Kaolinite, swelling

Montmorillonite clays absorb water readily, swell greatly and confer highly plastic properties to a soil. Thus soil stress (Section 14.8) occurs most frequently in these soils and less commonly in predominantly kaolinitic types. Similarly, a soil high in bentonite will show more aggressive corrosion than a soil with a comparable percentage of kaolinite. A chalky soil usually shows low corrosion rates. Clay mineralogy and the relation of clays to corrosion deserves attention from corrosion engineers. Many important relationships are not fully understood and there is need for extensive research in this area. 

Basic studies on the kinetics of swelling have been performed [1699]. Pure clays (montmoiillonite, illite, and kaolinite) with polymeric inhibitors were investigated, and phenomenologic kinetic laws were established. 

Fine particle migration can occur in the absence of water-swelling clays. Migrating fines can include the migrating clays kaolinite, illite, chlorite, and some mixed layer clays and fine silica particles (162,163). Fine particle migration is promoted when the... 

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

The crystals of 2 1 swelling clays are typically smaller than either kaolinite or fine-grained mica and thus have higher adsorption capacity and cation... 

Polyelectrolytes provide excellent stabilisation of colloidal dispersions when attached to particle surfaces as there is both a steric and electrostatic contribution, i.e. the particles are electrosterically stabilised. In addition the origin of the electrostatic interactions is displaced away from the particle surface and the origin of the van der Waals attraction, reinforcing the stability. Kaolinite stabilised by poly(acrylic acid) is a combination that would be typical of a paper-coating clay system. Acrylic acid or methacrylic acid is often copolymerised into the latex particles used in cement sytems giving particles which swell considerably in water. Figure 3.23 illustrates a viscosity curve for a copoly(styrene-... 

The CEC of clay minerals is partly the result of adsorption in the interlayer space between repeating layer units. This effect is greatest in the three-layer clays. In the case of montmorillonite, the interlayer space can expand to accommodate a variety of cations and water. This causes montmorillonite to have a very high CEC and to swell when wetted. This process is reversible the removal of the water molecules causes these clays to contract. In illite, some exchangeable potassium is present in the interlayer space. Because the interlayer potassium ions are rather tightly held, the CEC of this illite is similar to that of kaolinite, which has no interlayer space. Chlorite s CEC is similar to that of kaolinite and illite because the brucite layer restricts adsorption between the three-layer sandwiches. 

Type. The interlayer spaces of 2 1 silicates may be blocked by poorly ordered sheets of A1 hydroxy polymers, such as [Al(OH)2 5° +] (n > 6). Such A1 interlayers neutralize a considerable part of the surface charge and restrict swelling, and effectively convert 2 1 clays into materials similar to kaolinite. 

Many clay minerals have aluminosilicate layer structures. For example, in kaolinite, Al2(0H)4[Si205] (Fig. 7.5), the Al3+ are all in octahedral locations. Clay minerals of the smectite or swelling type, such as montmo-rillonite, can absorb large amounts of water between the aluminosilicate... 

The above results are related to the structural properties of the clay minerals. In the case of kaolinite, the tetrahedral layers of adjacent clay sheets are held tightly by hydrogen bonds. Therefore, only readily available planar external surface sites exist for exchange. With smectite, the inner peripheral space is not held together by hydrogen bonds, but instead it is able to swell with adequate hydration and thus allow for rapid passage of ions into the interlayer. 

De Sousa Santos, P., De Sousa Santos, H. and Brindley, G.W., 1966. Mineralogical studies of kaolinite-halloysite clays, 4. A platy mineral with structural swelling and shrinking characteristics. Am. Mineralogist, 51 1640-1648. 

Hofmann, U., Weiss, G.K., Mehler, A. and Scholz, A., 1956. Intracrystalline swelling, cation exchange, and anion exchange of minerals of the montmorillonite group and of kaolinite. Proc. Natl. Conf. Clays Clay Miner. 4th - Natl. Acad. Sci. Natl. Res. Counc., Pubi, 456 273-287. 

With kaolinite and non swelling materials, the external surface area obtained from xfe was in good agreement with the BET (N2) surface area. 

Clays are aluminosilicates with a two-dimensional or layered structure including the common sheet 2 1 alumino- and magnesium- silicates (montmorillonite, hectorite, micas, vermiculites) (figure 7.4) and 1 1 minerals (kaolinites, chlorites). These materials swell in water and polar solvents, up to the point where there remains no mutual interaction between the clay sheets. After dehydration below 393 K, the clay can be restored in its original state, however dehydration at higher temperatures causes irreversible collapse of the structure in the sense that the clay platelets are electrostatically bonded by dehydrated cations and exhibit no adsorption. 

Using MC simulations Delville and co-workers have investigated the clay-water interface [83-87], The number of hydration layers (2-3) increases suddenly during the swelling process [85]. For hydrated montmorillonite with interlayer sodium counterions it was determined that the water content of the pore is a function of the interlamellar distance. Water molecules are layered in successive shells, whose number (1-4) depends on the available interlayer space [87]. The MD study of structure of water in kaolinite [88] has indicated two types of adsorbed water molecules according to different orientations with respect to the structure of clay sheets with HH vector parallel or perpendicular to the surface. 

In both cases, an analysis of the diffusion front as a function of time shows a t2 dependence of the front line which indicates Fickian diffusion and allows for the determination of a diffusion coefficient according to x2 = 2Dt from the slope of the curves in Fig. 24. The inter-diffusion coefficient was measured at [1.15 + 0.05] x 10 9m2/s, while the self-diffusion coefficient was measured at [8.4 + 0.5] x 10 10m2/s, which is the same order of magnitude as that recorded for non-swelling technical-grade kaolinite at similar water content.97 This indicates... 

In Figure 29, the spectrum of an oil-sand sample shows the fundamental C-H peaks at 3.5 xm. From the two peaks in this region, one could determine the aromatic-aliphatic ratio of the hydrocarbons present in the sample. The fundamental water vibration is at approximately 3 xm (this peak would be substantially larger in a conventional emulsion sample), and the fundamental vibrations due to clays are at approximately 2.8 xm. The shape of the clay peaks indicates that kaolinite and a small amount of swelling clays such as bentonite are present in this sample. 

The mineralogy that comprises the clay component of the soil is also critical to contamination of soils by biological and chemical threat agents. For example, ricin was sorbed to four different clay minerals as described above (Figure 4.2). Kaolinite, a 1 1 clay mineral, sorbed very little ricin. Sepiolite, a fibrous clay mineral, sorbed much more ricin. Illite, a tetrahedrally substituted 2 1 clay mineral, sorbed similar amounts of ricin as the sepiolite. The octahedrally substituted clay mineral, montmorillonite, sorbed much greater quantities than all of the other clay minerals. Even with this clay mineral, the cation that was dominantly sorbed to the clay made a difference. The Na-saturated montmorillonite sorbed more than the Ca-saturated montmorillonite. This is thought to be due to the swelling of the interlayers of the clays. Na-saturated clays swell more so than do Ca-saturated ones. Similar results are shown with aflatoxin Bj (Jaynes et al. 2007). 

The surface structures of the three layer silicates studied-kaolinite, illite and montmorillonite - are essentially identical, since the surface atomic planes consist of tetrahedrons. Differences between them are due to the differences in their swelling capacities and charge... 

Martin (1959) and Bernard (1967) observed that clay swelling and/or dispersion accompanied by increased pressure drop resulted in incremental oil recovery. Tang and Morrow (1999) concluded that line mobilization (mainly kaolinite) increased recovery based on their observations (1) fired/acidized Berea core showed insensitivity of salinity on oil recovery, whereas unlired Berea core did show sensitivity and (2) for clean sandstones, the increase in oil recovery with the decrease in salinity was less than that for the clay sands. Figure 3.4 shows some of their results. In the tests, the reservoir CS core was used. The reservoir brine, CS RB, was used as connate brine for the entire CS core tests. 

At temperatures below 150°C, water that is physically attached to clays evaporates. Physically attached water can be present as water adsorbed onto the surface of particles or between the layers of the clay structure. The loss of water is endothermic and results in measurable weight loss. For kaolinite, the weight loss is usually minor, on the order of a percent or less. However, other clays, particularly those that swell when exposed to water such as bentonite can have considerable weight loss in this temperature regime (4-8 wt%) [6], For kaolinite, the changes due to loss of physical water do not alter the structure as determined by X-ray diffraction. 

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