Clay Crystals Research Articles

Study on the Properties of Waste Stone Powder-clay Slurry based on the Influence of Filter Press

A grouting material pressure effect simulation device (FSD) was used to study the performance of grout considering grouting pressure, slurry rheology, clay ash, slurry concentration and particle size composition of waste stone powder (FSD influencing factors). After the effect of filter pressing, the alkaline environment of the slurry became stronger, the number of active particles increased, and the CaCO3 and clay crystals were fully agglomerate, and the degree of crystallization increased. The cation exchange capacity increased, and the formation of calcium-silicon-aluminum matrix phase and aluminosilicate aggregates increased. The surface water between the matrix particles supports the crystal layer, and the plastic viscosity and yield stress are reduced. The free calcium oxide decreased, and the consolidation shrinkage rate after slurry hardening was less than 1%. The water-cement ratio is reduced, and the total time for slurry to be poured into the fracture to consolidate and form a mold and intermittent is shortened. The use of waste stone powder and clay in the coal mine grouting industry can not only reduce project costs, but also reduce soil erosion and soil pollution.

Molecular simulation of adsorption behaviors of methane and carbon dioxide on typical clay minerals

Knowledge of the interaction mechanisms between shale and CH4/CO2 is crucial for the implementation of CO2 sequestration with enhanced CH4 recovery (CS-EGR) in shale reservoir. As one of the main constituents of shale, clay minerals can profoundly affect the storage capacity of gases in nanopores. In this paper, the adsorption behaviors of both CO2 and CH4 on montmorillonite, illite as well as kaolinite under dry condition are investigated by Grand Canonical Monte Carlo (GCMC) simulation. The results exhibit that the maximum adsorption capacity of single-component CH4 and CO2 is associated with the types of clay crystals. Specifically, the montmorillonite has the strongest adsorption capacity for CO2, followed by illite and kaolinite, while the sequence in maximum adsorption capacity of CH4 is predicted in the order of kaolinite > montmorillonite > illite. These discrepancies are closely related to the characteristics of adsorbate molecules as well as the different structures of clay crystals. Meanwhile, the maximum adsorption capacity of CH4 in studied clay minerals gradually decreases as pore size increases, while nanopores with 2-nm basal spacing demonstrate the highest adsorption capacity for CO2. In addition, it is observed that the studied clay minerals tend to preferentially adsorb CO2 rather than CH4 during binary gas mixtures simulation. The selectivity of CH4/CO2 mixtures in montmorillonite and kaolinite exhibits various performances as the adsorption pressure increases, with the selectivity in montmorillonite being the largest, especially at low pressure. The cation exchange significantly enhances the electrostatic interaction with CO2 molecules, leading to a higher loading of CO2 as well as larger value of selectivity. These findings can provide basis and guidance for the CS-EGR project in shale reservoirs.

Production of Clay-Based Water Filter Using Biomass of Bacillus Subtillis, Sawdust, Activated Charcoal, Periwinkle and Snail Shell as Additives

A Significant proportion of rural households lacked access to improved and safe drinking water due to chemical and microbial contamination. Point-of-use (POU) water filters made from cheap, locally available ceramic materials and additives can achieve quality water parameters. Ceramic water filters were prepared by combining clay minerals with additives. Sawdust was used as a burnout material to achieve porosity and enhance the filtration rate. Silver nitrate, charcoal, periwinkle shell, snail shell, and biomass of Bacillus Subtilis were added in different ratios. The filter was formulated with charcoal, sawdust, snail shell, and periwinkle shell to remove microbes and treat heavy metals through the adsorption process. The filters were molded and fired in a temperature range of (700oC - 900oC). Characterization of the clay mineral, physiochemical and Microbial tests were conducted on the ceramic and water. Antimicrobial test was carried out on the biomass of Bacillus subtilis. Mineralogical (XRD) and elemental analysis of the clay, snail, and periwinkle shells showed high percentage composition of serpentine (a clay crystal), plagioclase, a mixture of feldspar minerals albite (sodium aluminosilicate - NaAlSi3O8), anorthite calcium aluminosilicate- CaAl2Si2O8) and Calcium (70-97 %composition) respectively. The results showed a greater proportion of silica in the clay, suggesting the material is silicate. Filtration rate was estimated at 1.125 L/hr. The result showed the filter has 96.72%, 99.26%, and 66.67% colony removal efficiency for heterotrophic bacteria, coliform, and fungi respectively. The filter showed about 70% - 96% efficiency for the treatment of physiochemical parameters in wastewater.

Swelling of compacted bentonite in organic solvents: Correlation of rate and extent of swelling with solvent properties

The swelling of clay minerals within shale formations during oil and gas exploration, and within compacted bentonite barriers for radioactive waste containment, presents a number of challenges to operators. Whilst much work has been devoted to understanding the interlayer swelling properties of clay mineral crystals, significantly less has been devoted to understanding coupled pore and interlayer swelling in reactive shale/compacted clay minerals. Here we study the swelling of compacted clay mineral tablets on exposure to a range of organic solvents, selected so that the effect of key solvent properties such as dielectric constant, density, octanol-water partition coefficient, viscosity and surface tension can be correlated with the swelling observed. We use a novel non-contact swelling meter to carry out the swelling tests, allowing us to access information on rate of swelling. Short-term swelling rate showed the strongest correlation to the solvent octanol-water partition coefficient. In long term swelling, good correlation was found between total linear swelling and viscosity, and the octanol-water partition coefficient.

Study on the Shale Hydration Inhibition Performance of Triethylammonium Acetate

Shale inhibitor is an additive for drilling fluids that can be used to inhibit shale hydration expansion and dispersion, and prevent wellbore collapse. Small molecular quaternary ammonium salt can enter the interlayer of clay crystal, and enables an excellent shale inhibition performance. In this paper, a novel ionic shale inhibitor, triethylammonium acetate (TEYA), was obtained by solvent-free synthesis by using acetic acid and triethylamine as raw materials. The final product was identified as the target product by Fourier transform infrared spectroscopy (FT-IR). The inhibition performance of TEYA was studied by the mud ball immersion test, linear expansion test, rolling recovery test and particle size distribution test. The results demonstrated that the shale inhibitor shows a good shale hydration inhibition performance. The inhibition mechanism was studied by FT-IR and X-ray diffraction (XRD), respectively; the results showed that triethylammonium acetate TEYA could enter the crystal layer of clay and inhibit it through physical adsorption.

A Kinetic Explanation for Combined Potassium Gains and Radiogenic 40Argon Losses of Diagenetic Illite-Rich Clay Separates

In this study, a kinetic model sketches the concomitant K gain and radiogenic 40Ar loss of clay separates recovered from progressively buried sediments. Published K-Ar ages of clay separates from the Mahakam Delta, the Texas Gulf Coast, and the North Sea were used to constrain the modeling. As compared with analytical results, the model simulates changes relative to depth or to deposition time of the K-Ar ages from fine- and coarse-grained clay crystals. The decrease in the K-Ar ages of detrital-rich coarse-grained fractions (>2 μm) is bracketed with depth by K addition rates between 0.2 and 3.5%/Ma and slightly higher 40Ar release rates between 0.5 and 4.5%/Ma. The former rate varies from 3.5 to 6%/Ma in the fine-grained fractions (<0.4 μm) and the latter rate varies from 0.7 to 6%/Ma in the same fractions. In fact, the K addition and the radiogenic 40Ar release rates record independent processes on different material sizes and types. Small K addition and 40Ar escape rates of about 1%/Ma also simulate analytical cases in which the mean K-Ar ages of the finer grained fractions remain about constant with increasing depth, confirming that the relationship between K-Ar age and stratigraphic depth cannot represent a temporary “steady state”, but a continuing dynamic process at a smaller rate. In turn, the modeled results help quantifying the illitization reactions in size separates consisting of authigenic and detrital clay materials from sediments covering stratigraphic intervals from 10 to 1000 Ma.

Widespread hydrothermal alteration overprinting epizonal Ordovician rocks in the Puna region of Argentina (Salta and Jujuy provinces)

X-ray-diffraction and textural studies under scanning electron microscopy (SEM) using backscattered electron images were employed to outline the thermal post-depositional evolution of Ordovician slates and metavolcanic rocks from four representative localities in southern Puna (the Sierra de Guayaos, the southern zone of the Sierra de Cobres, Cordón de Pozuelos, and Cordón del Gallego) and the Sierra de Cochinoca-Escaya in northern Puna of Argentina. In the case of a meta-andesite that in a previous study had displayed complex clay mineralogy, additional XRD analysis along with a detailed TEM study was performed.Clay mineralogy, Kübler index and chlorite geothermometry indicated that the rocks had undergone prograde metamorphic evolution attaining the epizone. Textural evidence proves that the metamorphic event was syntectonic with the folding that affected this succession, producing a conspicuous slate cleavage in sedimentary and volcanic rocks. Afterwards, the rocks were affected by hydrothermal alteration that produced retrograde changes in mineralogy at centimeter, micron and nanometer scales. The hydrothermal fluid partially dissolved the metamorphic minerals and enhanced the crystallization of clays, kaolinite being the most frequent clay in the altered rocks. Alunite-jarosite was identified in one slate and also evidences of metal transport, suggesting an acid hydrothermal fluid and temperatures between 100 and ~ 300 °C. These data confirm that the Ordovician successions of southern Puna were affected by widespread hydrothermal alteration, as the equivalent rocks in northern Puna. The hydrothermal event was probably associated with the intrusion of the Eastern Puna Magmatic Belt.In the meta-andesite outcropping in the Sierra de Cochinoca-Escaya, HRTEM images and compositional mapping reveal the steps in the paragenetic evolution of the hydrothermal event that produced the alteration of mafic phenocrysts and the formation of intergrowths between high-charge corrensite, trioctahedral vermiculite, and kaolinite.

Orbital asymmetric hybridization enhances surface Lewis acid-base reactions of charged clay catalysts

A strong electric field of 108–10 V/m could be produced from the surface charges of clay. In this study, the asymmetric hybridization of atomic orbitals in the electric field at the clay surface substantially enhances the Lewis acid-base reactions between the surface O and Cu2+/Ca2+/Mg2+/H2O. This has been confirmed by cationic adsorption kinetics, energies, critical coagulation concentrations (CCCs) and infrared spectral analyses of –OH and Si-O stretches for H2O and clay crystal respectively. The enhanced Lewis acid-base reaction energy for Cu2+, Ca2+ and Mg2+ at charged clay surface is found in an order of Cu2+(−27.21 kJ/mol) > Ca2+(−15.51 kJ/mol) > Mg2+(−6.061 kJ/mol). For surface H2O, a new blueshift adsorption peak (3612 cm−1) is observed in the infrared spectral analyses which indicate a strong Lewis acid-base reaction for H2O at charged clay surface. This study indicates that, for the catalytic activities of charged clay catalysts, the background cation types and concentrations, the electric field intensity and the orbital asymmetric hybridization effect at charged clay surface would be coupled and intertwined. Importantly, in those factors/effects the electric field and its initiated orbital asymmetric hybridization of surface atoms/cations should play the critical roles, and thus these two key factors should be emphasized in clay catalyst design.

A double structure model for hydro-mechano-chemical behavior of expansive soils based on the surface phenomena of mineral crystals

It is well known that the typical swelling behavior of expansive soils is mainly caused by the nanoscale electrochemical phenomena on the surface of their main constituent mineral (i.e., smectite). In this study, the hydro-mechano-chemical (HMC) model for unsaturated expansive soils, which combines the macroscale soil skeleton behavior and the nanoscale interlaminar behavior of mineral crystals based on the surface phenomena is proposed within a double structure framework. The soil skeleton behavior is modeled using the Cam clay type model based on Bishop's effective stress, which considers the degree of saturation-induced hardening. Thus, it is capable of describing hydraulic collapse. Furthermore, the interlaminar behavior is demonstrated through the interlaminar force equilibrium of clay mineral crystals. To describe the swelling process during wetting, namely the crystalline and osmotic swellings, the hydration and osmotic forces acting on the mineral crystals are related to the degree of saturation. Through simulations of a series of the suction-controlled oedometer tests and the swelling pressure tests with various solutions for FEBEX bentonite, it is indicated that the proposed model demonstrates that it can comprehensively describe the typical HMC behavior of expansive soils.

Illite and chlorite cementation of siliciclastic sandstones influenced by clay grain cutans

The distribution and amount of clay rim cements are different for Permian Rotliegend and Lower Triassic Bunter sandstones in the Southern Permian and German Triassic Basins, respectively. Both are similar fluvial-aeolian deposits in hot-arid endorheic basins. In both Permian and Triassic sandstones clay grain cutans can be present, but clay rim cement is often lacking or rare in Bunter sandstones. At first sight it would appear that the presence of cutans is thus not relevant for the development of clay cementation. However, at closer inspection, it appears that authigenic clay is indeed present in both cases. In Rotliegend sandstones, the authigenic clay mainly developed as rims around the clay grain cutans, which are often thin and well microlaminated with few intra-micropores and composed of platy particles. The clay crystals in the rim decrease the pore interconnectivity and lower permeability significantly. In Bunter sandstones, most of the authigenic clay developed within the cutans. These cutans are less well microlaminated, have ample micropores, and are composed of more equant-shaped particles. The latter looser structure facilitated clay authigenesis within the cutans and their micropores. This often led to exfoliation of the cutan laminae and expansion of the entire cutan. These expanded cutans also lower pore connectivity. The presence and thickness of clay rim cement on top of cutans and grains is thus not correlated with the thickness of the cutans but with the texture of the cutans. The latter determined where authigenic clays precipitated and the thickness of cutans is partly the result of clay authigenesis within the cutans. This demonstrates that the composition and the texture of sedimentary components constrained and controlled burial diagenesis.

Evaluation of geoenvironmental hazards at Qasr Al-Farid tomb, Mada’in Saleh, northwestern Saudi Arabia

Mada’in Saleh, northwest of Saudi Arabia, has attractive tombs carved in the outcrop cliffs of sandstone. The present study aims to evaluate the geoenvironmental hazards and to determine the main decay factors in the Mada’in Saleh tombs, using different analytical methods to support appropriate decisions. Besides field observations, meteorological data, optical, polarizing, scanning electron microscopy, and x-ray diffraction analysis were used to examine the stone samples. Mada’in Saleh outcrop cliffs are formed of Quweria sandstone (Cambrian). Petrographical analysis reveals that the sandstone detrital grains are composed of monocrystalline and polycrystalline quartz in addition to minor amounts of mica and clay minerals. According to SEM observations, the disintegration of clay minerals and salt crystallization are the major factors in the decay of Qasr Al-Farid’s tomb. The daily high temperature sometimes exceeds 44 °C; wind erosion and relative humidity can cause continuous wetting-drying cycles on the stone surfaces.

Effect of the surface hydration of clay minerals on the adsorption of cesium and strontium from dilute solutions

The use of clay minerals for the decontamination of liquid radioactive waste generated during the work of nuclear energy enterprises remains currently relevant. The effect of the surface hydration of a montmorillonite nanocrystal on the adsorption of cesium and strontium ions from dilute solutions was studied. As opposed to the generally accepted mechanism of the adsorption of cesium and strontium ions on active sites of clay mineral crystals, we considered the adsorption of radiocesium and radiostrontium by montmorillonite taking into account its colloidal chemical properties. When montmorillonite nanocrystals interact with water, a double electric layer with a mobile diffuse ionic atmosphere forms on the surface of the solid phase. The adsorption of cesium and strontium ions from dilute aqueous solutions confines itself to ion-exchange reactions of cesium and strontium ions of a dispersion medium with exchange cations of the diffuse ionic atmosphere of montmorillonite. Enhanced adsorption of cesium ions compared with strontium ions was explained by low charge density on the outer shell of cesium ions and the ability of cesium ions to overcome the diffuse ionic atmosphere easily and to be fixed firmly on the outer surface of the montmorillonite nanocrystal.

Molecular Dynamics in Nanocomposites Based on Renewable Poly(butylene 2,5-furan-dicarboxylate) In Situ Reinforced by Montmorillonite Nanoclays: Effects of Clay Modification, Crystallization, and Hydration.

This study deals with poly(butylene 2,5-furan-dicarboxylate), PBF, a renewable bio-based polyester expected to replace non-eco-friendly fossil-based homologues. PBF exhibits excellent gas barrier properties, which makes it promising for packaging applications; however, its rather low and slow crystallinity affects good mechanical performance. The crystallization of this relatively new polymer is enhanced here via reinforcement by introduction in situ of 1 wt % montmorillonite, MMT, nanoclays of three types (functionalizations). We study PBF and its nanocomposites (PNCs) also from the basic research point of view, molecular dynamics. For this work, we employ the widely used combination of techniques, differential scanning calorimetry (DSC) with broad-band dielectric relaxation spectroscopy (BDS), supplemented by polarized light microscopy (PLM) and thermogravimetric analysis (TGA). In the PNCs, the crystalline rate and fraction, CF, were found to be strongly enhanced as these fillers act as additional crystallization nuclei. The improvements in crystallization here correlate quite well with those on the mechanical performance recorded recently; moreover, they occur in the same filler order, in particular, with increasing MMT interlayer distance (from ∼1 to ∼3 nm). In the amorphous fraction of the polymer, the chain diffusion (calorimetric Tg and dynamic α process) is easier in the PNCs due to their slightly smaller length, while in the semicrystalline state, it decelerates by crystal-induced constraints. The local polymer dynamics (β process, below Tg) was found to be independent of the PNC composition, however, sensitive to structural changes of the matrix. Finally, a filler-induced dynamics was additionally recorded in the PNCs (α* process), arising possibly from the polymer located at the MMT surfaces. α* follows the changes in polymer chain length and decelerates with crystallization, whereas its activation energy decreases with mild hydration. The combined results on α* with the DSC and TGA findings, provide proof for weak MMT-PBF interactions. Overall, our results, along with data from the literature, suggest that such furan-based polyesters reinforced with properly chosen nanofillers could potentially serve well as tailor-made PNCs for targeted applications.

A method for extending a general constitutive model to consider the electro‐chemo‐mechanical phenomena of mineral crystals in expansive soils

SummaryThe mechanical behavior of expansive soils varies according to the chemical composition of the pore fluid. It is well known that electrochemical phenomena on the surface of clay mineral crystals considerably affect their macrostructural behavior. In particular, a change in the pore fluid composition causes osmotic consolidation or swelling. In this study, a model is constructed to describe the characteristic behavior of expansive soils by coupling the interlaminar behavior of clay mineral crystals and the soil skeleton behavior. The interlaminar behavior is derived from the electro‐chemo‐mechanical coupling equilibrium of mineral crystals, and the soil skeleton behavior is given by a general elastoplastic constitutive model for soils. This modeling approach extends a general model to consider the electro‐chemo‐mechanical phenomena of mineral crystals. Oedometer tests with the replacement of the cell fluid and the swelling pressure and deformation tests on expansive clays are simulated with the proposed model. The simulation results indicate that the proposed method can reasonably represent the typical behavior of expansive soils.

Facile preparation of attapulgite‐based aerogels with excellent flame retardancy and better thermal insulation properties

ABSTRACTA novel and environmentally friendly attapulgite‐based aerogel with a three‐dimensional fibrillary network structure was prepared by incorporation of nanometer‐sized natural clay crystals, in this case attapulgite (ATP), into degradable poly(vinyl alcohol) (PVA), cotton cellulose nanowhisker, and melamine using only a simple blending method and subsequently a freeze‐drying process. The ATP‐based aerogel exhibits an abundant porosity with an average mesopore size of 8.0 nm in diameter. Compared to fragile and rigid inorganic aerogels, the as‐prepared aerogel shows good flexibility and mechanical strength with a compressive strength of 9.65 × 104 Pa and 10.19 × 104 Pa at 20% and 40% of compressive strain, respectively. The limiting oxygen index (LOI) and vertical flame tests show that the resulting aerogel possesses excellent flame retardancy, with an LOI of 59.5%. Microcalorimetry test results show that the total heat release of the aerogel is as low as 5.1 KJ/g. Also, the sample shows a better thermal insulation property, with a thermal conductivity of about 0.045 W m−1 K−1 in air. Taking advantage of a simple and environmentally friendly fabrication, abundant natural clay resources, easy scalability, nearly no pollution emission in the process, and cost‐efficient production, the ATP‐based aerogel has great potential as ideal flame retardant and thermal insulation materials for many applications such as modern building construction or energy‐efficient coatings. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47849.

Implications and characterization of waste glass cullet – kaolinite clay ceramics

Cullet(x) reinforced ceramics (100 – x) made from Ukpor kaolinite clay by dry-pressing and fired at temperatures (T 0 C) for 900≥T≤ 1250 0 C with 0≤x ≤40% wt was investigated for its ceramics application. The chemical profile of the samples (cullet and clay) was determined by Atomic Absorption Spectroscopy (A.A.S) technique. Mineral composition was determined by XRD while SEM was employed to view the phase modification. The particle size of the raw materials was maintained at <180μm. The mechanical properties, micro-structure, and phase composition are discussed with respect to cullet content and temperature variation. It was observed that production temperature decreased with increase in cullet. Micro-structural study showed a granulated morphology and the formation of phase-boundary as granules fuse due to clay cullet crystallization with increase in cullet and temperature. Electrical insulation is greatly improved while thermal insulation is reduced due to the closure of pores with increase in cullet and temperature respectively. The mechanical properties of flexural strength, porosity, bulk and apparent density, shrinkage and water absorption were greatly modified for every 10% increase in cullet content. Production temperature greatly reduced with increase in cullet suggesting longer lifespan for the kilns and furnaces used. The study supports the utilization of cullet in the production of ceramics, a good reason to recycle waste to wealth but in excess of 20% cullet, production temperature must not exceed 1100 0 C due to development of cracks. Keywords: Bulk Density, cullet; porcelain; porosity; Ukpor clay (U.C); temperature

Hydrothermal alteration of the Ediacaran Volyn-Brest volcanics on the western margin of the East European Craton

The Ediacaran continental flood basalts and associated tuffs were studied to identify and quantify alteration processes by means of XRD and chemistry, supplemented by Mössbauer and FTIR spectroscopies, petrography, oxygen and iron isotopes, K-Ar dating, and organic geochemistry. Two superimposed alteration processes were identified: the Ediacaran hydrothermal alteration, induced by meteoric waters, heated and put in motion by the cooling basalt, and the Caledonian and/or Variscan potassic alteration. The degree of basalt alteration was quantified using as an index the sum of primary minerals in the bulk rock. The sequence of minerals dissolved and crystallized during the hydrothermal alteration was established. The alteration resulted in the loss of Ca (dissolution of plagioclases), compensated by the gain of water and Mg (crystallization of clays), and proceeded from the edges of the basalt flows in an oxidizing environment, evidenced by the increasing amount of hematite and Fe3+/Fe2+ ratio of the bulk rock. Cyanobacteria were active in the hydrothermal system, most probably responsible for the measured negative δ56Fe values and more reducing conditions at the stage of intense alteration. Chlorophaeite (palagonite), following quartz as the earliest petrographically identifiable basalt alteration product was found to vary systematically from fully isotropic to birefringent. The chlorophaeite was identified as a mixture of Fe-montmorillonite and Fe-saponite, identical with griffithite and oxysmectites, probably preceded by a finer-grained ferrosaponite at the isotropic stage. REE content of chlorophaeite indicates basaltic volcanic glass (sideromelane) as the major source of material. REE in clays are contained mostly in the dioctahedral smectite, while in the bulk rock mostly in phosphates. The smectite characteristics and Mg enrichment are indicative of the hydrothermal basalt alteration process, which perhaps was dominant also on Mars.Both mineral and chemical composition of tuffs vary continuously from basaltic to felsic, the latter close to the measured rhyodacite composition, dominated by quartz and feldspars. The basaltic tuffs resemble the most altered basalts but contain also abundant albite and chlorite, indicative of higher alteration temperatures, up to 220 °C. Tuff composition indicates stronger component of felsic volcanism in the trap formation than evidenced by the preserved bodies of effusive rocks.

Experimental and analytical investigations of volume change behaviour of saturated expansive soils in oedometer test

The chemical and mechanical behaviours of saturated bentonite were experimentally and analytically investigated. A series of oedometer tests on saturated bentonite was conducted. By replacing the cell fluid during the oedometer test, one-dimensional osmotic consolidation and swelling behaviour were observed. The experimental results were simulated numerically using a constitutive model by considering the influence of electrochemical phenomena of clay mineral crystals on the macrostructural behaviour. It was concluded that the typical mechanical swellability of water-saturated bentonite in oedometer test is affected by a positive dilatancy behaviour due to the lower shear strength. After the osmotic consolidation test, a lateral contraction of the specimen in the oedometer was observed; this affected the compressibility during the subsequent mechanical consolidation. It was also concluded that the concentration of Na+ in the pore fluid affects the specific mechanical properties of bentonite.

Clay minerals related to the late magmatic activity of the Piton des Neiges (Réunion Island): consequence for the primitive crusts

ABSTRACTThis paper describes a detailed petrographic and isotopic study of hypabyssal sheets of quartz-syenite that represent the ultimate differentiation product of the oceanite alkaline magmatic reservoir of the Piton des Neiges stratovolcano (Réunion Island). Clay minerals of the corrensite to chlorite series crystallized during the late-magmatic activity, with quartz, carbonates and accessory minerals from juvenile fluids filling the primary porosity of the quartz-syenite. It is proposed that a double chemical transfer occurred at the end of the crystallization process: degassing of the exsolved CO2-rich and SiO2-rich fluid from the magmatic chamber through the porous quartz-syenite and diffusion of Al, Fe and Mg from the intruded basalts affected by the juvenile fluids towards the primary porosity of the quartz-syenite, feeding the crystallization of late-magmatic clays in the residual primary pores after quartz and carbonate deposition. This process may be generalized to alkaline plutonism, as well as to the primitive crusts of terrestrial planets, and may be the first source of clays in early planets.

Crystal Growth of Layered Silicate Grafted with Organic Groups on Monodisperse Spherical Silica Particles

AbstractControl of the structure and morphology of clay crystals presents a challenge in the synthesis of materials for adsorption and catalysis. In the present study, direct crystallization of a phyllosilicate grafted with organosilyl (methylsilyl and phenylsilyl) groups on the surface of monodisperse spherical silica particles (2.6 μm) is reported. Methyl- and phenyltriethoxysilanes were allowed to react hydrothermally in a Teflon-lined autoclave with silica, MgCl2, and LiF in the presence of urea for 2 or 4 days. X-ray diffraction patterns revealed that the fine platy particles formed were a trioctahedral hectorite-like layered silicate. Greater temperature (150°C) was required to achieve homogeneous coverage of the original spherical silica particles with the hectorite-like particles. The diameter of the initial silica grains increased slightly to 3.0 μm after the hydrothermal reactions, while the original spherical shape and size distribution were maintained. Solid-state 29Si nuclear magnetic resonance analyses confirmed that the presence of resonances attributed to the RSi(OMg)(OSi)2 and RSi(OMg)(OH)(OSi) (R = methyl or phenyl) environments of the silicon proved the formation of covalent bonds between phyllosilicate sheets and the organic moieties. The crystallinity of the layered silicates increased when the reactions ran for a longer time (4 days).