Revision - Self reduction method

Copper

The concentrated ore is heated strongly with silicon dioxide (silica) and air or oxygen in a furnace or series of furnaces.

The Full Process

Large amount of copper are obtained from copper pyrite (CuFeS2) by smelting. Ores containing 4% or more copper are used and are treated by smelting process.

Concentration - Froth-Floatation process

The finely crushed ore is concentrated by Froth-Floatation process. The finely crushed ore is suspended in water containing a little amount of pine oil. A blast of air is passed through the suspension. The particles get wetted by the oil and float as a froth which is skimmed. The gangue sinks to the bottom.


Roasting

The concentrated ore is then roasted in a furnace in the presence of a current of air. Sulphur is oxidized to SO₂ and impurities of arsenous and antimony are removed as volatile oxides.
The following reaction takes place.

2CuFeS₂ + O₂ → Cu₂S + 2FeS + SO₂
S + O₂ è SO₂
4As + 3O₂ → As₂O₃
4Sb + 3O₂ → 2Sb₂O₃

Cuprous sulphide and ferrous sulphide are further oxidized into their oxides.

2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
2FeS + 3O₂ → 2FeO + 2SO₂

Smelting

The roasted ore is mixed with coke and silica (sand) SiO₂ and is introduced in to a blast furnace. The hot air is blasted and FeO is converted in to ferrous silicate (FeSiO₃).

FeO + SiO₂ → FeSiO₃

Cu₂ O + FeS → Cu₂ S + FeO


FeSiO₃ (slag) floats over the molten matte of copper.

Bessemerization

Copper metal is extracted from molten matte through bessemerization . The matte is introduced in to Bessemer converter which uphold by tuyers. The air is blown through the molten matte. Blast of air converts Cu₂S partly into Cu₂O which reacts with remaining Cu₂S to give molten copper.

2Cu₂ S + 3O₂ → 2Cu₂ O + 2SO₂
2Cu₂O + Cu₂ S → 6Cu + SO₂

The copper so obtained is called "Blister copper" because, as it solidifies, SO₂ hidden in it escapes out producing blister on its surface.

Removal of impurities from blister copper

Blister copper is 99% pure. It contains impurities mainly iron but little amount of As, Zn, Pb, Ag and Au may also be present. These impurities adversely affect the electrical as well as mechanical properties of copper. Therefore, they must be removed. Refining is used for this purpose.

Refining

Blister copper is refined by electrolysis. Blocks of blister copper are used as anodes and thin sheets of pure copper act as cathodes. The cathode plates are coated with graphite in order to remove depositing copper. The electrolyte is copper sulphate (CuSO₄) mixed with a little amount of H₂ SO₄ to increase the electrical conductivity. Optimum potential difference is 1.3 volt for this electrolytic process. During electrolysis, pure copper is deposited on the cathode plates and impurities which are soluble and fall to the bottom of the cell as anode mud or sludge.


Reactions during electrolysis at electrodes


Cu → Cu⁺² + 2e‾ (at the anode)
Cu⁺² +2e‾ → Cu (at the cathode)


We get copper is 100% pure copper from electrolytic refining.