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(a) Write the steps involved in the extraction of pure metals in the middle of the activity series from their carbonate ores.(b) How is copper extracted from its sulphide ore? Explain the various steps supported by chemical equations. Draw labelled diagram for the electrolytic refining of copper.
(a) As iron, zinc, lead, copper etc are moderately reactive metals, they are present as sulphides or carbonates and can be obtained from its ore by reduction or by electrolysis.
For example, Zinc ore is concentrated and roasted in the air to produce zinc oxide and carbon oxide. CO2 is formed when ZnCO3 is roasted in the air.
The equation for the reaction is given below:
$ZnCO_{3}(s)\rightarrow ZnO(s)+CO_{2}(g)$
Zinc oxide produced from ore is then heated with carbon to reduce it into metallic zinc.
$ ZnO(s) + C\rightarrow Zn(s)+CO(g)$
(b) Given below are the steps for the extraction of copper from its Sulphide ore:
1) Concentration of the ore: Removal of unwanted metals and gangue to purify the ore is done by Froth floatation method as it is a sulphide ore.
2) Roasting: Copper glance (Cu2S) is roasted in the presence of air. $2Cu_{2} S( s) +3O_{2}( g) \ \rightarrow 2Cu_{2} O( s) +2SO_{2}( g)$
3) Reduction: Copper oxide is then heated in the absence of air. Reduction of copper (I) oxide with copper (I) sulphide:
$2Cu_{2} O+Cu_{2} S\rightarrow 6Cu( s) +SO_{2}( g)$
This reaction is known as auto -reduction.
4) Reaction for electrolytic refining: The impure copper metal is made ANODE and the pure metal of copper is CATHODE copper sulphate as an electrolyte. Pure copper from electrolyte deposited on cathode soluble impurities goes into solution and insoluble impurities remain in the solution and deposited at bottom of ANODE.
$At\ anode\ :\ Cu^{2+}( aq) +2e^{-}\rightarrow Cu( s)$
$At\ cathode\ :\ Cu( s) \ \rightarrow Cu^{2+}( aq) +2e^{-}$
Updated on: 10-Oct-2022
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