瑞典专利SE1100941A1 Improved method and apparatus for foam flotation in a stirred vessel

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专利摘要:
A method of separating mixed particles in a flotation cell (1) using a fluidization zone (22) within the cell where particles become fluidized in a still zone of liquid moving through the fluidization zone (22). The fluidized fluid may be provided by the supply (21) or by recovered fluid from upper parts of the cell such as from the release zone (40). Bubbles are introduced into the lower part of the cell by a mechanical impeller (2) which also breaks up each channel in the mixing zone (5), or by separate aeration in the bottom of the cell or by insertion through a tube for recovery.
公开号:SE1100941A1
申请号:SE1100941
申请日:2009-05-26
公开日:2012-02-27
发明作者:Graeme John Jameson
申请人:Newcastle Innovation Ltd；
IPC主号:

专利说明:

101520253035PS54395SEOO2It is well known that the recovery of particulate mechanical cells then decreasesparticle size increases. In mechanical cells, backwater currents are formed in the liquid by turbulentagitation and when the intensity of the turbulence in the cell increases, backwater currents are createdgreater rotational speed. The gas bubbles move to the center of the backwater currentsand rotates with them. Larger rotational speeds lead to larger centrifugal forces such astends to cause the particles to detach from the bubbles. Consequently, in mechanicalcells under current practice, there is a built-in limitation in the maximumthe particle size that can be recycled efficiently. A built-in difficulty with mechanical cellsis that as the particle size increases, greater turbulent energy must be supplied to maintainthe particles in suspension in the cell, this thus leads to less and less probability ofthat the coarse particles will be able to remain attached to the bubbles.
Particles whose diameter is at or above the maximum size that can effectivelytreated in mechanical ﬂ otation cells are considered "coarse" particles. The meaning ofthe term "coarse particles" depends on the density of the particles. For sulphide and oxide minerals,where the density can be between 2500 to 7000 kg / ma, particles larger than100 to 150 micrometers in diameter as coarse particles. For lighter substances such as coal, whosedensity is in the range 1200 to 1800 kg / ma, coarse particles are those over 250 to 500micrometer.
The centrifugal forces acting on particles suspended in a sludge can be related tothe local shear rate or the local turbulent intensity in the totation cell.
For the purpose of generalization, general terms such as the level of turbulence, the turbulentthe intensity, energy loss rate or average shear rate be equivalentwith the specific speed of supply of mechanical energy (power per unit volume) into the working regions of the cellation cell or the energy loss rate mechanical energy pervolume unit of fluid in the active region. As an example, according to current practicethe specific power supply into ﬂ otation cells is usually in the order of 3 kWper cubic meter of working volume in the cell. The most active region of a mechanicalﬂ otation cell is, however, where contact between bubbles and particles takes place, in the region ofthe impeller, the stroke volume of which is usually in the order of one tenth ofﬂ otation cell volume. A more realistic estimate, based on the impeller's stroke volume,of the loss rate in the active region of the cell is thus 30 kW per cubic meter. TheIt is obvious that the level of turbulence in such cells is so high that coarse particles relaxfrom spinning bubbles, leading to low recovery in the coarse size fractions. For101520253035PS54395S E003to extend the upper limit for efficient collection of coarse particles by flotation isit is necessary to provide a process in which the specific energy supply ismuch lower than that found in mechanical cells.
Two important concepts regarding the suspension of particles in agitation tanks are thesuspended impeller velocity and cloud height (Handbook of Industrial Mixing,Edward L. Paul et al., Eds. Wiley lnterscience, New York, 2004). The just-suspendedthe impeller velocity is the rotatlon velocity of the impeller necessary tosuspend particles from the bottom of the tank so that no particles remain on the bottom for more than1 to 2 seconds. When the impeller speed increases to the overjust-suspended speeda well-mixed homogeneous layer is formed at the bottom of the tank. However, it has been shown thatthe particles are not necessarily distributed over the entire height of the liquid in the tank and inin some cases a sharp interface is visible which separates the homogeneous layer at the bottom of the tankfrom a clear liquid layer above. The height of the homogeneous layer is known as cloud height. Whenthe impeller speed is further increased lifting the particles higher and higher untilthe particle concentration is uniform throughout the vessel. Mechanical t otation cells of knowndesigns are driven by the principle that the particles, which are to be suspended, are fully formedsuspended in the liquid in the ﬂotation cell and that the particle concentration is so uniformas possible and substantially independent of the height within the cell. Known cells are driven byimpeller velocities well above the just-suspended value and contents of the cellis well mixed and substantially evenly distributed in the vessel. Thus the cloud height extendssubstantially to the top of the fluid layer in the cell.
The present invention avoids the need for the particles to be completely suspended inthe cell through the impeller and also the requirement that the cloud height should be extended to the top ofthe fluid in the ﬂotation cell. This invention is intended to overcome the inhabitantsthe disadvantages of mechanical cells by providing a low-energy environment fort otation that favors the attachment of coarse particles to bubbles.
SUMMARY OF THE INVENTIONIn one aspect, the present invention provides a method for separating selected onesparticles from a mixture of particles in a liquid within an cellotation cell includingsteps:feeding the mixed particles and liquid into a mixing zonecontaining bubbles in a lower part of the cell;1015202530PS54395SEOO4stirring the liquid in the mixing zone to provide a substantially smoothdistribution of particles, liquid and bubbles in the mixing zone while sufficient fluid flowprovided upwardly through the mixing zone into a fluidization zone above to movethe mixed particles upward into the fluidization zone;allow the selected particles to attach to bubbles within the fluidization zone and riseto the top of the fluidization zone;allow bubbles with attached selected particles to rise above the fluidization zone intoa release zone while removing other particles from the cell;forming a foam zone of bubbles and attaching selected particles to the top ofthe release zone; andremoval of selected particles with bubbles from the foam zone.
Preferably, the intensity of the agitation in the mixing zone is limited so that onesuspension cloud height formed by the agitation does not extend over the mixing zone andinto the fluidization zone.
Preferably, the fluidization zone is substantially still and free from any turbulence generatedin the mixing zone.
Preferably, the other particles are removed from the oxidized bedPreferably, the other particles are removed as waste from the lower part of the cell.
Preferably, the method includes the step of controlling the level of a boundary layer betweenthe release zone and the foam zone.
Preferably, the method includes the step of controlling the level of the top offfluidization zones.
Preferably, sufficient fluid flow is provided by feeding the mixedthe particles and the liquid into the mixing zone.
Preferably, sufficient fluid flow is provided at least in part by the introduction ofa fluidized fluid entering the mixing zone.1015202530PS54395SEOOPreferably, the fluidized fluid is provided by recovered fluid fromthe release zone into the mixing zone.
Preferably, the fluidized liquid is aerated before being introduced into the mixing zone.
Preferably, the supply of mixed particles is introduced at or below the top offluidization zones.
Preferably, the liquid is stirred in the mixing zone by rotation of a mechanicalimpeller within the mixing zone.
Preferably, bubbles are provided in the mixing zone by drawing air in tothe mixing zone through the mechanical impeller.
Preferably, bubbles entering the mixing zone are provided by a porous elementor diffusers.In another aspect of the invention, there is provided means for separating selected oneshydrophobic particles from a mixture of particles in a liquid, said deviceincludes:an cellotation cell arranged to receive a supply of a mixture of particles andfluid into the lower part of the cell;ﬂ uidising means arranged to supply bubbles and ﬂ uid into the cell insuch a velocity that a fluidized bed of particles is formed in a fluidization zone withincells;agitators operable in a mixing zone below the ﬂ uidization zone in itthe lower part of the cell to provide a substantially uniform distribution of particles,liquid and bubblori mixing zone;a release zone in the cell located directly above and connected tothe fluidization zone so that selected hydrophobic particles attach to bubbles rising to the topof the id uidization zone floats upwards within the release zone;waste separation means arranged to remove non-hydrophobic particles fromthe top of the fluidization zone; and101520253035PS54395SEOO6an overflow drain at the top of the cell arranged to remove themselected hydrophobic particles from a foam layer formed above the release zone.
Preferably, the waste separation means are arranged to remove non-hydrophobicparticles from the top of the fluidization zone.
Preferably, the waste separation means are arranged to remove non-hydrophobicparticles from below the release zone.
Preferably, the device includes first level control means arranged to maintainthe position of the boundary layer between the foam zone and the release zone within the cell.
Preferably, the device includes second level control means arranged tomaintain the position of the top of the fluidization zone within the cell.
Preferably, the fluidizing means includes a recycling tube arranged toremove liquid from the release zone and pump it back into the mixing zone.
Preferably, the recirculation tube includes an aerator arranged to dispersefine bubbles in to ﬂ uid passing through the tube for recycling.
Preferably, the oxidizing agent includes a porous element or diffuser located inthe lower part of the cell arranged to supply said bubbles into the cell.
Preferably, the agitator includes a mechanical impeller arranged to berotated in the mixing zone.
Preferably, the oxidizing agent includes a hollow drive shaft for the impeller arranged forto provide air through the hollow drive shaft for dissolution and shear to saidbubbles of the impeller.
Preferably, the device includes a waste disposal pipe having oneinlet end located in the boundary layer between the id uidisation zone and the release zone withinthe cell.101520253035PS54395SEO07Preferably, the flotation cell has a region with a reduced cross-sectional area abovethe release zone so that the layer gas velocity in the foam layer formed abovethe release zone is greater than the layer gas velocity in the release zone.
In one form of the invention, the flotation cell has a region of reduced cross-sectional area abovethe release zone so that the foam layer formed in the region will have an increased depth.
The invention provides a device for separating coarse particles byfoam t otation in which the contact between bubbles and particles takes place in an ﬂ uidizedBED. The fluidized medium is dispersed in the bottom of the fluidized bed throughouta rotary 'impeller, which helps to provide a uniform rising flow offluidized fluid and bubbles and prevents the formation of ducts that can lead tocircumventing and inefficient use of bubbles. The device consists of aupright cell or column with means for providing mixing and stirring.
New supply and air are introduced into a mixing zone at the bottom of the column, the air becomesdispersed into small bubbles by the action of the impetler. The well-mixed supply andthe dispersed bubbles enter a fluidization zone where the bubbles attach to non-dispersedwettable particles and transports them upwards into a release orsupernatant liquid zone and from there into a foam zone at the top of the vessel. The wasteremoved from the cell through a tube or port at the top of the fluidization zone. Means areprovided to control the position of the top of the release zone to a desired oneposition and thus the depth of the foam layer in the cell. In alternative devices is the bedfluidized by a recirculating stream drawn above the fluidized bed andinjected under the impeller. The recirculating flow can be aerated to provide thembubbles needed for ﬂ otation.
The particles are suspended by a vertical flow of water in the cell. Layer speed offthe water is such that it is above the lowest ﬂ unidated velocity of the particles but below itterminal velocity for a significant part of the particles. When operated in this waya liquid ﬂ unidised bed is formed. The weight of the particles is supported by the rising water and in onesuch a system, the level of turbulence is very low. The concentration of particles in the bed ismuch higher than that found in conventional flotation cells and consequentlybubbles that rise in the bed must push past the particles, making it inevitablesome non-wettable particles in their path come into contact with them and oneattachment is formed. The unidentified bed is thus a highly efficient environment for101520253035PS54395SE008separation of non-wettable from wettable particles.
The particles in the flotation stock feed are maintained in suspension by an upward flow of liquidwhich is substantially uniform across the cross-section of the cell. The layer liquid velocity in itthe vertical direction is sufficient to fluidize the particles and keep them separated fromeach other. Thus, when bubbles are introduced into the bed of idididized particles, they are free to rise inthe vessel and come into contact with hydrophobic particles lying in their path.
Usually the volumetric fraction of particles is in a packed bed where the particles moveat and support each other in the range 0.4 to 0.7. When the bed becomes fluidized, it is separatedthe particles apart and the volume fraction of particles decreases. If the bed is uniformand the volume fraction is constant throughout is Reynolds' number for the flow between the particlesusually well within the laminar flow order. The flow is thus still andturbulence is absent. In practice, however, it is difficult to maintain uniformityLiquid ﬂ unidisised beds and vertical channels tend to develop that allow itsuspended the liquid to bypass the bed. Once formed, it offers a channela lower hydraulic resistance to the flow of water through the bed than the bed itself does andthe water which is to support particles in the fluidized bed is diverted instead to ﬂ desolatethrough the channel, which prevents the bed from being uniformly fluidized. When air bubblesare introduced, the channel formation increases further.
In order to obtain the benefits of an unidirectional bed for the flotation of coarse particles, it isnecessary to form the bed in such a way as to channel gas or watersubstantially eliminated. It has been found that a fluidized bed with uniform propertiescan be achieved by using a rotary impeller or stirrer at the bottom ofﬂ otation cell. Sludge supply is introduced near the bottom of the cell and is distributed uniformlyby agitating the impeller. The design and operating speed of the impeller aresuch that a well-mixed zone is created at the bottom of the ﬂ uidized bed but thiszone is limited to the lower regions of the bed. The fluidized water canincluded in the supply that enters the cell near the impeller or it may come fromrecovery of fluid taken from above the fluidized bed in the cell. The bubblescan be derived from the dispersion of an air stream fed near the rotating impeller.
The mixing and pumping properties must obviously be such that any turbulencedeveloped by the impeller is limited to the region at the bottom of the fluidizedthe bed. For this purpose, the impeller may be surrounded by splash shots that allow a pile1015202530PS54395SE009degree of mixing but prevents swirling and development of large-scalecirculatory movements. The turbulence generated by the impeller is attenuated by the highthe concentration of particles in the fluidized bed so that in the upper regions ofthe bed rises the bubbles in a quiet environment that is conducive to the maintenance ofthe retention between bubbles and hydrophobic particles.
The flotation cell can, for the sake of clarity, be described in terms of four zones: onemixing zone, a fluidization zone, a release zone and a foam layer. INthe mixing zone mixes the new supply and bubbles and is uniformly dispersed over the cell.
The liquid and bubbles pass into the id uidisation zone where the liquid fluidizes the bedand retains the particles in suspension as the bubbles pass through the bedcollecting non-wettable particles as they rise. Above the fluidization zone isthe release zone which is essentially only liquid, it may also contain particleswhich have been trapped in the guards by rising bubbles, which are released from the guards and fallback in the fluidized bed. At the top of the cell, the foam zone is formed by bubblestransporting their load of attached particles. The foam is discharged from the cell asthe flotation product.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention will now be described with reference to the accompanying drawings in which:FIG. 1 is a schematic cross-sectional view of a flotation device according to the invention,FIG. 2 is a schematic cross-sectional view similar to FIG. 1 including an aeratedrecycling stream.
FIG. 3 is a schematic cross-sectional view similar to FIG. 2, showing a flotation column inwhich flow area of the fluidization zone and the foam zone are different.
FIG. 4 is a schematic cross-sectional view similar to FIG. 3, showing a flotation column therethe air is introduced through a porous diffuser.
FIG. 5 is a graph showing particle size versus fluid recovery percentagebed device according to the invention compared to a conventional mechanical cell.101520253035PS54395SE0010DETAILED DESCRIPTION OF THE PREFERRED PERFORMANCE! OFTHE INVENTION, AND WHEREAS THEREOFFIG. 1 shows a first preferred embodiment of the invention. A flotation cell 1 isprovided with a rotating impeller 2, which is attached to a hollow shaft 3 attached toshaft bearings 4 which are mounted in a fixed position relative to the cell 1 by means which do notis shown. The shaft 3 rotates in a housing 6 into which a controlled flow of air is let inthe conduit 7, which is inserted into the hollow shaft through an opening 8 and flows down the shaftthrough an opening 9 adjacent the center of the impeller 2. Bounce shots 10 are mounted onthe wall to prevent vortices. The invention is not limited to any particular type ofimpeller or splash shot design, the latter may include a stator contained inconventional flotation machines.
Conditioned supply of sludge enters through the inlet pipe 21 and is delivered tothe mixing zone 5 at the bottom of the cell 1, preferably below the impeller 2, which serves todisperse the new feed into the suspension at the bottom of the cell. An unidentified bedor fluidization zone 22 is established in the cell.
A waste removal pipe 23 is positioned so that its inlet 24 defines the upperthe boundary 25 of the fluidized bed. The waste removal pipe is mountedpreferably so that the position of the inlet 24 relative to the cell 1 can be adjusted in vertical andhorizontal directions to change the volume of the fluidized bed and optimizecell performance for a specific ore. Fluidized particles are drawn away through the tube 23by a siphon or other suitable fluid transfer device which is not shown and dischargedas the waste through line 26. At the bottom 27 of the cell is an outlet pipe 28 and acontrol valve 29 provided to allow emptying of the cell, to enableregular discharges of oversized particles that may have accumulated overtime at the bottom of the cell and also as an alternative discharge opening for the waste.
Air bubbles loaded with trapped particles rise out of the unidentified bed 22 tothe top of the cell where a foam layer 30 is formed. The foam ﬂ loosens from the cell beneath itprojecting edge 31 into the drain chute 32 to be emptied through the outlet pipe 33as the flotation product. The foam-liquid barrier layer 34 is maintained by appropriate means.
As an example, the level could be sensed by an ﬂ otter 35 whose vertical positioncould be measured by a device 36 which sends a signal to an actuator101520253035PS54395SEO01137 which opens or closes a valve 38 to change the rates of waste disposalso that the pulp level 34 is maintained at the desired position. The invention is not limited toany special form of level regulation.
In operation, a suitable conditioned supply containing particles in suspension entersthrough the tube 21 and is discharged into mixing zone 5 in the vicinity of the impeller 2 where it is mixedwith the contents at the bottom of the cell 1. A velocity field is induced in the immediatethe proximity of the rotary impeller, which is sufficient to cause mixing locally,thereby distributing the new feed so that the upward velocity of particles andwater in cell 1 is substantially uniform over a horizontal cross section above the impeller.
The extent of the homogeneous suspension cloud is limited to the vicinity ofimpeller. The rising velocity of the water in the supply is greater than the minimumﬂ the velocity of the particles but less than the terminal velocitythe particles tend to settle in the cell forming an expanded iduided bedabove the impeller, with a high concentration of particles. The bed moves slowlyupward under the influence of the fluidized water towards the inlet 24 of the pipe for removalof waste. Due to the presence of particles, the fluidized bed behaves as ifit would be a fluid of medium density greater than that of water and a substantial onehorizontal boundary layer 25 is formed at the boundary between the unidentified bed 22 andsupernatant liquid in the release zone 40. The viscosity of the compact fluidizedthe bed is significantly larger than that of water so ﬂ the field of fate generated by the impellertends to dissolve rapidly and the influence of the impellem does not penetrate far into itfluidized bed.
Air entering via the duct 7 passes downwards the hollow shaft 3 and is dispersed inbub na bubblorgenom actuation of the rotating impeller 2, which also distributesthe bubbles evenly over the horizontal cross section of the cell. The bubbles rise through itfluidized bed of particles. The probability of a collision between a hydrophobic particle and aair bubble is very high because the rising bubbles have to push the particles away fromtheir way as they rise. The probability of particle capture is thus also high.
The environment is particularly favorable for the capture of coarse particles because ﬂ the fate of itfluidized bed is relatively still. The turbulent backwater currents found inknown forms of mechanical flotation cells, which tend to cause centrifugal forcesleading to the release of coarse particles, is substantially absent in the fluidizedbed 22 above the impeller. The function of the impeller here is to provide mixing101520253035PS54395SE0012locally of the supply when it enters the cell, to distribute the air flow to bubbles and thatprevent channeling of water and air rising in the bed. Mixing effect ofthe impeller is limited to the region surrounding the lower part of the impellerfluidized bed, and does not extend to the lower part of the fluidized bedthe bed.
An advantage of the waste disposal configuration shown in FIG. 1 is that the position ofthe inlet 24 to the waste removal pipe determines the height of the fluidized bedthe bed. In an alternative embodiment, the waste is discharged through the outlet pipe 28 and acontrol valve 29 at the bottom of the cell. A control system that is not shown is provided tomaintaining the boundary layer 25 at the top of the fluidized bed 22 and the liquid level 34at their desired positions. In an alternative embodiment, the level of the boundary layer 25 may atthe top of the fluidized bed is detected by a float of suitable density or adifferential pressure sensor suitably located in the cell. In a further alternative embodiment isthe waste removed at any point below the top 25 of the fluidized bedthrough a riser pipe, not shown, which is connected to the outlet pipe 28 and the control valve 29.
An alternative embodiment is shown in FIG. 2. The device is essentially the same as itdepicted in FlG. 1, with additional features that allow recycling ofthe supernatant liquid from the release zone 40 within the ﬂuidated bed. Cell 1 isthus provided with an outlet opening 50, a pipe for recycling 51, a pump 52,and a return opening 53. In a further preferred embodiment, one is providedaerator 54 through which air entering through the tube 55 is dispersed into ﬁ n bubbleswithin the recycling stream. When air bubbles are introduced through the use ofthe recovery current, it is not necessary to use the impeller as a means ofmake small ﬂ otation bubbles. It has been found that the rotational speed necessary toproduce small bubblori the region of the impeller 2 is higher than the speed that isnecessary to distribute the iduidated water and to prevent the formation ofchannels in the unidentified bed. It is generally preferred to operate the impeller atthe lowest possible speed to save energy and to minimize turbulence asgenerated by the impeller in the ﬂ uidized bed. Where possible, it is thuspreferred to use the recovery stream to introduce bubbles.Although the alternative embodiment shown in FIG. 2 has the air intake throughthe line 7, down the hollow shaft 3 and is dispersed by the action of the rotary101520253035PS54395SE0013the impeller 2 which is also shown, it will be appreciated that this part of the device can be omitted thereadequate aeration is provided via the aerator 54. It has been left in FlG. 2 tofacilitate because it is possible that both methods can be used at the same time forto introduce bubbles, and a similar situation applies to the additional embodiments such asdescribed later with reference to FIG. 3 and FIG. 4.In operation, the supernatant liquid from the release zone 40 enters through the opening 50and passes through the pipe 51 for recovery under the influence of the pump 52.The recovery fate enters the bottom of cell 1, in the region affected by the impeller2, and mixed with particles in the mixing zone 5 of the cell. The total flow ofnew supplies from the pipe 21 and the recovery liquid is dispersed over the entire cross section ofthe cell and the water in the combined ﬂ fate penetrate upwards through the ﬂ uidized bed.In the absence of recovery, the flow of new supply to the flotation cell may fluctuate or stopentirely, in these cases, the supply of the water necessary tosuspend particulate matter the id uidized bed to cease. The advantage of useof the recovery fate is that an accumulation of water through the bed can be maintainedregardless of the flow rate of new supply and assist in stable operation of the bed.
Particles in the supply tend to settle in the fluidized bed, so thatthe supernatant liquid in the release zone 40 has a higher proportion of finer particles andwater than what is in the supply stream. The recycled water assists in the action ofthe impeller at the bottom of the cell and also while maintaining the bed in an ﬂ uidizedcondition.
An additional advantage is obtained if the air in the form of fine bubbles is dispersed inthe recovery current in an aerator 55. The recovery fate enters the tube 51 forrecovery through the opening 50 located above the ﬂudicated bed.The recycle stream may contain particles that have been sludged from itfluidized the bed by the rinsing action of the additional water included in saidCurrent. In the aerator 54, such particles will attach to air bubbles beforeentering the fluidized bed, assisting them to ascend through the cell and pass adjacent to thethe foam layer 30 to be recovered with the tation product. The use of aeration inthe recycling stream will thus lead to improved recycling of particles inthe cell. The invention is not limited to any particular aeration device, of which itThere are a number of well-known examples available on the market. For best results should1015202530PS54395S E0014the aeration return circuit must be designed to suit the specific characteristicsof the selected aeration device, taking into account the size of the bubble, the residence timeand internal shear rate.In the embodiment shown in Fig. 1, it is necessary to introduce a liquid supply to the bottomof the flotation cell so that it can rise and fluidize the bed of particles. It is understood that inIn the embodiment shown in FIG. 2, all recovery liquid can be provided bythe recycling stream so that it is not necessary to introduce new supplies to the bottom ofthe flotation cell. The new supplies can therefore enter at any position.
This feature may be advantageous in the operation of systems in which the supplies contain somehydrophobic. particles that have a much lower density than the material to be rejected inthe flotation process. Such particles can in any case rise to the top of the fluidized bedthe bed. When the feed mixture is directed to the top of the fluidization zone, the waste canremoved from the bottom of the ﬂ oxidation zone or from the mixing zone.
Another advantage of using a recycle stream shown in FIG. 2 relates tothe operating properties of the very fine particles in the fluidized bed. Althoughthe velocity of the layer liquid in the bed is maintained at a value sufficient to ﬂ identifya substantial fraction of the particles, would be the very ﬁ n particles that may be present in onesupplies in practice tend to be sludged out of the idudicated bed. lthe embodiment shown in FlG. 2, such particles could be recycled back tobottom of the fluidized bed and they would also be able to come into contactwith the air bubble vent device. The recycle stream with aeration providesthus an effective means of increasing the efficiency of trapping the next particles ina t otation supply current.
A portion of the liquid needed to fluidize the contents of the totation cell 1 in FIG. 2 harprovided by the recovery stream passing through an outlet port 50,a recovery pipe 51, a pump 52, and a re-entry opening 53. It will be appreciated thatthe use of a recycle stream is just one of your ways in which fluidizing fluidcan be provided. Liquid can thus be drawn from another part of the flotation circuitwhich cell is part of or can be created from a freshwater reservoir. It can tooadded as extra dilution water in the supply pulp to the flotation cell.101520253035PS54395SE0015Another preferred embodiment of the invention is shown in FIG. 3. The device issubstantially the same as shown in FIG. 2 with the additional feature that ithorizontal cross-sectional area of foam zone 30 is smaller than that of fluidization zone 22.
Thus, the vertical wall 60 of the fluidization zone 22 and the release zone 40 are coveredwith a conical reduction section 61 connecting to the bottom of a second space 62with vertical walls enclosing foam zone 30. It will be appreciated that if the flow rate of gaswhich is let into the flotation cell is constant, so is the layer gas velocity, which isthe gas flow rate divided by the flow range, is higher in foam zone 30 than influidization zone 22. This feature provides ﬂ flexibility in the operation of the cell, thenthe speed requirements in the two zones do not have to be the same. It is particularly beneficialfor the recovery of coarse particles to drive the foam zone with relatively highlayer gas velocities, in the range 2 to 4 cm / s, while the optimum value in the fluidizedthe bed can be in the range 0.5 to 1 cm / s. By providing a smallercross-sectional area in the foam zone, it is possible to maintain a higher gas velocity there whileit is operated with a lower value in the id uidization zone. The reduction in foam area can alsoobtained by using the winding of foam which is a known technique. Even if itthe reduced area feature is described with reference to an embodiment containing arecovered liquid stream shown in FIG. 2, it will be appreciated that the same features may be advantageousapplied to the embodiment shown in FIG. 1 which does not include a recycling stream.
In the embodiments shown in FIG. 2 and FIG. 3, the air is dispersed inthe recovery liquid in the aerator 54. The bubbling liquid passes into the cell 1 intomixing region 5 in the vicinity of the impeller. Under certain circumstances, such as whenthe recovery fluid may contain large particles that could potentially blockthe aerator, it may be preferable to introduce the bubbles through a porous diffuser ordistributor at the bottom of the cell itself. In the alternative preferred embodiment asshown in FIG. 4, the cell is provided with a porous element 71. Air under pressure floats throughthe inlet tube 72 into the distribution chamber 73, and then through the porous element71, flowing out to the contents of the flotation cell In the form of fine bubbles region 5 inthe proximity of the impeller 2. A flow of ﬂidifying fluid is maintained by the circulation pump52. The bubbles mix with the recovery liquid and rise upwards through the ﬂ uidizedthe bed. In the embodiment shown in FIG. 4 shows the main features of the embodiment IFIG. 3 which have been retained, in particular with reference to the reduction in column area infoam zones. It will be appreciated that the distribution of air through the porous diffuser shown in IFIG. 4 can be advantageously used in embodiments shown in FIG. 1 and FIG. 2. Although101520253035PS54395SE0016means for the production of fine bubbles are depicted in FIG. 4 as a porous plate asextending substantially over the vessel 1, other forms of diffusers could be used,such as pipes or conduits with porous walls or with suitably placed openings, orknown patent-protected devices for the introduction of bubblori flotation columns,EXAMPLEA flotation cell was constructed according to the invention and operated in batch mode. A sample ofhigh quality galenite was used as the suspended material and it was mixed withclassified silica particles as a source of non-suspended matter. Galenitescrushed and sieved to provide a sample in the size range of 45 to 1400micrometer. The silica in the size range 250 to 710 micrometers.
The galenite: silica mass ratio was 1:19 and the sample volume was 1.05 liters.
Cell diameter was 100 mm, with a foam zone of diameter 63 mm and height 150 mm.
The total height of the cell was 920 mm. The cell was equipped with an impeller with a diameter of70 mm driven at 150 rpm, with a top speed of 0.55 m / s. A clear transitioncould be seen through the transparent cell wall between the top of the idudication zone andthe release zone when fluidized with recycle fluid. The contents of the cell werefluidized with liquid taken from the release zone and recovered through abubble generator to enter the cell in the mixing zone below the impeller. Xantat (45g / ton) was used as a collector and MlBC (25 ppm) as a foaming agent. Malmenconditioned for 15 minutes at a pH of 8.5 before flotation. The air was supplied with onespeed of 2 l / min. The fluid level in the cell was maintained by the addition of additive water ata position 120 mm below the protruding edge of the cell. The flotation productwere collected until no additional particles appeared to be depleted from the cell.
The results of the flotation test are shown in Figure 5, for the purpose of making comparisons, data forflotation of galenite in a mechanical cell (from Jowett, A., 1980. Formation and disruption ofparticIe-bubble aggregates in ﬂ otation. ln Fine Particles Processing (Ed. P.
Somasundaran), pp. 720-754 (American Institute of Mining and Metallurgical Engineers:New York)). Jowett's results are typical data for mechanical cells. It can be seen thatthe recovery is quite low for ultrafine particles, and as the particle size increases, increasesthe recovery to a maximum of 97 percent at a size of 60 μm, for largersizes reduce recycling rapidly. With the fluidized bed cell according to thisrecovery, the recycling remained essentially 95-100 percent for particle sizes up to850 pm, beyond which there was a gradual decline. The results show that the range ofPS54395SEO017particle sizes of galenite particles recovered by flotation can be extended by more than tentimes by the use of a fluidized bed flotation cell of this invention.

权利要求:
Claims (1)
[1]
A method of separating selected particles from a mixture of particles in a liquid within a flotation cell including the steps of: feeding the mixed particles and the liquid into a mixing zone containing bubbles in a lower part of the flotation cell. cells; agitating the liquid in the mixing zone to provide a substantially uniform distribution of particles, liquid and bubblory to the mixing zone while providing sufficient fluid flow upwardly through the mixing zone into a liquidization zone above to move the mixed particles upward into the fluidizing zone; allowing the selected particles to adhere to bubbles within the fluidization zone and rise to the top of the id fluidization zone; allowing bubbles with attached selected particles to rise above the fluidization zone into a release zone while removing other particles from the cell; forming a foam zone of bubbles and attaching selected particles to the top of the release zone; and removing the selected particles with bubbles from the foam zone. A method according to claim 1, wherein the intensity of the agitation in the mixing zone is limited so that a suspension cloud height formed by the agitation does not extend over the mixing zone and into the fluidization zone. A method according to claim 1 or 2, wherein the fluidization zone is substantially still and free from any turbulence generated in the mixing zone. A method according to any one of the preceding claims, wherein the other particles are removed from the fluidized bed. A method according to any one of claims 1 to 3 wherein the other particles are removed as waste from the lower part of the cell. A method according to any one of the preceding claims, including the step of controlling the level of a boundary layer between the release zone and the foam zone. A method according to any one of the preceding claims, including the step of controlling the level of the top of the id oxidation zone. A method according to any one of claims 1 to 7, wherein the sufficient ﬂ outflow is provided by feeding the mixed particles and the liquid into the mixing zone. A method according to any one of claims 1 to 7, wherein the sufficient fluid flow is at least partially provided by introducing a fluidized liquid into the mixing zone. A method according to claim 9, wherein the fluidized liquid is provided by recovered liquid from the release zone into the mixing zone. A method according to either claim 3 or claim 4, wherein the fluidized liquid is aerated before it is introduced into the mixing zone. A method according to any one of the preceding claims, wherein the supply of mixed particles is introduced at or below the top of the fluidization zone. A method according to any one of the preceding claims, wherein the liquid is stirred in the mixing zone by rotation of a mechanical impeller within the mixing zone. A method according to claim 13, wherein bubbles are provided in the mixing zone by drawing air into the mixing zone through the mechanical impeller. A method according to any one of the preceding claims, wherein bubbles are provided into the mixing zone by a porous element or diffuser. An apparatus for separating selected hydrophobic particles from a mixture of particles in a liquid, said apparatus including a flotation cell arranged to receive a supply of a mixture of particles and liquid into the lower part of the cell; PS. agitators operable in a mixing zone below the id oxidation zone in the lower part of the cell to provide a substantially uniform distribution of particles, liquid and bubblori mixing zone; a release zone in the cell located directly above and connected to the id oxidation zone so that selected hydrophobic particles attached to bubbles rising to the top of the fluidization zone float upward within the release zone, waste separation means arranged to remove non-hydrophobic particles from the cell; and an overflow drain at the top of the cell arranged to remove the selected hydrophobic particles from a foam layer formed above the release zone. The device of claim 16, wherein the waste separating means is arranged to remove non-hydrophilic particles from the top of the fluidization zone. The device of claim 16, wherein the waste separating means is arranged to remove non-hydrophobic particles from below the release zone. Device according to any one of claims 16 to 18, including first level control means arranged to maintain the position of the boundary layer between the foam zone and the release zone within the cell. Device according to any one of claims 16 to 19, including second level control means arranged to maintain the position of the top of the fluidization zone within the cell. Device according to any one of claims 9 to 20, wherein the oxidizing means include a recycling tube arranged to remove liquid from the release zone and pump it back into the mixing zone. The device of claim 21, wherein the tube for recovery includes an aerator arranged to disperse the bubbles into fluid passing through the tube for recovery. A device according to any one of claims 16 to 21, wherein the fluidizing means includes a porous element or diffuser located in the lower part of the cell arranged to supply said bubbles into the cell. Device according to any one of claims 16 to 23, wherein the stirring means includes a mechanical impeller arranged to be rotated in the mixing zone. The device of claim 24, wherein the fluidizing means includes a hollow drive shaft for the impeller arranged to supply air through the hollow drive shaft for dissolving and shearing to said bubbles of the impeller. Device according to any one of claims 16 to 25, including a waste removal pipe having an inlet end located in the boundary layer between the fluidization zone and the release zone within the cell. Device according to any one of claims 16 to 26, wherein the flotation cell has a region of reduced cross-sectional area above the release zone so that the layer gas velocity in the foam layer formed above the release zone is greater than the layer gas velocity in the release zone.

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同族专利:

公开号 | 公开日

FI20116320A|2011-12-23|

MX2011012508A|2012-03-06|

US20120061298A1|2012-03-15|

AU2009346778A1|2012-01-12|

ZA201109484B|2014-05-28|

WO2010135760A1|2010-12-02|

CA2762841A1|2010-12-02|

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法律状态:
2014-04-08| NAV| Patent application has lapsed|

优先权:

申请号 | 申请日 | 专利标题

PCT/AU2009/000653|WO2010135760A1|2009-05-26|2009-05-26|Improved method and apparatus for froth flotation in a vessel with agitation|

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