What is concentration of an ore? Explain the methods of concentrating ores, with a diagram of froth flotation.

1. 1 · Define. Concentration (ore dressing) is the removal of gangue from the crushed and powdered ore.
2. 2 · Gravity separation. Heavier ore particles stay back while a stream of water washes away lighter gangue. Used for oxide ores like haematite.
3. 3 · Froth flotation. Ore + water + pine oil; air is blown in. Sulphide ore rises with the froth; gangue sinks. Used for copper pyrite and zinc blende.
4. 4 · Draw the froth flotation cell. [Tank with water and pine oil, compressed air pipe, stirrer, froth with ore at the top, gangue at the bottom, all labelled]
5. 5 · Magnetic separation. Ore falls on a belt over a magnetic roller; magnetic and non-magnetic parts fall in separate heaps. Tin stone is separated from wolframite.
6. 6 · Leaching. The ore dissolves in a suitable solvent but the gangue does not. Bauxite dissolves in sodium hydroxide solution.
7. 7 · Real-life link. Bauxite mined in Odisha is leached with caustic soda before aluminium for our vessels is made.
8. 8 · Close in one line. The method chosen depends on the nature of the ore and its gangue.

Scoring tip: Give the principle in one line and one example for each method. The froth flotation diagram must have every label.