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Fine particle electric separator
Fine-grain electrification is an important issue that has attracted attention and research at home and abroad. Especially fine-grained materials of less than 0.1 mm have made remarkable progress after research by scholars all over the world. One is dry electrification and the other is wet.
   1. Dry-type rotary electric separator
The electric sorter configuration is a nearly elliptical closed loop, and the cut surface of the tube is rectangular, and its construction diagram is shown in FIG. In the figure, hot air is sent at one place, material is fed at three places, and 2 is a regulating valve. The material flows along the pipeline along with the hot air. A corona pole is installed at the pipeline 4, and 5 is a grounding pole. The fine-grained material entering the pipeline is charged in the BC section. Regardless of whether the conductor or non-conductor ore particles obtain electric charge in the corona field, due to different electrical properties, the charge adsorbed by the conductor ore particles is immediately transmitted through the grounding pole 6 and is discharged to the 8 places with the air flow, between the two. The middle mine is sorted again with air circulation. The electrode size (referring to the length of BC and CD) can also vary depending on the time required to charge and transform the selected mineral.
Figure 1 Cyclone electric separator
1. hot air pipe connection port; 2. regulating valve; 3. material feeding inlet; 4. corona electrode;
5. Grounding pole; 6, 7. Static electrode; 8, 9. Mine hole; 10. Partition plate
If such an electric sorter is used to sort the minerals charged by friction, it is not necessary to install the corona pole 4, but the ore particles are rubbed against the pipe wall, and other materials are lined in the pipe wall to facilitate the charging of the ore particles. Simply install a static electrode at 6, 7 and sort the two minerals with positive and negative charges. The voltage used can reach 50 kV, and the sorting granularity is less than 5 micrometers. The sorting effect is better, and it has not yet formed a series of production products.
  Second, wet dielectric sorting machine
The sorting of such an electric sorter is carried out in a dielectric liquid, unlike the various dry sortings described herein. The principle is that the dielectric ore particles are polarized in a non-uniform electric field to produce different motions. When the dielectric constant of the sorted solid particles is less than the dielectric constant of the dielectric liquid, the electric field generates a repulsive force to the particles, and conversely, when the dielectric constant of the liquid is greater than the dielectric constant of the liquid, a suction force is generated.
According to the theoretical formula, the generated electricity (also known as the mass power) is:
Εm-ε L
F=ε L r 3------------EgradE
Εm+2ε L
(1)
Where F - electricity, N;
Εm, ε L , the dielectric constant of minerals and dielectric liquids;
When r 3 , E and gradE in the formula (1) are constant, then F is only related to εm and ε L .
When εm>ε L , F>0, the electrode attracts the ore particles;
When εm < ε L , the F < 0 electrode repels the ore. [next]
And when ε L =0.365 εm, F reaches the limit value (this is based on the actual measurement).
Since this sorting is a non-uniform electric field and is carried out in a liquid, the movement of fine-grained ore in the medium is necessarily related to dielectrophoretic force, electrostatic force, diffusion or osmotic pressure, gravity and viscous drag, etc., but since this is a Seed group movement, and these forces are not yet available for measurement and calculation, so only the effect of electricity is considered.
Using a mixture of a liquid dielectric constant of carbon tetrachloride and methanol, also using a mixture of kerosene and nitrobenzene, as needed formulated liquids of different dielectric permittivity. The average value can be obtained by the following formula.
ε 1 +ε 2
ε 1=--------------
2
(2)
Where ε 1 is the dielectric constant of the first dielectric liquid;
ε 2 - the dielectric constant of the second dielectric current body.
If the desired value is larger or smaller than the average of the two, the amount of the first dielectric liquid can be appropriately increased or decreased to adjust the appropriate value.
The power source of this type of electric separator is different from the general electric sorter, but uses an AC power supply of 2 to 5 kV, or a DC power supply.
Drum type dielectric sorting machine
This is a dielectric sorting machine developed in the United States. A plurality of filaments are mounted on the drum, and a sieve mesh is correspondingly formed. After the power is applied, a non-uniform electric field is formed between the drum and the sieve plate, and 2/3 of the drum is immersed in the dielectric liquid, and its construction is as shown in Fig. 2.
Figure 2 Drum type dielectric sorting machine
1. feeding to the mine; 2. rotating drum electrode; 3. screen electrode; 4. low dielectric constant ore; 5. intermediate dielectric liquid having a dielectric constant K;
6. High dielectric constant ore; 7. Key position of the separator; â— - Dielectric constant pillar (>K); â—‹ - Low dielectric constant ore (
After the feedstock is fed from the upper part of the drum to the drumhead, it is driven by the drum to the dielectric liquid. At this time, the ore enters the electric field action zone formed between the sieve and the drum, and the dielectric is affected by the non-uniform electric field. The ore with a constant larger than the liquid is sucked on the drum, while the dielectric constant is lower than the liquid but is repelled and falls to the left through the sieve hole. The ore particles sucked on the filament of the drum rotate with the drum. When leaving the key position of the partition plate of the sieve plate, it falls into the groove on the right side, because the field strength at this point becomes small, and it is affected by liquid resistance and gravity, so it can be discharged.
According to the US Bureau of Mines, the sorting of 28 complex mines shows that the effect is very good, but the production capacity is very low, which is its outstanding weakness.
2. High gradient electrical selection
This is the result of research in recent years. It is a progress in dielectric sorting and a new equipment developed for the selection of fine particles. Similar to high-gradient strong magnetic separation, the dielectric fiber is polarized in an electric field to increase the electric field gradient, thereby increasing the electric field ladder, and the dielectric fiber is completely similar to the high gradient. Magnetically selected steel wool media.
A non-conducting spherical object is placed in an insulating medium fluid and is subjected to a non-uniform electric field. When subjected to equilibrium, the dielectrophoretic force is:
1 →
Fe=---aVâ–½(E 2 )
2
(3)[next]
Where F e - dielectrophoretic force, N;
X - polarizability;
V - object volume, m 3 ;
→
▽ ——The electric field gradient can also be expressed by gradE.
The rest of the unit symbols are the same as before.
If the object is also like a magnetic object, if there is anisotropy, a is a tensor and cannot be calculated, but for a spherical object, the polarizability is:
(εm-ε L )
x=3ε L ---------------
(εm+2ε L )
(4)
Substituting the value and the spherical volume V=3/4лr 3 into the formula (3), the dielectrophoretic force of the spherical ore particles in the liquid is:
ε L (εm-ε L ) →
Fe=2лr 3 --------------▽(E 2 )
(εm+2ε L )
(5)
In the formula, r, E, εm, ε L and other symbols and units are the same as before.
Obviously, F e is directly related to the electric field strength and gradient. The larger the electric field intensity E is, the larger the gradient is, and the larger the dielectrophoretic force is, and the F e is determined by the shape and size of the filament, and the electric field strength is the parent polarization. It depends on the gradient produced. Figure 3 is a schematic diagram of the construction of a periodic high gradient electric separator. The dielectric used in the sorting tank is glass fiber, ball or rod-shaped titanate (such as barium titanate, etc.), ceramic fiber, etc., and is added to the sorting tank, which is filled with an insulating dielectric liquid.
Figure 3 Periodic high gradient electric separator
A. Parallel plate type; B. Cylinder type
1. Flow rate control valve; 2. Feeding valve; 3. Cleaning valve; 4. Sorting tank and medium;
5. Electrode; 6. Cleaning valve; 7. Feeding valve;
8. DC power supply and electric field control; 9. Automatic control device; 10. to valve
After the two plates are connected to the power source, the dielectric fibers are polarized, and positive and negative charges appear at both ends, forming a high-gradient unit electric field, thereby generating a large amount of electric power, trapping the ore particles, and collecting the ore particles. The clustering effect has established a new trapping point. Studies have shown that the power F e can exceed 50 to 150 times the gravity, and the cutting area captured in the electric field exceeds 100 times the radius of the fiber medium, but is limited to the dielectric body. The surface of the fiber or sphere, when equal to or larger than the diameter of the fiber or sphere, the non-uniformity of the dielectric approaches zero. As long as the power is interrupted, the ore particles trapped on the surface of the fiber or sphere can be washed away immediately, so the new method has great advantages.
Such equipment now developed into a continuous high gradient electric separator, and has been used in oil refining, metal and the vegetable oil industry, promising widely used in mineral processing, chemical industry, waste disposal, which processes up to micron particle size Grades, even colloidal particles can be separated by this device.