Explain the extration of zinc from zinc blende.

i) Crushing : The ore is crushed to a fine powder in ball mills
ii) Concentration of the ore : The crushed ore is concentrated by froth floatation process
iii) Roasting: The conc. ore is roasted in the presence of air (or) oxygen at about 1200K to form zinc oxide (ZnO).
$2\mathrm{ZnS}+3{\mathrm{O}}_2\stackrel{1200\mathrm{K}}{\to }2\mathrm{ZnO}+2{\mathrm{SO}}_2$
iv) Reduction: Zinc oxide obtained above is mixed with coke powder and heated to 1673K in a fire clay retort when it is reduced to zinc metal.
$\mathrm{ZnO}+\mathrm{C}\stackrel{1673\mathrm{K}}{\to }\mathrm{Zn}+\mathrm{CO}$
iv) Electrolytic refining : Anode is made with impure Zn . ZnSO₄ solution acidified with dill H₂SO₄. on passing electric current pure Zn gets deposited on the cathode.
At Anode : $\mathrm{Zn}\stackrel{ }{\to }{\mathrm{Zn}}^{+2}+2{\mathrm{e}}^{-}$
At cathode : ${\mathrm{Zn}}^{+2}+2{\mathrm{e}}^{-} \stackrel{ }{\to } \mathrm{Zn}$