As we know, Metals are required for a variety of purposes. For this we need their extraction from the minerals in which they are present and from which their extraction is commercially feasible. These minerals are known as Ores. Ores contain impurities called Gangue/Matrix and they are removed in the form of Slag (when Flux is added to it) in different processes.

Ores contain many impurities and there are few steps involved in extraction of the pure metals.

1. Concentration of the ore

2. Isolation of the metal from the concentrated ore

3. Purification of the isolated metal

   Concentration of the ores:

   Removal of the gangue from the ore is known as Concentration/dressing/benefaction.

   a. Hydraulic washing or Levigation: In this process an upward stream of running water is used to wash the powdered ore. The lighter gangue particles are washed away and the heavier ore particles are left behind. This is based on the difference in gravities of the ore and the gangue particles so it is a type of gravity separation.

   b. Magnetic Separation: If either of the ore of the gangue is capable of being attracted by a magnetic roller then magnetic separation is carried out. Example: Iron ores.

   c. Froth Floatation Method: In this process a slurry of the powdered ore is made with water. A rotating paddle is used to agitate the suspension and air is drawn into the suspension in presence of an oil. As a result froth is formed which carriers the mineral particles. To this slurry we add Froth Collectors (e.g. pine oil, xanthate, etc) which enhance the non-wettability of the mineral particles and Froth Stabilizers (e.g. aniline and cresols) that stabilize the froth. The froth is light and is removed. The ore particles are then obtained from this froth. Example: Sulphide Ores.

   d. Leaching: Leaching is often used if the ore alone but not the gangue is soluble in some suitable solvent. Example: Leaching of Alumina (Al2O3) from Bauxite.

   Extraction of crude metal from the concentrated ore:

   Two steps are involved in this process.

   a. Conversion of the ore into oxide

   i) Calcination: Calcination involves heating of the ore in the absence of air and the volatile matter escapes leaving behind the metal oxide.

   Example: ZnCO3→ ZnO+ CO2(g)

   ii) Roasting: Roasting involves heating of the ore in a regular supply of air. This is carried out at a temperature below the melting point of the metal.

   Example: 2ZnS+3O2→ 2ZnO+ 2SO2

   b. Reduction of Oxide to the metal

   In this process the metal oxide is heating with reducing agents such as C, CO or other active metals. The reducing agent( in this case carbon) combines with the oxygen of the metal oxide to form CO. Example: MxOy+ yC→ xM+ yCO

   Refining/ purification of the metal:

   1. Distillation: This is useful for low boiling metals like zinc and mercury containing high boiling point metals as impurities. The extracted metal in the molten state is distilled to obtain the pure metal as a distillate.

   2. Liquation: In this process low melting metal like tin can be made to flow on a sloppy surface. In this way it is separated from high melting impurities.

   3. Poling: The molten metal is stirred with logs of green wood. The impurities will then be removed either as gases or they get oxidized to form slag over the surface of the molten metal. Blister copper is purified by this method.

   4. Electrolytic Refining: In this method, the impure metal acts as an anode and the pure form of the same metal is used as a cathode. They are put in a suitable electrolyte containing the salt of the same metal. The metal we need gets deposited on the cathode in it’s pure form. Blister copper and Zinc are refined this way.