Hydrated halloysite

According to Sudo [1963], one of the important occurrences is in the Kanto volcanic ash soils. The principal clay minerals are (meta) halloysite, hydrated halloysite, and allophane. Randomly interstratified halloysite-hydrated halloysite occurs in the lower horizons and gives a basal reflection consisting of a broad band sometimes or 7 A reflection tailed toward lower angles. 

In view of the problems associated with the expanding 2 1 clays, the smectites and vermiculites, it seemed desirable to use a different clay mineral system, one in which the interactions of surface adsorbed water are more easily studied. An obvious candidate is the hydrated form of halloysite, but studies of this mineral have shown that halloysites also suffer from an equally intractable set of difficulties (JO.). These are principally the poor crystallinity, the necessity to maintain the clay in liquid water in order to prevent loss of the surface adsorbed (intercalated) water, and the highly variable morphology of the crystallites. It seemed to us preferable to start with a chemically pure, well-crystallized, and well-known clay mineral (kaolinite) and to increase the normally small surface area by inserting water molecules between the layers through chemical treatment. Thus, the water would be in contact with both surfaces of every clay layer in the crystallites resulting in an effective surface area for water adsorption of approximately 1000 tor g. The synthetic kaolinite hydrates that resulted from this work are nearly ideal materials for studies of water adsorbed on silicate surfaces. 

Kaolinite, ideally Al2Si205(OH)4, consists of 1 1 layers, alternating sequences of silicate and hydrated Al-octahedra (dioctahedral) sheets. There is potential for disorder in the specificity of the site occupied by Al and in the stacking of the sheets and layers, which give rise to the polymorphs dickite and halloysite. 

Halloysite [Al2Si205(0H)4] if hydrated with a single layer of water mol-... 

Tubular fibrous morphology has also been described for a hydrated kaolin (Honjo et al., 1954), a mineral known to have a structure different from that of kaolinite or halloysite. 

Another type of inclusion compd is the layer or sandwich compound. This includes certain hydrated clays (such as halloysite and montmoril-lonite) which form layer-or sandwich-inclusion compds with polar organic molecules (such as alcohols, glycols, some hydrocarbons, etc) which replace the water, loosely bound in clays (Ref 10, pp445-7)... 

Garrett, W.G. and Walker, G.F., 1959. The cation exchange capacity of hydrated halloysite and the formation of halloysite salt complexes. Clay Miner., 4 75-80. 

Swineford, A., McNewt, J.D. and Crumpton, C.F., 1954. Hydrated halloysite in Blue Hill Shale. Proc. Natl. Conf. Clays Clay Mina. 2nd-Natl. Acad. Sci. Natl. Res. Counc., Puhl., 327 158-170. 

Hydrated halloysite has the same structure as kaolinite with water (single layer of H20 molecules) sandwiched between the mineral layers (10-A spacing). This mineral is commonly encountered in tropical soils... 

If halloysite is air-dried, it retains 21—21 of the four formula waters, which corresponds roughly to one water interlayer per four silicate layers (Brindley and Goodyear, 1948). During dehydration, halloysite maintains a statistical distribution of hydrated and nonhydrated layers as described theoretically by Jefferson (1938). Roy and Osborn (1954) concluded from sealed hydro-thermal runs in simple aqueous solution that the 4-hydrate converts to the... 

The kaolinite mineral species studied are kaolinite, kaolinite d (disordered kaolinite), dickite and nacrite. These polytypes have been described by Bailey (1963) on the basis of sense and degree of displacement of 1 1 layers and the position of vacant octahedral positions in the layer sequence. For the hydrated kaolinitic minerals, we have used the terminology of Keller and Johns (1976) which is based on endellite as the completely hydrated species and halloysite as the partly or completely dehydrated species. The polytypes of chlorite have been described by Bailey and Brown (1962) and Hayes (1970). In Fig. 8.3b it is shown that montmorillonite, the mixed-layer clays and illite are located between pyrophyllite without interfoliar charge and the dioctahedral... 

The kaolin group includes kaolinite, nacrite, dickite and halloysite halloysite can also exist in a hydrated form having the formula Al2Si205(0H)4.2H20. Of all these, by far the most important is kaolinite, since it is the principal constituent of china clay, ball clay, fireclays, and many brick clays the other kaolin minerals are somewhat rare in Britain. 

S. B. Hendricks, On the crystal structure of the clay minerals Dickite, halloysite, and hydrated halloysite. Am. Miner. 23 295 (1938). S. B. Hendricks and M. E. Jefferson, Structure of kaolin and talc-pyrophyllite hydrates and their bearing on water sorption of the clays. Am. Miner. 23 863 (1938). 

S. Yariv and S. Shoval, The natiure of the interaction between water molecules and kaolin-like layers in hydrated halloysite, Clays and Clay Minerals 23 473 (1975). M. I. Cruz, M. Letellier, and J. J. Fripiat, NMR study of adsorbed water. II Molecular motions in the monolayer hydrate of halloysite, J. Chem. Phys. 69 2018 (1978). 

Filtrol, which had an estimated capacity of 100 to 150 tons per day and a bit over 25% of the market, used halloysite or bentonite treated with sulfuric acid to leach out some of the alumina. This was treated with ammonium hydroxide to produce a hydrated alumina, to which was added some of the leached clay, forming a gelatinous mixture of clay and hydrous alumina. The remainder of the leached clay reacts with sodium silicate and is heated to effect crystallization. After base exchange, the resulting zeolite is mixed with the clay-alumina matrix and spray dried to form microspheres (85). 

The hydrated form of halloysite occurs in ( lindrical tubes of overlapping kaolinite sheets. The outside diameters of the tubes range frx)m 0.05 to 0.20 im, with a median value of 0.07 p,m, and range in length frx)m a fraction to several micrometres. The specific surface area of halloysite ranges from 35 to 70 (Mitchell, 1976). 

Because of the interlayer water sheet in hydrated halloysite, intercalation (introduction between the imit cells) of chemicals can occur. This also results in a slightly higher cation exchange capacity for hydrated halloysite (5 to 40 meq/100 g) than for kaolinite (3 to 15 meq/100 g). Halloysite also may be more affected by chemicals than kaolinite. 

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