Gravity separation is a method of separating ores according to the difference in mineral density, which occupies an important position in contemporary mineral processing methods. The advantage of gravity separation is that it handles a wide range of ore size, it can sort the coarse-grained ores that other beneficiation methods can not help, gravity separation equipment is generally relatively simple structure, easy to manufacture, production does not consume expensive chemicals, while the discharge of the waste tailings on the environment is also less polluted.

There are several kinds of re-election methods:

 1, heavy media beneficiation

2, jigging beneficiation

3、Shaking table beneficiation

4, Chute beneficiation

5、Spiral beneficiation

6、Centrifugal concentrator

7、Wind power beneficiation

Now these re-election methods for a simple description and comparison.

First, heavy media beneficiation

Heavy media beneficiation refers to the density greater than 1000 kg/m3 in the medium for the beneficiation process. The density of the medium is generally chosen between the density of light minerals and heavy minerals in the mineral, when the density of the medium is strictly controlled (fluctuation range ≤ 20 kg/m3), the density difference can be only 50 ~ 100 kg/m3 of the two minerals effectively separated.

Heavy beneficiation has been applied in the industry for more than 70 years, mainly used in ore pre-selection, that is, in the coarse-grained conditions to select the veinstone or peridotite, reduce the amount of fine grinding and deep selection of the ore, and improve the grade of the selected ore. At present, it has been widely used in the treatment of iron, manganese, lead, zinc, tin, antimony, coal gangue, diamond and other metal and non-metal ores. The upper limit of the particle size of the selected stone is 50~150mm, and the lower limit is 2~3mm.

Heavy media beneficiation process includes ore preparation, media preparation, ore sorting, media removal, media regeneration and other operations. The disadvantage is that the media preparation, media removal and media regeneration requires a complete set of facilities, relatively complex. The advantages of heavy media beneficiation is (according to certain requirements of the preparation of media density), separation density can be precisely controlled, can make the density difference is very small minerals effectively separated. The processing capacity per unit area is large, and the cost of beneficiation is low. General small and medium-sized processing plant is less used.

Second, jigging beneficiation

Jigging beneficiation is one of the main methods of gravity beneficiation, belonging to the deep trough sorting operation. Jigging beneficiation, in addition to very fine materials, can deal with almost all kinds of particle size of mineral raw materials, process operation is simple, equipment processing capacity, and can be in a sorting in a certain final product, so the production is widely used. The treatment of raw coal by jigging accounts for about 40% of the total amount of coal separation. For metal ores, it is the main method to deal with coarse and medium grained iron ore, manganese ore and chrome ore. And a large number of used in the selection of unevenly embedded tungsten, tin ore coarser particles. The jigger is widely used to process gold-bearing alluvial ores, primary ores and alluvial ores containing niobium, tantalum, titanium and zirconium, and it is also the main method for separating diamonds. The greater the difference in density of the minerals to be separated in the ore, the wider the range of particle size can be selected. For example, for alluvial gold ore in the feed size of less than 25mm, can not be classified into the selection, recovery size lower limit can be 0.04mm. but for general metal ores to implement the classification into the selection can effectively improve the index of sorting and improve the equipment processing capacity.

In the specific gravity difference ≥ 1.25 and ore monomer dissociation under the premise of jigging machine can be selected particle size selection of coal for 150 ~ 2mm, selection of other minerals between the particle size range of 50 ~ 0.1mm, selection of alluvial gold, the lower limit of the particle size up to 0.04mm.

Third, shaking table beneficiation

Shaking table belongs to the flow film mineral processing equipment, from the plane chute development, later to its asymmetric reciprocating motion as a characteristic and self-contained system.

Shaking table is a commonly used equipment for sorting fine-grained ores, the effective size range is 3~0.019mm when dealing with metal ores, and the upper limit of particle size can reach 10 mm when selecting coal.The outstanding advantage of shaking table is high accuracy of sorting, and high grade concentrate or waste tailings can be obtained by one sorting, and multiple products can be received at the same time. Plane shaking table is easy to look after and convenient to adjust. The main disadvantage is that the equipment covers a large area, and the processing capacity per unit plant area is low. Standard shaking table (4500×1830) processing capacity of 0.12~2.2t/h. The finer the particle size, the smaller the processing capacity.

Fourth, chute beneficiation

Chute beneficiation belongs to the inclined flow sorting process. Slurry to a certain inclined inclined chute or inclined, driven by the water flow, the ore group loose stratification, the upper layer of fine minerals quickly discharged out of the tank, the lower layer of heavy minerals are retained in the tank or discharged from the lower part of the low speed. Separate pick up, that is, the concentrate and tailings.

Chute is the earliest appearance of mineral processing equipment. Its advantage is that the equipment structure is simple, low investment and production costs, coarse and medium grains chute also has a higher processing capacity, the disadvantage is that the sorting accuracy is low, the recovery rate is also low, the emergence of jig and shaking table, the use of chute is greatly reduced. Currently used more is the slime chute, used to deal with tungsten, tin, gold, platinum and other rare metal ores, micro-fine grained (-0.074mm) low-grade alluvial ores.

Fifth, spiral beneficiation

Spiral concentrator is bent into a spiral long trough in the beneficiation process, still belongs to the category of oblique flow beneficiation, but here the use of the slurry in the rotary movement of inertial centrifugal force, prompting the fine heavy minerals in the groove on the surface of the sub-band, and respectively, continuously discharged.

(A) spiral concentrator

Spiral concentrator has simple structure and no moving parts. Occupies an area of small, unit processing capacity is larger, operation and maintenance is relatively simple. The machine is suitable for processing sand ore containing less mud, feeding particle size in 2~0.1mm, with 0.5~0.1mm as the best. In the processing of high mud-containing vein ore grinding products should be deslimed or graded, otherwise it will reduce the quality of concentrate and recovery rate. The disadvantage is that the beneficiation is relatively low, and the selected concentrate generally needs to be re-processed and re-elected.

(ii) Spiral chute

Slurry flow in the spiral chute and sorting principle and spiral concentrator is basically the same. Only in the spiral chute groove surface has a larger gentle width, the slurry is laminar flow flow area is larger, so suitable for processing fine-grained ores.

Spiral chute also has a simple structure, large capacity, easy to operate, low production costs and other advantages, suitable for processing 0.6 ~ 0.03mm vein ore or sand ore, but high mud on the sorting is unfavourable. Beneficiation enrichment ratio is also lower.

Sixth, centrifugal beneficiation

Centrifugal beneficiation mainly with the help of centrifugal force, accelerating the settling of fine particle size and stratification speed, suitable for dealing with -0.1mm fine-grained minerals, due to the production cost is relatively high compared to the general method of gravity selection, and 37 ~ 19 micron particle size recovery effect is very good. At present, it is mainly used for processing micro fine grade materials with high value such as tungsten.

Compared with the shaking table, in the processing of 0.037 ~ 0.019mm materials, centrifugal concentrator has a small footprint, large capacity, saving power consumption and other advantages, but its beneficiation enrichment ratio are lower, and its concentrate needs to be selected with a belt chute in order to reach the final concentrate. Centrifugal concentrator is mainly used to replace the fabric chute process.

Seventh, wind beneficiation

Wind beneficiation is in the air medium according to the mineral density difference separation process of mineral raw materials, particle size and shape of the particles also have an impact on the separation. Compared with the re-election in the water medium, the advantages of wind beneficiation are:

(1) the operation does not consume water, the product does not need to be dehydrated, and no freezing occurs in winter transport.

(2) equipment structure is simple, infrastructure costs and operating costs are lower. However, there are also significant disadvantages of wind power beneficiation, which are manifested in:

(1) sorting accuracy is much lower than wet re-election, product quality is also poor;

2) Raw materials have to be de-dusted and graded before being selected.

3) It can not deal with wet ores.

(4) sorting process, the equipment should be strictly closed and dust collection, the diffusion of dust on the environmental pollution and health hazards to workers are greater.

Due to the wind ore dressing process is relatively complex, and the efficiency of ore dressing is low, so its application has greater limitations. At present, it is mainly used to deal with coal, asbestos and other non-metallic minerals, especially on the processing of mineral raw materials that should not be exposed to water.