Constituents of Fly Ash

Main constituents of fly ash are:

Silicon dioxide (SiO₂) = 30–60%

Aluminium oxide (Al₂O₃) = 15–30%

Unburnt fuel (carbon) = up to 30%

Calcium oxide (CaO) = 1–7%

Magnesium oxide (MgO) = small amount

Sulphur trioxide (SO₃) = small amount

The chemical composition of fly ash varies with the type of fuel burnt, load on boiler and type of separator, etc. High fineness, low carbon content, good reactivity are the necessary qualities of a good fly ash.