FIELD OF THE INVENTION
The present invention generally relates to ascertaining an useful and economic
application of large quantity of hematite fines generated during the pickling
operation of steel products in the steel plants. More particularly, the invention
relates to a process to convert hematite powder into magnetite for heavy media
separation.
BACKGROUND OF THE INVENTION
Large quantities and high purity hematite fines are generated during the pickling
operation of steel products in the steel plants. Prima facie the generated fines
are considered as waste, and their disposal causes huge cost and environmental
hazards. Therefore, a challenging prospect is the conversion of these hematite
fines into a value added product, for example magnetite.
The magnetite (Fe304) system has assumed an important technical field for
research due to its rich variety of application in the industry as pigment or
precursor for magnetic field. The aim of the research works mainly circumvent
the development of alternative methods of synthesis to reduce costs of
preparation and improve the rate and quality of the final products. Admittedly,
several chemical methods have been proposed to synthesize magnetite, however

the direct reduction of hematite by gaseous reductants in which the reaction
proceeds through the formation of Fe304 if the temperature is below 575°C is
most important since wusite phase is unstable under these conditions. (Figl).
For the experimental data revealed from prior art studies on gaseous reduction
of iron oxide, it can be summarized that the consecutive reduction of iron oxide
produces a complex series of heterogeneous reactions whose rates are
influenced both by chemical kinetic factors and mass (and/or heat) transfer
factors.
It is known that Nabi and Lu [1] investigated the kinetics and mechanism of
interfacial reactions between hematite and magnetite in hydrogen-water and
hydrogen-water-nitrogen mixture. Magnetite formation by the reduction of
hematite with iron in the presence of aqueous solution at 350-570° C, 1-2 kbar
pressure was studied by Matthews [2]. Srinivasan and Sheasby [3] studied the
reduction of hematite to magnetite using stabilized Zirconia cell over the
temperature range 923 to 1173 K. Unal and Bradshaw [4] investigated the rate
processes and structural changes in gaseous reduction of hematite to magnetite
using C0 gas and concluded that the rate measurement is strongly dependent
on C0 pressure while the influence of oxygen activity was of secondary
importance at 1000°C and negligible at 600°C. Hematite ore reduction to
magnetite with C0/C02 kinetics and microstructure was studied by Ettabirou et al

[5]. Feilmayr [6] et al. studied the reduction behavior of hematite to magnetite in
fluidized bed reactor using gas mixture of C0, C02, H20, H2, N2, and CH4 and at a
pressure of 10 bars absolute. Hematite to magnetite reduction monitored by
Mossbauer spectroscopy and X-ray diffraction was studied by Gaviria et al. [7].
Coarse hematite to magnetite and wustite under fluidized bed conditions
was studied by Weiss et al.[8]. They carried out detail experimental
investigations and cited morphological difference between hematite, magnetite
and wusite.
Betancur et al. [8] studied the dynamics of transformation from hematite to
magnetite by following two solid state methods. One of the procedures consisted
of a thermal treatment under a 20 % H2 and 80 % N2 atmosphere at 375°C,
whereas the second method involved a planetary ball mill to reduce the
transformation. The result of the first procedure evidenced a well-behaved
structural transformation for which highly stoichiometric Fe304 as a single phase
was obtained for treatment above 12.5 min. In contrast, a less stoichiometric
magnetite in the case of the ball milled samples was obtained.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process to convert
hematite powder into magnetite for heavy media separation.

Another object of the invention is to propose a process to convert hematite
powder into magnetite for heavy media separation which involves milling/mixing
of hematite with reductant, pelletisation and reduction to magnetite.
A still another object of the invention is to precisely determine the experimental
conditions (temperature, C0/C02 ratio, etc) for solid/gaseous reduction of
hematite into magnetite for industrial implementation.
A further object of the invention is to conduct characterization of select reduced
products in terms of mineralogy, chemistry and magnetic properties.
A still further object of the invention is to propose a process to convert hematite
powder into magnetite for heavy media separation which adapts a fluidized bed
for gaseous reduction of the hematite to magnetite.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process to convert hematite powder into
magnetite for heavy media separation providing known hematite powder which
was characterized by a known particle analyzer; providing a micropelletiser;
preparing pellets made from a mixture of hematite particles, coke fines and mill
scales; drying of the pellets in an oven for about 12 hours at temperature around
120°C; heating of the pellets at a temperature range of 450°C to 650°C wherein
a high temperature fluidized bed reactor (FBR) was used for heating; the pellets

cooled under gaseous atmosphere for about 60 - 90 minutes, the gaseous
mixture containing 5 - 20% hydrogen gas and 80 - 95% argon gas; and the size
of the pellets prepared in the micropelletiser is less than - 16 mesh.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - graphically depicts a prior art chemical method of direct reduction of
hematite by gaseous reductants.
Figure 2 - shows X-ray defraction pattern of hematite particles during phase
analysis in a particle analyzer.
Figure 3 - shows the result of particle size analysis of hematite particles in a
particle analyzer.
Figure 4 - shows XRD pattern of known magnetite sample.
Figure 5 - shows magnetic properties of known magnetite sample.

Figure 6 - shows XRD pattern of magnetite sample produced according to the
process of the present invention.
Figure 7 - shows magnetic properties of magnetite sample produced according
to the invention.
DETAIL DESCRIPTION OF THE INVENTION
Accordingly there is provided a process for conversion of hematite to magnetite
in a fluidized bed reactor using gaseous reductant. In a second aspect of the
invention there is provided a process for pelletisation of hematite particles in a
pot/muffle furnace through solid state reduction of mill scale and coke fines,
which provides the experimental samples for conversion of hematite to
magnetite using gaseous reductant. The present invention without delimiting the
scope uses a gas mixture of hydrogen and argon as gaseous reductant.
Materials
The materials used were hematite powder generated in steel plants. The powder
was characterized by a known particle analyzer. The gaseous reductant was a
mixture of H2 and Ar.

Equipment
High Temperature Fluidized Bed Reactor (FBR), Pot Furnace and Muffle furnace
was used for the process.
PROCESS
(a) Solid state reduction (In pot furnace/muffle furnace)
Different sizes of pellets (2-10 mm) were made from a mixture of hematite
particles, coke fines and mill scales. The pellets were dried at around 120°C for
12 hrs. in an oven. At around 750-1000 gms of pellets were placed in the pot
furnace/muffle furnace. The pellets were heated in the temperature of 500-
800°C and the time of heating was varied from 15-300 mins. For cooling
purpose, air/argon gas was used.
(b) Gaseous state reduction
For gaseous reduction of hematite particles, pellets in the size of less than - 16
mesh were prepared in micropelletiser. The pellets were dried at around 120°C
for 12 hrs. in an oven. The experiments were carried out in the temperature
range 450-650°C. A mixture of hydrogen gas (5-20 %) and argon gas (80-95%)
was allowed for a particular time period (60-90 mins.) After that the materials
were cool down using Argon gas.

RESULT AND DISCUSSION
The analysis of known hematite particles were done by conventional method.
The phase analysis (Fig. 2) and the particle size (Fig.3) were determined by the
particle analyzer. Similar analysis was also done for hematite particles. The
results are given below:
Analysis of hematite
All the particles are below 100µm
Mean particle size: 20.81µm
BET Surface Area: 3.2552 m2/g
Chemical Analysis : Fe203 = 92.30%
The chemical analysis of coke fines and mill scales are given below:
Coke fines


The detailed experimental matrix for the solid state reduction using mill scale and
coke fines in pot furnace/muffle furnace is given below. The best result obtained
in this case was the product contained 46.89 % of Fe304.
Experimental matrix
(a) Solid state reduction (Pot Furnace/Muffle furnace)



For the process of gaseous reduction of hematite to magnetite, a fluidized bed
reactor was used. In this case, a gas mixture of hydrogen and argon was used at
a predetermined temperature and rate. The best result obtained in this case was
96.32 % of Fe304. The experimental matrix in this case is given below:


The chemical analysis of known magnetite and the experimental product is given
below. The known magnetite contain 82.94% Fe304 whereas the experimental
product contains 96.32% Fe304. The X-RD plots (Fig. 4 and 6) of the known
magnetite and the experimental product has been provided . It can be seen
from the plots that the known magnetite contains some hematite but the
experimental magnetite contains almost all magnetite peaks. The magnetic
properties (Fig. 5 and 7) of both the known and experimental magnetite has
been given. Here also in experimental magnetite, the coercivity and magnetic
saturation value is more than the known sample. From the above results, it can
be seen that the experimental result is quite satisfactory.

Known Magnetite
Fe304: 82.94%
Fe203: 12.54%
Al203: 0.51%
Magnetic saturation = 76 emu/gm
Experimental Magnetite
Fe304: 96.32%
Fe203: Nil
FeO: 3.08%
Magnetic saturation = 82 emu/gm
From the above results and discussion, it can be concluded that the inventive
process for conversion of hematite to magnetite using a gas mixture of hydrogen
and argon is enabled to produce a product containing at least 96.32 % of
magnetite.

BENEFITS OF THE INVENTION
A process to utilize large quantities of hematite generated during pickling
of steel.
The magnetic produced after reduction of hematite find economic and
useful application in heavy media separation.
REFERENCES
[1] G.Nabi and W.K.Lu, Ind Eng. Chem. Fundam. Vol.13, No.3, No.4, 1974
pp 311-316.
[2] A. Matthews, American Mineralogist, Vol.61,1976, pp 927-932.
[3] M.V. Srinivasan and J.S.Sheasby, Metallurgial Transactions B, Vol.12 B,
March 1981, pp 177-185.
[4] A. Unal and A.V.Bradshaw, Metallurgical Transactions B,Vol.14Rb,
December, 1983, pp. 743-752.
[5] M. Ettabirou, B. Dupre and C.GIeitzer, Steel Research Vol. 57 No.7.
1986, pp 306-311.

[6] C.Feilmayr, A Thurnhofer, F Winter, H Mali and J Schenk, ISD.
International, Vol. 44, 2004, No.7, pp. 1125-1133.
[7] J.P. Gaviria A. Bone A. Pasquevich, D.M. Pasquevich, Physica B,
389, 2007, PP 198-201.
[8] B. Weiss, J.Sturn, S. Voglsam, S.Strobl, H.Mali, F. Winter and
J.Schenk, Steel Research. Int.81, 2010, No.2, pp. 93-99.
[9] J. Betancur et al. Hyper fine interact, Vol. 148/149, 2003, pp.163.

WE CLAIM:
1. A process to convert hematite powder into magnetite for heavy media
separation comprising:
- providing known hematite powder which was characterized by a know
particle analyzer;
- providing a micropelietiser;
- preparing pellets made from a mixture of hematite particles; coke fines
and mill scales;
- drying of the pellets in an oven for about 12 hours at temperature around
120°C;
- heating of the pellets at a temperature range of 450°C to 650°C, wherein:
- a high temperature fluidized bed reactor (FBR) was used for heating;
- the pellets were cooled under gaseous atmosphere for about 60 - 90
minutes, the gaseous mixture containing 5 - 20% hydrogen gas and
80-95% argon gas; and
- the size of the pellets prepared in the micropelietiser is less than - 16
mesh.

2. The process as claimed in claim 1, wherein the produced product
containing at least 96.32% of magnetite.
3. The process as claimed in claim 1, wherein the product contains Fe0 in
the range of 3.00% to 3.1%, and wherein the presence of Fe203 in the
product is substantially zero.
4. The process as claimed in any of the preceding claims wherein magnetic
saturation of the converted magnetite is 82 emu/gm.