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Extraction of Metals

Extraction of Copper.

Copper is sometimes found as native metal.

Copper ores include copper(II) oxide and copper(II) sulfide.
Copper(II) oxide can be reduced by reaction with carbon.

Some copper ores may contain only small amounts of copper.
These are called low grade ores and have less than 1% copper
but they are still used because copper is so valuable.
Bioleaching and phytomining are increasingly used
to extract copper from low grade ores (see below).

The traditional method of extraction is to heat the copper sulfide.
Copper(II) sulfide gives copper and sulfur dioxide during
thermal decomposition. Thermal decomposition means that the
compound breaks down into other substances when it is heated.
Thermal decomposition is an endothermic reaction.
copper(II) sulfide      copper  +  sulfur dioxide
CuS_(s)                           Cu_(s)       +       SO_2(g)
The impure copper which results is called blister copper.
The disadvantage of this method is that it uses a lot of energy.
If sulfur dioxide escapes into the atmosphere it causes pollution.
The advantage is that it is fast.

Bioleaching.
Some bacteria can live by using the energy of
the bond between sulfur and copper. This separates the
metal from the ore and is called bioleaching.
It has the advantage that it is very energy efficient
typically using only 30% to 50 % of the traditional method.
It has the disadvantage that it is very slow.

Phytomining.
Some plants absorb metal compounds (including copper)
when they grow. The plants can then be burned and the
metal is extracted from the ash. The process is called phytomining
and it can also be used to extract metals from contaminated land.
Brassicas (the cabbage family)
can extract metals including cadmium, cobalt and nickel.

Copper can also be extracted by displacement
from a copper salt solution using scrap iron.

Pure copper (99·99%) is needed for good electrical conductivity.
Pure copper is obtained by electrolysis.

About half of the copper used each year in the UK is recycled.

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