Laboratory studies have shown that manganese ore with a particle size of 4 – 0 mm can be effectively enriched by the method of continuous barrier magnetic separation, in which the separation of magnetic and non-magnetic particles and their removal from the separation zone occurs without the use of rolls or any other moving parts. At
work on a single barrier matrix satisfactory performance is achieved by enrichment in two steps and the induction of the background field of 0.6 T in the second separation technique. The double barrier matrix is easier to operate than the single.
It allows one to obtain satisfactory enrichment indices in one separation process with the induction of a background magnetic field of 0.75 T.
Magnetic enrichment of the granular part of manganese ore is carried out on electromagnetic roller separators. The enrichment process includes the attraction of magnetic particles to the roll, their removal from the magnetic field during rotation of the roll, and the subsequent unloading of magnetic particles into the magnetic separation product. The presence of rotating rolls gives rise to a number of disadvantages of these separators. For example, the power of the 4EVM-38/250 roller separator is 58 kW. Of these, 44 kW, that is, more than 75% of the power, is used to rotate four rolls and only 14 kW is spent on creating a magnetic field. The drive and the roller bearings immersed in the pulp require constant maintenance, significantly complicate and increase the cost of the separator, and reduce its reliability.
Various designs of barrier magnetic separators are known in which the separation of magnetic and non-magnetic particles and their removal from the separation zone occurs without the use of rolls or any other moving parts. In order to study the possibility of using such separators for the enrichment of manganese ore, laboratory studies were performed, the results of which are described below.
Manganese ore with a size of 4 – 0 mm of the Manganese mining and processing plant was subjected to enrichment. Two series of experiments were carried out.
In the first series of experiments, ore was enriched with a manganese content of 33.1%, free quartz -31.9%. Enrichment was carried out on a laboratory separator (Fig. 1). In the interpolar gap of its magnetic system 1 is placed a separation matrix consisting of ferromagnetic plates 2 installed with gaps 3 relative to each other.
The longitudinal faces of 4 ferromagnetic plates are rounded in cross section. To these faces are adjacent plates 5 made of non-magnetic material.
The angle of inclination of the matrix to the horizon is 300. Non-magnetic plates are made of transparent organic glass, which made it possible to monitor the movement of the separated grains.
With the indicated arrangement of the ferromagnetic plates, when the symmetry planes of the gaps between them are oriented along the magnetic field, magnetic forces directed from the gaps act on the longitudinal faces 4. These forces create a magnetic barrier that prevents the entry of magnetic grains under the action of gravity into the gap between the ferromagnetic plates. The theory of the formation of magnetic forces in the vicinity of ferromagnetic bodies located in a magnetic field is described in detail in the literature, for example [1].
The pulp of the material to be enriched from the feeder 6 was supplied above the edges 4 into the gaps between the non-magnetic plates 5. Below the edges 4, water was supplied from the device 7 to the gaps between the magnetic plates.
Non-magnetic particles under the action of gravity fell into the gaps between the magnetic plates and, under the action of a high-speed pressure of water, were transported to the device 8 for unloading the non-magnetic separation product. Magnetic particles could not overcome the magnetic barrier and, supported by a magnetic force above the edges 4 of the ferromagnetic bodies, were transported to the device 9 for unloading the magnetic separation product.
Preliminary studies have shown that in order to obtain tailings in one separation process, the induction of the background magnetic field should be no lower than 0.6 T. By background is meant the field in the air gap of the matrix without distortion by its ferromagnetic plates. The induction of such a field was measured with a teslameter in the gap between the matrix and the pole tip from the side of non-magnetic plates. With this induction, ore grains with increased magnetic susceptibility are attracted to the walls of the plates and accumulate in the gaps disrupting the separation process. In this regard, enrichment was carried out in two stages. At the first reception of separation, the background field induction was 0.3 T.
The resulting non-magnetic product, not containing grains with increased magnetic susceptibility, was refined by induction of a background field of 0.6 T. The separation results are shown in table 1.
Table 1. The results of the enrichment of manganese ore with a particle size of 4 – 0 mm on a single matrix in two stages of separation
The following conventions are adopted in the table: M1 and M2 – magnetic products of the first and second separation methods; N is a non-magnetic product of the second separation method; – weight yield of enrichment product; Mn and SiO2 are the content of manganese and free quartz in the enrichment products, respectively; Mn and SiO2 – extraction of manganese and free quartz into separation products; 1 is the enrichment efficiency according to T. G. Fomenko, defined as the product of the extraction of manganese into a magnetic product and the extraction of free quartz into a non-magnetic separation product.
The performance shown in the table is the expected specific performance, that is, per unit length of the power supply front.
In terms of the 4EVM-40 / 250A32 roller separator, which has a 5.5 m front supply width, the expected separator capacities will be 8 t / h, 12 t / h and 18 t / h.
The actual hourly capacity of the 4EVM-40 / 250A32 roller separator at 4-0 mm manganese ore does not exceed 12 t / h. In accordance with the results of laboratory experiments, when working with a barrier separator with such an expected productivity, a magnetic product with a manganese content of more than 41% will be obtained from ore with a manganese content of 33.1%. The manganese content in the tails will be less than 6%, and the content of free quartz in the sample will decrease from 31.86% to 12.1%, that is, by almost 20%.
From the above data it is seen that in the first separation technique at low induction, only 0.3 T, an average of half the magnetic product is recovered. This ensures that in the second separation method the unhindered passage of magnetic grains through the channel of the matrix during the induction of 0.6 T.
The main disadvantage of the sequential installation of two matrices is the inaccessibility for observation and maintenance from above of the matrix of the second separation technique. In addition, for the removal of the magnetic product of the first separation technique and its replacement with water in the second technique, a complicated gutter system is needed.
These disadvantages are absent in the double matrix. Its difference from the previous matrix consists only in the fact that ferromagnetic rods 10 are inserted inside non-magnetic plates 5. They are located along the rounded faces 4. The enriched material is fed into the gaps 3 above the ferromagnetic rods. Magnetic grains, which are kept from being lowered by a magnetic force directed from the gap between the rods, are transferred to the magnetic product. Non-magnetic grains under the influence of gravity fall down to the gap between the ferromagnetic plates where magnetic grains lost at the rods are separated from them. Further movement of the material is the same as in the previous matrix. The ore was enriched with a manganese content of 33.4%, free quartz – 29%. The enrichment results are shown in table 2.
It should be noted that at first experiments were carried out with the induction of 0.6 T with a specific productivity of 2 t / (hm). The non-magnetic separation product contained more than 10% manganese.
In this regard, further experiments were carried out with the induction of 0.75 T.
In general, separation on a double matrix is even more efficient than on a single matrix. For example, with a specific productivity of 3.5 t / (hm), a magnetic product with a manganese content of 42.3% and free quartz of 11.02% was obtained. The manganese content in the non-magnetic product was 6.7%. This is better than that obtained by enrichment with a specific productivity of 3.3 t / (hm) on a single matrix. However, to achieve such indicators, induction is required 25% higher than is necessary for using a single matrix. To create it with the same magnetic system, it is necessary to proportionally reduce the front of the power supply, and, consequently, the performance of the separator.
Table 2. The results of the enrichment of manganese ore with a particle size of 4 – 0 mm on a double matrix in one separation process
Conclusions
● Laboratory studies have shown that manganese ore with a particle size of 4 – 0 mm can be effectively enriched by continuous barrier magnetic separation, in which the separation of magnetic and non-magnetic particles and their removal from the separation zone occurs without the use of rolls or any other moving parts.
● When a single barrier matrix is operating, satisfactory performance is achieved by enriching in two steps and inducing a background field of 0.6 T in the second separation step.
● The double barrier matrix is easier to operate than the single. It allows one to obtain satisfactory enrichment indices in one separation process with the induction of a background magnetic field of 0.75 T.
INFORMATION SOURCES
● J. Svoboda. Magnetic Methods for the Treatment of Minerals. –
Amsterdam.:1987. – 692 c.
AUTHOR: TURKENICH A.M., Dr. tech. of sciences
© 2007 MHT