Copper Ores :
Copper Pyrite or Chalcopyrite – CuFeS2 or Cu2S.Fe2S3
Copper Glance or Chalcocite – Cu2S
Cuprite – Cu2O
Malachite – CuCO3 . Cu(OH)2
Azurite – (CuCO3)2 . Cu(OH)2
Copper pyrite is the major ores of copper. Copper pyrite and Copper glance are sulfide ores. Cuprite is oxide ores. Malachite and Azurite are carbonate ores.
Presentation :- Copper is found in free state in America, Sweden and Ural mountains. In India, copper is found in the combined state in the form of oxide, sulfide and carbonate ores. It is mainly found in Singhbhumi (Bihar), Rajsthan and Andhra Pradesh.
The main factory of Copper extraction in India is Indian Copper Cooperation Limited, Musabani Ghatshila, Jamshedpur.
Metallurgy of Copper :
Copper pyrite is the main ores of copper. In order to obtain copper from copper pyrite, first, large pieces of ores are obtained by hammering, crusher and using stemt mill in the form of a fine powder. After this the following steps are done in sequence.
Concentration of the ore :- After grinding copper pyrite ores, its concentration is done first by gravity separation method and then by froth floatation method.
To concentrate the ore by the froth flotation method, a fine powder of ore is poured into a pond filled with water and pine oil and a strong wind of air is passed through it, the concentrated ore obtained in the form of froths on the surface of the liquid.
Roasting of the concentrated ore :- The concentrated ore of copper pyrite is kept in a reflecting furnace and heated in the presence of low temperature and controlled air so that it gets oxidised without melting. In this way the concentrated ore gets roasted. The impurities of sulfure, arsenic and antimony present in the ore get oxidised to form their own oxides, which dissociate in the form of vapour.
S + O2 → SO2
4As + 3O2 → 2As2O3
Copper pyrite is oxidised to form copper sulfide (Cu2S), ferrous sulfide (FeS) and sulfure dioxide (SO2).
2CuFeS2 + O2 → Cu2S + 2FeS + SO2
Some part of copper sulfide and ferrous sulfide is converted into copper oxide (Cu2O) and ferrous oxide (FeO).
2Cu2S + 3O2 → 2Cu2O + 2SO2
2FeS + 3O2 → 2FeO + 2SO2
Smelting of the roasted ore :- The roasted ore of copper pyrite mixed with sand and cock is melted in blast furnace at high temperature. Sand contains SiO2 in excess and Cock contains carbon (C).
This process is called Smelting of the roasted ore. As a result of smelting of the roasted ore of copper pyrite, Cu2O and FeS present in it react as follows –
Cu2S + FeS → Cu2S + FeO
The FeO thus obtained reacts with the used slaking (SiO2) to form iron silicate which is called slag.
FeO + SiO2 → FeSiO3
The slag being lighter tends to collect at the top of the furnace. Which is separated by shedding. A mixture of ferrous sulfide and cuprus oxide gets deposited at the bottom of the furnace, which is called Matte.
Bessemerisation :- Bessemer’s Converter is a special shape pot made of steel. Its walls are made of fire proof bricks and the walls (lining or coating) are made of magnesia (MgO) and lime (CaO) or silica (SiO2).
In its upper part there is an outlet to drain the waste gas. In its lower part there are tuyers, through which strong blows of hot air are continuously applied. The Bessemer’s converter is mounted on a stand in such a way that it can be turned up and down.
Bessemer’s converter is used to get copper from Matte. This process is called Bessemerisation of matte. The lining of the bessemer’s converter used in the Bessemerisation of matte is made of Megnesia and Lime.
Mixing sand in molten matte and filling it in a bessemer’s converter. The following chemical reactions occur when tuyers blow air –
A :- The ferrous sulfide present in matte gets converted into ferrous oxide.
2FeS + 3O2 → 2FeO + 2SO2
B :- FeO combines with silica to form iron silicate which is called slag. Being light, it comes up.
FeO + SiO2 → FeSiO2