Smectite Suspensions Research Articles

Preparation and dispersive behaviors of reduced charge smectite

A series of reduced charge smectites (RCS) with gradually decreasing cation exchange capacity (CEC) were prepared by controlling the amount of Li used to saturate SAz-1 to study the dispersive characteristics of RCS in water and provide insight into the influence of the layer charge density on delamination of smectite in water. Results indicated that being well deliminated in water, high-CEC smectie suspension resulted in small flocs with fluffy structure after coagulation presumably due to a more porous type of coagulation with intense face-to-edge and edge-to-edge interactions of platelets. High-CEC smectie also resulted in suspension with higher viscosity due to the presence of larger number of particles and secondary electroviscous effect. Finally, this study demonstrated the possibility of tailor-made smectite suspensions with suitable dispersive properties for particular applications.

An In situ Time-Resolved XRD-PSD Investigation into Na-Montmorillonite Interlayer and Particle Rearrangement during Dehydration

AbstractX-ray diffraction with a position-sensitive detector (XRD-PSD) was used to make a time-resolved study of the dynamics of deposition and dehydration of Na-montmorillonite crystallites on flat substrates from deionized water suspensions. The static PSD geometry and simultaneous counting procedure allowed the acquisition of high-resolution data on the dynamics of interlayer and interparticle arrangements during dehydration. Three experimental datasets of Na-smectite dehydration are presented, each one representing different initial sample states (suspension, slurry and re-wetted thin film). The computer program NEWMOD was used to simulate one of the three datasets (dehydration of a smectite suspension) and thus obtain the apparent changes in relative proportions of different 00l values as smectite crystallites formed and dehydrated. Two types of diffracting domains formed: water-dispersed ‘packets’ of 1–2 smectite layers gaining long-range order in the c axis direction as water was lost to evaporation, and smectite layers deposited as hydrated crystallites with variable interlayer water contents. The experimental patterns show the rapid step-wise transition of Na-montmorillonite layers from d values of ∼55 to 18.5, 15.4 and 12.5 Å, with variations that depended upon how the hydrated smectite sample was prepared. The simulations show that there was a wide range of d values whose frequency distribution changed as dehydration proceeded and that transient d values occurred between the peaks observed experimentally. The data obtained in this study illustrate that XRD-PSD instruments have great potential in providing detailed data on the rapid kinetics of interlayer reorganization.

Effects of the Nature of the Exchangeable Cation and Clay Concentration on the Rheological Properties of Smectite Suspensions

AbstractThe rheological characteristics of purified bentonite suspensions as a function of exchangeable cation (Ca2+,NH4+,Li+)$({\rm{C}}{{\rm{a}}^{2 + }},{\rm{NH}}_4^ + ,\;{\rm{L}}{{\rm{i}}^ + })$ are studied at three different clay concentrations (40 gL−1, 60 gL−1, 80 gL−1). A Herschel-Bulkley model is used to determine rheological parameters such as yield value, consistency and fluidification index. The flow curves are typical for shear thinning fluids but differ on two points; presence of yield stress and/or thixotropy. The Li suspensions are not yield stress fluid, and the thixotropy is weakly expressed only for the 80 gL−1 suspension. On the contrary, Ca-clay suspension flow curves always present yield stress and a large thixotropic area. The NH4-clay suspensions exhibit an intermediate behavior as there is no thixotropy, but a yield stress appears for the most concentrated suspension. These differences in macroscopic mechanical properties are discussed with reference to the suggested microscopic clay organization in suspension.

Characterization of model soil colloids by cryo-scanning electron microscopy

The cryo-scanning electron microscopy (cryo-SEM) consists of the SEM examination of samples whose microstructure has been fixed by plunge-freezing into a liquid with a high thermal conductivity, such as nitrogen slush. The advantage of this cryo-preparation method is that it can transform the interstitial water of the samples into ice whose crystalline domain dimensions (a few nm to a few tens of nanometers) do not exceed those of the finest details that can be observed, and thus do not modify sample morphology at the observation scale. Cryo-SEM was applied to the study of wet-state model soil colloids: a soil humic acid, a commercial smectite, a synthetic ferrihydrite and their binary and ternary associations. The cryo-SEM images have given the following information: The smectite suspension behaved as a non-oriented network, the ferrihydrite suspension was formed from particles of various shapes and dimensions, and the humic acid exhibited a sponge-like structure. The micromorphology of the ferrihydrite–humic acid association was close to that of pure ferrihydrite, while the smectite-containing associations recalled the basic network of the smectite. The comparison of the images obtained by cryo-SEM, and by conventional SEM performed on the same samples after they had been freeze-dried, points out the morphologic modifications deriving from the conventional drying process. Besides SEM investigation, the soil colloids have been characterized by X-ray diffractometry, FTIR spectroscopy, elementary analysis and surface area determination.

Effects of clay-rich river-dam sediments on downstream fish and plant life

AbstractIn 1985, Dashidaira Dam, equipped with a flushing gate, was built on the Kurobe River in Toyama, Japan. Since the dam sediments were first flushed out in December 1991, benthic fish counts have decreased year by year due to repeated flushing of clay-rich dam sediments.In June 2001, the flushed dam water contained a low oxygen concentration (1 to 2 mg/l) and high concentrations of smectite and vermiculite. To establish the cause of the death of the benthic fish, living flatfish were collected from Toyama Bay in order to examine their gills, which showed tissue damage and chemical changes caused by adherent expandable clays, derived from the flushed dam sediments. For comparison, exposure experiments on rainbow trout were carried out using smectite suspensions. Examination by optical microscopy revealed that the gills had shrunk because of the smectite concentrations. Low oxygen concentrations and large amounts of expanding clays have a significant effect on downstream benthic life.

Mass spectrometric identification of an azobenzene derivative produced by smectite-catalyzed conversion of 3-amino-4-hydroxyphenylarsonic acid

The compound 3-amino-4-hydroxyphenylarsonic acid (3-amino-HPAA) reacts with smectite to form a soluble azobenzene arsonic acid compound. This reaction is of particular interest because it provides a possible mechanism for the formation of a new type of arsenic compound in natural water systems. 3-Amino-HPAA is a degradation product excreted by chickens that are fed rations amended with roxarsone. Roxarsone is used to control coccidial intestinal parasites in most of the broiler chickens grown in the United States. The structure of the azobenzene arsonic acid compound was first inferred from negative-ion and positive-ion low-resolution mass-spectrometric analyses of the supernatant of the smectite suspension. Elemental composition of the parent ion determined by high-resolution positive-ion mass spectrometric measurements was consistent with the proposed structure of the azobenzene arsonic acid compound.

Smectite-Type Clay Minerals as Nanomaterials

AbstractDilute aqueous smectite suspensions are well suited to convert into functional nanofilms. The functionalization is performed by ion exchange of amphiphilic molecules carrying the desired functionality. A functionalized clay mineral nanofilm is obtained by the organization of the molecules at the clay surface and by the organization of the elementary clay platelets in the film. Two techniques are presented: self-assembling and Langmuir-Blodgett (LB). Self-assembling is a very simple experiment, but the organizational order of the clay mineral particles is low. Nevertheless, films with nonlinear optical properties which are able to generate frequency-doubled light have been produced. The drawback of disorder of the clay platelets in the film can be largely overcome with the LB technique. Well organized films are obtained. In the presence of amphiphilic ruthenium(II)-bipyridine complexes, nonlinear optical properties are measured. In the presence of two dyes, oxacarbocyanine and rhodamine B, simultaneously adsorbed, efficient energy transfer between the donor (oxacarbocyanine) and the acceptor (rhodamine B) is measured. Fundamental research into the organization of molecules at clay mineral platelets is necessary to optimize the materials for specific applications.

Transport and retention of clay particles in saturated porous media. Influence of ionic strength and pore velocity

The aim of this work was to experimentally evaluate the role of ionic strength and pore velocity on clay suspension transport and retention through a saturated porous medium. A smectite suspension was injected into columns filled with a very fine quartz sand. Experiments were carried out at constant pore velocity with increasing ionic strength adjusted with a divalent electrolyte (CaCl 2) and at constant ionic strength (using three chemical conditions) with decreasing pore velocity. Typical colloid breakthrough curves show two important behaviors: a constant outlet concentration value after a transient phase, and a pronounced tailing effect at the end of the injection step. No differences were observed between the mean travel time of a solute tracer and that of the clay suspension. The classical advection–dispersion equation coupled with a first-order two-site kinetics model was used to reproduce the experimental breakthrough curves. The kinetic model consisted in a site with irreversible deposition and a reversible site used to reproduce the transient phase preceding the plateau of the experimental breakthrough curves. The particle fraction kept by the porous medium increases with ionic strength; consequently the kinetic parameters of the numerical model vary with chemistry. The irreversible sorption rate ( K irr: equivalent to a clean-bed filter coefficient) increases with ionic strength and was directly determined from experimental data. With increasing ionic strength, the deposition rate ( K d) for the reversible sorption increases whereas the release rate ( K r) decreases. The kinetic parameters of the reversible site show an evolution with pore velocity similar to that observed in kinetics model used for modeling solute transport in double porosity media. With decreasing pore velocities, the retention of clay particles increases but the kinetic deposition coefficient of the irreversible site decreases. Particle deposition can also be described and reinterpreted in terms of collector efficiency using the concept of the sphere-in-cell model. The collector efficiency, which adds a correction to the kinetic parameter with the residence time, is a more consistent way to represent particle retention. Its value increases with increasing ionic strength and decreasing pore velocity.

Changes in suspension properties of structural modified montmorillonites

Rheological changes were found in smectite (Wyoming- and Cheto-type montmorillonites) suspensions after structural modifications. The effect of the particle size and Na+ exchange on the flow curves of 6% wt/wt suspensions of smectites with and without Na2CO3 were examined. Mineralogical, structural and physicochemical characteristics were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), cationic exchange capacity (CEC), Mg2+, Al3+ determinations, particle size distribution and swelling index (SI). Grinding in an oscillating mill modified the particle sizes. The montmorillonite grain size and the structural disorder increased after larger grinding times. The grinding treatment modified the apparent viscosity and the yield stress of the montmorillonite suspensions. The homoionic Na Cheto-type montmorillonite with fine particle size (obtained by grinding) increased the flow properties. Nevertheless, rheological properties were lower than those of suspensions of the Wyoming-type montmorillonite. Montmorillonite-types reacted differently with Na2CO3 additions and this behavior may be related to their structural composition. The Na2CO3 activation improved the flow properties of the original Wyoming-type montmorillonite and after 30 s grinding.

A thermo-XRD study of Al-pillared smectites differing in source of charge, obtained in dialyzed, non-dialyzed and washed systems

The mechanism of Al-pillaring of the following smectites: montmorillonite, beidellite, saponite, hectorite and Laponite was investigated. For this purpose the products of three different preparation techniques that had been applied on the Keggin-ion smectite suspensions were studied by thermo-XRD analysis. These techniques included: (a) dialysis of the clay-Keggin ion suspensions; (b) aging of the smectites in the Keggin ion solution, and (c) separation between the clay and the supernatant after 24 h and washing the smectite to remove excess Na, Al and Cl. In the first stage after treating the smectite with the Keggin ion solution, the Keggin ion dissociated into smaller units. The adsorption of Al by the smectites took place in the first 24 h, but was very high relative to the cation exchange capacity of the smectites, indicating that the adsorbed species were hydroxy and/or chloro Al complexes. Thermo-XRD analysis showed that these adsorbed cations were monomers or very small oligomers. Large three-dimensional oligomers, which are essential for the formation of thermally stable pillared clays, were obtained inside the interlayer space after 7 days of dialysis or after thoroughly washing the smectites. At 600°C, the Al oxocation condensed with the silicate layer and the heated smectite did not swell in water. Pillared clays were obtained with montmorillonite, beidellite and saponite after 7 days of dialysis or repeated washings (in 5 days). Under the conditions used in the present study ([OH]/[Al] ratio of 2.3 and final Al concentration 0.07 M) Laponite and hectorite did not form thermally stable pillared clays.

Spectroscopy of Methylene Blue–Smectite Suspensions

Aqueoussuspensions of different Na-smectite type clay minerals were exchanged with methylene blue (Mb) and analyzed by visible spectroscopy. The spectra show bands of two types of monomers, protonated Mb, Mb-dimers, and higher aggregates. Their relative importance and the bandwidth was found to depend on parameters such as the particle morphology, the degree of dispersion, and the extent and location of the layer charge of the smectite. This can be qualitatively explained by the relative importance of three types of interactions, Mb–surface, H2O–surface, and Mb–Mb interactions. For hectorite and laponite at small loadings, H2O–surface interactions are dominant. Mb-islands are formed with a characteristic monomer absorption at 653 nm. Monomers at the surface absorb at 670 nm as found in barasym and saponite. Wyoming bentonite takes an intermediate position. As the loading increases Mb–Mb and Mb–surface interactions become dominant, giving rise to monomers absorbing at 670 nm, dimers, and higher aggregates. The bandwidths of the absorption bands reflect the structure of the clay particle associates.

Swelling and Texture of Iron-Bearing Smectites Reduced by Bacteria

AbstractMicrobial reduction of clay mineral structural Fe(III) decreases the swelling of nontronite gels, most importantly at intermediate oxidation states (40 to 80 cmol Fe(II) kg−1 clay). The purpose of this study was to establish whether microbial reduction of structural Fe(III) decreased the swelling of other Fe-bearing smectites and to discern the influence that organic compounds of microbial origin (bacterial cells, cell fragments and/or exudates) may have on clay swelling and texture. Structural Fe(III) was reduced by incubating smectite suspensions with either a combination of Pseudomonas bacteria or a mixture of anaerobic bacteria. The influence of organics on clay swelling was estimated on smectites suspended in either organic or inorganic media in the absence of bacteria. The gravimetric water content of the reduced clay gels equilibrated at various applied pressures was recorded as a function of Fe oxidation state. Transmission electron microscopy (TEM) was employed to determine the influence of bacteria and type of media on the texture of reduced smectite gels. Reduction of structural Fe(III) by bacteria decreased the swelling pressure of all Fe-bearing smectites. Increased clay swelling, due to the presence of organics (organic medium, exudates or cell fragments), was correlated to the total Fe content, the extent of structural Fe reduction, as well as the initial swelling characteristics of the Fe-bearing smectites. High structural Fe(II) contents (>50 cmol Fe(II) kg−1) resulted in increased attractive forces between clay platelets that decreased clay swelling, even in organic medium suspensions. Microbial reduction resulted in increased face-face association of individual clay layers, forming larger and more distinct crystallite subunits than in nonreduced clay gels. But, perhaps more importantly, microbial reduction of structural Fe(III) resulted in an increased association between crystallite subunits and, thus, an overall larger particle size and pore size distribution, due to the interaction of bacteria ceils, cell fragments and organic exudates.

Interaction of Methylene Blue with Reduced Charge Montmorillonite

Interaction of methylene blue (MB) with reduced charge Li−montmorillonites (RCM) in the aqueous suspensions was investigated using visible absorption spectroscopy. Dye cation agglomeration and protonation at the clay surface depended very sensitively on layer charge density. With increasing layer charge reduction, the content of agglomerates of MB cations decreased in favor of monomers and the protonated form of MB. Lower negative charge density on the clay basal surface induces a greater distance between neighboring MB cations sorbed at the clay surfaces, which suppresses dye agglomeration. Since each form of MB absorbs visible light at a different wavelength, different layer charge densities induce different colors of the resulting clay−dye suspension. Therefore, visible spectra of MB−smectite suspensions may be a simple but extremely sensitive method for the detection of layer charge density of smectites.

Linkage between ζ-potential and electron donicity of charged polar surfaces 2. Repeptization of flocculation caused by plurivalent counterions by means of complexing agents

Abstract Complete reversal of flocculation of a smectite (SWy-1) suspension previously flocculated by the addition of the plurivalent counterion La3+ was achieved by the addition of complexing agents, e.g. ethylenediamine tetraacetic acid trisodium salt (Na3EDTA) or (NaPO3)6. With the addition of La3+ ions, the particles' surface became more hydrophobic (the electron-donor surface tension parameter γ⊖ decreased from 36.4 to 12.3 mJ m−2) while the ζ-potential decreased (from −60 to −18.5 mV), and the attraction between the particles increased to 90% hydrophobic and 10% van der Waals. When the La3+ ions were removed by complexing agents, the surface hydrophilicity was restored (γ⊖ increased from 12.3 to 36.8 mJ m−2) and repeptization ensued, which was caused primarily by hydrophilic (85%) and secondarily (15%) by electrostatic repulsive forces. Washing with, or dialysis against, distilled water did not result in repeptization. The phenomenon of spontaneous repeptization of flocculated SWy-1 suspensions is also discussed.

Hydroxy‐Aluminum's Effect on Permeability of Clay‐Sand Mixtures

AbstractThe effect of the hydroxyl‐Al synthesis method on the hydraulic conductivity (HC) of a clay‐sand mixture in the presence of hydroxy‐Al was studied. Hydroxy‐Al precipitates were formed by adding Al(NO3)3 and NaOH solutions to continuously stirred smectite suspension. Aluminum nitrate was added either before or after NaOH. When the mixtures were leached with deionized water, HC reduction was much less when Al(NO3)3 was added prior to rather than after NaOH. Dispersion and transport of clay from the clay‐sand mixture occurred only when the NaOH was added prior to Al(NO3)3. The differences in behavior between the two systems is due to the location of hydroxy‐Al. When Al(NO3)3 is added to the clay followed by NaOH, hydroxy‐Al polymers interact with the clay particles to reduce swelling and dispersion. When clay and NaOH are mixed, followed by Al(NO3)3, precipitates form as a separate phase from the clay platelets.

Aqueous dissolution, solubilities and thermodynamic stabilities of common aluminosilicate clay minerals: Kaolinite and smectites

Determinations of the aqueous solubilities of kaolinite at pH 4, and of five smectite minerals in suspensions set between pH 5 and 8, were undertaken with mineral suspensions adjusted to approach equilibrium from over- and undersaturation. After 1,237 days, Dry Branch, Georgia kaolinite suspensions attained equilibrium solubility with respect to the kaolinite, for which Keq = (2.72 ± 0.35) × 107. The experimentally determined Gibbs free energy of formation (ΔGf,2980) for the kaolinite is −3,789.51 ± 6.60 kj mol−1. Equilibrium solubilities could not be determined for the smectites because the composition of the solution phase in the smectite suspensions appeared to be controlled by the formation of gibbsite or amorphous aluminum hydroxide and not by the smectites, preventing attempts to determine valid ΔGf0 values for these complex aluminosilicate clay minerals. Reported solubility-based ΔGf0 determinations for smectites and other variable composition aluminosilicate clay minerals are shown to be invalid because of experimental deficiencies and of conceptual flaws arising from the nature of the minerals themselves. Because of the variable composition of smectites and similar minerals, it is concluded that reliable equilibrium solubilities and solubility-derived ΔGf0 values can neither be rigorously determined by conventional experimental procedures, nor applied in equilibriabased models of smectite-water interactions.

Preparation and Handling of Dithionite-Reduced Smectite Suspensions

AbstractUsing Garfield, Washington, nontronite as the model mineral system, methods and apparatus were developed to prepare reduced suspensions in citrate-bicarbonate-dithionite (CBD) solution. These techniques were effective in removing excess, undesired solutes from reduced suspensions while maintaining a high Fe2+ content. They also enabled the preparation of dried, reduced films preferentially oriented with respect to the crystallographic c-axis. Supernatant solutions were collected and analyzed for Fe, Al, and Si, from which the extent of dissolution of the clay as a result of CBD treatment was assessed. Results indicated that very little Fe and Si were released to solution, but as much as about 8% of the total Al was solubilized. The highest levels of Al in solution were observed in CB treatments without dithionite.