Write down the chemical reactions taking place in different zones in the blast furnace during the extraction of iron.

Explanation

In the Blast furnace , reduction of iron oxides takes place in different temperature ranges. Hot air is blown from the bottom of the furnace and coke is burnt to give temperature upto about 2200K in the lower portion itself. The burning of coke therfore supplies most of the heat required in the process. The CO and heat moves to upper part of the furnace. In upper part, the temperture is lower and the iron oxides `(Fe_(2)O_(3)and Fe_(3)O_(4))` coming from the top are reduced in steps to `FeO` . Thus the reductions taking place in the lower temperature range and in the higher temperature range , depend on the points of corresponding intersections in the `Delta_(r)G^(Theta)` vs T plots . These reactions can be summarised as follows :
At 500-800 K (lower temperature range in the blast furnace)-
`3Fe_(2)O_(3)+COrarr2Fe_(3)O_(4)+CO_(2)`
`Fe_(3)O_(4)+4COrarr3Fe+4CO_(2)`
`Fe_(2)O_(3)+COrarr2FeO+CO_(2)`
At 900 -1500 K (higher temperature range in the blast furnace)
`C+CO_(2)rarr2CO`
`FeO+COrarrFe+CO_(2)`
Lime stone is also decomposed to CaO which removes silicate impurty of the ore as CaSiO3 slag is in molten state and separtes out from iron .
The iron obtained from Blast furnace contains about 4% carbon and many impurities in smaller amount (e.g.,S,P,Si,Mn). This is known as pig iron . Cast iron is different from and is made by melting pig iron with scrap iron and coke using hot air blast. It has slightly lower carbon content (about3%)and is extremely hard and brittle.
`Fe_(2)O_(3)+3Crarr2Fe+3CO`