Question

Give both chemical equations of leaching of silver in silver metallurgy by using sodium cyanide?

Answer 1

Leaching of silver is the extraction of silver from its ore using a sodium or potassium cyanide solution. Sodium or potassium cyanide dissolves the silver metal from its ore as silver cyanide. The soluble silver cyanide is then used to extract pure silver from it.

Complete step by step answer:
Leaching, in simple words, can be defined as the process of dissolving silver into a cyanide solution to change it into a liquid form from which silver can be extracted. This method of silver leaching was invented by the scientists, John S. MacArthur and Robert W. Forrest.
This process mainly comprises of two steps:
First, the silver ore is ground into fine tiny particles. These particles are then reacted with a dilute solution of sodium or potassium cyanide. The silver ore dissolves in the cyanide solution to form a soluble silver cyanide complex.
Now, the silver cyanide solution is treated with a zinc solution. Zinc lying above silver in the reactivity series displaces silver from the silver cyanide solution and silver is finally precipitated out. This is how pure silver is obtained from its ore through the leaching process.
The above two steps can be represented through two chemical equations showing the process of leaching of silver in silver metallurgy:
$(i)\ 4Ag + 8{CN}^{-} + 2H_2O + O_2\rightarrow4{[Ag\left(CN\right)_2]}^{-2} + 4{OH}^{-}$
$(ii)\ 2{[Ag(CN)_2]}^{-} + Zn\rightarrow[Zn(CN)_4]^{2-} + 2Ag$
In the first step, the insoluble silver changes into a soluble silver cyanide complex, and in the second step, the silver is separated out from its complex by forming a zinc cyanide complex.

Note: Reactivity series of metals represents the reactivity of one metal in relation to another. The metals which lie above can replace the ones which lie below in the reactivity series, but not vice-versa.