Copper
(Extraction)
Extraction Of Copper
Copper is widely distributed in
nature. It occurs in free as well as combined state. Blister copper is mainly
extracted from sulphide ores (copper pyrite). The extraction of Blister Copper
proceeds through following four steps.
Step I – Concentration
The sulphide ores are concentrated by
any of the following methods.
a. Gravity
Separation
The powdered ore is passed over a
wheel so that it falls in two section due to difference in specific gravity.
b. Forth
Floatation Process
The finely powdered copper pyrite ore
is introduced into water containing Rine oil. The suspension is vigorously
agitated with air. The stony matter settles to the bottom and the ore is
carried to the top in the forth. The object of this process is to increase the
concentration of copper in the ore.
Step II – Heating / Roasting
The concentrated ore is heated
strongly (roasted) in a multiple heater roaster (Reverberatory Furnace) in
excess of air in order to achieve the following.
1. To remove sulphur as sulphur
dioxide.
2. To remove arsenic and antimony as
their volatile oxides.
3. To convert the copper pyrite into
a mixture of cuprous sulphide and ferrous sulphide.
4. To partially oxidize cuprous
sulphide and ferrous sulphide to copper oxide and ferrous oxides respectively.
5. To remove fusible impurities and
moisture.
6. To change the ore into porous
form.
Step III – Smelting
The roasted ore is mixed with Silica
(SiO2) and smelted in a water jacketed
blast furnace about 5ft to 6ft high
and 1.6 m in diameter. It is a tower like structure made of steel sheet and
lined inside with firebricks. A blast of air is necessary for the combustion of
ore. This ore is blown through the pipes provided at the base. Since, most of
the heat is produced by the combustion of ore itself, therefore, small amount
of fuel is required. The cuprous oxide formed during roasting react with
unoxidized ferrous sulphide to form cuprous sulphide and ferrous oxide.
CuO + FeS —-> Cu2S + FeO
Silica act as flux, it reacts with
ferrous oxide to form fusible slag (Ferrous Silicate) because iron has more affinity
for oxygen than copper.
FeO + SiO2 —-> FeSiO3 (Slag)
Slag is removed from the slag hole
while a molten mass containing mostly cuprous sulphide, with a very little
ferrous sulphide is taken out from the bottom and is called Matte.
Step IV – Bessemerization
The molten is now transferred into
Bessemer converter. It is a pear shaped furnace made of steel plates and
provides with a basic lining like that of lime or Magnesium Oxide.
Diagram Coming Soon
The main features of this process is
that air is blasted through the molten matte. As a result, ferrous sulphide
still present gets oxidized to ferrous oxide and is removed as slag. Cuprous
sulphide is partially oxidized to oxide, which reacts with remaining cuprous sulphide
to form metallic copper.
Cu2S + 2Cu2O —-> 6Cu + SO2↑
The molten copper is run into sand
moulds and allowed to solidify. When it gives out absorbed SO2, it leaves
blister type appearance at the surface of the metal. The metal thus obtained is
known as Blister Copper. It is about 98% pure.
Refining
The crude copper obtained by the
above methods contain about 2% of impurities consisting of Fe, Ni, Zn and Ag.
It is refined by electrolysis. The process is carried out in a large tank lined
with lead. Thick plates of crude copper served as anode and thin plates of pure
copper act as cathode. The cathode is coated with oil which helps in easy
scraping of pure copper. These electrodes are dipped into electrolytic copper
sulphate solution. The electrolysis is then carried out by a current of 1.3
volts. The pure copper is deposited at the cathode while impurities like Fe,
Ni, Zn passes into solution and other like Ag and Au fall down as anode mud.
During electrolysis following reactions occur.
Cu0 —-> Cu11 + 2e- (At Anode)
Cu11 + 2e- —-> Cu0 (At Cathode)
Copper thus obtained is 99.99% pure
and is known as Electrolytic Copper.
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