Kaolinite group

Published images of serpentine and kaolinite group minerals characteristically consist of one dark-and-light-stripe pair per 0.7 nm, with dark and light bands of approximately equal thickness. 

An ONIOM study of the adsorption of Sarin on dickite (a 1 1 dioctahedral clay mineral of the kaolinite group)85 was recently published. For the calculations of the studied systems, the two-layered ONIOM method using combinations of quantum-mechanical methods was applied.43,86,87 The investigated systems of... 

The adsorbents have been prepared fi-om the halloysite (H) - mineral fi-om kaolinite group with an admixture of carbonaceous materials refinery waste deposits (RSI), sediment communal sewage (CSew) and cellulose (Ce), and the fiaction of these mixtures were within 30 - 70 wt.%. The mbcture of raw material was thermally (carbonaceous materials carbonization, 973 K) and hydrothermally (crystallization of the amorphous metahalloysite in alkaline solution to zeolitic structure of NaA type, 373 K) pretreated in order to cilitate their specific structure [1,2]. 

The different classes of clay minerals, namely, 1/1,2/1, and so on, have a differenf arrangemenf of tetrahedral and octahedral layers. Structural units of clays, fherefore, consist of either (1) alternating tetrahedral sheets (OT or 1/1 structure e.g., the kaolinite group) (2) a sandwich of one ocfahedral sheet between two tetrahedral sheets (TOT or 2/1 structure e.g., smectite clay minerals, of which fhe mosf common member is monf moril-lonite) or (3) an arrangement in which three TOT units alternate with a brucite layer (2/1/1 structure e.g., chlorite). 

The phyllosilicates in soil clays can be classified into three layer types, distinguished by the numbers of tetrahedral and octahedral sheets combined, and five groups, differentiated by the kinds of isomorphic cation substitutions that occur. The layer types are shown in Fig. 1.3, and the groups are described in Table 1.3. The 1 1 layer type consists of one tetrahedral and one octahedral sheet. In soil clays, it is represented by the kaolinite group, with the unit cell chemical formula [Si4](Al4)Oio(OH)8, where the cation enclosed in brackets is in tetrahedral coordination and that enclosed in parentheses is in octahedral coordination. Normally there is no significant isomorphic substitution for Si(IV) or Al(III) in this group, and, as is common with soil clay minerals, the octahedral sheet has two thirds of its cation sites occupied (dioctahedral phyllosilicate). 

Given the structure in Fig. 2.3 as a prototype of the monolayer arrangement of adsorbed water on kaolinite group minerals, there remains only the question of its single-particle properties. Proton and deuteron NMR measurements are instructive in this respect.As indicated in Table 2.1, NMR line shapes show whether a preferred orientation of water molecules exists on the NMR time scale, and NMR relaxation data can yield a value for the rotational correlation time, In the case of 10-A halloysite, the NMR signal from water protons or deuterons in the... 

The definition of adsorbed water adopted in Sec. 2.3 requires an arrangement of water molecules that differs significantly from that in an appropriate reference aqueous phase. For water on the surfaces of kaolinite group minerals the reference phase is bulk liquid water, whereas for water on vermiculite and smectite surfaces the reference phase is an aqueous solution because of the presence of exchangeable cations on the 2 1 layer silicates. On the ba,si.s of this definition, the consensus developed in Sec. 2.3 is that the spatial extent of adsorbed water on a phyllosilicate... 

Deeds CT, van Ohphen H, Bradley, WE (1966) Intersalation and Interlayer Hydration of Minerals of the Kaolinite Group. In Proceedings of the Int Clay Conf Pergamon Press Part 2 p 183... 

These minerals are hydrated aluminosilicates which are characterized by a sheetlike structure and can be conveniently divided into three groups (1) the kaolinite group, (2) the mont-morillonite group, and (3) the potash clay (or hydrous mica) group (Table 7.7). In the kaolinite group, all have the same chemical composition and differ only in individual crystal structures. The montmorillonite group can be represented by means of ion substitutions in the general chemical formula. For example, in montmorillonite itself, approximately 16% of the aluminum... 

Geometrical Parameters and Charges of Thymine and Uracil Adsorbed on Minerals of Kaolinite Group... 

Two works were devoted to the ab initio cluster calculations of the interactions between minerals of the kaolinite group with thymine (TH) and uracil (U). The key purpose of such studies was to determine (i) the equilibrium adsorption of selected nucleic acids, differing in chemical, molecular structure and functions (DNA, RNA) on specific clay mineral surfaces and (ii) the nature of the interaction between nucleic acids and clay using computational chemistry methods and modeling. An additional objective was to assess the effect of presence of water and sodium cation commonly occurring in soils on the process of adsorption. 

The clay minerals of kaolinite group have dioctahedral t-o structure. This type of structure consists of three planes of anions. On one side, there is a plane of bridging 0 of the r-sheet, on the other side there is a plane of OH". The middle anionic plane consists of the non-bridging oxygens of the f-sheets and OH". In the o-sheet, each octahedral cation is surrounded by three OH" from the plane of OH", one OH" and two non-bridging oxygens from the middle plane. 

Minerals of kaolinite group are composed of successive arrangement of parallel layers. Eaeh layer contains one tetrahedral (t) and one octahedral (o) sheets of atoms and ions, therefore known as t-o layer. The t-o l ers of kaolinites are electrieally neutral, and bonded to one another by weak bond. 

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