Describe the extraction of iron from its ore (ores, stages, and methods of extraction)

An ore is a rock or mineral from which a metal can be economically extracted. The main ores of iron used in industrial extraction are:

• Haematite (Fe₂O₃) — iron(III) oxide, the most important ore
• Magnetite (Fe₃O₄) — iron(II, III) oxide
• Siderite (FeCO₃) — iron(II) carbonate

Haematite is the most widely used ore because it contains a high percentage of iron and is abundant in many parts of the world.

The industrial extraction of iron from its ore is carried out in a tall furnace called a blast furnace. The blast furnace is continuously fed with three main materials from the top:

1. Iron ore (crushed and washed)
2. Coke (carbon-rich fuel obtained from coal)
3. Limestone (calcium carbonate, CaCO₃)

Hot air is blown into the furnace from the bottom through tubes called tuyeres. This creates the high temperatures needed for the chemical reactions to occur.

The extraction of iron in the blast furnace occurs in three main stages:

Stage 1: Production of Heat

Near the base of the furnace, where the hot air blast enters, coke burns in the oxygen of the air to produce carbon dioxide. This reaction releases a large amount of heat, raising the temperature inside the furnace to about 2000°C.

$\text{C} + \text{O}_2 \rightarrow \text{CO}_2 + \text{heat}$

Stage 2: Production of Reducing Agent

Higher up in the furnace, the carbon dioxide produced in Stage 1 meets more hot coke and is reduced to carbon monoxide. This carbon monoxide is the main reducing agent that will later remove oxygen from the iron ore.

$\text{CO}_2 + \text{C} \rightarrow 2\text{CO}$

Stage 3: Reduction of Iron Ore

At the higher regions of the furnace, carbon monoxide (and sometimes direct carbon) reduces the iron ore to molten iron. The haematite ore loses its oxygen to become pure iron.

$\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$

The molten iron, being denser, collects at the bottom of the furnace.

Limestone (calcium carbonate) plays an important role in the extraction process:

1. When heated in the furnace, limestone decomposes to produce quicklime (calcium oxide) and carbon dioxide:

$\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$

2. The quicklime (CaO) reacts with acidic impurities (such as silica, SiO₂) present in the ore to form molten slag:

$\text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3$

3. The slag, being less dense than molten iron, floats on top and can be easily removed. This helps purify the iron.

The iron and slag are tapped off separately at the bottom of the furnace. The iron obtained is called pig iron or cast iron, which contains about 2–4% carbon and other impurities.

Pig Iron (Cast Iron)

This is the crude iron obtained directly from the blast furnace. It contains 2–4% carbon and is brittle. It is used to make items such as water pipes, cooker bases, and railings.

Wrought Iron

Wrought iron is the purest form of commercial iron, containing about 99% iron and less than 0.25% carbon. It is produced by melting pig iron and stirring it in a furnace, which oxidizes the carbon and impurities to form slag. Wrought iron is malleable and can be hammered into shape at high temperatures. It is used to make nails, chains, gates, and farm equipment.

Steel

Steel is an alloy of iron containing 0.15–2% carbon. It is produced by removing impurities from molten pig iron using oxygen jets and then adding calculated amounts of carbon and other metals (such as manganese, nickel, or chromium) to achieve the desired properties. Steel is strong, hard, and widely used in construction, manufacturing vehicles, and making tools.

In a blast furnace, 1000 kg of haematite (Fe₂O₃) is fed into the furnace along with coke and limestone. Calculate the theoretical mass of iron produced if the ore is 80% pure Fe₂O₃.

Solution:

Molar mass of Fe₂O₃ = (2 × 56) + (3 × 16) = 112 + 48 = 160 g/mol

Mass of pure Fe₂O₃ in ore = 80% × 1000 kg = 800 kg = 800,000 g

Moles of Fe₂O₃ = 800,000 ÷ 160 = 5,000 moles

From the equation: Fe₂O₃ + 3CO → 2Fe + 3CO₂

1 mole of Fe₂O₃ produces 2 moles of Fe

Moles of Fe produced = 5,000 × 2 = 10,000 moles

Molar mass of Fe = 56 g/mol

Mass of iron produced = 10,000 × 56 = 560,000 g = 560 kg

Therefore, the theoretical yield of iron is 560 kg.

In Tanzania, iron and steel are used extensively in construction projects such as building bridges, school classrooms, and market stalls. For example, when constructing a classroom in Dodoma, builders use steel bars (reinforcement) made from iron extracted from ores to strengthen the concrete foundation. Understanding how iron is extracted helps engineers and technicians appreciate the quality control needed in producing strong construction materials, ensuring buildings last many years in Tanzania's climate.