FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A GRAVITY-MAGNETIC SPIRAL CONCENTRATOR.
2 APPLICANT (S)
Name : JSW STEEL LIMITED.
Nationality : An Indian Company incorporated under the Companies Act,
1956.
Address : JSW CENTRE,
BANDRA KURLA COMPLEX,
BANDRA(EAST),
MUMBAI-400051,
MAHARASHTRA,INDIA.
3
PREAMBLE TO THE
DESCRIPTION
COMPLETE
The following specification particularly describes the invention and the manner in which it
is to be performed.
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FIELD OF THE INVENTION
The present invention relates to a gravity-magnetic spiral
concentrator for improving efficiency of separation of magnetic and
non magnetic ore particles resulting in maximizing the iron ore
recovery. More particularly, the present invention is directed to
provide magnetic forces in addition to the gravitational forces to
assist the magnetic or weakly magnetic particles to laterally shift the
flow path towards the concentrate stream. The improved gravitymagnetic
spiral concentrator according to the invention utilizes
gravitational force in combination with controlled axially placed
directed magnetic forces to achieve separation efficiency in excess of
that which can be achieved using gravitational forces alone. Typically,
the gravity-magnetic spiral concentrator is formed by retrofitting a
conventional spiral concentrator with electro magnets positioned in
axial direction to the gravity flow path so as to enhance the
separation capability of the conventional spiral separator. Importantly
also, the apparatus is provided with control means to vary the
magnetic force induction, angle of force application to facilitate
separation of mineral/ore particles in a desired manner.
BACKGROUND OF THE INVENTION
The separation of ore particles in a normal spiral concentrator works
on the principles of gravity separation and the efficiency of separation
is a function of particle sizes, solids concentration in the feed, velocity
profile, particle settling rates, interstitial trickling etc. The ore particles
generally consist of magnetic and weakly magnetic mineral having
different specific gravity.
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In conventional spiral concentrator, the differences in the specific
gravities of different individual minerals or phases constituting the
mixture called the feed material are used to achieve the separation.
Generally, a stream of feed material flows over a downward sloping
helical surface around a central axis under the influence of
gravitational forces. The higher specific gravity particles which
generally form the concentrate flow towards the inner edge, while the
lower specific gravity material flow towards the outer edge and form
the tailings. Due to the very fines particle size, and the existence of
iron hydroxide phases, the specific gravity difference is not
appreciable to effectively separate the iron particle from that of
mineral matter. Further, due to drag force, the acceleration picked by
the particles and the resultant forces on the particles, tend to create
turbulence and mix up of useful iron particles along with mineral
particles and flow towards the middle of the spiral surface which from
the middling.
The phase and size analysis of the particles travelling towards the
middling path is analyzed to have magnetic or weakly magnetic ore
particles.
The generic geometry of spiral concentrators consisting of an open
trough that spirals vertically downwards in helical configuration
around the central axis (Wills, 1992). Feed is introduced at the top of
the spiral with solids concentration ranging from 15-45% by weight
and allowed to flow down the slopping surface. The particles in the
feed experience a number of forces during the motion and the
stratification of particles is affected by the gravitational forces
combined with differential settling rates due to the specific gravity
variation of the ore and mineral particles, interstitial trickling, drag
forces etc. (Mills, 1978). Conventionally the high specific gravity
particles move towards the inner edge, while lower specific gravity
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particles move towards the outer edge of the spiral. Some of the ore
particles which are predominantly of iron phases other than hematite
and magnetite are misplaced due to the close specific gravity values
with mineral matter, turbulence and flow towards the center of the
spiral called the middling.
An ore separator in which substantially co-directional magnetic and
gravitational forces are used to concentrate magnetic or weakly
magnetic minerals is disclosed in US Pat.No. 4565624; 1986 by
Martinez. A number of possible schemes have been proposed where in
a plurality of stationary permanent magnets or rotating magnets as
well as electromagnets with controlled magnetic force are located
beneath and along the length of an inclined surface of continuously
moving endless belts, spirals. Wet ore fed onto the belt or downward
sloping surfaces tends to move downward; while the magnetic or
weakly magnetic particles are attracted by the magnets located
beneath the sloping surface and are separated from the non magnetic
material and prevent build up of magnetic material on plate surface.
An alternative solution to the buildup of magnetic particles is disclosed
in Japanese Pat.No.143967. The Japanese patent discloses a separator
in which slurry of coal and iron ore flows along the bottom of a
separation tank. The iron ore sticks to the bottom of the tank which is
magnetized by electromagnetic coils while the non magnetic particles
are washed away. Scrapers are used to remove the buildup material
from the tank bottom.
While the above described gravity magnetic ore separator may under
certain circumstances, exhibit improved concentration capability for
magnetic or weakly magnetic minerals, no means is disclosed for
providing conventional gravity separators such as spirals with
magnetic forces to improve the ore concentration and yield
capabilities of such standard gravity separators.
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There has been thus a need to provide a modified and improved
gravity spiral concentrator involving modifying the conventional
gravity spiral separator with selectively disposed electro magnets to
apply controlled magnetic forces in combination with gravity force to
improve the recovery and concentration capabilities without limiting
the performance of the system.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to a gravitymagnetic
spiral concentrator for improving efficiency of separation of
magnetic and non magnetic ore particles resulting in maximizing the
iron ore recovery.
A further object of the present invention is directed to a gravitymagnetic
spiral concentrator wherein selective magnetic forces is
applied in addition to the gravitational forces to assist the magnetic or
weakly magnetic particles to laterally shift the flow path towards the
concentrate stream.
A still further object of the present invention is directed to a gravitymagnetic
spiral concentrator wherein axially placed magnetic forces
applied perpendicular to the flow path to shift the magnetic or weakly
magnetic particles towards the concentrate flow path resulting in
increased recovery of relatively fine sized magnetic or weakly
magnetic particles otherwise lost in the middling.
A still further object of the present invention is directed to a gravitymagnetic
spiral concentrator including retrofitting/adding axial
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magnetic forces to conventional gravity spiral concentrator to improve
both the capacity of the spiral and grade of concentrate produced.
A still further object of the present invention is directed to a gravitymagnetic
spiral concentrator wherein inclination, interval of
positioning and field intensity of the magnets are selected based on
the size and content of the magnetic or weakly magnetic particles in
the feed material and shall be proportional to counter the turbulence
forces and avoid/restrict drifting of the concentrate particle towards
middling path and also avoid any build up of magnetic material at one
place.
A still further object of the present invention is directed to a gravitymagnetic
spiral concentrator which would help eliminating a distinct
magnetic separation step that follows a conventional gravity
separation step and in addition, in conventional multistage
gravitational separators, a fewer steps would be needed to recover the
desired grade of the concentrate.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a gravitymagnetic
spiral concentrator comprising:
downward slopping spiral helical flow surface having a curved
cross section and supported on a central column over which
feed material flows under the influence of gravity for gravity
separation involving concentrates of heavy materials at the
inner edge, the middling at or about the central region and
tailings at the outer edges ;and
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electromagnets for applying magnetic forces perpendicular to
the flow path with means of varying the magnetic force
intensity and direction.
A further aspect of the present invention is directed to a gravitymagnetic
spiral concentrator wherein said electromagnets are
positioned to attract micro fines of magnetic and weakly magnetic iron
ore particles which does not normally respond to gravity separation.
A still further aspect of the present invention is directed to a gravitymagnetic
spiral concentrator comprising control means for varying the
position, angle and field intensity on the flow surface of the
concentrator.
A still further aspect of the present invention is directed to a gravitymagnetic
spiral concentrator wherein the electro magnets are
positioned at the lower half of the spiral helical flow surface to allow
basic gravitational segregation of the minerals first and subsequently
intensified by magnetic force application.
Another aspect of the present invention is directed to a gravitymagnetic
spiral concentrator wherein the inclination, interval of
positioning and field intensity of said electromagnets are selected
based on the size and content of the magnetic or weakly magnetic
particles in the feed material and proportional to counter the
turbulence forces and avoid/restrict drifting of the concentrate
particle towards middling path and also avoid any build up of
magnetic material at one place.
Yet another aspect of the present invention is directed to a gravitymagnetic
spiral concentrator wherein said electromagnets are
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positioned selectively in (a) regular intervals on the central column at
an inclination of 45 degree such that the magnetic force field is
directed towards the center of the spiral trough and (b) for producing
a time varying magnetic force adjacent to one another on the central
column along the bottom section of the spiral such that the feed
material flowing down the spiral trough is under the influence of time
varying magnetic forces along the bottom section of the spiral.
A further aspect of the present invention is directed to a method for
separating magnetic or weakly magnetic ore from feed material in a
spiral concentrator comprising the steps of involving a combination of
gravitational and axially positioned magnetic forces and involving
electromagnets for applying magnetic forces perpendicular to the flow
path with means of varying the magnetic force intensity and direction.
A still further aspect of the present invention is directed to a method
for separating magnetic or weakly magnetic ore from feed material
comprising carrying out gravity-magnetic spiral concentrating using a
conventional gravity spiral separator/concentrator modified by
retrofitting of selectively disposed magnetic means on a central
column/shaft supporting the spiral concentrator.
A still further aspect of the present invention is directed to a method
for separating magnetic or weakly magnetic ore from feed material for
separating magnetic or weakly magnetic material from feed material
mix including non magnetic material having lower specific gravity than
the said magnetic or weakly magnetic material comprising
providing said feed material at the top of the spiral in slurry
form rendering thereby gravity separation of the particles occur
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based on the specific gravity difference of the minerals while
the slurry travels downward on the sloping surface of the spiral,
applying selective directed magnetic force perpendicular to the
pulp flow path so as to augment said gravity separation by
attracting the magnetic or weakly magnetic material towards
the inner edge of the spiral surface where in the high gravity
concentrates flow thus improving the recovery.
A still further aspect of the present invention is directed to a method
for separating magnetic or weakly magnetic ore from feed material
comprising selectively providing number of electromagnetic means
across the length of the spiral equipment, magnetic force intensity,
and inclination of magnetic force application and particle size
manipulation to attract the magnetic and weakly magnetic particles
and wherein different portions are collected through separate ports
concentrates, middling and tailings at the bottom of spiral tray.
The above and other objects and advantages of the present invention
are described hereunder in greater details with reference to the
following accompanying non limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: shows a schematic diagram of an embodiment of the
gravity-magnetic spiral concentrator according to the present
invention wherein a conventional spiral is retrofitted with selectively
axially disposed electro magnets.
Figure 2: Illustrates an embodiment of the gravity-magnetic spiral
separator modified with electro magnets in accordance with the
principles of present invention in cut-section.
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Figure 3: shows a photograph of the actual performance of the
modified conventional spiral lab set up in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE
TO THE ACCOMPANYING FIGURES
The present invention is a modified spiral apparatus for separating
magnetic or weakly magnetic iron ore from feed material by using a
combination of gravitational and axially positioned magnetic forces.
The inventive apparatus is particularly useful to attract micro fines of
magnetic and weakly magnetic iron ore particles such as hematite,
goethite, limonite etc which does not normally respond to gravity
separation. The inventive separating spiral equipment comprises of;
downward slopping helical surface over which feed material flows
under the influence of gravity; electro magnets for applying magnetic
forces perpendicular to the flow path with means of varying the
magnetic force intensity and direction. The electro magnets are
located in the bottom section of the central column of the spiral
equipment at regular interval.
In the present invention in its preferred form involves more than
merely combining electromagnets with conventional gravity
separators to increase the forces acting on the particles. Such a
combination without optimum positioning and magnetic flux
adjustment will not achieve the desired results. The magnetic forces
in the present condition are designed to counter the drag and
turbulence forces and shift the flow path of the magnetic or weakly
magnetic particles towards the inner edge of the concentrate flow.
The intensity of the magnetic force applied is also essential to avoid
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build up of magnetic particles at one place. Accordingly, it is generally
desired in practice of the present invention that means for varying
the position, angle and field intensity on the flow surface of the
separator is included.
Modification of existing spiral gravity separator in accordance with the
present invention results in numerous advantages in processing of
feed materials such as iron ores to improve the recovery of magnetic
or weakly magnetic minerals. When modified in accordance with the
present invention, a conventional spiral gravity separator exhibits
increased weight recovery (weight of feed material divided by
concentration weight) and increased recovery of fine magnetic or
weakly magnetic particles otherwise lost in the middling.
With this modification in a conventional spiral, in certain cases, a
distinct magnetic separation step which follows a conventional gravity
separation step may be eliminated and in addition, in conventional
multistage gravitational separators, a fewer steps would be needed to
recover the desired grade of the concentrate.
The exemplary embodiment of gravity magnetic spiral and its working
methodology according to the present invention are described
hereunder with reference to accompanying figures:
Accompanying Figure 1 shows a schematic diagram of an
embodiment of a conventional spiral retrofitted with the electro
magnets according to the present invention. The modified spiral
separator 10 consists of a helical spiral trough 11 of curved cross
section supported on a central column 12. Feed material is iron ore
slurry which is a mixture of iron particles both magnetic and weakly
magnetic, gangue mineral particles such as silica, alumina etc which
have different specific gravity and magnetic properties. The feed
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material is introduced into the trough 11 near the top of the spiral. As
the feed material flows down the spiral trough 11, gravity separation
takes place. The heavy material such as iron rich particles move
towards the inner edge of the spiral trough 11. Mixed material of iron
ore particles primarily consisting of very fine size, low specific gravity
and weakly magnetic properties and some of the gangue particles
flows towards the middle and are called middling. The very low
specific gravity material, primarily consisting of silica and alumina
move towards the outer edge of the spiral trough 11 as tailings. The
different portions are collected through separate ports concentrates
13, middling 14 and tailings 15 at the bottom of the spiral 10.
The different particles during their flight down the spiral trough 11
experience different forces of increasing intensity with the distance of
travel. Due to effects of drag force and turbulence forces, acting on
the very fine iron ore particles, which are of magnetic or weakly
magnetic are forced to shift their flow path and get mixed up in the
middling path resulting in loss of recovery.
In order to improve the mineral concentrating and recovery
capabilities of the spiral separator 10, a number of electro magnets
16 for producing varying magnetic force are positioned axially at an
inclination at equal intervals along the central column 12. The electro
magnets are positioned at the lower half of the spiral 10 to allow
basic gravitational segregation of the minerals first and subsequently
intensified by magnetic force application. For inducing the required
magnetic forces, conventional electromagnets in conjunction with
control circuit may be used for producing varying magnetic force
intensities. The inclination, interval of positioning and field intensity
shall be based on the size and content of the magnetic or weakly
magnetic particles in the feed material and shall be proportional to
counter the turbulence forces and avoid/restrict drifting of the
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concentrate particle towards middling path and also avoid any build
up of magnetic material at one place.
In order to have significant effect on separation of magnetic or
weakly magnetic particles from the feed material and allow them to
flow towards the concentrate stream 13, it is desirable that the
magnetic means 16 be positioned in regular intervals on the central
column 12 at an inclination of 45 degree such that the magnetic force
field is directed towards the center of the spiral trough 11. In
addition, it is to be noted that although only four numbers of
electromagnetic assemblies 16 are shown in Figure 1, in particular
embodiments of the invention means for producing a time varying
magnetic force may be located adjacent to one another on the central
column 12 along the bottom section of the spiral 10, so that the feed
material flowing down the spiral trough 11 is under the influence of
time varying magnetic forces along the bottom section of the spiral
10. It may be further advantageous and improve the efficiency of
separation, if the magnetic means 16 are placed all along the length
of the spiral 10.
It is to be noted that, the conventional spirals currently in use are of
varying sizes in length and width and are made of fiber glass or fiber
glass reinforced plastic. The number of electromagnetic units 16 to be
used will be proportional to the size and dimensions of the specific
unit and the feed material characteristics.
Figure 2 illustrates an embodiment of the spiral separator modified
with electro magnets in accordance with the principles of present
invention in cut-section. The feed material flowing down the spiral
trough 11 gets segregated into three flow paths concentrate 13,
middling 14 and tailings 15 under the influence of gravitational
forces. An electro magnet capable of variable magnetic intensity is
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positioned on the central column of the spiral 12 at an inclination of
45 degrees such that the magnetic force field is directed towards the
middle section of the spiral trough 11 where the magnetic or weakly
magnetic particles flow mixed with gangue particles in a conventional
spiral equipment.
The magnetic field so directed towards the middling path, allows the
magnetic or weakly magnetic particles to be pulled towards the
source of the magnetic field and change their flight path from
middling 14 to concentrate path 13. The magnetic force so applied is
proportional to facilitate the shifting of the particle motion towards
the inner edge and does not result in buildup of the magnetic
particles at any specific place.
Once the magnetic or weakly magnetic particles drift towards the
concentrate path 13, the particles are continuously washed down by
the liquids flowing from the top and get accumulated in the
concentrate material.
The magnetic means 12 shall be capable of varying its position in
both vertical and axial directions and force intensities to suit the
dimensional requirements of the specific spiral under consideration.
Accompanying Figure 3 shows a photograph of the actual
performance of the modified conventional spiral lab set up in
accordance to the present invention.
The actual typical arrangement of the magnetic means 16 on the
central shaft 12 is shown. It can be seen that, subsequent to the
retrofit of electromagnets 16, the concentrate particle flow has
improved towards the inner edge of the spiral trough 11 compared to
conventional spiral equipment. In the embodiment of the present
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invention, the number of electromagnetic units 16 to be used will
depend on the size, shape and magnetic field area coverage required
and applicable to the spiral equipment 10 to be retrofitted and the
feed material characteristics.
A low grade iron ore particle consisting of a mixture of 100-150
micron sizes with a Fe concentration of 54 % has been experimented
to establish the efficacy of the system in accordance to the present
invention. Slurry of the iron ore particles is prepared with 23 % solids
and rest water similar to any actual plant operating condition. The
feed rate to the spiral was maintained at 2TPH. It is observed that the
minimum optimum voltage application to the electro magnets is 30 V.
First the sample was treated in the conventional spiral concentrator
and subsequently in the modified spiral retrofitted with
electromagnetic means. The new inventive process is tested and
established over 90 trials by varying the magnetic flux, feed solids
percentage and Fe concentration, feed flow rate. The averaged
optimum results are given in table 1.
The comparative performance results with conventional gravitational
and modified gravity –magnetic spiral separator are presented in
following Table 1.
Table 1:
Performance of Conventional spiral separation
Wt % T.Fe % Iron Recovery %
Concentrate 39.76 61.52 44.65
Middling 40.8 53.23 39.65
Tailing 19.44 44.23 15.70
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Performance of Modified Conventional spiral with
axially fitted electromagnets
Wt % T.Fe % Iron Recovery %
Concentrate 41.61 62.1 47.17
Middling 39.06 52.43 37.39
Tailing 19.33 43.75 15.44
It is observed that, the inventive step under the disclosure has
improved the recovery of the iron ore by 3% and has also improved
the grade of the concentrate by 1 %.
Trials data with varied degree of inclination of the magnets in steps of
15 deg directed towards attracting the iron particles from middling
path are as presented in following Tables 2(a) to (e).
Table 2(a) –(e)
Performance of Modified Conventional spiral with axially fitted
electromagnets_____________ _____ _____
_
WT% TFe% Recovery
Conc 40.60 61.58 45.67
Mid 39.90 53.12 38.72
Tail 19.50 43.83 15.61
Performance of Modified Conventional spiral with axially fitted
electromagnets_____________ _____ _____
_
WT% TFe% Recovery
Conc 40.84 61.83 46.11
Mid 39.94 52.81 38.52
Tail 19.22 43.79 15.37
_ _
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_
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_ _
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Performance of Modified Conventional spiral with axially fitted
electromagnets_____________ _____ _____
_
WT% TFe% Recovery
Conc 41.22 61.92 46.61
Mid 39.06 52.76 37.63
Tail 19.72 43.75 15.76
_ _ _ _
_Performance_ of Modified Co_nventional spi_ral with axially fitted
electromagnets_____________ _____ _____
WT% TFe% Recovery
Conc 41.61 62.1 47.17
Mid 39.06 52.43 37.39
Tail 19.33 43.75 15.44
_ _ _ _
_Performance_ of Modified Co_nventional spi_ral with axially fitted
electromagnets_____________ _____ _____
_
WT% TFe% Recovery
Conc 40.64 60.92 45.26
Mid 39.82 53.44 38.90
Tail 19.54 44.35 15.84
It is thus possible by way of the present invention to achieve
improved results in terms of iron recovery and concentrate grade in
actual plant operations involving the modified gravity–magnetic spiral
separator. In a possible alternative embodiment of the invention,
further improvements can be achieved by optimization of number of
electromagnetic means across the length of the spiral equipment,
magnetic force intensity, and inclination of magnetic force application
and particle size manipulation to attract the magnetic and weakly
magnetic particles.
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We Claim:
1. A gravity-magnetic spiral concentrator comprising:
downward slopping spiral helical flow surface having a curved
cross section and supported on a central column over which
feed material flows under the influence of gravity for gravity
separation involving concentrates of heavy materials at the
inner edge, the middling at or about the central region and
tailings at the outer edges ;and
electro magnets for applying magnetic forces perpendicular to
the flow path with means of varying the magnetic force
intensity and direction.
2. A gravity-magnetic spiral concentrator as claimed in claim 1
wherein said electromagnets are positioned to attract micro
fines of magnetic and weakly magnetic iron ore particles which
does not normally respond to gravity separation.
3. A gravity-magnetic spiral concentrator as claimed in anyone of
claims 1 or 2 comprising control means for varying the position,
angle and field intensity on the flow surface of the concentrator.
4. A gravity-magnetic spiral concentrator as claimed in anyone of
claims 1 to 3 wherein the electro magnets are positioned at the
lower half of the spiral helical flow surface to allow basic
gravitational segregation of the minerals first and subsequently
intensified by magnetic force application.
5. A gravity-magnetic spiral concentrator as claimed in anyone of
claims 1 to 4 wherein the inclination, interval of positioning
and field intensity of said electromagnets are selected based
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on the size and content of the magnetic or weakly magnetic
particles in the feed material and proportional to counter the
turbulence forces and avoid/restrict drifting of the concentrate
particle towards middling path and also avoid any build up of
magnetic material at one place.
6. A gravity-magnetic spiral concentrator as claimed in anyone of
claims 1 to 5 wherein said electromagnets are positioned
selectively in (a) regular intervals on the central column at an
inclination of 45 degree such that the magnetic force field is
directed towards the center of the spiral trough and (b) for
producing a time varying magnetic force adjacent to one
another on the central column along the bottom section of the
spiral such that the feed material flowing down the spiral
trough is under the influence of time varying magnetic forces
along the bottom section of the spiral.
7. A method for separating magnetic or weakly magnetic ore from
feed material in a spiral concentrator comprising the steps of
involving a combination of gravitational and axially positioned
magnetic forces and involving electro magnets for applying
magnetic forces perpendicular to the flow path with means of
varying the magnetic force intensity and direction.
8. A method for separating magnetic or weakly magnetic ore from
feed material as claimed in claim 7 comprising carrying out
gravity-magnetic spiral concentrating using a conventional
gravity spiral separator/concentrator modified by retrofitting of
selectively disposed magnetic means on a central column/shaft
supporting the spiral concentrator.
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9. A method for separating magnetic or weakly magnetic ore from
feed material as claimed in anyone of claims 7 or 8 for
separating magnetic or weakly magnetic material from feed
material mix including non magnetic material having lower
specific gravity than the said magnetic or weakly magnetic
material comprising
providing said feed material at the top of the spiral in slurry
form rendering thereby gravity separation of the particles occur
based on the specific gravity difference of the minerals while
the slurry travels downward on the sloping surface of the spiral,
applying selective directed magnetic force perpendicular to the
pulp flow path so as to augment said gravity separation by
attracting the magnetic or weakly magnetic material towards
the inner edge of the spiral surface where in the high gravity
concentrates flow thus improving the recovery.
10. A method for separating magnetic or weakly magnetic ore from
feed material as claimed in anyone of claims 7 to 9 comprising
selectively providing number of electromagnetic means across
the length of the spiral equipment, magnetic force intensity,
and inclination of magnetic force application and particle size
manipulation to attract the magnetic and weakly magnetic
particles and wherein different portions are collected through
separate ports concentrates, middling and tailings at the
bottom of spiral tray.