FIELD OF THE DISCLOSURE
The present disclosure relates to the production of high purity magnetite from
hematite. Particularly, the disclosure relates to a reactor for reduction of
hematite to magnetite using hydrogen gas.
BACKGROUND OF THE DISCLOSURE
The process to convert hematite, Fe2O3, into magnetite Fe3O4 has been
known for many years. Synthetic hematite is a basic reddish-brown iron
mineral frequently obtained as a byproduct during hydrochloric acid
regeneration in operations using this acid to clean or pickle steel products
prior to subsequent processing. Synthetic magnetite is utilized for its
magnetic and pigmentation properties.
Conversion of hematite into magnetite is known to occur in the presence of
hydrogen or carbon monoxide gas. The hydrogen or carbon monoxide gas
acts as a reduction agent and reduces the hematite, allowing magnetite to
form.
Reference may be made to G. Nabi and W.K. Lu [Ind. Eng.Chem. Fundam.,
Vol.13, No.4, 1974, pp311-316] wherein the kinetic studies of interfacial
chemical reaction were carried out with synthetic specimens by the weight
loss method, with negligible interference of mass transport processes. The
drawback is the consideration of initial rates of reaction and the experiments
were carried out at very low scale (25 mg) in a small (1.8 cm) reaction tube.
Reference may be made to A. Matthews [American Mineralogist, Vol. 61,
1976, pp.927-932] wherein magnetite is formed by the reduction of hematite
with iron in the presence of aqueous solution at 350-570 oC, 1-2 kbar
pressure. The drawbacks are due to this hydrothermal route, the process

kinetics is very slow and at a scale of 50-60 mg in a stainless steel cold-seal
bomb.
Reference may be made to M.V. Srinivasan and J.S. Sheasby [Metallurgical
Transactions B, March, 1981, pp.177-185] wherein the reduction of hematite
was investigated over the temperature range 923 to 1173 K using stabilized
zirconia cell. The drawbacks of the process were high temperature, reduction
was 85 to 90 %, material was taken only 80 g for experiments and the
equipment was small scale fluidized bed.
Reference may be made to A. Unal and A.V.Bradshaw [Metallurgical
Transactions B, Vol.14B, Dec., 1983, pp. 743-752] wherein rate processes
and structural changes in gaseous reduction of hematite particles to
magnetite were studied. The conclusion was that the rate is strongly
dependant on CO pressure while the influence of oxygen activity is of
secondary importance at 1000 oC and negligible at 600 oC. The drawbacks
were not doing detail analysis of reaction rates and sample weight for
experiment was only 200 mg. The reduction was carried out in a resistance
furnace.
Reference may be made to Feilmayr et al. [ISIJ, International, vol.44(2004),
No. 7 pp. 1125-1133] wherein hematite ore is reduced to magnetite in a
laboratory scale fluidized bed reactor at temperature from 623 to 873 K and
an absolute pressure of 10 bar. The effect of temperature and residence time
was studied. The drawbacks are the operation at high pressure and very low
scale (80 g).

Reference may be made to Sturn et al. [Chem. Eng. Technol. 2009, 32, No.3,
392-397] wherein hematite is reduced to magnetite in a laboratory scale
fluidized bed using H2 gas. The drawbacks are the operation which is at high
pressure of around 10 bars.
OBJECTS OF THE DISCLOSURE
In view of the foregoing limitations inherent in the prior-art, it is an object of
the disclosure to propose a reactor for the production of magnetite from
hematite.
Another object of the disclosure is to propose a reactor for the production of
magnetite from hematite at atmospheric pressure.
Still another object of the disclosure is to prepare a reactor for producing
magnetite from hematite at higher scale.
SUMMARY OF THE DISCLOSURE
Accordingly, there is provided a reactor (100) for reducing powdered
hematite into magnetite, the reactor comprising:
an inner reactor (2) housed inside an outer furnace (1), the inner reactor (2)
being fed powdered hematite through a feeding unit (4) coupled to the inner
reactor (2), the feeding unit (4) comprising a heating arrangement (5) below
to preheat and remove moisture from powdered hematite;
a reductant inlet (6) coupled to the inner reactor (2) through which reducing
gas is passed through for reducing powdered hematite to magnetite;
a burner (3) being installed between a space between the inner reactor (2)
and the outer furnace (1), inflammable gas being circulated in the said space
to burn inflammable gas for heating the inner reactor (2);

a by-product gas outlet (7) at the inner reactor (2) being configured to
release by-products generated during reduction; and
a discharged pipe (8) configured at the inner reactor (2) till a storage tank
(10) via a heat exchanger (9), the discharged pipe (8) being configured to
channel magnetite obtained from the inner reactor (2) to the storage tank,
the inner reactor (2), the heat exchanger (9) and the storage tank (10) being
maintained in inert atmosphere to prevent oxidation of magnetite obtained.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 shows schematic diagram of a reactor in accordance with various
embodiments of the disclosure.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
DISCLOSURE
Shown in FIG. 1 is the various components of a reactor (100) in accordance
with various embodiments of the disclosure.
The reactor (100) is being configured to reduce the powdered hematite into
magnetite in a batch process manner. The reactor (100) comprises an inner
reactor (2) housed inside an outer furnace (1).
The inner reactor (2) and the outer furnace (1) are made up of mild steel.
The inner reactor (2) is being coupled with a feeding unit (4) from the top.
The feeding unit (4) is configured to feed powdered hematite into the inner
reactor (2).
Hematite powder in accordance with an embodiment of the disclosure has the
particle size in the range of 5 to 100 µm. The BET surface area of the particle
is in the range of 1 to 5 m2/g and Fe2O3 may the in the range of 80-99%.

The powdered hematite is comprised of moisture which needs to be removed.
Therefore a heating arrangement (5) is employed below the feeding section
(4) to preheat and remove unwanted moisture from the hematite.
The inner furnace comprises a reductant gas inlet (6) coupled to the inner
reactor (2) through which reducing gas is passed for fluidizing to reduce
powdered hematite to magnetite and water vapour. The reducing gas is
passed counter currently to enable maximum reaction.
In accordance with an embodiment of the disclosure Hydrogen gas has been
used as a reductant. In another embodiment methane is used as reductant.
In still another embodiment carbon monoxide is used as the reductant.
The reduction reaction takes place at an atmospheric pressure for a period
ranging between 60 to 90 min. The temperature, to optimize reduction, is
maintained between 450-600 deg. C, therefore the inner furnace is
maintained around the same temperature.
A burner (3) is installed between space of the inner reactor (2) and the outer
furnace (1) to burn supplied inflammable gas (methane). The burning heats
up the inner furnace to raise upto temperature required.
In accordance with other embodiment of the disclosure, other gases may be
used in place maintaining the temperature of inner furnace.
The reduction of haematite produces magnetite and water vapour. The water
vapour is discharged through a by-product gas outlet (7). The by-product gas
outlet (7) is configured to release by-products generated during reduction.
The magnetite obtained has the following compositional range (all in wt. %)
Fe3O: 90 - 98 %, Fe2O3: 1 - 8%, FeO: 1 - 2%. The obtained magnetite has
magnetic saturation value in the range 80 to 85 emu/g.

A discharged pipe (8) is coupled to the inner reactor (2) till a storage tank
(10) via a heat exchanger (9). The discharged pipe (8) is configured to
channel magnetite obtained from the inner reactor (2) to the storage tank.
An inert atmosphere is maintained between discharged pipe (8), heat
exchanger (9) and the storage tank (10). This inert atmosphere is so
maintained to prevent oxidation of magnetite. Since the storage tank (10) is
at ambient temperature, the obtained magnetite is quenched as this
temperature since the obtained magnetite has the temperature of 450-600
deg. C.
The inert gas is argon or nitrogen or their mixture.
The heat exchanger (9) is being configured to bring down the temperature of
obtained magnetite from 450-600 deg. C which is the temperature of the
inner furnace to ambient temperature.
The obtained magnetite has purity more than 90 %.
Experimental Analysis
The following examples are given by way of illustration and should not be
construed to limit the scope of disclosure.
Example 1
For reduction of hematite particles, the experiments were carried out in the
temperature range 300-575 oC and 10 kg of materials were taken in the
reactor. Controlled amount of hydrogen gas was allowed for a particular time
period (60-90 min). After that the materials were cool down using argon gas.
Although hydrogen and argon gas was used, other suitable gas can also be
used. The product contained more than 95 % magnetite.

Example 2
The effect of hydrogen gas flow rate was examined in the reactor. The flow
rate of hydrogen was varied from 10 lpm to 30 lpm The results show that the
product containing magnetite marginally increases from 95.54 % to 96.32 %
at 30 lpm.
Example 3
The effect of temperature on the reduction of hematite particles were
examined. The temperature was varied from 300 oC to 575 oC. The variation
of temperature on the reduction is observed. It has been seen that as
temperature increases from 450oC to 525 oC, the product containing
magnetite is increased from 95.72 % to 98.64 %. The best result obtained at
around 525 oC, taking other parameters constant.
Example 4
The effect of time on the reduction of hematite particles were examined. The
time was varied from 60 to 90 min. It has been observed that as time
increases, the product containing magnetite increases from 90.45 % to 97.32
%, taking other parameters constant.
The advantages of the process are:
1. It is a simple reactor where hematite fines directly can be used.
2. Preheating and reduction of hematite is taken place in a single system.
3. The iron and steel plant wastes have been converted to useful valuable
product.
4. The process can utilize very fine hematite particles.
5. It can stop/reduce the import of magnetite.
6. The process is eco-friendly.
7. It reduces the energy consumption substantially.
8. The process is economically viable.
9. The product contains > 90 % of magnetite.

WE CLAIM:
1. A reactor (100) for reducing powdered hematite into magnetite, the
reactor comprising:
an inner reactor (2) housed inside an outer furnace (1), the inner
reactor (2) being fed powdered hematite through a feeding unit (4)
coupled to the inner reactor (2), the feeding unit (4) coupling a
heating arrangement (5) below to preheat and remove moisture from
powdered hematite;
a reductant inlet (6) coupled to the inner reactor (2) through which
reducing gas is passed through for reducing powdered hematite to
magnetite;
a burner (3) being installed between a space between the inner
reactor (2) and the outer furnace (1), inflammable gas being circulated
in the said space to burn inflammable gas for heating the inner reactor
(2);
a by-product gas outlet (7) at the inner reactor (2) being configured to
release by-products generated during reduction; and
a discharged pipe (8) configured at the inner reactor (2) till a storage
tank (10) via a heat exchanger (9), the discharged pipe (8) being
configured to channel magnetite obtained from the inner reactor (2) to
the storage tank, the discharge pipe (8), the heat exchanger (9) and
the storage tank (10) being maintained in inert atmosphere to prevent
oxidation of magnetite obtained.
2. The reactor (100) as claimed in claim 1, wherein the inert gas is argon
or nitrogen mixture.
3. The reactor (100) as claimed in claim 1, wherein the reductant is
Hydrogen or methane.

4. The reactor (100) as claimed in claim 1, wherein the reductant is
carbon monoxide.
5. The reactor (100) as claimed in claim 1, wherein the inner reactor (2)
and the outer furnace (1) is made up of mild steel.
6. The reactor (100) as claimed in claim 1, wherein the magnetite
obtained has magnetic saturation value in the range of 80 to 85
emu/g.
7. The reactor as claimed in claimed in claims 1, wherein the magnetite
obtained has compositional range (in wt.%): Fe3O4 : 90 to 98 %, Fe2O3
: 1 to 8%, FeO : 1-2%.
8. The reactor as claimed in claim 1, wherein hematite fed through the
feeding unit (4) has the particle size in the range of 5 to 100 µm, BET
surface area of the particle is in the range of 1 - 5 m2/g and Fe2O3 is in
the range of 80-99%.
9. The reactor (100) as claimed in claim 1, wherein the inflammable gas
is methane.