FIELD OF THE INVENTION
The present invention relates to a separation process using binary mixture of
spheres or beads. The particles which are smaller than pore size of the binary
mixture pass through the packed bed while larger particles are held back on the top
layer and along the height of the assembly and thus in the process sizing takes
place.
BACKGROUND OF THE INVENTION
In case of mineral beneficiation, sizing refers to the process of separating mineral
particles as per the particles size. Many a times, certain process or equipment
require feed particles of a certain size or size range therefore feed materials is
desirably sorted according to size in order to achieve the desired effect. The
attention to particle sizing is especially critical in the fine particle range due to the
poor efficiency of existing screen-type separators. Moreover, efficient sizing is
needed in every mineral processing plant for achieving desired liberation size and is
usually done for the following reasons:
1. Scalping
2. Size separation of the material into a coarse and fine fraction for
sized products or for processing in coarse and fine circuits
3. Dewatering
There are many types of sizing equipment, commercially available for the purpose of
sizing out particles. A number of problems are faced while sizing out the particles
such as:

1. blinding or clogging of screen panels due to the presence of near size
particles.
2. Maintenance after blinding of screens.
3. abrasion of screen panels.
4. Contaminated products due to holes in screens.
5. Added manpower requirements due to frequent screen panel changes.
6. Operational hard work
A number of attempts have been made in the past to overcome the above listed
problems. European patent EP1137497B1 describes the use of individual or nested
sieves to separate the particles of cohesive material according to size. US patent
US7810648B2 discusses the use of screen assembly for separating mineral particles
according to size. US Patent US20100282648 describes the use of vibrating
screening element submerged in a reservoir containing slurry to avoid the problems
of conventional screening processes and to improve the classification performance of
wet screening equipment. US patent US20120199521A1 describes the invention of
improved screen panel to withstand abrasion. Canadian patent CA2828181A1 relates
to an invention which discusses about innovative screen panels which have high
open area and low thickness. US patent US201000300943A1 discloses the invention
of using blends of virgin and recycled polyurethane as well as method of
manufacturing screen panels and methods of handling worn screen panels. Patent
no. WO1999010112A1 discloses the invention of an improved mineral screen
comprising a nonwoven mesh membrane in the form of an endless belt made of a
thermoplastics material. However, there is no invention disclosed in the art that
describes the screening of particle using packed bed of binary mixing of spheres.
The disclosed methods in the prior art have problems in terms of maintenance and
also designing of the screening media as per the feed requirements.

OBJECTS OF THE INVENTION
It is therefore an objective of the invention to provide a method for splitting the coal
or mineral feed into two products of different size.
It is a further objective of the invention to provide a method to use binary mixture of
spheres as a screening media to eliminate the problem of clogging or blinding of
screen panels.
It is a further objective of the invention to provide a screening media having pores,
thereby facilitating the mineral ores to pass through the pores easily and also
preventing clogging.
It is a further objective of the invention to provide a screening media to achieve
desired cut size.
It is a further objective of the invention to provide an apparatus to screen the
material according to its size.
SUMMARY OF THE INVENTION
The invention involves using metallic spheres or bead to act as screening media.
Two sized spheres of varying diameters are selected as per the sizing requirement of
the media. The volume density, ratio of small spheres and large spheres and height
of the filtering column are important factors and are dependent on the sizing
requirements. The feed material is mixed with water and then poured in a container
containing screening media of spheres. The container includes the screening media
along its length with a perforated plate at the bottom. The feed particles size as per
the current invention is below 500 microns.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 (a) Shows a schematic diagram of a side and bottom view of the container.
Figure 2 shows a schematic diagram of the apparatus according to the invention.
Figure 3: Size analysis of feed and undersize material.
DESCRIPTION OF THE INVENTION:
The process of screening an ore feed as per the current invention comprises the
following steps:
a) Preparing the slurry by mixing water and the ore feed, which needs to be
screened.
b) Preparing a binary mixture of steel spheres by vigorously shaking and tapping
it.
c) Placing the mixture of steel spheres in container which is open at one end
and closed at other end by a perforated plate.
d) Passing the slurry through a bed of binary mixture obtained in step b, to
capture over size particle.
e) Collecting underflow passed material and overflow deposited material
separately.
In the present description the term "ore" comprises coal as well as metallic, non-
metallic and mineral ores with a size is below 500 microns The term "binary" is
meant that two different size of spheres of required quantity are used for making
the packed bed mixture. In the present invention diameters of large spheres and
small spheres varies from 5-15mm and 1-2 mm respectively. Though the invention
has been described by developing a screening media comprising steel spheres of

two sizes however, steel spheres of more than two sizes can also be used. The
spheres as per the current invention can be made up of steel, metals or polymers.
Non-sticky polymers are preferred which do not stick to the ore feed slurry. Also, ore
particles of two different size classes can also be used for making the binary
mixture.
The ability of binary mixture to hold the particular size fraction depends upon its
porosity and the pore size. Further, Porosity and pore size of any packed bed, made
up of binary mixture of spheres, can be controlled by the size ratio and percentage
of large spheres by volume in the mixture, wherein size ratio is defined as ratio of
diameters of large spheres to diameter of small spheres. Sieving or screening takes
place when slurry containing suspended particles to be screened is passed through
the packed bed. The particles in the suspension which are smaller than the pore size
of the packed bed passes through the bed and are collected as undersize material
whereas, particles which are larger than the pore size gets blocked are recovered as
oversize material.
The ore particles encountered in real life situations are never perfectly spherical in
shape. Generally, Particles are considered to have three orthogonal axes and
dimensions measured along these axes are used to characterize the irregular
particles. Therefore, there also arises a probability that a particle having its size
larger than the pore size may pass through the bed depending upon orientation and
position of approach. This phenomenon is probabilistic in nature and it also
describes the inefficiency of screening process. This phenomenon is common to all
screening media. However, in the present case the bed height of the binary mixture
in the container plays an important role. Bed height controls the residence time of
particles in the system and also describes the probability with which these particles
are presented to different pores distributed along the bed height.

The invention is further elucidated on hand of the non-limiting example shown
in the drawing. As shown in figure 1(a) the container holds the binary mixture of
the spheres which will be used as a sieving media. This container is open at one end
and perforated at other to hold the binary mixture of spheres. Figure 1(b) shows the
container filled with binary mixture of spheres which will be used as the screening
media.
As shown in figure 2, feed containing ore particles of different size for which sieving
has to be done is fed from the top. Small particles which have their representative
size less than the pore size of the binary mixture pass through and are collected in a
container as undersize material. The operation may be continued until the media
gets choked due to pores blockage and there is no further recovery of undersize
material possible. The relative size of the underflow and overflow material may be
determined using any particle size technique commercially available. Large particles
can be recovered as oversize material by dismantling the entire bed and passing it
over the suitable to separate spheres (screening media) from ore particles.
Examples:
Embodiments of the present invention are further illustrated by the following
examples. The examples are for illustrative purposes only and thus should not be
construed as limitations in any way.
Example I: size ratio 5:1
Tests were conducted for different combinations of volume fractions of large sphere
in the total volume of the binary mixture for the size ratio of 5:1. Iron ore slimes
having d80 passing size of 90 microns was used as the feed material. Figure 3, shows
the Size analysis of underflow fraction i.e. sieved material obtained when a
combination of 60% volume fraction of large spheres and 40% small spheres was

used as the binary mixture i.e. screening media. It may be observed that d80 passing
size of the screened material is around 49 microns.
Example II: size ratio 10:1
Tests were conducted for different combinations of volume fractions of large sphere
in the total volume of the binary mixture for the said size ratio. Iron ore slimes
having d80 passing size of around 90 microns was used as the feed material. Figure
4, shows the Size analysis of underflow fraction i.e. sieved material obtained when a
combination of 60% volume fraction of large spheres and 40% small spheres was
used as the binary mixture i.e. screening media. Underflow material obtained was
observed to have d80 passing size 42 microns.
The current invention provides significant advantages in terms of ease of operation
and repeated use of the screening media. Further, screening media of the current
invention can be easily developed and customized depending upon the sizes of ore
feed that needs to be screened.
References:
Patent no. EP1137497B1
Patent no. US7810648B2
Patent no. US20100282648
Patent no. US20120199521A1
Patent no. CA2828181A1
Patent no. US201000300943A1
Patent no. WO1999010112A1

WE CLAIM :
1. A method for screening an ore feed, the method comprising:
a) preparing a slurry by mixing water and the ore feed;
b) preparing a binary mixture of spheres;
c) placing the binary mixture of spheres mixture in a container open at one end
and closed at other end by a perforated plate;
d) passing the slurry through a bed of binary mixture obtained in step c); and
e) collecting undersize particles as underflow and collecting oversize particles
which are trapped by the binary mixture.

2. The method according to claim 1, wherein the ore feed is coal, a metallic
mineral ore or a non-metallic mineral ore.
3. The method according to claim 1, wherein ore feed size is below 500 microns.
4. The method according to claim 1, wherein the slurry pulp density is in the
range of 15-35% solids by weight.
5. The method according to claim 1, wherein the spheres are made of steel.
6. The method according to claim 1, wherein the spheres are made of a non-
sticky polymer.
7. The method according to claim 1, wherein the spheres are made of a metal.
8. The method according to claim 1, wherein the binary mixture of spheres is
made of ore particles, wherein the sizes of spheres of binary mixture are
larger than sizes of the ore feed to be screened.

9. The method according to claim 1, wherein diameters of large spheres and
small spheres varies from 5 to 15mm and 1 to 2 mm respectively.
10. The method according to claim 1, wherein ratio of volume fraction of large
sphere to small sphere varies in the range of 40:60 to 70:30.
11. The method according to claim 1, wherein bed height of the binary mixture of
spheres is in the range of 8 to 12 cm.
12. An apparatus for screening of ore feed particles, the apparatus comprising:
a binary mixture of spheres of different sizes wherein diameters of large
spheres and small spheres varies from 5-15mm and 1-2 mm respectively,
a container open at one end and closed at bottom by a perforated plate, the
binary mixture of spheres being put in to the container.
13. The apparatus as claimed in claim 12, wherein the binary mixture of spheres
is mixed homogenously in the container.
14. The apparatus as claimed in claim 12, wherein bed height of the binary
mixture of spheres is in the range of 8 to 12 cm.
15. The apparatus as claimed in claim 12, wherein the spheres are made of steel.
16. The apparatus according to claim 12, wherein the spheres are made of a non-
sticky polymer.
17. The apparatus according to claim 12, wherein the spheres are made of a
metal.

18. The method according to claim 12, wherein the spheres of binary mixture are
ore particles itself, wherein the sizes of spheres of binary mixture are larger
than sizes of the ore feed particles to be screened.

ABSTRACT

The present invention relates to a method of splitting the feed in to differing size
products, wherein feed can be coal, metallic, non-metallic, mineral ores or the like.
According to the method, binary mixture of spheres or beads is prepared which is
characterized by its size ratio and percentage of large spheres in the mixture. The
obtained binary mixture is then placed in a container which is open at one end and
closed by a perforated plate at other end, to hold the binary mixture. Slurry
containing coal or ore particles of different size fractions is fed from the open end
and the coarse particles are deposited on the top and along the height of the binary
mixture and an oversize fraction is obtained. Fine particles pass through the bed of
binary mixture and collected as underflow of undersized material. The invention also
discloses an apparatus to carry out the method.