How is iron extracted?

Haematite and magnetite are the ores of iron.

i. Haematite is the principal ore of iron. The earthy impurities are removed and haematite is finely powdered. Methods like gravity separation, levigation are often used for concentration.

ii. If its magnetite ore, then magnetic separation is employed because magnetite has iron which is magnetic. The ore so obtained is subjected to roasting. Roasting is the process of heating the concentrated ore at a temperature below the melting point in a current of air.

iii. Impurities like sulphur, arsenic, phosphorous are removed as their gaseous oxides along with water. But silicon oxide will be present in large amounts.

A mixture of roasted haematite, coke and lime stone is fed into a blast furnace. Limestone (flux) acts as flux and helps in removal of silicon oxide(gangue) and forms slag. The reactions are given-

CaCO₃ CaO + CO₂

CaO + SiO₂ CaSiO₃

At the bottom of blast furnace coke combines with oxygen in hot current of air to form carbon dioxide and large amount of heat.

C + O₂ CO₂ + heat

This carbon dioxide rises up and is reduced by coke to produce carbon monoxide. This carbon monoxide reacts with iron oxide to produce iron.

CO₂ + C + heat 2CO

Fe₂O₃ + 3CO 2Fe + 3CO₂

Molten iron is denser than slag. Slag floats on molten iron and these are separated. This iron which is obtained from blast furnace is called pig iron.

This is further processed to get cast iron, steel etc.