Illite-producing reaction

Shaking in water prior to each drying cycle speeds reaction. For example, a K-Kinney smectite subjected to 64 WD cycles produced 42% illite layers, with shaking, compared with 30% for K-Kinney subjected to 50 WD cycles, and 32% for K-Kinney subjected to 75 WD cycles, without shaking. 

The experiments also indicate that WD may be an important mechanism for producing I/S at low temperatures in nature by a transformation mechanism (56). The percentage of illite layers formed by this mechanism is proportional to the number of WD cycles, and to the layer charge of the original smectite. Simple K-exchange does not produce stable illite layers in smectite therefore, these layers probably form by WD prior to deposition in subaqueous environments. The exception is found in high pH environments where illite layers may form without WD by chemical reaction, as has been reported previously for alkaline lakes (64, 65). 

Ca (aq), Mg (aq), and HCOjCaq). Silicate weathering is an incongruent process. The most important of these reactions involves the weathering of the feldspar minerals, ortho-clase, albite, and anorthite. The dissolved products are K (aq), Na (aq), and Ca (aq), and the solid products are the clay minerals, illite, kaolinite, and montmorillonite. The weathering of kaolinite to gibbsite and the partial dissolution of quartz and chert also produces some DSi,... 

As hydrolysis of the silicates and aluminosilicates continued (equation 1), dissolved sodium ions were continually produced, and acid was consumed. The pH of the water gradually increased. Formation of kaolinite was replaced by formation of montmoril-lonite and finally by production of illite. Silica was more soluble than alumina and as aluminosilicates were attacked by the water a protective coating of A1(0H) formed around the particles. This coating helped transport mineral particulates to the sediment. The reactions indicated by equation 1 were replaced by the family of reactions indicated in equation 2, written using the hydrolysis of albite as an example. 

Loughnan (22) gives this chemical composition for illite, pointing out that illite is characterized by substitutions in the silica sheet. Potassium collection and retention by silicate skeletons is a phenomenon recognized in lacustrine environments. As pH of the lake water increased, silica became more mobile than alumina. Formation of the relatively silica-poor illite resulted. Dehydration of the dissolved silica in the sediment s water (equation 3) produced quartz. The large amounts of illite from the reactions... 

The sequence of phases appearing in the mixtures composed of natural raw materials was also examined. In the mixture of calcium carbonate with quartz and clay minerals first reactions are the dehydroxylation of the latters. The kaolinite dehydroxylation at the temperature close to 450 °C is transforming in metakaolinite, which has, in disturbed form, the stmcture of initial mineral [18]. It is presenting high reactivity with calcium carbonate and the reaction of these eonrponents will start at this range of temperatures. For these reasons the mixture of marl with kaolinite produce C3S at 1100 °C and with illite even at 1000 °C [19]. 

KOH and silica produced by the above reaction are leaehed away, and kaolinite oceurs as residual deposits. If all the is not separated, then illite is formed instead of kaolinite. 

Soils and clays, in general, when calcined give off adsorbed, interlayer, and hydrated types of water. These effects produce endothermal peaks or loss of weight in DTA and TG, respectively. The endothermal peaks are followed by exothermal peaks that are caused by re-crystalliza-tion. Although many types of clay minerals such as montmorillonite, illite, and some shales show these effects, they are not suitable as pozzolans in concrete. Metakaolin, formed by heating kaolinite, seems to be the most suitable additive material for cement. Heating of kaolinite involves removal of adsorbed water at about 100°C and dehydroxylation at above 600°C, followed by the formation of metakaolinite, an almost amorphous product. The sequence of reactions is as follows ... 

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