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Copper is a reddish coloured lustrous metal. It is characterised by

1. Atomic number 29
2. Relative atomic mass 63.546
3. Relative density 8.93
4. Melting point 1083.4^OC
5. Boiling point 2582^OC
6. Is highly malleable and ductile.
7. a good conductor of heat and electricity.

Copper constitutes about 0.00001% of the earth’s crust. Its deposits, however are concentrated. In the combined state it exists as sulphides, carbonates. The main ores of copper are copper pyrites (CuFeS₂), Copper glance (Cu₂S), cuprite (Cu₂O) and malachite (CuCO₃Cu(OH)₂).

Copper is usually extracted by the smelting process. This process is also called as the dry process. This process consists of the following phases.

1. CONCENTRATION

The ore is concentrated by the froth floatation process.

2. ROASTING

In roasting the concentrated ore is heated strongly in a current of air. During roasting the impurities are oxidised and are then removed. The following reactions take place during roasting.

S + O₂ è SO₂

4As + 3O₂ è 2As₂O₃

4Sb + 3O₂ è 2Sb₂O₃

2CuFeS₂ + O₂ è Cu₂S + 2FeS + SO₂

2FeS + 3O₂ è 2FeO + 2SO₂

2Cu₂S + 3O₂ è 2Cu₂O + 2SO₂

3. SMELTING

the roasted ore is mixed with coke and silica and is transferred to a small blast furnace. The mixture is then heated in the presence of excess air. The following reactions take place inside the blast furnace.

FeS + Cu₂O è FeO + Cu₂S

2FeS + 3O₂ è 2FeO + 2SO₂

FeO + SiO₂ è FeSiO₃ (slag)

The lowest part of the furnace consists of a shallow hearth is which the molten mass, consisting of Cuprous Sulphide with a little iron sulphide, gets collected. This molten mass is also known as matte.

BESSEMERISATION

Th matte, obtained above, is transferred to another furnace, called the Bessemer converter. A little sand is added to it and a blast of hot air is blown through the mixture. The following reactions take place in the Bessemer converter.

2FeS + 3O₂ è 2FeO + 2SO₂

FeO + SiO₂ è FeSiO₃

2CuS + 3O₂ è 2Cu₂O + 2SO₂

Cu₂S + 2Cu₂O è 6Cu + SO₂

The molten copper is now poured off and is allowed to cool. During the process of cooling the sulphur dioxide comes out and large blisters are formed on the surface. The copper obtained from this process is 98% pure, and is refined electrolytically.