What is Gravity concentration

Gravity separation is the separation of two or more minerals of different specific gravity by their relative movement in response to the force of gravity and one or more other forces (such as centrifugal forces, magnetic forces), one of which is resistance to motion (drag force) by a viscous medium such as heavy media or water.

Gravity separation is one of the oldest technique in mineral processing but has seen a decline in its use since the introduction of methods like flotation, classification, magnetic separator and leaching. Gravity separation dates back to at least 3000 BC when Egyptians used the technique for separation of gold.

There are several methods that make use of the density differences of particles-

•     Heavy media or dense media separation (these include, baths, drums, larcodems, dyana whirlpool separators, and dense medium cyclones)

•     Shaking tables, such as the Wilfley table[4]

•     Spiral separators

•     Reflux Classifier

•     Jig concentrators are continuous processing gravity concentration devices using a pulsating fluidized bed.

•     Centrifugal bowl concentrators, such as the Knelson concentrator and Falcon Concentrator

•     Multi gravity separators (Falcon Concentrator, Knelson, Mozley (Enhanced Gravity Separator), Salter Cyclones (Multi-Gravity Separator) and the Kelsey Jig)

•     Sluice box

These processes can be classified as either dense medium separation or gravity separation. The difference between the two that gravity separation does not use a dense medium to operate, only water or air. Dense medium separation can be performed with a variety of mediums. These include, organic liquids, aqueous solutions, suspensions in water and suspensions in air. Of these, most industrial processes use suspensions in water. The organic liquids are not used due to their toxicity and difficulties in handling. The aqueous solution as a dense medium is used in coal processing in the form of a belknap wash and the suspension in air is used in water-deficient areas, like china, where sand is used to separate coal from the gangue minerals. The dense medium separation is also classified as absolute gravity separation as the sinks and the floats travel in different directions. The gravity separation is also called relative gravity separation as they separate particles due to their differences in the magnitude of the particle response to a driving force.