Diffuser arrangement and flotation cell

Abstract

A diffuser arrangement for a flotation cell (1) and a flotation cell. The diffuser arrangement (100) comprises a set of rods (3), the set of rods (3) including at least two rods (4) arranged parallel and on at least one horizontal imaginary plane (P) at a structural element of the cell.

Description

[0001] DIFFUSER ARRANGEMENT AND FLOTATION CELL

[0002] BACKGROUND

[0003] The invention relates to a diffuser arrangement for a f lotation cell .

[0004] The invention further relates to a flotation cell , comprising at least one diffuser arrangement .

[0005] There have been many problems over the years with flotation cells having excessive turbulence at the surface of the cel l and this type of problem can have a serious impact on the grade of froth concentrate being produced from the flotation cell and the recovery of the flotation cell .

[0006] BRIEF DESCRIPTION

[0007] Viewed from a first aspect , there can be provided a diffuser arrangement for a f lotation cell , the diffuser arrangement comprising a set of rods , the set of rods including at least two rods arranged parallel and on at least one hori zonal imaginary plane at a structural element of the cell .

[0008] Thereby a diffuser arrangement that helps the flotation cell succes sfully produce a froth concentrate without having to deal with excessive turbulence reducing the froth concentrate grade or recovery may be achieved . One of the main advantages of the diffuser arrangement is that it will not suffer from solids build up that can reduce its efficiency .

[0009] Viewed from a further aspect , there can be provided a flotation cell , comprising at least one diffuser arrangement as defined in the first aspect .

[0010] Thereby a flotation cell producing good froth concentrate may be achieved . A more quiescent area in the top regions of the flotation cel l may be achieved so that some of the entrained gangue has sufficient time to drain from the froth zone whereby the grade of froth concentrate is maintained . In these upper areas near the semi-froth zone the slurry velocity is reduced so there is the opportunity for smaller bubbles to collide into each other and form larger bubbles .

[0011] The diffuser arrangement and the flotation cell are characterised by what is stated in the independent claims . Some other embodiments 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 several separate inventions , especially if the invention is examined in the light of expressed or impl icit 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 applied to other embodiments .

[0012] Various embodiments of the aspects may comprise at least one feature from the following paragraphs :

[0013] In an embodiment , the overall shape of the set of rods in the hori zontal plane is roundish, such as round .

[0014] An advantage is that a symmetrical turbulence reducing effect may be provided .

[0015] In an embodiment , the rods in a set are arranged on one hori zonal imaginary plane .

[0016] An advantage is that the structure is simple and needs only a little space in vertical direction in the cell . In an embodiment , the rods are arranged on at least two hori zonal imaginary planes .

[0017] An advantage is that the effect of the diffuser arrangement on preventing turbulence and creating smaller bubbles may be advanced, and thus a more efficient flotation process may be achieved .

[0018] In an embodiment , the set of rods is arranged to surround an element of the flotation cell .

[0019] An advantage is that a symmetrical turbulence reducing ef fect may be provided around the element .

[0020] In an embodiment , the flotation cell comprises a vertically arranged blast tube for feeding slurry and air in the flotation cell , and wherein the set of rods is arranged around said blast tube , preferably concentrically with said blast tube .

[0021] An advantage is that a symmetrical turbulence reducing ef fect may be provided around the blast tube .

[0022] In an embodiment , the flotation cell comprises a launder and wherein the set of rods is arranged at said launder .

[0023] An advantage is that excessive turbulences at the launder may be prevented and high froth concentrate grade at the launder may be achieved .

[0024] In an embodiment , the set of rods is located at the inner perimeter of a flotation tank .

[0025] An advantage is that a broadly effective turbulence reducing field may be provided in the flotation tank . In an embodiment , the cross-section of at least one of the rods is roundish, such as round .

[0026] An advantage is that the shape is simple and may provide an equal turbulence reducing effect irrespective of flow direction .

[0027] In an embodiment , the cross-section of at least one of the rods is angular, such as triangular or quadrangular .

[0028] An advantage is that the turbulence reducing effects of the arrangement can be concentrated or directed in a desired way .

[0029] In an embodiment , the rods arranged on at least two at least two hori zonal imaginary planes are dimensioned so that in a cross-section of the set of rods , the outer edges of the rods make an angle with the hori zontal plane that is selected in range of 30 ° to 60 ° (upwards from the hori zontal plane ) or -30 ° to - 60 ° (downwards from the hori zontal plane ) .

[0030] An advantage is that the turbulence reducing effects of the arrangement may be optimi zed and thereby the recovery of valuable particles may be increased .

[0031] In an embodiment , the open cross-sectional area between the rods over the total cross-sectional area of the set is selected in range of 25 % - 75 % .

[0032] An advantage is that the turbulence reducing effects of the arrangement may be optimi zed while risk for clogging the diffuser arrangement may be substantially reduced, and thereby the recovery of valuable particles may be increased . In an embodiment , the flotation cell comprises at least one blast tube , and an impinger arranged on the longitudinal axis of the blast tube and at a di stance from the exit end thereof , the impinger configured to deflect a flow of slurry exiting from said exit end and to direct the flow radially outwards .

[0033] An advantage is that contacts between flotation gas bubbles and slurry particles may further be promoted, while turbulences on the upper part of the tank may be reduced, and thereby the recovery of valuable particles may be increased .

[0034] BRIEF DESCRIPTION OF FIGURES

[0035] Some embodiments illustrating the present disclosure are described in more detail in the attached drawings , in which

[0036] Figure 1 is a schematic view of a diffuser arrangement and a flotation cell in partial cross-section,

[0037] Figure 2 is a schematic view of a diffuser arrangement from bottom,

[0038] Figure 3 is a schematic side view of a detail of a diffuser arrangement in partial cross-section,

[0039] Figure 4 is a schematic side view of a detail of a diffuser arrangement in cross-section,

[0040] Figure 5 is a schematic side view of a detail of a diffuser arrangement in cross-section,

[0041] Figure 6 is a schematic side view of a detail of a diffuser arrangement in cross-section,

[0042] Figure 7 is a schematic side view of a detail of a diffuser arrangement , Figure 8 is a schematic side view of a detail of a diffuser arrangement ,

[0043] Figure 9 is a schematic side view of a detail of a diffuser arrangement ,

[0044] Figure 10 is a schematic side view of a detail of a diffuser arrangement in cross-section,

[0045] Figure 11 is a schematic view of a diffuser arrangement from top,

[0046] Figure 12 is a schematic view of a diffuser arrangement from top,

[0047] Figure 13 is a schematic view of a flotation cell from top,

[0048] Figure 14 is a schematic view of a flotation cell from top,

[0049] Figure 15 is a schematic view of a flotation cell from top,

[0050] Figure 16 is a schematic side view of a diffuser arrangement , and

[0051] Figure 17 is a schematic side view of a diffuser arrangement and a flotation cell in partial cross-section .

[0052] 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 .

[0053] DETAILED DESCRIPTION

[0054] Figure 1 is a schematic view of a diffuser arrangement and a flotation cell in partial cross-section .

[0055] In an embodiment , the flotation cel l 1 is so-called pneumatic flotation cell , where flotation gas , typically air, is introduced in a high-shear device such as a blast tube 2 with slurry infeed . In this description, the term "blast tube" covers means for feeding flotation gas as such or together with slurry in the flotation cell , Thus , the blast tube may be e . g . a sparger or a downcomer, etc .

[0056] The blast tube 2 creates fine flotation gas bubbles that are able to entrap also finer particles already during the bubble formation taking place in the blast tube . Surry and flotation gas bubbles exits the blast tube 2 through an outlet noz zle arranged in an exit end 5 of the blast tube in a flotation tank 9 .

[0057] In an embodiment , the flotation cell 1 comprises 2 to 40 blast tubes 2 , preferably 4 to 24 blast tubes . Typically, the blast tubes 2 are arranged vertically, i . e . their longitudinal axes are arranged in vertical direction Y .

[0058] In an embodiment , flotation gas is introduced in a selfaspirating manner in the blast tube due to the formation of a vacuum within the downcomer . Flotation cells 1 including this kind of blast tubes are often called as Jameson cells , and the blast tubes 2 as downcomers . Figure 1 is showing a downcomer of a Jameson cell .

[0059] In another embodiment , flotation gas is pressuri zed prior to its feeding in the blast tube .

[0060] In an embodiment , a set of rods 3 is arranged in a surrounding form around at least one of the blast tubes 2 , preferably around each blast tubes 2 arranged in the cell .

[0061] In an embodiment , the f lotation cell 1 comprises a launder 13 that is arranged to receive froth F overflow and discharge the overflow from the flotation cell . The flotation cell 1 may comprise further features and structures for directing and controlling flowing of slurry in the flotation tank 9, such as baffles 11.

[0062] Figure 2 is a schematic view of a diffuser arrangement seen from direction of the exit end.

[0063] In an embodiment, the set of rods 3 is arranged concentrically with a blast tube 2. In other words, centres of the surrounding rods 4 are on the longitudinal axis of the blast tube .

[0064] In an embodiment, the rods 4 are arranged so that the longitudinal axis of the blast tube is perpendicular to the overall shape of the rods 4. In other words, the longitudinal axis of the blast tube is perpendicular to an imaginary plane P on which the rod 4 lies.

[0065] In an embodiment, the set of rods 3 comprises 2 - 10 rods. The embodiment shown in Figure 2 comprises six rods. It is to be noted, however, that the number of the rods depends on e.g. the dimensions of the cell, and thus there may be dozens of rods, or even hundreds of rods in the flotation cell .

[0066] In an embodiment, the rods 4 in the set are fixed to each other by at least one support beam 7. The embodiment shown in Figure 2 comprises four support beams, but their number may vary. In an embodiment, such as shown in Figure 2, the set 3 is attached by the support beams 7 to the blast tube 2. Thus, the set 3 of the rods makes with the blast tube 2 a unit or module that can be assembled in or removed from the cell as a single unit. In an embodiment, the set 3 is attached to another element or part of the flotation tank 9, such as to the side wall or to the baffle thereof by e.g. the support beams 7. In an embodiment, such as shown in Figure 2, all the rods 4 in the set of rods are formed in a circular or ring-shaped form, and thus the set 3 round. However, in some embodiments the set - or its outer circumference - may have another shape. The shape may be, for instance, elliptic or polygonal, the latter with or without rounded vertexes.

[0067] In an embodiment, the outer diameter D of the set 3 is at least 1.5 times about the outer diameter d of the blast tube. In an embodiment the outer diameter D is at least two times the outer diameter d of the blast tube.

[0068] In an embodiment, such as shown in Figure 2, there is a gap 8 between the innermost rod 4 and the blast tube 2. The gap may prevent any solids build up in the interface of the diffuser arrangement and the blast tube.

[0069] In an embodiment, horizontal spacings Sh of all successive rods 4 are same in the set of rods. In another embodiment, horizontal spacings in the set of rods vary. The term "horizontal spacing" means here the distance between projections of successive rods 4 on a same horizontal plane. This projection can be seen in Figure 2. In an embodiment, the spacing of two successive rods 4 is selected so that an open cross-sectional area between the rods 4 of the set over the total cross-sectional area of the set (consisting of said of open cross-sectional area and a cross sectional area of the rods) is selected in range of 25 % - 75 %.

[0070] Figure 3 is a schematic side view of a detail of a diffuser arrangement in partial cross-section.

[0071] It is to be noted that the rods 4 disclosed in this description may be manufactured from metallic materials, such as steel, or composite materials, such as reinforced polymer composites .

[0072] The set of rods 3 comprises plurality of rods 4, i.e. at least two rods, such as 4 - 10 rods. In an embodiment, such as shown in Figure 1, the rods have a ring-shaped overall shape. The rods 4 are arranged on plurality of superposed horizonal imaginary planes P (shown in Figures 3 and 4, for instance) and have different outer ring-diameters. The rod 4 having the largest overall outer diameter is arranged on the lowest horizonal imaginary plane. The rest of the rods 4 are arranged so that their outer overall diameter decreases as the distance from the largest rod 4 increases.

[0073] In an embodiment, the cross-section of the rod 4 is angular, such as triangular or quadrangular. The embodiment shown in Figure 3 comprises rods 4 that have a shape of isosceles triangle, the base of which is arranged perpendicular to the vertical direction Y and the vertex point pointing upwards, i.e. away from the exit end 5 of said blast tube.

[0074] It is to be noted that rods 4 having non-symmetrical crosssections may be positioned many alternative ways in relation to the horizonal imaginary plane P or the vertical direction Y. Additionally, it is not necessary to position all the rods similarly. For example, one of the triangular rods shown in Figure 3 can be positioned so that its vertex point is pointing downwards, i.e. towards the exit end 5, etc.

[0075] In an embodiment, all the rods 4 in the set 3 have same cross-sectional shape and size. In another embodiment, the set 3 comprises rods having different shape and / or size.

[0076] In an embodiment, all the rods 4 in the set of rods are positioned so that an imaginary line L crosses the outer edges or periphery 6 of the rods and makes an angle A with the vertical direction Y. In an embodiment, said angle A is selected in range of -30° to -60°. The means here that the angle A is below the horizontal plane and the outer edges or periphery 6 increases when going downwards from one imaginary plane P to another imaginary plane P. In Figure 3 the angle A is about -45°.

[0077] Figure 4 is a schematic side view of a detail of a diffuser arrangement in cross-section.

[0078] In an embodiment, the cross-section of the rod 4 is roundish, such as round (such as shown in Figure 4) or oval.

[0079] In an embodiment, spacings S of all successive rods 4 are same in the set of rods. The term "spacing" means the distance of imaginary planes on which the rod 4 lies and which are perpendicular to the vertical direction Y. Figure 4 is showing two spacings SI and S2. In an embodiment, the spacing of two successive rods 4 is selected so that an open cross-sectional area OA between the rods 4 of the set over the total cross-sectional area AR of the set (consisting of said of open cross-sectional area OA and a cross sectional area of the rods) is selected in range of 25 % - 75 %. In Figure 4 is shown the open cross-sectional area OA between three rods 4.

[0080] In another embodiment, spacings in the set of rods vary. For instance, in Figure 4 the first spacing SI may be larger than the second spacing S2, or vice versa.

[0081] Figure 5 is a schematic side view of a detail of a diffuser arrangement in cross-section. In an embodiment, the rod 4 has a quadrangular cross-section. The cross-section may be square, parallelogram, trapezoid, for instance. In the embodiment shown in Figure 5, the cross-section of the rod is parallelogram having a longer dimension and a shorter dimension . The longer dimension is arranged perpendicular to the vertical direction Y . In another embodiments , the longer dimension may be arranged parallel with the longitudinal direction Y, or to some another angle in relation to said longitudinal direction Y .

[0082] In the embodiments shown in Figures , all rods 4 of the set of rods have similar cross-sectional shape and si ze . However, this is not always the case , i . e . in some embodiments the set of rods 3 comprises rods 4 having various cross- sectional shapes and / or si zes .

[0083] Figure 6 is a schematic side view of a detail of a diffuser arrangement in cross-section .

[0084] As already disclosed, all the rods 4 in the set of rods may be positioned so that an imaginary line L crosses the outer edges or periphery 6 of the rods and makes an angle A with the vertical direction Y .

[0085] In another embodiment , such as shown in Figure 6 , at least one rod 4 in the set of rods is positioned such that said imaginary line L does not cross the outer edge thereof . However, most of the rods 4 are on said line L as defined herein . In Figure 6, the outmost rod, or the largest in its overall diameter, is offset to the line L .

[0086] In an embodiment , the line L is not straight but curved . It can curve either downwards ( as shown in Figure 6 by dot- and-dash line ) or upwards .

[0087] Figure 7 is a schematic side view of a detail of a diffuser arrangement . In this embodiment , the rods 4 have a round cross-section, the spacing between two successive rods is 52 % and the angle A is +30 ° , as defined in the description relating to Figures 3 and 4 . The distance E between the exit end 5 and the rod 4 arranged closest to said exit end may vary depending on the details of the flotation cell. In an embodiment, the height position of the set of rods is selected so that it is in the pulp or slurry zone of the flotation cell.

[0088] Figure 8 is a schematic side view of a detail of a diffuser arrangement. In this embodiment, the rods 4 have a round cross-section, the spacing between two successive rods is 60 % and the angle A is +45°, as defined in the description relating to Figures 3 and 4.

[0089] Figure 9 is a schematic side view of a detail of a diffuser arrangement. In this embodiment, the rods 4 have a round cross-section, the spacing between two successive rods is 71 % and the angle A is +60°, as defined in the description relating to Figures 3 and 4.

[0090] Figure 10 is a schematic side view of a detail of a diffuser arrangement in cross-section. In an embodiment, the rod 4 that has the longest surrounding length is arranged uppermost in the set 3 of rods. For instance, if the rods are ring-shaped, the rod having the largest diameter is the uppermost one in the set of rods. The rest of the rod(s) 4 in the set of rods are arranged so that their surrounding length decreases as the distance from said upmost rod increases. In other words, the order of the rods is opposite to that shown e.g. in Figure 4.

[0091] In an embodiment, all the rods 4 in the set of rods are positioned so that an imaginary line L crosses the outer edges or periphery 6 of the rods and makes an angle A with the vertical direction Y. In an embodiment, said angle A is selected in range of +30° to +60°. The "+" means here that the angle A is above the horizontal plane and the outer edges or periphery 6 increases when going upwards from one imaginary plane P to another imaginary plane P. In Figure 3 the angle A is about 30°.

[0092] Figure 11 is a schematic view of a diffuser arrangement from top. The overall shape of the set of rods 3 shown in the previous Figures is round. However, other overall shapes are also possible. In an embodiment, the overall shape of the set of rods 3 is oval, such as shown in Figure 11. Other roundish shapes are possible, too. In an embodiment, the overall shape of the set of rods 3 is angular, such as hexagonal shown in Figure 12.

[0093] In an embodiment the overall shape of the rod 4 is surrounding so that the it has a continuous or closed shape, such as shown in Figures 2 and 12. In an embodiment the rod 4 has a curving or angular but discontinuous overall shape, such as shown in Figure 11. In an embodiment, the set of rods 3 may comprise both continuous and discontinuous rods.

[0094] Figure 13 is a schematic view of a flotation cell from top. As discussed in this description, the set of rods 3 can be arranged around a blast tube or downcomer. In another embodiments, the set of rods 3 is arranged to surround some another element or elements of the flotation cell 1, such as connecting launder ducts, transition ducts, internal or external launders, shafts in mechanical cells, such as a rotor shaft, open pipes, dart valve shafts, etc., i.e. anywhere where turbulence may occur. Thus, the diffuser arrangement 100 can be used also in the flotation technology based on mechanical cells, column cells, float-cells with fluidized beds, or in any flotation cell that produces a concentrate with or without froth, as far as gas bubbles or gas phase is appearing in the process. In an embodiment, the flotation cell 1 comprises a centre launder 15 for feeding slurry therein, and the set of rods 3 is arranged around said centre launder. In an embodiment, the set of rods 3 is arranged concentrically with the centre launder 15.

[0095] Figure 14 is a schematic view of a flotation cell from top. In an embodiment, such as shown in Figure 14, the set of rods 3 is located around the perimeter 14 of the flotation tank 9. The rod 4 having the longest surrounding length - or largest diameter in case of e.g. ring-like rods - is arranged closest to the wall of the flotation cell, and it may be the lowermost or uppermost rod in the set 3 of rods in embodiments where the rods are arranged on at least two horizontal imaginary planes.

[0096] Figure 15 is a schematic view of a flotation cell from top. The flotation cell 1 may have a polygonal, such as quadrangular, flotation tank 9. Figure 15 is showing four different embodiments of diffuser arrangements 100 in the flotation cell 1. It is to be noted that said embodiments, as well other embodiments described in this description, may be present in flotation cells in various combinations depending on e.g. the size, shape and purpose of said flotation cells .

[0097] In an embodiment, the diffuser arrangement 100 comprises straight rods. These rods may be arranged e.g. at the periphery of the flotation cell, or at a launder 13, such as shown in bottom right of Figure 15. In an embodiment, the rod may have two or more straight sections that are angled. In Figure 15 top left it is shown straight rods 4 having straight angle. In an embodiment , the rod 4 makes a closed angular loop . In Figure 15 bottom left it is shown rods 4 having rectangular overall shape .

[0098] In an embodiment , the diffuser arrangement 100 comprises a combination of closed loop rods and open end / discontinuous rods . In Figure 15 top right is shown an embodiment that comprises straight rods having angled sections and ringshaped rods .

[0099] In an embodiment , such as shown in Figure 2 , there is a gap 8 between the innermost rod 4 and the structural element at which the set of rods is arranged . The gap may prevent any solids build up in the interface of the diffuser arrangement and the blast tube .

[0100] Figure 16 is a schematic side view of a diffuser arrangement . In an embodiment , such as shown in Figure 16 , an impinger 10 is arranged below and coaxial with the blast tube and at a distance from the exit end 5 .

[0101] In an embodiment , the impinger 10 comprises a concave , such as domed or bowl , shape towards the respective blast tube .

[0102] The impinger 10 is configured to deflect a flow of slurry ( and flotation gas , typically air, mixed therewith) exiting from the exit end 5 and to direct said flow radially outwards to sidewalls of a flotation tank 9 and upwards towards upper parts of said flotation tank . In an embodiment , the set of rods 3 is arranged such that at least most of the flow bouncing or reflecting from the impinger 10 meets the rods 4 .

[0103] Figure 17 is a schematic side view of a diffuser arrangement and a flotation cell in partial cross-section . Figure 17 is showing embodiments of diffuser arrangements 100 arranged in three positions in the flotation cell 1 . The embodiments of arrangements 100 shown in Figure 17 and discus sed below may all be present in a very same flotation cell 1 , but this is not necessary in all embodiments .

[0104] In an embodiment , at least one set of rods 3 is arranged at the inner perimeter 14 of the flotation tank . Said set of rods 3 may circumvent all the inner periphery, but not necessary .

[0105] In an embodiment , the flotation cell 1 compri ses a launder 13 arranged around the upper part of the flotation cell for receiving the froth overflow . The launder may be an external launder, such as shown in Figure 17 , or an internal launder (not shown) arranged inside the flotation cell . At least one set of rods 3 may be arranged at the launder or wall thereof .

[0106] In an embodiment , the flotation cel l 1 comprises a feeder 15 for feeding slurry, and optionally also air, in the flotation cell . At least one set of rods 3 may be arranged around the feeder 15 .

[0107] It is to be noted that the positions and angles of the sets 3 , as well as number of the rods in the sets , may vary from those shown in Figure 17 . In embodiments of flotation cell 1 where froth or froth layer F is created, the set of rods 3 is arranged below the froth layer F .

[0108] The invention is not limited solely to the embodiments described 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 conj unction with or replace the attributes of another embodiment or application . The drawings and the related description are only intended to il lustrate the idea of the invention . The invention may vary in detail within the scope of the inventive idea de- fined in the following claims .

[0109] REFERENCE SYMBOLS

[0110] 1 I flotation cell

[0111] 2 blast tube

[0112] 3 set of rods

[0113] 4 rod

[0114] 5 exit end

[0115] 6 outer edge

[0116] 7 support beam

[0117] 8 gap

[0118] 9 flotation tank

[0119] 10 impinger

[0120] 11 baffle

[0121] 12 outlet noz zle

[0122] 13 launder

[0123] 14 perimeter

[0124] 15 feeder

[0125] 100 diffuser arrangement

[0126] A angle

[0127] AR area

[0128] D, d diameter

[0129] E distance

[0130] F froth

[0131] L imaginary line

[0132] OA open cross-sectional area

[0133] P imaginary plane

[0134] R radius

[0135] S spacing between two successive rods

[0136] Y vertical direction

Claims

CLAIMS1. A diffuser arrangement for a flotation cell (1) , the diffuser arrangement (100) comprising- a set of rods (3) ,- the set of rods (3) including at least two rods (4) arranged parallel and on at least one horizonal imaginary plane (P) at a structural element of the cell.

2. The diffuser arrangement as claimed in claim 1, wherein- the cross-section of the rod (4) is roundish, such as round .

3. The diffuser arrangement as claimed in claim 1, wherein- the cross-section of the rod (4) is angular, such as triangular or quadrangular.

4. The diffuser arrangement as claimed in any of the preceding claims, wherein- the overall shape of the rod (4) is roundish, such as ring-shaped .

5. The diffuser arrangement as claimed in any of claims 1- 3, wherein the overall shape of the rod (4) is straight or angular.

6. The diffuser arrangement as claimed in any of the preceding claims, wherein- the rods (4) are arranged on one horizonal imaginary plane (P) •7. The diffuser arrangement as claimed in any of claims 1- 5, wherein- the rods (4) are arranged on at least two horizonal imaginary planes (P) .

8. The diffuser arrangement as claimed in claim 7, wherein- the rods (4) are dimensioned and positioned so that in a cross-section of the set of rods (3) , the outer edges (6) of the rods make an angle (A) with the horizontal plane that is selected in range of +30° to +60° (upwards from the horizontal plane) or -30° to - 60 ° (downwards from the horizontal plane) .

9. The diffuser arrangement as claimed in any of the preceding claims, wherein- in a vertically arranged imaginary plane,- the open cross-sectional area (OA) between the rods (4) over the total cross-sectional area (AR) of the set is selected in range of 25 % - 75 %.

10. The diffuser arrangement as claimed in any of the preceding claims, wherein- in a horizontally arranged imaginary plane,- the projection of open cross-sectional area (OA) between the rods (4) over the projection of total cross-sectional area (AR) of the set is selected in range of 25 % - 75 %.

11. The diffuser arrangement as claimed in any of the preceding claims, wherein- the set of rods (3) is arranged to surround an element of the flotation cell (1) .

12. The diffuser arrangement as claimed in any of the preceding claims, wherein- the set of rods (3) is arranged at an inner periphery of an element of the flotation cell (1) .

13. The diffuser arrangement as claimed in claim 11, wherein- the flotation cell (1) comprises a vertically arranged blast tube (2) for feeding slurry and air in the flotation cell, and wherein- the set of rods (3) is arranged around said blast tube (2) , preferably concentrically with said blast tube (2) .

14. The diffuser arrangement as claimed in claim 8, wherein the flotation cell (1) comprises a launder (13) , and wherein- the set of rods (3) is arranged at said launder (13) .

15. The diffuser arrangement as claimed in claim 12, wherein- the set of rods (3) is located at the perimeter (14) of a flotation tank.

16. A flotation cell (1) , comprising at least one diffuser arrangement as claimed in any of the preceding claims.

17. The flotation cell as claimed in claim 16, comprising- the blast tube (2) as claimed in claim 13, and- an impinger (10) arranged under the blast tube and at a distance from the exit end (5) thereof and configured to deflect a flow of slurry exiting from said exit end (5) and to direct the flow radially outwards.

18. The flotation cell as claimed in claim 16 or 17, wherein- the height position of the set of rods (3) is selected so that it is in the pulp or slurry zone of the flotation cell (1) •

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