Jan Svoboda. Magnetic Techniques for the Treatment of Materials
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120 CHAPTER 2. REVIEW OF MAGNETIC SEPARATORS
Figure 2.66: MK III Sala-HGMS carousel unit.
Figure 2.67: A three-head HGMS 350 carousel machine (courtesy of Metso Min-
erals, Ltd.).
2.4. WET HIGH-INTENSITY MAGNETIC SEPARATORS 121
Figure 2.68: An isometric view of VMS.
a rotating drum, which carries separation chambers filled with matrix. The
non-magnetic and the middling fractions are collected in launders underneath
the magnet. Magnetizable particles are attracted to the matrix, placed in com-
partments along the periphery of the vertical wheel. When the matrix leaves
the region of the magnetic field during the rotation of the wheel, the captured
particles are flushed from the matrix. The magnetic product is thus washed o
from the matrix at the flush station in a direction opposite to that of the feed
and is collected in the trough at the bottom of the separator.
The maximum background magnetic induction generated by the magnet is
1.7 T, while stray magnetic induction outside the magnet is less than 5 mT.
Mild steel rods of 3 mm and 5 mm in diameter, with spacing of between 1.5
mm and 2.5 mm, are used as a matrix. Woven wire mesh has also been used in
some applications.
In order to increase the capacity of a magnetic separator, the width of the
working space must be increased. The VMS concept allows this very simply by
increasing the width of the wheel. Taking into account that the magnetic field in
the VMS separator is oriented vertically, perpendicularly to the increase of the
wheel width, the basic characteristics of the magnetic circuit remain unchanged,
i.e. the vertical length of the air gap, which determines the magnetomotive
force, or the number of ampere-turns needed to achieve the required magnetic
induction, is the same for any width of the wheel. Because of the increase in
the length of the conductor, energy consumption increases only linearly with
the wheel width. A throughput of up to 150 t/h was specified for the largest
separators VMS 100.
122 CHAPTER 2. REVIEW OF MAGNETIC SEPARATORS
Figure 2.69: A vertical ring of the VMS HGMS, with matrix compartments
(courtesy of
ˇ
ZB Spišská Nová Ves, Slovakia).
Figure 2.70: VMS high-gradient magnetic separator (courtesy of Ore Research
Institute, Czech Republic).
2.4. WET HIGH-INTENSITY MAGNETIC SEPARATORS 123
Figure 2.71: VMS-100 separators in a manganese ore beneficiation plant in the
Ukraine (courtesy of Ore Research Institute, Czech Republic).
By replacing the conventional horizontal rotor by a vertically rotating wheel,
Fig. 2.69, the VMS separator also addressed the problem of matrix clogging, an
onerous problem for most carousel WHIMS or HGMS machines. The reverse
flush and very low stray magnetic field in the flush section are additional features
of this separator.
The VMS magnetic separator, shown in Fig. 2.70, was manufactured in sev-
eral models and sizes by
ˇ
ZB Co. in the former Czechoslovakia. These separa-
tors were earmarked for incorporation into the Krivoy Rog and Kursk Magnetic
Anomaly iron ore beneficiation plants in the Ukraine. The proposed capacity
of the plants was 30 Mt/a and it was envisaged that at least forty VMS sep-
arators, each with capacity of 100 t/h, would be required. At the same time,
several units, Fig. 2.71, were installed in manganese ore beneficiation plants in
the Ukraine.
In many demanding applications, particularly when feebly magnetic admix-
tures from industrial minerals are to be removed, it is necessary to control the
residence time of the slurry in the separating zone and thus the flow velocity
through the matrix. To cater for such applications, the VMS separator was mod-
ified in such a way that the magnetic system was situated below the rotation
axis of the rotor. This VMKS separator, shown in Figure 2.72 and schematically
in Figure 2.73, generates a magnetic induction of 2 T and has a rotor diameter
of 3 m, width of 1.4 m and throughput of 10 t/h. It was successfully applied
to purification of kaolin [Z3].
124 CHAPTER 2. REVIEW OF MAGNETIC SEPARATORS
Figure 2.72: Continuous magnetic separator VMSK for purification of kaolin
(courtesy of Ore Research Institute, Czech Republic).
2.4. WET HIGH-INTENSITY MAGNETIC SEPARATORS 125
Figure 2.73: Sectional view of the VMKS separator for kaolin purification (Ore
Research Institute, Czech Republic).
SLON magnetic separator
It became obvious in the late eighties, that the use of an iron-clad solenoid and
application of the reverse flush of the matrix enhances the e!ciency, scalability
and availability of continuous high-gradient magnetic separators. The techni-
cal success of VMS separators prompted further innovative eort. The SLON
HGMS, developed in 1988 by Ganzhou Non-ferrous Metallurgy Research Insti-
tute, Ganzhou, China [X1], and shown in Figure 2.74, is based on the VMKS
concept. However, in order to improve the e!ciency of separation even further,
the pulsation of the slurry within the matrix was incorporated into the SLON
separator.
The pulse generator induces vertical pulses in the slurry within the matrix.
The particles are thus exposed to the pulsation force, which is much greater
than the force of gravity and acts in both directions [Y2]. By the pulsation
action, the mechanically entrained non-magnetic particles are removed from the
matrix, which results in improvement of the quality of the magnetic concentrate.
At the same time, the pulsation allows the magnetic particles in the slurry to
be exposed to the entire depth of the matrix, which increases the recovery of
the magnetic component.
The SLON separators are manufactured in several models, specifications of
three of which are listed in Table 2.6.
The separator is used, on a large scale, to beneficiate feebly magnetic iron and
ilmenite ores and appears to enjoy considerable commercial success in China.
126 CHAPTER 2. REVIEW OF MAGNETIC SEPARATORS
Figure 2.74: SLON-2000 pulsating high-gradient magnetic separator (courtesy
Ganzhou Non-Ferrous Metallurgy Research Institute, China).
Table 2.6: Parameters of SLON magnetic separators.
Parameter SLON-1000 SLON-1500 SLON-2000
Ring diameter [mm] 1000 1500 2000
Maximum magnetic in-
duction [T]
1 1 1
Input power [kW] 26 38 82
Pulsating stroke [mm] 0to30 0to30 0to30
Feed size [mm] -1 -1 -2
Feed solid density (%) 10 to 45 10 to 45 10 to 45
Throughput [t/h] 4to7 20 to 35 50 to 80
Mass of the machine [t] 6 20 50
2.4. WET HIGH-INTENSITY MAGNETIC SEPARATORS 127
Figure 2.75: SLON-1500 magnetic separators operating in Pang Zhi Hua il-
menite processing plant in China (courtesy of Ganzhou Non-ferrous
Metallurgy Research Institute, China).
It is set to make inroads into international markets. Figure 2.75 illustrates the
operation of a bank of SLON-1500 separators in the Pang Zhi Hua ilmenite
processing plant (China).
Other innovative designs of solenoid-based magnetic separators
Matrix blockage and insu!cient throughput was the main limitation to recovery
of uranium and gold from Witwatersrand ores and cyanidation residues by wet
high-intensity magnetic separation [C8]. In order to satisfy all the requirements
for a cost-eective and reliable machine that would be able to operate for a
su!ciently long period in industrial conditions, the Council for Mineral Tech-
nology (Mintek), Randburg, South Africa, designed and constructed a prototype
separator [S14] shown in Figure 2.76.
The design of the Mintek linear magnetic separator was based on a split-coil
magnet that consisted of two parallel short race-track coils, internally water-
cooled, separated by a gap through which the matrix could pass. This pair
of coils was enclosed in a steel cladding. The matrix consisted of woven mesh
screens held vertically on a flexible belt. The belt moved linearly in a horizontal
direction and inverted back on itself by means of pulleys. As the belt moved
round the pulleys, the matrix elements flared out, thus facilitating the removal
of ferromagnetic material and wood chips. The residual mechanically entrained
particles were then removed by a reverse flush on the lower side of the separator.
128 CHAPTER 2. REVIEW OF MAGNETIC SEPARATORS
Figure 2.76: The Mintek linear high-gradient magnetic separator.
Scale-up of the machine could be accomplished by increasing the width of the
belt and by the installation of two to four magnetic heads in a single machine
along the belt. Although the separator performed well on pilot-plant scale,
non-technical issues prevented the industrial application of the machine.
An innovative approach to the concept of the VMS separator was employed
by Magnetic Technology Consultants (MTC) (South Africa) who designed and
built a high-gradient separator (Figure 2.77) designed to treat weakly magnetic
materials [A6]. Figure 2.78 illustrates the MTC separator operating in a glass
sand plant. The feed material containing 0.08 % Fe
2
O
3
was upgraded to 0.022%
Fe
2
O
3
in the first pass and to 0.011% Fe
2
O
3
in the second pass.
Although the separator was designed primarily for wet applications, it was
successfully tested in a dry mode. A vacuum system with vacuum seals was used
to propel the pyroxenite ore through the matrix and high velocity of the ore and
thus high throughput were achieved.
2.5 Superconducting magnetic separators
Although high-intensity and high-gradient magnetic separators that use resis-
tive magnets meet, in most instances, the technological requirements of the
mining and materials industries, their cost-eectiveness is impaired by high en-
ergy consumption, the need to cool the windings, limited working volume and
considerable mass owing to the massive iron yokes or cladding. These disad-
vantages can, however, be overcome by using superconducting magnets, which
2.5. SUPERCONDUCTING MAGNETIC SEPARATORS 129
Figure 2.77: The MTC continuous HGMS separator (South Africa).
Figure 2.78: MTC HGMS separator at the glass sand plant. The feed into the
separator is on the right-hand side while the non-magnetic product
in the first pass is shown on the left.