How Copper is extracted from low grade Copper ore? Give reactions only.

Extraction

The chief and important ore of copper from which the metal is most isolated is copper pyrites (CuFeS2). It involves the following steps :

Concentration:Froth floatation process is used for concentrating the ore. The powdered ore is suspended in water and after adding little pine oil is stirred by means of air. The sulphide ore particles come to the surface & gangue remains at the bottom is rejected.

Roasting:The concentrated ore is heated strongly by the current of air on the hearth of reverberatory furnace where following reactions takes place.

S + O2→ SO2(S removed)

4As + 3O2→ 2As2O3(As & Sb removed)

The copper pyrite is partially converted into sulphide.2CuFeS2+ O2→ Cu2S + 2FeS + SO2

The sulphides are further partially converted into oxides.

2Cu2S + 3O2→ 2Cu2O + 2SO2
2FeS + 3O2→ 2FeO + 2SO2

Smelting: The orates ore (Cu2S + FeS + Cu2O + FeO) mixed with coke and sand is heated in water jacketed blast furnace.

Cu2O + FeS → Cu2S + FeO

This ferrous oxide combines with silica to form ferrous silicate as slag.

FeO + SiO2→ FeSiO3(slag)

The slag being lighter than molten mixture of Cu2S and FeS (Copper matte) floats & is removed. Copper matte contains 50% Cu.

Bassemerization:The molten copper matte is introduced into a small pear shaped furnace of steel plates called “Bessemer’s converter”.

Cu2S + 2Cu2O → 6Cu + SO2(self reduction reaction)

This copper obtained is known as blistered copper. It contains about 2% impurities mainly of As, Sn, Pb, Ag, Au, Ni, Zn etc.

Refining : It is done by two methods :

Poling :By this method, we can obtain 99.5% pure copper.

Electrolytic method :



Cathode : Pure copper

Anode : Impure copper

Electrolyte : 85% CuSO4containing 5% dilute H2SO4taken in a lead lined tank.

This method gives 99.9% pure copper.

Copper Pyrites (CuFeS2)
↓Crushed and sieved

Concentration by froth floatation

i.e., powdered ore + water + pine oil + air ® sulphide ore in the froth.
↓
Roasting in reveberatory furnace in pressure of air

S + O2→ SO2; 2As + 3O2→ 2As2O3

2Cu FeS2+ O2→ Cu2S + 2FeS + SO2
↓ sand + coke

Smelting in blast furnace in pressure of air

2FeS + 3O2→ 2FeO + 2SO2; FeO + SiO2→ FeSiO3(slag)