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Why is leaching of gold by metal cyanide...

Why is leaching of gold by metal cyanides carried out in the presence of oxygen? Give the chemical equation. Name the metal used as reducing agent.

Text Solution

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Leaching of gold by metal cyanides is carried out in the presence of oxygen because it is an oxidation reaction where Au is oxidised to `Au^(+)` which combines with `CN^(-)` ions to form soluble complex, i.e.
`4Au + 8KCN + 2H_(2)O +O_(2) to 4K[Au(CN)_(2)] +4KOH`
Zinc metal is used as the reducing agent, the pure metal is then displaced from the solution by active metal.
`2K[Au(CN)_(2)] +Zn to K_(2)[Zn(CN)_(4)]+2Au`
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