Mineral processing method----re-selection method

(1) mineral gravity separation principles and applications:

The re-election method is a method of sorting according to the difference in the specific gravity of the mineral and its different sedimentation speed in the medium.

In the process of re-election, the ore particles of different specific gravity are sorted in the moving medium due to their movement state-moving speed, direction and route.

The basic form of movement of the ore particles is to settle in the medium. When the ore particles settle in the medium, they are called a force: one is the gravity of the ore particles in the medium, and the gravity of a certain ore is certain in a certain medium; the other is the resistance, resistance and medium of the medium. The sedimentation velocity of the ore particles is related. In the initial stage of the sedimentation of the ore particles, due to the small resistance of the medium, the ore particles undergo acceleration settlement under the action of gravity. As the settling velocity increases, the resistance of the medium also increases. As the resistance of the medium increases gradually, the sedimentation acceleration of the ore particles gradually decreases. After a certain time, the acceleration is reduced to zero. At this time, the ore particles settle at a certain speed. This speed is called the final velocity of sedimentation. The final velocity of sedimentation is affected by many factors, the most important of which is the specific gravity, particle size and shape of the ore; the density and viscosity of the medium.

The results show that in a certain medium, the larger the particle size and specific gravity of the ore particles, the larger the sedimentation end velocity. If the particle size of the ore particles is the same, the final sedimentation velocity is larger than that.

In the re-election process, water, air, heavy liquid and suspension are used as the separation medium. Heavy liquid is a liquid with a specific gravity greater than water. The suspension is a two-phase liquid composed of water and solid particles suspended therein.

In daily life, we know that objects immersed in water are subject to the buoyancy of water. According to Archimedes' law, the magnitude of the buoyancy of water is equal in value to the weight of the same volume of water that is deposited by the sinking object. In non-flowing water, an object is subjected to two forces: the gravity of the object is vertically downward and the buoyancy of the liquid is vertically upward. If gravity and buoyancy are equal, the object is in equilibrium; when gravity is greater than buoyancy, the object sinks, and when gravity is less than buoyancy, the object floats.

If the density of the object and the liquid are uniform, the floating or sinking of the object can be determined according to the specific gravity of the object. When the specific gravity of the object is greater than the specific gravity of the liquid, it will sink, and it will float when it is smaller than the specific gravity of the liquid. The difficulty of mineral selection is usually approximately determined by the ratio of (δ2-Δ)/(δ1-Δ). Where δ1 is the specific gravity of small specific gravity ore, δ2

For the specific gravity of large proportion of ore particles, â–³ is the specific gravity of the medium. It is known from experience that it is easier to use the re-election method when this ratio is greater than 2.5, and it is more difficult if the ratio is less than 1.25.

It should be pointed out that when other conditions are the same, as the particle size of the mineral decreases, the difficulty of separation by specific gravity will increase. Because the weight of the fine ore is small, the sedimentation velocity is small, and thus the gravity is separated by gravity. Speed ​​and accuracy are greatly reduced. In order to solve this problem, the fine ore particles can be sorted by specific gravity or particle size under the action of centrifugal force.

Due to the difference in specific gravity and particle size, the settlement of the ore group will occur as shown in Figure 1-1. The large-sized particle d3 with smaller particle size and the small-sized particle d1 with larger particle size will settle at the same speed, d1 And d3 becomes equal drop particles, and d1/d3=l0 is called equal drop ratio. Therefore, when re-electing, the particle size of the ore particles will affect the accuracy of the ore sorting by specific gravity.

In order to sort the ore particles as much as possible by gravity, the ore before re-election must be sufficiently broken to allow the useful minerals to reach the monomer dissociation and reduce the maximum block size entering the re-election. Screening and grading are the separation of ore pellets into various grades for separate re-election operations. From the above concept of equal reduction ratio, it can be seen that the particle size is narrower during re-election, and the effect of particle size can be reduced, but the more accurate the classification of the ore particles by specific gravity.

According to the different principles of action, the re-election method can be divided into hydraulic or wind classification, washing, heavy medium dressing, jigging and dressing, chute dressing, and shaker dressing.

The re-election treatment has a large particle size range, and is particularly suitable for processing coarse-grained materials having a certain specific gravity difference. When selecting fine particles, the selection efficiency is often low. Compared with other methods, the re-election method is simple, low-cost, and easy to launch. Therefore, it is an indispensable job in almost all concentrators. The main applications are:

1 The selection of precious metals such as gold and platinum ;

2 The selection of tungsten and tin ore;

3 Treatment of sand ore containing rare metal element minerals, such as the separation of seashore sand ore containing zirconium and titanium minerals;

â‘£ hematite, limonite sorting;

⑤ sorting of manganese ore;

â‘¥ selected coal and coal gangue separation plant;

7 Separation of some non-metallic minerals from gangue, such as asbestos , mica , kaolin , sepiolite and diamond ;

8 For those non-ferrous metal ores such as copper , lead and zinc which are mainly treated by flotation, pre-enrichment by re-election method;

9 Re-election by particle size sorting process such as grading, de-sludge, etc.

(2) Main re-election methods and equipment:

According to the principle of action and the equipment used, re-election is divided into six types of operations: heavy medium dressing, classification, washing, jigging, shaker dressing, and chute dressing.

1) Jigging ore dressing:

Jigging is one of the most important re-election methods. The essence of the jigging process is to make the mixture of mineral particles of different specific gravity stratified by the specific gravity in the vertical moving variable medium (water or air) flow. The small specific gravity is located in the upper layer, and the larger specific gravity is located in the lower layer. Then, by means of the action of the machine and the action of the water flow, it is divided into products of different specific gravity and discharged separately.

The jigging beneficiation is suitable for the selection of coarse and medium granule materials. The upper limit of the particle size of the selected metal ore is 50mm, and the lower limit is 0.2-0.007mm. Usually used to sort between coarse ore between 18-2mm.

The jig is divided into a hydraulic jig and a wind jig. The wind jig is used very little. According to the structure and the movement of the water flow, the hydraulic jig can be divided into a piston type, a diaphragm type, a pistonless type, and a hydraulic power. There are five types of agitated and moving sieve jigs. The diaphragm jig is widely used, and it has various types of the above-mentioned dynamic diaphragm jig, the lower moving cone diaphragm jig, the side-moving diaphragm jig and the like. The basic structure of all types of jigs is similar, and his selection process is carried out in the jig room. The middle layer of the jigging room has a sieve plate, and a vertical alternating water flow is periodically fed from the sieve plate, and the ore is fed onto the sieve plate to form a dense material layer called a bed. Under the action of the rising water flow, the bed is The rushing well is gradually loose. When the momentum of the water flow is not too large, the looseness of the bed starts from the upper layer. The first is the fine ore with a small specific gravity, followed by the coarse ore with a small specific gravity and the fine ore with a large specific gravity. The grain is finally the coarser ore than the major one. At the end of the ascending water flow, the bed is fully loose, the ore particles begin to settle and stratify successively, and the coarser ore particles are the fastest sinking, located in the lower layer, followed by coarse ore particles with a small specific gravity and fine ore particles with a large specific gravity. The fine ore with a small specific gravity sinks the slowest and is located in the upper layer. When the water flow drops, the bed gradually becomes tight with the sedimentation of the ore particles, and the coarse ore particles sink to the sieve surface and lose their mobility. However, the fine ore particles can still move downward through the gap of the coarse ore under the inhalation of the descending water flow. This form of motion is called the gap motion. The water flow rises and falls down a complete cycle of change called a jigging cycle. The stratification process of the ore particles is not completed in a jigging cycle. During each jigging cycle, the ore particles are subjected to a certain sorting effect. After multiple cycles, the stratification of the ore particles is gradually improved. Large-scale ore particles will be concentrated in the lower layer to become heavy products, and small-weight ore particles will be concentrated in the upper layer to become light products.

In order to reduce the inhalation effect of the descending water flow on the small specific gravity fine ore particles, in order to improve the quality of the concentrate, the rising water in the jig is added in the jig. After sorting, the heavy products are discharged by the above-mentioned sieve discharge device, and the light products are discharged by the tail of the jig with the water flow.

This jig has high ore beneficiation efficiency and is suitable for sorting coarse ore-embedded ore. It is used in China to select tungsten or tin ore.

Its maximum ore size is up to 16mm and the minimum particle size is 0.5mm. The materials are sorted and classified and selected.

2) Shaker dressing:

Shaker beneficiation is one of the most widely used re-election methods for sorting fine-grained materials.

The basic structure of the shaker is divided into three main parts: the bed surface, the bed head and the frame. The bed surface is made of wood, which is inclined rectangular or diamond-shaped. The bed surface is slightly inclined to the tailings side. The bed surface is longitudinally nailed with wooden strips (called strips) or engraved with grooves. The ore is carried out on the bed surface. Sorting. The bed head is a mechanism for driving the bed surface to reciprocate and rock, which drives the bed surface to reciprocate asymmetrically in the longitudinal direction, that is, the bed surface is changed from the forward stroke to the backward stroke faster (acceleration), and the backward stroke is changed to the forward stroke. The time is slow (small acceleration) and the bed is driven by the motor. The frame is a shelf that supports the bed surface. The bed surface can be reciprocated on the shelf. The longitudinal and lateral slope of the bed can be adjusted by the relevant components of the frame.

There are two types of shaker surface: trapezoidal and diamond-shaped. The shaker surface produced in China is mostly trapezoidal, the ore end is wider, and the concentrate discharge end is narrower (such as the size of common industrial shaker is 4500mm×1800mm×1500mm) . The area utilization of the diamond-shaped bed surface is high, and the sorting efficiency is also improved due to the extension of the sorting belt, but the configuration and operation are inconvenient, and the bed surface is used more abroad.

The process of selecting the shaker is that the flushing water fed from the water tank flows through the thin layer in the oblique direction of the bed surface, that is, in the lateral direction. The slurry is fed to the bed by the feeding tank. Under the combined action of the flushing of the lateral water flow and the longitudinal reciprocating asymmetric movement of the bed surface, the ore particles with different specific gravities and different particle sizes move in different directions on the bed surface, the finest The slime flows directly along the inclined direction of the bed surface, and the ore particles that sink between the bed and the strip are stratified according to the difference in specific gravity and particle size due to the shaking of the bed surface and the eddy current formed by the flushing water in the groove. The ore particles with small specific gravity and large particle size are vortex washed to the upper layer, followed by the smaller specific gravity and smaller particle size. In the next layer, the ore particles with larger specific gravity and larger grain size are drilled through the ore particles. The gap between the two is located at the lowest level, and this process is called "separation separation."

The larger than the mineral grain is in the lower layer, because it is in contact with the bed surface, it is greatly affected by the movement of the bed surface, and is less affected by the lateral water flow. The small specific gravity of the ore in the upper layer is less affected by the movement of the bed surface and is mainly affected by the lateral flow. As a result, the longitudinal movement speed of the large specific gravity ore is large, the lateral movement speed is small, the longitudinal movement speed of the small specific gravity ore is small, and the lateral movement speed is large, and they will move in the direction of the respective combined speeds. Therefore, the larger ore particles move to the concentrate end, and the smaller specific gravity particles move to the tailings side. Finally, the ore belts with different specific gravity are formed, which are distributed in a fan shape, thus achieving the purpose of sorting.

The hydraulic classification of the shaker must be carried out before the selection, in order to reduce the influence of the size of the ore on the sorting.

The shaker has an upper limit of 2-3 mm and a lower limit of 0.037 mm. According to the different particle size, it can be divided into ore shaker and slime shaker. The 2~0.2mm material is selected as the ore shaker, and the material below 0.2mm is selected as the mud shaker. The difference between the two is that the type of the composite strip is different: the ore shaker generally adopts a higher strip, and the spacing is smaller; the slime shaker adopts a grooved bed surface, or the nail has a lower strip. Second, the strokes and strokes used are different: the ore shaker adopts large stroke and small stroke; the mud shaker adopts small stroke and large stroke. The third is that the inclined angle of the bed surface of the ore shaker is larger than the lateral slope; the inclination angle of the bed surface of the slime shaker is smaller than the lateral slope.

At present, China is widely used in three types: Hengyang type shaker, Yunxi type shaker and spring shaker.

The advantage of the shaker is that the beneficiation is stable and reliable, the distribution of the ore belt is clearly visible, and the ratio of rich ore (the ratio of concentrate grade to ore grade) is higher than many other beneficiation methods, up to more than 100 times, easy to handle, easy to adjust, and once The selection will result in the final concentrate and the discarded tailings. The disadvantage is that the productivity is low. When the processing capacity of the ore above 0.2mm is 0.7-0.5 tons/set, the number of units to be used is large, the floor space is large, and the water consumption is large.

The shaker is mainly used to select tungsten, tin, antimony, bismuth , chromium and other rare metals and precious metal ores. It can also be used to select iron or manganese ore. The selected particle size is less than 2mm. When sorting the object of more than 1mm, there is a tendency to be replaced by a jig. However, it is a very effective sorting equipment for sorting fine materials of 1mm or less, especially 0.1mm or less.

3) Chute dressing:

Slough beneficiation is a method of beneficiation using a bevel stream. The mixture of ore particles is fed into a chute with a small dip angle. Under the action of the impact of the water flow, the gravity of the ore particles (sometimes centrifugal force), and the frictional force, the specific gravity of the ore particles sinks in the groove. The small ore particles are taken away by the water flow to achieve the purpose of sorting by specific gravity.

There are many types of chutes. According to the force exerted by the ore particles, the gravity chute and the centrifugal chute can be divided. According to the selected strength, the coarse chute and the slime chute can be divided. The coarse-grained chute is often replaced by a jig because of the large amount of manual work required. Common chutes are shown in Table 4-3-1.

Table 4-3-1 List of common chute features

Coarse grain chute and ore chute are mainly used for gold, platinum, tin ore and other rare metal ore mines, such as monazite, zircon and other sand ore. The slime chute is often used for the selection of tungsten, tin and other ores. do not.

a. Centrifugal concentrator (also known as horizontal centrifugal chute): Centrifugal concentrator is an effective equipment for sorting fine granules. It has a high-speed rotating hollow cone rotating drum. After the slurry is fed, under the action of centrifugal force, the large proportion of the ore particles adheres to the inner wall of the drum, and the tailings are discharged from the gap of the drum edge. After a certain period of time, the ore is stopped and the concentrate is rinsed with water. Then give the mine and repeat the previous process. The time of each work cycle is approximately 2 minutes 30 seconds to 3 minutes 30 seconds. The entire beneficiation process of the centrifugal concentrator is automatically performed by the automatic control mechanism.

Centrifugal concentrators have been widely used as roughing equipment for tungsten and tin mud, and can be used to select other rare metal slime and fine-grained hematite. Its suitable ore feeding size is O.074~0.01mm, and it can effectively recover 0.037-0.019mm slime. The advantage is that the effective recovery has a low particle size lower limit and a high selectivity index. The shortcoming is intermittent operation, which cannot be continuously supplied to the mine. The power consumption and water consumption are larger than the fixed chute, and the drum slope cannot be adjusted.

b. Spiral concentrator (also known as spiral chute): The spiral concentrator is made up of 4-6 turns of spiral chute. The slurry moves downward along the groove after being fed from the upper end of the spiral groove. Under the combined action of gravity, centrifugal force, friction force and water flow force, the small specific gravity of the ore particles is close to the outer edge of the trough, and the larger ore particles are close to the inner edge of the trough. A hole is opened at a suitable portion of the bottom of the tank to discharge the concentrate (or medium mine), and the tailings are finally discharged from the tail end of the spiral groove. Concentrates (or intermediate mines) and tailings can also be taken from different locations at the end of the spiral groove.

In the spiral concentrator, the flushing water is also fed from the inner edge of the tank, so that the ore particles and the slime which are mixed with the heavy minerals can be washed out and play a supplementary role. Spiral concentrator for processing iron, tin, tantalum and niobium ore, alluvial particular process, good resolution monomers useful minerals obtained good indicator. It can also be used to treat flotation, magnetically select tailings, and recover heavy minerals from it. The selected particle size is generally 2-0.07 mm. The utility model has the advantages of simple structure, no moving parts, no power, simple operation and management, and low production cost. Small footprint and high productivity per unit area. The adaptability is large. When the amount of ore, ore concentration is changed, the recovery rate and concentrate grade have little effect. The disadvantage is that the height is large, the parameters of the equipment itself (pitch, spiral groove section, etc.) are not easy to adjust, and the effect of selecting the continuous body or the flaky ore is poor.

The spiral classifier models are divided into high-grade, low-lying and sunken. At present, the low-lying type has been eliminated, the sorghum type is used for the classification of coarse-ground products, and the submerged type is used for the classification of fine-grinding pulp.

4) Heavy medium dressing:

Heavy medium beneficiation is a beneficiation method in which the ore particles are sorted by specific gravity in a medium with a large specific gravity. The specific gravity of the heavy medium is between the specific gravity of the heavy ore and the specific gravity of the light ore. When the material is fed into the heavy medium, the ore particles with a specific gravity greater than the specific gravity of the heavy medium sink, and the ore particles with a specific gravity smaller than the specific gravity of the heavy medium float. The surface layer of heavy media. Then, the separated light and heavy minerals are separately intercepted, that is, the sorting process is completed.

This method of selection is mainly determined by the specific gravity of the ore particles, which is less affected by the particle size and shape. Therefore, his sorting accuracy is high, and it is possible to select minerals with small difference in specific gravity (such as a specific gravity difference of less than 0.1-0.05). . The range of particle sizes of the selected materials can also be wide. However, the ore particles with too small particle size, especially when the specific gravity and the specific gravity of the heavy medium are close, the sedimentation speed of the ore particles is small, so the separation process is slow and the sorting efficiency is greatly reduced. Therefore, heavy medium beneficiation has a certain limit on the lower limit of the ore particle size, and it is necessary to screen fine particles or deliming before selecting the fraction.

At present, heavy ore beneficiation is commonly used to treat minerals in which the minerals are coarse-grained or fine-grained. When the ore is broken to a certain particle size, a large number of gangues will be dissociated, and the useful minerals will appear as monomers or continuous organisms. The heavy medium beneficiation can separate a large number of gangues, thus entering the next stage of ore. The amount is greatly reduced, thereby increasing the production capacity of the concentrator and saving the cost of beneficiation. Therefore, the heavy medium ore dressing is often used as a pre-selection operation in the metal ore dressing plant, and a combined process with other beneficiation methods.

Heavy liquids and resuspensions as heavy media. The heavy liquid is an aqueous solution of some dense organic liquid or inorganic salt, which can be formulated into different densities by using an organic solvent or water. There are three commonly used heavy liquid methyl bromide or tetrabromoethane, mercuric iodide and potassium iodide of 1: 1.24 ratio of aqueous dubbed - Du nematic liquid solution, diiodomethane, thallium formate and malonate dubbed -. Krelich liquid, etc., because of limited source of heavy liquid, expensive, toxic, difficult to recycle, it is limited to laboratory use. The heavy suspension is used as a heavy medium in industrial production, so the heavy medium is generally referred to as a heavy suspension. The resuspension is a mixture of high specific gravity solid particles (generally referred to as suspended matter) and water. The commonly used suspended solids are: pyrite, magnetite, galena, ferrosilicon, etc., and the particle size of the suspended matter is mostly less than 0.074 mm. The heavy suspension has been widely used in the industry because of its wide source of raw materials, low price, non-toxicity, easy recycling, and no harmful effects on mineral processing.

There are many types of heavy medium mineral processing equipment, and the commonly used equipment is shown in Table 4-3-2. The commonly used heavy medium vibration chute mainly consists of a tank body, a transmission device, a separation partition plate and a frame.

When the heavy medium vibrating chute works, the heavy medium with higher concentration is first fed into the trough from the head end of the vibrating trough. Under the reciprocating shaking action of the trough body, the medium is transferred into the suspended state, and a certain flow is formed. Select the media bed of specific gravity. Then, the ore is fed from the head end of the tank, and due to the movement of the tank, the ore moves forward, and the stratification is started by the specific gravity. Heavy ore particles with a specific gravity greater than the specific gravity of the separation are passed through the bed of the medium, deposited on the bottom of the tank, and slid forward under the action of the tank, and discharged from the bottom of the separation separator. The light ore particles having a specific gravity smaller than the specific gravity of the separation are suspended in the upper layer of the medium bed, and are discharged from the upper surface of the separation separator according to the flow of the medium. The rising water in the tank is fed from the water chamber through the sieve holes of the two sieve plates, mainly to control and regulate the stability and uniformity of the medium bed, and to help the ore in the medium bed to move. The light and heavy products sorted out

The sieved medium and the removed dilute medium are recycled after being dehydrated.

The heavy medium vibration chute is used for the selection of ferrous metal ore such as hematite and manganese ore, and can also be used for the selection of other non-ferrous metal ores.

Table 4-3-2 Common heavy medium mineral processing equipment

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