Extraction of metals

Types of extraction

Methods of extraction

Many metals are found in the Earth's crust as ores. An ore is usually a compound of the metal mixed with impurities. When the metal is dug up, a method must be used to separate the metal from the rest of the ore. This is called extracting the metal.

The method of extraction depends on how reactive the metal is. The more reactive the metal, the more difficult it is to extract from its compound.

Electrolysis

Electrolysis is the most powerful extraction method. But it takes a lot of electricity and that makes it expensive. Hence, electrolysis is only used for the most reactive metals.

Examples of the different methods of extraction

Electrolysis: Used in extracting aluminium and extracting sodium from rock salt.

In the case of the rock salt, it is first melted in giant steel tanks:

The extraction of aluminium is dealt with in a separate quick learn within this topic.

Heating with Carbon monoxide: Used for extracting iron from iron ore using the blast furnace.

Roasting in Air: Used in extracting copper from copper (I) sulphide (copper pyrites).

The copper is extracted by roasting the ore in air.

Recycling metals

Metals are non-renewable resources. This means once dug up it cannot be replaced. Hence, the supply will eventually run out.

For example: it is expected that tin will run out within the next 15 years and copper in the next 40 years!

Therefore, the recycling of these two useful metals and others such as iron and aluminium is most important.

In recycling, metals are melted down before reshaping into their new use. However, this can be costly. Recycling companies will only recycle if it is economical!

The blast furnace

How to extract iron from its ore

The method

Three substances are needed to enable to extraction of iron from its ore. The combined mixture is called the charge:

Iron ore, haematite - often contains sand with iron oxide, Fe2O3.

Limestone (calcium carbonate).

Coke - mainly carbon.

The charge is placed a giant chimney called a blast furnace. The blast furnace is around 30 metres high and lined with fireproof bricks. Hot air is blasted through the bottom.

Several reactions take place before the iron is finally produced.

Oxygen in the air reacts with coke to give carbon dioxide:

The limestone breaks down to form carbon dioxide:

Carbon dioxide produced in 1 + 2 react with more coke to produce carbon monoxide:

The carbon monoxide reduces the iron in the ore to give molten iron:

The limestone from 2, reacts with the sand to form slag (calcium silicate):

Both the slag and iron are drained from the bottom of the furnace.

The slag is mainly used to build roads.

The iron whilst molten is poured into moulds and left to solidify - this is called cast iron and is used to make railings and storage tanks.

The rest of the iron is used to make steel.

The electrolysis of bauxite

How to extract aluminium from its ore

The method

The bauxite (red-brown solid) - aluminium oxide mixed with impurities - is extracted from the earth.

The extracted aluminium oxide is then treated with alkali, to remove the impurities. This results in a white solid called aluminium oxide or alumina.

The alumina is then transported to huge tanks. The tanks are lined with graphite, this acts as the cathode. Also blocks of graphite hang in the middle of the tank, and acts as anodes.

The alumina is then dissolved in molten cryolite - this lowers the melting point - saves money!

Electricity is passed and electrolysis begins. Electrolysis is the decomposition of a compound using electricity.

When dissolved, the aluminium ions and oxide ions in the alumina can move.

At the cathode:

Here the aluminium ions receive electrons to become atoms again:

At the anode:
The oxide ions lose electrons to become oxygen molecules, O:

Uses of aluminium:

1. Shiny metal - used as jewellery.

2. Low density - used to make aeroplanes and trains.

3. Non-toxic - used in drink cans.