Extraction of copper from copper pyrites (CuFeS2)

Copper is extracted from its principal ore copper pyrites (CuFeS₂). The ore is concentrated by froth flotation process. The concentrated ore is roasted in a reverberatory furnace when the following reactions occur.
 1. The volatiles like sulphur and arsenic escape as gases

    S + O₂ --------------> SO₂ 4AS + 3O₂ --------------->2AS₂O₃

 2. Copper pyrites is converted to a mixture of Cu₂S and FeS

    2CuFeS₂ + O₂ ---------------> Cu₂S + 2FeS + SO₂

3. The sulphides of Cu and Fe are partially oxidized

 2Cu₂S + 3O₂ <=======> 2Cu₂O + 2SO₂

 2FeS + 3O₂ <========> 2FeO + 2SO₂

Smelting in extraction of copper 

 The roasted ore mixed with silica as flux is heated in a blast furnace by a blast of hot air. Most of the FeO is removed as a slag and a molten mixture of Cu₂S and FeS called matte, get collected in the hearth of the furnace.

      FeO + SiO₂ -----------> FeSiO₃
      gangue + flux ------------> Slag

Bessemerisation in extraction of copper

The molten matte (CU₂S + FeS) is transferred to a Bessemer converter, a pear shaped vessel lined with MgO or SiO₂ and heated by hot air blown through tuyers and mounted in such a way that it can be filled in any direction. It is mixed with some silica as flux and heated by passing hot air through tuyers.
 The air oxidises FeS to FeO, which combine with silica forming a slag.

 2FeS + 3O₂ --------------> 2FeO + 2SO₂

 FeO + SiO₂ --------------> FeSiO₃

 The blast of air is continued when excess silica is absorbed by the basic lining (MgO) of the converter. Cuprous sulphide is partially oxidised by air to cuprous oxide which then combine with the remaining cuprous sulphide to form copper.

 2Cu₂S + 3O₂ -----------> 2Cu₂O + 2SO₂

 Cu₂S + 2Cu₂O -----------> 6Cu + SO₂

The molten copper is poured out and allowed to cool. The sulphur dioxide escaping from the melt gets trapped in the cooler parts of the surface giving a blistery appearance for copper and hence it is called blister copper. Blister copper is further refined by poling and electrolytic method, as described in the refining of metals. The air oxidises FeS to FeO, which combine with silica forming a slag.

 2FeS + 3O₂ --------------> 2FeO + 2SO₂

 FeO + SiO₂ --------------> FeSiO₃

The blast of air is continued when excess silica is absorbed by the basic lining (MgO) of the converter. Cuprous sulphide is partially oxidised by air to cuprous oxide which then combine with the remaining cuprous sulphide to form copper.

2Cu₂S + 3O₂ -----------> 2Cu₂O + 2SO₂

 Cu₂S + 2Cu₂O -----------> 6Cu + SO₂

The molten copper is poured out and allowed to cool. The sulphur dioxide escaping from the melt gets trapped in the cooler parts of the surface giving a blistery appearance for copper and hence it is called blister copper. Blister copper is further refined by poling and electrolytic method, as described in the refining of metals.

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