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Science

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 [crust: The outer layer of the Earth, on top of the mantle. It is between 6 and 48 kilometres thick and includes the continents and the ocean floor. ] contains metals and metal compoundscompounds: Substances formed by the chemical union (involving bond formation) of two or more elements. 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 [electrolysis: Electrolysis is the decomposition (separation or break-down) of a compound using an electric current. ], while a less-reactive metal such as iron may be extracted by reductionreduction: Reduction is a reaction in which oxygen is removed from a substance. Reduction also means a gain in electrons. 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.

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