Extractive Metallurgy of Copper

EXTRACTIVE METALLURGY OF COPPER

Occurrence:

It was named as cuprum by the Romans because they got it from the Island of Cyprus. Copper is found in the native state as well as combined state.

Ores of copper       Formula

Copper pyrites    CuFeS₂

Cuprite or ruby copper  Cu₂O

Copper glance    Cu₂S

The chief ore of copper is copper pyrite. It yields nearly 76% of the world production of copper. Extraction of copper from copper pyrites involves the following steps

i. Concentration of ore: The ore is crushed and the concentrated by froth floatation process.

ii. Roasting: The concentrated ore is roasted in excess of air. During the process of roasting, the moisture and volatile impurities are removed. Sulphur, phosphorus, arsenic and antimony are removed as oxides. Copper pyrite is partly converted into sulphides of copper and iron.

 2CuFeS₂ + O₂ → Cu₂S + 2 FeS + SO₂ ↑

iii. Smelting: The roasted ore is mixed with powdered coke and sand and is heated in a blast furnace to obtain matte (Cu₂S + FeS) and slag. The slag is removed as waste.

iv. Bessemerisation: The molten matte is transferred to Bessemer converter in order to obtain blister copper. Ferrous sulphide from matte is oxidized to ferrous oxide, which is removed as slag using silica.

2 FeS + 3 O2 → 2 FeO + 2 SO2 ↑

FeO + SiO2 → FeSiO3 (slag) (Iron silicate)

2 Cu₂S + 3O₂ → 2 Cu₂O + 2 SO₂ ↑

2 Cu₂O + Cu₂S → 6 Cu + SO₂↑ (Blister copper)

v. Refining: Blister copper contains 98% of pure copper and 2% of impurities and is purified by electrolytic refining. This method is used to get metal of a high degree of purity. For electrolytic refining of copper, we use:

Cathode: A thin plate of pure copper metal.

Anode: A block of impure copper metal.

Electrolyte: Copper sulphate solution acidified with sulphuric acid.

When electric current is passed through the electrolytic solution, pure copper gets deposited at the cathode and the impurities settle at the bottom of the anode in the form of sludge called anode mud.

Physical Properties of Copper

Copper is a reddish brown metal, with high lustre, high density and high melting point (1356°C). 

Chemical Properties of Copper

i.      Action of Air and Moisture: Copper gets covered with a green layer of basic copper carbonate in the presence of CO₂ and moisture.

2 Cu + O₂ + CO₂ + H₂O → CuCO₃.Cu(OH)₂

ii. Action of Heat: On heating at different temperatures in the presence of oxygen, copper forms two types of oxides CuO, Cu₂O.

iii. Action of Acids:

a) With dilute HCl and dilute H₂SO₄:

Dilute acids such as HCl and H₂SO₄ have no action on these metals in the absence of air. Copper dissolves in these acids in the presence of air.

2 Cu + 4 HCl + O₂ (air) →2 CuCl₂ + 2 H₂O

b) With dil. HNO₃:

Copper reacts with dil. HNO₃ with the liberation of Nitric Oxide gas.

3 Cu + 8 HNO₃ → Cu(NO₃)₂ + 2 NO ↑ + 2H₂O

Cu + 2 H₂SO₄ → CuSO₄ + SO₂ ↑ + 2 H₂O

iv) Action of Chlorine:

Chlorine reacts with copper, resulting in the formation of copper(II) chloride.

Cu + Cl₂  CuCl₂

v) Action of Alkalis:

Copper is not attacked by alkalis.

Uses of Copper:

i.                     It is extensively used in manufacturing electric cables and other electric appliances.

ii.                     It is used for making utensils, containers, calorimeters and coins,

iii.                     It is used in electroplating.

iv.                     It is alloyed with gold and silver for making coins and jewels