Extraction of metals

Metal ores are naturally occurring rocks that contain metals or metal compounds in sufficient amounts to make it worthwhile extracting them. The method used to extract a given metal from its ore depends upon the reactivity of the metal and how stable the ore is.

In each case the metal ions in the compound gain electrons to form atoms of the metal element.

Ores of very reactive metals have to be melted and electrolysed with a direct current (DC) supply of electricity.

The positive metal ions are attracted to the negative electrode where they accept electrons.

Example

sodium ions + electrons → sodium metal

Ores of reactive metals have to be heated with carbon or carbon monoxide in order to extract the metal.

Example

copper ions + carbon → copper metal + carbon dioxide

Ores of unreactive metals only need to be heated to obtain the metal.

Example

silver ions → silver metal + oxygen

Alloys

An alloy is a mixture of two or more elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone.

Alloys contain atoms of different sizes, which distort the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

Alloys have smaller particles between larger ones

It is more difficult for layers of atoms to slide over each other in alloys.

Copper, gold and aluminium are too soft for many uses. They are mixed with other metals to make them harder for everyday use:

• Brass which is used in electrical fittings, is 70% copper and 30% zinc.
• 18 carat gold used in jewellery, is 75% gold and 25% copper and other metals.
• Duralumin used in aircraft manufacture, is 96% aluminium and 4% copper and other metals.

Some alloys have more unusual properties. Nitinol is an alloy of nickel and titanium, and is known as a shape memory alloy. If nitinol is bent out of shape, it returns to its original shape when it is either heated or an electric current is passed through it. This property makes it useful for making spectacle frames - they will return to their original shape if they are put in hot water after they have been bent.