Smectite Particles Research Articles

Redox Properties of Structural Fe in Clay Minerals: 4. Reinterpreting Redox Curves by Accounting for Electron Transfer and Structural Rearrangement Kinetics.

Iron-bearing smectite clay minerals can act as electron sources and sinks in the environment. Previous studies using mediated electrochemical analyses to determine the reduction potential (EH) values of smectites observed that the relationship between the structural Fe2+(s)/FeTotal ratio in the smectite and EH varied based on the redox history of the smectite. We hypothesize that this behavior, referred to as redox hysteresis, results from the smectite particles not equilibrating with the applied EH over the course of the experiment (∼30 min). To test this hypothesis, we developed a model incorporating interfacial electron transfer kinetics and charge redistribution within the particle to simulate the mediated electrochemical experiments from previous studies. The simulated redox curves accurately matched the previously reported experimental redox curves of the smectite SWa-1, demonstrating that longer equilibration periods led to a decrease in redox hysteresis. We validated this experimentally by measuring the redox curve of SWa-1 after an equilibration period of at least 12 h. Furthermore, we extended the simulations to three other smectites (NAu-1, NAu-2, and SWy-2) and extracted their respective thermodynamic and kinetic parameters. This work offers a framework for interpreting and modeling redox reactions on clay surfaces, along with key parameters for four commonly studied smectites.

Illitization of montmorillonite in ammonium solutions under hydrothermal conditions

In diagenetic solutions, ammonium may be incorporated into smectites as an exchangeable cation and become fixed within the interlayer space of illites and other white micas. To study the potential impact of NH4+ on the smectite-to-illite transformation reaction, a series of hydrothermal experiments were carried out at 100, 150 and 200 °C, spanning reaction duration from 15 to 90 days, and two NH4+ concentrations (0.1 and 0.2 M). The solids resulting from these alteration experiments were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and transmission and analytical electron microscopy (TEM and AEM). The XRD analysis revealed that, under the specified experimental conditions, smectite incorporates NH4+ in the structure, leading to the formation of non-swelling layers, resulting in partial transformation to illite layers and producing packets of disordered illite/smectite (I/S). In addition, a minor XRD peak at ∼10 Å suggests the formation of discrete illite crystals. The FTIR spectra demonstrated the uptake of NH4+, with deformation bands observed at 1400 and 1430 cm−1, corresponding to exchangeable NH4+ in smectite and fixed NH4+ in high-charge layers, respectively. TEM analysis revealed that smectite particles exhibited wavy stacks comprising a few layers with abundant defects and lateral discontinuities. The interlayer spacing in these particles ranged from 12 to 15 Å and became thinner and more plate-like with increasing temperature and time. Moreover, they contained inclusions of 10–10.3 Å layers, either as discrete layers or in packets of several layers, indicating the formation of disordered mixed-layer illite-smectite. Lateral transitions from 12 to 15 Å to 10 Å layers were frequently observed and interpreted as reaction fronts due to local rearrangement. At 150 and 200 °C, isolated packets of 10 Å layers were identified as discrete illite crystals that precipitated directly from solution. Analysis of the chemical composition of individual particles revealed an increase in octahedral charge (MgVI for AlVI substitution) in smectite particles, followed by increase in tetrahedral charge in I/S particles. Interlayer NH4+ played a stabilizing role in the high-charge layers and favored the smectite-to-illite conversion process.

Smectite-bitumen interactions in non-aqueous bitumen extraction process

The non-aqueous extraction (NAE) is an alternative to the commercial water-based extraction technology used to liberate bitumen from oil sands. Although the impact of kaolinite, illite, chlorite, illite-smectite and montmorillonite on NAE process has been previously studied, the effect of different types of smectites has not been fully understood yet. In this work, mixtures of bitumen with bentonites dominated by saponite, hectorite, nontronite, beidellite and montmorillonite were reacted for several days and then washed with solvent (cyclohexane) to remove bitumen from the bentonites. The main goal was to better understand the impact of different smectites properties (specific surface area, pore structure characteristics, particle size, crystallite thickness, swelling ability, cation exchange capacity, layer charge and crystal-chemistry of smectites) on NAE process. The results showed that the porosity, particle size and swelling ability were the key parameters affecting the solvent-based bitumen recovery under the studied conditions. Samples with larger initial total pore volume and smaller particle size displayed reduced solvent bitumen extractability. The particle size of studied samples was affected primarily by swelling of smectites during the solvent bitumen extraction experiments. Smectites were swelling in water but not in cyclohexane. Swelling of smectite caused splitting of larger clay particles into many smaller particles. As a consequence, the efficiency of solvent bitumen extraction was significantly lower for fine grained samples, consisting of thin delaminated smectite particles, in which the bitumen was distributed among small-sized clay particles.

Potential of Mean Force for Face-Face Interactions between Pairs of 2:1 Clay Mineral Platelets.

Bottom-up modeling of clay behavior from the molecular scale requires a detailed understanding of the free energy between pairs of clay platelets. We investigate the potential of mean force (PMF) for hydrated clays in face-to-face interactions with free energy perturbation (FEP) methods through molecular dynamics simulations using simple overlap sampling (SOS). We show that PMF results for open systems with one finite in-plane dimension are affected by migration of counterions from within the interlayer space compared with fully confined closed system conditions. We compare PMFs for two common 2:1 clay sheet minerals Illite (IMt-1) and Na-smectite. The PMFs for the open illite systems exhibit a strong attractive energy well at a basal layer separation, d = 11 Å and interlayer water content, wIL = ∼0.4% while the attractive minimum for the closed system occurs at d = 12 Å, wIL = 3.5%. In contrast, net repulsion occurs between pairs of Na-smectite platelets for both open and closed systems (for d < 15-16 Å). The free energy is closely related to the distribution of counterions; while K+ ions are bound closely to the surfaces of the illite platelets, Na+ ions are more spatially disperse. This PMF results contradict prior findings for Na-smectite and prompted further comparisons with other published results. We find that most of the published results do not represent accurately the free energy for face-face interactions between pairs of clay platelets that are effectively infinite (with width/thickness O[104]). The PMF results presented in this paper form a reliable basis for mesoscale, coarse-grained modeling of illite and smectite particle assemblies. We show that the Gay-Berne potential provides a reasonable first-order model for upscaling, while the solvation potential proposed by Masoumi enables a more accurate representation of the computed PMFs.

Molecular dynamics simulation of organic contaminant adsorption on organic‐coated smectite clay

AbstractMolecular dynamics simulations are used to examine the adsorption and aggregation of tyrosine and glutamate molecules on a stack of smectite particles at three different organic loadings. The results reveal a strong affinity of the smectite surface for the organic molecules with the zwitterionic tyrosine molecules coating the exterior surfaces (and entering the interlayer region to a lesser extent), whereas the negatively charged glutamate molecules are generally found near the clay edge sites and in coordination with aqueous and coordinating Ca ions. Additional simulations examine the effects of the tyrosine and glutamate organic coatings on the adsorption of two organic contaminants, dimethyl phthalate (DMP) and perfluorobutanesulfonic acid (PFBS). The addition of these coatings did not prevent the DMP and PFBS molecules from accessing previously identified favorable adsorption domains. An analysis of the adsorption energetics shows an initial decrease in contaminant adsorption relative to pure mineral surfaces as tyrosine and glutamate are introduced to the system, followed by increasing adsorption with increasing organic loadings. Overall, this research advances the mechanistic understanding of the interplay between smectite surfaces, organic coatings, and organic contaminants.

Nucleation and dissociation of carbon dioxide hydrate in the inter- and intra-particle pores of dioctahedral smectite: Mechanistic insights from molecular dynamics simulations

The storage of CO2 in the form of gas hydrate is becoming common place in the field of carbon capture and storage. Natural gas hydrate deposits are typically rich in clay minerals, yet their potential effect on CO2 hydrate nucleation and dissociation is rarely elucidated. In the present work, the nucleation and dissociation of CO2 hydrate in the inter- and intra-particle pores of dioctahedral smectite particles were investigated using molecular dynamics simulations. The results show that the hydrate nucleation clearly occurred in the inter-particle pores, whereas clathrate-like structures were formed in the intra-particle pores or on the edge surface of smectite. The properties of smectite, specifically the layer charge distribution and the type of exchangeable cations, are the main factors affecting the nucleation and dissociation of CO2 hydrate by changing the structural ordering of water molecules. The diffusion of CO2 molecules into the intra-particle pores enhances the formation of clathrate-like structures with increasing water content, but it does not increase the structural ordering of water molecules. Increasing the temperature or adding electrolytes in the smectite particles have accelerated the CO2 hydrate dissociation. Overall, the nucleation and dissociation mechanisms of CO2 hydrate in the linked inter- and intra-particle pores of dioctahedral smectite particles not only substantially affects the carbon storage and methane extraction in hydrate reservoirs, but also have potentially important impacts on pore fluids transportation in marine sediments.

Effect of pedogenic iron-oxyhydroxide removal on the metal sorption by soil clay minerals

PurposeThe close association of Fe-oxyhydroxides and clay minerals might influence the sorption properties of these components. We aimed to study the effect of removing the pedogenic Fe-oxyhydroxides on the sorption of Cd, Cu, Pb, and Zn by the clay mineral particles in soils with contrasting pH.MethodsCompetitive batch sorption experiments before and after Fe-oxyhydroxide extraction in soils were carried out together with the direct analysis of the metal sorption on individual particles of ferrihydrite, smectite, and illite/smectite by TEM.ResultsFerrihydrite was a more effective metal sorbent than clay minerals, although its removal resulted in decreased sorption only for Cd, Cu, and Zn. Ferrhydrite coating blocked metals’ access for certain sorption sites on clay surfaces, which were only accessible for Pb as the most efficient competitor after removing the coating. This observation was the most remarkable for the smectite particles in the alkaline soil. Mineral surfaces sorbed higher Cu than Pb concentrations and higher Zn than Cd concentrations despite the former metals’ lower bulk sorption. Thus, organic surfaces and precipitation contributed to Pb and Cd’s retention to a greater extent than for Cu and Zn. The structural Fe of smectite also promoted the metal sorption in both soils.ConclusionRemoval of iron-oxyhydroxide coatings from the soil affects metal sorption selectively. Direct study of metal sorption on individual soil particles enables us to gain a more in-depth insight into soil minerals’ role in this process.

The "blue bottle" experiment in the colloidal dispersions of smectites

The Blue Bottle Experiment involves a reversible redox process of decolorizing methylene blue (MB) by reaction with glucose (Glc) at basic pH. The direction of the reaction is affected by the concentration of dissolved O2. In this work, the reactions that took place in the presence and absence of nanoparticles of smectites (a group of layered silicates) were compared. The method of absorption spectroscopy with a diode-array detector was chosen for studying the reaction. It was possible to measure the full spectrum in a fraction of a second, and thus several hundred spectra were obtained for each experiment. Spectral matrices were analyzed using the chemometric method of multivariate curve resolution (MCR). Analysis of the results revealed not only the formation of known reaction products (a leuco-form of MB, the oxidation products of Glc) but also some other processes related to the changes of the reactants in a basic environment, slow dye decomposition, glucose isomerization, and the formation of MB molecular aggregates. The injection of colloidal smectite particles into the reaction system effectively stopped the redox reaction of MB with Glc, which may be important for dye stabilization in hybrid materials with smectites. This property was not related to the type of smectite, which instead affected the molecular aggregation occurring in the heterogeneous systems.

A Mechanistic Exploration of Natural Organic Matter Aggregation and Surface Complexation in Smectite Mesopores

Soil minerals and organic matter play critical roles in nutrient cycling and other life-essential biogeochemical processes, yet the structural and dynamical details of natural organic matter (NOM) film formation on smectites are not fully understood on the molecular scale. XRD of Suwannee River NOM-hectorite (a smectite clay) complexes shows that the humic and fulvic components of NOM bind predominantly at the external surfaces of packets of smectite platelets rather than in the interlayer slit pores, suggesting that the key behavior governing smectite-NOM interactions takes place in mesopores between smectite particles. New molecular dynamics modeling of a ∼110 Å H2O-saturated smectite mesopore at near-neutral pH shows that model NOM molecules initially form small clusters of 2-3 NOM molecules near the center of the pore fluid. Formation of these clusters is driven by the hydrophobic mechanism, where aromatic/aliphatic regions associate with one another to minimize their interactions with H2O, and charge-balancing cations associated with the deprotonated carboxylate sites are located only at the outer surface of these clusters. Despite hydrophobicity driving the initial clustering, NOM clusters are formed more quickly when high-charge-density cations like Ca2+ are present vs low-charge-density cations like Cs+, as the former cations more effectively minimize the electrostatic repulsions between the negatively charged NOM molecules. Once the small hydrophobicity-driven NOM clusters form, the simulations show that Ca2+ promotes the aggregation of NOM clusters through tetradentate Ca2+ bridges involving carboxylate groups on two different NOM clusters. Importantly, our studies indicate that Ca2+ plays a crucial role in binding the NOM clusters to the smectite surface, which occurs through multiple quaternary complexes (Ob)-H2O-Ca2+-COO-NOM. In contrast, Cs+ never forms any coordination or acts like bridges between NOM molecules nor as ion bridges to the smectite surface. Additionally, we observe the formation of a metastable superaggregate involving all 16 NOM molecules several times in a Ca2+-bearing mesopore fluid. Superaggregates are never observed in the simulations involving Cs+. The modeling results are fully consistent with helium ion microscope images of NOM-hectorite complexes suggesting that NOM surface films develop when preformed NOM clusters interact with smectite surfaces. Overall, the binding of NOM clusters to the outer surfaces of smectite particles and the formation of large NOM aggregates at neutral pH occur through cation bridging, and cation bridging only occurs when high-charge-density cations like Ca2+ are present.

Evaporation and shrinkage processes of compacted bentonite-sand mixtures

The deterioration of compacted bentonite-sand mixtures (CBSMs) after suffering desiccation increases the hydraulic conductivity of clay barriers, posing risks to the environment. This work compressed bentonite-sand mixtures (BSMs) to various dry densities in order to conduct the free-drying tests, focusing on the evaporation and shrinkage processes. The compaction constrained the permeability of the mixtures and resulted in the delay in evaporation and shrinkage of the CBSMs’ internal parts (compared to their external parts). Subsequently, the secondary shrinkage occurred (i.e., the smaller volumetric shrinkage after the shrinkage limit reached). Compaction constrained the plate-like smectite particles in being propped up and led them to orientate. This structure reinforced the CBSMs’ shrinkage property and contributed to their lower air entry value, shrinkage limit, and final void ratio. During the design and maintenance of compacted clay barriers, secondary shrinkage and the reinforced shrinkage property are proposed to be taken into consideration.

Equimolar cation exchange of polyacrylamide in smectite

Smectite-polymer composites from cationic polyacrylamide (PAMS,τ40Cl) were prepared to investigate the adsorption behavior of the smectite after the intercalation procedure. PAMS,τ40Cl solutions with two different concentrations (γ = 5.18 g/L corresponds to 4.3 mmol/L and γ = 3 g/L corresponds to 4.3 mmol/L) were used to manufacture smectite-PAM+S,τ40 composites. The total amount of PAM+S,τ40 intercalated into the interlayer of the smectite was between 4.5 and 10%. This corresponds to coverage between 4 and 11 cmol(+)/kg, based on the cation exchange capacity (CEC) of the smectite. The smectite in the smectite-PAM+S,τ40 composites still possesses a CEC. The CEC decreased with increasing PAM+S,τ40 content. The CEC decrease was higher than the effective coverage. The amount of Na+ in the interlayer decreased compared to the initial amount with increasing PAM+S,τ40 content. PAM+S,τ40 prefers the interlayer with Na+. Smectite particles in the used raw bentonite (MX-80) are large enough for a planar covering of the basal surfaces by PAMS,τ40Cl. Furthermore, the distances between the charges at the basal surfaces of the smectite and in the oligomer are also large enough for planar covering. Evaluation of the mass spectrometer (MS) curve of m/z = 35 (Cl2) showed that PAM+S,τ40 does not saturate all charges of the smectite per unit cell. Some charges of PAM+S,τ40 are still saturated by Cl−. The exchange of PAM+S,τ40 for Na + in the interlayer of smectite takes place equimolar.

Investigation of hydrated smectite microstructure through wet environmental transmission electron microscopy

Water is an essential constituent of all biological materials as well as many non-biological materials. Not only the removal of water may result in undesirable morphological and structure change, the inability to sustain the hydrated conditions in the microscope also prevents the study of reactions which take place in aqueous environment. In order to overcome these problems we used wet environmental-cell transmission electron microscopy TEM (WETEM). Conventional TEM of dry smectite showed well-defined particle outlines (but without a specific shape) and typical smectite aggregates. Selected area electron diffraction (SAD) of dry particles showed stacking of smectite particles (i.e., aggregate) in very clear dot and ring patterns. In contrast, WETEM depicted well-dispersed clay particles showing a variety of different particle shapes. Analysis of SAD patterns obtained from dry and hydrated states illustrated a lattice change in different environments. The small lattice expansion in (h k 0) resulted from the expansion of the (0 0 l) plane resulting from the addition of water molecules in the crystal along the c-axis.

The chemical stabilization of methylene blue in colloidal dispersions of smectites

The model reaction of methylene blue (MB) with ascorbic acid (AA) to give the reduced leuco form of MB and dehydroascorbic acid was chosen to evaluate the chemical reactivity of the dye in aqueous solution and smectite colloidal dispersions. Saponite Sumecton (Sap) and montmorillonite Kunipia (Mt) from Kunimine Ind. were used. To obtain a large series of spectral data, UV–Vis absorption spectrophotometer equipped with a diode-array detector was used. The spectral components of the reaction were analyzed by chemometric methods. MB decomposition was evident only in aqueous solutions without smectites. The reaction kinetics was dependent on the AA concentration and the acidity of the solution but was not significantly affected by the concentration of MB. The half-life of the reaction without addition of HCl was in the range 69 to 23 s and further reduced in the presence of HCl. In the systems based on smectite colloidal dispersions, no similar reaction was observed. MB formed molecular aggregates depending on the surface properties of the smectite particles. Relatively complex spectral forms indicated the presence of monomers (672, 690 nm), J-aggregates (761 nm) and H-aggregates absorbing at a wavelength lower than 500 nm. Nothing indicated the bleaching of MB in smectite colloids as a consequence of the reaction with AA. The importance of this phenomenon to stabilize reactive dyes from the point of view of application and to interpret some of the earlier results of MB antimicrobial efficacy is discussed.

Clay, Water, and Salt: Controls on the Permeability of Fine-Grained Sedimentary Rocks.

The ability to predict the permeability of fine-grained soils, sediments, and sedimentary rocks is a fundamental challenge in the geosciences with potentially transformative implications in subsurface hydrology. In particular, fine-grained sedimentary rocks (shale, mudstone) constitute about two-thirds of the sedimentary rock mass and play important roles in three energy technologies: petroleum geology, geologic carbon sequestration, and radioactive waste management. The problem is a challenging one that requires understanding the properties of complex natural porous media on several length scales. One inherent length scale, referred to hereafter as the mesoscale, is associated with the assemblages of large grains of quartz, feldspar, and carbonates over distances of tens of micrometers. Its importance is highlighted by the existence of a threshold in the core scale mechanical properties and regional scale energy uses of shale formations at a clay content Xclay ≈ 1/3, as predicted by an ideal packing model where a fine-grained clay matrix fills the gaps between the larger grains. A second important length scale, referred to hereafter as the nanoscale, is associated with the aggregation and swelling of clay particles (in particular, smectite clay minerals) over distances of tens of nanometers. Mesoscale phenomena that influence permeability are primarily mechanical and include, for example, the ability of contacts between large grains to prevent the compaction of the clay matrix. Nanoscale phenomena that influence permeability tend to be chemomechanical in nature, because they involve strong impacts of aqueous chemistry on clay swelling. The second length scale remains much less well characterized than the first, because of the inherent challenges associated with the study of strongly coupled nanoscale phenomena. Advanced models of the nanoscale properties of fine-grained media rely predominantly on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, a mean field theory of colloidal interactions that accurately predicts clay swelling in a narrow range of conditions (low salinity, low compaction, Na+ counterion). An important feature of clay swelling that is not predicted by these models is the coexistence, in most conditions of aqueous chemistry and dry bulk density, of two types of pores between parallel smectite particles: mesopores with a pore width of >3 nm that are controlled by long-range interactions (the osmotic swelling regime) and nanopores with a pore width <1 nm that are controlled by short-range interactions (the crystalline swelling regime). Nanogeochemical characterization and simulation techniques, including coarse-grained and all-atom molecular dynamics simulations, hold significant promise for the development of advanced constitutive relations that predict this coexistence and its dependence on aqueous chemistry.

Temperature‐dependent residual shear strength characteristics of smectite‐bearing landslide soils

AbstractThis paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow‐to‐moderate shearing velocities. We performed ring‐shear tests on 23 soil samples at temperatures of 6–29°C. The test results show that the shear strength of smectite‐rich soils decreased when temperatures were relatively low. These positive temperature effects (strength losses at lower temperatures) observed for smectite‐bearing soils are typical under relatively slow shearing rates. In contrast, under relatively high shearing rates, strength was gained as temperature decreased. As rheological properties of smectite suspensions are sensitive to environmental factors, such as temperature, pH, and dissolved ions, we inferred that temperature‐dependent residual strengths of smectitic soils are also attributed to their specific rheological properties. Visual and scanning electron microscope observations of Ca‐bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth, whereas those at moderate shearing rates are not glossy and are slightly turbulent, indicating that platy smectite particles are strongly orientated at slow velocities. The positive temperature effect is probably due to temperature‐dependent microfriction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles. On the contrary, the influence of microviscous resistance, which appears in the vertical directions of the lamination, is assumed to increase at faster velocities. Our results imply that if slip‐surface soils contain high fractions of smectite, decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement.

Water retention and swelling behaviour of granular bentonites for application in Geosynthetic Clay Liner (GCL) systems

Geosynthetic Clay Liner (GCL) systems are used as efficient hydraulic barriers in landfills for the disposal of hazardous municipal wastes. Along with geotextiles, bentonite materials are chosen as one of the primary components of GCLs due to their high retention, adsorption, and swelling capacities. GCLs are manufactured using bentonites at a high total suction and hydrated through the uptake of liquid from the subsoil and the confined material as soon as they are installed. Bentonites may exhibit considerable volume change upon wetting. Depending on the confinement stress, the void ratio may significantly increase with a decrease in suction, particularly at higher degrees of saturation. To improve the hydraulic performance of GCLs, the swelling of the bentonites induced by the hydration should be limited when GCLs reach low suction values. The change in the hydrated void ratio is related to the pore structure evolution of the bentonites at different hydration levels. An improved understanding of the water retention and the void ratio evolution of bentonite materials during swelling is required, with particular attention given to the applications of GCL systems. The aim of this paper is to characterise the water retention and the swelling behaviour of granular bentonites for applications in GCLs. MX-80 granular bentonite, with an optimised grain size distribution, and Volclay GC-50 granular bentonite were selected, and their water retention behaviour was determined based on a new methodology. Reconstituted GCL specimens with MX-80 and Volclay GC-50 granular bentonites were tested with the same methodology to determine the water retention behaviour. An analysis of the water retention behaviour of the granular bentonites and reconstituted GCLs indicates that an adsorption mechanism controls the water retention behaviour for a wide range of total suction values. An analysis of the swelling potential of the granular bentonites indicates a significant increase in the hydrated void ratio for lower suction values. The increase in the void ratio is attributed to the modification of the smectite particles in the hydration path that results in new pore levels emerging in the bentonite structure. This change in the void ratio is expected to influence the hydraulic performance of the GCL in terms of diffusion and hydraulic conductivity.

The Depressing Effect of Clay Minerals on the Floatability of Chalcopyrite

ABSTRACTIn this work, the depressing effect of clay minerals on the floatability of chalcopyrite using PAX as collector was assessed through induction time and settling-turbidity measurements. The data obtained using these two techniques were correlated with the results of micro-flotation tests carried out to study the effect of kaolinite and smectite particles on the floatability of chalcopyrite at pH 9 and 10. The results indicate that these techniques can be confidently used to examine interactions between clay minerals and chalcopyrite, and their possible consequences on the flotation process. In particular, the use of settling-turbidity measurements to evaluate slime coating seems to be a useful technique that could be applied to study heterocoagulation in other mineral systems. It was found that the depressing effect of clay minerals was stronger at pH 10, which was correlated to a possible effect of Ca2+ from lime on the process of coagulation between clay minerals and chalcopyrite. Coating of bubbles with clays was detected in this work by visual observations and it is proposed as a mechanism that might explain the depressing effect of clays on the floatability of chalcopyrite. Further research is needed to propose a mechanism that explains this phenomenon.

Formation and Restacking of Disordered Smectite Osmotic Hydrates

AbstractClay swelling, an important phenomenon in natural systems, can dramatically affect the properties of soils and sediments. Of particular interest in low-salinity, saturated systems are osmotic hydrates, forms of smectite in which the layer separation greatly exceeds the thickness of a single smectite layer due to the intercalation of water. In situ X-ray diffraction (XRD) studies have shown a strong link between ionic strength and average interlayer spacing in osmotic hydrates but also indicate the presence of structural disorder that has not been fully described. In the present study the structural state of expanded smectite in sodium chloride solutions was investigated by combining very low electron dose, high-resolution cryogenic-transmission electron microscopy observations with XRD experiments. Wyoming smectite (SWy-2) was embedded in vitreous ice to evaluate clay structure in aqua. Lattice-fringe images showed that smectite equilibrated in aqueous, low-ionic-strength solutions, exists as individual smectite layers, osmotic hydrates composed of parallel layers, as well as disordered layer conformations. No evidence was found here for edge-to-sheet attractions, but significant variability in interlayer spacing was observed. Whether this variation could be explained by a dependence of the magnitude of long-range cohesive (van der Waals) forces on the number of layers in a smectite particle was investigated here. Calculations of the Hamaker constant for layer-layer interactions showed that van der Waals forces may span at least five layers plus the intervening water and confirmed that forces vary with layer number. Drying of the disordered osmotic hydrates induced re-aggregation of the smectite to form particles that exhibited coherent scattering domains. Clay disaggregation and restacking may be considered as an example of oriented attachment, with the unusual distinction that it may be cycled repeatedly by changing solution conditions.

Effect of Surface Charge and Elemental Composition on the Swelling and Delamination of Montmorillonite Nanoclays Using Sedimentation Field-flow Fractionation and Mass Spectroscopy

AbstractThe swelling properties of smectite-type clay particles (including montmorillonite) are of interest in various industries. A fundamental understanding of the surface properties of smectite particles at the sub-micron level would facilitate investigation of the effect of distributed properties such as charge and elemental composition. Swelling and delamination of SWy-2 Na-montmorillonite (Na-Mnt) nano-clay particles were studied here using size distributions obtained by sedimentation field-flow fractionation (SdFFF). Fractions were examined by electron microscopy and inductively-coupled optical emission spectroscopy (ICP-OES). Two distinct populations were observed in the size distribution of SWy-2 Na-Mnt particles (bimodal size distribution), with mean equivalent spherical diameters of ~60 nm and 250 nm, respectively. In contrast, the size distribution of STx-1 Ca-montmorillonite (Ca-Mnt) particles showed only one peak with a mean equivalent spherical diameter of ~410 nm, which changed to 440 nm after 4 days of hydration. Analyses of the fractions by ICP-OES obtained along the size distribution of Na-Mnt showed an abundance of Ca and Mg in the fractions below 250 nm, and confirmed the presence of Fe and Mg as isomorphous substituents. Electron micrographs of the fractions obtained from Na-Mnt size distributions were used to calculate the thickness of the clay particles. Bridging forces between pure orMgsubstituted montmorillonite and either Ca2+ or Na+ were calculated using semi-empirical methods. The results demonstrated that swelling and delamination of Na-Mnt clay particles are dictated by properties such as elemental composition and surface charge which are distributed along the size distribution.

황해 군산분지 표층 퇴적물의 점토광물 함량 분포 및 이동경향 연구

황해 군산분지 니질 퇴적물 이동양상을 알아보기 위하여, 표층 퇴적물과 코어 퇴적물 시료에 대한 점토광물 함량 공간분포 및 이동 경로 분석을 실시하였다. 표층 퇴적물의 점토광물 함량은 일라이트가 63.4~71.9%로 가장 우세하고, 다음으로 녹니석(15.1~20.2%), 고령석(10.3~17.2%), 스멕타이트(02~6.9%) 순으로 나타났다. 전반적으로 스멕타이트는 연구지역의 남부에서 상대적으로 높은 값을 보이며, 일라이트는 연구지역의 북쪽 중앙부, 그리고 고령석+녹니석은 연구지역의 북동부에서 상대적으로 높은 값을 보인다. 점토광물의 이동경로 파악을 위해 해저 수로 방향과 조석류 경로를 고려한 각 점토광물의 함량변화 추이를 살펴본 결과, 스멕타이트의 경우는 남쪽 황해 해곡에서 북쪽으로 갈수록 감소하는 뚜렷한 경향을 보였으나, 고령석+녹니석은 한국의 연안과 가까운 연구지역의 북동쪽에서 상대적으로 높은 함량을 보였다. 이러한 결과는 스멕타이트는 연구해역의 남쪽으로부터 반면, 고령석+녹니석은 한국 연안쪽으로부터 유입되었음을 보여준다. 코어 퇴적물 분석 결과, 현생 퇴적층에서 스멕타이트의 함량은 상부로 갈수록 감소하고, 대조적으로 고령석+녹니석의 함량은 증가하는 경향을 보인다. 이는 해수면 상승이 완료된 이후 중국으로부터 유입된 니질 퇴적물은 점차 감소하고 한국으로부터 유입된 니질 퇴적물은 상대적으로 증가했음을 보여준다. To understand the transport pathways of muddy sediment of the Kunsan basin in Yellow Sea, grain sizes and clay mineral of 32 surface sediments and a sediment core were analyzed. In the study area, illite is predominant (63.4~71.9%), followed by chlorite (15.1~20.2%), kaolinite (10.3~17.2%) and smectite (2~6.9%), According to the spatial distribution of the clay minerals, illite, kaolinite+chlorite and smectite show relatively higher contents in the center of the north, northeast, and the south of the study area, respectively. Considering the spatial distribution of clay mineral contents the sand ridge alignments and tidal current pathways, the smectite particles were probably derived from the south of the study area, but kaolinite and/or chlorite particles were mainly transported from the Korean coastal zone. Meanwhile, down-core variation in the contents of clay minerals of the core revealed a distinct change in fine-grained muddy sediment provenance: muddy sediment input from the Korean coastal areas has increased while the input from China has decreased since the last 5,000 year ago, by showing the amount decrease of smectite and the increase of kaolinite+chlorite at the top layer of the late Holocene muddy sediment unit of the core.