FIELD OF THE INVENTION

The present invention relates to a flotation unit. Further, the invention relates to a flotation plant. Further, the invention relates to a method maintenance of the flotation unit and/or plant. Further, the invention relates to uses of the flotation unit and/or plant.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides a flotation unit comprising at least one flo- tation tank and other equipment configured for imple ^¬ menting a flotation process for a feedstock subject of flotation. The flotation unit is built with self- supporting modules forming a modular storeyed structure having superimposed storeys. The self-supporting modules are transferable and hoistable as integral units and stackable on top of each other to form the storeys .

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 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 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 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 feed- stock 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 ^¬ clude 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. The technical effect of the invention is that as the modules are self-supporting units they can be trans ^¬ ported, transferred and hoisted as integral entities. The modules 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 inte ^¬ gral entities. During transportation, hoisting and use the equipment furnished into the modules are well protected inside the self-supporting framework which acts as a delivery package and thereby eliminates need for separate transportation packages for the equip ^¬ ment. At the site of installation the modules may be placed on top of each other to form the complete flo ^¬ tation unit or a plant having several flotation units in succession. Installing the flotation units at the installation site can be made safely and quickly with a small amount of labor and in short time. Capacity of the flotation plant can be easily increased by adding modules to a flotation unit or by adding flotation units. The modules and various equipment contained therein is accessible and easily replaceable for maintenance. After the dedicated plant lifecycle, the dismantling of the unit/plant can be made quickly.

In one embodiment of the flotation unit, the flotation unit comprises a first storey being the lowest storey of the unit. The first storey comprises at least one self-supporting module. The flotation unit comprises a second storey disposed on top of the first storey. The second storey comprising at least one self-supporting module stacked and aligned on the module of the first storey .

In one embodiment of the flotation unit the flotation unit comprises a third storey disposed above the sec ^¬ ond storey. The third storey comprises at least one self-supporting module. The number of the storeys is not limited to three storeys. In some other embodi ^¬ ments the flotation unit may comprise more than three storeys .

In one embodiment of the flotation unit, each module comprises

- a self-supporting framework having a shape of a rectangular parallelepiped, the self-supporting framework being stackable on top of another self- supporting framework of another module, and

equipment arranged inside the self- supporting framework, the equipment comprising compo- nents configured to enable operations of the flotation process. The various components may be configured to implement one or several functions for achieving the flotation, forming an overflow, for separating an overflow and/or conducting the overflow and/or the un- derflow within the flotation plant.

In one embodiment of the flotation unit, flotation is froth flotation. In one embodiment of the flotation unit, the flotation unit comprises gas adding equipment for adding gas to the feedstock subject of flotation.

In one embodiment of the flotation unit, the flotation unit comprises gas adding equipment for adding gas to the stream of the feedstock subject of flotation before entering the flotation tank.

In one embodiment of the flotation unit, the flotation unit comprises gas adding equipment for adding gas to the feedstock subject of flotation in the flotation tank .

In one embodiment of the flotation unit, the gas add- ing equipment includes a rotor inside the flotation tank .

In one embodiment of the flotation unit, 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 unit, the feedstock subject of flotation is slurry or pulp.

In one embodiment of the flotation unit, the flotation unit comprises mixing equipment.

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

In one embodiment of the flotation unit, the flotation tank having a bottom is disposed inside a framework, and the stator is connected to the framework through the bottom.

In one embodiment of the flotation unit, the flotation unit comprises a tank module. The tank module forms a flotation cell. The tank module is disposed at the level of the second storey. The second storey is de ^¬ fined by the height of the tank module. The tank mod ^¬ ule includes at least one flotation tank. The flota ^¬ tion tank, when in use, accommodates a volume of feed- stock subject of flotation, and an immersed equipment performing the flotation action in the feedstock subject of flotation.

In one embodiment of the flotation unit, the tank mod- ule is a rigid and self-supporting unit capable of be ^¬ ing transferable and hoistable as an integral entity.

In one embodiment of the flotation unit, the flotation tank accomodates mixing and bubble forming equipment including a rotor connected to a rotatable drive shaft for dispersing gas into the feedstock subject of flo ^¬ tation. In one embodiment of the flotation unit, the mixing and bubble forming equipment includes a stator dis ^¬ posed stationary around the rotor.

In one embodiment of the flotation unit, the flotation unit comprises a drive module. The drive module is disposed at the level of the third storey. The level of the third storey is defined by the height of the drive module. The drive module is removably stacked and aligned on top of the tank module. The dive module includes at least two drive units for the equipment immersed in the feedstock subject to flotation, the equipment performing the flotation action. The drive module is a rigid and self-supporting unit capable of being transferable and hoistable as an integral enti ^¬ ty.

In one embodiment of the flotation unit, the drive units are disposed to rotate the drive shafts.

In one embodiment of the flotation unit, the flotation unit comprises a foundation module. The foundation module is at the level of the first storey. The foun- dation module is a rigid and self-supporting unit ca ^¬ pable of being transferable and hoistable as an inte ^¬ gral entity. The tank module and the drive module may be stacked on top of the foundation module. In one embodiment of the flotation unit, the founda ^¬ tion module includes a pumping means for pumping, when in use, of a fluid obtained from the flotation tanks as an overflow and/or as an underflow. In one embodiment of the flotation unit, the flotation unit comprises a main pillar foundation. The main pillar foundation is at the level of the first storey. The main pillar foundation comprises a plurality of pillars having a height above the ground level. The tank module and the drive module are stacked on top of the main pillar foundation.

In one embodiment of the flotation unit, the flotation unit comprises a side module. The side module is dis ^¬ posed on the side and next to the foundation module or on the side and next to the main pillar foundation at the level of the first storey. The side 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 unit, side module includes a pumping means for pumping, when in use, of a fluid obtained from the flotation tanks as an over ^¬ flow and/or as an underflow.

In one embodiment of the flotation unit, the pumping means for pumping the overflow includes an overflow sump tank. The overflow sump tank is arranged to receive the overflow to be pumped.

In one embodiment of the flotation unit, the pumping means for pumping the overflow includes an overflow pump. The overflow pump is arranged to pump the overflow from the overflow sump tank.

In one embodiment of the flotation unit, the pumping means for pumping the underflow includes an underflow sump tank. The underflow sump tank is arranged to receive the underflow to be pumped.

In one embodiment of the flotation unit, the pumping means for pumping the underflow includes an underflow pump. The underflow pump is arranged to pump the underflow from the underflow sump tank. In one embodiment of the flotation unit, the flotation unit comprises an accessory module. The accessory mod ^¬ ule is located on the side and next to the tank module at the level of the second storey. The accessory mod ^¬ ule is a rigid and self-supporting unit capable of be ^¬ ing transferable and hoistable as an integral entity.

In one embodiment of the flotation unit, the accessory module is removably stacked on top of the side module.

In one embodiment of the flotation unit, the flotation unit comprises a side pillar foundation. The side pil ^¬ lar foundation is formed of a plurality of pillars lo- cated on the side of the foundation module at the lev ^¬ el of the first storey. The accessory module is remov ^¬ ably stacked on top of the side pillar foundation.

In one embodiment of the flotation unit, the flotation plant comprises an overflow receptacle for collecting an overflow overflowing from the flotation tank.

In one embodiment of the flotation unit, the overflow receptacle is disposed at a level of the second sto- rey.

In one embodiment of the flotation unit, 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 unit, the overflow receptacle is disposed inside the tank module. In one embodiment of the flotation unit, the overflow receptacle is disposed outside the tank module. In one embodiment of the flotation unit, the overflow receptacle is disposed inside the accessory module.

In one embodiment of the flotation unit, the flota- tion unit comprises an overflow channel to conduct away the overflow from the overflow receptacle.

In one embodiment of the flotation unit, the overflow channel is disposed at the level of the second storey.

In one embodiment of the flotation unit, the overflow channel is connected to the tank module to be trans ^¬ ferable and hoistable as an integral unit with the tank module.

In one embodiment of the flotation unit, the overflow channel is disposed inside the accessory module to be transferable and hoistable as an integral unit with the accessory module.

In one embodiment of the flotation unit, the drive module comprises a gas feed pipeline for supplying flotation gas. In one embodiment of the flotation unit, the gas feed pipeline is in fluid communication with the drive shaft. The drive shaft is hollow for conducting the flotation gas supplied by the gas feed pipeline. In one embodiment of the flotation unit, the drive module comprises an inner space. Measuring equipment is disposed in the inner space.

In one embodiment of the flotation unit, the drive module comprises a flow rate controller connected to the gas feed pipeline for controlling the rate of flow of the flotation gas. In one embodiment of the flotation unit, the drive module comprises measurement equipment for the meas ^¬ urement of liquid level in the flotation tank. In case of froth flotation there is a liquid layer and a froth layer on top of the liquid layer. The surface height of the liquid layer can be measured by the measurement equipment . In one embodiment of the flotation unit, the drive module comprises a maintenance platform.

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

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

In one embodiment of the flotation unit, the flotation unit includes a feed box for feeding feedstock subject of flotation to the flotation tank.

In one embodiment of the flotation unit, the flotation unit includes a discharge box for receiving and dis ^¬ charging underflow from the flotation tank. In one embodiment of the flotation unit, the feed box and/or the discharge box is attached to the ends of the tank module and located outside the tank module.

In one embodiment of the flotation unit, the drive module comprises a first self-supporting framework having a shape of a rectangular parallelepiped. The first self-supporting framework is stackable with an- other compatible 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 unit, the tank mod ^¬ ule comprises a second self-supporting framework having a shape of a rectangular parallelepiped. The sec ^¬ ond self-supporting framework is stackable with a com- patible another self-supporting framework of another module. The second self-supporting framework has an inner space. The flotation tank is disposed in the inner space of the second self-supporting framework. In one embodiment of the flotation unit, the founda ^¬ tion module comprises a third self-supporting frame ^¬ work having a shape of a rectangular parallelepiped. The third self-supporting framework is stackable with a compatible another self-supporting framework of an- other module. The third self-supporting framework has an inner space.

In one embodiment of the flotation unit, the pumping means is disposed in the inner space of the third self-supporting framework of the foundation module.

In one embodiment of the flotation unit, the side mod ^¬ ule comprises a fourth self-supporting framework having a shape of a rectangular parallelepiped. The fourth self-supporting framework is stackable with a compatible another self-supporting framework of another module. The fourth self-supporting framework has an inner space. In one embodiment of the flotation unit, the accessory module comprises a fifth self-supporting framework having a shape of a rectangular parallelepiped. The fifth self-supporting framework is stackable with a compatible another self-supporting framework of another module. The fifth self-supporting framework has an inner space.

In one embodiment of the flotation unit, each one of the modules comprises corners. The modules are de ^¬ signed to be supported by the corners. In one embodiment of the flotation unit, the modules have widths that differ from each other no more than 20%.

In one embodiment of the flotation unit, the modules have same width.

In one embodiment of the flotation unit, the height of the module containing the pumping means is 35 - 70 % of the total height of the pumping means containing module and the tank module.

In one embodiment of the flotation unit, the height of the module which contains the pumping means is 40 - 65%, more preferably 45 - 55%, of the total height of the module containing pumping means and the tank mod ^¬ ule .

In one embodiment of the flotation unit, the tank mod ^¬ ule includes 1 to 6, preferably 1 to 4, flotation tanks.

In one embodiment of the flotation unit, the volume of the flotation tank is 0.5 to 20 m ³ , more preferably 1 to 15 m ³ , most preferably 1 to 8 m ³ . According to a second aspect of the invention, the in ^¬ vention provides a flotation plant comprising a flotation unit according the first aspect of the invention. In one embodiment of the flotation plant, the flota ^¬ tion plant comprises at least two flotation units in succession .

In one embodiment of the flotation plant, the succes- sive flotation units are in fluid communication with each other.

In one embodiment of the flotation plant, the flota ^¬ tion plant comprises several groups of successive flo- tation units arranged in parallel.

In one embodiment of the flotation plant, the parallel groups of successive flotation units are in fluid com ^¬ munication with each other.

In one embodiment of the flotation plant, the flow of the feedstock subject of flotation between parallel groups of successive flotation units is arranged by means of pumps. Alternatively, it is also possible that there is a fall head between the groups and the flow of feedstock subject of flotation between the groups occurs by gravity.

In one embodiment of the flotation plant, the parallel groups of successive flotation units are not in fluid communication with each other. In this embodiment each group has its own through flow of feedstock subject of flotation which is independent from the flows of other parallel groups.

In one embodiment of the flotation plant, at least on one side, preferably on both sides, of the drive mod- ules and next to the drive modules there is a free space which is free of modules. The technical effect is that the free space enables easy lifting of the drive unit making the maintenance easy.

In one embodiment of the flotation plant, on one side of the tank modules and next to the tank modules, there is a free space which is free of modules. The technical effect is that the free space enables easy lifting of the drive unit making the maintenance easy.

In one embodiment of the flotation plant, the flota ^¬ tion plant comprises a conditioner for conditioning the feedstock subject of flotation before flotation operations. The conditioner is disposed to feed the conditioned feedstock to a first one of the flotation units in said succession of the flotation units.

According to a third aspect of the invention, the in- vention provides a method of maintenance of a flota ^¬ tion unit of the first and/or second aspect of the in ^¬ vention. In the method an uppermost module in the stack of modules is subject of maintenance, and the uppermost module is hoisted up and transferred aside from the top of the lower module and the uppermost module is replaced by a another uppermost module which is placed on top of the lower module.

According to a fourth aspect of the invention, the in- vention provides a method of maintenance of a flota ^¬ tion unit of the first and/or second aspect of the in ^¬ vention. In the method a lower module underneath the uppermost module is subject of maintenance, and the uppermost 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. In one embodiment of the method, after replacing of the lower module the originally uppermost module is returned on top of the lower module.

According to a fifth aspect of the invention, the in- vention provides use of the flotation unit according to the first aspect or use of the flotation plant ac ^¬ cording to the second aspect for separating material by flotation based on differences of buoyancy proper ^¬ ties of substances. For example there is buoyancy dif- ference when organic material is separated from aque ^¬ ous material .

According to a sixth aspect of the invention, the invention provides use of the flotation unit according to the first aspect or use of the flotation plant ac ^¬ cording to the second aspect for separating solid ma ^¬ terial by froth flotation based on differences of hy- drophilic properties of substances. Solid materials separated by froth flotation could be oil sands, car- bon, coal, talk, industrial minerals and mineral par ^¬ ticles. The minerals may include industrial minerals and ore. Froth flotation to solid material could be made based on natural hydrophilic/hydrophobic differ ^¬ ence or based on hydrophilic/hydrophobic differences made by addition of a surfactant or collector chemical or other chemical. According to a seventh aspect of the invention, the invention provides use of the flotation unit according to the first aspect or use of the flotation plant ac- cording to the second aspect for concentrating ore by froth flotation. An ore is a type of rock that contains sufficient minerals with important elements in ^¬ cluding metals that can be economically extracted from the rock. Metal ores are generally oxides, 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 hydro ^¬ philic/hydrophobic differences made by addition of a surfactant or collector chemical or other chemical.

According to an eighth aspect of the invention, the invention provides use of the flotation unit according to the first aspect or use of the flotation plant ac ^¬ cording to the second aspect for flotation of sub- stances 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 ninth aspect of the invention, the invention provides use of the flotation unit according to the first aspect or use of the flotation plant ac ^¬ cording to the second aspect for froth flotation 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 effective when flotation is made to ore containing pyrite, silica, chromite. PE and PP are durable against the ore con ^¬ taining 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 shows a perspective view of one embodiment of the three-storeyed flotation plant according to the invention, Figure 2 is a schematic side view of a second embodi ^¬ ment of the three-storeyed flotation plant according to the invention,

Figures 3 to 10 show as schematic cross-sectional views eight examples of different kinds combinations of modular three-storeyed flotation plants that can be assembled from the modules,

Figure 11 shows a schematic layout of an embodiment of a flotation plant according to the invention having three parallel rows of two successive flotation units and Figure 12 shows a schematic layout of a further embod ^¬ iment of a flotation plant according to the invention having three parallel rows of two successive flotation units .

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 of a storeyed modular struc- ture of the flotation unit and plant according to the invention can be implemented regardless of the specif ^¬ ic 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.

Referring to Figures 1 and 2, a froth flotation plant is built to a modular three-storeyed structure. The froth flotation plant has been assembled from self- supporting modules that when assembled together form a modular froth flotation plant having superimposed storeys. The self-supporting modules are transferable and hoistable as integral units and stackable on top of each other to form the storeyed structure. The modules from which the froth flotation plant has been built are removably stacked on top of each other to form the three-storeyed structure having a first storey I at the bottom, a second storey II in the middle above the first storey I and a top storey III above the second storey II.

With reference to Figures 1 - 10, each of the modules 2, 7, 11, 12, 17 in the froth flotation plant comprises a self-supporting framework 32, 34, 36, 38, 40 hav- ing a shape of a rectangular parallelepiped. The self- supporting framework is stackable on top of another self-supporting framework of another module. The mod- ules also comprise suitable equipment arranged inside the self-supporting framework 32, 34, 36, 38, 40. The equipment that can be different in different modules comprises a variety of components that are configured to enable and facilitate the froth flotation process in e.g. for mixing and forming bubbles in the fluid to be subject for froth flotation, for forming an overflow, for separating the overflow and/or for conducting the overflow and/or the underflow within the froth flotation plant. The equipment contained in the mod ^¬ ules 2, 7, 11, 12, 17 is explained in more detail in the following with reference to Figures 2 - 10.

As illustrated in Figures 2 to 4, and 6 to 10, a foun- dation module 11 is at the level of the first storey I. The foundation module 11 is a rigid and self- supporting unit that can be transferred and hoisted as an integral entity. The tank module 2 and the drive module 7 are stacked on top of the foundation module 11. As shown in Figure 5 the main foundation 1 may alternatively be formed of pillars 19.

The second storey II includes a tank module 2. The height of the tank module 2 defines the second storey II. The tank module 2 includes one to six froth flota ^¬ tion tanks 3. The neighboring flotation tanks 3 are in fluid communication with each other so that a continuous flow of underflow can flow through the successive flotation tanks. In the example shown in Figure 2, the tank module 2 includes four froth flotation tanks 3.

Preferably, the froth flotation tanks 3 are placed in the inner space 33 of the second self-supporting framework 34 without being attached to the framework bottom and framework sidewalls to provide for easy in- stalling and replacing of the tanks. The volume of the froth flotation tank 3 is 0.5 to 20 m ³ , more pref ^¬ erably 1 to 15 m ³ , most preferably 1 to 8 m ³ . The froth flotation tanks 3 and the overflow receptacle 21 are preferably made of a thermoplastic polymer, such as polyethylene PE or polypropylene PP which materials have good resistance against abrasion.

Referring to Figure 3, the froth flotation tanks 3, when in use, each accommodate a mixing and bubble forming equipment 4 including a rotor 5 connected to a rotatable drive shaft 6. The tank module 2 is a rigid and self-supporting unit that can be transferred and hoisted as an integral entity. For that purpose the tank module 2 comprises a second self-supporting framework 34 having a shape of a rectangular parallelepiped. The second self-supporting framework 34 is stackable with a compatible another self-supporting framework of another module. The second self- supporting framework has an inner space 35 and the froth flotation tanks 3 are disposed in the inner space of the second self-supporting framework 34. Preferably, the froth flotation tanks 3

As shown in Figure 2, the froth flotation plant includes a feed box 30 for feeding feedstock to be sub ^¬ ject for froth flotation to the flotation tank 3 and a discharge box 31 for receiving and discharging underflow from the flotation tank 3. The feed box 30 and the discharge box 31 are attached to the ends of the tank module 2 and located outside the tank module 2. The third storey III includes a drive module 7. The third storey III is defined by the height of the drive module 7. The drive module 7 is removably stacked on top of the tank module 2. The drive module 2 includes two to six drive units 8 corresponding to the number of the froth flotation tanks 3 in the tank module 2. In the example shown in Figure 2 the drive module 2 includes four drive units 8. The drive units 8 are ar- ranged to rotate the drive shafts 6. The drive module 2 is a rigid and self-supporting unit that can be transferred and hoisted as an integral entity. For that purpose the drive module 7 comprises a first self-supporting framework 32 having a shape of a rectangular parallelepiped. The first self-supporting framework is stackable with another compatible self- supporting framework of another module. The first self-supporting framework 32 has an inner space 33, and the drive units 8 are disposed in the inner space 33 of the first self-supporting framework 32.

As shown in Figures 2 to 10 the froth flotation plant comprises pumping means 9, 10 for pumping, when in use, of a fluid flow obtained from the froth flotation tank 3 as an overflow and/or as an underflow. The pumping means 9, 10 is always disposed at the level of the first storey I. In the examples shown in Figures 2 - 4, 8 and 9 the pumping means 9 for pumping the overflow are disposed inside the foundation module 11 which supports the stack formed of the tank module 2 and the drive module 7. Figure 2 shows that the same foundation module 11 that accommodates the pumping means 9 for pumping the overflow may also accommodate the pumping means 10 for pumping the underflow. The foundation module 11 comprises a third self-supporting framework 36 having a shape of a rectangular parallelepiped. The third self- supporting framework 36 is stackable with a compatible another self-supporting framework of another module. The third self-supporting framework has an inner space 37. The pumping means 9, 10 are disposed in the inner space 37 of the third self-supporting framework 36 of the foundation module 11. In the examples shown in Figures 5, 6, 7, 9 and 10 the froth flotation plant comprises a side module 12.

In the examples shown in Figure 6, 7, 9 and 10 the side module 12 is located on the side of and next to the foundation module 11 at the level of the first storey I .

The example in Figure 5 shows that a main pillar foun- dation 1 for supporting the stack of the tank module 2 and the drive module 7 may be formed of a plurality of pillars 19 having a height above the ground level thereby providing a free space having the height of the first storey I, so that the space below the froth flotation plant can be accessed. In the example shown in Figure 5 the side module 12 is located on the side of and next to a main pillar foundation 1 formed of pillars 19 at the level of the first storey I. The side module 12 is a rigid and self-supporting unit that can be transferred and hoisted as an integral en ^¬ tity. The side module 12 may include the pumping means 9, 10 for pumping of the overflow and/or the underflow. In the example shown in Figure 9, the side mod- ule 12 acts only as a support for the accessory module 17 which is placed removably on top of the side module 12. The side module 12 comprises a fourth self- supporting framework 38 having a shape of a rectangular parallelepiped. The fourth self-supporting frame- work 38 is stackable with a compatible another self- supporting framework of another module. The fourth self-supporting framework 38 has an inner space 39 that can accommodate the pumping means 9, 10 for pump ^¬ ing of the overflow and/or the underflow.

As can be seen in Figures 2 - 10 the pumping means 9 for pumping the overflow include an overflow sump tank 13. The overflow sump tank 13 is arranged to receive the overflow that is collected by overflow receptacles 21 and conducted via overflow channel 22 to the over ^¬ flow sump tank 13. An overflow pump 14 is arranged to pump the overflow away from the overflow sump tank 13. Referring to Figure 2, the pumping means 10 for pumping the underflow is a similar arrangement. An underflow sump tank 15 is arranged to receive the underflow of the froth flotation process coming via a pipeline from the discharge box 31 to the underflow sump tank 15. The pumping means 10 for pumping the underflow includes an underflow pump 16. The underflow pump 16 is arranged to pump the underflow away from the underflow sump tank 15.

In order to be able to create a continuous gravity flow of the overflow the height of the foundation mod ^¬ ule 11 or the side module 12 containing the pumping means 9, 10 is 35 - 70 % of the total height of the pumping means containing module 11, 12 and the tank module 2. The height of the module which contains the pumping means is 40 - 65%, more preferably 45 - 55%, of the total height of the pumping means containing module 11, 12 and the tank module 7.

As illustrated in Figures 5 - 10, the froth flotation plant may comprise an accessory module 17. The acces ^¬ sory module 17 is located on the side and next to the tank module 2 at the level of the second storey II. The accessory module 17 is a rigid and self-supporting unit that can be transferred and hoisted as an inte ^¬ gral entity. The accessory module 17 is removably stacked on top of the side module 12. The accessory module 17 comprises a fifth self-supporting framework 40 having a shape of a rectangular parallelepiped. The fifth self-supporting framework 40 is stackable with a compatible another self-supporting framework of anoth- er module. The fifth self-supporting framework 40 of the accessory module 17 has an inner space 41. A gangway 43 can be disposed on top of the fifth self- supporting framework 40.

Each one of the above disclosed modules 11, 2, 7, 12, 17 comprises corners, and the modules are designed to be supported by the corners. To provide stackability of the modules on top of each other, the modules 11, 2, 7, 12, 17 have widths that differ from each other no more than 20%. Preferably, the modules 1, 2, 7, 12, 17 have same width. A preferable embodiment of all the modules is that they are compatible to intermodal freight container standards whereby they have dimen- sions and corner fittings which enable intermodal transportability .

The example in Figure 8 shows that the froth flotation plant may comprise a side pillar foundation 18 at the level of the first storey I. The side pillar founda ^¬ tion 18 is formed of a plurality of pillars 20 and is located next to the main foundation 1. The accessory module 17 is removably disposed on top of the side pillar foundation 18. The side pillar foundation 18 formed of pillars 20 provides a free space having the height of the first storey I, so that the space below the froth flotation plant can be accessed.

With reference to Figures 2 - 10, the froth flotation plant comprises overflow receptacles 21 for collecting an overflow overflowing from the froth flotation tanks 3. The overflow receptacles 21 are disposed at a level of the second storey II. In the example shown in Figure 4, the overflow recep ^¬ tacle 21 is on one side of the tank module 2 and con ^¬ nected by brackets to the tank module 2 so as to be transferable and hoistable as an integral unit with the tank module 2.

In the examples shown in Figures 2, 3, 5, 6, 8, 9 and 10 the overflow receptacle 21 is disposed inside the tank module 2 at the tapered upper part of each froth flotation tank 3.

In the examples shown in Figures 4 and 7 the overflow receptacle 21 may be disposed outside the tank module 2. Figure 7 shows that the overflow receptacle 21 may be disposed in the inner space 41 of fifth self- supporting framework 40 of the accessory module 17 and connected by brackets to the fifth self-supporting framework 40.

As can be seen in Figures 2 - 10 the froth flotation plant comprises an overflow channel 22. The overflow channel 22 is located at the level of the second sto- rey II to conduct away the overflow from the overflow receptacle 21.

In the examples shown in Figure 3 and 4 the overflow channel 22 are connected brackets to the second self- supporting framework 34 of the tank module 2 so as to be transferable and hoistable as an integral unit with the tank module 2.

In the examples shown in Figures 5 - 10 the overflow channel 22 is disposed in the inner space 41 of the fifth self-supporting framework 41 inside the accessory module 17 to be transferable and hoistable as an integral unit with the accessory module 17. In all the shown examples of Figures 2 - 10 the drive modules 7 are identical. The various equipment fur ^¬ nished in the drive module 7 is disclosed in the fol- lowing with reference to Figure 3. The drive module 7 comprises a gas feed pipeline 23 for supplying flota ^¬ tion gas. The gas feed pipeline 23 is disposed in the inner space 33 of the first self-supporting framework 32 and supported to the first self-supporting frame ^¬ work 32. The gas feed pipeline 23 is connected in flu ^¬ id communication with the drive shaft 6 which is hol ^¬ low and thus are able to conduct the flotation gas. The drive module 7 comprises a cable tray 42 for sup ^¬ porting electric cabling 29. The cable trays and the cabling are disposed in the inner space 33 of the first self-supporting framework 32 and supported to the first self-supporting framework 32.

The gas feed pipeline 23 and the cable tray 42 are lo ^¬ cated in the inner space 33 of the self-supporting framework 32 so that they are above the level in rela ^¬ tion to the level of the drive units 8. Also they are offset in relation to the drive units 8 so that they do not hinder or interfere hoisting of the drive unit 8 in an upwards direction. During installing and removing the drive units 8 pass by the gas feed pipeline 23 and the cable tray 29.

The drive module 7 further comprises a flow meter 24 which is connected to the gas feed pipeline 23 for measuring the rate of flow of the flotation gas. A flow rate controller 25 is connected to the gas feed pipeline 23 for regulating the rate of flow of the flotation gas.

Also some additional equipment connectable to the drive module 7 is shown. The drive module 7 may also comprise measurement equipment 26 for the measurement of liquid level in each of the flotation tanks 3. The drive module 7 may also comprise a froth camera 28 for detecting bubble size of froth, when in use in froth flotation. Preferably, the self-supporting framework 2 also comprise a maintenance platform 27 that enables easy access to the inner space 33 of the self- supporting framework 32 for e.g. maintenance of the various equipment contained in the drive module 7.

The drive module 7 may also be equipped with a variety of other equipment that can be installed already at the manufacturing site. When needed, the drive module 7 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 . ) .

Figure 10 shows an example of the froth flotation plant wherein the side module 12 containing the overflow sump tank 13 and the overflow pump 14 is disposed in the middle of two parallel stacks formed of the foundation module 11, tank module 2 and the drive mod ^¬ ule 7. Thereby, the overflow channels 22 connected to both of the tank modules 2 can conduct the overflow to the same overflow sum tank 13. Referring back to Figures 1 and 2, the figures show that the flotation plant comprises at least two flota- tion units A in succession. The successive flotation units A are in fluid communication with each other.

The flotation plant comprises a conditioner 46 for conditioning the feedstock subject of flotation before flotation operations. The conditioner 46 is disposed to feed the conditioned feedstock to a first one of the flotation units A in the direction of flow in the succession of the flotation units A.

Referring to Figure 2, in the flotation process the feedstock subject of flotation (slurry or pulp) is first conditioned in the conditioner 46 which is shown schematically on the right hand side of Figure 2. The flow of the slurry is shown with small arrows. From the conditioner 46 the slurry flows through the feed- box 30 to the row of four flotation tanks (not shown in the right hand side first flotation unit Ai) which are inside the tank module 2 and in fluid communica- tion with each other so that the underflow from one flotation tank can flow to the neighboring flotation tank. The tank module 2 of the first flotation unit Ai is similar to the above described tank module 2 of the second flotation unit A ₂ . Flotation operations are performed in each of the flotation tanks and an over ^¬ flow flows from the flotation tanks to the overflow receptacles 21. The overflow which is also shown with small arrows is conducted via the overflow channel 22 to the overflow sump tank 13. From the last flotation tank in the row of four flotation tanks of the tank module the underflow flows to the discharge box 31. From the discharge box 30 the underflow flows to the feedbox 30 of the second flotation unit A which is on the left hand side in Figure 2. The tank module 2 of the first flotation unit Ai is at a higher level than the tank module 2 of the second flotation unit A ₂ to allow flow by gravity though the flotation units Ai and A ₂ . The separation of the overflow from the underflow in the second flotation unit A ₂ is similar to that of the first flotation unit Ai as disclosed above. From the last flotation tank 3 of the tank module 2 of the second flotation unit A ₂ the underflow flows via the discharge box 31 to the underflow sump tank 15.

Reference is made to Figures 11 and 12, which show that the the flotation plant ma comprise several groups Bi, B ₂ , B ₃ of successive flotation units Ai, A ₂ arranged in parallel.

Figure 11 shows a layout of the flotation plant having three groups Bi, B ₂ , B ₃ of successive flotation units Ai, A ₂ arranged in parallel. The parallel groups Bi, B ₂ , B ₃ are in fluid communication with each other. The flow of the feedstock subject of flotation between the parallel groups Bi, B ₂ , B ₃ be arranged by means of gravity or preferably by pumps. The through flow of feedstock subject of flotation via the groups is shown by arrows .

Figure 12 shows a layout of the flotation plant having three groups Bi, B ₂ , B ₃ of successive flotation units Ai, A ₂ arranged in parallel. The parallel groups Bi, B ₂ , B ₃ are not in fluid communication with each other. The through flow of feedstock subject of flotation in the individual groups is shown by arrows. Referring to Figures 3 to 10, in order to make the maintenance of the drive units easy at least on one side, preferably on both sides, of the drive modules 7 and next to the drive modules there is a free space which is free of any modules. Also on one side of the tank modules 2 and next to the tank modules, there is a free space which is free of modules. Maintenance of the flotation unit or 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 located underneath the uppermost module is subject of maintenance, then the uppermost module 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. Thereafter the original uppermost module can be re- turned on top of the changed lower module.

The flotation plant which is built of self-supporting modules to form a modular three-storeyed structure and in which the self-supporting modules are transferable and hoistable as integral units and stacked on top of each other is quick to install an dismantle. At most one self-supporting module is stacked on top of anoth ^¬ er module which contains equipment which requires reg ^¬ ular maintenance. Maintenance of such a module is easy since only one or two modules need to be lifted off and transferred aside in order to have access to the module that requires maintenance. The module contain ^¬ ing equipment which requires regular maintenance may be a tank module 2 wherein the equipment which re- quires maintenance is a flotation tank 3 contained in the tank module 2. The module which requires mainte ^¬ nance may also be the module which contains the pump ^¬ ing means pumping means 9, 10. In the method of maintenance a module is hoisted up from the top of another module having the equipment which requires regular maintenance to gain access to the equipment requiring maintenance, and maintenance to the equipment can be performed.

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.