Animated Solution for Chemistry - Metallurgy: The correct option(s) related to the extraction of iron from its ore in the blast furnace operating in the temperature range $900-1500\text{ K}$ is(are)

The extraction of iron in a blast furnace is a masterpiece of industrial chemistry, a towering inferno where raw earth is transformed into the backbone of modern civilization. But a blast furnace isn't just a hot pot; it's a carefully orchestrated sequence of temperature zones, each hosting its own unique chemical symphony. In this problem, we are zooming into the middle section of the furnace, where the temperature ranges from $900\text{ K}$ to $1500\text{ K}$. Let's break down exactly what happens in this crucial zone and evaluate our options.

Imagine the raw materials tumbling down from the top of the furnace: iron ore, coke, and limestone. As they descend into the $900-1500\text{ K}$ zone, the heat becomes intense enough to trigger the decomposition of limestone (${\text{CaCO}}_3$).

This newly formed calcium oxide ($\text{CaO}$) is highly basic. The iron ore contains acidic impurities, primarily silica (${\text{SiO}}_2$), which we call gangue. The basic $\text{CaO}$ acts as a flux, eagerly reacting with the acidic ${\text{SiO}}_2$ to form a molten compound called calcium silicate (${\text{CaSiO}}_3$), commonly known as slag.

This slag is lighter than molten iron and floats on top of it, protecting the iron from being re-oxidized. Because this vital purification step happens right in our temperature range, Option (A) is absolutely correct.

As the iron oxides are reduced and the metal melts, it trickles down towards the hearth at the bottom of the furnace. But it doesn't arrive pure. Along its fiery journey, the molten iron acts like a sponge, absorbing carbon from the burning coke, as well as traces of sulfur, phosphorus, and silicon.

The iron that collects at the very bottom is known as pig iron. Due to the intense carbon-rich environment it just passed through, pig iron typically contains about $4\%$ carbon. This high carbon content makes it quite brittle, but it is the essential first product of the blast furnace. Thus, Option (B) is a correct statement.

Now, let's talk about the reducing agent. While solid carbon (coke) can reduce iron oxide directly at very high temperatures, the heavy lifting in the middle and upper zones is done by carbon monoxide ($\text{CO}$) gas. But where does this $\text{CO}$ come from?

As carbon dioxide (${\text{CO}}_2$) gas rises from the combustion zone at the bottom, it encounters white-hot solid coke in the $900-1500\text{ K}$ region. Here, an endothermic reaction known as the Boudouard reaction takes place:

This reaction consumes heat but produces the vital $\text{CO}$ gas that will rise further up to reduce the incoming iron ore. Since this conversion happens precisely in our target temperature range, Option (C) is correct.

Finally, what comes out of the top of the furnace? The gases that escape are a mixture of the unreacted nitrogen (${\text{N}}_2$) from the air blast, carbon dioxide (${\text{CO}}_2$) produced from reduction and limestone decomposition, and some leftover carbon monoxide ($\text{CO}$).

Notice what is missing? There is no nitrogen dioxide (${\text{NO}}_2$). The conditions inside a blast furnace are highly reducing, making the formation of highly oxidized nitrogen species like ${\text{NO}}_2$ impossible. Therefore, Option (D) is incorrect.

By carefully analyzing the chemical environment and temperature profile of the blast furnace, we can confidently conclude that the correct statements are (A), (B), and (C). Mastering these zone-specific reactions is the key to conquering metallurgy questions in JEE!