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Title:
A TANK MODULE AND ITS USES, A FLOTATION PLANT, A METHOD OF CHANGING OF THE TANK MODULE AND A METHOD OF CHANGING THE SELF-SUPPORTING TANK
Document Type and Number:
WIPO Patent Application WO/2016/181026
Kind Code:
A1
Abstract:
A tank module (1) is a rigid and self-supporting unit capable of being transferable and hoistable as an integral entity. The tank module (1) comprises a self-supporting framework (2) having an inner space (3). The tank module (1) also comprises a flotation tank (4) which is disposed in the inner space (3) of the self-supporting framework (2). The flotation tank (4) has a tapered upper part (5). The tank module (1) also comprises an overflow receptacle (6) which is disposed in the inner space (3) of the self-supporting framework (2) in the area of the tapered upper part (5) of the flotation tank (4). The overflow receptacle (6) collects an overflow from the flotation tank, when in use.

Inventors:
TÄHKIÖ, Pekka (Matinkatu 24 A 13, Espoo, FI-02230, FI)
VAARNA, Valtteri (Fleminginkatu 5 C 73, Helsinki, FI-00530, FI)
LUUKKONEN, Matti (Töölönkatu 24 B 29, Helsinki, FI-00260, FI)
Application Number:
FI2015/050329
Publication Date:
November 17, 2016
Filing Date:
May 13, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
OUTOTEC (FINLAND) OY (Rauhalanpuisto 9, Espoo, FI-02230, FI)
International Classes:
B03D1/02; B03D1/14; B03D1/20; E04H5/00
Domestic Patent References:
2001-05-17
Foreign References:
EP0156699A11985-10-02
US20120061298A12012-03-15
DE202008018158U12011-12-22
Other References:
None
Attorney, Agent or Firm:
PAPULA OY (P.O. Box 981, Helsinki, 00101, FI)
Download PDF:
Claims:
CLAIMS

1. A tank module, the tank module being a rigid and self-supporting unit capable of being transferable and hoistable as an integral entity, the tank module com¬ prising

a self-supporting framework, the self- supporting framework having an inner space,

- a flotation tank, the flotation tank being disposed in the inner space of the self-supporting framework, and the flotation tank has a tapered upper tank part, and

- an overflow receptacle, the overflow recep¬ tacle being disposed in the inner space of the self- supporting framework in the area of the tapered upper tank part of the flotation tank, the overflow receptacle being arranged to collect an overflow from the flotation tank, when in use. 2. The tank module according to claim 1, wherein the self-supporting framework comprises a framework bottom and framework sidewalls defining the inner space.

3. The tank module according to claim 2, wherein the flotation tank is a self-supporting structure, and the flotation tank is disposed in the inner space of the self-supporting framework without being attached to the framework bottom and framework sidewalls. 4. The flotation tank module according to any one of the claims 1 to 3, wherein the flotation tank has a rectangular cross-sectional shape.

5. The tank module according to claim 4, wherein the flotation tank comprises a tank bottom and four tank sidewalls, and at least two of the tank sidewalls of the flotation tank lean against the framework side- walls .

6. The tank module according to claim 5, wherein the tank sidewalls comprise a planar wall part, the planar wall part having a width which is at least 70% of the total width of the tank sidewall, and at least two of the planar parts of the tank sidewalls lean against the framework sidewalls.

7. The flotation tank module according to any one of the claims 1 to 3, wherein the flotation tank has a circular cross-sectional shape. 8. The tank module according to any one of the claims 1 to 7, wherein the self-supporting framework is made of metal.

9. The tank module according to any one of the claims 1 to 8, wherein the overflow receptacle is made of plastics .

10. The tank module according to any one of the claims 1 to 9, wherein the flotation tank is made of plas- tics.

11. The tank module according to any one of the claims 1 to 10, wherein the flotation tank and the overflow receptacle are welded together to form an integral en- tity.

12. The tank module according to claim 10 or 11, wherein the wall thickness of the flotation tank is 5 - 30 mm .

13. The tank module according to any one of the claims 1 to 12, wherein the flotation tank and the overflow receptacle are made of a thermoplastic polymer. 14. The tank module according to claim 13, wherein the thermoplastic polymer is polyethylene (PE) or polypro¬ pylene (PP) .

15. The tank module according to claim 13, wherein the thermoplastic polymer is polyethylene.

16. The tank module according to claim 13, wherein the thermoplastic polymer is polypropylene. 17. The tank module according to any one of the claims 1 to 16, wherein the tank module comprises one to six, preferably one to four, flotation tanks and overflow receptacles . 18. The tank module according to claim 17, wherein the flotation tanks are arranged in a row and in fluid communication with each other inside the self- supporting framework. 19. The tank module according to any one of the claims 1 to 18, wherein the volume of the flotation tank is 0.5 - 20 m3, preferably 1 - 15 m3, most preferably 1 - 8 m3.

20. The tank module according to any one of the claims 1 to 19, wherein the flotation tank has a lower tank part below the tapered upper tank part, and the ta¬ pered upper tank part is narrower than the lower tank part .

21. The flotation tank module according to any one of the claims 1 to 20, wherein the flotation tank has a mouth at the upper end of the upper tank part. 22. The flotation tank module according to claim 21, wherein the overflow receptacle surrounds circumferen- tially the mouth of the flotation tank.

23. The flotation tank module according to claim 22, wherein an overflow lip is at the periphery of the mouth .

24. The flotation tank module according to claim 23, wherein the overflow lip comprises a separate lip mem- ber, and the lip member is connectable to the upper part of the flotation tank at a desired height posi¬ tion to obtain a suitable overflow height for the overflow . 25. The flotation tank module according to any one of the claims 1 to 24, wherein the overflow receptacle comprises a chute for collecting the overflow, when in use, and at least one outlet at the lower part of the overflow receptacle, and the chute is inclined towards the outlet.

26. The flotation tank module according to claim 25, wherein an angle (a) of inclination of the chute is 5° - 30°, more preferably 8° - 20°, most preferably 10° - 15°.

27. The flotation tank module according to any one of the claims 20 to 26, wherein the cross-sectional shape of the lower tank part is rectangular when the volume of the flotation tank is greater than 8 m3.

28. The flotation tank module according to any one of the claims 20 to 27, wherein the cross-sectional shape of the lower tank part being rectangular the mouth is rectangular or circular.

29. The flotation tank module according to any one of the claims 20 to 28, wherein the cross-sectional shape of the lower tank part is circular when the volume of the flotation tank is at most 8 m3.

30. The flotation tank module according to any one of the claims 20 to 29, wherein the cross-sectional shape of the lower tank part being circular the mouth is circular .

31. The tank module according to any one of the claims 1 to 30, wherein the tank module comprises an overflow channel for receiving and discharging the overflow from the overflow receptacle.

32. The tank module according to claim 31, wherein the overflow channel is disposed in the inner space of the self-supporting framework of the tank module. 33. The tank module according to claim 31, wherein the overflow channel is disposed outside the tank module.

34. The tank module according to any one of the claims 1 to 33, wherein self-supporting framework has a shape of a rectangular parallelepiped box and comprises a floor, two side walls, and two end walls defining the inner space, and is designed to withstand hydrostatic pressure exerted by a liquid filled in the flotation tank, when in use.

35. The tank module according to claim 34, wherein the floor, the side walls and the end walls each are sand¬ wich-structured elements. 36. The tank module according to any one of the claims 1 to 35, wherein flotation is froth flotation.

37. A flotation plant comprising a tank module according to any one of the claims 1 to 36.

38. Use of the tank module according to any one of the claims 1 to 36 for separating material by flotation based on differences of buoyancy properties of sub¬ stances .

39. Use of the tank module according to any one of the claims 1 to 36 for separating solid material by froth flotation based on differences of hydrophilic proper¬ ties of substances.

40. Use of the tank module according to any one of the claims 1 to 36 for concentrating ore by froth flota¬ tion. 41. Use of the tank module according to any one of the claims 1 to 36 for flotation of substances containing abrasive material.

42. Use of the tank module according to any one of the claims 1 to 36 for froth flotation of ore containing pyrite, silica, chromite.

43. A method of changing of the tank module according to any one of the claims 1 to 36, in which method the tank module subject of maintenance is replaced by an¬ other tank module.

44. A method of changing the flotation tank in the tank module according to any one of the claims 1 to 36, the method comprising steps of

- removing the flotation tank out from inside the framework, and

- installing another flotation tank into the framework .

45. The method according to claim 44, wherein in the installing step the flotation tank and the overflow receptacle attached to the flotation tank are in¬ stalled as one integral entity.

46. The method according to claim 44 or 45, wherein the steps of removing and installing include a lifting step .

Description:
A TANK MODULE AND ITS USES, A FLOTATION PLANT, A METHOD OF CHANGING OF THE TANK MODULE AND A METHOD OF CHANGING THE SELF-SUPPORTING TANK FIELD OF THE INVENTION

The present invention relates to a tank module. Fur ¬ ther, the invention relates to uses of the tank mod ¬ ule. Further, the invention relates to a method of changing of the tank module. Further, the invention relates to a method of replacing the self-supporting tank in a tank module.

SUMMARY OF THE INVENTION

According to an aspect, the present invention provides a tank module. The tank module is a rigid and self- supporting unit capable of being transferable and hoistable as an integral entity. The tank module com ¬ prises a self-supporting framework. The self- supporting framework has an inner space. Further, the tank module comprises a flotation tank. The froth flo ¬ tation tank is disposed in the inner space of the self-supporting framework. The flotation tank has a tapered upper tank part. Further, the tank module comprises an overflow receptacle. The overflow receptacle is disposed in the inner space of the self-supporting framework in the area of the tapered upper part of the froth flotation tank. The overflow receptacle is arranged to collect an overflow from the flotation tank, when in use.

The technical effect of the invention is that the maintenance of the tank module is easy since the over ¬ flow receptacle is inside the tank module together with the flotation tank(s). During transportation, hoisting and use the froth flotation tanks and the overflow receptacle are well protected inside the self-supporting framework which acts as a delivery package and thereby eliminates need for separate transportation packages for the tanks and overflow receptacles .

In this application the following definitions apply regarding flotation. Flotation involves phenomena related to the relative buoyancy of objects. The term flotation includes all flotation techniques. Flotation can be for example froth flotation, dissolved air flo ¬ tation (DAF) or induced gas flotation. Froth flotation is a process for separating hydrophobic materials from hydrophilic materials by adding gas, for example air, to process. Froth flotation could be made based on natural hydrophilic/hydrophobic difference or based on hydrophilic/hydrophobic differences made by addition of a surfactant or collector chemical. Gas can be add ¬ ed to the feedstock subject of flotation (slurry or pulp) by a number of different ways. In one embodiment gas can be added to the stream of feedstock subject to flotation before it is fed to the flotation tank. In one embodiment gas can be added to feedstock subject to flotation in the flotation tank. In one embodiment gas adding equipment can include gas dispersing equip- ment at the bottom of the tank. In one embodiment gas adding equipment can include a feedstock (slurry or pulp) jet for jetting the feedstock to air. In one embodiment gas adding equipment includes a rotor inside the tank. In one embodiment gas can be added under the rotor. In one embodiment gas is added by a pipe ending under rotor. The pipe can be inside the flota ¬ tion tank. The pipe can go through the bottom of the flotation tank. In one embodiment the rotor takes gas from the surface of sludge by vortex. In one embodi- ment is added by axis of the rotor. In one embodiment mixing equipment is arranged for mixing the slur ¬ ry/pulp. Mixing equipment could be for example a pump or a rotor. When the mixing is made by pump, the feedstock subject of flotation could be taken from one part of flotation tank and put back to another part of flotation tank. When mixing is made by the rotor, the rotor is inside the flotation tank. In one embodiment mixing equipment can include a rotor inside the flota ¬ tion tank. In one embodiment mixing equipment can include a stator inside the flotation tank. The stator is for boosting mixing and to diffuse air to the feed- stock (slurry or pulp) subject to flotation.

In one embodiment of the tank module, the self- supporting framework comprises a framework bottom and framework sidewalls defining the inner space.

In one embodiment of the tank module, the flotation tank is a self-supporting structure. The flotation tank is placed in the inner space of the self- supporting framework without being attached to the framework bottom and framework sidewalls. The flota ¬ tion tank is a part that wears in use due to abrasive conditions inside the tank. The tank being a self- supporting unit has an integral monocoque structure that is able to hold its form while it is used, trans- ferred and hoisted. The technical effect is that the self-supporting flotation tank can easily be installed into the self-supporting framework and also can easily be removed therefrom for maintenance or replacement since it the tank is not attached to the framework.

In one embodiment of the tank module, the flotation tank has a rectangular cross-sectional shape.

In one embodiment of the tank module, the flotation tank comprises a tank bottom and four tank sidewalls. At least two of the tank sidewalls of the froth flota ¬ tion tank lean against the framework sidewalls. In this embodiment the cross-sectional shape of the self- supporting flotation tank is rectangular or quadrangular whereby the tank can be designed to be a light ¬ weight structure since the framework may support the tank from outside. The framework can be designed to receive the majority of the forces exerted by the hy ¬ drostatic pressure which is caused by the liquid filled inside the tank. In one embodiment of the tank module, the tank side- walls comprise a planar wall part, the planar wall part having a width which is at least 70% of the total width of the tank sidewall, and at least two of the planar parts of the tank sidewalls lean against the framework sidewalls.

In one embodiment of the tank module, the flotation tank has a circular cross-sectional shape. In one embodiment of the tank module, the self- supporting framework is made of metal. The technical effect is that the framework is rigid, stiff and firm.

In one embodiment of the tank module, the overflow re- ceptacle is made of plastics. The technical effect is that the structure is endurable and light-weight whereby maintenance is seldom needed. However, when maintenance is needed light-weight elements are easy to handle.

In one embodiment of the tank module, the flotation tank is made of plastics. The technical effect is that the structure is endurable and light-weight whereby maintenance is seldom needed. However, when mainte- nance is needed the light-weight elements are easy to handle . 1. In one embodiment of the tank module, the flotation tank and the overflow receptacle are welded together to form an integral entity. The technical effect is that the entity has a good structural stiffness. Maintenance is easy because the tank and the recepta ¬ cle can be handled and installed as one entity.

In one embodiment of the tank module, the wall thick ¬ ness of the flotation tank is 5 - 30 mm. The technical effect of the wall thickness within this range is that the tank will not be too heavy so that it can be changed easily but yet it is stiff enough so that it can be easily installed. The tapering of the tank at its upper part makes it stiff so that the tank is stiff despite the relatively thin wall.

In one embodiment of the tank module, the flotation tank and the overflow receptacle are made of a thermo ¬ plastic polymer. The technical effect is wear re- sistance whereby the need for maintenance and the time needed for maintenance are minimized.

In one embodiment of the tank module, the thermo ¬ plastic polymer is polyethylene (PE) or polypropylene (PP) . The technical effect of these materials is that they are very resistant to abrasive wear. Especially, when the tank is in use it may accommodate a rotating rotor for gas adding and/or mixing, the mixing of the feedstock subject of flotation by a rotor causes the feedstock (which can be very abrasive) to flow against inner surface of the tank wall and thereby causes se ¬ verely abrasive wear conditions.

In one embodiment of the tank module, the thermo- plastic polymer is polyethylene (PE) . In one embodiment of the tank module, the thermo ¬ plastic polymer is polypropylene (PP) .

In one embodiment of the tank module, the tank module comprises one to six, preferably one to four, flota ¬ tion tanks and overflow receptacles.

In one embodiment of the tank module, the flotation tanks are arranged in a row and in fluid communication with each other inside the self-supporting framework.

In one embodiment of the tank module, the volume of the flotation tank is 0.5 - 20 m 3 , preferably 1 - 15 m 3 , most preferably 1 - 8 m 3 . The technical effect is that the tanks can be changed easily as they are not too big and heavy. The tanks are still big enough so that a significant volume of capacity can be subjected to maintenance by changing a few tanks. The mainte ¬ nance operations can be easily made for tanks which are not too big and heavy.

In one embodiment of the tank module, the flotation tank has a lower tank part below the tapered upper tank part, and the tapered upper tank part is narrower than the lower tank part.

In one embodiment of the tank module, the flotation tank has a mouth at the upper end of the upper tank part .

In one embodiment of the tank module, an overflow lip is at the periphery of the mouth.

In one embodiment of the tank module, the overflow lip comprises a separate lip member, and the lip member is connectable to the upper part of the flotation tank at a desired height position to obtain a suitable over ¬ flow height for the overflow. The technical effect is that the overflow heights of identical tanks can be made different with an adjustable lip member.

In one embodiment of the tank module, the overflow re ¬ ceptacle comprises a chute for collecting the over ¬ flow, when in use, and at least one outlet at the low- er part of the overflow receptacle, and the chute is inclined towards the outlet. The technical effect is that the flow of overflow by gravity is ensured by the inclination . In one embodiment of the tank module, an angle (a) of inclination of the chute is 5° - 30°, more preferably 8° - 20°, most preferably 10° - 15°. The technical ef ¬ fect of the angle of inclination especially for the angles 8° - 20°, most preferably 10° - 15°, is that the chute does not become blocked and does not wear excessively .

In one embodiment of the tank module, the cross- sectional shape of the lower tank part is rectangular when the volume of the flotation tank is greater than 8 m 3 . The technical effect is that such great tanks can be supported by sidewalls of the self-supporting framework in the inner space of which the tanks are installed in a tank module. The wall of the tank can be supported against the sidewall of the framework so that the framework bears loads exerted by the hydro ¬ static pressure of the liquid filled inside the tank.

In one embodiment of the tank module, the cross- sectional shape of the lower tank part being rectangu ¬ lar the mouth is rectangular or circular. The tech- nical effect of the circular mouth is that it stiffens the structure of the tank.

In one embodiment of the tank module, the cross- sectional shape of the lower tank part is circular when the volume of the flotation tank is at most 8 m 3 . The technical effect is that the round form gives the required stiffness for the tank up to this size class. In one embodiment of the tank module, the cross- sectional shape of the lower tank part being circular the mouth is circular. The technical effect of the circular mouth is that the entity formed by the tank and the overflow receptacle together is stiff to ena- ble easy handling, lifting and maintenance.

In one embodiment of the tank module, the tank module comprises an overflow channel for receiving and dis ¬ charging the overflow from the overflow receptacle.

In one embodiment of the tank module, the overflow channel is disposed in the inner space of the self- supporting framework of the tank module. The technical effect of this embodiment is that the overflow channel is well protected inside the self-supporting frame ¬ work .

In one embodiment of the tank module, the overflow channel is disposed outside the tank module. The tech- nical effect is that maintenance of the tanks and/or the tank module is easy since only the connection be ¬ tween the overflow receptacle and the overflow channel needs to be disconnected. During changing of the tanks there is no need to move the overflow channel.

In one embodiment of the tank module, self-supporting framework has a shape of a rectangular parallelepiped box and comprises a floor, two side walls, and two end walls defining the inner space, and is designed to withstand hydrostatic pressure exerted by a liquid filled in the froth flotation tank, when in use.

In one embodiment of the tank module, the floor, the side walls and the end walls each are sandwich- structured elements. In one embodiment of the tank module, flotation is froth flotation.

According to a second aspect of the invention, the in ¬ vention provides a flotation plant comprising a tank module according to the first aspect of the invention.

According to a third aspect, the present invention provides use of the tank module according to the first aspect of the invention for separating material by flotation based on differences of buoyancy properties of substances. For example there is buoyancy differ ¬ ence when organic material is separated from aqueous material . According to a fourth aspect, the present invention provides use of the tank module according to the first aspect of the invention for separating solid material by froth flotation based on differences of hydrophilic properties of substances. Solid materials separated by froth flotation could be oil sands, carbon, coal, talk, industrial minerals and mineral particles. The minerals may include industrial minerals and ore. Froth flotation to solid material could be made based on natural hydrophilic/hydrophobic difference or based on hydrophilic/hydrophobic differences made by addi ¬ tion of a surfactant or collector chemical or other chemical . According to a fifth aspect, the present invention provides use of the tank module according to the first aspect of the invention for concentrating ore by froth flotation. An ore is a type of rock that contains suf ¬ ficient minerals with important elements including metals that can be economically extracted from the rock. Metal ores are generally oxides, sulfides, sili ¬ cates, or metals such as native copper or gold. Froth flotation of ore could be made based on natural hydro- philic/hydrophobic difference or based on hydro- philic/hydrophobic differences made by addition of a surfactant or collector chemical or other chemical. According to a sixth aspect, the present invention provides use of the tank module according to the first aspect of the invention for flotation of substances containing abrasive material. The abrasive mineral may be, for example, pyrite, silica, chromite. The drive module being hoistable and transferable as one unit to gain access to the tanks enables that the tanks can easily be maintained or replaced when they are outworn and are at the end of their life. This is important especially with the use in connection with abrasive material. Use of the flotation plant which is easy to maintenance is effective when flotation is made to abrasive material.

According to a seventh aspect, the present invention provides use of the tank module according to the first aspect of the invention for froth flotation of ore containing pyrite, silica, chromite. Use of the tank module which is easy to maintenance and has preferably tanks made from PE or PP is effective when flotation is made to ore containing pyrite, silica, chromite. PE and PP are durable against the ore containing pyrite, silica, chromite. According to a seventh aspect, the present invention provides a method of changing of the tank module ac ¬ cording to the first aspect of the invention, in which method the tank module subject of maintenance is re ¬ placed by another tank module.

According to an eighth aspect, the present invention provides a method of changing the flotation tank in the tank module according to the first aspect of the invention, wherein the method comprises steps of re ¬ moving the flotation tank out from inside the framework, and installing another flotation tank into the framework .

In one embodiment of the method, in the installing step the flotation tank and the overflow receptacle attached to the flotation tank are installed as one integral entity.

In one embodiment of the method, the steps of removing and installing include a lifting step.

The embodiments of the invention described hereinbe- fore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment of the invention. An apparatus, a method, a composition or a use, to which the invention is related, may comprise at least one of the embodiments of the invention described hereinbefore.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to pro ¬ vide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the de- scription help to explain the principles of the inven ¬ tion. In the drawings:

Figure 1 is cross-section I-I from Figure 3, and shows an elevation view of a tank module according to a first embodiment of the invention,

Figure 2 is a cross-section II-II from Figure 1, Figure 3 is a cross-section III-III from Figure 1,

Figure 4 shows an axonometric view of an assembly formed of a froth flotation tank and an overflow receptacle attached thereto,

Figure 5 shows an axonometric view of the froth flota ¬ tion tank of Figure 4,

Figure 6 shows a cross-section VI-VI from Figure 4,

Figure 7 is a perspective view of a second embodiment of the tank module wherein the overflow channel is in ¬ side the self-supporting framework of the tank module, Figure 8 is an elevation view of a tank module accord ¬ ing to a third embodiment of the invention,

Figure 9 is the tank module of Figure 8 seen in the direction of IX-IX from Figure 8,

Figure 10 is an axonometric view of the self- supporting framework according to a third embodiment of the tank module of the present invention, Figure 11 shows as an axonometric view the floor ele ¬ ment, two side wall elements, and two end wall ele- ments of the self-supporting framework of Figure 10, separately,

Figure 12 is a cross-section from Figure 11,

Figures 13 to 15 show further examples of an assembly formed of a flotation tank and an overflow receptacle attached thereto in different forms, and Figures 16 to 18 show examples of the tank modules having tanks with a circular cross-sectional shape.

DETAILED DESCRIPTION OF THE INVENTION

Although flotation is disclosed in the following exam- pies by reference to froth flotation, it should be noted that the principles according to the invention can be implemented regardless of the specific type of the flotation, i.e. the flotation technique can be any of the known per se flotation techniques, such as froth flotation, dissolved air flotation or induced gas flotation.

Figures 1 - 3 show a tank module 1 which is intended to be utilized for implementing a froth flotation pro- cess, when in use. The tank module 1 is a rigid and self-supporting unit which can be transferred and hoisted as an integral entity.

The tank module 1 comprises a self-supporting frame- work 2, preferably made of metal. The self-supporting framework 2 has an inner space 3.

In the example shown in Figures 1 and 2, four froth flotation tanks 4 for receiving the liquid are ar- ranged in the inner space 3 of the self-supporting framework 2. The flotation tanks 4 are arranged in a row and in fluid communication with each other so that an underflow can flow through the tanks.

As can be seen in Figures 3-6, the froth flotation tanks 4 each have a tapered upper part 5. An overflow receptacle 6 is disposed in the inner space 3 of the self-supporting framework 2 in the area of the tapered upper part 5 of the froth flotation tank 4. When in use, during froth flotation the overflow receptacle 6 is arranged to collect an overflow overflowing from the froth flotation tank 4.

The self-supporting framework 2 comprises a framework bottom 7 and framework sidewalls 8, 9 defining the in- ner space 3. Each froth flotation tank 4 is a self- supporting structure. The froth flotation tanks 4 are placed in the inner space 3 of the self-supporting framework 2 without being attached to the framework bottom 7 and framework sidewalls 8, 9.

Each froth flotation tank 4 comprises a tank bottom 10 and four tank sidewalls 11. As can be seen in Figure 2, at least two of the tank sidewalls 11 of the froth flotation tank 4 lean against the framework sidewalls 8, 9. At the ends of the tank module 1 the three tank sidewalls 11 of the tank 4 lean against the framework sidewalls 8, 9, and the fourth tank sidewall 11 leans against the tank sidewall 11 of the neighboring self- supporting tank 4. The two froth flotation tanks 4 re- siding in the middle of the row each have two tank sidewalls 111 leaning against the opposite framework sidewalls 8 while the other two of the tank sidewalls 11 lean against tank sidewalls of the neighboring tanks 4.

As can be seen in Figures 2, 4 and 5 the self- supporting tank 4 has a generally rectangular cross- sectional shape having four tank sidewalls 11. As best seen in Figure 2, in the shown embodiment, each of the tank sidewalls 11 comprise a planar wall part 12. The planar wall part 12 has a width w which is at least 70% of the total width W of the tank sidewall. At least two of the planar parts 12 of the tank sidewalls 11 lean against the framework sidewalls 8, 9.

Although in the embodiment shown in Figures 1 and 2 there are four froth flotation tanks 4 and overflow receptacles 6 inside the framework 2, in other (not shown) embodiments the number of the froth flotation tanks 4 and overflow receptacles inside the framework can be less than four, i.e. one, two or three. Prefer- ably the number of the froth flotation tanks 4 and overflow receptacles 6 is two to four. The volume of the froth flotation tank 4 is 0.5 - 20 m 3 , preferably 1 - 15 m 3 , most preferably 1 - 8 m 3 Preferably, the froth flotation tank 4 is made of plastics. The wall thickness of the froth flotation tank 4 is preferably 5 - 30 mm. The froth flotation tank 4 and the overflow receptacle 6 are preferably made of a thermoplastic polymer, such as polyethylene PE or polypropylene PP. Preferably the overflow recep ¬ tacle 6 is also made of plastics, and of such plastics material which can be welded to the plastics material of the froth flotation tank 4 to enable that the froth flotation tank 4 and the overflow receptacle 6 can be welded together to form an integral entity.

Reference is now made to Figures 5 and 6. The froth flotation tank 4 and the overflow flow receptacle 6 are connected to each other by welding. The froth flo- tation tank 4 has a lower tank part 14 below the tapered upper tank part 5. The tapered upper tank part 5 is narrower than the lower tank part 13. The upper end of the froth flotation tank 4 forms an overflow lip 15. The overflow receptacle 6 is in a form of a pe ¬ ripheral chute 26 which surrounds the overflow lip 15 so that the overflow receptacle 6 can receive the overflow (froth) which overflows over the overflow lip 15 from the froth flotation tank 4. The overflow lip 15 comprises a separate lip member 25. The lip member 25 is connected to the upper part of the self- supporting tank 4 at a desired height position to ob- tain a suitable overflow height for the overflow.

In Figure 4 can be seen that outlets 24 are disposed at the lower part of the overflow receptacle 6. The chute 26 is inclined towards the outlets 24. The bot- torn of the chute 26 is straight. An angle a of incli ¬ nation of the chute 23 is 5° - 30°, more preferably 8° - 20°, most preferably 10° - 15°.

Figure 7 shows an embodiment of the tank module 1. The tank module 1 is a rigid and self-supporting unit which can be transferred and hoisted as an integral entity. The tank module 1 comprises a self-supporting framework 2, preferably made of metal. The self- supporting framework 2 has an inner space 3. Four froth flotation tanks 4 and overflow receptacles 6 are arranged in the inner space 3 of the self-supporting framework 2. The tank module 1 comprises also overflow channels 15 for receiving and discharging the overflow from the overflow receptacle 6. The overflow channels 15 are disposed in the inner space 3 of the self- supporting framework 2 of the tank module 1.

Figure 8 shows still another embodiment of the tank module 1. The tank module § may, for example, be as disclosed above with reference to Figure 1, but with an addition that the overflow channel 15 is disposed outside the tank module 1. The overflow channel 15 may be connected to the self-supporting framework of the tank module 1. In use, this enables easy access to the overflow channel 15 for maintenance. Referring to Figure 10, the self-supporting framework 2 has a shape of a rectangular parallelepiped box and comprises a floor 7, two side walls 8, and two end walls 9 defining the inner space 3. It may be designed to withstand hydrostatic pressure exerted by a liquid filled in the froth flotation tanks 4 when used with large tanks having a rectangular cross-section. The floor 7, the side walls 8 and the end walls 9 each may be, for example, sandwich-structured elements. In the embodiment shown in Figures 10 - 12 the floor 7, the side walls 8 and the end walls 9 may each com ¬ prise a rectangular frame 16, 17, 18 made of metal beams, the frame having a first side 19 and a second side 20, and a metal truss core sandwich structure. Referring to Figure 12, the truss core sandwich struc ¬ ture comprises a first sheet metal plate 21 having a periphery which is laser welded to the first side 19 of the frame 16, 17, 18, and a second sheet metal plate 22 having a periphery which is laser welded to the second side 20 of the frame, and a truss core TC is sandwiched between the first and second sheet metal plates. The truss core comprises cross profiles 23 made of sheet metal, said cross profiles 23 are laser welded to the first and second sheet metal plates. The truss core TC may comprise a plurality of V-shaped cross profiles 23. The V-shaped cross profiles 20 are arranged in parallel and spaced apart relationship to each other along the length of the frame 16; 17; 18 and transversally in relation to a longitudinal direc- tion of the frame. Figures 13 to 15 show three examples of possible shapes of the tank 4 and the overflow receptacle 6. In Figures 13 and 14 the lower tank part 14 of the tank 4 has a rectangular cross-sectional shape which is suit- able for tanks 4 having a volume greater than 8 m 3 . In Figure 13 the mouth 24 is circular and in Figure 8 the mouth 24 is rectangular.

Figure 15 shows an example wherein the lower tank part 14 of the tank 4 is circular in cross-section, i.e cylindrical, and also the mouth 24 and the overflow re ¬ ceptacle 6 are circular.

Figures 16 to 18 show further examples of the flota- tion tank modules 10 having integral assemblies of circular tanks 4 and overflow receptacles 6 as that shown in Figure 15.

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 in ¬ vention and its embodiments are thus not limited to the examples described above, instead they may vary within the scope of the claims.