FIELD OF THE INVENTION:
The present invention generally relates to the use of coal tar and wash oil,
one of the fractions of coal tar, produced during the coke making process of
coal as a reagent to enhance the hydrophobicity of the coal particles in a fine
coal flotation system to overall achieve the beneficiation of fine coal. More
particularly, the invention relates to a beneficiation process of coking coal
fines (-0.5 mm) to achieve an yield with acceptable ash value (14-15%).
BACKGROUND OF THE INVENTION:
Froth flotation is a process of separating valuable minerals from gangue
particles by utilizing the difference in their physico-chemical surface
properties. In case of coal, flotation is the most widely used method of
beneficiation used for the finer fraction (generally -0.5 mm) especially for the
metallurgical coal which can cover the cost of beneficiation. Coal flotation
makes use of the natural hydrophobicity of the carbonaceous matter in coal.
Air bubbles are introduced in the coal-water suspension where they get
attached to the hydrophobic particles and carry them to the froth phase. The
mineral matter in raw coal is comprised of hydrophilic minerals like clays
(such as kaolinite and montmorillonite), quartz, and carbonate minerals such
as calcite and dolomite, gypsum, and pyrite. These hydrophilic particles stay
wetted in the suspension and are removed later on. Several parameters affect
the coal flotation process which include material, chemical, operational and
equipment parameters. Among these parameters the chemical parameters
are the most easily controllable ones which can make the process more
efficient as well as economical. The type of reagents and their dosage are the
main chemical parameters. The reagents used for coal flotation are classified
as either collectors or frothers. The collectors used for coal flotation are
mostly organic compounds with basic purpose to selectively form a

hydrophobic layer on the coal surface in the flotation pulp and thus provide
conditions for attachment of the hydrophobic particles to air bubbles and
recovery of such particles in the froth product. Theoretically a high rank
bituminous coal should require very less amount of collector for flotation
owing to its natural hydrophobic nature. However, for low-rank coals or
weathered coals containing greater amounts of oxygen, large collector
dosages are required in order to obtain even moderate recovery of coal.
Hydrocarbons like kerosene, diesel oil, fuel oil etc. are the most commonly
used collectors for coal flotation. Since these oils are distillates of crude
petroleum oil, they are very costly with limited resources. Because of their
limited reserves they are preferred to be used as source of energy rather
than as a reagent in coal beneficiation. So they are used in only those coal
preparation plants where profit is substantially high and not for low rank or
oxidised coals where earning are low. Keeping this in mind a lot many
scientists have worked to develop new collectors for coal flotation. But again
the cost and availability of these collectors is a question and hence their
commercial use is still not confirmed. So in order to find better and cheap
reagents the search has become wider and this has led to the opening of new
sources of hydrocarbons such as the waste oils (all kinds like spent animal
oils, motor oils, edible vegetable oils etc.), by-products obtained during the
coke making process of coal etc.. The by-products of the coal coking process
i.e. coal tar and its derivatives have been used in coal flotation the details of
which are provided in Table 2.

However the above patent applications and the technologies hardly shows
much improvement in yield during the beneficiation of coking coal fines using
coal tar and wash oil as collector for flotation. Moreover the impetus for
establishing either coal tar or wash oil as a suitable collector for coking coal
fines is deficient as the above technologies deal with numerous different
fractions or derivatives which make the process quite complex. Hence simple
and easy processes to prove the suitability of coal tar as well as its derivative
wash oil, for use as collector during the flotation of coking coal fines is
required along with substantial increment in yield at low ash value.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a beneficiation process of
coking coal fines (-0.5 mm) to achieve an yield with acceptable ash value
(14-15%).
Another object of the invention is to propose a beneficiation process of coking
coal fines (-0.5 mm) to achieve an yield with acceptable ash value (14-15%)
which reduces the cost of flotation of coking coal fines by using cheaper
reagents.
A further object of the invention is to propose a beneficiation process of
coking coal fines (-0.5 mm) to achieve an yield with acceptable ash value
(14-15%) which allows utilization of otherwise waste coal tar and wash oil.
A still further object of the invention is to propose a beneficiation process of
coking coal fines (-0.5 mm) to achieve an yield with acceptable ash value
(14-15%), which uses both coal tar including its derivative wash oil as the
collector.

SUMMARY OF THE INVENTION
As per the invention, a process for beneficiation of coking coal fines i.e. less
than 0.5 mm comprises a flotation process where in pre-calculated amounts
of selected reagents is added to coal-water slurry inside a flotation cell
followed by vigorous mixing and then air is flown through the slurry to form
air bubbles and carry the low ash coal particles to the froth phase where it is
collected in a separate tray. The froth thus obtained is filtered and dried and
weighed to calculate the yield after which ash analysis of the froth is done to
determine its ash. The remaining slurry in the flotation cell is also transferred
to another tray and subjected to filtration and drying. After this its weight is
measured to get the yield of the tailings and ash analysis done. The flotation
test is performed in a standard laboratory mechanical flotation machine which
has a cell of capacity 2.5 liters. The amount of feed material (i.e. -0.5 mm
coking coal fines) taken depend on the pulp density of the slurry to be
prepared and in this case it is fixed at 10% by weight. After adding the feed
coal sample to the water in the cell, proper mixing of the coal-water slurry is
done by rotating the agitator of the cell at a constant speed of 800 rpm. This
speed of the agitator is fixed throughout the process. The mixing is done for
5 minutes after which a calculated amount of the collector which in this
invention is either coal tar or its derivative wash oil. The dosage of the
collector is varied from 0.25 kg/t to 2.0 kg/t with values as 0.25kg/t, 0.5 kg/t,
0.75kg/t, 1.00 kg/t, 1.25 kg/t, 1.5 kg/t, 1.75 kg/t and 2.00 kg/t. With these
dosages two sets of experiments are done, one with coal tar and the other
with wash oil. After the addition of collector mixing is again done for another
10 minutes. Finally Methyl Iso-butyl Carbinol (MIBC), a common frother used
for coal flotation is added at a dose of 0.1 kg/t which is fixed for all the tests.
Again a mixing for another 5 minutes is done so that a uniform mixing of the
reagents is done throughout the slurry. Then air at a fixed rate of 3 lpm is
flown through the slurry which resulted in the formation of air bubbles and

finally a stable froth. The low ash coal particles because of their hydrophobic
nature get attached to the air bubbles and come to the froth phase where
they are recovered in another tray using a scraper. The froth is collected for
2.5 minutes after which the air flow is cut off and agitator is switched off. The
only parameter which is varied during the flotation of coking coal fines using
coal tar or wash oil as the collector is the collector dosage. Whereas all the
other parameters i.e. pulp density (amount of feed and water), agitator
speed, airflow, frother dosage, conditioning time and collection time are
fixed.
These together with the other aspects of the invention, along with the various
features of novelty that characterize the invention, are pointed out with
particularity in the description, along with the abovementioned summary,
annexed hereto and form a part of the invention. For a better understanding
of the invention, its operating advantages and the specified object attained
by its uses, reference should be made to the accompanying drawings and
descriptive matter in which there are illustrated embodiments of the
invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
FIG. 1 shows a general flotation process.
FIG. 2 shows the mechanical flotation cell used in the current invention.
DETAILED DESCRIPTION OF THE INVENTION
As per the invention, a process for beneficiation of coking coal fines i.e. less
than 0.5 mm comprises a flotation process where in pre-calculated amounts
of selected reagents is added to coal-water slurry inside a flotation cell
followed by vigorous mixing and then air is flown through the slurry to form
air bubbles and carry the low ash coal particles to the froth phase where it is

collected in a separate tray. The froth thus obtained is filtered and dried and
weighed to calculate the yield after which ash analysis of the froth is done to
determine its ash. The remaining slurry in the flotation cell is also transferred
to another tray and subjected to filtration and drying. After this its weight is
measured to get the yield of the tailings and ash analysis done. The flotation
test is performed in a standard laboratory mechanical flotation machine which
has a cell of capacity 2.5 liters. The amount of feed material (i.e. -0.5 mm
coking coal fines) taken depend on the pulp density of the slurry to be
prepared and in this case it is fixed at 10% by weight. After adding the feed
coal sample to the water in the cell, proper mixing of the coal-water slurry is
done by rotating the agitator of the cell at a constant speed of 800 rpm. This
speed of the agitator is fixed throughout the process. The mixing is done for
5 minutes after which a calculated amount of the collector which in this
invention is either coal tar or its derivative wash oil. The dosage of the
collector is varied from 0.25 kg/t to 2.0 kg/t with values as 0.25kg/t, 0.5 kg/t,
0.75kg/t, 1.00 kg/t, 1.25 kg/t, and 1.5 kg/t. With these dosages two sets of
experiments are done, one with coal tar and the other with wash oil. After the
addition of collector mixing is again done for another 10 minutes. Finally
commonly used frothers Methyl Iso-butyl Carbinol (MIBC) & Pine oil were
used for coal flotation is added at a dose of 0.1 kg/t which is fixed for all the
tests. Again a mixing for another 5 minutes is done so that a uniform mixing
of the reagents is done throughout the slurry. Then air at a fixed rate of 3
lpm is flown through the slurry which resulted in the formation of air bubbles
and finally a stable froth. The low ash coal particles because of their
hydrophobic nature get attached to the air bubbles and come to the froth
phase where they are recovered in another tray using a scraper. The froth is
collected for 2.5 minutes after which the air flow is cut off and agitator is
switched off. The only parameter which is varied during the flotation of
coking coal fines using coal tar or wash oil as the collector is the collector

dosage. Whereas all the other parameters i.e. pulp density (amount of feed
and water), agitator speed, airflow, frother dosage, conditioning time and
collection time are fixed.
The feed coal used in the present invention is a medium coking coal and its
proximate analysis is given in Table 1 showing a fixed carbon content of more
than 50%.
Collectors are organic chemical compounds with basic purpose to selectively
form a hydrophobic layer on a given mineral surface in the flotation pulp and
thus provide conditions for attachment of the hydrophobic particles to air
bubbles and recovery of such particles in the froth product. The role of
collectors during flotation is very crucial and by the use of proper suitable
collector, the yield can be increased considerably. In case of coal both
aliphatic as well as aromatic hydrocarbons oils are used but aromatic or
highly branched compounds are known to give better performance. Coal tar
being composed of hundreds of polycyclic aromatic hydrocarbons
(compounds are mainly polycyclic aromatic hydrocarbons (PAHs), phenolic
compounds, and oxygenated and nitrogenated aromatic bases and, to a
lesser extent, their alkyl derivatives), indeed presents a good potential to be
used as collector for coal flotation. Wash oil is obtained during the fractional
distillation of coal tar at temperature 230-260 ºC. Wash oil is a mixture of
aromatic compounds mostly nitrogen based such as quinoline, isoquinoline,
carbazol and acridine with very low freezing point and excellent solvent
properties.


The results of the experimental work carried out are given in Table 2 for coal
tar and Table 3 for wash oil. The dosage of the collector with 0 kg/t shows
the flotation test without any collector and is taken as the base value. The
ash of the product without any collector is 15.84% and yield is only 35.36%.
As the coal tar is used the yield of the product increases with increase in
product ash also. The best result for coal tar is obtained at a dosage of 1.5
kg/t with yield of 52.5% at an ash of 17.04%. With the use of wash oil also
there is substantial increase in yield of the flotation product. Here better
results are obtained at all dosages but the optimum value of wash oil as
collector is 0.25 kg/t with product yield of 61.67% and ash of 14.19%.

WE CLAIM :
1. A beneficiation process for coking coal fines of size less than 0.5 mm
having fixed carbon content of more than 50%, the process
comprising:
mixing coal and water in the cell of a mechanical flotation machine
by rotating the agitator and adding coal tar or wash oil to the slurry;
mixing the slurry again after which a frother is added to the mixture
followed by further mixing for ; blowing air through the cell to form a
froth which is collected in a separate tray with a scraper for a time
period 1-4 mins.; and stopping the air flow and rotation of the
agitator and recovering the slurry left in the cell .
2. The process as claimed in claim 1, wherein the frother used is methyl
isobutyl carbinol (MIBC) with dosage of 0.1 kg/t.
3. The process as claimed in claim 1, wherein the frother used is pine oil
with dosage of 0.1 kg/t.
4. The process as claimed in claim 1, wherein the pulp density of the
slurry is 8-20% solids by weight and the volume of the slurry is same
as that of the flotation cell.
5. The process as claimed in claim 1, wherein the speed of the agitator of
the flotation cell is 800 rpm.

6. The process as claimed in claim 1, wherein the air flow through the
coal-water slurry is 2-5 lpm.