Extraction of Silver by cyanide process and its uses
Silver also occurs both in combined state as well as in free state. The important ores of silver are: Argentite (Ag2S), Copper silver glance, Horn silver, Ruby silver. The silver ores are found along with gold ores in some parts of India.
Silver is extracted from the ore-argentite (\(Ag_2S\)). The process of extraction of silver is called as cyanide process as sodium cyanide solution is used. The ore is crushed, concentrated and then treated with sodium cyanide solution. This reaction forms sodium argento cyanide \(Na [Ag(CN)_2]\).
\[ Ag_S + 4NaCN \rightleftharpoons 2Na [Ag(CN)_2] + Na_2S\]
The solution of sodium argento cyanide combines with zinc dust and forms sodium tetra cyanozicate and precipitated silver. This precipitated silver is called spongy silver.
\[ Zn + 2Na [ Ag (CN)_2] \rightarrow Na_2 [Zn(CN)_4] + 2Ag \]
The spongy silver is fused with potassium nitrate to obtain pure silver. Then the silver obtained is purified by electrolytic process.