FIELD OF INVENTIONS
The invention relates to an improved beneficiation method for recovering iron
values from ultra fine size fraction of iron ore slime. More particularly, the
invention relates to an improved method for beneficiation of low grade iron ore
feed exhibiting complex liberation characteristics and liberates at particle size
below 45 microns.
BACKGROUND OF THE INVENTION
Beneficiation of fine size feed is posing a huge challenge in the mineral sector.
The definition of fine size is often relative to the process operation. In mineral
industry however, particles of size below 150 microns are considered as critical
limit, since particles of these size ranges are difficult to treat. From fundamental
laws of physics, fineness of these particles is the major concern for its physical
separation. In gravity separation method, physical separation of ore and gangue
minerals are achieved through response difference of these two groups of
particles when they are subjected to body force or any other external force. In
case of simple gravity separator, acceleration due to gravity acts on mass of a
particle and the difference of weight between ore and gangue minerals helps
them to separate in the beneficiation process. In case of fine size feed, the mass
difference is low although the specific gravity difference of ore and gangue
minerals are significant which is due to small particle volume. Number of
particles per unit mass increases with decrease in particle size therefore, the
number density increase for fine size particles even at a level of fixed percent
solid in the slurry. This has two implications in minerals beneficiation process,
firstly, with the increase in number density function for fine size feed, the

probability of particles collision increase. Secondly, surface area of particles
increases manifold for fine particles and this leads to higher drag force on
particles. Therefore, mineral beneficiation at fine size range is difficult using body
force or applying any other external forces. Taking the advantage of higher
particle surface area, surface active reagents are used for beneficiation of fine
size feed. However, this process is also not efficient for a feed of wide size range
for example, a size range of below 150 microns. The disadvantages described
hereinabove, indicates that beneficiation of a fine size feed is difficult and needs
special attention.
In response to the above mentioned complexities for beneficiation of fine size
feed; mineral sector resorted to an easy solution, that is dumping most of this
fine size feed. In case of iron ore beneficiation, around 15 - 20% of the Run Off
Mine (ROM) is rejected as slime (fraction finer than 150 microns) in the waste
land or slime dam. At today's rate of steel production in India for example,
around 10 - 14 million tons of slime is being generated every year. Almost all
major steel producers in India with captive raw material resources have
accumulated more than 10 million tones of slime in their respective mine site. In
the near future, the rate of slime production would increase on two counts (i)
more quantity of iron ore will be mined to meet the ever increasing steel
production target and (ii) proportion of slime to ROM is taken to increase as ROM
quality is expected to deteriorate with time. The huge tonnage of slime produced
so far and projected slime generation over the next decade shall become an
environment concern to the populace. Furthermore, it has also been noticed that
this slime contains significant quantity of iron values and hence iron ore slime in

true sense is itself a huge reserve of iron ore. The Authorities involved in steel
making and environment maintenance are now exploring different options to
mitigate the threat involved in slime generation including the means and
methods to recover iron values from iron ore slime. At present, facilities are
being explored across the world for treating slime of size fraction below 150
micron and above 45 microns (i.e., coarser size fraction of slime). Although a few
plants for slime beneficiation treats coarser fraction of slime are known, however
they are restricted to magnetite type of iron ore with silica as the major impurity.
This technology cannot be implemented where the iron ore is compositionally
rich in hematite - goethite and contains alumina and silica rich gangue minerals.
It may be noted that slime of size fraction finer than 45 microns is not known to
be treated for iron ore beneficiation.
Use of hydrocyclone in dewatering of fine coal (US patent 4,128,474), removal of
grit and roots from feed (US patent application no. 538443), separation of oil
from fluid (US patent 4017390), as an apparatus for mixing fluid separating
fluids and separating solids from fluids (US patent 6811690, 6811699, 68117109,
6811713), are known. However, in the prior patents, the use of hydrocyclone
was mostly confined to separation of a heavier phase from a lighter phase in a
material flow by centrifugal force (US patent 5843211). However, use of
hydrocyclone for separating particles of size below 45 microns is a major
disadvantage of the prior art.
Froth floatation process is widely practiced in iron ore beneficiation. The
knowhow is limited to separation of removal of non-sulfide silicate gangue from
iron phases (US patent 5507395, 5525212, 5531330, 553626). US patent

(4422928, 6076682 and 5030340) on removal of silicate gangue minerals from
iron minerals through flotation. However, association of silicate and alumina
bearing gangue phases is typical problem of Indian iron ore. These gangue
phases are of diverse nature and it includes phases like silicates, alumino-silictes
and, alumina bearing minerals. Removal of all these phase through flotation is a
difficult task.
Major challenge before the selective flocculation is the removal of silicate as well
as alumina from iron bearing mineral phases. There are well documented
methods (US patents) (3397953, 3480761, 3545941, 3658772, 3776892,
3859212, 3975496, 4081357 and, 4090955) to remove silicon oxides from iron
oxides through selective flocculation method. Similarly, US patent Nos. 3755531,
3716617, 3575868 and, 3975496 describes selective flocculation method to
settle down iron compound as red mud from supernatant in alumina extraction.
There are also few US patent (3862027, 4604369, 4629556, 5368745 and,
6041939) which suggests methods to improve brightness of kaolin that is
removal of iron from alumina - silicate rich clay minerals. However, removal of
silica, alumina and, alumina-silicates from iron bearing mineral phases through
selective flocculation still remains as another major disadvantage of the known
flocculation methods.
In general, mineral beneficiation is not much effective at slime range of feed for
any mineral. Phosphate ore is beneficiated at this size range using floatation and
also selective flocculation. US patent 440635, 4584096, 4904375, 5221466,
6805242, 4113184, 4287053, 4324653, 4364824, and 4436616 details important

findings of phosphate beneficiation at slime size. Removal of iron mineral from
clay deposits at very fine size range (that is at slime size) using magnetic
separation is also practiced to improve the whiteness of the final product. Iron
ore beneficiation at slime range can be broadly classified into three categories
based on the feed types; (i) Magnetite - silica rich, (ii) Hematite - silica rich and,
(iii) Hematite - alumino - silicate combination. For the first type of feed,
concentrate of desired grade could be achieved through combination of magnetic
separation and flotation. The second category feed is treated using floatation.
Both the aforesaid feed types are being beneficiated in selected iron ore
beneficiation plant. Beneficiation for the third category of feed is evolving and at
present marginal success could be achieved primarily through gravity separation.
In all three cases, iron ore slime beneficiation is restricted to a size range of 150
- 45 microns. Thus, the prior art is silent on a process to treat a feed that
belongs to the difficult third category that is the feed containing mineralogical
assemblage such as Hematite - Goethite - alumino silicates and also loaded with
much higher volume of gangue mineral phases. Furthermore, treating a feed of
size below 45 micron adds further disadvantage to the prior art
methods/systems.
Thus, the existing practice for beneficiation of fine size feed is confined to feed
of size above 45 microns. The ultra fine fraction of feed i.e., size below 45
microns is presently wasted due to non-availability of suitable and established
technology.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved method to

separate particles of size below 10 microns from a slime feed of size below 45/30
microns, which eliminates the disadvantages of prior art.
Another object of the invention to propose an improved method to separate
particles of size above 10 microns from a slime feed of size below 45/30 microns,
and then enabled to recover iron values from ultra fine size fraction of iron ore
slime through flotation.
A still another object of the invention to propose an improved method to
separate particles of size below 10 microns from a slime feed of size below 45/30
microns through selective flocculation, which is capable to reduce the level of
silica and aluminium from 8 - 10% each in a feed to 2% in the concentrate.
A further object of the invention to propose an improved method to separate
particles of size below 10 microns from a slime feed of size below 45/30 microns,
which provides a concentrate having 64 to 66% of Fe content with the reject
including Fe below 45%.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved method for beneficiation of ultra fine
size fraction. The proposed method separates particles of size below 10 microns
from the rest and in this process of separation, ore minerals with higher specific
gravity reports to the coarser size fraction. The coarser and the finer fractions
are feed for two different unit operations namely; flotation system and selective

flocculation method and these two processes eventually produces product of
desired quality. The proposed flowsheet is capable of producing concentrate of
2.0% alumina from ultra fine size fraction of slime containing alumina as high as
10.0%. Rejects of this process assayed low iron content which is always less
than 45% and hence can be declared as plant waste as per the present
Government norm. This reject are also suitable for consumption through
identified waste utilization technique.
The inventive method deals with feed particles of size below 45 microns. The
method is also applicable for feed of size less than 30 microns. In a beneficiation
plant, feed of this size is available in slurry form. The process demands thorough
mixing of solid and water through a pump and sump combination to ensure (i)
uniform percent solid in the slurry all through, and (ii) breaking of agglomerate
which are often formed due to high surface charge associated with these fine
particles. The slurry is then treated in hydrocyclone in two stages. Hydro
cyclones are operated in both stages at low percent solids (10%) and at very
high pressure. Hydro cyclones used in both cases are also smaller in diameter;
usually in the ranges of 2 - 4 inch diameter. According to the flowsheet, the
underflow of 1st stage is used as feed for the 2nd stage operation. The overflow
of two stages of hydrocyclone operation is mixed together to form a common
(first) stream contains the finer size fraction and the gangue minerals. The
underflow fraction from the 2nd stage operation forms the second stream which
primarily contains coarser particles and ore minerals. Assay-wise, the underflow
fraction is enriched with higher metallic content as compared to the feed.
Hydrocyclone overflow and underflow is treated separately and hence the
flowsheet comprises three unit operation, the first one being hydrocyclone

operation and the other two unit operations treats the classified feed generated
through hydrocyclone operation. This flowsheet is most suitable for feed having
around 50% of material finer than 10 microns as no other operation is feasible
for treating such ultra fine feed.
The coarser stream which contains particles coarser than 10 microns and rich in
iron minerals is then treated through a flotation process to recover the iron
concentrate. This is a two stage process herein firstly, the underflow fraction of
the 2nd stage hydrocyclone operation is diluted to 20% solid by adding water,
and then the pH of the slurry is adjusted for 1st stage flotation. The flotation feed
is also conditioned with collector and frother prior to transferring the slurry to a
flotation machine. In the 1st stage of flotation, the froth phase contains more of
gangue minerals and hence it is a reverse flotation. The iron rich fraction is
collected through a tailing launder to have a quality product containing around
2.0% alumina. The froth phase which contains low percent solid (i.e., around
10% solid) is subjected to the 2nd stage of flotation. As a part of feed preparation
method the pH is adjusted and the slurry is conditioned in different collector. The
2nd stage flotation does not require any frother addition. This is also a reverse
flotation and hence the froth phase of this stage of flotation is the final reject of
the flotation circuit. The concentrate of the 1st and 2nd stage flotation together
forms flotation concentrate. This concentrate stream is transported to a vacuum
belt filter. The reject from the flotation circuit is pumped to 3rd thickener to
recover water. Thicker overflow is clarified water and it is to be reused. The
overflow contains solid which is dewatered using vacuum belt filter. The filtrate is
further treated in the 2nd thickener and the water recovered is reused in the
process plant. Solid from flotation reject is not discarded as the alumina content

in this fraction is around 4.5%. This fraction does not respond to any physical
beneficiation due to extremely poor liberation characteristics. However, this
fraction does respond well to chemical beneficiation as well as direct iron
smelting reduction process. This fraction is thus stored as feedstock for any of
the aforesaid process.
The overflow fractions from 1st and 2nd stage of hydrocyclone operation are
treated together to recover iron values through a known process of selective
flocculation. This stream is conditioned as part of feed preparation method prior
to selective flocculation. The slurry contains very fine particles of size less than
10 microns and these particles often tend to agglomerate due to high surface
area and surface charges. To ensure particles are free, the slurry is treated
through an ultrasonication unit and then pH of the slurry is adjusted to the
desired level using NaOH. The slurry is then transferred to a first thickener (that
is Thickener - 1) and dosage of causticized starch is added as flocculent to
initiate selective flocculation process. This is an effective process for feed of this
type which is extremely fine and loaded with alumina and silica bearing gangue
mineral phases. The concentrate comes out of the system as thickener underflow
and it is transported to a vacuum belt filter for dewatering. This dewatering step
reduces the moisture to the desired level of 8 - 10%. The overflow of thickener
- 1 is again transferred to a second thickener to recover water.
The second thickener receives slurry from the first thickener overflow including
filtrate of two different types of filters. A dosage of flocculent is added to this
thickener for faster settling of the suspended solids. The clarified water is taken
out as overflow and plant waste is drained out as thickener underflow. Waste is

further dewatered using a belt press filter to reduce the moisture content to
below 25% level and the filtrate is re-circulated to thickener - 2. Waste with 20 -
25% moisture level can easily be transported through roadways or conveyor
system. The clarified water is temporarily stored in a tank and from there it is
pumped to three different points namely; (i) to the feed tank of 1st stage
hydrocyclone, (ii) to the feed tank of 2nd stage hydrocyclone and, (iii) to the feed
tank of flotation cell. A separate small water tank receives fresh water supply
and is used to compensate water loss on washing and to flush the turbid process
water. Fresh water is primarily added to the flotation cell as wash water and to
the blower in the flotation system.
The inventive method is enabled to separate particle of size below 10 microns
from slime feed of size below 45/30 microns. The method includes a two stage
of hydrocyclone operation. The slurry of 10% solid is first treated on stage - I
hydrocyclone and it produces underflow and overflow. Underflow of stage - I
hydrocyclone is again treated in stage - II hydrocyclone. Overflow of stage - I
and II forms the finer fraction comprising particles less than 10 microns. The
underflow of stage - II hydrocyclone is the other fraction and it contains feed
material coarser than 10 microns size.
The hydrocyclones adapted for the invention, are having diameter of 2"/3", and
a throughput of 0.5 ton/hr. Operating conditions for the hydrocyclone is
completely different. The hydrocyclone is operated at very high feed inlet
pressure of 42 - 45 psi. Percent solid maintained in the feed slurry is 10 and it is
lower than the normal practice. Mass split can be maintained between 50:50 and

80:20 of underflow: overflow fraction in the 1st and 2 stage of hydrocyclone
operation. With two stages of hydrocyclone operation, alumina and silica content
is brought down to 3.0% each in the hydrocyclone underflow from head slime of
8 - 9% each.
The hydrocyclone underflow is treated in a two stage flotation circuit. In the first
stage of flotation, percent solid maintained is around 20% accordingly required
volume of additional water is added to the hydrocyclone underflow prior to
flotation. As a part of feed preparation method, pH of the slurry is adjusted to
10.0. The slurry is then conditioned using fatty acid as collector and pine oil as
frother for 15 and 5 minutes respectively. 1st stage flotation is a reverse flotation
wherein the concentrate is collected through a tailing launder and the froth
phase contains more of gangue minerals. In the 1st stage of flotation alumina
and silica content is reduced to 2.0% each in the concentrate.
The 2nd stage fraction is also a reverse flotation. The froth from the 1st stage of
flotation is treated in a scavenger circuit to recover iron values. Feed for the 2nd
stage flotation is again conditioned with amine base collector and the pH of the
slurry is maintained at 10.0.
The rejected from flotation system assays around 4 to 5 alumina and hence this
fraction cannot be rejected. This fraction does not respond to any physical
beneficiation method due to its extremely poor liberation characteristic. However,
metal recovery from this fraction through chemical leaching method as well as
direct smelting reduction is achieved. Therefore, this fraction is stored for future
use.

Overflow from 1st and 2nd stage of hydrocyclone operation is treated in a
thickener using selective flocculation method. The slurry is passed through an
ultrasonication system which disintegrates agglomerate present in the slurry. The
slurry is then conditioned by adding NaOH to maintain pH around 10.0. The
slurry is then transferred to the thickener along with flocculent (causticised
starch) for selective flocculation process to take place inside the thickener. The
thickener underflow is the concentrate and overflow is treated as process rejects.
The process reduces alumina and silica content from 8 - 12% each to 2.0% each
in the concentrate. The reject steam contains alumina and silica as high as 21%
each with iron content far less than 45%.
Concentrate from flotation and thickener is dewatered using a vacuum belt Filter
and the moisture content in the dewatered concentrate is 8 - 10%. The reject of
flotation circuit is sent directly to a belt press Filter for dewatering process. The
reject from selective flocculation process is too dilute for belt press filter and
hence it is First treated in thickener using flocculent. The overflow from the
thickener is clear process water which is reused in the plant. The underflow from
the thickener is further dewatered using belt press filter. Belt press Filter reduced
the moisture level in the waste to the targeted level that is below 25%.
The improved method reduces the silica and the alumina level from 8 - 10%
each in the feed to 2.0% each in the concentrate. The Fe content in the
concentrate is as high as 64.8 - 66%. The reject generated through this
beneficiation process contains Fe below 45% and hence the reject can be treated

as waste. The waste is consumed through known waste utilization technique and
thus the entire process plant becomes a zero waste plant. The improved method
of the invention enables to mitigate problem of generation huge volume of iron
ore slime during iron ore beneficiation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a generic flowsheet of the hydrocyclone operation.
Figure 2 shows an example of the hydrocyclone operation according to the
invention, wherein iron ore slime is used as feed.
Figure 3 shows the details of flotation circuit according to the invention.
Figure 4 shows the details of a selective flocculation system.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a two stage hydrocyclone operation; the underflow (UF1) of the
first stage (S1) of hydrocyclone operation is used as a feed for the second stage
(S2) of hydrocyclone operation. Overflow fraction (OF1, OF2) generated from the
first and second stage operation (S1, S2) together forms a common stream which
is treated in subsequent operation. The combined overflow fraction (COF)
contains finer fraction of the feed, in particular less than 10 microns size. The
underflow fraction (UF2) of the second stage (S2) hydrocyclone operation
contains the coarser and heavier fraction of the feed. Conversely, the finer and

the lighter gangue minerals mostly reports to the overflow fraction. Hydrocyclone
(HC) used for this purpose is small diameter hydrocyclone that is 2 - 4 inch
diameter with specific vortex and spigot diameter. This operation also demands
very high inlet pressure for the feed slurry which is much higher than the
conventional hydrocyclone operation. The process specification of the first stage
hydrocyclone operation (S1), and the second stage operation (S2) are selected to
respectively comply with inlet pressure, vortex finder diameter, and spigot
diameter of 45.0 psi, 42.0 psi, 14.1cm, 14.1cm; and 4.3cm, 4.3cm.
As shown in figure-2, in case of iron and ore slime, particles of size below 30
microns are used as the feed for the two stage hydrocyclone operation (S1, S2).
The underflow and the overflow fractions generated through two stages of
hydrocyclone operation (UF2, OF1, OF2) needs further beneficiation. Weight, iron,
alumina and, the silica distribution for each stream is marked for this specific
application. In this specific case along with classification of the feed, the process
separates gangue minerals. Thus the overflow fractions (OF1 and OF2) contains
more of gangue minerals.
As shown in Fig-3 the hydrocyclone underflow stored in a sump (UFS) is diluted
by adding process water to a level of 20% solid. This slurry is then pumped to a
mixing tank wherein a pH modifier (MPH) is added and the pH of the slurry is
maintained at 10.0. This slurry is then transferred to two successive conditioners
for conditioning for example, a first collector (CA1) (Fatty acid) and then a frother
(FA). The sizes of these two conditioner tanks (CA, FA) are fixed based on the
conditioning time in each case. The slurry flow is through the gravity flow from
one conditioner tank (CA1) to the next (FA), and also to flotation cell. Froth

coming out of the 1st stage flotation (SF) is collected in a first launder (U) and
through gravity flow it is transferred to a conditioner tank (CT). In this
conditioner tank (CT), the pH modifier (MPH) is added to maintain a constant
pH. The slurry is then conditioned with amine based collector in a second
collector for the 2nd stage flotation (SF2). The slurry flow from the conditioner
tank (CT) to the 2nd stage flotation (SF2) is also through gravity flow. The froth
from the 2nd stage flotation (SF2) is the final reject and it is collected in a second
launder (L2) and then pumped to the 3rd thickener and the thickener underflow
to a belt press (BPF) filter. The tailing of the 1st stage and 2nd stage flotation cell
(S1, S2) forms the concentrate are collected through a tailing launder (L3) to the
sump (UFS) and from the sump it is pumped to the vacuum belt filter (VBF) for
dewatering and the filtrate is pumped to 2nd thickener for reclaiming the process
water.
As shown in fig-4, the hydrocyclone overflow (HCDF) from 1st and 2nd stage
operation are collected in a sump (SMP) with recirculation facility. This is
primarily a mixing tank which helps maintaining an uniform percent of solid in
the slurry.
The slurry is then pumped to an ultrasonication unit (UST) which helps in
disintegrating agglomerates present in the slurry. The slurry is then pumped to a
conditioner tank (CT) wherein pH modifier (MPH) is added so as to maintain the
desired level of pH in the slurry. Prior to transferring the slurry to a thickener (T)
for selective flocculation process, a flocculent is added and properly mixed. The
concentrate (C) is taken out of the system as thickener underflow and then it is
pumped to vacuum belt filter (VBF1) for dewatering process. The tailings as

overflow (TS) is collected in an overflow launder (OL) and from there it is
pumped to the 2nd thickener. The overflow from the 2nd thickener constitutes
clarified water which is stored in a tank and from there continuously reused for
plant operation. The underflow of the 2nd thickener is plant waste. This waste is
dewatered using a belt press filter (VBF2) Filtrates from these two filters are
pumped to the 3rd thickener.
The present invention discloses a method to recover iron values from the slime
of particle size below 45 microns and thereby generating a plant waste which
can be used through waste utilization technique. This process enables to
eliminate the disadvantage associated with iron ore slime generation. The
process starts with hydrocyclone operation to separate particles of below 10
micron size from a feed of particle size below 45 microns or 30 microns.
Therefore, the hydrocyclone operation firstly ensures a size classification.
Objective of this classification process is two fold (i) to prepare feed for further
processing as processing the feed with particles size below 10 microns size is not
suitable for a size fraction coarser than 10 microns and vice versa, and (ii)
gangue mineral enrichment towards the fine size fraction thus, the classification
process also enriches coarser fraction with ore minerals. This classification
process is complex due to (i) presence of two broad category of particles i.e.,
iron ore and gangue minerals and (ii) feed particles of very fine size range.
Classification of feed with ore and gangue mineral is usually manageable as
gangue particles are predominantly finer in size in most of the mineral
beneficiation operation. An efficient classification method actually ensures gravity
separation. However, the process is lot more challenging for extremely fine size
feed.

The feed particles being very fine in size, according to the invention, the particles
have more surface area. Therefore, the surface chemistry, the surface charge of
these particles plays an important role and influence the process proposed for
beneficiation of the feed. It has been noticed that these particles often tend to
agglomerate to form pseudo larger particles. In the proposed method, these
pseudo large particles are disintegrated prior to the size classification. Smaller
size of the particles experiences high drag, force due to large surface area per
unit mass. This leads to a situation in which the particle having differential
acceleration attains an identical velocity in a quick span. Therefore, this type of
feed requires a system where in provision for high initial acceleration on particles
exists and the device also ensures early removal of the separated mass i.e.,
during the initial phase of movement of particles. Process condition for
hydrocyclone operation and the geometry of hydrocyclone are selected in
commensuration with the aforesaid requirement.
The underflow fraction from the 2nd stage of hydrocyclone operation (S2) is feed
for the flotation process. This feed contains particles of size above 10 microns
and enriched with iron minerals. Typically for a slime feed of below 30 microns
size, 40% of the head feed reports to flotation circuit (FC) and the feed contains
alumina of around 3.0%. Therefore, the target set on flotation process is to
improve the grade from 3.0% to the desired grade of 2.0% in the concentrate.
The flotation step is a two-stage operation. In the first stage (S1), fatty acid is
used as collector and pine oil as frother and this combination separates alumina
and silica rich fraction as froth. The flotation tailing contains iron ore concentrate
of 2.0% alumina. The froth also contains fine ore mineral phases and this is
separated through the 2nd stage of flotation. In the 2nd stage of flotation, amine

based collector is used to separate alumina and silica as froth and the iron
bearing mineral phases is collected as flotation tailing. The 2nd stage of flotation
(S2) improves the concentrate yield. Both these of flotation (S1, S2) are reverse
flotation and are sensitive to pH of the system which is maintained at 10.0 for
best flotation performance.
Overflow fractions (OF1, OF2) from 1st and 2nd stage of hydrocyclone operation is
treated together through a selective flocculation step. This feed material is the
most difficult fraction of the iron ore slime for any physical beneficiation owing to
its special characteristics. Particle size for this feed is less than 10 microns with
average size close to 5 microns which is an extremely fine size feed for any
physical separation. High surface area and surface charge associated with these
very fine particles often tend to create particle agglomerates. Furthermore, the
feed contains very high volume of gangue phase as compared the original slime.
The slurry containing this feed is also low in solid content that is close to 5%.
Ultrasonication technique is used for disintegration of agglomerates present in
the slurry and it is a prerequisite for improved performance of the subsequent
separation process. Surface charges of these particles are then modified so that
particles with iron bearing mineral phase flock together and the remaining
gangue phases remains in the dilute and dispersed phase. This phenomenon is
ensured through pH adjustment and also through use of specific flocculent.
Flocculent used in this process is causticised starch and pH of 10.0 is maintained
by adding NaOH.
Dewatering of concentrate and waste generated through slime beneficiation is
carried-out. Concentrate is generated through two streams namely, flotation
concentrate and selective flocculation concentrate. In both these process

surface active reagents are use to modify the particle surface thus, concentrate
particles do not hold moisture and it makes dewatering process easy. Normal
process of natural draining reduces moisture to 15% level. Moisture level is
further reduced to the desired level of 8 - 10% through the vacuum belt filter.
Unlike concentrate, dewatering of waste is difficult as it contain froth from
flotation process and very fine gangue minerals particles in dispersed state from
selective flocculation process. Froth from the flotation is dewatered using a belt
press filter. The overflow of the flocculation step is transferred to another
thickener to recover water and the underflow of the 2nd thickener is dewatered
using the same belt press filter used for dewatering the froth. Suitable flocculent
is added and pH maintained in the 2nd thickener for faster settling of solids.
TESTING METHODS
Tests were carried out using iron ore slime. By definition iron ore slime is a by
product of iron ore beneficiation plant. For a very long period iron ore slime is
mostly treated as an waste due to lack of technology for recovering iron values
from slime (with particle size below 150 microns) and also due to less demand
from the end users. However, in recent years system and method to treat good
quality iron ore slimes for particle size up to 45 microns are available. Slime
containing particle size below 45/30 microns is not amendable for beneficiation
as the available technology does not support beneficiation of this size fraction of
slime. This ultra fine size fraction (i.e., below 45/30 microns) constitute around

50% of the slime. Therefore, a process for beneficiation of the ultra fine size
fraction of slime is proposed. Representative slime samples of size fraction below
30 microns are collected from the slime dam at mine sites. These samples when
characterized, reveals that around 60% of the material is of size below 10
microns. These slime samples also contains agglomerates of very fine size
particles. Breaking these agglomerates to their original size is the first activity
and it is carried out through intense mixing using a slurry pump and sump
combination keeping 10% solid in the slurry. In the second stage, this slurry is
pumped to a hydro cyclone of 2" or 3" diameter depending on emphasis given to
either cyclone efficiency or throughput. A 2" diameter cyclone provides better
hydro cyclone efficiency. Inlet pressure maintained is around 45 psi. vortex
diameter and spigot diameter are adjusted depending on the intended mass split
in the underflow and the overflow fraction. Intended mass split for the present
case is 65% of the feed to report to the underflow fraction. The underflow of
stage - I hydrocyclone operation is again treated on the second stage
hydrocyclone. For stage - II operation, feed inlet pressure is kept at 42 psi with
intended mass split of 65% in the underflow, accordingly the spigot and the
vortex finder diameter are adjusted. The overflow of stage - I and II
hydrocyclone operation were mixed together which is around 58% of the feed.
This fraction contains particles below 10 micron size of the slime and it also
contains major part of the gangue minerals present in slime. This fraction is
subsequently treated using a beneficiation technique. The underflow fraction of
stage - II hydrocyclone operation is the other fraction which constitutes 42% of
the slime. This fraction contains particles coarser than 10 microns and also rich
with ore minerals as compared to the feed material. This upgraded product may

be used as feed for some iron making process or it may be upgraded further
using one more stage of beneficiation.
As mentioned earlier, the underflow from the 2nd stage hydrocyclone operation
needs further beneficiation in a flotation circuit for which necessary feed
preparation is prerequisite. The percent solid in the underflow is around 60 and
the same is diluted to 20% by adding process water. The pH for this slurry is
maintained at 10.0 by adding the required quantity NaOH solution. It is then
conditioned with fatty acid and pine oil for 15 and 5 minutes respectively in two
different conditioners. The conditioned slurry is then transferred to the floatation
cell. The concentrate is collected from the tailing launder and sent to the belt
filter for dewatering. Froth from the first stage of flotation is collected in a
conditioner which is then used for pH modification. The slurry is then transferred
to the next conditioner for conditioning it with amine based collector for 15
minutes. It is then transferred to the flotation cell for the 2nd stage of flotation.
The concentrate is once again collected through the tailing launder and is
dewatered using the belt filter. The froth of the 2nd stage flotation is pumped to
the 2nd thickener to recover water from this slurry. Fig. 3 shows schematic of the
flotation process.
Overflow from the 1st and the 2nd stage of hydrocyclone operation is treated
together for recovering iron values through the selective flocculation step. The
overflow generated through hydrocyclone operation contains very low percent
solid (around 5%) and it is treated at that level of percent solid. As a part of the

feed preparation step, the feed is passed through an ultrasonication unit to
disintegrate agglomerates formed during upstream operation. In the next step
pH of the slurry is adjusted to the desired level of 10.0 and it is an essential step
prior to fiocculation. The slurry is then transferred to the thickener and flocculent
is also added in the flowing slurry. Total settling time is around 30 minutes as
per the inventive process. The process is known as selective fiocculation as
flocculent binds the dispersed iron bearing phases in such a manner that these
particles flock together and get settled at the bottom. While, dispersing agents
(mainly pH modifier) alters the zeta potential of the gangue particles in such a
way that it keeps particles isolated and in disperse phase during fiocculation
process and then these particles flows out of the thickener along with the
overflowing water. The process detail of the selective fiocculation method is
schematically shown in Fig.4.

WE CLAIM
1. An improved method to separate particles of size below 10 microns from a
slime feed of size below 45/30 microns, comprising the steps of:
- treating in a first stage hydrocyclone operation a slurry containing 10% solid
which producing underflow and overflow;
- treating the underflow from the first stage hydrocyclone operation in a
second stage hydrocyclone operation which produces one each underflow
and overflow;
- the overflow of the first and second stage forming a first fraction having
particles size of less than 10 microns, the underflow of the second stage
forming a second portion containing feed material coarser than 10 microns
size.

2. The method as claimed in claim 1, wherein the hydrocyclones are operated at
a feed inlet pressure of 42 - 45 psi with a mass split maintained between
50:50:, and 80: 20 respectively for the first stage and second stage operation
in a ratio between the underflow and overflow, the two stages hydrocylcone
operations enabling reduction of alumina and silica content to about 3% in
hydrocyclone underflow from the head slime of 8 - 9% each.
3. The method as claimed in claim 1, wherein the underflow from the second
stage hydrocyclone operation is treated in a two - stage flotation circuit, the
first stage flotation maintaining around 20 percent solid through addition of
fresh water, adjusting the pH-value of slurry, conditioning of the slurry using

a collector and a frother for about 5 to 15 minutes, the concentrate is
collected and the froth being delivered for a second stage of flotation, and
wherein the second stage of flotation of the froth from the first stage of
flotation is conducted in a scavenger circuit to recover iron values including
further conditioning of the feed to maintain the pH-value of the slurry at 10.
4. The method as claimed any of the preceding claims, wherein both stages of
flotation are reverse flotation in which the concentrate is collected through a
tailing launder and the froth phase includes substantially gangue minerals,
and wherein the alumina and silica content in both stage of flotation is
reduced to about 2% each in the concentrate.
5. The method as claimed in claim 3, wherein the collector constitutes a fatty
acid and wherein the frother constitutes a pine oil. The collector used for the
second stage of flotation is amine based collector.
6. The method as claimed in any of the preceding claims, wherein the reject
from the flotation circuit includes around 4 to5% alumina with poor liberation
characteristics, and wherein the reject is susceptible to metal recovery
through one of chemical leaching process and direct smelting reduction
process.
7. The method as claimed in claim 1, wherein the overflow from the first and
second stage hydrocyclone operation is treated in a thickener by adapting
selective flocculation process in which the slurry is caused to pass through an
ultrasonication system allowing disintegration of the agglomerate present in
the slurry.

8. The method as claimed in claim 7, wherein the agglomerate-free slurry is
conditioned to maintain pH around 10.00, wherein the conditioned slurry is
added with flocculent and transferred to the thickener for selective
flocculation within the thickener, and wherein the thickener underflow
includes concentrate and the overflow constitutes the rejects, the selective
flocculation step reduces the alumina and silica content each from 8 - 12% in
the hydrocyclone overflow to below 2.0% in the concentrate, the reject
containing around 21% alumina and below 40% of iron.
9. The method as claimed in any of the preceding claims, wherein the
concentrate from the flotation circuit and the thickener is dewatered in a
vacuum belt fitter to achieve a moisture content of 8 to 10%, wherein the
reject from the thickener is further flocculated to produce clean water and
waste respectively from the overflow, the waste being treated in a belt press
filter to reduce the moisture content to a level below 25%, and wherein the
reject from the flotation circuit is directly sent to the belt press filter for
dewatering.
10.An improved method to separate particles of size above and below 10
microns from a slime feed of size below 45/30 microns as substantially
described and illustrated herein with reference to the accompanying
drawings.

The invention relates to an improved method to separate particles of size below
10 microns from a slime feed of size below 45/30 microns, comprising two steps
of treating the feed in hydrocyclone with underflow of 1st stage operation being
treated in the 2nd stage. This process produces underflow and overflow; the
overflow of the first and second stage forming a first fraction having particles
size of less than 10 microns and ore of gangue minerals; it is subsequently
treated through an innovative selective flocculation method. The underflow the
second fraction from hydrocyclone operation contains feed material coarser than
10 microns size and rich in ore minerals; is treated in two stage reverse flotation,
which is innovative as it separates alumina and silica rich gangue minerals. This
innovative method also suggests methods of dewatering upto required level and
thereby ensures optimal usage of water.