Silicate clay mineral

Secondary minerals. As weathering of primary minerals proceeds, ions are released into solution, and new minerals are formed. These new minerals, called secondary minerals, include layer silicate clay minerals, carbonates, phosphates, sulfates and sulfides, different hydroxides and oxyhydroxides of Al, Fe, Mn, Ti, and Si, and non-crystalline minerals such as allophane and imogolite. Secondary minerals, such as the clay minerals, may have a specific surface area in the range of 20-800 m /g and up to 1000 m /g in the case of imogolite (Wada, 1985). Surface area is very important because most chemical reactions in soil are surface reactions occurring at the interface of solids and the soil solution. Layer-silicate clays, oxides, and carbonates are the most widespread secondary minerals. 

Fig. 8-2 Structure of a 1 1 (kaolinite) and a (montmorillonite) layer-silicate clay mineral.

Boyd SA, Jaynes WF (1994) Role of layer charge in organic contaminant sorption by organo-clays. In Mermut AR (ed) Layer charge characteristics of 2 1 silicate clay minerals. CMS Workshop Lecture Series, vol 6, The Clay Minerals Society, Boulder, CO, pp 48-77... 

Most laboratory experiments demonstrating the utility of EO transport of organic compounds were conducted with kaolinite as the model clay-rich soil medium. Shapiro et al. (1989) used EO to transport phenol in kaolinite. Bruell et al. (1992) have shown that TCE can be transported down a slurry column by electroosmotic fluid flow, and more recently, Ho et al. (1995) demonstrated electroosmotic movement of p-nitrophenol in kaolinite. Kaolinite is a pure clay mineral, which has a very low cation exchange capacity and is generally a minor component of the silicate clay mineral fraction present in most natural soils. It is not, therefore, representative of most natural soil types, particularly those which are common in the midwestem United States. The clay content can impact the optimization and effectiveness of electroosmosis in field-scale applications, as has recently been discussed by Chen et al. (1999). 

The results show that the sorption of cyanide on soils and sediments is fast it reaches equilibrium within 10 minutes. The sorbed quantity, however, is low. From 10 4-10 3 mol/dm3 cyanide solutions, it is about 10 7 mol/g. This means an approximately 10-3 dm3/g distribution ratio for cyanide ion. This value is typical for the anion sorption of soils, and it is explained by the interfacial properties of soil components. The main mineral components of soils (primary silicates, clay minerals, oxides) have negative surface charges at pH applied (about 8.5), inhibiting the... 

Correns, C. The experimental chemical weathering of silicates. Clay Mineral. Bull. 249-265 (1961). 

In contrast to the decompositions of many solids (including the hydrates discussed in the previous chapter), the dehydrations of hydroxides show some common patterns of behaviour in two broad groups the dehydroxylations of (i) simple hydroxides (Mg(OH)2, Ca(OH)2, etc.) and (ii) extended silicates (clays, minerals. 

Layer of maximum accumulation of silicate clay minerals, or maximum development of blocky structure, or both... 

Absorbents, such as kaolin (a hydrated aluminum silicate clay mineral), pectin (a complex carbohydrate often extracted from fruits), and atta-pulgite (a hydrated magnesium aluminum silicate clay mineral), form a thickening powder that absorbs excess fluid and any bacterial toxins present (action of kaolin and attapulgite) and increases the consistency of the stool by forming a viscous colloidal solution (action of pectin). However, these agents may also absorb essential body enzymes and nutrients. 

Schwertmann, U. and Fechter, H., The point of zero charge of natural and synthetic ferrihydrites and its relation to adsorbed silicate, Clay Miner., 17, 471, 1982. 

Layer silicate clay minerals typically dissolve incongruently, with the octahedral sheet being more susceptible to hydrolysis and decomposition by acid attack than the tetrahedral (silica) sheet. Consequently, base cations from exchange sites and from the octahedral sheet initially dissolve out of these minerals at much faster rates than silica. This means that the residue of weathering is typically a siliceous material depleted in Ca, Mg, K, and Na. 

Laird, D.A. 1994. Evaluation of the structural formula and alkylammonium methods of determining layer charge, p. 79-103. In A.R. Mermut (ed.) Layer charge characteristics of 2 1 silicate clay minerals. Clay Miner. Soc., Boulder, CO. 

Aluminium, on the other hand, accumulates in the clay mineral fraction because it forms insoluble aluminosilicates and hydroxyoxides. The AI remains behind in the soil as other ions leach away. Iron also accumulates in soils but this is not apparent from Table 7.3 because the silicate clay minerals, with the exception of hydrous mica, are low in Fe. Iron precipitates in soils only as hydroxyoxides. Hydrous mica is altered parent material and is not reconstituted from the soil solution as are kaolinite, montmorillonite, and allophane. The <105° C water in Table 7.3 is, roughly speaking, adsorbed water the >105° C water is hydroxyl ions and water within crystal structures. 

The NH4" ion is almost identical in size with the K ion. Ammonium fixation takes place in silicate clay minerals (Ulite, vermic-ulite) in a similar way as potassium fixation. The relative content of this nonexchangeable ammonium rises with soil depth. 

The reviewed processes of dissolution and minerogenesis are capable of noticeably changing the composition of the host rocks. As a regular rule, relic rock-forming minerals are removed, and the secondary ones can both form and dissolve. An exception among the latter ones are secondary aluminum silicates, clay minerals, which practically insoluble in water. They as if replace relic minerals. 

CAS 1318-93-0 EINECS/ELINCS 215-288-5 ClassiTication Complex silicate clay mineral D nilion Specific type of Fuller s earth Fomtula AW, 4Si02 2HiO... 

Of all nano-silicate materials, the layer silicate ATP has an ideal composition for Mg5Sig02o(OH)2(OH2)4 as a natural silicate clay mineral. The distribution of Al ions among the five available octahedral positions in a chain can be accommodated either by vacancies in the octahedral positions or by some replacement of Si by Al. It is interesting to observe that a section through the above structure parallel to 010 presents the same sequence of layers of atoms as does a section of the mont-morillonite structure parallel to c when one layer of water molecules is present. The inorganic base exchange capacity, which amounts to less... 

The natural silicate minerals have been paid more attention to deal with the environment pollution and energy crisis. As a mass of natural the layer silicate clay mineral, attapulgite (ATP) and vermiculite (VMT) have a wide variety of industrial applications such as absorbent, catalyst carrier, densifying agent, adhesive, and food additive. In this chapter, we summarized the synthesis and photocatalytic performance of nano-silicates-based photocatalysts, which provided a general approach for the improvement and design of visible-light-driven photocatalysis. 

Structure Refined complex silicate clay mineral with a general composition of ... 

To provide molecular-scale detail about these surface reactions, four types of computer simulation for laya--type silicates (clay minerals) are utilized quantum mechanics (QM), molecular mechanics (MM), molecular dynamics (MD), and Monte Carlo (MC) (Fig. 1). Molecular modeling of a clay mineral and its hydrates is a nontfivial task because of the relatively large cell size required for simulation (up to hundreds of atoms for a solid clay mineral surface, plus layers of water molecules, which also require up to hundreds of atoms) and complex... 

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