Contents 3 Clay Minerals

Generally, clay mineral content was the most important factor determining K selectivity in soil, with weathering, fertilizers and organic residues affecting selectivity through their modifying effects on mineral surfaces. 

This information is reported as the percentage that each of the clay mineral type contributes to total identifiable clay mineral content of the noncarbonate clay-sized fraction of the surface sediments. These percentages were determined by x-ray diffraction, which is luiable to identify noncrystalline solids. Using this technique, clay minerals were found to comprise about 60% of the mass of carbonate-free fine-grained fraction. Most of the noncrystalline soUds are probably mixed-layer clay minerals. Carbonate was removed to facilitate the x-ray diffraction characterization of the clay minerals. In some cases, roimd off errors cause the sum of the percentages of kaolinite, illite, montmorillonite, and chlorite to deviate slightly from 100%. 

Sorption coefficients quantitatively describe the extent to which an organic chemical is distributed at equilibrium between an environmental solid (i.e., soil, sediment, suspended sediment, wastewater solids) and the aqueous phase it is in contact with. Sorption coefficients depend on (1) the variety of interactions occurring between the solute and the solid and aqueous phases and (2) the effects of environmental and/or experimental variables such as organic matter quantity and type, clay mineral content and type, clay to organic matter ratio, particle size distribution and surface area of the sorbent, pH, ionic strength, suspended particulates or colloidal material, temperature, dissolved organic matter (DOM) concentration, solute and solid concentrations, and phase separation technique. 

Jackson lignites are high in SiO and Al O, reflecting their higher ash (clay mineral) content. Deep-Basin Wilcox ashes are markedly lower in SiO and higher in Na O, SO, and CaO than are ashes from near-surface lignites. The most striking difference is in content, which increases with depth and is correlated... 

Influence of Clay Mineral Content. A number of authors like Thompson (1959), Heald and Renton (1966) and Sibley and Blatt (1976) have shown quantitatively that thin isolated sand intercalations or continuous sandstones possessing abundant clay bridges on their quartz grains have suffered more pressure solution and eventual removal of SiOj than sandstones with a smaller amount or total absence of clay bridges in the form of a film. This was also observed in the Saharan sandstones (Plate 13). It is, however, difficult to establish a quantitative statistical correlation between the amount of clay components and pressure solution. There is at the same time in the Saharan sandstones a clear inverse statistical correlation between the amount of clay minerals in the form of a film and the quartz cement (Fig. 4.12, Plates 13,14). This is in agreement with observations showing that the clay cement impedes in the sandstones the formation of overgrowth rims of quartz (Millot 1964 Heald and Larese 1974). 

Clay mineral content may possibly affect the alteration process and influence the distribution of organic compounds. It is especially sensitive when using pyrolysis (Peters, 1986). The abyssal plain samples have smectite as the main clay mineral (Martine Gerard, personal communication). The Shipboard Rock Eval pyrolysis gave the following parameters for MAP samples with TOC >1.3 wt% T ax from 400 to 430°C and PI average around 0.2 S2 range 2.15-4.73 mg C/g rock with HI 20-252 mg HC/g TOC. 

The characteristic feature of flow laminations is the directional orientation of the anisometric particles in the shearing speed gradient of the auger channel, the pressure head and the die. Figure 3 pictures the fracture surfaces of extruded clay-body columns after drying showing various flow laminations caused by different clay mineral content. 

As noted in Table I, the term clay refers to that part of the soil that is composed of particle sizes less than 2 /u.m. However, the term clay also can refer to the clay mineral content of a soil regardless of the particle size. Finally, the term clay often is used to denote a soil mass that possesses properties similar to those of a pure clay even though only a relative small percentage of the overall soil mass consists of clay-sized particles and/or clay minerals. For example, mixtures of sand and bentonite, a high-swelling clay, containing 4-10% (w/w) of bentonite typically possess some properties that are characteristic of clay soils, even though 90% (w/w) or more of these mixtures is made up of sand. 

A high clay mineral content is correlated with an increased particle surface area and sorption capacity for both inorganic and organic contaminants. Permeability is also reduced, increasing the residence time of leachate within the liner, and is important for contaminants (e.g. XOMs) which may be attenuated by processes (e.g. degradation) which are kinetically controlled... 

Kopf et al. (1981) found a correlation between the susceptibility and clay-mineral content Fciay (in volume percentage according X-ray analysis) for clay-, silt-, and sandstones (Cenozoic and Mesozoic sediments from the North German-Polish Basin) and derived an empirical equation (converted to SI units) ... 

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