Copper: Occurrence, principles of extraction, Properties and Uses

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.

Occurrence

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.

Ores

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.

2.    Roasting

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

3.    Smelting

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.

4.    Bessemerisation

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

5.    Refining

Blister copper contains about 2% of impurities and it is purified by electrolytic refining.

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.

Properties

Physical properties

Copper is a reddish brown metal, with high lustre, high density and high

melting point 1356 o C.

Chemical Properties

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.

Uses

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,

castings etc.