CHAPTER# 02 XII CHEMISTRY
Q Describe how 99.99% pure copper is obtained from its chalcopyrite ore.
METALLURGY OF COPPER
OCCURRENCE
Copper is widely distributed in free as well as incombined states mainly as
oxides, sulphides and carbonates – The chief ores are cuprite (Cu2O), Chalcocite
(Cu2S), Chalcopyrite (CuFeS2), malachite [CuCO3.Cu(OH)2] and azurite
[2CuCO3.Cu(OH)2].
EXTRACTION OF COPPER
Copper is extracted mainly from chalcopyrite which contains 6% Cu. Following
processes are used for its extraction.
(i) Concentration: The finely divided copper ore is added into oily water. This
mixture is then agitated by blowing air whereby stony matter floats on the surface
and pure ore is separated.
(ii) Roasting: The concentrated pure ore is heated strongly in a stream of air in a
furnace to remove volatile impurities. During heating the pure ore is converted
into FeO, Cu2S and SO2.
2CuFeS2 + 4O2 2FeO + Cu2S + 3SO2
The molten mixture of Cu2S and FeO is called matte.
(iii) Smelting: The roasted ore is mixed with silica, SiO2 which separates FeO as
ferrous silicate (FeSIO3) as a slag which floats on the surface of molten matte of
copper.
FeO + SiO2 FeSiO3
Bessemerization
The molten matte of copper containing Cu2S, un reacted FeO and SiO2, is heated
strongly in the presence of excess of air in the Bessemer Converter, where cuprous
sulphide is reduced to impure copper called blister copper.
2CuS + 3O2 2Cu2O + 2SO2
2Cu2O + Cu2S 6Cu + SO2
The un reacted FeO is then changes into ferrous silicate when reacts silica (SiO2).
REFINING OF COPPER
Blister copper is refined by electrolysis. A block of blister copper is dipped into
a tank containing CuSO4 solution and H2SO4 dilute. Blister copper acts as an anode
and a thin plate of pure copper is used as a cathode. On electrolysis pure copper
deposits at the cathode while blister copper dissolves from the anode into the
solution. Thus the impure copper dissolves on one electrode and appears as a pure
copper on the other electrode.
Cu Cu2+ + 2e at anode
Cu + 2e Cu
2+ at cathode
Where impurities are fall to bottom of cell as a sludge or anode mud. The copper
obtained in this condition is 100% pure copper.
