Field of the invention:

The invention relates to the froth flotation in mineral processing. The invention relates particu ^¬ larly to a stator for a froth flotation tank.

BACKGROUND OF THE INVENTION

Froth flotation is a process used in the re- fining of various metals. The purpose of froth flota ^¬ tion is to separate a desired mineral from undesired minerals of an ore referred to as gangue . The desired mineral is referred to as a valuable mineral. The froth flotation relies on the physical phenomena of hydrophobicity and selective surface wetting. Hydro- phobicity means the property of a molecule to be re ^¬ pelled from a mass of water. In froth flotation bodies extracted from an ore are crushed and milled to yield a dust of small particles having a size ranging, for example, from 0.1 mm to 5 ym. The dust of small parti ^¬ cles is mixed with water and wetted using a wetting agent which selectively wets exposed surfaces of the valuable mineral in particles. In the process of wet ^¬ ting molecules of the wetting agent attach to the ex- posed surfaces of the valuable mineral. The wetting agent may be referred to as a surfactant. The wetting agent has a molecular structure that causes a hydro ^¬ phobic surface to be formed over the wetted surfaces of the valuable mineral. The mixing and wetting pro- duce slurry. The slurry is introduced to a flotation tank. In the tank the slurry is agitated and aerated. In the process of aeration, particles having a wetted hydrophobic surface become attached to surfaces of air bubbles. The air bubbles rise to the surface of the tank and form froth. The froth is collected from the surface of the tank and provided to a laundering pro- cess. The gangue remaining at the bottom of the tank is allowed to flow to a neighboring tank where it is collected for further processing. The aeration and agitation are achieved by means of a rotor and a stator installed near the bottom of the tank. A flow of air is provided below the rotor, which causes the for ^¬ mation of air pockets in the rotor. Rotation of the rotator causes air to flow towards outer edges of ro ^¬ tor blades. From the rotor blade edges the air flows to stator blades which results in formation of bubbles from the air.

The effectiveness of the froth flotation de ^¬ pends on the rate and amount of bubble production in the slurry. With increased efficiency of air bubble formation it is possible to form more forth from the slurry. With better forth formation there is less need for circulating slurry via several forth flotation tanks before a desired amount of valuable mineral is obtained from an amount of slurry.

The problems in prior art solutions include high power consumption and hence high operating cost. There is a need for increased pumping capacity. Simi ^¬ larly, existing rotor and stator arrangements are not effective when sizes of the tanks used for flotation vary.

Another problem in prior art solutions is stator weight. A heavy stator may require sturdy sup ^¬ ports for the stator in a flotation tank. Sturdy supports may restrict flow of slurry into an interior space below the stator defined by the supports.

SUMMARY OF THE INVENTION:

According to an aspect of the invention, the invention is a stator of a gas dispersion mechanism to be used in a froth flotation tank, the stator comprising: an annular top plate having an inner circumference; an annular array comprising a plurality of radi- al stator blades, each stator blade having an inner edge and an outer edge, the inner edges of the stator blades defining an interior space for a rotor, inner edges of at least two stator blades of the plurality of stator blades defining an inner circumference of the annular array, the at least two stator blades hav ^¬ ing innermost inner edges among the plurality of sta ^¬ tor blades, the annular array being disposed below the annular top plate and being coaxial with the annular top plate; and an annular bottom plate disposed below the annular array, the annular bottom plate being coaxial with the annular array, the annular bottom plate having an inner circumference, the inner circumference of the annular bottom plate having a radius which is smaller than a radius of the inner circumference of the annular array, the difference between the radius of the inner circumference of the annular bottom plate and radius of the inner circumference of the annular array forming a flow guide for guiding a flow of slur- ry towards an axis of the annular bottom plate.

According to another aspect of the invention, the invention is a rotor-stator assembly of a gas dis ^¬ persion mechanism to be used in a froth flotation tank, the rotor-stator assembly comprising: a stator comprising an annular top plate having an inner circumference, an annular array comprising a plurality of radial stator blades, each stator blade having an inner edge and an outer edge, the inner edges of the stator blades defining an interior space for a rotor, inner edges of at least two stator blades of the plu ^¬ rality of stator blades defining an inner circumference of the annular array, the at least two stator blades having innermost inner edges among the plurali ^¬ ty of stator blades, the annular array being disposed below the annular top plate and being coaxial with the annular top plate, and an annular bottom plate disposed below the annular array, the annular bottom plate being coaxial with the annular array, the annu ^¬ lar bottom plate having an inner circumference, the inner circumference of the annular bottom plate having a radius which is smaller than a radius of the inner circumference of the annular array, the difference be ^¬ tween the radius of the inner circumference of the an ^¬ nular bottom plate and radius of the inner circumference of the annular array forming a flow guide for guiding a flow of slurry towards an axis of the annu- lar bottom plate; and a rotor comprising a plurality of rotor blades defining an interior space of the rotor, the rotor comprising an rotor top plate having an aperture for gas supply to the interior space, the ro ^¬ tor top plate being disposed above the plurality of rotor blades, the rotor being coaxial with the annular top plate, the rotor being positioned to protrude a depth from an opening formed by the inner circumference of the annular bottom plate.

According to another aspect of the invention, the invention is a froth flotation tank comprising the rotor-stator assembly.

In one embodiment of the invention, the at least two stator blades, the inner edges of which de ^¬ fine the inner circumference of the annular array have innermost inner edges among the plurality of stator blades in the annular array of stator blades.

In one embodiment of the invention, the annu ^¬ lar array comprises a plurality of stator blades, the annular array has an inner circumference and an outer circumference and the plurality of stator blades ex ^¬ tend radially from the inner circumference of the an ^¬ nular array to the outer circumference of the annular array. The inner edges of the stator blades may define the inner circumference. The outer edges of the stator blades may define the outer circumference.

In one embodiment of the invention, the sta ^¬ tor comprises a cylindrical member disposed between the annular array and the annular bottom plate, the cylindrical member being coaxial with the annular array .

In one embodiment of the invention, a height of the cylindrical member is from 50% to 150% of a height of the annular array of stator blades.

In one embodiment of the invention, the inner circumference of the annular array is substantially similar to the inner circumference of the cylindrical member.

In one embodiment of the invention, the outer circumference of the annular array is substantially similar to the outer circumference of the cylindrical member .

In one embodiment of the invention, a radius of the outer circumference of the annular top plate is from 20% to 45% larger than a radius of the outer circumference of the annular array.

In one embodiment of the invention, a thick- ness of stator blades decreases in radial direction from a maximum thickness at the inner circumference of the annular array to a minimum thickness at the outer circumference of the annular array.

In one embodiment of the invention, the sta- tor blades have a rectangular edge facing an axis of the annular array.

In one embodiment of the invention, the sta ^¬ tor depends from a superstructure of the froth flota ^¬ tion tank.

In one embodiment of the invention, the sta ^¬ tor is mounted on a plurality of support bars standing on a bottom of the froth flotation tank.

In one embodiment of the invention, a width of the flow guide is from 20% to 80% of the width of the annular array.

In one embodiment of the invention, the rotor comprises an annular collar for an inward flow of slurry, the annular collar being disposed below the plurality of rotor blades.

In one embodiment of the invention, the depth of protrusion is from 5% to 50% of a height of the ro- tor .

In one embodiment of the invention, the depth of protrusion is from 5% to 30% of a height of the ro ^¬ tor .

In one embodiment of the invention, the depth of protrusion is from 5% to 20% of a height of the ro ^¬ tor .

The embodiments of the invention described hereinbefore may be used in any combination with each other. At least two of the embodiments may be combined together to form a further embodiment of the invention. A stator, a rotor-stator assembly or a flotation tank to which the invention is related may comprise at least one of the embodiments of the invention de ^¬ scribed hereinbefore.

It is to be understood that any of the above embodiments or modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as excluding alternatives .

The benefits of the present invention relate to improved suction of a rotor-stator assembly in a froth flotation tank and thereby enhanced pumping capacity and reduced energy consumption in froth flotation tanks.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illus- trate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings: Fig. 1A illustrates a stator according to an embodiment of the invention;

Fig. IB illustrates a top view of the stator of Fig. 1A;

Fig. 1C illustrates a lateral section view of the stator of Fig. 1A and IB;

Fig. 2A illustrates a stator according to an embodiment of the invention;

Fig. 2B illustrates a top view of the stator of Fig. 2A;

Fig. 2C illustrates a lateral section view of the stator of Fig. 2A and 2B;

Fig. 3 illustrates a rotor in one embodiment of the invention;

Fig. 4 illustrates a rotor and stator arrangement in one embodiment of the invention;

Fig. 5A illustrates a rotor-stator assembly in one embodiment of the invention;

Fig. 5B illustrates a rotor-stator assembly in one embodiment of the invention; and

Fig. 6 illustrates a flotation tank compris ^¬ ing a stator according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

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

Figure 1A illustrates a stator in one embodi- ment of the invention.

In Figure 1A there is a stator 100. The sta ^¬ tor comprises an annular top plate 106. To the bottom of annular top plate 106 there is fixed an annular ar ^¬ ray 104 of stator blades such as stator blade 124 and stator blade 126. Stator blades in the annular array 104 extend transversely and radially from an inner circumference to an outer circumference of the annular array 104. Annular array is mounted on a cylindrical member 102. Cylindrical member 102 has an inner circumference which may be smaller than the inner circumference of annular array 104. In one embodiment of the invention, cylindrical member 102 has an inner circumference which is equal to the inner circumference of annular array 104. Cylindrical member 102 has an outer circumference which may be larger than the outer circumference than the outer circumference of annular ar- ray 104. In one embodiment of the invention, cylindrical member 102 has an outer circumference which is equal to the outer circumference of annular array 104. Cylindrical member 102 is mounted on an annular bottom plate 108. Inner circumference of annular bottom plate 108 may be smaller than the inner circumference of cy ^¬ lindrical member 102. Annular array 104 of stator blades and cylindrical member 102 define an interior space for a rotor (not shown) . Height of annular array 104 may be substantially equal to cylindrical member 102. Height of annular array 104 may be 75% to 125% of the height of cylindrical member 102. In one embodi ^¬ ment of the invention, the height of annular array 104 is substantially half of the height of stator 100.

In one embodiment of the invention, annular top plate 106, annular array 104 of stator blades and annular bottom plate 108 are integrated. The integra ^¬ tion may comprise at least one welding, securing or attaching with bolts or screws and molding.

Figure IB illustrates the stator 100 of Fig- ure 1A as seen from above in one embodiment of the in ^¬ vention. In Figure IB annular array 104 is illustrated as exposed so that the portion of annular top plate 106 covering annular array 104 is not shown. However, still the actual inner circumference of annular top plate 106 is the same as in any of the embodiments de ^¬ scribed in Figure 1A. Annular top plate 106 has an outer circumference 110 and an inner circumference 112. In Figure IB there is illustrated annular array 104 which consists of stator blades such as stator blade 124 and 126. Annular array 104 of stator blades has an outer circumference 120 and an inner circumfer- ence 122. Outer circumference 110 of annular top plate 106 may extend outer circumference 120 of annular ar ^¬ ray 104 by one quarter to one third of the width of annular array 104. The protrusion of annular top plate 106 in relation to outer circumference 120 of annular array 104 may be in the range of 50 mm to 120 mm de ^¬ pending on the size of the flotation tank in which stator 100 is installed. The larger the flotation tank, the larger the protrusion. The width of annular top plate is thus the width of annular array 104 plus the width of the protrusion. Stator blades in annular array 104 extend radially outwards in relation to lon ^¬ gitudinal axis 101 of stator 100. Stator blades extend radially outwards from an inner circumference 122 of annular array 104 to an outer circumference 120 of an- nular array 104. In annular array 104 stator blades may be circumferentially equally spaced. The number and width of stator blades in annular array 104 may vary depending on the size of the flotation tank into which stator 100 is designed to be installed. The thickness of a stator blade in annular array 104 may vary from 30 mm to 60 mm. The thicknesses of stator blades may be increased depending on the slurry load in the flotation tank in which stator 100 designed to be installed. Top surfaces of blades in annular array 104 are fixed to annular top plate 106, for example, so that inner circumference 122 of annular array 104 and inner circumference 112 of annular top plate 106 are aligned. The fixing may be by means of welding. Blades in annular array 104 may be secured to annular top plate 106 with bolts. Bottom surfaces of blades in annular array 104 are fixed to the top of cylindrical member 102. The fixing may be by means of welding. Blades in annular array 104 may be secured to cylin ^¬ drical member 102 with bolts. Cylindrical member 102 has an outer circumference 130 and an inner circumference 132. Cylindrical member 102 may have a hollow structure and have in inner wall corresponding to in ^¬ ner circumference 132 and an outer wall corresponding to outer circumference 130. The inner and outer wall of cylindrical member 102 may be mutually connected with annular top and bottom plates (not shown) and possible other connecting means (not shown) . Outer circumference 130 of cylindrical member 102 may be aligned with outer circumference 120 of annular array 104. Inner circumference 132 of cylindrical member 102 may be aligned with inner circumference 122 of annular array 104. Annular bottom plate 108 has in inner circumference 142 and an outer circumference 140.

When stator 100 is installed into a flotation tank, an opening defined by inner circumference 142 of annular bottom plate 108 guides slurry into the inte- rior space defined by annular array 204 where a rotor such as rotor 300 in Figure 3 may be suspended or oth ^¬ erwise mounted.

In one embodiment of the invention, inner circumference 132 of cylindrical member 102 is larger than inner circumference 142 of annular bottom plate 108. A difference between inner circumference 132 of cylindrical member 102 and inner circumference 142 of annular bottom plate 108 is referred to with numeral Wb . The extension of annular bottom plate 108 radially towards axis 101 by width Wb may be referred to as flow adjustor. Therefore, inner circumference 142 of annular bottom plate 108 is smaller than inner circumference 132 of cylindrical member 102. The width Wb may be between 50% and 300% of the length of stator blades in radial direction from inner circumference 122 to outer circumference 120 of annular array 104. The benefit of flow adjustor is to guide slurry into the region of a rotor such as rotor 300 in Figure 3 and to change flow field around the rotor and stator 100 for better mixing and gas dispersion. The effectiveness of suction from opening formed by inner cir- cumference 142 of annular bottom plate into rotor is enhanced. Furthermore, pumping capacity is increased because of enhanced suction intensity. The flow ad- justor enhances turbulence in a low region of a flota ^¬ tion tank in which stator 100 is installed. As a re- suit, the mixing and bubble dispersion efficiency is improved. The idea of flow adjustor changes flow pat ^¬ tern and fluid kinetics around stator 100 and a rotor installed in interior region of stator 100.

Cylindrical member 102 induces an additional vortex around a bottom region of the flotation tank in which stator 100 may be installed. Cylindrical member 102 also enhances turbulence in a lower region of the flotation tank in which stator 100 may be installed.

Stator blades in annular array 104 subdue swirling flow produced by a rotor thereby forming jet flows in radial direction away from stator 100 and to ^¬ ward the wall in the flotation tank in which stator 100 may be installed. This creates favorable condi ^¬ tions for air bubble dispersion and mixing.

The protrusion of annular top plate 106 in relation to outer circumference 120 of annular array of stator blades is to guide air-slurry mixture hori ^¬ zontally in the radial direction away from stator 100 and to avoid undesired upward flow, which would dis- turb froth in the froth layer.

In one embodiment of the invention, stator blades in annular array 104 are thicker at inner circumference 122 of annular array 104 facing axis 101 than at outer circumference 122 facing away from axis 101. The thicknesses of stator blades at the inner circumference 122 of annular array 104 are illustrated with line 180. The thicknesses of stator blades at the outer circumference of annular array 104 are illus ^¬ trated with line 182. The difference in the thickness of each stator blade makes the blades stronger at an interior space defined by inner circumference 122 of annular array 104. The flurry currents to which flanks of the blades are subjected to are stronger closer to the interior space.

Figure 1C illustrates a lateral section view of stator 100 of Figure 1A and Figure IB.

Figure 2A illustrates a stator according to an embodiment of the invention.

In Figure 2A there is a stator 200. Stator 200 comprises an annular top plate 206. To annular top plate 206 is fixed an annular array 204 of stator blades such as blades 224 and 226. Annular top plate 206 is fixed to top surfaces of the stator blades. The fixing is achieved by means of at least one of welding or securing with bolts. Stator 200 also comprises an annular bottom plate 208. To annular bottom plate 208 is fixed annular array 204 of stator blades. Annular bottom plate 208 is fixed to bottom surfaces of the stator blades. The fixing is achieved by means of at least one of welding or securing with bolts.

In one embodiment of the invention, annular top plate 206, annular array 204 of stator blades and annular bottom plate 208 are integrated. The integra ^¬ tion may comprise at least one of welding, securing or attaching with bolts and molding.

Figure 2B illustrates a top view of the sta- tor of Figure 2A. In Figure 2B annular top plate 206 is removed to reveal annular array 204 of stator blades. Stator 200 has axis 201. Annular array 204 comprises a plurality of stator blades such as stator blade 224 and stator blade 226. Annular array 204 of stator blades has in outer circumference 220 and an inner circumference 222. Stator blades in annular array 204 extend transversely and radially from inner circumference 222 to outer circumference 220. The sta- tor blades in annular array 204 may be equally spaced. Annular array 204 of stator blades is mounted on annu ^¬ lar bottom plate 208. Annular bottom plate 208 has an outer circumference 240 and an inner circumference 242. Outer circumference 240 of annular bottom plate 208 may be aligned with outer circumference 220 of an ^¬ nular array of stator blades 204. In Figure 2B a dif ^¬ ference between inner circumference 222 of annular ar- ray 204 and inner circumference 242 of annular bottom plate 208 is referred to with numeral Wb . The exten ^¬ sion of annular bottom plate 208 radially towards axis 201 by width Wb may be referred to as flow adjustor. Therefore, inner circumference 242 of annular bottom plate 208 is smaller than inner circumference 222 of annular array 204. The width Wb may be between 50% and 300% of the length of stator blades in radial direc ^¬ tion from inner circumference 222 to outer circumference 220 of annular array 204. The benefit of flow ad- justor is to guide slurry into the region of a rotor such as rotor 300 in Figure 3 and to change flow field around the rotor and stator 200 for better mixing and gas dispersion. The effectiveness of suction from opening formed by inner circumference 242 of annular bottom plate into rotor is enhanced. Furthermore, pumping capacity is increased because of enhanced suc ^¬ tion intensity. The flow adjustor enhances turbulence in a low region of a flotation tank in which stator 200 is installed. As a result, the mixing and bubble dispersion efficiency is improved. The idea of flow adjustor changes flow pattern and fluid kinetics around stator 200 and a rotor installed in interior region of stator 200.

An opening defined by inner circumference 242 of annular bottom plate 208 guides slurry into the in ^¬ terior space defined by annular array 204 where a ro- tor such as rotor 300 in Figure 3 may be suspended or otherwise mounted.

Stator blades in annular array 204 subdue swirling flow produced by a rotor thereby forming jet flows in radial direction away from stator 200 and to ^¬ ward the wall in the flotation tank in which stator 200 may be installed. This creates favorable condi ^¬ tions for air bubble dispersion and mixing.

In one embodiment of the invention, blades in annular array 204 are thicker at inner circumference 222 of annular array 204 facing axis 201 than at outer circumference 220 facing away from axis 201. The thicknesses of stator blades at the inner circumfer ^¬ ence 222 of annular array 204 are illustrated with line 280. The thicknesses of stator blades at the out ^¬ er circumference 220 of annular array 204 are illus ^¬ trated with line 282. The difference in the thickness of each stator blade makes the blades stronger at an interior space defined by inner circumference 222 of annular array 204. The flurry currents to which flanks of the blades are subjected to are stronger closer to the interior space.

Figure 2C illustrates a lateral section view of the stator of Figure 2A and Figure 2B.

Figure 3 illustrates a rotor in one embodi ^¬ ment of the invention.

In Figure 3 there is illustrated a rotor 300 to be rotated in an interior space defined by an annu ^¬ lar top plate of a stator, an annular array of stator blades and an annular bottom plate of a stator. The annular top plate of a stator may be the annular top plate of Figure 1A or Figure 2A. The annular array of stator blades may be annular array of Figures 1A and 2A. The annular bottom plate of a stator may be the annular bottom plate of Figures 1A and 2A. The interior space may be also defined by a cylindrical member, on top of which the annular array of stator blades is mounted. Rotor 300 comprises a rotor annular top plate 310. Rotor annular top plate 310 has an inner circumference which allows an air supply pipe 320 to be fit ^¬ ted in an opening formed by the inner circumference. Air supply pipe 320 is cylindrical and has a conduit 322 for air. Rotor 300 comprises an annular array 312 of rotor blades which extend in transverse direction from an inner circumference of annular array 312 such as rotor blades 302A, 302B, 302C and 302D. Annular ar- ray 312 of rotor blades extends radially from an inner circumference of array 312 to an outer circumference of array 312. The inner circumference of array 312 forms a slurry space 304. Annular array 312 of rotor blades extends axially from rotor annular top plate 310. Annular array 312 has an outer circumference which is substantially similar to the outer circumference of rotor annular top plate 310 axially close to the rotor annular top plate 310. Outer circumference of annular array 312 diminishes in the axial direction away from rotor annular top plate 310. The outer circumferences of annular array 312 in axial direction form a curvilinear profile when viewed laterally. Blades in annular array 312 have a curvilinear peripheral configuration and extend from an inner radial lo- cation at a first axial end to an outer radial loca ^¬ tion at a second axial close to annular top plate 310. A collar 330 is fitted to encircle a lower axial por ^¬ tion of slurry space 304. Collar 330 is attached to lower axial portions of blades in array 312. Collar 330 guides slurry from a lower portion of flotation tank (now shown) into slurry space 304. Slurry space 304 is also defined a plurality of slurry space walls 308 each of which have at least one opening 306. Be ^¬ tween adjacent rotor blades there may also be openings such as opening 307.

Figure 4 illustrates a rotor and stator ar ^¬ rangement in one embodiment of the invention. The ar- rangement 400 comprises rotor 300 as described in as ^¬ sociation with Figure 3 and stator 200 as described in association with Figure 2A. Annular array 204 of stator blades has inner circumference 222 and outer cir- cumference 220. Annular array 204 of stator blades is mounted on an annular bottom plate, which has an outer circumference 240 and an inner circumference 242. In ^¬ ner circumference 242 of the annular bottom plate is smaller than inner circumference 222 of annular array 204. The difference between inner circumference 242 of the annular bottom plate and inner circumference 222 of annular array 204 of stator blades is illustrated with reference numeral Wb .

Figure 5A illustrates a rotor-stator assembly 500 in one embodiment of the invention. Rotor-stator assembly 500 comprises rotor 300 as described in asso ^¬ ciation with Figure 3. Rotor-stator assembly 500 also comprises stator 200 as described in association with Figure 2. Stator 200 comprises stator top annular plate 206 mounted on annular array 204 of stator blades. Stator annular array 204 is mounted on annular stator bottom plate 208. Cylinder 320 supplying air to slurry space 304 of rotor 300 is also illustrated in Figure 5. Rotor 300 is mounted inside an interior space defined by annular array 204 of stator blades, stator annular top plate 206 and stator annular bottom plate 208. Rotor 300 is depended via cylinder 320 from a superstructure of the flotation tank (not shown) so that collar 330 protrudes by a depth from stator annu- lar bottom plate 208. A space may be left between ro ^¬ tor 300 and stator 200 which allows vibrations in ro ^¬ tor 300. The depth is referred to using reference nu ^¬ meral Db . The depth may be from 10% to 20% of the height of rotor 300. Stator 200 may be mounted on a plurality of legs such as leg 502. The height at which collar 330 of rotor 300 depends above the bottom of the flotation tank is referred to using reference nu- meral Hb . Beneath rotor 300 on the bottom of the flo ^¬ tation tank may be attached a vortex breaker 504 coax ^¬ ial with rotor 300. Vortex breaker may be cruciform.

Figure 5B illustrates a rotor-stator assembly 550, in one embodiment of the invention. In the embod ^¬ iment described in Figure 5B stator 200 has been re ^¬ placed with stator 100 of Figure 1A.

Figure 6 illustrates a flotation tank com ^¬ prising a stator according to an embodiment of the in- vention.

In Figure 6 there is illustrated a flotation tank 600. Flotation tank has a cylindrical side wall 602. Flotation tank 600 comprises a superstructure 604 mounted over flotation tank 600, from which rotor 300 depends. Rotor 300 is suspending in a position relative to a stator 610 where a lower portion of rotor 300 protrudes from an opening in stator annular bottom plate, as described in association with in Figure 5. Stator 610 may be stator 100 illustrated in Figure 1A or stator 200 illustrated in Figure 2A. Stator 610 may be mounted on pillars or legs on the bottom of flota ^¬ tion tank 600. On the bottom of flotation tank 600 may be a cruciform vortex breaker coaxial with rotor 300, as illustrated in Figure 5. Rotor 300 aerates slurry 612 in flotation tank. Rotor 300 receives an air supply via hollow pipe 320 and via a pipeline 608 mounted on superstructure 604. Rotor 300 is rotated by motor 606, which may be an electrical motor. Rotation of ro ^¬ tor blades in rotor 300 cause a pumping effect and a suction of slurry 612 through collar 330 into slurry space 304 within rotor 300. Slurry 612 becomes aerated in slurry space 304 because of incoming air flow into rotor 300 via hollow pipe 320. Aerated slurry escapes from slurry space 304 due to increasing pressure in slurry space 304 and incoming slurry flow via collar 330. Aerated slurry escapes through openings in slurry space walls 308 such as openings 306 and 307. Escaped aerated slurry reaches stator blades of the annular array of stator blades which remove a rotational com ^¬ ponent from aerated slurry flow. Stator blades of sta ^¬ tor 610 also cause a shearing action in relation to rotor blades of rotor 300 which yields small-sized bubbles. Aerated slurry exits as radial jets spaces between stator blades in annular array of stator blades. Bubbles, to the surfaces of which valuable mineral is attached, travel towards a surface of liq- uid in flotation tank 600. Bubbles from a layer of froth 614 which may be recovered from the surface.

The embodiments of the invention described hereinbefore may be used in any combination with each other. At least two of the embodiments may be combined together to form a further embodiment of the invention. A flotation tank, a rotor-stator assembly or a stator to which the invention is related may comprise at least one of the embodiments of the invention de ^¬ scribed hereinbefore.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.