FIELD OF THE INVENTION
The present invention relates to a process for improving the liberation properties
of iron ore. More particularly, the invention relates to a process for effective
separation of iron from gangue materials.
BACKGROUND OF THE INVENTION
Basic raw material for iron and steel industry is iron ore availability of which
indicates a growing economy of a country. Fortunately, India is known to have
huge reserves of quality iron ore to cater for the growing demand for domestic
iron and steel industry as well as to contribute towards the large external trade
demand.
The most important type of iron ore found in India are hematite and magnetite.
Nearly 61% of hematite ore deposits are found in the eastern part of India and
82% of magnetite ore deposits are located in southern part of India, especially in
the state of Karnataka. India possesses around hematite resources of around
11,464 million tons of which about 6,013 million tonnes are reserves and 5,442
million tonnes are residual resources. About 2,842 million tons (25.8%) are
medium grade lumpy ore resources while 945 million tons (8.4%) are high-grade
lumpy ore. Out of the fines resources about 2,543 million tons (22%) are
medium grade ore, 39.9 million tonnes (1%) are high-grade and 17.7 million
tons (1%) resources are of blue dust range. The residual are low grade,
unclassified resources of lumps and fines or high, medium, low or unclassified
grades of lumps and fines mixed. Major problem faced with the processing of
Indian iron ore is that the iron ores although are very rich in iron content, they
also have a high content of gangue material for example, silica and aluminium
which obstruct the iron and steel production due to reduction in the performance

of the blast furnace lowers. Iron ore sample found is a part of banded iron ore
formation. Hematite and goethite are major constituents of iron ore samples.
Hematite in the ore sample occurs as specularite with inter granular micro-pore
spaces. Goethite is profuse and occurs as colloform product in cavities in addition
with the weaker bedding planes. Hematite and goethite are very friable during
mining and processing due to inter-granular pore spaces and voids along the
weaker bedding planes. These friable particles break down and account for the
iron content of the slime. Ore samples, having magnetite and martite do not
participate in the formation of the slime as they are very massive . Numerous
cavities are contained in most of the bulk ore sample and are mainly occupied
with clay in the form of kaolinite. Kaolinite is in greater concentration in the slime
as it is friable, easily crushable into ultrafine size during the mining and
processing activities. Hematite and goethite in the ore sample are closely related
to clay forming interlocking complex. This interlocking characteristic continues in
the slime leading to a considerable percentage of interlocked clay
hematite/claygoethite.
Iron processing depend mainly on the type of ROM ore feed and optimum
product. Dry screening into lumps and fines is practised for high quality of flaky
ore and blue dust, because, if wet treatment is used, a substantial part of good
quality material is rejected in the form of slimes. Another advantage of dry
screening is that the dry screened fines retain ultra-fines particle which may later
be used in sintering. Ore types having gangue material which strictly adhere to
the useful metal surface are subjected to wet screening -> classification or
scrubbing -> wet screening -> classification. Mineral processing plants at mines
like Barsua, Bolani, Bailadila, Donamalai, Dalli, Gua, Kiriburu, Meghahatuburu,
Noamundi and Rajhara use dry screening for direct ore mined from the face.

The present invention introduces new concept of crushing by shear. In this
method the iron ore is crushed by shearing instead of conventional impact
method. Shear crushing enable effective liberation of iron particle and gangue
material, hence make it convenient for beneficiation compared to the
conventional method.
OBJECTS OF THE INVENTION
It is therefore an object of this invention to propose a process for improving
liberation characteristics of iron ore (haematite) including its separation from
gangue material.
Another object of this invention is to propose a process for effective separation
of iron from gangue materials which is based on shear crushing to improve the
liberation characteristics of iron and gangue material.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process for effective separation of iron from
gangue materials, which improves liberation characterisitcs of iron ore including
effective separation from gangue material. According to the invention, a specific
crushing method based on shear has been developed which enables liberating
iron particle and gangue material more effectively.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 Size distribution of iron ore for two types of crushing method
Figure 2 Distribution of iron ore for two methods in different size fraction
Figure 3 Distribution of silica for two methods in different size fraction

Figure 4 Distribution of silica for two methods in different size fraction
Figure 5 QEMSCAN analysis of 200 size fraction sample for two methods
DETAILED DESCRIPTION OF THE INVENTION:
Materials: A haematite type of iron ore has been taken, the bulk chemistry of
which is presented in table 1.
Crushing and Grinding: The iron ore is first screened to – 5mm. By
conventional method it is crushed by impact and screened in different screens.
In the second case, - 5mm iron ore is crushed by shear method and screened in
same fashion. The scheme of screening and grinding is shown in figure 1. Before
screening 10-20 kg sample drawn from a bulk quantity of 100 kg of iron ore.
Characterization of the samples
Bulk chemistry analysis: Bulk chemistry of iron ore is analyzed by using ICP-OES
following EURO – Standard no 682-1.
Liberation study with QEM SCAN: QEM SCAN technique is utilised to
characterise the as-it-is ore as well as the product material coming out from
conventional method in respect of the product material produced by the
inventive technique.
QEMSCAN is an automated technique based on SEM-EDS system attached to a
sophisticated image analysis software for fast characterisation of phases, natural

as well as synthetic, to deliver different information which is suitable for
beneficiation purpose.
The SEM system basically uses Back-scattered electron (BSE) and Energy
Dispersive Spectrometer (EDS) to identify the phases in the sample. The samples
are mounted in a cold-mount of 25mm diameter and coated by carbon to make
those samples conducting. The proportionate graphite powder with appropriate
size was mixed with the sample to separate out different particles, which
facilitated analysis of the sample on particle by particle basis. A database based
on BSE toning and X-ray spectrum was created to distinguish different iron ore
phases present in the sample. The individual particles are then identified on the
basis of BSE brightness in a scale of 0-255. In addition, the X-Ray spectrum also
identifies the phase composition. Both of those data are matched with the pre
stored database and accordingly phases are identified. A number of several
analysis modes are available in the software. Out of them ‘Particle Mineral
Analysis’ mode are identified to get the results.
Sink and float study
As iron ore has specific gravity greater then 5, so a solution of specific gravity
4.1 has been chosen for the analysis. This specific gravity has been obtained by
mixing water and Cleric solution. After separating and drying of sink and float
that sink material has been analysed for its iron, silica and alumina content.
Results and Discussion
Table 1 shows the bulk chemistry of sample. The iron content of the ore is
around 64% and silica and alumina content are 2.29 and 2.39 % respectively.

For experimentation the sample size taken as below 5 mm. Then the sample is
crushed by conventional method i.e ball mill and second lot of sample is crushed
by invented method. Figure 1 shows the size distribution of these two above
mentioned method.

It is found that with the invented method, the mass fraction in finer size is
greater than the conventional method. To eliminate the size effect, the bulk
chemistry analysis has been performed with each fraction of each method.
Figures 2, 3 and 4 respectively present the quantitative analysis of Fe, Silica and
alumina for each fraction of the two methods.
Figure 2 presents the distribution of Fe in different fraction for the two method
under discussion. It is clear from the graph that the distribution is quite different.
In case of conventional method, the liberation of Fe in finer size is higher than
the invented method which is not desirable because the finer size (less than 150
micron.) gets deposited to the slime pond as slime. By using the invented
method, it becomes possible to extract more iron in coarser size.
Figures 3 and 4 present the distribution of Silica and alumina in the different
fractions. These two compounds are most detrimental for blast furnace. In case

of silica, there is a markable difference in the two methods in the finer size
fraction (-0.5 mm), but in case of Alumina, the difference is not that much.
In order to elude the validity of the inventive process, a liberation study has been
conducted by QEM SCAN method. Figure 5 shows the liberation graph from QEM
SCAN study.
These has been taken for the sample of below 200 micron because in bulk
chemistry this size fraction has shown the most prominent difference. Here it is
found that liberated Fe for invented method is higher in smaller fraction. Hence
it can be separated easily.
Float and sink analysis has been performed for the sample. Results are shown in
the Table 2 . As iron has specific gravity of more than 4.1 so that the report is in
sink and the report on impurities is shown in float. It was noticed from the result
that in case of invented method the percentage of Fe is more. This is expected
as the liberation of Fe, in the invented crushing method found to be higher.


Conclusion
Here a methodology for iron ore grinding has been described. In which the
mechanism is different from the conventional technique. In conventional
technique, mainly grinding take place by impact method. In the invented
method, grinding of iron ore has been done by shearing. It was found that these
two method has different distribution of Fe in different size fraction. In the
smaller size fraction the gangue material accumulated in case of invented
method. Also in this range the liberation of iron is also good. This method is a n
alternative to conventional method with good liberation and separation
efficiency.

WE CLAIM :
1. A process for effective separation of iron from gangue materials, comprising :
- subjecting the iron ore to a grinding step by shearing techniques;
- screening the iron ore sample to below 5mm, wherein the original sample
containing around 64% of Fe.

2. The process as claimed in claim 1 wherein the original sample crushed in,
conventional method and by the invented method, wherein crushing in the
inventive method is done by shearing method.
3. The process as claimed in claim 1, wherein the bulk chemistry shows a
difference in two methods (invented and conventional), and wherein
4. The process as claimed in claim 1, wherein only two gangue material namely
silica and alumina are taken into consideration in case of the former method.
5. The process as claimed in claim 1, wherein the liberation study is done by
QEM SCAN method.
6. The process as claimed in claim 1, wherein the liberation study is validated
through the float and sink method.