Natural clay minerals

The genetic heritage and origin of clay minerals have been described by many research groups, including Esquevin (1958), Millot (1970), Velde (1977), and Eberl (1984) and, most recently, Velde and Meunier (2008). Three basic genetic mechanisms were found to be operational inheritance neoformation and transformation  

While inheritance dominates in the sedimentary environment at generally ambient conditions characterized by slow reaction rates, layer transformation requires a considerable input of activation energy, and thus is found preferentially in the diagenetic and hydrothermal realms, where higher temperatures prevail. In between these two environments, the weathering environment exists in which all three mechanisms discussed above can be operational. Hence, when these three mechanisms occur in three different geologic environments, it leads to nine pos-sibiUties of clay mineral formation in nature, attesting to the exceptional variability and complexity of day mineral chemistries. 

Rain water contains considerable amounts of carbon dioxide, and also a certain amount of nitric acid, which renders the overall pH value slightly acidic at between 5 and 6. In the temperate-humid climate zone, this acidity is increased to below 5 by humic acids of the soil overlying the bedrock. On the other hand, in the tropical-humid climate zone the groundwater may be close to neutral, owing to the interaction with soil solutions produced by intensified bacterial decomposition of plant material. 

While rain and soil solutions dissolve easily soluble ions such as K, Na, Ca, and Mg from the minerals of the parent rocks, the degree to which Fe, AP, and Si are attacked and solubilized depends to a large extent on the pH and Eh values of the leaching solutions. The environmental conditions determine also the degree of reprecipitation of hydroxides into the surrounding soil, in particular iron and aluminum hydroxides and oxihydroxides. Freely moving water and 

Muscovite Igneous and metamorphic rocks Crystallization mostly under higher pressure-temperature conditions To illite, montmorillonite and glauconite Residual 

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In presenting an initial attempt to integrate the knowledge of clay mineral stabilities in various chemical and physical environments it is hoped that a more systematic approach can be made to the interpretation of natural clay mineral assemblages in their different environments. 

VELDE (B.) and BYSTROM-BRUZEVITZ (A.M.), 1972. Transformation of natural clay minerals at elevated temperatures and pressures. Geol. For. 

The natural clay minerals are hydrous aluminum silicates with iron or magnesium replacing aluminum wholly or in part, and with alkali or alkaline earth metals present as essential constituents in some others. Their acidic properties and natural abundance have favored their use as catalysts for cracking of heavy petroleum fractions. With the exception of zeolites and some specially treated mixed oxides for which superacid properties have been claimed, the acidity as measured by the color changes of absorbed Hammett bases is generally far below the superacidity range. They are inactive for alkane isomerization and cracking below 100 °C and need co-acids to reach superacidity. 

Hectorite is a natural clay mineral that is not considered acutely toxic, therefore no toxicity values have been established. However, hectorite may contain small amounts of crystalline silica in the form of quartz. 

The development of clay minerals as solid-acid catalysts has been impeded by the general use of natural clay minerals often contaminated with impurities which are difficult to remove. Clay minerals are often used as supports for homogeneous catalysts, such as zinc chloride. 

One of the questions that can be answered with the help of adsorption measurements concerns the microtexture of natural clay minerals. Several idealized models for the texture of soil clays (see [5]) have been considered, but rather than assuming one model a priori, one should try to gain useful information from experimental relationships between the size of clay particles and apparent density or surface area and internal porosity, as described in Sections 6.1 and 6.2.1. Experiments aiming at the evaluation of the microtextures of clay minerals were carried out by Ben Ohoud and van Damme [95], who studied kaolinite, sepiolite, palygorskite and 20 monoionic montmorillonite samples. The accessible surface area S of consecutive fractions of size r was measured by N2 adsorption using the classical BET method, whereas the open porosity P was measured from the amounts of adsorbed N2 at a relative vapor... 

Natural clay minerals kaoUnite, bentonite, attapulgite, montmorillonite, clarit, Fuller s earth, zeolites, synthetic clays or zeolites... 

Fig. 1.5 Processes of genesis, transformation and destruction of clay minerals in nature. Clay minerals occurring in clay are produced by rock weathering, transformed during diagenesis, and destroyed by metamorphism. These processes are discussed in section 1.4.2.

Nanoclay is low-cost nanofitler for PNCs since it can be richly sourced from natural clay minerals. Nanoclay has a layered structure consisting of tetrahedral and octahedral sheets [30]. It is commonly referred to 1 1 or 2 1 clay-based ratio of tetrahedral and octahedral sheets. The 1 1 clay includes the typical examples of... 

The field of clay-polymer nanocomposite technology is attracting a great amount of attention (169). Among clay minerals, the 2 1 natural clay mineral montmorillonite has been used for clay nanocomposite applications. The structure of nanocomposites, the dynamics of confined polymer clay nanocomposites using NMR and computer simulations, rheology of clay nanocomposites have been... 

Synthetic hectorite, which closely resembles the natural clay mineral hectorite in both structure and composition, forms clear gels. It is free from natural clay impurities and is compatible with anionic and nonionic surfactants. The thickening efficiency of synthetic hectorite (commercially available under the trade name Laponite from Southern Clay Products, Inc.) is better than natural hectorite and natural bentonite in tap water [61]. 

Preliminary studies of the interaction of leachate with natural clay mineral liners, has revealed the development of a black sludge material. The formation of a sulphide sludge at the leachate clay interface is well documented and has been acknowledged to be a significant factor in the blinding of pores and the consequent reduction in the permeability of clay mineral liners (Bisdom et al. 1983 Brune et al. 1991). It is postulated that this material may act as a sink for metals and other contaminants in leachate, by microbially controlled precipitation. Specific micro-organisms exist that are able to reduce sulphates and initiate the precipitation of metal sulphides, in this way (Brune et al. 1991 Watson et al. 1995). 

For the natural clay minerals in Table 9.1 (i.e., excluding Laponite which is a synthetic clay), the predominance of the clay samples with large 7 values (taken arbitrarily as 7 >2 mJ/m ) tend to be lithium-saturated clays followed in abundance by cesium-saturated clays. It has been known for some... 

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