Chemical elements
  Aluminium
    Isotopes
    Energy
    Preparation
    Physical properties
    Chemical properties
      Aluminium subfluoride
      Aluminium trifluoride
      Aluminium trichloride
      Aluminium tribromide
      Aluminium iodide
      Aluminium chlorate
      Aluminium perchlorate
      Aluminium bromate
      Aluminium periodate
      Aluminium suboxide
      Alumina
      Aluminium sesqui-oxide
      Aluminium peroxide
      Aluminium hydroxides
      Aluminates
      Tricalcium aluminate
      Sodilim aluminate
      Aluminium sesqui-sulphide
      Aluminium selenide
      Aluminium telluride
      Aluminium sulphite
      Aluminium sulphate
      Alums
      Sodium alum
      Potassium alum
      Ammonium alum
      Hydroxylamine alum
      Silver alum
      Pseudo-alums
      Aluminium dithionate
      Aluminium selenite
      Aluminium selenate
      Aluminium chromate
      Aluminium molybdate
      Aluminium silicomolybdate
      Aluminium tungstate
      Aluminium silicotungstate
      Aluminium phosphotungstate
      Aluminium nitride
      Aluminium phosphide
      Aluminium arsenide
      Aluminium nitrate
      Aluminium Phosphates
      Basic aluminium arsenite
      Aluminium carbide
      Aluminium carbonate
      Aluminium thiocyanate
      Aluminium oxalate
      Aluminium alkyls
      Aluminium Hydrocarbon
      Aluminium acetylacetonate
      Aluminium silicide
      Aluminium silicates
      Leucite
      Nephelite
      Spodumene
      Topaz
      Beryl
      Tourmaline
      Axinite
      Sodalite
      Hauynite
      Kaolinite
      Aluminosilicic acids aluminosilicates
      Aluminium Borides
      Aluminium Boride
      Aluminium Boride
      Aluminium borocarbides
      Aluminium borate
      Aluminium sodium perborate
    Applications
    PDB 1a6e-1zca
    PDB 2b8w-3i62
    PDB 3kql-5ukd

Kaolinite, H4Al2Si2O9






Kaolinite, H4Al2Si2O9, is a rare, white mineral. It crystallises in the monoclinic system (a:b:c = 0.5748:1:0.5997; β = 96°19'); density, 2.62; hardness, 2.5. The best crystals are found near Amlwch in the island of Anglesey; they are six-sided plates or pyramids with a perfect basal cleavage. The mean refractive index is 1.563; the birefringence (0.004) is much lower than that of mica, which resembles kaolinite in appearance. The water is only expelled from kaolinite at high temperatures (above 330°); hence, when the formula is written in the usual way, Al2O3.2SiO2.2H2O, it must be remembered that the water is "water of constitution" and not water of crystallisation. Chemically, kaolinite is best regarded as an acid.

The silicates described above are naturally occurring substances. A number of artificial aluminium silicates, however, are of considerable industrial importance and may therefore be mentioned. These are the substances prepared by Gans and known technically as permutits. Sodium permutit is practically an artificial zeolite of the composition 2SiO2Al2O3.Na2O.6H2O. It is prepared by heating together china-clay, sodium carbonate and quartz in the requisite proportions and treating the mass with water. Other substances may be added in the preparation; a mixture of 2.5 to 3 parts of china-clay, 5 to 6 of alkali carbonate, and 1.5 to 2.4 parts of borax, for instance, has been particularly specified. The permutit is of a granular or leafy, porous character.

Sodium permutit, like certain natural zeolites, is able to exchange its sodium for other metals with remarkable ease. If, for instance, a solution of calcium or magnesium chloride is allowed to percolate through a column of the permutit, a solution of sodium chloride, free from calcium or magnesium, is obtained. If now, a concentrated solution of sodium chloride is percolated through the permutit, the calcium of magnesium is expelled from it and replaced by sodium. The application of sodium permutit to the softening of boiler water will therefore be obvious without further explanation.

The sodium or calcium permutits can readily be made to exchange sodium or calcium for manganese, by treatment with a manganous salt solution. When this product is acted upon by potassium permanganate solution, the latter is reduced, and a manganese-potassium permutit produced which is covered with very finely divided higher oxides of manganese. This material is a valuable oxidising agent, and, when exhausted, can readily be regenerated by allowing potassium permanganate to percolate through it; its commercial uses are for removing iron from, and oxidising the organic matter and bacteria in water. These results are easily brought about by allowing the contaminated water to flow through a layer of the permutit; in sterilising water by this means it may be necessary, in addition, first to add a little' permanganate to the water.


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