Question

In the extraction of iron using blast furnace to remove the impurity (X), chemical (Y) is added to the ore. X and Y are respectively

• A. SiO₂, MgCO₃
• B. FeO, SiO₂
• C. SiO₂, CaCO₃
• D. SiO₂, FeCO₃

Hint:

Remember the principle of slag formation: Acidic impurity + Basic flux \(\rightarrow\) Slag, or Basic impurity + Acidic flux \(\rightarrow\) Slag. For iron extraction, the impurity (SiO₂) is acidic, so the flux (CaCO₃ \(\rightarrow\) CaO) must be basic.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question concerns the metallurgy of iron, specifically the role of flux in a blast furnace. A blast furnace is used to reduce iron oxides (from the ore) to molten iron. The ore contains impurities that must be removed. This is done by adding a chemical called a flux, which reacts with the impurity to form a molten substance called slag.
Step 2: Identifying the Impurity and Flux:
- Impurity (X): The primary impurity in iron ores like hematite (Fe₂O₃) is sand, which is silicon dioxide (SiO₂). SiO₂ is an acidic oxide. This is also known as the 'gangue'.
- Chemical Added (Y): To remove the acidic impurity (SiO₂), a basic flux is required. The chemical added to the blast furnace charge is limestone, which is primarily calcium carbonate (CaCO₃). At the high temperatures inside the furnace, limestone decomposes to form calcium oxide (CaO), which is a basic oxide, and carbon dioxide.
\[ \text{CaCO}_3(s) \xrightarrow{\text{heat}} \text{CaO}(s) + \text{CO}_2(g) \] - Slag Formation: The basic flux (CaO) then reacts with the acidic impurity (SiO₂) to form a molten slag, calcium silicate (CaSiO₃).
\[ \text{CaO}(s) + \text{SiO}_2(s) \rightarrow \text{CaSiO}_3(l) \] The molten slag is less dense than the molten iron and floats on top, allowing it to be tapped off separately.
Step 3: Matching with Options:
- Impurity (X) is SiO₂.
- Chemical added (Y) is CaCO₃.
This corresponds to the pair (SiO₂, CaCO₃).
Step 4: Final Answer:
The impurity X is SiO₂ and the chemical Y added is CaCO₃. Therefore, option (C) is correct.