Write down the reactions taking place in a blast furnace related to the metallurgy of iron in the temperature range 500K to 800K. What is the role of limestone in the metallurgy of iron?

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Hint:Reduction of Iron oxides takes place during this process. Metallurgy is the branch of science and technology concerned with the properties of metals and their production and purification.

Complete answer:
At the top, the temperature is as low as 500−800 K. It is called a reduction zone. In the lower temperature range, carbon is the reducing agent and in the higher temperature range, CO is the reducing agent. In the reduction zone (500−800 K), following reactions occur:

\begin{matrix} 3 F e_{2} O_{3} + C O \to 2 F e_{3} O_{4} + C O_{2} \\ F e_{3} O_{4} + 4 C O \to 3 F e + 4 C O_{2} \\ F e_{2} O_{3} + C O \to 2 F e O + C O_{2} \end{matrix}

Role of limestone in metallurgy:
>Limestone decomposes in the hot furnace, forming calcium oxide (

C a O

) which removes silica impurity of ore as slag.

C a C O_{3} C O_{2} C a O S i O_{2}

(Impurity)(Slag)

C a S i O_{3}

>Limestone is also used to remove impurities from the blast furnace when making iron. The impurities are mostly silicon dioxide (also known as sand). The calcium carbonate in the limestone reacts with the silicon dioxide to form calcium silicate (also known as slag).

C a C O_{3} (s) \to C a O (s) + C O_{2} (g) C a O (s) + S i O_{2} (l) \to C a S i O_{3} (s)

>Molten calcium silicate is less dense than the molten iron so it floats on top of the iron and can easily be removed.
>Limestone can be crushed and used to build roads. The waste slag from the blast furnace can also be used for this purpose.

Note:At the top of a blast furnace temperature is 500K to 800K and it is known as “Reduction Zone” as reduction of iron oxides takes place here.Most limestone is obtained by quarrying, where the rock is blasted out of the ground in huge pits.