FIELD OF INVENTION
The present invention generally relates to a beneficiation method which is useful
in recovering fine minerals from a low grade feed of very fine size. The invention
further relates to a feed preparation method using hydrocyclone. More
particularly, the invention relates to a process for separating particles of size
below 10 microns from a slime feed of size below 30 microns in a two-stage
hydrocyclone operation.
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 have a special significance
as the particles of such size range are difficult to treat. From fundamental laws of
physics, fineness of these particles is the major concern for its physical
separation. In mineral beneficiation processes, 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 the ore and gangue minerals
enable them to get separated in the beneficiation process. In case of a fine size
feed, the mass difference is substantially low in spite of the fact that the specific
gravity difference of ore and gangue minerals are significant and it is due to
small particle volume. Number of particles per unit mass inversely varies with the
particle size which suggests that number density increases for fine size particles
even at a fixed percent solid in the slurry. Such a phenomenon has two
implications in mineral beneficiation process.

Firstly, with the increase in number density function for fine size feed, the
probability of particle collision increases. Secondly, surface area of the particles
undergoes a manifold increase for the fine particles which leads to higher drag
force on the particles. Therefore mineral beneficiation at fine size range is
difficult using the body force or applying any other external forces. Taking the
advantage of availability of higher particle surface area, the prior art processes
use surface active reagents for beneficiation of fine size feed. However, this
process is inefficient for the feed of wide size range for example, for the entire
size range of below 150 microns. The prior art therefore indicates that
beneficiation of fine size feed is difficult and needs a novel and innovative
solution.
In an attempt to address the above mentioned complexities for beneficiation of
the fine size feed, mineral sector resorted to an easy solution for example,
dumping of most of the 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. Accordingly, almost all of the major
steel producers perforce store more than 10 million tones of slime in their
respective mine site. In the near future, the rate of slime production is expected
to increase on two counts (i) more quantity of iron ore has to be mined to meet
the persistent increase in steel production target and (ii) increase of slime to
ROM due to deterioration of ROM quality with time. The huge tonnage of slime
so produced including projected slime generation over next decade shall have a
serious repercussion. Furthermore, it has also been noticed that the slime
contains significant quantity of iron values and hence iron ore slime in true sense
is itself a huge reserve of iron ore. At present, a pilot scale facility across the
world for treating the slime of size fraction below 150 micron and above 45
microns (i.e. coarser size fraction of slime) is being experimented.

A few countries recently commissioned commercial plants for slime beneficiation
to treat coarser fraction of slime for magnetic 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. However, it may be noted that worldwide slime of size fraction
finer than 45 microns is not being treated for iron ore beneficiation.
In case of beneficiation of other metallic minerals, a feed is often crushed and
ground to below 75 microns for better liberation and then beneficiated primarily
through flotation. These plants are specially designed to restrict the generation
of ultra fines (below 45 microns) to the minimum. Generation of ultra fines is
termed as over grinding and it is always considered detrimental for plant
performance. Impurities present in the ultra fine size tend to get entrapped in
the froth during flotation and affects adversely the process performance.
Therefore, the prior art of beneficiation for fine size feed is still confined to feed
of size above 45 microns. Accordingly, the ultra fine fraction of feed i.e. size
below 45 microns is presently wasted due to non-availability of suitable and
established technology. Therefore, in the beneficiation of other metallic minerals
as well as in iron mineral, beneficiation of feed below 45 micron is an urgent
need.
US patent 4,128,474 adapts hydrocyclones for dewatering of fine coal.

US patent application no.538443 uses hydrocyclones for removal of grit and
roots from feed.
US patents 4844817 adapt hydrocyclones for separation of oil from water.
US patent 4017390 utilizes hydrocyclones for removal of solid pollutants from
fluid.
US patents 6811690, 6811699, 6811709, 6811713 each utilizes hydrocyclones
for mixing fluid, separating fluids, and separating solids from fluids.
Thus, the prior art teach utilization of hydrocyclones which is confined to
separation of a heavier phase from a lighter phase in a material flow.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a beneficiation process for
separating particles of size below 10 microns from a slime feed size below 45/30
microns, which eliminates the disadvantages of prior art.
Another object of the invention is to propose a beneficiation process for
separating particles of size below 10 microns from a slime feed size below 45/30
microns, which adapts a two stage hydrocyclone operation.

SUMARY OF THE INVENTION
According to the invention, a feed containing particles of size below 45 microns is
selected. In a beneficiation plant, a feed so selected is available in a slurry form.
As the process demands a thorough mixing of the solid with water, a pump and
sump combination is utilized to ensure (i) uniform percent of solid in the slurry is
present all thorough, and (ii) breaking of agglomerates often formed due to high
surface charge associated with these fine particles is ensured. The slurry is then
treated in a hydrocyclone in two stages. Hydro cyclones are operated in both
stages with low percentage of solids (10%) and at very high pressure. The Hydro
cyclones used in both cases are of small diameter for example, in the range of 2-
4 inch diameter. In the process, the underflow of the first stage is used as the
feed for the second stage operation. The overflow of the two stages of the
hydrocyclone is mixed together which forms a common stream. This stream
contains the finer size fraction and gangue minerals. The underflow fraction from
the second stage operation forms a stream separate from the common stream
which primarily contains coarser particles and ore minerals. Assay-wise, the
underflow fraction is enriched with the metallic content as compared to the feed.
In some cases, an up gradation through two stages of the hydro cyclone
operation (i.e. underflow from the 2nd stage of hydrocyclone operation) is found
suitable in respect of the concentrate, for the next stage of metallurgical process.
In other cases, concentrate in the hydrocyclone is a feed for the next stage of
beneficiation. Usually it involves one more unit operation. Therefore, the process
flow comprises three unit operation the major one being hydrocyclone operation
which treats a maximum tonnage and the other two unit operations together
treats the entire feed material. The process is most suitable for the feed having
around 50% of material finer than 10 microns as no other operation is feasible
for treating such ultra fine feed. Adaptation of hydrocyclone for beneficiation of
such fine size feed material is indeed a novel and innovative approach.

The process is also viable for feed of size less than 30 microns.
Adaptation of hydrocyclone for separating particles of size above 10 microns
from particles of size below 10 microns from a feed of size below 45 microns is a
novel and innovative approach which further improves the downstream process
operation leading to beneficiation of such ultra fine feed material.
According to the invention the coarser fraction (i.e., stage - II underflow) is
upgraded with ore minerals. This fraction is often a final beneficiated product
which is ready for some of the downstream metallurgical operation. In case, a
superior grade concentrate is required then this fraction is subjected to one
stage of unit operation.
The throughput of the hydrocyclones used for this process is 0.5 ton/hr.
Operating condition for this hydrocyclone is different than those of the prior art
hydrocyclone.
The inventive process is enabled to prepare feed of particle size less than 10
microns. The feed material thus prepared though contains a very high level of
gangue minerals, still is capable to respond to the process configured for
particles less than 10 microns size.

The inventive process though extensively tested with iron ore slime is found
suitable for other slime feed containing metallic ore minerals. The process helps
in removal of ultra fine particles (that is particles less than 10 micron size) from
the slime feed. This often helps in lowering the impurities level and makes the
hydrocyclone product suitable for further beneficiation e.g., flotation. Removal of
these ultra fine particles also helps in reducing the possibilities of entrapment of
the impurities into the froth phase during flotation.
The inventive method is cost effective and involves initial capital investment on
small size and small diameter hydrocyclones in banks can be fed by a common
pump sump arrangement with feed distributor in between. One bank of
hydrocyclone occupies a space identical to that occupied by a single large
hydrocyclone. Thus, there is no space constraint in use of these hydrocyclones.
The wear and tear inside the hydrocyclone is not evident and it is due to the fact
that the slurry is very dilute in percent solid and also contains very fine size
particles. Chocking of slurry pipe line, pump and in hydro cyclone is not
encountered during the several rounds of tests conducted.
BRIEF DESCRIPTIONS OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a process flowsheet of the inventive beneficiation process.
Figure 2 shows a process flow chart according to the invention with iron ore
slime as an example.

DETAILED DESCRIPTION OF THE INVENTION
This invention discloses a novel and innovative method to separate particles of
size below 10 micron from a feed of particle size below 45 microns or 30
microns. Therefore, a size classification of the feed particles is first resorted to.
Objective of this classification process is two fold for example (i) to prepare feed
for further process as the process applicable for feed size below 10 microns is
not suitable for the coarser size fraction of coarser than 10 microns and vice
versa, and (ii) particle degeneration which shows gangue mineral enrichment
towards the fine size fraction. Thus, the step of classification enriches the
coarser fraction with ore minerals. This classification process is complex due to
(i) presence of two category of particles i.e. ore and gangue minerals, and (ii)
feed particles of very fine size. Classification of a feed with ore and gangue
mineral is usually manageable as gangue particles are predominantly finer in size
in most of the mineral beneficiation operations. The invention adapts an
improved classification step to actually ensure gravity separation as well.
Fineness of the feed in general makes the classification process complex and
challenging.
The feed particles are very fine for this feed and it provides the particles a higher
surface area. Therefore, surface chemistry, surface charge of these particles
plays an important role and influences the process designed for beneficiation of
the feed. It has been noticed that these particles often tend to agglomerate to
form a pseudo larger particles. In the suggested method of classification these
pseudo large particles are disintegrated prior to classification. Smaller size of the
particles experiences high drag force due to large surface area per unit mass.
Such phenomenon leads to a situation where the particles having differential
acceleration attaining the identical velocity in quick span.

Therefore, this type of feed requires a system where provision for high initial
acceleration on the particles exists and the hydrocydones also ensure early
removal of the products i.e. during initial phase of journey of particles. Process
condition for hydrocyclone operation and the geometry of hydrocyclone are
selected keeping the aforesaid requirement in mind.
As shown in figure 1, the process warrants a two stage hydrocyclone operation;
the underflow of the first stage of hydrocyclone operation is used as feed for the
second stage of hydrocyclone operation. Overflow fractions generated from the
first and the second stage operation together forms a product of the total
operation. The combined overflow fraction contains finer fraction of the feed,
usually it is less than 10 microns size. The underflow fraction of the second stage
hydrocyclone operation contains the coarser fraction of the feed. In the process
of classification the lighter and the finer gangue minerals mostly reports to the
overflow fraction. Hydrocyclone used for this purpose is a small diameter
hydrocyclone that is 2 - 3 inch diameter with specific vortex and spigot diameter.
This operation also demands very high inlet pressure which is much higher than
the conventional hydrocyclone operation. The selection of hydrocyclone and the
operating conditions are the two unique and innovative features of the invention.
As shown in figure 2, iron ore slime is used as feed. In the case of iron ore slime,
particles of size below 30 microns are used as feed for the two stage
hydrocyclone operation. The underflow and the overflow fractions generated
through two stage of hydrocyclone operations needs further beneficiation and
hence in this specific case the method is a part of the total flowsheet. The
weight, iron, alumina and, the silica distribution in each of the stream is marked
for this specific application. As described hereinabove, is enabled to classify the
feed including separation of gangue minerals. The overflow fraction contains
more of gangue minerals.

EXAMPLE
A test was carried out using iron ore slime. By definition iron ore slime is a by
product of iron ore beneficiation plant having particle size below 150 microns.
Iron ore slime is generally treated as waste due to lack of suitable technology for
recovering iron values from the slime and also due to less demand from the end
users. However, in the recent years, the beneficiation process to treat good
quality of iron ore slime for particle size up to 45 microns and 30 microns has
been introduced. In contrast, a slime containing particle size below 45/30
microns is not amenable to beneficiation as the available technology does not
support beneficiation of this size fraction of the slime. This ultra fine size fraction
(i.e.' below 45/30 microns) constitute around 50% of the slime. Therefore a
process suitable for beneficiation of the ultra fine size fraction of slime is
proposed herein. Representative slime samples of size fraction below 30 microns
were collected from the slime dam at mine sites. These samples were
characterized which revealed that around 60% of the material is of size below 10
microns. These slime samples also contain 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 a sump
combination at 10% solid level. In the second stage this slurry is pumped to a
hydrocyclone of 2" or 3" diameter depending on the trade off between the
cyclone efficiency and the required throughput A 2" diameter cyclone provides
better hydro cyclone efficiency. Inlet pressure was maintained around 45 psi.
Vortex diameter and spigot diameter is suitably adjusted depending on the
intended mass split in the underflow and the overflow fraction. Intended mass

split for the experimented case is 65% of the feed to be available in the
underflow fraction. The underflow of stage-1 hydrocyclone operation was again
treated on second stage hydrocyclone. For stage - II operation, feed inlet
pressure was kept at 42 psi with intended mass split of 65% in the underflow,
accordingly the spigot and the vortex finder diameter was adjusted. The overflow
of stage - 1 and II hydrocyclone operation were mixed together which is around
58% of the feed. This fraction contains less than 10 micron size fraction of the
slime and it also contains major part of the gangue minerals present in slime.
This fraction was subsequently treated using a suitable 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. A process flow
chart of the invention is shown in figure 1. A typical iron ore slime results is
shown in figure 2.

WE CLAIM
1. A process for separating particle of size below 10 microns from a slime
feed of size below 30 microns in a two stage of hydrocyclone
operation, the method comprises :
providing iron ore slime including agglomerates having an average size
around 10 microns.
breaking the agglomerates and intense mixing with water at 10 percent
solid level to form a slurry by adapting a combination of a slurry pump
and a sump;
supplying the prepared slurry into at least one hydrocyclone;
treating in a first stage the slurry containing 10% solid which produces
underflow and overflow;
treating the underflow of the first stage in a second stage to obtain a finer
fraction constituting an overflow of the second stage which comprises
particles of size less than 10 microns;
extracting the underflow of the second stage containing fraction coarser
than 10 microns size feed material.

2. The process as claimed in claim 1, wherein the at least one
hydrocyclone is operated at high feed inlet pressure of 42-45 psi,
wherein the solid fraction is maintained in the feed slurry at around
10%, and wherein the mass split is maintained between 50:50 to
80:20 for the underflow and overflow fractions.
3. A process for separating particle of size below 10 microns from a slime
feed of size below 30 microns in a two stage of hydrocyclone
operation, as substantially described and illustrated herein with
reference to the accompanying drawings.
4. The suggested method in addition to size classification also upgrades
the coarser fraction (i.e., stage - II underflow) with ore minerals. This
fraction is often a final beneficiated product which is ready for some of
the downstream metallurgical operation. In case superior grade
concentrate is required then this fraction is subjected to one stage of
unit operation.

The invention relates to a process for separating particle of size below 10
microns from a slime feed of size below 45 micron or 30 microns in a two stage
of hydrocyclone operation, the method comprises : providing iron ore slime
including agglomerates having an average size around 10 microns; breaking the
agglomerates and intense mixing with water at 10% solid level to form a slurry
by adapting a combination of a slurry pump and a sump; supplying the
prepared slurry into at least one hydrocyclone; treating in a first stage the
slurry containing 10% solid which produces underflow and overflow; treating
the underflow of the first stage in a second stage to obtain a finer fraction
constituting an overflow of the second stage which along with overflow from 1st
stage of hydrocyclone operation comprises particles of size less than 10
microns; extracting the underflow of the second stage containing fraction
coarser than 10 microns size feed material.