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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


extraction of copper CuFeS2

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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