Copper occurs in both states either in a free state or in a combined state. In a combined state, it is found as Copper pyrites, copper glance , Cuprite and Malachite.
Element Symbol: Cu
Atomic Number: 29
Atomic Weight: 63.546
Appearance: Reddish-orange solid metal
Group: Group 11 (transition metal)
Note : Copper pyrites is the common ore of copper
Extraction of Copper from Pyrites ( Sulphide ore )
- Crushing & Concentration
- Roasting
- Smelting
- Bessemerisation
- Purification process
1. Crushing & 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.
2. 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.
3. 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 SiO2 to form ferrous silicate as slag.
- 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.
4. Bessemerisation
- 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.
- 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.
5. Purification process
- The blister copper still contains certain impurities which can be purified by the electrolytic refining process.
Electrolytic refining process
Blister copper consists of about 2% of impurities consisting of silver, Glod, Zinc, Nickel etc.
It is mostly purified by the electrolytic method. A block of impure copper is the anode, a strip of pure copper is cathode while solution of CuSO4 containing dil H2SO4 is electrolyte.
On passing current, impure copper dissolves and an equivalent amount of pure copper is deposited at cathode. Impurities are collected below anode as anode mud.
