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Smectites are effective binders of aflatoxin in aqueous solutions. Unfortunately, their efficacy is reduced in guts because of interference by biomolecules and essential nutrients within the gut. Tunnel structures in palygorskite and sepiolite may function as molecular sieves and may, therefore, serve as alternatives or complements to smectites in binding aflatoxins but not larger biological compounds. The objective of the current work was to determine the effect of heat treatment on aflatoxin B1 (AfB1) adsorption and selectivity for biomolecules by two palygorskites (Plg_PK and Plg_CN), sepiolite (Sep), and a palygorskite-smectite mixture (Plg-Sm) in comparison with a smectite (Sm-37GR). The clays were heated at 250, 400, 500, and 600°C while phase and structural changes were characterized by X-ray diffraction and infrared spectroscopy. Comparative AfB1 adsorption was determined in aqueous and in simulated gastric fluids. The clay structures collapsed irreversibly in Sm-37GR and folded in fibrous clays with heating at 400°C or more. Sm-37GR adsorbed more AfB1 than all of the other clays; the estimated adsorption capacity followed the trend Sm-37GR (44 g kg–1) > Plg_PK (18.12 g kg–1) > Sep (12.7 g kg–1) > Plg_CN (11.4 g kg–1) > Plg-Sm (9.0 g kg–1). This trend appeared to be correlated with the abundance of smectite in the clays. Sepiolite had greater binding strength for AfB1 than the other clays. With intact clay structures, heating induced a negligible effect on AfB1 adsorption by the fibrous clays while in Sm-37GR and Plg-Sm, adsorption increased with heating at 250°C. Tunnel folding and structural collapse that had occurred at 400°C caused an abrupt decline in AfB1 adsorption irrespective of the clay type. The sepiolite clay adsorbed the least pepsin (370 g kg–1) while smectite adsorbed the most (1430 g kg–1). Consequently, in the simulated gastric fluid, adsorption declined by 25–30% in sepiolite, 52–60% in smectite, and remained unaffected in the palygorskites. Aflatoxin B1 adsorption probably occurred through H-bonding at the surface with the silanol group in palygorskite and sepiolite. No evidence that AfB1 molecules occupied the tunnels of the natural or heated palygorskite or sepiolite was observed in the present study. Palygorskite and sepiolite had a much smaller adsorption capacity for AfB1 than the smectite but also adsorbed less pepsin; therefore, both may be effective aflatoxin binders in gastrointestinal systems. [ABSTRACT FROM AUTHOR]

The Bursa-Orhaneli and Keles-Harmanalan coal deposits were developed in swampy and fluvial-lacustrine environments in western Anatolia under the E–W-trending graben zone during the Neogene. The present study aimed to determine the mineralogical and geochemical properties of clays interlayering the coal seams to define the origin of clay minerals, in particular, smectite. These deposits, comprising argillaceous sediment, marl, coal seam, mudstone, organic-rich shale, and sandstone, were deposited in a lacustrine environment accompanied by volcanogenic materials. The characteristics of sediments and their parent rocks were examined using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, palynology, and chemical analyses. The association of abundant smectite with quartz, amphibole, accessory chlorite, and a decrease in feldspar in fluvial-lacustrine sediments compared to those in the smectite accompanied by feldspar and volcanic glass and the absence of quartz and amphibole in the pyroclastic units suggest that smectite had detrital and authigenic origins. Flaky smectite shows either detrital, irregularly outlined coating and filling pores of terrigenous sediments or in situ precipitation edging resorbed feldspar and devitrified volcanic glass. Chemical analyses of the smectite-rich fraction show montmorillonite compositions with an average structural formula of: (Ca0.42Na0.25K0.08)(Al2.76Fe0.47Mg0.59Ti0.07Mn0.002)(Si7.65Al0.35)O20(OH)4. The positive correlation of Al2O3 vs. TiO2 and K2O vs. Rb may be related to the abundant detrital input. Feldspar and biotite were replaced by illite during diagenesis. An increase in the Ni/Co and V/(V + Ni) ratios in the altered units also suggest oxic, suboxic to anoxic conditions, under the control of a dry, warm to subtropical climate in fresh water and lakes during the Late Eocene to Middle Miocene. The slight enrichment of light rare earth elements (LREE) compared to heavy rare earth elements (HREE) with positive Eu and positive/negative Ce anomalies reflect fractional crystallization of feldspar. The δ18O and δD values of smectite and illite fractions and the wide range of δ34S isotope values (–1.5 to 15‰) for pyrite and chalcopyrite associated with coal indicate a signature of both diagenetic and partial hydrothermal origin. [ABSTRACT FROM AUTHOR]

Myanmar has a drier sub-tropical climate than countries that typically contain Ni laterite deposits, but hosts a Ni laterite deposit at Tagaung Taung. Given that Ni enrichment processes in the Tagaung Taung deposit are poorly understood, we investigated the geochemical and mineralogical evolution of two weathering profiles developed on different bedrocks in the central part of Myanmar: a partly serpentinized harzburgite at Tagaung and an almost completely serpentinized peridotite at Budaung. The whole-rock geochemical data indicate that Si was retained relative to Fe and Al in the weathering profiles. Nickel has been enriched to contents as high as 4.89 wt.% NiO in the saprolite layers at Tagaung, whereas the saprolite layers at Budaung contain ≤ 1.55 wt.% NiO. Smectite is the main mineral that formed in the saprolite layers at Tagaung, whereas secondary serpentine dominates the saprolite layers at Budaung. Microscopic observations indicate that Ni-smectite (> 10 wt.% NiO), which is only observed at Tagaung, formed as a replacement product of orthopyroxene. In addition to the high Ni fixation capacity of smectite relative to secondary serpentine, Ni-rich pore water derived from the dissolution of olivine likely contributed to the high Ni contents of smectite. Our results imply that high-grade Ni laterite deposits may develop on unaltered or partly serpentinized harzburgite under the climatic conditions typical of Myanmar. [ABSTRACT FROM AUTHOR]

Soils contaminated with heavy metals (HMs) are among the common problems of geo-environmental issues all around the world. Modification of clay soils using polymers is an effective method to improve the soils’ geo-environmental properties. Despite the extensive research done on the process of interaction between polymers and clay soils, very limited research has been undertaken with respect to the study of interactions between polymers and contaminated soils. The primary objective of this study was to determine the mechanisms involved in the partitioning and retention of Pb contaminants in interaction with smectite-polymer mixtures. Two procedures for determining the interaction of smectite-polymer mixtures with the HM contaminant Pb were used. In the first procedure (procedure A), smectite samples were first exposed to the polymer before being brought into contact with the HM contaminants. In the second procedure (procedure B), smectite samples previously contaminated with the Pb were brought into contact with the polymer. A series of batch equilibrium tests, buffering capacity and pH measurements, X-ray diffraction analyses, and scanning electron microscope photograph evaluations were conducted to determine the retention capacity of Pb in these two series of samples. The results state that the addition of 3% polymer to the samples contaminated with 200 cmol/kg soil Pb contaminant resulted in a 72% increase in Pb contaminant retention relative to the untreated smectite. In general, the results of this study indicate that more effective partitioning of Pb contaminants was achieved with procedure B samples because of the solidification of the polymer and polymer-bonding mechanisms. [ABSTRACT FROM AUTHOR]

This study reveals mineral and deformation processes associated with faulting of lacustrine unconsolidated sediments in the Guadix-Baza Basin (Betic Cordillera, S Spain) affected by the Baza Fault. Brittle carbonate and silt sediments develop deformation bands frequently sealed by dolomite crystallization, whereas ductile clay-rich sediments form clay smearing bands where late crystallization of gypsum can be observed. Granular flow and local cataclasis were the main deformation mechanisms in the brittle deformation bands. Flow alignment, grain-boundary sliding, and extrusion were predominant in the clay smearing bands. These water and clay-rich bands reduced shear strength of the faulting process due to their lubricating effect. Beidellitic smectite defines shear foliation of the smeared bands, but Mg-Fe, a K-rich smectite (Fe + Mg > 1 and K content up to 0.8 a.p.f.u), crystallizes in the micropores surrounding brittle clasts produced by deformation pressure shadows. These data suggest that the interaction of micromechanical events, which increased sediment porosity by the generation of pressure shadows, and the flow and concentration of saline fluids in these pores promoted structural diagenesis processes that favoured the beginning of local illitization. [ABSTRACT FROM AUTHOR]

Silicate glasses are durable materials in our daily life, but corrosion rate accelerates under alkaline aqueous environment. Such situation has raised concerns, for example, in nuclear waste disposal where vitrified wastes encounter to alkaline leachate from surrounding concrete materials. Here we report volcanic glass example surviving with a hyperalkaline groundwater (pH > 11) and high flow rate for about 4000 years. The tiny glass fragments were extracted from the volcanic ash layer sandwiched between ultramafic sediments using microanalytical techniques. Sharp elemental distributions at the glass surface, where amorphous-like smectite precursors and crystalline smectites coexist, suggest the corrosion by an interface-coupled dissolution–precipitation mechanism rather than inter-diffusion. The corrosion rate was maintained at, the minimum, 2.5 orders of magnitude less than the rate observed for fresh glass, even in the presence of Fe and Mg that might have consumed Si through the silicate precipitation. [ABSTRACT FROM AUTHOR]

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A calcium bentonite clay from Boane region (Mozambique) was subjected to an Na2CO3 activation process. The methylene blue test together with energy-dispersive X-ray spectroscopy (EDX) analysis indicated the successful ion exchange of Ca2+ by Na+ ions since the cation exchange capacity (CEC) increased from 67.5 to 74 meq/100 g and the Na/Ca ratio from 2.91 up to 15.8, as the concentration of Na2CO3, activation temperature, and activation time were varied from 2 to 6 wt.%, from 25 to 65 °C, and from 2 to 4 h, respectively. However, the increase in the CEC did not follow the same trend as the increase in the Na/Ca ratio, and for the case of Na2CO3 concentration, the increase in the CEC was limited. The X-ray diffraction (XRD) patterns also confirmed that Ca-rich bentonite was effectively modified into Na-bentonite since after the activation, the d(001) decreased from 1.52 nm to 1.30 nm. The statistical design of the experiments showed that as well as the time and the temperature × time linear interactive effect, all the other independent factors and their interactive effects had a significant influence on the CEC. The response surface methodology (RSM) indicated that higher values of the CEC can be obtained under the optimal activation conditions of 4 wt.% Na2CO3, at a temperature of 45 °C, and with an activation time of 3 h. A statistical model was used to predict the CEC, and the R2 value was 0.99529, which denotes a satisfactory result in predicting the CEC. [ABSTRACT FROM AUTHOR]

In this study, raw smectite (Sm), from the Guarapuava–Parana–Brasil region, was saturated with copper ions (Cu-Sm) by ion exchange and the samples Sm and Cu-Sm were used in crystal violet (CV) adsorption and applied as an antimicrobial and antifungal hybrid pigment. Samples (Sm and Cu-Sm) were used to remove crystal violet (CV) dye from aqueous media, simulating wastewater. Samples after use as adsorbents were characterized and named smectite/adsorbed dye (Sm/Dye) and copper smectite/adsorbed dye (Cu-Sm/Dye); and they were applied as hybrid pigments with antimicrobial action. The Sm and Cu-Sm were characterized by X-ray diffractometry (XRD), energy dispersive X-ray fluorescence (EDXRF), vibrational spectroscopy (FTIR), Zeta potential (ζ), scanning electron microscopy (SEM), and colorimetry (CIE L*a*b*), enabling the identification of the presence of intercalated copper ions and on the smectite surface. The adsorption assays were carried out to evaluate the effects of initial dye concentration and contact time. Tests for application as a hybrid pigment showed good compatibility with commercial white paint being applied on plaster blocks and later photoaging and chemical stability tests were performed in acid and basic environments, both were discussed by colorimetry (CIE L*a*b*), thus being able to relate it to the color variation (∆E). The samples (Sm, Cu-Sm, Sm/Dye, and Cu-Sm/Dye) were dispersed in white paint at 10% and 20% (% w/w) to evaluate the ability to inhibit different microorganisms. The modification with copper ions promoted an increase in the adsorptive capacity relative to the raw smectite and provided antibacterial and antifungal action to the hybrid pigment against Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Candida albicans. The Cu-Sm and Cu-Sm/Dye samples showed excellent results against all studied microorganisms and reveal successful materials that can be used in environments that require microbiological protection.

Biodiesel is nowadays added in 5–10% v/v to diesel, and its production involves the parallel creation of a vast glycerol amount as a by-product. Despite its many applications, there is a surplus of glycerol (Gly) that has boosted the search for new applications of this compound, now transformed into an industrial synthesis intermediate or platform chemical. Its transcarbonation is a type of reaction that occurs under mild conditions, using weak or moderate basic catalysts, and allows the parallel production of glycols of industrial interest with high selectivity, such as ethylene glycol. In this research, we have studied the activity of a Tunisian clay rich in inorganic carbonates that give it a weak basic character. The raw clay (RC) has been fully characterized by XRD, FTIR, SEM-EDS and nitrogen porosimetry. Subsequently, it has been employed as a catalyst to react glycerol (G) with ethylene carbonate (EC) to obtain glycerol carbonate (GC) and ethylene glycol (EG). The main operating variables and their effects on glycerol conversion and initial reaction rate were analyzed: catalyst concentration (2–6% w/w glycerol), reagent molar ratio (EC:G 1.5:1 to 3:1), and temperature (80–110 °C). Then, an appropriate kinetic model was selected from the results obtained under various reaction conditions, including the total deactivation of order 1 of the catalyst. The kinetic constant activation energy in this reaction using Tunisian smectite was found to be around 183.3 kJ·mol−1. In the second phase of the investigation, we explored the reuse of smectite using the kinetic model to appreciate the effect of cycle-to-cycle deactivation. It can be seen that the kinetic constant of the main reaction generally decreases with the number of cycles at low temperature and goes through a maximum at high operating temperature, while the deactivation constant increases with the number of catalytic cycles. The catalyst shows more stability, in general, at higher temperatures.

Smectites, like other clay minerals, have been shown to promote ice nucleation in immersion freezing mode and likely contribute to the population of ice nucleating particles (INPs) in the atmosphere. Smectites are layered aluminosilicates, which form platelets that depending on composition might swell or even delaminate in water by intercalation of water molecules between their layers. They comprise among others montmorillonites, hectorites, beidellites, and nontronites. In this study, we investigate the ice nucleation (IN) activity of a variety of natural and synthetic smectite samples with different exchangeable cations. The montmorillonites STx-1b and SAz-1, the nontronite SWa-1, and the hectorite SHCa-1 are all rich in Ca2+ as the exchangeable cation, the bentonite MX-80 is rich in Na+ with a minor contribution of Ca2+, the synthetic Laponite is a pure Na+ smectite. The bentonite SAu-1 is rich in Mg2+ with a minor contribution of Na+, and the synthetic interstratified mica-montmorillonite Barasym carries NH4+ as the exchangeable cation. In emulsion freezing experiments, all samples except Laponite exhibited one or two heterogeneous freezing peaks with onsets between 239 K and 248 K and a quite large variation in IN activity, yet without clear correlation with the exchangeable cation, with the type of smectite, or with mineralogical impurities in the samples. To further investigate the role of the exchangeable cation, we performed ion exchange experiments. Replacing NH4+ with Ca2+ in Barasym reduced its IN activity to the one of other Ca-rich montmorillonites. In contrast, stepwise exchange of the native cations in STx-1b once with Y3+ and once with Cu2+ showed no influence on IN activity. However, aging of smectite suspensions in pure water up to several months revealed a decrease in IN activity with time, which we attribute to the delamination of smectites in aqueous suspensions, which may proceed over long timescales. The dependence of IN activity on platelet stacking and thickness can be explained if the hydroxylated chains forming at the edges are the location of ice nucleation in smectites, since the edges need to be thick enough to host a critical ice embryo. We hypothesize that at least three smectite layers need to be stacked together to host a critical ice embryo on clay mineral edges and that the larger the surface edge area is the higher the freezing temperature. Comparison with reported platelet thicknesses of the investigated smectite samples suggests that the observed freezing temperatures are indeed limited by the surface area provided by the mostly very thin platelets. Specifically, Laponite, which did not show any IN activity, is known to delaminate into single layers of about 1 nm thickness, which would be too thin to host a critical ice embryo. [ABSTRACT FROM AUTHOR]

Understanding the behavior of secondary minerals under alkaline conditions is important for predicting the potential alteration of the constituent minerals in radioactive-waste disposal facilities. A previous study reported the formation of uncommon Fe- and Mg-bearing clays under natural alkaline conditions in the Philippines; these were referred to as iron-magnesium-silicate-hydrates (F-M-S-H) and nontronite-like minerals. The current study aimed to investigate the structural and chemical characteristics and to understand the formation pathways of these clays by performing a detailed characterization. F-M-S-H comprised tetrahedral–octahedral–tetrahedral (TOT) layers, imperfect interlayer hydroxide sheets, and interlayer Ca ions. The systematic changes in the characteristics of F-M-S-H at different sampling depths, such as the gradual decrease of the interlayer hydroxide sheets to form smectitic domains, were caused by the differing interaction periods between each sediment at different sampling depths and alkaline seepage. Furthermore, F-M-S-H was ferrous in form prior to oxidation. In contrast, a nontronite-like mineral comprised nontronite and part of an interlayer hydroxide sheet. This mineral was inferred to be formed under chemically different conditions from F-M-S-H, and probably formed in the presence of aqueous Fe3+ and Mg ions. [ABSTRACT FROM AUTHOR]

Atmospheric mineral dust is derived from arid/semi-arid region, undergoes long-range transport, and can impact surface biogeochemical processes in the pristine marine region. This study reports fluxes of mineral dust (wet and dry deposition), their clay mineralogy, and associated seasonal variability over the Northeastern Arabian Sea. Dust sources are assessed using mineral composition and their ratios as well as satellite retrievals during 2012–2015. The average wet deposition flux (293 mg m−2 day−1) of mineral dust is three times higher than dry deposition flux (96 mg m−2 day−1). A clear distinction is observed in the mineral composition of wet and dry deposited dust with smectite and palygorskite being dominant during the wet period and illite and chlorite being dominant during the dry period. Mineralogical composition and their ratios indicate that major dust sources to the Northeastern Arabian Sea are from northeast Africa, Arabian Peninsula, and southwest Asia. These observations are corroborated with the satellite retrievals, aerosol optical depth, and back trajectory analyses. [ABSTRACT FROM AUTHOR]

Lithofacies belonging to mud-flat and palustrine deposits (lake margin) in the Miocene of the Madrid Basin (Spain) have been studied. Four lithofacies corresponding to mud flat (1 and 3) and palustrine (2 and 4) deposits have been differentiated. Units 1 and 3 consist mainly of mudstones and carbonates (calcretes and diolocretes). The clay fraction is dominated by trioctahedral smectite (up to 79%) with illite and kaolinite as minor components. The d(060) spacing value shows reflections at 1.52 and 1.50 Å indicating also the presence of dioctahedral phyllosilicates. Unit 2 consists predominantly of lutites (claystones), locally with carbonate and chert nodules. The clay fraction is dominated by sepiolite (up to 96%) with variable contents of smectite and subordinate illite. The d(060) spacing value shows reflections at 1.51 and 1.52 Å indicating trioctahedral clay minerals. Unit 4 consists mostly of carbonates (limestones) with mudstone and lutite inserts. The clay fraction shows different contents of sepiolite, palygorskite and dioctahedral smectite. The analysis of a selection of trace elements (Cr, Co, Th, La, Sc) has allowed us to determine the characteristics of the source area as dioritic, somewhat different from those of the nearby materials from the Batallones sector. Sepiolite shows FWHM values ranging between 0.68 and 1.10 (2θ), indicating "low crystallinity sepiolite". Differences in the conditions of formation of magnesian smectite and palygorskite have been observed in the mud-flat and palustrine deposits. The formation of sepiolite mainly by neoformation in palustrine deposits with different hydrochemistry is remarkable, leading to differences in fibre size and crystallinity of the fibrous clay mineral. Authigenic transformation processes from previous Al-rich phases would be responsible for the formation of saponite and palygorskite in mud flat and palustrine environments, with different pH conditions. [ABSTRACT FROM AUTHOR]

The arrangement of bisphenol A molecules into organoclays and their interactions with the intercalated surfactant were studied. The organoclays were prepared via solid-state intercalation of four cationic surfactants, such as dodecyltrimethyl-, tetradecyltrimethyl-, hexadecyltrimethyl-, and didodecyldimethyl-ammonium, as bromide salts, at different loading levels into the interlayers of two natural clays. The natural clays, the prepared organoclays, and the spent organoclays were characterized by X-ray powder diffraction, infrared spectroscopy, and scanning electron microscopy. X-ray powder diffraction measurements showed successive interlayer expansions of the d001 basal spacing due to the intercalation of the cationic surfactants and the bisphenol A sorption. The increased d001 basal spacing of the organoclays after bisphenol A sorption indicates that the molecules are integrated between the alkyl chains of the surfactant in the organoclays interlayers. Infrared spectroscopy was employed to probe the intercalation of the cationic surfactants and the sorbed bisphenol A. New characteristic bands attributed to the bisphenol A phenol rings appear in the range 1518–1613 cm−1 on the infrared spectra of the spent organoclays, proving the presence of bisphenol A in the hydrophobic interlayers. Scanning electron microscopy of the organoclays before and after BPA sorption shows that their morphology becomes fluffy and that the presence of the organic molecules expands the clay structure. [ABSTRACT FROM AUTHOR]

Based on molecular dynamics (MD) and density function theory (DFT) simulation, the adsorption mechanisms of Cs+ and Sr2+ on the illite/smectite(I/S) were investigated. The results show that the adsorption of Cs+ is mainly located in the planar sites(PS) and edge sites(ES) of I/S, whereas Sr2+ adsorption occurs primarily in the planar sites(PS) and interlayer sites(IS) of I/S. The adsorption of Cs+ on illite/smectite is mainly the result of the hybridization of p-p and p-d orbitals between Cs+ ions and Si/Al-O tetrahedra. In the coexistence of Cs+ and Sr2+, Sr2+ occupies the central adsorption site on the surface. [ABSTRACT FROM AUTHOR]

Exploring the sensitivity of reservoir is the foundation of oil and gas exploration and exploitation. The damage degree of water sensitivity is affected by the clay mineral content and microscopic pore throat structure of the illite/smectite mixed layer. This study proposed a method for reservoir characterization based on digital core technology to reveal the influence of clay mineral content and micropore structure on the production of the illite/smectite mixed layer. The micropore throat characteristic parameters of the reservoir were obtained by using high-resolution micro computed tomography technology. The mineral quantitative analysis technology was used to determine the clay mineral content of the illite/smectite mixed layer. The distribution characteristics, pore radius distribution characteristics, throat length distribution characteristics, shape factor, and coordination number of the clay minerals of the illite/smectite mixed layer of the glutenite reservoir were analyzed. With the Upper Wuerhe Formation in Mahu Depression as an example, the accuracy of the proposed evaluation method was verified on the basis of the production data. Results show that the clay mineral content in the illite/smectite mixed layer and the increase in production are negatively correlated. The output of the area with the clay mineral content less than 30% in the illite/smectite mixed layer gradually increases. High-quality reservoir has the following microscopic pore throat characteristics: the distribution frequency of coordination number 5 exceeds 0.12, the average pore radius is greater than 6.34 µm, and the average throat length is greater than 8.58 µm. This study provides new technical methods and study ideas for understanding the sensitivity characteristics of glutenite reservoirs. [ABSTRACT FROM AUTHOR]

The new Luxor city was proposed by the Egyptian government as a new constructional and building site in order to face the increasing population density around the two banks of the river Nile. It is important prior construction of buildings to characterize the foundation soil. So, vertical electrical resistivity survey and mineralogical investigation were conducted for this purpose. The results obtained from the interpretation of the sounding data indicate that the lithological succession of the study area consists of four geoelectric layers. The top layer corresponds to the surface loose sediments of conglomerate, gravel, and sand. The second geoelectric layer is composed of sand and gravel. The third layer is composed of silty clay, sandy clay, and clayey sand. The fourth geoelectric layer is composed of dry sandstone. The X-ray diffraction (XRD) results of samples collected from the clay-rich layer revealed the presence of smectite mineral as predominate clay minerals which is characterized by its swell potentiality on wetting. Accordingly, the clay zone recorded within the third layer must be taken into consideration during designing the foundations at new Luxor city especially this layer was located at shallow depth range between 1.6 and 7.5 m and attains a relatively big thickness that reach up to 33.5 m in some parts. This study emphasizes the importance of the integration of geophysical investigation and mineralogical analysis of the foundation soil for optimal characterization of a site. [ABSTRACT FROM AUTHOR]

In this study, a detailed characterization of the clayey waste of the Kırka boron plant was undertaken before the development of a sulfuric acid roasting-water leaching process for the extraction of lithium from this waste. The effects of roasting temperature (650-800°C) and sulfuric acid/waste ratio (90-260 kg H2SO4/1000 kg waste on a dry basis) on the extraction of lithium were investigated. By roasting the waste sample, which contained 0.37% Li2O with dolomite, smectite and borax as the main phases, at temperatures between 650°C and 800°C in the absence of sulfuric acid as the additive, CaMgSiO4 was found to form as the dominant phase after the decomposition of dolomite and smectite present in the sample. On the other hand, the X-ray diffraction analyses of the waste sample subjected to sulfuric acid treatment without roasting showed the in-situ formation of various hydrated calcium sulfate phases for all sulfuric acid/waste ratios tested. Besides, at the highest acid/waste ratio of 260, a hydrated magnesium sulfate phase was also identified in the sample. The application of the sulfuric acid roasting-water leaching process under the optimum roasting temperature of 750°C and the acid/waste ratio of 180 was found to lead to a lithium extraction of 85.7%. The applied sulfuric acid roasting-water leaching process appeared to be an attractive process with its attributes including low roasting temperature, high extraction percentage and no requirement for gypsum as the external sulfation agent. [ABSTRACT FROM AUTHOR]

Analyses of clay minerals within the Early Cretaceous Weald Basin, Southeast England reveal kaolinite, illite and chlorite as the main detrital clay minerals while glauconite and smectite are subordinates. A kaolinite-rich assemblage which characterized the sand-dominated Ashdown and Tunbridge Wells Sand formations and an illite-dominated assemblage associated mostly with the Wadhurst Clay and Weald Clay formations are recognized. Kaolinite was enriched in the Ashdown and Tunbridge Wells Sand formations during warm and humid climate with high precipitation that encouraged chemical weathering and leaching, while cold and dry conditions favoured the concentration of illite in the Wadhurst Clay and Weald Clay formations. Rainfall patterns associated with warm climate were drastically reduced during the drier climatic conditions. Most clay minerals are detrital in origin, with chlorite being more prominent than previously recognized. Contrary to previous studies and assumptions, this study revealed that authigenic clay minerals are present in the Hastings Beds, with vermiform and mica-replacive kaolinite being the most common, consistent with humid depositional environments. Isolated authigenic illite is also present, along with a chloritized grain, providing evidence for mesodiagenesis. The absence of dickite and occurrence of kaolinite, suggest that authigenic illite formed in relatively shallow burial conditions, indicating a maximum burial depth of 2500 m–3000 m, about 1000 m deeper than previous estimates of 1500 m–2000 m. Authigenic clay minerals are absent in the Weald Clay Formation possibly because of hindered flow of meteoric water and limited growth space for authigenic minerals. This study is significant in: 1) reinforcing multiple methods to facilitate a robust and balanced knowledge of formation and transformation of clay minerals; 2) investigating detrital and authigenic clay mineral assemblages when assessing the palaeoenvironments of sedimentary basins. [ABSTRACT FROM AUTHOR]

In this study, the He gas permeability of films made of natural smectite and butenediol vinyl alcohol copolymers, which are polymers with high gas barrier properties, was measured in a wide range of compositions from 100% natural smectite to 100% polymer between 40°C and 160°C. The gas permeation behavior was discussed in terms of activation energy. Since butenediol vinyl alcohol copolymers form intra/intermolecular hydrogen bond networks, it was found that the activation energy of gas permeation is reduced by the addition of clay, which may be due to the suppression of the mobility of polymer molecules by clay. Moreover, the gas barrier deterioration was more suppressed with high temperature than with the polymer alone. The calculated gas permeability of the 25-µm coating layer at 160°C was less than 10 mL m−2 day−1 bar−1 in the polymer range of 10–40 wt%, indicating excellent gas barrier properties even at high temperatures. [ABSTRACT FROM AUTHOR]

In the last decades, clays have been used in sectors such as health and cosmetics. This requires products that are increasingly pure and present homogeneous properties, hardly found in natural clays. The use of synthetic clays can be a solution. For this, it is necessary to explore techniques for their production. The main focus of this study was to synthesize a smectite clay in a simple, fast and economic way at low temperature and pressure, called static and dynamic methods. To regulate the pH of the reaction and bring it closer to the ideal synthesis conditions, two different acids were used: nitric acid (the most widely used in the literature) and hydrochloric acid (more accessible and cheaper). The results showed characteristics of uniform crystalline material with a porous structure similar to that of the smectite group. Small particle sizes of approximately 100 nm were observed by scanning electron microscopy. Stevensite clay was obtained by both synthesis methods using two different acids; the static method with hydrochloric acid stood out. The greater practicality in its development provides a more viable option for large-scale industrial production. [ABSTRACT FROM AUTHOR]

The hydro-swelling of smectite clay minerals in low-permeability reservoirs further decreases the reservoir permeability and results in low oil recovery. Currently, the traditional chemical anti-swelling agents are widely used, but most of them are only effective in the short term and are not environmentally friendly. Here, we report the use of Fe(III) reducing microorganisms (FeRM) as a novel green anti-swelling agent to enhance oil recovery from low-permeability reservoirs. The results showed that FeRM (Proteus hauserifective) inhibited/reduced the hydro-swelling of smectite clay minerals through a three-step biochemical mineralization reaction process. The structural Fe(III) reduction in minerals by FeRM can be an important driving force for illitization. The maximum inhibition efficiency (36.6%) and shrinkage efficiency (69.3%) were achieved at 35 °C and 0.1 Mpa. Furthermore, core displacement tests showed that FeRM reduced the waterflooding injection pressure by 61.1%, increased the core permeability by 49.6%, and increased the oil recovery by 8.1%. Finally, the mechanism of FeRM-enhanced oil recovery was revealed. This study demonstrates that using FeRM to inhibit/reduce the hydro-swelling of clay minerals holds great potential to enhance the oil recovery from low-permeability reservoirs. [ABSTRACT FROM AUTHOR]

We conduct frictional experiments using cuttings collected at Nankai Trough IODP Site C0002 over 980.5–3262.5 mbsf (meters below seafloor) depth interval to better understand the frictional properties through the accretionary prism. The experiments are conducted at the in situ effective normal stresses (9–37 MPa) under brine-saturated conditions, and the slip velocity is abruptly changed in a stepwise manner to either of 0.3, 3, or 33 µm/s after the steady-state friction is reached. The friction coefficient (μ) of the cuttings samples ranges from 0.45 to 0.60, with a slight increase in μ with increasing depth, related to decreasing smectite content. The velocity dependence of friction (a − b) is positive at all depths and ranges from 0.001 to 0.006, which indicates a velocity-strengthening behavior; these values are consistent with relatively homogeneous deformation microstructures. The critical slip distance (Dc) ranges from 0.5 to 123 μm, with relatively large values obtained for the smectite-rich samples. The changes in both the friction coefficient and rate- and state-friction parameters are likely associated with mineralogical change and consolidation with increasing depth. Although all of the cuttings samples collected from Site C0002 exhibit a velocity-strengthening behavior, a slight decreasing trend in a − b with increasing depth indicates either a nearly neutral velocity dependence or a possible transition to velocity-weakening behavior at greater depths, which may be attributed to the occurrence of slow earthquakes in the Nankai accretionary prism. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To evaluate the effect of diosmectite on visceral hypersensitivity and intestinal transit in a rat chronic stress model and on the faecal microbiota. MATERIALS AND METHODS: Wistar rats (175-225 g; n=10) were randomized into four groups: diosmectite/control, diosmectite/stress, vehicle/control, and vehicle/stress. Diosmectite (500 mg/kg, PO) was administered for five days for assessment of visceral hypersensitivity and intestinal transit and for three weeks for assessment of faecal microbiota. The stress procedure was a daily chronic passive water avoidance session. Intestinal transit was evaluated by faecal output in the hour following the last stress session. Visceral sensitivity in response to colorectal distension (CRD) was assessed at baseline and 30 min after the last stress session. In another group of rats, faecal material was collected before and after treatment with diosmectite or vehicle; genomic DNA was extracted and sequenced to characterize the faecal microbiota. RESULTS: Under nonstressed conditions, diosmectite treatment did not modify intestinal transit compared to the vehicle group (p=0.33). After the stress procedure, a trend towards reduction in stress-induced stool production was observed with diosmectite compared to vehicle (6.3±1.1 vs. 4.9±1.2 respectively; p=0.38). In the control condition, the number of CRD-evoked abdominal contractions was 20±4 after diosmectite and 24±2 after vehicle (p=0.75). In the stressed condition, the number of contractions increased to 34.4±2.4 after vehicle (p<0.05 compared to control). Stress-related hypersensitivity was attenuated after diosmectite treatment (26.9±2.2; p<0.05 compared to vehicle). No relevant changes were observed in the faecal microbiotic profile after treatment with diosmectite or vehicle. CONCLUSIONS: Diosmectite treatment attenuates stress-induced visceral hypersensitivity; this effect may contribute to the therapeutic effect of diosmectite in IBS in humans. [ABSTRACT FROM AUTHOR]

The chemical structure of different soil organic matter (OM) pools in water-stable macro- and free microaggregates isolated from the surface horizons of Haplic Chernozem in contrasting variants of land use (steppe and long-term bare fallow) is studied using solid-state 13C-NMR spectroscopy. It is observed that the degree of OM protection increases with a decrease in the size of structural units, which is confirmed by integral characteristics of OM chemical structure, such as lower degrees of OM decomposition, aromaticity, and hydrophobicity of microaggregates as compared with macroaggregates. A negative effect of the long-term bare fallow regime causes a sharp increase in the integral indicators of the chemical structure in all studied OM pools, being more pronounced in free microaggregates. The proposed multiple linear regression models for the C/N value prediction ( = 0.993, P < 0.05 for discrete (free and occluded) OM and = 0.996, P < 0.05 for the clay-bound OM and the residue fraction) clearly explain its increase in the bare fallow, reflecting the maximum nitrogen losses in OM, which in its status approaches the degraded one. According to the proposed model, the size of clay particles is determined by a set of factors. The best model with all its parameters being significant ( = 0.997, P < 0.05) clearly demonstrates that the average diameter of clay particles increases with a decrease in the amount of OM hydrophobic fragments, the share of smectites in clay, and increase in the content of the clay-bound carbon. [ABSTRACT FROM AUTHOR]

Simultaneous removal of mycotoxins has been poorly addressed, and a limited number of studies have reported the efficacy of feed additives in sequestering a large spectrum of mycotoxins. In this study, a new mycotoxin-adsorbing agent was obtained by properly mixing a tri-octahedral smectite with a lignocellulose-based material. At a dosage of 1 mg mL−1, these materials simultaneously adsorbed frequently occurring mycotoxins and did not exert a cytotoxic effect on intestinal cells. Chyme samples obtained by a simulated GI digestion did not affect the viability of Caco-2TC7 cells as measured by the MTT test. In addition, the chyme of the lignocellulose showed a high content of polyphenols (210 mg mL−1 catechin equivalent) and good antioxidant activity. The properties of the individual constituents were maintained in the final composite, and were unaffected by their combination. When tested with a pool of seven mycotoxins at 1 µg mL−1 each and pH 5, the composite (5 mg mL−1) simultaneously sequestered AFB1 (95%), FB1 (99%), ZEA (93%), OTA (80%), T-2 (63%), and DON (22%). HT-2 adsorption did not occur. Mycotoxin adsorption increased exponentially as dosage increased, and occurred at physiological pH values. AFB1, ZEA and T-2 adsorption was not affected by pH in the range 3–9, whereas OTA and FB1 were adsorbed at pH values of 3–5. The adsorbed amount of AFB1, ZEA and T-2 was not released when pH rose from 3 to 7. FB1 and OTA desorption was less than 38%. Langmuir adsorption isotherms revealed high capacity and affinity for adsorption of the target mycotoxins. Results of this study are promising and show the potential of the new composite to remove mycotoxins in practical scenarios where several mycotoxins can co-occur. [ABSTRACT FROM AUTHOR]

The use of clays as resource of supplementary cementitious materials (SCMs) for a new generation of low-carbon cements and concretes is currently the subject of intense research efforts. To this purpose, a large number of clay resources have been explored, characterized and evaluated. This paper introduces the basic knowledge and concepts on clay occurrence and clay mineralogy, before presenting up-to-date knowledge on properties and occurrence of clay resources suitable for use as SCMs. Occurrence, distribution and chemical and mineralogical selection criteria are discussed for kaolinitic clays, which often show superior reactivity and performance. 2:1 clay mineral resources have received somewhat less attention as SCM resources, however recent developments indicate significant potential for calcined impure common clays, and are reviewed. An overview of ubiquitous clay mineral-bearing waste materials also identifies important opportunities for alternative clay sourcing in mining or extraction residues, and dredged or excavated sediments. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the oxalic acid activation of bentonites containing different types of smectites, analyse their surface modification as a function of acid concentration and create good quality bleaching earths. In particular, two different bentonite samples (one containing aluminum and one containing ferruginous smectite), after being characterized through XRD, XRF and FT-IR analysis, are treated with oxalic acid at a concentration of 0.5, 0.7 and 1 M. Their structural modifications after treatment are observed through FT-IR spectra and surface area and porosity measurement (using the BET equation and the BJH method, respectively) combined with the determination of the main structural metals' extraction from them (using an atomic adsorption spectrometer). The results showed that the ferruginous smectite is more susceptible to oxalic acid activation compared to the aluminum smectite, and all the final products have developed extra porosity in their structure while retaining the structure of smectite (even at 0.5 M acid concentration). The activated samples were used as bleaching earths in soybean oil, and the results proved that Lovibond yellow and red colours as well as the chlorophyll of oil (measured spectrophotometrically) were reduced to the values set by the specifications. [ABSTRACT FROM AUTHOR]

Gypsiferous soils contain sufficient gypsum to influence soil physico-chemical, mineralogical, mechanical properties and geotechnical conditions and as a consequence, affect plant growth and crop production. So physico-chemical and mineralogical properties of 6 soil profiles located on the gypsiferous parent material with semi-arid climate in north of Urmia, West Azerbaijan province, Iran, were investigated. Based on standard methods, morphological, physico-chemical and mineralogical properties of these soils were determined. Soils with higher gypsum content had lighter color, lighter texture, lower values of organic carbon and cation exchange capacity and higher values of electrical conductivity. These parameters were reversely changed with decreasing gypsum content of soils. Semi-quantitative analysis of clay minerals indicated the presence of smectite, illite, chlorite, kaolinite and palygorskite were as major clay minerals with decreasing order from smectite to palygorskite. The origin of illite, chlorite and kaolinite were related to the inheritance from parent material. Smectite group of clay minerals has been resulted from three origins of inheritance from parent material, transformation of illite and palygorskite and neoformation, but the transformation and neoformation are the main pathways for its formation. Palygorskite has pedogenic origin and has been formed via neoformation. The comparison of clay mineralogy of soils with different gypsum values revealed the presence of higher smectites in soils with higher gypsum. Palygorskite was identified just in soils with higher gypsum. In soils with lower values of gypsum, illite and chlorite were the predominant clay minerals and palygorskite did not identified.

Background and aims: The pathophysiology of SARS-CoV-2-associated diarrhea is unknown. Using an experimental model validated for rotavirus-induced diarrhea, we investigated the effects of SARS-CoV-2 on transepithelial ion fluxes and epithelial integrity of human intestinal cells. The effect of the antidiarrheal agent diosmectite on secretion was also evaluated following its inclusion in COVID-19 management protocols. Methods: We evaluated electrical parameters (intensity of short-circuit current [Isc] and transepithelial electrical resistance [TEER]) in polarized Caco-2 cells and in colonic specimens mounted in Ussing chambers after exposure to heat-inactivated (hi) SARS-CoV-2 and spike protein. Spectrofluorometry was used to measure reactive oxygen species (ROS), a marker of oxidative stress. Experiments were repeated after pretreatment with diosmectite, an antidiarrheal drug used in COVID-19 patients. Results: hiSARS-CoV-2 induced an increase in Isc when added to the mucosal (but not serosal) side of Caco-2 cells. The effect was inhibited in the absence of chloride and calcium and by the mucosal addition of the Ca2+-activated Cl– channel inhibitor A01, suggesting calcium-dependent chloride secretion. Spike protein had a lower, but similar, effect on Isc. The findings were consistent when repeated in human colonic mucosa specimens. Neither hiSARS-CoV-2 nor spike protein affected TEER, indicating epithelial integrity; both increased ROS production. Pretreatment with diosmectite inhibited the secretory effect and significantly reduced ROS of both hiSARS-CoV-2 and spike protein. Conclusions: SARS-CoV-2 induces calcium-dependent chloride secretion and oxidative stress without damaging intestinal epithelial structure. The effects are largely induced by the spike protein and are significantly reduced by diosmectite. SARS-CoV-2 should be added to the list of human enteric pathogens.

Mineral carbonation of alkaline mine residues is a carbon dioxide removal (CDR) strategy that can be employed by the mining industry. Here, we describe the mineralogy and reactivity of processed kimberlites and kimberlite ore from Venetia (South Africa) and Gahcho Kué (Canada) diamond mines, which are smectite-rich (2.3–44.1 wt.%). Whereas, serpentines, olivines, hydrotalcites and brucite have been traditionally used for mineral carbonation, little is known about the reactivity of smectites to CO2. The smectite from both mines is distributed as a fine-matrix and is saponite, Mx/mm+Mg3(AlxSi4−x)O10(OH)2·nH2O, where the layer charge deficiency is balanced by labile, hydrated interlayer cations (Mm+). A positive correlation between cation exchange capacity and saponite content indicates that smectite is the most reactive phase within these ultramafic rocks and that it can be used as a source of labile Mg2+ and Ca2+ for carbonation reactions. Our work shows that smectites provide the fast reactivity of kimberlite to CO2 in the absence of the highly reactive mineral brucite [Mg(OH)2]. It opens up the possibility of using other, previously inaccessible rock types for mineral carbonation including tailings from smectite-rich sediment-hosted metal deposits and oil sands tailings. We present a decision tree for accelerated mineral carbonation at mines based on this revised understanding of mineralogical controls on carbonation potential.

In uniaxially stretched films, the refractive indices perpendicular to the stretching direction have the same value, and so, the out-of-plane birefringence is half that of the in-plane birefringence. This means that these values cannot be controlled independently in uniaxially stretched films. The same relationship was previously observed when needle-shaped nanoparticles were added to uniaxially stretched films. This paper presents a method to achieve the three-dimensional birefringence control of uniaxially stretched films. When we added plate-shaped smectite nanoparticles to uniaxially stretched films, different relationships were observed for the in- and out-of-plane birefringence. The magnitude of the out-of-plane birefringence increased more than would be expected according to the usual relationship. According to our results, uniaxially stretched films with no out-of-plane birefringence and negative in-plane birefringence can be formed by adding smectite nanoparticles to polymer films with negative in-plane birefringence. Using our method, the three-dimensional birefringence of uniaxial polymers can be controlled, and the possibility of the uniaxial films could be drastically extended. [ABSTRACT FROM AUTHOR]

The results of the adsorption study of methylene blue dye as the low molecular weight toxins marker from its aqueous solutions by carbon, silicon and polymer enterosorbents are presented. It has been shown that the activated carbons modification by water-soluble cellulose polyelectrolyte makes it possible to increase their adsorption capacity. The applicability of Langmuir, Freundlich, Temkin and Redlich – Peterson adsorption models for the approximation of experimental adsorption isotherms of methylene blue on the enterosorbents has been estimated. It has been established that the three-parameter Redlich – Peterson equation describes this process better than others. This was evident from the comparison of the regression coefficients, constants and parameters values of these equations.

The Sinanpaşa basin, one of the Neogene basins formed in the extensional tectonic regime in Western Anatolia, is located on the eastern margin of Western Anatolia basins containing different types of evaporites, lignite, uranium and clay minerals. Miocene sequence was initiated with alluvial fan- fluvial units and followed by lacustrine sediments. River floodplains and lakeshore marshes locally contain economic coal levels. Since middle-late Miocene, the products of Afyon volcanism were deposited into a subaerial or a subaqueous environment alternating with lake sediments. Dominant clay minerals are illite and smectite within the sediments coexistence with the volcanics. These minerals were accompanied by chlorite, kaolinite, and zeolite in some samples. Feldspar, dolomite, thenardite, and gypsum are locally observed too. Sepiolite mineral enrichments are also noteworthy in shallow-coastal lacustrine environments where organic matter is abundant. Clay minerals are mostly detritic and developed due to the weathering of volcaniclastics and sedimentary rocks in temperate/humid climatic conditions. In particular, smectite and kaolinite minerals were formed in situ/authigenic under subaqueous conditions due to the acidic/basic character of tuffs. As a result, different clay mineral types have been developed due to the mineralogical composition of source rocks, climatic factors (humid/semi-humid, arid), paleotopography, depositional environment and diagenetic factors.

In this work, hybrid materials were prepared from natural clay (ARC) and algae Codium fragile (COD), using two different heating methods, one conventional (ARCCOD E) and the other with microwaves (ARCCOD MO). The characterization of the materials obtained was carried out by XRD and FT-IR. The results show appreciable differences of the hybrids in relation to the starting materials, indicating in both cases a possible intercalation of water and COD biomass in the ARC structure, which is more evident in ARCCOD E. The microwave effect would produce a higher degree of delamination in ARCCOD MO, while in ARCCOD E, the original ARC structure would seem to be more preserved. Preliminary tests show oil sorption capacities of the hybrids similar to the starting materials.

Shale belongs to low-porosity and low-permeability reservoir, so it is difficult for fluid to enter pores through displacement. However, in the process of shale hydraulic fracturing, most of the fracturing fluid does not flowback after entering strata. It indicates that reaction may take place when fluid enters into strata, resulting in low flowback rate of fracturing fluid. Imbibition experiment and physicochemical properties test show that there is imbibition effect in shale. There are two stages: one is the initial rapid water absorption, while the other is later osmotic water absorption. The first stage is affected by the seam network system, while the other stage is mainly affected by the content of clay minerals. As clay minerals swell by absorbing water, the original fracture network system gradually expands, and porosity grows, permeability improves and recovery rate increases. The physicochemical properties test shows that (1) imbibition is influenced by both capillary force and mineral components. The higher the clay content is, especially the content of chlorite and illite/smectite (I/S) , the stronger the imbibition capacity is. (2) Shale with strong imbibition capacity also has strong seam-making capacity, which not only provides convenience for hydraulic fracturing but is more conducive to exploitation. [ABSTRACT FROM AUTHOR]

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Accurate determination of clay minerals can be challenging due to the natural occurrence of interlayered phases, i.e., layers of different clay species such as illite and smectite. The overlap of peaks of the constituent minerals (e.g., illite and smectite), and the similarity of diffraction patterns when not treated with ethylene glycol, hampers identification, especially when the clay content is low. We investigated the occurrence of interlayered illite/smectite in a rock sample from Rodalquilar, Spain, using X-ray diffraction, scanning electron microscopy and reflectance spectroscopy in the short-wave infrared wavelength range. For the first time, a precise determination of interlayered I/S conducted on the extracted clay fraction treated with ethylene glycol using such different approaches was provided. X-ray diffraction results demonstrated the presence of an I/S peak at around 8.4° in the untreated fraction coupled with a peak splitting at 6.7° and 9.4° 2θ when solvated with ethylene glycol. While spectroscopy indicated the occurrence of interlayered structures as a mixture of the two constituent minerals, the results of X-ray analysis showed that the interlayered clay consisted of two discrete phases (illite and smectite). The two discrete phases were observed in both the whole rock analysis and in the extracted clay fraction. This study shows that X-ray diffraction and validation with a scanning electron microscope is a mandatory, integrating tool for detecting interlayered phases since reflectance spectroscopy alone cannot be used to differentiate between interlayered clay minerals and non-interlayered mixtures. This work highlights the limits and advantages of three sensors (X-ray diffraction, scanning electron microscopy and reflectance spectroscopy) to investigate clay mixtures and interlayering, representing a significant contribution to confidence in the interpretation of interlayered clays, this being essential in mineral exploration and prospecting. [ABSTRACT FROM AUTHOR]

Smectites are common clay minerals in surface and near surface terrestrial environments and have recently been shown to be ubiquitous on Mars. Because these minerals are products of water-rock interaction, the thermodynamics of their interaction with fluids constitutes a vital part of resolving the utility of smectite mineralizations as petrogenetic and paleoenvironmental indicators on both Mars and Earth's near surface environments. Smectites, and other clay minerals of comparable compositional complexity, have been purported to be disequilibrium solids whose complexity derives from steep chemical gradients in their environments of formation rather than from crystal-chemical constraints. Solubility investigations of several natural smectites wherein none exhibited the predicted inverse correlation between pH-1⁄3pAl and pSi(OH)4 were adduced by May et al. (1986) as empirical proof of the disequilibrium solid concept, and hence they asserted unequivocally that "it is obviously impossible to obtain valid ion activity quotients for smectite solubilities in these systems." However, the unattainability of equilibrium smectite solubility in those experimental systems was probably an artifact of the extremely high fluid-to-solid ratios employed therein. In subsequent experimental studies using significantly lower fluid-to-solid ratios, smectite-fluid interactions (Kittrick and Peryea 1989; Gaboreau et al. 2020), and chlorite-fluid interactions (Aja and Dyar 2002) yielded solubility data amenable to laws of chemical thermodynamics and thus invalidated the disequilibrium solid model. Therefore, the notion of smectite metastability and/or instability anchored on the disequilibrium solid model is false and warrants a more constrained definition of smectite metastability. [ABSTRACT FROM AUTHOR]

Smectite clays such as acid clay or bentonite have various characteristic values such as the adsorption amount of methylene blue (MB adsorption amount), the amount of exchangeable cations (Na+, K+, Mg2+, Ca2+) or the cation-exchange-capacity (CEC). Generally, the MB-adsorption amount has been quantified by the standard test method (JBAS-107-91) established by the Japan Bentonite Industry Association or the Japanese Industrial Standards (JIS Z 2451) established by the Japan Industrial Standards Committee, and the amount of exchangeable cations (Na+, K+, Mg2+, Ca2+) and the CEC have been quantified by the method established by the Soil Standard Analysis and Measurement Method Committee. We emphasized the simplicity and speed of measurement, and conducted repeated studies to further simplify these measurement methods. As a result, following simple measurement methods were proposed. In the measurement of MB adsorption amount, at first, the sample is dispersed at room temperature in an aqueous solution of sodium oxalate having a predetermined concentration. Next, a predetermined concentration of MB aqueous solution is added to shake for a predetermined time. Finally, the MB concentration of the separated supernatant is measured using a spectrophotometer and the MB adsorption amount (mmol/100 g) is calculated from the concentration value of MB. The two simple measurement methods were obtained on the amounts of exchangeable cations and the CEC. One is a method of measuring the amounts of exchangeable cations (Na+, K+, Ca2+) eluted by replacing with NH4+ ions by using a convenient measuring device such as a simplified type of ion meter. Another is a method of measuring the amounts of exchangeable cations (Na+, K+, Mg2+, Ca2+) and the CEC at once by using an ion chromatography. [ABSTRACT FROM AUTHOR]

Aflatoxins in contaminated corn do not degrade in corn fermentation solution (CFS) during biofuel production; rather, they are enriched in the co-product, dried distillers grain. Aflatoxin B1 (AfB1) is the most toxic form of all aflatoxins. Removing AfB1 from CFS is desirable to minimize its toxicity to animals. Smectites can adsorb AfB1 from aqueous solutions and, therefore, inactivate the toxin, but proteins in CFS inhibit the adsorption of AfB1 by smectites. The current study aimed to minimize the interference by CFS in adsorption of AfB1 on smectite by modifying a calcium-smectite (Ca-3MS) with a small nutritive organic compound, e.g. carnitine, choline, arginine, histidine, or tryptophan. The organo-smectites were characterized by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, and adsorption of AfB1 in CFS by these composites was examined. Various degrees of intercalation of the organic nutrients into the smectites were observed with XRD and FTIR. After immersing the smectite and organo-smectites in the CFS, the d001 values of Ca-3MS expanded to ~1.82 nm due to protein interaction, but the organo-smectites were confined to ~1.39 nm, which indicated that the protein had limited access to the organo-smectite interlayers. The IR bands at ~1652, 1544, 1538, and 1454 cm–1 from the organo-smectites revealed, however, that complete protein inhibition was not achieved. The organo-smectites were capable of adsorbing AfB1 in simple aqueous solution with maximal adsorption capacity up to 0.55 mol kg–1. Significantly greater (p ≤ 0.05) AfB1 adsorption was achieved by choline- and carnitine-modified smectites compared with the original Ca-3MS in the presence of competing protein (pepsin) in simple aqueous solution. In real CFS, both AfB1 adsorption capacities (Qmax) and affinities (K) by all organo-smectites were greater (Qmax = up to 0.45 mol kg–1 and K = up to 0.165 μM–1) than those by Ca-3MS (Qmax = 0.22 mol kg–1 and K = 0.031 μM–1). The study suggested that using smectites modified with an organic nutritive compound could be an effective, economical, and safe strategy for removing mycotoxins, including aflatoxins, during biofuel production. [ABSTRACT FROM AUTHOR]

Natural smectites bind aflatoxins from water effectively, but the complex chemical environment in the guts of mammals and other animals can limit binding of aflatoxins. Many efforts have been made to enhance the adsorption capacity and affinity of smectites for aflatoxins in the presence of biological compounds. The main objective of the present study was to modify smectite structures by pillaring and cation exchange to enhance aflatoxin B1 adsorption capacity and selectivity. Smectite was pillared with Al and Al-Fe polycations or saturated with Ca, Mg, Zn, or Li. Structural changes in smectites with or without heat treatment were determined using X-ray diffraction and Fourier-transform infrared spectroscopy. Equilibrium aflatoxin B1 adsorption to the smectites was measured in aqueous solution and in simulated gastric fluid. Pillaring with the polycations expanded smectites in the z-direction to 18.6 Å and the expansion was stable after heating at 500°C. Changes in the Al–OH–Al infrared bands in the stretching region supported the formation of pillared clays. Migration of Mg, Zn, and Li into the octahedral sites of the smectite was observed as Mg and Zn saturation yielded a d spacing of 15 Å at 200°C which collapsed to 9.6 Å at 400°C. The 14.6 Å peak of the Li-saturated smectite collapsed to 9.6 Å at 200°C while the 15 Å Ca-saturated smectite peak was stable up to 400°C. The unheated Al- and AlFe-pillared smectites adsorbed significantly more aflatoxin B1 from an aqueous suspension than did unpillared clay. In both water and simulated gastric fluid, heat treatment decreased aflatoxin B1 adsorption to pillared smectites, but heat treatment increased aflatoxin B1 adsorption to unpillared smectites. Without heat treatment, smectites saturated with divalent cations (Ca, Mg, Zn) adsorbed more aflatoxin B1 from an aqueous suspension than the smectite saturated with a monovalent cation (Li). Ca-saturated smectite showed the greatest aflatoxin B1 adsorption, 114 g kg–1, from aqueous suspension after 400°C heat treatment. The Zn-, Mg-, and Li-saturated smectites showed maximum aflatoxin adsorption of 107, 93, and 90 g kg–1, respectively, after 200°C heat treatment. From simulated gastric fluid with pepsin, the 200°C heated, Zn-saturated smectite had maximum aflatoxin B1 adsorption of 68 g kg–1. Pillared smectites effectively adsorbed aflatoxin B1 from aqueous suspension, but Ca- and Zn-saturated smectites after heat treatment might improve the selectivity of smectites for aflatoxin B1 over pepsin and enhance the efficacy of smectite as a feed additive. [ABSTRACT FROM AUTHOR]