The process of extraction of metals by dissolving the ore in a suitable chemical reagent and the precipitation or displacement of the metal by more reactive or electropositive metal is called hydrometallurgy.
For example:
Conc. argentite Ag2S is first treated with a dilute solution of NaCN to form the soluble complex sodium dicyanoargantate (I).
Ag2S + 4NaCN → 2Na[Ag(CN)2] + Na2S
Sodium dicyanoargentate (I) (soluble)
In the above complex, Zn metal is mixed and Ag metal is obtained by replacement.
2Na[Ag(CN)2] + Zn → Na2 [Zn(CN)4] + 2Ag ↓
