Kaolinite structure

Schematic representation of the kaolinite structure. It reveals the 1 1 structure due to the alternation of silica-type (black) and gibbsite-type layers (white). Furthermore, the edge surface exposes aluminol and siianol groups.

Clay Activation. The clay is heated to about 700 °C to destabilize the kaolinite structure by removing hydroxyl ions as water. This can be either a batch process with the clay in crucibles in a directly fired kiln, or a continuous process in a tunnel kiln, rotary kiln, or other furnace. 

Magnetic and flotation techniques can reduce the Ti02 content of Georgia kaolinites from 1.7—2.0% to 0.2—0.4%. Leaching experiments by Dolcater et al. (1970) indicate that on an average 15% (range 0—30%) of the Ti in seven samples (six from Georgia) was in the kaolinite structure. Thus, present data indicate that some Ti does occur in the kaolinite layer, presumably in the octahedral sheet. 

Bailey, S.W. and Langston, R.B., 1969. Anauxite and kaolinite structures identical. Clays Clay Miner., 17 241-243. 

Gruner, J.W., 1944. The kaolinite structure of amesite, and additional data on chlorites Am. Mineralogist, 29 422- 432. 

Figure 3. [100] Projection of the kaolinite structure showing the position of the inner and inner-surface-hydroxyl groups of kaolinite.

The best-known example of a 1 1 (two-sheet) type clay is kaolinite. A pictorial impression of the ideal kaolinite structure is given in Figure 11.1. The upper and lower basal surfaces of the two-sheet layer are clearly quite different. The layer repeat distance, or c-spacing, is c. 0.72 nm, which is the distance between atom centres in two contiguous layers. This is approximately the same as the sum of the atomic radii and therefore in an ideal structure there is insufficient space to accommodate any interlayer material such as intercalated water. 

Kaolinite structure is composed of a layer incorporating two networks tetrahedral network made of tetrahedrons [Si04] and octahedral network made of octahedrons [Al(0,0H)d. The latter is similar to network in gibbsite structure, Al(OH)3, with nearly equal lengths of corresponding a and b axes. The networks unite at an insignificant change of interatomic distances. Such structure provides a sharply polar character of the layer. When packed into a structure, the layers are bound to each other by very weak bonds, that is why their stmcture is always not completely ordered. 

Neder RB, Burghaimner M, Grasl T, Schulz H, Bram A, Fiedler S (1999) Refinement of the kaolinite structure from single-crystal synchrotron data. Clays Clay Minerals 47 487-494 Nelmes RJ, Allan DR, McMahon Ml, Belmonte SA (1999a) Self-hosting incotmnensurate structure of barium IV. Phys Rev Lett 83 4081-4084... 

Interstitial infilling in reordered kaolinite structure Oxidation... 

The collapsed kaolinitic structure acts as a source or framework for several different aluminosilicate complexes formed in HTA ash samples. Common minerals found are as follows anorthite... 

Fig. 5 Perspective drawing of the kaolinite structure taken from Brindley (Reproduced by permission of MIT Press from G.W. Brindley, Ion Exchange in Clay Minerals, in Ceramic Fabrication Processes, Ed. by W.D. Kingery, John Wiley, New York, 1958, pp. 7-23) [13]...

Bish, D.L. 1993. Rietveld refinement of the kaolinite structure at 1.5 K. Clay Clay Miner. 41 738-744. 

Morton JD, Semrau JD, Hayes KF (2001) An X-ray absorption spectroscopy study of the structure and reversibility of copper adsorbed to montmorillonite clay. Geochim Cosmocliim Acta 65 2709-2722 Muller B, Sigg L (1992) Adsorption of lead(II) on the goethite surface Voltammetric evaluation of surface complexation parameters. J Coll Interf Sci 148 517-532 Neder RB, Burghammer M, Grasl T, Schulz H, Bram A, Fiedler S (1999) Refinement of the kaolinite structure from single-crystal synchrotron data. Clays Clay Miner 47 487-494 Needleman HL (1983) Low level lead exposure and neuropsychological performance In Lead versus health - Sources and effects of low level lead exposure. Rutter M, Russell JR (eds) Wiley, Chichester, p 229-248... 

Fig. 2.1 Agglomerate of clay minerals crystallites with adsorbed water layers. Top insert cell of kaolinite structure right insert capillary forces in water bridges between the crystallites...

Brindley and Robinson [1946a] used improved X-ray diffraction techniques to show that the unit cell was triclinic with a = 91.8° instead of 90° and contained one kaolinite layer. The new cell enabled them to index the reflections observed in X-ray patterns more satisfactorily than Gruner had done without calling into question the actual kaolinite structure proposed by Pauling. 

The most recent experimental determination of the kaolinite structure is that by Drits and Kashaev [I960]. The structure is triclinic with one kaoUnite molecule per unit cell. The parameters given are... 

Bailey [1966], following Newnham [1961], consider the compressions and rotations to be sufficient to match the smaller distances in the network shown in Figure 5, but not sufficient to match the larger. They propose that the bases of the tetrahedra are tilted so that some of the bonds between silicons and the apical oxygens of the tetrahedra are not normal to the xyO plane, but point away from each other to come into correspondence with the oxygen network at the octahedral-tetrahedral junction. For dickite, this seems to be an adequate explanation, because one of the oxygens in the basal tetrahedra is clearly depressed into the structure compared with the other two (see Figure 8) as would occur if the tetrahedra were tilted outward. For the kaolinite structure, however, this explanation does not appear to suffice because... 

The structure of the unit cell projected on to the Oyz plane is shown in Figure 8. The obvious differences, to the kaolinite structure (see Figure 3), apart from the different origins for the unit cells chosen by the respective authors, are the depression of one oxygen (marked A in Figure 8) 0.17 A above the base of the tetrahedra and the varying heights of the three hydroxyls in the base of the octahedra. 

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