METALLURGY OF COPPER
 
 
 
IMPORTANT ORES OF COPPER
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   Copper pyrite or chalcopyrite (CuFeS2).
   Chalocite (Cu2S) or copper glance.
   Malachite green [CuCO3.Cu(OH)2].
   Azurite blue [2CuCO3.Cu(OH)2].
   Bornite (3Cu2S.Fe2S3) or peacock ore.
   Melaconite (CuO) etc.
EXTRACTION OF COPPER FROM SULPHIDE ORE
   Large amount of copper are obtained from copper pyrite (CuFeS2) by smelting. Ores containing 4% or    more copper are treated by smelting process. Very poor ores are treated by hydro-metallurgical process.
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EXTRACTION OF COPPER BY SMELTING PROCESS
   Following steps are involved in the extraction of copper.
CONCENTRATION
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   The finely crushed ore is concentrated by Froth-Floatation process. The finely crushed ore is suspended in    water containing a little amount of pine oil. A blast of air is passed through the suspension. The particles    get wetted by the oil and float as a froth which is skimmed. The gangue sinks to the bottom.
ROASTING
   The concentrated ore is then roasted in a furnace in the presence of a current of air. Sulphur is oxidized    to SO2 and impurities of arsenous and antimony are removed as volatile oxides.
   The following reaction takes place.
2CuFeS2 + O2 è Cu2S + 2FeS + SO2
S + O2 è SO2
4As + 3O2 è As2O3
4Sb + 3O2 è 2Sb2O3
   Cuprous sulphide and ferrous sulphide are further oxidized into their oxides.
2Cu2S + 3O2 è 2Cu2O + 2SO2
2FeS + 3O2 è2FeO + 2SO2
SMELTING
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   The roasted ore is mixed with coke and silica (sand) SiO2 and is introduced in to a blast furnace. The hot    air is blasted and FeO is converted in to ferrous silicate (FeSiO3).
FeO + SiO2 è FeSiO3
Cu2O + FeS è Cu2S + FeO
   FeSiO3 (slag) floats over the molten matte of copper.
BESSEMERIZATION
 
   Copper metal is extracted from molten matte through bessemerization . The matte is introduced in to    Bessemer converter which uphold by tuyers. The air is blown through the molten matte. Blast of air    converts Cu2S partly into Cu2O which reacts with remaining Cu2S to give molten copper.
2Cu2S + 3O2 è 2Cu2O + 2SO2
2Cu2O + Cu2Sè 6Cu + SO2
   The copper so obtained is called "Blister copper" because, as it solidifies, SO2 hidden in it escapes out    producing blister on its surface.
IMPURITIES IN BLISTER COPPER AND THEIR EFFECTS
 
   Blister copper is 99% pure. It contains impurities mainly iron but little amount of As, Zn, Pb, Ag and Au    may also be present. These impurities adversely affect the electrical as well as mechanical properties of    copper. Therefore, they must be removed.
REFINING OF COPPER
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   Blister copper is refined by electrolysis. Blocks of blister copper are used as anodes and thin sheets of pure    copper act as cathodes. The cathode plates are coated with graphite in order to remove depositing    copper. The electrolyte is copper sulphate (CuSO4) mixed with a little amount of H2SO4 to increase the    electrical conductivity. Optimum potential difference is 1.3 volt for this electrolytic process. During    electrolysis, pure copper is deposited on the cathode plates and impurities which are soluble and fall to the    bottom of the cell as anode mud or sludge.
ELECTROCHEMICAL CHANGES DURING ELECTROLYSIS
 
Cu è Cu+2 + 2e- (at the anode)
Cu+2 +2e-è Cu (at the cathode)
This electrically refined copper is 100% pure.
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