Gravity Separation
Gravity separation is one of the oldest and most common methods of separating and recovering minerals from ore, and has been used for thousands of years. Gravity separation is particularly useful for minerals that are not very dense, such as coal and certain industrial minerals, as well as for certain heavy minerals, where even a small difference in density can make a large difference in recovery.
Gravity separation is based on the differences in specific gravity of minerals and gangue. In general, specific gravity is calculated by comparing the relative weights of equal volumes of compounds. The difference in specific gravity between minerals and gangue results in different terminal velocities and therefore different paths of particles in the water.
Gravity separators, such as the Knelson separator, are typically used to separate minerals which are mineralogically similar, but with different specific gravities. In this way, minerals with higher specific gravity are relatively easy to isolate, while those with lower specific gravity are much more difficult to isolate. This is because the lower specific gravity particles travel further down the separator bed than the higher specific gravity particles.
Gravity separation is used in many industries, such as coal, agriculture, and mineral beneficiation, as well as in water treatment and wastewater treatment processes. It is also used for many research and engineering applications, such as for the separation of cells and particles.
Gravity separation is most effective when there is a large difference in the specific gravity of minerals and gangue. When this difference is smaller, it is more difficult to separate the two when using gravity. In such cases, other separation methods can be used, such as flotation, magnetic separation, and electrostatic separation.
Gravity separation is also limited by the fact that it cannot separate materials that are of similar compositions and densities. For example, it is difficult to separate plastics from metals using gravity since both have similar densities.
Gravity separation is a simple process, but it can be affected by a number of factors. These include the particle size distribution, density, and the surface properties of the particles. It is therefore important to understand how the process works in order to be able to optimize it for different applications.
