Flotation Cell

Abstract

A flotation cell for treating particles suspended in slurry and for separating the slurry into an underflow and an overflow is disclosed. The flotation cell includes a flotation tank including a center, a perimeter, a bottom, and a side wall; and a launder and a launder lip surrounding the perimeter of the flotation tank. The flotation tank further includes blast tubes for introducing slurry infeed into the flotation tank. A flotation line, as well as a use of the flotation line is also disclosed.

Claims

1. A flotation cell for treating particles suspended in slurry and for separating the slurry into underflow and overflow, the flotation cell comprising: a flotation tank comprising a center, a perimeter, a bottom, and a sidewall; and a launder and a launder lip surrounding the perimeter of the flotation tank; the flotation tank having a height, measured as the distance from the bottom to the launder lip, at the perimeter of the flotation tank at most 20% lower than at the center of the flotation tank; and underflow arranged to be removed from the flotation tank via a tailings outlet arranged at the side wall of the flotation tank, characterized in that the flotation tank further comprises blast tubes for introducing slurry infeed into the flotation tank, a blast tube comprising: an inlet nozzle for feeding slurry infeed into the blast tube, an inlet for pressurized gas, the slurry infeed subjected to the pressurized gas as it is discharged from the inlet nozzle, an elongated chamber arranged to receive under pressure the slurry infeed, an outlet nozzle configured to restrict flow of slurry infeed from the outlet nozzle, and to maintain slurry infeed in the elongated chamber under pressure, and an impinger configured to contact a flow of slurry infeed from the outlet nozzle and to direct the flow of slurry infeed radially outwards and upwards of the impinger.

2. The flotation cell according to claim 1, wherein the outlet nozzle is configured to produce a supersonic shockwave into the slurry infeed, the supersonic shockwave inducing formation of flotation gas bubble-particle agglomerates.

3. The flotation cell according to claim 1, wherein it comprises 2 to 40 blast tubes, preferably 4 to 24 blast tubes.

4. The flotation cell according to claim 1, wherein the blast tubes are arranged concentric to the perimeter of the flotation tank at a distance from the center of the flotation tank.

5. The flotation cell according to claim 4, wherein a distance of an outlet nozzle from the center of the flotation tank is 10 to 40% of the diameter of the flotation tank, measured at a distance of the outlet nozzle from the bottom of the flotation tank; preferably 25% of the diameter of the flotation tank.

6. The flotation cell according to claim 1, wherein the blast tubes are arranged parallel to the side wall of the flotation tank, at a distance from the side wall.

7. The flotation cell according to claim 6, wherein a distance of an outlet nozzle from the side wall of the flotation tank is 10 to 40% of the diameter of the flotation tank, measured at a distance of the outlet nozzle from the bottom of the flotation tank; preferably 25% of the diameter of the flotation tank.

8. The flotation cell according to claim 1, wherein the blast tubes are arranged at equal distance from each other so that a distance between any two adjacent outlet nozzle is the same.

9. The flotation cell according to claim 1, wherein the height of the flotation tank to diameter of the flotation tank, measured at a distance of the outlet nozzle from the bottom of the flotation tank, ratio is 0.5 to 1.50.

10. The flotation cell according to claim 1, wherein the volume of the flotation tank is at least 20 m.sup.3, preferably 20 to 1000 m.sup.3.

11. The flotation cell according to claim 1, wherein the diameter of an outlet nozzle is 10% to 30% of the diameter of an elongated chamber of a blast tube.

12. The flotation cell according to claim 11, wherein the diameter of the outlet nozzle is 40 to 100 mm.

13. The flotation cell according to claim 1, wherein a distance from a bottom of the impinger to the outlet nozzle is 2 to 20 times the diameter of the outlet nozzle.

14. The flotation cell according to claim 13, wherein the distance to a distance of the outlet nozzle from the bottom of the flotation tank ratio is lower than 1.0.

15. The flotation cell according to claim 1, wherein a slurry fraction, taken out from the flotation tank via an outlet arranged at the side wall of the flotation tank, is recirculated into blast tubes as infeed slurry.

16. The flotation cell according to claim 15, wherein the slurry infeed comprises 40% or less slurry fraction.

17. The flotation cell according to claim 1, wherein it further comprises a conditioning circuit.

18. The flotation cell according to claim 17, wherein the conditioning circuit comprises a pump tank in fluid communication with the flotation tank, in which pump tank infeed of fresh slurry and a slurry fraction taken from the flotation tank via an outlet are arranged to be combined into slurry infeed.

19. The flotation cell according to claim 18, wherein the outlet is arranged at the side wall of the flotation tank, at a distance from the bottom of the flotation tank.

20. The flotation cell according to claim 19, wherein the distance is 0 to 50% of the height of the flotation tank.

21. The flotation cell according to claim 17, wherein the conditioning circuit further comprises a pump arranged to intake the slurry fraction from the flotation tank and to forward slurry infeed from the pump tank.

22. The flotation cell according to claim 17, wherein the conditioning circuit further comprises a distribution unit arranged to distribute slurry infeed into blast tubes.

23. The flotation cell according to claim 1, wherein the slurry infeed comprises 100% fresh slurry.

24. A flotation line comprising a number of fluidly connected flotation cells, wherein at least one of the flotation cells is a flotation cell according to claim 1.

25. The flotation line according to claim 24, wherein the flotation cell is preceded by a flotation cell.

26. The flotation line according to claim 24, wherein the flotation cell is preceded by a mechanical flotation cell.

27. The flotation line according to claim 25, wherein the flotation line comprises: a rougher part with a flotation cell; a scavenger part with a flotation cell arranged to receive underflow from the rougher part; and a scavenger cleaner part with a flotation cell arranged to receive overflow from the scavenger part, wherein the last flotation cell of the scavenger part and/or the scavenger cleaner part is a flotation cell according to claim 1.

28. The flotation line according to claim 27, wherein the flotation cell is preceded by a mechanical flotation cell.

29. Use of a flotation line according to claim 24 in recovering particles comprising a valuable material suspended in slurry.

30. The use according to claim 29 in recovering particles comprising nonpolar minerals such as graphite, sulphur, molybdenite, coal, and talc.

31. The use according to claim 29 in recovering particles comprising polar minerals.

32. The use according to claim 31 in recovering particles from minerals having a Mohs hardness of 2 to 3, such as galena, sulfide minerals, PGMs, and/or REO minerals.

33. The use according to claim 32 in recovering particles comprising Pt.

34. The use according to claim 31 in recovering particles comprising Cu from minerals having a Mohs hardness from 3 to 4.

35. The use according to claim 34 in recovering particles comprising Cu from low grade ore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0110] The accompanying drawings, which are included to provide a further understanding of the current disclosure and which constitute a part of this specification, illustrate embodiments of the disclosure and together with the description help to explain the principles of the current disclosure. In the drawings:

[0111] FIG. 1 is a 3D projection of a flotation cell according to an embodiment of the invention,

[0112] FIG. 2 depicts a flotation cell according to an embodiment of the invention, as seen from above,

[0113] FIG. 3 depicts a flotation cell according to an embodiment of the invention in side view,

[0114] FIG. 4 is a vertical cross-section of the flotation cell of FIG. 3 along a section A-A,

[0115] FIG. 5 is a schematic illustration of a flotation cell according to the invention, detailing the dimensions of the flotation cell,

[0116] FIGS. 6a and b are schematic drawings of flotation lines according to embodiments of the invention, and

[0117] FIG. 7 shows schematic vertical cross-sections of embodiments of flotation tanks according to the invention.

[0118] FIG. 8 is a schematic presentation of forms of the bottom structure according to embodiments of the flotation cell.

DETAILED DESCRIPTION

[0119] Reference will now be made in detail to the embodiments of the present disclosure, an example of which is illustrated in the accompanying drawings.

[0120] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the flotation cell, flotation line and its use based on the disclosure. Not all steps of the embodiments are discussed in detail, as many of the steps will be obvious for the person skilled in the art based on this disclosure.

[0121] For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components.

[0122] The enclosed FIGS. 1-5 and 7 illustrate a flotation cell 1 in some detail. The figures are not drawn to proportion, and many of the components of the flotation cell 1 are omitted for clarity. FIGS. 6a-b illustrate in a schematic manner embodiments of the flotation line. The direction of flows of slurry is shown in the figures by arrows.

[0123] The flotation cell 1 according to the invention is intended for treating mineral ore particles suspended in slurry and for separating the slurry into an underflow 400 and an overflow 500, the overflow 500 comprising a concentrate of a desired mineral.

[0124] Referring in particular to FIGS. 1-5, the flotation cell 1 comprises a flotation tank 10 that has a centre 11, a perimeter 12, a bottom 13 and a side wall 14. The flotation cell 1 further comprises a launder 2 and a launder lip 21 surrounding the perimeter 12 of the flotation tank 10.

[0125] In the accompanying figures, launder 2 is a perimeter launder. It is to be understood that a launder 2 may comprise, alternatively or additionally, a central launder arranged at the centre 11 of the flotation tank 10, as is known in the technical field. A launder lip of a central launder may face towards the perimeter 12 of the flotation tank 10, or towards the centre 11 of the flotation tank 10, or both. The overflow 500 is collected into the launder 2 or launders as it passes over a launder lip 21, from a froth layer formed in the upper part of the flotation tank 10. The froth layer comprises an open froth surface A.sub.f at the top of the flotation tank 10.

[0126] Underflow 400 is removed from or led out of the flotation tank via a tailings outlet 140. According to an embodiment, the tailings outlet 140 may be arranged at the side wall 14 of the flotation tank 10 (see FIG. 4). The tailings outlet 140 may be arranged at the side wall 14 of the flotation tank 10 at a distance L.sub.6 from the bottom 13 of the flotation tank 10. The distance is to be understood as the distance of the lowest point of the tailings outlet 140 or outlet opening in the side wall 14 of the flotation tank 10 from the tank bottom 13. The distance L.sub.6 may be 1 to 15% of the height H of the flotation tank 10. For example, the distance L.sub.6 may be 2%, or 5% or 7.5%, or 12% of the height H. Alternatively, the tailings outlet 140 may be arranged at the bottom 13 of the flotation tank 10 (see FIG. 1). In any case, the tailing outlet 140 is arranged at a settling zone B, at the lower part of the flotation tank 10. The tailings outlet 140 may be controlled by a dart valve, or by any other suitable manner known in the field, to control the flow rate of underflow from the flotation tank 10. Even if the tailings outlet 140 is controlled by internal or external structures such as up-flow or down-flow, respectively, dart boxes, the tailings outlet 140 is ideally located at the lower part of the flotation tank 10, i.e. near or adjacent to the bottom 13 of the flotation tank, or even at the bottom 13 of the flotation tank 10. More specifically, underflow 400 or tailings are removed from the lower part of the flotation tank 10, and at or near the side wall 14 of the flotation tank 10.

[0127] The flotation tank 10 may further comprise a froth crowder 6 shaped to direct froth in the open froth surface A.sub.f towards the launder lip 21. The froth crowder 6 may be a central froth crowder, as shown in FIG. 2, or an internal perimeter froth crowder arranged within the flotation tank 10 at a desired depth, at the sidewall of the flotation tank 10.

[0128] A central froth crowder 61 is arranged concentric to the centre 11 of the flotation tank 10. The central froth crowder 61 may have a shape of a cone or a truncated cone. The central froth crowder 61 may have a shape of a pyramid or a truncated pyramid. In other words, a vertical cross-section of a central froth crowder 61 may be an inverted triangle with a vertex pointing towards the bottom 13 of the flotation tank. In case the central froth crowder 61 is has a truncated structure or shape, the vertex is only functional, i.e. it is to be visualised as the lowest point of the structure or shape as continued to a complete untruncated form, whereby a included angle α may be identified irrespective of the actual shape or form of the central froth crowder. The included angle α may be 20 to 80°. For example, the included angle α may be 22°, or 37.5° or 45°, or 55°, or 63.75°, or 74°. In an embodiment, the central froth crowder 61 is arranged to block 25 to 40% of the open froth surface A.sub.f.

[0129] Alternatively or additionally to the central froth crowder 61, the flotation tank may comprise an internal perimeter crowder 62, arranged in the side wall 14 of the flotation tank 10 so that a lowest point 620 of the internal perimeter crowder is located at a distance h.sub.2 from the bottom 13 of the flotation tank 10. The distance h.sub.2 may be ½ to ⅔ of the height H of the flotation tank 10. The internal perimeter crowder 62 may be formed to comprise a diagonal intake starting from the lowest point 620, and angled towards the centre 11 of the flotation tank 10, and extending between a first part of the side wall 14 of the flotation tank 10 and a second part of the side wall 14 so that an angle of inclination of the diagonal intake in relation to the first part of the side wall 14 is 20 to 80°. The angle of inclination may be for example 22°, or 37.5° or 45°, or 55°, or 63.75°, or 74°. The internal perimeter crowder 62 may be arranged to block ⅕ to ¼ of a pulp area A.sub.p, which is measured at a distance h.sub.1 of an outlet nozzle 43 of a blast tube 4 from the bottom 13 of the flotation tank 10, at a mixing area A. The mixing area A, i.e. the part or zone of the flotation tank in vertical direction where the slurry is agitated or otherwise induced to mix the ore particles suspended in the slurry with the flotation gas bubbles, is formed roughly at a vertical section of the flotation tank 10 around the lower parts of the blast tubes 4 and the impingers 44 (see FIG. 5).

[0130] Additionally or alternatively, the flotation tank 10 may further comprise a bottom structure 7 (see FIGS. 5 and. 7), arranged on the bottom (13), and having a shape that allows particles suspended in slurry to be mixed in a mixing zone created over the bottom structure 7, and to settle down in a settling zone surrounding the bottom structure 7.

[0131] The shape of the bottom structure 7 may be defined as follows (see FIG. 8): the vertical cross-section of the bottom structure may be understood to display a form of a functional triangle 700 that comprises a first (top) vertex 71, pointing away from the bottom 13 of the flotation tank 10; a second vertex 71a; and a third vertex 71b, the two latter disposed at the bottom 13 of the flotation tank 10. A first side a is formed between the first vertex 71 and the second vertex 71a. A second side b is formed between the first vertex 71 and the third vertex 71b. A base c is formed between the second vertex 71a and the third vertex 71b, the base c being thus parallel to and on the bottom 13 of the flotation tank 10. A central axis 70 of the functional triangle 700 is substantially concentric with the centre 11 of the flotation tank 10. “Substantially” in this context is to be understood so that during manufacturing and/or installation of the bottom structure 7, it is possible that slight deviations from the centre 11 of the flotation tank 10 may naturally occur. The intention is, nevertheless, that the two axes, central axis 70 of the functional triangle (which is also the central axis of the bottom structure 7) and the centre of the flotation tank 10 are coaxial.

[0132] A base angle α between the first side a and the base c (and/or between the second side b and the base c), in relation to the bottom 13 of the flotation tank 10 is 20 to 60°. For example, the angle α may be 22°, or 27.5° or 35°, or 45°, or 53.75°. Further, an included angle β between the first side a and the second side b is 20 to 100°. Preferably, the included angle β is 20 to 80°. For example, the included angle β may be 22°, or 33.5°, or 45°, or 57.75°, or 64°, or 85.5°. The functional triangle may therefore be an isosceles triangle or an equilateral triangle.

[0133] The functional triangle is in essence a form which may be identified though the abovementioned features, regardless of the actual form of the bottom structure 7, which may be, depending on the cross-section and other structural details of the flotation tank 10, for example a cone, a truncated cone, a pyramid, or a truncated pyramid. A cone or a truncated cone may be suitable from for a flotation tank with a circular cross-section. A pyramid or a truncated pyramid may be a suitable form for a flotation tank with a rectangular cross-section.

[0134] The bottom structure 7 comprises a base 73, corresponding to the base c of the functional triangle 700 (i.e. the base c of the functional triangle 700 defines the base 73 of the bottom structure 7), and arranged on the bottom 13 of the flotation tank 10. Further, the bottom structure comprises a mantle 72. The mantle 72 is defined at least by the first vertex 71, the second vertex 71a and the third vertex 71b of the functional triangle 700. Therefore, irrespective of the actual form of the bottom structure 7, the functional triangle 700 defines the extreme physical dimensions of the bottom structure 7. For example, in case the bottom structure 7 has an irregular form yet being rotationally symmetrical, it would fit into the functional triangle 700 in its entirety (see the last image of FIG. 8). In an embodiment, the mantle 72 is at least partly defined by the first side a and the second side b of the functional triangle. An example of such an embodiment is a bottom structure 7 having the form of a truncated cone (see the middle image of FIG. 8). In an embodiment, the mantle 72 is defined essentially entirely by the first side a and the second side b of the functional triangle 700, i.e. the bottom structure 7 has the form of a cone (see the first image of FIG. 8).

[0135] The bottom structure 7 has a height h.sub.4, measured from the topmost part of the bottom structure 7 to the bottom 13 of the flotation tank 10. In case the form of the bottom structure is a cone or a pyramid, the topmost part is also the first vertex 71 of the functional triangle 700. In case the bottom structure 7 has some sort of truncated form, the height h.sub.4 is measured from the level top of the truncated form (see middle image of FIG. 8) to the bottom 13 of the flotation tank 10. The height h.sub.4 is greater than ⅕ and less than ¾ of the height H of the flotation tank 10. Further, the diameter d.sub.3 of the base 73 of the bottom structure 7 may be ¼ to ¾ of a diameter d.sub.1 of the bottom 13 of the flotation tank 10. In case a flotation tank 10 and/or the bottom structure 7 has a non-circular cross-section, the diameters are measured as the maximal diagonals of the respective parts (base 73 and bottom 13). In an embodiment, the surface area of a base 73 of the bottom structure 7 is less than 80% of the surface area of the bottom 13 of the flotation tank 10. The surface area of the base 73 may be 25 to 80% of the surface area of the bottom 13 of the flotation tank 10.

[0136] Further, the volume of the flotation tank 10 taken by the bottom structure 7 may be 30 to 70% of the volume of the flotation tank 10 taken by the mixing zone A.

[0137] The bottom structure 7 may additionally comprise any suitable support structures and/or connecting structures for installing the bottom structure 7 into the flotation tank 10, on the bottom 13 of the flotation tank 10. The bottom structure 7 may be made of any suitable material such as metal, for example stainless steel.

[0138] The flotation tank 10 has a height H, measured as the distance from the bottom 13 of the flotation tank 10 to the launder lip 21. At the perimeter 12 of the flotation tank 10, the height H is at most 20% lower than the height H at the centre 11 of the flotation tank 10. In other words, the flotation tank 10 may have different vertical cross-sections (see FIG. 7)—for example, the side wall 14 of the flotation tank 10 may include at its lower part a section that is inclined towards the centre 11 of the flotation tank 10.

[0139] Further, the flotation tank 10 has a diameter D, measured at a distance h.sub.1 of an outlet nozzle 43 from the bottom 13 of the flotation tank 10. In an embodiment, the height H to diameter D ratio H/D of the flotation tank 10 is 0.5 to 1.5.

[0140] The flotation tank 10 may have a volume of at least 20 m.sup.3. The flotation tank 10 may have a volume ranging from 20 to 1000 m.sup.3. For example, the volume of the flotation tank 10 may be 100 m.sup.3, or 200 m.sup.3, or 450 m.sup.3, or 630 m.sup.3.

[0141] The flotation tank 10 comprises blast tubes 4 for introducing slurry infeed 100 into the flotation tank 10. A blast tube 4 comprises an inlet nozzle 41 for feeding slurry infeed 100 into the blast tube 4; an inlet 42 for pressurized air or other gas, so that the slurry infeed 100 may be subjected to pressurized air or other gas as it is discharged from the inlet nozzle 41; an elongated chamber 40 arranged to receive under pressure the slurry infeed 100; an outlet nozzle 43 configured to restrict flow of slurry infeed 100 from the outlet nozzle 43, and to maintain slurry infeed in the elongated chamber 40 under pressure.

[0142] Flotation gas is entrained through a turbulent mixing action brought about by the jet, and is dispersed into small bubbles in the slurry infeed 100 as it travels under pressure downwards through the elongated chamber 40 to an outlet nozzle 43 configured to restrict the flow of slurry infeed 100 from the outlet nozzle 43, and further configured to maintain slurry infeed 100 under pressure in the elongated chamber 40.

[0143] According to an embodiment, the outlet nozzle 43 may further be configured to produce a supersonic shockwave into the slurry infeed, the supersonic shockwave inducing formation of flotation gas bubble —particle agglomerates. For example, and to the outlet nozzle 43 may induce a supersonic shockwave into the slurry infeed 100 as it exits the blast tube 40. In addition, the supersonic shockwave may extend to the slurry adjacent or surrounding the outlet nozzle so that even outside the blast tube, the creation of small size flotation gas bubble-particle agglomerates is thus possible.

[0144] For restricting the flow, an outlet nozzle 43 may comprise a throttle such as a throat-like restricting structure. From the outlet nozzle 43, more specifically from the throttle, slurry infeed 100 issues under pressure into the flotation tank 10. As the slurry infeed 100 passes through the outlet nozzle 43, or through the throttle of the outlet nozzle 43, flotation gas bubbles are reduced in size by the pressure changes, and by the high-shear environment downstream of the outlet nozzle 43. The velocity of the gas-liquid mixture in outlet nozzle 43, or in the throttle, may exceed the speed of sound when the flow of infeed slurry 100 becomes a choked flow and flow downstream of the throttle becomes supersonic, and a shockwave forms in the diverging section of the outlet nozzle 43. In other words, the outlet nozzle 43 is configured to induce a supersonic shockwave into slurry infeed 100. The flow of slurry infeed 100 becomes choked when the ratio of the absolute pressure upstream the outlet nozzle 43 to the absolute pressure downstream of a restricting structure of the outlet nozzle 43 exceeds a critical value. When the pressure ratio is above the critical value, flow of slurry infeed 100 downstream of the restricting structure of the outlet nozzle 43 becomes supersonic and a shockwave is formed. Small flotation gas bubbles in slurry infeed 100 mixture are split into even smaller by being forced through the shockwave, and forced into contact with hydrophobic ore particles in slurry infeed 100, thus creating flotation gas bubble-ore particle agglomerates.

[0145] An outlet nozzle 43 may be disposed inside the flotation tank 10 at a desired depth. An outlet nozzle 43 may be positioned at a vertical distance L.sub.5 from the launder lip 21, the distance L.sub.5 being at least 1.5 m. In other words, the length of the portion of a blast tube 4 disposed inside the flotation tank 10 below the launder lip 21 level is at least 1.5 m. In an embodiment, the distance L.sub.5 is at least 1.7 m, and the distance h.sub.1 of the outlet nozzle 43 from the bottom 13 of the flotation tank 10 is at least 0.4 m. For example, the distance L.sub.5 may be 1.55 m, or 1.75 m, or 1.8 m, or 2.2 m, or 2.45 m, or 5.25 m; and the distance h.sub.1, irrespective of the distance L.sub.5, may be 0.45 m, 0.55 m, 0.68 m, 0.9 m, or 1.2 m. Further, the ratio of the distance L.sub.5 to the height H of the flotation tank 10 may be 0.9 or lower. The depth at which the blast tubes 4 are disposed inside the flotation tank 10 may depend on a number of factors, for example on the characteristics of the slurry and/or valuable mineral to be treated in the flotation cell 1, or on the configuration of a flotation line in which the flotation cell 1 is arranged. The ratio of a distance h.sub.1 of an outlet nozzle 43 from the bottom 13 of the flotation tank 10 to height H of the flotation tank 10, h.sub.1/H may be 0.1 to 0.75.

[0146] A diameter of an outlet nozzle 43 may be 10 to 30% of the diameter of an elongated chamber 40 of a blast tube 4. The diameter of an outlet nozzle 43 may be 40 to 100 mm. For example, the diameter of an outlet nozzle 43 may be 55 mm, or 62 mm, or 70 mm.

[0147] A blast tube 4 further comprises an impinger 44 configured to contact a flow of slurry infeed 100 from the outlet nozzle 43 and to direct the flow of slurry infeed 100 radially outwards and upwards of the impinger 44. Slurry infeed 100 exiting from the outlet nozzle 43 is therefore directed to contact the impinger 44. A distance L.sub.3 from a bottom 440 of the impinger 44 to the outlet nozzle 43 may be 2 to 20 times the diameter of the outlet nozzle 43. For example, the distance L.sub.3 may be 5 times, 7 times, or 12 times, or 15 times the diameter of the outlet nozzle 43.

[0148] The ratio of the distance L.sub.3 to the distance h.sub.1 of an outlet nozzle 43 from the bottom 13 of the flotation tank 10, L.sub.3/h.sub.1, may be lower than 1.0. Further, a distance h.sub.3 of a bottom 440 of the impinger 44 from the bottom 13 of the flotation tank 10 may be at least 0.3 m. For example the distance h.sub.3 may be 0.4 m, or 0.55 m, or 0.75 m, or 1.0 m.

[0149] The impinger 44 may comprise an impingement surface intended for contacting the flow of slurry infeed 100 exiting the outlet nozzle 43. The impingement surface may be made of wear-resistant material to reduce the need for replacements or maintenance.

[0150] The slurry, which in essence is a three-phase gas-liquid-solid mixture, rising out of the impinger 44 enters the upper part of the flotation tank 10, and the flotation gas bubbles rise upwards and separate from the liquid to form a froth layer. The froth rises upwards and discharges over the launder lip 21 into the launder 2 and out of the flotation cell 1 as overflow 500. The tailings or underflow 400, from which the desired material has substantially been removed, pass out from the flotation tank 10 through an outlet arranged at or near the bottom 13 of the flotation tank 10.

[0151] Some of the coarse hydrophobic particles that are carried into the froth may subsequently disengage from flotation gas bubbles and drop back into the flotation tank 10, as a result of bubble coalescence in the froth. However, the majority of such particles fall back into the flotation tank 10 in such a way and position that they may be captured by bubbles newly entering the flotation tank 10 from the blast tubes 4, and carried once more into the froth layer.

[0152] There may be 2-40 blast tubes 4, or 4-24 blast tubes 4 arranged in a flotation cell 1. In an embodiment, there are 16 blast tubes 4. In another embodiment, there are 24 blast tubes 4. In yet another embodiment, there are 8 blast tubes 4. The exact number of blast tubes 4 may be chosen according to the specific operation, for example the type of slurry being treated within the flotation cell 1, the volumetric feed flowrate to the flotation cell 1, the mass throughput feed to the flotation cell 1, or the volume or dimensions of the flotation tank 10. In order to properly disperse flotation gas within the flotation tank 10, 4 to 6 blast tubes 4 may be employed.

[0153] The blast tubes 4 may be arranged concentric to the perimeter 12 of the flotation tank 10 at a distance from the centre 11 of the flotation tank 10. This may be the case when the flotation tank 10 is circular in cross-section. The blast tubes 4 may be further arranged so that each blast tube 4 is located at a distance L.sub.1 of an outlet nozzle 43 from the centre 11 of the flotation tank 10, the distance being preferably equal for each blast tube 4. For example, the distance L.sub.1 may be 10 to 40% of the diameter D of the flotation tank 10. According to different embodiments of the flotation cell 1, the distance L1 may be 12.5%, or 15%, or 25% or 32.5% of the diameter D of the flotation tank 10.

[0154] The blast tubes 4 may be arranged parallel to the side wall 14 of the flotation tank 10, at a distance from the side wall 14. This may be the case when the flotation tank 10 is rectangular in cross-section. A distance L.sub.2 of the outlet nozzle 43 of a blast tube 4 from the side wall 14 of the flotation tank 10 may be 10 to 40% of the diameter D of the flotation tank 10. In an embodiment, the distance L.sub.2 is 25% of the diameter D of the flotation tank 10. According to different embodiments of the flotation cell 10, the distance L.sub.2 may be 12.5%, or 15%, or 27% or 32.5% of the diameter D of the flotation tank 10. Additionally, the parallel arranged blast tubes 4 may be further arranged at a straight line within the flotation tank 10.

[0155] Further, in all the above mentioned embodiments, the blast tubes 4 may be arranged at equal distance from each other so that a distance between any two adjacent outlet nozzle 43 is the same.

[0156] A slurry fraction 300 may be taken out from the flotation tank 10 via an outlet 31 arranged at the side wall 14 of the flotation tank 10. This slurry fraction 300 is recirculated into blast tubes 4 as infeed slurry. In an embodiment, the slurry infeed 100 comprises 40% or less of slurry fraction 300. In an embodiment, the slurry infeed 100 comprises 50% or less of slurry fraction 300. For example, the slurry infeed may comprise 5%, or 12.5%, or 20%, or 30%, or 37.5%, or 45% of slurry fraction 300. Alternatively, the slurry infeed 100 may comprise 0% of slurry fraction 300, i.e. no recirculation of slurry taken from the flotation tank 10 back to the flotation cell takes place, but the slurry infeed 100 comprises 100% of fresh slurry 200, for example from a previous flotation cell (that is, underflow 400 from a previous flotation cell), or from a previous process step.

[0157] The slurry fraction 300 may be recirculated to all of the blast tubes 4 of the flotation tank 10, or, alternatively, to some of the blast tubes 4, while other blast tubes 4 receive fresh slurry 200, comprising either the underflow 400 of a previous flotation cell, or a slurry flow from some preceding process step, depending on the location of the flotation cell 1 within a flotation line 8. The outlet 31 may be arranged at a distance L.sub.4 from the bottom 13 of the flotation tank 10. The distance is to be understood as the distance of the lowest point of the outlet or outlet opening in the side wall 14 of the flotation tank 10 from the tank bottom 13. The distance L.sub.4 is 0 to 50% of the height H of the flotation tank 10. The outlet 31 may advantageously be positioned at a settling zone where the particles suspended in slurry and not captured by the flotation gas bubbles and/or the upwards flow of slurry descend towards the bottom 13 of the flotation tank 10. In an embodiment, the outlet 31 is arranged at the lower part of the flotation tank 10. For example, the distance L.sub.4 may be 2%, or 8%, or 12.5%, or 17, or 25% of the height H of the flotation tank 10. Even if the outlet 31 is controlled by internal or external structures such as up-flow or down-flow dart boxes, respectively, the outlet 31 is ideally located at the lower part of the flotation tank 10, i.e. near or adjacent to the bottom 13 of the flotation tank. More specifically, slurry fraction 300 is removed from the lower part of the flotation tank 10.

[0158] The flotation cell 1 may also comprise a conditioning circuit 3. The conditioning circuit 3 may comprise a pump tank 30, or other such additional vessel, in fluid communication with the flotation tank 10. In the pump tank 30 infeed of fresh slurry 200 and a slurry fraction 300 taken from the flotation tank 10 via the outlet 31 are arranged to be combined into slurry infeed 100, which is then led into blast tubes 4 of the flotation tank 10. The fresh slurry 200 may be for example underflow 400 from a preceding flotation cell, or in case the flotation cell 1 is the first flotation cell of a flotation line, an infeed of slurry coming from a grinding unit/step or a classification unit/step. It is also possible that slurry fraction 300 and fresh slurry 200 are distributed into the blast tubes 4 without being first combined in a pump tank 30.

[0159] The combined slurry may be recirculated to all of the blast tubes 4 of the flotation tank 10, or, alternatively, to some of the blast tubes 4, while other blast tubes 4 receive fresh slurry 200, comprising either the underflow 400 of a previous flotation cell, or a slurry flow from some preceding process step, depending on the location of the flotation cell 1 within a flotation line 8.

[0160] The outlet 31 may be arranged at the side wall 14 of the flotation tank 10, at a distance L.sub.4 from the bottom 13 of the flotation tank 10. The distance L.sub.4 may be 0 to 50% of the height H of the flotation tank 10. For example, the distance L.sub.4 may be 2%, or 8%, or 12.5%, or 20%, or 33% of the height H of the flotation tank 10.

[0161] Additionally, the conditioning circuit may comprise a pump 32 arranged to intake the slurry fraction 300 from the flotation tank 10, and to forward slurry infeed 100 from the pump tank 30 to the blast tubes 4. The slurry fraction 300 may comprise low settling velocity particles such as fine, slow-floating particles. The slurry fraction may be taken from or near the bottom of the flotation tank 10. Additionally or alternatively, the conditioning circuit 3 may further comprise a distribution unit (not shown in the figures), arranged to distribute slurry infeed 100 into the blast tubes 4. The pump 32 may also be used to forward the slurry infeed 100 into the blast tubes 4. In order to distribute the slurry infeed 100 evenly into the blast tubes 4, a distribution unit may be utilized. The distribution unit may, for example, comprise a feed pipe inside the flotation tank 10, configured to distribute slurry fraction 300 directly into the blast tubes 4. For example, the distribution unit may comprise conduits arranged outside the flotation tank 10, leading to a separate feed distributor configured to distribute slurry fraction 300, or a combination of slurry fraction 300 and fresh slurry 200 into the blast tubes 4.

[0162] According to another aspect of the invention, flotation lines 8 is presented in FIGS. 6a and 6b. A flotation line 8 comprises a number of fluidly connected flotation cells 1a, and at least one of the flotation cells is a flotation cell 1 according to the above described embodiments of the flotation cell 1 according to the invention. In an embodiment of the flotation line 8, the flotation cell 1 according to the invention is preceded by a flotation cell 1a. A flotation cell 1a may be of any type known in the field. Alternatively or additionally, the flotation cell 1 may be preceded by mechanical flotation cell 1b (see FIG. 6a).

[0163] In an embodiment of the flotation line 8, it comprises a rougher part 81 with a flotation cell 1a; a scavenger part 82 with a flotation cell 1a arranged to receive underflow 400 for the rougher part 81; and a scavenger cleaner part 820 with a flotation cell 1a arranged to receive overflow 500 from the scavenger part 82 (see FIG. 6b). In the flotation line 8, the last flotation cell 1 of the scavenger part 82, and alternatively or additionally, the last flotation cell 1 of the scavenger cleaner part 820 is a flotation cell 1 according to the invention, with blast tubes 4. Additionally, in the flotation line 8, as described above, the flotation cell 1 according to the invention, with blast tubes 4, may be preceded by a mechanical flotation cell 1b.

[0164] The flotation line 8 may be preceded by other processes such as grinding, classification, screening, heavy-medium process, coarse particle recovery process, spirals, and other separation processes; and other flotation processes. A number of processes may follow the flotation line 8, such as regrinding, cleaner or other flotation processes, centrifuging, filtering, screening or dewatering.

[0165] According to a further aspect of the invention, the flotation line 8 may be used in recovering particles comprising a valuable material suspended in slurry. In an embodiment, the use may be directed to recovering particles comprising nonpolar minerals such as graphite, sulphur, molybdenite, coal, talc.

[0166] According to another embodiment, the use may be directed to recovering particles comprising polar minerals.

[0167] In a further embodiment, the use is directed to recovering particles from minerals having a Mohs hardness of 2 to 3, such as galena, sulfide minerals, PGMs, REO minerals. In a yet further embodiment, the use is specifically directed to recovering particles comprising platinum.

[0168] In a further embodiment, the use is directed to recovering particles comprising copper from mineral particles having a Mohs hardness of 3 to 4. In a yet further embodiment, the use is specifically directed to recovering particles comprising copper from low grade ore.

[0169] The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A flotation cell to which the disclosure is related, may comprise at least one of the embodiments described hereinbefore. It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.