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Title:
A FROTH FLOTATION METHOD AND A FROTH FLOTATION ARRANGEMENT
Document Type and Number:
WIPO Patent Application WO/2019/008216
Kind Code:
A1
Abstract:
The invention is based on the idea of a froth flotation method for treating mineral ore particles suspended in slurry, comprising a flotation tank for separating the slurry into an underflow (19) and an overflow (20). The arrangement comprises a primary line comprising at least three flotation tanks connected in series, wherein each subsequent flotation tank is arranged to receive the underflow (19) from the previous flotation tank. The method comprising the steps of: feeding a slurry (8) to a tank (2) through a slurry inlet (15), the tank (2) has at least 200 m3 volume, and the tank (2) comprises an available froth surface area (Afroth). The tank (2) comprises a froth collection launder (7) comprising a froth overflow lip (6), and the overflow lip (6) has total length of the overflow lips (L tot) in horizontal direction (x). There is an effective height (h) from a bottom (5) of the tank to the lip (6) of the froth collection launder (7). The tank has a diameter (D) at the height of the impeller, where the diameter of the tank is calculated as an average at the height of an impeller (h3). The ratio between the effective height (h) and the diameter (D) of the tank (h/) is less than 1,5. Introducing gas bubbles to the tank through a gas supply (4), mixing the slurry (8) and the gas with the impeller (3) within the tank (2), and capturing the valuable material from the slurry (8) to the gas bubbles creating a froth (12). The third tank or subsequent tank in the series comprises a ratio L tot/ √A froth between a total length of the overflow lips (L tot) in horizontal direction (x) and a square root of an available froth surface area (A froth) is 4-20. The method further comprises the steps of: causing the froth (12) to flow over the froth overflow lip (6) of the froth collection lauder (7) by controlling the froth level (14), wherein the froth overflow lip (6) of the third tank or subsequent tank in the series comprises an edge portion (13) with variable height (h) in the vertical direction (y), and controlling the froth level (14) to be vertically higher than the vertically lowest edge height (h1) of the lip (6) and vertically lower than the vertically highest edge height (h2) of the lip (6), and controlling the slurry level (17) to be lower than the vertically lowest edge height (h1) of the lip (6). The application also relates to a froth flotation arrangement.

Inventors:
MIETTINEN, Tatu (Tallbergin puistotie 7 B 14, Helsinki, 00200, FI)
GRAU, Rodrigo (Opiskelijantie 10, Pori, 28600, FI)
YANEZ, Alejandro (Jääkärinkatu 4 A 12, Helsinki, 00150, FI)
MÖNKÄRE, Zakaria (Fredrikinkatu 43 E 36, Helsinki, 00120, FI)
TUOMINEN, Jere (Ohrakaskensyrjä 13 B, Espoo, 02340, FI)
Application Number:
FI2017/050504
Publication Date:
January 10, 2019
Filing Date:
July 04, 2017
Export Citation:
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Assignee:
OUTOTEC (FINLAND) OY (Rauhalanpuisto 9, Espoo, 02230, FI)
International Classes:
B03D1/02; B03D1/14; B03D103/02
Domestic Patent References:
WO2003078013A22003-09-25
Foreign References:
DE363816C1922-11-14
US6019898A2000-02-01
Attorney, Agent or Firm:
PAPULA OY (P.O. Box 981, Helsinki, 00181, FI)
Download PDF:
Claims:
CLAIMS

1. A froth flotation method for treating mineral ore particles suspended in slurry, comprising a flotation tank (2) for separating the slurry (8) into an underflow (19) and an overflow (20), wherein the arrangement comprises

- a primary line (1) comprising at least three flotation tanks (2) connected in series, wherein each subsequent flotation tank (2) is arranged to receive the underflow (19) from the previous flotation tank (2),

the method comprising the steps of:

feeding a slurry (8) to a tank (2) through a slurry inlet (15) -the tank (2) has at least 200 m3 volume, and the tank (2) comprises an available froth surface area (Afroth),

- the tank (2) comprises a froth collection launder (7) comprising a froth overflow lip (6), and the overflow lip (6) has total length of the overflow lips

(L tot) in horizontal direction (x), and

-there is an effective height (h) from a bottom (5) of the tank to the lip (6) of the froth collection launder (7),

-the tank has a diameter (D) at the height of the impeller, where the diameter of the tank is calculated as an average at the height of an impeller (h3),

-wherein the ratio between the effective height (h) and the diameter (D) of the tank (h/D) is less than 1,5,

introducing gas bubbles to the tank through a gas supply (4), mixing the slurry (8) and the gas with the impeller (3) within the tank (2), capturing the valuable material from the slurry (8) to the gas bubbles creating a froth (12),

characterize d in that the third tank or subsequent tank in the series comprises a ratio L tot/ J A froth between a total length of the overflow lips (L tot) in horizontal direction (x) and a square root of an available froth surface area (A froth) is 4-20,

the method further comprises the steps of: causing the froth (12) to flow over the froth overflow lip (6) of the froth collection lauder (7) by controlling the froth level (14), wherein the froth overflow lip (6) of the third tank or subsequent tank in the series comprises an edge portion (13) with variable height (h) in the vertical direction (y), and controlling the froth level (14)to be vertically higher than the vertically lowest edge height (hi) of the lip (6) and ver- tically lower than the vertically highest edge height (h2) of the lip (6), and controlling the slurry level (17) to be lower than the vertically lowest edge height (hi) of the lip (6).

2. A froth flotation method according to claim 1, characterized in that the method further comprises the steps of: the controlling the slurry level

(17) for controlling the flow of the froth (12) over the overflow lip (6).

3. A froth flotation method according to any of claims 1-2, characterized in that in the method 20-100% of the total length (L tot)of the froth overflow lips (6) in horizontal direction(x) comprises the edge portion (13) with variable height (h).

4. A froth flotation method according to any of claims 1-3, characterized in that the edge portion (13) with variable height (h) comprises undulated edge, serrate edge or columns projecting in vertical direction (y).

5. A froth flotation method according to any of claims 1-4, charac- t e r i z e d in that in the method the froth level (14) controlling is performed at least in a range defined by the distance between the vertically (y) lowest edge height (hi) and the vertically (y) highest edge height (h2) of the froth overflow lip (6) which is at least 2 cm, preferably 5 cm.

6. A froth flotation method according to any of claims 1-5, charac- t e r i z e d in that a distance between the lengths in the overflow lips open for the froth (12) to flow over the froth overflow lip (6) in horizontal direction (x) at the froth level (14) is less than 50 cm.

7. A froth flotation method according to any of claims 1-6, characterized in that in the method the ratio L eff/ L tot between effective length of the overflow lips (L eff) and the total length of the overflow lips (L tot) in horizontal direction is in range of 0,2-0,6 where the effective length of the overflow lips (L eff) is the sum of lengths in the overflow lips open for the froth (12) to flow over the froth overflow lip (6) in horizontal direction (x) at the froth level (14).

8. A froth flotation method according to any of claims 1-7, charac- t e r i z e d in that in the method a ratio L tot/ J A froth between a total length of the overflow lips (L tot) in horizontal direction (x) and a square root of an available froth surface area (A froth) is preferably 8 - 16.

9. A froth flotation arrangement for treating mineral ore particles suspended in slurry, comprising a flotation tank (2) for separating the slurry (8) into an underflow (19) and an overflow (20), wherein the arrangement comprises

- a primary line (1) comprising at least three flotation tanks (2) connected in series, wherein each subsequent flotation tank (2) is arranged to receive the underflow (19) from the previous flotation tank (2),

-a tank (2) comprising an impeller (3) within the tank (2) and a gas supply (4),

-the tank (2) has at least 200 m3 volume, and the tank (2) comprises an available froth surface area (Afroth),

- the tank (2) comprises a froth collection launder (7) comprising a froth overflow lip (6), and the overflow lip (6) has total length of the overflow lips (L tot) in horizontal direction (x), and

-there is an effective height (h) from a bottom (5) of the tank to the lip (6) of the froth collection launder (7),

-the tank has a diameter (D) at the height of the impeller, where the diameter of the tank is calculated as an average at the height of an impeller (h3),

-wherein the ratio between the effective height (h) and the diameter

(D) of the tank (h/D) is less than 1,5,

c h a r a c t e r i z e d in that the third tank or subsequent tank in the series comprises a ratio L tot/ J A froth between a total length of the overflow lips (L tot) in horizontal direction (x) and a square root of an available froth surface area (A froth) is 4-20,

the froth overflow lip (6) of the third tank or subsequent tank in the series comprises an edge portion (13) with variable height (h) in the vertical direction (y), and the arrangement comprises means for controlling the froth level (14) to be vertically (y) higher than the vertically lowest edge height (hi) of the froth overflow lip (6) and vertically (y) lower than the vertically highest edge height (h2) of the froth overflow lip (6).

10. A froth flotation arrangement according to claim 9, c h a r a c t e r i z e d in that the ratio L tot/ jA froth between a total length of the overflow lips (L tot) in horizontal direction (x) and a square root of an available froth sur- face area (A froth) is preferably 8 - 16.

11. A froth flotation arrangement according to any of claims 9-10, c h a r a c t e r i z e d in that the ratio between a height from a bottom (5) of the tank (2) to the lip (6) of the froth collection launder (7) and the square root of a pulp area h/ jA pulp is less than 1,5, where the pulp area (A puiP) is calculated as an average from the cross sectional areas of the tank (2) at the height of the impeller (h3).

12. A froth flotation arrangement according to any of claims 9-11, characterized in that the arrangement comprises means for controlling the slurry level (17) to be lower than the vertically lowest edge height (hi) of the froth overflow lip (6).

13. A froth flotation arrangement according to any of claims 9-12, characterized in that a ratio L eff/ L tot between effective length of the overflow lips (L eff) and the total length of the overflow lips (L tot) in horizontal direction (x) is in range of 0,2-0,6, where the effective length of the overflow lips (L eff) is the sum of the lengths in the overflow lips open for the froth (12) to flow over the froth overflow lip (6) in horizontal direction (x).

14. A froth flotation arrangement according to any of claims 9-13, characterized in that in the height variation (dh) in the edge portion (13) is at least 2 cm, preferably 5 cm.

15. A froth flotation arrangement according to any of claims 9-14, characterized in that the length in the overflow lip open for the froth to flow over the overflow lip (L eff) in horizontal direction (x) increases towards the vertically highest edge height (h2) of the froth overflow lip (6).

16. A froth flotation arrangement according to claim 15, characterized in that the edge portion (13) with variable height comprises undulat- ed edge or serrate edge.

17. A froth flotation arrangement according to any of claims 9-16, characterized in that the gas supply (4) comprises a pipe delivering gas to the bottom part of the tank or a conduit formed to an agitator (9) comprising the impeller (3).

18. A froth flotation arrangement according to any of claims 9-17, characterized in that the flotation tank (2) comprises an agitator comprising an impeller (3) and a stator (18).

Description:
A FROTH FLOTATION METHOD AND A FROTH FLOTATION ARRANGEMENT

FIELD OF THE INVENTION

[0001] The invention relates to a froth flotation method and a froth flotation arrangement, and particularly to a froth flotation method and a froth flotation arrangement for treating mineral ore particles suspended in slurry.

BACKGROUND OF THE INVENTION

[0002] A froth flotation method and arrangement is used for treating mineral ore particles suspended in slurry.

BRIEF DESCRIPTION OF THE INVENTION

[0003] An object of the present invention is thus to provide a method and an arrangement having an improved froth collection lauder lip loading and a froth recovery. The objects of the invention are achieved by a method and an arrangement which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

[0004] The invention is based on the idea of a froth flotation method for treating mineral ore particles suspended in slurry, comprising a flotation tank for separating the slurry into an underflow and an overflow. The arrangement comprises a primary line comprising at least three flotation tanks connected in series, wherein each subsequent flotation tank is arranged to receive the underflow from the previous flotation tank. The method comprises the steps of: feeding a slurry to a tank through a slurry inlet, the tank has at least 200 m 3 volume, and the tank comprises an available froth surface area. The tank comprises a froth collection launder comprising a froth overflow lip, and the overflow lip has total length of the overflow lips in horizontal direction. There is an effective height from a bottom of the tank to the lip of the froth collection launder. The tank has a diameter at the height of the impeller, where the diameter of the tank is calculated as an average at the height of an impeller. The ratio between the effective height and the diameter of the tank is less than 1,5. Introducing gas bubbles to the tank through a gas supply, mixing the slurry and the gas with the impeller within the tank, capturing the valuable material from the slurry to the gas bubbles creating a froth. The third tank or subsequent tank in the series comprises a ratio between a total length of the overflow lips in horizontal direction and a square root of an available froth surface area is 4-20. The method further comprises the steps of: causing the froth to flow over the froth overflow lip of the froth collection lauder by controlling the froth level, wherein the froth overflow lip of the third tank or subsequent tank in the series comprises an edge portion with variable height in the vertical direction, and controlling the froth level to be vertically higher than the vertically lowest edge height of the lip and vertically lower than the vertically highest edge height of the lip, and controlling the slurry level to be lower than the vertically lowest edge height of the lip.

[0005] The invention is based on the idea of a froth flotation arrangement for treating mineral ore particles suspended in slurry, comprising a flotation tank for separating the slurry into an underflow and an overflow. The arrangement comprises a primary line comprising at least three flotation tanks connected in series, wherein each subsequent flotation tank is arranged to receive the underflow from the previous flotation tank. The arrangement further comprising a tank comprising an impeller within the tank and a gas supply. The tank volume comprises at least 200 m 3 and the tank comprises an available froth surface area. The tank comprises a froth collection launder comprising a froth overflow lip, and the overflow lip has total length of the overflow lips in horizontal direction, and there is an effective height from a bottom of the tank to the lip of the froth collection launder. The tank has a diameter at the height of the impeller, where the diameter of the tank is calculated as an average at the height of an impeller. The ratio between the effective height and the diameter of the tank is less than 1,5. The third tank or subsequent tank in the series comprises a ratio between a total length of the overflow lips in horizontal direction and a square root of an available froth surface area which is 4-20. The froth overflow lip of the third tank or subsequent tank in the series comprises an edge portion with variable height in the vertical direction, and the arrangement comprises means for controlling the froth level to be vertically higher than the vertically lowest edge height of the froth overflow lip and vertically lower than the vertically highest edge height of the froth overflow lip.

[0006] An effect of the method and arrangement of the invention is a better froth handling. The froth overflow lip comprising an edge portion with variable height in the vertical direction reduces the cross sectional surface for the froth to flow over the overflow lips while the total length of the overflow lips remains the same. This allows to adjust the overflow lip load. Further, the method and arrangement of the invention allows the use of multiple internal collection launders to decrease the travel time of bubble-particle aggregates. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figure 1 shows a froth flotation tank;

Figure 2 illustrates a part view of a froth collection launder;

Figures 3a-d show an overflow lip edge;

Figure 4 shows a froth flotation tank;

Figure 5 shows a top view of a froth flotation tank;

Figure 6 shows a primary line in a froth flotation arrangement.

DETAILED DESCRIPTION OF THE INVENTION

[0008] Figures 1 and 4 show a froth flotation tank 2. The froth flotation tank 2 comprising an impeller 3 within the tank 2 and a gas supply 4. The tank 2 volume comprises at least 200 m 3 . The tank 2 volume comprises the volume of the tank 2 surrounding the slurry 8 measured from the bottom 5 of the tank 2 to height of a lip 6 of the froth collection launder 7. The tank 2 contains slurry 8 which is a mixture of solid particles in a carrier liquid, e.g. mineral particles in water.

[0009] The agitator 9 disperses air in the slurry 8, pumps slurry 8, keeps solids in the suspension and provides an environment in the tank 2 for interaction of bubbles and hydrophobic particles and their subsequent attachment and therefore separation of valuable mineral particles from the undesired gangue mineral particles. Further, the agitator may also comprise a stator 18 for providing a more stable air dispersion as shown in Figure 1. A stator 18 surrounds the impeller 3.The agitator 9 comprises an impeller 3 and a drive assembly for rotating the impeller. The drive assembly may comprise a motor 10 and a drive shaft 11.

[0010] A gas supply 4 comprises pressurized or self-aspirating gas supply. Examples of pressurized gas supply systems are pipes or tubes delivering gas to the bottom part of the tank. Gas may be supplied to the impeller 3 area also through conduits formed to the agitator 9.

[0011] The bubble— particle aggregates move up in the froth flotation tank 2 by buoyancy forming a froth layer 12 on the surface. The froth 12 comprises water, bubbles and particles. [0012] The tank 2 further comprises a froth collection launder 7. The froth collection launder 7 is an inclined drainage module which collects froth 12 from the surface. In the Figures the froth collection launders 7 are located on the top of the tank 2, and enable the transportation of froth 12 or concentrate product out of the tank 2. The out of the tank 2 transported froth 12 or concentrate product form the overflow 20 separated from the slurry 8. The froth flotation tank 2 can have one or more froth collection launders 7 which can be either internal or external, double, radial, depending on the capacity of the froth collection launder 7 necessary for the froth 12 removal. For example, in Figure 5 two different types of froth collection launders 7 are shown, a central froth collection launder 7 in the middle of the tank 2 and an internal froth collection launder 7 adjacent a periphery of the tank 2.

[0013] The froth collection launder 7 comprises a froth overflow lip 6. The ratio L tot/ J A froth between a total length of the overflow lips 6 in hori- zontal direction x and a square root of an available froth surface area is 4-20. The available froth 12 surface area A froth is the horizontal area at the top of the tank 2 which is open for the froth 12 to flow at the height of the lip 6. The available froth 12 surface area A froth is shown with a hatch pattern in Figure 5.

[0014] The froth overflow lip 6 comprises an edge portion 13 with variable height in the vertical direction y. The arrangement comprises means for controlling the froth level 14 to be vertically higher than the vertically lowest edge height hi of the lip and vertically lower than the vertically highest edge height h2 of the lip 6.

[0015] In a froth flotation method for treating mineral ore particles suspended in slurry valuable material is extracted from a slurry. In a flotation tank the slurry is separated into an underflow 19 and an overflow 20. The arrangement comprises a primary line comprising at least three flotation tanks connected in series, wherein each subsequent flotation tank is arranged to receive the underflow 19 from the previous flotation tank.

[0016] Froth flotation is a physical separation method for separating particles based on differences in the ability of air bubbles to selectively adhere to specific mineral surfaces in a mineral/water slurry 8.The slurry 8 is fed to a tank 2 through a slurry inlet 15 and the underflow 19 is discharged through a underflow outlet 16. The tank 2 comprises at least 200 m 3 volume. The tank 2 further comprises a froth collection launder 7 comprising a froth overflow lip 6.

[0017] There is an effective height h from a bottom 5 of the tank to the the impeller, where the diameter of the tank is calculated as an average at the height of an impeller h3. The ratio between the effective height h and the diameter D of the tank h/D is less than 1,5. This ratio describes the shape of the tank 2 and together with a volume of the tank 2 means a relatively shallow large tank 2.

[0018] The third tank or subsequent tank in the series comprises the ratio L tot/ J A froth between a total length of the overflow lips L tot in horizontal direction x and a square root of an available froth surface area A froth is 4-20.. Further, in the method gas bubbles are introduced to the tank 2 through a gas supply 4, the slurry 8 and the gas is mixed with the impeller 3 within the tank 2. The formed bubble— particle aggregates move up in the froth flotation tank 2 by buoyancy forming a froth 12 layer on the surface. Thus the valuable material is captured from the slurry 8 to the gas bubbles creating a froth 12. The froth 12 is caused to flow over the froth overflow lip 6 of the froth collection lauder 7 by con- trolling the froth level 14, wherein the froth overflow lip 6 comprises an edge portion 13 with variable height h in the vertical direction y. The froth level 14 is controlled to be vertically higher than the vertically lowest edge height hi of the lip 6 and vertically lower than the vertically highest edge height h2 of the lip 6. The slurry level 17 is controlled to be lower than the vertically lowest edge height hi of the lip.

[0019] The froth overflow lip 6 comprising an edge portion 13 with variable height h in the vertical direction y reduces the cross sectional surface for the froth 12 to flow over the overflow lips 6 while the total length of the overflow lips L tot remains the same. This allows to adjust the overflow lip 6 load.

[0020] An effect of the edge portion 13 with variable height h in the vertical direction y is that the amount of the froth 12 flow over the overflow lip 6 can be set to be adequate to prevent the froth 12 from drying on the overflow lip 6 surface. Thus the overflow lip 6 surface remains clean.

[0021] The risk of froth 12 drying on the overflow lip 6 surface is sig- nificant with large froth flotation tank 2 sizes. In large froth flotation tanks 2 multiple internal froth collection launders 7 are necessary for obtaining a more effective froth transportation required due to the increase of the travel time of bubble- particle aggregates which results in a high drop-back and a low froth recovery. Multiple internal froth collection launders 7 means an increase to the length of the overflows lip 6 in a froth collection tank 2.

[0022] Preferably a distance between the lengths in the overflow lips open for the froth 12 to flow over the froth overflow lip 6 in horizontal direction x at the froth level 14 is less than 50 cm. This means that the froth 12 layer adjacent to an overflow lip 6 has an open flow path into the froth launder 7 at less than 50 cm intervals. An excessive length between the open flow paths for the froth 12 creates easily dead zones where the froth 12 does not move.

[0023] It is not necessary to provide all overflow lips 6 of the froth collection launders 7 with edges portions 13 with variable heights h. For instance, 20-100% of the total length of the overflow lips L tot in horizontal direction comprises the edge portion 13 with variable height h.

[0024] The effective length of the overflow lips L e ff is calculated at the height of the froth top surface level 14.

[0025] In the arrangement the ratio between a height from a bottom 5 of the tank 2 to the lip 6 of the froth collection launder 7 and the square root of a pulp area h/ jA pulp is less than 1,5, where the pulp area A pu i P is calculated as an average from the cross sectional areas of the tank 2 at the height h3 of the impeller 3.

[0026] Figure 2 illustrates a part view of a froth collection launder 7. The froth 12 layer is above the slurry 8 in vertical direction y. The froth level 14 is vertically higher than the vertically lowest edge height hi of the froth overflow lip 6 to allow the flow of the froth 12 over the overflow lip 6. The froth level 14 is vertically lower than the vertically highest edge height h2 of the lip 6. In the method the slurry level 17 may be controlled for controlling the flow of the froth 12 over the overflow lip 6.

[0027] The slurry level 17 is vertically y lower than the vertically low- est edge height hi of the froth overflow lip 6 to prevent the flow of the slurry 8 over the overflow lip 6.

[0028] The edge portion 13 with a variable height h allows a refined controlling of the flow of the froth 12 over the overflow lips 6. As the froth level 14 rises the increase of the cross sectional surface for the froth 12 to flow over the overflow lips 6 is smaller than with a straight edge.

[0029] In large froth flotation launder 7 sizes it is important to accelerate the froth 12 flow flowing over the overflow lips 6 and thereby prevent the drying of the froth on the surface of the overflow lips 6. Therefore in a froth flotation method and the arrangement a ratio L tot/ (A froth) between a total length of the overflow lips L tot in horizontal direction x and a square root of an available froth surface area A froth is preferably between 8-16 as it provides optimal travel time of the bubble-particle aggregates but not too much overflow lip 6 length.

[0030] Figures 3a-d show several shapes of froth overflow lip edges 13. The froth overflow lip edgesl3 comprise notched lip edges 13.

[0031] In a froth flotation method and the arrangement the ratio L e ff/

L tot between effective length of the overflow lips L e ff and the total length of the overflow lips L tot in horizontal direction (x) is in range of 0,2-0,6. The effective length of the overflow lips L e ff is the sum of lengths in the overflow lips 6 open for the froth 12 to flow over the overflow lip 6 in horizontal direction x at the froth level 14.

[0032] In Figure 3a the overflow lip edge portion 13 comprises columns projecting in vertical direction y. In Figure 3b the overflow lip edge portion 13 comprises a mixture of columns and serrated edge portion. In Figure 3c the overflow lip edge portion 13 comprises a serrated edge portion 13. In Figure 3a the overflow lip edge portion 13 comprises an undulated edge portion 13.

[0033] In the Figures 3b-d the length in the overflow lip open for the froth 12 to flow over the froth overflow lip 6 in horizontal direction x increases towards the vertically highest edge height of the lip h2. Thus, the effective length L eff of the overflow lip 6 increases towards the vertically highest edge height of the lip h2.

[0034] The height variation dh in the edge portion 13 is at least 2 cm, preferably 5 cm. The froth level 14 controlling can be performed at least in a range defined by the distance between the vertically lowest edge height hi and the vertically highest edge height h2 of the froth overflow lip 6 which is at least 2 cm, preferably 5 cm. As the froth and slurry level varies a too small distance between the vertically lowest edge height hi and the vertically highest edge height h2 of the froth overflow lip 6 allows the froth to flow over the vertically highest edge height h2. An adequate distance prevents the over flow due to the level variation.

[0035] Figure 6 shows a froth flotation arrangement with three flotation tanks 2. The arrangement can comprise more than three flotation tanks 2. The flotation tank 2 separates the slurry 8 into an underflow 19 and an overflow 20. The primary line 1 comprises three flotation tanks 2 which are connected in series. Each subsequent flotation tank 2 is arranged to receive the underflow 19 from the previous flotation tank 2.

[0036] The amount of floatable mineral in the slurry 8 reduces after each subsequent tank 2. Therefore the thickness of the froth 12 layer above the slurry 8 decreases after each subsequent tank 2. Then keeping up the adequate froth 12 flow over the froth overflow lips 6 becomes more important.

[0037] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

[0038] Part list: 1 a primary line; 2 a tank; 3 an impeller; 4 a gas supply; 5 a bottom; 6 a froth overflow lip; 7 a froth collection launder; 8 a slurry; 9 agitator; 10 a motor; 11 a drive shaft; 12 a froth; 13 an edge portion; 14 a froth level; 15 a slurry inlet; 16 a underflow outlet; 17 a slurry level; 18 a stator, 19 an underflow, 20 an overflow.

[0039] A froth available froth surface area; dh a height variation; h height; hi, h2 an edge height; h3 a height of the impeller; L e ff the effective length of the overflow lips; L tot a total length of overflow lips; y vertical direction; x horizontal direction.




 
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