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Difficulty: MediumChemical Industries, Raw Materials, and Siting Factors

At the Ajaokuta steel complex in Kogi State, Nigeria, iron ore and coal are major raw materials utilized in heavy metallurgical manufacturing. During the blast furnace operation, limestone (CaCO3CaCO_3) is also added as an essential raw material. Which of the following best describes the primary industrial function of limestone in this process?

  1. A
    It acts directly as the primary reducing agent converting iron(III) oxide into molten metallic iron in the furnace.
  2. It thermally decomposes into calcium oxide (CaOCaO), which reacts with silica impurities (SiO2SiO_2) to form removable molten slag (CaSiO3CaSiO_3).Answer
  3. C
    It functions as an added catalyst to shift the chemical equilibrium position to increase the overall yield of iron.
  4. D
    It reacts with amphoteric oxides by acting as a strong basic solvent to release pure oxygen gas into the upper furnace.

Answer

Limestone thermally decomposes into calcium oxide (CaOCaO), which reacts with silica impurities (SiO2SiO_2) to form removable molten slag (CaSiO3CaSiO_3).
In heavy metallurgical chemical processing (such as iron extraction at Ajaokuta), raw materials serve distinct chemical roles. Limestone (CaCO3CaCO_3) decomposes under heat to produce calcium oxide (CaOCaO), a basic flux. CaOCaO combines with acidic impurities like silica (SiO2SiO_2) in iron ore to form molten calcium trioxosilicate(IV) (CaSiO3CaSiO_3 or slag), which floats on molten iron and is easily removed.

Step-by-Step Solution

1
Identify the chemical transformation of limestone (CaCO3CaCO_3) at high temperatures in the blast furnace.
Limestone undergoes thermal decomposition: CaCO3(s)→CaO(s)+CO2(g)CaCO_3(s) \rightarrow CaO(s) + CO_2(g).
High heat inside the blast furnace breaks down limestone into basic calcium oxide and carbon(IV) oxide.
2
Determine the reaction of calcium oxide with sandy/earthy impurities present in the iron ore.
Calcium oxide acts as a basic flux reacting with silicon(IV) oxide: CaO(s)+SiO2(s)→CaSiO3(l)CaO(s) + SiO_2(s) \rightarrow CaSiO_3(l).
Iron ore contains acidic silica impurities (SiO2SiO_2) which must be removed to prevent contamination of the produced iron.
3
Evaluate the physical separation of the resulting byproduct.
Molten calcium trioxosilicate(IV) (CaSiO3CaSiO_3, slag) floats on top of the denser molten iron and is tapped off separately.
Slag removal cleans the iron and prevents re-oxidation of molten iron by furnace gases.

Key Concept

Industrial raw material roles and fluxing in heavy metallurgy (blast furnace operation)
Estimated Time:1m 0s
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Topics

Chemical Industries, Raw Materials, and Siting Factors

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