Extraction of Silver

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 +2H2 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.

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