FROTH FLOTATION UNIT

Abstract

A froth flotation unit for treating mineral ore particles suspended in slurry includes a tank, a gas supply for introducing flotation gas into the slurry to form froth, and a first froth collection launder including a first froth overflow lip facing towards the centre of the tank. The froth flotation unit has a pulp area of at least 15 m.sup.2 measured at a mixing area. The froth flotation unit further includes a second froth collection launder with a first froth overflow lip facing the perimeter of the flotation tank, and a froth blocker arranged between the first froth overflow lip and the second froth overflow lip. A froth flotation line, its use, and a froth flotation method are also disclosed.

Claims

1.-44. (canceled)

45. A froth flotation unit for treating mineral ore particles suspended in slurry and for separating the slurry into an underflow and an overflow, the froth flotation unit comprising: a tank with a centre and a perimeter, a gas supply for introducing flotation gas into the slurry to form froth, and a first froth collection launder comprising a first froth overflow lip facing towards the centre of the tank, wherein the froth flotation unit has a pulp area of at least 15 m.sup.2, measured at a mixing area, wherein the froth flotation unit further comprises: a second froth collection launder arranged inside the first froth collection launder, the second froth collection launder comprising a first froth overflow lip facing the perimeter of the flotation tank, and a froth blocker arranged between the first froth overflow lip and the second froth overflow lip.

46. The froth flotation unit according to claim 45, wherein the second froth flotation launder comprises a second overflow lip facing the centre of the tank.

47. The froth flotation unit according to claim 45, wherein a second froth blocker is arranged inside the second lip.

48. The froth flotation unit according to claim 45, wherein the first froth collection launder comprises a second overflow lip facing the perimeter of the tank.

49. The froth flotation unit according to claim 48, wherein the tank further comprises: a third froth collection launder comprising: a first froth overflow lip facing the centre of the tank, the launder arranged on the perimeter of the tank, and that the first froth collection launder comprises a second overflow lip facing the perimeter of the tank, and that a third froth blocker is arranged between first froth overflow lip of the third launder and the second froth overflow lip of the first froth collection launder.

50. The froth flotation unit according to claim 45, wherein the first froth collection launder is arranged on a perimeter of the tank.

51. The froth flotation unit according to claim 45, wherein the pulp area comprises the combined area of open froth surfaces formed between any two froth overflow lips, and/or inside a froth overflow lip.

52. The froth flotation unit according to claim 51, wherein an open froth surface is dividable into two open froth subsurfaces by a froth blocker, one open froth subsurface on the side of the first froth overflow lip and one open froth subsurface on the side of the second froth overflow lip, so that the two open froth subsurfaces are completely separated by the froth blocker; or so that the two open froth subsurfaces are partially separated by the froth blocker and have a fluid connection.

53. The froth flotation unit according to claim 45, wherein the cross-section of the froth blocker in the radial direction of the tank is a functional triangle comprising a first vertex pointing towards a bottom of the tank, a second vertex, and a third vertex so that a top side, drawn from the second vertex to the third vertex and radially in plane with a horizontal drawn through the centre of the tank; a first side, drawn from the first vertex to the second vertex and facing a froth overflow lip adjacent to the second vertex; and a second side, drawn from the first vertex to the third vertex and facing the froth overflow lip adjacent to the third vertex, are formed.

54. The froth flotation unit according to claim 53, wherein froth blocker is arranged to have a form which allows a froth load to be balanced between an open froth subsurface on the first side of the functional triangle and an open froth subsurface on the second side of the functional triangle.

55. The froth flotation unit according to claim 53, wherein a first angle formed between a vertical line drawn from the first vertex to the top side of the functional triangle and the first side is 0-30.

56. The froth flotation unit according to claim 55, wherein a second angle between the vertical line of the functional triangle and the second side is 20-45.

57. The froth flotation unit according to claim 56, wherein the functional triangle is a scalene triangle wherein the second angle is at least 50, preferably at least 100, larger than the first angle.

58. The froth flotation unit according to claim 52, wherein the area of an open froth surface is arranged to be varied so that the relationship between the two open froth subsurfaces separated by a froth blocker is changed.

59. The froth flotation unit according to claim 58, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is arranged to be varied by changing the vertical position of the froth blocker in relation to the height of a froth overflow lip next to the froth blocker, and/or by moving the position of the first vertex of the functional triangle in relation to the froth overflow lip next to the froth blocker.

60. The froth flotation unit according to claim 58, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is arranged to be varied by moving the froth blocker vertically in relation to the height of the first froth overflow lip next to the froth blocker, and/or by moving the position of the first vertex of the functional triangle in relation to the centre of the tank.

61. The froth flotation unit according to claim 52, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is arranged to be varied by moving the froth blocker vertically in relation to the height of the first froth overflow lip next to the froth blocker.

62. The froth flotation unit according to claim 61, wherein an open froth surface is dividable into two open froth subsurfaces by a froth blocker, one open froth subsurface on the side of the first froth overflow lip and one open froth subsurface on the side of the second froth overflow lip, so that the two open froth subsurfaces are partially separated by the froth blocker and have a fluid connection.

63. The froth flotation unit according to claim 45, wherein the froth blocker is a continuous circle.

64. The froth flotation unit according to claim 45, wherein the froth blocker comprises individual circle arcs and discontinuation points between the arcs so that a fluid connection between the open froth subsurfaces is formed.

65. The froth flotation unit according to claim 45, wherein the froth blocker is a segment of the tank.

66. The froth flotation unit according to claim 65, wherein the froth blocker is a circle segment of the tank.

67. The froth flotation unit according to claim 65, wherein the froth blocker is arranged to be movable along a rotational axis so that the position of the first vertex may be changed in relation to centre of the tank.

68. The froth flotation unit according to claim 67, wherein the rotational axis is parallel to a chord of the tank.

69. The froth flotation unit according to claim 45, wherein the gas supply is arranged into the tank.

70. The froth flotation unit according to claim 45, wherein the tank comprises a mixing device.

71. The froth flotation unit according to claim 70, wherein the mixing device comprises a gas supply.

72. The froth flotation unit according to claim 45, wherein the pulp area is at least 40 m.sup.2, measured at the mixing area.

73. The froth flotation unit according to claim 45, wherein a distance between froth overflow lip and the first side of a froth blocker or the second side of a froth blocker is at most 500 mm, preferably from 100 to 500 mm.

74. A flotation line comprising at least one froth flotation unit according to claim 45.

75. The flotation line according to claim 74, wherein a froth flotation unit is arranged into a downstream end of the flotation line.

76. The flotation line according to claim 74, wherein it comprises at least two conventional flotation units and/or at least two additional froth flotation units arranged to treat the slurry before it is arranged to be treated in the froth flotation unit.

77. The use of a froth flotation line according to claim 74, wherein recovering mineral ore particles comprising a desired mineral.

78. The use of the froth flotation line according to claim 77, wherein recovering mineral ore particles comprising a desired mineral from low grade ore.

79. The use of the froth flotation line according to claim 78, wherein recovering mineral ore particles comprising Cu from low grade ore.

80. The froth flotation method for treating mineral ore particles suspended in slurry, wherein the slurry is separated into an underflow and an overflow in a froth flotation unit according to claim 45, wherein an open froth surface of a flotation tank is divided into two open froth subsurfaces by a froth blocker arranged between a first overflow lip of a first froth collection launder and a first overflow lip of a second froth collection launder.

81. The froth flotation method according to claim 80, wherein the two open froth subsurfaces are completely separated by the froth blocker.

82. The froth flotation method according to claim 80, wherein the two open froth subsurfaces are partially separated by the froth blocker and have a fluid connection.

83. The froth flotation method according to claim 80, wherein the area of an open froth surface is varied so that the relationship between the two open froth subsurfaces separated by a froth blocker is changed.

84. The froth flotation method according claim 80, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is varied by changing the vertical position of the froth blocker in relation to the height of a froth overflow lip next to the froth blocker.

85. The froth flotation method according to claim 80, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is varied by moving the position of the first vertex of the functional triangle in relation to the froth overflow lip next to the froth blocker.

86. The froth flotation method according to claim 80, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is varied by moving the froth blocker vertically in relation to the height of the first froth overflow lip next to the froth blocker.

87. The froth flotation method according to claim 80, wherein the relationship between the two open froth subsurfaces separated by a froth blocker is varied by moving the position of the first vertex of the functional triangle in relation to the centre of the tank.

88. The froth flotation method according to claim 80, wherein the froth blocker is arranged to be movable along a rotational axis so that the position of the first vertex may be changed in relation to centre of the tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] 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 invention and together with the description help to explain the principles of the invention. In the drawings:

[0086] FIGS. 1a-c are a schematic illustration of an exemplary embodiment of the unit according to the invention.

[0087] FIGS. 2a-c are a schematic illustration of another exemplary embodiment of the unit according to the invention.

[0088] FIGS. 3a-c are a schematic illustration of another exemplary embodiment of the unit according to the invention.

[0089] FIGS. 4a-c are a schematic illustration of yet another exemplary embodiment of the unit according to the invention.

[0090] FIGS. 5a-b are a schematic illustration of yet another exemplary embodiment of the unit according to the invention.

[0091] FIG. 6 is a schematic three-dimensional projection of an exemplary embodiment of the unit according to the invention.

[0092] FIGS. 7a-b are schematic cross-sectional illustrations showing the geometry of a froth blocker according to the invention.

[0093] FIG. 8 is a schematic illustration of a flotation line according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0094] Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0095] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the unit, use, line and method 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. The figures are not drawn to proportion, and many of the components of the flotation unit 10 and the flotation line 50 are omitted for clarity. The forward direction of flow of slurry 1 is shown in the figures by arrows.

[0096] For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components.

[0097] In FIGS. 1 to 6, a tank 11 of a flotation unit 10 receives a flow of suspension, that is, a flow of slurry 1 comprising ore particles, water and flotation chemicals such as collector chemicals and non-collector flotation reagents. The collector chemical molecules adhere to surface areas on ore particles having a desired mineral to be floated, through an adsorption process. The desired mineral acts as the adsorbent while the collector chemical acts as the adsorbate. The collector chemical molecules form a film on the areas of the desired mineral on the surface of the ore particle to be floated. Typically, the desired mineral is a valuable mineral contained in the ore particle. In reverse flotation, the mineral may be the invaluable part of the slurry suspension thus collected away from the concentrate of the valuable material. For example in reverse flotation of Fe, silicate-containing ore particles are floated while the valuable Fe-containing ore particles are collected from the underflow or tailings.

[0098] The collector chemical molecules have a non-polar part and a polar part. The polar parts of the collector molecules adsorb to the surface areas of ore particles having the valuable minerals. The non-polar parts are hydrophobic and are thus repelled from water. The repelling causes the hydrophobic tails of the collector molecules to adhere to flotation gas bubbles. An example of a flotation gas is atmosphere air introduced, for example by blowing, compressing or pumping, into flotation unit 10 or a tank 11 of the flotation unit 10. A sufficient amount of adsorbed collector molecules on sufficiently large valuable mineral surface areas on an ore particle may cause the ore particle to become attached to a flotation gas bubble. This phenomenon may be called mineralization. In low mineralization, less than optimal amount of ore particles are attached to flotation gas bubbles, leading to brittle froth and problems in recovering the desired ore particles from the froth layer to a froth overflow lip and froth collection launder.

[0099] Ore particles become attached or adhered to gas bubbles to form gas bubble-ore particle agglomerates. These agglomerates rise to the surface of the flotation tank 11 at the uppermost part of the tank 11 by buoyancy of the gas bubbles, as well as with the continuous upwards flow of slurry induced by mechanical agitation and/or the infeed of slurry 1 into the tank 11. The gas bubbles form a layer of froth 3, and the froth 3 gathered to a surface of slurry in froth flotation unit 10, comprising the gas bubble-ore particle agglomerates is let to flow out of flotation unit 10 as an overflow 1b via a froth overflow lip 121a into a froth collection launder 21.

[0100] The collected slurry overflow 1b may be led to further processing or collected as a final product, depending on the point of a flotation line, at which the overflow 1b is collected. Further processing may comprise any necessary process steps to increase the product grade, for example regrinding and/or cleaning. Tailings may be arranged to flow as an underflow 1a via an outlet to a subsequent flotation cell and finally out of the process as gangue or final residue.

[0101] The slurry 1 is first introduced into an overflow flotation unit 10, in which the slurry 1 is treated by introducing flotation gas into the slurry by a gas supply 12 (see FIG. 4a, 5b) which may be any conventional means of gas supply. For example, the gas may be led into the tank via a mixing device 14 (FIG. 1a-4a), or into a tank without a mixing device via gas inlets (FIG. 5b), as is the case in a column flotation cell. The flotation gas may be introduced into the tank 11. The flotation gas may be incorporated into to slurry prior to leading the slurry 1 into the flotation tank 11b in a separate pre-treatment tank 11a, as is the case in a dual flotation cell (FIG. 5a).

[0102] The slurry may be agitated mechanically by a mixing device 14, i.e. the tank 11 comprises a mixing device 14, which may be, for example, a rotor-stator type agitator disposed in the flotation tank 11 (FIG. 1a, 2a, 3a), or by a pump 14, 12 in a so-called self-aspirating tank, as shown in FIG. 4a (the pump acts as both a mixing device 14 and a gas supply 12), or by utilising any other type of mechanical agitation known in the art. There may be one or more auxiliary agitators disposed in the flotation tank 11 in the vertical direction of the flotation tank 11, as well.

[0103] In an embodiment of the froth flotation unit 10, as seen in FIG. 1a, the tank 11 comprises a centre 111 and a perimeter 110, and a first froth collection launder 21 comprising a first froth overflow lip 121a facing towards the centre 111 of the tank 11. The first froth collection launder 21 may be arranged at the perimeter 110 of the tank 11.

[0104] A second froth collection launder 22 comprising a first froth overflow lip 122a, also facing the perimeter 110 of the tank, is arranged inside the first froth collection launder 21. Between the first froth collection launder 21 and the second froth collection launder 22, a froth blocker 31 is arranged. More specifically, the froth blocker 31 is arranged between the first froth overflow lip 121a of the first froth collection launder 21 and the first froth overflow lip 122a of the second froth collection launder 22.

[0105] The froth blocker 31 may be positioned and moved so that it is capable of dividing an open froth surface A.sub.1 into two subsurfaces A.sub.1a, A.sub.1b, one open froth subsurface A.sub.1a on the side of the first froth overflow lip 121a and one open froth subsurface A.sub.1b on the side of the second froth overflow lip 122a, so that the two open froth subsurfaces are completely separated by the blocker (FIG. 1b); or so that the two open froth subsurfaces A.sub.1a, A.sub.1b are partially separated and have a fluid connection (FIG. 1c).

[0106] The froth flotation unit 10 comprises a pulp area A, which is the effective froth surface area, i.e. the largest possible area on which froth may be formed, of the tank 11, measured as an area of pulp at the height of a mixing area 140, and which is in principle available for the formation of a froth layer 3.

[0107] The mixing area 140 depends on the type of flotation tank, and can be for example flotation tank 10 comprising a rotor 14, the mixing area 140 is defined as the mean cross-sectional area of the tank at the rotor height (FIG. 1a, 2a, 3a). In a self-aspirating tank 10 (FIG. 4a), the mixing area 140 is defined as the mean cross-sectional area of the tank 10 at the pump 14, 12 height. In a flotation unit 10 where the gas supply 12 into the slurry is arranged into a pre-treatment tank 11a prior to leading the slurry into the flotation tank 11b, i.e. in a dual flotation tank (FIG. 5a), the mixing area 140 is the cross-sectional area at the height of a slurry inlet 100. In a flotation tank 10 where gas 2 is supplied via gas supply spargers 12a (not shown in detail), i.e. a column flotation cell (FIG. 5b), the mixing area 140 is defined as the cross-sectional area of the tank 10 at the gas supply sparger 12a height.

[0108] The pulp area A is the combined area of open froth surfaces A.sub.1, A.sub.2, A.sub.3 formed between any two forth overflow lips 121a, 122a and/or inside a froth overflow lip 122b. The pulp area A may be at least 15 m.sup.2. In an embodiment, the pulp area A may be at least 40 m.sup.2. For example the pulp area A may be 40-400 m.sup.2. For example, the pulp are A may be 75 m.sup.2, 100 m.sup.2, 150 m.sup.2, 360 m.sup.2.

[0109] The second froth flotation launder 22 may comprise also a second overflow lip 122b facing the centre 111 of the tank 11. There may be a second froth blocker 32 arranged inside the second overflow lip 122b, as shown in FIG. 2a-c.

[0110] The first froth collection launder 21 may also comprise a second overflow lip 121b facing the perimeter 110 of the tank 11. In other words, the first froth collection launder 21 may be arranged at a distance from the perimeter 110 of the tank 11, as can be seen in FIG. 3a-c. A third froth blocker 33 may be arranged on the perimeter 110 of the tank 11, between the perimeter 110 and the second overflow lip 121 b.

[0111] A third froth collection launder 23 may be arranged on the perimeter 110 of the tank 11. The third froth collection launder 23 comprises a first froth overflow lip 123a facing the centre 111 of the tank 11. The third froth blocker 33 may be arranged may be arranged between the first overflow lip 123a of the third froth collection launder 23 and the second froth overflow lip 121b of the first froth collection launder 21 (not shown in the figures).

[0112] A distance d between a froth overflow lip 121a, 121b, 122a, 122b, 123a and the first side a or the second side b of the froth blocker 31, 32, 33 is at most 500 mm. Preferably, the distance d is 100-500 mm, for example 110 mm, 175 mm, 230 mm, 295 mm, 340 mm, 400 mm.

[0113] Therefore the pulp area A may be comprised of for example two open froth surfaces A.sub.1, A.sub.2 (FIGS. 1b-c and 2b, 4c), three open froth surfaces A.sub.1, A.sub.2, A.sub.3 (3b-c, 4b), four open froth surfaces (not shown in the figures), depending on the number of froth collection launders 21, 22, 23 and their positions, and the number of overflow lips 121a, 121b, 122a, 122b, 123a, as well as the number of froth blockers 31, 32, 33 arranged between the overflow lips 121a, 121b, 122a, 122b, 123a or inside the overflow lip 121b, 122b.

[0114] An open froth surface A.sub.1 may be divided into two open froth subsurfaces (A.sub.1a, A.sub.1b) by the froth blocker 31 so that a first open froth subsurface A.sub.1a is formed on the side of the first froth overflow lip (121a) and a second open froth subsurface A.sub.1b is formed on the side of the second froth overflow lip 122a so that the two open froth subsurfaces are completely separated from each other.

[0115] In that case, the froth blocker 31, 32, 33 may have a form of a continuous circle (FIG. 1b, 2b, 3b, 4b).

[0116] An open froth surface A.sub.1 may be divided into two open froth subsurfaces (A.sub.1a, A.sub.1b) by the froth blocker 31 so that a first open froth subsurface A.sub.1a is formed on the side of the first froth overflow lip (121a) and a second open froth subsurface A.sub.1b is formed on the side of the second froth overflow lip 122a so that the two open froth subsurfaces are partially separated and have a fluid connection (see for example FIG. 1c, 2c, 6).

[0117] In that case, the froth blocker 31, 32, 33 may comprise individual circle arcs 31a, 31b, 31c and discontinuation points 34a, 34b, 34c (see FIG. 6) between the arcs 31a, 31b, 31c so that a fluid connection between the open froth subsurfaces A.sub.1a, A.sub.1b. Circular froth blockers 31, 32, 33 or froth blockers comprising individual circle arcs 31a, 31b, 31c may be moved as described above.

[0118] Alternatively, the froth blocker 31, 32, 33 may be a segment of the tank 11, as can be seen in FIG. 1c, 2c, 3c, 4c. This kind of arrangement may be preferable in a froth flotation unit 10 in which the tank 11 has a cross-section deviant from a circle, for example, if the cross-section is rectangular or partially rectangular. In a cylindrical tank 11, more specifically, the froth blocker 31, 32, 33 may be a circle segment 35a, 35b, 35c of the tank 11 (see FIG. 2c).

[0119] A froth blocker 31, 32, 33 of the aforementioned segment or circle segment 35a, 35b, 35c type may be moved along a rotational axis x so that the position of the first vertex 301 may be changed in relation to the centre of the tank. The rotational axis x may be parallel to a chord c of the tank 11. Each of the open froth surfaces A.sub.1, A.sub.2, A.sub.3 may be divided into open froth subsurfaces A.sub.1a, A.sub.1b, respectively, depending, again, on the number and position of froth blockers 31, 32, 33.

[0120] The area of an open froth surface A.sub.1 may be varied so that the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 is changed.

[0121] The relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 may be varied by changing the vertical position of the froth blocker 31, 32, 33 in relation to a height H of a froth overflow lip 121a, 122a, 121b, 122b, 123a next to the froth blocker 31, 32, 33. Alternatively or additionally, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 may be varied by moving the position of the first vertex 301 of the functional triangle 300 in relation to the froth overflow lip 121a, 122a, 121b, 122b, 123a next to the froth blocker 31, 32, 33.

[0122] In an embodiment, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31, 32, 33 may be varied by moving the froth blocker 31, 32, 33 vertically in relation to the height H of the first froth overflow lip 121a, 122a, 123a next to the froth blocker 31, 32, 33. Alternatively or additionally, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31, 32, 33 may be varied by moving the position of the first vertex 301 of the functional triangle 300 in relation to the centre 111 of the tank 11.

[0123] The froth blocker 31, 32, 33 may be arranged to be moved by any suitable actuator or regulating unit known in the art, powered for example by an electric motor, or by hydraulic or pneumatic transfer equipment.

[0124] The froth blockers 31, 32, 33 may have a cross-section in the form of a functional triangle 300, in the radial direction of the tank 11, as can be seen in FIG. 7a-b. The functional triangle 300 comprises a first vertex 301 pointing towards the bottom 112 of the tank 11, a second vertex 302 and a third vertex 303. A top side t of the functional triangle 300 is formed by a line drawn from the second vertex 302 to the third vertex 303, radially in plane with a horizontal drawn through the centre 111 of the tank 11. A first side a is formed by a line drawn from the first vertex 301 and the second vertex 302. Side a faces the froth flotation lip 121a adjacent to the second vertex 302. A second side b is formed by a line drawn first vertex 301 to the third vertex 303. Side b faces the froth flotation lip 122a adjacent to the third vertex 303. In reality, the froth blocker may have uneven sides t, a, b, as can be seen in FIG. 7b, due to manufacturing factors such as materials or manufacturing methods, but in effect, the shape of the functional triangle 300 may always be detectable from the cross-section of the froth blocker 31, 32, 33.

[0125] The froth blocker may be manufactured from plastic, metal or a composite material by any suitable manufacturing method.

[0126] A first angle is formed between a vertical line n drawn from the first vertex 301 to the top side t of the functional triangle 300 and the first side a. The first angle may be 0-30, for example 2.5; 3.8; 5; 9.3; 15.5; 21.6; 27.20,

[0127] A second angle is formed between the vertical line n and the second side b. The second angle may be 20-45, for example 21.5; 25; 31.2; 37.5; 40.3; 44.8.

[0128] The functional triangle 300 may be in form a scalene triangle with unequal sides a, b. The second angle is, in that case, at least 5, preferably at least 100 larger than the first angle .

[0129] The froth flotation unit 10 described above may be a part of a froth flotation line 50 (see FIG. 8). A flotation line 50 is an arrangement for treating the slurry 1 for separating valuable metal containing ore particles from ore particles suspended in the slurry in several fluidly connected flotation units 10, 51 which may be of any conventional type known to a person skilled in the art. At least one of the flotation units may be a froth flotation unit 10 according to this disclosure. Preferably, the at least one froth flotation unit 10 is arranged into a downstream end of the flotation line 50. The flotation line 50 may comprise at least two conventional flotation units 51a, 51b, and/or at least two additional froth flotation units 10a, 10b arranged to treat the slurry 1 before it is led into the froth flotation unit 10.

[0130] A froth flotation line 50 comprising at least one froth flotation unit 10 according to the present disclosure may be used in recovering mineral ore particles comprising a valuable mineral from a low-grade ore. More specifically, the froth flotation line 50 may be used in recovering mineral ore particles comprising copper (Cu) from low grade ore. The amount of Cu may be as low as 0.1% by weight of the feed, i.e. infeed of slurry into the flotation arrangement.

[0131] In the froth flotation method for treating mineral ore particles suspended in slurry, the slurry 1 is separated into an underflow 1a and an overflow 1b in a froth flotation unit 10 according to the present disclosure. An open froth surface A.sub.1 of a flotation tank 11 is divided into two open froth subsurfaces A.sub.1a, A.sub.1b by a froth blocker 31 arranged between a first overflow lip 121a of a first froth collection launder 21 and a first overflow lip 122a of a second froth collection launder 22, as described above in connection with the forth flotation unit 10. The two open froth subsurfaces A.sub.1a, A.sub.1b may be completely separated by the blocker 31. Alternatively, the two open froth subsurfaces A.sub.1a, A.sub.1b may be partially separated and have a fluid connection.

[0132] The area of an open froth surface A.sub.1 may be varied so that the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 is changed. In more detail, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 may be varied by changing the vertical position of the froth blocker 31 in relation to the height H of a froth overflow lip 121a, 122a next to the froth blocker 31. Alternatively or additionally, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 may be varied by moving the position of the first vertex 301 of the functional triangle 300 in relation to the froth overflow lip 121a, 122a next to the froth blocker 31.

[0133] In an embodiment, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 may be varied by moving the froth blocker 31 vertically in relation to the height H of the first froth overflow lip 121a next to the froth blocker. Alternatively or additionally, the relationship between the two open froth subsurfaces A.sub.1a, A.sub.1b separated by a blocker 31 may be varied by moving the position of the first vertex 301 of the functional triangle 300 in relation to the centre 111 of the tank 11.

[0134] In an embodiment, the froth blocker 31 may be arranged to be movable along a rotational axis x so that the position of the first vertex 301 may be changed in relation to centre 111 of the tank 11.

[0135] 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.