FIELD OF INVENTION
The present invention relates to an apparatus which generates information on
theoretical yield of the coal and minerals concentrate at different impurities level.
More particularly, the invention relates to an improved float-sink apparatus
adaptable to determine beneficiation prospects of coal, metallic, non-metallic ore
and, industrial minerals in a beneficiation process. The invention further relates
to a method of operating an improved float-sink apparatus.
BACKGROUND OF THE INVENTION
In case of coal or any other mineral, beneficiation prospect of the feed is
evaluated by graphically developing a curve which indicates theoretical yield
values of the concentrate at different impurities level. The theoretical yield values
are considered as the maximum achievable yield at the corresponding impurities
level in the concentrate. This is a valuable information as it directly shows the
liberation status of the feed, concentrate yield versus grade relation and loss of
values in the reject. The theoretical yield values are compared with the actual
yield values of the plant or machine to arrive at the efficiency of the plant or the
machine. The general expression for the efficiency is = [(Actual
yield)/Theoretical Yield)] * 100.
Theoretical yield for coal is determined through a series of float - sink tests. The
process starts with the preparation of heavy media liquids of specific gravity 1.3

to 2.2 with intervals of 0.1. These liquids are prepared by mixing benzene, tetra-
chloro-ethylene and, bromoform in different proportions. The float - sink tests
are conducted with feed coal at size ranges identical to the size ranges fed in the
washery. The coal is first tested on 1.3 specific gravity liquid and the float
obtained is the purest coal in the feed. The sink is again treated on the next
higher specific gravity liquid which is 1.4. The process continues till float and sink
fractions are obtained from 2.2 specific gravity liquid. At the end of the process
along with one sink fraction, float fractions from each specific gravity liquids are
generated. All these fractions are then analysed for their ash content. Ash
content of the float from 1.3 specific gravity liquid is minimum which increases
successively for the rest of the float fractions and the lone sink fraction shows
the highest ash content. This trend is universal for coal as the specific gravity of
ash containing minerals is higher than pure coal matter. These set of data is
used to generate the theoretical yield - ash curve of washed (clean coal) and is
often described as the washability curve.
Although in case of coal the process described hereinabove is well established,
however in case of minerals such process is not that established as the liquids
used for float - sink tests of coal cannot be used in minerals as the specific
gravity of minerals are much higher than that of coal. In case of minerals, the
application of float - sink tests is industry specific and often not conclusive by
itself. For example, the known beneficiation methods followed in beach sand
minerals involves testing of the feed in bromoform (a liquid of specific gravity
2.88). The liquid separates all heavy minerals from the silicates. The heavy

minerals are then washed with acetylene prior to semi quantitative estimation of
minerals through microscopical method. In iron ore industry two different types
of methods are being used, but none of them is self sufficient. In the first
method, the atomised Ferro-silicon is mixed in different proportions with water to
create suspended solutions of solid which could provide mixtures of different
specific gravity. Thereafter, the feed iron ore is tested in the mixtures having low
to high specific gravity. The float fractions and the lone sink fraction are then
chemically analysed for their iron content. In case of minerals float fraction
contains more of impurities and the sink represents the purest form of minerals.
The known method is not self sufficient because of the difficulties in preparation
of high specific gravity medium through this prior art method. Therefore, this
known method fails to allow extension of the theoretical yield - grade curve to a
desired grade concentrate level. In the second method, three separate specific
gravity liquids namely; ethylene bromide, di-iodomethane and clarici solution of
specific gravity 2.96, 3.30 and 4.03 respectively, are used in a sequence. These
liquids are immiscible to one another and thus, liquids of intermediate specific
gravity cannot be generated by mixing which remains the major disadvantages
of this known method. The second method generates a few discrete theoretical
yield values corresponding to concentrate grade, instead of a continuous curve
and thereby the purpose of the tests is often partly defeated. Furthermore, a
liquid of specific gravity higher than 4.03 is often required to separate iron
concentrate of desired grade from a poorly liberated ore. In such cases, the
theoretical yield of the concentrate cannot be obtained from this test.

In addition, the float - sink analysis is carried out with organic liquids which are
not environment friendly and often hazardous. Most of these liquids are costly
and not readily available in the market. Owing to these disadvantages, the float
- sink tests are not a regular practice in mineral sector resulting to either yield
loss or deterioration of the concentrate quality in the plant.
In the suggested method a complete fluidization is defined as the state where
the volume of voidage becomes equal to the volume of the particles. Position of
particles during complete fluidization depends on the force balance of three
important forces acting on the particle. These forces are weight, buoyancy and,
drag. Particles of same size include same buoyancy and drag assuming an
uniform voidage around the particles. However, weight of these particles differs
which is the function of the respective specific gravity. Therefore, depending on
the specific gravity these particles attain their terminal velocity. The heaviest
category of particles show highest terminal velocity and reaches to the bottom of
the fluidization column earlier than other category of particles. The next category
of heavier particles follows the trend and forms the next layer. The process
continues and layers are formed with successive layers each lighter than the
previous. However, these layers are not very stable and some degree of mixing
cannot be avoided, as these particles realize more drag due to less voidage
around them as soon as they tend to settle to the bottom. With this increased
drag, the particles again get partially fludized and allow the fluid to flow through
the bed. Therefore, these layers are dynamic in nature and a partial mixing is
expected. During fluidization, there is another possibility for example, some of
the particles tend to

remain in the fluidized state at applied superficial water velocity as these
particles attain zero terminal velocity. To allow these particles to segregate, the
superficial water velocity is lowered to the next lower level. The process is
continued in steps till all fluidized particles are segregated and settled to the
bottom.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of generating a
relationship between theoretical yield and grade level of concentrates (of coal
including minerals) for determining the benefication prospects of coal and
mineral.
Another object of the invention is to propose a method of generating a
relationship between theoretical yield and grade level of concentrates (of coal
including minerals) for determining the beneficiation prospects of coal and
minerals, which is equally effective for clean coal including all kinds of minerals.
A still another object of the invention is to propose a method of generating a
relationship between theoretical yield and grade level of concentrates (of coal
including minerals) for determining the beneficiation prospects of coal and
minerals, which is cost-effective and easy to implement.
Yet another object of the invention is to propose a method of generating a
relationship between theoretical yield and grade level of concentrates (of coal
including minerals) for determining the beneficiation prospects of coal and
minerals, which is environment - friendly.

A further object of the invention is to propose a method of generating a
relationship between theoretical yield and grade level of concentrates (of coal
including minerals) for determining the beneficiation prospects of coal and
minerals, which is enabled to handle larger volume of feed materials including
heterogeneous type of feed.
A still further object of the invention is to propose an improved float - sink
apparatus to implement the method of the invention.
SUMMARY OF THE INVENTION
The known float - sink apparatus uses liquids of different specific gravity to
classify the feed into different specific gravity classes. According to the invention,
the improved float - sink apparatus adapts a fluidization technique for the same
purpose. The apparatus primarily constitutes a fluidization column wherein the
superficial water velocity is controlled by a pump, and a by pass line including a
valve. A homogenization chamber is placed below the fluidization column to
reduce the turbulence of water flow inside the fluidization column. The
homogenization chamber and the fluidization column are separated by a first fine
mesh screen, and a concentric cylinder of smaller height is fitted inside the
fluidization column which holds the particle before and after fluidization. A
second fine mesh screen is placed between the fluidization column and an upper
outlet of the fluidization column is provided to prevent elutriation of coarser
particle. The upper outlet has the provision of draining out the overflow water

vis-a-vis re- circulating the water to a tank. The pump draws water from the tank
which are connected via a water line. Flow of water is measured through a
rotameter. An outlet valve is provided at the bottom of the fluidization column to
drain out the water from the column at the end of the fluidization test. According
to the inventive method, the feed is fluidized with a superficial water velocity
which causes the particle to segregate based on their specific gravity. After the
fluidization and consequent particle segregation steps, the superficial water
velocity is brought down to zero and then the water in the column is drained out.
This process enables segregation of particles in layers with a downward
increasing density. These layers are then separated and chemically analysed.
Data generated from the testing process establish a theoretical yield - grade
relationship for the concentrate.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1(a) shows a schematic diagram of an improved float - sink apparatus
according to the invention.
Fig. 1(b) shows a schematic diagram of a small cylinder disposable inside the
apparatus of Fig. 1(a) during the test.
Fig. 2 schematically shows a step of feed preparation in a process to determine
the beneficiation prospects of coals and all minerals according to the invention.

Fig. 3 schematically shows a step adopted for separating fractions of different
specific gravity material from a composite closed size feed.
DETAILED DESCRIPTION OF THE INVENTION
The prior art discussion establishes that the process of particle segregation based
on their specific gravity through fluidization is possible for particle of similar size
and shape. However, in practice, feed containing particles of same size and
shape is not achievable although a process can be designed to prepare feed
close to the theoretical assumption. According to the invention, the feed is
prepared by screening a feed of close sized fractions and then each of these
fractions is separately tested in the fluidization apparatus. The influence of
particles shape is thus eliminated as the same cannot be controlled in any of the
beneficiation process.
As shown in figure - 1, a small cylinder holds particles for which float - sink test
is to be carried out. On completion of the test, this cylinder again holds all the
settled particles. This is taken out after the fluidization test from the fluidization
column. The upper half of this small cylinder contains lighter particles and the
rest (bottom) half contains the heavier particles. These two fractions are
separated after each cycle of operation.
Now figure - 2 shows that the feed is prepared from -10.0 mm size fraction. The
main purpose of the feed preparation step is to generate closed size fractions

from the feed. Each of these size fractions is then separately tested in the
machine to generate relationship between theoretical yields and concentrate
grade for each size fraction as well as for the entire feed.
Figure - 3 further shows that the sink is indicated by dark colour and marked by
the numeral S whereas the float is of a lighter colour and indicated by the
numeral F. It may be noted that these set of operation segregate the pure heavy
and light material at the initial phase and then the intermediate fractions are
repeatedly fluidized so as to ensure a complete segregation of lighter and
heavier particles from the near gravity fractions.
EXAMPLE
As shown in fig. 2, the feed particles are screened to close size range using
manual/mechanical sieves. Each of these size fractions is tested separately to
find out the theoretical yield - grade relation for each size fractions. One such
size fraction is transferred to a small cylinder (11) and the total particle volume is
maintained little less than the cylinder volume. The fluidization column (4) having
a plurality of sample collection ports (7). The small cylinder (11) filled with
particles and placed at the bottom of the fluidization column (4). The flanges at
the bottom of the fluidization column (4), the small cylinder (11) and, a
homogenization chamber (6) are tightened with screws. A water pump (2) is
then switched on with a by pass valve full open and this allows water to flow
through the

fluidization column (4) at a lower superficial water velocity. An overflow line (8)
which otherwise is connected to a sump (1) is placed in the drain at the initial
stage of the test and a fresh water line (9) to the sump (1) is also kept full open.
Draining of turbid water through the overflow line (8) is allowed to continue for
some time so that slime/very fine particles adhering to the coarse particles are
drained. Once the water inside the fluidization column (4) is reasonably clear the
overflow line (8) is again placed on the sump and a valve of the fresh water line
(9) that supplies water to the sump (1) is completely closed. The circuit is then a
closed circuit.
In the next stage, the superficial water velocity in the fluidization column (4) is
increased in steps by manipulating the valve placed in a bypass line (5). The
superficial water velocity is increased till the fluidized bed attains a volume which
is twice of the particle volume. For any particular particle type a mark is inserted
on the fluidized column (4) before commencement of the test. The superficial
water velocity is maintained for few minutes in this state to allow the particles to
segregate. In the subsequent stages, the superficial water velocity is reduced in
steps which causes all particles to settle inside the small column as per their
density with the lighter particles settling at the top. The Bypass valve is again
fully opened and then the pump (2) is switched off. Water in the fluidized column
(4) is drained out by opening the valve placed just below the homogenization
chamber (6).

The small column in which particles have settled is then taken out and placed
upside down on a steel plate. The small cylinder (11) is then lifted a bit and
dragged over the plate so that particles come out to form the bed. The particle
bed is then divided into two parts i.e., the lighter and heavier fraction. The
process is repeated several times to generate sufficient quantity of light and
heavy fraction. Following the steps of Fig. 3 fluidization tests are carried out with
these two fractions to generate eight different specific gravity fractions. In case
of iron ore feed, each of these fraction is then weighted and chemically analysed
for its iron, alumina content. Other chemical components may be analysed as per
the feed and the benefication requirement. With these data the theoretical yield
and grade (with respect to total iron, alumina and silica) is plotted. Similar curve
is generated for other metallic, non-metallic minerals and, coal.
The invention provides an improved float - sink apparatus, which uses the
fundamental principle of fluidization in separating particles of different specific
gravity when the feed is prepared with closed size particles.
According to the inventive method water is only used as opposed to the prior art
method in which chemicals of different specific gravities are used for separating
particle. Therefore, the method of this invention is environment friendly, not
hazardous and less costly.
The inventive method can be used for the feed with wide size distribution and
also for larger - volume of feed since, the method does not require using costly

and hazardous chemical. It may be noted that larger quantity of feed material is
often essential for the feed constituting heterogeneous particles.
The present method is useful for coal, metallic and, non-metallic ores and
industrial minerals. For the existing methods, for metallic and non-metallic
minerals, a theoretical yield - grade relationship is drawn based on float - sink
analysis, due to limitation in the availability of various types of specific gravity
liquids. Thus, inferences drawn through interpolation from the set of the few
data points, which often mislead the operator. In contrast thereto, the inventive
method is enabled to generate a large number of points and provides more
reliable data.
The inventive method is adaptable to all coal, metallic, non-metallic ore and
industrial mineral mines and beneficiation processes. The operation is easy, quick
and does not demand a lot of skill.
The improved apparatus provided by the invention, is portable and hence can be
used in the mine site, inside the beneficial plant. Even the apparatus has its use
for the concentrate and reject stream as the test results indicates misplacement
of quality grade coal or ore particles in either of the stream.

The apparatus is capable to indicate the process efficiency including efficiency of
any unit operation. The apparatus is further adaptable for sensitivity study of a
plant with fluctuation in feed grade, throughput and operating parameters.
The apparatus is capable to generate data adaptable in optimising a plant
operation and also in designing a new plant. Therefore, a major contribution of
this apparatus is improving the concentrate yield.
The method additionally indicates the liberation status of coal, metallic, non-
metallic ore and industrial minerals and predicts their response to gravity
separation methods.

WE CLAIM
1. An improved float-sink apparatus adaptable to determine beneficiation
prospects of coal, metallic, non-metallic ore and industrial minerals,
comprising:
- a fluidization column (4) having a plurality of sample collection ports (7),
is enabled to accommodate a cylinder (11) filled with particles at the
bottom of the column (4);
- a homogenization chamber (6) disposable at the further bottom of the
column (4), the chamber (6), the cylinder (11), and the column (4) can be
releasably attached together via screw means;
- a water sump (1) connected to a pump (2) for supply of water at a lower
superficial water velocity to the column (4), the sump (1) being provided
with a fresh water inlet pipe (9), and a removable overflow line (8) for
draining-out the turbid water including very fine particles produced during
the test;
- a first valve with a bypass line (5) capable of being manipulated to step-
wise increase the velocity of the superficial water till such time the volume
of the fluidized bed attains double the particle volume;
- a second valve disposed below the homogenization chamber (6) which is
enabled to open for draining out water from the fluidized column (4) when
the increased superficial velocity after maintaining for a predetermined
period to allow the particles to segregate, is reduced in stages to cause

settling of all the particles, and the pump (2) being de-activated with the
first valve fully-opened; and
- a steel plate on which the cylinder (11) can be dragged over to enable the
particles to come out from the fluidized bed, the particles being divisible
into two fractions capable of generating a plurality of fractions with
different specific gravity, each fraction after weighting and chemical
analysis provide a large plurality of data adaptable to produce an accurate
graphical relationship between the theoretical yield and grade of the coal
and other minerals.
2. The apparatus as claimed in claim 1, wherein a first fine mesh screen is
placed between the homogenization chamber (6) and the fluidization
column (4).
3. The apparatus as claimed in claim 1, wherein a second fine mesh screen
is disposed between the fluidization column (4) and an outlet configured
on the upper part of the column (4).
4. An improved float-sink apparatus adaptable to determine beneficiation
prospects of coal, metallic, non-metallic ore and industrial minerals, as
substantially described and illustrated herein with reference to the
accompanying drawings.

The invention relates to an improved float-sink apparatus adaptable to determine
beneficiation prospects of coal, metallic, non-metallic ore and industrial minerals,
comprising a fluidization column (4) having a plurality of sample collection ports
(7), is enabled to accommodate a cylinder (11) filled with particles at the bottom
of the column (4); a homogenization chamber (6) disposable at the further
bottom of the column (4), the chamber (6), the cylinder (11), and the column
(4) can be releasably attached together via screw means; a water sump (1)
connected to a pump (2) for supply of water at a lower superficial water velocity
to the column (4), the sump (1) being provided with a fresh water inlet pipe (9),
and a removable overflow line (8) for draining-out the turbid water including
very fine particles produced during the test; a first valve with a bypass line (5)
capable of being manipulated to step-wise increase the velocity of the superficial
water till such time the volume of the fluidized bed attains double the particle
volume; a second valve disposed below the homogenization chamber (6) which
is enabled to open for draining out water from the fluidized column (4) when the
increased superficial velocity after maintaining for a predetermined period to
allow the particles to segregate, is reduced in stages to cause settling of all the
particles, and the pump (2) being de-activated with the first valve fully-opened