CHEMISTRY

JAMB 2008 - Question 31

Chemistry 2008 JAMB Past Questions - Question 31: The substance that is used in the steel industry for the removal of carbon, sulphur and phosphorus impurities from pig iron is

Choose the correct answers from the options given.
The substance that is used in the steel industry for the removal of carbon, sulphur and phosphorus impurities from pig iron is
A:
B:
C:
D:
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Correct Answer

A

Explanation

The substance used in the steel industry for the removal of carbon, sulfur, and phosphorus impurities from pig iron is **calcium oxide (CaO)**, commonly known as **lime**.

Here's how it works:

- **Carbon:** During the steelmaking process, impurities like carbon are removed by **oxidation**. CaO reacts with carbon to form carbon monoxide (CO):

  CaO + C -> CaC₂O₄ + CO

  The CO gas bubbles out of the molten metal, taking a significant amount of carbon with it.

- **Sulfur:** CaO reacts with sulfur to form calcium sulfide (CaS), which then floats to the surface as slag and is removed:

  CaO + S -> CaS

- **Phosphorus:** Similar to sulfur, CaO reacts with phosphorus to form calcium phosphate (Ca₃(PO₄)₂) that becomes part of the slag and is removed:

  3CaO + P₄ -> Ca₃(PO₄)₂

**Other materials** can also be used along with CaO in specific situations, such as:

- **Fluorspar (CaF₂)**: Helps improve the fluidity of slag and promote further removal of sulfur and phosphorus.
- **Dolomite (CaMg(CO₃)₂)**: Similar to CaO, acts as a flux and provides magnesium oxide (MgO) which also aids in desulfurization.
- **Iron ore**: Can be added to oxidize excess silicon present in pig iron.

However, **CaO remains the primary and most widely used substance for removing these impurities due to its effectiveness, affordability, and readily available sources.**

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