Question

Copper can be extracted by hydrometallurgy but not zinc. Explain.

Answer 1

The reduction potentials of zinc and iron are lower than that of copper. In hydrometallurgy, zinc and iron can be used to displace copper from their solution.

\[\ce{Fe{(s)} + Cu^{2+}_{ (aq)} -> Fe^{2+}_{ (aq)} + }\]

But to displace zinc, more reactive metals i.e., 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.

\[\ce{2K_{(s)} + 2H2O_{(l)} -> 2KOH_{(aq)} + H2_{(g)}}\]

As a result, these metals cannot be used in hydrometallurgy to extract zinc. Hence, copper can be extracted by hydrometallurgy but not zinc.

Answer 2

\[\ce{Zn(E^{\circ}_{Zn^{2+}/Zn} = -0.76 V)}\] is much more reactive than \[\ce{Cu(E^{\circ}_{Cu^{2+}/Cu} = +0.34 V)}\]. Copper ions can easily be replaced from Cu²⁺ ion solution by Zn.

\[\ce{Zn_{(s)} + Cu^{2+}_{ (aq)} -> Zn^{2+}_{ (aq)} + Cu_{(s)}}\]

Thus, hydrometallurgy can be used to extract copper. However, due to its high reactivity, zinc is difficult to remove from a solution that contains Zn²⁺ ions. This is because water reacts with metals that are more reactive than zinc, such as aluminium, magnesium, calcium, etc. Therefore, hydrometallurgy cannot be used to extract zinc.