Extraction of Copper

Extraction of Copper

Extraction of Copper

Copper Atomic Number: 29
Copper Electronic configuration: [Ar]3d104s1

The copper metal is extracted from copper pyrites. The various steps involved during extraction are:

  1. Concentration:
    The ore is concentrated by froth floatation process.

  2. Roasting:
    The concentrated ore is heated in the presence of excess of air in a reverberatory furnace. During heating temperature is kept below its melting point. Following changes are observed.

    1. Moisture is expelled

    2. Sulphur, arsenic and phosphorus impurities are expelled in form of their volatile oxides.

      S + O SO2

      4As + 3O 2As2O3

    3. Copper pyrite ore is converted to ferrous sulphide and cuprous sulphide

      2CuFeS2 + O Cu2S + 2FeS + S02

  3. Smelting:
    Mixture of roasted ore, powdered coke and sand is heated in blast furnace. Following changes are observed:

    1. Oxidation of ferrous sulphide takes place and ferrous oxide thus formed reacts with silica to form fusible slag, FeSiO3.

      2FeS + 3O2  2FeO + 2SO2

    2. Cuprous oxide which is formed as a result of oxidation is partially converted back into cuprous sulphide.

      Cu2S + 3O 2Cu2O + 2SO2

      Cu2O + FeS  Cu2S + FeO

      From the base of the furnace molten mass called matte is removed.

  4. Bessemerisation:
    The matte is transferred to bassemer converter, which is a pear-shaped furnace, lined from inside with magnesium oxide. Air blast in bessemer converter is added through Tuyers. The following reactions take place in the bessemer converter

    2Cu2S + 3O2  2Cu2O + 2SO2

    2FeS + 3O2  2FeO + 2SO2

    The iron oxides forms slag with silica.

    FeO + SiO2  FeSiO3

    The cuprous oxide reacts with more of Cu2S to form copper.

    2Cu2O + Cu2 6Cu + SO2

    After the completion of reaction, the molten copper is poured off. As it cools, it gives up the sulphur dioxide dissolved in it which comes out in the form of bubbles thus giving the shape of blisters to the surface of copper, which is therefore, known as Blister copper.

  5. Purification:

    1. Poling: The blister copper is purified by melting it in a reverberatory furnace where it is exposed to an oxidising atmosphere. The impurities are expelled as volatile oxides. During this process the molten mass is stirred with long poles of green wood. The process is known as poling. The reducing gases evolved from the wood prevent the oxidation of copper.

    2. Electrolytic purification: The crude copper obtained is then purified by electrolysis. Impure copper is made anode and a thin strip of pure copper is made cathode. An aqueous solution of copper sulphate, acidified with dil. H2SO4 is used as electrolyte. During electrolysis anode starts dissolving due to oxidation whereas copper cathode becomes thicker due to decomposition of copper.

      At anode: Cu  Cu2+ + 2e-

      At cathode: Cu2+ +2e-  Cu

      Impurities fall under anode and cathode mud.

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