FI ELD OF THE INVENTION
The present invention generally relates to a beneficiation process for low
grade iron ore having ultrafine liberation. In particular, the invention is
related to beneficiation of high alumina content iron ore having about 50% Fe
and about 9% Al2O3 using crushing, classifiaction, jigging, coarser grinding,
pre-concentration, finer grinding, and two stage advance gravity
concentration to produce final concentrate with 3% Al2O3 and reject/tailings
with less than 45% Fe. More particularly, the invention relates to a process
for beneficiation of low grade iron ore possessing critical liberation
characteristic.
BACKGROUND OF THE INVENTION
India is endowed with large reserves of high grade hematite ore. However,
steady consumption of these iron ores is now a concern forcing to develop
beneficiation strategies to utilize low grade iron ores. India being the fourth
largest producer of iron ores in the world requires around 110 million tons
(MT) of finished steel production from the current level of ~ 40 MT by the
year 2019-20. To produce 110 Mt finished steel, around 170 MT of quality
iron ore (+63% Fe) is required. Besides that around 100 MT of quality ore is
expected to be exported. All together, 270 MT of prepared quality ore is
required which corresponds to mining of around 400 Mt of run-off-mine
(ROM) ore every year. It has been estimated that at this rate of mining the
proven reserve of iron ore in India may last about 32-35 years only. Current
mining practice adopts a cut off grade of 58% Fe content. As a result of
which lot of low grade insitu deposits are locked in operating mines. Besides
these in-situ deposits huge stockpiles of low grade ore has been created in all
operating mines in course of removal of overburden and selective mining
during mine development. This low grade ore can’t be utilised due to low
industrial value and marketability.

To meet the future demand and projected requirement of steel plants,
existing reserves of high grade hematite (>63% Fe) may not last beyond 25-
30 years. Accordingly, it is highly desirable to utilize these low grade reserves
to cater for increased future demand of steel making. New mining
infrastructure are also expected to contain deposits of increasingly inferior
grades. In addition to this, stringent environmental regulations involved in
opening of new mines, problems involved in handling, disposal of tailings
(slimes), and utilizing of iron ore at 45% Fe as a cut-off fixed by statutary
Authorities, it is the need of hour to effectively beneficiate low grade iron ore.
Apart from the reserves of low grade iron ore, the known washing
methodology adopted in mining industries which had discarded the slimes as
well as fines containing Fe value between 45%-55% have added 10-15 Mt
every year and have been dumped somewhere as a big heap or in tailing
pond. It is required to utilize these lost minerals in main stream by making
sinter/ pellet using advance and cost effective techniques of beneficiation.
The main difficulty in processing and utilization of lean grade iron ores
originates from their compositional characteristics, soft nature of some of the
ores and high alumina content as well. The composition of the Indian iron
ores is typified by high iron content with relatively higher amount of alumina
(as high as 10% to 15%). Alumina and Silica content should be within the
permissible limit for better fluidity of slag which in turn reduces the coke
consumption in blast furnace. Iron ore is being beneficiated all round the
world to meet the quality requirement of Iron and Steel industries. However,
each source of Iron ore has its own peculiar mineralogical characteristics and
requires the specific beneficiation and metallurgical treatment to get the best
product out of it. The choice of the beneficiation treatment depends on the
nature of the gangue present and its association with the ore structure.
Several techniques such as washing, jigging, magnetic separation, advanced
gravity separation and flotation are being employed to enhance the quality of

the Iron ore. Washing, jigging and classification are being carried out for the
beneficiation of Iron ores in many steel plants.
US patent 3414402 describes a method for beneficiation of low grade iron ore
for limonitic and sideritic ores. This technology treats normally nonmagnetic,
iron ores utilizing either a fluidized bed or dilute phase reduction technique to
produce a mixture of reduced metallic iron and gangue, followed by a
controlled heat treatment step of the mixture after which a relatively simple
grinding permits facile and high yield magnetic separation of the iron from
the gangue.
US patent 4548795 A decribes a method for treatment of aluminous materials
where leaching process employing acidic chloride solutions, whereby the iron
content of aluminous materials such as lower grade iron-containing bauxite
ores is reduced, enabling the obtention of valuable products such as
metallurgical grade alumina and refractory grade bauxite, previously
obtainable only from higher grade low-iron aluminous materials.
US 4697744 A describes a process for producing iron oxide fine powder of
high purity from an oxide iron ore such as hematite or magnetite by only
physical processing is disclosed, which comprises the steps of: providing a
preliminarily ground raw material powder of an oxide iron ore or a mixture
thereof having the impurity content in a specific range; classifying the raw
material iron ore powder under such conditions that fine particles smaller
than 10 Ūm in diameter are removed from the ore powder; optionally treating
the classified powder with an acid solution; refining the classified, optionally
acid-treated iron ore powder by means of gravity concentration; and finish
grinding the refined powder to reduce the particle size to a desired level.
US patent 3273993 A, US patent 1588420 A, US patent 2468586 describe
processes of utilization of low grade iron ore having silica rich impurities using
reduction roasting followed by magnetic separation technique.

US patent 3337328 A and US patent 3502271A explain beneficiation
processes for treating lean grade iron ore having silca rich impurities using
gravity concentration, magnetic sepration and flotation process.
CN patent 1548234A and CN patent 101413057 describe about ore dressing
processes for treating poor hematite, low grade ores and complicated ores.
These ore are firstly liberated using stage wise milling then beneficiated with
the combination of gravity process, magnetic process and flotation process.
CN patent 103495495A teaches a beneficiation method for super-low-grade
iron ore. The method comprises the steps of smashing, screening, grinding
treatment, GK screen sifting, high-frequency screen sifting, permanent
magnet magnetic separator treatment, high-gradient magnetic separator
treatment, shaking table reselection treatment and gangue recycling machine
screening treatment.
OBJECTS OF THE INVENTION
An object of the invention is to propose a process to beneficiate low grade
iron ore having high impurities of alumina.
Another object of the invention is to propose a process to beneficiate low
grade iron ore having difficult liberation characteristic.
A still another object of the invention is to propose a beneficiation process for
low grade iron ore involving crushing, scrubbing, grinding, classification and
gravity concentration steps.
Yet another object of the invention is to propose a cost effective beneficiation
process to recover iron values from high alumina iron ore.
A further object of the invention is to propose a beneficiation process to
produce concentrate from low grade iron ore which can be used as raw
material for sinter making and pellet making.

A still further object of the invention is to propose a process of recovering
iron values from discarded iron ore.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a beneficiation process for
low grade iron ore slimes having 51% Fe and 9% Al2O3, which interalia,
comprises steps of two stage crushing using primary and secondary crusher
to produce 8 mm size then scrubbing and classification using scrubber, screen
and classifier. Combination of screen and classifier produce three size
fractions -8+1 mm, -1+0.15 mm and -0.15 mm. Size fraction -0.15 mm was
discarded as waste. Size fraction -8+1 mm was treated separately through
jigging process and produce iron concentrate with 63.42% Fe and 3.03%
Al2O3 for sinter making. Reject obtained from jigging process contains
substantial amount of iron values but having interlocking structure therefore
it was ground down to 0.5 mm size using ball mill to liberate the iron values
from material. Ground material obtained from ball mill and size fraction -
1+0.15 mm were mixed together and subjected to wet screening to remove
the particles of size 75 micron in the overflow. Oversize fraction of screen
was treated through pre-concentration process using HG spiral. This process
enriches the hydrocyclone underflow material and directly removes undesired
material. By doing this, unnecessary load on downstream process reduce.
Again HG spiral concentrate material is ground down to liberation size i.e. 75
micron of material using a ball mill so that most of the iron particles become
free from gangue minerals. Further ground material of ball mill having size 75
micron and undersize fraction (-75 µ) of screen are combined together and
subjected to hydrocyclone for classifying the material at 10 micron cut size.
Hydrocuclone overflow material i.e. -10 micron is discard as waste and
underflow material is treated in two stage FM spirals for achieving the pellet
grade concentrate. Finally a concentrate with assay 61.56% Fe and 3.54%

Al2O3 was produced which will be used a raw material for pellet making.
Overall waste generated from the process was having 44.23% Fe.
These together with the other aspects of the invention, along with the various
features of novelty that characterize the invention, are pointed out with
particularity in the description, along with the abovementioned summary,
annexed hereto and form a part of the invention. For a better understanding
of the invention, its operating advantages and the specified object attained
by its uses, reference should be made to the accompanying drawings and
descriptive matter in which there are illustrated embodiments of the
invention.
BRI EF DESCRIPTION OF THE ACCOMPANYING DRAWING AND
TABLES
Figure 1 shows a schematic flow sheet with material balance illustrating
different steps performed as per the process of the current invention.
Figure 2 shows XRD pattern of low grade iron ore sample.
Figure 3 shows microscopic characters of the low-grade iron ore showing the
modes of occurrence of various minerals.
Figure 4 shows the modal distribution of iron-bearing mineral, interlocked
grains and the gangue minerals.
Table 1 Dry screening analysis of as received sample
Table 2 Wet screening size wise chemical analysis of ore crushed to 8 mm
size

Table 3 Result of scrubbing, wet screening, classification of sample crushed
to -8 mm size
Table 4 Jigging results of -8+1 mm washed fines at 40 stokes/minute
Table 5 Jigging results of -8+1 mm washed fines at 50 stokes/minute
Table 6 Jigging results of -8+1 mm washed fines at 60 stokes/minute
Table 7 Jigging results of -8+1 mm washed fines at 70 stokes/minute
Table 8 Jigging results of -8+1 mm washed fines at 80 stokes/minute
Table 9 Optimum result of wet screening of ground product
Table 10 Optimum result of HG spiral treating -500+ 75 micron size fraction
Table 11 Optimum result of hydrocycone treating mixed sample of -75 µ size
Table12 Optimum result of fine mineral spiral separator treating hydrocyclone
underflow sample
Table 13. Optimum result of scavanging of middling and tailing product using
FM spiral separator
Table 14. Optimum result of WHIMS treating hydrocyclone underflow sample
at current of 8 amps.
Table 15. Optimum result of reverse flotation treating hydrocyclone underflow
sample
DETAI LED DESCRI PTION OF THE INVENTION
Representative low grade iron ore sample was collected from Katamati mines
of TATA Steel. The dry screen analysis result is presented in Table 1. It was
found that the sample contains more than 18 wt% material that are coarser
than 30 mm. This sample consists of 51.41% Fe, 7.77% Al2O3 and 8.72%
SiO2. Specific gravity of the sample was found to be 3.68. This sample was
characterized using X-ray differaction (XRD) methodology to identify the

minerals present in the low grade iron ore sample. Figure 2 shows the XRD
pattern of the iron ore sample which shows that hematite, goethite, gibbsite
and minor traces of quartz are present in the ore. An optical microscopic
study was carried out using Leitz (Leica) Orthoplan microscope with DFC
420C Digital camera attachment. Magnification of the order of 50, 100 and
200 were used to examine the minerals present in the ore and its association.
From the microscopic studies, it was found that the ore contains goethite and
hematite as the main iron bearing minerals. Major gangue minerals are iron-
rich clay and quartz and amorphous silica. The type of hematite observed
here are martite, specular hematite, microplaty hematite. Hematite varies
widely in its size from minute plates to coarse anhedral aggregates. Individual
morphological types tend to dominate in a single micro band with adjacent
bands sometimes containing different forms. Primary hematite bands consist
of fine hematite crystallites which occur in the form of vermicular and platy
grains with abundant sub-micron sized pores. The martite bands consist of
euhedral, subhedral and tabular martite grains. Some martite grains show
skeletal texture that formed due to alteration and replacement of hematite
lamellae by iron rich clay. Martite aggregates also occur as short
discontinuous band and patches within the fine grained hematite aggregates.
The voids besides having specular hematite grains also contain secondary
minerals such as clay and goethite. Most of the specular hematite grains vary
in length between 10-80 micron and few are less than 10 micron in length.
Very fine crystallites of hematite are mostly within 1-5 micron size
intermittently interlocked with iron rich clay as matrix. In the banded iron
ores, the bands are variously replaced by goethite. Goethite is intimately
intergrown with hematite due to extensive replacement giving rise to micron
scale intergrowth. Voids are partially filled up with irregular patches of
goethite. Goethite occurs as massive mass and colloform bands. Coarse
fibrous and granular goethite occurs in hematite ore fragments. At many
instances, goethite becomes alumina rich and grades into limonite. In the

lateritic type, goethite forms a network binding clay and silica within such
complex networks. The various characters described above are presented
pictorially in Figure 3. Liberation analysis of sample was carried using a
known stereo-zoom microscope and the modal distribution of iron-bearing
mineral, interlocked grains and the gangue minerals were determined which
is shown in Figure 4. It can be visualized from the figure that the sample has
a very poor liberation characteristics because above 1 mm size, more than
50% grains remain as interlocked grains. However, the liberation of iron
minerals slowly improves and at -100 micron size, there is a sharp increase in
the liberation of the iron minerals. But from the graph it becomes apparently
clear that most of the locked iron bearing phases shall be liberated below 75
microns. This is in conformity to the microscopic observation on the crystal
sizes of the iron-bearing minerals, especially that of hematite. Therefore,
after processing the material at coarser sizes and recovering the possible
valuables, the remaining material are to be ground and processed below 75
microns.
Based on characterization study, as received sample was first crushed to
below 30 mm using primary crusher and then product of primary crusher was
further crushed to below 8 mm so that interlocked gangue minerals from iron
minerals could be liberated in coarser range. Bond work index of the raw
sample was found to be 12.15 KWH/ton. Size wise chemical analysis of
crushed sample (-8mm) is presented in Table. The -8 mm crushed ore was
subjected to scrubbing, washing followed by wet screening at 1mm.
Scrubbing and washing was carried out to remove the coated impurities of
clay minerals from surface the sample. The -1mm material was further
subjected to classification using screw classifier followed by desliming of the
classifier overflow (-0.15mm) using hydrocyclone for possible enrichment.
Hydrocyclone was found unsuitable for further unsuitable therefore classifier
overflow sample (-0.15 mm) was discarded as waste. The size and size-wise
chemical analysis and the results of scrubbing, classification and desliming

are given in Tables. Washed fines (-8+1 mm) from scrubbing and wet
screening option was subjected to jigging in air pulsated jig supplied by
Humblotz Wedag with varying frequencies viz. 40, 50, 60 , 70 and 80
stokes/minute. Parameters which were kept fixed throughout all the
experiments were air pressure, jigging time and water flow rate. Values of air
pressure, jigging time and water flow rate were 0.4 bar, 6 minutes and 175
liter per minute respectively. Results of all experiments are given in Tables 4-
8. Optimum result was obtained with frequency 40 stokes /minute which is
given in Table 4. Results given in Table 4 shows that concentrate with 21.7%
yield, assaying 63.13% Fe, 3.1% Al2O3 and 2.21% SiO2 can be obtained.
Bond work index of reject sample obtained from jigging was found to be
11.58 KWH/ton. This reject sample and -1+0.15 mm fraction were clubbed
together and ground to below 500 µ size using a ball mill and subjected to
classification using wet screen having aperture size of 75 micron. Optimum
test result of wet screening is given in Table 9 which shows that 44% of +75
µ size had lower Fe content and this was treated separately in 7 turn high
gradient (HG) spiral separator as pre-concentrator to remove the gangue
material (45% Fe) at this stage. Optimum test result of HG spiral separator is
given in Table 10. Concentrate and middling product of HG spiral separator
were mixed and ground to below 75 µ size using a ball mill. Ball mill was
operated at pulp density of 65% solid by weight. This ground product was
combined with -75 µ size fraction and subjected to desliming. Desliming was
carried out using 100 mm hydrocyone to remove the ultrafine fraction in the
overflow. Parameters which were maintained during hydrocycone operation
were vortex finder diameter, spigot diameter, operating pressure and pulp
density of slurry having values 25 mm, 15 mm, 10 psi and 10% solid
respectively. Optimum test result of desliming is presented in Table 11. The
deslimed material was further treated separately through two stage 7 turn
fine spiral (FM) separator, wet high intensity magnetic separator (WHI MS)
and reverse flotation to asses the efficiency of the process. Optimum test

results of FM spiral separator (2 stage), WHIMS and reverse flotation are
given in Tables 12-15 respectively. From the results, it was found that 2 stage
FM spiral separator has the advantage over the WHIMS and flotation due to
high yield of iron concentrate with high grade. Concentrate obtained from FM
spiral separator has 17.4% yield with 61.47% Fe and 3.39% Al2O3 which
could be used a raw material for pellet making. Rejects obtained after
washing was mixed with tailings obtained from HG spiral separator, FM spiral
separator and hydrocycone, and considered as waste as it contains less than
45% Fe.

WE CLAIM:
1. A process for beneficiation of low grade iron ore, the process comprising the
steps of:
crushing a low grade iron ore of size < 100 mm to size fraction below 8 mm, the
low grade iron comprising alumina 8-10 wt% and 48-52 wt% Fe;
scrubbing, screening and classifying the crushed low grade iron ore to produce
three size fractions -8+1 mm, -1 + 0.15 mm and -0.15 mm;
feeding of size fraction -8+1 mm in a jig, and obtaining a first concentrate and a
first tailing, and collecting the first concentrate;
mixing -1 + 0.15 mm size fraction with the first tailing and grinding to 0.5 mm size
in a ball mill for further liberation;
collecting and feeding the mixed first tailing to wet screening for classifying into
oversize (-0.5 mm+ 75 micron) and undersize (-75 micron);
feeding the oversize fraction (-0.5 mm + 75 micron) to high gradient (HG) spiral
separator in slurry form and collecting a second concentrate and a second tailing;
grinding the second concentrate to 75 micron size by ball milling;
mixing the undersize (-75 micron) with the second concentrate and feeding to a
hydrocyclone, collecting the overflow and underflow fraction of the hydrocyclone;
feeding the underflow fraction into a Fine mineral (FM) spiral separator and
obtaining a third concentrate and a third tailing; and
collecting the third tailing and feeding the third tailing into FM spiral and
generating fourth concentrate and fourth tailing.
2. The process as claimed in claim 1, wherein the jig is operated at a frequency 40-
80 stokes/minute, under air pressure 0.3-0.4 bar, with jigging time 5-6 minutes,
and at water flow rate 175 liter per minute.

3. The process as claimed in claim 1, wherein the pulp density of 65-70% solid by
weight of said mixed first tailing is maintained.
4. The process as claimed in claim, wherein the screen used during said wet
screening has an aperture size of 75 micron.
5. The process as claimed in claim 1, wherein said HG spiral separator constitutes a
7 turn HG spiral separator.

6. The process as claimed in claim 5, wherein the HG spiral separator is operated
at pulp density of 20-30% solid by weight.
7. The process as claimed in claim 1, wherein the pulp density maintained during
said finer grinding in ball mill for the second concentrate is 55-65% solid by
weight.

8. The process as claimed in claim 1, wherein the hydrocyclone is operated by
maintaining feed slurry density of 10% solid by weight.
9. The process as claimed in claim 8, wherein the hydrocyclone is operated with an
feed inlet pressure at 10 psi.

10. The process as claimed in claim 1, wherein fine mineral (FM) spiral separator
constitutes a 7 turn FM Spiral separator.
11. The process as claimed in claim 10, wherein said fine mineral (FM) spiral
separator is operated at 25-35% solid by weight.