Extraction of Silver

Extraction of Silver

Silver Atomic Number: 47
Silver Electronic configuration: [Kr]³d¹⁰4s¹

Silver occurs in native state as well as in combined state. Silver is extracted from Argentite ore (Ag₂S).

Cyanide process:
This process is also called Mac Arthur Forest Process. The process involves the following steps:

1. Concentration of ore:
   The crushed and fine powdered ore is concentrated by froth flotation process.
   
2. Cyanidation:
   The finally powdered concentrated ore is treated with dilute solution (0.4 to 6%) of sodium cyanide in presence of a current of air to form sodium argentocyanide.
   
   Ag₂S + 4NaCN  2Na[Ag(CN)₂)] + Na₂S
   
   The air blown in converts sodium sulphide to sodium sulphate thus shifting the equilibrium to right side.
   
   4Na₂S + 50₂ +2H₂O  2Na₂SO₄ + 4NaOH + 2S
   
   The soluble sodium argentocyanide is separated out by filtration.
   
3. Recovery of Silver:
   Zinc powder in finely divided state is added to clear filtrate to precipitate Ag as a dark amorphous mass.
   
   2Na[Ag(CN)₂] + Zn  Na₂[Zn(CN)₄] + 2Ag
    
4. Refining:
   Silver obtained by the above method is contaminated with impurities of lead, copper and gold. Impurities are removed by:
   
   Electrolytic Refining: Pure silver is obtained by the electrolysis of AgNO₃ solution containing 10% HNO₃ and using the impure silver as anode and pure silver plate as cathode. During electrolysis copper passes into solution as copper nitrate while gold collects as anodic mud. Silver is deposited at cathode.
   
   Anode : Ag  Ag⁺ + e^-
   
   Cathode : Ag⁺ + e^-  Ag
   
   Note: Same process can be applied for gold as well.