Q. Explain about Gravity Separation?
This is one of the simplest processes of concentration of ores. It is based on the difference in the specific gravities of the gangue and ore. In this process, the crushed ore is kept on top of a sloping table, which is prepared to vibrate. A stream of water is goes in the direction perpendicular to the slope. The lighter particles are thrown up by vibration and are replaced by the water stream. The heavier mineral particles settle to the base and are collected. This process of gravity separation is called as tabling. Casseterite or tin-stone, pitchblende and chromite are concentrated by this method.
A modification of the above process is sinking and float method. In this the powdered ore is suspended in a liquid whose specific gravity is intermediate between the ore and the densities of gangue. The lighter material floats and the heavier material sinks. In this process, the difficulty is in finding a liquid of the proper specific gravity. A solution of calcium chloride in after is usually used. Suspensions of sand in water giving liquids of specific gravities up to 3.2 are also used. Thus, due to technical problems this process is rarely used in concentration of low grade ores, but it is widely used in cleaning coal.