Problem 106 - A Complete Resource Book in Chemistry for JEE Main

Question

The chemical processes in the production of steel from haematite ore involve (a) reduction (b) oxidation (c) reduction followed by oxidation (d) oxidation followed by reduction

Step-by-Step Solution

Answer

(d) oxidation followed by reduction.

Step 1: Understand the Context of Steel Production

Steel production generally starts with iron ores like hematite (5e3O4"). Hematite is primarily iron (III) oxide, and in order to produce steel, the iron content needs to be extracted and purified.

Step 2: Identify the Initial Process

Hematite, being primarily iron (III) oxide (5e3O4), must first undergo a reduction process. The iron ore is reduced to iron by removing oxygen, usually in a blast furnace using carbon (coke) as a reducing agent.

Step 3: Consider Additional Processes

After reduction, the raw iron (known as pig iron) may go through additional processes to be purified of impurities such as carbon. During this stage, some controlled oxidation may occur to remove excess carbon and other elements.

Step 4: Determine Correct Sequence for Steel Production

In the production of steel from haematite, the essential process starts with the reduction of the iron ore to remove oxygen and extract iron. This is typically followed by any necessary oxidation to adjust carbon levels and impurities, if present.

Key Concepts

Reduction Process

The reduction process is a key step in the production of steel from haematite, the iron-containing ore. This stage is critical as it involves removing oxygen from the iron ore to extract pure iron. Haematite, chemically known as iron(III) oxide (Fe₂O₃), must undergo a chemical reaction where its oxygen is extracted. This is typically achieved in a blast furnace, where carbon in the form of coke acts as a reducing agent.

In this process, the carbon combines with oxygen from the haematite, forming carbon dioxide and liberating the iron:

• The overall chemical reaction can be represented as:

\[\text{Fe}_2\text{O}_3 + 3\text{C} \rightarrow 2\text{Fe} + 3\text{CO}_2\]
The furnace is maintained at high temperatures to facilitate this reaction, ensuring the efficient conversion of iron oxide to metallic iron. This forms a crude iron product known as pig iron, which still contains some impurities.

Oxidation in Metallurgy

Oxidation, although typically associated with rusting or corroding of metals, plays an interesting role in metallurgy, especially in the steel production process. Once the initial reduction has taken place, the pig iron obtained requires further purification. This is where controlled oxidation comes into play.

During this phase, oxygen is deliberately introduced to remove excess carbon from the pig iron. The process typically forms carbon dioxide or monoxide and helps adjust the carbon content to desired levels suitable for strong and durable steel.

• This oxidation converts unwanted impurities into oxides, making them easier to remove.
• Key reactions involve carbon converting to carbon dioxide and other impurities like silicon, phosphorous, and sulphur forming their respective oxides.

This harmonizing step is what allows the transformation from pig iron to steel, ensuring that the material properties are suited for various applications.

Blast Furnace

The blast furnace is the heart of the steel production process. It is a large steel structure lined with heat-resistant bricks that operates continuously, forming liquid iron from iron ore. This essential metallurgical apparatus carries out reduction and offers conditions suitable for the subsequent production steps.

Using a blast of hot air and compounds like coke and limestone, the furnace maintains high temperatures around 2000°C. This environment is necessary for breaking down iron ore:

• The upper parts of the furnace are loaded with iron ore, coke, and limestone, where initial reactions start.
• As these materials descend through the furnace, they encounter hotter zones facilitating reduction, primarily using coke.
• Gasses like carbon dioxide are produced and removed, while liquid iron trickles down to the bottom.

This process not only reduces iron oxide but also produces slag, which is removed to improve the iron quality. Thus, the blast furnace is fundamental to preparing raw iron before it undergoes further refining to become steel.