During the extraction of iron in the blast furnance, slag is produced using

Step 1: Analyze the question The question asks which substance is used to produce slag in the blast furnace during iron extraction.

Step 2: The concept Iron ore (mainly haematite, Fe₂O₃) contains impurities, chiefly silica (SiO₂, sand). These impurities must be removed. This is done by adding a flux, a substance that combines with the impurities to form a molten waste called slag. In the blast furnace, the flux is limestone (CaCO₃).

Step 3: The reactions

1. Limestone decomposes in the heat: CaCO₃ → CaO + CO₂

2. The calcium oxide (a basic oxide) reacts with silica (an acidic oxide): CaO + SiO₂ → CaSiO₃ (calcium silicate, the slag)

The slag is molten and less dense than the molten iron, so it floats on top of the iron. It can be tapped off separately and is often used for road construction or making cement.

Step 4: Check the other options

• A. Carbon (coke): It is the fuel and reducing agent (it forms CO, which reduces Fe₂O₃ to Fe). It does not form slag.
• B. Cryolite: It is used in the extraction of aluminium, not iron.
• C. Limestone: It is the flux that forms slag. ✔
• D. Oxygen: The hot air blast supplies oxygen to burn the coke, but it does not make slag.
• E. Sulphur: It is an impurity in iron, not a slag-forming agent.

Answer: C. Limestone.

Exam tip: Remember "Limestone = Loses impurities". In the blast furnace, coke is the fuel and reducing agent, and limestone is the flux. Cryolite belongs to aluminium extraction (the Hall-Héroult process), which is a common distractor in NECO and JAMB.