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In the soils of western Jilin Province in northeastern China, some significant gaps have been observed between the fraction of the soil existing as clay-size particles (<0.002 mm) and the amount attributable to crystalline clay minerals, and that the relative proportions of crystalline clay minerals to the total clay-size fraction (CP) apparently varies with latitude. The purpose of the present study was to identify the reason for this discrepancy and to explain the dependence on latitude. The grain sizes and mineral compositions of the whole soils from western Jilin Province, China, were analyzed by laser particle-size analysis (LPSA) and X-ray diffraction (XRD), and the <0.002 mm particle-size fraction was analyzed by XRD and X-ray fluorescence (XRF). The results confirmed that the percentage gaps between the clay fraction and clay minerals increased with increasing latitude. The theoretical illite percentage calculated from K2O content was compared with the illite percentage measured by XRD, and the results suggested that the measured illite accounted for only a small proportion of the theoretical illite. Structures of some special minerals below the identification threshold of XRD was suggested to be the reason for the percent gaps. The grain size and mineral crystallization both changed with latitude: the soil particle size and the CP decreased. In addition, clay minerals were more sensitive to climate than particle sizes were, and the CP of clay minerals in the soils within 0~180 cm depth all decreased with increasing latitude; however, the grain size showed patterns with latitude only in relatively shallow soil layers. The present study provides a reference and error analysis for the testing of clay minerals in alpine regions, and more suitable methods may be considered for development of clay-mineral testing in future studies.
Fe-reducing micro-organisms can change the oxidation state of structural Fe in clay minerals. The interactions with complex clays and clay minerals in natural materials remain poorly understood, however. The objective of this study was to determine if Fe(III) in loess was available as an electron acceptor and to study subsequent mineralogical changes. The loess samples were collected from St. Louis (Peoria), Missouri, USA, and Huanxia (HX) and Yanchang (YCH), in the Shanxi Province of China. The total Fe concentrations for the three samples was 1.69, 2.76, and 3.29 wt.%, respectively, and Fe(III) content was 0.48, 0.69, and 1.27 wt.%, respectively. All unreduced loess sediments contained Fe (oxyhydr)oxides and phyllosilicates. Bioreduction experiments were performed using Shewanella putrefaciens CN32 with lactate as the sole electron donor and Fe(III) in loess as the sole electron acceptor with and without anthraquinone-2, 6-disulfonate (AQDS) as an electron shuttle. Experiments were performed in non-growth (bicarbonate buffer) and growth (M1) media. The unreduced and bioreduced solids were analyzed by X-ray diffraction, Mössbauer spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy/energy dispersive spectroscopy. Despite many similarities among the three loess samples, the extent and rate of Fe(III) reduction varied significantly. In the presence of AQDS the extent of reduction in the non-growth experiment was 25% of total Fe(III) in HX, 34% in Peoria, and 38% in YCH. The extent of reduction in the growth experiment was 72% in HX, 94% in Peoria, and 65% in YCH. The extent of bioreduction was less in the absence of AQDS. Overall, AQDS and the M1 growth medium significantly enhanced the rate and extent of bioreduction. Fe(III) in (oxyhydr)oxides and phyllosilicates was bioreduced. Siderite was absent in control samples, but was identified in bioreduced samples. The present research suggests that Fe(III) in loess sediments is an important potential source of electron acceptors that could support microbial activity under favorable conditions.
The formation of 2:1 and 1:1 phyllosilicates in Fe–Si–O–H systems occurs in various geological and engineering settings; however, the identification and characterization of these minerals is very challenging due to the limited amount that is accessible, the very small particle size, and often the large degree of heterogeneity of these samples. To overcome these drawbacks, the synthesis of iron-rich phyllosilicates was attempted in this study with an initial Fe/Si molar ratio ranging from 0.50 to 2.33. The synthesis was performed at 150°C under hydrothermal conditions over a period of 7 days. Synthesis products were characterized by X-ray diffraction and fluorescence, by infrared, Raman, and Mössbauer spectroscopies, and by transmission electron microscopy. Results revealed that the stability field of the 2:1 clay mineral was wider than that of the 1:1 clay mineral. The 2:1 clay mineral was less sensitive to redox conditions compared to the 1:1 clay mineral. In addition, a heterogeneity of phases formed (iron oxides, nontronite, cronstedtite, or greenalite) was identified.
Synthetic dyes in industrial effluents pose a significant risk to human health and the environment, so much effort has been expended to degrade them using various methods, including the use of clay minerals as catalysts. The purpose of this study was to advance understanding of the mechanisms for clay-catalyzed degradation of crystal violet (CV) and other triarylmethine dyes using three different vermiculite clays (Llano, Texas, VTx-1; Ojen, OV; and Russian, RV), a montmorillonite (SWy-1), and a Spanish sepiolite (SEP). While OV, RV, SWy-1, and SEP showed almost no activity with respect to dye degradation, VTx-1 caused complete removal of the dye from solution up to the equivalent of 200% of the cation exchange capacity of the clay. While large amounts of dye were removed from the solution, no change in basal spacing was observed by X-ray diffraction. The kinetics of removal of CV from solution began after a lag period of >10 days in a process that can be described by pseudo-second order kinetics. By comparison, adsorption of CV onto SWy-1 and SEP was immediate, without any lag period. Sonication treatment of the VTx-1 vermiculite suspension caused the CV removal process to begin immediately. Fourier-transform infrared measurements of adsorption of CV on clays revealed that for the OV and RV vermiculites, SEP sepiolite, and SWy-1 montmorillonite the spectra were similar to the original dye; the spectra of the VTx-1-dye differed considerably, however, exhibiting vibrations of methylene groups (—CH2—) which were not present in the CV molecule. The significant changes in the IR spectrum indicated that CV underwent degradation on the surface of the VTx-1 vermiculite. Carbon-content analysis led to the conclusion that degradation products remained bound to the clay. Similar effects were observed for two other triarylmethine dyes (malachite green and methyl green) added to VTx-1, indicated that it may, therefore, be considered suitable as a sorbent to remove and decompose such dyes from industrial effluents. Pretreatment by sonication would remove the need for long incubation times.
The Al13 polycation is the predominant hydroxy-Al species in partially neutralized solutions. However, the existence of the Al13 species and the factors governing its formation in terrestrial environments still remain obscure. The objective of this study was to investigate the influence of pyrogallol, a common polyphenol in soils, on the formation of Al13 tridecamer. Hydroxy-Al solutions with an OH/Al molar ratio of 2.2 (pH 4.53) at pyrogallol/Al molar ratios of 0, 0.01, 0.05, 0.1 and 0.5 were prepared and mixed with 0.5 M sodium sulfate to form aluminum sulfate precipitation products. The solid-state 27Al nuclear magnetic resonance (NMR) spectra of the precipitates show that the pyrogallol perturbed the formation of Al13 tridecamer species as indicated by the decrease in the intensity of resonance peak, observed at 62.5 ppm, with increase in the pyrogallol/Al molar ratio. The crystallization of the precipitated Al sulfates was also hampered by pyrogallol, resulting in the formation of X-ray non-crystalline products at a pyrogallol/Al molar ratio of 0.50. The absorbance at 465 and 650 nm of the hydroxy-Al-pyrogallol solutions, the C coprecipitated, the electron spin resonance and 13C CPMAS-NMR spectra of the precipitates indicate the concomitant enhanced abiotic humification of pyrogallol by the X-ray amorphous Al species.
The golden age of human rights is over, as is the time when rights protection systems developed in a favorable context. Multilateralism is under attack from all sides, authoritarian countries are in the majority around the world, and democracies are increasingly fragile. The resurgence of claims about national sovereignty against universal human rights is part of a global geopolitical context in which authoritarianism and populism are permeating national political scenes. In this context, it is important to understand how regional systems for the protection of human rights manage to continue functioning, to convince states to implement the judgments of the courts, and to avoid denouncing their jurisdiction.
Stacking disorder in celadonite, a dioctahedral mica with Fe and Mg as major octahedral cations and which generally adopts the 1M stacking sequence, was investigated mainly by using transmission electron microscopy (TEM). The selected-area electron diffraction patterns with 0kl reflections along the [100] beam direction correspond to the 1M stacking but those along the [110], \$\end{document}, [010], [310], and \$\end{document} directions are frequently streaked along the [001]* direction or contain extra spots from twinned domains. Three-dimensional stacking analyses using sets of two high-resolution TEM images along different directions of the same area of one crystal indicate that all stacking faults involve only 180° layer rotations. These stacking faults produce greater peaks of 0kl reflections than expected in powder X-ray diffraction (XRD) patterns. Simulation of the XRD patterns indicated that 180° layer rotations occur at >10% of total interlayer regions in one celadonite specimen. The interlayer region of celadonite is characterized by a near-zero ditrigonal rotation angle, a small surface corrugation of the basal oxygen plane, and a small amount of Al substitution in the tetrahedral sheets. These features suggest that there is no preference for any of the six stacking angles around the interlayer region. The abundance of 180° layer rotation rather than ±60° and ±120° in the present specimens may be related to their ribbon-like morphologies elongated along the a axis.
Developing low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L−1 showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.
Fougerite (IMA 2003-057) is a mixed M(II)-M(III) hydroxysalt of the green rust group, where M(II) can be Fe or Mg, and M(III) is Fe. The general structural formula is: where A is the interlayer anion and n its valency, with 1/4 ≼ x/(1+y) ≼ 1/3 and m ≼ (1−x+y). The structure of green rusts and parent minerals can accommodate a variety of anions, such as OH−, Cl−, ${\rm{CO}}_3^{2 - },\;{\rm{SO}}_4^{2 - }$. The structure of the mineral was studied by Mössbauer, Raman and X-ray absorption spectroscopies (XAS) at the FeK edge. Mössbauer spectra of the mineral obtained at 78 K are best fitted with four doublets: D1 and D2 due to Fe2+ (isomer shift δ ≈ 1.27 and 1.25 mm s−1, quadrupole splitting ΔEQ ≈ 2.86 and 2.48 mm s−1, respectively) and D3 and D4 due to Fe3+ (δ ≈ 0.46 mm s−1, ΔEQ ≈ 0.48 and 0.97 mm s−1, respectively). Microprobe Raman spectra obtained with a laser at 514.53 nm show the characteristic bands of synthetic green rusts at 427 and 518 cm−1. X-ray absorption spectroscopy shows that Mg is present in the mineral in addition to Fe, that the space group is and the lattice parameter a ≈ 0.30–0.32 nm. The mineral forms by partial oxidation and hydrolysis of aqueous Fe2+, to give small crystals (400–500 nm) in the form of hexagonal plates. The mineral is unstable in air and transforms to lepidocrocite or goethite. The name is for the locality of the occurrence, a forested Gleysol near Fougères, Brittany, France. Its characteristic blue-green color (5BG6/1 in the Munsell system) has long been used as a universal criterion in soil classification to identify Gleysols. From a thermodynamic model of soil-solution equilibria, it was proposed that for the eponymous mineral, Fougères-fougerite, OH− may be the interlayer anion. In other environments, the interlayer anion may be different, and other varieties of fougerite may exist. Fougerite plays a key role in the pathways of formation of Fe oxides.
The Kütahya kaolinite deposits are the most important source of raw materials for the ceramics industry in Turkey. To date, no detailed mineralogical or geochemical characterizations of these materials have been carried out; the present study aims to fill that gap. The Kütahya kaolinite deposits formed by alteration of dacite and andesite tuffs related to Neogene volcanism whichwas associated withe xtensional tectonics. The kaolinite deposits contain silica and Fe- and Ti-bearing phases (pyrite, goethite, and rutile) in vertical and subvertical veins that diminish and then disappear upward. Mineralogical zonation outward from the main kaolinite deposit is as follows: kaolinite ± smectite + illite + opal-CT + feldspar; feldspar + kaolinite + quartz + smectite + illite; quartz + feldspar + volcanic glass. The veins and mineral distributions demonstrate that hydrothermal alteration was the main process in the development of the kaolinite deposits of the area. The very sharp, intense, diagnostic basal reflections at 7.2 and 3.57 Å, as well as non-basal reflections, well defined pseudohexagonal to hexagonal crystallinity with regular outlines, ideal differential thermal analysis-thermal gravimetric curves, and ideal, sharp, infrared spectral bands indicate well crystallized kaolinite. Micromorphologically, the development of kaolinite plates at the edges of altered feldspar and devitrified volcanic glass indicates an authigenic origin. Lateral increase in (SiO2+Fe2O3+MgO+Na2O+CaO+K2O)/(Al2O3+TiO2) from the center of the kaolinite deposit outward also indicates hydrothermal zonation. Enrichment of Sr in altered and partially altered rocks relative to freshvolca nic-rock samples demonstrates retention of Sr and depletion of Rb, Ba, Ca, and K during hydrothermal alteration of sanidine and plagioclase within the volcanic units. In addition, depletion of heavy rare earth elements (HREE) relative to light rare earth elements (LREE) in the kaolinized materials may be attributed to the alteration of hornblende. The negative Eu anomaly suggests the alteration of feldspar by hydrothermal fluids. The isotopic data from kaolinite and smectite indicate that hydrothermalalteration processes developed at 119.1–186.9°C and 61.8–84.5°C, respectively. Thus, the kaolinite deposits formed by hydrothermal alteration of volcanic glass, feldspar, and hornblende by a dissolutionprecipitation mechanism which operated under acidic conditions within Neogene dacite, andesite, and tuffs.
Former SHGAPE president Walter Nugent passed away in 2021. On April 1, 2023, historians gathered at the Organization of American Historians (OAH) annual meeting in Los Angeles, California, to remember him. William Deverell, Nancy Unger, Donna Gabaccia, Alan Lessoff, Charles Postel, and Annette Atkins spoke about Walter Nugent as a scholar, a colleague, a mentor, and a friend; then the audience joined in with their own memories and stories. The following roundtable is a lightly edited version of the panelists’ comments from that day, including an introduction that William Deverell wrote for the journal. We have included a Walter Nugent Reading List at the end—a selected bibliography of his books and articles, as well as works about him.
The polymer model provides a relatively simple and robust basis for estimating the standard Gibbs free energies of formation (ΔGfo) and standard enthalpies of formation (ΔHfo) of clay minerals and other aluminosilicates with an accuracy that is comparable to or better than can be obtained using alternative techniques. The model developed in the present study for zeolites entailed the selection of internally consistent standard thermodynamic properties for model components, calibration of adjustable model parameters using a linear regression technique constrained by ΔGfo and ΔHfo values retrieved from calorimetric, solubility, and phase-equilibrium experiments, and assessments of model accuracy based on comparisons of predicted values with experimental counterparts not included in the calibration dataset. The ΔGfo and ΔHfo predictions were found to average within ±0.2% and ±0.3%, respectively, of experimental values at 298.15 K and 1 bar. The latter result is comparable to the good accuracy that has been obtained by others using a more rigorous electronegativity-based model for ΔHfo that accounts explicitly for differences in zeolite structure based on differences in framework density and unit-cell volume. This observation is consistent with recent calorimetric studies indicating that enthalpies of transition from quartz to various pure-silica zeolite frameworks (zeosils) are small and only weakly dependent on framework type, and suggests that the effects on ΔHfo of differences in framework topology can be ignored for estimation purposes without incurring a significant loss of accuracy. The relative simplicity of the polymer model, together with its applicability to both zeolites and clay minerals, is based on a common set of experimentally determined and internally consistent thermodynamic properties for model components. These attributes are particularly well suited for studies of the effects of water-rock-barrier interactions on the long-term safety of geologic repositories for high-level nuclear waste (HLW).
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/eNvs. 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 preconsolidation 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.
The presence of pharmaceutical pollutants in the environment is one of the most pressing environmental problems. Adsorption from solution is an effective way to remove pharmaceuticals from liquid media, but the problem then is to separate the adsorbent from the liquids. The objective of the present study was to remove nitrofurazone from aqueous solutions using a bentonite/magnetite composite, prepared by co-precipitation of magnetite with bentonite, which could then be collected by magnetic separation. The bentonite/magnetite composite was characterized using diverse techniques, such as X-ray diffraction, scanning electron microscopy, low-temperature N2 adsorption/desorption, laser diffraction, and magnetization measurements. The particle size of the composite material did not exceed 50 μm and the particle size distribution was mono-modal with a maximum at 3.2 μm. The strong hysteresis in the magnetization curve revealed that the bentonite/magnetite particles were ferromagnetic. Adsorption of nitrofurazone by the bentonite/magnetite composite from aqueous solutions was measured and the amount of nitrofurazone adsorbed was 3.2×10–2 mmol/g. The adsorption kinetics of nitrofurazone to the bentonite/magnetite composite followed a pseudo-second-order kinetics equation. Upon adsorption, hydrogen bonds were formed between the amide groups of nitrofurazone and oxygen groups in bentonite.
Adsorption by synthetic 2-line ferrihydrite and hematite of glyphosate and phosphate, separately and together, was compared with adsorption results for goethite, gibbsite and two kaolinites in order to determine adsorption differences and similarities, in particular competition and phosphate preference, of these variable-charge minerals. Hematite rapidly adsorbed both compounds, while adsorption by ferrihydrite was slow, in particular of glyphosate, probably because of very slow diffusion of the bulky glyphosate molecules into interior sites in ferrihydrite particles. Accordingly, the Langmuir adsorption capacity of glyphosate (GAC) was considerably smaller (1.85 µmol m−2)than GAC for hematite (2.61 µmol m−2). The phosphate adsorption capacities (PAC) for ferrihydrite and hematite were more alike, 2.91 µmol m−2 and 2.85 µmol m−2, respectively. Differences between surface coordination (mono- or bidentate) may also contribute to the observed differences but conflicting information about the nature of the surface complexes makes this a difficult contributary factor to assess. The minerals were found to exhibit great variation in extent of competition and phosphate preference. Little competition and phosphate preference characterized hematite adsorption, while phosphate almost completely outcompeted glyphosate on goethite; ferrihydrite adsorption fell between these extremes. These differences may be attributed to different numbers of common (competitive) and specific (selective) adsorption sites on the three Fe oxides with a decreasing number of common sites in the order: goethite>>ferrihydrite>hematite, i.e. almost all goethite sites are common but with strong phosphate preference, while most hematite sites are specific for either glyphosate or phosphate. Alternatively, the result may be explained by adsorption in more planes, e.g. glyphosate adsorption onto the inner-Helmholtz-plane-adsorbed phosphate. For all six minerals compared, desorption of glyphosate following phosphate addition was found to be significantly correlated with the difference between the amounts of phosphate and glyphosate adsorbed indicating that this difference may be used as a competition index for predicting the influence of phosphate on glyphosate adsorption.