How Extraction of Copper from Copper Pyrites? - QS Study
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Extraction of copper from copper pyrites involves the following steps.

Crushing and concentration

The ore is crushed and then concentrated by froth-floatation process.

Roasting

The concentrated ore is heated strongly in the reverberatory furnace, in excess of air. During roasting,

  • Moisture is removed.
  • The volatile impurities are removed.
  • Sulphur, phosphorus, arsenic and antimony which are present as impurity are removed as volatile oxides.

S + O2 → SO2

P4 + 5O2 → 2P2O5

4As + 3O2 → 2As2O3

  • The copper pyrite is partly converted into sulphides of copper and iron.

2CuFeS2 + O2 → Cu2S + 2FeS + SO2

2FeS + 3O2 → 2FeO + 2SO2

Smelting

The roasted ore is mixed with powdered coke and sand and is heated in a blast furnace. It is made of steel plates lined inside with fire clay bricks. Hot air at 800°C is introduced from the tuyers near the base of the furnace. As a result, the following changes occur.

  • 2FeS + 3O2 → 2FeO + 2SO2
  • FeO + SiO2 → FeSiO3 (fusible slag)
  • 2Cu2S + 3O2 → 2Cu2O + 2SO2
  • Cu2O + FeS → Cu2S + FeO
  • FeO + SiO2 → FeSiO3 (fusible slag)

As a result of smelting, two separate molten layers are formed at the bottom of the furnace. The upper layer consists of slag and is removed as a waste while the lower layer is called matte. It chiefly consists of cuprous sulphide and some unchanged ferrous sulphide.

Refining: Blister copper contains about 2% of impurities and it is purified by electrolytic refining.