Clay properties octahedral sheet

Some of expanding clays in soils have the attributes of vermiculite, some of smectite, and some have features of both. The variation in properties is largely related to the layer charge. The charge is dependent on the original charge on the 2 1 layer of the parent mineral and the amount of ferrous iron in the octahedral sheet. The oxida-... 

Acid activation has long been known as a preparation method for porous materials. In general, the acid solution dissolves the octahedral sheets of the clay and produces a significant modification over the tetrahedral sheets [11]. The solids obtained have higher surface area and better adsorptive and catalytic properties than the original clays, depending on the starting material and the conditions of the treatment [12-15]. The activation of metakaolin has been reported only in a few articles, and the application of the solids obtained to different catalytic reactions has been described [3,7,16-18]. 

Conceptually, the next simplest clay mineral is pyrophyllite, which is produced by attaching tetrahedral sheets above and below an octahedral layer (Fig. 6), compared with just one octahedral sheet for kaolin [15]. The resulting chemical composition of pyrophyllite is AI2Si4Ol0(OH)2, which is equivalent to the mineral formula Al20 4Si02-II20. The structure and properties of pyrophyllite are summarized in Table 2. 

Specific minerals in each group are distinguished by a combination of chemical composition, whether the octahedral sheet is dioctahedral or trioc-tahedral, the existence or absence of interlayer molecular species (principally water), and by the degree of disorder in the layer stacking. A full discussion of these factors is not necessary here the interested reader should look at Moore and Reynolds (1997). The following will discuss only the most common clay minerals and their properties, especially those which may be related to surface properties. 

Simple Models. The surface chemical properties of clay minerals may often be interpreted in terms of the surface chemistry of the structural components, that is, sheets of tetrahedral silica, octahedral aluminum oxide (gibbsite) or magnesium hydroxide (brucite). In the discrete site model, the cation exchange framework, held together by lattice or interlayer attraction forces, exposes fixed charges as anionic sites. 

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