The geochemistry of minerals in intermediate to deep sedimentary rocks (2–10 km depth) is not known sufficiently well to predict accurately the effect of human activities, such as carbon dioxide sequestration or fracking. To carry out real-time experiments, a high-pressure environmental chamber (HPEC) was constructed for in situ X-ray diffraction (XRD) studies to 1000 bars and to 200°C. In the HPEC, a liquid, e.g. a brine, plus sample in suspension, is pressurized by gas, e.g. CH4 or CO2, or liquid, e.g. supercritical CO2. The unique aspect of this chamber is that the sample + liquid (~2 mL) form a dynamic system, and particles can move freely in the liquid while being illuminated by the X-ray beam. Several HPECs were constructed of Ti alloy, stainless steel, or carbon-fiber polyether ketone to be resistant to corrosion under basic or acidic conditions. These HPECs are compatible with standard transmission-mode diffractometers with sealed-tube X-ray sources (Mo radiation is being used at the University of Illinois at Chicago — UIC) or with brilliant X-ray sources. In addition, to allow long-duration studies or, for example, to study the effect of micro-organisms on these mineral reactions, a large-bore (~25 mL) reaction vessel system was devised that could be examined regularly at appropriate P/T conditions or off-line. Calibration of the HPEC and XRD pattern processing is discussed and illustrated. The potential significance of these devices goes beyond understanding the deep sedimentary environment, because materials and reactions can be studied while using nearly any liquid as an immersion agent. As an example, experimental results are given for the d001 values of montmorillonite clay vs. temperatures to 150°C at P(CO2) = 500 bars in a NaCl-rich brine.

Dissolution of amorphous silica or silicate is an important reaction to release silicic acid in natural water and this reaction is affected by several factors. The existence of a natural organic compound, tropolone, because of its abundance, is of particular importance. In the present study, the dissolution of amorphous silica in the presence of tropolone (HL) was investigated in an aqueous solution under acidic conditions. The dissolution is controlled by the reaction between silicic acid and tropolone (Si(OH)4 + 3HL + H+ ⇌ SiL3+ + 4H2O), where the conditional formation constant K = [SiL3+]/[Si(OH)4][HL]3[H+]). The solubility of amorphous silica in the presence of tropolone was significantly greater than that in pure water due to the formation of the Si-tropolonate complex in the solution. The acceleration of silica dissolution by tropolone depends on the reaction pH and tropolone concentration. The solubility of the amorphous silica in the tropolone solution at pH 1 was approximately ten times greater than in the 0.1 mol/dm3 HCl used as a reference. This increase in the solubility correlates to a K value of the Si-tropolone complex at each pH. From the solubility experiments, the conditional formation constants (log K) of the Si-tropolonate complex at each reaction pH 1, 2, and 3 were 6.39, 5.88, and 5.77, respectively. The significant acceleration of the dissolution of amorphous silica by tropolone at pH 1 can be attributed to the large formation constant of the Si-tropolonate complex.

The Hercynian metamorphic event is poorly characterized in internal zone complexes of the Betic Cordillera (Spain), as it has been, to a great extent, overprinted by the mineral assemblages formed during the Alpine event. Identification of the signals of the Hercynian episode is easier in series largely unaffected by the Alpine event, such as Intermediate units between the Maláguide and the Alpujárride Complexes, which consist of a set of thrust slices. With the aim of characterizing the Hercynian paragenesis, a detailed comparison of the mineral assemblages of Paleozoic and overlying Triassic sequences, unaffected by the pre-Alpine event, was carried out. Mineral assemblages were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, electron microprobe, and transmission-analytical electron microscopy. A rapid increase in the illite crystallinity values was observed at the Triassic—Paleozoic transition in the upper tectonic slices. In addition, the diagenetic to anchizonal dickite-, sudoite-, and pyrophyllite-bearing assemblages, characterizing the Triassic rocks, contrast with Paleozoic assemblages consisting of white K-mica ± paragonite + chlorite + mica-chlorite and chlorite-vermiculite mixed layers + garnet, suggesting that this assemblage corresponds to the Hercynian metamorphic event. This assemblage records temperatures on the order of 400ºC and an intermediate pressure regime. Paleozoic rocks contain, in addition, tobelite, which comprises some of the detrital grains and strongly masks the illite crystallinity values. Tobelite has been identified only in the upper thrust slices, suggesting that changes in the detrital input is primarily responsible for the disappearance of tobelite at the transition from the Maláguide to the Alpujárride domain. Tobelite appears finely intergrown with white K-mica and its origin is uncertain. It could have been inherited as tobelite, but a more likely hypothesis is that the intergrowths of white K-mica and tobelite were formed at low temperature from an NH4-bearing mica precursor.

The structures of one synthetic and two natural chlorites of the chlinochlore type were explored using X-ray diffraction, magic-angle spinning nuclear magnetic resonance (NMR) and Mössbauer spectroscopy. Rietveld refinements indicated that all structures are of the trioctahedral ordered IIb polytype. Mössbauer spectra provided the ratio IIFe/IIIFe but gave no evidence for the presence of IIIFe in the brucite-like sheet. We also report unit-cell parameters, Mössbauer isomeric shifts, Si NMR chemical shifts as well as 27Al isotropic shifts and quadrupolar coupling parameters. Very broad 29Si NMR peaks from the natural samples prevented us from obtaining accurate information on the Si-Al ordering in the tetrahedral sheets; the limitations of 29Si NMR as applied to natural chlorites are discussed. High-resolution 3QMAS NMR resolved the 27Al signal of the M4 octahedral site in the brucite-like sheet from the other three Al signals of crystallographically inequivalent octahedral positions.

The structural significance of micas with Na-K intermediate composition, and their chemical and structural evolution at increasing metamorphic grade have been investigated in Triassic rocks from the transition between the Maláguide and Alpujárride complexes (Internal zones of the Betic Cordillera, Spain). Micas were studied by X-ray diffraction (XRD) and by scanning and transmission electron microscopy (SEM/TEM). Three samples, belonging to the late diagenesis and to the low and medium anchizone, were selected for this study. Na-bearing mica appears as submicroscopic packets intergrown in parallel with K-mica, becoming more compositionally uniform with increasing grade. The diagenetic sample contains illite, minor paragonite, and two main populations of intermediate Na-K micas, with average compositions Ms60Prg40 and Ms35Prg65, respectively, where Ms represents muscovite and Prg, paragonite. The lattice-fringe images of mica packets with intermediate compositions suggest the presence of random mixed-layered paragonite-muscovite. Under low anchizonal conditions the amount of discrete paragonite increases and the Na-K intermediate mica has a mean composition of Ms40Prg60. The TEM images suggest that the packets with intermediate composition are solid solutions of paragonite and illite. Micas with Na-K intermediate composition are lacking in the sample with the highest metamorphic grade. In this sample, paragonite and muscovite coexist with mica, with composition intermediate between paragonite and margarite. The lattice-fringe images of these Na-Ca-bearing packets suggest that they consist of irregularly shaped domains enriched either in Na or in Ca.

Our data indicate that Na+K-bearing micas have several origins: detrital stacks of K- and Na-bearing micas coexist with authigenic phases, formed from dickite in the diagenetic, coarse-grained samples, and perhaps from smectite-bearing mixed-layers or detrital illite, in the fine-grained rocks. The changes observed at increasing metamorphic grade can be related to the influence of the lithology, the metamorphic grade, and the different geological settings. Intermediate Na-Ca mica appears to have grown from paragonite, with calcite as the source of Ca.

Dioctahedral smectite samples of a wide range of compositions (beidellites, montmorillonites, nontronites, Fe-rich montmorillonites and Al-rich nontronites) were studied by infrared (IR) spectroscopy. A special sample-preparation technique was used to eliminate the contribution of molecular water. The OH-stretching regions of the spectra were decomposed and curve-fitted, and the individual OH-stretching bands were assigned to all the possible types of OH-bonded cation pairs that involve Al, Mg and Fe. The integrated optical densities of the OH bands were assumed to be proportional to the contents of the specific types of OH-linked cation pairs with the absorption coefficients being the same for all individual OH bands. Good agreement between the samples’ octahedral cation compositions calculated from the IR data and those given by crystal-chemical formulae was obtained for a representative collection of samples in terms of a unique set of individual OH-band positions that vary within narrow wavenumber intervals. This has allowed us to minimize the ambiguity in spectra decomposition caused by the poor resolution of smectite spectra and confirmed the validity of the resulting band identification.

The bands associated with specific OH-bonded cation pairs in the spectra of smectites are, on the whole, shifted to greater wavenumbers with respect to the corresponding bands in micas. In addition to OH bands that refer to the smectite structure, AlOHAl and AlOHFe bands of the pyrophyllite structural fragments were identified. The band-position variation ranges overlap in a few cases (AlOHFe and MgOHMg; AlOHAl of smectite and AlOHFe of pyrophyllite-like component).

Unambiguous interpretation of the OH-stretching vibrations was found to be possible only for smectite samples with known chemical compositions, so that IR data cannot be used for quantitative determination of octahedral cation composition of mixtures of dioctahedral 2:1 phyllosilicates. In the case of the studied monomineral smectites with known chemical compositions, IR data provided information on the short-range order/disorder in the distribution of octahedral cations along cation-OH-cation directions. This information can be employed, in conjunction with the data of other spectroscopic and diffraction techniques, in the analysis of short-range octahedral cation distribution.

Pillared clays (PILCs) with magnetic properties are materials with potential for wide application in industry and the environment, but only a few studies of these types of materials have been carried out. The purpose of this study was to advance knowledge of the preparation and magnetic properties of pillared clays by examining in detail a series of magnetic Ti-pillared clays (Ti-M-PILCs). Samples were synthesized at ambient temperature by sodium borohydride reduction of ferrous ions added by ion-exchange to Ti-pillared montmorillonite (Ti-PILCs). The properties of the Ti-M-PILCs were investigated using a superconducting quantum interference device (SQUID) and Mössbauer spectroscopy. Hysteresis, zero-field-cooled (ZFC), and field-cooled (FC) regimes were measured on different precursor materials prepared by calcination of Ti-PILCs at temperatures between 200 and 600°C. Hysteresis loops, recorded between −7 and 7 T in the temperature range 200–300 K, were observed in most samples depending on the preparation of clays. The ZFC/FC measurements were made after heating from 2 to 300 Kunder an applied magnetic field of 39.8 kA m−1. The influence of the calcination temperature of the starting Ti-PILCs on the structural and magnetic properties of the Ti-M-PILCs was examined. The presence of two different Fe-alloy distributions was found; a dispersed one for the less-calcined Ti-PILCs and clusters for the more-calcined ones.

While there is increasing recognition of the role of race in shaping global politics, the extent to which the construction and operation of international order is entangled with race remains underexplored. In this article, I argue for the centrality of race and racialization in understanding the constitution of international order by theorizing the constitutive connections between race and international order and showing how the two can be examined as intertwined. I do this, first, by articulating conceptualizations of both international order and race that center on processes of regulation and regularization. Second, I bring these together to suggest that race be understood as a form of order that functions to reproduce a historically emergent form of hierarchy and domination across a range of spaces and contexts. Third, I operationalize these conceptualizations by outlining and historicizing some of the key features of this racialized and racializing international order, specifically coloniality, the racial state, and racial capitalism, and thereby illustrate important aspects of the persistence of this order. Centering race in the study of international order, I suggest, helps us better understand how racializing hierarchies and racialized inequalities persist in the present and are reproduced through structures and practices of international order.

‘Liminal’, from the Latin limen, denotes both thresholds and, curiously, the home. Since its original use by the anthropologist Arnold van Gennep in 1909 to label the central stage in a transformational rite of passage, the term has been used in very many contexts: from writings concerning sociology within both local and global contexts to an internet aesthetic of eerie empty spaces, a sort of loose understanding of modern spiritualities and plenty of art gallery labels.

The Weches Formation of the Claiborne Group (Eocene) in northeast Texas consists of clayey sandstones and mudrocks, both with variable proportions of dark green to brown clay peloids deposited in a marginal to open marine setting on the Gulf Coast margin. The composition of the dark green peloids, from two localities, has been investigated using X-ray diffraction, back-scattered electron microscopy with X-ray analysis, electron energy-loss spectroscopy (EELS), Mössbauer spectroscopy, chemical analysis and Fourier transform infrared spectroscopy. These peloids were previously described on the basis of their color as glauconite (Yancey and Davidoff, 1994); our results, however, show that the dark green indurated pellets are predominantly composed of mixed-layer clays with a high proportion of Fe-rich 7 Å serpentine layers coexisting with a mixed-layer phase containing glauconite, nontronite and vermiculite layers, in addition to discrete illite and kaolinte. Analyses by EELS of single particles with a chemical composition consistent with them being the Fe-rich clay indicate that the Fe is >95% ferric, while Mössbauer analyses of the bulk magnetically separated fraction for the same samples indicates a ferric iron content of ∼60–70%, despite the variable relative proportions of expandable and 7 Å layers. Taking into account that there is a significant amount of 2:1 layers containing ferric Fe, we interpret these data as indicating that the Fe in the 7 Å layers has a significant amount of Fe2+ even taking into account the high ferric Fe ratio from the EELS analysis when the coexisting 2:1 layers are considered. Thus, these 1:1 layers are closer to berthierine in composition than to odinite. The vermiculite layers in the Texas clay may indicate partial ‘verdinization’ of expandable 2:1 clay. A possible reaction is smectite → vermiculite → berthierine-like phase. We estimate a temperature of 20°C for the seawater in which the Texas clay formed, the lower end of the range for modern occurrences of odinite.

Landfill leachate is one of the most difficult effluents with which to deal from an environmental perspective because of its concentration and complex composition, including refractory and toxic components such as heavy metals or xenobiotic organic compounds. The objective of the present study was to use organically modified bentonite (OMB) to dispose of landfill leachate >10 y old. The OMB was synthesized using a new method, which removed four steps (filtering, washing, drying, and grinding) from the traditional process. After treatment using OMB, the chemical oxygen demand concentration (COD concentration, an index of the organic pollutants in the landfill leachate, was determined using the potassium dichromate method) of the landfill leachate sample decreased from 2400 to 245 mg/L in 5 h, i.e. the organic pollutants reduction efficiency was as high as 90%. Gas chromatography-mass spectrometry results indicated that most of the organic compounds were removed during the process. The modified and unmodified bentonite contained in the OMB deal with the hydrophobic and hydrophilic organic pollutants, respectively, resulting in significant degradation of the leachate. The study results have provided a new cost-effective method for treatment of landfill leachate.

Clay–organic interaction is an important natural process that underpins soil ecosystem services. This process can also be tailored to produce clay–organic nanocomposites for industrial and environmental applications. The organic moiety of the nanocomposites, typically represented by a toxic surfactant, could be replaced by hydrochar formed from biomolecules (e.g. glucose) via hydrothermal carbonization. The effect of montmorillonite (Mnt) and glucose dosage on hydrochar formation, however, has not been clarified. In addition, the mechanisms by which Mnt-hydrochar nanocomposites (CMnt) can detoxify and remove carcinogenic Cr(VI) from aqueous solution are not well understood. In the current study, research milestones in terms of clay–organic interactions are summarized, following which the synthesis and characterization of CMnt for Cr(VI) adsorption are outlined. Briefly, 1 g of Mnt was reacted with 75 mL of glucose solution (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol L−1) by hydrothermal carbonization at 200°C for 16 h. The resultant CMnt samples were analyzed for chemical composition, functional groups, morphological features, and Cr(VI) adsorptive properties. Mnt promoted the conversion of glucose to hydrochars, the particle size of which (~80 nm) was appreciably smaller than that formed in the absence of Mnt (control). Furthermore, the hydrochars in CMnt had an aromatic structure with low hydrogen substitution and high stability (C/H atomic ratio 0.34–0.99). The weakened OH (from hydrochar) and Si–O–Si stretching peaks in the Fourier-transform infrared (FTIR) spectra of CMnt are indicative of chemical bonding between Mnt and hydrochar. The CMnt samples were effective at removing toxic Cr(VI) from acidic aqueous solutions. Several processes were involved, including direct reduction of Cr(VI) to Cr(III), complexation of Cr(III) with carboxyl and phenolic groups of hydrochar, electrostatic attraction between Cr(VI) and positively charged CMnt at pH 2 followed by indirect reduction of Cr(VI) to Cr(III), and Cr(III) precipitation.

Clays are extremely variable materials with different mineral compositions, and they are the main ingredients in ceramics applications. Their properties play specific roles in influencing the technological properties and performance of ceramics products. Evaluating the various properties can help to determine the best way to utilize clay materials, such as the locally available Bombawuha (BC) and Denkaka (DC) clays mined from Ethiopia's Bombawuha and Denkaka areas, respectively. The objective of this study was to examine these materials for the purpose of using them to produce quality electrical porcelain insulators. The clay samples were characterized for their chemical composition, mineralogy, thermal properties, plasticity, and particle-size distribution, using atomic absorption spectrometry (AAS), X-ray diffractometry (XRD), differential thermal analysis coupled with thermogravimetric analysis (DTA-TGA), the Atterberg plasticity test, and sieve hydrometer analysis. Based on the characteristics, suitable clay materials were selected and mixed with feldspar and quartz to formulate various porcelain body compositions which were fired at three different temperatures (1200, 1250, and 1300°C) and dwell times (1.5, 2.0, and 2.5 h). The mineralogy, water adsorption, apparent porosity, bulk density, dielectric strength, flexural strength, and microstructure of the fired bodies were measured. The results revealed that, compared to DC, BC contains kaolinite as the major mineral with appreciable amounts of silica (46.72 wt.%), alumina (35.32 wt.%), and fluxing oxides but smaller amounts of CaO. BC contains greater clay fractions (20.58 wt.%); and has a middle-range plasticity index (PI = 11.2 wt.%), thus making BC suitable for producing porcelain insulators. A test-body composition of 40 wt.% BC, 40 wt.% feldspar, and 20 wt.% quartz, fired at 1250°C for 2 h, exhibited water adsorption of 0.17 wt.%, apparent porosity of 0.42 wt.%, bulk density of 2.45 g/cm3, a dielectric strength of 8.22 kV/mm, and flexural strength of 43.63 MPa and, thus, satisfied the required properties for quality porcelain insulators.

Sorption and transformation of 1-naphthol by a K-smectite (K-SWy-2) were studied using batch sorption isotherms, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The sorbents included three preparations of the reference smectite clay (SWy-2): (1) whole clay containing naturally occurring carbonate impurities, (2) SWy-2 with the removal of carbonate impurities, and (3) the carbonate-free SWy-2 fraction amended with calcite. For the whole clay and carbonate-free clay amended with calcite, >80% of added 1-naphthol disappeared from aqueous solution within 24 h, corresponding to a sorbed concentration of ≥2 mg/g of clay. In contrast, only 35% of the added 1-naphthol disappeared from solution in the carbonate-free clay after 24 h of exposure. For the clays from the three preparations in this study, <1% of sorbed 1-naphthol could be recovered by methanol extraction from the clays. The XRD data suggested that 1-naphthol was intercalated in the smectite, but was not conclusive because the 1-naphthol sorption range (1.5–2.8 mg/g of clay) in this study had relatively minor effects on the XRD patterns. The FTIR spectra of sorbed 1-naphthol-clay complexes demonstrated structural Fe3+ reduction. The spectra also showed evidence of the transformation of 1-naphthol. It suggests that reduction of structural Fe3+ may be coupled to oxidation/polymerization of 1-naphthol. Further transformation of oxidized 1-naphthol, such as by oxidative coupling reactions, is implicated by formation of a dark gray color on the clay and the inability to extract sorbed 1-naphthol.

Organo-clays are of interest in the modification of anion transport properties in engineered barriers. In the present study, surface charge and wettability were assessed for tracking changes in the effective diffusion coefficient (Deff) by the formation or suppression of bound H2O layers on the external surfaces of clays. Bentonite samples modified with three different organic cations in amounts of 0 to 400% of the cation exchange capacity were used. Diffusive transport was determined in H2O→D2O exchange experiments in a newly constructed cell adapted to the attenuated total reflectance (ATR) accessory of a Fourier-transform infrared (FTIR) spectrometer at two different dry bulk densities and various degrees of water saturation.

All organo-clay combinations showed changes in surface charge after the addition of organic cations, from a negative value of 99 mmolc/kg for the original bentonite to a maximum positive value of 230.5 mmolc/kg for hexadecylpyridinium (HDPy)-montmorillonite. The positive charge resulted from adsorption of the organic cation in excess of the CEC. Hydrophobic surface properties with contact angles >90° were obtained for HDPy-montmorillonite samples with monolayers of organic cations on the external surfaces only. Here, where hydrophobicity suppressed the formation of bound H2O layers, the largest Deff o f 2.7×10−10 m2/s was observed in the high dry bulk density range (1.0–1.5 g/cm3) under water-saturated conditions. In the low dry bulk density range (0.6–0.9 g/cm3) this effect was weakened significantly because, with increasing pore size, the effect of bound H2O layers was reduced. In the high dry bulk density range at partial water saturation (40%), diffusive transport was hindered by the small water volume. Previous work found that, in the high dry bulk density range and water-saturated state, Deff was 2.4×10−11 m2/s for the original bentonite. Deff for all hydrophilic organo-clay samples was ⩽2.1×10−11 m2/s, somewhat less than for the hydrophobic sample. In hydrophilic organo-clay samples, retardation factors that retard the value for Deff, up toa magnitude of 0.5, include an increase in dry bulk density and a decrease in water saturation. In the water-saturated state at high dry bulk densities, hydrophobic surface properties suppressing the formation of bound H2O layers can increase Deff by one order of magnitude.