A new method for the magnetic separation of weakly magnetic ores and a device for its creation have been developed, which can increase the magnetic field induction in the separation zone to 1.8 – 2.0 T. A description of the method and device, as well as an example of calculating the electric field at which the separation of the magnetic grain from the magnetic roller.
The results of laboratory studies are presented that confirm the high efficiency of the method.
Currently, for the cleaning of non-magnetic granular materials from magnetic inclusions worldwide, tape roller separators are widely used [1]. The enriched material from the feeder enters the tape and with it envelopes the rotating magnetic roller.
Magnetic grains are pressed against the tape under the influence of magnetic force, and non-magnetic grains fall into the non-magnetic separation product. At the place of separation of the tape from the roller, the magnetic grains exit the magnetic field and fall under the influence of gravity into the magnetic product. A magnetic roller is a set of sequentially alternating iron disks and disks made of strong rare-earth (Nd – Fe – B) permanent magnets. Magnetic disks adjacent to one iron disk on both sides face each other with the same poles. This allows you to create induction on the surface of the roller up to 2 T.
To clean quartz sand, zircon and other materials from weakly magnetic inclusions, you must have as much as possible high induction in the separation zone, that is, on the surface of the tape. Therefore, for these purposes, it is made of thin, durable, wear-resistant material with a thickness of 130 – 150 microns. In fig. 1 shows a graph of the magnitude of the magnetic induction on the distance x to the surface of the roller. The graph shows that if the induction on the surface of the iron disks is 1.8 T, then with the distance from the surface of the roller, it quickly falls and already at a distance of 150 microns, that is, on the surface of the tape where the separation process takes place, it decreases to 1.2 – 1.3 T. In addition, the service life of such a tape does not exceed 2 – 3 months. The cost of the tape is 800 – 1000 US dollars.
The listed disadvantages of tape roller separators are absent in PCT roller magnetic separators with electrical removal of the magnetic product [2]. The separator circuit is shown in Fig. 2. The separator includes an electrically conductive magnetic roller 1, a non-magnetic electrode 2, a feeder 3, a device for receiving non-magnetic 4 and magnetic 5 separation products. The roller and electrode are connected to the opposite terminals of the high voltage source.
The principle of operation of the separator is as follows. Dry granular material, which is a mixture of magnetic and non-magnetic grains, is fed from the feeder 3 to the roller 1. Non-magnetic grains are not held on the rotating roller and are crumbled into the device for receiving a non-magnetic product 4. Magnetic grains under the influence of magnetic force
are held on the roller and during its rotation exit the unloading zone of the non-magnetic product and enter the zone of the electric field, which is created between the electrically conductive magnetic roller 1 and the electrode 2.
The roller is connected mainly to the positive charge terminal of the high voltage source, and the electrode to negative terminal.
Since the roller is positively charged, the electrons from the magnetic grains transfer to the roller, and they receive a positive charge, that is, the same as the roller. Therefore, the grains repel from the roller and move to the negative electrode. Since the electrode is made of non-magnetic material, the magnetic grains are not held onto it and are crumbled into the device for receiving the magnetic product 5. The jumping of individual magnetic grains between the roller and the electrode can be repeated.
In these separators, the enriched material is fed directly to the open surface of the roller, where magnetic induction reaches 1.8 – 1.9 T.
Detachment of magnetic grains from the magnetic roller will occur if the force of their repulsion from the roller under the action of electric charges is greater than the force of magnetic attraction to the roller.
The separation condition is expressed by the inequality
where is the specific magnetic susceptibility, density and radius of the grain; H, grH – intensity and gradient of the magnetic field near the surface of the roller; E is the electric field strength at the surface of the roller; ? 0 = 8.85 • 10-12 F / m is the dielectric constant of the vacuum; ? 0 = 4? • 10–7 gn / m — magnetic permeability of the vacuum.
The left side of this inequality describes the dependence of the specific electric force acting on the grain on the grain parameters and the electric field strength, and the right part describes the dependence of the specific magnetic force acting on the same grain on the magnetic properties of the grain and magnetic field parameters. Specific forces are understood to mean forces that act on a unit mass of grain. When the electric field becomes large enough for the transition of mobile charges from grain to roller, the charges of grain and roller become the same and the magnetic grain is repelled from the magnetic roller.
As an example, we determine the electric field strength required to detach a grain of radius r = 0.1 mm having magnetic susceptibility? = 200 • 10–8 m3 / kg and density? = 4 • 103, from the roller, which has the field characteristic shown in Fig. 1. According to the schedule, at a distance of 0.1 mm from the surface of the roller, that is, in the center of the grain, the field strength H = 1.1 • 103 kA / m and the field gradient grH = 3.2 • 103 kA / m2. Substituting the values of the given parameters into the equation, we obtain that the electric field strength E, necessary for separating the grain from the roller, is 370 kV / m. Since the grain does not receive the maximum electric charge, for separation
grain need to create a little more tension. For example, if the potential difference between the roller and the electrode, the gap between which is 10
mm, is 10 kV, then the electric field is equal to 1000 kV / m, that is, it is quite enough to separate the grain from the roller.
A general view of the PCT two-roller separator with a roller length of 100 mm is shown in Fig. 3. Above the rollers, a drum separator with induction on the drum surface of 0.36 T is visible. The enriched material enters the drum, where grains with increased magnetic susceptibility are removed.
Next, sequentially on two rollers the material is cleaned of weakly magnetic grains.
The cleaning performance depends on the properties of the material being enriched and its performance. In fig. Figure 4 shows the dependence of the Fe2O3 content in purified quartz sand of the Volnogorsk Combine on
specific productivity of a roller separator with electric removal of a magnetic product. The content of Fe2O3 in the sand before treatment was 0.071%. As a result of purification at a productivity of 5 t / (h • m), the Fe2O3 content decreased to 0.02%. The yield of magnetic product is less than 6%.
Silica sand with an iron content of 700 ppm was also cleaned. As a result of two separation methods with a specific separator capacity of 0.5 t / (h • m), the iron content in the purified sand decreased to 16 – 20 ppm.
Thus, a new method of magnetic separation of weakly magnetic ores and a device for its creation can increase the magnetic field induction in the separation zone to 1.8 – 2.0 T. The results of laboratory tests confirm the high efficiency of the method.
List of references:
● Svoboda J. Magnetic Methods for the Treatment of Minerals. –
Amsterdam: Elsevier Science Publishers B. V., 1987.
● Turkenich A. M. Low magnetic material separation method associated with
a magnetic product electrical removal and a device for carrying out said
method. Int. Appl. Nr: PCT / UA2005 / 000026. Int. Pab. Nr .: WO
2006/112803, 10.26.2006.
AUTHOR: TURKENICH A.M.
© 2007 MHT