Chemistry (Metals)

Metals are very useful. Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them. For example, iron ore is used to make iron and steel. Copper is easily extracted, but ores rich in copper are becoming more difficult to find. Aluminium and titanium are metals with useful properties, but they are expensive to extract. Most everyday metals are mixtures called alloys.

Methods of Extracting Metals

The Earth's crust contains metals and metal compounds such as gold, iron oxide and aluminium oxide, but when found in the Earth these are often mixed with other substances. To be useful, the metals have to be extracted from whatever they are mixed with. A metal ore is a rock containing a metal, or a metal compound, in a high enough concentration to make it economic to extract the metal.

The method used to extract metals from the ore in which they are found depends on their reactivity. For example, reactive metals such as aluminium are extracted by electrolysis, while a less-reactive metal such as iron may be extracted by reduction with carbon or carbon monoxide.

Thus the method of extraction of a metal from its ore depends on the metal's position in the reactivity series:

Reactivity and Extraction Method

Metals - in decreasing order of reactivityReactivity

• potassium
• sodium
• calcium
• magnesium
• aluminium

extract by electrolysis carbon

• zinc
• iron
• tin
• lead

extract by reaction with carbon or carbon monoxide hydrogen

• copper
• silver
• gold
• platinum

extracted by various chemical reactions

Note that gold, because it is so unreactive, is found as the native metal and not as a compound, so it does not need to be chemically separated. However, chemical reactions may be needed to remove other elements that might contaminate the metal.

Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores such as

haematite contain iron oxide. The oxygen must be removed from the iron oxide to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions.

Carbon is more reactive than iron, so it can push out or displace the iron from iron oxide. Here are the equations for the reaction:

iron oxide + carbon    →    iron + carbon dioxide

2Fe₂O₃ + 3C    →    4Fe + 3CO₂

In this reaction, the iron oxide is reduced to iron, and the carbon is oxidised to carbon dioxide.

In the blast furnace, it is so hot that carbon monoxide can be used to reduce the iron oxide in place of carbon:

iron oxide + carbon monoxide    →    iron + carbon dioxide

Fe₂O₃ + 3CO    →    2Fe + 3CO₂

The raw material for extracting iron and their function in the process

Raw materialContainsFunction iron ore (haematite) iron oxide a compound that contains iron coke carbon burns in air to produce heat…