Note: Descriptions are shown in the official language in which they were submitted.
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MINERAL SEPARATION PROCESS
The present invention relates to a selective wet magnetic separation process
for beneficiation
(separating and concentrating) of weakly paramagnetic lithium-mica minerals
from a milled
feed stream containing weakly paramagnetic lithium-mica minerals, highly
magnetic ferrous
waste and nonmagnetic gangue, using a sequence of wet magnetic separators,
such as Low
Intensity Magnetic Separators ("LI MS"), Wet High Gradient Magnetic Separators
("WHGMS")
and Vertical Pulsating Wet High Gradient Magnetic Separators ("VPWHGMS") to
obtain
concentrated paramagnetic lithium-mica minerals therefrom suitable for further
processing
to extract the lithium. The present invention also relates to a magnetic
separation apparatus
for beneficiation of weakly paramagnetic lithium-mica minerals from a milled
feed stream
containing weakly paramagnetic lithium-mica minerals, highly magnetic ferrous
waste and
nonmagnetic gangue. The process of the present invention can be used to
achieve >90%
recovery of weakly paramagnetic lithium-mica minerals to a concentrate.
BACKGROUND OF INVENTION
Beneficiation is used in the mining and allied industry to improve the
economic value of a
mineral ore feed by removing "gangue" minerals (worthless or low-value
contaminants) to
provide a higher grade or concentrated valuable product. Beneficiation can
however be a
wasteful process in terms of both energy and chemicals, and provide low
recovery of the
valuable product. Beneficiation processes typically use high energy milling,
chemical
surfactants and other agents to improve mineral concentration. Physical means
of
beneficiating ores can also be used to extract different materials to discrete
process streams
based on their contrast in physical characteristics such as for example
colour, radiometric,
magnetic or electrostatic susceptibility, density, shape or particle size. For
example, magnetic
separation can be used "indirectly" to remove magnetic contaminants from the
desired
mineral ore, or to "directly" remove a magnetic target mineral from
nonmagnetic
contaminants.
Wet milling is required to liberate or separate the desired minerals (such as
lithium-mica or
lithium-spodumene) from gangue.
Various beneficiation processes can be used on wet, milled feed in combination
to achieve a
desired beneficiation efficiency or purity. For example, pegmatites and
spodumene hosted
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lithium deposits (which are currently the world's largest source of lithium)
have been known
to be beneficiated using dense media separation plus chemical froth floatation
technologies
as a precursor to extracting the lithium from the spodumene. Floatation
technologies require
the use of costly consumable surfactants such as fatty acids which may be
harmful to the
environment and can require remediation. One of the key parameters in
floatation is the
particle size distribution of the feed and it has been shown in several
studies that the optimal
size range for floatation is relatively narrow, approximately 20 p.m to 150
p.m which requires
energy intensive milling of the ore, and which can also generate fine
particles which cannot
be economically recovered. Froth floatation is widely used; however it has
been found that
spodumene producers typically recover only 60% to 70% of the desired spodumene
content
of the ore, meaning that 30% to 40% of the lithium is lost through process
wastes.
Furthermore, beneficiation processes for spodumene are complex and typically
involve
multiple stages of crushing, grinding, hydraulic sorting, attrition scrubbing,
conditioning,
multi- stage chemical floatation plus dense media separation. This is time
consuming, costly,
labour intensive and the complexity can lead to low overall plant availability
and mass
recovery. Moreover, the use of acidic reagents for floatation can create
hazardous acidic
tailings.
Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate
LiAl(SiO3)2, is not
magnetic or paramagnetic, and so cannot be separated from gangue minerals and
concentrated by magnetic separation. Magnetic separation has been known to be
used to
indirectly concentrate spodumene by removing minor magnetic contaminants from
spodumene ores, but not to directly concentrate the spodumene.
Extensive potentially economic deposits of lithium also occur in lithium-mica
minerals within
granites in Europe and elsewhere, which also contain gangue minerals,
principally quartz and
feldspar. However, lithium has never been extracted commercially from lithium-
mica and so
to exploit these deposits commercially there is a need to develop an
environmentally
sustainable and economic method for separation and concentration of the
lithium-mica
minerals from gangue minerals as a precursor to extracting the lithium from
the mica.
Micas are chemically the most variable mineral group among all rock-forming
minerals. Not
all mica minerals contain lithium, but those that do can also, but not always,
contain iron
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within their crystal matrix or as impurities in the form of sub-microscopic
inclusions of iron
oxides, which makes them very weakly magnetic or paramagnetic.
Lithium-mica minerals such as zinnwaldite KLiFeAl(AlSi3)010(OH,F)2 (potassium
lithium iron
aluminium silicate hydroxide fluoride) and polylithionite
KL11.7N1a0.3A1S14010F(OH) are more
complex minerals than spodumene LiAl(Si206) (lithium aluminium inosilicate)
and contain less
lithium. Pure zinnwaldite for example contains eight elements with lithium
accounting for
only 1.59% of the mineral's mass, whereas spodumene contains only four
elements of which
lithium accounts for 3.73% of the pure mineral's mass.
Given the very high energy cost of drying milled feed before dry magnetic
separation, there
is a need for an efficient beneficiation process using wet magnetic separation
instead of dry
magnetic separation.
Given the very low contrast in magnetic susceptibility of weakly paramagnetic
lithium-mica
and gangue, single-stage wet magnetic separation cannot sufficiently recover
or concentrate
the lithium-mica and so there is a need for an improved method of multi-stage
wet magnetic
separation with recycle streams to obtain acceptable recovery and concentrate
grade.
Given lithium-mica minerals' disadvantages of lower grade and higher mineral
complexity
compared to spodumene there is a need for a beneficiation process for lithium-
mica minerals
with improved mineral recovery efficiency, with fewer processing steps,
improved specificity
for a particular ore, at lower cost and lower environmental impact. There is
also a need for a
beneficiation process that does not require the use of environmentally
damaging chemical
reagents or processes.
Alternative technology is the direct flotation of lithium-mica using fatty
acid reagents. This
involves adding acid to reduce the pH, resulting in acidic waste and produces
low recovery to
a concentrate.
The major sources of commercially mined lithium are from brine solutions
(principally in
South America) and spodumene containing ores (principally in Western
Australia). To date,
there has been no commercial production of lithium from lithium-mica granite
ores or
concentrates.
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There have been several efforts to beneficiate lithium-mica minerals in the
laboratory.
Importantly, these prior art efforts focussed on nonmagnetic lithium-mica
minerals such as
lepidolite using gravity or density separation or floatation or on
paramagnetic lithium-mica
minerals using dry magnetic separation and none of these prior art efforts
have involved the
proposed sequence of indirect concentration using Low Intensity Magnetic
Separation
("LIMS") followed by direct concentration using and Wet High Gradient Magnetic
Separation
("WHGMS") or Vertical ring Pulsating Wet High Gradient Magnetic Separation
("VPWHGMS").
Other processes have been described to remove lithium-mica minerals as waste
from a
valuable mineral, but not to directly concentrate paramagnetic lithium-mica
minerals for the
purpose of recovering lithium.
From a review of other known methods for the beneficiation of mica minerals,
whether or
not they are lithium-mica minerals, recovery efficiencies as high as those
demonstrated by
the invention process are not known in the prior art. Similarly, the
paramagnetic properties
of many mica materials are unknown and their utility as a means of separation
is previously
undescribed in academic and patent literature.
The use of magnetic separation of one material from another or the removal of
magnetic
particles from streams depends upon their motion in response to the magnetic
force and to
other competing external forces, namely gravitational, inertial, hydrodynamic
and centrifugal
forces all of which need to be considered when designing an efficient process.
A necessary
condition for the successful separation of more strongly magnetic from less
strongly magnetic
particles in a magnetic field is that the magnetic force acting on more
magnetic particles must
be greater than the sum of all the competing forces. In one embodiment, the
present
invention uses vertical fluid flow and pulsation of the slurry to assist the
separation of
paramagnetic mica minerals.
The granite ore containing lithium-mica may contain low concentrations of
ferrous minerals.
Milling ores in preparation for their beneficiation by separating or
liberating the different
minerals from each other invariably introduces highly magnetic ferrous waste,
which may
include swarf from crushing and grinding media. Ferrous minerals and swan f
have been found
to foul high-intensity magnetic separators used to extract and concentrate
paramagnetic
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minerals. The highly magnetic swan f often contains chrome, which has been
found to be
deleterious to the subsequent process of extracting lithium from lithium-mica
minerals.
CN108057513 discloses a method for the extraction of potassium feldspar
concentrate and
iron lepidolite concentrate from lithium-containing granite pegmatite waste.
The method
comprises the steps of: mineral separation and classification; ball-milling
screening and
classification; gravity separation; and magnetic separation to provide the
potassium feldspar
concentrate and the iron lepidolite concentrate.
SUMMARY OF INVENTION
According to a first aspect of the invention, there is provided a wet magnetic
separation
process for efficiently beneficiating (separating and concentrating)
paramagnetic lithium-
mica minerals from a milled feed stream containing weakly paramagnetic lithium-
mica
minerals mixed with both highly magnetic ferrous waste and nonmagnetic gangue,
in which
the process comprises:
feeding the milled feed stream containing weakly paramagnetic lithium-mica
minerals, highly magnetic ferrous waste and nonmagnetic gangue into a Low
magnetic field
Intensity Magnetic Separator ("LIMS") having a first magnetic field strength
to provide a first
waste stream comprising highly magnetic waste material, and an indirectly
concentrated first
product stream comprising paramagnetic lithium-mica minerals together with
nonmagnetic
gangue;
subsequently feeding the first product stream into a first Wet High Gradient
Magnetic
Separator ("WHGMS") having a second magnetic field strength that is greater
than the first
magnetic field strength of the LIMS to provide a second waste stream
comprising
nonmagnetic gangue and residual carryover paramagnetic lithium-mica minerals,
and a
second product stream comprising directly concentrated paramagnetic lithium-
mica minerals
and a reduced concentration of nonmagnetic gangue when compared to the first
product
stream, and further comprising one or more of:
feeding the second waste stream into a second WHGMS to recover additional,
residual
carryover paramagnetic lithium-mica minerals and to provide a third product
stream
comprising concentrated paramagnetic lithium-mica minerals and a reduced
concentration
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of nonmagnetic gangue compared to the second waste stream, and a third waste
stream
comprising nonmagnetic gangue; and/or
feeding the second product stream, and optionally the third product stream,
into a
third WHGMS to provide a fourth product stream comprising a further
concentrated
paramagnetic lithium-mica minerals preferably of higher lithium grade when
compared to the
second product stream and a fourth waste stream of nonmagnetic material;
and/or
optionally feeding the fourth waste stream comprising nonmagnetic gangue and
residual carryover paramagnetic lithium-mica minerals into the second WHGMS to
recover
additional paramagnetic lithium-mica minerals to the third product stream.
A series of low and high magnetic field strength separations may be used to
achieve a high
beneficiation mass yield of particular paramagnetic lithium-mica minerals, and
overcome the
difficulty of separating materials with very low contrast of magnetic
susceptibility.
The process may comprise the use of vertical fluid flow and pulsating slurry
feed in
combination with the series of low and high magnetic field strength
separations to achieve a
high beneficiation yield of particular paramagnetic lithium-mica minerals.
The milled feed stream is preferably a slurry.
The LIMS preferably has a first magnetic field strength sufficient to separate
the first highly
magnetic waste stream, whilst also being insufficient to attract paramagnetic
lithium-mica
minerals.
The first WHGMS may also be referred to herein as a "Rougher".
The second WHGMS may also be referred to herein as a "Scavenger".
The third WHGMS may also be referred to as a "Cleaner".
The second waste stream comprising nonmagnetic gangue produced by the Rougher
WHGMS
preferably comprises residual or carryover paramagnetic lithium-mica minerals
mixed with
nonmagnetic gangue.
The fourth product stream preferably has an increased concentration of
paramagnetic
lithium-mica minerals compared to the second and third product streams. The
fourth waste
stream comprising nonmagnetic gangue produced by the Cleaner WHGMS preferably
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comprises a low concentration of remaining paramagnetic lithium-mica minerals
(for example
residual or carry-over paramagnetic lithium-mica minerals) mixed with
nonmagnetic gangue
which optionally may be recycled to the Scavenger WHGMS for recovery of
residual carryover
paramagnetic lithium-mica minerals.
Optionally the fourth waste stream may comprise a decreased concentration of
paramagnetic
lithium-mica minerals mixed with an increased concentration of nonmagnetic
gangue
resulting in a lithium concentration below a predetermined minimum amount. The
predetermined minimum amount may be selected to correspond to an amount of
lithium
content that is considered to be uneconomic to use for further extraction in
which case the
fourth waste stream may be considered the final waste stream and no further
beneficiation
is required.
According to a second aspect of the present invention, there is provided an
apparatus for the
wet magnetic separation of wet milled paramagnetic lithium-mica minerals from
a feed
stream containing weakly paramagnetic lithium-mica minerals mixed with highly
magnetic
ferrous waste and nonmagnetic gangue, the apparatus comprising:
a slurry feed source comprising milled weakly paramagnetic lithium-mica
minerals
mixed with nonmagnetic gangue and highly magnetic ferrous waste materials;
a LIMS having a first magnetic field strength, the LIMS being configured to
receive the
slurry feed source, and further comprising a first waste outlet configured to
provide a first
highly magnetic waste stream, and a first product outlet configured to provide
a first product
stream comprising paramagnetic lithium-mica minerals together with nonmagnetic
gangue;
a Rougher WHGMS having a second magnetic field strength, the Rougher WHGMS
being configured to receive the first product stream from the LIMS, and
further comprising a
second waste outlet configured to provide a second waste stream comprising
nonmagnetic
gangue and residual carryover paramagnetic lithium-mica minerals, and a second
product
outlet configured to provide a second product stream comprising concentrated
paramagnetic
lithium-mica minerals and a reduced concentration of nonmagnetic gangue when
compared
to the first product stream,
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in which the second magnetic field strength is greater than the first magnetic
field
strength, and one or more of:
a Scavenger WHGMS operable to receive the second waste stream from the Rougher
WHGMS, and in which the Scavenger WHGMS further comprises a third product
outlet
configured to provide a third product stream comprising concentrated
paramagnetic lithium-
mica minerals and a reduced concentration of nonmagnetic gangue compared to
the second
waste stream; and/or
a Cleaner WHGMS operable to receive the second product stream from the Rougher
WHGMS, and/or the third product stream from the Scavenger WHGMS, to provide a
fourth
product stream comprising an increased concentration of paramagnetic lithium-
mica
minerals compared to the second and third product streams, and a fourth waste
stream which
optionally may be recycled to the Scavenger WHGMS for recovery of residual
carryover
paramagnetic lithium-mica minerals.
Optionally the fourth waste stream may comprise a decreased concentration of
paramagnetic
lithium-mica minerals mixed with an increased concentration of nonmagnetic
gangue
resulting in a lithium concentration below a predetermined minimum amount. The
predetermined minimum amount may be selected to correspond to an amount of
lithium
content that is considered to be uneconomic to use for further extraction in
which case the
fourth waste stream can be considered the final waste stream and no further
beneficiation is
required
The term "milled" is used to refer to the solid materials having reduced
particle size, to
separate or liberate different minerals from each other, by processes
including crushing,
grinding and classification or optionally scrubbing and classification.
Size classification of the particles is required to ensure the bulk of the
material feed is of a
size suitable for magnetic separation. Preferably the feed stream has a
maximum particle size
of 1-3 mm. Preferably, the feed stream has a minimum particle size in the
range of between
10 p.m and 50 p.m.
The wet magnetic separation process may further comprise desliming the milled
feed stream
containing paramagnetic lithium-mica minerals, preferably by use of a
hydrocyclone to
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provide a deslimed, milled feed stream containing paramagnetic lithium-mica
minerals
comprising particles having an average particle size (d50) greater than 10
p.m, preferably
greater than 20 p.m, preferably greater than 50 p.m. Desliming the milled feed
stream to
remove ultrafine particles (that are not readily separated by magnetic
separation or by other
beneficiation means) with an average particle size (d50) of 10 p.m or less,
preferably 20 pm or
less, preferably 50 p.m or less reduces the feed mass by between 10% and 25%
while losing
to waste less than 5% to 10% of the contained paramagnetic lithium-mica
minerals, and
increasing the pulp density.
The feed stream or feed source may comprise a plurality of feed stream
fractions. Each feed
stream fraction may comprise a milled feed stream containing paramagnetic
lithium-mica
minerals comprising particles having a maximum particles size within a
predetermined
maximum particle size range. The feed stream or feed source may comprise a
plurality of
feed stream fractions, in which one or more, preferably each feed stream
fraction, comprises
particles within a different predetermined maximum particle size range. The
predetermined
maximum particle size range within one feed stream fraction may overlap with
the
predetermined maximum particle size range of one or more other feed stream
fractions. The
predetermined maximum particle size range within one feed stream fraction may
be distinct
from the predetermined maximum particle size range of one or more other feed
stream
fractions.
The process may comprise feeding each feed stream fraction or a combination of
one or more
feed stream fractions into a WHGMS and obtaining a paramagnetic lithium-mica
mineral
concentrate product stream therefrom. One or more, for example each, feed
stream fraction
may be fed, for example separately fed or in combination, into the same WHGMS,
or into
separate WHGMS.
The milled feed stream containing paramagnetic lithium-mica minerals or feed
source is
derived from igneous rock which may be granite. The igneous rock may have been
formed
during the Variscan orogeny. The igneous rock may form for example part of the
Cornubian
batholith, the Bohemian batholith, the Mondenubian batholith or the Central
French Massif.
The milled feed stream containing paramagnetic lithium-mica minerals or feed
source is
preferably derived from naturally deposited lithium-mica-bearing rock,
sediments or
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anthropogenically generated waste streams or lithium-mica storage dams derived
from
naturally deposited lithium-mica-bearing rock or sediments.
The milled feed stream containing paramagnetic lithium-mica minerals or feed
source
preferably comprises a slurry containing between 10% and 50% w/w solids,
preferably
grading between 500 and 15,000 ppm lithium.
The WHGMS preferably provides a magnetic field with a magnetic field strength
of less than
2 Tesla, preferably less than 1.5 Tesla, for example in the range of between
0.2 and 1.5 Tesla.
The WHGMS is preferably a VPWHGMS.
Pulsation may be provided by for example an actuated diaphragm configured to
provide
pulsation to the slurry feeding the corresponding WHGMS, preferably a VPWHGMS.
The
WHGMS preferably comprises one or more VPWHGMS. The VPWHGMS may use an
actuated
diaphragm pulsation mechanism with a stroke length between 0 mm and 40 mm, and
a stroke
rate between 0 Hz and 400 Hz.
At least one of the WHGMS is a VPWHGMS. The vertical orientation of the
separator ring
enables magnetic particle flushing in the opposite direction to the flow of
feed material. This
enables the more strongly magnetic and or coarse particles to be removed
without passing
through the full depth of the separator matrix. Additionally, flushing may
take place near the
top of rotation of the vertical ring where the magnetic field is the lowest,
thereby reducing
residual attraction of paramagnetic particles. These benefits reduce magnetic
matrix
plugging and increase mechanical availability.
Preferably, the first and/or second and/or third WHGMS is a VPWHGMS.
Preferably, each of
the first and second and third WHGMS is a VPWHGMS. For example, in one
embodiment,
each of the WHGMS is a VPWHGMS.
In one embodiment, the apparatus comprises a first "Rougher" WHGMS and a
second,
"Scavenger" WHGMS having a magnetic field strength preferably equal to or
greater than the
magnetic field strength of the Rougher WHGMS, in which the Scavenger WHGMS is
operable
to receive the second waste stream from the Rougher WHGMS and to recover
additional
paramagnetic lithium-mica minerals therefrom to provide a third product stream
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concentrated paramagnetic lithium-mica minerals mixed with a reduced
concentration of
nonmagnetic gangue, and a third waste stream therefrom.
In one embodiment, the process comprises feeding one or more waste streams
from one or
more first "Rougher" WHGMS or a third "Cleaner" WHGMS into a second
"Scavenger"
WHGMS having a magnetic field strength preferably equal to or greater than the
magnetic
field strength of the Rougher WHGMS to provide the third product stream
comprising
concentrated paramagnetic lithium-mica minerals mixed with a reduced
concentration of
nonmagnetic gangue, and a third waste stream. The third waste stream may
comprise a
decreased concentration of paramagnetic lithium-mica minerals mixed with an
increased
concentration of nonmagnetic gangue in a lithium concentration below a
predetermined
minimum amount. The predetermined minimum amount may be selected to correspond
to
an amount of lithium content that is considered to be uneconomic to use for
further
extraction.
The apparatus may further comprise a Cleaner WHGMS operable to receive one or
more
product streams from the Rougher WHGMS and/or the Scavenger WHGMS to provide a
fourth product stream comprising an increased concentration of paramagnetic
lithium-mica
minerals compared to the first, second or third product streams, and a fourth
waste stream.
The process may comprise feeding a product stream obtained from the Rougher
WHGMS into
a Cleaner WHGMS to provide a fourth product stream comprising an increased
concentration
of paramagnetic lithium-mica minerals compared to the second product stream
obtained
from the Rougher WHGMS, and fourth waste stream.
In one embodiment, the Scavenger WHGMS is in communication with a Cleaner
WHGMS.
The Cleaner WHGMS preferably has a third magnetic field strength preferably no
greater than
the magnetic field strength of the Scavenger WHGMS.
In one embodiment, the process comprises feeding a second product stream
obtained from
one or more Rougher WHGMS into a Cleaner WHGMS. The magnetic Field strength of
the
Cleaner WHGMS is preferably no greater than the magnetic field strength of the
Scavenger
WHGMS. The Cleaner WHGMS provides a fourth product stream comprising an
increased
concentration of paramagnetic lithium-mica minerals compared to the magnetic
product
stream obtained from one or more Rougher WHGMS, and a fourth waste stream. The
fourth
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waste stream may contain paramagnetic lithium-mica minerals in a concentration
above a
predetermined minimum amount. As such, the fourth waste stream may be
recycled, for
example reintroduced into one of the WHGMS (for example the first or second or
third or a
fourth WHGMS) in order to further extract any residual carryover paramagnetic
lithium-mica
minerals remaining within the fourth waste stream.
The apparatus may comprise one or more of: LIMS, WHGMS, scavenger WHGMSs
and/or
cleaner WHGMSs, and any combination thereof, operable to receive one or more
waste
streams.
One or more waste streams may be fed into one or more of: the LIMS, WHGMS, a
scavenger
WHGMS and/or a cleaner WHGMS, and any combination thereof.
The apparatus may comprise one or more of: additional LIMS(s), WHGMS(s),
VPWHGMS(s),
scavenger WHGMS(s), cleaner WHGMS(s), or any combination thereof, operable to
receive
one or more product streams.
One or more product streams are preferably fed into one or more of: a further
LIMS, a
WHGMS, a VPWHGMS, a scavenger WHGMS, a cleaner WHGMS, or any combination
thereof.
Preferably, the process further includes pulsation of the slurry fed to at
least one of the
magnetic separators. Preferably, the process further includes pulsation of one
or more,
preferably of at least the first VPWHGMS. Preferably, the process further
includes pulsation
of the second VPWHGMS. Preferably, the process further includes pulsation of
one or more,
preferably each of the first, second and third VPWHGMS, or any combination
thereof.
Pulsation assists the separation of weakly paramagnetic lithium-mica mineral
particles by
agitating the feed material in the separation zone, for example a slurry, and
keeping particles
in a loose state, thereby minimizing the risk of blockages, accumulation or
entrapment on the
faces of the magnetic matrix and maximising contact of weakly paramagnetic
particles to the
magnet while reducing particle momentum aiding in magnetic attraction.
The process and apparatus of the present invention has been found to be more
tolerant of
fine particles as well as of larger particle sizes, and to recover particles
of lower magnetic
susceptibility than conventional beneficiation processes. As a result, the
process of the
present invention is more time and energy efficient and lower cost than
conventional
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beneficiation processes, produces higher mass recovery and does not require
the use of
chemicals.
Preferably, the wet magnetic separation process for beneficiation of
paramagnetic lithium-
mica minerals is an exclusively magnetic separation process. In one
embodiment, the wet
magnetic separation process of the present invention does not involve any
additional
beneficiation steps.
The process of the present invention has been found by the inventor in pilot-
scale testwork
to provide improved recovery efficiency compared to conventional beneficiation
processes
including dense media separation and/or floatation. Furthermore, the process
of the present
invention involves fewer processing steps, is more economical and more
environmentally
friendly than conventional beneficiation processes. The process of the present
invention does
not use environmentally damaging processes or reagents, such as surfactants.
The waste
products are principally chemically unaltered silica sand and feldspar which
can be disposed
of safely.
Embodiments of the present invention will now be described in further detail
in relation to
the accompanying Figures.
BRIEF DESCRIPTION OF FIGURES
Figure 1 and Figure 2 are schematic illustrations of the magnetic separation
process for
extracting weakly paramagnetic lithium-mica minerals by sequentially
extracting
paramagnetic magnetic fractions of an ore according to one embodiment of the
present
invention.
DETAILED DESCRIPTION OF FIGURES
Figure 1 shows an embodiment of the magnetic separation apparatus 10 for
extracting
paramagnetic lithium-mica minerals from a milled feed stream containing
paramagnetic
lithium-mica minerals 2A, highly magnetic waste materials and nonmagnetic
gangue.
By way of example, the comminution apparatus 12 is operable to produce a
milled feed
stream containing paramagnetic lithium-mica minerals 2A. The comminution
apparatus 12
may for example be a device that is configured to break, crush, grind, vibrate
and/or mill the
mineral feed source 1A, 1B. Preferably, the comminution apparatus is a milling
device, for
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example, a wet milling device. The comminution apparatus 12 provides a milled
feed slurry
stream containing paramagnetic lithium-mica minerals 2A having predetermined
maximum
particle size, for example, of no more than 3 mm. The comminution apparatus 12
also
provides a milled waste stream containing paramagnetic lithium-mica minerals
2B having
maximum particle size which is found to be greater than the predetermined
maximum
particle size. The waste stream 2B is recycled and reintroduced to the
comminution
apparatus 12 as recycled mineral feed stream 1B.
The apparatus 10 further comprises a cyclone 14 comprising an inlet 16
operable to receive
the milled feed stream containing paramagnetic lithium-mica minerals 2A. The
cyclone 14
further comprises an outlet 18 to provide a deslimed, milled feed stream
containing
paramagnetic lithium-mica minerals 4 therethrough. The cyclone is operable to
produce a
deslimed, milled paramagnetic lithium-mica mineral feed stream having an
average particle
size (d50) of 10 p.m or more, for example 50 km or more.
The apparatus 10 further comprises a Low Intensity Magnetic Separator ("LIMS")
20 in
communication with the outlet 18 of the cyclone 14 to receive the deslimed,
milled feed
stream containing paramagnetic lithium-mica minerals 4 therefrom.
The LIMS 20 is operable to have a first magnetic field strength to produce a
first highly
magnetic waste stream (not shown) and a first product stream comprising
paramagnetic
lithium-mica minerals and nonmagnetic gangue 5.
The apparatus 10 further comprises a first, "Rougher" WHGMS 22 in
communication with the
LIMS 20 to receive the first product stream containing paramagnetic lithium-
mica mineral 5
therefrom.
The Rougher WHGMS 22 is operable to have a second magnetic field strength
higher than the
first magnetic field strength of the LIMS 20.
The Rougher WHGMS 22 is operable to provide a second waste stream 7 and a
second
product stream 6 comprising paramagnetic lithium-mica minerals and a reduced
concentration of nonmagnetic gangue.
The apparatus 10 may further comprise one or more of: a second, "Scavenger"
WHGMS
and/or a third, "Cleaner" WHGMS.
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Figure 2 shows an embodiment where the second nonmagnetic waste stream E is
fed into a
Scavenger WHGMS 3. The Scavenger WHGMS has a magnetic field strength
preferably equal
to or greater than the magnetic field strength of the Rougher WHGMS 2. The
Scavenger
WHGMS 3. provides a third product stream F comprising concentrated
paramagnetic lithium-
mica minerals, and a third waste stream G.
The apparatus further comprises a Cleaner WHGMS 4. in communication with the
Rougher
WHGMS 2. The Cleaner WHGMS 4 receives the second product stream D from the
Rougher
WHGMS 2 and provides a fourth product stream H comprising an increased
concentration of
paramagnetic lithium-mica minerals compared to the product stream D or product
stream F,
and a fourth waste stream I.
It is to be understood that one or more waste streams may be recycled and
reintroduced into
any one of: LIMS, one or more WHGMS, scavenger WHGMS and/or cleaner WHGMS, or
any
combination thereof, in order to further extract and concentrate paramagnetic
lithium-mica
minerals therefrom.
The present invention has been found in pilot-scale testing to increase
lithium-mica recovery
efficiency with low energy consumption and without requiring any nonmagnetic
beneficiation
steps or the use of environmentally harmful chemicals. The process of the
present invention
can be used to achieve >90% recovery of paramagnetic lithium-mica minerals to
a
concentrate.
The operating principle of the invention relies on a series of magnetic
separation steps which
are tuned to enable the selective recovery of materials with different
magnetic
susceptibilities. The applicant has achieved this through tailoring the forces
required for
particle capture at each magnetic separation step. To initially analyse the
forces involved in
particle capture, an idealised situation describing the separation process can
be applied. A
spherical paramagnetic particle in a fluid moving at a constant velocity,
approaches a
fe rromagnetic/ferri magnetic object of circular cross section. A uniform
magnetic field applied
perpendicular to the object axis magnetises the object and a magnetic force
acting on the
particle is developed. If the magnetic force is large enough to overcome the
competing
hydrodynamic force and gravity then the particle will adhere to the magnetised
matrix. This
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is the underlying principle by which the method described is tuned to a
particular separation
challenge. The equation that describes the relationship is given below.
FM = V = Mp = (dH/dX)
where;
FM is the magnetic force required
V is the volume of the particle
Mp is the magnetic susceptibility of the particle
dH/dX is the magnetic gradient seen across the particle.
The magnetic force required for separation becomes proportional to three
terms: the volume
of the particle, the particle magnetisation (gauss/gram), and the field
gradient over the
dimensions of the particle. In the process of the present invention, all of
these terms are
tuned to improve the recovery yield of the material. The dynamics of this
sequence of
separations become readily interpretable by substitution into the formula. For
each of the
target magnetic separation steps of the present invention, a range of
parameters for
practising the invention is defined.
The process of the invention is particularly suited to the magnetic
beneficiation of lithium-
mica minerals that are weakly paramagnetic and with low contrast in magnetic
susceptibility
to the gangue. In a general sense, lithium-mica minerals suitable for
beneficiation by this
process can be described by the general formula:
X2Y4-6Z8020(OH, F)4,
in which;
X is K, Na, or Ca or less commonly Ba, Rb, or Cs;
Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, Sn etc.;
Z is chiefly Si or Al, but also may include Fe3+ or Ti.
Structurally, lithium-mica minerals can be classed as dioctahedral (Y = 4) and
trioctahedral (Y
=6).
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One example of a paramagnetic lithium-mica mineral suitable for concentration
using the
invention is Zinnwaldite KLiFeAl(AlSi3)010(OH,F)2 (potassium lithium iron
aluminium silicate
hydroxide fluoride).
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