Extracting metals and making alloys
Metals are very useful. Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them: most everyday metals are mixtures called alloys.
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 become 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 high enough concentration to make it economic to extract the metal.
Ores are mined. They may need to be concentrated before the metal is extracted and purified. The economics of using a particular ore may change over time. For example, as a metal becomes rarer, an ore may be used when it was previously considered too expensive to mine.
Metals are produced when metal oxides are reduced (have their oxygen removed). The reduction method depends on the reactivity of the metal. For example, aluminium and other reactive metals are extracted by electrolysis, while iron and other less reactive metals may be extracted by reaction with carbon or carbon monoxide.
|Metals (in decreasing order of reactivity)||Method of extraction|
|extract by electrolysis|
|extract by reaction with carbon or carbon monoxide|
|extracted in various ways|
The method of extraction of a metal from its ore depends on the metal's position in the reactivity series.
Gold, because it is so unreactive, is found as the native metal and not as a compound [compound: A compound is a substance formed by the chemical union (involving bond formation) of two or more elements. ]. It does not need to be chemically extracted from its ore, but chemical reactions may be needed to remove other elements that might contaminate the metal.
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