The 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.

To determine the dependency of rheological properties on mineralogical characteristics, eleven organophilic hectorite and nine organophilic saponite samples were prepared from hydrothermally synthesized smectites and a quaternary ammonium salt containing mainly octadecyl groups as alkyl chains and were examined by X-ray powder diffraction (XRD), particle size, chemical, and rheological procedures. The rheological properties of the organophilic products dispersed in toluene were found to depend chiefly on (1) particle size, (2) the expansion behavior of the stacked clay platelets, in which the amount and location of negative charge of the silicate layer affected the expandability, and (3) the amount of methanol added as a polar activator. By the addition of 2–4% methanol, apparent viscosities of the hectorite clays were drastically increased at low shear rate, although even a 10% addition did not significantly affect the saponite clays. Under the most suitable gellation conditions, the saponite clays showed lower apparent viscosity than the hectorite clays. Inasmuch as the former had its negative charge near the surface of the silicate layer and formed strong bonds to the organic ion, the expansion of the platelets was apparently difficult. An optimum layer charge for increasing the viscosity was found; specifically 0.45–0.50 and 0.50–0.55 equivalents per half unit cell for saponite and hectorite clays, respectively. Because the saponite clays contained a denser population of organic ions than the hectorite clays, the ion density in the interlayer of both clays was considered to be the same, i.e., about 0.4 organic ions per unit ab area.

Viscosity and light-transmission measurements of dilute suspensions of montmorillonites having different exchangeable cations were used to calculate relative particle sizes as a function of cation composition, where particle size is expressed as the number of clay plates per tactoid relative to the number of plates per tactoid for Li-montmorillonite, after exchange of Li, Na, K, Cs, and Mg by Ca. Tactoid sizes increased in the order Li < Na < K < Mg < Ca, with the number of plates per tactoid relative to Li-montmorillonite varying from 1.5 for Na- to 6.1 for Ca-montmorillonite. The results for tactoid sizes derived from light transmission and those derived from viscosity data are in reasonable agreement with each other and with literature data for similar systems. Upon exchange of Ca-counterions for Li-, Na-, or K-coun-terions, a sharp initial decrease in tactoid size was observed over approximately the first 30% of cation exchange. Upon further exchange, tactoid sizes changed only slightly, but when Ca was exchanged for Cs or Mg, a much more gradual decrease in particle size was observed.

The effect of freezing and thawing on the rheological behavior of illite suspensions was studied by examining viscosity and plasticity. Stability of suspensions was characterized by a hysteresis loop of thixotropy. Thermal gravimetric and differential scanning calorimetry analysis were also used. After initial freezing and thawing, the flow curves of the suspensions show an increased viscosity, an “irregular up line”, and a greater hysteresis loop of thixotropy. The ratios of mean viscosity of previously frozen (F) and control (O) samples (ηF/ηO) for non-expandable 2:1 phyllosilicates ranges from 1.3 to 2.1. Addition of monovalent (0.1% Na2SiO3) and divalent cations (0.3% CaCl2 or BaCl2) increase and decrease the shear-stress difference between F and O samples, respectively. Prior freezing of clay samples results in an increase of plasticity by ∼20–30%. The thermal analysis data of F samples show an increase in weight loss, and a decrease in enthalpy of dehydration. The changes of physico-chemical properties from cycles of freezing and thawing are long lasting. The freezing memory effect of illite-type clays is expected to play an important role in ceramic processing, i.e., casting processes, plastic formation, and sintering.

Electrophoretic mobility of imogolite has been reported as positive (migration toward the negative electrode) below pH 9, and zero above pH 9. However, when mobility of dilute imogolite suspensions (5 × 10−3 kg/m3) was measured, it was found to be negative above pH 9. The reason that imogolite does not behave as a negative colloid when the clay concentration is not very dilute is because the imogolite forms floccules large enough to prevent migration. Imogolite has a PZNC at about pH 6, and has a PZC at pH 8.5–9.0 showing a relatively low absolute mobility under alkaline conditions compared to that under acid conditions. The fact that imogolite behaves like this is understandable given the location of negative charge appearing on the inside surface of the thin fibrous tube, according to the structural model of imogolite.

Aqueous suspensions of allophane show relatively high viscosity, presumably because of strong particle interaction between the unit particles. To test this hypothesis, we measured the particle weight and particle size of allophane during a dispersion using the light scattering method. The particle weight was more than several hundred times larger than that of the unit particle, and the size was 100–400 nm, whereas the Stokes’ diameter of the particles in the sample was less than 50 nm. Particle weight and size varied with the pH of the sample. Particle sizes were cross-checked by ultrafiltration through membrane filters. The experimental findings show that the unit particles of allophane within dilute dispersions appear to be associated like strings of beads, forming domains (primary floccules) about 100 nm in diameter. When these domains coagulate under certain conditions, they do not grow analogously but form clusters, such as secondary floccules, then precipitate. Formation of secondary flocculation of loose structure accounts for the maximum relative viscosity at the transition pH between dispersion and coagulation.

Bentonite cake is usually formed on the excavated trench surface that is supported by the bentonite slurry during construction of slurry cutoff walls. The lower hydraulic conductivity of bentonite cakes formed during construction of slurry cutoff walls in comparison to backfill materials provides an additional benefit. In the present study, the hydraulic conductivities of bentonite cakes made using three different bentonites were estimated using the modified fluid-loss test under various pressures. Both the hydraulic conductivities of bentonite cakes and cutoff-wall backfill are important in evaluating the in situ hydraulic performance of slurry cutoff-wall construction. Three bentonite slurry concentrations of 4, 6, and 8% were used to fabricate bentonite cakes that represent common field conditions. X-ray diffraction, cation exchange capacity, and swell-index data were collected to characterize the bentonites. Two modified methods for analyzing fluid-loss test results were used to estimate bentonite cake hydraulic conductivities. In addition, the viscosity as a function of time was measured to explain the sealing capacities of the bentonite slurries. The bentonite-cake hydraulic conductivities ranged from 2.15×10−11 m/s to 2.88×10−10 m/s, which were 10 to 500 times lower than the cutoff wall backfill design. Experimental results for 4 and 6% bentonite slurries were relatively similar, but the 8% slurries were noticeably different. Calculated bentonite-cake thickness and stress distribution indicated that the local void ratio and hydraulic conductivity may vary across the cake thickness. The considerably lower bentonite-cake hydraulic conductivities compared to the cutoff wall backfill design show its significance in slurry cutoff-wall construction practices.

The behavior of fine-grained mineral systems is dependent on pore-fluid characteristics. The systematic analysis of previously published studies supports the development of a fabric map in the pH and ionic concentration space as a working hypothesis. This conceptual study is complemented with an extensive battery of tests where surface charge and particle interactions are controlled through pore-fluid characteristics. The macro-scale tests include sedimentation, viscosity and liquid limit, and involve a wide range of solid volume fractions (suspension to sediment) and strain levels. Experimental results permit the development of an updated fabric map on the pH-ionic concentration space which takes into consideration all experimental results. The fabric map is structured around a critical pH level and a threshold ionic concentration beyond which van der Waals attraction prevails.

A modified procedure for bentonite purification and a new method for the quantitative characterization of bentonite using smectite content are reported. Bentonite found in a drill core of Tsunagi Mine, Niigata, Japan was evaluated by the new method to demonstrate the substantial increase in smectite content from 40% in the original bentonite to 75% after purification using a new procedure. Powder samples were prepared by putting blocks of bentonite into acetone to remove water without mechanical crushing. The powdered, acetone-dried bentonite was purified by a dispersion-sedimentation method in water after cation exchange of the interlayer Ca2+ ion with Na+ ion by the reaction of raw bentonite with aqueous NaCl. The purification was evaluated using X-ray diffraction and thermogravimetric analyses (TG). The raw bentonite contained feldspar, quartz, and cristobalite, and feldspar and quartz were removed by the new purification procedure. The purification was evaluated quantitatively by comparing the TG data before and after the purification. The purified bentonite swelled in water to give a stable aqueous suspension and 3 g of purified bentonite dispersed in 60 mL of water was stable for several days. The replacement of interlayer sodium with dibehenyldimethylammonium gave an organophilic clay, which swelled in toluene. The bentonite has potential practical uses as a purified bentonite and an organophilic bentonite.

Hydrophobicity, high viscosity, and dispersion are important properties for organo-montmorillonites, and all organo-montmorillonite configurations have yet to be fully characterized with respect to this property. High-viscosity montmorillonite (Mnt) is useful in gels and as an adsorber. The current study focused on modifying Mnt using organic cations and anions of various chain lengths in batch experiments with various concentrations and ratios. The viscosity of organic Mnt reached up to 395 mP.s. Molecular dynamics simulations and X-ray diffraction (XRD) were used to identify the conditions and arrangement of organic cations and anions in the Mnt interlayer area. The intercalation mechanism of organic cations and anions was also determined, providing a theoretical basis for the preparation of high-viscosity Mnt.

The behavior of mineral mixtures can be significantly different from the behavior of the individual components of the mixture due to differences between the mechanical and chemical properties of the individual minerals, and their ensuing effects on interparticle interactions and fabric formation. This study examines mixtures of kaolinite and calcium carbonate at different mass fractions using sedimentation, viscosity, and liquid-limit tests. These macroscale tests represent a wide range of solid-volume fractions and strain levels, with emphasis on high water-content conditions to magnify the effects of electrical forces. The results demonstrate that interparticle interactions depend on mineral surface-fluid effects, particle geometry, relative particle size, and solids content. With small solids contents, the kaolinite/calcium carbonate mixture behavior is a function of electrostatic interactions between oppositely charged mineral particles that promote flocculation; however, with large solids contents, the specific surface area of the minerals is the controlling factor. These results are relevant to many natural soil environments and to the possible development of engineered mineral mixtures for industrial applications.

Permeability is often the limiting factor in clay-based barrier systems designed to attenuate miscible or immiscible contaminant transport. One critical aspect of barrier design is prediction of the effects of permeant conditions on physicochemical properties (e.g swelling) of the clay component and thus, ultimately, the permeability of the barrier. To this end, the permeability of an organically modified bentonite to ethanol-water solutions was determined to approximate the effects of organo sorption-induced swelling. The bentonite was modified with a substituted alkylammonium cation: benzyloctadecyl-dimethylammonium (BODMA). Powder X-ray diffraction (XRD) measurements were used to measure interlayer expansion and to estimate aggregate particle densities at any given ethanol concentration. Permeability measurements were conducted on samples under confining overburden stresses of 43 kPa (∼2.5 m of saturated soil) using a hydraulic gradient of ∼300. Sample thickness was continuously monitored during measurements of volumetric flow so that sample strain, void ratio and porosity could be calculated from changes in sample pore volumes. For calculations of porosity and void ratio, the swelling solid volume, determined from XRD, was assumed to include the sorbed layer (crystalline water/ethanol), the thickness of which is not normally considered in engineering applications. Exposure of the BODMA bentonite to increasing ethanol concentrations increased the swell volume of the clay. Measured coefficients of permeability for the BODMA bentonite decreased from ∼1 × 10−7m s−1 for pure water to ∼8 × 10−10m s−1 for pure ethanol. Exposure of the organo clay to ethanol-water solutions containing 0.2 M NaCl increased the effect of ethanol on clay swelling and permeability. Probable consequences of the effects of sorption-induced swelling on permeability and the performance of organo clay-based permeable reactive barriers are discussed.