FIELD OF THE INVENTION
The present invention relates to an improved process for conversion of hematite
which is a waste material from steel plants to magnetite using ammonia gas.
More particularly the invention relates to a process for production of high purity
magnetite from hematite.
BACKGROUND OF THE INVENTION
Several processes to convert hematite, that is, Fe2O3, into magnetite Fe3O4 are
known in the art Synthetic hematite is a basic reddish brown iron mineral
frequently obtained as a byproduct during hydrochloric acid regeneration in the
process of cleaning or pickling steel products prior to subsequent processing.
Synthetic magnetite is utilized for its magnetic and pigmentation properties.
Conversion of hematite into magnetite occurs 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 the 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 interracial 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.
Reference may also 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 °C, 1-2 kbar pressure.

The drawbacks are due to this hydrothermal route, the process kinetics is very
slow.
Reference may further 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 drawback of the process was high temperature and also reduction was
85 to 90 %.
Reference may once again be made to A.Unal and A.V.Bradshaw [Metallurgical
Transactions B, Vol.l4B, 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 °C and
negligible at 600 °C. The drawbacks were not doing detail analysis of reaction
rates.
Reference may be incorporated herein to P.E.Cavanagh et.al.[ US patent no.
666059, dated June 17, 1957] wherein the hematite is reduced to magnetite
with the help of strongly reducing gas at a temperature of from 1800 to 2000 °F.
The drawbacks are the high temperature and the product quality.
Reference may be also incorporated herein 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.

The non-patent literature by Pineau et al. [Thermochimica Acta, 447(2006)
pp.89-100] teaches a process in which hematite ore is reduced to magnetite by
pure H2 in the temperature range of 220-680 °C. It concluded that the rate of
reduction of iron oxide with hydrogen is higher than CO. The drawbacks are the
use of pure H2 which is costly and low scale operation.
The non-patent literature by Gaviria et al. [Physica B 389(2007), pp. 198-201]
discloses a process, in which hematite is reduced to magnetite by a mixture of H2
and Ar at temperatures between 260 and 360 °C. The drawbacks are the use of
very less raw material (90 mg) and use of a furnace not fluidized bed.
The non-patent literature by Sturn et al. [Chem. Eng. Technol. (2009, 32, No.3,
392-397] describes a method in which hematite is reduced to magnetite in
fluidized bed using H2 gas. The drawbacks are the operation which is at high
pressure of around 10 bars.
Prior published patent US 2010/0129264, describes a method in which magnetite
is produced by reducing powdered hematite at a temperature range of 700 to
1300 °C. The drawbacks are the high temperature operation.
The non-patent literature publisehed by Hosokai et.al. [Environ. Sci.Technol.
2011, 45, 821-826] wherein iron is produced by reducing hematite at
temperature of 700°C using ammonia gas where magnetite is an intermediate
product.
Thus, the prior art fail to discuss any process to produce magnetite from
hematite at atmospheric pressure and low temperature and at higher scale (1000
g) using ammonia gas. The purpose of this development also is to use

abundantly available hematite waste generated in the pickling plants to produce
magnetite which is a value added product.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved process
for production of magnetite from hematite which obviates the drawbacks of the
prior art.
Another object of the present invention is to propose an improved process to
produce magnetite from hematite, in which the energy consumption is
significantly reduced.
A still another object of the present invention is to propose an improved process
to produce magnetite from hematite, which substantially reduces the CO2
emission.
Yet another object of the present invention is to provide an improved process to
produce magnetite from hematite, in which process very fine hematite particles
are used.
A further object of the present invention is to propose an improved process for
production of magnetite from hematite, which is implemented at a preferred
temperature range of about 400-600 °C and a more preferred temperature range
of about 450-550 °C, thereby maintains an optimum level of performance.

A Still further object of the present invention is to propose an improved process
for production of magnetite from hematite, which produces a product having at
least 85 % pure magnetite, and a magnetic saturation level of greater than 78
emu/g.
Yet further object of the present invention is to propose an improved process for
production of magnetite from hematite, which is scalable and can be run at high
commercial production levels to produce high amount of high purity magnetite.
DETAIL DESCRIPTION OF THE INVENTION
Accordingly, there is provided an improved process for production of magnetite
from hematite.
Thus, the invention constitutes a process of reducing powdered hematite into
magnetite with a gas mixture of ammonia and argon, wherein the hematite is
reduced in a Fluidized Bed Reactor with the flow of the gas mixture, while
holding the solids for a specific time at a temperature to effect the reduction to
magnetite.
The present invention uses a large quantities of hematite generated during
pickling of steel in steel plant. The magnetite produced after reduction of
hematite finds; application in dense heavy media separation.
The products produced by the process of present invention may be of different
particle sizes and shapes and different specific surface areas.
According to the inventive process, pellets in the size of less than -16 mesh (1
mm) were prepared in micropelletiser. A known binder is used for this purpose.

The pellets were dried at around 110-120 °C for 12-15 h in an oven. 1000 g of
dried pellets were charged in the fluidized bed reactor. The experiments were
carried out in the temperature range 400-600 °C. A mixture of ammonia gas (6-
18 %) and argon gas (82-94%) was allowed to flow for a particular time period
(60-120 min). After that the material was cooled using flowing argon gas. After
the desired time, the gas flow was stopped and the product was withdrawn from
bottom part of the reactor.
Accordingly, the improved process for the production of magnetite from
hematite, which comprises:
i. forming hematite pellets of size in the range of 0.5 to 1 mm,
ii. drying the pellets at temperature ranging between 110 to 120 °C
for a period of 12 to 15 hours,
iii. charging of pellets into a fluidized bed reactor and raising
temperature in a range of 300-600 °C,
iv. mixing 6 to 18% of ammonia with 82-94% of argon gas and
passing through the reactor to fluidize and for reduction reaction
at atmospheric pressure for a period ranging between 60 to 120
min and cooling in an inert gas atmosphere to obtain the
magnetite, and
v. collecting the magnetite by a known method.

In an embodiment of the present invention, the hematite used having the
particle size in the range of 5 to 100 urn, BET surface area of the particle in a
range of 1 to 5 m2/g and Fe2O3 in the range of 80-99%.
In an embodiment of the present invention, the obtained magnetite is having
following compositional range:
Fe3O4 : 95 to 98%
Fe2O3 : 0.5 to 1%
FeO : 1-4%
In an embodiment of the present invention, the obtained magnetite has
magnetic saturation value in the range of 78 to 85 emu/g
The uniqueness of the present invention is that in the disclosed porcess produces
magnetite from hematite at atmospheric pressure and at low temperature (400-
600°C). Also the products produced by the process of the present invention have
a purity of more than 95 % and a magnetic saturation of more than 82 emu/g.
The following examples are given by way of illustration and should not be
construed to limit the scope of invention.
Example 1
For reduction of hematite particles, pellets in the size of less than -16 mesh were
prepared. The pellets were dried at around 110- 120 °C for 12-15 h in an oven.
The experiments were carried out in the temperature range 400-600 °C and
1000 g of pellets were taken. A mixture of ammonia gas (6-18 %) and argon gas
(82-94%) was allowed for a particular time period (60-120 min). After that the

materials were cool down using argon gas. Although a gas mixture of ammonia
and argon was used, a gas mixture of ammonia and nitrogen can also be used.
The product contained more than 98 % magnetite.
Example 2
The effect of % of ammonia gas in a mixture of ammonia and argon gas was
examined. The % of ammonia was varied from 6 % to 18 % in the mixture. The
results show that the product containing magnetite increases from 82.60 % to
98.24 % at 12 % mixture of ammonia and argon and thereafter it remains
almost constant upto 18 % of ammonia in a mixture of ammonia and argon.
Example 3
The effect of temperature on the reduction of hematite pellets was examined.
The temperature was varied from 400 °C to 600 °C. The variation of temperature
on the reduction is observed. It has been seen that as temperature increases
from 400 °C to 600 °C, the product containing magnetite is increased and then
reduced from 97.29 % to 82.69 % at 600°C.The best result obtained at around
500 °C, taking other parameters constant.
Example 4
The effect of time on the reduction of hematite pellets was examined. The time
was varied from 60 to 120 min. It has been observed that as time increases, the
product containing magnetite increases from 91.45 % to 97.73 %, taking other
parameters constant.

The advantages of the process are:
1. The iron and steel plant wastes have been converted to useful valuable
product.
2. The process can utilize very fine hematite particles.
3. It can stop/reduce the import of magnetite.
4. The process is eco-friendly.
5. It reduces the energy consumption substantially.
6. The process is economically viable.
7. The product contains > 95 % of magnetite.

WE CLAIM :
1. An improved process for production of magnetite from hematite, which
comprises:
i. forming hematite pellets of size in the range of 0.5 to 1 mm,
ii. drying the pellets at temperature ranging between 110 to 120 °C
for a period of 12 to 15 hours,
iii. charging of the pellets into a fluidized bed reactor and raising the
temperature in the range of 400-600 °C,
iv. mixing 6 to 18% of hydrogen with 82-94% of argon gas and
passing through the reactor to fluidize for a reduction reaction at
atmospheric pressure for a period ranging between 60 to 120 min,
and cooling the mixture in an inert gas atmosphere to obtain the
magnetite, and
v. collecting the magnetite by known method.
2. A process as claimed in claim 1 wherein the hematite used comprises a
particle size in a range of 5 to 100 urn, BET surface area of the particle in
a range of 1 to 5 m2/g and Fe2o3 is in a range of 80-99%
3. A process as claimed in claims 1 to 2, wherein the obtained magnetite
have the following compositional range:

Fe3O4 : 95 to 98%
Fe2O3 : 0.5 to 1%
FeO : 1-4%
4. A process as claimed in claims 1 to 3 wherein the obtained magnetite
have Magnetic saturation value in the range of 78 to 85 emu/g.
5. A process as claimed in claim 1, wherein as received hematite can be used
without pelletizing.
6. An improved process for production of magnetite from hematite as
sustantially described herein with reference to the disclosed examples.

ABSTRACT

The invention relates to an improved process for production of magnetite from
hematite, which comprises: forming hematite pellets of size in the range of 0.5
to 1 mm.drying the pellets at temperature ranging between 110 to 120 °C for a
period of 12 to 15 hours,charging of the pellets into a fluidized bed reactor and
raising the temperature in the range of 400-600 °C, mixing 6 to 18% of
hydrogen with 82-94% of argon gas and passing through the reactor to fluidize
for a reduction reaction at atmospheric pressure for a period ranging between
60 to 120 min, and cooling the mixture in an inert gas atmosphere to obtain the
magnetite, and collecting the magnetite by known method.