What is the role of zinc metal in the extraction of silver ?
Silver is extracted from the ore-argentite (Ag2S). This 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 results into sodium argento cyanide Na[Ag(CN)2]. The reaction is as follows:
AgS + 4NaCN ⇌ 2Na[Ag(CN)2] + Na2S
The solution of sodium argento cyanide combines with zinc dust. It forms sodium tetra cyanozicate and precipitates silver. This precipitated silver is called as spongy silver. The reaction is as follows:
Zn + 2Na[Ag(CN)2] → Na2[Zn(CN)4] + 2Ag
The spongy silver is fused with potassium nitrate to get pure silver. This silver obtained is purified by electrolytic process.