Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Inv_nt n
Field: This invention relates to mixing and aera~
tion impellers. 5pecifically this invention provides a
method and apparatus for mixing and aerating mediums,
including slurries processed in flotation machines to recover
mineral values therefrom,
State of the Art: In recent years the mineral
processing industry has found i~ necessary to trea~ ever
increasing tonnages of lower and lower grade ores. This, in
turn, has dictated the use of correspondingly increasingly
large processing equipment, including rlotation machines.
A slurry is prepared from a ground mixture of ore
and a liquid which is typically water with selected condition-
ing, collecting and frothing agents The slurry is fed into a
flotation machine comprised of one or more flotation cells.
In the flotation cells, means are typically employed to both
aerate and physically mix the slurry. Aeration and mixing
are desired to simultaneously produce bubbles in the slurry
and to bring ore particles in contact with the bubblesO As
is knownl ore particles having desired mineral values tend
to be carried~to the surface of the slurry to form a froth
which may be regarded as a concentrate of the desired
mineral value to be recovered. As known, in the flotation
process, some particles, which tend to be the heavier
particles which are frequently rich in the desired mineral
~alue, tend to settle to the bottom of the flotation cell~
In order to improve the efficiency of the flotation machine
process it is desirable to thoroughly mix and suspend all
particles in the slurry without overmixing or agitating
which could reduce the opportun1ty for bubbles to transport
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-~esired particles to the surface (froth),
Heretsfore the mixing operation within the flotation ~` -'
cell has been effected by a variety of mixing means. For
,example, a ship-type propeller could be' used within the slurry. ~'
It would be xotated to produce a generally downward flow and ~ ~'
-~n turn generate a circulating current which i5 deflected
from the bottom of the cell. However, such a propeller would ~ ~ -
not usually be reversible to vary the flow currents within
*he cell to minimize the collection of solids near the '
-bottom of the cell. Such limitation would be more severe
~when the ship-type propeller is used with means for the
introduction of gas to enhance mixing. Further, the flow
currents above the propeller are less pronounced. In turn,
mixing is less effacious. Moreover, solids could build-up
on the cell bottom in the flow vortex. A ship-type propeller
- ' may be more readily subject to the build-up of corrosion and
precipitates on the propeller blades. '
; ~Turbine-type impellers have been used in flotation
cells and can be either unidirectional or reversible ~in ;
rotation) depending upon the design of the impeller blades,
However, the flow patterns through such an impeller are such ;
that the bottom of the cell cannot be readily swept by 10w
to prevent the build-up of solids on the bottom which settle
-out from the slurry.
-':Modern aeration impellers in common use ~e~g.,
~those-manufactured by the Galigher Co. of Salt Lake City,
-Utah, ~and sold under the trademark "AGITAIR"~ can be
-r~ve~sed to improve impeller lifeO Flow through such
impellers is generally upward under and downward to the
impeller and then radially outward~ The flow currents along
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the bottom of the cell are not pronounced. In turn,
mixing is less thorough because a direct outward flow of
fluid is not directed at the bottom to sweep it clean and
keep the heavier particulate matter suspended in the slurry.
Injecting gas into such an impeller is effected
so that a slurry gas mixture is pumped by the turbine blades~
The gas fluid interfaces tend to accelerate erosion and,
when the gas is chemically capable of contributing to
corrosion (e,g., air)~ corrosion of the impeller. Further,
lQ the gas tends to decrease the efficiency of the impeller
because it inhibits laminar flow and by its mere presence
reduces the volume of slurry processed.
The Outokumpu OK-16 pneumatic flotation machine
uses an impeller such as the one shown on page 148 of
Mining Magazlne, August 1976 tpublished by Mining Journal
Ltd, London, England). Gas is directed into the fluid
before it passes through the impeller blades. Impellers
of this type also suffer increased erosion and corrosion
across the turbine ~lades by virtue of the presence of the
gas which is generally compressed air, Further, such an ~ ~
impeller does not direct a flow of slurry to the bottom to ~ -
sweep the bottom of the cell. Therefore, not all matter
is suspended within the slurry for processing. The
processing of the slurry throughout the system is thus less
efficient and in turn less economical.
UOS. Patent No.3,843,101 (Green) also discloses an - ~
impeller which may be regarded as a flotation machine im- ~ ;
peller.
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Brief Descrl~tion of the Invention
An impeller for rotation by a shat is comprised
of a hub and a plurality of first flutes interspaced between ~;
and joined to a plurality of second flutes~ The hub may be
removably adapted to the shaft~ The impeller rotates in a
plane substantially normal to the shaft. The first and;~
second flutes are adapted to the hub and extend radially
outward from the hub. Each of the flutes has a trough
beginning proximate the hub which extends angularly downward ;~
for the first flutes and angularly upward for the second
flutes as the flutes extend radially outward. The bases of ;; ;
the flutes form the outer rim of the impeller.
The impeller preferably includes means to receive
compressed air from a source and means to exhaust the
compressed air radially outward from the rim, The hub may
be formed to receive air from a hollow shaft and communicate
it to at least one passage formed through at least one flute ~
to the outer rim of the impeller. A plurality of passages .
may be formed in the impeller which have distal ends at the
outer rim. The distal ends may be preferably interconnected
to form a con~tinuing slot along the rim. Most preferably the
impeller is formed from upper and lower substantially
symmetrical members positioned proximate each other to form
a gap which is connected to receive compressed air from the ;
hub and to form a continuing slot along the outer rim of
the impeller.
The impeller has a height measured in the axial
direction at its outer rim. Preferably the impeller has a
diameter to height ratio from about twenty to one ~20:1) to
~bout one to one (1~ The first and second flutes are
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preferably formed as one unitary structure and shaped in a
periodic pattern, They may be smoothly shaped to ~e
generally sinusoidal in shape at the rim and in cross section
normal to the radius of the impeller along the length o~ the
flutes. They may also be shaped to form a trapezoid having
,
substantially equal vertical side members in cross section
normal to the radius of the impeller along the lengt~ of the
flutes. The flutes are preferably formed from a strong and
slightly flexible material, Further, the impeller may have
a shroud positioned above and below the impeller proximate
thereto. The shroud may include a plate in a plane normal
to the shaft with support means adapted thereto and a ~;
plurality of fins adapted thereto, The fins are radially
oriented about the perimeter of the impeller.
A flotation machine for recovering mineral values
has a cell containing a slurry and means to agitate the slurry,
An improved impeller is used which constitutes the agitation
means. The impeller rotates in a plane substantially normal
to its rotation shaft. The impeller has hub means and a
20 plurality of first flute means interspaced between a plurality ;
of second flute means. Preferably the impeller has means to
receive compressed gas and means to exhaust the gas into the
slurry along the rim of the impeller,
The slurry in a flotation machine may be agitated
by rotating an impeller within the slurry to cause the slurry
to be simultaneously directed angularly upward and angularly
downward from the impeller~ The rate of rotation of the
impeller is selected to establish separate slurry flow
currents above and below the impeller, By positioning the
impeller properly within the cell of a flotation machine~
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one current is directed to the bottom of the cell to sweep
acros~ the bottom and the other is directed upward towards
the surface of the cell. The suction for the flow upward
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is from below the impeller; and the suction for the flow
downward is rom above the impeller,
Pxeferably the impeller is selected to ha~e a
diameter to height ratio between about 20:1 and about 1:1,
Uost preferably, the impeller is selected to have a diameter ;;
to height ratio between about 10:1 and about 1:1 when
positioned within a cell sized so that the cell cross-
sectional wndth to impeller diameter ratio is between about
1-1/2:1 and about 10:1, Further, the impeller is preferably
rotated at a rate so that the peripheral speed is between
about two (2) meters per second and about fifteen ~15) meters
per second.
Brief Description of the Drawings
In the drawings, which illustrate the best mode
presently contemplated for carrying out the invention:
FIG. 1 is a perspective side view of an impeller
of the instant invention;
FIG; 2 is a cross-sectional side view of an ;,
impeller within a flotation machine cell of a Flotation
machine of the instant invention;
FIGo 3 is a side perspective side view of an
; impeller of the instant invention and appears with Fig~ 1
on the first page of drawings;
FIG, 4 is a side view of an impeller of the instant
invention with shroud means positioned proximate thereto; and
FIG~ 5 is a top view of the impeller and shroud of
FIG D 4
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Description of the Illustrated Embodiment
. The ayitation and aeration impeller shown in FIG. -:
1 has a hub 10 and a plurality of first flutes 12 interspaced
and connected between a plurality of second flutes 14. The :~
hub 1~ constitutes hub means for removably adapting the
impeller illustrated in FIG~ 1 to a shaft (not shown), The
shaft provides rotational torque to rotate the impeller of
FIG. 1 in a plane 16 which is substantial:Ly normal to the
axis 18 of the hub 10 and shaft (not shown).
The first flutes 12 are provided with a trough 20
which commences proximate the hub 10 and extends radially
and downwardly away from the plane 16. Similarly, the ~:
second flutes 14 contain a trough 22 which commences
proximate the hub and extends radially and upwardly away
from the plane 16. As best seen in FIG. 2, the troughs
20 and 22 of the first and second flutes 12 and 14 extend
downwardly and upwardly at a discrete acute angle 24 and
26 with respect to the plane 16. The angles 24 and 26 are
here shown to be equal with a common base 27. Upon rotating
an impeller of the type illustrated in FIGS. 1 and 2 in a :
medium such as a slurry 28, it has been found that flow is
di~ected from the first flutes 12 downward as indicatecl by
the arrow 30 and by the second flutes upward as indicated :
by the arrow 32. As more fully discussed hereina~ter~
the flow pattern above and away from and downward away from
the plane 16 of the im~eller results in improved agitation~
As best seen in FIG, 1~ the flutes 12 and 1~ are
formed as a unitary structure with the bases 34 and 36 of
the flutes forming a substantially circular (in projection)
rim 38. The flutes 12 and 14 may be formed to be ~mooth,
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continuous surfaces which may be regarded as generally
sinusoidal in appearance. That is, a cross~section normal
ko the radius 41 of the impeller along the length 33 of the
flutes 12 and 14 would result in the wavy shape which may be
regarded as generally sinusoidal., A smooth contiguous surface
i5 desirable to reduce drag as the impeller is rotated and
to avoid the build-up of deposits. Further, a smooth
contiguous surface tends to minimize the corrosion and erosion
which might be experienced in a slurry environment.
lu Referring to FIG. 3, khe impeller therein illustrated
has 1utes 12 and 14 formed to be essentially trapezoids with
sides 40, 42 substantially equal in vertical length 43 in
cross section normal to the radius 41 along the length 33 of ~;
the flutes 12, 14. That is, a cross section normal to the
radius 41 of the impeller in the plane 16 would show a trape- ;
zoidal shape with the trapezoid having a base 47, equal
vertical sides 40 and 42, and another base 48 which would be
the line 48 interconnecting two adjacent flute vertical , !
surface extremities 49a 49b. Here too a smooth surace is
2û desired to reduce drag, ~o avoid build-up of deposits and
to minimize corrosion and erosion~ ;
It might also be noted that the flutes 12, 14 of
FIGS. 1, 2 and 3 are each generally formed to be a periodic
pattern about the hub 10. Further, each ~lute may be
regarded as having an axis or center line 39 with surfaces
4û and 42 on either side formed to be substankially symmetric
or mirror images o each other~ Thus, the impeLler of FIGS.
- 1 and 2 may be rotated either in a clockwise or counterclock-
wise direction as desired by the user. In practice~ i,t may
~0 be desirable to operate the impeller in first clockwise
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1~973125
direction for a period of time and then in a counterclock-
wise direction. In this way the surface erosion experienced
by the impeller as the fluid (slurry 28) passes down and
out of a particular flute ~12, 14) will shift from one side
40 to the other side 42 of each flute 12, 14~
Referring in more detail to FIG, 2, which is a
section of the impeller of FIG, 1 along the section lines ~,
2-2, it can be seen that the hub 10 as illustrated is in
effect an elongated hub or shaft extending upward away from
10- the plane 16 f~r connection to a shaft and external rotation
means. The hub 10 is hollow and receives a gas which is
preferably a compressed gas such as air from an external
source which transmits the gas down the length of the hub
10 in an axial direction towards the flutes 12, 14. It can
further be seen that the flutes 12 and 14 are formed to have
a passage which as here shown is a continuous gap 50
extending from the hub 10 outwardly to the rim 38 of the ;
impeller. Although one or more passages may be employed
to communicate the compressed gas 52 from the hub to the
rim of the impeller, it is preferre~ to use the continuous
gap 50 to form a continuous or an unbroken slot 54 along
the outer rim o~ the impeller,
As best seen in FIG, 2, the flutes 12 and 14 are
formed as two substantially symmetrical members which are
; bolted to the hub 10 by a plurality of nuts and bolts 56.
Spacers 58 are provided along the shafts of the bolts 56 to
provide for the gap 50~ Further additional spacers or
supports 60 may be provided along the radial length of the
gaps 50 to provide structural strengkh and minimize vibration.
30 An end spacer 62 proximat~ the rim 38 may not be desired in
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some circumstances, In particular, it may be desirable to ;~
fabricate the flutes 12 and 14 from a strong yet flexible
substance such as plastic elastomers or rubber compounds,
Certain flexing in the flutes 12 and 14 has been found to
be desirable to minimize the build-up of crud (i.e., solid
scales adhering to the sufaces of the impeller).
Referring to FIGS. 4 and 5~ it can be seen that an
impeller substantially similar to the impellers of FIGSo 1,
2 and 3 is illustrated with shroud means positioned proximate
thereto. The shroud means includes a plate 70 and support
means 71. The shroud plate 70, as here shown, has a plurallty ~ -
of fins 73 secured thereto. The fins are oriented radially `~
and are po~itioned preferably symmetrically about the
perimeter or rim 38 of the impeller, The support means 71
is comprised of an arm 74 and leg 75 Each -arm 74 is secured
to a fin 73. The legs 75 are sized in length 76 to support
the shroud on the bottom 82 of a cell 80 (FIG. 2).
Alternately, the support means 71 may be attached directly
to the plate 70 and provided with structure to suspend it
from above the impeller. An aperture 77 is formed in the
plate 70 concentric to the hub 10 or shaft of the impeller
to act as an inlet or suction for the impeller.
It should be particularly noted -that the impeller
of the instant invention (may be regarded as a double-fluted
impeller) permits a cross mixing flow which tends to more
thoroughly mix and suspend the particulate matter in a slurry
28. More particularly, the flow as the impeller is rotated
is such that the fluid traveling axially upward towards the
impeller, as shown by the double dot arrows 32, continues to
pass upward away from the plane 16 as it exits the second
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flutes 14 and at the same time fluid traveling axially
downward as shown by the single dash arrows 30 continues ~;
to pass downward as it exits the first flutes 12 angularly ~`
downward away from the plane 160 In this way 1uid above
the impeller is circulated downward and to the area below
the impeller while at the same time fluid below the impellex
is circulated upward to the area above the impeller. There-
by more thorough mixing and aeration is effected.
; The cross mixing feature as best seen in FIG 2
generates what might be regarded as a figure-eight flow
pattern within the cell 80 of a flotation machine By
positioning the impeller of the instant invention and rotating
it at a selected speed, flow exiting the first flutes 12 may ``
be directed outwardly to the side of the cell 80 and then
downward to the bottom 82 of the cell. The flow current so
extablished in effect sweeps the bottom so that particulate
matter in the slurry does not settle out and collect on the
bottom of the tank. Indeed, as the flow passes or sweeps
along the bottom 82 of the cell 80 and draws particulate
matter into the slurry 28, the slurry is directed upward
towards the tQp of the cell by the second flutes 14.
Accordingly, a more complete mixing of the particulate
matter in the slurry is effected with a minimum of
segregation of the coarse and heavy particles which are
not easily suspended by any of the other types of impellers
presently known.
The cross mixing feature hereinbefore discussed,
can be increasea or decreased depending upon the desires of
the user by changing impeller diameter to height ratio, In
particular, the impeller of the instant invention may be
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regarded as having a h0ight which is measured in the axial
direction at the rim 38 of the impeller, That is, the
distance between the uppermost portion and lowermost portion ~
of adjacent flutes may be regarded as the height 84 of the ~ ;
impeller. It has been found that the impeller diameter 86
to impeller height 84 tFIG, 1) ratio may be varied from
approximately 20:1 to 1:1. However, pract:ical use in
flotation of chemical applications has been found to be best
in the range of ratios of about 10:1 to 1:1. Further, it
has been noted that the more nearly the ratio approaches 1:1,
the more effective is the intermixing of materials on each ` ;
side of the impeller, That is, the agitation in the tank
i5 more violent yet even and thorough.
As known to those skilled in the artt it is
desirable to introduce a gas to both improving the mixing
of the slurry 28 within the flotation machine and to provide
bubbles to carry mineral value particles to the slurry
surface 90 (FIG. 2) to form a froth 92. In the past, air
or gas has been ihtroduced in such a manner as to impinge
directly on turbine blades or other impeller structure there-
by significantly increasing the erosion experienced by that
structure. In turn the wear life of an impeller has been
significantly shortened and in turn the cost of the process
increased. In ~he instant invention, gas (which may be
; compressed air) 52 is passed down a hollow shaft into the
hub 10 and thence outwardly through the flutes 12, 14 to
exit through the slot 54 at the rim 38 of the impeller in
an outward radial direction~ It may be noted that as the
impeller is rotated through a medium such as the slurry
28~ the increased flow of the medium at the rim ~4 of the
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impeller as it exits the flutes 12 and 14 produces a reduced
pressure area 88 immediately adjacent the rim 33. The ~as
52 exits from the slot 54 into the reduced pressure area 88
Thus it may be seen that the pressure of the gas 52 as
supplied may be reduced because it need not overcome the full
pressure of the medium such as the slurry 28 as it exists at
the depth 94 the impeller is located within the cell 80.
This in turn produces an economy because the gas 52 need
not be compressed to as high a pressure as heretofore ~
required. It should also be noted that as the gas 52 exits ~;
from the slot 54 into the reduced pressure area ~8, its
~elocity accelerates because of the reduced pressure in the
area 88. Further, the centrifugal movement of the impeller
tends to pump the gas 52 out through the slot 5~. As a
result, the gas pressure may be even lower or selected to
achieve greater penetration into the slurry as desired. It
may also be noted that the turbulence created radially outward
o the low pressure zone 88 by the intermixing or cross mixing
hereinbefore described provides an excellent area for
intermixing of the gas with the medium or slurry 28. In
addition, introducing the gas at the rim does not interfere
with the efficiency of the pumping action of the flutes 12
and 14. That is, in impellers heretofore known the gas is
introduced in such a manner that the efficiency of the
pumping action is reduced in that a combined gas and
slurry/medium is pumped by the impeller/propeller because
the air or gas is introduced at or near the eye of the
impeller tadjacent the hub 10)~ It may also be noted that
by introducing the ~as at the rim 38, the impeller is not
su~jected to a ~as liquid interface. This in turn reduces
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the turbulent wear and erosion assoicated thexewith on
impeller structure, Only the small bubbles which may be
already entrapped in the slurry come into contact with the
surfaces of the flutes 12, 14.
In operation it has been determined that an
impeller with a diameter to height ratio from between 10:1
to about 1:1 is preferred for a flotation machine having a
cell cross-sectional width 96 to impeller diameter ratio from
about 1-1/2:1 to about 10:1. Further, for an impeller as
above described, it has been determined that the optimum
rotational speed of the impeller should be from a peripheral
speed of about 2 meters per second to about 15 meters per
second. Peripheral speed is the actual linear speed of any
point on the rim 38 of the impeller as it rotates. For
example, an impeller having a two (2) meter circumference
and rotating at a peripheral speed of two (2) meters per
second would turn at the rate of one revolution per second.
For the machine and impeller described in the
paragraph next above, it has been found that air may be
introduced preferably at a relatively low pressure from
about 5 pounds per square inch above atmospheric pressure
to about 1/2 pound per square inch above atmospheric
pressure. Usually the air pressure may be less than 1-1/2
pounds per square inch above atmospheric pressure~ Further,
such an impeller may preferably have a gap 50 which may be
sized between one millimeter to five millimeters.
It may be noted that the impeller configurations
illustrated in FIGS, 1 through 4 act to reduce the tendency
to sand-in a flotation machine cell. In the less efficient
systems heretofore known~ the impeller is typically located
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1073125
closer to the kank bottom 82 to generate more pronounced flow
~urrents near the bottom to produce more thorough mixing,
~pon shutdown, the layer of solids on the cell bottom 82 plus
the additional solids settling out of a sLurry 28, tends to
raise the level of solids to and above the bottom of the im-
peller. That is, there is a tendency to "sand-in" the
impeller making a subsequent re-start difEicult~ Further,
for flotation cells using impellers heretofore known, the
inefficient mixing leaves heavier particulate matter behind
which tends to concentrate the slurry in operation.
As stated herein, the impeller of the instant
invention more thoroughly mixes the slurry. The heavier
particles tend to be mixed so that less material collects on
the cell bottom 82 and the slurry 82 tends to not concentrate.
Upon shutdown, fewer solids are available to settle to the
bottom. The impeller is therefore generally free of settled
solids in a static state and can be started or re-started
without the usual problems associated with other impellers -~
known in the art which may become mired in solids which
build-up from the bottom of the cell 80 The use of a ; -
shroud such a~s that illustrated in FIGS~ 3 and 4 further
prevents solids from settling around the impeller and
virtually eliminates the sand-in problem for the impeller of
the instant invention.
It has also been found that use of the impeller of
the instant invention results in significant power sa~ings.
For example, a 2n horsepower synchronous AC motor ~3 phase,
60~Z) may be used to power simultaneously an impeller in two
100 cubic oot flotation cellsO Using an AGITAR~M impeller
manufactured by the Galigher Company o~ Salt ~ake City, ~tah,
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about 12.85 horsepower are required to operate the two
impellers in a water slurry~ Using an impeller of the
instant invention under si~ilar conditions, only about 9~2
horsepower are required, That is, a net savings of about ;~
29 percent in horsepower required may be realized while
experiencing improved mixing as herein set forth,
Comparable power savings have been noted for 500 cubic
foot flotation cells and may be expected in other sizes of
flotation cells,
It may be noted that the impeller and method
herein disclosed are very versatile, That is~ it can be
readily adapted to existing flotation machines and other
equipment for which mixing and aeration or gas injection is
desirable hy adjusting diameter height and rotation speed,
A wide range of agitation capacity gas dispersion and froth
surface characteristics can thereby be achieved, Further,
the self-cleaning aspects of this impeller, by virtue of its
: flexib~ity, commend its use for fibrous or random waste ~ ;
materials. That is, the flexing of the impeller and the
absence of protruding blades makes it virtually impossible .
to clog this impeller in virtually any medium,
It may also be noted that the descriptions and
illustrations herein set forth are merely illustrative of
the principles of the invention, Those skilled in the art
will recognize that other embodiments may readily be devised
in incorporating the principles of the invention set forth
in the claimsq
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