Illitization of smectite

When the size of the exchanged cation is similar to the pore sizes in the crystal lattice (e.g., potassium [Bouabid et al. 1991] and lithium ions [Komadel et al. 2003]), they can be built into the crystal lattice and decrease the layer charge. As an example, the illitization of smectites is mentioned. 

It is generally agreed on the basis of TEM evidence (e.g., Rask et ai, 1997) and on the basis of chemical substitution in the several structural sites of illite (e.g., Lanson and Champion, 1991 Awwiller, 1993 Lynch et ai, 1997) that the illitization of smectite, like other replacement reactions in late diagenesis, proceeds through a dissolution/precipitation mechanism. Similar to other replacement minerals, illite also occurs as cements in sandstones as well as in shales, where it forms overgrowths on detrital illite particles and discrete crystals (cements) (e.g., Lanson and Champion, 1991 Rask et at, 1997). 

Amouric M, Olives J (1991) Illitization of smectite as seen by high-resolution transmission electron microscopy. Eur J Mineral 3 831-835... 

All of the I/S produced by WD are randomly interstratified, with the possible exception of the Black Jack sample (Figure 3) and the most illitic Kinney sample (Figure 4), both of which show signs of partial R1 ordering between illite and smectite layers. For these samples, the 001 XRD reflections are displaced towards larger angles, and a very weak superlattice reflection is visible at small angles. 

Concerning clay minerals (illite and smectite), Capuano (1992) proposed a simple linear dependency of the mineral-water fractionation factor over reciprocal temperature ... 

In the Goldenville Group, the Moshers Island Formation also has two compositional members an upper one explained by mixtures of chlorite, kaolinite illite, and smectite, and a lower one explained by only illite and smectite. 

The problem with limited selectivity includes some of the minerals which are problems for XRD illite, muscovite, smectites and mixed-layer clays. Poor crystallinity creates problems with both XRD and FTIR. The IR spectrum of an amorphous material lacks sharp distinguishing features but retains spectral intensity in the regions typical of its composition. The X-ray diffraction pattern shows low intensity relative to well-defined crystalline structures. The major problem for IR is selectivity for XRD it is sensitivity. In an interlaboratory FTIR comparison (7), two laboratories gave similar results for kaolinite, calcite, and illite, but substantially different results for montmorillonite and quartz. 

The molar ratio of Al Si in clay minerals is variable, kaolinite (0.85), mica-illite (0.61), and smectitic clays (0.35) (McCarthy et al. 1987). Bituminous coal tends to have higher concentrations of kaolinite, while lignite and subbituminous coals contain mica-illite or smectitic clays. McCarthy et al. (1987) predicted that the higher the Al Si ratio of the clay minerals the... 

Intact soil cores (6.7 cm i.d.) were taken with spilt spoon at depths of 1 to 2 meters from a field test site located approximately 50 km east of Cincinnati, Ohio. The soil in this interval consists mainly of quartz (60%) and clay minerals (35%) with minor amounts of plagioclase and potassium feldspar. The majority of clay is illite and smectite, with minor amount of kaolinite. Soil chemical properties were analyzed prior to, and after, electroosmosis, in order to evaluate the effects of electroosmosis on the distribution of elements within the soil column. Sampled cores were wrapped in aluminum foil and stored at 12°C until the EO cell was assembled. 

In natural soils which commonly contain illite and smectite, there can be a significant charge imbalance between Si4+ and Al3+ in the structures of these clay minerals. This results in a net negative charge on the clay mineral surfaces, resulting in more adsorption of mobile cations. When an acid front encounters these adsorbed mobile cations, they are very easily displaced by the H ion, which by virtue of its small size is strongly adsorbed to the clay surface. As a result, the measured CEC of such clay-bearing soils is predicted to increase, as we have observed in our experiments. 

Rates of ion exchange on kaolinite, smectite, and illite are usually quite rapid. Sawhney (1966) found that sorption of cesium on illite and smectite was rapid, while on vermiculite, sorption had not reached an equilibrium even after 500 h (Fig. 5.5). Sparks and Jardine (1984) found that potassium adsorption rates on kaolinite and montmorillonite were rapid, with an apparent equilibrium being reached in 40 and 120 min, respectively. However, the rate of potassium adsorption on vermiculite was very slow. Malcom and Kennedy (1969) studied Ba-K exchange rates on kaolinite, illite, and montmorillonite using a potassium ion-specific electrode to monitor the kinetics. They found >75% of the exchange occurred in 3 s, which represented the response time of the electrode. The rate of Ba-K exchange on vermiculite was characterized by a rapid and slow rate of exchange. 

So-called mixed-layer chlorite-vermiculites are common in marine sedimentary rocks, but it appears that in most, if not all, instances the vermiculite layers will not contract when saturated with potassium and the expanded layers are probably some form of smectite. These clays probably formed from volcanic material, montmorillonite or chlorite, rather than from the degradation of micas and illites. 

Clay mineral diagenesis also may play a role in dolomite formation during burial. The commonly observed conversion of smectites to illite can result in the release of the magnesium necessary for dolomite formation (e.g., McHargue and Price, 1982). Dolomite formation is observed near and within shale beds however, this process again appears to be a localized mechanism and probably is incapable of producing large quantities of dolomite. 

The mixed-layer structure of illite and smectite was obtained by alternating layers of illite and smectite. To allow comparison to other 1.0-nm structures, a layer spacing of exactly 1.0 nm was used for muscovite and biotite, and a layer spacing of exactly 2.0 nm was used for the 2-layer illite/smectite structure. 

IHite/Smectite. Another common intergrowth of sheet silicates is the mixed-layering of illite and smectite. As discussed above, illite and smectite are clay minerals whose basic structures resemble the mica muscovite. Their compositions may differ significantly from muscovite, but they generally have a lower occupancy of the interlayer sites than mica. Numerous other compositional differences are possible for smectite however, this discussion will be restricted to a dioctahedral illite and a dioctahedral smectite containing potassium and vacancies in the interlayer sites as given above. 

In principle, actual sequences of illite and smectite layers can be observed directly with HRTEM imaging. However, since the illite and smectite layers differ only slightly in their compositions (subtle differences in K, Al, and Si), they may be difficult to differentiate in HRTEM images. Indeed, the two different layer types are barely distinguishable near the Scherzer focus (Figure 10a), but the two layers are clearly visible for overfocus conditions (Figure 10b). This image allows direct observation of the sequence S-I-S-I-I-I-S-I-I-I-I-I-S-I from top to bottom. 

ATR-FTIR and the HF/3-21G(d,p) level of theory [103], it was predicted that salicylic acid is adsorbed strongly onto illite. Salicylate forms surface complexes predominantly with the Al3+ octahedra located on the edges of the illite grains. The authors of DFT studies [104, 105] show that the ordering for the best sorption of dioxine and furane on the surface of smectites follows the order Mg2+ > Fe2+ > Fe3+ > Li+, which was obtained also in the case of adsorption of nitrogen heterocyclics on smectites [106]. 

The most powerful methods for the study of adsorption mechanism of nitroaromatic compounds on clay minerals have become in situ spectroscopic investigations. Handerlein et al. [152, 153] and Weissmahr et al. [154-156] have investigated the adsorption of NACs particularly on illites, montmorillonites and homoionic kaolinites. The substituted nitrobenzenes on the surface of smectites were investigated by Boyd et al. [157, 158], The main focus in the experimental study of adsorption of NACs on the surface of clay minerals is the influence of the type of clay mineral, the effect of exchangeable cation of the mineral, the effect of the structure and the kind of substituents of NAC compound on the position and orientation of NACs to the surface of mineral, the character of interaction between NACs and the surface of mineral, the adsorption energy. 

Clay minerals are hydrous aluminum phyllosilicates made of sheets or layers composed of tetrahedra and octahedra. This mineral type includes the following groups kaolinite, smectite, illite, and chlorite. In the case of smectite, each layer comprises two sublayers of tetrahedra with an inserted octahedral layer, where, between layers, an interlayer space where the exchangeable cations are located is formed [131-133], In Figure 2.24... 

As indicated in Table 1, the three 2 1 groups differ from one another in two principal ways. The layer charge decreases in the order illite > vermiculite > smectite, and the vermiculite group is further distinguished from the smectite group by the extent of isomorphic substitution in the tetrahedral sheets. Among the smectites, those in which substitution of Al for Si exceeds that of Fe2+ or Mg for Al are called beidellite, and those in which the reverse is true are called montmorillonite. The sample chemical formula in Table 1 for smectite thus represents montmorillonite. In any of these 2 1 clay... 

In reality, soil clays are often not so well defined. Interstratification is common, with, for example, intergrades of vermiculite and illite or smectite and illite being found. This means that some layers in the clay... 

The mineralogical compositions of the LTA s from lignites in Shelby, Nacogdoches, and Rusk Counties appear to be rather similar. The mineral matter in the lignites of Panola County is different in that large amounts of detrital clays such as illite and smectite, and rather low quantities of bassanite and pyrite are present. 

The transformation of smectite to mixed layer smectite-illite, and ultimately to illite, with increasing temperature is an extremely important reaction in many sedimentary basins, including the northern Gulf of Mexico Basin (Hower et al., 1976 Boles and Franks, 1979 Kharaka and Thordsen, 1992). The water and solutes released and consumed by this transformation are major factors in the hydrogeochemistry of these basins, because of the enormous quantities of clays involved. Several reactions conserving aluminum or maintaining a constant volume have been proposed for this transformation (Hower et al., 1976 Boles and Franks, 1979). The reaction proposed below (Equation (4)) conserves aluminum and magnesium, and is probably a closer approximation based on the composition of formation waters in these systems ... 

Figure 13 Ternary plots of mole fraction Al203(A)-CaO + Na20 in silicates (CN)-K20(K) (note that the lower part of the ternary diagrams, A < 40, is not shown). The plagioclase-K-feldspar join, at A = 50, and illite and smectite compositions (thick bars) as in Figure 12. Fields encompassing data from Fore Arc and Trailing Edge tectonic settings are shown in stippled patterns (after Me Lennan et al., 1990).

Fluids can be released from solids by mineral dehydration thus adding fluids to the compaction-driven fluid flux in a sedimentary column undergoing burial. The relative contribution of such diagenetic processes to the compaction-driven flow, can be estimated. Dehydration of smectite may be important (Burst, 1969), but at greater depths illitization of kaolinite may be significant (Eq. (2)). Bjprlykke et al. (1986) and... 

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