Occurrence and principles of extraction of iron

Iron is the second most plentiful metal on this planet, followed by aluminium. Since it is a reactive metal, it is not available in a free state. Iron is found as oxides such as hematite, magnetite, limonite, iron pyrites, and siderite in the combined form. Iron pyrites is a common ore, but it is not usually used to produce iron due to the high content of Sulphur. Iron is an essential metal and makes up for a significant part of the biological system. The extraction of iron requires the involvement of various principles and processes of chemistry. 

Occurrence of Iron

Iron is non existent in the free state; instead, it is found in a combined form. Some primary ores of iron are as follows:

Hematite (Fe2O3)

Limonite (Fe2O3.3H2O)

Iron Pyrites (FeS2)

Magnetite (Fe3O4)

Siderite (FeCO3)

Mineral and Ore Defined

A mineral is a substance in which a helpful metal or compound is found. An ore is that mineral in which a particular metal occurs in some significant amount and can be extracted economically. Some common examples of iron ore are hematite and limonite etc.

Extraction of iron 

The extraction of iron is mainly from its oxide, i.e., hematite, and the process of extraction of iron involves the following steps.

• Concentration 

Concentration is the process of removing unwanted and useless material from ore. 

For this, the ore is broken down into smaller pieces with the help of a jaw crusher, and then the crushed ore is concentrated on a process known as gravity separation. It is washed with water in gravity separation to remove clay, sand, and other impurities.

• Calcination

In this method, the concentrated ore is heated in a shallow kiln in the presence of an excess of air. In this process, moisture is eliminated, and impurities such as C, S, P, As, and Pb are also removed from their volatile oxide.

S + O2 → SO2 ↑

The carbonates and sulphides are changed into oxides. 

FeCO3 → FeO + CO2 ↑

Ferrous oxide is oxidised to ferric, and therefore there is no formation of slag.

4FeO + O2 → 2Fe2O3

FeO+ SiO2 → FeSiO3 (Slag) 

• Smelting or Reduction

The calcined ore is mixed with coke, a reducing agent, and limestone flux and is reduced in a blast furnace. Reactions in the blast furnace are different since there is a temperature difference in different zones.

Reactions of blast furnace 

The following reactions in the blast furnace are as follows. 

Zone of Combustion

This zone is close to the end of the furnace. In this zone, combustion of carbon takes place since combustion is an exothermic process, the maximum temperature in this zone. 

2C + C → 2CO + 58 kcal. 

C + O2 → CO2 + 97 kcal.

Zone of Fusion 

This zone lies above the combustion zone; this zone is where the iron melts and moves down while the lighter slag floats over the molten metal, thereby preventing the oxidation of iron by a blast of air.

Zone of adsorption

This is the middle portion of the blast furnace, and the rising CO2 is reduced to carbon monoxide here. This reaction is endothermic, and so this zone has the lowest temperature. 

CO2 + C → 2CO 

The following reactions also occur in this zone.

Reduction of Fe2O3, which escaped to reduce in the reduction zone.

Fe2O3 + 3C → 2Fe + 3CO ↑

Limestone decomposes and forms CaO, which reacts with SiO2 to form slag; hence, this zone is also known as the slag formation zone.

CaCO3 → CaO + CO2

CaO + SiO2 → CaSiO3 ( Slag)

Zone of Reduction

This zone is at the top portion of the furnace, and here the calcined ore is reduced to iron, and carbon dioxide rises. The process of extraction of iron is complete here:

3Fe2O3 + CO ⇆ 2Fe3O4 + CO2 ↑

Fe3O4 + CO ⇄ 3 FeO + CO2 ↑

FeO + CO2 ⇄ Fe + CO2 ↑

The reactions mentioned above in the blast furnace lead to the extraction of iron

Wrought Iron/ Malleable Iron

Wrought iron is the perfect form of iron available for commercial purposes. It is made by heating cast iron in a furnace lined with Hematite  (Fe2O3 ), which reacts with carbon in cast iron to produce pure iron and carbon monoxide gas, both of which escape. It is another method of extraction of iron.

Fe2O3 + C → 2Fe + 3CO

Limestone is then added to it as flux, which results in slag formation. Impurities such as S and Si enter the slag, which can then be separated to yield pure iron without hassle.

Conclusion 

Iron is an important element, and studying the occurrence and extraction of iron is necessary. Iron is used extensively for various purposes, such as wrought iron and steel manufacturing. While there are many ways of extracting iron, the reaction in a blast furnace and the Wrought iron/ Malleable iron method are the most discussed ones. The iron extracted from this method is tough, malleable, and ductile and can be used for making chains, bolts, frameworks, etc. There are other methods of extracting iron, although these two are the most commercially accepted and viable methods.