Basic Principles of Metallurgy

Metallurgy involves the extraction of pure metals from ores through various processes. The first stage in this process is the concentration of ores, where impurities (gangue) are separated from the desired metal. The method used depends on the physical properties of the metal and gangue, the metal's reactivity, and environmental considerations.

1. Concentration of Ores: The removal of gangue from ores to increase the concentration of the desired metal. Different methods are used based on the properties of the ore and gangue.

a) Separation Based on Gravitation: Heavier ore particles can be separated from lighter gangue using gravity-based methods.

Wilfley Table Method: A vibrating table with wooden riffles is used. Water flows over the table, carrying away lighter gangue while heavier ore particles settle between the riffles.
Hydraulic Separation Method: Ore is ground into fine powder and released into a tapered tank. A strong water jet pushes out lighter gangue while heavier metal particles settle at the bottom. Based on gravitational force, separating particles by weight.

b) Magnetic Separation Method

• It is used when one component is magnetic and the other is not.
• The powdered ore is passed over a conveyor belt with two rollers:
• One is nonmagnetic, and the other is an electromagnetic.
• Magnetic metal particles stick to the magnetic roller while nonmagnetic gangue falls off.
• Example: Cassiterite (SnO₂) contains ferrous tungstate (FeWO₄), which is magnetic and can be separated.

Magnetic separation

c) Froth Flotation Method

Based on the hydrophilic (water-attracting) and hydrophobic (water-repelling) properties of particles. Metal sulphides (ZnS, CuFeS₂) are hydrophobic and get coated with oil, while gangue is hydrophilic and remains in water.

Process:

• Finely ground ore is mixed with water and oil (e.g., pine or eucalyptus oil) in a tank.
• Air is blown, forming foam (froth).
• Sulphide ore particles attach to the froth and float, while gangue sinks.

Froth floatation method

d) Leaching (Chemical Separation)

The ore is soaked in a specific solution that dissolves the metal but leaves gangue behind. Example: Bauxite (Al₂O₃) is purified using NaOH, which dissolves alumina but not impurities.

It is used for aluminium, gold, and silver extraction.