AU2018434575B2 - Flotation cell - Google Patents

Abstract

A flotation cell (1) is disclosed for treating particles suspended in slurry and for separating the slurry into an underflow (400) and an overflow (500). The flotation cell comprises a flotation tank (10) with a centre (11), a perimeter (12), a substantially horizontal level bottom (13), and a side wall (14); a launder (2) and a launder lip (21) surrounding the perimeter (12) of the tank (11); and a bottom structure (7) arranged on the bottom (13), and having a shape that allows particles suspended in slurry to be mixed in a mixing zone (A) over the bottom structure, and to settle down in a settling zone (B) surrounding the bottom structure. The flotation tank further comprises blast tubes (4) for introducing slurry infeed (100) into the tank. In addition, a flotation line and use of the flotation line are disclosed.

Description

FLOTATION CELL TECHNICAL FIELD

The current disclosure relates to a flotation cell

for separating valuable material containing particles from

particles suspended in slurry and to a flotation line and its

use.

SUMMARY

.0 A flotation cell is provided for treating particles

suspended in slurry and for separating the slurry into an

underflow and an overflow. The flotation cell comprises a

flotation tank comprising a centre, a perimeter, a

substantially horizontal, level bottom, and a side wall; a

.5 launder and a launder lip surrounding the perimeter of the

tank; and a bottom structure arranged on the bottom and having

a shape that allows particles suspended in slurry to be mixed

in a mixing zone over the bottom structure, and to settle down

in a settling zone surrounding the bottom structure. The !0 flotation cell is characterized in that the flotation tank

further comprises blast tubes for introducing slurry infeed

into the flotation tank. A blast tube comprises an inlet nozzle

for feeding slurry infeed into the blast tube; an inlet for

pressurized gas, the slurry infeed subjected to the pressurized

gas as it is discharged from the inlet nozzle; an elongated

chamber arranged to receive under pressure the slurry infeed;

and an outlet nozzle configured to restrict flow of slurry

infeed from the outlet nozzle, and to maintain slurry infeed

in the elongated chamber under pressure; and in that the blast

tubes are disposed at a position relative to the bottom

structure so as to induce mixing at the mixing zone.

According to another aspect, a flotation line is

provided. The flotation line comprises a number of fluidly connected flotation cells, and at least one of the flotation cells is a flotation cell as described above.

According to a further aspect, use of the flotation

line is intended for recovering particles comprising a valuable

material suspended in slurry.

With the flotation cell described herein, the

recovery of fine particles in a flotation process may be

improved. The particles may, for example, comprise mineral ore

particles such as particles comprising a metal.

.0 In froth flotation for mineral ore, upgrading the

concentrate is directed to an intermediate particle size range

between 40 pm to 150 pm. Fine particles are thus particles

with a diameter of 0 to 40 pm, and ultrafine particles can be

identified as falling in the lower end of the fine particle

.5 size range. Coarse particles have a diameter greater than 150

pm. In froth flotation of coal, upgrading the concentrate is

directed to an intermediate particle size range between 40 pm

to 300 pm. Fine particles in coal treatment are particles with

a diameter of 0 to 40 pm, and ultrafine particles those that !0 fall into the lower end of the fine particle size range. Coarse

coal particles have a diameter greater than 300 pm.

Recovering very coarse or very fine particles is

challenging, as in a traditional mechanical flotation cell,

fine particles are not easily entrapped by flotation gas

bubbles and may therefore become lost in the tailings.

Typically in froth flotation, flotation gas is introduced into

a flotation cell or tank via a mechanical agitator. The thus

generated flotation gas bubbles have a relatively large size

range, typically from 0.8 to 2.0 mm, or even larger, and are

not particularly suitable for collecting particles having a

finer particle size.

Fine particle recovery may be improved by increasing

the number of flotation cells within a flotation line, or by

recirculating the once-floated material (overflow) or the tailings flow (underflow) back into the beginning of the flotation line, or to precedent flotation cells. A cleaner flotation line may be used in order to improve recovery of fine particles. In addition, a number of flotation arrangements employing fine flotation gas bubbles or even so-called microbubbles have been devised. Introduction of these smaller bubbles or microbubbles may be done prior to feeding the slurry into the flotation cell, i.e. the ore particles are subjected to fine bubbles in a feed connection or the like to promote .0 formation of ore particle-fine bubble agglomerates, which may then be floated in flotation cells such as flash flotation cells or column cells. Alternatively, fine bubbles or microbubbles may be introduced directly into the flotation cell, for example, by spargers utilizing cavitation. These .5 kinds of solutions are not necessarily feasible in connection with mechanical flotation cells, as the turbulence caused by mechanical agitation may cause the ore particle-fine bubble agglomerates to disintegrate before they are able to rise into the froth layer to be collected into overflow and thus !0 recovered. Column flotation cells act as three phase settlers where particles move downwards in a hindered settling environment counter-current to a flow of rising flotation gas bubbles generated by spargers located near the bottom of the cell. While column flotation cells may improve the recovery of finer particles, the particle residence time is dependent on settling velocity, which may impact on the flotation of large particles. In other words, while the aforementioned flotation solutions may have a beneficial effect for recovery of fine particles, the overall flotation performance (recovery of all valuable material, grade of recovered material) may be undermined by the negative effect on recovery of larger particles.

To overcome the above problems, so-called pneumatic

flotation cells are used, where flotation gas is introduced in

a high-shear device such as a downcomer with slurry infeed,

thereby creating finer flotation gas bubbles that are able

entrap also finer particles already during the bubble formation

in the blast tube. However, such high-throughput flotation

cells may require a vacuum to be created in the downcomer to

effectively achieve the required bubble formation rate to

entrap the desired particles in the short time slurry infeed

.0 resides in the blast tube.

Once having exited the downcomer, the flotation gas

bubble- particle agglomerates rise immediately towards the

froth layer on the top part of the flotation cell, and no

further entrapment of particles take place in the part of the

.5 flotation cell downwards from the blast tube outlet. This may

lead to significant part of particles comprising a desired

material (mineral) to simply drop to the bottom of the

flotation tank and ending up in tailings, which reduces the

recovery rate of the flotation cell. !0 However, typically the so-called high-throughput

flotation cells or pneumatic flotation cells of the Jameson

cell type do not include any flow restriction for controlling

the pressure within the downcomer after the formation of

flotation air bubble-particle agglomerates has taken place.

Such control of pressure is advantageous also in view of the

pressure at which flotation gas bubbles are formed (effect on

bubble size), but also for the adjustment of relative pressure

at which they are to be used in the flotation tank. In that

way, the coalescence of bubbles may be minimized after their

formation. This is especially advantageous, as the rate of

entrapment of particles by flotation gas bubbles decreases as

the bubble size increases (provided that the air to liquid

ratio remains the same).

In addition, the so-called high-throughput flotation cells may be used in coal liberation operations, where there typically is a flotation line comprising one or two such flotation cells at the end of the liberation circuit for the recovery of especially fine coal particles. In the liberation circuit, a process water recirculation system circulating water from the end part of the circuit (i.e. from the flotation line and a dewatering circuit) back to the front circuit (beginning of the liberation circuit). Flotation chemicals, .0 especially frothers, typically cause problems in the processes preceding the flotation line. The problems may be alleviated to some extent by minimizing the use of frothers in the flotation line, but if not enough frother is added into the flotation process, the froth formation in blast tubes according .5 to state of the art may suffer, which leads to unstable process conditions and especially unstable downcomer operation and froth layer in a flotation cell, which in turn affects the recovery of desired particles negatively. Recovery of particles within the entire particle size distribution of a !0 slurry is affected as bubble size increases with lower frother dosage, in particular that of coarse particles. In prior art downcomers, flotation gas is introduce in a self-aspirating manner due to the formation of a vacuum within the downcomer. There is a very short residence time of flotation air to be entrained into the slurry, so the system is very sensitive to process variations. Frothers need to be constantly added to overcome the effect of restriction to air flowrate needed to maintain or even increase the vacuum inside the downcomer to keep the conditions as constant as possible for bubble-particle engagement, as frothers prevent bubbles from coalescing and rising back into the airspace not filled by slurry inside the downcomer. However, adding an amount of frothers required by the steady utilization of a prior art downcomer creates problems in other parts of the process, particularly in coal operations, as described above. Therefore the solution has been to decrease the frother dosage, which affects the downcomer vacuum, bubble formation, as well as bubble size and surface area negatively, and decreases recovery of desired particles significantly, making the high-throughput flotation cells known in the prior art inefficient in that application. By using a flotation cell disclosed herein, the amount of frother required to optimize the flotation process may be .0 significantly reduced without significantly compromising bubble formation, bubble to particle engagement, stable froth layer formation or the recovery of desired material. At the same time, problems associated with recirculating process water from downstream circuit to front circuit can be .5 alleviated. A blast tube operating under pressure is completely independent of the flotation tank. A better flotation gas flowrate may be reached, and finer bubbles created, and frother usage optimized, as the blast tube operation is not dependent of frother dosage. !0 In the solutions known from prior art, problems relate especially to limitations to the amount of flotation gas that can be supplied relative to the amount of liquid flowing through the downcomer, and to the need for relatively high concentrations of frothers or other expensive surface-active agents to produce small bubbles. With the flotation cell presented here, flotation of fine and ultrafine particles comprising, for example, mineral ore or coal may be improved by reducing the size of the flotation gas bubbles introduced to slurry infeed in a blast tube, by increasing the flotation gas supply rate relative to the flow rate of particles suspended in the slurry, and by increasing the shear intensity or energy dissipation rate either in or adjacent to the blast tube. The probability of finer particles attaching to or being entrapped by smaller flotation gas bubbles is increased, and the recovery rate of desired material such as a mineral or coal, improved. In a flotation cell disclosed herein, sufficiently small flotation gas bubbles, so-called ultra-fine bubbles, may be created to ensure efficient entrapment of fine ore particles. Typically, ultra-fine bubbles may have a bubble size distribution of 0.05 mm to 0.7 mm. For example, decreasing the mean flotation gas bubble size to a diameter of 0.3 to 0.4 mm means that the number of bubbles in 1 m3 of slurry may be as high as 30 to 70 million, and the total mean surface area 2 .0 of the bubbles 15 to 20 M . In contrast, if the mean bubble 2 size is around 1 mm, the number of bubbles in 1 m of slurry 2 is around 2 million, and the total mean surface area 6 M . In the flotation cell it may thus be possible to reach 2.5 to 3 times higher bubble surface area than in flotation cells

_5 according to prior art solutions. It goes without saying that

the effect of such increase in bubble surface area in recovery

of valuable material comprising particles is significant.

At the same time, recovery of coarser particles may

be kept at an acceptable level by achieving a high flotation !0 gas fraction in the slurry, and by the absence of high

turbulence areas in the region below the froth layer. For

example, the known benefits of mechanical flotation cells may

be employed, even though there may not necessarily be any

mechanical agitation present in the flotation cell. Further,

the upwards motion of slurry or pulp within the flotation tank

increases the probability of also coarser particles rise

towards the froth layer with the flow of slurry.

One of the effects that may be gained with the

flotation cell disclosed herein is the increased depth or

thickness of a froth layer. A thicker froth layer contributes

to increased recovery of smaller particles, and a separate

froth washing step, typical for column flotation cells, may be

discarded.

By disposing a number of blast tube blast tubes into the flotation cell, the probability of collisions between flotation gas bubbles, as well as between gas bubbles and particles can be increased. Having a number of blast tubes may ensure an improved distribution of flotation gas bubbles within a flotation tank, and the bubbles exiting the blast tubes are distributed evenly throughout the flotation tank, the distribution areas of individual blast tubes have the possibility of intersecting each other and converging, thus .0 promoting an extensively even flotation gas bubble distribution into the flotation tank, which in turn may affect the recovery of especially smaller particles beneficially, and also contribute to the aforementioned even and thick froth layer. When there are several blast tubes, collisions between _5 flotation gas bubbles and/or particles in the slurry infeed from different blast tubes are promoted as the different flows intermingle and create local mixing subzones. As the collisions are increased, more bubble-particle agglomerates are created and captured into the froth layer, and therefore recovery of !0 valuable material may be improved. By generation of fine flotation gas bubble or ultra fine bubbles, by bringing them into contact with the particles, and by controlling the flotation gas bubble- particle agglomerates-liquid mixture of slurry, it may be possible to maximize the recovery of hydrophobic particles into the forth layer and into the flotation cell overflow or concentrate, thus increasing the recovery of desired material irrespective of its particle size distribution within the slurry. It may be possible to achieve a high grade for a part of the slurry stream, and at the same time, high recovery for the entire slurry stream passing through a flotation line. By disposing the blast tubes at a position relative to the bottom structure, slurry mixing can be induced and improved at a mixing zone surrounding the bottom structure.

For example, the outlet nozzles of the blast tubes may be disposed at a suitable depth, i.e. disposing them at a specific vertical distance from the launder lip, the distribution of flotation gas bubbles may be optimized in an even and constant manner. As the residence time of bubbles within a mixing zone may be kept high enough by a suitable depth of the blast tube outlet nozzles, the bubbles may be able to contact and adhere to the fine particles in the slurry efficiently, thus improving the recovery of smaller particles, and also promoting froth .0 depth, stability and evenness at the top of the flotation tank. By a "mixing zone" is meant herein a vertical part or region of the flotation tank in which active mixing of particles suspended in slurry with flotation gas bubbles takes place. In addition to this mixing zone created into an entire .5 vertical section of the flotation tank, separate and regional individual mixing subzones may be created at areas where slurry flows directed radially outwards by individual impingers meet and become intermingled. This may further promote contacts between flotation gas bubbles and particles, thereby !0 increasing the recovery of valuable particles. Further, this additional mixing may eliminate the need for a mechanical mixer for suspending solids in the slurry. By a "settling zone" is meant a vertical part of region of the flotation tank in which particles not associated with flotation gas bubbles or otherwise not able to rise towards the froth zone on the top part of the flotation tank descend and settle towards the tank bottom to be removed in the tailings as underflow. The settling zone is below the mixing zone. The flotation cell, and the flotation line and its use disclosed herein have the technical effect of allowing the flexible recovery of various particle sizes, as well as efficient recovery of valuable mineral containing ore particles from poor ore raw material with relatively low amounts of valuable mineral initially. The advantages provided by the structure of the flotation line allow the accurate adjustment of the flotation line structural parameters according to the target valuable material at each installation.

By treating the slurry according to this disclosure,

recovery of valuable material containing particles may be

increased. The initial grade of recovered material may be

lower, but the material (i.e. slurry) is also thus readily

prepared for further processing, which may include, for

.0 example, regrinding and/or cleaning.

In this disclosure, the following definitions are

used regarding flotation.

Basically, flotation aims at recovering a concentrate

of ore particles comprising a valuable mineral. By concentrate

.5 herein is meant the part of slurry recovered in overflow or

underflow led out of a flotation cell. By valuable mineral is

meant any mineral, metal or other material of commercial value.

Flotation involves phenomena related to the relative

buoyancy of objects. The term flotation includes all flotation !0 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 or

nitrogen or any other suitable medium, to the 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 added to the

feedstock subject of flotation (slurry or pulp) by a number of

different ways.

A flotation cell meant for treating mineral ore

particles suspended in slurry by flotation. Thus, valuable

metal-containing ore particles are recovered from ore

particles suspended in slurry. By flotation line herein is meant a flotation arrangement where a number of flotation cells are arranged in fluid connection with each other so that the underflow of each preceding flotation cell is directed to the following or subsequent flotation cell as an infeed until the last flotation cell of the flotation line, from which the underflow is directed out of the line as tailings or reject flow. Slurry is fed through a feed inlet to the first flotation cell of the flotation line for initiating the flotation process. A flotation line may be a part of a larger flotation

.0 plant or arrangement containing one or more flotation lines.

Therefore, a number of different pre-treatment and post

treatment devices or stages may be in operational connection

with the components of the flotation arrangement, as is known

to the person skilled in the art.

_5 The flotation cells in a flotation line are fluidly

connected to each other. The fluid connection may be achieved

by different lengths of conduits such as pipes or tubes, the

length of the conduit depending on the overall physical

construction of the flotation arrangement. Alternatively, the !0 flotation cells may be arranged in direct cell connection with

each other. By direct cell connection herein is meant an

arrangement, whereby the outer walls of any two subsequent

flotation cells are connected to each other to allow an outlet

of a first flotation cell to be connected to the inlet of the

subsequent flotation cell without any separate conduit. A

direct contact reduces the need for piping between two adjacent

flotation cells. Thus, it reduces the need for components

during construction of the flotation line, speeding up the

process. Further, it might reduce sanding and simplify

maintenance of the flotation line. The fluid connections

between flotation cells may comprise various regulation

mechanisms.

By "neighbouring", "adjacent", or "adjoining"

flotation cell herein is meant the flotation cell immediately following or preceding any one flotation cell, either downstream or upstream, or either in a rougher flotation line, in a scavenger flotation line, or the relationship between a flotation cell of a rougher flotation line and a flotation cell of a scavenger flotation line into which the underflow from the flotation cell of the rougher flotation line is directed.

By a "flotation cell" is herein meant a tank or vessel

in which a step of a flotation process is performed. A

.0 flotation cell is typically cylindrical in shape, the shape

defined by an outer wall or outer walls. The flotation cells

regularly have a circular cross-section. The flotation cells

may have a polygonal, such as rectangular, square, triangular,

hexagonal or pentagonal, or otherwise radially symmetrical

_5 cross-section, as well. The number of flotation cells may vary

according to a specific flotation line and/or operation for

treating a specific type and/or grade of ore, as is known to

a person skilled in the art.

The flotation cell may be a froth flotation cell, !0 such as a mechanically agitated cell, for example, a TankCell,

a column flotation cell, a Jameson cell, or a dual flotation

cell. In a dual flotation cell, the cell comprises at least

two separate vessels, a first mechanically agitated pressure

vessel with a mixer and a flotation gas input, and a second

vessel with a tailings output and an overflow froth discharge,

arranged to receive the agitated slurry from the first vessel.

The flotation cell may also be a fluidized bed flotation cell

(such as a HydroFloat TM cell), wherein air or other flotation

gas bubbles which are dispersed by the fluidization system

percolate through the hindered-setting zone and attach to the

hydrophobic component altering its density and rendering it

sufficiently buoyant to float and be recovered. In a fluidized

bed flotation cell axial mixing is not needed. The flotation

cell may also be an overflow flotation cell operated with constant slurry overflow. In an overflow flotation cell, the slurry is treated by introducing flotation gas bubbles into the slurry and by creating a continuous upwards flow of slurry in the vertical direction of the first flotation cell. At least part of the valuable metal containing ore particles are adhered to the gas bubbles and rise upwards by buoyancy, at least part of the valuable metal containing ore particles are adhered to the gas bubbles and rise upwards with the continuous upwards flow of slurry, and at least part of the valuable metal .0 containing ore particles rise upwards with the continuous upwards flow of slurry. The valuable metal containing ore particles are recovered by conducting the continuous upwards flow of slurry out of the at least one overflow flotation cell as slurry overflow. As the overflow cell is operated with .5 virtually no froth depth or froth layer, effectively no froth zone is formed on the surface of the pulp at the top part of the flotation cell. The froth may be non-continuous over the cell. The outcome of this is that more valuable mineral containing ore particles may be entrained into the concentrate !0 stream, and the overall recovery of valuable material may be increased. All of the flotation cells of a flotation line may be of a single type, that is, rougher flotation cells in the rougher part, scavenger flotation cells in the scavenger part, and scavenger cleaner flotation cells of the scavenger cleaner flotation line may be of one single flotation cell type so that the flotation arrangement comprises only one type of flotation cells as listed above. Alternatively, a number of flotation cells may be of one type while other cells are of one or more type so that the flotation line comprises two or more types of flotation cells as listed above. Depending on its type, the flotation cell may comprise a mixer for agitating the slurry to keep it in suspension. By a mixer is herein meant any suitable means for agitating slurry within the flotation cell. The mixer may be a mechanical agitator. The mechanical agitator may comprise a rotor-stator with a motor and a drive shaft, the rotor-stator construction arranged at the bottom part of the flotation cell. The cell may have auxiliary agitators arranged higher up in the vertical direction of the cell, to ensure a sufficiently strong and continuous upwards flow of the slurry.

A flotation cell may comprise one or more froth

crowders. A froth crowder herein is meant a froth blocker, a

.0 froth baffle, or a crowding board, or a crowding board device,

or any other such structure or side structure, for example, a

sidewall, inclined or vertical, having a crowding effect, i.e.

a crowding sidewall, which can also be a crowding sidewall

internal to the flotation tank, i.e. an internal perimeter

.5 crowder.

By utilizing a froth crowder, it may be possible to

direct so-called "brittle froth", i.e. a loosely textured froth

layer comprising generally larger flotation gas bubbles

agglomerated with the mineral ore particles intended for !0 recovery, more efficiently and reliably towards the froth

overflow lip and froth collection launder. A brittle froth can

be easily broken, as the gas bubble-ore particle agglomerates

are less stable and have a reduced tenacity. Such froth or

forth layer cannot easily sustain the transportation of ore

particles, and especially coarser particles, towards the froth

overflow lip for collection into the launder, therefore

resulting in particle drop-back to the pulp or slurry within

the flotation cell or tank, and reduced recovery of the desired

material. Brittle froth is typically associated with low

mineralization, i.e. gas bubble-ore particle agglomerates with

limited amounts of ore particles comprising a desired mineral

that have been able to attach onto the gas bubbles during the

flotation process within a flotation cell or tank. The problem

is especially pronounced in large-sized flotation cells or tanks with large volume and/or large diameter. With the flotation cell at hand, it may be possible to crowd and direct the froth towards the froth overflow lip, to reduce the froth transportation distance (thereby reducing the risk of drop back), and, at the same time, maintain or even reducing the overflow lip length. In other words, the handling and directing of the froth layer in a froth flotation cell or tank may become more efficient and straightforward. It may also be possible to improve froth recovery and .0 thereby valuable mineral particle recovery in large flotation cells or tanks from brittle froth specifically in the later stages of a flotation line, for example, in the rougher and/or scavenger stages of a flotation process. Further, with the flotation cell described herein, _5 the area of froth on the surface of the slurry inside a flotation tank may be decreased in a robust and simple mechanical manner. At the same time, the overall overflow lip length in a froth flotation unit may be decreased. Robust in this instance is to be taken to mean both structural simplicity !0 and durability. By decreasing the froth surface area of a flotation unit by a froth crowder instead of adding extra froth collection launders, the froth flotation unit as a whole may be a simpler construction, for example, because there is no need to lead the collected froth and/or overflow out of the added crowder. In contrast, from an extra launder, the collected overflow would have to be led out, which would increase the constructional parts of the flotation unit. Especially in the downstream end of a flotation line, the amount of desired material that can be trapped into the froth within the slurry may be very low. In order to collect this material from the froth layer to the froth collection launders, the froth surface area should be decreased. By arranging a froth crowder into the flotation tank, the open froth surface between the froth overflow lips may be controlled. The crowder may be utilized to direct or guide the upwards-flowing slurry within the flotation tank closer to a froth overflow lip of a froth collection launder, thereby enabling or easing froth formation very close to the froth overflow lip, which may increase the collection of valuable ore particles. The froth crowder may also influence the overall convergence of flotation gas bubbles and/or gas bubble-ore particle agglomerates into the froth layer. For example, if the gas bubbles and/or gas bubble-ore particle agglomerate .0 flow becomes directed towards the centre of a flotation tank, a froth crowder may be utilized to increase the froth area at the perimeter of the tank, and/or closer to any desired froth overflow lip. In addition, it may be possible to reduce the open froth surface in relation to the lip length, thereby _5 improving the efficiency of recovery in the froth flotation cell. By a "blast tube" is meant a dual high-shear device in which flotation gas is introduced into slurry infeed, thereby creating finer flotation gas bubbles that are able !0 entrap also finer particles already during the bubble formation in the blast tube. In particular, a blast tube in the flotation cell disclosed herein operates under pressure, and not vacuum is needed. By "overflow" herein is meant the part of the slurry collected into the launder of the flotation cell and thus leaving the flotation cell. Overflow may comprise froth, froth and slurry, or in certain cases, only or for the largest part slurry. In some embodiments, overflow may be an accept flow containing the valuable material particles collected from the slurry. In other embodiments, the overflow may be a reject flow. This is the case in when the flotation arrangement, plant and/or method is utilized in reverse flotation. By "underflow" herein is meant the fraction or part of the slurry which is not floated into the surface of the slurry in the flotation process. In some embodiments the underflow may be a reject flow leaving a flotation cell via an outlet which typically is arranged in the lower part of the flotation cell. Eventually the underflow from the final flotation cell of a flotation line or a flotation arrangement may leave the entire arrangement as a tailings flow or final residue of a flotation plant. In some embodiments, the underflow may be an accept flow containing the valuable mineral particles. This is the case in when the flotation cell or

.0 flotation line is utilized in reverse flotation.

By "reverse flotation" herein is meant an inverse

flotation process typically utilized in the recovery of iron.

In that case, the flotation process is directed for collecting

the non-valuable part of the slurry flow into the overflow.

_5 The overflow in reverse flotation process for iron contains

typically silicates, while the valuable iron-containing

mineral particles are collected in the underflow. Reverse

flotation may also be used for industrial minerals, i.e.

geological mineral mined for their commercial values which are !0 not fuel, nor sources of metals, such as bentonite, silica,

gypsum, and talc.

By "downstream" herein is meant the direction

concurrent with the flow of slurry towards the tailings

(forward current, denoted in the figures with arrows), and by

upstream herein is meant the direction counter current with or

against the flow of slurry.

By "concentrate" herein is meant the floated part or

fraction of slurry of ore particles comprising a valuable

mineral. In normal flotation, concentrate is the part of the

slurry that is floated into the froth layer and thereby

collected into the launders as overflow. A first concentration

concentrate may comprise ore particles comprising one valuable

mineral, whereas a second concentration concentrate may

comprise ore particles comprising another valuable mineral.

Alternatively, the distinctive definitions first, second, may refer to two concentrations concentrates of ore particles comprising the same valuable mineral but two distinctly different particle size distributions. By a "rougher flotation, rougher part of the flotation line, rougher stage and/or rougher cells" herein is meant a flotation stage that produces a concentrate. The objective is to remove a maximum amount of the valuable mineral at as coarse a particle size as practical. The primary objective of a .0 rougher stage is to recover as much of the valuable minerals as possible, with less emphasis on the quality of the concentrate produced. The rougher concentrate is normally subjected to further stages of cleaner flotation in a rougher cleaner .5 flotation line to reject more of the undesirable minerals that have also reported to the froth, in a process known as cleaning. The product of cleaning is known as cleaner concentrate or final concentrate. Rougher flotation is often followed by scavenger !0 flotation that is applied to the rougher tailings. By a scavenger flotation, a scavenger part of the flotation line, scavenger stage and/or a scavenger cell is meant a flotation stage wherein the objective is to recover any of the valuable mineral material that was not recovered during the initial rougher stage. This might be achieved by changing the flotation conditions to make them more rigorous than the initial roughing, or, in some embodiments of the flotation cell, by the introduction of microbubble into the slurry. The concentrate from a scavenger cell or stage could be returned to the rougher feed for re-floating or directed to a regrinding step and thereafter to a scavenger cleaner flotation line. By "cleaner flotation, a rougher/scavenger cleaner line, cleaner/cleaning stage and/or a cleaner cell" is meant a flotation stage wherein the objective of cleaning is to produce as high a concentrate grade as possible. By "pre-treatment and/or post-treatment and/or further processing" is meant, for example, comminution, grinding, separation, screening, classification, fractioning, conditioning or cleaning, all of which are conventional processes as known to a person skilled in the art. A further processing may include also at least one of the following: a further flotation cell, which may be a conventional cleaner .0 flotation cell, a recovery cell, a rougher cell, or a scavenger cell. By "slurry surface level" herein is meant the height of the slurry surface within the flotation cell as measured from the bottom of the flotation cell to the launder lip of .5 the flotation cell. In effect, the height of the slurry is equal to the height of a launder lip of a flotation cell as measured from the bottom of the flotation cell to the launder lip of the flotation cell. For example, any two subsequent flotation cells may be arranged in a stepwise fashion in a !0 flotation line so that the slurry surface level of such flotation cells is different (i.e. the slurry surface level of the first of such flotation cells is higher than the slurry surface level of the second of such flotation cells). This difference in the slurry surface levels is defined herein as "step" between any two subsequent flotation cells. The step or the difference in slurry surface levels is a difference allowing the flow of slurry be driven by gravity or gravitation force, by creating a hydraulic head be-tween the two subsequent flotation cells. By a "flotation line" herein is meant an assembly or arrangement comprising a number of flotation units or flotation cells in which a flotation stage is performed, and which are arranged in fluid connection with each other for allowing either gravity-driven or pumped slurry flow between flotation cells, to form a flotation line. In a flotation line, a number of flotation cells are arranged in fluid connection with each other so that the underflow of each preceding flotation cell is directed to the following or subsequent flotation cell as a infeed until the last flotation cell of the flotation line, from which the underflow is directed out of the line as tailings or reject flow. It is also conceivable that a flotation line may comprise only one flotation stage performed either in one flotation cell or, for example, in two or more

.0 parallel flotation cells.

Slurry is fed through a feed inlet to the first

flotation cell of the flotation line for initiating the

flotation process. Flotation line may be a part of a larger

treatment plant containing one or more flotation lines, and a

.5 number of other process stages for the liberation, cleaning

and other treatment of a desired material. Therefore, a number

of different pre-treatment and post-treatment devices or

arrangements may be in operational connection with the

components of the flotation line, as is known to the person

!0 skilled in the art.

By "ultra-fine bubbles" herein is meant flotation gas

bubbles falling into a size range of 0.05 mm to 0.7 mm,

introduced into the slurry in a blast tube. In contrast, "normal" flotation gas bubbles utilized in froth flotation

display a size range of approximately 0.8 to 2 mm. Larger

flotation gas bubbles may have a tendency to coalesce into

even larger bubbles during their residence in the mixing zone

where collisions between particles and flotation gas bubbles,

as well as only between flotation gas bubbles take place. As

ultra-fine bubbles are introduced into slurry infeed prior to

its feeding into a flotation tank, such coalescence is not

likely to happen with ultra-fine bubbles, and their size may

remain smaller throughout their residence in the flotation cell, thereby affecting the ability of the ultra-fine bubbles to catch fine particles.

In an embodiment of the flotation cell, the outlet

nozzle is configured to produce a supersonic shockwave into

the slurry infeed, the supersonic shockwave inducing formation

of flotation gas bubble - particle agglomerates.

A supersonic shockwave is created when the velocity

of slurry infeed passing through the outlet nozzle exceeds the

speed of sound, i.e. the flow of slurry infeed becomes choked

.0 when the ratio of the absolute pressure upstream the outlet

nozzle to the absolute pressure downstream of the throttle of

the outlet nozzle exceeds a critical value. When the pressure

ratio is above the critical value, flow of slurry infeed

downstream of the throttle part of the outlet nozzle becomes

_5 supersonic and a shock wave is formed. Small flotation gas

bubbles in slurry infeed mixture are split into even smaller

by being forced through the shock wave, and forced into contact

with hydrophobic ore particles in slurry infeed, thus creating

flotation gas bubble-ore particle agglomerates. The supersonic !0 shockwave produced into the slurry infeed at the outlet nozzle

discharge carries into the slurry within the flotation tank

immediately adjacent to an outlet nozzle, thereby promoting

the formation of flotation gas bubbles also in the slurry

outside the outlet nozzles. After exiting the outlet nozzle,

fine ore particles may contact the small flotation gas bubbles

a second time, as there are several of such blast tubes/outlet

nozzles discharging into a common mixing area in which the

probability of secondary contacts between bubbles and

particles is increased by the intermixing flows of slurry

exiting the blast tubes.

In an embodiment of the flotation cell, a height of

the flotation tank, measured as the distance from the bottom

to the launder lip, is at the perimeter of the flotation tank

at most 20 % lower than at the centre of the flotation tank.

In an embodiment of the flotation cell, the vertical

cross-section of the bottom structure is a functional triangle

comprising a first vertex pointing away from the bottom of the

flotation tank, a second vertex and a third vertex; a first

side between the first vertex and the second vertex; a second

side between the first vertex and the third vertex; and a base

between the second and third vertexes on the bottom of the

flotation tank; and a central axis substantially concentric

with the centre of the flotation tank.

.0 In a further embodiment of the flotation cell, the

base angle between the first side and the base, or second side

and the base in relation to the bottom of the flotation tank

is 20 to 600.

In a further embodiment of the flotation cell, the

.5 included angle between the first side and the second side is

20 to 1000, preferably 20 to 80°.

In a further embodiment of the flotation cell, the

bottom structure comprises a base on the bottom of the

flotation tank and defined by the base of the functional !0 triangle, and a mantle defined at least by the first, second

and third vertexes of the functional triangle.

In a yet further embodiment of the flotation cell,

the mantle is at least partly defined by the first and second

sides of the functional triangle.

In an embodiment of the flotation cell, a height of

the bottom structure is greater than 1/5 and less than 3/4 of

a height of the flotation tank (10), measured as the distance

from the bottom to the launder lip.

By arranging a bottom structure at the bottom of a

flotation tank, the bottom structure extending upwards in the

flotation tank, it may be possible to obtain better

distribution of fine and/or small particles suspended in

slurry. At the centre of the flotation tank, particles cannot

descend and settle, as the flow of slurry infeed from the blast tubes may reach the raised centre part of the flotation tank, which ensures good mixing at that part. Particles that may have already detached from flotation gas bubbles and began their descent may be recaptured by the bubbles on account of the turbulent conditions in the mixing zone. On the other hand, the flotation tank bottom nearer the tank perimeter has a zone of a sufficient depth that allows for unfloated, most likely valueless particles to settle down and descend to be efficiently removed from the flotation tank. This settling

.0 zone is not affected by the slurry infeed flow from the blast

tubes. Further, such relatively calm zone may inhibit formation

of short circuiting of the slurry flows within the flotation

tank, where the same slurry material keeps recirculating within

the tank without being properly separated or settled. The above

.5 features may promote increased recovery of fine particles.

In an embodiment of the flotation cell, the flotation

tank further comprises a central froth crowder arranged at a

distance from the bottom of the flotation tank.

In a further embodiment of the flotation cell, a !0 height of the bottom structure is 1/3 to 3/4 of the distance

of the central froth crowder from the bottom of the flotation

tank.

In an embodiment of the flotation cell, the flotation

tank further comprises an internal perimeter froth crowder, a

lowest point of the internal perimeter froth crowder arranged

at a distance from the bottom of the flotation tank.

In a further embodiment of the flotation cell, the

ratio of a height of the bottom structure to the distance of

the lowest point of the internal perimeter forth crowder from

the bottom of the flotation tank is 1.0 or lower.

In an embodiment of the flotation cell, a diameter of

a base of the bottom structure is 1/4 to 3/4 of a diameter of

the bottom of the flotation tank.

In an embodiment of the flotation cell, the surface

area of a base of the bottom structure is 25 to 80 % of the

surface area of the bottom of the flotation tank.

In an embodiment of the flotation cell, the ratio of

height of the flotation tank, measured as the distance from

the bottom to the launder lip, to diameter of the flotation

tank, measured at a height of the outlet nozzle from the bottom

is 0.5 to 1.5; i.e. the ratio of tank height to tank diameter

is 0.5 to 1.5.

.0 In an embodiment of the flotation cell, the volume of 3 the flotation tank is at least 20 m , preferably 20 to 1000 3 m .

By arranging a flotation tank to have a sufficient

volume the flotation process may be better controlled. The

.5 ascent distance to the froth layer on the top part of the

flotation tank does not become too large, which may help to

ensure that the flotation gas bubble-ore particle agglomerates

remain together until the froth layer and particle drop-back

may be reduced. Further, a suitable bubble rise velocity may !0 be reached to maintain a good concentrate quality. Utilizing

flotation cells with a sufficient volumetric size of increases

the probability of collisions between gas bubbles created into

the flotation cells, for example, by means of a rotor, and the

particles comprising valuable mineral, thus improving the

recovery rate for the valuable mineral, as well as the overall

efficiency of the flotation arrangement. Larger flotation

cells have a higher selectivity as more collisions between the

gas bubbles and the ore particles may take place due to the

longer time the slurry stays in the flotation cell. Therefore,

most of the ore particles comprising valuable mineral may be

floated. In addition, the backdrop of buoyant ore particles

may be higher, which means that ore particles comprising very

low amount of valuable mineral drop back into the bottom of

the flotation cell. Thus, the grade of overflow and/or concentrate from larger flotation cells may be higher. These kinds of flotation cells may ensure high grade. Further, the overall efficiency of the flotation cell and/or the entire flotation line may be improved. In addition, in case the first flotation cells in a flotation line have a relatively large volume, there may be no need for large subsequent flotation cells, but rather, the flotation cells downstream from the first flotation cell or cells may be smaller and therefore more efficient. In flotation processes of certain minerals, it

.0 may be easy to float a significant part of the ore particles

comprising valuable mineral with high grade. In that case it

may be possible to have flotation cells of smaller volume

downstream in the flotation line and still achieve high

recovery rate.

_5 In an embodiment of the flotation cell, the flotation

cell comprises 2 to 40 blast tubes, preferably 4 to 24 blast

tubes.

The number of blast tubes directly influences the

amount of flotation gas that can be dispersed in the slurry. !0 In conventional froth flotation, dispersing an increasing

amount of flotation gas would lead to increased flotation gas

bubble size. For example, in a Jameson cell, an air-to-bubble

ratio of 0.50 to 0.60 is utilized. Increasing the average

bubble size will affect the bubble surface area flux (Sb)

detrimentally, which means that recovery may be decreased. In

the flotation cell, with pressurized blast tubes,

significantly more flotation gas may be introduced into the

process without increasing the bubble size or decreasing Sb,

as the flotation gas bubbles created into the slurry infeed

remain relatively small in comparison to the conventional

processes. On the other hand, by keeping the number of blast

tubes as small as possible, costs of refitting existing

flotation cells, or capital expenditure of setting up such flotation cells may be kept in check without causing any loss of flotation performance of the flotation cells.

In an embodiment of the flotation cell, the blast

tubes are arranged concentric to the perimeter of the flotation

tank at a distance from the centre of the flotation tank.

In an embodiment of the flotation cell, the blast

tubes are arranged parallel to the sidewall of the flotation

tank, at a distance from the side wall.

The exact number of blast tubes within a flotation

.0 cell may depend on the flotation tank size or volume, on the

type of material to be collected and other process parameters.

By arranging a sufficient number of blast tubes into a

flotation cell, and by arranging them in a specific manner in

relation to the flotation tank centre and perimeter and/or

.5 side wall, even distribution of ultra-fine bubbles may be

ensured, as well as even mixing effect caused by the shear

forces within tank secured.

In an embodiment of the flotation cell, a blast tube

further comprises an impinger configured to contact a flow of

!0 slurry infeed from the outlet nozzle and to direct the flow of

slurry infeed radially outwards and upwards of the impinger.

An impinger deflects the flow of slurry infeed

radially outwards to the flotation tank sidewall and upwards

towards the flotation tank upper surface (i.e. to the froth

layer) so the fine flotation gas bubble - ore particle

agglomerates do not short circuit into the tailings. All of

the slurry infeed from the blast tubes are forced to rise up

towards the froth layer at the top region of the flotation

tank before gravity has the chance to influence the particles

not adhered to flotation gas bubbles, forcing them to descend

and eventually report to tailings flow or underflow. Thereby

the probability of valuable material containing particles

short-circuiting may be diminished. Slurry is highly agitated

by the energy of the deflected flow, and forms mixing vortexes in which the size of the bubbles may be further reduced by the shear forces acting upon them. The high-shear conditions favourably also induce high number of contacts between flotation gas bubbles and particles in the slurry within the flotation tank. As the flow of slurry is forced upwards towards the froth layer, turbulence reduces and the flow becomes relatively uniform, which may contribute to the stability of the already formed bubbles, and flotation gas bubble- particle agglomerates, especially those comprising coarser particles.

.0 By arranging the outlet nozzle and the impinger at an

optimum distance from each other, the impinger may be

configured to deflect and direct the flow of slurry infeed

radially outwards and upwards of the impinger to create the

earlier mentioned mixing zones within the flotation tank, and

.5 to promote the ascent of particles towards the froth layer. At

the same time, it may be necessary to minimise the wear caused

by high-velocity flows of slurry on the impinger. By

positioning the outlet nozzle and the impinger at a certain

relation to each other, it may be possible to optimise the !0 flotation process within a flotation cell equipped with blast

tubes, as well as minimise wear to the impinger parts.

In a further embodiment of the flotation cell, the

volume of the flotation tank taken by the bottom structure is

30 to 70 % of the volume of the flotation tank taken by the

mixing zone.

By arranging the bottom structure to have a certain

size, especially in respect to the mixing zone, the mixing

zone and the settling zone may be designed to have desired

characteristics (size, depth, turbulence, residence time of

particles in the mixing zone, settling speed and probability

of valueless fraction in the settling zone etc.). In a

conventional flotation cell, a majority of this area (without

any mechanical mixing at the bottom of the flotation tank)

would be subjected to sanding, as there is little or no mixing.

If the area fills up with solids, a risk of this solid matter

slumping in and at the same time blocking a tailings outlet

and/or a recirculate outlet located at the settling zone.

In an embodiment of the flotation cell, it further

comprises a conditioning circuit.

In a further embodiment of the flotation cell, the

conditioning circuit comprises a pump tank in fluid

communication with the flotation tank, in which pump tank

infeed of fresh slurry and a slurry fraction taken from the

.0 flotation tank via an outlet are arranged to be combined into

slurry infeed.

In yet another embodiment of the flotation cell, the

outlet is arranged at the sidewall of the flotation tank, at

a distance from the bottom of the flotation tank.

_5 In yet another embodiment of the flotation cell, the

distance of the outlet from the bottom of the flotation tank

is 0 to 50 % of the height of the flotation tank.

In a further embodiment of the flotation cell, the

conditioning circuit further comprises a pump arranged to !0 intake the slurry fraction from the flotation tank and to

forward slurry infeed from the pump tank.

In a further embodiment of the flotation cell, the

conditioning circuit further comprises a distribution unit

arranged to distribute slurry infeed.

By taking slurry from the bottom of a flotation cell

it may be ensured that the finer particles settled to the

bottom of the flotation tank may be efficiently reintroduced

into the part of the flotation tank where active flotation

process takes place, before the finer particles are reported

to tailings. Thus, the recovery rate of valuable material may

be improved as the particles comprising even minimal amounts

of valuable material may be collected into the concentrate.

By recirculating into blast tubes a slurry fraction

from the lower part of the flotation tank via an outlet arranged at the side wall of the flotation tank, the recirculated fraction becomes thus obtained at a zone where the slurry by most parts comprises particles descending or settling towards the tank bottom. Due to the probabilistic nature of a flotation process, the particles may, however, still comprise valuable material. Especially at the settling zone closest to the flotation tank side wall, the slurry may comprise such valuable material comprising particles that have not been captured by the flotation gas bubbles and/or by the

.0 upwards directed flow of slurry near the impingers at the

mixing zone. At this position, the slurry is also affected by

the flow of slurry infeed from a single blast tube creating

turbulence. There is thus a higher probability of particles

comprising valuable material not being captured by the

.5 flotation gas bubbles and/or the upwards directed flow of

slurry. In order to recover valuable material from these

particles as well, it may be favourable to treat this slurry

fraction again in the same flotation cell, for example, as a

part of the slurry infeed. Therefore, the overall recovery may

!0 be further improved

In an embodiment of the flotation cell, the flotation

tank further comprises a tailings outlet for removing

underflow.

In a further embodiment of the flotation cell, the

tailings outlet is arranged at the side wall of the flotation

tank, at a distance from the bottom of the flotation tank.

In a yet further embodiment of the flotation cell,

that the distance of the tailings outlet from the bottom of

the flotation tank is 1 to 15 % of a height of the flotation

tank, measured as the distance from the bottom to the launder

lip.

The tailings outlet may be positioned at the bottom

of the flotation tank, or at the side wall of the flotation

tank, at the settling zone.

By disposing a tailings outlet at the side wall of the flotation tank, underflow may be removed at a zone where the slurry by most parts comprises particles descending or settling towards the tank bottom. In the flotation cell, the settling zone is deeper near the side wall of the flotation tank. At this area, mixing action and turbulence created by the blast tubes does not affect the settling particles, which, for the most part, do not comprise any valuable material, or comprise only a very small amount of valuable material. At .0 this part, the settling action is also most pronounced due to the lack of turbulence interfering the descent by gravity of the particles. In addition, friction forces created by the tank side wall further decrease the turbulence and/or flows. Thus, taking underflow out of the flotation tank at a position _5 arranged on this relatively calm settling zone, it may be ensured that as little as possible of the valuable material comprising particles are removed from the flotation tank these particles should, rather, be floated, or, if for some reason having ended up in the settling zone, recirculated back !0 into the flotation tank as slurry infeed through the blast tubes. Further, by removing underflow from the settling zone near the side wall of the flotation tank, the entire volume of the flotation tank may be efficiently utilized - there is no need to configure a separate lower settling zone below the blast tubes, as is the case in, for example, a Jameson cell. In some embodiments, it is even foreseeable that the volume of the flotation tank may be decreased at the centre of then tank, thereby decreasing the volume of the settling zone where the turbulence caused by slurry infeed from the blast tubes may influence the probability of particles settling towards the bottom of the tank, and allowing full use of the flotation tank volume. The volume of the flotation tank may be decreased at the centre of the tank, for example, by arranging a bottom structure at the flotation tank bottom, at the centre of the tank. In addition, it may be possible to dispose the blast tubes (the outlet nozzles) relatively deep into the flotation tank, and still ensure a sufficient calm settling zone at the side wall of the flotation tank. Also, this further promotes to the efficient use of the entire volume of the flotation tank. In an embodiment of the flotation line, the flotation cell is preceded by a flotation cell. The preceding flotation cell may be of any suitable type. .0 In an embodiment of the flotation line, the flotation cell is preceded by a mechanical flotation cell. In a further embodiment of the flotation line, the flotation line comprises a rougher part with a flotation cell; a scavenger part with a flotation cell arranged to receive .5 underflow from the rougher part; and a scavenger cleaner part with a flotation cell arranged to receive overflow from the scavenger part, wherein the last flotation cell of the scavenger part and/or the scavenger cleaner part is a flotation cell as disclosed herein. !0 In a yet further embodiment of the flotation line, the flotation cell is preceded by a mechanical flotation cell. An embodiment of the use of the flotation line is particularly intended for recovering mineral ore particles comprising nonpolar minerals such as graphite, sulphur, molybdenite, coal, and talc. Treatment of slurries for the recovery of such industrial minerals as bentonite, silica, gypsum, or talc, may be improved by using reverse flotation. In recovering industrial minerals, the goal of flotation may be, for example, the removal of dark particles into the overflow reject, and recovery of white particles into the underflow accept. In that kind of process, some of the lighter, finer white particles may end up into the overflow. Those particles could be efficiently recovered according to the present disclosure. In reverse flotation, particles comprising undesirable material are removed from the slurry by arranging the gas bubbles to adhere to those particles and removing them from the flotation cell in the overflow, whereas the valuable material comprising particles are recovered in the underflow, thus inversing the conventional flotation flows of accept into overflow and reject into underflow. Typically, in reverse flotation, the large mass pull of invaluable material may cause significant problems in controlling the flotation process.

.0 An embodiment of the use of the flotation line is

particularly intended in recovering particles comprising polar

minerals.

An embodiment of the use of the flotation line is

particularly intended in recovering particles from minerals

_5 having a Mohs hardness of 2 to 3, such as galena, sulfide

minerals, PGM minerals, and/or REO minerals.

A further embodiment of the use of the flotation line

is particularly intended in recovering particles comprising

Pt. !0 An embodiment of the use of the flotation line is

particularly intended in recovering particles comprising Cu

from minerals having a Mohs hardness from 3 to 4.

A further embodiment of the use of the flotation line

is particularly intended in recovering particles comprising Cu

from low grade ore.

Valuable mineral may be, for example, Cu, or Zn, or

Fe, or pyrite, or metal sulfide such as gold sulfide. Mineral

ore particles comprising other valuable mineral such as Pb,

Pt, PGMs (platinum group metals Ru, Rh, Pd, Os, Ir, Pt), oxide

mineral, industrial minerals such as Li (i.e. spodumene),

petalite, and rare earth minerals may also be recovered,

according to the different aspects of the present disclosure.

For example, in recovering copper from low grade ores

obtained from poor deposits of mineral ore, the copper amounts may be as low as 0,1 % by weight of the feed, i.e. infeed of slurry into the flotation line. The flotation line may be very practical for recovering copper, as copper is a so-called easily floatable mineral. In the liberation of ore particles comprising copper, it may be possible to get a relatively high grade from the first flotation cells of the flotation line. Recovery may be further increased by a flotation cell according to the disclosure. By using the flotation arrangement according to the .0 present disclosure, the recovery of such low amounts of valuable mineral, for example, copper, may be efficiently increased, and even poor deposits cost-effectively utilized. As the known rich deposits have increasingly already been used, there is a tangible need for processing the less favourable .5 deposits as well, which previously may have been left unmined due to lack of suitable technology and processes for recovery of the valuable material in very low amounts in the ore.

BRIEF DESCRIPTION OF THE DRAWINGS

!0 The accompanying drawings, which are included to provide a further understanding of the current disclosure and which constitute a part of this specification, illustrate embodiments of the disclosure and together with the description help to explain the principles of the current disclosure. In the drawings: Fig. 1 is a 3D projection of a flotation cell according to an embodiment of the invention, Fig. 2 depicts a flotation cell according to an embodiment of the invention, as seen from above, Fig. 3 depicts a flotation cell according to an embodiment of the invention in side view, Fig. 4a is a vertical cross-section of the flotation cell of Fig. 3 along a section A-A,

Fig. 4b shows a vertical cross-section of a further

embodiment of the flotation cell of Fig. 3 along the section

A-A,

Fig. 5 is a schematic illustration of a flotation

cell according to an embodiment of the invention, detailing

the dimensions of the flotation cell,

Fig. 6a and 6b are schematic drawings of flotation

lines according to embodiments of the invention,

Fig. 7 shows schematic vertical cross-sections of

.0 embodiments of flotation tanks according to the invention, and

Fig. 8 is a schematic presentation of forms of the

bottom structure according to embodiments of the flotation

cell.

_5 DETAILED DESCRIPTION

Reference will now be made in detail to the

embodiments of the present disclosure, an example of which is

illustrated in the accompanying drawings.

The description below discloses some embodiments in !0 such a detail that a person skilled in the art is able to

utilize the flotation cell, flotation line and its use based

on the disclosure. Not all steps of the embodiments are

discussed in detail, as many of the steps will be obvious for

the person skilled in the art based on this disclosure.

For reasons of simplicity, item numbers will be

maintained in the following exemplary embodiments in the case

of repeating components.

The enclosed figures 1-5 and 7-8 illustrate a

flotation cell 1 in some detail. The figures are not drawn to

proportion, and many of the components of the flotation cell

1 are omitted for clarity. Figures 6a and 6b illustrate in a

schematic manner embodiments of the flotation line. The

direction of flows of slurry is shown in the figures by arrows.

The flotation cell 1 according to an embodiment of the invention is intended for treating mineral ore particles suspended in slurry and for separating the slurry into an underflow 400 and an overflow 500, the overflow 500 comprising a concentrate of a desired mineral. Referring in particular to figures 1-5, the flotation cell 1 comprises a flotation tank 10 that has a centre 11, a perimeter 12, a bottom 13 and a side wall 14. The flotation cell 1 further comprises a launder 2 and a launder lip 21 .0 surrounding the perimeter 12 of the flotation tank 10. In the accompanying figures, launder 2 is a perimeter launder. It is to be understood that a launder 2 may comprise, alternatively or additionally, a central launder arranged at the centre 11 of the flotation tank 10, as is known in the .5 technical field. A launder lip of a central launder may face towards the perimeter 12 of the flotation tank 10, or towards the centre 11 of the flotation tank 10, or both. The overflow 500 is collected into the launder 2 or launders as it passes over a launder lip 21, from a froth layer formed in the upper !0 part of the flotation tank 10. The froth layer comprises an open froth surface Af at the top of the flotation tank 10. Underflow 400 is removed from or led out of the flotation tank via a tailings outlet 140. According to an embodiment, the tailings outlet 140 may be arranged at the side wall 14 of the flotation tank 10 (see Fig. 5). The tailings outlet 140 may be arranged at the side wall 14 of the flotation tank 10 at a distance L6 from the bottom 13 of the flotation tank 10. The distance is to be understood as the distance of the lowest point of the tailings outlet 140 or outlet opening in the side wall 14 of the flotation tank 10 from the tank bottom 13. The distance L 6 may be 1 to 15 % of the height H of the flotation tank 10. For example, the distance L 6 may be 2 %, or 5 % or 7.5 %, or 12 % of the height H. Alternatively, the tailings outlet 140 may be arranged at the bottom 13 of the flotation tank 10 (see Fig. 1). In any case, the tailing outlet 140 is arranged at a settling zone B, at the lower part of the flotation tank 10. The tailings outlet 140 may be controlled by a dart valve, or by any other suitable manner known in the field, to control the flow rate of underflow from the flotation tank 10. Even if the tailings outlet 140 is controlled by internal or external structures such as up-flow or down-flow, respectively, dart boxes, the tailings outlet 140 is ideally located at the lower part of the flotation tank .0 10, i.e. near or adjacent to the bottom 13 of the flotation tank, or even at the bottom 13 of the flotation tank 10. More specifically, underflow 400 or tailings are removed from the lower part of the flotation tank 10, and at or near the side wall 14 of the flotation tank 10. _5 The flotation tank 10 has a height H, measured as the distance from the bottom 13 of the flotation tank 10 to the launder lip 21. At the perimeter 12 of the flotation tank 10, the height H is substantially equal to or greater than the height H at the centre 11 of the flotation tank 10. In other !0 words, the flotation tank 10 may have different vertical cross sections (see Fig. 7) - for example, the side wall 14 of the flotation tank 10 may include at its lower part a section that is inclined towards the centre 11 of the flotation tank 10. Further, the flotation tank 10 has a diameter D, measured at a distance hl of an outlet nozzle 43 from the bottom 13 of the flotation tank 10. In an embodiment, the height H to diameter D ratio H/D of the flotation tank 10 is 0.5 to 1.5. The flotation tank 10 may have a volume of at least 20 m 3 . The flotation tank 10 may have a volume ranging from 20 to 1000 m 3 . For example, the volume of the flotation tank 10 3 may be 100 m , or 200 m 3 , or 450 m 3 , or 630 m 3 .

The flotation tank 10 comprises blast tubes 4 for introducing slurry infeed 100 into the flotation tank 10. A blast tube 4 comprises an inlet nozzle 41 for feeding slurry infeed 100 into the blast tube 4; an inlet 42 for pressurized air or other gas, so that the slurry infeed 100 may be subjected to pressurized air or other gas as it is discharged from the inlet nozzle 41; an elongated chamber 40 arranged to receive under pressure the slurry infeed 100; an outlet nozzle 43 configured to restrict flow of slurry infeed 100 from the outlet nozzle 43, and to maintain slurry infeed in the elongated chamber 40 under pressure.

.0 Flotation gas is entrained through a turbulent mixing

action brought about by the jet, and is dispersed into small

bubbles in the slurry infeed 100 as it travels downwards

through the elongated chamber 40 to an outlet nozzle 43

configured to restrict the flow of slurry infeed 100 from the

.5 outlet nozzle 43, and further configured to maintain slurry

infeed 100 under pressure in the elongated chamber 40.

According to an embodiment, the outlet nozzle 43 may

further be configured to produce a supersonic shockwave into

the slurry infeed, the supersonic shockwave inducing formation !0 of flotation gas bubble - particle agglomerates. For example,

and to the outlet nozzle 43 may induce a supersonic shockwave

into the slurry infeed 100 as it exits the blast tube 40. In

addition, the supersonic shockwave may extend to the slurry

adjacent or surrounding the outlet nozzle so that even outside

the blast tube, the creation of small size flotation gas bubble

- particle agglomerates is thus possible.

For restricting the flow, an outlet nozzle 43 may

comprise a throttle such as a throat-like restricting

structure. From the outlet nozzle 43, more specifically from

the throttle, slurry infeed 100 issues under pressure into the

flotation tank 10. As the slurry infeed 100 passes through the

outlet nozzle 43, or through the throttle of the outlet nozzle

43, flotation gas bubbles are reduced in size by the pressure

changes, and by the high-shear environment downstream of the outlet nozzle 43. The velocity of the gas-liquid mixture in outlet nozzle 43, or in the throttle, may exceed the speed of sound when the flow becomes a choked flow and flow downstream of the throttle becomes supersonic, and a shockwave forms in the diverging section of the outlet nozzle 43. In other words, the outlet nozzle 43 is configured to induce a supersonic shockwave into slurry infeed 100. The flow of slurry infeed 100 becomes choked when the ratio of the absolute pressure upstream the outlet nozzle 43 to the absolute pressure .0 downstream of a throttle or other restricting structure of the outlet nozzle 43 exceeds a critical value. When the pressure ratio is above the critical value, flow of slurry infeed 100 downstream of the throttle of the outlet nozzle 43 becomes supersonic and a shockwave is formed. Small flotation gas _5 bubbles in slurry infeed 100 mixture are split into even smaller by being forced through the shockwave, and forced into contact with hydrophobic ore particles in slurry infeed 100, thus creating flotation gas bubble-ore particle agglomerates. An outlet nozzle 43 may be disposed inside the !0 flotation tank 10 at a desired depth. An outlet nozzle 43 may be positioned at a vertical distance L5 from the launder lip 21, the distance L5 being at least 1.5 m. In other words, the length of the portion of a blast tube 4 disposed inside the flotation tank 10 below the launder lip 21 level is at least 1,5 m. In an embodiment, the distance L5 is at least 1.7 m, and the distance hl of the outlet nozzle 43 from the bottom 13 of the flotation tank 10 is at least 0.4 m. For example, the distance L5 may be 1.55 m, or 1.75 m, or 1.8 m, or 2.2 m, or 2.45m, or 5.25 m; and the distance hi, irrespective of the distance L 5 , may be 0.45 m, 0.55 m, 0.68 m, 0.9 m, or 1.2 m. Further, the ratio of the distance L5 to the height H of the flotation tank 10 may be 0.9 or lower. The depth at which the blast tubes 4 are disposed inside the flotation tank 10 may depend on a number of factors, for example, on the characteristics of the slurry and/or valuable mineral to be treated in the flotation cell 1, or on the configuration of a flotation line in which the flotation cell 1 is arranged. The ratio of a distance hi of an outlet nozzle 43 from the bottom 13 of the flotation tank 10 to height H of the flotation tank 10, hi/H may be 0.1 to 0.75. A diameter of an outlet nozzle 43 may be 10 to 30

% of the diameter of an elongated chamber 40 of a blast tube 4. The diameter of an outlet nozzle 43 may be 40 to 100 mm. For .0 example, the diameter of an outlet nozzle 43 may be 55 mm, or 62 mm, or 70 mm. By arranging an outlet nozzle to have a certain diameter, the velocity of the slurry infeed may be maintained at a level favourable for the creation of small size flotation _5 gas bubbles, and for the probability of these bubbles to contact the ore particles in the slurry. Especially, to maintain a shockwave after the outlet nozzle, a slurry velocity of 10 m/s or higher needs to be maintained. By designing the outlet nozzle in relation to the blast tube size, the effect !0 of slurry infeed flow rate in different types of flotation cells may be accounted for. A blast tube 4 may further comprise an impinger 44 configured to contact a flow of slurry infeed 100 from the outlet nozzle 43 and to direct the flow of slurry infeed 100 radially outwards and upwards of the impinger 44. Slurry infeed 100 exiting from the outlet nozzle 43 is therefore directed to contact the impinger 44. A distance L3 from a bottom 440 of the impinger 44 to the outlet nozzle 43 may be 2 to 20 times the diameter of the outlet nozzle 43. For example, the distance L3 may be 5 times, 7 times, or 12 times, or 15 times the diameter of the outlet nozzle 43. The ratio of the distance L 3 to the distance hi of an outlet nozzle 43 from the bottom 13 of the flotation tank 10, L 3 /hi, may be lower than 1,0. Further, a distance h 3 of a bottom

440 of the impinger 44 from the bottom 13 of the flotation

tank 10 may be at least 0,3 m. For example, the distance h3 may be 0.4 m, or 0.55 m, or 0.75 m, or 1.0 m.

The impinger 44 may comprise an impingement surface

intended for contacting the flow of slurry infeed 100 exiting

the outlet nozzle 43. The impingement surface may be made of

wear-resistant material to reduce the need for replacements or

maintenance.

The slurry, which in essence is a three-phase gas

.0 liquid-solids mixture, rising out of the impinger 44 enters

the upper part of the flotation tank 10, and the flotation gas

bubbles rise upwards and separate from the liquid to form a

froth layer. The froth rises upwards and discharges over the

launder lip 21 into the launder 2 and out of the flotation

_5 cell 1 as overflow 500. The tailings or underflow 400, from

which the desired material has substantially been removed,

pass out from the flotation tank 10 through an outlet arranged

at or near the bottom 13 of the flotation tank 10.

Some of the coarse hydrophobic particles that are

!0 carried into the froth may subsequently disengage from

flotation gas bubbles and drop back into the flotation tank

10, as a result of bubble coalescence in the froth. However,

the majority of such particles fall back into the flotation

tank 10 in such a way and position that they may be captured

by bubbles newly entering the flotation tank 10 from the blast

tubes 4, and carried once more into the froth layer.

There may be 2-40 blast tubes 4, or 4-24 blast tubes

4 arranged in a flotation cell 1. In an embodiment, there are

16 blast tubes 4. In another embodiment, there are 24 blast

tubes 4. In yet another embodiment, there are 8 blast tubes 4.

The exact number of blast tubes 4 may be chosen according to

the specific operation, for example, the type of slurry being

treated within the flotation cell 1, the volumetric feed

flowrate to the flotation cell 1, the mass throughput feed to the flotation cell 1, or the volume or dimensions of the flotation tank 10. In order to properly disperse flotation gas within the flotation tank 10, 4 to 6 blast tubes 4 may be employed.

The blast tubes 4 may be arranged concentric to the

perimeter 12 of the flotation tank 10 at a distance from the

centre 11 of the flotation tank 10. This may be the case when

the flotation tank 10 is circular in cross-section. The blast

tubes 4 may be further arranged so that each blast tube 4 is

.0 located at a distance Li of an outlet nozzle 43 from the centre

11 of the flotation tank 10, the distance being preferably

equal for each blast tube 4. For example, the distance Li may

be 10 to 40 % of the diameter D of the flotation tank 10.

According to different embodiments of the flotation cell 1,

_5 the distance Li may be 12.5 %, or 15 %, or 25 % or 32.5% of

the diameter D of the flotation tank 10.

The blast tubes 4 may be arranged parallel to the

side wall 14 of the flotation tank 10, at a distance from the

side wall 14. This may be the case when the flotation tank 10 !0 is rectangular in cross-section. A distance L2 of the outlet

nozzle 43 of a blast tube 4 from the side wall 14 of the

flotation tank 10 may be 10 to 40 % of the diameter D of the

flotation tank 10. In an embodiment, the distance L2 is 25 %

of the diameter D of the flotation tank 10. According to

different embodiments of the flotation cell 10, the distance

L 2 may be 12.5 %, or 15 %, or 27 % or 32.5% of the diameter D

of the flotation tank 10. Additionally, the parallel arranged

blast tubes 4 may be further arranged at a straight line within

the flotation tank 10.

Further, in all the above mentioned embodiments, the

blast tubes 4 may be arranged at equal distance from each other

so that a distance between any two adjacent outlet nozzle 43

is the same.

The flotation tank 10 comprises a bottom structure 7

(see esp. Figs. 2, 4a, 4b, 5 and 8), arranged on the bottom

(13), and having a shape that allows particles suspended in

slurry to be mixed in a mixing zone A created by the flow of

slurry infeed 100 from the outlet nozzles 43 of the blast tubes

4 over the bottom structure 7, and to settle down in a settling

zone B surrounding the bottom structure 7.

The shape of the bottom structure 7 may be defined as

follows (see Fig. 8): the vertical cross-section of the bottom

.0 structure may be understood to display a form of a functional

triangle 700 that comprises a first (top) vertex 71, pointing

away from the bottom 13 of the flotation tank 10; a second

vertex 71a; and a third vertex 71b, the two latter disposed at

the bottom 13 of the flotation tank 10. A first side a is

_5 formed between the first vertex 71 and the second vertex 71a.

A second side b is formed between the first vertex 71 and the

third vertex 71b. A base c is formed between the second vertex

71a and the third vertex 71b, the base c being thus parallel

to and on the bottom 13 of the flotation tank 10. A central !0 axis 70 of the functional triangle 700 is substantially

concentric with the centre 11 of the flotation tank 10.

"Substantially" in this context is to be understood so that

during manufacturing and/or installation of the bottom

structure 7, it is possible that slight deviations from the

centre 11 of the flotation tank 10 may naturally occur. The

intention is, nevertheless, that the two axes, central axis 70

of the functional triangle (which is also the central axis of

the bottom structure 7) and the centre of the flotation tank

10 are coaxial.

A base angle a between the first side a and the base

c (and/or between the second side b and the base c), in relation

to the bottom 13 of the flotation tank 10 is 20 to 600. For

example, the angle a may be 22°, or 27.5° or 35°, or 45°, or

53,750. Further, an included angle B between the first side a and the second side b is 20 to 1000. Preferably, the included angle B is 20 to 800. For example, the included angle @ may be

220, or 33.50, or 450, or 57.750, or 640, or 85.50. The

functional triangle may therefore be an isosceles triangle or

an equilateral triangle.

The functional triangle is in essence a form which

may be identified though the abovementioned features,

regardless of the actual form of the bottom structure 7, which

may be, depending on the cross-section and other structural

.0 details of the flotation tank 10, for example, a cone, a

truncated cone, a pyramid, or a truncated pyramid. A cone or

a truncated cone may be suitable from for a flotation tank

with a circular cross-section. A pyramid or a truncated pyramid

may be a suitable form for a flotation tank with a rectangular

.5 cross-section.

The bottom structure 7 comprises a base 73,

corresponding to the base c of the functional triangle 700

(i.e. the base c of the functional triangle 700 defines the

base 73 of the bottom structure 7), and arranged on the bottom !0 13 of the flotation tank 10. Further, the bottom structure

comprises a mantle 72. The mantle 72 is defined at least by

the first vertex 71, the second vertex 71a and the third vertex

71b of the functional triangle 700. Therefore, irrespective of

the actual form of the bottom structure 7, the functional

triangle 700 defines the extreme physical dimensions of the

bottom structure 7. For example, in case the bottom structure

7 has an irregular form yet being rotationally symmetrical, it

would fit into the functional triangle 700 in its entirety

(see the last image of Fig. 8). In an embodiment, the mantle

72 is at least partly defined by the first side a and the

second side b of the functional triangle. An example of such

an embodiment is a bottom structure 7 having the form of a

truncated cone (see the middle image of Fig. 8). In an

embodiment, the mantle 72 is defined essentially entirely by the first side a and the second side b of the functional triangle 700, i.e. the bottom structure 7 has the form of a cone (see the first image of Fig. 8).

The bottom structure 7 has a height h 4 , measured from

the topmost part of the bottom structure 7 to the bottom 13 of

the flotation tank 10. In case the form of the bottom structure

is a cone or a pyramid, the topmost part is also the first

vertex 71 of the functional triangle 700. In case the bottom

structure 7 has some sort of truncated form, the height h4 is .0 measured from the level top of the truncated form (see middle

image of Fig. 8) to the bottom 13 of the flotation tank 10.

The height h4 is greater than 1/5 and less than 3/4 of the

height H of the flotation tank 10. Further, the diameter d 3 of the base 73 of the bottom structure 7 may be 1/4 to 3/4 of a

.5 diameter di of the bottom 13 of the flotation tank 10. In case

a flotation tank 10 and/or the bottom structure 7 has a non

circular cross-section, the diameters are measured as the

maximal diagonals of the respective parts (base 73 and bottom

13). In an embodiment, the surface area of a base 73 of the !0 bottom structure 7 is less than 80 % of the surface area of

the bottom 13 of the flotation tank 10. The surface area of

the base 73 may be 25 to 80 % of the surface area of the bottom

13 of the flotation tank 10.

Further, the volume of the flotation tank 10 taken by

the bottom structure 7 may be 30 to 70 % of the volume of the

flotation tank 10 taken by the mixing zone A.

The bottom structure 7 may additionally comprise any

suitable support structures and/or connecting structures for

installing the bottom structure 7 into the flotation tank 10,

on the bottom 13 of the flotation tank 10. The bottom structure

7 may be made of any suitable material such as metal, for

example, stainless steel.

The flotation tank 10 may further comprise a froth

crowder 6 shaped to direct froth in the open froth surface Af towards the launder lip 21, as shown in Figs. 4b and 5. The froth crowder 6 may be a central froth crowder 61, and/or an internal perimeter froth crowder arranged within the flotation tank 10 at a desired depth, at the sidewall of the flotation tank 10.

A central froth crowder 61 is arranged concentric to

the centre 11 of the flotation tank 10. The central froth

crowder 61 may have a shape of a cone or a truncated cone. The

central froth crowder 61 may have a shape of a pyramid or a

.0 truncated pyramid. In other words, a vertical cross-section of

a central froth crowder 61 may be an inverted triangle with a

vertex pointing towards the bottom 13 of the flotation tank.

In case the central froth crowder 61 is has a truncated

structure or shape, the vertex is only functional, i.e. it is

_5 to be visualised as the lowest point of the structure or shape

as continued to a complete untruncated form, whereby a included

angle a may be identified irrespective of the actual shape or

form of the central froth crowder. The included angle a may be

20 to 800. For example, the included angle a may be 22°, or !0 37.5° or 45°, or 55°, or 63.75°, or 74°. In an embodiment, the

central froth crowder 61 is arranged to block 25 to 40 % of

the open froth surface Af.

Alternatively or additionally to the central froth

crowder 61, the flotation tank may comprise an internal

perimeter crowder 62, arranged in the side wall 14 of the

flotation tank 10 so that a lowest point 620 of the internal

perimeter crowder is located at a distance h 2 from the bottom

13 of the flotation tank 10. The distance h 2 may be 1/2 to 2/3

of the height H of the flotation tank 10. The internal

perimeter crowder 62 may be formed to comprise a diagonal

intake 14c starting from the lowest point 620, and angled

towards the centre 11 of the flotation tank 10, and extending

between a first part 14a of the side wall 14 of the flotation

tank 10 and a second part 14b of the side all 14 so that an angle of inclination B of the diagonal intake 14c in relation to the first part 14a of the side wall 14 is 20 to 800. The angle of inclination B may be, for example, 220, or 37.50 or

450, or 550, or 63.75°, or 74°. The internal perimeter crowder

62 may be arranged to block 1/5 to 4 of a pulp area Ap, which

is measured at a distance hi of an outlet nozzle 43 of a blast

tube 4 from the bottom 13 of the flotation tank 10, at a mixing

area A. The mixing area A, i.e. the part or zone of the

flotation tank in vertical direction where the slurry is

.0 agitated or otherwise induced to mix the ore particles

suspended in the slurry with the flotation gas bubbles, is

formed roughly at a vertical section of the flotation tank 10

around the lower parts of the blast tubes 4 and the impingement

bowls 44 (see Fig. 5).

_5 A slurry fraction 300 may be taken out from the

flotation tank 10 via an outlet 31 arranged at the side wall

14 of the flotation tank 10. This slurry fraction 300 is

recirculated into blast tubes 4 as infeed slurry. In an

embodiment, the slurry infeed 100 comprises 40 % or less of !0 slurry fraction 300. In an embodiment, the slurry infeed 100

comprises 50 % or less of slurry fraction 300. For example,

the slurry infeed may comprise 5 %, or 12.5%, or 20 %, or 30

%, or 45 % of slurry fraction 300. Alternatively, the slurry

infeed 100 may comprise 0 % of slurry fraction 300, i.e. no

recirculation of slurry taken from the flotation tank 10 back

to the flotation cell takes place, but the slurry infeed 100

comprises 100 % of fresh slurry 200, for example, from a

previous flotation cell (that is, underflow 400 from a previous

flotation cell), or from a previous process step.

The slurry fraction 300 may be recirculated to all of

the blast tubes 4 of the flotation tank 10, or, alternatively,

to some of the blast tubes 4, while other blast tubes 4 receive

fresh slurry 200, comprising either the underflow 400 of a

previous flotation cell, or a slurry flow from some preceding process step, depending on the location of the flotation cell

1 within a flotation line 8. The outlet 31 may be arranged at

a distance L 4 from the bottom 13 of the flotation tank 10. The

distance is to be understood as the distance of the lowest

point of the outlet or outlet opening in the side wall 14 of

the flotation tank 10 from the tank bottom 13. The distance L4 is 0 to 50 % of the height H of the flotation tank 10. The

outlet 31 may advantageously be positioned at a settling zone

where the particles suspended in slurry and not captured by

.0 the flotation gas bubbles and/or the upwards flow of slurry

descend towards the bottom 13 of the flotation tank 10. In an

embodiment, the outlet 31 is arranged at the lower part of the

flotation tank 10. For example, the distance L 4 may be 2 %, or

8 %, or 12.5 %, or 17, or 25 % of the height H of the flotation

_5 tank 10. Even if the outlet 31 is controlled by internal or

external structures such as up-flow or down-flow dart boxes,

respectively, the outlet 31 is ideally located at the lower

part of the flotation tank 10, i.e. near or adjacent to the

bottom 13 of the flotation tank. More specifically, slurry !0 fraction 300 is removed from the lower part of the flotation

tank 10.

The flotation cell 1 may also comprise a conditioning

circuit 3. The conditioning circuit 3 may comprise a pump tank

30, or other such additional vessel, in fluid communication

with the flotation tank 10. In the pump tank 30 infeed of fresh

slurry 200 and a slurry fraction 300 taken from the flotation

tank 10 via an outlet 31 are arranged to be combined into

slurry infeed 100, which is then led into blast tubes 4 of the

flotation tank 10. The fresh slurry 200 may be, for example,

underflow 400 from a preceding flotation cell, or in case the

flotation cell 1 is the first flotation cell of a flotation

line, an infeed of slurry coming from a grinding unit/step or

a classification unit/step. It is also possible that slurry fraction 300 and fresh slurry 200 are distributed into the blast tubes 4 without being first combined in a pump tank 30.

The combined slurry may be recirculated to all of the

blast tubes 4 of the flotation tank 10, or, alternatively, to

some of the blast tubes 4, while other blast tubes 4 receive

fresh slurry 200, comprising either the underflow 400 of a

previous flotation cell, or a slurry flow from some preceding

process step, depending on the location of the flotation cell

1 within a flotation line 8.

.0 The outlet 31 may be arranged at the side wall 14 of

the flotation tank 10, at a distance L4 from the bottom 13 of

the flotation tank 10. The distance L4 may be 0 to 50 % of the

height H of the flotation tank 10. For example, the distance

L4 may be 2 %, or 8 %, or 12.5 %, or 20 %, or 33 % of the

.5 height H of the flotation tank 10.

Additionally, the conditioning circuit may comprise

a pump 32 arranged to intake the slurry fraction 300 from the

flotation tank 10, and to forward slurry infeed 100 from the

pump tank 30 to the blast tubes 4. The slurry fraction 300 may

!0 comprise low settling velocity particles such as fine, slow

floating particles. The slurry fraction may be taken from or

near the bottom of the flotation tank 10. Additionally or

alternatively, the conditioning circuit 3 may further comprise

a distribution unit (not shown in the figures), arranged to

distribute slurry infeed 100 into the blast tubes 4. The pump

32 may also be used to forward the slurry infeed 100 into the

blast tubes 4. In order to distribute the slurry infeed 100

evenly into the blast tubes 4, a distribution unit may be

utilized. The distribution unit may, for example, comprise a

feed pipe inside the flotation tank 10, configured to

distribute slurry fraction 300 directly into the blast tubes

4. For example, the distribution unit may comprise conduits

arranged outside the flotation tank 10, leading to a separate

feed distributor configured to distribute slurry fraction 300, or a combination of slurry fraction 300 and fresh slurry 200 into the blast tubes 4.

According to another aspect of the disclosure,

flotation lines 8 are presented in figures 6a and 6b. A

flotation line 8 comprises a number of fluidly connected

flotation cells la, and at least one of the flotation cells is

a flotation cell 1 according to the above described embodiments

of the flotation cell 1. In an embodiment of the flotation

line 8, the flotation cell 1 is preceded by a flotation cell

.0 la. A flotation cell la may be of any type known in the field.

Alternatively or additionally, the flotation cell 1 may be

preceded by mechanical flotation cell lb (see Fig. 6a).

In an embodiment of the flotation line 8, it comprises

a rougher part 81 with a flotation cell la; a scavenger part

_5 82 with a flotation cell la arranged to receive underflow 400

for the rougher part 81; and a scavenger cleaner part 820 with

a flotation cell la arranged to receive overflow 500 from the

scavenger part 82 (see Fig. 6b). In the flotation line 8, the

last flotation cell 1 of the scavenger part 82, and !0 alternatively or additionally, the last flotation cell 1 of

the scavenger cleaner part 820 is a flotation cell 1, with

blast tubes 4. Additionally, in the flotation line 8, as

described above, the flotation cell 1, with blast tubes 4, may

be preceded by a mechanical flotation cell lb.

The flotation line 8 may be preceded by other

processes such as grinding, classification, screening, heavy

medium process, coarse particle recovery process, spirals, and

other separation processes; and other flotation processes. A

number of processes may follow the flotation line 8, such as

regrinding, cleaner or other flotation processes, centrifuging, filtering, screening or dewatering.

According to a further aspect, the flotation line 8

may be used in recovering particles comprising a valuable

material suspended in slurry. In an embodiment, the use may be directed to recovering particles comprising nonpolar minerals such as graphite, sulphur, molybdenite, coal, talc. According to another embodiment, the use may be directed to recovering particles comprising polar minerals. In a further embodiment, the use is directed to recovering particles from minerals having a Mohs hardness of 2 to 3, such as galena, sulfide minerals, PGMs, REO minerals. In a yet further embodiment, the use is specifically directed to recovering particles comprising platinum. .0 In a further embodiment, the use is directed to recovering particles comprising copper from mineral particles having a Mohs hardness of 3 to 4. In a yet further embodiment, the use is specifically directed to recovering particles comprising copper from low grade ore. _5 The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A flotation cell to which the disclosure is related, may comprise at least one of the embodiments described hereinbefore. It is !0 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. Any reference to background art or other prior art in this specification is not an admission that such background art or other prior art is common general knowledge in Australia or elsewhere. In this specification, the term "comprising" is intended to denote the inclusion of a stated integer or integers, but not necessarily the exclusion of any other integer, depending on the context in which that term is used. This applies also to variants of that term such as "comprise" or "comprises".

Claims (11)

1. A flotation cell for treating particles suspended in slurry and for separating the slurry into an underflow and an overflow, the flotation cell comprising a flotation tank comprising a centre, a perimeter, a substantially horizontal level bottom, and a side wall; a launder and a launder lip surrounding the perimeter of the tank; and a bottom structure arranged on the bottom, and having .0 a shape that allows particles suspended in slurry to be mixed in a mixing zone (A) over the bottom structure, and to settle down in a settling zone (B) surrounding the bottom structure; wherein the flotation tank further comprises blast tubes for introducing slurry infeed into the tank, a blast _5 tube comprising an inlet nozzle for feeding slurry infeed into the blast tube; an inlet for pressurized gas, the slurry infeed subjected to the pressurized gas as it is discharged !0 from the inlet nozzle; an elongated chamber arranged to receive under pressure the slurry infeed; and an outlet nozzle configured to restrict flow of slurry infeed from the outlet nozzle, and to maintain slurry infeed in the elongated chamber under pressure; and in that the blast tubes are disposed at a position relative to the bottom structure so as to induce mixing at the mixing zone; wherein the outlet nozzle is configured to produce a supersonic shockwave into the slurry infeed, the supersonic shockwave inducing formation of flotation gas bubble - particle agglomerates.

2. The flotation cell according to claim 1, wherein a

height (H) of the flotation tank, measured as the distance

from the bottom of the flotation tank to the launder lip, at

the perimeter of the flotation tank is at most 20 % lower than

at the centre of the flotation tank.

3. The flotation cell according to claim 1 or claim 2,

wherein the vertical cross-section of the bottom structure is

a functional triangle comprising a first vertex pointing away

.0 from the bottom of the flotation tank, a second vertex and a

third vertex; a first side between the first vertex and the

second vertex; a second side between the first vertex and the

third vertex; and a base between the second and third vertexes

on the bottom of the flotation tank; and a central axis

_5 substantially concentric with the centre of the flotation tank.

4. The flotation cell according to claim 3, wherein the

base angle (a') between the first side (a) and the base (c), or

second side (b) and the base in relation to the bottom of the !0 flotation tank is 20 to 600.

5. The flotation cell according to claim 3 or claim 4,

wherein the included angle (B) between the first side (a) and

the second side (b) is 20 to 1000, preferably 20 to 800.

6. The flotation cell according to any one of claims 3

to 5, wherein the bottom structure comprises a base on the

bottom of the flotation tank and defined by the base of the

functional triangle, and a mantle defined at least by the

first, second and third vertexes of the functional triangle.

7. The flotation cell according to claim 6, wherein the

mantle is at least partly defined by the first and second sides

(a, b) of the functional triangle.

8. The flotation cell according to any one of claims 1 to 7, wherein a height (h4 ) of the bottom structure is greater than 1/5 and less than 3/4 of a height (H) of the flotation tank, measured as the distance from the bottom to the launder lip.

9. The flotation cell according to any one of claims 1 to 8, wherein the flotation tank further comprises a central froth crowder arranged at a distance (h 5 ) from the bottom of .0 the flotation tank.

10. The flotation cell according to claim 9, wherein a height (h4 ) of the bottom structure is 1/3 to 3/4 of the distance (h5 ). -5 11. The flotation cell according to any one of claims 1 to 10, wherein the flotation tank further comprises an internal perimeter froth crowder, a lowest point of the internal perimeter froth crowder arranged at a distance (h 2 ) from the !0 bottom of the flotation tank.

12. The flotation cell according to claim 11, wherein the ratio of a height (h 4 ) of the bottom structure to the distance (h 2 ) is 1, 0 or lower.

13. The flotation cell according to any one of claims 1 to 12, wherein a diameter (d 3 ) of a base of the bottom structure is 1/4 to 3/4 of a diameter (di) of the bottom of the flotation tank.

14. The flotation cell according to any one of claims 1 to 13, wherein the surface area of a base of the bottom structure is 25 to 80 % of the surface area of the bottom of the flotation tank.

15. The flotation cell according to any one of claims 1

to 14, wherein a height(H) of the flotation tank, measured as

the distance from the bottom to the launder lip, to diameter

(D) of the flotation tank, measured at a height (hi) of the

outlet nozzle from the bottom, ratio (H/D), is 0.5 to 1.5.

16. The flotation cell according to any one of claims 1

to 15, wherein a blast tube further comprises an impinger

configured to contact a flow of slurry infeed from the outlet

.0 nozzle and to direct the flow of slurry infeed radially

outwards and upwards of the impinger.

17. A flotation line comprising a number of fluidly

connected flotation cells, wherein at least one of the

.5 flotation cells is a flotation cell according to any one of

claims 1 to 16.

18. The flotation line according to claim 17, wherein the flotation cell is preceded by a flotation cell. !0

19. The flotation line according to claim 18, wherein the

flotation line comprises

a rougher part with a flotation cell;

a scavenger part with a flotation cell arranged to

receive underflow from the rougher part; and

a scavenger cleaner part with a flotation cell

arranged to receive overflow from the scavenger part, wherein

the last flotation cell of the scavenger part and/or the

scavenger cleaner part is a flotation cell according to any

one of claims 1-16.

20. Use of a flotation line according to anyone of claims

17 to 19 in recovering particles comprising a valuable material

suspended in slurry.

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