FROTH FLOTATION CELL

Abstract

A froth flotation cell for treating mineral ore particles suspended in slurry includes a tank, a gas supply, a first froth collection channel, a second froth collection channel arranged between the centre of the tank and the first froth collection channel, and a radial froth collection launder including a radial froth overflow lip, and extending from the first froth collection channel towards the second froth collection channel. The froth flotation cell further includes a radial froth crowder including a crowding sidewall, and extending from the second froth collection channel to the first froth collection channel. Further, a froth flotation line, its use and a froth flotation method are presented.

Claims

1.-52. (canceled)

53. A froth flotation cell for treating mineral ore particles suspended in slurry and for separating the slurry into an underflow and an overflow, the froth flotation cell comprising: a tank with a centre and a perimeter, a gas supply for introducing flotation gas into the slurry to form froth, a first froth collection channel surrounding the perimeter of the tank so that an open froth surface (A.sub.f) is formed inside the first froth collection channel, a second froth collection channel arranged between the centre of the tank and the first froth collection channel and substantially concentric with the first froth collection channel, the second froth collection launder comprising a first froth overflow lip facing towards the centre of the tank, and a radial froth collection launder comprising a radial froth overflow lip, and extending from the first froth collection channel towards the second froth collection channel and in fluid communication with the first froth collection channel, wherein the froth flotation cell has a pulp area (A.sub.p) of at least 15 m.sup.2, measured at the height of a mixing area, defined as the part or zone of the flotation tank in vertical direction where the slurry is agitated, and wherein froth collected into the second froth collection channel is arranged to be directed to the first froth collection channel, wherein the froth flotation cell further comprises a radial froth crowder comprising a crowding sidewall, and extending from the second froth collection channel to the first froth collection channel.

54. The froth flotation cell according to claim 53, wherein the radial froth collection launder comprises a first radial froth overflow lip and a second radial froth overflow lip opposite the first radial froth overflow lip.

55. The froth flotation cell according to claim 53, wherein at least one radial froth overflow lip is arranged to face a crowding sidewall of a radial froth crowder.

56. The froth flotation cell according to claim 53, wherein the radial froth collection launder comprises a sidewall which is a crowding sidewall.

57. The froth flotation cell according to claim 56, wherein a radial froth crowder comprises a crowding sidewall and a froth collection lip opposite the crowding sidewall, and that the froth collection lip is arranged to face a crowding sidewall of a radial froth collection launder.

58. The froth flotation cell according to claim 53, wherein a radial froth crowder comprises a first crowding sidewall and a second crowding sidewall.

59. The flotation cell according to claim 53, wherein the froth flotation cell comprises radial froth collection launders and/or radial froth crowders arranged so that the open froth surfaces (A.sub.f) formed between each radial froth collection launder and/or radial froth crowder are identical in surface area.

60. The froth flotation cell according to claim 53, wherein the first froth collection channel comprises a first froth overflow lip facing towards the centre of the tank.

61. The froth flotation cell according to claim 60, wherein the first froth overflow lip is arranged at the top of a vertical sidewall of the first froth collection channel.

62. The froth flotation cell according to claim 53, wherein the first froth collection channel comprises a side structure facing towards the centre of the tank, the side structure arranged to crowd froth away from the first froth collection channel.

63. The froth flotation cell according to claim 62, wherein the side structure has an angle of inclination of 20-80 in relation to the vertical (n) of the tank.

64. The froth flotation cell according to claim 53, wherein the second froth collection channel further comprises a second overflow lip facing towards the perimeter of the tank.

65. The froth flotation cell according to claim 64, wherein the second overflow lip is arranged at the top of a vertical sidewall of the second froth collection channel.

66. The froth flotation cell according to claim 53, wherein the second froth collection channel further comprises a side structure facing towards the perimeter of the tank, the side structure arranged to crowd froth away from the second froth collection channel.

67. The froth flotation cell according to claim 66, wherein the side structure has an angle of inclination of 20-80 in relation to the vertical (n) of the tank.

68. The froth flotation cell according to claim 53, wherein the radial froth collection launder is arranged to collect froth and direct the collected froth to the first froth collection channel.

69. The froth flotation cell according to claim 53, wherein the radial froth crowder is arranged in fluid communication with the first froth collection channel and the second froth collection channel, and further arranged to direct froth from the second froth collection channel to the first froth collection channel.

70. The froth flotation cell according to claim 53, wherein the radial froth collection launder is arranged to have a shape that prevents flotation gas bubbles from colliding under the radial froth collection launder and froth from moving away from the radial froth collection launder.

71. The froth flotation cell according to claim 53, wherein the radial froth collection launder is arranged to have a shape that directs froth to flow into the radial froth collection launder.

72. The froth flotation cell according to claim 53, wherein the cross-section of the radial froth collection launder in the radial direction of the tank is a substantially V shaped form comprising an apex pointing towards the bottom of the tank, an first inclined sidewall (c) and a second inclined sidewall (d) extending from the apex so that an apex angle is formed between the first and the second inclined sidewalls (c, d), and a first radial froth overflow lip at the top of the first inclined sidewall (c) and a second radial froth overflow lip at the top of the second inclined sidewall (d).

73. The froth flotation cell according to claim 53, wherein the radial froth collection launder comprises a vertically extending first sidewall and a vertical extending second sidewall opposite the first sidewall, a first radial froth overflow lip at the top of the first sidewall and a second radial froth overflow lip at the top of the second sidewall, and a substantially V shaped inclined bottom with an apex pointing towards a bottom of the tank and having an apex angle , the first and second sidewalls and the bottom defining a channel for directing froth to the first froth collection channel.

74. The froth flotation cell according to claim 73, wherein the first sidewall and the second sidewall have a length of at least 50 mm.

75. The froth flotation cell according to claim 71, wherein the angle is 20-160, preferably 20-80.

76. The froth flotation cell according to claim 53, wherein the radial froth crowder is arranged to have a shape that directs froth towards the radial overflow lips of radial froth collection launders next to the radial froth crowder.

77. The froth flotation cell according to claim 53, wherein the cross-section of the radial froth crowder in the radial direction of the tank has a functional V shape comprising an apex pointing towards the bottom of the tank, and an inclined first side (a) and an inclined second side (b) extending from the apex so that an angle is formed between the first and the second sides (a, b); the first side (a) facing the first radial froth overflow lip of an adjacent first radial froth collection channel and the second side (b) facing the second radial froth overflow lip of an adjacent second radial froth collection launder.

78. The froth flotation cell according to claim 77, wherein the angle is 20-80.

79. The froth flotation cell according to claim 53, wherein a surface area (A.sub.C) of a radial froth crowder is larger than a surface area (A.sub.L) of a radial froth collection launder, measured at the height (H) of the froth surface; preferably, the ratio of A.sub.C/A.sub.L is at least 2, more preferably at least 3.

80. The froth flotation cell according to claim 53, wherein the tank comprises open froth surfaces (A.sub.f) between froth collection channels and radial froth collection launders, and inside the second froth collection launder.

81. The froth flotation cell according to claim 80, wherein an open froth surface (A.sub.f) between any two radial froth collection launders is dividable into two open froth subsurfaces (A.sub.fa, A.sub.fb) by a radial froth crowder, one open froth subsurface (A.sub.fa) on the side of the first radial froth overflow lip of a first radial froth collection launder, and one open froth subsurface (A.sub.fb) on the side of the second radial froth overflow lip of a second froth collection channel; so that the two open froth subsurfaces (A.sub.fa, A.sub.fb) are completely separated by the radial froth crowder.

82. The froth flotation cell according to claim 80, wherein a radial froth crowder is arranged to have a form which allows a froth load to be balanced between an open froth subsurface (A.sub.fa) on the first side (a) of the functional V shape and an open froth subsurface (A.sub.fb) on the second side (b) of the functional V shape.

83. The froth flotation cell according to claim 80, wherein the area of open froth surface (A.sub.f) is arranged to be varied so that the relationship between open froth subsurfaces (A.sub.fa, A.sub.fb) between two radial froth collection launders and an open froth subsurface (A.sub.fc) inside the first overflow lip of the second froth collection channel is changed.

84. The froth flotation cell according to claim 80, wherein the relationship between the two open froth subsurfaces (A.sub.fa, A.sub.fb) separated by a radial froth crowder is arranged to be varied by changing the vertical position of the radial froth crowder in relation to the height (H), measured from the bottom of the tank, of a radial froth overflow lip next to the radial froth crowder.

85. The froth flotation cell according to claim 53, wherein the gas supply is arranged into the tank.

86. The froth flotation cell according to claim 53, wherein the tank comprises a mixing device.

87. The froth flotation cell according to claim 86, wherein the mixing device comprises the gas supply.

88. The froth flotation cell according to claim 53, wherein pulp area (A.sub.p) is at least 40 m.sup.2, measured at the mixing area.

89. The froth flotation cell according to claim 53, wherein it has a volume of at least 150 m.sup.3, or at least 250 m.sup.3, or at least 400 m.sup.3.

90. The froth flotation cell according to claim 53, wherein a radial froth collection launder is arranged to be supported by the second froth collection channel.

91. The froth flotation cell according to claim 53, wherein comprising an equal number of radial froth collection launders and radial froth crowders arranged alternately on a circumference surrounding the second froth collection channel; wherein the radial froth collection launders are arranged to be supported by the second froth collection channel.

92. The froth flotation cell according to claim 53, wherein the radial froth collection launder comprises a straight radial froth overflow lip, or a zigzag radial froth overflow lip.

93. The froth flotation cell according to claim 53, wherein the radial froth collection launder comprises a straight radial froth overflow lip.

94. A flotation line comprising a rougher part with at least two rougher flotation cells connected in series and arranged in fluid communication, and a scavenger part with at least two scavenger flotation cells connected in series and arranged in fluid communication, in which flotation line a subsequent flotation cell is arranged to receive underflow from a previous flotation cell, wherein at least one of the flotation cells is a froth flotation cell according to claim 53.

95. The flotation line according to claim 94, wherein the scavenger part comprises at least one froth flotation cell.

96. The flotation line according to claim 94, wherein the rougher part comprises at least one froth flotation cell.

97. The flotation line according to claim 94, wherein it comprises at least two rougher or scavenger flotation cells and/or at least two additional froth flotation cells arranged to treat the slurry before it is arranged to be treated in the froth flotation cell.

98. Use of a froth flotation line according to claim 94, wherein recovering mineral ore particles comprising a valuable mineral.

99. The use of a froth flotation line according to claim 98, wherein recovering mineral ore particles comprising a valuable mineral from low grade ore.

100. The use of a froth flotation line according to claim 99, wherein recovering mineral ore particles comprising Cu from low grade ore.

101. 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 cell according to claim 53, wherein the froth floatation cell comprises a first radial froth collection launder with a first radial overflow lip and a second radial froth collection launder with a second radial overflow lip, and an open froth surface (A.sub.f) of a flotation tank is divided into two open froth subsurfaces (A.sub.fa, A.sub.fb) by the radial froth crowder arranged between a first radial overflow lip of the first radial froth collection launder and the second radial overflow lip of the second radial froth collection launder, one open froth subsurface (A.sub.fa) on the side of the first radial froth overflow lip and one open froth subsurface (A.sub.fa) on the side of the second radial froth overflow lip; so that the two open froth subsurfaces (A.sub.fa, A.sub.fb) are completely separated by the radical froth crowder.

102. The froth flotation method according to claim 101, wherein the two open froth subsurfaces (A.sub.fa, A.sub.fb) are completely separated by a radial froth crowder.

103. The froth flotation method according to claim 101, wherein the area of an open froth surface (A.sub.f) is varied so that the relationship between open froth subsurfaces (A.sub.fa, A.sub.fb) between two radial froth collection launders and an open froth subsurface (A.sub.fc) inside the first overflow lip of the second froth collection channel is changed.

104. The froth flotation method according to claim 101, wherein the relationship between the two open froth subsurfaces (A.sub.fa, A.sub.fb) separated by a radial froth crowder is varied by changing the vertical position of the radial froth crowder in relation to the height (H) of a radial froth overflow lip next to the radial froth crowder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0114] 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:

[0115] FIG. 1a-c are a schematic transverse cross-section of a froth flotation cell according to exemplary embodiments of the invention.

[0116] FIG. 1d is a further cross-section along the line D-D of FIG. 1a of a froth flotation cell according to the exemplary embodiment invention.

[0117] FIG. 1e is a further cross-section along the line E-E of FIG. 1c of a froth flotation cell according to the exemplary embodiment invention.

[0118] FIG. 1f is a further cross-section along the line F-F of FIG. 1a of a froth flotation cell according to the exemplary embodiment invention.

[0119] FIG. 1g is a further cross-section along the line G-G of FIG. 1c of a froth flotation cell according to the exemplary embodiment invention.

[0120] FIG. 1h is a cross-section of another exemplary embodiment of the froth flotation cell according to the invention.

[0121] FIG. 1i is a further cross-section along the line I-I of FIG. 1h of a froth flotation cell according to the exemplary embodiment invention.

[0122] FIG. 1j is a cross-section of another exemplary embodiment of the froth flotation cell according to the invention.

[0123] FIGS. 2a-c are schematic radial cross-sections showing details of embodiments of a froth flotation cell according to the invention.

[0124] FIG. 3a-d are schematic three-dimensional projections of exemplary embodiments of the froth flotation cell according to the invention.

[0125] FIG. 4 is a schematic illustration of an exemplary embodiment of the froth flotation cell according to the invention.

[0126] FIG. 5 is a schematic illustration of another exemplary embodiment of the cell according to the invention.

[0127] FIG. 6a-b are a schematic illustration of yet another exemplary embodiment of the cell according to the invention.

[0128] FIGS. 7a-b are flow chart illustrations of embodiments of a flotation line according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0129] Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0130] The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the froth flotation cell, line, use 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 froth flotation cell 10 and froth flotation line 1 are omitted for clarity. The forward direction of flow of slurry 1 is shown in the figures by arrows.

[0131] For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components.

[0132] In FIGS. 1a-j and 3a-d to 6b, a tank 11 of a froth flotation cell 10 receives a flow of suspension, that is, a flow of slurry 100 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.

[0133] 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 froth flotation cell 10 or a tank 11 of the flotation cell 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.

[0134] Ore particles become attached or adhered to gas bubbles to form gas bubble-ore particle agglomerates. These agglomerates rise to the surface 113 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 100 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 cell 10, comprising the gas bubble-ore particle agglomerates is let to flow out of froth flotation cell 10 as an overflow 50 via the froth overflow lips 121a, 122a-b, 123a-b into froth collection channels 21, 22 or into a radial froth collection launder 23.

[0135] Any or all of the froth overflow lips including the first froth overflow lip 121a of the first froth collection channel 21, the first froth overflow lip 122a of the second froth collection channel 22, the second froth overflow lip 122b of the second froth collection channel 22, the first froth overflow lip 123a of a radial froth collection launder 23, the second froth overflow lip 123a of a radial froth collection launder 23 and/or a froth overflow lip 123a, 123b of a radial structure may be straight or winding, e.g. a zigzag or wavy lip. While zigzag lips may be used, lip length is preferably reduced by using radial froth crowders 31 or radial structures having at least one side wall arranged as a crowder instead.

[0136] The collected slurry overflow 50 may be led to further processing or collected as a final product, depending on the point of a flotation line 1 at which the overflow 50 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 la via an outlet to a subsequent flotation cell and finally out of the process as gangue or final residue.

[0137] The slurry 100 is first introduced into a froth flotation cell 10, in which the slurry 100 is treated by introducing flotation gas into the slurry by a gas supply 12 (see FIG. 5, 6b) 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. 4, 5), or into a tank without a mixing device via gas inlets (FIG. 6b), 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 100 into the flotation tank 11b in a separate pre-treatment or conditioner tank 11a, as is the case in a dual flotation cell (FIG. 6a).

[0138] 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. 4), or by a pump 14, 12 in a so-called self-aspirating tank, as shown in FIG. 5 (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.

[0139] In an embodiment of the froth flotation cell 10, as seen in FIG. 1a-c, 1h, 3a-d and 4, it comprises a tank 11 with a centre 111 and a perimeter 110, and a first froth collection channel 21 surrounding the perimeter 111 of the tank 11 so that an open froth surface A.sub.f is formed inside the first froth collection channel 21.

[0140] The first froth collection channel 21 may comprise a first froth overflow lip 121a facing towards the centre 111 of the tank 11, i.e. the first froth collection channel may act as a froth collection launder (see FIGS. 1a-b and FIGS. 3a-b). In that case, the first froth collection channel 21 may comprise a vertical sidewall 210 also facing towards the centre 111 of the tank 11. The sidewall 210 ends in the first froth overflow lip 121a, i.e. the first froth collection lip 121a is arranged at the top of the sidewall 210.

[0141] Alternatively, the first froth collection channel 21 may comprise a side structure 212 facing towards the centre 111 of the tank 11 (see FIGS. 3c-d). The side structure 212 is arranged to crowd froth 3 away from the first froth collection channel 21, towards the centre 111 of the tank 11. The side structure 212 is inclined so that in relation to the vertical n of the tank 11, the side structure 212 has an angle of inclination of 20-40 or even 20-80. The angle of inclination may for example be 24, 28.5, 30, 35 or 37.5.

[0142] The froth flotation cell 10 further comprises a second froth collection channel 22 arranged between the centre 111 of the tank 11 and the first froth collection channel 21. The second froth collection channel 22 comprises a first froth overflow lip 122a facing towards the centre 111 of the tank 11.

[0143] The froth flotation cell 10 may also comprise a central froth crowder 32 arranged inside the second froth collection channel 22, as shown in FIGS. 1a-c and 3a-d. The central froth crowder 32 may be positioned on the centre 111 of the tank 11, for example axially along the centre axis of the tank 11. The central froth crowder 32 may be conical or frustoconical with its narrow end pointing towards the bottom 112 of the tank 11. The central froth crowder 32 may be adjusted to control an open froth surface formed inside the second froth collection channel 22. For this purpose, the vertical position of the central froth crowder may be arranged to be varied in relation to the height, measured from the bottom of the tank, of the first froth overflow lip 122a of the second froth collection channel 22.

[0144] The second froth collection channel 22 may further comprise a second overflow lip 122b facing towards the perimeter 110 of the tank 11. In that case, similarly to the first froth collection channel 21, the second froth collection channel 22 may comprise a vertical sidewall 220 also facing towards the centre 111 of the tank 11. The sidewall 220 ends in the second froth overflow lip 122b, i.e. the second froth collection lip 122b is arranged at the top of the sidewall 220.

[0145] Alternatively, the second froth collection channel 22 may further comprise a side structure 222 facing towards the perimeter 110 of the tank 11. The side structure 222 is arranged to crowd froth 3 away from the second froth collection channel 22, towards the perimeter 110 of the tank 11. The side structure 222 is inclined so that in relation to the vertical n of the tank 11, the side structure 222 has an angle of inclination of 20-40 or even 20-80. The angle of inclination may for example be 24, 28.5, 30, 35 or 37.5.

[0146] Froth 3 collected into the second froth collection channel 22 is arranged to be directed to the first froth collection channel 21. This may be realized for example by separate connecting pipe or pipes or other conduits (not shown in the figures).

[0147] The froth flotation cell 10 also comprises a radial froth collection launder 23 extending from the first froth collection channel 21 towards the second froth collection channel 22.

[0148] A radial froth collection launder 23 comprises at least one radial froth overflow lip 123a. In an embodiment, it may comprise a first radial froth overflow lip 123a and a second radial froth overflow lip 123b opposite the first (see FIG. 2a), i.e. both sides of the radial froth collection launder act as collecting structures allowing overflow of froth and/or slurry to be collected into the radial froth collection launder 23. At least one radial froth overflow lip 123a is arranged to face a crowding sidewall 310 of a radial froth crowder 31, which allows the crowding effect from the froth crowder to efficiently push and direct material in the froth 3 layer towards the radial froth collection launder 23. Both the first and the second radial froth overflow lips 123a, 123b may be arranged to face a crowding sidewall 310, 320 of radial froth crowders 31, between which the radial froth collection launder is situated (see for example FIG. 3c).

[0149] A radial froth collection launder 23 may also comprise a sidewall 230a which is a crowding sidewall, i.e. one side of the radial launder 23 is not collecting froth but provides a crowding effect (see FIG. 2b). This crowding sidewall is arranged to face a froth collection lip 302 of an adjacent radial froth crowder 31, to push and direct the flow of froth and/or slurry towards this collecting structure.

[0150] A radial froth collection launder 23 is in fluid communication with the first froth collection channel 21. There may be at least one radial froth collection launder 23 in the froth flotation cell 10. In an embodiment, the froth flotation cell 10 may comprise four such radial froth collection launders 23, as illustrated for example in FIGS. 1a, 1c, 3a and 3c. In another embodiment, the froth flotation cell 10 may comprise eight such radial froth collection launders 23, as illustrated for example in FIGS. 1b, 1h, 3b and 3d. The number of radial froth collection launders 23 may be readily chosen according to the size (tank diameter, tank volume, pulp area A.sub.p) of the froth flotation cell, and/or according to any other relevant flotation process parameter. The froth collection launders 23 may be arranged symmetrically with respect to each other and/or the centre 111 of the tank 11. For example, they may be arranged with a separation of substantially 30, 60 or 90 degrees with respect to a central longitudinal axis of the tank 11.

[0151] A radial froth collection launder 23 may be arranged to collect froth 3 from the surface 113 of the tank 11, and to direct the collected froth 3 to the first froth collection channel 21. A radial froth collection launder 23 is arranged in fluid communication with the first froth collection channel 21. Any or all radial froth collection launders 23 may be arranged separate from the from the second froth collection channel 22 (see FIGS. 1a-c and 3a-d) so that they are not in fluid communication, at least a direct fluid communication, with the second froth collection channel 22. Any or all radial froth collection launders 23 may therefore be shorter than the radial distance between the first froth collection channel 21 and the second froth collection channel 22.

[0152] Alternatively or additionally, any or all radial froth collection launders 23 may be arranged to be supported by the second froth collection channel 22 (see FIGS. 1h-j). This may be arranged as a structural connection, e.g. a direct structural connection 124, between a radial froth collection launder 23 and the second froth collection channel 22. The radial froth collection launders 23 may therefore be at least as long as the radial distance between the first froth collection channel 21 and the second froth collection channel 22. Depending on the length of the radial froth collection launders 23, any or all of them may be arranged to divide the open froth surfaces A.sub.f into separated subsurfaces but they may also be arranged so that they do not divide the open froth surfaces A.sub.f into separated subsurfaces, i.e. they facilitate direct connection of the subsurfaces.

[0153] A radial froth collection launder 23 may arranged to have a shape that prevents flotation gas bubbles from colliding under the radial froth collection launder 23, and a shape that also prevents froth 3 from moving away from the radial froth collection launder 23. Further, the radial froth collection launder 23 may be arranged to have a shape that directs froth 3 to flow into the radial froth collection launder.

[0154] This shape is realized by the radial froth collection launder 23 having at least one radial froth overflow lip 123a, 123b for gathering froth.

[0155] For example, the froth collection launder 23 may have a shape in which the cross-section of a radial froth collection launder 23 in the radial direction of the tank 11 is substantially V shaped form (see FIG. 2a) comprising an apex 123c pointing towards the bottom 112 of the tank 11, a first inclined sidewall c and a second inclined sidewall d extending from the apex 123c so that an apex angle is formed between the first and the second inclined sidewalls c, d, and a first radial froth overflow lip 123a at the top of the first inclined sidewall c and a second radial froth overflow lip 123b at the top of the second inclined sidewall d.

[0156] A radial froth collection launder 23 may also have a cross-section in the radial direction of the tank 11 of a functional V shape (see FIG. 2a, where this alternative form may be seen within the radial froth collection launder 23a. The functional V shape comprises an apex pointing towards the bottom 112 of the tank 11, and an inclined first sidewall and an inclined second sidewall extending from the apex so that an apex angle is formed between the first and the second sides. The apex angle may be even 20-160. The at least one froth overflow lip 123a, 123b for gathering froth is formed above the functional V shape. The structure may comprise one or more additional side walls extending from the functional V shape e.g. vertically or in an inclined fashion. A low profile of the radial collection launder 23, for example one with apex angle being 120-160 is advantageous in reducing the spatial volume the launder 23 takes in the tank 11. The at least one froth overflow lip 123a, 123b may then be formed directly at the edge and/or edges of the functional V shape or on top of a side wall extending only a short distance therefrom. In particular, the invention allows reducing the length of the overflow lip 123a, 123b while improving recovery of froth 3.

[0157] A sidewall 230b, c arranged as a crowding sidewall may be inclined, as shown in FIG. 2b, to increase the crowding effect.

[0158] Alternatively, the froth collection launder 23 may comprise a vertically extending first sidewall 230a and a vertically extending second sidewall 230b opposite the first sidewall 230a. The first and the second sidewalls 230a, 230b may have a length of at least 5 mm, to ensure that the radial froth collection launder 23 extends sufficiently deep into the layer of froth 3 on the surface of the tank 11, and that the vertical sidewall may efficiently direct froth 3 to flow over radial froth overflow lips 123a, 123b of the radial froth collection launder 23.

[0159] A first radial froth overflow lip 123a may be arranged at the top of the first sidewall 230a, and a second radial froth overflow lip 123b is arranged at the top of the second sidewall 230b, i.e. the first and second sidewalls 230a, 230b both end, at their upper parts (the parts extending closer towards the surface 113 of the tank 11), into the radial froth overflow lips 123a, 123b. The first and second sidewalls 230a, 230b are connected from their lower parts (the parts extending closer towards the bottom 112 of the tank 11) by a substantially V shaped inclined bottom 230c with an apex 123c pointing towards the bottom 112 of the tank 11. The first and second sidewalls 230a, 230b and the bottom 230c together define a channel 231 for directing froth 3 to the first froth collection channel 21. The bottom 230c may comprise an inclined first sidewall and an inclined second sidewall extending from the apex 123c so that an apex angle is formed between the first and the second sides. The angle may be a freely chosen value between 20-80.

[0160] A radial froth collection launder 23 may have a substantially rectangular cross-section in the horizontal direction of the tank 11, i.e. the first and second sidewalls are straight. In an embodiment, for example as illustrated in FIGS. 1a-c and 3a-d, the first and second sidewalls may be so inclined that the radial froth collection launder 23 is broader or wider closer to the first froth collection channel 21 and narrower closer to the second froth collection channel 22, i.e. the channel 231 may expand towards the flow of froth 3 into the first froth collection channel 21.

[0161] Alternatively or additionally, the apex 123c may have a substantially level height in relation to the bottom 112 of the tank 11 through the length of the radial froth collection launder 23. In an embodiment, the height of the apex 123c may decrease along its extension from the second froth collection channel 22 towards the first froth collection channel 21, so that the channel 231 deepens in the direction of flow of froth 3 towards the first froth collection channel 21.

[0162] By arranging the shape of radial froth collection launder 23 in the above manner, it may be possible to maintain a substantially constant transport distance d between a radial froth crowder and a radial froth overflow lip 123a, 123b of a radial froth collection launder 23. Further, the shape of the radial froth collection launder 23 as seen from the above (see FIGS. 1a-c and 1h) may improve the collection of froth from corner areas where a radial froth collection launder 23 meets the first froth collection channel 21 or the second froth collection launder 22.

[0163] A radial froth collection launder 23 has a surface area A.sub.L measured at the froth 3 surface height H (from the bottom 112), i.e. the area formed between the first and the second sidewalls 230a, 230b, c, d and at least the first froth collection channel 21 from which the radial froth collection launder 23 extends (see FIG. 1d). This surface area corresponds to the reduction in area of the open froth surface A.sub.f the radial froth collection launder effect in the froth flotation cell 10.

[0164] The froth flotation cell 10 further comprises a radial froth crowder 31 extending from the second froth collection channel 22 to the first froth collection channel 22.

[0165] A radial froth crowder 31 comprises a crowding sidewall 310 (see FIGS. 2a-c). In an embodiment, a radial froth crowder 31 comprises a crowding sidewall 310, 320 and a froth collection lip 302 (i.e. the top edge 302 of the sidewall 310, a, may act as a froth collection lip 302) opposite the crowding sidewall, and that the froth collection lip 302 is arranged to face a crowding sidewall 230a of a radial froth collection launder 23. The radial froth crowder 31 of such a structure may therefore act as a collecting structure as froth and/or slurry from the open froth surfaces A.sub.f may overflow the froth collection lip 302. In an embodiment, the froth collection lip 302 of a radial froth crowder 31 may be arranged to face a radial froth overflow lip 123a of a radial froth collection launder 23 (see FIG. 2c). This kind of construction allows for efficient recovery of valuable mineral ore particles in the froth flotation cell 10. In case the radial froth crowder 31 is arranged to act as a collecting structure, a sidewall a is arranged to have a vertical portion (see FIGS. 2b, 2c) that efficiently directs flow of slurry and/or froth over the top edge 302 of the sidewall a, acting as a froth overflow lip 302. In other words, at the side of the froth overflow lip 302, the radial froth crowder may be arranged to have a shape similar to a radial froth collection launder, as described above.

[0166] In an embodiment, a radial froth crowder 31 may comprise a first crowding sidewall 310 and a second crowding sidewall 320, i.e. the radial froth crowder 31 is arranged to act as a conventional froth crowder.

[0167] A radial froth crowder 31 may be arranged in fluid communication with the first froth collection channel 21 and the second froth collection channel 22. Further, the radial froth crowder 31 may be arranged to direct froth from the second froth collection channel 21 to the first froth collection channel, so that the transportation of collected froth overflow may be substantially increased in volume and efficiency. A radial froth crowder 31 may be arranged to divide the open froth surfaces A.sub.f into separated subsurfaces but it may also be arranged so that it does not divide the open froth surfaces A.sub.f into separated subsurfaces, i.e. facilitating direct connection between the subsurfaces. Using the radial froth crowder 31 in combination with the second froth collection channel 22 allows notable simplification and lightening of the structure of the froth flotation cell 10. The second froth collection channel 22 allows notable improvements in terms of volume and weight for covering the area between the perimeter 110 and the centre 111.

[0168] There may be at least one radial froth crowder 31 in the froth flotation cell 10. In an embodiment, the froth flotation cell 10 may comprise four such radial froth crowders 31. The number of radial froth crowders 31 may, similarly to the number of radial froth collection launders 23, be readily chosen according to the size (tank diameter, tank volume, pulp area Ap) of the froth flotation cell, and/or according to any other relevant flotation process parameter. In an embodiment, the froth flotation cell 10 comprises an equal number of radial froth collection launders 23 and radial froth crowders 31, arranged in an interleaving manner (see FIGS. 1a and 1c). The angular separation between neighbouring radial froth collection launders 23 and/or radial froth crowders 31 may be constant.

[0169] The froth flotation cell 10 may comprise an equal number of radial froth collection launders 23 and radial froth crowders 31 arranged alternately, i.e. so that each radial froth collection launder is followed by a radial froth crowder and vice versa, when moved circumferentially in the region between the first froth collection channel 21 and the second froth collection channel 22. Any or all of the radial froth collection launders 23 may be arranged to be supported by the second froth collection channel 22 as described above (see FIG. 1j).

[0170] A radial froth crowder 31 may be arranged to have a shape that directs froth 3 towards radial froth overflow lips 123a, 123b of radial froth collection launders 23a, 23b next to radial froth crowder 31. The shape is arranged to prevent froth 3 from being gathered by the crowder 31.

[0171] This shape may be realized by the radial froth crowder 31 having sidewalls arranged to prevent froth 3 from going over them. For example, the radial froth crowder 31 may have a cross-section in the radial direction of the tank 11 of a functional V shape 300. The functional V shape 300 comprises an apex 301 pointing towards the bottom 112 of the tank 11, and an inclined first sidewall a, 310 and an inclined second sidewall b, 320 extending from the apex 301 so that an angle is formed between the first and the second sides a, b. The angle is 20-80. The angle may for example be 24, 28.5, 31, 35 or 37.5. Preferably the angle is about 30. The structure may comprise one or more additional side walls extending from the functional V shape e.g. vertically or in an inclined fashion.

[0172] The first side 1 faces the first radial froth overflow lip 123a of an adjacent first radial froth collection launder 23a, and the second side b faces the second radial froth overflow lip 123b of an adjacent second radial froth collection launder 23b. The radial froth crowder 31 is arranged between two radial froth collection launders 23 (see FIG. 2a-c).

[0173] In an embodiment, a radial froth collection launder 23 comprises a first froth overflow lip 123a and a second froth overflow lip 123b, and a radial froth crowder 31 comprises a first crowding sidewall 310 and a second crowding sidewall 320. In a further embodiment, the froth flotation cell is arranged to have an equal number of such radial froth collection launders 23 and radial froth crowders 31, arranged alternating and symmetrically (at equal distances from each other) on the perimeter 110 of the tank 11. These kinds of constructions allow a structure of the radial froth collection launders 23 that is light, and that takes only a small amount of space, i.e. does not reduce the volume of the tank 11 or the area of the open froth surfaces significantly.

[0174] Further, the radial froth collection launders 23 and/or radial froth crowders 31 within the froth flotation cell 10 may be arranged so that the open froth surfaces A.sub.f formed between each radial froth collection launder and/or radial froth crowder are identical in surface area.

[0175] Similarly to a radial froth collection launder 23, a radial froth crowder 31 may have a substantially rectangular cross-section in the horizontal direction of the tank 11, i.e. the first and second sides a, b are straight. In an embodiment the first and second sides a, b may be so inclined that the radial froth crowder 31 is broader or wider closer to the first froth collection channel 21 and narrower closer to the second froth collection channel 22, i.e. a channel formed by the functional V shape may expand towards the flow of froth 3 into the first froth collection channel 21. The apex 301 may have a substantially level height in relation to the bottom 112 of the tank 11 through the length of the radial froth crowder 31. In an embodiment, the height of the apex 301 may decrease along its extension from the second froth collection channel 22 towards the first froth collection channel 21, so that the channel formed by the functional V shape deepens in the direction of flow of froth 3 towards the first froth collection channel 21, i.e. the bottom of the radial froth crowder 31 may be inclined or raked towards the first froth collection channel 21 so that the radial cross-section of the froth crowder 31 is widening towards the tank perimeter 110. In this way, the transport distance d between a radial froth crowder 31 and the adjacent radial froth overflow lip 123a may be kept constant throughout the entire radial length which the radial froth crowder 31 and the radial froth collection launder 23 extend from the second froth collection channel 22 to the first froth collection channel 21.

[0176] A radial froth crowder has a surface area A.sub.C measured at the froth 3 surface height H (from the bottom 112), i.e. the area formed between the first and the second sidewalls 310, 320, a, b and the first and second froth collection channels 21, 22 from which the radial froth collection launder 23 extends (see FIG. 1d). This surface area corresponds to the reduction in area of the open froth surface A.sub.f the radial froth crowder 31 effects in the froth flotation cell 10. Preferably, the surface area A.sub.C of a radial froth crowder 31 is larger than the surface area A.sub.L of a radial froth collection launder 23. In an embodiment, the ratio A.sub.C/A.sub.L is at least 2. In an embodiment, the ratio A.sub.C/A.sub.L is at least 3.

[0177] This kind of arrangements are particularly suitable when a radial froth collection launder 23 comprises a first froth overflow lip 123a and a second froth overflow lip 123b, and a radial froth crowder 31 comprises a first crowding sidewall 310 and a second crowding sidewall 320. Alternatively or additionally, the above arrangements may be made even more advantageous when the froth flotation cell is arranged to have an equal number of such radial froth collection launders 23 and radial froth crowders 31, arranged alternating and symmetrically (at equal distances from each other) on the perimeter 110 of the tank 11.

[0178] The tank 11 may comprise open froth surfaces A.sub.f between froth collection channels 21, 22 and radial froth collection launders 23, as well as inside the second froth collection channel 22. An open froth surface A.sub.f between any two radial froth collection launders 23a, 23b may be divided into two open froth subsurfaces A.sub.fa, A.sub.fb by a radial froth crowder 31 so that one open froth subsurface A.sub.fa is formed on the side of the first radial froth overflow lip 123a of a first radial froth collection launder 23a, and one open froth subsurface A.sub.fb on the side of the second radial froth overflow lip 123b of a second radial froth collection channel 23b. The two open froth subsurfaces A.sub.fa, A.sub.fb are completely separated by the radial froth crowder 31 (see FIG. 2).

[0179] The open froth surfaces A.sub.f between froth collection channels 21, 22 may be automatically balanced with each other since they are located on a circumference with constant radial distance from the central axis of the tank 11. However, the froth surfaces A.sub.f between froth collection channels 21, 22 may be imbalanced with respect to any or all froth surfaces A.sub.fc inside the second froth collection channel 22. The open froth surfaces A.sub.f between froth collection channels 21, 22 may be balanced or arranged to be balanced with respect to the open froth surfaces A.sub.fc inside the second froth collection channel 22 by moving any or all radial froth crowders 31 vertically upwards or downwards. Specifically, all radial froth crowders 31 may be arranged to be vertically at the same height. Alternatively or additionally, the froth surfaces A.sub.f between froth collection channels 21, 22 may be balanced or arranged to be balanced with respect to the open froth surfaces A.sub.fc inside the second froth collection channel 22 by moving the central froth crowder 32 vertically upwards or downwards.

[0180] In an embodiment, a radial froth crowder 31 may arranged to have a form which allows a froth load to be balanced between an open froth subsurface A.sub.fa on the first side a of the functional V shape 300 and an open froth subsurface A.sub.fb on the second side b of the functional V shape 300.

[0181] In an embodiment, the area of open froth surface A.sub.f is arranged to be varied so that the relationship between open froth subsurfaces A.sub.fa, A.sub.fb between two radial froth collection launders 23a, 23b and an open froth subsurface A.sub.fc inside the first overflow lip 122a of the second froth collection channel 22 is changed.

[0182] In an embodiment, the relationship between the two open froth subsurfaces A.sub.fa, A.sub.fb separated by a radial froth crowder 31 is arranged to be varied by changing the vertical position of the radial froth crowder 31 in relation to the height H, measured from the bottom 112 of the tank 11, of a radial froth overflow lip 123a, 123a next to the radial froth crowder 31.

[0183] An angle formed between a radial froth crowder 31 and a radial froth collection launder 23 may not be too steep to avoid collisions between gas bubbles, which could lead to the bubbles merging. Therefore the area of open froth surfaces or subsurfaces need to be influenced not by moving a radial froth crowder 31 closer or further away from a radial froth collection launder 23, but by changing the vertical position of the radial froth crowder 31. By moving the radial froth crowder 31 lower in the vertical direction of the tank 11, the open froth subsurface may be decreased and froth crowded towards a radial froth overflow lip 123a, 123b. By moving the radial froth crowder 31 higher, the crowding effect is decreased, but at the same time, it may also be ensured that froth 3 does not flow inside the radial froth crowder 31. By moving the radial froth crowder 31, the difference of height between the apex 301 of the radial froth crowder 31 and the apex 123c of the radial froth collection launder 23 may essentially be varied (see FIG. 2).

[0184] The radial froth crowder 31 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.

[0185] The froth flotation cell 10 may have a pulp area A.sub.p of at least 15 m.sup.2, measured at a mixing area 140 (see FIG. 4, 5, 6a-b). In an embodiment, the froth flotation cell 10 may have a pulp area A.sub.p of at least 40 m.sup.2. A pulp area A.sub.p may be understood as 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 layer of froth 3.

[0186] The mixing area 140 depends on the type of flotation cell. In a flotation cell 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. 4). In a self-aspirating flotation cell 10 (FIG. 5), 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 cell 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. 6a), 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. 6b), the mixing area 140 is defined as the cross-sectional area of the tank 10 at the gas supply sparger 12a height.

[0187] The froth flotation cell 10 may have a volume of at least 150 m.sup.3. In an embodiment, the froth flotation cell 10 may have a volume of at least 250 m.sup.3. In an embodiment, the froth flotation cell 10 may have a volume of at least 400 m.sup.3. The volume of the froth flotation cell 10 may be understood to mean the volume of the tank 11, 11b.

[0188] The froth flotation cell 10 described above may be a part of a froth flotation line 1 (see FIG. 7a-b). A flotation line 1 is an arrangement for treating the slurry 100 for separating valuable metal containing ore particles from ore particles suspended in the slurry in several fluidly connected froth flotation cells 10, and flotation cells 15a, 15b which may be of any conventional type known to a person skilled in the art.

[0189] According to an aspect of the invention, a flotation line 1 comprises a rougher part 1a with at least two rougher flotation cells 15a connected in series and arranged in fluid communication, and a scavenger part 1b with at least two scavenger flotation cells 15b connected in series and in fluid communication. A subsequent flotation cell is arranged to receive underflow 40 from a previous flotation cell. Overflow 50 from each flotation cell 15a, 15b is led out of the flotation line 1 into further treatment, for example regrinding, cleaning, conditioning or further flotation according to processes commonly known in the art.

[0190] At least one of the flotation cells in the flotation line 1 may be a froth flotation cell 10 according to this disclosure. Preferably, the at least one froth flotation cells 10 is arranged into a downstream end of the flotation line 1. In an embodiment, the scavenger part 1b comprises at least one froth flotation cell 10 according to this disclosure. Alternatively or additionally, the rougher part 1a of the flotation line 1 may comprise at least one froth flotation cell 10.

[0191] According to an embodiment, the flotation line 1 may comprise at least two rougher or scavenger flotation cells 15a, 15b, and/or at least two additional froth flotation cells 10a, 10b arranged to treat the slurry 1 before it is led into the froth flotation cell 10 (see FIG. 7b).

[0192] A froth flotation line 1 comprising at least one froth flotation cell 10 according to the present disclosure may be used in recovering mineral ore particles comprising a valuable mineral, especially but not necessarily from a low-grade ore. More specifically, the froth flotation line 1 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 100 into the flotation line.

[0193] In the froth flotation method for treating mineral ore particles suspended in slurry, the slurry 100 is separated into an underflow 40 and an overflow 50 in a froth flotation cell 10 according to the present disclosure. An open froth surface A.sub.f of a flotation tank 11 is divided into two open froth subsurfaces A.sub.fa, A.sub.fb by a radial froth crowder 31 arranged between a first radial overflow lip 123a of a first radial froth collection launder 23a and a second radial overflow lip 123a of a second radial froth collection launder 23.

[0194] In an embodiment, the two open froth subsurfaces A.sub.fa, A.sub.fb are completely separated by a radial froth crowder 31. According to another embodiment, the area of an open froth surface A.sub.f is varied so that the relationship between open froth subsurfaces A.sub.fa, A.sub.fb between two radial froth collection launders 23a, 23b and an open froth subsurface (A.sub.fc) inside the first overflow lip 122a of the second froth collection channel 22 is changed. According to an embodiment, the relationship between the two open froth subsurfaces A.sub.fa, A.sub.fb separated by a radial froth crowder 31 is varied by changing the vertical position of the radial froth crowder 31 in relation to the height H of a radial froth overflow lip 123a, 123b next to the radial froth crowder 31.

[0195] 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.