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  Extraction of silver

Extraction of silver from the Argentite ore:

Silver is extracted from argentite ore by the Mac-Arthur and Forrest’s cyanide procedure. The various steps included in this procedure are as follows:

1. Concentration:

The crushed ore is concentrated by froth-floatation procedure.

2. Treatment of the ore with NaCN:

The concentrated ore is treated with 0.4-0.6 percent solution of sodium cyanide for many hours. The mixture is continuously agitated by a current of air, and hence Ag present in the ore is transformed into soluble sodium argento complex.

Ag2S + 4NaCN ↔ 2Na [Ag(CN)2] + Na2S
                       Sodium argento cyanide (soluble)

3. Precipitation of silver:

The solution having sodium argento cyanide is filtered to eliminate insoluble impurities and filtrate is treated with zinc dust, silver acquires precipitated.

2Na [Ag(CN)2] + Zn → Na2[Zn(CN)4] + 2Ag↓

4. Electrolytic refining:

The impure silver is then purified by electrolytic refining. The impure silver made the anode whereas a thin sheet of pure silver acts as the cathode. The electrolyte is silvernitrate acidified with 1percent nitric acid. On passing electricity, pure silver gets deposit at the cathode.

5. Extraction of silver from silver coins:

Silver coins are Ag-Cu alloys. Ag can be acquired from such an allloy by dissolving the alloy in concentrated HNO3, a solution having a mixture of AgNO3 and Cu(NO3)2  is  acquired. The solution is then boiled to expel excess of nitric acid, then the solution is treated with concentrated HCl, silver is precipitated as AgCl. AgCl is separated and transformed to silver by fusing with excess Na2CO3.

4AgCl + 2Na2CO3 → 4Ag↓ + 4NaCl + 2CO2 + O2

The silver so obtained is purified by the fusion with borax and followed by electrolytic purification.

 

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