This disclosure concerns mineral processing. In partic ular, this disclosure concerns separation of minerals from their ores by flotation.

BACKGROUND

The energy consumption of comminution processes, espe cially grinding, typically constitutes a significant part of overall energy consumption in mineral pro cessing. As such, significant effort has been invested in reducing energy consumption of grinding. This may generally be achieved by lowering the degree of liber ation of ore, i.e. by increasing the average size of ore particles prior to concentration. Robust so called standard mechanical flotation units are best suited for separation of particles within a size range of approx imately 20 ym to 150 ym. Consequently, alternative so lutions are required to increase the recovery of average particle size of ore beyond 150 ym.

In light of this, it may be desirable to develop new solutions related to separation of the coarser and finer particles.

Generally, there is a need for improving the efficiency of the flotation in processes for liberating valuable minerals from mineral ore.

SUMMARY

The flotation arrangement according to the current dis closure is characterized by what is presented in claim

1. The flotation plant according to the current disclosure is characterized by what is presented in claim 21.

Further, the method according to the current disclosure is characterized by what is presented in claim 23.

The grinding of the ore before flotation gives a rather uneven result, i.e. it gives a wide range of particles of different sizes. Provided is a flotation arrangement, which is able to handle and recover a broad particle size distribution of particles containing both finer and coarser particles in an energy and water efficient way. By first treating the ore using a robust first flotation unit, and then leading the underflow (tailings) to a second flotation unit (for removal of coarser parti cles), and subsequently leading the underflow from the second flotation unit to a third flotation unit (for removal of finer particles) an energy and water effi cient flotation process may be achieved.

DEFINITIONS

This summary of definitions is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

Throughout this specification, "flotation" may refer to separation of a mixture by adhering a substance in said mixture at an interface. In flotation, separation of a mixture may be based on differences in the hydrophobi- city of substances in said mixture. Herein, "separation" may refer to the extraction or removal of a substance from a mixture for use or rejection.

Further, "froth" may refer to a dispersion, comprising a greater portion by volume of flotation gas dispersed as bubbles in lesser portion by volume of a flotation liquid. Generally, froth may or may not be stabilized by solid particles.

In this disclosure, a "layer" may refer to a generally sheet-formed element arranged on a surface. A layer may or may not be path-connected. Some layers may be locally path-connected and disconnected. Although a layer may generally comprise a plurality of sublayers of different material compositions, a "froth layer" may refer to a layer comprising, or comprising substantially, or con sisting essentially of, or consisting of froth.

Throughout this specification, slurry being "fed to a froth layer" may refer to feeding said slurry onto, and/or into, and/or immediately below, e.g., at most 50 cm, or at most 40 cm, or at most 30 cm, or at most 20 cm, or at most 10 cm below, said froth layer. Additionally or alternatively, in embodiments, wherein a height of a launder lip defines a height of an upper surface of a froth layer, slurry being fed to said froth layer may refer to feeding said slurry into a tank at said launder lip height and/or at a position at most 60 cm, or at most 50 cm, or at most 40 cm, or at most 30 cm, or at most 20 cm below said launder lip height.

Herein, a "unit" may refer to a device suitable for or configured to perform at least one specific process. Naturally, a "flotation unit" may then refer to a unit suitable for or configured to subject material to flo tation. A unit may generally comprise one or more parts, and each of the one or more parts may be classified as belonging to an arrangement of said unit.

A "device" may refer to a set of parts of said unit suitable for or configured to perform at least one spe cific subprocess of said process. Generally, a device may comprise any component(s), for example, mechanical, electrical, pneumatic, and/or hydraulic component(s), necessary and/or beneficial for performing its specific subprocess.

In this disclosure, "a means for creating bubbles" is an arrangement for providing flotation gas and may refer to an arrangement of parts of a flotation unit suitable for or configured to supply flotation gas into a tank of said flotation unit. Generally, a flotation gas sup ply arrangement may comprise any part(s) suitable or necessary for supplying flotation gas into a tank, for example, one or more spargers, e.g., jetting and/or cav itation sparger(s), and/or one or more static mixers.

In this specification, a "tank" may refer to a recepta cle suitable for or configured to hold a fluid, for example, a liquid.

Further, "slurry" may refer to a dispersion, comprising solid particles suspended in a continuous phase of flo tation liquid. As such, a "volume of slurry" may refer to a certain amount of slurry. In flotation, slurry may be commonly referred to as coarse slurry or as fine slurry depending on its properties.

Throughout this specification, "classification" may re fer to sizing of solid particles in slurry to form at least two, i.e., two, three, or more, slurry fractions based on differences in the settling velocities of solid particles in said slurry. In practice, classification of slurry results in coarser particles in said slurry being preferentially directed to one or more coarser slurry fractions and finer particles in said slurry be ing preferentially directed to one or more finer slurry fractions.

Throughout this specification, a "agitation" may refer stirring, mixing and/or disturbing a fluid, e.g., a liq uid or a slurry.

Throughout this disclosure, a "fluidized-bed" may refer to a solid-fluid mixture, which exhibits fluid-like properties. As known to the skilled person, a fluidized bed may be maintained by passing pressurized fluid (s), i.e., liquid(s) and/or gas(es), through a particulate medium.

Consequently, "fluid bed flotation" or "fluidized-bed flotation" may refer to flotation, wherein a fluid bed / fluidized bed is maintained in a volume of slurry by suitably passing flotation liquid and/or flotation gas through said volume of slurry, and a "fluidized-bed flo tation unit" may refer to a unit suitable for or con figured to subject material to fluidized-bed flotation.

Generally, maintaining a fluidized bed in a tank of a flotation unit may increase recovery of coarser parti cles. Additionally or alternatively, when coarse slurry is fed to a froth layer for froth-interaction flotation and a fluidized bed is maintained in a volume of slurry below said froth layer, coarser particles of said coarse slurry that have inadvertently dropped into said volume of slurry may settle through said fluidized bed and may be recollected more efficiently to the froth layer.

Throughout this specification, a "dewatering system" refers to a solid-liquid separation arrangement. A solid-liquid separation arrangement may comprise one or more of a dewatering cyclone, a gravitational sedimen tation device, e.g., a thickener or a inclined plate settler; a centrifuge; and a filtration device, e.g., a pressure filter, a tube press, a vacuum filter, or a rotary-drum filter. Preferably, the dewatering system comprises a dewatering cyclone. The dewatering system, such as especially a dewatering cyclone, used in combi nation with a robust first standard flotation section is advantageous, when the dewatering system is located after the first section and before the second flotation section. The standard flotation system evens the stream and minimizes variations in the mass fed to the dewater ing system. This may solve many problems.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood from the following detailed description read in light of the accompanying drawings, wherein:

FIG. 1 shows a schematic view of the flotation arrangement of this disclosure.

FIG. 2 shows a schematic view of the flotation arrangement of this disclosure.

FIG. 3 shows a schematic view of the flotation arrangement of this disclosure.

Unless specifically stated to the contrary, any drawing of the aforementioned drawings may be not drawn to scale such that any element in said drawing may be drawn with inaccurate proportions with respect to other elements in said drawing in order to emphasize certain structural aspects of the embodiment of said drawing.

Moreover, corresponding elements in the embodiments of any two drawings of the aforementioned drawings may be disproportionate to each other in said two drawings in order to emphasize certain structural aspects of the embodiments of said two drawings.

DETAILED DESCRIPTION

Generally, in standard flotation, such as when using standard mechanically agitated flotation cells, under flow from a first primary flotation section may comprise considerable amounts of coarser particles of valuable mineral (s) mixed with finer gangue particles. Standard mechanical flotation cells only separate effectively within a narrow size range of approximately 20 microns to 150 microns depending on the ore type and the liber ation of the ore, and may vary. Thus, coarser particles are not fully recovered by these standard flotation units. This can result in a substantial loss of valuable coarse minerals. One application of so called "coarse flotation" is treatment of the tailings or an underflow stream from a first flotation treatment section to in crease the overall recovery of valuable material. This may be fresh tailings from the ongoing current process or from reclaimed tailings ponds. Any captured minerals from the tailings stream may then be reground and sub jected to further standard flotation to improve product grade. However, this is energy consuming. Excessive classification devices can be utilized, which also are energy consuming.

The current disclosure describes an arrangement, which provides an improvement by treating all solids within the underflow stream from a first flotation section within a second flotation section, such as a coarse flotation unit, and then further treating the underflow from the second flotation section in a third flotation section, such as a fine flotation section.

By using the combination of the different floatation units as disclosed herein, many advantages may be achieved. The first flotation section recovers a large mass pull of a certain range. Thus, the following flo tation sections may be optimized to remove particles with another size distribution. The second flotation section can be adjusted to remove coarse particles. The third flotation unit can be adjusted to remove fine particles. Thereby, also the different flotation sec tions can be sized in an optimal way to achive an overall good yield using the complete flotation arrangement. The mass to be handled vs. the size of the equipment may be optimized when it is clear what particle sizes should be removed in each section. The described combination enables a controlled selection of units and devices, and the yield can be increase.

It may be beneficial to dewater the stream to increase the percentage of solids before the second flotation unit. The amount of solids may be above 50 or above 55 weight-%. This may be done using a dewatering system before the second flotation unit. Removing water and increasing the solids content may improve the efficiency and reduce the size of the second flotation section. In addition, the separated water can be utilized enabling savings in process water usage. A dewatering stage and a dewatering system 5 in combination with the first flotation unit (such as standard mechanically agitated flotation cells) and the second flotation unit (for coarser particles) can provide an advantage. The de watering system is not a classification system.

Coarse flotation processes that can handle high per centages of solids in the feed are preferred. One such process is separation-in-froth or other froth interac tion processes, or fluidized-bed flotation technology. The second flotation unit may require water to maintain its operations, and thus the water separated and recov ered using the dewatering system may be utilized.

The current invention improves upon this by treating the entire solids portion of the tailings stream as a whole to improve both coarse and fine recovery without initial classification.

The tailings from the first flotation section (such as standard flotation) is fed directly in to a second flo tation section (a coarse flotation unit). As described, There may be a dewatering stage of the initial tailings / underflow from the first flotation section, but clas sification is not needed. All minerals and particle sizes should stay in the feed to the second flotation section. The second flotation unit(s) of the second sec tion will recover valuable minerals, which may be led to regrinding and further upgrading in a standard flo tation section. The tailings from the second flotation unit(s) will be treated further in a third flotation section (fine flotation unit(s)). This section will be specifically focused on fine particle recovery. One ex ample of this is the column cell or shockwave treatment, or other cells with pneumatical agitation. Tailings from the third flotation units will be final tailings. Con centrate can be sent back for further upgrading.

The benefits of the arrangement, plant and method of this disclosure include providing:

- Improved recovery of both coarse and fine particles.

- Simplified flow sheet for improved recovery.

- No pre-classification units between the first and the second flotation sections are required, which reduces the upstream equipment requirements.

- Less, or no additional water addition to the flotation process. Since tailings may be directly processed from unit to unit, the percentage of solids most likely would not increase (depending on yield to concentrate), or if they did increase would not increase much. This would negate the need to add process water to maintain a per centage of solids below a maximum desired value.

- Smaller unit size of the second flotation unit may be achieved by first using a robust first standard flota tion system for removing a large mass of valuable mate rial. Thus, the underflow from the first flotation sys tem is significantly smaller than the feed to the first flotation system.

The arrangement, plant and method of this disclosure provides a way to improve the recovery of the flotation process in an energy and water effective way. Flotation uses large amounts of water, so water balance control is important. Robust standard flotation uses less water, so placing such a flotation section first optimizes the water consumption. Further, it evens the stream by re moving certain parts of the mineral ore. There is over all less material to be treated in the more water con suming second (coarse) flotation unit, and the third (fine) flotation unit. After the first flotation unit (such as robust standard technology) and the second flo tation unit (such as coarse flotation unit(s)), third flotation unit(s) providing small bubbles is arranged to recover the last of the valuable material. The oper ation window is the same, because the robust technology can even the stream by removing mass and stabilize the water consumption. The use of water is optimized in the second flotation section and it can be operated in a more stable state.

Thus, described is a flotation arrangement comprising: a first flotation section, a second flotation section, and a third flotation section, wherein: the first flotation section includes at least a first flotation unit (1) comprising a mechanical agitator, the second flotation section includes at least a second flotation unit (2), which is connected to the first flotation unit (1), and the second flo tation unit comprises i) a fluid bed device comprising devices for cre ating a fluid bed, and/or ii) a froth device comprising devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer close proximity thereof, or above the froth layer, or any combinations thereof, and

- the third flotation section includes at least a third flotation unit (3), which is connected to the second floatation unit (2) and comprises devices for pneumatical gas addition, wherein underflow from the first flotation unit (1) is arranged to be led to the second flotation unit (2), and the third flotation unit (3) is connected for receiving underflow from the second flotation unit (2).

According to one embodiment, the first flotation unit (1) is i) at least one device comprising a closed vessel for a pressurized flotation, wherein flotation concentrate is removed by pressure from the ves sel, and/or ii) at least one device comprising a flotation ves sel and:

- an inlet (22) connected for receiving feed to be handled in said flotation vessel and arranged to a lower part of the flotation vessel (21),

- an overflow means (15) for removing flotation con centrate, arranged to an upper part of the flota tion vessel (21), and

- an outlet (25) for removing underflow, arranged to a lower part of the flotation vessel (21).

The above described alternatives represent robust flo tation technology suitable for the first floatation sec tion. According to one embodiment, the first flotation unit (1) comprises means for adding air with mechanical ag itation. According to one embodiment, the mechanical agitator comprises means for mixing a slurry and creat ing bubbles therein. The robust technology using me chanical agitation creates bubbles, which can remove particles with a large particle size distribution. Thus, the mass pull to the following sections is reduced and a rather homogenous underflow from the first flotation section can be provided.

According to one embodiment, the arrangement does not include a hindered bed classification device upstream to the second flotation unit. The flotation arrangement of described provides a solution where a hindered bed classification device is not needed, which is an ad vantage.

According to one embodiment, the arrangement further comprises a dewatering system (5) between the first flo tation unit and the second flotation unit. According to one embodiment, the dewatering system (5) comprises a dewatering cyclone. Dewatering the stream before the second flotation section provides a way to control and optimize the water balance in the process.

According to one embodiment, the first flotation unit (1) comprises at least three flotation vessels arranged in series such that the outlet for removing underflow of a preceding flotation vessel is connected to the inlet of a following flotation vessel. Using at least three flotation vessels enables removing a large part of the valuable material efficiently. An example of suitable robust flotation vessels for the first flota tion unit may be the so-called TankCell®. Treating the ore stream in several vessels may ensure maximum recov ery of the valuable material in the first flotation section.

According to one embodiment, the first flotation unit comprises a flotation vessel and the flotation vessel comprises devices for creating a froth layer.

According to one embodiment, the second flotation unit comprises i) a fluid bed device comprising devices for cre ating a fluid bed, and ii) a froth device comprising devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer close proximity thereof, or above the froth layer, or any combinations thereof.

The advantage is of this embodiment is that a device combining these two technologies may recover an even larger amount of the coarse particles in the feed.

According to one embodiment, the second flotation (2) comprises devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer close proximity layer to close proximity thereof, or above the froth layer, or any combinations thereof. According to one embodiment, the first flotation unit (1) comprises at least one flotation vessel and the flotation vessel com prises a device comprising - an inlet connected for receiving feed to be handled in said flotation vessel and arranged to a lower part of the flotation vessel,

- an overflow means for removing flotation concentrate, arranged to an upper part of the flotation vessel, and

- an outlet for removing underflow, arranged to a lower part of the flotation vessel.

One example of such a flotation vessel is a TankCell®. The robust flotation technology described in this em bodiment is suitable for many kinds of feed, since it does not easily clog. A rater large mass can be removed, so in case a mill is used its operation does not need to be very strictly adjusted, which facilitates opera tion of the flotation arrangement. In particular, the outlet for removing underflow enables the handling of a large range of different particle sizes before the sec ond flotation unit.

According to one embodiment, the first flotation unit (1) comprises a flotation vessel and the flotation ves sel comprises a closed vessel for a pressurized flota tion, wherein flotation concentrate is removed by pres sure from the vessel. The pressure enables moving the slurry / material to be handled up in the vessel and removing it.

According to one embodiment, the third flotation unit (3) comprises a flotation vessel that comprises devices for pneumatical gas addition.

According to one specific embodiment, this flotation vessel comprises a froth separation device comprising devices for creating a froth layer, comprising - an inlet connected for receiving feed to be handled in said flotation vessel and arranged to an upper part of the flotation vessel, and

- an overflow means for removing flotation concentrate, arranged to an upper part of the flotation vessel.

One example of this is a so-called column flotation cell. One advantage with this embodiment is that it can be used without screening or classification before the third flotation unit. It is able to process a rather broad range of particles, even coarse. The whole under flow from the second flotation unit may thus be led to the third flotation unit. For example, if there is only a very little amount of fine material to be removed, the third flotation unit of this embodiment is advantageous, because it can recover the finer material even if there is coarse material in the feed.

According to another very specific embodiment of the third flotation unit, the flotation vessel comprises a downcomer for slurry infeed, the downcomer equipped with a nozzle for feeding pressurized flotation gas in slurry therein. Furthermore, the flotation the downcomer may comprise an outlet nozzle configured to induce a super sonic shockwave into the slurry as it exits the down comer. The flotation arrangement of this embodiment may also comprise a separation unit arranged for preventing large particles entering in the third flotation unit. Further, the separation unit may comprise a grizzly and/or a grating.

According to one embodiment, the flotation arrangement comprises means for leading the underflow from the sec ond flotation unit (2) directly to the third flotation unit (3). In case screening / classification is not needed and the third flotation unit can handle the com plete underflow from the second flotation unit, it is beneficial to feed the underflow directly to the third flotation section.

Further described is a flotation plant comprising the flotation arrangement according to any one of the em bodiments described herein.

According to one embodiment, the plant comprises a pre milling section comprising a mill selected from the group consisting of an autogenous grinding mill, a semi- autogenous grinding mill, and a high-pressure grinding roll or any combination thereof. The combination of pre milling, a first robust flotation section, the second flotation section for coarse particles, and the third flotation section, is especially effective. The standard flotation can handle the material from the pre-milling well and remove a large mass and even the stream (un derflow). Thus, the other flotation sections, when placed after the first section, can be ideally sized and adjusted to remove particles of a certain size distri bution. The stream fed to the second (coarse) flotation unit is more even. The combination can reduce the energy required for milling as there is no need to regrind all underflow from first flotation unit.

Described is also a flotation method wherein the method is performed in an arrangement comprising a first flo tation section, a second flotation section, and a third flotation section, wherein: the first flotation section includes at least a first flotation unit (1) comprising a mechanical ag itator, the second flotation section includes at least a second flotation unit (2), which is connected to the first flotation unit (1), and the second flotation unit comprises i) a fluid bed device comprising devices for creating a fluid bed, and/or ii) a froth device comprising devices for creating a froth layer, wherein particles are fed for interaction with froth layer in the froth layer, under the froth layer close proximity thereof, or above the froth layer, or any combinations thereof, and - the third flotation section includes at least a third flotation unit (3), which is connected to the second floatation unit (2) and comprises devices for pneumatical gas addition, wherein underflow from the first flotation unit (1) is led to the second flotation unit (2), and the underflow from the second flotation unit (2) is led for to the third flotation unit (3).

Figure 1 illustrates one embodiment of the flotation arrangement of this disclosure. It shows a first flota tion unit 1, a second flotation unit 2 and a third flotation unit 3. The figure also shows that the ar rangement includes means for feeding a stream containing feed material to be treated 11. Means for feeding the underflow 12 from the first flotation unit 1 to the second flotation unit 2. An overflow including valuable coarse material is led out from the second flotation unit via line 22. It can be led for example to recovery via regrinding. The underflow from the second flotation unit 2 is led to the third flotation unit 3 via line 21. Overflow 31 comprising the valuable fine material to be recovered, and underflow 32 (tailings).

Figure 2 illustrates another embodiment of the flotation arrangement of this disclosure. At least part of the underflow from the second flotation unit 2 is lead to a screening device 4, wherein the underflow is separated into tailings and a stream 21, which is led to the third flotation unit 3 to be further treated.

Figure 3 illustrates yet another embodiment of the flo- tation arrangement of this disclosure. The arrangement further comprises a dewatering system 5 between the first flotation unit 1 and the second flotation unit 2. A liquid / water steam 52 is separate in the dewatering system and a dewatered stream 51 is led to the second flotation unit 2. Optionally, at least part of the stream 52 may be recirculated to the second flotation unit 53.

It will be understood that any benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. The term "comprising" is used in this specification to mean including the feature(s) or act(s) followed there after, without excluding the presence of one or more additional features or acts. It will further be under- stood that reference to 'an' item refers to one or more of those items.