According to the activity series of metals, the reduction potentials of zinc and iron are lower than that of copper. In hydrometallurgy, these elements can be used to displace copper from their solution.

Fe_(s) + Cu²⁺_(aq)   →   Fe²⁺_(aq)   + Cu_(s)

However, in order to displace zinc, more reactive metals like the metals having lower reduction potentials than zinc such as Mg, Ca, K, etc. are required. But all these metals react with water with the evolution of H₂ gas as exemplified below.

2K_(s)  + 2H₂O _(l)   →  2KOH _(aq) + H_2(g)

So these metals cannot be used in hydrometallurgy to extract zinc.

And thus copper can be extracted by hydrometallurgy but not zinc.