What is the role of lime stone in the extraction of iron from the concentrated hematite ore ?

Explanation

Concentration ore is mixed with lime stone and coke, and fed into blast furnace. Coke acts as fuel, CO formed from it acts as reducing agent and lime stone acts as flux.
Reactions in the blast furnance.
(i) Zone of combination : Hot air is blown from the bottom of the furnance coke burns to give `CO_(2)` temperature rises to 2200 K.
`C + O_(2) rarr CO_(2)`
The `CO_(2)` reacts wwith overlying coke to from CO.
`CO_(2) + C rarr 2CO`.
(ii) Zone of reduction : In the upper part of the furnance where the temperature range is 500 K to 800 K CO reduces iron oxides to iron.
`Fe_(2)O_(3) + 3CO rarr 2Fe + 3CO_(2)`
(iii) Zone of slag formation : In the middle part of the furnance where the temperature range is 800 K to 1000 K limestone decomposes to CaO, which removes silicate impurity to form slag.
`CaCO_(3) rarr CaO + CO_(2)`
`CaO + SiO_(2) rarr CaSiO_(3)`.