Iron Extraction Blast Furnace Metallurgy

Introduction

The metallurgy that deals with metal, iron and its alloy is ferrous metallurgy. In ancient times iron has been used for several applications by humans. It is a metallic element with the atomic number 26 and has some unique characteristics. They are very dense and are abundant in the earth's crust. About five percent of the earth's crust is covered by metal iron. The abundance is in fourth place. Iron is placed in the d block or transition elements. The pure metals of iron have many advantages. So, it is very important to extract iron in its pure form. The discovery of a blast furnace in the 15th century made the extraction process easier.

Define Iron Extraction by Blast Furnace Metallurgy.

The huge container used for the extraction of iron is a blast furnace. The ore of Iron is hematite containing iron (III) oxide, Fe₂ O₃. From the formula itself, the removal of Oxygen is necessary. Removing oxygen is done by reaction reduction. Coke is used and is because of the reason that carbon is more reactive than iron and can easily displace iron from iron oxide. High temperature is present in the blast furnace, and it further leads to the burning of carbon and carbon gets converted into carbon monoxide.

Iron Extraction Procedure

There are mainly three steps in the iron extraction process. They are

• The concentration of Ore − The ore of iron contains many impurities other than the water-soluble sand and clays. These impurities can be separated with the help of a concentration, and it can be done by the limited supply of oxygen. The process is called calcination, it is a thermal decomposition process. Such impurities are given the name gangue. Sulphur and carbonates are removed by this process.

• Extracting Iron from the concentrated ore − After concentrating the ore iron is extracted by reaction with the limestone and coke. This process is done with the help of a blast furnace. At the top of the blast furnace, the compounds such as concentrated ore, coke, and limestone are introduced. Then from the bottom of the blast furnace hot air is blown. High temperature is needed for this process and carbon monoxide is produced by the burning of coke.

  $$\mathrm{C+CO_2→2CO}$$

  Then the carbon monoxide participates in reactions. And the process is taking place in the upper part of a blast furnace since the temperature there is low. The temperature at which the reaction takes place is 500K-800K. That is

  $$\mathrm{3Fe_2 O_3+CO→2Fe_3 O_4+CO_2}$$

  $$\mathrm{Fe_3 O_4+4CO→3Fe+4CO_2}$$

  $$\mathrm{Fe_2 O_3+CO→2FeO+CO_2}$$

  $$\mathrm{3FeO+CO_2→Fe+CO_2}$$

• Purification of Iron − The iron obtained from the blast furnace is impure. The impurities mainly consist of silicate, and they can be removed by the limestone. Limestone removes the impurities present in iron in the form of slag and which can be easily removed from iron in the molten state. That is,

  $$\mathrm{CaCO_3 (s) → CaO(s) + CO_2 (g)}$$

  $$\mathrm{CaO(s) + SiO_2 (s) → CaSiO_3 (l)}$$

  The iron obtained after this procedure has a 3 to 4 percentage of carbon content, and some other impurities. And are called pig iron. It is a brittle and hard metal. So, it is very important to reduce the amount of carbon content, and it can be done by melting again with some scraps of coke and iron and then allowing it into the blast furnace. Then the obtained iron contains only two to three percent carbon content and this iron is called cast iron.

What is Calcination?

Calcination is a process that involves that purification method. A limited supply of oxygen is required for this process. Volatile impurities are easily removed with the help of this process. This process is commonly used for limestone, in which the calcium carbonate is converted into calcium oxide with the removal of carbon dioxide gas.

$$\mathrm{CaCO_3→CaO+CO_2}$$

What is Roasting?

This process involves the heating of ores at a high temperature that is at a temperature higher than the melting point with excess oxygen. The process of roasting involves several reactions such as oxidation, pyrohydrolysis, reduction, etc. It is mainly used in sulphide ores for example Zinc sulphide.

$$\mathrm{2ZnS+3O_2→2ZnO+CO_2}$$

What are the Differences between Calcination and Roasting?

Some of the differences between calcination and roasting are tabulated below.

Calcination	Roasting
The process of heating ores of metal under a reduced supply of oxygen where it will remove volatile impurities is calcination.	The process that involves heating ores of metal with an access amount of oxygen thereby removing impurities is roasting.
Mainly useful for carbonated ores.	Mainly useful for sulphide ores.
Volatile and toxic compounds are produced.	Toxic gases and compounds are produced.
Reverberatory furnaces with closed holes are used for this process	A reverberatory furnace with open holes is used for this process.
The organic components present in the ores are mainly escaped as gases and holes are formed in the ores.	Phosphorus, arsenic, and sulphur impurities are escaped as gaseous oxide.

What Happens in the Blast Furnace?

The ore of iron and haematite undergo several reactions and will result in the formation of the metal, iron. It is a high-temperature process. And mainly involves three steps concentration of ore, extraction of iron, and purification of iron. The whole process happening here at the blast furnace is the removal of oxygen present in the ore, so it is a reduction process.

What is Wrought Iron/Malleable Iron?

The purest form of iron is wrought iron or malleable iron. In a furnace lined with hematite heating of cast iron will produce the wrought iron. And is the commercially available iron. The reaction is,

$$\mathrm{Fe_2 O_3+3C→2Fe+3CO}$$

Conclusion

The extraction of iron from its ore is a complex process since it involves the use of a blast furnace. The introduction of the ore of iron and several other chemical compounds in the blast furnace result in the extraction of iron. The main raw material used for the extraction process is coke, which contains carbon. Iron is easily available and possesses many applications. Calcination is also involved in the process of extraction. The iron obtained is called pig iron, which then undergoes some additional process to obtain cast iron, and which is treated with hematite to produce the purest form of iron, wrought iron.

FAQs

1. Which is harder pig iron or cast iron?

Cast iron is harder than pig iron.

2. What is metallurgy?

The production of metal from its ore is called the metallurgical process.

3. What is steel?

The alloy of iron that is made by combining carbon is steel. The properties of steel are better than iron in case of rusting, resistance, strength, etc.

4. Is Iron slag and ore magnetic?

Yes, the slag obtained from the blast furnace and the ore of iron, and hematite are all magnetic.

5. What is the function of slag?

Slag acts as a protective covering for the molten metal since it floats on its surface and protects metals from oxidation.