The extraction of Iron and its impact on the environment

GENERAL OVERVIEW

Iron is extracted through a method called reduction. Raw materials used in the extraction of iron are:

- Haematite (contains iron(III) oxide, Fe2CO3) [Figure 1: Haematite]

Figure 1: Haematite

- Coke (contains carbon, C) [Figure 2: Raw coke]

Figure 2: Raw coke

- Limestone (contains calcium carbonate) [Figure 3: Limestone]

Figure 3: Limestone

Oxygen has to be removed from iron(III) oxide chemically to obtain iron. Iron(III) oxide is reduced when oxygen is removed from it. A blast furnace is used for this process [Figure 4].

Figure 4: A blast furnace

WHAT IS A BLAST FURNACE?
A blast furnace is a structure which spans over 50 metres, and the walls of the furnace are lined with refractory bricks. It is heated by blasts of hot air, and the temperature at the centre of the furnace is about 1500°C.

HOW IS IRON EXTRACTED FROM ITS ORE?

Haematite, coke and limestone are fed into the furnace through the top. The following process takes place inside the blast furnace:

Coke is added to haematite as it acts as a reducing agent for iron(III) oxide. Carbon, which comes into contact with haematite, reduces some of the iron(III) oxide. 

Reduction of iron(III) oxide:
iron(III) oxide + carbon --> iron + carbon dioxide
2 Fe2CO3 (s) + 3 C (s) --> 4 Fe (l) + 3 CO2 (g)

When carbon dioxide (made from coke burning in the hot blasts of air) reacts with more hot coke, carbon monoxide is formed (this is why hot air is blasted: to produce heat, and allow the coke to burn). Carbon monoxide reduces most of the iron(III) oxide.

Coke burning in oxygen:
carbon + oxygen --> carbon dioxide
C (s) + O2 (g) --> CO2 (g)

Carbon dioxide reacting with more hot coke to form carbon monoxide:
carbon dioxide + carbon --> carbon monoxide
CO2 (g) + C (s) --> 2 CO (g)

Carbon dioxide reducing iron(III) oxide:
iron(III) oxide + carbon monoxide --> iron + carbon dioxide
Fe2CO3 (s) + 3 CO (g) --> 2 Fe (l) + 3 CO2 (g)

Due to the high temperature inside the furnace, iron forms as a liquid. It sinks to the bottom of the surface, where it is tapped off.

Limestone is added to remove acidic impurities (silicon dioxide, SiO2: sandy bits of rock found in the haematite ore).

Limestone decomposing in the hot furnace:
calcium carbonate --> calcium oxide + carbon dioxide
CaCO3 (s) --> CaO (s) + CO2 (g)

Calcium oxide is a base, therefore it reacts with with silicon dioxide to form molten calcium silicate (or slag).

Formation of calcium silicate:
calcium oxide + silicon dioxide --> calcium silicate
CaO (s) + SiO2 (s) --> CaSiO3 (l)

At the base of the furnace, slag floats on top of the molten iron. It is then cooled and used for making roads. The following figure depicts the inside of a blast furnace, and how iron is extracted from haematite [Figure 5].

Figure 5: The inside of a blast furnace

IMPACTS ON THE ENVIRONMENT DUE TO THE EXTRACTION OF IRON

Impacts on the environment due to the extraction of iron from haematite does not only start during the extraction of iron from the ore - it starts when the raw materials are being mined and transported. The following are problems which arise from these processes:

From mining and transporting of raw materials
- Air pollution
- Noise pollution
- Loss of land (due to mining of haematite, coke and limestone)

From extraction of iron from haematite
- Atmospheric pollution (from gases such as carbon dioxide - which contributes to the greenhouse effect; carbon monoxide, which is poisonous, and sulfur dioxide, which is also poisonous and causes acid rain)
- Tailings (normally produced as slurry) are large amounts of waste produced by ore mills, and they are dumped into ponds which come from natural valleys. 
- Loss of land (from the building and size of chemical plant)
- Noise pollution
- Disposal of slag (some of the slag do not end up being used to make roads - instead, they are simply dumped)

SOLUTIONS IN PLACE TO ADDRESS PROBLEMS

Recycling is one solution which can address problems caused by the extraction of iron. This is done through recycling and using scrap metals instead of extracting and mining for raw materials. For example, old iron (in forms such as cars) can be melted and reused.

Through recycling, not only can production costs be reduced - raw materials and energy can be saved as there would be no need for those raw materials to be extracted, and for iron to be extracted from haematite. The different types of pollution mentioned above can be avoided, and there would be no waste products produced. Thus, these waste materials will not be present to cause harm to the environment.