Belle van Zuylenlaan 3, Culemborg clear Nederlands
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Fly ash originates in the minerals present in pulverized coal. Only a small proportion of the inorganic elements is originally organically bound. Important minerals in coal are kaolinite, illite, quartz, pyrite, feldspar, calcite. During the burning of pulverized coal these minerals undergo conversion processes such as melting and oxidation.

fly ash micro
production scheme
  Element1 Range2
  SiO2 56 ± 3
  Al2O3 6.7 ± 1.2
  Fe2O3 25 ± 3
  CaO 4.4 ± 1.7
  K2O3 1.9 ± 0.5
  Na2O3 0.92± 0.37
  MgO 1.7 ± 0.4
  P2O5 0.84 ± 0.44
  TiO2 1.2 ± 0.3
  Cl ≤ 0.01
  S (as SO3) 0.74 ± 0.38
  Loss on Ignition (LOI) 3.9 ± 1.8
  1 expressed as an oxide; this does not mean they
    actually are available as an oxide
  2 shown is average ± standard deviation
  3 as Na2Oeq: 2.2 ± 0,5 % m/m

Fly ash is a fine powder: it has an average particle size of about 20 µm. The particles are mainly spherical in shape, because the glass-like particles in a molten state take on a globular form. The density is approximately 2200 kg/m3. This is lower than theoretically would be expected, but the encapsulation of gas bubbles cause this lower density.

SiO2 and Al2O3 are the main components, and to a lesser degree Fe2O3 en CaO. These elements are named oxides, as usual in geology and cement chemistry. But this does not mean that this is actually true. The most important mineral phase is a glass-like compound containing the major part of the available SiO2 en Al2O3. In addition, mineral phases such as mullite, quartz, hematite and magnetite are present. These minerals can also be found in nature.

Concentration of main components in fly ash.
(Source: fly ash quality control database 2009)

fly ash | applications | composition | downloads