Talc, clay mineral

According to these approaches, one assumes a given chemistry and/or morphology of the solid surface. Yet, the same function cannot simultaneously describe a macro-heterogeneous surface solid such as talc, clay minerals or crystalline silicas, having basal and lateral surfaces and a micro-heterogeneous one like the surface of an amorphous silica. Therefore many authors tried to develop resolution methods without making any assumption for the shape of the distribution function. 

Washing and dewatering by air displacement of cakes are possible. AppHcations are in the treatment of minerals, in the sugar industry, and in the treatment of municipal sewage sludge and fillers like talc, clay, whiting, etc. 

The vertical recessed plate automatic press, shown schematically in Figure 15 and described previously, is another example of a horizontal belt pressure filter. Cycle times ate short, typically between 10 and 30 minutes, and the operation is fully automated. The maximum cake thickness is about 35 mm washing and dewatering (by air displacement) of cakes is possible. Apphcations include treatment of mineral slurries, sugar, sewage sludge, and fillers like talc, clay, and whiting. 

Clay minerals that are composed of two tetrahedral layers and one octahedral layer are referred to as 2 1 clay minerals or TOT minerals. The apical oxygens of the two tetrahedral sheets project into the octahedral sheet. The 2 1 stmcture has a basal spacing (nominal thickness) of 1.0 nm (10 E). Pyrophjlhte [12269-78-2] Al2Si40 Q(0H)2, is the dioctahedral mineral, ie, AF" in the octahedral sites, and talc [14807-96-6], Mg3Si402Q(0H)2, is the trioctahedral, ie, in the octahedral sites. Both these minerals are essentially free of substitution in the octahedral site and therefore do not have a net... 

Talc and Pyrophyllite. Talc (qv) and pyrophjlhte are 2 1 layer clay minerals having no substitution in either the tetrahedral or octahedral layer. These are electrostatically neutral particles (x = 0) and may be considered ideal 2 1 layer hydrous phyUosiHcates. The stmctural formula of talc, the trioctahedral form, is Mg3Si402Q(0H)2 and the stmctural formula of pyrophylUte, the dioctahedral form, is Al2Si402Q (OH)2 (106). Ferripyrophyllite has the same stmcture as pyrophylUte, but has ferric iron instead of aluminum in the octahedral layer. Because these are electrostatically neutral they do not contain interlayer materials. These minerals are important in clay mineralogy because they can be thought of as pure 2 1 layer minerals (106). 

Smectites are stmcturaUy similar to pyrophylUte [12269-78-2] or talc [14807-96-6], but differ by substitutions mainly in the octahedral layers. Some substitution may occur for Si in the tetrahedral layer, and by F for OH in the stmcture. Deficit charges in smectite are compensated by cations (usually Na, Ca, K) sorbed between the three-layer (two tetrahedral and one octahedral, hence 2 1) clay mineral sandwiches. These are held relatively loosely, although stoichiometricaUy, and give rise to the significant cation exchange properties of the smectite. Representative analyses of smectite minerals are given in Table 3. The deterrnination of a complete set of optical constants of the smectite group is usually not possible because the individual crystals are too small. Representative optical measurements may, however, be found in the Uterature (42,107). 

Examples are the mica group (e.g., KMg3(OF[)2Si3A10io) of which biotite, (K(Mg,Fe)3(OH)2Sl3A10io) (Figure 1.55) and talc (Mg3(OFl)2Si40io) are members, and contains a sandwich of two layers with octahedrally coordinated cations between the layers and clay minerals such as kaolin, Al4(OH)8Sl4C3io. 

If layers of silicon tetrahedra are condensed on both sides of a hydrargillite layer, a substance is obtained having the composition AU3i Oio(OH)t. This is the clay mineral pyrophyllite. The substance MgaSi40io(OH) obtained similarly from a brucite layer (Fig. 7-10) is the mineral talc. Both of these substances, involving the loose superposition of neutral layers, are very soft, with extreme basal cleavage.70... 

Talc and Pyrophyllile. Talc and pyrophyllite are 2 1 layer clay minerals having no substitution in eiflier the tetrahedral or octahedral layer. These are electrostatically neutral particles i t = 0) and may be considered ideal 2 1 layer hydrous phyllosilieates. Talc and pyrophyllite are found in metamorphic rocks that arc rich in Mg and Al. respectively... 

The three-sheet or 2 1 layer lattice silicates consist of two silica tetrahedral sheets between which is an octahedral sheet. These three sheets form a layer approximately 10 A thick. The oxygens at the tips of the tetrahedra point towards the center octahedral sheet and substitute for two-thirds of the octahedrally coordinated hydroxyls. The 2 1 clay minerals include the mica and smectite groups which are by far the most abundant of the clay minerals. The pure end members of this type are talc, a hydrous magnesium silicate pyrophyllite, a hydrous aluminum silicate and minnesotaite, a hydrous iron silicate. 

In addition to MC and MD simulations, several quantum-chemical studies of hydrated clay minerals with or without exchangeable cations in the interlayer space have been performed at the ab initio and semiempirical level of theory. The total energy of hydrated layered silicates (talc and pyrophyllite) without exchangeable counterions, the position and interactions of interlayer water... 

Hydrotalcite (HT) is a clay mineral which on crushing becomes a fine powder, similar to talc. It is a hy-droxycarbonate of Mg and A1, of the general formula Mg6Al2(0H)i6C03 - 4H20, and occurs in nature in foliated and controlled plates and/or fibrous masses. Anionic clays of the HT type have been of importance in catalysis since 1970. Their interesting properties for catalytic applications are ... 

The various types of compounds which have been purified with peroxygens and which will be discussed here are petroleum products, miscellaneous organic chemicals, surfactants, natural oils, waxes and gums, natural sugars and starches, synthetic polymers, inorganic acids and salts, clays, talc and minerals. 

Pyrophyllite is the simplest layer aluminosilicate in which two tetrahedral Si04 layers are condensed on to the octahedral A106 layer to produce a three-sheet layer, the composition of the unit cell being [Al2(OH)2(Si205)2]2. Another ideal structure in which A1 is replaced by Mg is that of talc. In both cases the three-sheet layer is electrically neutral and the layers are stacked in the ABAB... sequence. Because of the cohesive strength of this ideal structure, neither pyrophyllite nor talc occurs in the form of the very fine particles which generally characterize clay minerals. 

Geologically and genetically, clay minerals are difficult to define simply and adequately, but broadly they are layer lattice silicates of secondary origin. In the same classification are the micas, talc, chlorites, and serpentines which are not strictly clay minerals. In this context, secondary origin means that mineral formation has arisen from the weathering of primary or igneous rock, e.g. granites and basalts. 

The most significant representative, talc, is hydrated magnesium silicate having the formula Mg3(Si205)2 (OH)2, i.e. molecular composition 3 MgO. 4 Si02. H2O, It has a layer structure similar to that of clay minerals, which is the cause of ready cleavability and of the macroscopically laminar character of some varieties. Its density lies in the range 2.6 —2.8 g/cm. The talc structure does not provide conditions for major substitution by other elements. 

We describe in Chapter 5 the formation of composite layers formed by the sharing of the remaining vertices of a tetrahedral A2XS layer with certain of the vertices of an octahedral layer AX3, both layers being based on the plane 6-gon net. These complex layers are the structural units in two important classes of minerals, the clay minerals (including kaolin, talc, and the bentonites) and the micas. One of these layers is illustrated as an assembly of tetrahedra and octahedra in Fig. 5.44 (p. 191). 

The term clay refers to fine-grained aluminosilicates that have a platy habit and become plastic when mixed with water [11], Dozens of minerals fall under the classification of clays and a single clay deposit can contain a variety of individual clay minerals along with impurities. Clay minerals are classified as phyllosilicates because of their layered structure [12], The most common clay mineral is kaolinite, although others such as talc, montmorillonite, and vermiculite are also abundant. Each of the... 

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