The Relation Between Composition and Swelling in Clays
TL;DR: In this paper, the authors reviewed the mechanism of hydration and swelling of different types of clays and some theories proposed as to the cause of the clays' hydration, including broken bonds on the edges of the sheets.
Abstract: The phenomenon of swelling is associated with the hydration of clay; however, all clays do not swell when hydrated. Steps in the mechanism of hydration and swelling of different types of clays as observed and interpreted by several investigators and some theories proposed as to the cause of hydration and swelling are reviewed. The concept of clays as colloidal electrolytes that dissociate to a greater or less extent when dispersed in water seems to explain most satisfactorily the significant relation between the degree of swelling on hydration and the composition of the clay minerals. In the kaolinite group, in which there are generally no replacements, the small number of exchangeable cations associated with the clay structure are presumed to be held by broken bonds on the edges of the sheets. Even though kaolinite, as shown by Marshall, is more highly ionized than montmorillonite, this greater ionization, because of the small number of cations present and their location on the edges of the sheets, cannot pry the units apart or leave the sheets sufficiently charged to cause the mineral to exhibit the phenomenon of swelling. In the montmorillonite structure, on the other hand, isomorphous replacements, most commonly of magnesium and ferrous iron for aluminum in the octahedral layer, and, to a slight degree, replacement of aluminum for silicon in the tetrahedral layer, give the structure a net residual charge of 0.7 to 1.10 milliequivalents, which is neutralized by cations held electrostatically and located, for the most part, between the sheets. On hydration such a structure tends to ionize, the degree of ionization depending on (a) the nature of the exchangeable cation and (b) the kind and extent of isomorphous replacements. The characteristically great swelling of sodium montmorillonite as compared with calcium montmorillonite can be correlated with its much greater ionization. The differences in swelling of different montmorillonites have been correlated with the nature and extent of octahedral substitution and are attributed to the effect of these replacements on the anionic strength of the structural unit and its consequent degree of ionization as influenced by the changes in polarization throughout the structure caused by these replacements. Hydrous mica, with the same structure as montmorillonite, is characterized by even a greater degree of isomorphous replacements and, consequently, a greater charge. However, a large part of this charge is neutralized by fixed, nonexchangeable and nonionizable potassium, and ionization of the exchangeable cations is unable to overcome the effect of this fixed potassium. It is probable that the greater replacements in the hydrous mica structure, as in the montmorillonite structure, have a depressing effect on ionization. The result is that hydrous micas are characterized by a very low degree of swelling.
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TL;DR: Stucki et al. as mentioned in this paper studied the role of bacteria-mediated changes in the oxidation state of iron in soil clay minerals in determining the chemical and physical properties of soils and sediments.
130 citations
01 Jan 1990
TL;DR: In this article, the effects of clays on the water holding capacity of the soil are discussed. And the most important of these effects is associated with their effects on the clay microstructure at different levels of organisation, which is strongly influenced also by the climatic conditions, the soil organisms, the topography, and the length of time for soil genesis.
Abstract: Clays have several important influences on the properties and the performance of soils, and one of the most important of these is associated with their effects on the water holding capacity of the soil For soils with appreciable contents of clays, the uptake and the release of water gives rise to changes in bulk volume (swelling and shrinking), and this alters the clay microstructure at different levels of organisation The nature and the quantities of the clays in any soil are of fundamental importance to the behaviour of the soil, but this behaviour is strongly influenced also by the climatic conditions, the soil organisms, the topography, and the length of time for soil genesis
96 citations
01 Jan 2013
TL;DR: In this paper, structural changes of smectites were characterized by a variety of chemical, instrumental, and spectroscopic methods, including the use of synchrotron X-ray sources, infrared, UV-visible, and scanning, environmental-sample, and high-resolution electron microscopy.
Abstract: Structural Fe in clay minerals plays a large role in determining and influencing the chemical and physical properties and behaviour of this ubiquitous inorganic fraction of natural soils and sediments. Almost all clay minerals contain some Fe in their crystal structures, so the impact of Fe is great. Moreover, the effects of Fe are greatly amplified by its facile susceptibility to changes in oxidation state (redox modification), which are in fact larger than the effects of its mere presence in the mineral structure. Iron(III) is the more common oxidation state in the smectite structure under natural conditions, but bacterial activity in soils and sediments readily reduces it temporarily to Fe(II). In the laboratory, both sodium dithionite and bacteria were used extensively to effect reduction, followed by a plethora of subsequent characterizations. A variety of other reducing agents were also tried in the laboratory, with mixed results and with none of them being as effective as either dithionite or bacteria. Multiple redox cycles transform the smectite to a more illitic form, with both fixed K and residual Fe(II) increasing with each cycle. The surface reactivity of the smectites toward pesticides, chlorinated and various other organics, and redox-active metals is greatly increased once the structural Fe had been reduced. The cation exchange and fixation capacities increase, whereas specific surface area and swelling in water decrease. Recent studies also showed that reaction with redox-active anions (e.g. nitrate) is possible with polycations-exchanged, redox-modified smectites. Structural changes were characterized by a variety of chemical, instrumental, and spectroscopic methods, including the use of synchrotron X-ray sources, infrared, UV–visible, and scanning, environmental-sample, and high-resolution electron microscopy. In summary, Fe in smectites provides a robust means by which the properties and behaviour of soils and sediments change dynamically over space and time as environmental conditions fluctuate in response to global climate patterns and anthropogenic activity. Many opportunities await the curious and adventurous ones who decide to probe this phenomenon in order to advance understanding and uncover more avenues for meaningful exploitation.
90 citations
Cites background from "The Relation Between Composition an..."
...If this is true, then why are the observed effects just the opposite [Foster, 1953, 1955; Egashira and Ohtsubo, 1983; Stucki et al., 1984b, 2000; Lear and Stucki, 1985; Gates et al., 1993]....
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...This phenomenon was first observed by Foster [Foster, 1953, 1955], who found that the blue-gray form of Wyoming montmorillonite swelled to about half the water volume as the olive-green form, and that the Fe2+/Fe3+ ratio of the blue-gray form was double that of the olive-green form....
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TL;DR: In this article, X-ray diffraction and electron microscopy were employed in conjunction with core flooding experiments to investigate clay migration phenomena in sandstones of 500 millidarcy permeability.
Abstract: X-RAY diffraction and electron microscopy were employed in conjunction with core flooding experiments to investigate clay migration phenomena. Severe water sensitivity or loss of permeability was observed in a suite of sandstones in spite of the almost total absence of montmorillonite or swelling mixed layer clays. Clay migration was found to cause total or partial plugging even in sandstones of 500 millidarcy permeability. Bacterial plugging was ruled out by prefiltering and bactericide treatments of waters. X-ray diffraction and electron microscopy analyses were performed on the sandstones and produced effluents. The direct cause of damage was displacement of submicroscopic natural clay crystals of needle-shaped mica and hexagonal-shaped kaolinite (Rex, 1965). The mobile clays were identified as authigenic crystals that are present on the pore walls and are dislodged by changes in water chemistry combined with water movement. Flooding sandstones with alkali metal brines “sensitized” the cores, i.e. triggered clay dispersion upon subsequent flooding with fresh water. Flooding with divalent calcium brine prevented water sensitivity and suppressed the undesirable effect of alkali metal brines. A double layer expansion effect is suggested as the dispersion mechanism.
86 citations
TL;DR: The isoelectric point (IEP) of the edge surface of a montmorillonite sample was determined by using electrophoretic mobility measurements and characterizes the intrinsic reactivity of edges, that is, the protonating capacity of edge groups in absence of any electric field generated by structural charges.
Abstract: Fil: Pecini, Eliana Melisa. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Bahia Blanca. Instituto de Quimica del Sur; Argentina. Universidad Nacional del Sur; Argentina
80 citations
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TL;DR: In this paper, the spectral and x-ray properties of water and ionic solutions have been deduced quantitatively in good agreement with experiment using a model of the water molecule derived from spectral and X-ray data.
Abstract: On the basis of the model of the water molecule derived from spectral and x-ray data and a proposed internal structure for water, the following properties of water and ionic solutions have been deduced quantitatively in good agreement with experiment. (1) The crystal structure of ice. (2) The x-ray diffraction curve for water. (3) The total energy of water and ice. (4) The degree of hydration of positive and negative ions in water. (5) The heat of solutions of ions. (6) The mobility of hydrogen and hydroxyl ions in water. And the following inferred in a qualitative way. (7) The density and density changes of water. (8) The explanation of the unique position of water among molecular liquids. (9) The dielectric properties of water and ice. (10) The viscosities of dilute ionic solutions. (11) The viscosities of concentrated acids.
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