Extraction of Metals

General Description.

A solid element or compound which occurs naturally
in the Earth's crust is called a mineral.
A mineral which contains a high enough percentage of a metal
for economic extraction is called a metal ore.
Economic extraction means that the cost of
getting the metal out of the ore is sufficiently less than
the amount of money made by selling the metal.

The most common metal ores are oxides and sulfides.
Sulfides are the oldest ores, formed in the Earth's history
when there was a lot of sulfur from volcanic activity.
Oxides formed later when photosynthesis in plants
released large amounts of oxygen into the atmosphere.

Metal ore deposits are a finite resource
(there are only a certain amount of them)
and non-renewable
(once used, they are gone and will not be replaced).

Many metals are obtained today from recycling
(melting and refining) scrap metals.
About half of the aluminium, copper, lead, steel and tin
which are used in the UK come from recycled scrap metal.

A metal above carbon in the reactivity series
may be extracted from its ore by electrolysis.

A metal below carbon in the reactivity series (zinc to silver)
may be extracted from its ore by heating with carbon.
The metal is displaced from its non-metal anion
by the more reactive carbon.
Carbon is used because it is readily available and cheap
(coke or charcoal are both carbon).
The metal in the ore is said to be reduced by reaction with carbon.

Hydrogen may be used to reduce metals
which are lower than itself in the reactivity series,
but since it is more expensive than carbon
it is only used on a large scale for the extraction of tungsten,
to avoid the formation of tungsten carbide.

Gold and platinum occur in the Earth as native metal,
which means that they are found as the element, not the compound,
and so do not need to be reduced.
Silver and copper may also be found as native metal.

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