This is based on the fact that more electropositive metal can displace less electropositive metal from its salt solution. The ore is treated with such chemical reagents which converts it into soluble compound. By the addition of more electropositive metal to filtrate, the metal present in ore can be precipitated.
Example: Extraction of copper from malachite ore:
CuCO3.Cu(OH)2 2CuO + H2O + CO2
The solution of copper sulphate, scrap iron is added which precipitates copper.
This method is used for the extraction of noble metals like gold, silver etc. from the native state. The finely powdered ore is brought in contact with mercury, which combines with the particles of the metal present in The ore and form amalgam. The metal is recovered from the amalgam by subjecting it to distillation, where the mercury distills over leaving behind the metal.