The crushed ore of argentite (Ag2S) is leached with sodium cyanide solution. This reaction forms sodium argento cyanide Na[Ag(CN)2]
Step 1:
Ag2S + 4NaCN ⇌ 2Na[Ag(CN)2] + Na2S
The solution of sodium argento cyanide combines with zinc dust and forms sodium tetra cyano zincate and precipitated silver.
Step 2:
Zn + 2Na[Ag(CN)2] → Na [Ag(CN)2] + 2 Ag↓ In the step 2, redox reaction take place.