Explain the extraction of Zinc form Zinc blende.

Explanation

"Zinc blende (ZnS)"is an improtant source for 'Zn' metal.
Extraction of Zinc : Zinc blende ore is treated in the following stages.
i) Crushing : The ore is crushed to a fine powder in ball mills.
ii) Concentration of the ore : The ore is concentrated first by gravity process. The crushed ore is washed with a stream of water on a wilfley's tables have a corrgated top and are under a rocking motion .Due to this motion, the lighter gangue particles are washed away by the steam. The heavier ore particles settle to the bottom of the table.
The partially concentrated ore is further concentrated by froth floatation process. The ore particles go with the froth.
The concentrated oere is subjected further to electromagnetic separation , if iron oxide is present in the gangue .Iron oxide is magnetic and so forms a heap nearer to the magnetic pole.
iii) Roasting : The concentrated ore thus obtained is roasted in rotary shelf burner which is provided with horizonatl shelves and raking arms .The ore is added at the top zinc oxide is collected from the bottom .The following reactions take place.
`2ZnS+3O_(2)rarr2ZnO+2SO_(2)`
`ZnS+2O_(2)rarrZnSO_(4)`
`2ZnSO_(4)rarr2ZnO+2SO_(2)+O_(2)`
iv) Reduction : Three methods are in partice for the reduction of the oxide to the metal. The most commonly used method is the Belgian process. In this process the roasted ore is mixed with coal or coke intimately and is taken in fireclay or earthern were retorts .The retorts are made of fireclay which are bottle shaped tubes.These are closed at one closed at one end .The other end is connected toair cooled earthern were condenser. A large number of retorts are placed in tiers in a large furnace and heated in `1100^(@)C` by burinig the gas . 'prolongs' made of sheet iron are attached to the condensers. The metal condenses in these earthern were condensers and the prolongs .The metal powder collected is mixed with some zinc oxide and is known as "Zinc dust" .Some of the zinc meatal is collected in the fused state .This is solidified in moulds .This metal is called "Zinc Spelter".
`ZnO+CrarrZn+CO`
`ZnO+COrarrZn+CO_(2)`
Electrolytic refining : very pure zinc is obtained by electrolysis. The electrolysis is zinc sulphate solution containing a little `H_(2)SO_(4)` Impure zinc is made the anode and the pure zinc plates are made the cathode .