolinite basal surfaces. Slab models with vacuum-terminated surfaces were used to obtain detailed structural properties and binding energies at both levels of theory, while classical molecular dynamics simulations of aqueous pores were used to characterize MB adsorption at infinite dilution and at higher concentration in which MB dimers and one-dimensional chains formed. Results for the neutral MB molecules are compared with those for the corresponding cation. Simulations of the aqueous pore indicate preferred adsorption on the hydrophobic siloxane surface, while charge-balancing chloride ions adsorb at the aluminol surface. At infinite dilution and in the gas-phase models, MB adsorbs with its primary molecular plane parallel to the siloxane surface to enhance hydrophobic interactions. Sandwiched dimers and chains are oriented perpendicular to the surface to facilitate the strong hydrophobic intermolecular interactions. Compared with quantum results, the hybrid force field predicts a weaker MB adsorption energy but a stronger dimerization energy. The structure and energetics of adsorbed MB at infinite dilution are consistent with the gas-phase binding results, which indicate that monomer adsorption is driven by strong interfacial forces rather than by the hydration properties of the dye. These results inform spectroscopic studies of MB adsorption on mineral surfaces while also revealing critical areas for development of improved hybrid force fields.

Molecular Dynamics Simulations of Pyrophyllite Edge Surfaces: Structure, Surface Energies, and Solvent Accessibility

Abstract: Atomistic simulations of 2:1 clay minerals based on parameterized forcefields have been applied successfully to provide a detailed description of the interfacial structure and dynamics of basal planes and interlayers, but have made limited progress in exploring the edge surfaces of these ubiquitous layer-type aluminosilicates. In the present study, molecular dynamics simulations and energy-minimization calculations of the edge surfaces using the fully flexible CLAYFF forcefield are reported. Pyrophyllite provides an ideal prototype for the 2:1 clay-mineral edge surface because it possesses no structural charge, thus rendering the basal planes inert, while crystal-growth theory can be applied to identify two major candidates for the structure of the edge surfaces. Models based on these candidate structures reproduced bulk crystal bond distances accurately when compared to X-ray data and ab initio molecular simulations, and the predicted edge surface bond distances were in agreement with those determined via ab initio simulation. The calculated surface free energy and surface stress led to an accurate prediction of pyrophyllite nanoparticle morphology, while surface excess energies calculated for the edge surfaces were always negative. These results are consistent with the observed pyrophyllite nanoparticle morphology, with the concept of negative interfacial energies, and conditions that may give rise to them including a role in the stabilization of layer-type nanoparticulate minerals. Molecular dynamics simulations of hydrated nanoparticle edge surfaces indicated five reactive surface oxygen sites on the dominant candidate edge, in agreement with a recent model of proton titration data for 2:1 clay minerals. These promising results illustrate the potential for classical mechanical atomistic simulations that explore edge surface phenomena at much greater length- and times-scales than are currently possible with computationally expensive ab initio methods.

Organo-clays as sorbents of hydrophobic organic contaminants: sorptive characteristics and approaches to enhancing sorption capacity

Abstract: When clay minerals, notably smectites, intercalate organic cations, their interlayer surfaces change from hydrophilic to hydrophobic. The resultant intercalates, known as organo-clays (OCs), have a large affinity for hydrophobic organic contaminants (HOCs). Organo-clays are used as sorbents of HOCs in wastewater treatment and as sorptive barriers in landfill liners. The structural and sorptive characteristics of OCs with respect to HOCs have been studied extensively, and a large volume of literature has accumulated over the past few decades. The interactions of OCs with HOCs and the various approaches to improving the sorption capacity of OCs are reviewed here, with particular reference to the application of novel analytical techniques, such as molecular modeling, to characterizing the OC–HOC interaction.

Ceramic Membranes Prepared from a Silicate and Clay-mineral Mixture for Treatment of Oily Wastewater

Abstract: The application of ceramic membranes is limited by the high cost of raw materials and the sintering process at high temperatures. To overcome these drawbacks, the present study investigated both the preparation of ceramic membranes using cost-effective raw materials and the possibility of recycling the membranes for the treatment of oily wastewater. Ceramic membranes with a pore size of 0.29–0.67 μm were prepared successfully at temperatures as low as 1000–1100°C by a simple pressing route using lowcost base materials including diatomite, kaolin, bentonite, talc, sodium borate, and barium carbonate. The typical steady-state flux, fouling resistance, and oil-rejection rate of the low-cost virgin membranes sintered at 1000°C were 2.5 × 10−5 m3m−2s−1 at 303 kPa, 63.5%, and 84.1%, respectively, with a feed oil concentration of 600 mg/L. A simple burn-out process of the used membranes at 600°C in air resulted in >95% recovery of the specific surface area (SSA) of the virgin membranes, a significantly increased steady-state flux, decreased fouling resistance, and increased oil-rejection rate. The typical steady-state flux, fouling resistance, and oil-rejection rate of the low-cost ceramic membrane sintered at 1000°C and subsequently heat treated at 600°C for 1 h in air after the first filtration were 5.4 × 10−5 m3m−2s−1 at 303 kPa, 27.1%, and 92.9%, respectively, with a feed oil concentration of 600 mg/L. The present results suggest that the low-cost ceramic membranes used for oily wastewater filtration can be recycled by simple heat-treatment at 600°C in air. As the fouling resistance of the low-cost ceramic membranes decreased with a decrease in pore size, the preferred pore size of the membranes for oily wastewater filtration is <0.4 μm.

Formation and restacking of disordered smectite osmotic hydrates

Abstract: Author(s): Gilbert, B; Comolli, LR; Tinnacher, RM; Kunz, M; Banfield, JF | Abstract: Clay swelling, an important phenomenon in natural systems, can dramatically affect the properties of soils and sediments. Of particular interest in low-salinity, saturated systems are osmotic hydrates, forms of smectite in which the layer separation greatly exceeds the thickness of a single smectite layer due to the intercalation of water. In situ X-ray diffraction (XRD) studies have shown a strong link between ionic strength and average interlayer spacing in osmotic hydrates but also indicate the presence of structural disorder that has not been fully described. In the present study the structural state of expanded smectite in sodium chloride solutions was investigated by combining very low electron dose, highresolution cryogenic-transmission electron microscopy observations with XRD experiments. Wyoming smectite (SWy-2) was embedded in vitreous ice to evaluate clay structure in aqua. Lattice-fringe images showed that smectite equilibrated in aqueous, low-ionic-strength solutions, exists as individual smectite layers, osmotic hydrates composed of parallel layers, as well as disordered layer conformations. No evidence was found here for edge-to-sheet attractions, but significant variability in interlayer spacing was observed. Whether this variation could be explained by a dependence of the magnitude of long-range cohesive (van der Waals) forces on the number of layers in a smectite particle was investigated here. Calculations of the Hamaker constant for layer-layer interactions showed that van der Waals forces may span at least five layers plus the intervening water and confirmed that forces vary with layer number. Drying of the disordered osmotic hydrates induced re-aggregation of the smectite to form particles that exhibited coherent scattering domains. Clay disaggregation and restacking may be considered as an example of oriented attachment, with the unusual distinction that it may be cycled repeatedly by changing solution conditions.

Salt diffusion through a bentonite-polymer composite

Abstract: Bentonites are commonly used as chemical containment barriers to minimize liquid flow and contaminant transport. However, chemicals can adversely affect bentonite performance to the extent that modified bentonites have been developed to improve chemical resistance relative to traditional (unmodified) bentonites. The present study focused on the diffusion of potassium chloride (KCl) through a bentonite-polymer composite, or BPC, that was known to behave as a semipermeable membrane. Specifically, the effective diffusion coefficients, D *, for chloride (Cl−) and potassium (K+) were measured and correlated with previously measured membrane efficiency coefficients, ω, for the BPC. The values of D * at steady-state for chloride ![Formula][1] and potassium ![Formula][2] decreased as the ω values increased. The decrease in ![Formula][3] and ![Formula][4] was approximately a linear function of (1 − ω), which is consistent with previous research performed on unmodified Na-bentonite contained within a geosynthetic clay liner (GCL). In contrast to the previous GCL tests, however, ![Formula][5] values for the BPC generally were greater than the ![Formula][6] values, and the differences between ![Formula][7] and ![Formula][8] decreased as KCl concentration increased. The apparent discrepancy between ![Formula][9] and ![Formula][10] is consistent with excess sodium (Na+) in the BPC prior to testing and the requirement for electroneutrality during testing. Also, despite an apparent linear trend in diffusive mass flux for K+, lack of agreement between the ratio of the diffusive mass flux of K+ relative to that for Cl− as required on the basis of electroneutrality at steady state suggested that steady-state diffusive mass flux for K+ had probably not been achieved due to continual K+-for-Na+ cation exchange. Nonetheless, the excess Na+ and bentonite modification did not affect the fundamental correlation between D * and ω, which requires that D * approaches zero as ω approaches unity ( D * → 0 as ω → 1). [1]: /embed/mml-math-1.gif [2]: /embed/mml-math-2.gif [3]: /embed/mml-math-3.gif [4]: /embed/mml-math-4.gif [5]: /embed/mml-math-5.gif [6]: /embed/mml-math-6.gif [7]: /embed/mml-math-7.gif [8]: /embed/mml-math-8.gif [9]: /embed/mml-math-9.gif [10]: /embed/mml-math-10.gif

Prediction of compressibility data for highly plastic clays using diffuse double-layer theory

Abstract: Montmorillonite-rich clays are important in many engineering applications. The compressibility of such plastic clays at high consolidation pressures is important for predicting routine settlement and for applications in nuclear-waste repositories. Laboratory measurement of compressibility data at high consolidation pressures is not only time consuming but very expensive also. Theoretical predictions can help to determine the compressibility of plastic clays at high consolidation pressures. A linear relationship between e / e N vs . 1/√ P ( eN is the normalization void ratio at normalization pressure N and P is the consolidation pressure) was derived using diffuse double-layer theory. The compressibility data of several plastic clays in published studies were found to support the derived relationship. A generalized theoretical equation was proposed to predict the compressibility data over a wide range of consolidation pressures using an experimentally measured void ratio at low consolidation pressure. The compressibility data for different plastic clays were predicted accurately up to maximum consolidation pressures that ranged from 0.7 to 30 MPa using an experimentally measured void ratio near the pre-consolidation pressure. The pre-consolidation pressures for different clays considered here ranged from 25 to 133 kPa. The proposed predictive model is supported by experimental data, is simple, and does not require knowledge of clay-surface and pore-fluid parameters.

Influence of grinding and sonication on the crystal structure of talc

Abstract: Talc is an important industrial mineral with a broad range of applications. Particle size and crystal structure have a significant influence on the potential uses. The present study examined the influence of grinding and ultrasound treatment on talc from a new deposit, Gemerska Poloma, in Slovakia. The general knowledge that grinding produces progressive structural disorder leading to amorphization, whereas sonication has a negligible effect on the talc crystal structure, was confirmed by X-ray diffraction (XRD), infrared (IR) spectroscopy, and transmission electron microscopy (TEM). Partial reduction of particle size along with delamination was observed by XRD after sonication, low-angle laser light scattering (LALLS), scanning electron microscopy (SEM), and TEM. The specific surface area (SSA) increased slightly after prolonged sonication, but grinding initially caused a rapid increase in SSA followed by a drastic decrease after prolonged grinding time of up to 120 min which was attributed to the aggregation of amorphized talc. Sonication and grinding had different influences on the thermal behavior of the talc studied. Sonication decreased slightly the dehydroxylation temperature, whereas grinding added a significant mass loss at low temperature, arising from the dehydration of hydrated Mg cations released from the talc structure during amorphization. The initial high whiteness value of talc decreased slightly after grinding or sonication. Thermogravimetry was suggested as a useful tool to track and predict changes in the talc structure upon sonication and grinding.

Effect of surface charge and elemental composition on the swelling and delamination of montmorillonite nanoclays using sedimentation Field-Flow fractionation and mass spectroscopy

Abstract: The swelling properties of smectite-type clay particles (including montmorillonite) are of interest in various industries. A fundamental understanding of the surface properties of smectite particles at the sub-micron level would facilitate investigation of the effect of distributed properties such as charge and elemental composition. Swelling and delamination of SWy-2 Na-montmorillonite (Na-Mnt) nano-clay particles were studied here using size distributions obtained by sedimentation field-flow fractionation (SdFFF). Fractions were examined by electron microscopy and inductively-coupled optical emission spectroscopy (ICP-OES). Two distinct populations were observed in the size distribution of SWy-2 Na-Mnt particles (bimodal size distribution), with mean equivalent spherical diameters of ~60 nm and 250 nm, respectively. In contrast, the size distribution of STx-1 Ca-montmorillonite (Ca-Mnt) particles showed only one peak with a mean equivalent spherical diameter of ~410 nm, which changed to 440 nm after 4 days of hydration. Analyses of the fractions by ICP-OES obtained along the size distribution of Na-Mnt showed an abundance of Ca and Mg in the fractions below 250 nm, and confirmed the presence of Fe and Mg as isomorphous substituents. Electron micrographs of the fractions obtained from Na-Mnt size distributions were used to calculate the thickness of the clay particles. Bridging forces between pure orMgsubstituted montmorillonite and either Ca2+ or Na+ were calculated using semi-empirical methods. The results demonstrated that swelling and delamination of Na-Mnt clay particles are dictated by properties such as elemental composition and surface charge which are distributed along the size distribution.

Measuring the layer charge of dioctahedral smectite by o–d vibrational spectroscopy

Abstract: Layer charge (LC) is a fundamental property of smectite but its measurement remains challenging and tedious to apply on a high-throughput basis. The present study demonstrates that the position of a sharp, high-energy O—D stretching band of adsorbed D2O (νO—D, at ~2686–2700 cm−1), determined by infrared spectroscopy, correlates with LC and provides a simple method for its measurement. Twenty nine natural dioctahedral smectites and 14 reduced-charge montmorillonites with LC determined previously by different methodologies were saturated with D2O and examined by attenuated total reflectance infrared spectroscopy (ATR-IR). The samples included smectites in Mg, Ca, Na, Li, K, and Cs forms and covered the full range of the smectite LC (0.2 to 0.6 e per formula unit). Statistically significant correlations were found between νO—D and LC values determined with each of the two main methods of LC determination: the structural formula method (R2 = 0.96, σ = 0.02, ~0.2 < LC < 0.6) and the alkylammonium method (R2 = 0.92, σ = 0.01, 0.27 < LC < 0.37). These correlations were based on Li- and Na-saturated smectites, respectively, but other cationic forms can be employed provided that the exchangeable cations are of sufficiently high hydration enthalpy (e.g. Mg2+ or Ca2+, but not K+ or Cs+). The new method is fast, low-cost, implemented easily in laboratories equipped with ATR-FTIR, and applicable to samples as small as ~5 mg.

Sorption of neptunium on clays and clay minerals – a review

Abstract: During recent decades, the search for possible repositories for high-level nuclear waste has yielded large amounts of sorption data for actinides on different minerals. Clays and clay minerals are of special interest as potential host-rock formations and backfill materials, by virtue of their good retardation properties. Neptunium (Np) is one of the actinides which is considered in long-term scenarios due to its long-lived nuclide 237Np (t1/2 = 2.1 × 106 y). Because neptunium sorption is heavily dependent on the experimental conditions, comparison of sorption data from different experiments is challenging. Normalizing reported data with respect to the surface area of the sorbent enables conversion of conventional distribution coefficients (Kd) to normalized (Ka) values, which improves comparability among the results of different experiments. The present review gives a detailed summary of sorption data of Np on clays and clay minerals and examines critically the applicability of the Ka approach.

Diagenetic and Paleoenvironmental Controls on Late Cretaceous Clay Minerals in the Songliao Basin, Northeast China

Abstract: Sedimentary and diagenetic processes control the distribution of clay minerals in sedimentary basins, although these processes have seldom been studied continuously in continental sedimentary basins. The Songliao Basin, northeast China, is a large continental, petroleum-bearing basin, and provides a unique study site to understand the sedimentary and diagenetic processes that influence clay assemblages. In this paper, the clay mineralogy of a 2500 m-thick Late Cretaceous (late Turonian to Maastrichtian) terrestrial sedimentary succession (SK-1s and SK-1n cores), retrieved by the International Continental Scientific Drilling Program in the Songliao Basin, was examined. The objective was to determine the diagenetic and paleoenvironmental variations that controlled the formation of clay mineral assemblages, and to determine the thermal and paleoenvironmental evolution of the basin. The results from both cores show that illite is ubiquitous through the succession, smectite is frequently encountered in the upper strata, and ordered mixed-layer illite-smectite (I-S), chlorite, and kaolinite are abundant in the lower strata. Burial diagenesis is the primary control on the observed decrease of smectite and increasing illite, I-S, and chlorite with depth. Observations of clay-mineral diagenesis are used to reconstruct the paleotemperatures and maximum burial depths to which the sediments were subjected. The lowermost sediments could have reached a maximum burial of ~1000 m deeper than today and temperatures ~50°C higher than today in the latest Cretaceous. The transition of smectite to I-S in the SK-1 cores and the inferred paleotemperatures provide new constraints for basin modeling of oil maturation at elevated temperatures in the Songliao Basin. Authigenic kaolinite and smectite are enriched in sandstones with respect to the coeval mudstones from the SK-1n core, as a result of early diagenesis with the participation of primary aluminosilicates and pore fluids. In the upper part of both SK-1 cores, variations in smectite and illite were controlled primarily by paleoenvironmental changes. Increases in smectite and decreases in illite from the late Campanian to Maastrichtian are interpreted as resulting from increasing humidity, a conclusion consistent with previous paleoenvironmental interpretations.

Interaction of corroding iron with bentonite in the ABM1 experiment at Äspö, Sweden: A microscopic approach

Abstract: Bentonite and iron metals are common materials proposed for use in deep-seated geological repositories for radioactive waste. The inevitable corrosion of iron leads to interaction processes with the clay which may affect the sealing properties of the bentonite backfill. The objective of the present study was to improve our understanding of this process by studying the interface between iron and compacted bentonite in a geological repository-type setting. Samples of MX-80 bentonite samples which had been exposed to an iron source and elevated temperatures (up to 115oC) for 2.5 y in an in situ experiment (termed ABM1) at the Aspo Hard Rock Laboratory, Sweden, were investigated by microscopic means, including scanning electron microscopy, μ-Raman spectroscopy, spatially resolved X-ray diffraction, and X-ray fluorescence. The corrosion process led to the formation of a ~100 mm thick corrosion layer containing siderite, magnetite, some goethite, and lepidocrocite mixed with the montmorillonitic clay. Most of the corroded Fe occurred within a 10 mm-thick clay layer adjacent to the corrosion layer. An average corrosion depth of the steel of 22–35 μm and an average Fe2+ diffusivity of 1–26×10–13 m2/s were estimated based on the properties of the Fe-enriched clay layer. In that layer, the corrosion-derived Fe occurred predominantly in the clay matrix. The nature of this Fe could not be identified. No indications of clay transformation or newly formed clay phases were found. A slight enrichment of Mg close to the Fe–clay contact was observed. The formation of anhydrite and gypsum, and the dissolution of some SiO 2 resulting from the temperature gradient in the in situ test, were also identified. © 2014, Clay Minerals Society. All right reserved.

Geology and conditions of formation of the zeolite-bearing deposits southeast of ankara (central turkey)

Abstract: The pyroclastic sediments studied here contained varied amounts of zeolite and were formed in the saline alkaline Tuzgolu Basin following the alteration of dacitic volcanic materials during the Early to Late Miocene. The present study focused on the geological-geochemical properties of the zeolites and describes their formation. Mineralogical and chemical compositions were determined by X-ray diffraction, scanning electron microscopy, optical microscopy, and inductively coupled plasma mass spectrometry. Results indicated that the zeolitic tuffs consisted mainly of heulandite/clinoptilolite (Hul/Cpt), chabazite, erionite, and analcime associated with smectite. Smectite, calcite, and dolomite are abundant in the clay and carbonate layers which alternate with the zeolitic tuffs. K-feldspar, gypsum, and hexahydrite (MgSO4·6H2O) were also found in some altered tuffs and clay-marl layers as accessory minerals. The zeolite and other authigenic minerals showed weak stratigraphic zonation. Some vitric tuff layers contained no zeolite minerals and others were found to consist of almost pure Hul/Cpt and chabazite layers with economic potential. The rare earth elements (REE), large ion lithophile elements (LILE), and high-field strength elements (HFSE) in the Hul/Cpt-rich tuffs and vitric tuffs were enriched or depleted relative to the precursor rock, while many major elements were slightly or significantly depleted in all zeolitic tuffs. The amounts of REE in the chabazite- and erionite-rich tuffs were generally smaller than those in the precursor rock. The middle and heavy REE (MREE and HREE, respectively) were abundant in the Hul/Cpt-rich tuffs, tuffs, and smectitic bentonites. Chondrite-normalized REE values of the sample groups are characterized by sub-parallel patterns with enrichment in LREE relative to HREE. The mineral assemblages and geological setting indicated that zeolite diagenesis occurred in a saline-alkaline basin. The δ18O and δD compositions of the Hul/Cpt, chabazite, and smectite indicated that the minerals formed at low to moderate temperatures and that some of the zeolitization occurred due to diagenetic alteration under closed-system conditions that varied according to the nature of the basin and with the composition and physical properties of the volcanic materials.

Modification of montmorillonite with alkyl silanes and fluorosurfactant for clay/fluoroelastomer (fkm) nanocomposites

Abstract: The main objective of the present work was to functionalize nanoclays with organosilanes and surfactant in order to facilitate the dispersion of the nanofillers in the host fluoroelastomer (FKM) polymer matrix. Better dispersion was achieved by improving interaction between the clay polymer nanocomposite (CPN) constituents. The first part of this study investigated modification of montmorillonite (Mnt) using different saturated and unsaturated alkyl silanes and an alkyl hydrocarbon ammonium quaternary surfactant. Silicon magic angle spinning nuclear magnetic resonance spectroscopy, thermal gravimetric analysis (TGA), elemental analysis, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy were used to characterize the silane-grafted clays. Results indicated that the amount of silane grafted depended on the specific structure of the silane. Silane-grafted Mnt was also modified with ionic surfactants intercalated between the clay layers. A 169% increase in the clay basal spacing (from initial spacing of 10.0 A to 26.9 A) was achieved. The second part of the study successfully synthesized FKM nanocomposites containing custom-functionalized Mnt, with the aim of producing reinforced high-performance materials. The effects of clay modification on the morphology and thermal properties of the CPN were studied using XRD, TGA, scanning electron microscopy, and transmission electron microscopy. The CPN made with the modified clay exhibited greater thermal stability than the CPN of the commercially available modified Mnt, with a degradation onset point ~ 40°C higher.

The illite–aluminoceladonite series: distinguishing features and identification criteria from x-ray diffraction and infrared spectroscopy data

Abstract: Al-rich K-dioctahedral 1M and 1Md micas are abundant in sedimentary rocks and form a continuous compositional series from (Mg,Fe)-poor illite to aluminoceladonite through Mg-rich illite. The complexity and heterogeneity of chemical composition and structural features, as well as the lack of reliable diagnostic criteria, complicate the identification of these mica varieties. The objectives of the present study were to reveal the structural and crystal-chemical variability in the illite—aluminoceladonite series, and to define the composition ranges and identification criteria for the mica varieties in the series. A collection of illite and aluminoceladonite samples of various compositions was studied by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. Analysis of the relationships between unit-cell parameters and cation composition showed that the series includes three groups, (Mg,Fe)-poor illites, Mg-rich illites, and aluminoceladonites, each characterized by a unique combination of unit-cell parameter variation ranges. The distinctive features of aluminoceladonite are reduced values of csinβ and |ccosβ/a| in combination with b parameters that are smaller than those for Mg-rich illites, and slightly greater than those of (Mg,Fe)-poor illites. The compositional boundary between illite and aluminoceladonite occurs at Si = ~3.7 and Mg + Fe2+ = ~ 0.6 atoms per O10(OH)2. A new approach to the interpretation of the FTIR spectroscopy data involving new relationships between band positons and cation composition of (Mg,Fe)-poor illites, Mg-rich illites, and aluminoceladonites provides additional diagnostic features that include the band positions and profile in the regions of Si—O bending, Si—O stretching, and OH-stretching vibrations. A sharp maximum from the AlOHMg stretching vibration at ~3600 cm−1, the presence of a MgOHMg stretching vibration at 3583–3585 cm−1, as well as characteristic band positions in the Si—O bending (435–, 468–472, and 509–520 cm−1) and stretching regions (985–1012 and 1090–1112 cm−1), are typical of aluminoceladonite.

Composition and genesis of the nickel-chrome-bearing nontronite and montmorillonite in lateritized ultramafic rocks in the muratdaği region (uşak, western anatolia), turkey

Abstract: Widespread lateritized ultramafic rocks in the southern part of the Muratdagi region of Turkey constitute a significant source of Ni-Cr-bearing ore with economic potential. However, no mineralogical or geochemical characterizations of these important materials have been performed previously. The aim of the present study was to describe the mineralogy, geochemistry, and genesis of Ni-Cr-bearing smectite in garnierite and ferruginous saprolite associated with the lateritized ophiolite-related ultramafic rocks. The lateritic zones are well developed over serpentinized harzburgitic mantle peridotites. The lateritized units and related bedrocks were examined using polarized-light microscopy, X-ray diffraction, scanning and transmission electron microscopies, and chemical and isotopic methods. The garnierite-containing saprolites are enriched in smectite, Fe-(oxyhydr)oxide phases, and opal-CT. Micromorphological images revealed that flaky smectite and, locally, Fe-rich particles, alunite, gypsum, gibbsite, and sulfur crystals developed along the fractures and dissolution voids. The development of saprolite demonstrates chemical weathering. The presence of silicified and Fe-(oxyhydr)oxide phases associated with gypsum, alunite, and local native sulfur in vertical and/or subvertical fractures and fault infillings are indicative of hydrothermal processes along the extensional, tectonically related fault systems. Chemical weathering and hydrothermal processes, which probably started during the Oligocene and Miocene, led to the formation of nontronite, Fe-bearing montmorillonite, and local Fe-rich kaolinite. Nickel and Cr are concentrated significantly in the saprolite zone and are positively correlated with Fe2O3 content, which is controlled by the formation of nontronite, montmorillonite, and Fe-(oxyhydr)oxide phases. Nickel-Cr-bearing nontronite and montmorillonite precipitated from alkaline water as a result of the increasing (Fe2O3+Al2O3+Cr2O5+Ni+Co)/(MgO+SiO2) ratio under the control of both chemical weathering and hydrothermal processes. The Fe and Mg (associated with Ni and Cr) required for the formation of smectite were supplied by solutions from both chemical weathering and hydrothermal alteration of Ni-Cr-bearing olivine and pyroxene in the harzburgitic bedrock; the Al was supplied by schists, granite, and volcanic units.

Transport and Exchange Behavior of Ions in Bentonite During Electro-Osmotic Consolidation

Abstract: Electro-osmotic consolidation is considered to be an efficient technique for dewatering and consolidation of soft soil. In the present study, four experiments were conducted on a Na-rich bentonite using two reactive electrodes (copper and iron) and two inert electrodes (graphite and stainless steel) to study the transport and exchange behavior of ions during electro-osmotic consolidation. The results showed that the changes in pH and ion contents were limited to the zone close to the electrode due to the buffering capacity of bentonite and the significant reduction in electric current density. The ion concentration profiles indicated that Na+ ions were largely responsible for carrying the pore water to the cathode. The reactive electrodes are better at transporting Na+ ions and therefore induce better drainage than inert electrodes. Ion-exchange reactions occurred between the Cu2+ and Fe2+/Fe3+ ions released and pre-existing Na+ ions in the electrical double layer, causing decreased water adsorption capacity and plasticity index. The swelling and shrinkage characteristics of the bentonite were thus reduced, and electroosmotic consolidation may therefore provide a new way to improve the stability of expansive soils and slopes.

Clay-mineral transformations and heavy-metal release in paddy soils formed on serpentinites in eastern taiwan

Abstract: Serpentinites, which contain high concentrations of Cr and Ni, weather easily into layer silicates and are therefore a possible source of metal contamination in soils. In the present study three soil profiles formed on serpentinites in a paddy field in eastern Taiwan were investigated to understand pedogenic clay-mineral transformations and to determine the relationship between the mineralogical characteristics and labile Cr and Ni in the soil. To this end, physicochemical analyses, micromorphology, X-ray diffraction, and Fourier transform infrared spectroscopy were employed. Serpentine and chlorite were the dominant minerals in the soil parent material, with smaller amounts of pyroxene, amphibole, and talc. Progressive weathering and the release of cations from the parent material resulted in the pedogenic formation of smectite, vermiculite, and interstratified chlorite-vermiculite, demonstrated by their presence in all Ap and AC horizons but their absence from the C horizons. Serpentine, pyroxene, amphibole, and talc are proposed to be transformed to low-charge smectite, while chlorite transformed to vermiculite through an interstratified chlorite-vermiculite phase. The surface soils were enriched in oxalate-extractable Fe relative to the subsoils, which was probably generated by the artificial flooding and draining of the paddy soils. The artificial flooding, which typically releases Fe, may also drive the observed partial hydroxyl interlayering of smectite and incomplete interlayer OH sheets of chlorite. Labile Cr and Ni (extracted with 0.1 N HCl) ranging from 4.7 to 26.8 mg kg−1 and from 56 to 365 mg kg−1, respectively, increased significantly toward the surface soil, consistent with weathering. The heavy metals released may pose a threat to the environment as well as to human health by entering the food chain.

Reactivity of Callovo-Oxfordian Claystone and its Clay Fraction With Metallic Iron: Role of Non-Clay Minerals in the Interaction Mechanism

Abstract: In order to better understand the possible interactions between steel canisters and a claystone host rock, in this case the Callovo-Oxfordian rock (COx), the present study investigated in detail, under conditions relevant to high-level radioactive waste repositories (anoxic conditions, temperature of 90°C), the reactions between metallic iron and: (1) COx; (2) the clay fraction extracted from COx (CF); and (3) mixtures of CF with quartz, calcite, or pyrite. Batch experiments were then carried out in the presence of NaCl-CaCl2 background electrolyte, for durations of 1, 3, and 9 months. Solid and liquid end-products were characterized by a combination of techniques including liquid analyses, transmission and scanning electron microscopies, X-ray diffraction, N2 adsorption at 77 K, and Mossbauer spectroscopy. The interaction between CF and metallic iron appeared to proceed by means of pathways similar to those illustrated in previous studies on interactions between metallic iron and purified clays. In spite of the many similarities with previous studies, significant differences were observed between the behavior of COx and CF, particularly in terms of pH and Eh evolution, iron consumption, chemical composition of the neoformed particles, and textural evolution. Such differences demonstrate the important role played by non-clay minerals in reaction pathways. The addition of carbonates or pyrite to CF did not lead to significant change in reactivity. In contrast, under the conditions used in the present study, i.e. for relatively low iron:clay ratios, the presence of quartz strongly influenced reaction pathways. In the presence of quartz, magnetite was observed only in trace abundances whereas the amounts of magnetite were significant in experiments without quartz. Furthermore, filamentous serpentine particles with a small Al:Si ratio appeared which could develop from an FeSiAl gel that only forms in the presence of quartz. Considering that most clay rocks currently being considered for radioactive waste disposal contain significant amounts of quartz, the results obtained in the present study may be of significant interest for predicting the long-term behavior of clay barriers in such sites.

Surface and Interface Properties of Lauroyl Sarcosinate-Adsorbed CP+-Montmorillonite

Abstract: Catanionic surfactant systems are used as drug-delivery vehicles and as nanocompartments in the formation of biomaterials and nanosized particles. Clay minerals are compatible with organic tissues and also have biomedical applications. The aim of the present study was to combine the properties of catanionic surfactants and clay minerals to obtain new materials with potential uses in medicine, waste-water treatment, and antibacterial applications. The surfactants chosen to make the catanionic surfactant were cetylpyridinium (CP) and lauroyl sarcosinate (SR), which interact strongly in aqueous media and cause specific aggregations such as ion-pair amphiphiles and needle- and leaf-like structures. Aside from the aqueous solution, new ternary systems are formed with different structures and properties through the addition of montmorillonite (Mnt). The surface and interlayer structures of the different Mnt-CP-SR samples prepared by using CP and SR in amounts equal to various ratios of cationic exchange capacity of the clay mineral were studied. They were also compared with the structured surfactant aggregates formed in aqueous media. The Mnt-CP-SR samples were subjected to X-ray diffraction (XRD), thermogravimetric analyses, and zeta-potential measurements to elucidate the interlayer- and external-surface structures. The XRD analyses showed the formation of a compact structure in the interlayer region resulting from the interaction between randomly oriented pyridinium and negatively charged SR head groups. The triple interactions among the Mnt surface, CP, and SR were more complex than the double interactions between the Mnt and cationic surfactant, and the CP played a dominant role in the formation of external and interlayer surface structures regardless of the amount and order of the addition of SR. The new findings support new applications for organoclays in the fields of biomedicine, remediation of polluted water, and nanocomposite materials.

Native morphology of hydrated spheroidal halloysite observed by environmental transmission electron microscopy

Abstract: Natural mineral materials such as tabular and spheroidal halloysites have recently been suggested as candidates for intercalating metal ions or organic molecules. Their potential use as nano-adsorbents is related to their porous structure and water content. Although the two morphologies can coexist in natural deposits, spheroidal halloysites remain poorly characterized whereas much literature exists on tubular halloysites. The present study investigates the native morphology, internal porous structure, and behavior upon dehydration of spheroidal halloysite from Opotiki (New Zealand). This mineral was characterized in its natural hydrated state using a transmission electron microscope equipped with an environmental cell (EC-TEM). The sample was placed in a sealed block in which water vapor-saturated air circulated at a pressure of 30 Torr. The observed particles consisted of almost complete spheroids displaying polyhedral external surfaces. 1:1 layers stack concentrically as a pore-free, onion-like structure. The dynamic processes of dehydration created by slow depressurization of the cell resulted in a decrease in the layer-to-layer distance ( d 001 ) from ~10 A to ~7 A due to the loss of interlayer water molecules. Irreversible formation of spurious ‘internal pores’ was recorded during this process. These pores were not indigenous to the hydrated 10 A halloysite and resulted from the collapse of the native layers. They cannot account for the physical chemical properties of spheroidal halloysite. Spheroidal halloysites would have a lower propensity for intercalating ions or molecules than tubular halloysites. Isolated facets were also observed in high-resolution-TEM and displayed a pseudo-hexagonal morphology. The three-dimensional microstructure of the spheroid appeared bent along the three pseudo equivalent y i directions of the kaolinite-like single layers. An analogy with polyhedral serpentine has allowed the proposal of a formation process of hydrated spheroidal halloysite triggered by enrichment in divalent ions in the growth system.

A Critical Appraisal of Debye Length in Clay-Electrolyte Systems

Abstract: The equivalent diffuse double layer (DDL) thickness in clay-electrolyte systems is a very useful parameter for analyzing the engineering behavior of clays under different environmental conditions. The equivalent DDL thickness is generally assumed to be equal to the characteristic (Debye) length. The present work examined critically the applicability of characteristic length to define equivalent DDL thickness under various clay-surface and pore-fluid conditions. A critical analysis is presented of the changes in the equivalent DDL thickness and characteristic length under the influence of different clay-surface and electrolyte properties. The equivalent DDL thickness was found to be smaller than the characteristic length for a wide range of surface and pore-fluid parameters normally encountered in engineering practice. An accurate and simple power relationship was developed to predict the equivalent DDL thickness from the characteristic length, which is applicable to a wide range of clay-electrolyte systems.

CEC AND 7Li MAS NMR STUDY OF INTERLAYER Li+ IN THE MONTMORILLONITE–BEIDELLITE SERIES AT ROOM TEMPERATURE AND AFTER HEATING

Abstract: The objective of the study was to contribute to the understanding of the influence of the structure and the 2:1 layer dimension of smectites on cation exchange capacity (CEC) reduction and the hydration behavior of Li-saturated smectites after heating. Five montmorillonites extracted from bentonites of different provenance were saturated with Li+ and heated to 300°C. Initial montmorillonites and montmorillonites with reduced layer charge (RCM) were characterized by comprehensive mineralogical analysis supplemented by CEC measurements, surface-area measurements by Ar adsorption, and 7Li, 27Al, and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The CEC of the initial montmorillonites varied between 89 and 130 cmol(+)/kg while the CEC of the RCM prepared at 300°C varied between 8 and 25 cmol(+)/kg. The lateral dimension of the 2:1 layers varied between 70 and 200 nm. The greatest decrease in CEC was observed for the montmorillonite with the largest diameter of the 2:1 layers and the smallest decrease was observed for the montmorillonite with the smallest diameter of the 2:1 layers. 7Li MAS NMR revealed an axially symmetric chemical environment of the hydrated interlayer Li+ with ηΔ = 0 for the chemical shift anisotropy tensor for unheated montmorillonites with >33% tetrahedral layer charge (ξ). The chemical environment is typical of innersphere hydration complexes of interlayer Li+. An axially non-symmetric chemical environment of the interlayer Li+ with ηCS of close to one was observed for all RCM. While the remaining CEC of RCM prepared at 300°C reflected the variable CEC at the edges, and thus the lateral size or aspect ratio of the 2:1 layers, the hydration complex of interlayer Li+ was strongly determined by the isomorphic substitutions in the dioctahedral 2:1 layers.

Mid-Infrared Features of Kaolinite-Dickite

Abstract: Transformation of kaolinite to dickite is a common diagenetic reaction. The present report is part of a wider study to investigate the pathways of this polytype change. Fourier-transform infrared spectroscopy (FTIR) was used to attempt quantification of the relative proportions of kaolinite and dickite, validated by X-ray diffraction (XRD) results, in order to link mineral and structural features during the mineralogical changes. A group of kaolinite and dickite samples was investigated: 13 samples from the Froy and Rind oil fields (North Sea), three kaolinite specimens with different crystal order and particle size (KGa-2, kaolinite API 17, Keokuk kaolinite), and two dickite-rich samples (Natural History Museum collection). Six FTIR spectral features were analyzed: (1) intensity ratio of the minima at 3675 and 3635 cm−1; (2) position of the band at ~1115 cm−1; (3) difference between the frequency of the bands at ~1030 and ~1000 cm−1; (4) intensity ratio of the bands generating shoulders at ~922 and ~900 cm−1; (5) position of the band at ~370 cm−1; and (6) intensity of the band at ~268 cm−1. Correlation of the features above with polytype relative proportions derived from XRD showed non-linear behavior, with maximum curvature at the dickite end, which precludes kaolinite-dickite quantification. Increasing kaolin particle size is known to cause decreased intensity of the FTIR spectra. A model was developed to test whether this effect is consistent with the non-linear progression of the IR features. The relative intensity of kaolinite and dickite IR features were calculated in a series of kaolinite-to-dickite transformations, where the size of particles increases with dickite proportion, and where dickite-dominated particles reach a larger size than kaolinite-dominated particles. The results indicated that the differential particle size increase is possibly the cause of the lack of linearity between IR- and XRD-measured dickite proportions.

Key Steps Influencing the Formation of Aluminosilicate Nanotubes by the Fluoride Route

Abstract: Imogolite is usually formed by means of a three-step process involving the use of large amounts of water with long crystallization times and low yields, preventing large-scale synthesis. These drawbacks can be overcome by synthesis in the presence of fluoride, an approach which has been demonstrated to be suitable for the synthesis of other phyllosilicates. In the present study, the nature of the Al and Si sources, the Al/Si molar ratio, the volume of H2O for the redispersion of the gel after desalination, the F/Si molar ratio, as well as the crystallization temperature and time have been varied to investigate their role in the crystallization of imogolite. The structural properties of the as-synthesized samples were characterized by X-ray diffraction, infrared spectroscopy, and 29Si, 27Al, and 19F magic angle spinning nuclear magnetic resonance spectroscopy. The results show that the imogolite nanotubes can be prepared with high yields (>55%) from AlCl3·6H2O and Na4SiO4 aqueous solutions with an Al/Si molar ratio of 2.5, addition of HF for a F/Si molar ratio of 0.1–0.2, and 4 days of crystallization at 98°C.

Sediment-Hosted Kaolin Deposit from Çakmaktepe (Uşak, Turkey): its Mineralogy, Geochemistry, and Genesis

Abstract: Because of their geochemical properties, the Cakmaktepe (Usak) kaolin deposits have been considered as primary. New sedimentological, mineralogical, and geochemical data suggest that the Cakmaktepe kaolins are secondary deposits of sedimentary processes after hydrothermal alteration of the source rocks. The kaolins in the Cakmaktepe deposit were formed from the hydrothermal alteration of calcalkaline Karaboldere volcanics (KBV). The kaolinized materials were then reworked and accumulated in a lacustrine basin. The argillic alteration zones were associated with faults, and lateral zonation of minerals was observed in the KBV. Smectite was the major phyllosilicate in the ‘outer zone’. The alteration mineralogy of the ‘inner zone’ was similar to that of the Cakmaktepe kaolins and consisted mainly of kaolinite with minor amounts of smectite and alunite. The trace-element abundances in the kaolinized volcanics and the Cakmaktepe kaolins indicated hypogene conditions. The δ18O values of the Cakmaktepe kaolins ranged from 0.2 to 5.92%, which indicated that the Cakmaktepe kaolinites were formed at temperatures between 92 and 156°C, and the δD values ranged from −91.68 to −109.45‰. The irregular edge-to-face morphology, the variation in grain-size, a few broken crystals of kaolinite, the deficiency of dissolution-replacement and crystallization mechanisms, and the the low sphericity, very angular, and poorly sorted quartz crystals in the kaolins all result from transport processes. The sedimentary structures, including trough cross-lamination, tool marks, and load casts, indicate transportation by turbulent waters and deposition of kaolin layers in a shallow lake.

Clay-Polymer Nanocomposite-Supported Brominating Agent

Abstract: The conventional methods of direct bromination of organic compounds with elemental bromine have several major drawbacks such as handling difficulty, corrosive effect, and toxicity, in addition to over-bromination and problems with isolation of products from the reaction mixture. Supported catalysts and reagents have become popular in the synthesis of organic chemicals over recent decades because they have overcome almost all of the drawbacks noted above. In the present study, a new clay polymer nanocomposite (CPN)-supported brominating agent was prepared from montmorillonite (Mnt) and styrene-co-vinyl pyridinium polymer. The reagent was obtained by the direct interaction of a two-fold excess of poly(styrene-co-N-methyl-4-vinylpyridinium) bromide with Na-montmorillonite (NaMnt) through ion exchange between Na+ of the NaMnt and pyridinium ions in the copolymer to provide CPN3 with free methylpyridinium bromide side chains. The structure of the CPN3 prepared was characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Treatment of the CPN3 with bromine using the bromide ions which remained led to the perbromide-supported reagent, CPN4. The activity of the resulting CPN4 brominating reagent was examined through direct bromination of some alkenes, arenes, and carbonyl compounds and compared with the effectiveness of a crosslinked polymeric perbromide reagent. The yields obtained from application of the reagent were moderate to excellent. The advantages of this reagent, such as stability at room temperature, ease of regeneration from the polymeric by-product, and the yields of the brominated products, confirm the viability of using a CPN-supported brominating agent as a reactive reagent in organic chemistry synthesis.