CA3184601A1

CA3184601A1 - Flotation arrangement and method

Info

Publication number: CA3184601A1
Application number: CA3184601A
Authority: CA
Inventors: Ian SHERRELL; Antti Rinne
Original assignee: Metso Outotec Finland Oy
Current assignee: Metso Finland Oy
Priority date: 2020-06-30
Filing date: 2021-06-23
Publication date: 2022-01-06
Also published as: CN217313904U; AU2021300601A1; CN113856913A; EP4171826A4; CL2022003789A1; EP4171826A1; WO2022003242A1

Abstract

A flotation arrangement (100) and method. The arrangement comprises mill (2) arranged for producing slurry, a flotation section (12) comprising at least one flotation unit (1) provided with a feed system (3), an overflow means (4), and an outlet (5), as well as a fluid bed device comprising de vices for creating a fluid bed and/or a froth device comprising devices for creating a froth layer, particles being fed for interaction with the froth layer. The flotation section (12) is followed by a first classification unit (6), the flotation section (12) is arranged for receiving, from the mill (2), slurry feed from which particles under 300 µm are not removed, and the flotation section (12) is operably connected to an inlet (7) of the first classification unit for classification of said under flow exiting from the flotation section (12) into a fine underflow stream (F) and a coarse underflow stream.

Description

2 FLOTATION ARRANGEMENT AND runnlop BACKGROUND
The invention relates to a flotation arrangement.
The invention further relates to a method for flotation.
There are needs for improving the effectiveness of the flotation in processes for liberating valuable minerals form mineral ore.
BRIEF DESCRIPTION
Viewed from a first aspect, there can be provided a flota-tion arrangement, comprising a mill arranged for producing slurry, a flotation section comprising at least one flota-tion unit, provided with a feed system for receiving slur-ry to be handled in said flotation unit, an overflow means for removing flotation concentrate, an outlet for removing underflow. The flotation unit comprises a fluid bed device comprising devices for creating a fluid bed and/or a froth device comprising devices for creating a froth layer, wherein particles are fed for interaction with the froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth layer, or any combi-nations thereof. The flotation section is followed by a first classification unit, and the flotation section (12) is arranged for receiving, from the mill, slurry feed from which particles under 300 pm are not removed. The flota-tion section is operably connected to an inlet of the first classification unit for classification of said un-derflow exiting from the flotation section into a fine un-derflow stream (F) and a coarse underflow stream that is tailings.
Thereby a flotation arrangement where it is handled a broad particle size distribution of particles containing both finer and coarser particles is achieved. It is sur-prisingly discovered that a very effective flotation of coarser particles containing valuable minerals is achieved due to fact that said coarser particles are combined with finer particles. Some portion of finer particles, however, containing valuable minerals arrives in underflow of flo-tation, from where they are recovered in first classifica-tion unit. Additionally, the arrangement allows upgrading of the fine particles.
Viewed from a second aspect, there can be provided a meth-od for flotation, the method comprising - creating a slurry feed in a mill, - feeding the feed from which particles under 300 pm are not removed from the mill to a flotation section compris-ing at least one flotation unit, wherein the flotation unit (1) comprises a fluid bed device comprising devices for creating a fluid bed and/or a froth device comprising devices for creating a froth layer, wherein particles are fed for interaction with the froth layer in the froth lay-er, under the froth layer to close proximity thereof, or above the froth layer, or any combinations thereof, - removing a flotation concentrate as an overflow from the flotation section, - removing an underflow from the flotation section, - feeding the underflow to a first classification unit, and - classifying the underflow into a fine underflow stream and a coarse underflow stream in the first classification unit.
Thereby a method for flotation handling a broad particle size distribution of particles containing both finer and coarser particles is achieved. It is surprisingly discov-ered that a very effective flotation of coarser particles containing valuable minerals is achieved due to fact that

3 said coarser particles are combined with finer particles.
Some portion of finer particles, however, containing valu-able minerals arrives in underflow of flotation, from where they are recovered in a first classification unit.
Additionally, the method allows upgrading of the fine par-ticles.
The arrangement and the method are characterised by what is stated in the independent claims. Some other embodi-ments are characterised by what is stated in the other claims. Inventive embodiments are also disclosed in the specification and drawings of this patent application. The inventive content of the patent application may also be defined in other ways than defined in the following claims. The inventive content may also be formed of sever-al separate inventions, especially if the invention is ex-amined in the light of expressed or implicit sub-tasks or in view of obtained benefits or benefit groups. Some of the definitions contained in the following claims may then be unnecessary in view of the separate inventive ideas.
Features of the different embodiments of the invention may, within the scope of the basic inventive idea, be ap-plied to other embodiments.
In one embodiment, the flotation unit comprises devices for creating a fluid bed. An advantage is that valuable particles are floated and at least most of fine particles are recovered. This allows an immediate disposal of coarse tailings. Another advantage is that the fine particles can processed downstream in standard flotation equipment with a higher separation efficiency.
In one embodiment, the flotation unit comprises devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the

4 froth layer to close proximity thereof, or above the froth layer, or any combinations thereof. An advantage is that the size of the flotation unit may be reduced, a high throughput per flotation unit volume may be achieved, and an immediate interaction with froth/bubbles leading to a potentially higher recovery.
In one embodiment, the flotation unit comprises the devic-es for creating a fluid bed and the devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth layer, or any combinations thereof. An advantage is that the recov-ery of coarse valuable minerals to concentrate may be max-imized.
In one embodiment, the classification unit comprises a classification cyclone. An advantage is that simple struc-ture without moving parts can be achieved.
In one embodiment, the fine underflow stream from the first classification unit is arranged to be fed to a flo-tation system comprising at least one flotation vessel. An advantage is that valuable minerals may be recovered.
In one embodiment, the flotation vessel is a fluid bed de-vice comprising devices for creating a fluid bed. An ad-vantage is that recovery of near-floating particles may be improved with added buoyancy of fluid bed.
In one embodiment, the flotation vessel is a device com-prising devices for creating a froth layer, wherein parti-cles are fed for interaction with froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth layer, or any combinations thereof. An advantage is that recovery of particles may be improved due to immediate addition to the froth layer.
In one embodiment, the flotation system comprises at least

5 three flotation vessels arranged in series such that the outlet for removing underflow of a preceding flotation vessel is connected to the inlet of a following flotation vessel. An advantage is that valuable minerals in the un-derflow may be recovered.
In one embodiment, the flotation vessel comprises the de-vice comprising an inlet connected for receiving feed to be handled in said flotation vessel and arranged to a low-er part of the flotation vessel, an overflow means for re-moving flotation concentrate, arranged to an upper part of the flotation vessel, and an outlet for removing under-flow, arranged to a lower part of the flotation vessel. An advantage is that a high recovery may be achieved due to a high energy input and good mixing properties.
In one embodiment, the flotation vessel comprises a me-chanical agitator for agitating surry in said vessel. An advantage is that separation of particles containing valu-able minerals from other particles may be intensified.
In one embodiment, the flotation vessel comprises a me-chanical agitator for creating bubbles in said vessel. An advantage is that separation of particles containing valu-able minerals from other particles may he intensified.
In one embodiment, the flotation vessel comprises a closed vessel for a pressurized flotation, wherein flotation con-centrate is removed by pressure from the vessel. An ad-vantage is that a high recovery may be achieved since there are no losses in the froth.

6 In one embodiment, the flotation vessel comprises devices for pneumatical gas addition. An advantage is that a bet-ter product grade and/or improved recovery of fine parti-cles may be achieved.
In one embodiment, at least one of the flotation vessels is a froth separation device comprising devices for creat-ing a froth layer, comprising an inlet connected for re-ceiving feed to be handled in said flotation vessel and arranged to an upper part of the flotation vessel, an overflow means for removing flotation concentrate, ar-ranged to an upper part of the flotation vessel, and an outlet for removing underflow, arranged to a lower part of the flotation vessel. An advantage is that a high product grade may be achieved.
In one embodiment, the flotation vessel comprises a down-comer for slurry infeed, the downcomer equipped with a nozzle for feeding pressurized flotation gas in slurry therein. An advantage is that a high recovery may be achieved resulting from a localized high energy input.
Another advantage is that especially fines recovery may be enhanced.
In one embodiment, the downcomer comprises an outlet noz-zle configured to induce a supersonic shockwave into the slurry as it exits the downcomer. An advantage is that flotation of fine and ultrafine particles comprising for example mineral ore or coal may be improved.
In one embodiment, the arrangement comprises a second sep-aration unit arranged for preventing large particles en-tering in the first classification unit. An advantage is that particles containing valuable minerals but too large for entering in the fine underflow stream may be recov-ered.

7 In one embodiment, the second separation unit is arranged before the flotation unit for preventing large particles entering in said flotation unit and the first classifica-tion unit. An advantage is that it is possible to avoid feeding in the flotation unit particles containing valua-ble minerals but too large for entering in the fine under-flow stream.
In one embodiment, the second separation unit is arranged between the flotation unit and the first classification unit. An advantage is that particles containing valuable minerals but too large for entering in the fine underflow stream may be recovered.
In one embodiment, the second separation unit comprises a grizzly or a grating. An advantage is that a simple struc-ture of the separation unit may be achieved.
In one embodiment, the second classification unit is con-nected to the mill for returning large particles back to the mill for further grinding. An advantage is that large particles containing valuable minerals may be grinded in size that may enter in the fine underflow stream.
In one embodiment, the flotation unit is deployed in an open-circuit configuration. An advantage is that a config-uration that is simple, has reduced energy usage and low capex and running costs may he achieved.
In one embodiment, the flotation unit is deployed in a closed-circuit configuration. An advantage is that recir-culation of particles may enhance recovery of valuable minerals.

8 BRIEF DESCRIPTION OF FIGURES
Some embodiments illustrating the present disclosure are described in more detail in the attached drawings, in which Figure 1 is a schematic view of an arrangement and a meth-od, Figure 2 is a schematic view of another arrangement and method, Figure 3 is a schematic view of a flotation system and a method, Figure 4 is a schematic view of another flotation system and a method, and Figure 5 is a schematic view of a third flotation system.
In the figures, some embodiments are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.
DETAILED DESCRIPTION
Figure 1 is a schematic view of a flotation arrangement 100 and a method.
The arrangement 100 comprises a mill 2 arranged for pro-ducing slurry, and a flotation section 12 comprising at least one flotation unit 1.
The mill 2 may be e.g. an autogencus grinding mill, or a semi-autogenous grinding mill, or a high-pressure grinding roll.

9 In the embodiment shown in Figure 1, the flotation section 12 includes one flotation unit 1. In another embodiments, there may be two, three or even more flotation units in the flotation section. If there are plurality of flotation units, they all may be of same type, or alternatively, there may be at least two types of flotation units.
The flotation unit 1 comprises a feed system 3 arranged to receive slurry to be handled in said flotation unit 1 from which slurry particles under 300 pm are not removed. The location of the feed system 3 depends on the type of the flotation unit 1. Thus, the feed system 3 may be located to a lower part, to an upper part or to a mid-part of the flotation unit 1.
The flotation unit 1 further comprises an overflow means 4 for removing flotation concentrate from said flotation unit, and an outlet 5 for removing underflow from said flotation unit.
In embodiments comprising plurality of flotation units, the units are in series such that a first of the of flota-tion units 1 is arranged to receive slurry to be handled in the flotation section 12, and the outlet 5 of a preced-ing flotation unit 1 is connected to the feed system 3 of a following flotation unit 1. The last one of the plurali-ty of flotation units 1 is arranged to remove underflow from the flotation section 12.
The arrangement 100 further comprises a first classifica-tion unit 6 comprising an inlet 7. The inlet 7 is arranged for receiving underflow from the flotation section 12. The first classification unit 6 is adapted for classification of the underflow into a fine underflow stream F and a coarse underflow stream that is tailings.

In an embodiment, the flotation unit 1 comprises a fluid bed device comprising devices for creating a fluid bed in the flotation unit 1. In another embodiment, the flotation unit 1 comprises a froth device that has devices for cre-5 ating a froth layer in the flotation unit 1. The froth layer may interact with particles of the product stream.
In an embodiment, the product stream is arranged to be fed in the froth layer, under the froth layer to close proxim-ity thereof, or above the froth layer, or any combinations

10 thereof. The term "close proximity" means distance of 20 cm or less from the froth layer in this description.
In an embodiment, the product stream is arranged to be fed in the froth layer, under the froth layer not more than 2 cm therefrom, or above the froth layer, or any combina-tions thereof.
In an embodiment, the flotation unit 1 comprises both the devices for creating a fluid bed and the devices for cre-ating a froth layer.
In an embodiment, the first classification unit 6 compris-es a cyclone. In another embodiments, the first classifi-cation unit 6 comprises, in addition to or as an alterna-tive to a cyclone, one or more of a non-mechanical sedi-mentation classifier, e.g., a settling cone; a mechanical sedimentation clas-sifier, e.g., a rake classifier or a spiral classifier; a free-settling classifier; and a hin-dered-settling classifier, e.g., a hydrosizer.
In an embodiment, the fine underflow stream F is fed from the first classification unit 6 to a flotation system 20 comprising at least one flotation vessel 21. The flotation system 20 is discussed more detailed in connection with Figures 3 and 4.

11 Figure 2 is a schematic view of another arrangement and a method.
In an embodiment, the arrangement comprises a second sepa-ration unit 13 that is arranged for preventing large par-ticles entering in the first classification unit 6. The large particles may contain valuable minerals, but they are too large for entering in the fine underflow stream F.
In an embodiment, such as shown in Figure 2, the second separation unit 13 is arranged between the flotation unit 1 and the first classification unit 6. In another embodi-ment, the second separation unit 13 is arranged before the flotation unit 1 for preventing large particles entering also in the flotation unit 1.
In an embodiment, the second classification unit 13 com-prises a grizzly or a grating.
In an embodiment, such as shown in Figure 2, the second classification unit 13 is connected to the mill 2 so that large particles can be returned to the mill 2 for further grinding.
Figure 3 is a schematic view of a flotation system and a method and Figure 4 is a schematic view of another flota-tion system and method. The flotation system 20 is ar-ranged in fluid communication with the first classifica-tion unit 6 described in this description so that the fine underflow stream F created in the first classification unit 6 is fed to the flotation system 20 that comprises at least one flotation vessel 21.
In an embodiment, the first classification unit 6 is oper-ated in an open-circuit configuration, i.e. without recir-

12 culation of material back into the first classification unit 6.
In an embodiment, the flotation vessel 21 is one of the following:
a fluid bed device comprising devices for creating a fluid bed, or a device comprising devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer to close proxim-ity thereof, or above the froth layer, or any combinations thereof, or a device comprising devices for pneumatical gas addition, or a closed vessel for a pressurized flotation, wherein flo-tation concentrate is removed by pressure from the vessel, or a device (such as shown in Figure 3) comprising an inlet 22 connected for receiving feed to be handled in said flo-tation vessel and arranged to a lower part of the flota-tion vessel 21, an overflow means 15 for removing flota-tion concentrate, arranged to an upper part of the flota-tion vessel (21), and an outlet 25 for removing underflow, arranged to a lower part of the flotation vessel 21. The term 'close proximity" means distance of 20 cm or less from the froth layer in this description.
In an embodiment, the flotation system 20 comprises at least three flotation vessels 21 arranged in series such that the outlet 25 for removing underflow of a preceding flotation vessel 21 is connected to the inlet 22 of a fol-lowing flotation vessel 21. In an embodiment, all the flo-tation vessels 21 in the flotation system 20 are of same type. In another embodiment, there are at least two types of flotation vessels 21 in the flotation system 20.

13 In an embodiment, the flotation vessel 21 comprises a me-chanical agitator for agitating surry in said vessel. Ad-ditionally, or alternatively, a mechanical agitator may be used for creating bubbles in the vessel.
In an embodiment, (such as shown in Figure 4) the flota-tion vessel 21 is a froth separation device comprising de-vices for creating a froth layer, wherein an inlet 22 con-nected for receiving feed to be handled in said flotation vessel is arranged to an upper part of the flotation ves-sel 21, an overflow means 15 for removing flotation con-centrate is arranged to an upper part of the flotation vessel 21, and an outlet 19 for removing underflow is ar-ranged to a lower part of the flotation vessel 21.
In an embodiment, the flotation vessel 21 comprises at least one downcomer that feeds slurry in the vessel. The downcomer is equipped with a nozzle for feeding pressur-ized flotation gas in slurry therein. Additionally, the downcomer comprises an outlet nozzle that is configured to induce a supersonic shockwave into mixture of gas and slurry as it exits the downcomer.
Figure 5 is a schematic view of a third flotation system.
As already disclosed, in an embodiment the flotation ves-sel 21 is a closed pressurized vessel where pressurized flotation may take place and wherefrom the flotation con-centrate is removed by pressure. In an embodiment, no froth is created in the vessel, but loaded bubbles are collected before a froth is generated.
An inlet 22 may be arranged to a lower part of the flota-tion vessel 21, an overflow means 15 may be arranged for removing flotation concentrate to an upper part of the flotation vessel 21, and an outlet 19 for removing under--Flow may he arranged to a lower part of the flotation yes-

14 sel 21. The flotation vessels 21 may be installed on the same level (as shown), since flowing from a vessel to next vessel takes place by virtue of pressure created in the vessels.
In an embodiment, an outlet 19 for removing underflow may be arranged to an upper part of the flotation vessel 21.
In an embodiment, the pressurized vessel comprises a me-chanical agitator. One example of this kind of vessel is known as "Direct Flotation Reactor- (DFR).
It is to be noted here that all the flotation vessels 21 arranged in the flotation system 20 may be of same type, or alternatively, there may be at least two types of flo-tation vessels.
The invention is not limited solely to the embodiments de-scribed above, but instead many variations are possible within the scope of the inventive concept defined by the claims below. Within the scope of the inventive concept the attributes of different embodiments and applications can be used in conjunction with or replace the attributes of another embodiment or application.
The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the inventive idea de-fined in the following claims.

REFERENCE SYMBOLS
1 flotation unit 5 2 mill 3 feed system 4 overflow means 5 outlet 6 classification unit 10 7 inlet of classification unit 12 flotation section 13 second separation unit

15 overflow means flotation system 15 21 flotation vessel 22 inlet of flotation vessel outlet for underflow 100 arrangement fine underflow stream

Claims

16

1. A flotation arrangement (100), comprising - a mill (2) arranged for producing slurry, - a flotation section (12) comprising at least one flota-tion unit (1), provided with - a feed system (3) for receiving slurry to be handled in said flotation unit (1), - an overflow means (4) for removing flotation concentrate, - an outlet (5) for removing underflow, wherein the flotation unit (1) comprises - a fluid bed device comprising devices for creat-ing a fluid bed and/or - a froth device comprising devices for creating a froth layer, wherein particles are fed for inter-action with the froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth layer, or any combinations thereof, the flotation section (12) being followed by a first clas-sification unit (6), wherein the flotation section (12) is arranged for receiving, from the mill (2), slurry feed from which particles under 300 pm are not removed, and the flotation section (12) is operably connected to an inlet (7) of the first classification unit for classification of said underflow exiting from the flotation section (12) in-to - a fine underflow stream (F) and - a coarse underflow stream that is tailings.

2. The arrangement as claimed in claim 1, wherein - the flotation unit (1) comprises the devices for creat-ing a fluid bed.

3. The arrangement as claimed in claim 1, wherein - the flotation unit (1) comprises the devices for creat-ing a froth layer, wherein particles are fed for interac-tion with froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth lay-er, or any combinations thereof.

4. The arrangement as claimed in claim 1, wherein - the flotation unit (1) comprises the devices for creat-ing a fluid bed and the devices for creating a froth lay-er, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth layer, or any combi-nations thereof.

5. The arrangement as claimed in any of the preceding claims, wherein the first classification unit (6) is a cy-clone.

6. The arrangement as claimed in any of the preceding claims, wherein the fine underflow stream (F) from the first classification unit (6) is arranged to be fed to a flotation system (20) comprising at least one flotation vessel (21).

7. The arrangement as claimed in claim 6, wherein the flo-tation vessel (21) is - a fluid bed device comprising devices for creating a fluid bed or - a device comprising devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer to close proxim-ity thereof, or above the froth layer, or any combinations thereof, or - a device comprising devices for pneumatical gas addi-tion, or - a device comprising a closed vessel for a pressurized flotation, wherein flotation concentrate is removed by pressure from the vessel, or - a device comprising - an inlet (22) connected for receiving feed to be handled in said flotation vessel and arranged to a lower part of the flotation vessel (21), - an overflow means (15) for removing flotation concen-trate, arranged to an upper part of the flotation vessel (21), and - an outlet (25) for removing underflow, arranged to a lower part of the flotation vessel (21).

8. The arrangement as claimed in claim 7, wherein - the flotation vessel (21) is - the device comprising devices for pneumatical gas addi-tion, or - the device comprising a closed vessel for a pressurized flotation, wherein flotation concentrate is removed by pressure from the vessel, or - the device comprising - an inlet (22) connected for receiving feed to be handled in said flotation vessel and arranged to a lower part of the flotation vessel (21), - an overflow means (15) for removing flotation concen-trate, arranged to an upper part of the flotation vessel (21), and - an outlet (25) for removing underflow, arranged to a lower part of the flotation vessel (21).

9. The arrangement as claimed in claim 8, wherein - the flotation vessel (21) is - the device comprising a closed vessel for a pressurized flotation, wherein flotation concentrate is removed by pressure from the vessel, or - the device comprising - an inlet (22) connected for receiving feed to be handled in said flotation vessel and arranged to a lower part of the flotation vessel (21), - an overflow means (15) for removing flotation concen-trate, arranged to an upper part of the flotation vessel (21), and - an outlet (25) for removing underflow, arranged to a lower part of the flotation vessel (21).

10. The arrangement as claimed in claim 9, wherein - the flotation system (20) comprises at least three flo-tation vessels (21) arranged in series such that the out-let (25) for removing underflow of a preceding flotation vessel (21) is connected to the inlet (22) of a following flotation vessel (21).

11. The arrangement as claimed in claim 9, wherein - the flotation vessel (21) comprises the device compris-ing - an inlet (22) connected for receiving feed to be handled in said flotation vessel and arranged to a lower part of the flotation vessel (21), - an overflow means (15) for removing flotation concen-trate, arranged to an upper part of the flotation vessel (21), and - an outlet (25) for removing underflow, arranged to a lower part of the flotation vessel (21).

12. The arrangement as claimed in claim 11, wherein the flotation vessel (21) comprises - devices for creating a froth layer.

13. The arrangement as claimed in claim 9, wherein - the flotation vessel (21) comprises a closed vessel for a pressurized flotation, wherein flotation concentrate is removed hy pressure from the vessel.

14. The arrangement as claimed in any of claims 11 - 13, wherein the flotation vessel (21) comprises - a mechanical agitator for agitating surry in said ves-sel.

15. The arrangement as claimed in any of claims 11 - 14, wherein the flotation vessel (21) comprises - a mechanical agitator for creating bubbles in said ves-sel.

16. The arrangement as claimed in claim 7, wherein - the flotation vessel (21) comprises devices for pneumat-ical gas addition.

17. The arrangement as claimed in claim 16, wherein - the flotation vessel (21) is a froth separation device comprising devices for creating a froth layer, comprising - an inlet (22) connected for receiving feed to be handled in said flotation vessel and arranged to an upper part of the flotation vessel (21), and - an overflow means (15) for removing flotation concen-trate, arranged to an upper part of the flotation vessel (21).

18. The arrangement as claimed in claim 16 or 17, wherein the flotation vessel (21) comprises - an outlet (19) for removing underflow, arranged to a lower part of the flotation vessel (21).

19. The arrangement as claimed in claim 17, wherein - the flotation vessel (21) comprises a downcomer for slurry infeed, the downcomer equipped with a nozzle for feeding pressurized flotation gas in slurry therein.

20. The arrangement as claimed in claim 19, wherein - the downcomer comprises an outlet nozzle configured to induce a supersonic shockwave into the slurry as it exits the downcomer.

21. The arrangement as claimed in any of the preceding claims, comprising - a second separation unit (13) arranged for preventing large particles entering in the first classification unit (6).

22. The arrangement as claimed in claim 21, wherein - the second separation unit (13) is arranged before the flotation unit (1) for preventing large particles entering in said flotation unit (1) and the first classification unit (6).

23. The arrangement as claimed in claim 21, wherein - the second separation unit (13) is arranged between the flotation unit (1) and the first classification unit (6).

24. The arrangement as claimed in any of claims 21 - 23, wherein - the second separation unit (13) comprises a grizzly or a grating.

25. The arrangement as claimed in any of claims 21 - 24, wherein - the second separation unit (13) is connected to the mill (2) for returning large particles back to the mill (2) for further grinding.

26. The arrangement as claimed in any of the preceding claims, wherein - the flotation unit (1) is deployed in an open-circuit configuration.

27. The arrangement as claimed in any of claims 1 - 25, wherein - the flotation unit (1) is deployed in a closed-circuit configuration.

28. A method for flotation, the method comprising - creating a slurry feed in a mill (2), - feeding the feed from which particles under 300 pm are not removed from the mill (2) to a flotation section (12) comprising at least one flotation unit (1), wherein the flotation unit (1) comprises a fluid bed device comprising devices for creating a fluid bed and/or a froth device comprising devices for creating a froth layer, wherein particles are fed for interaction with the froth layer in the froth layer, under the froth layer to close proximity thereof, or above the froth layer, or any combinations thereof, - removing a flotation concentrate as an overflow from the flotation section (12), - removing an underflow from the flotation section (12), - feeding the underflow to a first classification unit (6), and - classifying the underflow into a fine underflow stream and a coarse underflow stream in the first classification unit (6).