Question

Write a short note on electrochemical principles of metallurgy.

Write a note on the electrochemical principles of metallurgy.

Answer 1

1. Reduction of oxides of active metals such as sodium, potassium etc. by carbon is thermodynamically not feasible.
2. Such metals are extracted from their ores by using electrochemical methods.
3. In this method the metal salts are taken infused form or in solution form.
4. The metal ion present can be reduced by treating the solution with a suitable reducing agent or by electrolysis.
5. Gibbs free energy change for the electrolysis is ∆G° = −nFE°
   n = number of electrons involved in the reduction
   F = Faraday = 96500 coulombs
   E° = electrode potential of the redox couple.
6. If E° is positive, is negative and the reduction is spontaneous.
7. Hence a redox reaction is planned in such a way that the emf of the net redox reaction is positive.
   A more reactive metal displaces a less reactive metal from its salt solution.
   eg; \[\ce{Cu^{2+}_{(aq) } + Zn_{(s)} -> Cu_{(s)} + Zn^{2+}_{(aq) }}\]
8. Zinc is more reactive than copper and displaces copper from its salt solution.

Answer 2

Electrolysis or the addition of a reducing element are the methods used to reduce metal ions in solution or in their molten form. Electrochemical principles form the basis of the reduction techniques.

As we have already observed, the change in the system’s Gibbs free energy is connected to the electrode potential E0 of a redox pair (M/Mⁿ⁺) as:

ΔG° = −nE°F    ...(i)

where n represents how many electrons are engaged in the redox process. Larger negative electrode potential values are seen in more reactive metals. It is therefore very challenging to minimise them. According to Eq. (i), the value of ΔG° will be negative if there is a positive difference between the E° values of the two redox couples. The more reactive metal will enter the solution in this situation, while the less reactive metal will exit it. Stated otherwise, the more reactive metal will push out the less reactive metal in this situation. For instance,

\[\ce{Cu^{2+}_{ (aq)} + \underset{metal}{\underset{More reactive}{Fe_{(s)}}} -> \underset{metal}{\underset{Less reactive}{Cu_{(s)}}} + Fe^{2+}_{ (aq)}}\]

Mⁿ⁺ ions are released and deposited at the cathode, or negative electrode, during the electrolysis process. Therefore, electrodes should be manufactured of appropriate materials, taking into account the reactivity of the metal produced. Sometimes, a flux is required to increase the conductivity of the molten mass.