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The presence of swelling clay minerals, such as smectites, is known to be one of the main parameters controlling the mobility of radium in natural environments due to the high adsorption capacities of these materials. However, experimental data and modeling from literature allowing to investigate the adsorption properties of radium towards smectite in a wide range of acidic conditions (2 < 7) are scarce. Moreover, the role of the smectite crystal chemistry (charge location in the layer) remains unclear. Therefore, experimental data for the adsorption of radium onto a swelling clay mineral with a tetrahedral charge (beidellite) are presented here in the 2–7 pH range. Different batch experiments were conducted in order to investigate the effects of both ionic strength (i.e., from 0.027 to 0.11 M in sodium chloride medium) and presence of competing major cations (i.e., magnesium). Experimental data were interpreted using a multi-site ion-exchange model that takes into account the adsorption of major cations (including H + ), which usually compete with trace elements for sorption onto mineral surfaces in natural environments. The ability of the proposed model to predict experimental distribution coefficient (K d ) values under various conditions of ionic strength and aqueous cation compositions was tested, and results were compared with those obtained using previously published models. The evolution of radium adsorption on beidellite with pH variation is better reproduced by using a multi-site ion-exchange model, as proposed in this study, than by using a single-site model as that reported in literature. Finally, the implication of the results obtained in this study for the mobility of radium in natural environments was discussed. The significant role of smectites in the adsorption of radium at low pH conditions (pH ≤ 6) in complex mixtures, which are representative of natural matrices, was demonstrated based on comparison with experimental data previously obtained on organic material and Fe(III)-oxy/hydroxides. The multi-site model proposed in this study for beidellite, coupled with a model from literature for organic matter, was applied in order to predict the role played by the beidellite in the adsorption properties of a virtual complex mixture containing various proportions of beidellite and organic matter. The model shows that smectite can contribute from 80 to 100% to the total adsorption of radium of the complex mixture for pH < 3. Moreover, the predicted results were in good agreement with experimental data from literature obtained with natural peat. Finally, the multi-site ion-exchange model proposed in this study for beidellite could be applied in many natural environments characterized by acidic pH, such as naturally acidic soils (pH ≤ 5) and acid mining environments (pH ≤ 1), where predicting 226 Ra exchange onto swelling clay minerals requires accounting for the effects of the major cations present in these systems. [ABSTRACT FROM AUTHOR]

The dissolution rate of beidellite, a dioctahedral smectite with tetrahedral charge that is a common swelling clay mineral in surface and subsurface natural environments, was studied in acidic solutions at 25 °C under far from equilibrium conditions. A <0.3 μm size fraction of SBId1 beidellite ((Si 7.148 Al 0.852 )(Al 3.624 Mg 0.18 Fe(III) 0.224 )O 20 (OH) 4 M + 0.948 ) purchased from the Clay Mineral Society was used as the starting material, and experiments were performed in stirred flow-through reactors using HCl solutions with pH values ranging from 1 to 3. Several hydrodynamic conditions were tested using different flow rates with stirred and non-stirred particles. The aqueous Al/Si ratio measured at the outlet of the reactor was followed as a function of time and compared to solid stoichiometry values to assess the mechanisms occurring at the solid/solution interface. The reversible adsorption of Al 3+ in the smectite interlayer space was evidenced for pH > 1.1, and the presence of an amorphous Si-enriched layer can be reasonably assumed in some cases from the interpretation of the aqueous concentrations and the characterization of the solid phase (X-ray diffraction and FTIR spectroscopy). Beidellite dissolution rates normalized to the sample mass (mol g −1 s −1 ) were obtained from Si and Al concentrations under steady state dissolution conditions. Calculated rates were compared with those previously reported for montmorillonite in several publications. The beidellite dissolution rates are, on average, ten times lower than those of montmorillonite. This implies that the smectite crystal chemistry (i.e., amount of Al 3+ versus Mg 2+ or Fe 3+ substitution in the structure) has a strong effect on its stability and should be considered in reactive transport models in which the dissolution properties of smectites are taken into account. [ABSTRACT FROM AUTHOR]

Five-membered cyclic organic carbonates (COC) are of interest for their ability to modify the surface properties of smectites and enhance the hydraulic resistance of bentonites to saline leachates. The mechanism of interaction of glycerol carbonate (GC) and several other hydroxyl containing cyclic organic carbonates (generally having progressively greater molecular masses) with sodium montmorillonite (Na + -Mt) was studied using powder X-ray diffraction and infrared spectroscopy. The 001 reflection for GC/Na + -Mt intercalates varied with the amount COC added, and the measured d 001 value increased from 1.29 nm to as large as 2.22 nm at equal-mass coverage of the COC to Na + -Mt. In general, when intercalated, the cyclic carbonyl (C O) stretch and the fundamental hydroxyl (O–H) stretch bands of COC derivatives were red-shifted with respect to these bands for neat COC, indicating strong ion-dipole interaction of the carbonyl group with interlayer Na + , and H-bonding of the OH group with both interlayer water and Mt surfaces. A stable and highly ordered intercalate was produced at a 1:1 mass loading with Mt in which about 6 GC molecules per unit cell (~ 7 molecules per Na + ion) replaced most of the interlayer water. [ABSTRACT FROM AUTHOR]

Smectites are clay minerals of interest due to their natural availability, extraordinary surface properties, and high swelling capacity in the presence of water. The behaviour of smectites and other layered phyllosilicates is largely affected by the appearance of isomorphous substitutions with a lower nuclear charge in their layer structures. These substitutions are the origin of negative net layer charge, and their distribution in the mineral layer impacts on the electrostatic properties of the mineral surfaces. The present density functional theory study shows that octahedral Mg(II) and tetrahedral Al(III) substitutions in aluminium-rich dioctahedral smectites tend to avoid each other and disperse in the layer structure. This behaviour is explained and demonstrated to originate from geometry deformations around the substitutions which are larger than the unsubstituted species. [ABSTRACT FROM AUTHOR]

We report an FPMD (first-principles molecular dynamics) study of the interfacial structures and acidity constants of the edge surfaces of ferruginous smectites. To understand the effects of Fe oxidation states on the interfacial properties, we investigated both the oxidized and reduced states of the (0 1 0)-type edges of two clay models with different Fe contents. The coordination states of edge Fe atoms are determined from the free energy curves for the desorption of the H 2 O ligands. The results of both clay models show that for Fe(III), only the 6-coordinate states are stable, whereas for Fe(II), both the 6- and 5-coordinate states are stable. Using the FPMD-based vertical energy gap technique, the p K a values of the edge sites are evaluated for both oxidation states. The results indicate that for both clay models, both the octahedral and tetrahedral sites become much less acidic upon Fe reduction. Therefore, the comparison reveals that the interfacial structures and protonation states are strongly dependent on the Fe oxidation states. Using the calculated results, we have derived the pH-dependent surface complexing mechanisms of ferruginous smectites. [ABSTRACT FROM AUTHOR]

The relationships between clay minerals and associated iron and arsenic-rich phases are a main scientific issue in reactive mine waste-dumps. Therefore, this paper documents the composition and morphology of the fine fraction (< 2 μm), including the nano-sized Fe and As precipitates, associated with clay minerals in three distinctive sulfide-rich waste-dumps: Cerdeirinha , Lapa Grande , and Penedono (Northern Portugal). The obtained results indicated that the study sites have similar relative proportions of the detrital materials. However, major differences were observed in the remainder phases, which is in accordance with the mineralogy that was inherited from the respective ore deposits. In general, the clay mineral assemblage is dominated by the presence of illite, halloysite(7 Å), and beidellite. There are also associated minerals, such as jarosite and goethite, as well as amorphous As-rich nanoprecipitates with specific morphologies. Moreover, the results suggested that AMD conditions control the physical–chemical transformations, namely constraining the stability of the secondary phases formed by weathering in the waste dumps. Acidity is responsible for the degradation of the clay minerals, which is reflected in their crystalochemistry, structural order–disorder, and morphology. On the contrary, jarosite is more stable, being a dominant mineral in such environmental conditions. The stability of amorphous ferric arsenates or its evolution to a more crystalline phase is dependent on the Fe:As ratio, which is lower in Penedono . The study of the secondary products, especially the nanoparticles, puts in evidence their ability to control the mobility of trace elements, suggesting potential applications in environmental technology, including remediation of reactive mine waste-dumps. [ABSTRACT FROM AUTHOR]

This paper describes the petrographic properties and the clay mineralogy of Eocene sandy sediments of the Chu-Saryssu basin (South-Central Kazakhstan), in which dioctahedral smectite formed during shallow burial diagenesis (eogenesis). Evidence from petrography and clay mineralogy supports the successive occurrence of kaolinite and dioctahedral smectite during the eogenetic processes, which may have resulted from a change from wet and humid to semi-arid or arid climatic conditions. An original result of this study is the predominantly beidellitic nature of the authigenic smectite, which was determined via X-ray diffraction (XRD, using the Hofmann–Klemen test) and Fourier transform infrared spectroscopy (FTIR) investigations and chemical microanalysis. The crystal-chemical investigations indicate a rather homogeneous chemical composition of the smectite at the regional scale, and the following unit formula is proposed: (Si 4 + 3.65 Al 3 + 0.35 )(Al 3 + 1.65 Fe 3 + 0.21 Mg 2 + 0.14 )O 10 (OH) 2 Na + 0.10 Mg 2 + 0.11 Ca 2 + 0.04 K + 0.07 . This type of smectite has been interpreted as representative of mixed layers of montmorillonite and beidellite. The fact that the smectite that formed primarily in the unconsolidated sandy sediments is close to beidellite, rather than montmorillonite, may have a major impact on the rate of further illitization in the Chu-Saryssu basin. Indeed, the crystal chemistry of beidellite is more favorable to illitization, and the presence of this mineral provides new insights concerning the different rates of illitization between sandstones and shale formations observed worldwide. [ABSTRACT FROM AUTHOR]

In this study, an Al-pillared smectite was synthesized and changes in its colloidal properties were investigated. The pillaring solution was prepared by mixing 0.4 mol L−1NaOH and 0.2 mol L−1AlCl3.6H2O solutions. Intercalated clays were heated to obtain the pillared clay, and X-ray diffractometry (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy and N2sorption/desorption isotherms analysis were done to characterize the changes in clay properties. Moreover, adsorption experiments were carried out in order to evaluate the capacity of the pillared clays to remove Cu2+from an aqueous solution and to characterize the interaction between adsorbent and adsorbate. The results indicate that the natural clay has a basal spacing of 1.26 nm, whereas the pillared clays reached 1.78 nm (500°C) and 1.80 nm (350°C) after calcination. XRF analysis revealed an increase in the Al3+in the pillared clay as compared to the natural clay. The surface area and pore volume (micro and mesoporous) were higher for the pillared clays. Experimental data from the adsorption experiment were fit to Langmuir and Freundlich and Temkin adsorption models, and the former one was the best fit (highestr2value) for all the clays and lower standard deviation (Δg%) for the natural clay. On the other hand, the Temkin model exhibited Δg% value lower for the pillared clays. Thermodynamics parameters demonstrate that the Cu2+adsorption process is spontaneous for all the clays, but with higher values for the pillared materials. In addition, application of the Dubinin–Radushkevich model revealed that the bond between the metal and the clay are weak, characterizing a physisorption. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Development of eco-friendly corrosion inhibitor based on Ca2+-exchanged beidellite. [•] Improvement of corrosion inhibition by progressive release of Ca2+ from host mineral. [•] Role of beidellite in trapping aggressive corrosion species such as Cl−, Na+ and H+. [•] Valorization of natural Moroccan clay mineral. [•] Ca2+-BDT modified the physicochemical properties of electrolyte near zinc surface. [ABSTRACT FROM AUTHOR]

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Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occurs preferentially in specific sites within the former octahedral sheet. The rehydroxylation of dehydroxylated A1-rich and A1,Mg-rich 2:1 layers occurs as trans-vacant (tv) structural arrangements, regardless of whether the initial structure was tv or cis-vacant (cv). In nontronite (Fe-rich 2:1 layer clay), the dehydroxylate pseudo-cv structure is probably directly reconstructed into the rehydroxylated cv structure without migration of octahedral cations. Rehydroxylation occurs preferentially in the R3+-Or-R3+ former octahedral structural arrangements (Or = residual oxygen) over R2+-Or-R (R = R3+ or R2+ = A13+, Fe3+ or Mg2+, Fe2+). In the case of the R2+ octahedral substitution, the interlayer cation is attracted to the electrostatically undersaturated residual oxygen of the R2+-Or-R arrangement, which blocks the ability of water molecules to pass through the ditrigonal cavity and rehydroxylate the previously dehydroxylated local arrangement. The pyrophyllite-like type of octahedral R3+-Or-R3+ arrangements, formed due to the lack of tetrahedral substitution and resulting in the absence of interlayer cations, is thus favored for rehydroxylation over the mica-like R3+-Or-R3+ arrangements where Al occurs in the tetrahedral sheet. The valence of the interlayer cation and the charge density of the 2:1 layer clay mineral, which controls the interlayer cation content, also affect the degree of rehydroxylation.Dehydroxylated 2:1 layer minerals with a high-rehydroxylation potential, including beidellite and illite, use all the adsorbed water molecules that persist above 200 °C for rehydroxylation; the water vapor from the ambient environment also becomes a source of H2O molecules for rehydroxylation. The high demand for water molecules to use for rehydroxyltion results in a noticeable gain of mass in the temperature interval between 200 and 350 °C even during heating. [ABSTRACT FROM AUTHOR]

Abstract: This study focuses on acid activated beidellite and its adsorption ability for the herbicide simazine. After acid activation, the non-silicon atoms, such as Al, Mg, and Fe, which are located in the octahedral sheet, and sodium ions between the clay mineral layers were leached from the parent clay mineral. The basal spacing increased after acid activation. The acid activated beidellites were used to remove simazine from water. The simazine molecules can enter into the destroyed alumino silicate interlayer spaces and can be adsorbed from contaminated water. [Copyright &y& Elsevier]

Abstract: Nanocomposites of polyaniline (PANI) with organophilic montmorillonite (O-MMT) and hydrophilic montmorillonite (Na-MMT) were prepared. The nanocomposites were characterized using FT-IR, D.C. electrical conductivity measurement and cyclic voltammetry techniques. It was found that PANI/Na-MMT nanocomposite has lower (5.8%) and PANI/O-MMT nanocomposite has higher (29.4%) conductivity compared to pure polyaniline. Cyclic voltammetry experiments showed that both nanocomposites are electroactive. The anticorrosive properties of a 100μm thickness coating of nanocomposites on iron coupons were evaluated and compared with pure polyaniline coating. According to the results PANI/MMT nanocomposites have enhanced corrosion protection effect in comparison to pure polyaniline coating. Results showed also that the PANI/Na-MMT and PANI/O-MMT nanocomposites have considerably different corrosion protection efficiencies in various corrosive environments. [Copyright &y& Elsevier]

Abstract: In the current work, a sensitive, rapid and convenient electrochemical method was developed for the determination of Sudan I utilizing the excellent properties of montmorillonite calcium (MMT-Ca). Compared with the unmodified carbon paste electrode (CPE), MMT-Ca modified CPE not only significantly enhances the oxidation peak current of Sudan I but also lowers the oxidation overpotential, suggesting that the MMT-Ca modified CPE can remarkably improve the determining sensitivity of Sudan I. The experimental conditions such as determining medium, the content of MMT-Ca and accumulation time were optimized for the determination of Sudan I. The oxidation peak current is proportional to the concentration of Sudan I over the range from 0.05mgL−1 (2.01×10−7 mol L−1) to 1.0mgL−1 (4.03×10−6 mol L−1), and the limit of detection is 0.02 mg L−1 (8.06×10−8 mol L−1) for 2-min accumulation. Finally this newly-proposed sensing method was successfully employed to detect Sudan I in practical samples and good recovery was achieved. [Copyright &y& Elsevier]

Abstract: Tri-octahedral Li–Mg smectites (hectorites) were synthesized at temperatures ranging from 25 to 250°C, in the presence of solutions highly enriched in lithium. After removing all the exchangeable lithium from the synthesized clays, Li isotope fractionation (Δ7Liclay-solution) was determined. This fractionation was linked to Li incorporation into the structural octahedral site, substituting for Mg2+. As predicted, experimental Δ7Liclay-solution inversely correlates with temperature, and ranges from −1.6‰±1.3‰ at 250°C to −10.0‰±1.3‰ at 90°C, and then stays relatively constant down to 25°C. The relatively constant isotope fractionation factor below 90°C may be due to high concentrations of edge octahedra in low crystallinity smectites. The isotopic fractionation factor (α), for a given temperature, does not depend on the solution matrix, nor on the amount of structural Li incorporated into the clay. Empirical linear laws for α as a function of 1/T (K) were inferred. Smectite Li contents and smectite-solution distribution coefficients (D Li/Mg) increase with temperature, as expected for a substitution process. The fractions of dissolved Li incorporated into the smectite octahedral sites are small and do not depend on the duration of the experiment. In a seawater-like matrix solution, less Li is incorporated into the smectites, probably as a result of competition with dissolved Mg2+ ions for incorporation into the octahedral sites. The high Li contents observed in marine smectites are therefore best explained either by a significant contribution from basalts, by adsorption processes, or by the influence of seawater chemical composition on distribution coefficients. We also calculate, using present-day estimates of hydrothermal water and river fluxes, that a steady-state ocean would require a relatively large global clay-water Li isotope fractionation (−12‰ to −21‰). This study demonstrates the ability of laboratory experiments to quantify the impact of secondary phases on the Li geochemical cycle and associated isotope fractionations. [Copyright &y& Elsevier]

Abstract: Toluene isopropylation is carried out over modified montmorillonite clays. Effect of ion exchange and pillaring on the catalytic activity and selectivity is noted. Elemental analysis results give the extent of metal incorporated. Enhanced porosity is evident from X-ray diffraction as well as surface area – pore volume measurements. 29Si NMR shows the resonance for T (3Si, 1Al) units which shifts proportional to the amount of pillar metal present. Among the different modifications mixed metal oxide pillaring is found to be most effective in catalytic activity, p-cymene selectivity and lowering deactivation. [Copyright &y& Elsevier]

Abstract: Platinum sub colloids (nm range) were synthesized in the presence of a surfactant (CTAB) by micellar technique in which the metal particles ensured long-term stability in the aqueous dispersion and were prevented from agglomeration. When this surfactant stabilized Pt hydrosol was allowed to react with aqueous suspension of Na+ montmorillonite or Li+ hectorite, the cationic exchange reaction between Na+/Li+ and organic cation (CTA+) took place with simultaneous incorporation of the reduced Pt particles into the organoclay host. Finely divided and well-dispersed Pt particles (nm range) were generated by this method in the interlamellar space of the montmorillonite and hectorite. The catalyst samples with different metal loadings were synthesized and characterized with UV–Vis spectroscopy, XRD, TEM and AAS techniques. From the TEM micrographs it was confirmed that the diameter of the Pt particles intercalated was in the nanometer range. The catalytic activity of the synthesized catalysts was studied towards the selective hydrogenation of C cinnamaldehyde using a batch type high pressure reactor at different temperatures and hydrogen pressures. The catalytic activity of the catalysts and their selectivity towards cinnamyl alcohol were discussed in detail. The activity and selectivity of 1wt.% Pt loaded montmorillonite catalyst was found to be appreciable. [Copyright &y& Elsevier]

Abstract: Proton uptake on montmorillonite edge surfaces can control pore water pH, solute adsorption, dissolution kinetics and clay colloid behavior in engineered clay barriers and natural weathering environments. Knowledge of proton uptake reactions, however, is currently limited by strong discrepancies between reported montmorillonite titration data sets and by conflicting estimates of edge structure, reactivity and electrostatics. In the present study, we show that the apparent discrepancy between titration data sets results in large part from the widespread use of an erroneous assumption of zero specific net proton surface charge at the onset of titration. Using a novel simulation scheme involving a surface chemistry model to simulate both pretreatment and titration, we find that montmorillonite edge surface chemistry models that account for the “spillover” of electrostatic potential from basal onto edge surfaces and for the stabilization of deprotonated Alng sites through bond-length relaxation at the edge surface can reproduce key features of the best available experimental titration data (the influence of pretreatment conditions on experimental results, the absence of a point of zero salt effect, buffer capacity in the acidic pH range). However, no combination of current models of edge surface structure, reactivity and electrostatics can quantitatively predict, without fitted parameters, the experimental titration data over the entire range of pH (4.5 to 9) and ionic strength (0.001 to 0.5 mol dm−3) covered by available data. [Copyright &y& Elsevier]

Abstract: Natural and synthetic clay minerals have been transformed into Si-pillared mesoporous structures and then grafted with SH functions, for heavy metal ion trapping in polluted soils. The techniques and the limits encountered were detailed, with assessments of transformations by FTIR spectrometry and X-ray diffraction analyses. Adsorption isotherms of Cd2+ and Pb2+ were measured after 1 day shaking in calcium nitrate suspensions. Tests of Cd and Pb plant uptake were pursued by ray-grass cultivation on polluted soil amended or not with a functionalized synthetic beidellite during 3 months. Natural beidellite, hectorite and vermiculite were transformed into SH-grafted pillared clays but difficulties were encountered to keep a regular and significant interlayer distance until the last step. The well crystalline high-charge vermiculite of Santa Olalla (Spain), after Li-saturation, exchange with alkyl-ammonium cations, formation and grafting of interlayer Si-pillars, showed the highest capacity of Cd2+ and Pb2+ fixation among the 3 functionalized tested clay minerals. The cadmium uptake by ray-grass grown on polluted soil has been quite depressed by amendments with 0.17 or 0.5% of functionalized synthetic beidellite, but these amendments were inefficient for lead. [Copyright &y& Elsevier]

Molecular dynamics simulations were performed to provide a systematic study of aqueous uranyl adsorption onto the external surface of 2:1 dioctahedral clays. Our understanding of this key process is critical in predicting the fate of radioactive contaminants in natural groundwaters. These simulations provide atomistic detail to help explain experimental trends in uranyl adsorption onto natural media containing smectite clays. Aqueous uranyl concentrations ranged from 0.027 to 0.162 M. Sodium ions and carbonate ions (0.027–0.243 M) were also present in the aqueous regions to more faithfully model a stream of uranyl-containing groundwater contacting a mineral system comprised of Na-smectite. No adsorption occurred near the pyrophyllite surface, and there was little difference in uranyl adsorption onto the beidellite and montmorillonite, despite the difference in location of clay layer charge between the two. At low uranyl concentration, the pentaaquouranyl complex dominates in solution and readily adsorbs to the clay basal plane. At higher uranyl (and carbonate) concentrations, the mono(carbonato) complex forms in solution, and uranyl adsorption decreases. Sodium adsorption onto beidellite occurred both as inner- and outer-sphere surface complexes, again with little effect on uranyl adsorption. Uranyl surface complexes consisted primarily of the pentaaquo cation (85%) and to a lesser extent the mono-(carbonato) species (15%). Speciation diagrams of the aqueous region indicate that the mono(carbonato)uranyl complex is abundant at high ionic strength. 01igomeric uranyl complexes are observed at high ionic strength, particularly near the pyrophyllite and montmorillonite surfaces. Atomic density profiles of water oxygen and hydrogen atoms are nearly identical near the beidellite and montmorillonite surfaces. Water structure therefore appears to be governed by the presence of adsorbed ions and not by the location of layer charge associated with the substrate. The water oxygen density near the pyrophyllite surface is similar to the other cases, but the hydrogen density profile indicates reduced hydrogen bonding between adsorbed water molecules and the surface. [ABSTRACT FROM AUTHOR]

Smectites affecting water and soil exchangeable cations, especially potassium and ammonium related to plants, are common swelling clay minerals in sediments and paleosols that can record paleoenvironmental and paleoclimatic information. Paleoenvironmental and paleoclimatic interpretations are potentially ambiguous, because smectite minerals may have either detrital or pedogenic origins. This study analyzes smectites in Lower Eocene paleosols of the Qaidam Basin, China, with the goal of determining their origin and paleoclimatic significance. Twelve smectite-rich vertisol samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) in the Dahonggou (DHG) section of the Lulehe Formation. The samples from DHG section contained predominant dioctahedral smectites (60–65%) in the <2 μm clay fractions. Minor dioctahedral illites, dioctahedral interstratified illite-smectite (I-Sm), kaolinite, and traces of dioctahedral chlorites and palygorskites were present. The chemical data and FTIR spectra revealed both tetrahedral substitutions (i.e., Al for Si) and octahedral substitutions (i.e., Mg and minor Fe for Al) in the dioctahedral smectites. Montmorillonite comprised the dominance of the fine-clay fractions (< 0.2 μm) with minor contributions of beidellite, as determined by the Greene-Kelly test (GK-test), geochemical and FTIR analyses. SEM observations revealed two morphological types of dioctahedral smectites, the less abundant one with typical 'honeycomb' structure, interpreted as neoformed, and the other occurring as thin, well-defined plates and irregular masses considered to be detrital. DSC revealed two dehydroxylation temperatures (500–550 °C and 600–700 °C), indicating the presence of trans- vacant (t v) and cis- vacant (cv) layers, respectively. The cv layers were attributed to montmorillonite originating as catchment-delivered detritus, as the study Lulehe Formation exhibited no evidence of volcanic ash layers or diagenesis that would have promoted formation of montmorillonite with high dehydroxylation temperatures. The tv layers represented pedogenic beidellite formed via solution crystallization in a floodplain pedogenic environment. The accumulation of abundant inherited montmorillonite and neoformed beidellite in paleosols of the Lulehe Formation was probably promoted by a relatively warm climate with alternating wet-dry seasons during the Early Eocene. Admixture of detrital montmorillonite makes paleoclimatic reconstructions based on bulk-smectites concentrations and isotopic compositions unreliable, showing that integrated clay mineralogical analyses of the type undertaken in this study are necessary to identify the provenance and paleoclimatic significance of smectites in sediments. • Two subtypes of smectite, montmorillonite and beidellite, occur in Lulehe palesosols. • Predominant montmorillonite with high thermal ability has a detrital origin. • Minor beidellite with low dehydroxylation temperatures has a pedogenic origin. • Smectite accumulation/formation increased during EECO due to seasonal wet and dry. • Smectites in soils can be of multiple origin making their paleoenvironmental interpretation complex. [ABSTRACT FROM AUTHOR]

• Swelling pressure trend of smectites with monovalent interlayer cations was studied. • Variables used are interlayer cation, d-spacing, dry density, total charge and location. • Swelling pressure decreased as the interlayer cation progressed down the group. • Swelling behavior of Li-smectite was different from other cation-smectites. Interlayer cations largely determine the swellability of expansive clays. An atomic level study was carried out to determine the effect of monovalent interlayer cations on the swelling behavior of two different smectite minerals to establish their swelling pressure trends. Montmorillonite and beidellite clay minerals were simulated with five different alkaline metals as interlayer cations: Li+, Na+, K+, Rb+, and Cs+. A molecular dynamics simulation method was employed with varying charge balancing cations, layer charges and charge locations. The swelling pressure of homoionic smectite decreased as the interlayer cation progressed down the group from Li+ to Cs+ yielding the following trend: Li+ > Na+ > K+ > Rb+ > Cs+. The effects of layer charge and charge location were also evident. The outcome of this study is useful for the selection of smectite buffer materials for use in high-level radioactive waste disposal repositories. [ABSTRACT FROM AUTHOR]

A predictive model is developed for estimating the amount of clay water and the hydration thermodynamic properties as a function of relative humidity (R.H.), for any 2:1 clay composition. From a methodology performed by Gailhanou et al. (2017) upon MX80-Na smectite, based on experimental water adsorption isotherms and structural data, a regular solid solution between anhydrous and highly hydrated clay end-members is parameterized, providing a set of 4 thermodynamic parameters Δ Cem. W H , Δ Cem. W S , W H and W S characterizing the theoretical mechanisms of adsorption of the clay water versus the relative humidity. To complete literature data, water adsorption isotherms are acquired at 25 °C and 45 °C for five natural 2:1 clays, with various compositions, interlayer charges and interlayer cations (Na, Ca, K, Mg). The amounts of clay water are extracted from the total adsorbed water amounts by removing the contribution of capillary water and the thermodynamic entities of the hydration reaction are calculated and are closely related to the nature of the clay (characterized by its interlayer and tetrahedral charges and the nature of the interlayer cation), allowing two predictive models, for di-octahedral smectites and for tri-octahedral 2:1 clays. These two models are assessed by using experimental data for other clay minerals provided by literature. For a given 2:1 clay composition, the model allows - to predict quite well the clay water adsorption isotherm, - to provide hydration thermodynamic properties (G, H, S) for the di-octahedral model and for the tri-octahedral model and-to predict the thermodynamic properties of formation for some hydrated clays of fictive compositions. Image 1 • Five natural 2:1 clays, (dioct and trioct) with various interlayer cations. • Adsorption - desorption isotherms performed at 25 °C and 45 °C. • Extraction of clay water properties from adsorption isotherms. • Prediction of the thermodynamic properties of hydration for 2:1 clays. [ABSTRACT FROM AUTHOR]

Abstract: A simple, efficient and environmentally benign protocol has been developed for the conversion of glycals into 2-(d-glycero-1,2-dihydroxy ethyl) furan derivatives using montmorillonite KSF as inexpensive and environmentally benign solid acid to afford excellent yields with high selectivity. [Copyright &y& Elsevier]