The present invention relates to an improved process for the reduction of hematite to magnetite using hydrogen gas. The invention particularly relates to a process for the production of high purity magnetite from hematite, which is a waste material from steel plants.
The products produced by the process of present invention may be of different particle sizes and shapes and different specific surface areas.
Specially , the inventions relates to a process of reducing powdered hematite into magnetite with hydrogengas, wherein the hematite is reduced in a gas fired reactor with the flow of reduction gas, while holding the solids for a specific time at a temperature to effect the reduction to magnetite.
The invention relates to a process to utilize large quantities of hematite generated during pickling of steel in steel plant. The magnetite produced after reduction of hematite will find application in coal washeries. BACKGROUND OF THE INVENTION
It has been known for many years to convert hematite, Fe2O3, into magnetite Fe3O4. 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).
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 350-570oC, 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.
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 drawback of the process was high temperature ,reduction was 85 to 90 % and material was taken only 80 g for experiments.
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 1000oC and negligible at 600oC.The drawbacks were not doing detail analysis of reaction rates and sample weight for experiment was only 200mg.

Reference may be made 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 range of 1800 to 2000oF.The drawbacks are the high temperature and the poor product quality.
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 Pineau et al. [Thermochimica Acta, 447(2006) pp.89¬100] wherein hematite ore is reduced to magnetite by pure H2 in the temperature range of 220-680oC.It concluded that the rate of reduction of iron oxide with hydrogen is higher than CO. The drawbacks are the use of pure H2in the experiments which is costly and low scale operation(100 mg).
Reference may be made to Gaviria et al. [Physica B 389(2007), pp. 198-201] wherein hematite is reduced to magnetite by a mixture of H2 and Ar at temperatures between 260 and 360oC.The drawbacks are the use of very less raw material (90 mg) and use of a furnace.
Reference may be made to Sturn et al. [Chem. Eng. Technol. 2009, 32, No.3, 392-397] wherein 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.

Reference may be to Nickels et al. [Patent No. US 2010/0129264, dated May, 27, 2010] wherein magnetite is produced by reducing powdered hematite at a temperature range of 700 to 1300oC.The drawbacks are the high temperature operation.
According to literature, patent survey and available information, it may be
mentioned that at present no process is available to produce magnetite from
hematite at atmospheric pressure ,low temperature and at higher scale (10 kg). 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
The main object of the present investigation is to provide an improved process for
the production of magnetite from hematite which obviates the drawbacks as detailed
above.
Another object of the present invention is to provide an improved process to produce magnetite from hematite, anindustrial waste whereby the energy consumption is significantly reduced.
Yet another object of the present invention is to provide an improved process to produce magnetite from hematite, anindustrial waste whereby the CO2 emission is significantly reduced.
Yet another object of the present invention is to provide an improved process to produce magnetite from hematite, an industrial waste whereby very fine hematite particles are used.

Another object of the present invention is to provide a process and a product there of that includes a more preferred temperature range of about 300-575oC and a most preferred temperature range of about 400-550oC, thereby providing a level of optimum performance.
Still another object of the present invention isto provide a product that is at least 90 % pure magnetite, and further has magnetic saturation greater than 80 emu/g.
Yet another object of the present invention is to provide a scalable process that may be run at high commercial production levels to produce high amounts of high purity magnetite, or may further be downscaled for smaller runs.
Hematite materials were charged directly without any processing into the gas fired reactor. The experiments were carried out in the temperature range 300-575oC. Hydrogen gas of controlled amount was allowed to flow for a particular time period (60-90 min). After that the material was cooled using flowing argon gas. After desired time, gas flow is stopped and the product is withdrawn from bottom part of the reactor.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides a scaled up improved process for
reduction of hematite to magnetite, which comprises:
i. charging of hematite materials directly without any processing into the reactor and raising the temperature in the range of 300-575oC,
ii. passing hydrogen gas through the reactor to fluidize and for reduction reaction at atmospheric pressure for a period ranging between 60 to 90 min and cooling thereof in inert gas atmosphere to obtain magnetite,

iii. collecting magnetite by known method.
In an embodiment of the present invention hematite used may have the particle size may be in the range of 5 to 100 µm, BET surface area of the particle may be range of 1 to 5 m2/gand Fe2O3may the in the range of 80-99%
In anembodiment of the present invention the obtained magnetite may have the following compositional range:

In anembodiment of the present invention the obtained magnetite may have Magnetic saturation value in the range of 80 to 85 emu/g
Novelty of the present invention is that itreduces hematite to magnetite at
atmospheric pressure , low temperature (300-5750C)and at a scale of 10 kg. Also the products produced by the process of present invention have purity more than 90 % and magnetic saturation more than 80 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, the experiments were carried out in the temperature range 300-575oC and 10kg of materials were taken. 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. 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 300oC to 575oC.The variation of temperature on the reduction is observed. It has been seen that as temperature increases from 450oC to 525oC, the product containing magnetite is increased from 95.72 % to 98.64 %. The best result obtained at around 525oC, 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. 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 >90% of magnetite.

We claim
1. A scaled up improved process for the reduction of hematite to magnetite,
which comprises:
i. charging of 10 kg of hematite material directly into the reactor and raising the temperature in the range of 300-575oC,
ii. temperature is raised through burning of cheap methane gas
iii. passing hydrogen gas through the reactor to fluidize and for reduction reaction at atmospheric pressure for a period ranging between 60 to 90 min and cooling thereof using argon gas at atmosphere to obtain magnetite
iv. collecting magnetite by known method
2. A process as claimed in claim 1 wherein the used hematite have the particle size in the range of 5 to 100 µm, BET surface area of the particle is in the range of 1 to 5 m2/g and Fe2O3 is in the range of 80-99%
3. A process as claimed in claimed in claims 1 to 2 wherein the obtained magnetite have the following compositional range:


4. A process as claimed in claims 1 to 3 wherein the obtained magnetite have magnetic saturation value in the range of 80 to 85 emu/g
5. A scaled up improved process for the reduction of hematiteto magnetite as wherein described with reference to the examples accompanying this specification.