Synthesis kaolinite

Linares, J. and Huertas, F., 1971. Kaolinite synthesis at room temperature. Science, 171 896-897. 

Subsequent work showed that a modification of the synthesis procedure produced a 10A hydrate which> if dried carefully, would maintain the interlayer water in the absence of excess water (27). This material is optimal for adsorbed water studies for a number of reasons the parent clay is a well-crystallized kaolinite with a negligible layer charge, there are few if any interlayer cations, there is no interference from pore water since the amount is minimal, and the interlayer water molecules lie between uniform layers of known structure. Thus, the hydrate provides a useful model for studying the effects of a silicate surface on interlayer water. 

Characterization of Interlayer Water. X-ray diffraction studies of the 10A hydrate show no hkl reflections indicating a lack of regularity in the stacking of the kaolin layers. In addition to the 10A hydrate, two other less hydrated kaolinites were synthesized. Both have one molecule of water for each formula unit in contrast to the 10A hydrate which has two. These less hydrated clays consequently have smaller d(001) spacings of 8.4 and 8.6 A. The synthesis conditions for these two hydrates are described in (22.). By studying the interlayer water in the 8.4 and 8.6A hydrates, it was possible to formulate a model of the water in the more complicated 10A hydrate. 

In acids soils, particularly those with kaolinite clay minerals, soluble Fe + concentrations tend to rise to high levels because of low CEC and because conditions do not favour precipitation of Fe(II) oxides or carbonates or synthesis of silicates. 

Eberl, D., 1970. Low-temperature synthesis of kaolinite from amorphous material at neutral pH. Conf. Clay Minerals Soc., 19th, Abstr., p. 17. 

It was demonstrated in [9] that mechanical activation of a mixture of Ca(OH)2 with AI2O3 (at molar ratio 1 4) in a vibratory mill results in partial interaction with the formation of calcium hydroaluminate 4Ca0-3Al203-H20. The authors [9] showed that mechanochemical synthesis of 3Ca0-Al203 H20 occurs starting from Ca(OH)2+Al(OH)3 and Ca(OH)2+ kaolinite mixtures during their activation at room temperature. 

Cordierite synthesis method based on mechanical activation of mixtures of hydrated oxides of calcium, aluminium and silicon, as well as natural hydrated compounds (talc, kaolinite and gibbsite), has been developed in [2, 3]. Mechanical activation of these mixtures does not lead to the formation of new phases but provides good mixing at the cluster level giving aggregates that form cordierite during the subsequent thermal treatment. 

In industry, cordierite is usually obtained by calcination of the mixtures containing talc, kaolinite and silica at 1300-1450°C for 20-60 h. The product contains the impurity phases spinel, mullite, clinoenstatite, etc., that worsen the exploitation characteristics of cordierite. Since the mentioned minerals contain structural water, chemical interaction between them during mechanical activation can be considered from the viewpoint of soft mechanochemical synthesis. Mechanical activation of this mixture does simplifies the interaction between its components. It is sufficient to heat this mixture for 2 h at a temperature of 1260°C to obtain practically homogeneous cordierite without impurity phases (Fig. 7.2) [2-9]. 

However, the synthesis process most extensively studied by solid-state NMR is that of carbothermal reduction of aluminosilicate minerals such as kaolinite, which are mixed with finely divided carbon and heated in nitrogen at > 1400°C (Neal et al. 1994, MacKenzie et al. 1994a). Under carbothermal conditions the clay decomposes to a mixture of mullite and amorphous silica (MacKenzie et al. 1996b), the latter forming SiC which reacts with the mullite to form P-sialon, in some cases via other sialon phases such as X-sialon (see below). The precise reaction sequence and the nature of the intermediates has been shown by the NMR studies to depend on various factors including the nature of the aluminosilicate starting mineral (MacKenzie er a/. 1994a). 

Carbothermal synthesis and its variant, silicothermal synthesis, have proved attractive routes for preparing sialons from readily available clay mineral raw materials. The clay is mixed with fine carbon and/or silicon powder and reacted in a stream of purified nitrogen at > 1400°C. The 3-sialon product carbothermally synthesised from kaolinite has the composition Si3Al303N5 (z = 3), controlled by the Si02 Al203 ratio of the clay... 

Dimirkou, A., loannou. A., and Kalliannou, Ch., Synthesis-identification of hematite and kaolinite-hematite (k-h) system, Commun. Soil Sci. Plant Anal., n, 1091, 1996. 

The laboratory synthesis at 2(fC of trioctahedral (Mg-bearing) layer silicate clays from solution has been found to be much easier than that of dioctahedral clays (e.g., kaolinite, montmorillonite). Provide a mechanism-based explanation for this, given that Al(OH)j is least soluble in the pH range of 5-9, while Mg(OH)2 is least soluble above pH 10. 

Experiments involved synthesis of muscovite from gels or reaction of paragonite or kaolinite with KCl solutions. 

It had recently been shown that thermal disruption of the kaolinite mineral layer structure produced a highly reactive disordered aluminosilicate with a silica to alumina molar ratio of two. Higher calcination temperatures produced what is known as mullitized kaolin, which also contained some reactive free silica (86). This served to supply the additional silica needed for the synthesis of zeolite Y, which has a silica to alumina molar ratio in the 4.5 to 5.0 range. 

Kaolinite clay and limestone with different mass ratios were mixed thoronghly with sodium hydroxide solutions for 1 h, and then transferred to a 1 L autoclave. The mixture was hydrothermally reacted at different temperature and pressure values for 8 h. The synthesis conditions such as kaolinite/limestone mass ratio (K/L= 0.3), NaOH concentration (9M), solution temperature (200 °C), and reaction pressure (15 bar) were optimized. The obtained Ca-Na-Al203-Si02was washed thoroughly with double distilled water to reach a supernatant pH of 7.5. Then the samples were mixed with different concentrations of Cu(N03)2.3H20 for 24 hours, fdtered, dried at 110 C for 4 h and then calcinated at 550 °C for 4 hrs. 

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