Notes On Extraction Of Copper And Zinc From Their Oxides - CBSE Class 12 Chemistry

Copper occurs in combined state as sulphides, oxides and carbonates. Copper pyrites (or) chalcopyrites and copper glance are its sulphide ores. Cuprite is its oxide ore, while malachite and azurite are its carbonate ores.

Sulphide Ore Composition
Copper pyrites or Chalcopyrites CuFeS2
Copper glance Cu2S

Oxide Ore Composition
Cuprite Cu2O

Carbonate Ore Composition
Malachite CuCo3.Cu(OH)2
Azurite 2CuCO3.Cu(OH)2



Most ores of copper are sulphide ores and some of them may contain iron. Hence, the sulphide ores are first roasted (or) smelted to give oxides. The oxides are then reduced to metallic copper using coke.

       2Cu2S         +     3O2       →       2Cu2O     +      2SO2
Copper Sulphide       Oxygen         Cupric oxide      Sulphur dioxide

         Cu2O         +      C            →     2Cu       +        CO
Cupric oxide             Coke                Copper          Carbon monoxide

But concentrated sulphide ore containing iron as an impurity is mixed with silica and heated in a reverberatory furnace. During this process, most of the iron sulphide is converted into its oxide, which further reacts with silica to form a fusible slag of iron silicate. Copper is produced in the form of copper matte, which contains copper sulphide and iron sulphide.

The molten matte is now introduced into a converter provided with a lining of silica. A blast of sand and hot air is blown into it. During this process, the remaining iron is removed in the form of slag, while copper sulphide is reduced to metallic copper.

The metallic copper then melts and sinks to the bottom of the converter. This molten copper is poured into moulds. When the molten mass is allowed to cool down, SO2 gas escapes. As a consequence, the copper so obtained has a blistered appearance. Hence, the product is called blister copper.

Blister copper contains 98 per cent copper and is refined through electrolysis.


Extraction of zinc:

Zinc occurs widely in nature in the form of sulphide, oxide and carbonate ores. Zinc blende is its sulphide ore, zincite its oxide ore and calamine is its carbonate ore.

Sulphide Ore Composition
Zinc blende ZnS

Oxide Ore Composition
Zincite ZnO

Carbonate Ore Composition
Calamine ZnCO3


The reduction of zinc oxide to zinc occurs at a higher temperature than that required for the reduction of copper oxide to copper. Coke is used for the reduction of zinc oxide.

Depending on whether sulphide or carbonate ores used for the extraction, the concentrated ore is either roasted (or) calcined.

The zinc oxide obtained after roasting (or) calcination is reduced to zinc in vertical retorts where zinc oxide is powdered, mixed with coke and clay and then made into small briquettes. These are placed in vertical retorts that are lined internally with clay bricks. Producer gas is used as the fuel to heat the charge.

At high temperatures of 1400 - 1500 0C, coke reduces zinc oxide to zinc and itself gets oxidised to carbon monoxide. The zinc metal is distilled off and collected by rapid chilling, thus obtained Zinc is 97 % pure and is called zinc spelter.

Summary

Copper occurs in combined state as sulphides, oxides and carbonates. Copper pyrites (or) chalcopyrites and copper glance are its sulphide ores. Cuprite is its oxide ore, while malachite and azurite are its carbonate ores.

Sulphide Ore Composition
Copper pyrites or Chalcopyrites CuFeS2
Copper glance Cu2S

Oxide Ore Composition
Cuprite Cu2O

Carbonate Ore Composition
Malachite CuCo3.Cu(OH)2
Azurite 2CuCO3.Cu(OH)2



Most ores of copper are sulphide ores and some of them may contain iron. Hence, the sulphide ores are first roasted (or) smelted to give oxides. The oxides are then reduced to metallic copper using coke.

       2Cu2S         +     3O2       →       2Cu2O     +      2SO2
Copper Sulphide       Oxygen         Cupric oxide      Sulphur dioxide

         Cu2O         +      C            →     2Cu       +        CO
Cupric oxide             Coke                Copper          Carbon monoxide

But concentrated sulphide ore containing iron as an impurity is mixed with silica and heated in a reverberatory furnace. During this process, most of the iron sulphide is converted into its oxide, which further reacts with silica to form a fusible slag of iron silicate. Copper is produced in the form of copper matte, which contains copper sulphide and iron sulphide.

The molten matte is now introduced into a converter provided with a lining of silica. A blast of sand and hot air is blown into it. During this process, the remaining iron is removed in the form of slag, while copper sulphide is reduced to metallic copper.

The metallic copper then melts and sinks to the bottom of the converter. This molten copper is poured into moulds. When the molten mass is allowed to cool down, SO2 gas escapes. As a consequence, the copper so obtained has a blistered appearance. Hence, the product is called blister copper.

Blister copper contains 98 per cent copper and is refined through electrolysis.


Extraction of zinc:

Zinc occurs widely in nature in the form of sulphide, oxide and carbonate ores. Zinc blende is its sulphide ore, zincite its oxide ore and calamine is its carbonate ore.

Sulphide Ore Composition
Zinc blende ZnS

Oxide Ore Composition
Zincite ZnO

Carbonate Ore Composition
Calamine ZnCO3


The reduction of zinc oxide to zinc occurs at a higher temperature than that required for the reduction of copper oxide to copper. Coke is used for the reduction of zinc oxide.

Depending on whether sulphide or carbonate ores used for the extraction, the concentrated ore is either roasted (or) calcined.

The zinc oxide obtained after roasting (or) calcination is reduced to zinc in vertical retorts where zinc oxide is powdered, mixed with coke and clay and then made into small briquettes. These are placed in vertical retorts that are lined internally with clay bricks. Producer gas is used as the fuel to heat the charge.

At high temperatures of 1400 - 1500 0C, coke reduces zinc oxide to zinc and itself gets oxidised to carbon monoxide. The zinc metal is distilled off and collected by rapid chilling, thus obtained Zinc is 97 % pure and is called zinc spelter.

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