FIELD OF INVENTION
The present invention is related to a beneficiation process of iron ore slime. More
specifically, the invention is related to beneficiation process of iron ore slime by
gravity separation to recover iron values from pre-concentrated iron ore slime of
size finer than 45 micron. The invention further relates to a method of
beneficiation of high alumina low grade iron ore which show complex liberation
characteristics and liberates at a particle size of less than 45 micron.
BACKGROUND OF THE INVENTION
Impurities in iron ore such as alumina and silica are separated by beneficiation
process and about 15-20% of the total iron ore input is discarded as slime
(fraction of iron ore finer than 150 micron) in to slime ponds during the
beneficiation process. Approximately 10 - 14 million tons of slime is generated
every year in India during beneficiation process of iron ore. Almost all major
steel producer with captive raw material resources have accumulated more than
10 million tones of slime in their respective mine site. The rate of slime
production is likely to increase with time as more quantity of iron ore will be
mined to meet the ever increasing steel production target. Further, proportion of
slime to Run off

mine (ROM) will increase as ROM quality will deteriorate with time. The huge
tonnage of slime thus produced is becoming an environmental concern.
Furthermore, it has also been noticed that slime contains significant quantity of
iron values and hence, iron ore slime in true could be a source of iron ore.
Different research groups are exploring the exploring the ways to reduce slime
generation and also to recover iron values from iron ore slime.
At present, processes are developed across the world for treating slime of size
fraction below 150 micron and above 45 microns (i.e., coarser size fraction of
slime). However, beneficiation of ultra-fine size feed (fraction finer than 45
micron) is still a big challenge for the steel industry. Fine size of these particles is
the major concern for the physical separation. In conventional gravity separation
method, physical separation of ore and gangue minerals is achieved by
acceleration due to gravity on different mass of particles. In case of ultra-fine
size feed, mass difference is low in spite of the fact that the specific gravity
difference of ore and gangue minerals is significant. Number of particles per unit
mass increases with decrease in particle size therefore, number density increases
for ultra-fine size particles even at a fixed percent solid in the slurry. This has
two implications in mineral beneficiation process. Firstly, with increase in number
density function for ultra-fine size feed, the probability of particle collision
increases. Secondly, surface area of particles increase manifold for ultra-fine
particles and this leads to higher drag force on particles. Particle collision and

drag force both enhance turbulence on ultra-fine size particles and as a result,
settling rates of particles become uncontrollable. Therefore, it is difficult to
beneficiate the particles using conventional gravity separation techniques like
tabling, conventional spirals etc.
US patent 2907459 describes the use of table to concentrate ores having the size
finer than 0.25 mm. US patent 4078996 describes about the use of vibrating
table for the gravimetric separation of fine particles of size less than 250 micron.
This invention relates to a vibrating table allowing very fine particles (50 micron)
to be separated with output rates greater than for existing tables. US patent
5472096, 629595 describe the use of spiral separator for separation of ash from
coal of size fraction less than 1.0 mm. US patent 5184731 describes the use of
spiral for separation of heavy mineral particles from lighter rock particles. Use of
conventional spiral in beneficiation of iron ore tailings was restricted for the size
range of 3mm to 300 micron as described in US patent 4416768, 20120260772.
Now a days, enhanced gravity separators like Kelsey jig, Campbell jig, Falcon
separator, and the Mozely MGS and flotation machines are widely used for
beneficiation at fine and ultrafine size range. However, all of enhanced gravity
machines are mechanical in nature and generally have higher costs both from a
capital and operating perspective.

Froth flotation process is widely practiced in iron ore beneficiation for feed size of
around 75 micron. The knowhow is limited to separation of removal of non-
sulfide silicate gangue from iron phases (US patent 5507395, 5525212,
5531330). Tata Steel Ltd. has filed a patent application no. 816/KOL/2010 on
beneficiation of iron ore of slimes of below 45 micron through flotation route.
However, there is no process disclosed in the art that describes beneficiation of
slime with size fraction finer than 45 microns through gravity separation route.
Beneficiation of iron ore slime of size below 45 micron through gravity separation
remains a challenge as discussed in the above section and hence, there is need
of a process that can beneficiate iron ore slime of size less than 45 micron.
OBJECTS OF THE INVENTION
An object of the invention is to develop a process to beneficiate iron ore slime of
size less than 45 microns.
Another object of the invention is to develop a beneficiation process of ultrafine
iron ore slime via pre-concentration followed by gravity separation.
Still another object of the invention is to develop a process to recover iron values
from pre-concentrated high alumina iron ore slimes.

Another object of the invention is to propose a beneficiation method to produce
the concentrate from iron ore slime which can be used as raw material for pellet
making.
Still another object of the invention is to develop a process of recovering iron
values from discarded iron ore slime.
Still another object of the invention is to develop a beneficiation process which
can enable utilization of rejected iron ore slime.
Summary of the invention
According to the process of current invention, high alumina iron ore slime of size
less than 45 micron is collected from beneficiation plant. The slime is then
thoroughly mixed with water using a mechanical stirrer and further by pump and
sump combination to ensure uniform percentage of solid in the slurry. This step
also ensures breaking of agglomerate which are often formed due to high
surface charge on the surface of fine particles.
The feed slurry is then treated on a pre-concentrated unit which removes
gangue mineral present in finer size fraction to upgrade feed material. This

separation is done at a particular cut size with optimum condition of operating
and process parameters of pre-concentrated unit. The concentrate obtained from
pre-concentration unit is again mixed with water to maintain the required
percentage solid in the slurry. This slurry is further processed in a gravity
separation process for recovery of iron values.
In a gravity separation process, 8.5 turns fine mineral spiral is employed to
separate gangue minerals from pre-concentrated feed. During spiral operation,
three operating parameters a) feed flow rate b) percentage solid and c) product
splitter position are controlled to achieve better separation. Flow on spiral trough
is controlled to minimize turbulence that entrains fine particles in the outer
section of the trough. Furthermore, adjustment of flow on fine mineral spiral
trough is done to ensure a more laminar flow regime to allow the fine heavy
mineral particles to settle on the trough surface and migrate to the concentrate
collection area. Finally, concentrate and tailings both are collected separately in
product launders through product splitter. Position of product splitter is adjusted
to achieve the desired grade and recovery of iron concentrate during the
operation. Both samples are analyzed for chemical analysis. The design of
experiments is predefined for optimum recovery of iron values from ultra-fine
iron ore slime. This design approach gives the optimum condition of operating

parameters for desired grade and recovery of concentrate. The combination of
pre-concentration and gravity separation process gives high grade Fe
concentrate with low alumina content. The obtained concentrate is suitable as a
raw material which is pelletized to feed in blast furnace.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
Figure 1 shows a schematic flow diagram illustrating different steps performed as
per the process of the current invention.
Figure 2 shows EPMA image of pre-concentrated feed along with point analysis,
Magnification 400.
DETAILED DESCRIPTION OF THE INVENTION
Iron ore fines of finer size are generally termed as slime. Slime size fraction
below 45 microns when characterized shows that slime comprises major iron
bearing minerals such as hematite and goethite along with gangue bearing
minerals such as kaolinite, gibbsite and quartz. Around 67% of the material is of
size below 25 microns which is very fine in nature. The complex relationship of
iron bearing minerals and gangue bearing minerals in finer size range makes
beneficiation process difficult to recover iron values. The iron ore is high alumina
low grade iron ore containing alumina more than 6%.

The first step of the process involves hydro cyclone operation to separate
particles of below 10 micron size from a feed of particle size below 45 microns.
Hydro cyclone operation does size classification. The feed particles are very fine
in this feed and it provides particles more 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 also been
noticed that these particles often tend to agglomerate to form 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. This will lead to a
situation wherein particle having differential acceleration attaining an identical
velocity in quick span. Therefore, this type of feed requires a system where in
provision for high initial acceleration on particles exists and the machine also
ensures early removal of the separated mass i.e., during the initial phase of
journey of particles. Process condition for hydro cyclone operation and the
geometry of hydro cyclone were selected keeping the aforesaid requirement in
mind. During the operation, hydro cyclone is operated with the targeted cut size
close to 10 micron to remove particles of 10 micron to bring down the alumina
content to 3.0% in the hydro cyclone underflow from head slime of 6-7%
alumina. The solid concentration during the hydro cyclone operation is

maintained in the range of 10-15 wt. %. The pre-concentration process of iron
ore slime using hydro cyclone reduces the load for further process and improves
the efficiency of the process. The optimum conditions of operating parameters
used to pre-concentrate the iron ore slime in two stage hydro cyclone operation
are shown in Table 1. wherein the spiral separator comprises of 8.5 turns or
more. The iron ore fines of size less than 40 microns are pre-concentrated with
at least two stage hydro cyclone operations.


Underflow of stage-2 hydro cyclone is further treated with spiral separator. The
concentrate obtained from hydro cyclone unit contains particles of size above 10
microns with alumina less than 3%. Therefore, the target set on spiral separator
was to improve the grade from 3.0% to the desired grade of 2.0% in the
concentrate. The size-wise chemical analysis of pre-concentrated feed is given in
Table 3. Micro-analysis of pre-concentrated feed using EPMA coupled with EDS is
shown in Figure 2. Figure 2 reveals that most of the alumina and silica are
associated with goethite phase which is present in major mass fraction. The
concentrate obtained from hydro cyclone unit is mixed with water to condition
the solid particles present in the slurry. This slurry is fed to top of fine mineral
spiral separator consisting 69 cm trough diameter and a pitch of 39 cm with 8.5
turns through a slurry pump & sump combination. The slurry fed in to the spiral
concentrator has a solid concentration of 10 to 20 Wt.%. As slurry gravitates
down word, light suspended particles (gangue bearing minerals) migrate
outward by centrifugal force, whilst heavy particles (iron bearing minerals) settle
in the flow (to regions of lower velocity) and travel inward toward the central
column. During operation with fine mineral spiral, three parameters such as feed
flow rate, percentage solid and product splitter position are controlled to achieve
better separation. All these parameters of fine mineral spiral separator are
adjusted to control of turbulence generated by particles collision and drag force
on ultrafine particles across the entire trough to controlled settling. Due to low

settling rate encountered by ultrafine particles, the separation processes takes
longer residence time to fully develop. Therefore, fine mineral spiral consisting
8.5 turns or more is used to provide a longer residence time which is required for
useful separation to occur. During spiral operation, concentrate and tailings are
collected separately in product launders via discharge hose pipes. For obtaining
the best result, three factor three level Box-Behnken design of experiments
optimization is carried out. Factors with corresponding levels used in the
experiments are presented in Table 4. The process of the current invention is
able to recover iron values in the range of 55 -60 %. As per the process of the
current invention, concentrate of high grade iron consisting less than 2% AI203
is achieved with 55.85% recovery of iron values from a pre-concentrated feed
consisting of 63.01% Fe, 2.81% AI203 which is shown in Table 5. The obtained
product can be used as raw material for making pellets before charging it in blast
furnace.
Table 3: Size wise chemical analysis of pre concentrated feed



The process of the current invention results in recovering iron values from the
discarded slime via an inventive gravity separation method. The method involves
understanding of liberation characteristics of the fine particles and accordingly
devising a suitable process. The process further results in producing concentrate
from the discarded slime having alumina content less than 2 % and hence,
make them suitable for use in blast furnace.

WE CLAIM:
1. A process for recovering iron values from iron ore fines of size less than 45
microns, the process comprising:
pre-concentrating a slurry of iron ore fines of size less than 45 microns in a
hydro cyclone;
collecting a concentrate of iron ore fines of size greater than 10 microns;
mixing the concentrate with water to prepare a slurry;
feeding the slurry to the top of a spiral separator with a flow rate of 2.1 to 4.3
m3/hour; and
collecting a concentrate for further re-use.
2. The process as claimed in claim 1, wherein the iron ore is high alumina iron
ore containing alumina more than 6%.
3. The process as claimed in claim 1, wherein splitter position of the spiral
separator is maintained in the range of 3-6 centimeter.
4. The process as claimed in claim 1, wherein the spiral separator comprises of
8.5 turns or more.

5. The process as claimed in claim 1, wherein the iron ore fines of size less than
40 microns are pre-concentrated with at least two stage hydro cyclone
operations.
6. The process as claimed in claim 1, wherein the slurry fed in to the spiral
concentrator has a solid concentration of 10 to 20 Wt.%.
7. The process as claimed in claim 1, wherein the iron ore slurry pre-
concentrated in the hydro cyclone has a solid concentration in the range of 10-15
wt%.
8. The process as claimed in claim 1, wherein the first stage hydro cyclone
operating parameters - vortex finder diameter, spigot diameter and feed inlet
pressure are 14.1 mm, 4.3 mm and 42 psi respectively.
9. The process as claimed in claim 1, wherein the second stage hydro cyclone
operating parameters - vortex finder diameter, spigot diameter and feed inlet
pressure are 14.1 mm, 3.2 mm and 42 psi respectively.

10. The Iron values recovered as per the process claimed in claim 1 to claim 9,
wherein alumina percentage in the recovered iron values is less than 2% after
the spiral concentrator treatment.
11. The Iron values recovered as per the process claimed in claim 1 to claim 9,
wherein alumina percentage in the iron values is less than 3% after the hydro
cyclone treatment.
12. The process as claimed in claim 1 to claim 9, wherein the iron ore is
recovered in the range of 55 to 60 wt%.

ABSTRACT

A process for enriching iron values from ultra-fine iron ore slime.
The current invention provides a process to enrich iron values from ultra-fine iron
ore slime. High alumina iron ore slime of size less than 45 micron is collected
from beneficiation plant. The slime is then thoroughly mixed with water using a
mechanical stirrer. The feed slurry is then treated on a pre-concentrated unit
which removes gangue mineral present in finer size fraction to upgrade feed
material. This separation is done at a particular cut size with optimum condition
of operating and process parameters of pre-concentrated unit. The concentrate
obtained from pre-concentration unit is again mixed with water to maintain the
required percentage solid in the slurry. This slurry is further processed in a
gravity separation process for recovery of iron values.