Reduction of Metal Ores by electrolysis

Metals above carbon in the reactivity series could be extracted from their compounds by a competition reaction with a more reactive metal. However, the more reactive metal is often very expensive and although the method is efficient it is uneconomical.

Instead, electrons are given directly to metal cations by a direct electric current.

In terms of energy costs, it would be cheaper to electrolyse aqueous solutions of more reactive metal compounds rather than the molten compound. However, water contains low concentrations of H⁺_(aq) and, as hydrogen is below most metals in the reactivity series, these are preferentially discharged so that H₂ gas is produced at the cathode.

2H⁺_(aq) + 2e^- à H₂

K⁺_(aq) + e^- à K

This type of equation is called an ion-electron equation, or a half equation, i.e. notice that the Hydrogen ions are being reduced because they are gaining electrons.

This means that more reactive metals can only be extracted from their compounds using electrolysis of the molten compound.