FIELD OF THE INVENTION

The present invention relates to a flotation plant. Further, the invention relates to uses of the flota ^¬ tion plant. Further, the invention relates to a drive module. Further, the invention relates to uses of the drive module. Further, the invention relates methods of maintenance of a flotation plant.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides a flotation plant. The flotation plant com- prises at least one flotation tank. The flotation tank, when in use, accommodates a mixing and/or bubble forming equipment including a rotor connected to a ro- tatable drive shaft. The flotation plant comprises a drive module. The drive module is disposed on top of the flotation tank and includes at least two drive units for the rotation of the drive shafts. The drive module is a rigid and self-supporting unit capable of being transferable and hoistable as an integral enti ^¬ ty.

The technical effect of the invention is that the drive module being a self-supporting unit can be transferred and hoisted as an integral entity. During transportation and hoisting at the time of maintenance and also when other modules are hoisted the drive units and all the other necessary equipment furnished into the drive module are well protected inside the self-supporting framework which acts as a delivery package and thereby eliminates need for separate transportation packages for the drive units and other furnishings. At the site of use the drive module may be placed on top of the flotation tanks. When the tanks need maintenance, the drive module together with its drive units can be lifted off and transferred aside to enable access to the flotation tanks. Also for the maintenance of the equipment furnished inside the drive module, if needed, the drive module can be transferred as one entity to a site of maintenance.

In this application the following definitions apply regarding flotation. Flotation involves phenomena re- lated to the relative buoyancy of objects. The term flotation includes all flotation techniques. Flotation can be for example froth flotation, dissolved air flotation (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 of flotation before it is fed to the flotation tank. In one embodiment gas can be added to feedstock subject of 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 em- bodiment 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 gas is added by axis of the rotor. In one embodi- ment 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 in- elude a stator inside the flotation tank. The stator is for boosting mixing and to diffuse air to the feed ^¬ stock (slurry or pulp) subject of flotation.

In one embodiment of the flotation plant, the flota- tion plant comprises a tank module. The tank module includes the flotation tank. The tank module is a rig ^¬ id and self-supporting unit capable of being transferable and hoistable as an integral entity. The drive module is removably stacked on top of the tank module. The tank module being a self-supporting unit can be transferred and hoisted as an integral entity. The tank module can be assembled and furnished at the site of manufacture, e.g. in an engineering workshop, and then transported to the site of installation as one integral entity. During transportation, hoisting and use the flotation tank(s) is/are well protected inside the self-supporting framework of the tank module which acts as a delivery package and thereby eliminates need for separate transportation packages for the tank(s) and overflow receptacles.

In one embodiment of the flotation plant, the drive module comprises a first self-supporting framework having a shape of a rectangular parallelepiped. The first self-supporting framework is stackable with a compatible another self-supporting framework of another module. The first self-supporting framework has an inner space. The drive units are disposed in the inner space of the first self-supporting framework.

In one embodiment of the flotation plant, the tank module comprises a second self-supporting framework having a shape of a rectangular parallelepiped. The second self-supporting framework is stackable with a compatible another self-supporting framework of another module. The second self-supporting framework has an inner space. The flotation tank is disposed in the in ^¬ ner space of the second self-supporting framework.

In one embodiment of the flotation plant, the second self-supporting framework of the tank module comprises a framework bottom and framework sidewalls. The flota ^¬ tion tank is a self-supporting structure. The self- supporting flotation tank is placed inside the second self-supporting framework without being attached to the framework bottom and the framework sidewalls. The flotation tank is a part that wears in use due to abrasive conditions inside the tank. The flotation tank being a self-supporting and integral monocoque structure that is able to hold its form while it is used can be transferred and hoisted as an integral unit. The technical effect is that the self-supporting tank can easily be installed into the second self- supporting framework of the tank module and also can easily be removed therefrom for maintenance or re ^¬ placement since it is not attached to the bottom or sidewalls of the framework after the drive module has been first hoisted and transferred aside to permit ac ^¬ cess to the tank module. The self-supporting tank may have any suitable cross-sectional shape, e.g. circu ^¬ lar, rectangular, quadrangular.

In one embodiment of the flotation plant, the tank module comprises 1 to 6 flotation tanks, preferably 1 to 4 flotation tanks, arranged in a row and in fluid communication with each other in the inner space of the second self-supporting framework. In one embodiment of the flotation plant, the drive module comprises 2 to 6 drive units, preferably 2 to 4 drive units .

In one embodiment of the flotation plant, the drive module comprises corners and the drive module is de ^¬ signed to be supported by the corners.

In one embodiment of the flotation plant, the tank module comprises corners and the tank module is de- signed to be supported by the corners.

In one embodiment of the flotation plant, the widths of the drive module and the tank module are different from each other at most 20%.

In one embodiment of the flotation plant, the drive module and the tank module have same width.

In one embodiment of the flotation plant, the flota- tion plant comprises an overflow receptacle for col ^¬ lecting an overflow of containing concentrate, the overflow overflowing from the flotation tank. The overflow receptacle is disposed at a level of the tank module .

In one embodiment of the flotation plant, the overflow receptacle is connected to the tank module to be transferable and hoistable as an integral unit with the tank module.

In one embodiment of the flotation plant, the overflow receptacle is disposed inside the tank module. In one embodiment of the flotation plant, the overflow receptacle is disposed outside the tank module. In one embodiment of the flotation plant, the flota ^¬ tion plant comprises an overflow channel for receiving the overflow from the overflow receptacle and for conducting away the overflow from the overflow receptacle .

In one embodiment of the flotation plant, the overflow channel is disposed outside the tank module.

In one embodiment of the flotation plant, the overflow channel is disposed at a level of the tank module and connected thereto to be transferable and hoistable as an integral unit with the tank module.

In one embodiment of the flotation plant, the drive module comprises a gas feed pipeline for supplying flotation gas.

In one embodiment of the flotation plant, the gas feed pipeline is in fluid communication with the rotor shaft. The rotor shaft is hollow for conducting the flotation gas supplied by the gas feed pipeline.

In one embodiment of the flotation plant, the drive module comprises a flow meter. The flow meter is connected to the gas feed pipeline for measuring the rate of flow of the flotation gas.

In one embodiment of the flotation plant, the drive module comprises a flow rate controller. The flow rate controller is connected to the gas feed pipeline for controlling the rate of flow of the flotation gas. In one embodiment of the flotation plant, the drive module comprises measurement equipment for the meas ^¬ urement of liquid level in the flotation tank.

In one embodiment of the flotation plant, the drive module comprises a maintenance platform.

In one embodiment of the flotation plant, the drive module comprises a camera for detecting bubble size of the overflow.

In one embodiment of the flotation plant, the drive module comprises cabling for supplying electric power for the flow meter, for the flow rate controller, for the measurement equipment and/or for the camera.

In one embodiment of the flotation plant, the flota ^¬ tion plant includes a feed box for feeding the feed ^¬ stock subject of flotation to the flotation tank. In one embodiment of the flotation plant, the flota ^¬ tion plant includes a discharge box for receiving and discharging underflow from the flotation tank.

In one embodiment of the flotation plant, the feed box and/or the discharge box is attached to the ends of the tank module and disposed outside the tank module.

In one embodiment of the flotation plant, the flota ^¬ tion plant has at most three storeys comprising a first storey, the first storey being the lowest storey of the plant, and the first storey having a height above ground; a second storey, the second storey in ^¬ cluding the tank module and being above the first sto ^¬ rey and defined by the height of the tank module, and a third storey, the third storey including the drive module and being above the second storey and defined by the height of the drive module. In one embodiment of the flotation plant, the flota ^¬ tion plant comprises a foundation disposed at the first storey for supporting the stack of the tank mod ^¬ ule and the drive module. In one embodiment of the flotation plant, the founda ^¬ tion is formed of a plurality of pillars.

In one embodiment of the flotation plant, the founda ^¬ tion is formed of a self-supporting foundation module placed at the first storey. The foundation module is a rigid and self-supporting unit capable of being trans ^¬ ferable and hoistable as an integral entity.

In one embodiment of the flotation plant, the flota- tion plant comprises a first pump for pumping the overflow .

In one embodiment of the flotation plant, the flota ^¬ tion plant comprises a second pump for pumping the un- derflow.

In one embodiment of the flotation plant, the first pump and/or the second pump is disposed at the first storey .

In one embodiment of the flotation plant, flotation is froth flotation.

In one embodiment of the flotation plant, the flota- tion plant comprises gas adding equipment for adding gas to the feedstock subject of flotation. In one embodiment of the flotation plant, the flota ^¬ tion plant comprises gas adding equipment to the stream of the feedstock subject of flotation before entering the flotation tank.

In one embodiment of the flotation plant, the flota ^¬ tion plant comprises gas adding equipment for adding gas to the feedstock subject of flotation in the flo ^¬ tation tank.

In one embodiment of the flotation plant, the gas add ^¬ ing equipment includes a rotor inside the flotation tank . In one embodiment of the flotation plant, the gas add ^¬ ing equipment includes a hollow rotatable drive shaft, and the rotor is connected to the drive shaft.

In one embodiment of the flotation plant, the feed- stock subject of flotation is slurry or pulp.

In one embodiment of the flotation plant, the flota ^¬ tion plant comprises mixing equipment. In one embodiment of the flotation plant, the mixing equipment includes a rotor inside the flotation tank.

In one embodiment of the flotation plant, the mixing equipment includes a stator inside the flotation tank.

In one embodiment of the flotation plant, the flota ^¬ tion tank having a bottom is disposed inside a frame ^¬ work, and the stator is connected to the framework through the bottom.

According to a second aspect of the invention, the in ^¬ vention provides use of the flotation plant according to the first aspect for separating material by flota ^¬ tion based on differences of buoyancy properties of substances. For example there is buoyancy difference when organic material is separated from aqueous mate- rial.

According to a third aspect of the invention, the in ^¬ vention provides use of the flotation plant according to the first aspect 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 fourth aspect of the invention, the invention provides use of the flotation plant according to the first aspect 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 fifth aspect of the invention, the in- vention provides use of the flotation plant according to the first aspect for flotation of substances con ^¬ taining 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 sixth aspect of the invention, the invention provides use of the flotation plant according to the first aspect for froth flotation of ore con ^¬ taining pyrite, silica, chromite. Use of the flotation plant 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 of the invention, the present invention provides a drive module for a flota ^¬ tion plant. The flotation plant includes a flotation tank and a mixing and/or bubble forming equipment in- side the tank. The bubble forming and mixing equipment including a rotor connected to a rotatable drive shaft. The drive module is a rigid self-supporting unit capable of being transferable and hoistable as an integral entity. The drive module comprises a self- supporting framework having a shape of a rectangular parallelepiped. The self-supporting framework defines an inner space inside the self-supporting framework. The drive module comprises at least two drive units. The drive units are connectable to the drive shaft of the mixing and/or bubble forming equipment for the ro ^¬ tation of the drive shaft. The drive units are sup- ported to the self-supporting framework in the inner space of the self-supporting framework.

According to an eighth aspect of the invention, the invention provides a method of maintenance of a flota ^¬ tion plant according to the first aspect of the inven ^¬ tion. In the method a lower module underneath the up ^¬ permost module is subject of maintenance, and the up ^¬ permost module is hoisted up from the top of the lower module and transferred aside for gaining access to the lower module.

In one embodiment of the method, while the uppermost module is away from the top of the lower module, maintenance operations are performed for the lower module .

In one embodiment of the method, while the uppermost module is away from the top of the lower module, the lower module is replaced by another lower module.

According to a ninth aspect of the invention, the invention provides use of the drive module according to the seventh aspect of the invention for separating ma- terial by flotation based on differences of buoyancy properties of substances. For example there is buoyan ^¬ cy difference when organic material is separated from aqueous material. According to a tenth aspect of the invention, the invention provides use of the drive module according to the seventh aspect of the invention for separating solid material by froth flotation based on differences of hydrophilic properties of substances. Solid materi- als separated by froth flotation could be oil sands, carbon, coal, talk, industrial minerals and mineral particles. The minerals may include industrial miner- als and ore. Froth flotation to solid material could be made based on natural hydrophilic/hydrophobic dif ^¬ ference or based on hydrophilic/hydrophobic differ ^¬ ences made by addition of a surfactant or collector chemical or other chemical.

According to an eleventh aspect of the invention, the invention provides use of the drive module according to the seventh aspect of the invention for concentrat- ing ore by froth flotation. An ore is a type of rock that contains sufficient minerals with important ele ^¬ ments including metals that can be economically ex ^¬ tracted from the rock. Metal ores are generally ox ^¬ ides, sulfides, silicates, or metals such as native copper or gold. Froth flotation of ore could be made based on natural hydrophilic/hydrophobic difference or based on hydrophilic/hydrophobic differences made by addition of a surfactant or collector chemical or other chemical.

According to a twelfth aspect of the invention, the invention provides use of the drive module according to the seventh aspect of the invention for flotation of substances containing abrasive material. The abra- sive mineral may be, for example, pyrite, silica, chromite. The drive module being hoistable and trans ^¬ ferable as one unit to gain access to the tanks ena ^¬ bles that the tanks can easily be maintained or re ^¬ placed 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 flo ^¬ tation plant which is easy to maintenance is effective when flotation is made to abrasive material. According to a thirteenth aspect of the invention, the invention provides use of the drive module according to the seventh aspect of the invention for froth flo- tation of ore containing pyrite, silica, chromite. Use of the flotation plant which is easy to maintenance and has preferably tanks made from PE or PP is effec ^¬ tive when flotation is made to ore containing pyrite, silica, chromite. PE and PP are durable against the ore containing pyrite, silica, chromite.

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 em- bodiments of the invention and together with the de ^¬ scription help to explain the principles of the inven ^¬ tion. In the drawings:

Figure 1 is a schematic side view of a first embodi- ment of the flotation plant according to the invention,

Figure 2 is a schematic cross-section II-II from Figure 1 ,

Figure 3 is a schematic cross-section corresponding to Figure 2 of second embodiment of the flotation plant according to the invention, Figure 3 is a schematic cross-section corresponding to Figure 2 of third embodiment of the flotation plant according to the invention, Figure 4 is a schematic cross-section corresponding to Figure 2 of fourth embodiment of the flotation plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Although flotation is disclosed in the following examples 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 and 2 show a froth flotation plant that is configured for implementing froth flotation. In this embodiment the froth flotation plant has been assembled from self-supporting modules that together form a modular froth flotation plant. The modules from which the froth flotation plant has been built are removably stacked on top of each other to form a three-storeyed structure having a first storey I at the bottom, a second storey II in the middle and a top storey III. A tank module 1 disposed in the second storey II.

A foundation 24 disposed at the first storey I is for supporting a stack formed by a tank module 6 and a drive module 5 placed on top of the tank module 6. The second storey II includes the tank module 6. The tank module 6 is above the first storey I. The second sto ^¬ rey II is defined by the height of the tank module 6. The third storey II disposed above the second storey II includes the drive module 5 which is the uppermost module in the stack of modules. The third storey II is defined by the height of the drive module 5. The foundation 24 may be formed of a plurality of pil ^¬ lars 25 (illustrated by dashed line in Figure 2), or as shown in Figure 2 as a self-supporting foundation module 26 at the first storey I. The foundation module 26 is a rigid and self-supporting unit capable of be ^¬ ing transferable and hoistable as an integral entity. At the first storey I there preferably are also dis ^¬ posed a first pump 27 for pumping an overflow (froth) that overflows out from froth flotation and a second pump 28 for pumping an underflow that underflows out from froth flotation.

Referring to Figures 1 to 4, the tank module 6 in ^¬ cludes four froth flotation tanks 1. The neighboring flotation tanks 1 are in fluid communication with each other so that a continuous flow of underflow can flow through the successive flotation tanks. As can be seen in Figures 2 to 4, each froth flotation tank 1 accommodates a mixing and bubble forming equipment 2 in- eluding a rotor 3 connected to a rotatable drive shaft 4. The drive shaft 4 is preferably hollow to provide a supply channel for the flotation gas via the drive shaft 4 to the rotor 3 which releases the flotation gas as bubbles into the liquid inside the froth flota- tion tank. A stationary stator 43 is arranged to surround the rotor 3. The stator 43 is attached through the bottom 44 of the flotation tank 1 to the framework 9 of the tank module 6. The drive module 5 is disposed on top of the froth flotation tanks 1 so that the drive module 5 is remov ^¬ ably stacked on top of the tank module 6. The drive module 5 includes four drive units D for the rotation of the drive shafts 4.

The drive module 5 is a rigid and self-supporting unit that can be transferred and hoisted as an integral en- tity. The drive module 5 comprises a first self- supporting framework 7 having a shape of a rectangular parallelepiped, the first self-supporting framework 7 being stackable with another compatible self- supporting framework of another module, the first self-supporting framework having an inner space 8, and the drive units D are disposed in the inner space 8 of the first self-supporting framework 7. The drive module 5 being a self-supporting structure comprises corners 11 by which the drive module 6 can be supported during transferring and hoisting as well as when being installed in the froth flotation plant. A preferable embodiment of the drive module 5 and its framework 7 is that they are compatible to intermodal freight container standards whereby they have dimen ^¬ sions and corner fittings which enable intermodal transportability . Referring to Figures 2 to 4, the tank module 6 is a self-supporting unit which can be transferred and hoisted as an integral entity. The tank module 6 in ^¬ cludes a second self-supporting framework 9 having an inner space 10. The second self-supporting framework 9 of the tank module 1 comprises a framework bottom 29 and framework sidewalls 30 which together define the inner space 10. The four froth flotation tanks 1 are arranged in a row inside the inner space 10 of the self-supporting framework 2. The froth flotation tanks 1 are each self-supporting structures. In order to enable easy installation and replacing the froth flotation tanks 1 are placed in the inner space 10 of the self-supporting framework 9 without being attached to the framework bottom 29 and the framework sidewalls 30. The tank module 6 being a self-supporting structure comprises corners 12 by which the tank module 6 can be supported during transferring and hoisting as well as when being installed in the froth flotation plant.

A preferable embodiment of the tank module 6 and its framework 9 is that they are compatible to intermodal freight container standards whereby they have dimen ^¬ sions and corner fittings which enable intermodal transportability .

The widths of the drive module 5 and the tank module 6 may differ from each other at most 20% to enable their stacking. In the shown embodiments the drive module 5 and the tank module 6 have same width.

Figure 1 shows that the froth flotation plant includes a feed box 22 for feeding feedstock to the froth flo- tated to the flotation tank 1 and a discharge box 23 for receiving and discharging underflow from the flo- tation tank 1. The feed box 22 and the discharge box 23 are attached to the opposite ends of the tank mod ^¬ ule 6 and disposed outside the tank module 6.

Referring to Figures 2 to 4, the froth flotation plant comprises overflow receptacles 13 arranged at the lev ^¬ el of the upper part the tank module 6. The overflow receptacles 13 are arranged to collect the overflow that overflows from the froth flotation tanks 1. In the embodiments shown in Figures 1 to 3 the overflow receptacles 13 are inside the second self-supporting framework 9 of the tank module 6 and each of the re ^¬ ceptacles are connected to the froth flotation tanks 1 to be transferable and hoistable as an integral unit with the tank module 6. Preferably, the froth flota- tion tanks 1 are made of plastics, e.g. polypropylene or polyethylene. Preferably, the overflow receptacles 13 are made of same material as the froth flotation tanks .

Figure 4 shows alternative embodiment wherein the overflow receptacle 13 is disposed outside the tank module 6. In this example the overflow receptacle 13 is arranged in the inner space 35 of an accessory mod ^¬ ule 36 that is placed next to the tank module 6 at the level of the second storey II. The overflow receptacle 13 is supported by brackets 37 to a self-supporting framework 38 of the accessory module 36.

Referring again to Figures 2 to 4, the froth flotation plant comprises an overflow channel 14. The overflow channel 14 is disposed outside the tank module 6 at one side of the tank module 6. The overflow channel 14 receives the overflow from the overflow receptacle 13 and conducts the overflow away from the overflow re ^¬ ceptacle 13.

Figure 2 shows an embodiment wherein the overflow channel 14 is arranged in an inner space 31 of an ac ^¬ cessory module 32 that is placed next to the tank mod ^¬ ule 6 at the level of the second storey II. The over- flow channel 14 is supported by brackets 33 to a self- supporting framework 34 of the accessory module 32.

Figure 3 shows an embodiment wherein the overflow channel 14 is disposed at a level of the tank module 6 and connected thereto to be transferable and hoistable as an integral unit with the tank module 6.

Referring to Figures 1 - 4, at the level of the first storey I there is a pump sump module 39 including a first pump 27 for pumping the overflow which comes via the overflow channel 14 to a first sump tank 40 where- from the settled overflow can be pumped away by the first pump 27 to further processing. As shown in Figure 1, the pump sump module 39 may also include a sec ^¬ ond pump 28 for pumping the underflow which comes from the flotation tank 1 via the discharge box 23 to a second sump tank 41 wherefrom it can be pumped away by the second pump 28 to further processing. Preferably, in the embodiments of the Figures 2 and 4, the pump sump module 39 acts as a foundation on top of which the accessory module 32, 36 is placed so as to be ele- vated to the second storey II level.

As can be seen in Figures 1 to 4, the drive module 5 comprises a gas feed pipeline 15 for supplying flota ^¬ tion gas and electric cabling 21 supported on a cable tray 42. The gas feed pipeline 15 and the cable tray extend along the length of the drive module 5.

The gas feed pipeline 15 and the cable tray 42 are disposed in the inner space 8 of the first self- supporting framework 7 so that they are above the level in relation to the level of the drive units D. Also they are offset in relation to the drive units D so that they do not hinder or interfere hoisting of the drive unit D in an upwards direction. During in- stalling and removing the drive units D pass by the gas feed pipeline 15 and the cable tray 42.

The gas feed pipeline 15 is connected in fluid commu ^¬ nication with the hollow drive shaft 4.

The drive module 5 further comprises a flow meter 16 which is connected to the gas feed pipeline 15 for measuring the rate of flow of the flotation gas. A flow rate controller 17 is connected to the gas feed pipeline 15 for regulating the rate of flow of the flotation gas. The drive module 5 may also comprise measurement equipment 18 for the measurement of liquid level in a flotation tank (not shown) , when in use in froth flotation. The drive module 5 may also comprise a froth camera 20 for detecting bubble size of froth, when in use in froth flotation. Preferably, the first self- supporting framework 7 also comprise a maintenance platform 19 (see also Figure 1) that enables easy ac ^¬ cess to the inner space 8 of the first self-supporting framework 7 for e.g. maintenance of the various equip ^¬ ment contained in the drive module.

The drive module 5 may also be equipped with a variety of other equipment that can be installed already at the manufacturing site. When needed, the drive module 5 may contain e.g.

- a water pipeline for supplying water to an overflow receptacle which receives the overflow from the froth flotation tank,

- a gas suction pipeline for recirculating the flotation gas (needed for work safety reasons e.g. in froth flotation of molybdenum wherein the flotation gas is poisonous),

- a roofing on top of the drive module, and shields that cover the sides of the self-supporting space frame metal beam framework for shielding the equipment furnished inside the framework from harsh environmental conditions (sunshine, rain, sandstorm, ice, snow etc) .

It should be noted that although the above embodiments disclose the froth flotation tanks to be in the tank module, the invention is not limited to that. Within the scope of the invention, the froth flotation plant may be implemented e.g. with conventional froth flota ^¬ tion tanks that are fixed structures and are not placed in the inner space of the self-supporting framework. The drive module that can be hoisted and transferred as an integral unit according to the in ^¬ vention is equally usable in connection with e.g. such conventional froth flotation tanks or any other froth flotation tanks which are placed next to each other.

Maintenance of the modular flotation plant is easy and can be performed quickly. If an uppermost module in the stack of modules is subject of maintenance, the uppermost module is simply hoisted up and transferred aside and is replaced by another uppermost module. If a lower module disposed underneath the uppermost mod ^¬ ule is subject of maintenance, then the uppermost mod ^¬ ule is hoisted up from the top of the lower module and transferred aside for gaining access to the lower mod ^¬ ule. While the uppermost module is away from the top of the lower module, maintenance operations are per ^¬ formed for the lower module. Alternatively, the lower module can simply be replaced by another lower module.

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.