Method for dry magnetic separation of weakly magnetic materials with electrical removal of magnetic product and device for its implementation. The invention relates to the field of dry separation of weakly magnetic materials by magnetic properties, in particular, in mining, chemical, pharmaceutical and other industries.
A known method of dry magnetic separation of materials comprising supplying an enriched material to a rotating horizontal drum in a magnetic field created by a fixed magnetic system of permanent magnets that is inside the drum and covers less than half its circumference, attracting magnetic grains to the surface of the drum under the influence of magnetic force , removal of non-magnetic grains under the action of centrifugal force and gravity into a non-magnetic separation product, drum output of magnetic ren from the magnetic field zone, where they are gravity separated from the drum and enter the magnetic product
separation [1].
The disadvantage of this method is that the retention of magnetic grains on the drum occurs at a distance from the surface of the magnetic system, where the magnetic forces are much less than on its surface and this limits the possibilities for extracting grains with the lowest magnetic susceptibility inherent in the magnetic system.
This separation method is carried out in a device that includes a drum with a horizontal axis of rotation, a magnetic system that is inside the drum and covers less than half the circumference, a feeder for feeding enriched material to the drum, a device for receiving non-magnetic and magnetic separation products [1].
The principle of operation of the separator is as follows. The enriched material is fed from above onto the surface of the rotating drum. Magnetic grains are attracted to the drum, and non-magnetic grains are removed into the device for receiving a non-magnetic product. In the subsequent movement, together with the rotating drum, the magnetic grains exit the magnetic field, where they are separated by gravity from the drum and enter the device for receiving the magnetic product.
The disadvantage of this device is the presence of a drum. Its outer surface is removed from the surface of the magnetic system by a distance equal to the thickness of the shell of the drum plus the gap between the inner surface of the drum and the magnetic system. The value of this distance is more than 10 mm. At such a distance from the magnetic system, the magnetic field strength and its gradient are much less than on the surface of the magnetic system. This limits the possibilities for extracting grains with the lowest magnetic susceptibility inherent in the magnetic system.
The prototype of the proposed method of dry magnetic separation of materials is a method that includes
- feeding the enriched material onto a horizontal endless ribbon that bends around a roller drawn from permanent magnets along the entire circumference of the roller;
- the attraction of magnetic grains to the surface of the tape under the influence of magnetic force;
- removal of non-magnetic grains under the action of centrifugal force and gravity into a non-magnetic separation product, removal of magnetic grains by a moving tape from the magnetic field of the roller, where they are separated by gravity from the tape and enter the magnetic separation product [2].
The disadvantage of this method is that the retention of magnetic grains on the tape occurs at a distance from the surface of the roller, where the magnetic forces are much less than on the surface of the roller and this limits the possibilities for extracting grains with the lowest magnetic susceptibility incorporated in the magnetic system of the roller.
This separation method is carried out in a device including a roller with a horizontal axis of rotation, which is composed of permanent magnets creating a magnetic field along the entire circumference of the roller, a horizontal non-magnetic tension roller, an endless tape that goes around the magnetic and tension rollers, a feeder for feeding enriched material onto the tape A device for receiving non-magnetic and magnetic separation products [2].
The principle of operation of the device is as follows. The enriched material is fed from above to the outer surface of the tape. Magnetic grains are pressed against the tape by magnetic force, and non-magnetic grains are removed into a device for receiving a non-magnetic product. After the tape leaves the magnetic roller, the magnetic grains exit the magnetic field, where they are separated by the force of gravity from the tape and enter the device for receiving the magnetic product.
The disadvantage of this device is the presence of tape. Its outer surface, on which the enriched material is fed, is removed from the surface of the magnetic roller by a distance equal to the thickness of this tape. This limits the possibilities for extracting grains with the lowest magnetic susceptibility inherent in the roller magnetic system. Therefore, they strive to make the tape as thin as possible. Known separators with a tape thickness of 150 microns.
The operation of belt separators is complicated by the roll off of the tape from the rollers, the ingress of magnetic material on the magnetic roller, the rapid wear of expensive tape, especially thin. The basis of the invention is the task to improve the method [2] of dry magnetic separation of materials and a device for its implementation by creating conditions for removing from the surface of the magnetic roller of the magnetic grains drawn to it without the use of a tape, thereby achieving the possibility of supplying an enriched material
directly to the surface of the magnetic roller, where the magnetic field strength and its gradient are the largest, as well as operating costs are reduced and the reliability of the separator is increased.
The solution of this problem is achieved by the fact that in the method of dry magnetic separation of materials, including feeding the enriched material into a magnetic field created by a magnetic roller rotating around a horizontal axis, holding magnetic grains in a magnetic field under the action of a magnetic force that is directed to the surface of the roller, removing non-magnetic grains from a magnetic field under the action of gravity into a non-magnetic separation product, the removal of magnetic grains during rotation of the magnetic roller outside the non-magnetic removal zone x grains and the subsequent removal of magnetic grains in the magnetic separation product, according to the invention, the enriched material is supplied directly to the surface of the magnetic roller, which is electrically conductive, and to ensure separation of the magnetic grains from the roller and their subsequent removal into the magnetic product, they create outside the non-magnetic removal zone grain electric field between the magnetic roller and a non-magnetic electrode, applying voltage of the opposite sign to them, with a voltage at which eskaya force coming off the magnetic grains on the surface of the roller, greater than the magnetic force pressing these grains to the surface of the roller.
The parameters of the magnetic grain, the parameters of the magnetic and electric fields, at which the separation of grain from the magnetic roller is ensured, satisfy the inequality
The electric field, which is created at the surface of the magnetic roller in the zone of separation of magnetic grains from it, is more than 1 kilovolt per meter.
The solution of this problem is also achieved by the fact that in the device for implementing the method of dry magnetic separation of weakly magnetic materials, which includes a roller made of permanent magnets with a horizontal axis of rotation, a feeder for supplying enrichable material, a device for receiving non-magnetic and magnetic separation products, according to the invention, the roller is electrically conductive, and along the entire length of the magnetic roller and with a gap relative to it from the side of the device for receiving the magnetic product is located ktrod.
The gap between the electrode and the roller is more than 5 mm
The surface of the electrode facing the roller is concave. The electrode is made in the form of a set of electrically conductive non-magnetic bodies installed with a gap relative to each other.
The electrode and the roller are electrically isolated from one another, mounted on dielectric elements and connected to unlike terminals of the high voltage source.
The electrode is connected to a negative high voltage source. The voltage between the electrode and the magnetic roller is more than 1 kilovolt.
The causal relationship between the features of the invention and the achieved result (separation of magnetic grains from a magnetic roller without the use of tape) is as follows. According to the invention, the enriched material is fed to a conductive magnetic roller. Under the action of magnetic force, magnetic grains are attracted directly to the surface of the roller. In the unloading zone of the magnetic product between the roller and the electrode creates a difference in electrical potentials. Under the influence of this potential difference, mobile electric charges, whose sign is opposite to the sign of the roller, pass from magnetic grains to the roller. As a result, magnetic grains receive an electric charge of the same name with the charge of the roller and are repelled from it. After separation from the magnetic roller, the grains move to the electrode, which is non-magnetic and does not hold the magnetic grains.
The movement of some grains between the roller and the electrode can occur many times, but in the end they all inevitably pass into the magnetic product.
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
The left side of this inequality describes the dependence of the specific electric force acting on the grain on the grain parameters and electric field strength [1], and the right side of the inequality describes the dependence of the specific magnetic force acting on the same grain on magnetic properties of the grain and magnetic field parameters [1] . Here, specific forces are understood to mean forces that act on a unit mass of grain.
With an electric field strength of more than 1 kilovolt per meter, the potential difference between the magnetic grain and the conductive magnetic roller becomes large enough for the mobile charges to transfer from grain to the roller, after which the grain and roller charges become the same and the magnetic grain is repelled from the magnetic roller.
The electrode is connected to a negative source of high voltage, since the mobility of electrons is higher than positive ions, and they are more easily transferred to a positively charged roller.
The voltage between the electrode and the magnetic roller of more than 1 kilovolt ensures the creation of the necessary electric field strength with a gap width between the roller and the electrode large enough to prevent electrical breakdowns.
Testing the method of removing the magnetic product using an electric field was performed on a laboratory roller separator. The roller was recruited from alternating conductive magnetic and iron disks. On the side of the roller where the unloading of the magnetic product is provided, a non-magnetic electrode was located. The distance between the roller and the electrode is 10 mm. The magnetic field strength on the surface of the roller was 0.95 T.
The roller rotated at a speed of 35 revolutions per minute. A mixture of weakly magnetic ilmenite and non-magnetic rutile was fed to the roller. Rutile immediately removed from the roller and entered the non-magnetic separation product. Ilmenite was held by magnetic forces on the surface of the roller and during its rotation passed into the gap between the roller and the electrode. With an electric field voltage of more than 4 kilovolts, ilmenite was completely detached from the roller and entered the magnetic separation product.
In FIG. 1 shows a cross-sectional view of a roller magnetic separator with electrical removal of a magnetic product.
The separator includes an electrically conductive magnetic roller 1, a non-magnetic electrode 2, a high voltage source (not shown in the figure), feeder 3, devices 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.
Dry granular enriched material, which is a mixture of magnetic and non-magnetic grains, is fed from feeder 3 to roller 1.
Non-magnetic grains are not held on a rotating roller and are crumbled into a device for receiving a non-magnetic product 4. Magnetic grains under the influence of magnetic force are held on the roller and, when it is rotated, leave the unloading zone of the non-magnetic product and enter the zone of the electric field that is created between the electrically conductive magnetic roller 1 and electrode 2. The roller is connected mainly to the positive terminal of the high voltage source, and the electrode to the negative terminal.
Since the roller is positively charged, the electrons of the magnetic grains transfer to the roller and these grains receive a positive charge, that is, the same as the roller.
Therefore, they repel from the roller and move towards the electrode. Since the electrode is made of non-magnetic material, the magnetic grains are not held on it and show off in the device for receiving the magnetic product 5.
Leaping of individual magnetic grains between the roller and the electrode can occur repeatedly. A causal relationship between the essential features of the device and the achieved result is that the inventive device allows you to implement the essential features of the inventive method of enrichment of weakly magnetic materials.
The roller is electrically conductive to enable the transfer of mobile charges to it from a magnetic grain attracted to it. The electrode is located on the side of the magnetic product, since it is from this side that an electric field must be created, which is necessary to separate the magnetic attracted to it from the roller
grains. The electrode is located along the entire length of the magnetic roller, since the enriched material is fed to the roller along its entire length.
When the gap between the electrode and the roller is more than 5 mm, it is possible to create the necessary electric field voltage without electric breakdown between the roller and the electrode at such an electric field strength that ensures the transition of mobile charges from magnetic grains to electrically conductive magnetic
roller.
The electrode surface facing the roller is concave to create close conditions for the separation of grains from the roller over the entire length of the arc of the circumference of the roller, where the magnetic product is unloaded. The electrode is made in the form of a set of electrically conductive non-magnetic bodies installed with a gap relative to each other, which is necessary for the exit of magnetic grains through these gaps from the space between the roller and the electrode into the magnetic product after they are separated from the roller. Magnetic grains do not accumulate on the electrode due to the fact that all elements of the electrode are non-magnetic.
The electrode and the roller are electrically isolated from one another and are mounted on dielectric elements to prevent electrical breakdown between them.
The electrode and the roller are connected to the opposite terminals of the high voltage source to create a potential difference between them.
Using the proposed enrichment method and device for its implementation allows the separation of weakly magnetic materials on a roller magnetic separator without tape. The separator can be mass-produced using standard equipment.
INFORMATION SOURCES
● Derkach VG, Special methods of mineral processing,
M., Nedra, 1966 – p. 333.;
● Svoboda J., Magnenic Methods for the Treatment of Minerals, Elsevier
Science Publishers B.Y., Amsterdam – Oxford – New York – Tokyo, 1987 – p.
286.;
AUTHOR: TURKENICH A.M., Dr. tech. of sciences
© 2007 MHT