Some aspects of the crystal structure of illite are not understood properly yet, in spite of its abundance and significance as a component of soils, sediments, and low-grade metamorphic rocks. The present study aimed to explore the role of hydronium cations in the interlayer space of illite in a theoreticalexperimental approach in order to clarify previous controversial reports. The infrared spectroscopy of this mineral has been studied experimentally and by means of atomistic calculations at the quantum mechanical level. The tetrahedral charge is critical for the stability of the hydronium cations, the presence of which has probably been underestimated in previous studies. In the present study, computational studies have shown that the hydronium cations in aqueous solutions are likely to be intercalated in the interlayer space of illite, exchanging for K cations. During the drying process these cations are stabilized by hydrogen bonds in the interlayer space of illite.

Terrestrial resource extraction has been a part of the human experience for eons. Soon, humanity may move away from digging in the earth the extracting resources among the stars.

Recent measurements from Mars document X-ray amorphous/nano-crystalline materials in multiple locations across the planet. Despite their prevalence, however, little is known about these materials or what their presence implies for the history of Mars. The X-ray amorphous component of the martian soil in Gale crater has an X-ray diffraction pattern that can be fit partially with allophane (approximately Al2O3⋅(SiO2)1.3–2⋅(H2O)2.5–3), and the low-temperature water-release data are consistent with allophane. The chemical data from Gale crater suggest that other silicate materials similar to allophane, such as Fe-substituted allophane (approximately (Fe2O3)0.01–0.5(Al2O3)0.5–0.99⋅(SiO2)2⋅3H2O), may also be present. In order to investigate the properties of these potential poorly crystalline components of the martian soil, Fe-free allophane (Fe:Al = 0), Fe-poor allophane (Fe:Al = 1:99), and Fe-rich allophane (Fe:Al = 1:1) were synthesized and then characterized using electron microscopy and Mars-relevant techniques, including infrared spectroscopy, X-ray diffraction, and evolved gas analysis. Dissolution experiments were performed under acidic (initial pH values pH0 = 3.01, pH0 = 5.04), near-neutral (pH0 = 6.99), and alkaline (pH0 = 10.4) conditions in order to determine dissolution kinetics and alteration phases for these poorly crystalline materials. Dissolution rates (rdiss), based on the rate of Si release into solution, show that these poorly crystalline materials dissolve approximately an order of magnitude faster than crystalline phases with similar compositions at all pH conditions. For Fe-free allophane, logrdiss = –10.65–0.15 × pH; for Fe-poor allophane, logrdiss = –10.35–0.22 × pH; and for Fe-rich allophane, logrdiss = –11.46–0.042 × pH at 25°C, where rdiss has the units of mol m–2 s–1. The formation of incipient phyllosilicate-like phases was detected in Fe-free and Fe-rich allophane reacted in aqueous solutions with pH0 = 10.4 (steady-state pH ≈ 8). Mars-analog instrument analyses demonstrate that Fe-free allophane, Fe-poor allophane, and Fe-rich allophane are appropriate analogs for silicate phases in the martian amorphous soil component. Therefore, similar materials on Mars must have had limited interaction with liquid water since their formation. Combined with chemical changes expected from weathering, such as phyllosilicate formation, the rapid alteration of these poorly crystalline materials may be a useful tool for evaluating the extent of aqueous alteration in returned samples of martian soils.

The adsorption of [M(bpy)3]2+ ions (M = Ru or Os) by clay films immersed in pure water and in electrolyte solutions was investigated by electrochemical quartz crystal microbalance (EQCM), UV-visible spectroscopy and powder X-ray diffraction. In water, the adsorption of the cations resulted in a decrease in the mass of the films. This decrease in mass is attributed to the expulsion of some 50 water molecules from the clay interlayer spaces for each cation adsorbed. Water is lost to make room for the large metal complex cations in the interlayer spaces, and because of decreases in the volume of the interlayer spaces during adsorption of the cations. In 0.05 M NaCl or 0.05 M Na2SO4, UV-visible measurements show a rapid initial adsorption of the cations by ion exchange, followed by a slower additional adsorption of the cations above the clay’s CEC, presumably as ion pairs with the electrolyte counter ions. The EQCM show initial reductions in the mass of the films that were two to three times larger in pure water. These initial mass decreases were followed by smaller mass ‘re-increases’ at longer times that were not observed in water. The larger initial mass losses are attributed to the loss of more water from the clay interlayer spaces. In 0.5 M Na2SO4 or 1.0 M NaCl, adsorption of the cations never exceeded the clay’s CEC. The initial decreases in mass upon addition of the cations all but disappeared, leaving only the smaller positive mass changes at longer times.

When present at elevated levels in drinking water, arsenic is toxic, and magnesian clays are gaining recognition as a source of elevated arsenic in groundwater. In the crust and upper mantle of Earth, arsenic incorporation into clay minerals is influenced by geochemical conditions associated with hydrothermal fluids and metamorphic processes (e.g. serpentinization), meaning that As is a useful tracer of fluid-flow in the deep Earth. To improve understanding of arsenic speciation in groundwater, sediments, soils, and hydrothermal-metamorphic systems, the present study examined arsenic incorporation into magnesian clays by synthesis of serpentine minerals (200oC, 10 d) with varied concentrations of Si, Al, As5+, and As3+. The synthesis experiments produced two distinct crystal types, tubular and platy serpentines, each with 10–15% randomly interstratified talc layers. X-ray absorption spectroscopy indicated that As5+ and As3+ occurred in the tetrahedral sheet. Single-crystal analysis revealed that tubular crystals contained up to 1 wt.% arsenic [Mg2.8(Si1.8As0.2)O5(OH)4] (mean 0.2 wt.% As). The mean composition of platy, high-Al crystals is (Mg1.8Al0.7)(Si2.0)O5(OH)4, and that of platy, medium-Al crystals with As3+ is (Mg2.07Al0.52) (Si1.97As3+0.03)O5(OH)4. Charge, geometry, and radius of tetrahedral AsO43– oxyanions are similar to tetrahedral SiO44–, and this facilitates fixation of As5+ into the tetrahedral sheet of clay minerals. The geometry and size of the larger As3+ in tetrahedral sites (as a pyramidal AsO33– oxyanion) may limit incorporation relative to As5+. Arsenic-bearing Mg clays crystallize in alkaline environments where AsO43– or AsO33– are the dominant As species and where high pH accompanies crystallization of serpentine, talc, chlorite, or Mg-smectite. The presence of tetrahedral As in these clays raises the possibility of tetrahedral As in other Mg clays (e.g. sepiolite or kerolite) as well.

Art librarians face many changes in the professional relationship with their users. Technological and cultural evolutions lead us to learn new skills to adapt ourselves to these new audiences. But are these changes really so new to librarians? Librarians have always had to embrace new technological expertise for library catalogues, databases and digital libraries. We know that librarianship is a profession where communication is primordial; communication with library users, and also with the general public – there's not much new here vis-à-vis the traditional missions of librarians. Still, librarians must become more competent than ever at conversing with patrons, to better understand their needs and their ways of expressing those needs, particularly their need to interact with our libraries and collections. Diverse examples from French art libraries illustrate how library professionals tend to use new media, technologies, and cultural trends to enable their institutions to disseminate knowledge and contribute to a more open society that can partake freely of the riches and learning history that art libraries have to offer.

Low-temperature FTIR spectroscopy was used to characterize the v(OH) region of kaolin-group minerals including well ordered to poorly ordered kaolins from Georgia, Brazil, and England, along with samples of discrete dickite and nacrite. Low-temperature FTIR spectra were useful in resolving dickite- and nacrite-like features present in the spectra of kaolins when cooled to <30 K. These features were not resolved at room temperature and only partially resolved at liquid N2 temperature (77 K). The room-temperature and low-temperature positions of the ν(OH) bands of kaolinite, dickite, and nacrite were linearly correlated with the interatomic OH⋯O distances and this relationship served as the basis for polytype/disorder identification. Dickite or dickite-like disorder was found in high Hinckley-Index kaolinite from Keokuk, Iowa, and from Cornwall, England. Dickite- and nacrite-like features were observed in both high- and low-Hinckley-index kaolinite and the amounts of these stacking sequences generally increased with decreasing Hinckley Index.

Ion-exchange modeling is used widely to describe and predict ion-adsorption data on clay minerals. Although the model parameters are usually optimized by curve fitting experimental data, this approach does not confirm the identity of the adsorption sites. The purpose of the present study was to extend to divalent cations a previous study on the retention of monovalent cations on Na-saturated montmorillonite (NaMnt) which optimized some of the model parameters using density functional theory (DFT) simulations. The adsorption strength of divalent cations increased in the order Mg2+ < Cd2+ < Ca2+ < Sr2+ < Ba2+. After adding adsorption of metal hydroxide species (MOH+), the three-site ion-exchange model was able to describe adsorption data over a wide pH range (pH 1–10) on NaMnt. X-ray diffraction (XRD) analyses were conducted to investigate the interlayer dimension of clay samples under various conditions. The cation retention strengths of divalent cations did not correlate with interlayer dimensions. The XRD analyses of the Mnt showed a d001 value of 19.6 Å when saturated with alkaline earth cations, 22.1 Å with Cd2+, 15.6 Å with Na+, and 15.2 Å with H+. In the case of Na+, the 15.6 Å peak decreased gradually and disappeared, and new peaks at 22.1 and 19.6 Å appeared when the percentages of Mg2+ and Ba2+ adsorbed increased on NaMnt. The peak shifted from 22.1 to 20.3 and 19.6 Å when the pH increased for all cations except Cd2+, which stayed constant at 22.1 Å. The coexistence of multiple d001 peaks in the XRD patterns suggested that the interlayer cations were segregated, and that the interlayer ion–ion interactions among different types of ions were minimized.

Accidental discharges of the hazardous nuclear fission products 137Cs+ and 90Sr2+ into the environment, such as during the Fukushima Dai-ichi nuclear accident, have occurred repeatedly throughout the ‘nuclear age.’ Numerous studies of the fate and transport of 137Cs+ and 90Sr2+ in soils and sediments have demonstrated their strong and selective binding to phyllosilicate clay minerals, primarily by means of cation exchange into interlayer sites. The locally concentrated amounts of these radioactive beta-emitters that can be found in these host minerals raise important questions regarding the long-term interplay and durability of radioisotope—clay associations, which is not well known. The present study goes beyond the usual short-term focus to address the permanence of radioisotope retention in clay minerals, by developing a general theoretical understanding of their resistance to the creation of defects. The present study reports ab initio molecular dynamics (AIMD) calculations of the threshold displacement energy (TDE) of each symmetry-unique atomic species comprising the unit cell of model vermiculite. The TDE values determined are material specific, radiation independent, and can be used to estimate the probability of Frenkel-pair creation by direct electron—ion collision, as could be induced by the passage of a high-energy electron emitted during the beta-decay of 137Cs, 90Sr, and daughter 90Y. For 137Cs and 90Sr, the calculated probability is ~36%, while for 90Y the probability is much greater at ~89%. The long-term retention picture that emerges is that decay will progressively alter the clay interlayer structure and charge, probably leading to delamination of the clay, and re-release of residual parent isotopes. Further work examining the effect of Frenkel defect accumulation on the binding energy of parent and daughter radionuclides in the interlayer is thus justified and potentially important for accurate long-term forecasting of radionuclide transport in the environment.

‘Ghassoul’ clay is a Mg-rich clay from Morocco which is of great industrial use and interest, but its characterization is still incomplete. The purpose of this study was to provide further details regarding the structure and characteristics of this important commercial clay mineral. Mineralogical and physicochemical characterizations of the raw form of ‘Ghassoul’ clay from Jbel Ghassoul in Morocco, and of its <2 µm size fraction, purified and Na+-saturated, were carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR), and differential and thermogravimetric analysis (DTA/TG). The XRD data revealed that the raw Ghassoul clay consists mainly of a Mg-rich trioctahedral smectite, stevensite, together with quartz and dolomite. The IR spectra consisted of vibrations typical of trioctahedral smectites. The DTA/TG curves were also similar to those of trioctahedral smectites. Chemical analysis confirms that this Mg-rich trioctahedral smectite is a stevensite characterized by a limited isomorphic substitution of Si4+ by Al3+. The thermal transformations examined by in situ XRD as a function of the firing temperature from 100 to 1200°C indicated that stevensite was transformed to enstatite (MgSiO3) at temperatures >800°C and that quartz was transformed to cristobalite when the temperature exceeded 1100°C. These transformations were irreversible. The specific surface area and cation exchange capacity (CEC) of the ‘Ghassoul’ clay are 133 m2/g and 75 meq/100 g, respectively. The main exchangeable cation is Mg2+ (53 meq/100 g).

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.