Extraction of Copper from Copper pyrite

The principle ore of copper is copper pyrite and copper is extracted from this ore. The different steps in extraction of copper are:

 

Crushing and Concentration:

 

The ore obtained from mines are broken down into small piece by jaw crusher and then pulverized. The ore being sulphide ore is concentrated by froth floatation process. Pulverized ore is kept in water containing pine oil and the mixture is agitated by passing compressed air. Ore forms froth with pine oil and comes to the surface and is skimmed off while impurities are left in water.

Extraction of Copper from Copper pyrite

Roasting

The concentrated ore is heated in excess supply of air on the hearth of reberberatory furnace below its melting point. The different changes during roasting are:

a. Moisture and volatile impurities are driven out.

b. Non-metallic impurities like sulphur, phosphorous, arsenic etc. are removed as their oxides.

S + O2      →             SO2

P4 + SO2        →       2P2O5

c. Copper pyrite dissociates into individual sulphide

2CuFeS2 + O2    →         Cu2S + 2FeS + SO2     major r × n

Small amount of metal sulphides are oxidized to oxides.

2FeS + 3O2     →       2FeO   + SO2             minor reaction

2Cu2S + 3O2   →       2CuO  + 2SO2

Smelting

The roasted ore, coke and silica (flux) is charged a water jacketed blast furnace when hot air is passed into blast furnace. Fes if oxidized to FeO which combines with S1O2 to form ferrous silicate as slag.

                        2FeS + 3O2      →     2FeO + 2SO2

                        FeO + S1O2    →       FeS1O3

                                    Flux                             Ferrous Silicate

 

 

As long as Fes is present in the mixture Cu2O can’t be formed as copper has higher affinity for sulphur than oxygen. In molten state FeS & Cu2S are missible and the molten mixture of Cu2S and FeS is called copper malte. The lower end of blast furnace has two openings for slag and copper matte.

Extraction of Copper from Copper pyrite

Fig: Blast Furnace for extraction of copper

 

Bassemerisation

 

The molten matte is mixed with little silica and charged into a Bessemer converter. Lined internally by basic lining of CaO or MgO. Hot air is blown into the mixture which converts remaining FeS. To FeSiO3.

                        2FeS + 3O2     →     2FeO + 2SO2

                        FeO + SiO2     →   FeSiO3 (slag)

The slag is removed and air is passed. The air oxidized Cu2S partially to Cu2O which then reduces remaining Cu2S to metallic copper. During this process no external reducing agent is used so it is an example of self-reduction.

                        2CuS + 3O2   →    2Cu2O + 2SO2

                        2Cu2O + Cu2S    →   6Cu + SO2

 

The reaction is highly exothermic and copper obtained is in molten state. During solidification, SO2 escapes forming blisters on the surface of metal. This variety of copper containing about 2% of impurity is blister copper.

Extraction of Copper from Copper pyrite

Refining:

 

Blister copper consists of about 2% of impurities consisting of cliver, Glod, Zinc, Nicket etc. It is mostly purified by electrolytic method. A block of impure copper is anode, a strip of pure copper is cathode while solution of CuSO4 containing dil H2SO4 is e;ectrolyte. On passing current, impure copper dissolves and equivalent amount of pure copper is deposited at cathode. Impurities are collected below anode as anode mud.

             CuSO4 (aq)      →      Cu++ + SO4

            At cathode: Cu++ + 2e   →     Cu

            At anode:        Cu         →      Cu++ + 2e

Extraction of Copper from Copper pyrite

Physical Properties:

 

  • It is a transition metal having characteristic red color.
  • It is highly malleable & ductile and has high electrical and thermal conductivity
  • It has high melting point 10830c and bpt 2320c
  • It has specific gravity 8.93

 

Chemical properties

 

Action of air:

Dry air has no effect but moist air containing CO2gas forms a green layer of basic copper carbonate.

Cu + O2+ CO2 + H2O     →  CuCO3Cu(OH)2

                                Moist air                                  basic copper carbonate

 

On heating in air 9000c, copper forms cupric oxide or black oxide of copper,

4Cu + O2         900 →               2CuO

Cupric oxide

On further heating above 11000c, copper gives cuprous oxide or red oxide of copper.

4Cu + O2         1000 →            2Cu2O

Cuprous oxide

Action of water:

Water has no effect on copper.

Action of Alkalis:

Alkalis has no effect on copper.

 

Action of Acids:

 

a) With HNO3

dil HNO3 does not react with copper while moderately conc. HNO3 (1:1) is reduced  to Nitric oxide by copper.

3Cu + 8HNO3              →           3Cu (NO3)2 + 2NO + 4H2O

moderately conc.

 

Conc. HNO3 is reduced to Nitric oxide by copper.

Cu + 4HNO3              →             Cu (NO3)2 + 2NO2 + 2H2O

Conc

 

b) With H2SO4 :

dil. H2SO4  alone does not react but hot dil. H2SO4  in presence of air gives CuSO4

2Cu + 2H2SO4 + O2                 →           2CuSO4+2H2O

Hot & dil.

 

With hot and conc. H2So4, Coppe gives So2 gas.

Cu + 2H2SO4            →              CuSO4 +SO2+2H2O

Hot & conc.

 

c) With HCl:-

Copper reacts with hot and conc HCl in presence of air forming cupric chloride.

2Cu+4HCl+ O2                   →                2CuCl2+2H2O

 

5) Displacement reaction:-

 

Copper can displace metals lying below it in electrochemical series from their salt solution.

 

Cu+2AgNo3              →              Cu (No3)2+2Ag

3Cu+2Aucl3                 →           3Cucl2+2Au

 

Uses of Copper:-

i) It is in making electrical cables.

ii) It is used in making coins.

iii) It is used in making allays like brass, German Silver.

iv) It is Rold Gold, constantan, bell metal etc.

iv) It is used in making utensits.

v) It is used in making scientifi equipments like calioriemeter boilers etc.

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