• Hydraulic washing: This process separates the heavier ore particles from the lighter gangue particles. This is done by washing them in a stream (jet) of water over a vibrating, sloped table with grooves. Denser ore particles settle in grooves. Lighter gangue particles are washed away (Fig. 14.10).

• Froth floatation: In this process, separation of the ore and gangue particles is done by preferential wetting. This process is generally used for sulfide ores of copper, lead, and zinc. The finely powdered ore is mixed with water and suitable oil in a large tank. A current of compressed air agitates the mixture. The ore particles are wetted by oil and form froth at the top, which is removed. The gangue particles wetted by water settle down. Ore preferentially wetted by oil is removed as froth. Gangue wetted by water is removed after it settles down (Fig. 14.11).

• Magnetic separation: This process is used in the extraction of metals which exhibit magnetic properties. For example, in the extraction of iron, crushed magnetite ore (iron) particles are separated using their magnetic property. The pulverized ore is moved on a conveyor belt. Electromagnetic wheel of the conveyor attracts only the magnetic particles into a separate heap. Only the magnetic particles are attracted by the magnetic wheel. These particles fall separately into a different heap (Fig. 14.12).

• Chemical separation: This process utilizes the difference in some chemical properties of the metal and gangue particles for their separation. For example, in the Bayer’s process of aluminium extraction, the bauxite ore is treated with hot sodium hydroxide solution. Water-soluble sodium aluminate formed is filtered to separate the undissolved gangue particles. Sodium aluminate (NaAlO2) is further processed to get aluminium oxide (Al2O3).