Extraction of Silver from Argentite

Symbol: Ag
Latin name: Argentum
Atomic number: 47
Valency : 1
Occurance: Silver is found in free as well as combined state.

The chief ore of silver are:

  • Silver Glance (Ag2S)
  • Horn Silver (AgCl)
  • Bromyrite (AgBr)
  • Pronstite silver (Ag3AsS3)

Extraction of silver:

Silver is extracted from argentite by cynide process. The steps involved in exraction process are as follows.

1. Crushing and pulverization: The sulphide ore crushed in jaw crusher and powdered in ball mills.

2. Concentration: The concentration process is carried out by froth floatation process. The powdered ore is suspended in water and after adding pine oil, it is stirred by the means of blast of air. The particles of the sulphide ore being preferentially wetted by oil comes to the surface along with froth which is taken out and the gangue particles remains at the bottom which are then removed.

3. Cyanide treatment:

The concentrated ore is changed into cyanide by reacting it with dilute solution (about 0.5%) of sodium cyanide.
$$\ce{Ag2S + 4NaCN->$\underset{\text{Sodium argentocyanide}}{\ce{2Na[Ag(CN)2]}}$ + Na2S}$$
The current of air is passed through this solution continuously for 8-10 hours. Since, the reaction is reversible , the reaction is made to proceed forward by consuming Na2S with the help of air.
$$\ce{Na2S + O2->Na2SO4}$$

4. Recovery of silver: The above solution is filtered to remove the insoluble impurities. Then, it is treated with scrap zinc dust. Since, zinc is more electropositive, so it displaces Ag from its solution.
$$\ce{2Na[Ag(CN)2] + Zn->$\underset{\text{Sodium zincocyanide}}{\ce{Na2[Zn(CN)4]}}$ + 2Ag v }$$
This soluble complex is removed by the method of filtration. The silver, thus obtained is 95% pure and called as spongy silver.

5. Refining: Silver still contains some impurities. So, it is purified by electrolytic refining. Impure silver is made as anode while pure silver is made cathode. The electrolytic tank containing silver nitrade solution is made acidic with 1% nitric acid. On passing current, pure silver gets deposited at cathode. Impurities lies down as anode mud. Thus obtained silver is 99.9% pure. The cell reaction is represented by:
$$\ce{AgNO3->Ag^+ NO3^-}$$
At anode: $$\ce{Ag – ^e->Ag ^+}$$
At cathode: $$\ce{Ag + ^e->Ag }$$

Electrorefining

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One Response to “Extraction of Silver from Argentite”

  1. Isabel

    This is really good and well explained information