Question

What are important ores of copper? How is copper extracted from copper pyrites?

Answer 1

Copper is extracted from its principal ore copper pyrites (CuFeS2). The oreis concentrated by froth flotation process. The concentrated ore is roasted in a reverberatory furnace when the following reactions occur

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Answer 2

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The ore obtained from mines are broken down into small piece by jaw crusher and then pulverized. The ore being sulphide ore is concentrated by froth floatation process. Pulverized ore is kept in water containing pine oil and the mixture is agitated by passing compressed air. Ore forms froth with pine oil and comes to the surface and is skimmed off while impurities are left in water.

Extraction of Copper from Copper pyrite

Roasting

The concentrated ore is heated in excess supply of air on the hearth of reberberatory furnace below its melting point. The different changes during roasting are:

a. Moisture and volatile impurities are driven out.

b. Non-metallic impurities like sulphur, phosphorous, arsenic etc. are removed as their oxides.

S + O2      →             SO2

P4 + SO2        →       2P2O5

c. Copper pyrite dissociates into individual sulphide

2CuFeS2 + O2    →         Cu2S + 2FeS + SO2     major r × n

Small amount of metal sulphides are oxidized to oxides.

2FeS + 3O2     →       2FeO   + SO2             minor reaction

2Cu2S + 3O2   →       2CuO  + 2SO2

Smelting

The roasted ore, coke and silica (flux) is charged a water jacketed blast furnace when hot air is passed into blast furnace. Fes if oxidized to FeO which combines with S1O2 to form ferrous silicate as slag.

                       2FeS + 3O2      →     2FeO + 2SO2

                       FeO + S1O2    →       FeS1O3

                                   Flux                             Ferrous Silicate

 

 

As long as Fes is present in the mixture Cu2O can’t be formed as copper has higher affinity for sulphur than oxygen. In molten state FeS & Cu2S are missible and the molten mixture of Cu2S and FeS is called copper malte. The lower end of blast furnace has two openings for slag and copper matte.

Extraction of Copper from Copper pyrite

Fig: Blast Furnace for extraction of copper

 

Bassemerisation

 

The molten matte is mixed with little silica and charged into a Bessemer converter. Lined internally by basic lining of CaO or MgO. Hot air is blown into the mixture which converts remaining FeS. To FeSiO3.

                       2FeS + 3O2     →     2FeO + 2SO2

                       FeO + SiO2     →   FeSiO3 (slag)

The slag is removed and air is passed. The air oxidized Cu2S partially to Cu2O which then reduces remaining Cu2S to metallic copper. During this process no external reducing agent is used so it is an example of self-reduction.

                       2CuS + 3O2   →    2Cu2O + 2SO2

                       2Cu2O + Cu2S    →   6Cu + SO2

 

The reaction is highly exothermic and copper obtained is in molten state. During solidification, SO2 escapes forming blisters on the surface of metal. This variety of copper containing about 2% of impurity is blister copper.

Extraction of Copper from Copper pyrite

Refining:

 

Blister copper consists of about 2% of impurities consisting of cliver, Glod, Zinc, Nicket etc. It is mostly purified by electrolytic method. A block of impure copper is anode, a strip of pure copper is cathode while solution of CuSO4 containing dil H2SO4 is e;ectrolyte. On passing current, impure copper dissolves and equivalent amount of pure copper is deposited at cathode. Impurities are collected below anode as anode mud.

            CuSO4 (aq)      →      Cu++ + SO—4

           At cathode: Cu++ + 2e   →     Cu

           At anode:        Cu         →      Cu++ + 2e