Gravity beneficiation

China is an ancient country with a long history and developed culture. It began to smelt copper more than 4,000 years ago. In 1637, Song Yingxing's "Heavenly Creations" recorded many examples of the application of gravity sorting. Such as: cereal selected windmill wind, water power extraction clay classification method, selected by panning method yields tin and iron sand sand.

China's first election coal plant was built in 1917. At present, there are more than 500 large and small coal preparation plants in China, all of which have gravity selection equipment. Among them are small re-election equipment and large-scale modern re-election equipment.

Re-election concept

Gravity beneficiation is a method of sorting ore in a certain fluid medium according to the difference in mineral density. Re-election is carried out in a fluid medium, usually water, and sometimes air or heavy medium (heavy liquid or resuspension).

The essence of re-election is summarized as a loose-layered-separation process. The loose action of the fluid must obey the requirement of stratification of the granules. The problem of re-election theory is simply to explore the relationship between looseness and stratification. The layered ore layers are discharged under mechanical action, that is, sorting is achieved.

Looseness is a condition, stratification is the goal, and separation is the result.

Basic principle of reselection

Most re-election processes include two stages: loose-stratified and transport-separated. In the moving medium, the loose ore clusters form stratification of different density (or particle size) ore particles due to differences in the state of motion during settling. The layer of the good layer (ie the layer of material consisting of the ore particles) is separated by the transport of the moving medium. The basic law can be summarized as: loose (settling) stratification (transport) separation. In fact, loose stratification and separation of operations are almost always occurring. But looseness is a condition of stratification, and stratification is the basis of separation. Settlement is the most basic form of exercise. Looseness can be seen as a special form of sedimentation of ore particles in an ascending medium stream.

1. The difference in density of different minerals in the ore is the basic condition for re-election

The density and particle size of the ore particles determine the weight of the particles and are the basic forces that drive the particles to move in the medium. The different weights of the ore particles are subject to different gravitational fluid dynamics and other mechanical forces in the medium, and their speed and motion. The trajectory is also different.

2. Mechanical action provides media to form motion and promote material stratification

The reselection process must not only be carried out in the medium, but must also be carried out in the moving medium. The ore particles are not easy to loose in the static medium, and the positions of the ore particles of different densities, particle sizes and shapes cannot be transferred to each other, and even if the layering is reached, it is difficult to achieve separation. Only a moving medium can loosen the tight material layer. Mechanical action is the source of energy for media motion.

3. The medium is both a medium for transmitting mechanical forces and at the same time completing product transportation.

The medium is important for re-election. The medium used for re-selection is water, air, and heavy liquid with a density greater than water. Under the action of buoyancy and resistance generated by the medium, the ore particles with different properties have different movement states, and the separation is achieved according to the difference. The medium uses mechanically powered loose particles to create conditions for stratification and at the same time undertake the task of transporting products.

Reselection method

According to the movement form of the medium and the purpose of the work, there are several operation methods for re-election.

(1) Classification (2) Washing (3) Heavy medium dressing

(4) Jigging ore dressing (5) Shaker beneficiation (6) Chute dressing

(7) spiral beneficiation (8) centrifugal force beneficiation (9) wind beneficiation

Grading and washing are operations that are separated by particle size and are often used in the preparation of ore before the selection. Other local arts are substantive sorting operations.

Common features of various re-election processes:

(1) There must be a difference in density (or particle size) between the ore particles;

(2) The sorting process is carried out in a moving medium;

(3) Under the combined action of gravity, fluid dynamics and other mechanical forces, the ore particles are loose and stratified by density (or particle size);

(4) Separate the layers of materials, achieve separation under the movement of moving media, and obtain different final products.

Application of re-election method

Re-election is suitable for processing ore or other materials with a large density difference between useful minerals and gangue. It is an effective method for treating ore, medium and fine (substantially bound to be larger than 25 mm, 25-2 mm, 2-0.1 mm) ore. In the treatment of fine slime (less than 0.1 mm), the efficiency is not high, the modern film-forming equipment can effectively recover the particle size to 20-30 microns, and the centrifugal concentrator can reach 10 microns.

The re-election method is a method for treating tungsten, tin, gold ore, especially for the treatment of gold and tin. Re-election in the coal preparation industry is the main method.

Reselection characteristics

(1) The granularity of useful mineral inlays restricts the sorting effect;

(2) There are many sorting equipment and the process is relatively complicated;

(3) The ore size of the re-election treatment is wide, up to several tens of millimeters;

(4) The structure of the re-election equipment is generally simple, does not consume expensive materials, and the operation is low;

(5) Less environmental pollution.

Re-election advantage

It is capable of processing ore of various particle sizes at low cost, and processing equipment for coarse (greater than 25 mm), medium (25 to 2 mm) and fine (2 to 0.075 mm) ore, which has high processing capacity, low energy consumption and cost. Generally low, so willing to use it under possible conditions. The re-election equipment for processing fine particles (less than 0.075 mm) has low processing capacity and poor sorting effect, but re-election is still available when other beneficiation methods are difficult to work.

Re-election process for gold ore in a typical re -election process

Reselection is the most effective method of ore and coal, gold, tungsten, tin, treatment, also used to recover the density of the relatively large thorianite, iron titanium, rutile, zircon, monazite, tantalite, columbite and other rare non-ferrous metals and minerals, but also for sorting coarse and disseminated few fine disseminated hematite ore and manganese ore and asbestos, non-metallic minerals such as diamond and solid waste.

The gold grade of the ore deposit of Zijinshan Gold Mine is only 0.8g/t. The concentrator uses the heap leaching-slot re-election-cyanide carbon leaching process to recover the gold in the ore, and obtains a satisfactory technical and economic index. The recovery rate of gold is obtained. More than 80%, the economic and social benefits of the concentrator are very significant. The production process of the concentrator is shown in Figure 1.

Raw ore (-1000mm)

Figure 1 Production process principle of Zijinshan Gold Mine Concentrator

In the gold ore processed by Henan Jinyuan Gold Mining Co., Ltd., more than 51% of the gold is present in a natural gold state with a particle size greater than 0.06 mm. In order to recover this part of the gold economically, reasonably and efficiently, the concentrator set up a re-election operation in the grinding circuit, and used two KC-XD40 Nielsen concentrators to recover the coarse gold. The production process is shown in Figure 5- 10-2. In the case of grinding product particle size of -0.075mm, 55%, and ore concentration (solid mass fraction) of 36%, the gold concentrate yield of Nielsen concentrator is 0.03%, and the gold grade of concentrate is 2800~3500g/ t, the recovery rate of gold in concentrate is 38%.

Another reprocessing process for processing gold ore is shown in Figure 2, and the re-election equipment used is the Nielsen concentrator.

Coarse gold re-fining process at Jinyuan Concentrator

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