Smectite Particles Research Articles

Distribution of Clay Minerals In the Northern North Sea Basin During the Paleogene and Neogene: A Result of Source-Area Geology and Sorting Processes

Abstract: Clay-mineral compositions have been analyzed in samples from the Danish, Norwegian, British, and Dutch North Sea sectors and from onshore Denmark and Germany, comprising both wells and outcrops (clay pits and cliff sections). The time slices investigated comprise from the Paleogene, the post-Ekofisk Fm. interval of the Paleocene, the entire Eocene, and the entire Oligocene. The Neogene time slices investigated comprise the following Miocene intervals: the Vejle Fjord Fm., the Klintinghoved Fm., the Arnum Fm., and the Gram Fm. There were not enough samples from offshore wells to make a detailed stratigraphic subdivision of the Paleogene. It was, however, possible to refer Miocene samples to specific lithostratigraphic units. The onshore Danish nomenclature was applied, and seismic sections were used to correlate between wells and outcrops. Existing biostratigraphic data were used to control the stratigraphic interpretation. The distribution of the most dominant clay minerals—smectite, chlorite, kaolinite and illite—are shown on maps comprising the Paleocene, Eocene, Oligocene, and the formations Vejle Fjord Fm., Klintinghoved Fm., Arnum Fm., and Gram Fm. from the Miocene. The investigation has shown that the source-rock composition plays an important role in the clay-mineral content of the sediments. For example, smectite makes up a higher proportion in periods with substantial supply of volcanic material, especially in the Paleocene and early Eocene. In source areas, where metamorphic rocks dominate, chlorite is present in the sediment adjacent to these areas. The illite content in sediments increases where the source area is dominated by granites and/or gneisses. Sorting of the supplied suspended material generally controls the depositional area for the minerals. For example, the larger particles of kaolinite are generally more abundant in nearshore areas, whereas the relatively small smectite particles normally dominate in the central parts of the sedimentary basins. Illite and chlorite are relatively abundant in areas between those rich in smectite, present in the central part of the basin, and those rich in kaolinite, present in the marginal parts of the basin. Climatic conditions during erosion and deposition seem to play an important role, especially in the distribution of chlorite, which is rather sensitive to chemical weathering. This means that chlorite makes up a greater proportion of the sediment in periods with colder climate, such as in the Oligocene and late Miocene. The uplift of surrounding areas seems to be an important factor for the amount of detrital material transported to the North Sea. The elevation of marginal areas also played an important role in the reworking of Paleogene sediments during the Neogene. Mass flows, including turbidity currents, have redistributed marginal kaolinite-rich sediments, deposited in marginal areas of the basin, to more basin-central locations, especially in the Paleocene Viking Graben. Diagenetic modification of the originally supplied clay minerals seems to be minor since the highest contents of smectite occur in the oldest and deepest areas with more than 3 km of overburden. The reason for this is believed to be the extremely low permeability of the very fine-grained smectite-dominated clays hindering water from being expelled from the sediments, combined with low contents of K-bearing minerals necessary for the formation of illite from smectite.

Short-term impact of de-vegetation on organic/inorganic interactions and cation transfers in uppermost soil horizons

The soil solutions of a natural soil covered by grass and of the same soil after grass removal were collected and analyzed after each rainfall and percolation through the two soils during a fifteen-month experiment. To identify and quantify the water–mineral–plant interactions during this period of time, plastic tubes containing calcite and smectite particles were inserted into the two soils, some powder of both being recovered after three and fifteen months, water leached and the leachates analyzed. The contents of various elements including the rare-earth elements were measured in the soil solutions and the water leachates, to identify the extent of the interactions and evaluate the contribution of the plants. The immediate impact of de-vegetation was recorded in the soil solutions that exported systematically more Si and Ca, and often more Mg from de-vegetated soil. The supplement of exported Si was probably released by altering microorganisms as a response to de-vegetation, whereas that of Mg resulted probably from dissolution of oxy-hydroxides and that of Ca from partial dissolution of the calcite reference mineral. The removed elements were about 50 times higher in the soil solutions than in the plain rainwater before percolation through the soils. The contents of the dissolved organic carbon and ammonia of the soil solutions from de-vegetated soil were about one third higher than in those of the vegetated soil.On the basis of the elemental contents of the soil solutions that percolated through the two soils, removal of plants did not significantly affect adsorption of the nutrient K on the inserted smectite and calcite during the initial three months. However, less K was adsorbed on smectite and calcite of the de-vegetated soil than on the same minerals of the same soil covered with grass during the following twelve months, indicating in turn that more K was removed from de-vegetated soil within a one-year time.

Clay mineralogy in southern Africa river muds

AbstractThe composition, morphology and crystal order of clay minerals in silt-sized sediments carried in suspensions from 25 major rivers across tropical southern Africa have been studied by X-ray diffractometry and scanning and transmission electron microscopy. Our goal was to determine the spatial variability of clay-mineral associations in diverse geological settings, and in climatic conditions ranging from humid Angola and Zambia to hyperarid Namibia and the Kalahari. Specific attention was paid to the micromorphology and chemical composition of smectite particles. The relative abundance of smectites, illite/mica, kaolinite and chlorite enabled identification of regions characterized by different physical and chemical processes: (1) negligible chemical weathering is documented in Namibia, where river muds mostly contain illite/mica or smectite derived from Damara metasedimentary or Etendeka volcanic rocks; (2) kaolinite documenting intense weathering, reaches a maximum in the Okavango, Kwando and Upper Zambezi, sourced in subequatorial Angola and Zambia; (3) suspended-load muds in the Limpopo and middle Zambezi catchments display intermediate features, with varied assemblages and smectite compositions reflecting diverse parent lithologies. Clay mineralogy and chemical composition are confirmed as a most effective tool to unravel present and past climatic conditions on a continental scale.

Adsorption, aggregation, and desorption of proteins on smectite particles.

We report on adsorption of lysozyme (LYS), ovalbumin (OVA), or ovotransferrin (OVT) on particles of a synthetic smectite (synthetic layered aluminosilicate). In our approach we used atomic force microscopy (AFM) and quartz crystal microbalance (QCM) to study the protein-smectite systems in water solutions at pH ranging from 4 to 9. The AFM provided insights into the adhesion forces of protein molecules to the smectite particles, while the QCM measurements yielded information about the amounts of the adsorbed proteins, changes in their structure, and conditions of desorption. The binding of the proteins to the smectite surface was driven mainly by electrostatic interactions, and hence properties of the adsorbed layers were controlled by pH. At high pH values a change in orientation of the adsorbed LYS molecules and a collapse or desorption of OVA layer were observed. Lowering pH to the value ≤ 4 caused LYS to desorb and swelling the adsorbed OVA. The stability of OVT-smectite complexes was found the lowest. OVT revealed a tendency to desorb from the smectite surface at all investigated pH. The minimum desorption rate was observed at pH close to the isoelectric point of the protein, which suggests that nonspecific interactions between OVT and smectite particles significantly contribute to the stability of these complexes.

Water retention behaviour and microstructural evolution of MX-80 bentonite during wetting and drying cycles

MX-80 bentonite used in engineered barrier systems would be subjected to wetting and drying cycles. To assess the response of the material under such circumstances, a comprehensive experimental characterisation of the water retention behaviour of compacted MX-80 granular bentonite was performed in this study. A new methodology is proposed to investigate this behaviour under a constant volume condition for specimens prepared at different dry densities. The material was subjected to different hydraulic paths, including cyclic variations of the water content. As a result, an irreversible modification of the retention behaviour was observed when the material approached a fully saturated state during the first main wetting, and a new hydraulic domain was consequently created. The water retention capacity of the material increased as a result of such modification. Microstructural observations were performed at different stages of the hydraulic paths to relate the permanent change in the retention behaviour to the evolution of the fabric during the wetting and drying cycles. A clear transition from a double-structured to a single-structured fabric, followed by a permanent change of the microfabric, was found following the first wetting. Available data on the hydration of smectite particles were used to relate the microstructural evolution to the change in the water retention properties. This correlation shows the evolution of the active porosity at the particle level within the microstructure, which consequently affects the macroscopic response of the bentonite in terms of its water retention behaviour.

The Interaction Between Bentonite and Water Vapor. I: Examination of Physical and Chemical Properties

AbstractThe influence of water vapor on bentonites or smectites is of interest in many different fields of applied mineralogy such as nuclear-waste sealing or casting in the foundry industry. The water vapor affects the smectite surface and perhaps its structure probably leading to mostly unfavorable changes in its properties. In this first part of the present study, the influence of hot water vapor (200°C) on the physicochemical and mineralogical properties of smectite-group minerals was studied. After the steam treatment, turbidity measurements, methylene-blue sorption, water adsorption, and cation exchange capacity (CEC) were measured on both untreated and treated samples. Mineralogical changes were monitored by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) was used to measure O, Al, and Si. Only a few parameters showed differences between the untreated and vapor-treated samples. Sedimentation volumes (SV) decreased following the treatment. As shown by XRD and XPS, the crystalline structure of smectite remained unaffected by the steam treatment. Equivalent sphere diameters (ESD) were not affected systematically by the steam treatment. Differences in CEC values between untreated and treated samples were observed, but only for smectites with monovalent interlayer cations. From the variety of different measurements the conclusion of the present study was that steam treatment changes the charge properties at or near the smectite particle surface.

Clay Fabric in Electrokinetic Dewatering

Electrokinetic dewatering, a promising way to separate the clay particles from water in suspensions, has been researched for many years on topics like equipment design, parametric optimization, and ion migration.1 However, little work has been done on the clay fabric which affects the performance to a considerable degree during electrokinetic dewatering since different fabrics have different electrokinetic properties. Therefore, if we could figure out fabric and control it intentionally, a breakthrough in improving the productivity and lowering the energy consumption will be possible.Suspensions come from four corners mining plant in central Florida, which contains approximately one-third phosphate, one-third sand and one- third clay. Clay, mainly smectite here, plays the key role in dewatering due to the relatively small particle size and large surface area. Smectite plate is a 2:1 structure with permanent negative charge on the two faces, and pH-dependent charge on the edge.2 It is this property that makes the behavior of smectite complex in electrokinetic dewatering under the effect of both pH and electrical force simultaneously. To dissociate the effect of the two mechanisms, a natural settling experiment at different pH and an electrokinetic dewatering experiment were conducted.In the natural settling experiment, suspensions at acid environment reach stable state very fast and show a “gel” like behavior. However, suspensions in neutral and alkaline environment remains to be liquid like ones. The SEM results (Fig 1) of the sediments samples prepared by freeze-drying show that smectite particles in the presence of acid show edge-face fabric and flocculate into “honeycomb” structure as a result of the edge-face attraction and face-face repulsion (Fig 1a), while particles in neutral suspensions mainly display edge-edge, and in alkaline environment show all fabrics (edge-edge, edge-face, face-face) without dominating part.In the electrokinetic dewatering experiment, an electric field of 4V/cm was applied for 13 minutes. The SEM results (Fig 1b) elucidates that honeycomb forms at lower layer near anode where H+ exists due to electrolysis of water during the separation process, but appears to be more compressed compared with that of natural settling (Fig. 1a), which should be due to the electrical force. The middle and upper layer with a slightly alkaline environment looks much more disordered than the lower layer.Intuitively, we could infer that the rigid “gel” like honeycomb is not desirable for separation of particles compared with “soft” suspensions. In addition, the cells of the honeycomb are likely to trap water, which weakens electro-osmosis. The significance of this work exists in the difference of the electrokinetic properties between disordered plates and flocculated honeycomb. If the difference is quantified, then measures could be taken to control the fabric intentionally. Thus, we can predict the process more accurately and achieve a better performance. References A. Mahmoud, J. Olivier, J. Vaxelaire, A. F. Hoadley, Electrical field: a historical review of its application and contributions in wastewater sludge dewatering,Water research, 44(2010), 8. G. Lagaly, S. Ziesme . Colloid chemistry of clay minerals : the coagulation of montmorillonite dispersions. Advances in Colloid and Interface Science, 100-102(2003), 105–128.

Networking and rheology of concentrated clay suspensions “matured” in mineral medicinal water

This work studied the influence of "maturation" conditions (time and agitation) on aggregation states, gel structure and rheological behaviour of a special kind of pharmaceutical semisolid products made of concentrated clay suspensions in mineral medicinal water. Maturation of the samples was carried out in distilled and sulphated mineral medicinal water, both in static conditions (without agitation) and with manual stirring once a week, during a maximum period of three months. At the measured pH interval (7.5-8.0), three-dimensional band-type networks resulting from face/face contacts were predominant in the laminar (disc-like) clay suspensions, whereas the fibrous (rod-like) particles formed micro-aggregates by van der Waals attractions. The high concentration of solids in the studied systems greatly determined their behaviour. Rod-like sepiolite particles tend to align the major axis in aggregates promoted by low shearing maturation, whereas aggregates of disc-like smectite particles did not have a preferential orientation and their complete swelling required long maturation time, being independent of stirring. Maturation of both kinds of suspensions resulted in improved rheological properties. Laminar clay suspensions became more structured with time, independently from static or dynamic maturation conditions, whereas for fibrous clay periodic agitation was also required. Rheological properties of the studied systems have been related to aggregation states and networking mechanisms, depending on the type of clay minerals constituents. Physical stability of the suspensions was not impaired by the specific composition of the Graena medicinal water.

Reaction of smectites with iron in aerobic conditions at 75 °C

The stability of six dioctahedral smectites with different crystal chemistry was studied in the presence of iron to simulate the possible reactions of clay minerals in contact with Fe canister in a nuclear waste repository. The batch experiments were performed at 75°C for 35days in air. The reaction products were examined by XRD, QXRD, FTIR, BWA analyses and UV–Vis spectroscopy. The reaction of bentonites with metal iron led to the consumption of iron and the formation of magnetite and 7-Å phyllosilicate. The original smectites were partially transformed from Al-rich to Fe-bearing. Appearance of the dioctahedral–trioctahedral domains in the octahedral sheets of smectites resulted in the partial destabilization and/or partial dissolution of the smectite structure indicated by the increase of the layer charge, splitting of the smectite particles and partial disruption of the smectite layers. Benefits of NIR spectroscopy were found in identification of FeMgOH and FeFeOH groups, which were not recognized in the MIR region of reacted iron–bentonite mixtures due to overlapping with other absorption bands. The comparison of the present study with the paper of Osacký et al. (2010) showed that smectites reacted differently with iron in air and nitrogen atmosphere. In the aerobic conditions more iron was consumed and less amount of magnetite was formed. The distinct experimental conditions (aerobic versus anaerobic) had the greatest effect on the layer charge and thickness of the smectite particles. Less pronounced changes of the layer charge and thickness of the smectite particles were observed for the iron–bentonite mixtures reacted in the aerobic conditions. It indicated that smectite destabilization was inhibited in the aerobic conditions.

Evolution with depth from detrital to authigenic smectites in sediments from AND-2A drill core (McMurdo Sound, Antarctica)

AbstractWe have examined the nature and origin of smectites in glaciomarine sediments of the AND-2A drill core (McMurdo Sound, Antarctica) by means of X-ray diffraction (XRD) analyses on the clay fraction, field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM) observations and SEM-EDS microanalyses on smectite particles. Relying on the smectite variation throughout the drill core it was possible to split the sequence into three units. Smectites throughout the core are either detrital or authigenic. Detrital smectites are close to montmorillonite-beidellite in composition while newly-formed smectites frequently have higher Fe-Mg contents and intermediate compositions between the saponite and nontronite field, with lower amounts in the montmorillonite-beidellite field. In the upper sedimentary sections (Unit I, and Unit II, 36-440 mbsf, 0.7-16.5 Ma) smectites are interpreted to be predominantly detrital, whereas in the lower portion of the core (Unit III, 440-1123.20 mbsf, 16.5-20.2 Ma) authigenic smectites are the most common feature. The predominance of mica, the abundance of chlorite, and the nature of smectites in the upper units indicate physical weathering under cold and dry climate, and a dominant provenance for the clay minerals from the Transantarctic Mountains. Smectites in the lower unit are considered mostly authigenic and they are most likely to be the result of early diagenetic processes, being formed from the alteration of volcanic material (glass, pyroxenes and feldspars) and/or through precipitation from fluids of a possible hydrothermal origin. Our survey attests to the importance of discriminating between a detrital and authigenic nature of smectites as the occurrence of authigenic clay minerals in ancient sedimentary successions might lead to incorrect palaeoclimatic interpretations, since they can be affected by diagenetic processes, thus obliterating the climatic signal.

Dynamics of Confined Reactive Water in Smectite Clay–Zeolite Composites

The dynamics of water confined to mesoporous regions in minerals such as swelling clays and zeolites is fundamental to a wide range of resource management issues impacting many processes on a global scale, including radioactive waste containment, desalination, and enhanced oil recovery. Large-scale atomic models of freely diffusing multilayer smectite particles at low hydration confined in a silicalite cage are used to investigate water dynamics in the composite environment with the ReaxFF reactive force field over a temperature range of 300-647 K. The reactive capability of the force field enabled a range of relevant surface chemistry to emerge, including acid/base equilibria in the interlayer calcium hydrates and silanol formation on the edges of the clay and inner surface of the zeolite housing. After annealing, the resulting clay models exhibit both mono- and bilayer hydration structures. Clay surface hydration redistributed markedly and yielded to silicalite water loading. We find that the absolute rates and temperature dependence of water dynamics compare well to neutron scattering data and pulse field gradient measures from relevant samples of Ca-montmorillonite and silicalite, respectively. Within an atomistic, reactive context, our results distinguish water dynamics in the interlayer Ca(OH)(2)·nH(2)O environment from water flowing over the clay surface, and from water diffusing within silicalite. We find that the diffusion of water when complexed to Ca hydrates is considerably slower than freely diffusing water over the clay surface, and the reduced mobility is well described by a difference in the Arrhenius pre-exponential factor rather than a change in activation energy.

Mineral characterization of soil type ranker formed on serpentines occurring in southern Belgrade environs Bubanj Potok

The paper addresses the issue of health risk associated with the presence of chrysotile in the soil type ranker formed on massive serpentines occurring in the area of Bubanj Potok, a settlement located in the southern Belgrade environs, Serbia. Characterization of the ranker soil was conducted by scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy and transmission 57Fe M?ssbauer spectroscopy. Scanning electron microscopy figures showed regular shaped smectite (montmorillonite) particles, aggregates of chlorite, and elongated sheets of serpentines minerals antigorite. X-ray diffraction analysis confirmed the presence of detrital mineral quartz polymorph as well as minor amounts of other mineral species. Micro-Raman spectroscopy identified the presence of dominant minerals, such as montmorillonite, kaolinite, muscovite, gypsum, calcite, albite, amphiboles (hornblende/kaersutite) and orthoclase. Important polymorph silica modifications of quartz, olivine (forsterite), pyroxene (enstatite/ferrosilite, diopside/hedenbergite), and serpentine (antigorite/lizardite/chrysotile) were identified.

Delamination of smectite in river-borne suspensions at the fluvial/marine interface – An experimental study

Fine fractions (<2 μm) from smectite-rich flood-plain sediments from the Elbe and Weser rivers in Germany were treated in the laboratory with synthetic sea salt solutions at different concentrations and for different periods of time to document sheet delamination of smectite particles at the fluvial/marine interface and thus simulate changes in clay minerals at the mouth of a river. The project consisted of two steps: (1) Pilot tests were made in 0.5% salt solutions (brackish environment) showing a nearly 2-min delay of the clearing of the clayey suspensions, when the suspension was redispersed 15 and 30 min later after the first measurement. This was due to an obviously increased number of fine laminae from disintegrated smectite particles. (2) X-ray diffraction studies (XRD) of the clayey material from suspensions in 0.0, 0.5, 1.0, and 3.0% salt solutions after standing 10 min, and one and three weeks were made to document alteration reactions of smectite. An aliquot was pipetted periodically from each series, and oriented clay-mineral specimens were analyzed by XRD in air-dried, glycol- and glycerin-solvated states. The peak intensities in the XRD patterns of the clay minerals smectite, random-ordered mixed-layer illite/smectite (I–S), kaolinite, chlorite, and illite did not change in the salt-free series during the experiments. In contrast the peak intensities of smectite and I–S mineral in the air-dried and glycerin-solvated states after suspension in saline solutions decreased significantly. The d-values of the smectitic materials in the air-dried state also decreased after contact with the saline solutions, and in the glycerin-solvated state the full-width-at-half-maximum (FWHM) of the 001 smectite reflection increased by about 20%, indicating a reduction in grain size. The variations in FWHM, d-values and peak intensity of the smectitic material are assumed to be caused by an exchange of Na for Ca in the interlayer spaces and subsequent delamination of the particles along the Na-activated interlayers. Only those smectite particles in which adjacent sheets are still stabilized by the remaining Ca are preserved after contact with seawater. The experiments show that delamination of smectite and I–S mixed-layer minerals is likely to occur in the brackish environment at the mouth of a river. However, formation of these fine laminae is expected to be a transitional stage in the development of clay particle size, owing to the formation of flocs and aggregates in the higher salt concentrations of seawater.

Filtering of Clay Colloids in Bentonite Detritus Material

AbstractBentonite clay consists of two types of materials, small nanoscale smectite particles and larger accessory material particles. When used as a barrier, it is important that as little material as possible is lost. This loss may occur if water with low salinity passes by the bentonite clay. First, the clay will swell and then the smectite particles can solubilize. This study investigates under which circumstances the material can form a filter cake of the accessory material and slow down or stop the penetration of smectite through the filter cake. It has been shown that it is possible to form such a filter cake and that the filter cake can be further improved by adding other particles.

The card-house structure of mud: Energy between particles and its effect on bubble formation.

A model of mud as a lyophobic colloid [Verwey and Overbeek (1948)] leads to a card-house structure of platelets, typically kaolinite or smectite particles. Because of isomorphous substitution, each platelet carries a distributed negative charge. The structure is immersed in water which, especially so for sea water, carries positive and negative ions, and the positive ions tend to cluster on both sides of the platelets, so that the composite platelet charge is zero, but each platelet is analogous to a sheet of longitudinal electrical quadrupoles. The charge distribution causes parallel platelets to repel each other, but which can attach so that one platelet edge can touch the face of another platelet. The energy associated with such attachments is discussed, and it is conjectured that it is associated with van der Waals and London attraction forces. Recent sound transmission experiments by Carey at Dodge Pond in Connecticut support the contention that sediment mud invariably contains vapor bubbles, and other work such as that of Boudreau et al. (2005) suggests that the bubbles are considerably flattened, with shapes that have been described as corn-flakes. Present paper conjectures as to whether these shapes are associated with the card-house structure of mud.

Abrasivity by bentonite dispersions

Bentonites are used for various industrial applications. Their physicochemical properties depend on the mineralogical and chemical composition, the type of smectite, the grain size distribution, the cation exchange capacity (CEC), the dominant interlayer cation (Na +, Ca 2+, Mg 2+), and the layer charge density. All these parameters can be measured with acceptable precision. Nevertheless, the performance of a bentonite in a given application is often unpredictable. An additional relevant parameter is the “microfabric” describing the arrangement of minerals and/or the intergrowth of the minerals with glass. The microfabric is supposed to affect different bentonite properties such as swelling capacity and rheology. The present study focuses on the influence of different microfabrics on the abrasivity by bentonite dispersions. The abrasivity of bentonite dispersions mainly depended on two factors: 1) on the amount of hard and sharp accessory minerals and volcanic glass and 2) the grain size distribution, which was produced by different grinding techniques. The abrasivity increased with decreasing grain size, which was caused by breaking the hard components (minerals and glass) leading to an increased number of sharp edges. In addition, there was evidence for a subordinate influence of the type of exchangeable cations. This influence is explained by the different relative arrangements of smectite particles towards the surfaces of hard and sharp minerals. Na + exchanged glass rich samples showed higher abrasion values than the Ca 2+ exchanged samples.

Smectite suspension structural behaviour

Smectite suspensions, at low solids contents, are known to be naturally high in volume with diverse structural properties. The changing structural properties of smectite aqueous suspensions in the absence and presence of calcium ions were investigated using an acoustosizer and an advanced cryo-SEM technique to further understand and thereby control their environmental impact. In the absence of Ca(II) ions, smectite particles are present as a colloidally stable sol due to electrical double layer repulsion of the negatively charged platelets. The smectite network is observed to be extended throughout the suspension via clay platelets networking with an edge–edge (EE) orientation due to high basal surface repulsion. After the initial addition of Ca(II) ions, the smectite negative zeta potential reduces and the smectite platelets coagulate forming 2 µm aggregates. The platelets are randomly orientated, lettuce-like, coagulated aggregates with a high presence of both edge–edge (EE) and edge–face (EF) orientations. After equilibration, the smectite platelets forming an orientated honeycomb cellular structure comprised of face–face (FF) multiply sheet aggregates. The voids in the cellular structure are larger than prior to Ca(II) addition, measured at 2–8 µm. The changing structural properties of a smectite suspension in the absence and presence of Ca(II) greatly influence smectite stability and in turn, mineral processing and/or environmental management. Adequate time is required to allow suppression of the initial swelling of the smectite, full Ca(II) exchange and platelet aggregation.

Influence of clay addition on the properties of olive oil in water emulsions

The behaviour of olive oil-in-water emulsions (O/W) was studied in the presence of smectite particles. The distribution of these particles in the emulsions and the effect of their interaction with the surfactant on the stability of the emulsions were investigated. Whereas the variation of surfactant and/or clay content did not seem to affect the nature of the emulsion, it had a significant influence on emulsion stability. This observation led to two main assumptions on the distribution of clay particles within the emulsion, either exclusively in the continuous phase, or also at the oil-water interface. In the absence of clay, the variation of surfactant concentration (from 0 to 17% (w/w)) allowed to distinguish 3 domains. In the first concentration domain (0–4.2%) emulsions stability increased with the content of surfactant. Within the second domain (4.2–8.5% (w/w)), a slight decrease in stability was observed due to flocculation by depletion. For surfactant concentrations equal or higher than 8.5% (3rd domain), emulsion stability increased sharply, probably due to the development of interactions between surfactant molecules as they came closer to their gelling concentration. The effect of clay addition to the aqueous phase (up to 10% (w/w)) on the physicochemical properties of the studied emulsions was assessed from stability, drop size, interfacial tension, rheological and acido-basic analyses. A model based on the location of clay particles either in the bulk or at the interface could be proposed, in which clay particles would interact with surfactant molecules in the bulk phase, and form a mechanical barrier around the oil droplets, thus increasing emulsion stability .

Characteristics of Clay Minerals in the Northern South China Sea and Its Implications for Evolution of East Asian Monsoon since Miocene

Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.

Rheological Behavior of Smectite Dispersions: The Influence of Suspension Concentration and Exchangeable Cation

The mechanical behaviors of smectite materials in water are very sensitive to many parameters, such as concentration, particle size and morphology, exchangeable cation nature, and chemical environment (pH, ionic strength). The literature usually provides general rules for sodium and calcium bentonites. However, it appears that the quantitative results present a large range of values. This study has established the relationships between the smectite nature (mineralogy, morphology, reactivity) and its rheological behavior according to the exchangeable cation. To develop a complete rheological study, we need 800 g of montmorillonite purified and saturated with or . Huge production necessitates optimized process with accurate control of the powder quality and the chemical environment. Smectite particles have been extracted from a natural bentonite and then saturated with sodium or calcium. Then, each sample was characterized with classical methods like X-ray diffractometry (XRD), and laser granulometry but also cutting-edge technologies like scanning transmission electron microscopy on wet samples (Wet STEM). The Na-smectite dispersion contains a lot of small units whereas the Ca-smectite dispersion contains a few large units. Rheological study consists in flow curves obtained with a high-resolution rheometer. Logarithmic representation of the rheograms permits detecting a yield stress, it separates solid and fluid behavior. The rheological datas (viscosity, consistency, and yield stress) allow defining the limits depending on the concentration and on the saturation state. A Newtonian law could be applied to around 4% for Na- and Ca-smectites. Seaward of these concentrations, the dispersions are shear thinning and modelled by Ostwald law. Finally a yield stress appears at 6% for Na-smectite and 11% for Ca-smectite, the flow curves could be modelled by Hershel-Bukley law. Results are in accordance with the bibliography.