Na-montmorillonite Suspensions Research Articles

Rheological and Electrokinetic Properties of Sodium Montmorillonite Suspensions: I. Rheological Properties and Interparticle Energy of Interaction

In this article, we describe the rheology of Na montmorillonite suspensions as a function of pH, at constant ionic strength. The observed behavior is discussed quantitatively in terms of the potential energy of interaction between particles, keeping in mind the anisotropic nature of clay particles. The extended DLVO model that includes electrostatic, van der Waals, and polar acid–base contributions to the total energy is used. It is found that face-to-face interactions are virtually independent of pH, whereas edge-to-edge interactions are most attractive at the isoelectric point of edges (pH∼7). The most significant variations occur in face-to-edge potential energy, with strong attractions at pH<7. Steady-state viscometry showed that the yield stress decreases up to an order of magnitude between pH 3 and pH 7, with a much slower rate of decrease in the 7–11 pH interval. Concerning oscillatory measurements, it is found that both the elastic (G′) and viscous (G′′) moduli are practically independent of frequency. It is also demonstrated that G′>G′′, the difference being larger at acid pH values. These results, in addition to potential energy calculations, suggest the existence of an elastic, coagulated structure up to pH 7, whereas as the pH is increased such structure is more relaxed because of electrostatic repulsions. Similar conclusions are reached when creep–recovery data are analyzed.

Luminescence of Silica-Pillared Clays and Gels Derived from Aminofunctional Silanes

Silica-pillared clays were prepared by reacting Na-montmorillonite aqueous suspensions with (3-aminopropyl)triethoxysilane (APTEOS). It was indicated that cubic octamers [NH3+(CH2)3SiO3/2]8 derived from APTEOS are intercalated with two different conformations of the alkyl chains. Namely, the cubic octamers are intercalated with the alkyl chains parallel to the silicate layers at low concentration of APTEOS, and then intercalated with the alkyl chains normal to the silicate layers with increase in APTEOS. Gels were prepared from the reaction of APTEOS with acetic acid and by the conventional sol-gel process using (3-aminopropyl)trimethoxysilane (APTMOS). The luminescence spectra of the gel prepared by the sol-gel process and the intercalated clays were similar to that of silica gels. The gel from APTEOS with acetic acid showed broad visible luminescence. The luminescence spectra and the structures of these materials were described.

Yield Stress of Na-Montmorillonite Suspension in an Electrostatically Dispersed State

Yield Stress of Na-Montmorillonite Suspension in an Electrostatically Dispersed State

Interaction of Cationic Surfactants with Iron and Sodium Montmorillonite Suspensions

Calorimetry, static technique, and X-ray diffraction (XRD) analysis were employed to study the adsorption of cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) on Fe–montmorillonite and Na–montmorillonite suspensions. The results show that the process of adsorption is exothermic and that the type of clay and the alkyl chain length of surfactant affect the amount of adsorption and the enthalpy of adsorption significantly but that the effect of temperature is very limited in the temperature range studied. The magnitudes of adsorption amount and adsorption enthalpy follow the order Na-montmorillonite > Fe-montmorillonite, CTAB > DTAB. The basal spacings determined by X-ray powder diffraction indicate that the CTAB adsorbed between the clay interlayers in a bilayer arrangement, while the DTAB formed bilayers or monolayers at saturation adsorption between the Na-montmorillonite and Fe-montmorillonite interlayers, respectively. The adsorption mechanism is also discussed on the basis of the experimental data.

Study on the thixotropy of aluminum magnesium hydroxide- Na-montmorillonite suspension

In this paper, the thixotropy of the aqueous suspension consisting of aluminum magnesium hydroxide (AMH) possessing permanent positive charges and Na-montmorillonite possessing permanent negative charges was studied. Besides positive thixotropy and negative thixotropy, a novel thixotropic phenomenon was found, i.e., a given system studied may display, early and late, positive M28.8nthixotropic character and negative thixotropic character, we describe it as “complex thixotropy”. The content of the suspension and electrolyte may influence the forms of thixotropy of the suspension studied.

Flow characteristic of dilute Na montmorillonite suspension

The objective of this paper was to study the flow properties of dilute Na montmorillonite suspensions. Until now, a very dilute Na montmorillonite suspension has been treated as a Newtonian fluid. However, this paper shows a different behavior. Consistency curves of dilute suspensions, measured over different measuring times, may exhibit a different behavior from that of a perfect Newtonian fluid with a concentration of 33–36 kg/m 3. The simple viscoelastic model a Maxwell model proposed by the authors in a previous paper analyzes this behavior. The theoretical analysis predicted that the consistency curve measured in au extremely short measuring time shows negative shear-rate thixotropy, and the loop disappears as time increases. The experimental results confirmed the validity of the analysis. The consistency curves of a dilute clay suspension over extensive measuring times allow estimation of the relaxation time and the shear modulus of the suspension as well as the coefficient of viscosity.

Adsorption Enthalpy and Adsorption Isotherm of Tetradecylpyridinium Bromide on Na-Montmorillonite

The adsorption enthalpy and the adsorption isotherm of tetradecylpyridinium bromide (TPB) onto a Na–montmorillonite suspension and the dilution enthalpy of the TPB solution have been determined at 298.15 K. The dilution process is endothermic and the adsorption process is exothermic. For ion exchange adsorption, the interaction between TP+and the montmorillonite is much stronger than that between Na+and the montmorillonite because the cumulative adsorption enthalpy increases dramatically with adsorption amount. For molecular adsorption, however, the interaction between TPB and the clay is much weaker.

Rheological study on thixotropic flow: effect of time scale on flow types measurement

The object of this study is to clarify the dependence of the flow type of a clay suspension (shear-rate thixotropy or negative shear-rate thixotropy) on the time scale of measurement. First, we propose a dynamic analysis of thixotropic flow by introducing a parameter expressing the degree of softening into the Maxwell model. Then, using the above analysis, we show theoretically the dependence of the type of flow on the time scale of measurement. When a clay-water system develops structure, we measure several consistency curves for the sample by changing the time scale of measurement from shorter to longer times compared to the relaxation time T M. We are thus able to find curves that demonstrate different mechanical characteristics i.e., curves showing negative shear-rate thixotropy over shorter measurement times and curves showing shear-rate thixotropy over longer measurement times. Furthermore, we are able to predict that the measurement time that indicates changes in flow types decreases as the structure of the clay-water system develops. Finally, we performed consistency experiments for Na-montmorillonite suspensions at mass concentrations 57 kg/m 3 and 60 kg/m 3 to investigate the validity of the analysis; the experimental results did indeed confirm the validity of the analysis (i.e., it was proved that thixotropic properties of a clay dispersion system depend on the length of the measurement time T). Further, an increase in the mass content greatly affects the thixotropic properties.

Humic Substances and pH Effects on Sodium- and Calcium-Montmorillonite Flocculation and Dispersion

Humic substances (HS) are important factors in soil particle associations. Little is known, however, about the mechanism of clay-HS interaction and their effects on aggregation at various pH levels have not been adequately studied to date. In this study, flocculation and dispersion characteristics of homoionic montmorillonite were studied as a function of the exchangeable cation (Na+ and Ca2+), humic acid (HA), and fulvic acid (FA) concentration (0–40 mg L-1), and pH (4, 6, 8, and 10). Flocculation values (FV) of Na-montmorillonite increased with increasing concentrations of HS at all pH levels. For pH values of 4, 6, and 8, a sharp increase in FV was observed with increasing HS concentration up to 10 mg L-1 (37.5 g kg-1 clay). Only slight increases in FV were observed for HS concentration >10 mg L-1 at these pH values. In contrast, for suspensions at pH 10, HS concentrations up to 10 mg L-1 had little effect on the FV, but further addition of HS caused an increase in FV up to 141 mmol L-1. In contrast to Na-montmorillonite suspensions, addition of Ca-humate or Ca-fulvate to Ca-montmorillonite resulted in no effect on the FV. The effect of HS on the stability of Na-montmorillonite suspensions is explained by interactions between negatively charged HS molecules and the edge charge of the clay. These interactions are affected by pH and by the charge and configuration of the HS macromolecule. In pure clay systems at pH values below the point of zero charge (PZC) of edge sites, edge-edge (E-E) and edge-face (E-F) interactions among clay platelets are the dominant flocculation mechanisms. At pH values above the PZC of the edge sites, only F-F associations occur. In the presence of HS at pH values below the PZC, negative HS molecules are adsorbed to positive edge sites causing edge-charge reversal (from positive to negative). Consequently, increased electrolyte concentrations are required for flocculation relative to Na-montmorillonite suspensions without HS. The second flocculation mechanism we propose is based on a random distribution of the HS macromolecules among the montmorillonite tactoids. The FV of such a mixture is higher than the FV of montmorillonite suspensions. The term mutual flocculation (heteroflocculation) has been suggested to describe this mechanism.

Flow Characteristics of Na-montmorillonite Suspension in the Region of Newtonian Flow

Flow Characteristics of Na-montmorillonite Suspension in the Region of Newtonian Flow

Rheological Behavior of Na-Montmorillonite Suspensions at Low Electrolyte Concentration

AbstractThe prevailing concept that positive-edge to negative-face attraction accounts for the rheological behavior of montmorillonite suspensions at low electrolyte concentration was investigated. In one experiment, Mg2+ released from Na-montmorillonite was measured at several NaCl concentrations; in a second experiment, the viscosity, η, and the extrapolated shear stress, θ, were measured at several clay concentrations, pHs, and NaCl concentrations; and in a third experiment, the absorbance, A, was measured at two wavelengths (450 and 760 nm) at different clay and electrolyte concentrations. The released Mg2+ decreased with increasing NaCl concentration until it became zero at a NaCl concentration between 0.01 and 0.02 M, depending on pH. Thereafter, it increased with increasing NaCl concentration. Both θ and η were highly correlated with the amount of released Mg2+. Also, A remained constant until the NaCl concentration corresponded to that at the minimum of θ. Thereafter, it increased and became linearly related to θ. These results suggest: (1) positive-edge to negative-face interaction cannot solely account for the rheological properties of montmorillonite at low electrolyte concentration, and (2) the release of octahedral Mg2+ from montmorillonite affects θ, because it reduces the negative charge on the particles and, thereby, the repulsive force between them.

On the bulk and surface electric conductivity in montmorillonite suspensions

Experimental results on the electrical conductivity of Na-montmorillonite suspensions in solutions of different electrolyte concentrations and pH values are used for the determination of the relative conductivity increment, ΔK, and the surface conductivity, κ σ , of such suspensions. A previous estimation of the conductivity, K ∞, of the liquid media employed is required. Hence, different methods for the evaluation of K ∞ are discussed. Best results are obtained when K ∞ is computed theoretically, a good qualitative agreement being found with the general physical principles of the phenomenon of electrical conductivity in suspensions. A comparison is carried out between the experimental values of ΔK and those deduced from a detailed theoretical analysis; again, the qualitative agreement is, generally speaking, good, but theory seems to underestimate the results. Reasonable values of κ σ are obtained only if the clay particles are idealized as oblate spheroids, worse results being found if they are considered spherical in shape. The experimental conductivity data allow the estimation of the axial ratio of the spheroids.

Flocculation of clay suspensions by an anionic soil conditioner

Ca- and Na-montmorillonite and Na-kaolinite were flocculated from suspension by two anionic soluble polymers. Light absorbance at 280 nm served as degree of flocculation measure. A prerequisite for flocculation was that salt concentration in clay suspension should exceed 1.0 and 0.2 meq. l −1 for Na- and Ca-montmorillonite, respectively. Furthermore it was shown that the clay had to adsorb a minimum amount of polymer: 0.8 mg/g for a 0.735 g l −1 Na-montmorillonite suspension and 1.0 mg/g for a 0.436 g l −1 Ca-montmorillonite suspension. Saturation adsorptions of polymers on Na- and Ca-clays were estimated to be 4.6 and 7.0 mg/g. These levels of adsorption stabilized the suspension and prevented flocculation. Na-polymetaphosphate (Calgon) added to a Na-montmorillonite suspension after the polymer addition retarded flocculation whereas its addition at a level >2.7 mg/g prior to the polymer addition prevented flocculation. Increasing the pH of the Na-kaolinite suspension from 6.5 to 8.2 considerably reduced its flocculation by the polymer. The effects of both pH and Na-polymetaphosphate indicate the importance of the positively charged sites on the clay in adsorption of anionic polymers and contribute to understanding of flocculation mechanisms.

Investigation into the existence of edge—face coagulated structures in Na-montmorillonite suspensions

Download options Please wait... Article information DOI https://doi.org/10.1039/F19807600225 Article type Paper Download Citation J. Chem. Soc., Faraday Trans. 1, 1980,76, 225-235 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Investigation into the existence of edge—face coagulated structures in Na-montmorillonite suspensions B. Rand, E. Pekenć, J. W. Goodwin and R. W. Smith, J. Chem. Soc., Faraday Trans. 1, 1980, 76, 225 DOI: 10.1039/F19807600225 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Brian Rand Erdogan Pekenć James W. Goodwin Robert W. Smith

Electrical Conductivity of Na—Montmorillonite Suspensions

AbstractThe electrical conductivity of Na-montmorillonite suspensions in various salt and clay concentrations was measured. The weight conductance of the clay suspension was found to decrease with increase in clay concentration between 0 and approximately 0·5 g clay/100 ml, then rose to a plateau at 6–10 g clay/100 ml. The weight conductance of the clay suspensions also increased with an increase in the salt solution concentration. If the model of two resistors in parallel is used in interpreting the experimental data, these changes can be attributed to an increase in the mobility of the adsorbed Na ions. It is proposed that the two resistors in series model is more realistic in describing the conductivity of the suspensions. This model predicts the observed weight conductance changes of the suspensions, while the mobility of the adsorbed ions remains constant. A constant mobility of the adsorbed Na ions in clay-water systems of low to medium salt and clay concentrations also is predicted by the diffuse double layer.

Flocculation of Na-montmorillonite by electrolytes

AbstractThe flocculation of a Na-montmorillonite suspension by Na, Ca, and Al chlorides was investigated using the optical absorbance method. The flocculation of the clay was found to be irreversible with a degree of irreversibility that increases with electrolyte concentration. The flocculation values of Na, Ca and Al chlorides were found to be equal to 8, 0·25 and 0·032 mmol/l respectively. The ratio of the flocculation values of the different salts is in reasonable agreement with the ratio predicted by current theories of colloid stability.

Small Angle X-Ray Scattering from Montmorillonite Clay Suspensions. II

Small angle x-ray scattering has been used to study the interactions between clay platelets in a number of samples. Sodium montmorillonite clays have been studied in concentrations ranging from 5% to 85% by weight. The scattering from the samples with concentrations from 10% to 40% was analyzed by Fourier transformation to obtain the distribution functions for the platelet spacing. For the higher concentrations, the scattering curves were interpreted by fitting the data with theoretical curves for aggregates of platelets. The most probable platelet spacing ranged from 116 Å for the 10% concentration to 13 Å for the 85% concentration. If one plots platelet spacing as a function of grams of H2O per gram of clay for this series of samples, a reasonably linear relation is obtained. The effect of adding NaCl, CaCl2, and AlCl3 to 2% sodium montmorillonite suspensions was studied. Until the salt concentration is raised to a critical value, the scattering curve is identical to the curve obtained for dilute Na montmorillonite suspensions with no salt added. The latter scattering curve has been previously interpreted [R. Hight, Jr., W. T. Higdon, and P. W. Schmidt, J. Chem. Phys. 33, 1656 (1960)] as being due to independent montmorillonite layers 10 Å thick. The critical concentration decreased as the valence of the added salt was increased. Above the critical concentration, the scattering data show that aggregation takes place, with the aggregates consisting of about 6 to 8 platelets and with a platelet spacing of 19 to 21 Å. Calcium montmorillonite suspensions show essentially identical behavior. Fresh hydrogen montmorillonite samples show no aggregation, but in samples aged about four months, the scattering curves indicate the presence of aggregates with a platelet spacing of 22–24 Å and with 2 or 3 platelets per aggregate.