Copper: Occurrence, principles of extraction, Properties and Uses
Atomic mass : 63.54
Valency : 1 and 2
Atomic number : 29
Symbol : Cu
Position in the periodic table : Period Number -4, Group Number -11.
Copper was known to the earliest races of mankind. It was named as cuprum by the Romans because they used to get it from the island of Cyprus. Copper is found in the native state as well as in the combined state. Native copper is found in large quantities in Michigan (USA). In India, copper is mainly found in Singhbhum (Bihar), Khetri and Darbia (Rajasthan) and in Tamilnadu.
i) Copper pyrite, CuFeS2.
ii) Cuprite or Ruby copper, Cu2O.
iii) Copper glance, Cu2S.
The chief ore of copper is copper pyrite. It yields nearly 76% of the world production of copper.
Extraction from copper pyrites
Extraction of copper from copper pyrites involves the following steps.
1. Crushing and concentration
The ore is crushed and then concentrated by froth-floatation process.
The concentrated ore is heated strongly in the reverberatory furnace, in excess of air. During roasting,
i) Moisture is removed.
ii) The volatile impurities are removed.
iii) Sulphur, phosphorus, arsenic and antimony which are present as impurity
are removed as volatile oxides.
S + O2 ® SO2
P4 + 5 O2 ® 2P2O5
4As + 3O2 ® 2As2O3
iv) The copper pyrite is partly converted into sulphides of copper and iron.
2CuFeS2 + O2 ® Cu2S + 2FeS + SO2
2FeS + 3O2 ® 2FeO + 2SO2
The roasted ore is mixed with powdered coke and sand and is heated in a blast furnace. It is made of steel plates lined inside with fire clay bricks. Hot air at 800 o C is introduced from the tuyers near the base of the furnace. As a result, the following changes occur.
2FeS + 3O2 ® 2FeO + 2SO2
FeO + SiO2 ® FeSiO3 (fusible slag)
2Cu2S + 3 O2 ® 2Cu2O + 2SO2
Cu2O + FeS ® Cu2S + FeO FeO + SiO2 ® FeSiO3 (fusible slag)
As a result of smelting, two separate molten layers are formed at the bottom of the furnace. The upper layer consists of slag and is removed as a waste while the lower layer is called matte. It chiefly consists of cuprous sulphide and some unchanged ferrous sulphide.
The molten matte is transfered to a Bessemer converter. The Bessemer is mounted on a horizontal axis and is fitted with small pipes called tuyeres through which a blast of hot air and fine sand is admitted.
Any sulphur, arsenic and antimony still present escape as their respective oxides. Ferrous sulphide present in matte is oxidised to ferrous oxide which combines with silica to form slag
2FeS + 3O2 ® 2FeO + 2SO2
FeO + SiO2 ® FeSiO3 (slag)
Some of the cuprous sulphide undergoes oxidation to form cuprous oxide which then reacts with more cuprous sulphide to give copper metal. The impure metal thus obtained is called blister copper and is about 98% pure.
2Cu2S + 3O2 ® 2Cu2O + 2SO2
2Cu2O + Cu2S ® 6Cu + SO 2
Blister copper contains about 2% of impurities and it is purified by electrolytic refining.
This method is used to get metal of high degree of purity. For electrolytic
refining of copper,
i) A block of impure copper metal acts as anode
ii) A thin plate of pure copper metal acts as cathode
iii) Copper sulphate solution acidified with sulphuric acid is taken as electrolyte.
When electric current is passed through the electrolytic solution pure copper get deposited on the cathode ,impurities settle near the anode in the form of sludge called anode mud.
Copper is a reddish brown metal, with high lustre, high density and high
melting point 1356 o C.
i) Action of air and moisture
Copper gets covered with a green layer of basic copper carbonate, in the
presence of CO2 and moisture
2Cu + O2 + CO2 + H2O ® Cu(OH)2 . CuCO3
(Green) Copper Carbonate
ii) Action of Heat
Copper when heated to redness (below 1370K) in the presence of oxygen
or air, first it gets converted to black cupric oxide and further heating to above 1370K, it gets converted into red cuprous oxide.
2Cu + O2 --- Below 1370K -- > 2CuO
4Cu + O2 --- Above 1370K -- > 2Cu2O
iii) Action of acids
a) With dil.HCl and H2SO4
Dilute acids such as HCl and H2SO4 have no action on these metals in the
absence of air or an oxidising agent. Copper dissolves in these acids in the
presence of air
2Cu + 4HCl + O2 (air) ® 2CuCl2 + 2H2O
b) 2Cu + 2H2SO4 + O2 (air) ® 2CuSO4 + 2H2O
With dil. HNO3
Copper reacts with dil.HNO3 with the liberation of NO gas.
3Cu + 8HNO3(dil) ® 3Cu(NO3)2 + 2NO + 4H2O
c) With con.HNO3 and con. H2SO4
Copper reacts with con.HNO3 and con.H2SO4 with the liberation of
NO2 and SO2 respectively.
Cu + 4HNO3 (con) ® Cu(NO3)2 + 2NO2 + 2H2O
Cu + 2H2SO4 (con) ® CuSO4 + SO2 + 2H2O
iv) Action of chlorine
Chlorine reacts with copper, resulting in the formation of copper chloride.
Cu + Cl2 ® CuCl2
v) Action of alkalis
Copper is not attacked by alkalies.
1. It is extensively used for making electric cables and other electric appliances.
2. It is used for making utensils, containers, calorimeters, coins, ...... etc. 3. It is used in electroplating.
4. It is alloyed with gold and silver for making coins and jewellery.
Alloys of Copper
Alloy % composition Uses
i) Brass Cu = 60-80, Zn = 20-40 For making utensils, condenser
tubes, wires, .....etc.
ii) Bronze Cu = 75-90, Sn = 10-25 For making cooking utensils,
statues, coins ...etc.
iii) Gun metal Cu = 87, Sn = 10, Zn = 3 For making gun barrels, gears,