FIELD OF THE INVENTION:
The present invention relates to a process and system for enriching the iron content of low
grade iron ore utilizing blast furnace flue dust .
The present invention further relates to a process and system for enriching the iron content
of low grade iron ore utilizing blast furnace flue by self-reducing blast furnace flue dust and
low grade iron ore simultaneously, and specifically, it relates to treatment of low grade iron
ore of size less than 3mm through reduction roasting-magnetic separation technique to
produce a concentrate with enriched iron content. The reduction roasting is carried out
using blast furnace flue dust.
BACKGROUND AND PRIOR ART:
Blast furnace flue dust is a by-product of blast furnace iron making process. The gas ejected
during the iron making process contains lot of dust particles which are recovered during the
dust catching process. These dust particles contain valuable iron ore and coal particles. In
addition minor amount of CaO, Al2O3 and about 6-8% SiO2 is also present. The iron content
of the flue dust is about 30-35% while the Carbon content is about 25-30%.
Low grade iron ore which is the ore used for reduction roasting using flue dust contains Fe
about 50% and SiO2 and Al2O3 about 10-12%. The major mineral phases present in low
grade iron ore are goethite, hematite, kaolinite and quartz. The physical separation of low
grade iron ore has been attempted by many researchers worldwide. A similar kind of low
grade iron ore available in Tata Steel’s captive iron ore mines contain lot of goethite mineral.
Presence of goethitic mineral is problematic for beneficiation since most of the goethite is
associated with alumina and is present as aluminous goethite. The grade of this goethite is
very low and contains up to 15% Al2O3. In view of this any physical beneficiation process is
incapable of upgrading the low grade iron ore to more than 60% Fe with economically
justifiable yield.
Alternative techniques to beneficiate these ores have been tried. Similarly the blast furnace
flue dust is also a problem for steel industry in view of its low Fe content and also alkali
content. Alternative techniques to recover carbon content or utilize the carbon content of
flue dust have been tried by various researchers.

The Institute of Gas Technology has developed a fluidized-bed process for recovering direct
reduced iron from blast furnace flue dust - a material currently considered to be a waste
from the iron and steel industry. In the process, a portion of the carbon in the flue dust is
combusted to supply energy for the endothermic reaction between carbon and steam. The
reaction produces reducing gases comprised of carbon monoxide and hydrogen both of
which react with iron oxides to produce reduced iron. Up to 95 percent of the iron oxides
contained in the waste stream can be reduced to elemental iron. The vitiated reducing gases
emanating from the process can be used as fuel in the plant. The yield of iron depends upon
the quantity of iron oxide present in the flue dust and generally ranges from 20 to 30 percent
of the waste stream.
The Fe3O4 nanoparticles were prepared from a mixed solution of ferrous and ferric sulfate
obtained by leaching the blast furnace (BF) flue dust with sulfuric acid. The factors affecting
particle size, morphology, magnetic and other properties of Fe3O4 nanoparticles were
investigated carefully. The phase structure, particle size and magnetic properties of the
samples were characterized by means of X-ray diffraction (XRD) and transmission electron
microscopy (TEM), vibrating sample magnetometer (VSM) and thermo gravimetric
differential thermal analyzer (TG-DTA). The results showed that the as-prepared Fe3O4
nanoparticles had pure phase, narrow size distribution, good dispersion and crystallinity, and
exhibited the attractive magnetic property with high saturation magnetization of 105 emu/g.
The synthesized magnetic materials show the potential application in the fields of
information storage, biomedicine, catalyst, chemical sensors, etc.
In one more research work, plant waste materials such as blast furnace flue dust and sludge
were utilized as macro pellets and use of these macro pellets in the production of sinter.
Wastes addition as pellets to the sinter modifies the productivity of the laboratory grade
sinter machine as well as the better mechanical strength of sinter. At the same it also
decreases the coke rate for sinter production. The maximum productivity achieved is
5t/m(2)/day at basicity 2.2(super fluxed sinter). Microstructure of the sinter of basicity 2.2
revels that it consists of re-oxidized hematite (Fe2O3) and few magnetite (Fe3O4) phases
with some slag phase of calcium silicate(CaSiO3). X-ray diffraction also confirms the presence
of hematite and magnetite as the main constituents of the sinter. Although using these
waste made pellets in the sintering process leads to decrease the coke consumption,

simultaneously it is used as secondary raw material and at the same time it is eco-friendly
also due to recirculation of hazardous wastes.
In yet another study a possible solution for use of blast furnace flue dust which generates
from the Egyptian Iron and Steel Company by forming self-reducing briquettes composed of
flue dust and mill scale with different mass ratios, used in electric arc furnace to produce
steel was studied. The results indicated that the mechanical properties of the briquettes
improved with increasing mill scale ratio in the mixture, whereas the reduction percentages
decreased with decreasing temperatures. The addition of coke breeze fines to the briquette
mixture (1 mill scale : 1 flue dust) improved the compressive strength of the produced
briquette. XRD analysis and microscopic structure of briquette containing 11% coke reduced
at 1100 degrees C for 2 h in isolated atmosphere, showed that the iron phase was
predominate phase and the quantity of metallic iron increased.
Blast furnace (BF) flue dust is one of pollutants emitted by iron and steel plants. The
recycling of BF flue dust can not only reduce pollution but also bring social and
environmental benefits. In this study, leaching technique was employed to the treatment of
BF flue dust at first. A mixed solution of ferrous and ferric sulfate was obtained and used as
raw material to prepare nanometer-sized black iron oxide pigment (Fe(3)O(4), magnetite)
with NaOH as precipitant. The optimal technological conditions including total iron ion
concentration, Fe(3+)/Fe(2+) mole ratio, precipitant concentration and reaction temperature
were studied and discussed carefully. The spectral reflectance and oil absorption were used
as major parameters to evaluate performance of pigment. Furthermore, Fe(3)O(4) particles
were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM).
Under optimized conditions obtained pigment has low average spectral reflectance (<4%),
good oil absorption (similar to 23%), high black intensity, and narrow size distribution 60-70
nm.
In one of the Chinese patent CN105695735 BF flue dust along with limestone powder is used
in the pelletizing of steel roll oily sludge. Pellets of size 30-50mm were produced which were
further subjected for converter production lines for use.
In another patent US3652260 Blast furnace dust and converter dust are mixed with each
other and then formed into green pellets containing 7 to 20 percent by weight of carbon.
These pellets, after being dried at a temperature below 250 (degree) C., are charged into a

rotary reducing furnace, in which the pellets are reduced by means of the carbon
component contained therein.
In one of the patent JP2016188414, a method a of recycling blast furnace wet dust is
suggested. This comprises of : a step of charging the blast furnace wet dust or a mixture dust
formed by mixing iron oxide-containing dust with the blast furnace wet dust into a furnace
body of a hot metal mixer car after the furnace body discharges molten pig iron; a step of
holding the furnace body after the charging step; and a step of injecting the molten pig iron
into the furnace body after the holding step.
The method of recycling blast furnace wet dust is characterized in that mass ratio of carbon
to iron of the blast furnace wet dust or mix dust injected in the charging step is 0.5 or more
and a temperature in the blast body in the charging step is 1000°C or more.
The research work so far carried out has mostly concentrated on utilization of BF flue dust in
metallurgical plant either in production of pellets for charging in converter or for production
of nano sized iron powder after reduction.
OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a process and system for enriching the
iron content of low grade iron ore utilizing blast furnace flue dust.
It is a further object of this invention to propose a process and system for enriching the iron
content of low grade iron ore utilizing blast furnace flue dust by a techno-economically
feasible route for upgrading low grade iron ore utilizing blast furnace flue dust as a
reductant.
Another object of this invention is to propose a process and system for enriching the iron
content of low grade iron ore utilizing blast furnace flue dust by self-reducing the hematite
mineral present in blast furnace flue dust thus upgrading the overall Fe content of the flue
dust.
A further object of this invention is to propose a process and system for enriching the iron
content of low grade iron ore utilizing blast furnace flue dust by a techno-economically
feasible process for utilizing the waste blast furnace flue dust in pelletization process.

These and other objects and advantages of the invention will be apparent to a person skilled
in the art on reading the ensuing description when read in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention is provided a process for enriching the iron content of low grade
iron ore utilizing blast furnace flue dust.
In accordance with this invention is provided a process for upgrading iron content of waste
blast furnace flue dust and low grade iron ore by crushing the low grade iron ore to less than
0.075mm, blending this low grade ground iron ore with fine blast furnace flue dust,
subjecting the blended mixture to green pelletizing to form green pellets of size 8-18mm,
subjecting the green pellets to reduction roasting in a muffle furnace at predetermined
temperatures, grinding the reduced pellets to less than 0.075mm and then subjecting this
ground material to magnetic separation in a low intensity magnetic separator. The low grade
iron ore of size -10mm is crushed to less than 0.075mm and blended with as obtained blast
furnace flue dust. The blast furnace flue dust is used as a reductant cum ore wherein it only
supplies the reducing agent but also supplies iron values which are further reduced to
magnetite. The reduced mass is further subjected to grinding to below 0.075mm and then
subjected to wet low intensity magnetic separation to separate magnetic from non-magnetic
fraction.
The low grade iron ore contains about 48-50% Fe, 9-10% SiO2 and 10-11% Al2O3. The low
grade iron ore can neither be directly utilized in blast furnace as a lump ore nor it can utilized
in iron ore sintering or iron ore pelletization process. This is because of the high levels of
gangue minerals silica and alumina. The presence of these gangue minerals increases the
slag volume thereby demanding more heat in the form of coke. However the presence of
such high content of iron values cannot be ignored and such ores cannot be rejected. Any
value addition of this low grade ore that makes it suitable for blast furnace or sintering or
pelletization will not only increase the iron reserves but will also conserve the energy.
Reduction roasting is one such process that adds value to the ore by upgrading the iron

content to desired levels. Reduction roasting requires an external fuel/reductant that can
reduce the hematite phase to magnetite phase.
The blast furnace flue dust which is normally considered a waste for metallurgical plants
contains valuable carbon and iron content. The typical chemistry of blast furnace flue dust is
25-30%C, 30-35% Fe, 6-8% SiO2, 3-5% Al2O3 and 2-4% CaO. The blast furnace flue dust has
the potential to be used as a reductant wherein the iron contained in it as well as the
external source of iron oxide can be reduced to magnetite. This potentiality of blast furnace
flue dust triggered the need to develop a process to enrich iron content and lower the
gangue content of low grade iron ore. The desired specifications of such iron ore require
more than 62% Fe.
The process involves crushing and grinding of low grade iron ore to less than 0.075mm
followed by classification at 0.075mm to separate the below 0.075mm from above 0.075mm
fraction. The oversize of the classification is again recirculated to grinding process. This
process is repeated until all the oversize fraction is ground to less than 0.075mm. Similarly
the blast furnace flue dust was initially screened at 0.075mm and the oversize was ground to
less than 0.075mm. Both the ground low grade iron ore and the ground blast furnace flue
dust are blended in a certain proportion and subjected to green pelletizing in disc pelletizer.
The pelletizing process was carried out after adding water in the blended mixture such that
the total moisture content of the mixture is maintained at 10%. The size of the green balls is
maintained between 8-18mm. The disc pelletizer parameters like inclination, moisture
content and feed rate were optimized to get the green balls of desired size.
The green balls of the blended material are then subjected to reduction roasting in a muffle
furnace or in a rotary kiln. The temperature of the muffle furnace is maintained between
800-900°C. The time of reduction was varied between 30 minutes to 90 minutes. The
atmosphere of the furnace was maintained oxidizing so that the reductant present in the
blended pellets are oxidized to CO thus generating reducing gases. The carbon present in
the blended and coming from blast furnace flue dust is the source of reductant as well as
heat energy. The reduction roasted material is taken out of the muffle furnace after the
completion of the experiment and is ground to a size below 0.075mm The below 0.075mm
ground material is then subjected to low intensity magnetic separation at an intensity of
1000 gauss.

The magnetic concentrate recovered from low intensity magnetic separator is dried,
weighed and analysed for determination of Fe, SiO2 and Al2O3 content.
The separation of iron from rest of the slag is done through a wet low intensity magnetic
separator. However before separating the same the reduction roasted material is crushed to
less than 0.075mm so that most of the iron (Fe) gets liberated at this finer size. The
preferential separation of iron bearing material from gangue matrix phase is done by
subjecting the ground reduction roasted -0.075mm material to a wet low intensity magnetic
separation at magnetic field intensity between 500-1500 gauss. The magnetic iron gets
attracted to the magnetic drum and is scarped at the other end of the magnetic separator
while the non-magnetic material containing mostly gangue phase of silica and alumina and
other unburnt carbon values is collected at the tailing collection end of the magnetic
separator.
Since most of the gangue mineral phases are liberated at -0.075mm size, it is seen that there
is a sharp separation of silica and alumina in magnetic and non-magnetic fractions. The yield
of magnetic concentrate ranges from 45% to 60%. The final concentrate is above the desired
Fe specifications of 62%, thus it can be easily utilized in sintering or pelletizing process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 shows the process flow sheet to self-reduce flue dust and low grade iron ore
DETAILED DESCRIPTION OF THE INVENTION:
According to this invention is provided a process and system for enriching the iron content
of low grade iron ore utilizing blast furnace flue dust.
The low grade iron ore contains about 48-50% Fe, 9-10% SiO2 and 10-11% Al2O3. The low
grade iron ore can neither be directly utilized in blast furnace as a lump ore nor it can utilized
in iron ore sintering or iron ore pelletization process. This is because of the high levels of
gangue minerals silica and alumina. The presence of these gangue minerals increases the
slag volume thereby demanding more heat in the form of coke. However the presence of
such high content of iron values cannot be ignored and such ores cannot be rejected. Any
value addition of this low grade ore that makes it suitable for blast furnace or sintering or
pelletization will not only increase the iron reserves but will also conserve the energy.

Reduction roasting is one such process that adds value to the ore by upgrading the iron
content to desired levels. Reduction roasting requires an external fuel/reductant that can
reduce the hematite phase to magnetite phase.
The blast furnace flue dust which is normally considered a waste for metallurgical plants
contains valuable carbon and iron content. The typical chemistry of blast furnace flue dust is
25-30%C, 30-32% Fe, 6-8% SiO2, 3-5% Al2O3 and 2-4% CaO. The blast furnace flue dust has
the potential to be used as a reductant wherein the iron contained in it as well as the
external source of iron oxide can be reduced to magnetite. This potentiality of blast furnace
flue dust triggered the need to develop a process to enrich iron content and lower the
gangue content of low grade iron ore. The desired specifications of such iron ore require
more than 62% Fe.
This novel process where the blast furnace flue dust is self-reduced along with low grade iron
ore comprises the following process steps
1. Crushing and grinding of low grade iron ore
2. Classification at 0.075mm
3. Recirculation of +0.075mm to crushing and grinding step
4. Blending the ground low grade iron ore with blast furnace flue dust in the ratio 1:1
5. Formation of green pellets of size 6-18mm
6. Reduction roasting of green pellets at temperature between 800-900°C
7. Maintaining a reduction time between 30-90 minutes as per the desired
specifications of final product.
8. Cooling the reduced pellets in ambient atmosphere conditions.
9. Grinding the reduced pellets to -0.075mm
10. Low Intensity Magnetic separation of ground material.
The process involves crushing and grinding of low grade iron ore to less than 0.075mm
followed by classification at 0.075mm to separate the below 0.075mm from above 0.075mm
fraction. The oversize of the classification is again recirculated to grinding process. This
process is repeated until all the oversize fraction is ground to less than 0.075mm. Similarly
the blast furnace flue dust was initially screened at 0.075mm and the oversize was ground to
less than 0.075mm. Both the ground low grade iron ore and the ground blast furnace flue
dust are blended in a certain proportion and subjected to green pelletizing in disc pelletizer.

The pelletizing process was carried out after adding water in the blended mixture such that
the total moisture content of the mixture is maintained at 10%. The size of the green balls is
maintained between 8-18mm. The disc pelletizer parameters like inclination, moisture
content and feed rate were optimized to get the green balls of desired size.
Roasting is a step of the processing of certain ores. More specifically, roasting is a
metallurgical process involving gas–solid reactions at elevated temperatures with the goal of
purifying the metal component(s). Often before roasting, the ore has already been partially
purified, e.g. by froth floatation, magnetic separation or gravity separation. The concentrate
is mixed with other materials to facilitate the process. The technology is useful but is also a
serious source of air pollution.
Roasting consists of thermal gas–solid reactions, which can include oxidation, reduction,
chlorination, sulfation, and pyrohydrolysis. In roasting, the ore or ore concentrate is treated
with very hot air. This process is applied to both oxide and sulphide minerals. During roasting
of steel slag the iron containing phases i.e goethite and hematite gets reduced to magnetite.
The objective is to convert into magnetite so that during the further physical separation
process the metallic iron can be recovered easily at low magnetic intensities. The balanced
equations for the reduction roasting of steel slag are:
3Fe2O3 + CO → 2Fe3O4+ CO2 ……………………………… (1)
FeO + CO → Fe + CO2 (2)
The key operating variables of a reduction roasting process include:
• Size of the steel slag
• Size of the reductant (Coal)
• Time of reduction
• Temperature of reduction
• Ratio of coal to slag
The green balls of the blended material are then subjected to reduction roasting in a muffle
furnace or rotary kiln. The temperature of the muffle furnace is maintained between
800-900°C. The time of reduction was varied between 30 minutes to 90 minutes. The

atmosphere of the furnace was maintained oxidizing so that the reductant present in the
blended pellets are oxidized to CO thus generating reducing gases. The carbon present in
the blended and coming from blast furnace flue dust is the source of reductant as well as
heat energy. The reduction roasted material is taken out of the muffle furnace after the
completion of the experiment and is ground to a size below 0.075mm The below 0.075mm
ground material is then subjected to low intensity magnetic separation at an intensity of
1000 gauss.
The magnetic concentrate recovered from low intensity magnetic separator is dried,
weighed and analysed for determination of Fe, SiO2 and Al2O3 content.
The separation of iron from rest of the slag is done through a wet low intensity magnetic
separator. However before separating the same the reduction roasted material is crushed to
less than 0.075mm so that most of the iron (Fe) gets liberated at this finer size. The
preferential separation of iron bearing material from gangue matrix phase is done by
subjecting the ground reduction roasted -0.075mm material to a wet low intensity magnetic
separation at magnetic field intensity between 500-1500 gauss. The magnetic iron gets
attracted to the magnetic drum and is scarped at the other end of the magnetic separator
while the non-magnetic material containing mostly gangue phase of silica and alumina and
other unburnt carbon values is collected at the tailing collection end of the magnetic
separator.
The final magnetic concentrate is much above the specifications of 62% Fe and is mostly
acceptable for blending with iron ore in iron ore sintering. The following example shows
typical concentrate and tailing grade and yield values.
Table 1: Example 1 of Reduction roasting-magnetic separation of low grade iron ore and flue
dust


In one more example shown below in Table 2, it is seen that the yield of concentrate
increases but at the same time the grade of concentrate measured in terms of Fe value
decreases.
Table 2: Example 2 of Reduction roasting-magnetic separation of low grade iron ore and flue
dust

In the invention claimed , the BF flue dust has been utilized in self-reduction of flue dust
along with beneficiation cum reduction roasting of low grade iron ore. Thus this is an entirely
new and innovative process where the beneficiation of low grade iron ore is achieved to
desired level of concentrate by reduction roasting cum magnetic separation route. The
advantages of the proposed process are that the self-reduction of low grade iron ore and
blast furnace flue dust will recover a concentrate (product) that will contain relatively higher
proportion of iron values compared to the feed. Also the gangue content of the product will
be less than 7%. This product can be directly recycled in iron ore sintering process, where in
the product will serve the following purpose
1. It will add iron values thereby reducing the specific iron ore consumption in iron ore
sintering.
2. It will help in utilizing the blast furnace flue dust with simultaneous saving in
coal/coke required for reduction roasting of low grade iron ore.
3. The problem of alkali recycling which is faced when directly recycling the flue dust
can be eliminated by the use of this innovative process. The alkalis are removed
during the magnetic separation process.

WE CLAIM:
1. A process for enriching the iron content of low grade iron ore utilizing blast
furnace flue dust ,said process comprising the steps of:
crushing and grinding the low-grade iron ore to a size of less than 0.075 mm,
the low-grade iron ore comprising 48-50% Fe with 9-10% SiO2 and 10-11% Al2O3
blending the low-grade iron ore and the blast furnace flue dust in a ratio of
1:1 to form a composite, said flue dust comprising Fe 30-32% and 25-30% Carbon ,
reduction roasting of the composite at the temperature of 800-900 deg. C to
form a reduced composite,
crushing the reduced composite to particles having a size less than 0.075 mm,
followed by
magnetically separating the particles to obtain iron ore enriched in iron
content.
2. The process as claimed in claim 1, wherein the low-grade iron ore is crushed and
grounded by ball mill.
3. The process as claimed in claim 1, wherein the reduction roasting is performed in a
muffle furnace.
4. The process as claimed in claim 1, wherein the reduction roasting is performed in a
rotary kiln.
5. The process as claimed in claim 1, wherein the reduction roasting is performed for 30
to 90 minutes.
6. The process as claimed in claim 1, wherein the classification of the low-grade iron ore
and the reduced composite is done in hydrocyclone.