Aluminosilicate clays

The intercalates of sheet aluminosilicates (clays) and of graphite are demonstrated to be efficient catalysts for a variety of reactions, and results obtained using several analytical techniques, including magic angle spinning KMR, are presented. For the clay family,... 

This i>aper describes two broad types of intercalation conpomds which are based on graphite on the one hand and sheet aluminosilicate (clay) hosts on the other. Taken together these provide a rich veiriety of examples of heterogeneously catalysed reactions. Appropriately cation exchanged clays, for example, act as efficient catalysts for a number of commercially important proton catalysed reactions (10-13) (see Table I). Graphite intercalates, whilst also capable of... 

Elephantiasis, oedema of the lower leg consequent to obstruction of the lymphatic drainage, is endemic in bare-footed subjects in the Cameroons and other regions of Africa. The identification of aluminosilicate clay... 

Intercalation in layered solids is a long-established phenomenon. It has been suggested [ 1 ] that the first example, dating from over two thousand years ago, involved intercalation in kaolinite (an aluminosilicate clay) and explains the secret behind the production of fine Chinese porcelain, hi modern times, many thousands of papers have been devoted to intercalation chemistry in clays, graphite and other materials. 

Clays are silicate minerals that may be platy or fibrous and are usually of exceedingly fine grain size, ranging from colloidal, a few nanometers in diameter, to a maximum of about a tenth of a micrometer. Similarly to other aluminosilicates, clays show considerable range in chemical composition with concomitant structural modifications (Fig. 2.13). A few of the clay minerals described as fibrous are briefly mentioned here. 

The hot-water separation process involves extremely complicated surface chemistry with interfaces among various combinations of solids (including both silica sand and aluminosilicate clays), water, bitumen, and air. The control of pH is critical. The preferred range is 8.0—8.5, achievable by use of any of the monovalent bases. Polyvalent cations must be excluded because they tend to flocculate clays and thus raise viscosity of the middlings in the separation cell. 

Such NACs do not exhibit linear isotherms when they sorb under certain conditions with aluminosilicate clays (Fig. 11.66 Haderlein and Schwarzenbach, 1993 Hader-lein et al., 1996). Rather they show saturation behavior indicating an association with specific sites on the solid surfaces. This specific site interaction is also indicated by the observations of competitive effects among different NACs in sorption experiments. Further, the sorption enthalpies have been found to be much greater than excess enthalpies of aqueous solution of these sorbates (e.g., 4-methyl-2-nitro-phenol exhibits a sorption enthalpy of-41.7 kJ-mol"1). These data all indicate that there is a strong specific interaction of NACs with the aluminosilicate clay surfaces. 

Table 11.2 Adsorption of Nonionic Nitroaromatic Compounds (NACs) to Aluminosilicate Clays (a) Surface Area Factors,/saf, for Different Clays Expressing Maximum Sorption Sites Relative to Kaolinite, and (b) KNAC EDA Values (L- mol 1 sites) Measured for Several NACs on K+-Kaolinite Allowing Estimates of KNACd Values Due to Electron Donor-Acceptor Interactions (Eq. 11-20) ...

The retardation of subsurface transport of TNT arises from this compound s absorption into NOM and adsorption onto mineral siloxane surfaces covered with weakly hydrated cations like potassium (but not sodium and calcium). While components of feldspars exhibit some siloxane surfaces, here we anticipate that most of the silox-anes occur in the aluminosilicate clay minerals (e.g., illite) because these particles have such high specific surface areas (Table 11.3). Hence, the total for TNT may be found at this site ... 

The mineralogical composition of Sahara dust particles shows the predominance of aluminosilicates (clays). Illite is also present in many cases while quartz particles are rare. Scanning Electron Microscopy (SEM) results on dust composition transported over different regions in the Mediterranean Basin have shown that Al-rich clay minerals such as illite and kaolinite are very common in PM10 for Cypms and dominant for Crete. Dust particles are also very rich in calcium which is distributed between calcite, dolomite and sulphates and Ca-Si particles (e.g. smectites) whereas iron oxides are often detected [43]. 

Walker WJ, Cronan CS, Patterson HH. 1988. A kinetic-study of aluminum adsorption by aluminosilicate clay-minerals. Geochim Cosmochim Acta 52 55-62. 

May H.M., Kinniburgh D.G., Helmke P.A. and Jackson M.L. (1986) Aqueous dissolution, solubilities and thermodynamic stabilities of common aluminosilicate clay minerals Kaolinite and smectites. Geochim. Cosmochim Acta 50, 1667-1677. 

Aluminosilicate clays (kaolinite) with a cation exchange capacity of 2.2meq/100g were blended with calcium oxide and starch prior to spray addition of the epoxide. The reaction proceeded at ambient temperature without mixing. Greater reaction efficiencies are claimed.43... 

Adsorption isotherms, 178-190 Freundlich, 179 Langmuir, 183 S-type, 178-179 L-type, 178-179 C-type, 178-179 H-type, 178-179 Aerobic decomposition, 323 Alkalinity, 82—91 Definition, 88 Types of alkalinity, 82 Aluminosilicate clays, 102 Aluminum cation, 103, 160 Acidity, 160 Complexation, 160 Polymeric aluminum, 160 Exchangeable, 160,162 Hydrolysis, 69, 75 Solubility, 71 Soluble complexes, 69 Aluminum hydroxide, 78-80 Solubility, 78 pH effect, 79... 

In the study of soil science, most attention has historically been paid to the aluminosilicate clays, which dominate the properties of temperate soils, the first to be scientifically studied. More recently, the importance of the amorphous aluminosilicates has been shown in young soils, in soils derived from volcanic ash and in leached, acidic soil (e.g. podzols or spodosols). The hydrous oxides are especially important components of old, highly weathered soils, such as those found in the tropics (e.g. oxisols). This is an important distinction as the charge on the aluminosilicate clays is predominantly a permanent negative charge, while the amorphous aluminosilicates and hydrous oxides have a variable,... 

Aluminosilicate Clay Minerals (Phyllosilicates). The aluminosilicate clay minerals are sheet silicates. They are sometimes referred to as phyllosilicates, but strictly this term should also include the micas, which are primary minerals. 

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