(i) Argentite is Ag2S. Silver is extracted form its ore argentite (silver glance, Ag2S) as follows :
(1) Silver glance is concentrated by froth flotation.
(2) Leaching : The concentrated ore is ground to fine powder and dissolved in dilute solution of sodium cyanide.
Ag2S + 4NaCN → 2NaAg(CN)2 + Na2S
Oxygen of air converts Na2S to Na2SO4 thereby preventing reaction to take place in the revesible direction
(3) Recovery of silver.
Silver is precipitated out by adding electropositive metal, Zn.
2Na[Ag(CN)2] + Zn → Na2[Zn(CN)4] +2Ag
(ii) For development, activated grains are preferentially reduced by mild reducing agents like hydroquinone
AgBr (s) + e- → Ag(s) + Br-
(Reducing of activated AgBr to elemental silver.)
The photographic film is permanently fixed by immediately washing out any non activated AgBr
AgBr(s) + 2Na2S2O3 → Na3Ag(S2O3)2 + NaBr
hypo soluble
