By kaolinite

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. 

The effects of organic molecules and phosphate on the adsorption of acid phosphatase on various minerals, and kaolinite in particular, have been investigated by Huang et al. [97]. The Langmuir affinity constant for AcP adsorption by kaolinite follows the series tartrate (K — 97.8) > phosphate (K= 48.6) > oxalate (K — 35.6) > acetate (K= 13.4). At low concentration, acetate even promoted the adsorption of acid phosphatase. It was considered that competitive interactions between anionic adsorbates can occur directly through competition for surface sites and indirectly through effects of anion adsorption on the surface charge and protonation. 

Bar-Yosef B, Meek D (1987) Selenium sorption by kaolinite and montmorillonite. Soil Sci (144) 11-19 Beard BL, Johnson CM (2004) Fe isotope variations in the modem and ancient earth and other planetary bodies. Rev Minerd Geochem 55 319-357... 

Now we might consider what is in fact the common clay mineralogy of sandstones. Shelton (1964), Bucke and Mankin (1971) find it to be most often dominated by kaolinite. This mineral although hydrous, is conspicuous by its lack of alkalis. Thus one could suspect that alkali activity in pore solutions of sandstones is, or was, frequently low, lower at any rate than adjacent mica-bearing shales. Laboratory studies by Hanshaw and Coplen (1973) and Khareka and Berry (1973) would give a plausible explanation for such a phenomenon. If solutions are forced hydrostatically across the argillaceous membrane, ionic species in solution are selectively... 

Studies of hydrothermal alteration products associated with ore mineralization in acidic rocks have established the general propensity for the original minerals to be replaced by illite, sericite or hydromica in the innermost zone near the source of hydrothermal fluids and by kaolinite or expandable minerals further from the vein or center of fluid emanation. The newly-formed "mica" can be 2M, 1M, or lMd in polymorph and range compositionally from muscovite to a low potassium, silicic species which can be assimilated in the term illite (Lowell and Guilbert, 1970 Schoen and White, 1966, 1965 Kelly and Kerr, 1957 Bonorino, 1959 Tomita, e al., 1969 Yoder and Eugster, 1955 Meyer and Hemley, 1959, among many authors). 

V is characterized by kaolinite-illite-chlorite assemblages beyond the stability of an expanding mixed layered potassic dioctahedral mineral and below the thermal stability of pyrophyllite. The establishment of such conditions will be difficult in that the non-appearance of a mineral is a poor diagnostic and, as we have seen, kaolinite is frequently eliminated from sediments before its upper stability limit in the presence... 

Wang and Xing (2005) observed that the fractions sorbed by kaolinite are more aliphatic than those sorbed by montmorillonite. Feng et al. (2005) showed that... 

Random displacements of nb/3 parallel to b are present in chamosite as in kaolinite (Brindley,1961). Youell (1955) has shown that in many chamosites there is disorder parallel to the a-axis. The better ordered chamosites are rich in iron, and the less well ordered contain less iron and more aluminum. Oxidation of Fe2+ to Fe3+ also increases the disorder. Both mechanisms cause a larger ion to be replaced by a smaller. This results in a decrease in the size of the octahedral sheet thus decreasing the misfit between the octahedral and tetrahedral sheets. Decreasing the strain within the layers apparently allows more shifting between layers. Youell (1955) noted that disordered chamosite is almost invariably accompanied by kaolinite, and ordered chamosite by siderite . 

Gay minerals and zeolites are interesting with respect to possibilities for geometric influences. Activation can be produced, as in enzyme catalysis, by constraining the reactive molecule, via surface complexation, in a configuration in which it is destabilized relative to that of the free molecule, yet still accessible to other reactants. A possible example is hydrazine complexed with kaolinite. The conformation of hydrazine is flattened relative to that of the free molecule (See Giff Johnston s paper in Part m of this volume). It has been shown that hydrazine is readily air-oxidized by kaolinite (Coyne, submitted for publication). 

The final ratio between the <001> and the < hkO > size of the crystals was about 1.6, significantly lower than the value observed in crystals obtained by kaolinite conversion. 

Examination of the Predynastic (ca. 5500 B.P.) bone from Tel-Roba showed the effect of contamination from the soil and solutions. Near the surface of the bone (Figure 5), the apatite groundmass is covered by kaolinite... 

Frost and Griffin (11) studied the effect of pH on the adsorption of As by kaolinite and montmorilIonite and observed that the maximum adsorption of As(V) on both clays occurred at pH 5, while the adsorption of As (III) increased with increasing pH. At pH 5, both clays removed more As(V) than As(III), while at pH 8 more As(III) was removed than As(V) (the authors presented the adsorption isotherm at pH 5 the isotherm at pH 8 can be constructed from the data presented). 

Maynard, J. B., Kinetics of silica sorption by kaolinite with application to seawater chemistry. Am. J. Sci., 275, 1028-1048 (1975). 

Bar-Yosef B. and Meek D. (1987) Selenium sorption by kaolinite and montmorillonite. Soil Sci. 144, 12-19. 

The fallacy of assigning single values to the sorption of metal cations is evident from Figs. 10.13 and 10.14, which show Pb adsorption by kaolinite and Cd by montmorillonite. Lead adsorption has been measured as a function of pH. Clearly, a sorption isotherm equation is needed to... 

Figure 10.13 Adsorption of Pb from DuPage landfill leachate by kaolinite at 25°C, as a function of pH, Dashed vertical lines show the Pb concentration at. saturation with Pb-hydroxy-carbonate solid. Reprinted with permission from R. A. Griffin and N. F, Shimp. Envir. Sci. Technol. 10(13) 1256-i261. Copyright 1976 American Chemical Society.

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