The mechanism of silicon transfer in the blast furnace was examined through fundamental experiments, chemical analyses of metal and slag drips taken from the end of raceway during operation and measurements of PO2 at the same place.
The (FeO) content in slag averages about 15wt% and oxygen partial pressure PO2 averages 10-12 atm at the end of raceway.
These data imply that siliconization reaction via SiO gas from coke ash and slag occurs chiefly in the zone above and below tuyere level, respectively.
Slag-metal reaction occurs chiefly in the zone below tuyere level and desiliconization reaction proceeds until (FeO) content in slag is reduced to about 0.2wt %.
In the hearth, the slag-metal reaction, i.e. Si+2(FeO)=SiO2+2Fe, changes from desiliconization to siliconization reaction and [Si] content in metal approaches [Si]eq, at (FeO)=0.2wt %.
If the [Si] content of dripping metal is more than [Si]eq at (FeO)=0.2wt% or (FeO) content in slag is more than 0.2wt%, siliconization reaction does not occur any more.
The measured [Si] content agrees with the above equilibrium one in many blast furnaces. In some blast furnaces, however, the measured values are lower than the equilibrium ones. It is indicated that hot metal is tapped before the above equilibrium one is reached in these cases.
