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  Extraction from copper pyrites

Extraction from copper pyrites:

Extraction of copper from copper pyrites includes the steps shown below:

1. Crushing and concentration:

The ore is first crushed and then concentrated by froth-floatation procedure.

2. Roasting:

The concentrated ore is heated strongly in reverberatory furnace, in the excess of air. During roasting,

i) Moisture is eliminated.
ii) The volatile impurities are eliminated.
iii) Phosphorus, Sulphur, arsenic and antimony that are present as impurity are eliminated as volatile oxides.

S + O2 → SO2
P4 + 5O2 → 2P2O5
4As + 3O2 → 2As2O3

iv) The copper pyrite is partially transformed into sulphides of copper and iron.

2CuFeS2 + O2 → Cu2S + 2FeS + SO2
2FeS + 3O2 → 2FeO + 2SO2

3. Smelting:

The roasted ore is mix with powdered coke and sand and then heated in a blast furnace. It is made up of steel plates lined within with fire clay bricks. Hot air at 800°C is introduced from the tuyers close to the base of the furnace. As an outcome, the following changes take place.

2FeS + 3O2 → 2FeO + 2SO2
FeO + SiO2 → FeSiO3 (fusible slag)
2Cu2S+ 3O2→ 2Cu2O + 2SO2
Cu2O + FeS → Cu2S + FeO
FeO + SiO2 → FeSiO3 (fusible slag)

As an outcome of smelting, two separate molten layers are generated at the bottom of the furnace. The upper layer comprises of slag and is eliminated as a waste whereas the lower layer is termed as matte. It mainly consists of cuprous sulphide and few unchanged ferrous sulphide.

4. Bessemerisation:

The molten matte is transferred to a Bessemer converter. The Bessemer is mounted on horizontal axis and is fitted with small pipes termed as tuyeres via which a blast of hot air and fine sand is entered.

Any arsenic, sulphur, and antimony yet present escape as their respective oxides. Ferrous sulphide present in matte is oxidised into ferrous oxide that joins with silica to form slag.

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

A few of the cuprous sulphide undergoes oxidation to form cuprous oxide which then reacts with additional cuprous sulphide to provide copper metal. The impure metal so obtained is termed as blister copper and is around 98% pure.

2Cu2S + 3O2 → 2Cu2O + 2SO2
2Cu2O + Cu2S → 6Cu + SO2

5. Refining:

Blister copper has around 2% of impurities and it is purified by electrolytic refining.

Electrolytic Refining:

This technique is used to acquire metal of high degree of purity. For electrolytic refining of copper,

i) A block of impure copper metal performs as anode.
ii) A thin plate of pure copper metal performs as cathode.
iii) Copper sulphate solution acidified with sulphuric acid is carried as electrolyte.

Whenever electric current is passed via the electrolytic solution pure copper get deposited on the cathode, impurities settle close to the anode in the form of sludge termed as anode mud.

 

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