`E^(@)` value of `Zn^(2+)//Zn=-0.76V` is less then that of `Cu^(2+)//Cu=+0.34V`. This means that zinc is a stronger reducing agent than copper. In solution `Cu^(2+)` ions can be easily displaced by reducing agents like Fe and Zn which donot react with water.
`Fe(s)+Cu^(2+) (aq) to Fe^(2+) (Aq)+Cu(s)`
In order to isolate zinc by hydrometallurgy, we require stronger reducing agents like Ca, Mg , Al etc. However, all of them react with water to evolve hydrogen gas. Therefore, these cannot be used for the purpose. Thus, zinc cannot be extracted by hydrometallurgy.
