The purpose of mineral processing is to separate useful minerals (or useful components) from the raw ore and enrich them to form an artificial bonanza (or compound) with a single component, the so-called concentrate.The mineral processing process should be completed by taking advantage of the differences in the properties of each mineral in the ore.Gravity mineral processing is based on the different densities between ore particles, so the gravity, hydrodynamics and other mechanical forces in the moving medium are different, so as to realize the process of sorting ore particle groups by density, referred to as selection.In the process of metal ore dressing, the density of the recovered target metal mineral is higher than that of gangue. At this time, the heavy product obtained by sorting is concentrate and the light product is tailings.

During the reselection process, the separation of minerals is gradually completed during the movement.In other words, ore particles of different properties should have different motion conditions—direction of motion, speed, acceleration and trajectory-in the reselection equipment, so as to achieve the purpose of mineral separation.At the same time, all reselection processes must be carried out in a certain medium.When materials composed of ore particles of different particle sizes and densities move in a flowing medium, due to the differences in their properties and the different flow methods of the medium, the ore particles are subjected to different media resistance and their motion states are also different.The ore particle group is not easy to loose in the stationary medium, and it is difficult for ore particles of different densities, particle sizes, and shapes to transfer to each other. Even if they reach stratification, it is difficult to achieve separation.For reselection, the role of the medium is very important.The media used for reselection include air, water, heavy liquid, and heavy suspension.

Among them, the most used is water. Air is available in dry areas where there is a shortage of water or when processing certain special ores. At this time, it is called wind mineral processing.Heavy liquids are liquids with a density greater than water or aqueous solutions of high-density salts, in which minerals can be strictly separated by density, but because such liquids are expensive, they are limited to laboratory use.A resuspended solution is a mixture of high-density solid particles and water. Its apparent density is higher than that of the light product and lower than that of the heavy product, so it can play the same role as the heavy liquid.The mineral processing method that uses resuspended liquid as the medium is called heavy medium mineral processing.With the increase of the density of the sorting medium, the difference in the movement condition of ore particles of different properties also increases, and the better the sorting effect within a certain range.

In the process of reselection, although the role of the medium is very important, the role of the medium is an external factor. The root cause of the separation of minerals is the difference in their own properties, that is, the difference in particle density, particle size and shape.The density and particle size together determine the gravity of the particles, which is the basic force that drives the movement of the particles in the medium.In the process of mineral processing, the operation that basically separates the ore according to the density difference is the ore sorting operation.However, when the density difference between minerals is not large, the particles of different particle sizes can also settle at different rates in the medium to achieve separation by particle size. This kind of operation is called grading operation.At this time, the shape of the ore particles also affects the speed of their movement in the medium, which is also an important factor in the separation process.