Silver is extracted from the argentite ore by the Mac-Arthur and Forrest’* cyanide process. The various steps involved in this process are as follows :
(a) Concentration : The crushed ore is concentrated by froth floatation process.
(b) Treatment of ore with NaCN : The concentrated ore is treated with 0.4 – 0.6% solution of sodium cyanide. This mixture is agitated by a current of air. So that Ag present in the ore is converted into soluble sodium argento complex.
(c) Precipitation of Silver : The solution containing sodium argento cyanide is filtered to remove insoluble impurities and filtrate is treated with zinc dust, silver gets precipitated.
2Na[Ag(CN)2] + Zn → Na2 [Zn(CN)4] + 2Ag
(d) Electrolytic refining : Impure silver is made anode and a thin sheet of pure silver act as cathode. Silver nitrate acidified with 1% nitric acid acts as an electrolyte. On passing electricity pure silver gets deposited at the cathode.
