Title: A process for removing gangue matter of alumina and silica from iron ore
rejects slime and low grade iron ore.
FIELD OF INVENTION:
This invention relates to a process for removing gangue matter of alumina and
silica from iron ore rejects slime and low grade iron ore.
BACKGROUND OF INVENTION:
Now here an attempt has taken to make the process techno-economic by
recycling of alkali. Effective or optimize process of acid and alkali recovery
helps us to established the process feasibility. In current experimental approach,
we have designed the experiment such a way it minimize the loss of alkali. The
gangue removal methodology developed by us in slurry extraction is a novel
process where chemical used are regenerated in a closed operation.
Successful studies for extraction of gangues are on laboratory scale. Further
studies are needed to carry out for suitable to bench scale resulted from
laboratory study.
Reject or slime of iron ore has gangue content of around 14% to 16%. This
gangue can be leached out economically by proposed process, which needs the
requirements of the various industries Aluminosilicate, which is one of the
essential constituent of iron bearing materials and it, is deleterious in the

manufacture of iron and steel. The invention is related to removal of gangue
from iron bearing materials like iron ore /concentration / reject / slime.
Aluminosilicate & gibbsite is of the main harmful constituent to ferrous
metallurgy and it adversely affects the blast furnace operation. The removal of
gangue from iron bearing materials involves smelting process, physical
separation and chemical leaching. Chemical leaching is relatively simple
process as it can directly treat the sinter fines without strict requirements for the
particles size.
The aim is to treat iron oxide bearing materials containing gangue matter of
aluminosilicate, quartzite, gibbsite like iron ore/concentrate/rejects/slime to
remove alumina and silica there form.
For a more detailed understanding of the invention and for further objects and
understanding thereof, reference to be had to the flow diagram.
Generally, an iron oxide bearing material is treated with a quantity of a
particular alkali with specific temperature, stirring and time span.
In this process, the slurry of insoluble material and pregnant liquor is filtered
and residue is washed with water.
Now here an attempt has taken to make the process techno-economic by
recycling of alkali and acid.

Effective or optimize process of alkali recovery helps us to established the
process feasibility. In current experimental approach, we have designed the
experiment such a way it minimize the loss of alkali.
The present patent is specific to high temperature roasting with possibility of
substantial of loss iron content.
Various mineral acids are nitric, hydrochloric, sulphuric and hydrofluoric.
Both of the methodology like alkali roasting and acid leaching is silent about
the regeneration of chemical used therein.
OBJECTS OF INVENTION:
The main object of this invention is to propose a process for removing gangue
of aluminosilicate and quartzite from low grade iron ore;
Other object is to propose a process wherein leaching of alumina and silica
gangue matter from iron bearing minerals is done with regeneration of
chemicals;
Another object is to propose a process wherein the final left over is used as
value added product or otherwise further processing;
Yet another object is to propose a process which is techno-economic by
recycling of alkali and acid, thereby minimizing the loss of alkali;

Further object is to propose a cost effective and simple process for removal of
gangue.
SUMMARY OF THE INVENTION:
According to this invention there is provided a process for removing gangue
matter coating alumina and silica from low grade iron ore and iron ore reject
slime comprising:
i) adding the sodium hydroxide to iron ore at 80-95°C to form alumino-
silicate sodium salt;
ii) subjecting the soluble alumino-silicate sodium salt to the step of
washing following by filtration;
iii) regenerating sodium hydroxide from sodium alumino-silicate salt at a
temperature range of 80 to 90°C for 60 to 90 minutes.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1: shows the block diagram illustrating the flow chart of the present
invention.
Fig 2: shows the dissolution, X% of the main gangue contents and enriching
iron value.

DETAILED DESCRIPTION OF THE INVENTION:
The present invention is related generally to leaching of alumina and silica from
low grade / reject iron ore and more precisely to novel process of leaching
gangue matter from iron bearing minerals by caustic solution with regeneration
of chemicals using atmospheric gas. The process has three stages i.e. extraction,
filtration cum washing and regeneration of caustic solution and the final left
over is used as value added product or otherwise further processing.
According to this invention there is provided a process for removing gangue
matter from low grade iron ore comprising:
Extracting gangue from the iron ore by the addition of sodium hydroxide at 80
to 95°C;
Subjecting the soluble aluminosilicate-sodium salt to the step of washing and
followed by filtration;
Regenerating1 of sodium hydroxide from spent of aluminosilicate-sodium at a
temperature range of 80 to 90°C for 60 to 90 minutes.
Controlling factors
a. Surface area
Surface are also depends upon the quality of mixing that place inside the
reaction vessel. The process generally comprises sizing of ore, below 25-
micron size ore. The surface are area increases, agitator is used which
creates a more vigorous mixing with slurry.

b. Slurry ratio & Temperature
As described in the experiments and shown in the figure below. This
relates to tap density when a fixed quantity of gangue powder is trapped
in a closed measuring cylinder till the volume of the powder remains
constant and does not decrease with further tapings.
c. Regeneration1
Regeneration of the solution is the conversion of sodium salt to sodium
hydroxide by the use of calcium hydroxide
Soluble sodium salt + Ca (OH)2 CaCO3 + 2NaOH
The generated sodium hydroxide is used for the digestion of iron ore. Calcium
hydroxide can be either purchased from market or the calcium carbonate can be
heated at around 850°C for converting it to calcium oxide which when comes in
contract with water become as calcium hydroxide. This depends on the market
value of each product and costs involved for either processing or purchasing.
All the studies carried out for regeneration have yielded around 85%
conversion to sodium hydroxide.
The generation was carried out in different temperature from 30°C to 95°C and
it was found that around 85°C to 90°C, taking 45 minutes to complete the
reaction. Calcium salt produced in this process has purity of around 97-98% and
can be sold in the market.

A. Extraction:
Extraction refers to digestion of gangue present in ore to form sodium alumina
and silicate or sodium aluminosilicate. The required quantity of sodium
hydroxide is dissolved in water and iron ore material is added after the
temperature of the caustic solution reaches greater than 90°C. Extraction studies
ware carried at various temperatures with various slurry ratios in order to
optimize the same. The extraction temperature of around 95 °C with 1:15 slurry
ratio was decided as the optimum because of the higher phosphorus leach out as
can be seen in the Table 1, The extraction is carried at this temperature and
slurry ratio for a period of 120 minutes, which is optimum reaction time,
established by the experimental results and further increase in time of extraction
hardly leach the value obtained, which is evident from experimental results
given in the tables and figure.
Hence, the optimum time for extraction is 120 minutes at around 95 °C with
1.15 slurry ratio at reaction speed 800-900rpm.
The process generally comprises sizing of ore, below 25-micron size ore.
Thereafter, the solution is removed and the leached ore washed with water.
As in case of most leaching operations, the particle size directly affects leaching
time and one may vary the particle size by, for example, crushing and
screening.
This process may be carried out in a batch or continuous way. Conventional
equipment and procedure may be used in both the case. In continuous process,
multiple stage extraction procedure can be used whereby pregnant liquor is
recycled through leaching stages to maximize utilization of leaching reagent.

The present invention is combined of gangue removal with high iron recovery
and also increases the iron grade of the de-gangue product thereby making this
low grade reject more valuable and usable in iron production. Therefore, the
practice of the invention would be worth nothing for conserving the iron ore
resources through the world. The leach reactor was made of torsion with
loading capacity of 1 kg ore.
Two modes of the operations were used.
1. Circulating operation: In such a test, the leach solution was continuously
recycled at a constant reaction speed, through tapping until the apatite
and iron phase in ore was dissolved to minimum level. The bulk solution
was sampled at a certain time interval.
2. Single-phase operation: The fresh leach solution was added after single
operation by filtration
B. Filter cum washing:
In the filtration process, the soluble sodium salt of aluminum and silica goes out
from residue. This is crucial step to remove the sodium of required specification
by varying counter current washing to ensure the residue free from sodium.
Extraction:
1. NaOH + Coal -NaAlO2 or Na3SiO2 + Insoluble residue

Filtration cum washing
2. NaAlO2 or Na3SiO2 + Insoluble residue + H2O Insoluble
Residue + NaAlO2 or Na3SiO2
Regeneration:
3. NaAlO2 or Na3SiO2 + Flue gas Soluble sodium salt +
Si02 or Al2O3
4. CaO + H2O Ca(OH)2
Soluble sodium salt + Ca (OH)2 CaCO3 + 2NaOH
Following the out comes of experiments;
1. Gangue matter (alumina + silica) can be selectively removed from iron
ore by leaching with sodium hydroxide. A properly leached ore contains
gangue at a level of 4.0%. The iron loss from the ore can be limited to
less than 2%.
2. The leached ore has to be washed in a counter current loop operation in
order to reduce the alkalinity of residue .
The results show that gangue present in goethite, limonite, quartzite and
kaolinite can removed by alkali leaching, but those occurring in iron phase
could not. Hydrofluoric acid is most effective among the all kind of

inorganic and organic acids. Similarly, sodium hydroxide is the most
efficient leaching reagent between the all alkali and alkaline earth hydroxide.
Main advantage of this process are i) ease leaching of gangue matter in the
main process stream, ii) 85-90% recovery of ore, iii) improved iron value of
leached ore, now here an attempt has taken to make the process techno-
economic by recycling of alkali. Effective or optimize process of acid and
alkali recovery helps us to established the process feasibility. In current
experimental approach, we have designed the experiment such a way it
minimize the loss of alkali.
3. The gangue removal methodology developed by us in slurry extraction is
a novel process where chemical used are regenerated in a closed
operation.
4. Successful studies for extraction of gangues are on laboratory scale.
Further studies are needed to carry out for suitable to bench scale resulted
from laboratory study.
5. Reject or slime of iron ore has gangue content of around 14% to 16%.
This phosphorus can be leached out economically by proposed process,
which needs the requirements of the various industries.
6. The process consists of three step namely;
a. Extraction
b. Filtration cum washing
c. Regeneration

Table 2: Result of feed and treated ore with varying different parameters

Table 3: Optimum analysis of the ore and leachate


WE CLAIM:
1. A process for removing gangue matter coating alumina and silica from low
grade iron ore and iron ore reject slime comprising:
i) adding the sodium hydroxide to iron ore at 80-95 °C to form alumino-
silicate sodium salt;
ii) subjecting the soluble alumino-silicate sodium salt to the step of
washing following by filtration;
iii) regenerating sodium hydroxide from sodium alumino-silicate salt at a
temperature range of 80 to 90°C for 60 to 90 minutes.
2. The process as claimed in claim 1, wherein the step of extraction is
preformed preferably by preparing a slurry of sodium hydroxide dissolved in
water in a ratio from 1:5 to 1:20 and adding the iron ore material at a
temperature greater than 90°C at a reaction speed of 800 to 900 rpm for a period
of 120 minutes to form sodium-alumino silicate and sodium silicate.
3. A process as claimed in claim 1, wherein the step of filtration and
regeneration are carried out for a period of 1 hour and 30 minutes
respectively.
4. The process as claimed in claim 1, wherein for the step of regeneration,
the salt used is selected from calcium oxide and calcium hydroxide.

5. The process as claimed in claim 1, wherein the particle size of iron ore is
below 25 micron.
6. The process as claimed in claim 1, wherein the concentration of sodium
hydroxide 25% by weight.
7. The process as claimed in claim 1, wherein the 85% of sodium hydroxide
is regenerated.
8. The process as claimed in claim 1, wherein the 85% yield of ore having
iron value of 67-68%.

A process for removing gangue matter coating alumina and silica from low
grade iron ore and iron ore reject slime comprising: adding the sodium
hydroxide to iron ore at 80-95°C to form alumino-silicate sodium salt;
subjecting the soluble alumino-silicate sodium salt to the step of washing
following by filtration; regenerating sodium hydroxide from sodium alumino-
silicate salt at a temperature range of 80 to 90°C for 60 to 90 minutes.