Minerals halloysite

The admixture of clay mineral (halloysite) to carbonaceous deposit (as for waste materials) remarkably enriches the texture of mineral-carbon adsorbents in mesopores and leads to the decrease of magnitude of micropores volume with dimension of 0.4 - 2 nm. In the case of hard coal and kaolinite mixture this char contains the maximum sub- and micropores at the lowest content of mesopores. 

Individual kaolinite layers are 7 A thick, so that the stacked layers produce a repeat distance (c-axis spacing) of 7 A, a fact used to identify kaolinite in soils by x-ray diffraction. The mineral halloysite, which has the same 1 1 layer structure as kaolinite, diflFers from kaolinite in the fact that it has a single sheet of water molecules between the layers. This increases the c-spacing to 10.1 A. Mild heating of halloysite will dehydrate and collapse it irreversibly to the kaolinite 7-A spacing. 

See also brick clays, china clay, FIRECLAY and the clay minerals halloysite, kaolinite, montmorillonite, etc. 

Endeiiite. Obsolete name for the clay mineral halloysite (q.v.) some authorities, however, would preserve the name for those halloysites containing an excess of water. 

Hedicke-Hbchstotter K, T.im GT, Altstadt V (2009) Novel polyamide nanocomposites based on silicate nanotubes of the mineral halloysite. Compos Sci Technol 69(3-4) 330-334 Hermanutz F, Gahr F, Utadingen E, Meister F, Kosan B (2008) New developments in dissolving and processing of cellulose in ionic liquids. Macromol Symp 262(l) 23-27 Hyden WL (1929) Manufacture and poperties of regenerated cellulose films. Ind Eng Chem 21 (5) 405-410... 

Hedicke-Hochstotter, K, Lim, G.T. Altstadt, V. (2009) Novel polyamide nanocomposites based on silicate nanotubes of the mineral halloysite. Composites Science and Technology, 69, 330-334. 

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). 

Hydrothermal clay-silica deposits (kaolinite, halloysite, sericite, montmorillonite and silica) and zeolite deposits occur in Tertiary-Quaternary volcanic regions. These deposits are distributed in areas of epithermal gold mineralization. 

Halloysite is an economically viable material that can be mined from deposits as a raw mineral. The size ofhalloysite tubules varies within 0.5-10 microns in length and 15-200 nm in inner diameter, depending on the deposit. There are between 15 and 20 aluminosilicate layers rolled in the multilayer tubule walls with a layer spacing of... 

Price, R., Gaber, B. and Lvov, Y. (2001) In-vitro release characteristics of tetracycline, khellin and nicotinamide adenine dinudeotide from halloysite a cylindrical mineral for delivery of biologically active agents. Journal of Microencapsulation, 18, 713—723. 

Gaber,B.,Price,R.,Santos,J.P.andVittal, V. (2001) Entrapment and controlled release of active agents from halloysite. Rocks Minerals, 76, 211-215. 

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. 

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... 

One of the four compositional groups of clay minerals, the kandites include the minerals kaolinite, dickite, halloysite, and metahalloysite all have virtually the same composition. The first two minerals are common and widely used in the production of ceramics the latter two occur in tubular fibrous form. 

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. 

Bates, T. F., and J. J. Comer (1959). Further observations on the morphology of chrysotile and halloysite. Clays and Clay Minerals. Monograph 2. Pergamon Press, New York. 

De Putter, T., Andre, L., Bernard, A., Dupuis, C., Jedwab, J., Nicaise, D. Perruchot, A. 2002. Trace element (Th, U, Pb, REE) behaviour in a cryptokarstic halloysite and kaolinite deposit from Southern Belgium importance of accessory mineral formation for radioactive pollutant trapping. Applied Geochemistry, 17, 1313-1328. 

Kaolins. The kaolin minerals include kaolinite. dickite. and nacrite which all have composition AUOi 2 SiO 2 FLO halloysite (7 At. AGO, 2 SiO, 2 H.O and halfoysile (10 A). Al 0, 2 SiO 4 H 0 The struclural formulas for kaolinite and halloysite tIO At. which are shown in Figure I, are AbSiaOiotOH)). and AljSi.iO, i(OH) -4 H,(). respectively. The so-called fire day mineral is a h-axis disordered kaolinite halloysite (7 A) and halloysite (10 A) are disordered along both the a- and h-Mcs Indeed, most variations in the kaolin group originate as structural polymorphs, related to variations in layer slacks. 

Halloysite has a chemical composition similar to kaolinite, but with a higher water content. The layers of halloysite are like those in kaolinite, but they are stacked with highly random displacements parallel to the layers, as opposed to the regular stacking found in kaolinite. The interlayer distance is greater in halloysite, allowing for the presence of a sheet of water molecules. A small ion-exchange capacity is measurable in kaolinite and halloysite minerals, which arises from a small amount of iso-morphous replacement of Si4+ or Al3+ in the framework 234). 

Clay (mineral) A group of fine-grained and platy aluminum silicate minerals. Kaolinite (ALSiiOs/OH ), montmorillonite ((Al,Mg)g(Si40io)4(OH)8-12H20), and halloysite (Al2Si205(0H)4-2H20) are common clay minerals. 

Hashimoto, 1. and 3ackson, M.L., 1960. Rapid dissolution of allophane and Kaolinite-Halloysite after dehydration. Clay and Clay Minerals, 7th Conf., pp. 102-113. 

Certain minerals can interfere in the test. They include halloysite, palygor-skite, antigorite, hornblende, and others. 

One of the major differences in the reported chemical composition of the kaolinite minerals is in the H20+and H20 values. In part, these variations may be real but many must be due to the presence of halloysite and other impurities, variation in grain size and surface area, and in the methods of dehydration. H20 increases linearly with increase in surface area and with decrease in grain size. 

Keller et al. (1971) reported on the occurrence of halloysite formed by the action of hot spring waters on rhyolitic volcanic rock in Michoacan, Mexico and suggested that high concentrations of Si and Al in solution, low pH (about 3.5) and sulfate as the solvent anion allows the formation of halloysite rather than other kaolinite minerals. 

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