Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Method for Froth Flotation
FIELD OF THE INVENTION
This invention relates to a method for the separation of particles of oil or
hydrophobic
minerals from a water or mineral pulp or slurry. In particular the invention
relates to a
new and useful method for froth flotation.
BACKGROUND OF THE INVENTION
In the mining and mineral processing industries froth flotation has long been
used as a
means to separate or concentrate valuable or desirable minerals from waste
materials or
gangue. In flotation, finely ground particles of an ore are typically added to
water to
produce a slurry that is then treated with a reagent to make the surface of
one or more
mineral components sufficiently hydrophobic such that the mineral surface will
preferentially adhere to an air bubble rather than remain wetted. The
remainder of the
ore is preferably made or kept sufficiently hydrophilic to enable the
hydrophobic and
hydrophilic components to be separated from each other when placed in an
aerated
volume of water. That is, when immersed in water and subjected to an injected
stream
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of air, small bubbles attach to the hydrophobic mineral components causing
them to
float to the surface where they can be collected and removed for further
processing. The
remaining hydrophilic components tend to settle at the bottom of the volume of
water
and can be extracted therefrom using a variety of mechanical methods. To aid
in the
separation of the mineral components a further chemical may be added to
produce a
controllable froth. Depending upon the nature of the minerals contained within
an ore,
the component sought to be concentrated may be the hydrophobic component that
is
separated with the froth or, in other cases, the desired component may be
hydrophilic
and may remain immersed in the water.
For separation to be achieved in a flotation system air bubbles must come into
contact
with hydrophobic particles within the flotation cell or the phase separation
vessel. To
achieve a desired throughput and to ensure that all of the hydrophobic
component has
the opportunity to be exposed to injected air, flotation cells have previously
tended to
be relatively large pieces of equipment that often contain an impeller to
agitate the slurry
and to disperse bubbles throughout the cell. While relatively effective, such
equipment
tends to be expensive to manufacture, difficult or essentially impossible to
transport
from site to site, and can consume relatively large amounts of energy through
the use of
electric motors needed to drive the impeller.
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SUMMARY OF THE INVENTION
The present invention provides a method for froth flotation that permits the
separation of fine particles of oil or hydrophobic minerals from an aqueous
mineral pulp or slurry by creating an improved environment for the
attachment of air bubbles onto hydrophobic particles to permit subsequent
separation in a flotation cell or phase separation vessel. Utilization of the
inventive method allows for the use of substantially smaller separation
vessels than conventional flotation cells and systems while attaining
generally the same or comparable levels of recovery. In
particular,
employment of the method described herein substantially reduces the
volume of air that is required during the flotation process, thereby allowing
for the use of smaller vessels which in turn can have a significant impact on
the capital cost of equipment, the size of the processing plant necessary to
house the equipment and the overall operating costs of the plant.
Accordingly, in one of its aspects the invention provides a method of froth
flotation comprising the steps of delivering a pressurized stream of feed
slurry and a pressurized stream of air to a contactor vessel, said feed slurry
including a mixture of particles of oil or hydrophobic materials and water;
through the use of a flow obstruction, disposed within a flow path of the
contactor vessel between in input and an output thereof, maintaining said
contactor vessel at a pressure of from 18 to 25 pounds per square inch
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gauge and causing said feed slurry and said stream of pressurized air to
intermix within said contactor vessel to create a mixture having a slurry-to-
air
ratio, measured after said flow obstruction, of from between about 1:1 to 1:5,
said mixing of said feed slurry and said air within said pressurized contactor
vessel allowing for the attachment of air bubbles to said particles of oil or
hydrophobic materials forming particle-bubble aggregates; maintaining the
flow of said feed slurry and said pressurized air through said contactor
vessel at a rate of from 1 to 3.5 meters per second, said contactor vessel
constructed to permit a slurry retention time of from 1 to 2 seconds at a flow
rate through said contactor vessel of from 1 to 3.5 meters per second; and,
thereafter, discharging the contents of said contactor vessel through said
flow obstruction into a separation vessel where said particle-bubble
aggregates form a froth for removal as a concentrate.
In a further aspect the invention provides a method of froth flotation for the
separation of a hydrophobic material from a hydrophilic material in an
aqueous slurry containing particles of both hydrophobic and hydrophilic
materials, the method comprising the steps of delivering a pressurized
stream of said slurry to a contactor vessel; injecting a stream of pressurized
air into said slurry within said contactor vessel, said air injected at a rate
sufficient to establish a slurry-to-air ratio, measured after a flow
obstruction
disposed within a flow path of the contactor vessel between an input port
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and an output port of the contactor vessel, of from between about 1:1 to 1:5
within said contactor vessel; maintaining said contactor vessel at an internal
pressure of from 18 to 25 pounds per square inch gauge such that said
slurry and permitting said stream of pressurized air to intermix to aid in the
attachment of air bubbles to at least a portion of said hydrophobic material
in
said slurry; maintaining said slurry and said air within said contactor vessel
for a retention time of from 1 to 2 seconds; and, thereafter discharging said
slurry and said air from said contactor vessel into a separation vessel where
said hydrophobic material with air bubbles attached thereto forms a froth for
removal as a concentrate.
Further aspects and advantages of the invention will become apparent from
the following description taken together with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show more clearly
how it may
be carried into effect, reference will now be made, by way of example, to the
accompanying drawings which show the preferred embodiments of the present
invention
in which:
Figure 1 is a schematic side sectional view of an apparatus for froth
flotation for use in
accordance with a preferred embodiment of the method comprising the present
invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention may be embodied in a number of different forms. However,
the
specification and drawings that follow describe and disclose only some of the
specific
forms of the invention and are not intended to limit the scope of the
invention as defined
in the claims that follow herein.
An apparatus constructed for use when practicing a preferred embodiment of the
method
comprising the present invention is shown schematically in side sectional view
in Figure
1. Figure 1 depicts a contactor vessel 1 that is connected to a flotation cell
or phase
separation vessel 2. Contactor vessel 1 includes a slurry input port 3, an air
input port
4 and an output port 5, and has a generally hollow interior 6. While the
contactor vessel
shown in Figure 1 is a pipe chamber, it will be appreciated from a complete
understanding of the invention that other physical forms of vessel 1 could
also be
employed while remaining within the broad scope of the invention.
When assembled for operation, the slurry input port 3 of contactor vessel 1 is
operatively
connected to a source of pressurized slurry. Typically, the slurry would be
comprised
of an aqueous mixture of finely ground minerals or other materials that have
previously
undergone any conditioning stages that may be necessary in order to obtain
separation
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of various components my means of froth flotation. For example, depending upon
the
nature of the minerals or materials contained within the slurry, a variety of
different
commonly used flotation reagents may be added for purposes of making one of
the
components of the slurry hydrophobic and/or rendering other components
hydrophilic
(or otherwise depressing certain elements or components). In addition, in some
instances it may also be desirable to add floculants, froth enhancers,
stabilizers, or other
chemicals or reactants that are commonly used in the flotation field.
Referring again to Figure 1, when assembled in an operative state air input
port 4 of
contactor vessel 1 is connected to a source of pressurized air for injecting
air into the
generally hollow interior 6 of the contactor vessel. In this manner,
pressurized slurry
entering contactor vessel 1 through slurry input port 3 is intermixed with
pressurized air
injected through air input port 4 causing air bubbles to come into contact
with
hydrophobic materials within the slurry. This allows for the attachment of air
bubbles
to the hydrophobic particles forming particle-bubble aggregates. To help
assist in the
intermixing of the injected air with the stream of pressurized slurry, in one
embodiment
of the invention slurry input port 3 is arranged at an angle of approximately
45 degrees
to the longitudinal axis of contactor vessel 1. In an alternate embodiment the
relative
positions of slurry input port 3 and air input port 4 may be reversed from
that shown in
Figure 1.
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Output port 5 of contactor vessel 1 is connected to flotation cell 2 by means
of piping
7 such that the contents of the contactor vessel (including the pressurized
slurry and
injected air) may be delivered to flotation cell 2 as they exit the contactor
vessel. In a
preferred embodiment of the invention the contents of the contactor vessel are
pumped
through output port 5, into piping 7 and eventually through a generally
cylindrical
vertically oriented distributor 8 that is situated preferably at or near the
center of
flotation cell 2. In the embodiment shown in Figure 1, distributor 8 has an
enclosed
upper end and a series of rectangular shaped slots 9 positioned about its
vertical axis and
through which the aerated slurry passes. Once released into the flotation
cell, the
particle-bubble aggregates within the slurry will separate from the
hydrophilic
component of the slurry by means of traditional froth flotation. That is, the
particle-
bubble aggregates will tend to float upwardly through the separation vessel
and
accumulate at or near the top of the vessel where they can be collected and
removed as
a concentrate. A froth launder 10 may be used to help collect the froth and
direct it out
of flotation cell 2 for further processing. The hydrophilic materials within
the slurry
settle at the bottom of the flotation cell and may be removed by any one of a
variety of
commonly used methods. In these regards, the embodiment shown in Figure 1
indicates
the use of a hopper 11 situated on the bottom of flotation cell 2 which tends
to collect
and direct settled hydrophilic materials to an outlet port 12.
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In accordance with one aspect of the present invention, during its operation
contactor
vessel 1 is maintained in a pressurized state in order to help assist in the
attachment of
air bubbles to particles of hydrophobic materials prior to the discharge of
the slurry and
air from the contactor vessel into flotation cell 2. It has been found that
maintaining the
contents of contactor vessel 1 in a pressurized environment helps to assist in
the
intermixing of air that is injected into the slurry and encourages a more
consistent and
effective attachment of air bubbles to hydrophobic particles. It will be
appreciated that
depending upon the nature of the materials undergoing separation and the
volume and
throughput of the equipment in question, the optimum pressure under which
contactor
vessel 1 should be maintained may vary. However, a pressure of from about 18
to about
25 pounds per square inch gauge has been found to be most effective. It has
also been
determined that where contactor vessel 1 is a pipe chamber, sizing the chamber
in a
manner such that the velocity of slurry travelling therethough is from about 1
to about
3.5 meters per second such that a retention time of from approximately 1 to 2
seconds
is established permits effective particle-bubble attachment at an enhanced
throughput.
In order to maintain the interior of contactor vessel 1 in a pressurized state
during its use
the invention contemplates the employment of a flow obstruction 13 that
effectively
hinders the flow of material through the contactor vessel, thereby creating
back pressure
which tends to establish and maintain a pressurized state within hollow
interior 6 of
contactor vessel 1. It will be appreciated that the use of a flow obstructions
will also
PP=109PWR
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have the result of increasing the velocity of material exiting the contactor
vessel through
the orifice or opening in the flow obstruction. It is expected that under most
conditions
the velocity of materials flowing through flow obstructions 13 will be from
about 10 to
about 20 meters per second.
Flow obstruction 13 may take any one of a wide variety of different mechanical
structures that range from a simple reduction in the cross sectional area of
the interior
of the contactor vessel or the piping that connects contactor vessel 1 to
flotation cell 2,
to more complex fixed or adjustable orifice plates, muscle valves or pinch
valves. The
particular structure of flow obstruction 13 will to a large part be dependent
upon the end
use of contactor vessel 1 and the amount of flexibility and control over the
operation of
the vessel that is desired.
In cases where it is desirable to be able to adjust or modify the operation of
contactor
vessel 1, there may be included a pressure sensor 117 in communication with
hollow
interior 6 of the contactor vessel to allow for the monitoring of its internal
working
pressure. As pressure sensor 17 senses fluctuations in the pressure within
contactor
vessel 1, signals may be generated to alert an operator so that adjustments
can be made
to either the rate of delivery of pressurized slurry to the contactor vessel
and/or the rate
of delivery of pressurized air and/or the operation of flow obstruction 13
(where the
mechanism comprising the flow obstruction allows for the adjustment of the
orifice or
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flow passageway therethrough). Through altering the amount of slurry and/or
air
delivered to the contactor vessel and/or the functioning of the flow
obstruction, an
operator will be able to effectively adjust and maintain the internal pressure
of contactor
vessel 1 within a pre-determined range.
Complete automation of the process may be achieved through the utilization of
a
microprocessor control 18 and an actuator connected to flow obstruction 13 to
adjust the
size of the opening therethrough. Typically such an actuator would be an
electric,
hydraulic or pneumatic solenoid. Signals generated by pressure sensor 17 may
be
directed to microprocessor control 18 which in turn is connected to the
actuator to
permit automated adjustment of flow obstruction 13.
If desired, microprocessor
control 18 may also be connected to a throttle valve (not shown) or other
structure (for
example, the slurry pump) so that the microprocessor is able to adjust the
flow of
pressurized slurry into contactor vessel 1. In this manner, microprocessor
control 18 is
able to automatically compensate for varying operational conditions that may
result in
a fluctuation of pressure within the contactor vessel 1, thereby maintaining a
desired
pressure therein. Microprocessor control 18 may also be connected to valves,
compressors or other devices used to generate the stream of pressurized gas
injected into
the slurry as a further means to control the overall process parameters. It
will further be
appreciated that where flow obstruction 13 is a fixed orifice, control of
internal
pressures with the contactor may be achieved through using the microprocessor
to
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control the rate of delivery of the feed slurry and/or the injected air.
It will therefore be appreciated by those skilled in the art from a complete
understanding
of the above invention that the described apparatus and method provides a
mechanism
for separating particles of oil or hydrophobic minerals or other materials
from a water
or mineral pulp or slurry by creating an improved environment for the
attachment of air
bubbles to hydrophobic particles, thereby allowing for the subsequent
separation of the
hydrophobic and hydrophilic materials in a flotation cell or phase separation
vessel. The
air/hydrophobic particle contact is created under pressure inside a contact
chamber and
outside of the separation vessel. In this manner the described method and
apparatus
provides for an efficient environment for attaching air bubbles to the
hydrophobic
material before the slurry is released into the separation vessel.
It has been found that through the use of contactor vessel 1, and with the
establishment
of a pressurized environment within which the slurry and air stream are
intermixed, a
maximum slurry/gas volume flow ratio of from approximately 1:1 to
approximately 1:5
,measured after the flow obstruction, can be established while transporting
material
through the contactor vessel. Such slurry-to-air ratios are considerably less
that those
commonly used in the art. When the contents of contactor vessel 1 are
delivered to the
flotation cell the expansion of the gas on discharge will provide a gas:slurry
volume
ratio in the flotation cell as high as approximately 2.5:1 and a gas velocity
in the
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separation vessel as high as 4 centimeters per second. Accordingly, not only
does the
pressurized state of contactor vessel 1 enhance the bubble-hydrophobic
particle
attachment, but it also forces the attachment of pressurized bubbles of air to
the
hydrophobic particles. Upon release into the flotation cell the pressurized
bubbles
expand to provide an enhanced gas lift during the separation process. This
structure has
proven to permit the use of separation tank volumes that can be in the range
of 2 to 3
times smaller than that required by conventional mechanical cells, while
attaining the
same or similar rates of recovery. In addition, the described method generally
permits
the use of separation vessels that do not require internal agitators or
impellers.
It is to be understood that what has been described are the preferred
embodiments of the
invention and that it may be possible to make variations to these embodiments
while
staying within the broad scope of the invention. Some of these variations have
been
discussed while others will be readily apparent to those skilled in the art.
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