Mineral processing is an important process of extracting useful minerals from the raw ore and separating them from the chondrites, so as to improve the mineral grade and meet the requirements of industrial utilisation. In the complex process of mineral processing, hydrocyclone, as a kind of high-efficiency separation equipment, plays a variety of indispensable roles by virtue of its unique working principle and structural characteristics. It has the advantages of simple structure, small footprint, large processing capacity, high separation efficiency, and occupies an important position in the modern mineral processing industry.
一.The working principle of hydrocyclone
The main structure of hydrocyclone is in the shape of a cylinder cone, which is composed of feed pipe, overflow pipe, sand sinking port and other parts. When the slurry with a certain pressure from the feed pipe along the tangential direction into the cyclone, it will be in the cylinder to do high-speed rotary movement, forming the inner and outer two spiral flow field. Under the combined effect of centrifugal force, centripetal force and gravity of the fluid itself, the particles in the slurry are separated according to the differences in particle size, density and other properties. Coarse particles and particles with high density are thrown to the wall and spiral downward along the wall due to large centrifugal force, and finally discharged from the sand sinking port as sand-settled products; while fine particles and particles with low density move upward along with the inner helix, and discharged through the overflow pipe as overflow products.
二.The specific role of hydrocyclones in mineral processing
1.Classification
Classification is a key part of the mineral processing process, the purpose of which is to separate mineral particles of different sizes according to specific requirements for subsequent separate processing. Hydrocyclones are widely used in classification operations to achieve efficient classification of mineral particles. For example, in the grinding circuit, hydrocyclones often form a closed loop system with ball mills and other grinding equipment. The slurry discharged from the ball mill enters the hydrocyclone, and after classification, the coarse-grained slurry (sinker) returns to the ball mill for further regrinding, while the fine-grained slurry (overflow) enters the subsequent sorting operation. In this way, it can effectively control the particle size composition of the grinding products, avoid the occurrence of over-crushing phenomenon, and improve the grinding efficiency and recovery of useful minerals. Compared with traditional mechanical classification equipment such as spiral classifier, hydrocyclone has significant advantages such as high classification efficiency, high classification accuracy, large processing capacity and small footprint. In some large-scale mineral processing plant, the use of hydrocyclone classification, can make the particle size of the grinding product more uniform, for the subsequent flotation, re-election and other sorting operations to provide more suitable into the selection of materials, so as to enhance the technical and economic indicators of the entire beneficiation process.
2.Desliming
In many ores, often accompanied by a large number of clay minerals and other fine-grained mud impurities. The existence of these mud impurities will have a negative impact on the subsequent separation operations, such as in the flotation process, fine mud will be adsorbed on the surface of the useful minerals, hindering the effective role of the trapping agent and the minerals, reducing the grade and recovery of flotation concentrates; in the re-election process, the fine mud will interfere with the mineral stratification according to the density, affecting the effect of re-election. Hydrocyclone can be used to remove the fine mud impurities in the ore. When the slurry enters the cyclone, the fine-grained mud is easier to be discharged with the overflow due to its small mass and relatively weak centrifugal force, while the coarse-grained minerals remain in the sediment, thus realising the desliming of the slurry. In the processing of some non-ferrous metal ores or rare metal ores containing a large number of clay minerals, the use of hydrocyclone for pre-demuding can effectively improve the conditions of the sorting operation and improve the sorting index. 3.Concentration
Concentration is an important operation to reduce the water content of the slurry and increase the concentration of the slurry, which is conducive to subsequent transport, storage and further processing. Hydrocyclones also play an important role in thickening operations. When the slurry enters the cyclone, under the action of centrifugal force, most of the water is discharged with the overflow, while the solid particles are enriched in the bottom sand sinking port, which makes the concentration of the sand sinking significantly improved. Compared with the traditional concentration equipment such as thickener, hydrocyclone has the advantages of simple structure, small footprint and fast processing speed. In some of the site space limitations of the mineral processing plant or the need to quickly achieve the slurry concentration occasions, hydrocyclone concentration role is particularly prominent. For example, in the tailings treatment process, through the hydrocyclone to concentrate the tailings slurry, can reduce the volume of tailings discharge, reduce the cost of tailings treatment, but also conducive to the subsequent comprehensive use of tailings or stockpile disposal.
3.Re-election Auxiliary Role
Re-election is a beneficiation method that separates minerals based on their density differences. Hydrocyclone can be used as the auxiliary equipment of re-election to further strengthen the effect of re-election. In the process of re-election, hydrocyclone can pre-grade and concentrate the ore slurry, so that the particle size and concentration of the ore slurry into the re-election equipment is more in line with the re-election requirements, thus improving the sorting precision and efficiency of re-election. For example, when dealing with alluvial gold ore, the slurry is first classified and concentrated by hydrocyclone, and the coarse-grained and highly concentrated slurry is sent to the jig machine and other re-election equipment, which can effectively improve the recovery rate of gold. In addition, hydrocyclone can also be used in conjunction with other re-election equipment such as shaking table to re-grade and re-select the re-election products, further purify the concentrate and reduce the tailings grade.
4.Pre-treatment before flotation
Before flotation operation, appropriate pretreatment of the slurry is essential to improve the flotation effect. Hydrocyclone can be used for pre-treatment of slurry before flotation, through classification and desliming, etc., to improve the properties of slurry and create favourable conditions for flotation. As mentioned above, desliming can remove the fine mud impurities in the slurry and reduce its adverse effect on flotation; classification can make the slurry size more uniform, which is conducive to the full effect of flotation chemicals and minerals. At the same time, the hydrocyclone can also adjust the slurry concentration and flow rate, affecting the surface properties of mineral particles and suspension state, to further optimise the flotation process.
By virtue of its unique working principle and efficient separation performance, hydrocyclone plays a variety of important roles in mineral processing, such as classification, desliming, concentration, re-election auxiliary and pre-treatment before flotation. It can not only effectively improve the technical indicators of the mineral processing process, improve the recovery rate of useful minerals and concentrate grade, but also reduce production costs and reduce environmental pollution. With the continuous development of mineral processing technology and the increasing requirements for the comprehensive utilisation of resources, hydrocyclone is expected to play a greater role in mineral processing, the application prospects in the field of mineral processing will be more broad, providing strong support for the sustainable development of the mining industry.
三.Factors affecting hydrocyclone performance and optimisation measures
1.Structural parameters
Cyclone diameter: the larger the diameter, the larger the treatment capacity, but the separation size also increases accordingly. In practical application, according to the treatment capacity and the required separation particle size to choose the appropriate diameter of the cyclone. For fine grading, a small diameter cyclone is usually used; while for large-scale coarse grading or dewatering operations, a larger diameter cyclone can be used.
Cone angle: the cone angle affects the residence time and centrifugal force distribution of the slurry in the cyclone. Smaller cone angle is conducive to fine grading, can improve the grading accuracy; larger cone angle is suitable for coarse grading and dewatering operations, can increase the amount of sand discharged.
Diameter of overflow pipe and sand sinker: if the diameter of overflow pipe increases, the overflow particle size becomes thicker, and the processing capacity increases; if the diameter of sand sinker increases, the amount of sand sinking increases, but the content of fines in the sand sinking may also increase. Reasonable adjustment of the ratio of the two diameters can optimise the separation effect.
2.Operating parameters
Feed pressure: Feed pressure directly affects the rotational speed and centrifugal force of the slurry in the cyclone. Increased pressure, increased centrifugal force, separation of fine particle size, but too high a pressure will lead to increased wear and tear of equipment, increased energy consumption, and may make the overflow run coarse. According to the actual situation should choose the appropriate feed pressure, generally between 0.1 – 0.3MPa.
Ore concentration: the concentration of ore has a greater impact on the performance of hydrocyclone. Concentration is too high, the viscosity of the slurry increases, and the mutual interference between the particles intensifies, which will reduce the grading efficiency and separation accuracy; concentration is too low, the processing capacity decreases. Different minerals and operational requirements have different suitable feed concentration, usually between 10% – 30%.
Feeder flow: stable feeder flow is the key to ensure the normal operation of hydrocyclone. Flow fluctuation will lead to unstable flow field in the cyclone, affecting the separation effect. By installing flow control devices to ensure that the feed flow rate is stable within the design range.
3.Optimisation measures
Equipment selection and combination: According to the nature of minerals, processing scale and process requirements, reasonably select the type and specification of hydrocyclone, and use multiple cyclones in series or parallel to meet different operational requirements. For example, in the grading operation, the tandem cyclone group of coarse grading and then fine grading can be used to improve the grading effect.
Application of wear-resistant materials: As the hydrocyclone is subject to high-speed scouring of the slurry during the working process, the wear and tear is more serious. The use of wear-resistant materials to manufacture key components of the cyclone, such as rubber lining, polyurethane, etc., can effectively extend the service life of the equipment and reduce equipment maintenance costs.
By virtue of its unique working principle and significant performance advantages, hydrocyclone plays a vital and diversified role in many aspects of mineral processing, such as particle size classification, desliming, dewatering and concentration, as well as re-election assistance. With the continuous development of mineral processing technology and the increasing requirements for the efficient use of resources, the application prospect of hydrocyclone will be more broad. Through in-depth study of the factors affecting its performance, and take reasonable optimisation measures, and constantly improve the equipment structure and operation process, hydrocyclone will continue to play an important role in improving the efficiency of mineral processing, reducing production costs, promoting the comprehensive utilisation of resources and environmental protection, etc., and provide a strong support for the sustainable development of the mineral processing industry.
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