Kaolinite properties

Property Kaolinite nhte Hahoysite Montmoril-lonite Attapulgite... 

Refra.ctories, Refractory products are prepared from a wide variety of naturally occurring materials such as chromite [1308-31 -2] and magnesite [546-93-0] or from clays predominandy composed of kaolinite. Increasingly, higher purity synthetic materials are being used to obtain special properties. On the other hand, for many refractory uses, a somewhat lower fusion point than that provided by kaolinite may be adequate, so that clay materials having a moderate amount of other components as, for example, iUite, may be satisfactory. High alumina clays are also used extensively for the manufacture of special types of refractories. 

Montmorillonite clays absorb water readily, swell greatly and confer highly plastic properties to a soil. Thus soil stress (Section 14.8) occurs most frequently in these soils and less commonly in predominantly kaolinitic types. Similarly, a soil high in bentonite will show more aggressive corrosion than a soil with a comparable percentage of kaolinite. A chalky soil usually shows low corrosion rates. Clay mineralogy and the relation of clays to corrosion deserves attention from corrosion engineers. Many important relationships are not fully understood and there is need for extensive research in this area. 

During caustic waterflooding the alkali can be consumed by the dissolution of clays and is lost in this way. The amount lost depends on the kinetics of the particular reaction. Several studies have been performed with kaolinite, using quartz as a yardstick, because the kinetic data are documented in the literature. The initial reaction rate has been found pH independent in the pH range of 11 to 13 [517]. The kinetics of silica dissolution could be quantitatively described in terms of pH, salinity, ion-exchange properties, temperature, and contact time [1549]. 

Clays used in foundries include hydrous alumina silicates, known as bentonites. Their properties provide cohesion and plasticity in the green state and also high strength when dried. There are three clays that are commonly used in foundries western bentonite [sodium bentonite, burnout point 1290°C (2350°F)], southern bentonite [calcium bentonite, burnout point 1065°C (1950°F)], and fire clay [kaolinite, burnout point 1425°C (2600°F)]. 

The micellization and adsorption properties of industrial sulfonate/ ethoxylated nonionic mixtures have been assessed in solution in contact with kaolinite. The related competitive equilibria were computed with a simple model based on the regular solution theory (RST). Starting from this analysis, the advantage of adding a hydrophilic additive or desorbing agent to reduce the overall adsorption is emphasized. 

The porous medium properties for the different tests are presented in Table II. The tests are carried out in a porous medium constituted of silica sand, kaolinite (4%), mixed with heavy crude oil and water. 

Adsorption of nonionic and anionic polyacrylamides on kaolinite clay is studied together with various flocculation properties (settling rate, sediment volume, supernatant clarity and suspension viscosity) under controlled conditions of pH, ionic strength and agitation. Adsorption and flocculation data obtained simultaneously for selected systems were correlated to obtain information on the dependence of flocculation on the surface coverage. Interestingly, optimum polymer concentration and type vary depending upon the flocculation response that is monitored. This is discussed in terms of the different properties of the floes and the floe network that control different flocculation responses. Flocculation itself is examined as the cumulative result of many subprocesses that can depend differently on system properties. 

Flocculation is indeed dependent on polymer adsorption, and there are hypotheses correlating the two phenomena, but often these have been put forth without detailed measurement of the two phenomena simultaneously (10-13). In this paper, flocculation is investigated as a function of polymer and solution properties and hydrodynamic conditions by measuring different properties of the system, including adsorption, using well characterized kaolinite and polymer samples prepared specifically for this purpose. Also, the role of concentration and charge density of polyacrylamide and polyacrylamide-polyacrylic acid co-polymers in determining kaolinite flocculation is examined under controlled hydrodynamic conditions. 

Kaolinite, 2 345t 6 659-664, 686-687, 718 composition in bauxite used for alumina production, 2 346t structure and composition, 6 668 in unit layer mixtures, 6 671 Kaolins, 6 686. See also Kaolin dry process, 6 673-675 estimated total production, 6 683 grades for polymer applications, 6 694t properties relating to applictions, 6 686t uses, 6 686-696 wet process, 6 675-679 Kapok, 11 297... 

Matsumara [23] noticed that starch particles exhibit slight exothermie properties during wetting, whieh was thought to cause localized stress resulting from the expansion of air retained in the tablet matrix. Unfortunately, this explanation, if valid, would be limited to a few substances such as aluminium silicate and kaolinite. List and... 

As a function of their structural properties, clays interact differently with organic and inorganic contaminants. Two major groups of clay minerals are selected for discussion here (a) kaolinite, with a 1 1 layered structured aluminosilicate and a surface area ranging from 6 to 39 m g" (Schofield and Samson 1954) and (b) smectites with a 2 1 silicate layer and a total surface area of about 800m g" (Borchardt 1989). 

Kaolinite crystals in the subsurface are submicron sized and exhibit a platelike morphology. They usually are found mixed with other layered structured minerals. In a comprehensive review, Dixon (1989) summarizes the structural properties of kaohnite. This mineral is composed of tetrahedral and octahedral sheets constituting a 0.7 mn layer in a triclinic unit cell. Two thirds of the octahedral positions are occupied by Al the tetrahedral positions are occupied by Si and Al, which are... 

Clay minerals with their own surface properties affect the near surface water in different ways. The adsorbed water in the case of kaolinite consists only of water molecules ( pure water), whereas water adsorbed on a smectite-type mineral is an aqueous solution, due to the presence of exchangeable cations on the 2 1 layer sihcate. Sposito (1989) noted the generally accepted description that the spatial extent of adsorbed water on a phyUosilicate surface is about 1.0 nm (two to three layers of water molecules) from the basal plane of the clay mineral. 

Based on their molecular properties as well as the properties of the solvent, each inorganic or organic contaminant exhibits an adsorption isotherm that corresponds to one of the isotherm classifications just described. Figure 5.1 illustrates these isotherms for different organic contaminants, adsorbed either from water or hexane solution on kaolinite, attapulgite, montmorillonite, and a red Mediterranean soil (Yaron et al. 1996). These isotherms may be used to deduce the adsorption mechanism. 

Based on these rate laws, various equations have been developed to describe kinetics of soil chemical processes. As a function of the adsorbent and adsorbate properties, the equations describe mainly first-order, second-order, or zero-order reactions. For example. Sparks and Jardine (1984) studied the kinetics of potassium adsorption on kaolinite, montmorillonite (a smectite mineral), and vermiculite (Fig. 5.3), finding that a single-order reaction describes the data for kaolinite and smectite, while two first-order reactions describe adsorption on vermiculite. 

The conversion of parathion is affected by soil constituents in the order kaolinite > smectite > organic matter and is related inversely to the adsorption affinity of these materials for this contaminant (Mingelgrin and Saltzman 1977). Although the extent of hydrolysis differs among soils, it is apparent that soil-surface degradation of parathion is caused by hydrolysis of the phosphate ester bond. The presence of water in the soil-parathion system led to a decrease in the surface-induced degradation of the organic molecule and diminished the effect of natural soil properties on its persistence. 

Fig. 16.13 Charge properties as a function of pH of an oxidic-kaolinitic Oxisol B horizon (Brazil) with ca. 300 g kg Fe oxides as determined (left) by Na and Cl adsorption from a) 0.2 b) 0.1 and c) 0.01 M NaCI solution and (right) by potentiometric titration in a) 1 b) 0.1 c) 0.01 and d) 0.001 M NaCI solution (Van Raij 8c Peech, 1972 with permission).

Schwertmann, U. Kampf, N. (1984) Properties of goethite and hematite in kaolinitic soils of southern and central Brazil. Soil Sci. 139 344-350... 

The nature of the interfacial structure and dynamics between inorganic solids and liquids is of particular interest because of the influence it exerts on the stabilisation properties of industrially important mineral based systems. One of the most common minerals to have been exploited by the paper and ceramics industry is the clay structure of kaolinite. The behaviour of water-kaolinite systems is important since interlayer water acts as a solvent for intercalated species. Henceforth, an understanding of the factors at the atomic level that control the orientation, translation and rotation of water molecules at the mineral surface has implications for processes such as the preparation of pigment dispersions used in paper coatings. 

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