Wrought iron is obtained by heating cast iron in a furnace with?

Analysis of the Question

The question asks for the substance used in a furnace to convert cast iron into wrought iron. This process is known as the "puddling process" or "reverberatory furnace process."

Concept Explanation

Cast iron contains a high percentage of carbon (about 2% to 4.5%) and other impurities like silicon, sulfur, and phosphorus, which make it brittle. To produce wrought iron (which is almost pure iron), these impurities must be removed through oxidation.

When cast iron is heated in a reverberatory furnace, it is lined with haematite ($Fe_2O_3$). The haematite acts as an oxidizing agent. It reacts with the carbon and other impurities in the cast iron to oxidize them:

• Carbon is oxidized to carbon(IV) oxide ($CO_2$), which escapes as a gas.
• Silicon is oxidized to silicon(IV) oxide ($SiO_2$), which forms slag.

Step-by-Step Solution

1. Identify the goal: The goal is to reduce the carbon content of cast iron to produce wrought iron.
2. Identify the process: The process involves heating cast iron in a furnace lined with an oxidizing agent.
3. Evaluate the options: • Magnetite ($Fe_3O_4$): While it is an iron ore, it is not the standard lining used in the puddling furnace for this specific conversion. • Haematite ($Fe_2O_3$): This is the specific iron ore used to line the furnace. It provides the oxygen necessary to burn off the excess carbon and impurities. • Carbon(II) oxide ($CO$): This is a reducing agent, not an oxidizing agent. It would not help remove carbon from the iron. • Calcium trioxosilicate(iv) ($CaSiO_3$): This is a slag component, not the primary oxidizing agent used to line the furnace.
4. Conclusion: The haematite ($Fe_2O_3$) reacts with the carbon in the molten cast iron: $Fe_2O_3 + 3C \rightarrow 2Fe + 3CO$

Correct Answer

The correct option is B.

Exam Tip

When studying metallurgy, always distinguish between reducing agents (like $CO$ used in the Blast Furnace to extract iron from ore) and oxidizing agents (like haematite used in the Puddling Furnace to purify iron). Remember: Blast Furnace = Reduction; Puddling Furnace = Oxidation.