Silver and its Compounds
Ores : Argentite (silver glance) Ag2S, Horn silver (AgCl), Ruby silver (Pyrargyrite) 3Ag2S. Sb2S3.
Extraction : Cyanide process or Mac Arthus-Forrest cyanide process : This method depends on the fact that silver, its sulphide or chloride, forms soluble complex with alkali cyanides in the silver. This implies that silver compounds will dissolve in solution of alkali cyanides in the presence of blast of air.
4Ag + 8NaCN + 2H2O + O2 4Na [Ag(CN)2] + 4NaOH
4Ag + 8CN– + 2H2O + O2
Or
Ag2S + 4NaCN
AgCl + 2NaCN
The reaction with the sulphide is reversible and accumulation of Na2S must be prevented. A free excess of air is continuously passed through the solution which oxidizes Na2S into sulphate and thiosulphate.
2Na2 + 2O2 + H2O → Na2S2O3 + 2NaOH
Na2S2O3 + 2NaOH + 2O2 → 2Na2SO4 + H2O
2Na[Ag(CN)2] + 4NaOH + Zn → Na2ZnO2 +4NaCN + 2H2O + 2Ag
Compounds of silver : AgNO3, Ag2S, AgCl, AgBr, AgI, and AgO