Oxidation Reduction

The cyanide leaching of gold and silver introduced in Section 6.2.4 is worth looking at again through a slightly different lens — as a genuine oxidation–reduction pair, not just a solubility trick.

The oxidation step

Leaching gold with cyanide in the presence of air converts the metal itself: $Ag \rightarrow Ag^+$ or $Au \rightarrow Au^+$. That's an oxidation of the metal, driven by atmospheric $O_2$:

The reduction step

The gold is then recovered from solution by a displacement reaction with zinc:

Here zinc is the reducing agent — it gives up electrons more readily than gold does, pushing $Au^+$ back down to metallic $Au(s)$ while zinc itself goes into solution as the cyanide complex.

--- …