Question

Which of the following metal is leached by the cyanide process?

• A. $\mathrm{Al}$
• B. $\mathrm{Ag}$
• C. $\mathrm{Cu}$
• D. $\mathrm{Na}$

Answer 1

The correct option is B

$\mathrm{Ag}$

The explanation for correct option (B) $\mathrm{Ag}$

Leaching by cyanide process:

• Leaching is a process that is used widely in metallurgy where the treatment of ores takes place with chemicals to convert the valuable metals while the impurities remain insoluble.
• The metals such as gold and silver can be leached with a dilute solution of sodium cyanide or potassium cyanide in the presence of air.
• The chemical reaction can be depicted as:

$\mathrm{Ag}\left(\mathrm{s}\right)+2{\mathrm{CN}}^{-}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to \left[\mathrm{Ag}{\left(\mathrm{CN}\right)}_2{]}^{-}\right(\mathrm{aq})+4{\mathrm{OH}}^{-}(\mathrm{aq})$

• The silver complex formed with cyanide is a water-soluble complex.
• Further reduction takes place in presence of Zinc with the cyanide complex. The chemical reaction can be depicted as:

$\left[\mathrm{Ag}{\left(\mathrm{CN}\right)}_2{]}^{-}\right(\mathrm{aq})+2\mathrm{Zn}(\mathrm{s})\to 2[\mathrm{Zn}{\left(\mathrm{CN}\right)}_4{]}^{2-}\left(\mathrm{aq}\right)+\mathrm{Ag}\left(\mathrm{s}\right)$

• The complex formed between the zinc and cyanide is also a water-soluble complex

Explanation for incorrect options:

Metals such as Aluminum, Copper, and Sodium cannot be leached by the cyanide process. Thus options B, C, and D stand incorrect.

Hence, the correct option is A i.e. $\mathrm{Ag}$.