Question

In a blast furnace, iron oxide is reduced by:
This question has multiple correct options
[A] A hot blast of air
[B] Carbon monoxide
[C] Carbon
[D] Silica

Answer 1

Hint: We often come across the term blast furnace in metallurgy. In the blast furnace, iron ore is placed with coke and to this a blast of hot air forms a gas which is responsible for the reduction. You can use this to answer the given question.

Complete Solution :
> We know that a blast furnace is a huge furnace made up of steel which is lined with refractory material so that the high heat produced inside does not escape. Now let us discuss the reactions taking place inside the blast furnace.
> Let us take the example of iron extraction from its ore to answer this question.
> Iron is obtained from Hematite and magnetite. These two are the most common ore of iron.
- Iron is extracted from hematite by introducing the ore along with limestone and coke in the blast furnace. The main impurity in hematite is iron bearing metal silicates.
- Extraction process begins by adding carbon or coke to the molten ore in a blast furnace where reduction of ferrous oxides takes place. Coke that is basically carbon reacts with oxygen in the blast furnace and forms carbon monoxide and carbon monoxide reduced iron oxides. We can write the reactions as-
\[\begin{align}
 & 2C(s)+{{O}_{2}}(g)\to 2CO \\
 & 3CO+F{{e}_{2}}{{O}_{3}}\to 2Fe+3CO \\
\end{align}\]
- Then, a flux mainly limestone is added to form lime-silica slag which floats on top of the furnace and can be removed.
- Limestone decomposes due to the heat in the furnace and forms calcium oxide which reacts with silicon based impurity.
\[CaC{{O}_{3}}(s)\rightleftharpoons CaO(s)+C{{O}_{2}}(g)\]
- Calcium oxide reacts with the impurity and forms a slag which can be removed from the molten metal. We can write the reaction as-
\[CaO+Si{{O}_{2}}\to CaSi{{O}_{3}}\]
- The slag helps to protect it from re-oxidation and also removes the impurities whose solubility is greater in slag than in ferrous metal.
We can understand from the above discussion that iron oxide is reduced by carbon monoxide.

So, the correct answer is “Option B”.

Note: 

> A blast furnace is generally used during the extraction of pig iron from ores but it is also used for extraction of copper and lead.
> As we can see that both oxides and sulfides are found in the furnace at the same time but the oxides are converted into slag in presence of silica and the molten matte is settled in the bottom.