Metals - Sources, Oxidation and Reduction
Rocks, minerals and ores
Most metals are found in the Earth as part of a chemical compound. Naturally occuring compounds are called minerals. Rocks are mixtures of different minerals. Some rocks are metal ores. Very unreactive metals like gold can be found in the Earth as elements. Metal ores contain metal compounds and unwanted rock. The metal must be extracted from the ore.
The cost of the metal is higher if:
- The ore is difficult to obtain
- The method of extraction is expensive
- The ore contains a low percentage of the metal
Iron is cheap as iron ore (haematite) is plentiful and inexpensive to extract. Gold has a high price because the ore is rare. Aluminium ore (bauxite) is plentiful but aluminium is expensive as it costs a lot to extract.
Some metals can be extracted by heating with Carbon, e.g. extracting iron.
iron oxide + carbon --> carbon dioxide + iron
Other metals must be extracted by electrolysis, e.g. extracting aluminium
aluminium oxide -----------> aluminium + oxygen