Aluminium extraction

Aluminium is the most abundant (found in large quantities) metal on Earth. But it is expensive, largely because of the amount of electricity used up in theextraction process.

Aluminium ore is called bauxite. The bauxite is purified to yield a white powder -aluminium oxide - from which aluminium can be extracted.

The extraction is done by electrolysis. But first the aluminium oxide must be melted so that electricity can pass through it. Aluminium oxide has a very high melting point (over 2000°C) so it would be expensive to melt it. Instead, it is dissolved in moltencryolite - an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.

Diagram showing cell for aluminium extraction

The diagram shows an aluminium oxide electrolysis tank. Both the negative electrode (cathode) and positive electrode (anode) are made of graphite, a form of carbon.

Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.

Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away. As a result, the positive electrodes have to be replaced frequently. This adds to the cost of the process.

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Atoms

Atoms consist of electrons surrounding a nucleus that contains protons and neutrons. Neutrons are neutral, but protons and electrons are electrically charged: protons have a relative charge of +1 and electrons have a relative charge of -1.

Atoms and elements

All substances are made of tiny particles called atoms. An element is a substance that is made of only one sort of atom. There are about 100 different elements. These are shown in the periodic table, which is a chart with all the elements arranged in a particular way. The horizontal rows in the periodic table are called periods and the vertical columns are called groups. The elements in a group have similar properties to each other.

Metals and non-metals

The metals are shown on the left of the periodic table, and the non-metals are shown on the right. The dividing line between metals and non-metals is shown in red on the table below. You can see that most of the elements are metals.

The periodic table divided into non-metals and metals

Chemical symbols

The atoms of each element are represented by a chemical symbol. This usually consists of one or two different letters, but sometimes three letters are used for newly discovered elements. For example, O represents an oxygen atom, and Na represents a sodium atom.

The first letter in a chemical symbol is always an UPPERCASE letter, and the other letters are always lowercase. So, the symbol for a magnesium atom is Mg and not mg, MG or mG.

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