Philip F. Low

Physical Chemistry of Clay-Water Interaction

Publisher Summary Clay and water are two of the most common substances in the earths crust. Separately and together they influence daily lives of individuals. Frequently, the mutual interaction between clay and water controls the formation of clouds and the infiltration of rain water into the soil. It is often responsible for the failure of buildings and highways and the decreased production of oil wells. It affects the quality of paper coatings and ceramics. This chapter provides a critical review of the recent literature on clay–water interaction. Understanding the nature and properties of the two components help to understand the nature of clay–water interaction.

Direct measurement of the relation between interlayer force and interlayer distance in the swelling of montmorillonite

Abstract Oriented gels of eight Na-montmorillonites having values of the surface charge density, σ, ranging from ≈ 28,000 to 56,000 esu/cm2 were confined in a close chamber between a N2-gas piston and a porous ceramic plate in contact with a solution of 10−4 N NaCl. Successively higher pressures up to 6.9 bars were applied by the N2-gas piston while the NaCl solution was maintained at atmospheric pressure. After equilibration at each applied pressure, the c axis spacing of the silicate layers was measured by X-ray diffraction. Subsequently, the thickness of a silicate layer was subtracted from this spacing to obtain the corresponding interlayer separation, λ. Since, at equilibrium, the swelling pressure, II, is equal to the applied pressure, it was thus possible to determine II as a function of λ for each montmorillonite. We found that II is an exponential function of 1 λ . Also, at any value of II, the value of λ is independent of the value of σ. Neither of these findings is consistent with the double-layer (i.e., osmotic) theory of swelling. Therefore, an additional force, which is the dominant force at the observed values of λ, must be responsible for swelling. In view of an empirical relation that exists between II and any property of the water in the swollen system, we postulate that this additional force results from the in-depth perturbation of the water by the surfaces of the montmorillonite layers.

Frost Phenomena on Mars

The hypothesis that the Martian wave of darkening might be a frostheaving phenomenon has been examined. Consideration of the water-vapor sorption characteristics of a silicate mineral surface at temperatures below freezing leads to the conclusion that, without strongly deliquescent salts to attract and retain liquid water in the Martian soil, frost-heaving phenomena are not to be expected on Mars. On the other hand frost-heaving phenomena involving the freezing and thawing of ammonia may be common in the soils of Jupiter.

EFFECTS OF OXIDATION STATE OF OCTAHEDRAL IRON ON CLAY SWELLING

Three montmorillonites and a nontronite were reduced by sodium dithionite to obtain different amounts of Fe2+ in their octahedral sites. The mass ratio of water to clay, mw/mc was determined as a function of Fe2+ at several values of the swelling pressure, n. The value nVmc decreased markedly with increasing Fe2+ at each value of II for each clay. Moreover, curves of II vs. mymc for the different clays were displaced downwards as Fe2+ increased. A straight line was obtained when ln(II + 1) was plotted against l/(w/mc) however, at some oxidation states of three of the samples this line exhibited a sharp break at a specific value of l/(w/mc. The slope of the line decreased for each clay as Fe2+ increased, and an increase in Fe2+ was accompanied by an increase in the cation exchange capacity. These observations are thought to be due to a collapse or partial collapse of the superimposed clay layers resulting from the increase in cation-exchange capacity.РезюмеТри монтмориллониты и нонтронит восстанавливались при помощи дитионита натрия, чтобы получить различные количества Fe2+ в их октаэдрических местах. Отношение массы воды до массы глины, м,/мг, определялось как функция Fe2+ при нескольких величинах давления набухания, П. Значение мв/мг уменьшалось значительно с увеличением Fe2+ при всех величинах П для каждой глины. Кроме того, кривые П как функции м,/мг для различных глин перемещались вниз, когда Fe2+ увеличивалось. Прямая линия получалась для функции 1п(П + 1) в зависимости от 1/(мв/мг); однако, при некоторых состояниях окисления трех образцов эта линия имела острый перелом при опреде¬ленном значении 1/(мв/мг). Наклон линии уменьшался для каждой глины, тогда как Fe2+ увеличи¬валось, и увеличению Fe2+ сопутствовало увеличение катионообменной способности. Предполагается, что эти наблюдения были в результате полного или частичного разрушения наложенных глинистых слоев, получающихся в следствие увеличения катионообменной способности. [Е.G.]ResümeeDrei Montmorillonite und ein Nontronit wurden mittels Na-Dithionit reduziert, um verschiedene Fe2+-Gehalte auf den Oktaederplätzen zu erhalten. Das Mengenverhältnis von Wasser zu Ton, mw/mc wurde als eine Funktion von Fe2+ bei verschiedenen Werten des Quelldruckes, II, bestimmt. Der mw/mc-Wert nahm mit zunehmendem Fe2+ bei jedem n-Wert für jeden Ton beachtlich ab. Darüberhinaus verlagerten sich die Kurven, bei denen II gegen mw/mc für die verschiedenen Tone aufgetragen sind, mit zunehmendem Fe2+ nach unten. Eine gerade Linie wurde erhalten, wenn ln(II + 1) gegen l/(mw/mc) aufgetragen wurde; jedoch zeigte diese Linie bei einigen Oxidationszuständen bei 3 der Proben einen scharfen Knick bei einem spezifischen Wert von l/(mw/mc). Die Neigung der Linie nahm für jeden Ton ab, wenn Fe2+ zunahm, und eine Zunahme des Fe2+ wurde von einer Zunahme der Kationenaustausch-kapazität begleitet. Man nimmt an, daß diese Beobachtungen mit einem Zusammenbruch oder einem teilweisen Zusammenbruch der überlagerten Tonlagen zusammenhängen, der von der Zunahme der Kationenaustauschkapazität herrührt. [U.W.]RésuméTrois montmorillonites et une nontroni te ont été réduites par une dithionite de sodium pour obtenir différentes quantités de Fe2+ dans leurs sites octaèdraux. La proportion de masse d’eau à argile mw/mc a été déterminée en fonction de Fe2+ à plusieurs valeurs de la pression de gonflement H. La valeur mw/mc a diminué de manière marquée au fur et à mesure de l’augmentation de Fe2+ à chaque valeur de n pour chaque argile. De plus, les courbes de II vs. mw/mc, pour différentes argiles ont été déplacées vers le bas au fur et à mesure de l’augmentation de Fe2+. On a obtenu une ligne droite lorsqu’on a relevé ln(n + 1) vs. 1/(mw/mc); cette droite a cependant exhibé une cassure nette à une valeur spécifique de l/(mw/mc) à certains états d’oxidàtion des trois échantillons. L’inclinaison de la droite a diminué pour chaque argile au fur et à mesure de l’augmentation de Fe2+, et une augmentation de Fe2+ a été accompagnée d’une augmentation de la capacité d’échange de cations. On croit que ces observations sont dues à l’affaissement ou l’affaissement partiel des couches d’argile superimposées résultant de l’augmentation de la capacité d’échange de cations. [D.J.]

Rheological behavior of Na-montmorillonite suspensions at low electrolyte concentration

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

EFFECT OF SWELLING ON THE INFRARED ABSORPTION SPECTRUM OF MONTMORILLONITE

The i.r. spectra of mixtures of different Na-montmorillonites were determined at several water contents between 2 and 22 g of water/g of montmorillonite. It was found that Si—O absorption is represented by four closely-spaced bands, one of which is pleochroic. The pleochroic band appeared only at higher water contents. All of these bands, excepting that with the highest wave number, shifted in frequency with increasing isomorphous substitution. None of them shifted in frequency with increasing water content.The absorption coefficient for the principal Si—O absorption decreased with increasing isomorphous substitution but increased with increasing water content. Niether isomorphous substitution nor water content appeared to have any significant effect on absorption due to O—H stretching or H—O—H bending in the interlayer water.At a critical water content for each montmorillonite, an abrupt change occurred in the absorption coefficient for the principal Si—O absorption. This change was ascribed to a sudden rearrangement of the particles.

Relation between the heat of immersion and the initial water content of Li-, Na-, and K-montmorillonite

Abstract The heat of immersion, Q, and the interlayer spacing, λ, of Li-, Na-, and K-montmorillonite were determined at several values of the mass ratio of water to montmorillonite, mw/mc, by microcalorimetry and X-ray diffraction, respectively. For Li-montmorillonite, Q decreased and λ increased monotonously with increasing mw/mc. However, for Na- and K-montmorillonite, Q decreased rapidly from positive to negative values, passed through a minimum, increased to positive values again, passed through a maximum, and then decreased gradually to 0. Concurrently, λ increased continuously with mw/mc to a specific value, jumped to an appreciably higher value, and increased continuously thereafter. Comparison of the curves of Q vs mw/mc with those of λ vs mw/mc showed that the minimum in Q occurred at the same mw/mc as the jump in λ, that the depth of the minimum correlated with the magnitude of the jump in λ, and that its width correlated with the range of mw/mc over which the jump in λ occurred. The minimum in Q was deeper and wider for the K-montmorillonite than for the Na-montmorillonite. With all of the three homoionic montmorillonites, Q remained measureable until mw/mc exceeded 6.0 g/g. These results were interpreted to mean that Q is governed by the energy required to dissociate the exchangeable cations and expand the montmorillonite layers and by the energy released in hydrating these cations and the surfaces of the layers but that it does not become negligible until the layers are far apart.

EFFECTS OF pH and ELECTROLYTE CONCENTRATION ON PARTICLE INTERACTION IN THREE HOMOIONIC SODIUM SOIL CLAY SUSPENSIONS

The relation between shear stress and shear rate was determined with a Fann viscometer at each of several values of clay concentration, NaCI concentration, and pH for suspensions of Na-saturated clay extracted from Cecil, Putnam, and Hoytville soils. The predominant clay minerals in these soils were kaolinite, montmorillonite, and illite, respectively. Then values of the extrapolated shear stress were obtained by extrapolating the linear portions of the respective shear curves. Theory and practice indicate that extrapolated shear stress is a criterion of particle-particle interaction; for the Cecil kaolinitic soil clay, these values decreased with increasing NaCI concentration at low pH values but increased with increasing NaCl concentration at high pH values. As a result, curves of extrapolated shear stress versus pH at different NaCl concentrations intersected at or near a common point. However, for the Putnam (smectitic) and Hoytville (illitic) soil clays, extrapolated shear stress increased with increasing NaCl concentration and decreased with increasing pH. Moreover, these curves of different NaCl concentrations tended to converge with increasing pH but did not intersect. The findings were interpreted to mean that the edges of the Cecil clay were amphoteric with an isoelectric point at the point of intersection of the curves whereas the edges of the Putnam and Hoytville clays were negatively charged with a charge density that increased with increasing pH. Consequently, the particle arrangement in the Cecil kaolinitic soil clay changed from edge-to-face at low pH values to edge-to-edge at high pH values, and the particle arrangement in the Putnam and Hoytville 2:1 soil clays was edge-to-edge at all pH values.

The molar absorptivity of interparticle water in clay―water systems

Abstract Infared spectroscopy was used to study the molar absorptivity, ϵ, for OD stretching of HDO mixed in different proportions with various clay minerals. The value of ϵ was found to decrease with increasing m c m w , the mass ratio of clay to water, according to the empirical equation ϵ = ϵ0 exp( β ϵ m c m w ), where ϵ0 is the value of ϵ for bulk HDO and βϵ is a constant that is proportional to the specific surface area of the clay. Theoretical equations were used to relate the infrared absorption intensity to the arrangement and interaction of the interparticle water molecules. It was found that both ( ∂u ∂Q 1 ) 2 , the square of the partial derivative of the dipole moment with respect to the normal coordinate of vibration, and τ, the transition moment relaxation time, obeyed empirical equations of the same form as the one which describes the variation in ϵ. The changes in ( ∂u ∂Q 1 ) 2 and τ were interpreted to mean that water next to clay surfaces has a different charge distribution and a slower rate of rotation than bulk water. Also, since ϵ was independent of the surface charge density and, hence, of the concentration of the counterions, it was concluded that the particle surfaces are responsible for these differences. As shown by an analysis of the data, the effect of the particle surfaces on the adjacent water extends to at least 40 A.

Swelling pressure of montmorillonite layers versus H-O-H bending frequency of the interlayer water

The in-depth perturbation of vicinal water by the surfaces of montmorillonite layers was investigated by relating the swelling pressure, Π, of the montmorillonite layers to the H-O-H bending frequency, ν2, of the interlayer water. For this purpose, an oriented montmorillonite gel was deposited on a porous filter in an environmental chamber. On its underside the filter was in contact with a solution maintained at atmospheric pressure. By admitting nitrogen gas at a known pressure to the environmental chamber, water was squeezed from the gel into the solution until equilibrium was reached and Π equalled the applied pressure. Then the gel was divided into 2 parts. One part was used for the gravimetric determination of the water content, mw/mc. It was possible, therefore, to determine mw/mc as a function of Π. The other part of the sample was transferred to an FTIR spectrometer where the ν2 of the water within it was measured by attenuated total reflectance. Thus, the same samples were used to determine the dependence of both Π and ν2 on mw/m{inc}. It was found that Π and ν2 were both exponential functions of mc/mw and so a linear relation was found between ln(Π + 1) and ln(ν2/ν2°), where ν2° is the H-O-H bending frequency of bulk water. These results strongly support the conclusion that the in-depth perturbation of the water by the surfaces of the montmorillonite layers is primarily responsible for both the development of Π and the departure of ν2 from ν2°.