Purest form of commercial iron is:

Wrought iron

The correct answer is Option (3) → Wrought iron

Let us delve into the different forms of iron and clarify why wrought iron is considered the purest form of commercial iron.

1. Pig Iron

Composition: Pig iron has a high carbon content (about 3-4%), along with other impurities such as sulfur, phosphorus, and silicon.

Properties:

Brittleness: Due to its high carbon content, pig iron is brittle and cannot be easily worked into shapes.

Not suitable for structural applications: Its brittleness limits its usability, so it is primarily used as a raw material for further processing.

Production: It is produced by smelting iron ore in a blast furnace, where coke and limestone are used as reducing agents and flux, respectively.

2. Cast Iron

Composition: Cast iron contains a higher carbon content than wrought iron (about 2-4%) and is usually alloyed with silicon and other elements.

Properties:

Strength and brittleness: While cast iron is strong, its higher carbon content also makes it brittle compared to wrought iron.

Excellent castability: Cast iron can be easily cast into complex shapes, which is why it's commonly used for engine blocks, pipes, and cookware.

Types: There are different types of cast iron (e.g., gray iron, ductile iron) based on the microstructure, which influences their properties.

3. Wrought Iron

Composition: Wrought iron contains a very low carbon content (typically less than 0.08%) along with small amounts of other elements like silicon and manganese. This low carbon content contributes to its unique properties.

Properties:

Malleability: Wrought iron can be easily shaped and formed without breaking, making it ideal for forging and working into various shapes.

Ductility: It can be drawn into wires, which is beneficial for applications that require flexibility.

Corrosion Resistance: Wrought iron has good resistance to corrosion due to its structure, especially when compared to cast iron.

Production: Wrought iron is produced by further refining pig iron through processes such as the puddling process, where impurities are removed and the iron is worked to remove slag. It can also be produced using direct reduction methods.

Applications: Commonly used in construction (railings, gates, and ornamental work), as well as in blacksmithing.

4. Haematite

Composition: Haematite is an iron ore with the chemical formula \(Fe_2O_3\), consisting mainly of iron oxide.

Properties:

Raw material: It is not a form of iron itself, but a source from which iron is extracted. The iron content in haematite is typically around 70%.

Mining and Processing: Haematite is mined and then processed (usually in a blast furnace) to produce pig iron, which can then be refined into wrought iron or steel.

Summary

Wrought iron is the purest commercial form of iron due to its low carbon content and the absence of significant impurities. Its excellent malleability and ductility make it suitable for various applications.

In contrast, pig iron and cast iron contain higher carbon levels, leading to brittleness, and haematite is simply a raw material for iron production.

This detailed understanding of the different forms of iron helps clarify why wrought iron is recognized as the purest form among the options provided.