Kaolin minerals water

Kaolin most commonly originates by the alteration of feldspar or other aluminum siHcates via an intermediate solution phase (97,98) usuaHy by surface weathering (26,99) or by rising warm (hydrothermal) waters. A mica, or hydrated alumina soHd may form as an intermediate phase during the alteration from parent material to kaolin minerals. 

The 1 1 kaolin structures are chemically simpler the tetrahedral sites are occupied by silicon and the octahedral sites by aluminum. There is a minor amount of substitution, largely of ferric iron for aluminum, but the amounts are generally only a few tenths of a percent by weight of oxide. The kaolin minerals do not expand in the presence of water and their surface area, approximately 10 to 15 m2/g, represents the external area of the crystals. 

GIESE AND COSTANZO Water on the Surface of Kaolin Minerals... 

Kaolin Minerals. The 1 1 structures include a group of aluminosilicate minerals which are termed collectively the kaolin minerals specifically these are kaolinite, dickite, nacrite, and halloysite. The basic 1 1 layer for all of these minerals has the composition AlgSigOj-fOHJj, there is a small amount of substitution of iron for aluminum, ana fluoride for hydroxyl ion. All, except halloysite, are normally anhydrous and do not expand (as do the smectites) upon exposure to water and most organic molecules. As a result, they generally have a rather small surface area, on the order of 10 nr... 

When the water has been driven off, the residue still retains some of the crystalline features of the original kaolin mineral, and is therefore called meta-kaolin . Chemically, however, it behaves as if it were simply a mixture of finely divided silica and alumina. 

It must be borne in mind that many clays (as opposed to clay minerals) are impure, and these impurities can have a marked effect on the products formed and the temperatures of the various reactions. Nevertheless, the breakdown of kaolin minerals about 450°C is little affected by impurities, and it is this breakdown, which occurs during firing, that gives clay its unique properties. Before it breaks down, clay is sensitive to the action of water and can be moulded in the wet state when the structure has been broken down by firing, and when the constituents have recombined at higher temperatures, the clay retains its shape well and is unaffected by water. 

Water frequently forms an intercalate with kaolinite, in the form of the mineral halloysite which has the formula Al2Si20s(0H)2 2H2O. The addition of the two molecules of water increases the thickness of the layer from 7 A to 10 A. Kaolinite itself can be hydrated by a relatively simple chemical treatment to produce both a dihydrate, similar to halloysite, and a monohydrate with a thickness of about 8.6 A. Kaolin minerals do not form fibers as readily as do the serpentines. These minerals are described in more detail by Giese (1988). 

Wada, K., 1965. Intercalation of water in kaolin minerals. Am, Mineral, 50 924-941. 

Periodically, these mixtures were centrifuged and an aliquot of the clay-free supemate taken for counting analysis. Two naturally-occurring clays were selected for the experiments one was labeled kaolin (for the mineral kaolinite) while the second was referred to as attapulgite (or polygorshite). Both were obtained from the Source Clay Mineral Repository (3) as standard clays representative of each class of clay and were used as received. Stable, colloidal suspensions of each were prepared by ultrasonically dispersing weighed quantities of each clay in triple-distilled water. 

The over-all picture of what happens to the soil waters, as illustrated by Tables II and IV, is that initially they rapidly attack the rocks, kaolinizing chiefly plagioclase plus biotite and K-spar. As they penetrate more deeply, the reaction rate slows down, and both kaolinite and mont-morillonite are weathering products. Also, an important part of the Ca2+ comes from solution of small amounts of carbonate minerals. 

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