Zinc blende is chemically zinc sulphide (ZnS). It undergoes following reactions :
`2ZnS+3O_(2) overset("Heat")to 2ZnO+2SO_(2) " " ("Roasting")`
`ZnO+C("coke") overset("Heat")to Zn+CO " " ("Reduction")`
Zinc metal is in crude or impure form. It can be refined with the help of electro-refining. In this method, impure zinc is made anode while a plate of pure metal acts as the cathode. The electrolyte is aqueous zinc sulphate containing a small amount of dilute `H_(2)SO_(4)`. On passing electric current, `Zn^(2+)` ions from the electrolyte migrate towards cathode and are reduced to zinc metal which gets deposited on the cathode.
`underset(("Electrolyte"))Zn^(2+)(aq)+2e^(-) to Zn(s)`
From anode, an equivalent amount of zinc gets oxidised to `Zn^(2+)` ions which migrate to the electrolyte
`Zn(s) to Zn^(2+) (aq)+2e^(-)`
