Problem 17 - A Complete Resource Book in Chemistry for JEE Main

Question

In the extraction of iron slag is produced which is (a) \(\mathrm{CaSiO}_{3}\) (b) \(\mathrm{FeSiO}_{3}\) (c) \(\mathrm{CO}\) (d) \(\mathrm{MgSiO}_{3}\)

Step-by-Step Solution

Answer

(a) \( \mathrm{CaSiO}_{3} \)

Step 1: Understanding the Process

In the extraction of iron, iron ore is reduced in a blast furnace. Lime stone (calcium carbonate) is added to remove impurities in the iron ore as a flux. The major impurity is silica (SiO_2).

Step 2: Formation of Slag

The limestone decomposes to produce calcium oxide and carbon dioxide. The calcium oxide reacts with the silica in the ore to form calcium silicate (slag). The reaction can be represented as: \( \text{CaO} + \text{SiO}_2 \to \text{CaSiO}_3 \).

Step 3: Choosing the Product

Based on the reaction, the product formed is calcium silicate. Comparing this with the options given: (a) \( \text{CaSiO}_3 \) matches the product obtained from the reaction.

Key Concepts

Slag Formation

In the world of iron extraction, slag plays a crucial role. Essentially, slag is a byproduct formed during the extraction of iron from its ore. It is created to help remove impurities from the iron. This happens when limestone, which is primarily calcium carbonate, is introduced into the blast furnace as a flux. A flux is a substance that aids in melting and helps in removing impurities.
Limestone decomposes under the high temperatures of the furnace to form calcium oxide and carbon dioxide. This calcium oxide then reacts with silica, a common impurity in iron ore, to form calcium silicate. This chemical reaction can be written as \[ \text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3\]This compound, calcium silicate, is the slag. Its formation is vital as it "floats" on the molten iron, preventing contamination from impurities and making the iron purer for further use. Slag is not waste; it can be used in various applications like road building and cement manufacturing.

Blast Furnace

A blast furnace is a large steel structure that's key to extracting iron from its ores like hematite or magnetite. Inside the blast furnace, all the core processes of iron extraction occur.
The furnace operates at very high temperatures, often reaching up to 2000°C. These extreme conditions are necessary to chemically alter the iron ore sequence and produce molten iron. A blast of air, enriched with oxygen, is blown into the lower part of the furnace, igniting the coke (carbon) present and producing intense heat.

• The top of the furnace is where iron ore, coke, and limestone enter.
• Hot air is blown in from the bottom, ascending upwards.
• As the materials descend, reactions occur, leading to the melting and separation of iron and slag.

This high-heat environment is also effective in initiating the reaction between calcium oxide and silica impurities leading to slag formation, as mentioned earlier.

Calcium Silicate

Calcium silicate plays a crucial role in the process of iron extraction. It is the specific kind of slag formed when calcium oxide reacts with silica impurities in the iron ore.When the limestone decomposes in the blast furnace, it forms calcium oxide. This oxide is quite active; it readily reacts with the silica present as an impurity. As these two substances combine, they form calcium silicate \[ \text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3\]Calcium silicate is a useful material beyond the iron smelting process. It has a very stable chemical structure, making it valuable in industries such as construction, where it is used in making bricks and tiles. This transformation of potential waste into a functional product is an excellent example of efficient resource utilization.