Used when the ore is soluble in some suitable solvent
(i) eg. Leaching of Alumina From Bauxite
• Bauxite usually contain SiO2, Iron oxides, TiO2 etc as impurities
• Powdered ore is digested with conc NaOH at 473 - 523 K and 35-36 bar pressure
• Al2O3 and SiO2 are leached out as Sodium aluminate and Sodium silicate.
• The impurities are left behind
• The aluminate is neutralised by passing CO2 so that hydrated aluminium oxide is precipitated(seeded with fresh Hydrated Al2O3
• The sodium silicate *** in the solution
• Hydrated alumina is Filtered, dried and heated to give pure Al2O3
(ii) eg. - Leaching of Silver and Gold
• Leached with a dilute solution of NaCN or KCN in presence of air
• The metal is obtained later by Displacement
