THE COMPOSITION OF CLAY

The composition of clay is dependent on its history , i.e. the way it was formed and the events which took place afterwards. It is of vital importance for the composition of clay whether the clay was immediately deposited on the place where it was formed without having been altered under the influence of the environment or whether the clay was transported over a long distance. In this paragraph we will have a closer look at the composition of clay which is often quite 

The Dutch magazine KGK (Klei Glas Keramiek = Clay Glass Ceramics) reports the results of an extensive physical and chemical research of five clay deposits in the area between the rivers Rhine and river Meuse in the Netherlands. The chemical part involved both main and trace elements. The analysis of trace elements was carried out within the framework of an Act on the requirements for the environmental quality of soil materials in relation to, for example, the chemical composition of baked clay products. One of the things which have to be investigated in the baked product is the degree in which incorporated pollutions leach out (are extracted) under the influence of the weather, and especially under the influence of water. The analysis of one of the five deposits is represented in table 8.2. 

Some of the mentioned trace elements have natural origins, others are the result of for example industries. The latter are only considered to be pollutants when their contents exceed a certain norm value. This subject is, however, beyond the scope of this book. 

It should be born in mind that this is a overall clay composition. When we compare the representations of a clay composition in both tables, we notice that chemists apply the existing nomenclature rules (chapter 3, Chemistry). Furthermore the above represention proves that clay contains a number of silicate minerals. The structure of these silicate minerals and of quartz was already discussed in the chapter on Geology and Minerology. In the next paragraph we will concentrate on a certain group of silicates, the so-called clay minerals. Without these minerals clay would not possess its specific clay properties. 

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TABLE OF THE COMPOSITION OF CLAYS AKD rOBOELAUf WEEN FREE FROM WATER. 

In intumescent fire retardant application, clay was combined with ammonium polyphosphate and pentaerythritol in the polypropylene matrix. The fire retarding properties depended on the composition of clay. Ammonium polyphosphate played the role of carbonization catalyst and pcnlacrylhrilol the role of carbonization agent. 

Properties of clays and clayey rocks, and also the processes in them depend on a number of factors. Then the mathematical simulation of the properties and processes, as one of the methods of their examination, is a rather difficult problem. Physically it is clear that the speciflc properties of clay rocks (low permeability, plasticity in moist condition) are caused by the existence of clay minerals in their composition, and these properties are a manifestation of surface capacities, which exist between particles of the clay minerals, which are included in the composition of clays. The most useful conception of the activity of surface capacities is the conception of disjoining pressure between colloid particles, Mitchell (1976). In this work we provide a description of the physical and mechanical clay properties and transport processes in them. The description is based on methods of theory of filtration consolidation. Nikolaevskiy (1996), and also on the theory of stability of lyophobic colloids (theory of Deijaguin-Landau-Verwey-Overbeeck, or DLVO theory), which uses the conception of disjoining pressure. 

The chemical composition of fly ash is the same as the composition of clays. The most important components are Si02 and AI2O3 the pozzolanic activity of material augments with increasing amount of sihca and iumina [115]. The pozzolanic activ-... 

Like cements, the composition of clay is established by either XRF or AAS/ICP-AES. However, it is necessary to modify the method of preparation of the fused bead by using a mixture of lithium tetraborate and lithium metaborate as the flux rather than lithium tetraborate alone. 

The group-names used in this book are given in italics and synonyms of the same groups in parentheses. The compositions of clay mineral species are given in next chapters. 

Antipow-Karatajew and Tsyurupa [1964], reviewing the results of Russian investigations on the composition of clay fractions of soils derived from igneous rocks in the different climatic zones of the USSR and parts of South East Asia, pointed out that hydrous mica predominates in almost all soils investigated, except in soils from humid subtropical or tropical zones. 

Water-Based Muds. About 85% of all drilling fluids are water-based systems. The types depend on the composition of the water phase (pH, ionic content, etc), viscosity builders (clays or polymers), and rheological control agents (deflocculants or dispersants (qv)). 

Transmission electron micrographs show hectorite and nontronite as elongated, lath-shaped units, whereas the other smectite clays appear more nearly equidimensional. A broken surface of smectite clays typically shows a "com flakes" or "oak leaf surface texture (54). High temperature minerals formed upon heating smectites vary considerably with the compositions of the clays. Spinels commonly appear at 800—1000°C, and dissolve at higher temperatures. Quartz, especially cristobalite, appears and mullite forms if the content of aluminum is adequate (38). 

Clay particles are so finely divided that clay properties are often controlled by the surface properties of the minerals rather than by bulk chemical composition. Particle size, size distribution, and shape the nature and amount of both mineral and organic impurities soluble materials, nature, and amount of exchangeable ions and degree of crystal perfection are all known to affect the properties of clays profoundly. 

This depends very largely on the composition of the body and the temperature to which it is fired. The addition of a clay grog will normally reduce the tensile strength but the degree of reduction depends on the proportion used, the grain-size distribution of the grog, and the particle shape. The... 

Table 1 shows chemical compositions of clay catalysts measured by XRF analysis. Si02 and AI2O3 are main components of the three clay catalysts with minor amount of Na20, Fc203 and others. The Si/Al ratio increased from HH [Pg.434]

Clays or shales have the ability to absorb water, thus causing the instability of wells either because of the swelling of some mineral species or because the supporting pressure is suppressed by modification of the pore pressure. The response of a shale to a water-based fluid depends on its initial water activity and on the composition of the fluid. The behavior of shales can be classified into either deformation mechanisms or transport mechanisms [1765]. Optimization of mud salinity, density, and filter-cake properties is important in achieving optimal shale stability and drilling efficiency with water-based mud. 

The primary characteristic necessary for a liner, cover, or cutoff wall is low permeability, which essentially enables them to slow down the seepage or diffusion of chemicals. Clay is therefore the main material used to construct these containment systems. The thickness and chemical compatibility of containment systems are of concern in assessing the performance of a system. For example, clay liners are constructed as a simple liner that is 2 to 5 ft thick. In composite and double liners, the compacted clay layers are usually between 2 and 5 ft thick, depending on the characteristics of the underlying geology and the type of liner to be installed. Regulations specify that the clay used can only allow water to penetrate at a rate of less than 1.2 in./yr. However, the effectiveness of clay liners can be reduced by fractures induced by freeze-thaw cycles, drying out, and the presence of some chemicals. 

There are a number of different clays, and some of the most common are listed in Table 55. The composition of each clay can be expressed by a formula that differs slightly from the general formula given above. Chemical composition alone, however, is not sufficient for characterizing clays their crystal structure provides the best way of characterizing any type of clay (see Textbox 21). In many clays, for example, the atoms are grouped in... 

Table 2 gives the compositions of the same four clay samples in atomic percent. The atomic percent is defined as the number of atoms of an element per unit volume divided by the number of atoms per unit volume of the substance containing the element. This is similar to mole fraction when the atomic percent is converted to fractional value. 

The zinc oxide ores of any economic value are represented by smithsonite and calamine. Willemite, franklinitc and other zinc oxide minerals are quite rare. The gangue minerals are usually represented by calcite ferooxides, dolomite and hemimorphite. The composition of gangue minerals, however, varies considerably and may also contain clay, talk, Fe-hydro-xide and other minerals. 

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