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METALLURGY OF COPPER
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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. |
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EXTRACTION
OF COPPER FROM SULPHIDE ORE
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| 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. For latest information , free computer courses and high impact notes visit : www.citycollegiate.com |
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EXTRACTION
OF COPPER BY SMELTING PROCESS
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| Following steps are involved in the extraction of copper. | |||
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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. | |||
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ROASTING
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| 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. |
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2CuFeS2 + O2 è
Cu2S + 2FeS + SO2
S + O2 è SO2 4As + 3O2 è As2O3 4Sb + 3O2 è 2Sb2O3 |
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| Cuprous sulphide and ferrous sulphide are further oxidized into their oxides. | |||
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2Cu2S + 3O2 è
2Cu2O + 2SO2
2FeS + 3O2 è2FeO + 2SO2 |
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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). | |||
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FeO + SiO2 è
FeSiO3
Cu2O + FeS è Cu2S + FeO |
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| FeSiO3 (slag) floats over the molten matte of copper. | |||
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BESSEMERIZATION
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| 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. | |||
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2Cu2S + 3O2 è
2Cu2O + 2SO2
2Cu2O + Cu2Sè 6Cu + SO2 |
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| The copper so obtained is called "Blister copper" because, as it solidifies, SO2 hidden in it escapes out producing blister on its surface. | |||
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IMPURITIES
IN BLISTER COPPER AND THEIR EFFECTS
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| 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. | |||
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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. |
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ELECTROCHEMICAL
CHANGES DURING ELECTROLYSIS
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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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| For latest information , free computer courses and high impact notes visit : www.citycollegiate.com | |||