Question

In the manufacture of iron, a mixture of limestone, coke, and iron ore is added to the blast furnace.

In this context,

(i) State the purpose of adding limestone to the furnace.

(ii) Give the equation for the reduction of iron ore.

(iii) Name the substance which is collected along with cast iron at the bottom of the furnace.

(iv) Write the chemical equation for the formation of the substance named in (iii) above.

Answer 1

Iron$\left(\mathrm{Fe}\right)$ extraction process

(i) Purpose of limestone addition to the furnace

Limestone$\left({\mathrm{CaCO}}_3\right)$ is used for the removal of impurities from blast furnace during the manufacturing of Iron.

Mainly, impurities are found in form of Silicon dioxide$\left({\mathrm{SiO}}_2\right)$ which is commonly known as sand.

Limestone chemically known as Calcium carbonate$\left({\mathrm{CaCO}}_3\right)$ decomposes to give Calcium oxide$\left(\mathrm{CaO}\right)$ and Carbon dioxide gas$\left({\mathrm{CO}}_2\right)$.

The formed Calcium oxide $\left(\mathrm{CaO}\right)$ reacts with Silicon dioxide$\left({\mathrm{SiO}}_2\right)$ and produces Calcium silicate$\left({\mathrm{CaSiO}}_3\right)$.

${\mathrm{CaCO}}_3\left(\mathrm{s}\right)\to \mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{SiO}}_2\left(\mathrm{s}\right)\to {\mathrm{CaSiO}}_3\left(\mathrm{s}\right)$

Hence, limestone acts as a flux in iron$\left(\mathrm{Fe}\right)$ manufacturing.

(ii) Chemical equation for the reduction of iron ore

Reduction of iron ore, Haematite$\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ takes place in presence of Carbon monoxide$\left(\mathrm{CO}\right)$ and ${\mathrm{Fe}}^{3+}$ of metal oxide converts into free metal $\mathrm{Fe}$.

Carbon dioxide gas$\left({\mathrm{CO}}_2\right)$ is released in this reduction reaction.

This reaction occurs in upper region of blast furnace.

${\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+3\mathrm{CO}\left(\mathrm{g}\right)\to 2\mathrm{Fe}\left(\mathrm{s}\right)+3{\mathrm{CO}}_2\left(\mathrm{g}\right)$

(iii) Substance produced at bottom of the furnace

The reaction between limestone$\left({\mathrm{CaCO}}_3\right)$ and Silicon dioxide$\left({\mathrm{SiO}}_2\right)$ which occurs in the middle region of the blast furnace produces Calcium silicate.

This Calcium silicate$\left({\mathrm{CaSiO}}_3\right)$ which is a fusible slag is collected along with cast iron$\left(\mathrm{Fe}\right)$ at the bottom of the furnace.

(iv) Chemical equation for the formation of Calcium silicate

The Calcium oxide $\left(\mathrm{CaO}\right)$ formed as a result of the decomposition of Calcium carbonate$\left({\mathrm{CaCO}}_3\right)$ reacts with Silicon dioxide$\left({\mathrm{SiO}}_2\right)$ and produces Calcium silicate$\left({\mathrm{CaSiO}}_3\right)$.

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{SiO}}_2\left(\mathrm{s}\right)\to {\mathrm{CaSiO}}_3\left(\mathrm{s}\right)$

In this way, Calcium silicate(slag) is formed in the middle region of a blast furnace.