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Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?
A
Galena
B
Copper pyrite
C
Sphalerite
D
Argentite
Detailed Solution
Leaching is the selective dissolution of the desired mineral in a suitable reagent, leaving behind the impurities.
Argentite or silver glance, $Ag_2S$, is an ore of silver.
Silver is extracted from argentite by the MacArthur-Forrest cyanide process, which is a leaching process: the ore is treated with a dilute solution of NaCN in the presence of air.
$Ag_2S + 4NaCN \rightarrow 2Na[Ag(CN)_2] + Na_2S$
Silver dissolves as the soluble complex and is later recovered by displacement with zinc. Gold is leached in the same way: $4Au + 8KCN + 2H_2O + O_2 \rightarrow 4K[Au(CN)_2] + 4KOH$
Galena (PbS), copper pyrite ($CuFeS_2$) and sphalerite (ZnS) are concentrated by froth flotation.
So the exception is argentite.
Argentite or silver glance, $Ag_2S$, is an ore of silver.
Silver is extracted from argentite by the MacArthur-Forrest cyanide process, which is a leaching process: the ore is treated with a dilute solution of NaCN in the presence of air.
$Ag_2S + 4NaCN \rightarrow 2Na[Ag(CN)_2] + Na_2S$
Silver dissolves as the soluble complex and is later recovered by displacement with zinc. Gold is leached in the same way: $4Au + 8KCN + 2H_2O + O_2 \rightarrow 4K[Au(CN)_2] + 4KOH$
Galena (PbS), copper pyrite ($CuFeS_2$) and sphalerite (ZnS) are concentrated by froth flotation.
So the exception is argentite.