FLOTATION METHOD

Abstract

A flotation arrangement for treating suspended metalliferous mineral particles is presented. The arrangement comprises a primary flotation line with a coarser section comprising at least two coarser primary flotation cells and a scrubber section comprising at least two scrubber primary flotation cells, and a secondary flotation line comprising at least two secondary flotation cells. A first secondary flotation cell is arranged to receive the primary overflow from the at least one coarser primary flotation cell, and another secondary flotation cell is arranged to receive the primary overflow from the at least one coarser primary flotation cell.The additional secondary flotation cell is arranged in fluid communication with a previous secondary flotation cell, and the underflow from the first secondary flotation cell is arranged to flow to the additional secondary flotation cell, or is arranged to be combined with the secondary underflow from the additional secondary flotation cell.

Description

FLOTATION METHOD Field of Invention The present disclosure relates to a flotation arrangement and its use, to a flotation plant, and to a flotation method for separating metal ore particles containing valuable metals from metal ore particles suspended in a slurry. Compendium of Invention The arrangement according to the current disclosure is characterized by what is presented in claim 1. The use of the floating arrangement according to the current disclosure is characterized by what is presented in claim 48. The flotation plant according to the current disclosure is characterized by what is presented in claim 59. The flotation method according to the current disclosure is characterized by what is presented in claim 69. A flotation system is provided for treating metal ore particles suspended in a slurry. The flotation system comprises flotation cells for separation of the slurry into reflux and overflow. The separation is carried out with the aid of a flotation gas. The flotation arrangement comprises a primary flotation line comprising a rougher portion with at least two rougher primary flotation cells connected in series and arranged in fluid communication, overflow from a first rougher primary flotation cell arranged to flow directly into a secondary flotation line; the primary flotation line further comprising a scrubber portion with at least two scrubber primary flotation cells connected in series and arranged in fluid communication, overflow from the scrubber primary flotation cells arranged to flow back to the rougher flotation cell of the primary flotation line, or to a regrind stage and then to a cleaner scrubber flotation line.In the primary flotation line, a downstream primary flotation cell is arranged to receive the primary underflow from a upstream primary flotation cell. The secondary flotation line comprises at least two secondary flotation cells, where in the secondary flotation line, a first secondary flotation cell is arranged in fluid communication with at least one rougher primary flotation cell, and arranged to receive the primary overflow from at least one rougher primary flotation cell for the recovery of a first concentrate.The flotation arrangement is characterized in that at the secondary flotation line, another secondary flotation cell is arranged in fluid communication with at least one other rougher primary flotation cell, and arranged to receive the primary overflow from at least one other rougher primary flotation cell for the recovery of a first concentrate; the further secondary flotation cell is arranged in fluid communication with a prior secondary flotation cell, and the underflow from the first secondary flotation cell is arranged to flow to the further secondary flotation cell, or is arranged to be combined with the secondary underflow from the further secondary flotation cell. The use of a flotation arrangement according to the present disclosure is intended to be employed in the recovery of metalliferous ore particles comprising valuable mineral. The flotation plant according to the invention comprises a flotation arrangement according to the present disclosure. The flotation method for treating metal ore particles suspended in a slurry in flotation stages in which the slurry is separated into underflow and overflow with the aid of flotation gas comprises subjecting the slurry to primary flotation comprising at least two rougher flotation stages in series and in fluid communication, the primary overflow from a first rougher stage being directed to secondary flotation; the primary flotation further comprising at least two scrubbing flotation stages in series and in fluid communication, the primary overflow from the scrubbing stages being directed toward the first rougher stages, or in regrind and then cleaner flotation, and in primary flotation, the primary overflow from a previous flotation stage is directed toward a subsequent flotation stage.In the flotation method, the slurry is further subjected to a secondary flotation comprising at least two secondary flotation stages in fluid communication, wherein the primary overflow from at least a first rougher flotation stage is directed to a first secondary flotation stage for recovery of a first concentrate, the at least first rougher flotation stage and the first flotation stage being in series and in fluid communication.The flotation method is characterized in that in the secondary flotation the primary overflow from at least one further rougher flotation stage is directed to a further secondary flotation stage in series and in fluid communication with the at least one further rougher flotation stage, for the recovery of a first concentrate, the at least one further rougher flotation stage and the further secondary flotation stage being in series and in fluid communication; the next secondary flotation stage and a previous secondary flotation stage are in fluid communication; and the underflow from the first secondary flotation stage is directed to the next secondary flotation stage, or is combined with the secondary underflow from the next secondary flotation stage. With the invention described herein, the focus of slurry treatment can be shifted toward efficient separation of the valueless fraction of the ore particles and the recovery of a maximum amount of valuable particles. In other words, ore particles comprising very small or even minimal amounts of valuable material can be recovered for further processing. This can be especially beneficial for poor-quality ores, i.e., ores with very little valuable material initially, e.g., from poor ore deposits that may have previously been considered economically too insignificant to justify utilization. Essentially, ore particles comprising a relatively high amount of valuable minerals are treated only once in a primary flotation line, which can be understood as a treatment line comprising rougher and / or scrubber cells. The underflow from the primary flotation cells is directed downstream along the primary flotation line to ensure that the majority of the valuable mineral material is recovered in the primary line. At the same time, the overflow from the primary flotation cells is directed to a secondary flotation line, which can be understood as a treatment line comprising scrubber cells, for the efficient separation of any unwanted particles from the material recovered from the flotation cells of the primary line.By directing the secondary bottom reflux from a first secondary flotation cell downstream along the secondary waterline, it can further be ensured that most of the valuable mineral material is recovered. Furthermore, when the underflow from a primary flotation cell(s), or from a secondary flotation cell(s), is sent downstream along the primary or secondary line in the direction of slurry flow, or the primary overflows into the secondary line, by gravity, energy consumption can be reduced while achieving very efficient recovery of the valuable mineral. It is possible to achieve a high grade for a portion of the slurry stream while simultaneously achieving high recovery of the entire slurry stream passing through the flotation arrangement. Retreating the slurry stream in several adjacent flotation cells in this manner ensures effective mineral recovery without any significant increase in energy consumption, as the slurry flows do not need to be pumped in an energy-consuming manner, but rather by utilizing the inherent hydraulic head of the slurry flows downstream within the flotation arrangement and plant. At the beginning or end of the flotation arrangement, it is therefore possible to recover a high grade of metal particles comprising valuable ore, while at the end of the flotation arrangement, it can be used to recover the largest possible amount of metalliferous ore particles comprising even a small amount of valuable ore. The overflow degree is increased through the use of secondary flotation lines, while the primary line in particular ensures efficient overall recovery of the metalliferous ore particles comprising valuable ore. The flotation arrangement allows the grade to be increased without high-energy pumping, thus providing significant advantages over the prior art. The flotation arrangement, its use, the flotation plant, and the flotation method according to the invention have the technical effect of enabling flexible recovery of various particle sizes, as well as efficient recovery of metalliferous ore particles containing valuable mineral from lean ore feedstock with relatively low amounts of valuable mineral initially. The advantages provided by the waterline structure allow precise adjustment of the waterline structural parameters according to the target valuable material at each installation. By treating the slurry in accordance with the present invention as defined by this disclosure, the recovery of metal ore particles containing valuable material can be increased. The initial grade of the recovered material may be lower, but the material (i.e., slurry) is also readily prepared for further processing, which may include, for example, regrind and / or cleaning. Arranging flotation lines so that at least some or all of the flotation cells (i.e., the flotation cell bottoms) are on the same level increases construction speed, simplifies planning and construction, and therefore reduces costs. This so-called uniplanarity of flotation cells or flotation lines could offer advantages through reduced investment costs, since installing a plant requires less fieldwork and less space. This could be especially advantageous when increasing the size of the flotation cell. Again, this could be desirable from the perspective of optimizing process performance while reducing capital investment costs.In the case where the flotation cells are arranged in a uniplanar manner, the flow of the suspension from the flotation cell to the next flotation cell can be achieved by pumping action, for example by low-head pumps. According to some embodiments of the invention, the waterlines may also be arranged in a graded manner, so that at least some of the flotation cells (i.e. the bottoms of the flotation cells), whether at the primary waterline or at the secondary waterline, are positioned at different levels: for example, the bottom of a first primary flotation cell of a primary waterline may be arranged above the bottom of the next primary flotation cell(s) (rougher or scrubber primary flotation cell), and / or above the bottom of the first secondary flotation cell into which the overflow from the first primary flotation cell is directed.In this way, the surface level of the suspension of at least some of the flotation cells following the first primary flotation cells is lower, thus creating a stage between any two following flotation cells in direct fluid connection with each other. The stage thus created allows for a hydrostatic head or hydrostatic pressure differential (hydraulic gradient) to be achieved between the two subsequent flotation cells, allowing slurry flow from one cell to the next by gravity, without separate pumps. The hydraulic gradient forces the slurry flow toward the tailings outlet or waterline outlets. This can reduce the need for additional pumping. Furthermore, the pumping power requirement can be reduced as the material flow is directed downstream by gravity due to the drop in slurry surface levels. This can even be applied to configurations where the slurry surface levels of adjacent flotation cells on the waterline are at the same level.The reduced need for energy-intensive pumping will lead to savings in energy consumption, as well as simplified construction of the flotation operation, and a reduced requirement for construction space. By directing the at least one first primary overflow directly to at least one stage of the first secondary flotation for the recovery of a first concentrate, the process does not include any grinding steps between the primary flotation stage and the secondary flotation stage. By eliminating the grinding step, the hydraulic head of the slurry flow is not lost between two subsequent stages, and only gravity can be used to drive the slurry flow. Therefore, the first primary overflow can be separated from the lower-quality additional primary overflow. The first primary overflow can be floated separately from the additional primary overflow, thereby increasing the recovery of the metalliferous ore particles comprising valuable mineral. Basically, the purpose of flotation is to recover a concentrate of metal ore particles comprising a valuable mineral. A concentrate refers to the portion of the recovered suspension in the overflow or underflow that exits a flotation cell. A valuable mineral refers to 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 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 can be performed based on the natural hydrophobic / hydrophilic difference or based on hydrophobic / hydrophilic differences produced by the addition of a surfactant or collecting chemical. Gas can be added to the raw material subject to flotation (slurry or slurry) in several different ways. A flotation arrangement is understood to mean an assembly comprising at least two flotation units or flotation cells arranged in fluid connection with one another to allow either gravity-driven slurry or pumped slurry to flow between the flotation cells, forming a flotation line. The arrangement is intended to treat ore particles suspended in the slurry by flotation. Thus, ore particles containing valuable metals are recovered from the ore particles suspended in the slurry. The slurry is fed through a feed inlet to the first flotation cell of the waterline to initiate the flotation process. The flotation arrangement may be part of a larger flotation plant containing one or more flotation arrangements.Therefore, a number of different pre-treatment and post-treatment devices or stages may be in operative connection with the components of the flotation arrangement, as is known to those skilled in the art. By waterline is meant a part of the flotation arrangement where several flotation cells are arranged in fluid connection with one another such that the underflow from each preceding flotation cell is directed to the next or subsequent flotation cell as an inlet feed up to the last flotation cell of the waterline, from which the underflow is directed off-line as tailings or reject flow. In connection with the method for flotation according to the present invention, by flotation is meant the complete flotation process carried out in a waterline. The flotation cells in a flotation arrangement are fluidly connected to each other. The fluid connection can be achieved through different lengths of conduits, such as pipes or tubes, with the length of the conduit depending on the overall physical construction of the flotation arrangement. Alternatively, the flotation cells may be arranged in a direct cell connection with one another. A direct cell connection refers to an arrangement whereby the outer walls of any two subsequent flotation cells are connected to one another to allow an outlet of a first flotation cell to be connected to the inlet of the subsequent flotation cell without any separate conduit. Direct contact reduces the need for piping between two adjacent flotation cells. This thus reduces the need for components during waterline construction, speeding up the process. Furthermore, it can reduce sanding and simplify waterline maintenance. The fluid connection between the flotation cells and the flotation units can be direct, i.e., the two flotation cells (belonging to the same or different waterlines) can be immediately adjacent to each other. Alternatively, the two flotation cells can be placed at a distance from each other and connected via a pipe, channel, or other means known in the art. The fluid connection between the flotation cells can comprise various regulating mechanisms. A “neighboring,” “adjacent,” or “contiguous” flotation cell means a flotation cell immediately after or before any flotation cell, whether downstream or upstream, or whether in a primary line, in a secondary line, or in the relationship between a flotation cell of a primary line and a flotation cell of a secondary line to which overflow from the flotation cell of the primary line is directed. A flotation cell is understood to mean a tank or vessel in which a step of a flotation process is carried out. A flotation cell is typically cylindrical in shape, the shape being defined by an outer wall or walls. Flotation cells regularly have a circular cross-section. Flotation cells may have a polygonal section, such as rectangular, square, triangular, hexagonal, or pentagonal, or otherwise a radially symmetrical cross-section. The number of flotation cells may vary according to a specific flotation arrangement and / or operation for treating a specific type and / or grade of mineral, as is known to a person skilled in the art. In relation to the flotation method according to the present invention, a flotation step is understood to mean the flotation process that takes place in a flotation cell. The flotation cell may be a froth flotation cell, such as a mechanically agitated cell or tank cell, a column flotation cell, a Jameson cell, or a double flotation cell. In a double flotation cell, the cell comprises at least two separate vessels, a first mechanically agitated pressure vessel with a mixer and a flotation gas inlet, and a second vessel with a tailings outlet 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™ cell), wherein air or other flotation gas bubbles dispersed by the fluidization system percolate through the hindered configuration zone and adhere to the hydrophobic component, altering its density and making it sufficiently buoyant to float and be recovered.In a fluidized bed flotation cell, axial mixing is not required. The flotation cell may also be of a type where a mechanical flotation cell (i.e., a flotation cell comprising a mechanical agitator or mixer) comprises a microbubble generator for generating microbubbles in the suspension within the flotation cell. The size distribution of the microbubbles is smaller than that of conventional flotation gas bubbles introduced by the mixer or other gas introduction system, which typically range in size from 0.8 to 2 mm. The size range of the microbubbles may be from 1 pm to 1.2 mm. The microbubbles may be introduced by a microbubble generator comprising a suspension recirculation system or a direct spreader system. The flotation cell may also be an overflow flotation cell operated with constant overflow of slurry. In an overflow flotation cell, the slurry is treated by introducing flotation gas bubbles into the slurry and creating a continuous upward flow of slurry in the vertical direction of the first flotation cell. At least some of the valuable metal-containing ore particles adhere to the gas bubbles and rise by floatation, at least some of the valuable metal-containing ore particles adhere to the gas bubbles and rise with a continuous upward flow of slurry, and at least some of the valuable metal-containing ore particles rise with the continuous upward flow of slurry.The ore particles containing valuable metal are recovered by conducting the continuous upward flow of slurry out of at least one overflow flotation cell in the form of a slurry overflow. When the overflow cell is operated with virtually no froth depth or froth layer, a froth zone does not effectively form on the slurry surface at the top of the flotation cell. The froth can be discontinuous over the cell. The result is that more ore particles containing valuable mineral can be entrained into the concentrate stream, and the overall recovery of valuable material can be increased. All flotation cells in a flotation arrangement according to the invention may be of a single type, i.e., the rougher flotation cells in the rougher portion, the scrubber flotation cells in the scrubber portion, and the secondary flotation cells in the secondary waterline may be of a single flotation cell type, such that the flotation arrangement comprises only one type of flotation cells as mentioned above. Alternatively, several flotation cells may be of one type while other cells are of one or more types, such that the flotation arrangement comprises two or more types of flotation cells as mentioned above. Depending on its type, the flotation cell may comprise a mixer for agitating the suspension to keep it in suspension. A mixer is understood to mean any means suitable for agitating the suspension 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 structure being arranged at the bottom 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 upward flow of suspension. Overflow refers to the portion of the suspension collected in the flotation cell tundish and thus leaving the flotation cell. The overflow may comprise froth, froth, and suspension, or in certain cases, either alone or as the majority of the suspension. In some embodiments, the overflow may be an acceptable flow containing the valuable material particles collected from the suspension. In other embodiments, the overflow may be a reject flow. This is the case when the flotation arrangement, plant, and / or method is used in reverse flotation. Bottom reflux refers to the fraction or portion of the suspension that does not float on the surface of the suspension during the flotation process. In some embodiments, bottom reflux may be a reject flow exiting a flotation cell through an outlet typically located at the bottom of the flotation cell. Eventually, the bottom flowback from the final flotation cell of a flotation line or flotation arrangement may leave the entire arrangement as a tailings flow or final residue from a flotation plant. In some embodiments, the bottom flowback may be an accepted flow containing valuable metal ore particles. This is the case when the flotation arrangement, plant, and / or method is used in reverse flotation. Reverse flotation refers to a reverse flotation process typically used in iron recovery. In this case, the flotation process aims to collect the non-valuable portion of the slurry flow in the underflow. The overflow in the reverse flotation process for iron typically contains silicates, while metalliferous ore particles containing valuable iron are collected in the underflow. Reverse flotation can also be used for industrial minerals, i.e., geological minerals mined for their commercial value that are neither fuel nor sources of metals, such as bentonite, silica, gypsum, and talc. Downstream means the direction concurrent with the suspension flow (direct current, indicated in the figures by arrows), and upstream means the direction countercurrent to or against the suspension flow. Concentration refers to the floating portion or fraction of the suspension of metal ore particles comprising a valuable mineral. A first concentration may comprise metal ore particles comprising one valuable mineral, while a second concentration may comprise metal ore particles comprising another valuable mineral. Alternatively, the distinctive definitions "first" and "second" may refer to two concentrations of metal ore particles comprising the same valuable mineral but with two distinctly different particle size distributions. A rougher flotation, a rougher part of the waterline, a rougher stage, and / or rougher cells refers to a flotation stage that produces a rougher concentrate. The objective is to remove a maximum amount of the valuable mineral to as coarse a particle size as possible. Complete liberation is not necessary for rougher flotation; only sufficient liberation to release enough valuable mineral gangue to obtain a high recovery. The primary objective of a rougher stage is to recover as much valuable mineral as possible, with less emphasis on the quality of the concentrate produced. The harder concentrate typically undergoes further stages of cleaning flotation on a rougher waterline to reject more of the unwanted minerals also found in the froth, in a process known as cleaning. The cleaned product is known as cleaning concentrate or final concentrate. Rougher flotation is often followed by scrubbing flotation, which is applied to harder tailings. A scrubbing flotation, a scrubbing portion of the waterline, a scrubbing stage, and / or a scrubbing cell is a flotation stage in which the objective is to recover any valuable mineral materials that were not recovered during the initial rougher stage. This could be achieved by changing the flotation conditions to make them more stringent than the initial hardness, or, in some embodiments of the invention, by introducing microbubbles into the slurry. The concentrate from a scrubbing cell or stage may be returned to the rougher feed for refloating or directed to a regrind stage and then to a cleaner flotation line. By cleaner flotation, a cleaner / scrubber line, a cleaner / cleaner stage and / or a cleaner cell is meant a flotation stage where the objective of cleaning is to produce as high a grade of concentrate as possible. Pretreatment and / or post-treatment and / or further processing means, for example, pulverizing, crushing, separating, screening, classifying, fractionating, conditioning, or cleaning, all of which are conventional processes known to those skilled in the art. Further processing may also include at least one of the following: an additional secondary flotation cell, which may be a conventional cleaner flotation cell, a recovery cell, a rougher cell, or a scrubber cell. The suspension surface level is the height of the suspension surface in the flotation cell, measured from the bottom of the flotation cell to the top of the flotation cell trough. In effect, the suspension height is equal to the height of the top of the trough of a flotation cell, measured from the bottom of the flotation cell to the top of the flotation cell trough. For example, any two flotation cells below may be arranged in a staggered manner on a waterline such that the suspension surface level of said flotation cells is different (i.e., the suspension surface level of the first of said flotation cells is higher than the suspension surface level of the second of said flotation cells). This difference in suspension surface levels is defined as a "step" between any two flotation cells below.The stage or difference in suspension surface levels is a difference that allows the suspension flow to be driven by gravity or gravitational force, creating a hydraulic drop between the two following flotation cells. In one embodiment of the flotation arrangement, the at least one of the secondary flotation cells of the secondary waterline is arranged in direct fluid communication with the rougher first primary bloom cell from which it is arranged to receive primary overflow. Direct fluid communication means that two neighboring, adjacent, or contiguous flotation cells are connected so that no additional process steps, such as grinding, are arranged between any two flotation cells or flotation stages. This should not be confused with the previous definition of direct cell connection. In certain cases of conventional froth flotation processes, the overflow from a first flotation cell may initially be directed to a regrind stage or to another additional processing stage before being directed to a secondary flotation cell. This is especially typical for conventional flotation operations, which include a rougher stage or a scrubber stage followed by a cleaner stage. In the flotation arrangement, plant, and method according to the present invention, such further processing step may be abandoned, and the primary flotation cell, from which the primary overflow is directed, may be roughened to a secondary flotation cell, and that secondary flotation cell may thus be in direct fluid connection with each other. Similar direct fluid communication may also be provided between two other flotation cells of the flotation arrangement. In one embodiment of the flotation arrangement, the primary waterline comprises at least four primary flotation cells, or 3-10 flotation cells, or 4-7 flotation cells. In one embodiment of the flotation arrangement, the rougher portion of the primary waterline comprises at least two rougher primary flotation cells, or 2-6 rougher primary flotation cells, or 2-4 primary flotation cells. In one embodiment of the flotation arrangement, the scrubber portion of the primary waterline comprises at least two scrubber primary flotation cells, or 2-6 scrubber primary flotation cells, or 2-4 scrubber primary flotation cells. Having a sufficient number of primary flotation cells (rougher primary flotation cells and / or a scrubber) allows for high-grade production for part of the concentrate, while also ensuring high recovery of the desired valuable mineral throughout the primary line, thus preventing any valuable mineral from ending up in the tailings stream. To the extent possible, metal ore particles comprising a valuable mineral can be floated, while simultaneously reducing the pumping energy required to achieve this. In one embodiment of the flotation arrangement, the secondary line comprises at least two secondary flotation cells, or 2-10 secondary flotation cells, or 4-7 secondary flotation cells. Even a small number of secondary flotation cells can be sufficient to clean the overflow from the primary flotation cells to a reasonable level, i.e., increase the grade of the concentrate recovered from the primary line. The underflow from even a low number of secondary flotation cells has a high enough volume to be sent for further treatment in the primary line to further increase recovery. In one embodiment of the flotation arrangement, the number of secondary flotation cells in series on the secondary waterline is equal to or less than the number of primary flotation cells in series on the primary waterline. The overflow from a primary cell or cells into the first flotation cell or cells of the secondary waterline may be of higher quality (i.e., higher grade) than the overflow from primary flotation cells located downstream on the primary waterline into the additional secondary flotation cell or cells of the secondary waterline. The additional secondary waterline may therefore require more capacity to efficiently treat the slurry. Furthermore, excessive treatment in the first secondary flotation cell or cells may lead to increased pumping requirements, which would lead to undesirable higher energy consumption. The effect of this type of embodiment is that while minimal pumping is performed to boost the slurry flows, at least a portion of the concentrate can be recovered at a very high grade. In one embodiment of the flotation arrangement, a secondary flotation cell is arranged to receive primary overflow from 1-3 rougher primary flotation cells, or from 1-2 rougher primary flotation cells. In another embodiment of the flotation arrangement, a secondary flotation cell is arranged to receive primary overflow from at most two rougher primary flotation cells. In another embodiment of the flotation arrangement, a secondary flotation cell is arranged to receive primary overflow from at most one rougher primary flotation cell. In another embodiment of the flotation arrangement, the additional secondary flotation cell is arranged to receive primary overflow from at least two rougher primary flotation cells. In this way, the overflows from the various rougher primary flotation cells do not mix to a very high degree. Each overflow can be treated as best as possible to ensure sufficient treatment, and only a small number of secondary flotation cells acting as recovery cells are needed to achieve high-grade concentration. In one embodiment of the flotation arrangement, the underflow from the further secondary flotation cell is arranged to flow back to the rougher part of the primary waterline at a point downstream of the rougher primary flotation cell from which the further secondary flotation cell is arranged to receive primary overflow. In another embodiment of the flotation arrangement, the underflow from the further secondary flotation cell is arranged to flow back to another, rougher primary flotation cell downstream of the first primary flotation cell from which the further secondary flotation cell is arranged to receive primary overflow. In another embodiment of the flotation arrangement, the lower reflux from the additional secondary flotation cell is arranged to be combined with the overflow. In one embodiment of the flotation arrangement, the first secondary cell of the first secondary line has at least one additional rougher primary flotation cell downstream of the rougher primary flotation cell from which a further secondary flotation cell is arranged to receive primary overflow. In one embodiment of the flotation arrangement, the secondary flotation line further comprises an additional secondary flotation line comprising at least one additional secondary flotation cell arranged to receive primary overflow from at least one other rougher primary flotation cell. In another embodiment of the flotation arrangement, the bottom reflux from the additional secondary flotation cell is arranged to flow into the additional secondary flotation cell. In another embodiment of the flotation arrangement, the first secondary flotation cell is arranged to receive primary overflow from the first rougher primary flotation cell, and the further secondary flotation cell is arranged to receive primary overflow from at least two rougher primary flotation cells. The additional secondary flotation cell can act as a recovery cell. This arrangement can prevent metal ore particles comprising valuable mineral from ending up in the tailings stream, thereby ensuring good recovery of the desired concentrate. Using an additional secondary flotation cell can ensure that all available valuable mineral is recovered from the primary line slurry flow in the overflow or concentrate. The loss of ore particles comprising valuable mineral can be minimized, further improving the froth recovery efficiency of the flotation arrangement and the plant. Similarly, when using the flotation arrangement in reverse flotation, as much ore particles comprising valuable material as possible can be recovered in the underflow from the primary line. The underflow from the additional secondary flotation cell can be directed to the regrind circuit or stage to ensure the recovery of ore particles comprising valuable mineral from that slurry flow as well. Furthermore, the need for pumping can be reduced while the underflow from the secondary flotation line is efficiently retreated. After this operation, with an additional secondary flotation cell acting as a recovery cell, a significant portion of the metalliferous ore particles comprising valuable mineral can be effectively floated. From the first line, at a location where the high-grade concentrate has already been extracted, a sufficient amount of primary overflow can still be collected to efficiently float the desired concentrate away. Furthermore, the underflow from the additional secondary flotation cell can be directed to a further processing stage. The underflow may be especially suitable for an additional grinding stage. By additional secondary flotation cell is meant a flotation cell from which the overflow is directed away from the flotation arrangement, for example directly to a further processing stage such as a grinding stage or a frothing stage. The underflow from the additional secondary flotation cell may be directed back upstream, into the first rougher primary flotation cell of a primary flotation line, or to a rougher primary flotation cell upstream of the rougher primary flotation cell from which the overflow is received in the additional secondary flotation cell; or away from the flotation arrangement, either as tailings flow directed to further treatment outside the flotation arrangement, for example regrind, or as an inlet to another flotation arrangement for further concentration recovery. In one embodiment of the flotation arrangement, the underflow from a further secondary flotation cell is arranged to flow to the last of the at least one rougher primary flotation cells from which the primary overflow to the further secondary flotation cell was received, or to a rougher primary flotation cell downstream of the last of the at least one rougher primary flotation cells from which the primary overflow to the further secondary flotation cell was received. When the underflow from secondary flotation tanks is returned downstream to the primary line, in the direction of slurry flow, energy consumption can be reduced while achieving highly efficient recovery of the valuable mineral. A high grade can be achieved for a portion of the slurry stream, while simultaneously achieving high recovery of the entire slurry stream passing through the flotation arrangement. By directing the underflow from a secondary flotation cell downstream, energy-intensive pumping can be avoided.Retreating the slurry flow in multiple adjacent flotation cells in this manner ensures effective mineral recovery without any significant increase in energy consumption, as the slurry flows do not need to be pumped in an energy-consuming manner, but rather utilize the inherent hydraulic head of the slurry flows downstream within the flotation arrangement and plant. The slurry is returned for further treatment to a position in the flotation arrangement where a similar slurry is already being treated. In effect, any pumping required to drive the slurry flow can be minimized, while the slurry is still conveyed to multiple treatment stages in the flotation arrangement. Furthermore, slurry fractions with similar or identical properties can be combined for further treatment.The primary floatline bottom flow combined with a secondary floatline bottom flow can have very similar properties, for example, the amount of ore particles that still comprise valuable mineral, or ore particles with the same size distribution. This allows the flotation process to be optimized. In one embodiment of the flotation arrangement, the first secondary flotation cell of the secondary bloom line has a larger volume than the further secondary flotation cell of the secondary float line. The first primary flotation cell can have a higher-grade concentrate in its overflow than subsequent primary flotation cells on the primary waterline. Overflows from those subsequent primary flotation cells can be treated in smaller secondary flotation cells, thus achieving a shorter flotation time. This type of arrangement can also ensure a higher-grade concentrate from the additional secondary flotation cells on the secondary waterline. In one embodiment of the flotation arrangement, the additional secondary flotation cell of the secondary waterline has a larger volume than the first flotation cell of the secondary waterline. In one embodiment of the flotation arrangement, the first rougher primary flotation cell has at least 150 m3 of volume, or at least 500 m3 of volume, or at least 2000 m3 of volume. In one embodiment of the flotation arrangement, the second, rougher primary flotation cell has at least 100 m3 of volume, or at least 300 m3 of volume, or at least 500 m3 of volume. The use of flotation cells with a volumetric size of at least 400 m3 increases the probability of collisions between gas bubbles created in the flotation cells, for example, by means of a rotor, and particles comprising valuable ore, thereby improving the recovery rate for the valuable ore as well as the overall efficiency of the flotation arrangement. Larger flotation cells have greater selectivity, as more collisions occur between gas bubbles and ore particles due to the longer time the suspension remains in the flotation cell. Therefore, most of the ore particles containing valuable ore are able to float. Furthermore, the bottom of the floating ore particles can be higher, meaning that ore particles comprising a very low amount of valuable ore fall back to the bottom of the flotation cell.Therefore, the degree of overflow and / or concentration of larger flotation cells can be higher. These types of rougher primary flotation cells can ensure high quality. In one embodiment of the flotation arrangement, the second rougher primary flotation cell is equal in volume to the first rougher primary flotation cell, or less in volume than the first rougher primary flotation cell. In one embodiment of the flotation arrangement, the first secondary flotation cell in fluid communication with a rougher primary flotation cell is 100-2000 m3 in volume, preferably 400-1000 m3 in volume. The use of flotation cells with a volumetric size of at least 400 m3 increases the probability of collisions between gas bubbles created in the flotation cells, for example, by a rotor, and the particles comprising valuable ore, thereby improving the recovery rate for the valuable ore as well as the overall efficiency of the flotation arrangement. As mentioned above, larger flotation cells have greater selectivity, as more collisions occur between gas bubbles and ore particles due to the longer time the suspension remains in the flotation cell. Therefore, most of the ore particles containing valuable ore can be floated.Furthermore, the bottom of the floating ore particles can be higher, meaning that ore particles containing very little valuable mineral fall back to the bottom of the flotation cell. Therefore, the degree of overflow and / or concentration of larger flotation cells can be greater. In one embodiment of the flotation arrangement, the additional secondary flotation cell of the secondary waterline in fluid communication with a rougher primary flotation cell is 100-2000 m3 in volume, preferably 300-1000 m3 in volume. The use of flotation cells with a volumetric size of at least 300 m3 increases the probability of collisions between gas bubbles created in the flotation cells, for example, by means of a rotor, and the particles comprising valuable mineral, thereby improving the recovery rate for the valuable mineral as well as the overall efficiency of the flotation arrangement. In an arrangement where there is a secondary waterline cleaning the overflow from a rougher primary flotation cell, and where the underflow from such secondary waterline is carried back to a subsequent rougher primary flotation cell downstream, it is important to obtain a higher grade from the rougher primary flotation cell than to obtain a high recovery of metalliferous ore particles comprising valuable ore in the overflow from the rougher primary flotation cell. This is because the underflow from the secondary waterline can be re-treated in the primary waterline where any remaining ore particles comprising valuable ore are recovered.While some valuable material is returned to the primary waterline, the energy required to pump the lower reflux back to the primary waterline is not crucial, as the rougher primary flotation cells later ensure recovery. However, it is not always preferable to use flotation cells larger than 1000 m3, as efficient mixing is difficult to achieve in such a large cell. Without efficient mixing, ore particles comprising relatively small amounts of valuable mineral fall back to the bottom of the flotation cell, which can negatively affect the recovery rate. With a flotation arrangement of the above embodiment, it may be possible to produce or recover at least some part of the concentrate with a very high grade. If the rougher primary flotation cells have a relatively large volume, there may not be a need for subsequent large flotation cells. Rather, the flotation cells (primary or secondary) downstream of the rougher primary cell(s) may be smaller and therefore more efficient. In the flotation process for certain minerals, it may be easy to float a significant portion of the ore particles comprising high-grade valuable mineral. In that case, it may be possible to have smaller volume flotation cells downstream of the primary flotation line and still achieve a high recovery rate. In one embodiment of the flotation arrangement, the volume of the first secondary flotation cell in fluid communication with the at least one rougher primary flotation cell is 2-50% of the aggregate volume of the at least one rougher primary flotation cell, preferably 3-30% of the aggregate volume of the at least one primary flotation cell. In one embodiment of the flotation arrangement, the volume of the additional secondary flotation cell of the secondary line in fluid communication with the at least one rougher primary flotation cell is 2-50% of the aggregate volume of the at least one rougher primary flotation cell, preferably 3-30% of the aggregate volume of the at least one rougher primary flotation cell. Aggregate volume refers to the combined volume of the rougher primary flotation cells from which a secondary flotation cell receives primary overflow. For example, the additional secondary flotation cell may receive primary overflows from more than one rougher primary flotation cell in the primary line. In that case, the aggregate volume is the combined volume of the rougher primary flotation cells. In these methods, a portion of the concentrate is produced with a high grade. When the secondary flotation cells in the secondary flotation line(s) are smaller, the ore particles remain in the flotation cell for a shorter period of time, meaning there is less time to float the desired concentrate. The resulting concentrate therefore has a higher grade. Constructing the secondary flotation cell(s) of the secondary waterline smaller in the direction of slurry flow than the flotation cell(s) of the primary waterline could provide efficiency benefits. The effect could be especially noticeable if the flotation cell(s) of the secondary waterline are at least 10% smaller than those of the primary waterline. For example, at least one flotation cell of the secondary waterline might be at least 20 or 30% smaller than at least one primary flotation cell of the primary waterline. In one embodiment of the flotation arrangement, the flow of slurry between at least two fluidly connected flotation cells is driven by gravity. In a further embodiment of the flotation arrangement, the flow of slurry between the first rougher primary flotation cell and a further rougher primary flotation cell is gravity driven. In a further embodiment of the flotation arrangement, the flow of slurry between the first secondary flotation cell and a further secondary flotation cell is gravity driven. In a further embodiment of the flotation arrangement, the flow of slurry between a rougher primary flotation cell and a secondary flotation cell in fluid connection with the rougher primary flotation cell is gravity driven. In another embodiment of the flotation arrangement, the flow of slurry between the first rougher primary flotation cell and the first secondary flotation cell is gravity driven. In a further embodiment of the flotation arrangement, the flow of slurry between a further rougher primary flotation cell and a further secondary flotation cell is gravity driven. By arranging for gravity-driven slurry flow, energy savings can be achieved, as no additional pumping is required to drive the slurry downstream. By avoiding energy-intensive pumping in the flotation arrangement, significant energy savings can be achieved while ensuring efficient recovery of valuable mineral material from low-grade ores, i.e., those containing very little valuable mineral to begin with. It may be possible to produce some portion of the concentrate with a high grade, yet still achieve good overall recovery of the desired valuable mineral. Only negligible amounts of the valuable mineral may end up in the tailings stream. The invention aims to improve the mineral recovery process while simultaneously reducing the energy consumption of the process. This is possible by utilizing the inherent slurry flows of the process, i.e., by moving the slurry flow toward retreatment in downstream flotation cells. By arranging the flotation process in this manner, it is possible to direct the slurry flow by gravity. In some embodiments, the slurry flow can also be directed by low-intensity pumping, or by a suitable combination of both, i.e., gravity and low-intensity pumping.For example, it is possible to handle the slurry flow by means of a low head pump or by gravity, where the underflow from an additional secondary flotation cell is arranged to flow towards the last of the rougher primary flotation cells from which the primary overflow was received, or towards a rougher primary flotation cell downstream of the last of the at least one primary flotation cells from which the primary overflow was received. A low-head pump refers to any type of pump that produces a low pressure to propel a slurry flow downstream. Typically, a low-head pump produces a maximum head of up to 1.0 meters; that is, it can be used to propel the slurry flow between two adjacent flotation cells with a difference of less than 30 cm in the slurry surface level. A low-head pump typically has an impeller to create axial flow. In one embodiment of the flotation arrangement, the primary overflow from at least one scrubber primary flotation cell is arranged to flow directly to a regrind stage. In a further embodiment of the flotation arrangement, the combined primary overflow from the scrubber flotation cells is arranged to flow directly to a regrind stage. In one embodiment of the flotation arrangement, the combined secondary overflow from the at least two secondary flotation cells is arranged to flow to a further processing stage. In one embodiment of the flotation arrangement, the bottom reflux from the last scrubbing primary flotation cell is arranged to flow to a further processing stage, or to exit the flotation arrangement as tailings. In one embodiment of the flotation arrangement, the bottom reflux from the last secondary flotation cell of the secondary waterline is arranged to flow to a further processing stage, or to exit the flotation arrangement as tailings. In a further embodiment of the flotation arrangement, the further processing step comprises at least one step selected from: a grinding step, a conditioning step, a flotation step. By further processing is meant any suitable process step, such as a grinding step or a chemical addition step, or any other process step typically used in connection with the flotation arrangement and known to one skilled in the art. The grinding step may comprise at least one mill, which may be any suitable mill known to one skilled in the art. In one embodiment of the flotation arrangement, the flotation arrangement comprises two primary flotation lines, and the first secondary flotation cell of the secondary flotation line is arranged to receive the overflow from the rougher first primary flotation cells of both primary flotation lines. In such arrangements, it may be possible to have a larger volume of suspension inflow into a secondary flotation line. Therefore, it may be feasible to use larger volume flotation cells also in the secondary line, the benefits of which, primarily related to efficiency, have already been discussed earlier in this disclosure. In one embodiment of the flotation arrangement, the primary flotation cells and / or the secondary flotation cells comprise a froth flotation cell. In one embodiment of the flotation arrangement, a third rougher primary flotation cell, and any subsequent rougher primary flotation cell after the third rougher primary flotation cell, comprises a froth flotation cell. In a further embodiment of the flotation arrangement, the first rougher primary flotation cell and a second rougher primary flotation cell of the primary waterline function as overflow flotation cells. In a further embodiment of the flotation arrangement, the flotation gas is introduced into the flotation cell where the slurry is separated into overflow and underflow. In a further embodiment of the flotation arrangement, the flotation cell into which flotation gas is introduced comprises a mixer. In a further embodiment of the flotation arrangement, the flotation gas is introduced into a preparation flotation cell in which a mixer is arranged. A preparation flotation cell is understood to mean a flotation vessel in which the slurry can be prepared for flotation, typically by introducing flotation gas and employing mechanical agitation, before the slurry is conveyed to a second vessel where the actual flotation process is carried out. The preparation flotation cell may, for example, be the first vessel of a double flotation cell described earlier in this disclosure. In one embodiment of the flotation arrangement, the ore particles comprise Cu or Zn, or Fe, or pyrite, or metal sulfide such as gold sulfide. The ore particles comprising other valuable minerals such as Pb, Pt, PGMs (platinum group metals Ru, Rh, Pd, Os, Ir, Pt), oxide ore, industrial minerals such as L¡ (i.e., spodumene), petalite, and rare earth minerals may also be recovered, in accordance with the different aspects of the present invention. An embodiment of the use of a flotation arrangement according to the invention is particularly intended for the recovery of metalliferous ore particles comprising a valuable mineral from a low-grade ore. An embodiment of the use of a flotation arrangement according to the invention is intended for the recovery of metalliferous ore particles comprising Cu from low-grade ores. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the first rougher primary flotation cell has at least 150 m3 of volume, or at least 500 m3 of volume, or at least 2000 m3 of volume, and wherein the slurry flow is gravity driven. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the second, rougher primary flotation cell has at least 100 m3 of volume, or at least 300 m3 of volume, or at least 500 m3 of volume, and wherein the slurry flow is gravity driven. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the flow of slurry between the primary flotation cells of the primary waterline is driven by gravity. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the flow of slurry between the secondary flotation cells of the secondary line is driven by gravity. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the flow of slurry between a rougher primary flotation cell and a secondary flotation cell in fluid connection with the rougher primary flotation cell is driven by gravity. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the flow of slurry between the rougher first primary flotation cell and the first secondary flotation cell is gravity driven. An embodiment of the use of a flotation arrangement according to the invention is intended for a flotation arrangement wherein the flow of slurry between a further rougher primary flotation cell and a further secondary flotation cell of the secondary waterline is driven by gravity. An embodiment of the use of a flotation arrangement according to the invention is intended for the recovery of metal ore particles comprising Fe by reverse flotation. In one embodiment of the flotation plant, the plant comprises at least two, or at least three flotation arrangements according to the invention. In one embodiment of the flotation plant, the plant comprises at least a first flotation arrangement for recovering a first concentrate and at least a second flotation arrangement for recovering a second concentrate. In one embodiment of the flotation plant, the primary flotation cells of the at least one first flotation arrangement for recovering the first concentrate and the primary flotation cells of the at least one second flotation arrangement for recovering the second concentrate are arranged in series. In one embodiment of the flotation plant, the plant further comprises an arrangement for further treatment of the suspended metal ore particles so that the second concentrate differs from the first concentrate. In one embodiment of the flotation plant, the arrangement for further treatment of the suspended metal ore particles comprises a grinding stage, arranged between a first flotation arrangement and a second flotation arrangement. In this case, the second concentrate recovered from the second flotation arrangement may have a similar mineralogy to the first concentrate recovered from the first flotation arrangement, but the particle size distribution of the slurry that is conducted to the second flotation arrangement after the grinding stage may be different. In one embodiment of the flotation plant, the plant for the further treatment of the suspended metal ore particles comprises an arrangement for the addition of flotation chemicals, arranged between a first flotation arrangement and a second flotation arrangement. In this case, the second concentrate recovered from the second flotation arrangement may have a different mineralogy than the first concentrate recovered from the first flotation arrangement, the use of flotation chemicals used was naturally determined by the desired valuable mineral to be recovered by the second flotation arrangement. In one embodiment of the flotation plant, a flotation arrangement is provided to recover metal ore particles comprising Cu and / or Zn, and / or pyrite, and / or a sulfide metal, such as gold. In one embodiment of the flotation plant, the flotation arrangement is arranged to recover metalliferous ore particles comprising Cu from low-grade ores. For example, in the recovery of copper from low-grade ores obtained from poor ore deposits, the amount of copper can be as low as 0.1% by weight of the feed, i.e., slurry input into a flotation arrangement. The flotation arrangement according to the invention can be very practical for the recovery of copper, since copper is a so-called easily floatable mineral. In the liberation of metalliferous ore particles comprising copper, it may be possible to achieve a relatively high grade from the first primary flotation cells without any additional pumping between the flotation cells. By using the flotation arrangement according to the present invention, the recovery of such low quantities of valuable mineral, e.g., copper, can be efficiently increased, and even poor deposits can be profitably utilized. As the known rich deposits have already been increasingly utilized, there is a tangible need to process less favorable deposits, which may previously have been left unexploited due to a lack of appropriate technology and processes for the recovery of valuable material in very low quantities from the ore. In a further embodiment of the flotation plant, a flotation arrangement is provided to recover Fe by reverse flotation. In reverse flotation, ore particles comprising undesirable material are removed from suspension by arranging gas bubbles to adhere to those particles and removing them from the flotation cell in the overflow, while ore particles comprising valuable mineral material are recovered in the underflow, thereby reversing the conventional flotation flows of acceptance in the overflow and rejection in the underflow. Typically in Fe reverse flotation, the large attraction of large masses of valuable material, most commonly silicates, can cause significant problems in controlling the flotation process. Inevitably, some of the ore particles comprising valuable Fe end up in the overflow (especially the fines and light particles).By directing this overflow to a secondary waterline for reprocessing, at least some of the metalliferous ore particles comprising the Fe can be processed in the secondary waterline overflow and thus recovered. Similarly, the treatment of slurries for the recovery of such industrial minerals as bentonite, silica, gypsum, or talc can be enhanced using reverse flotation in the same manner as for Fe. In the recovery of industrial minerals, the objective of flotation may be, for example, the removal of dark particles in the overflow reject, and the recovery of white particles in the underflow accept. In such a process, some of the lighter, finer white particles may end up in the overflow. Those particles could be efficiently recovered by the invention according to the present disclosure. In one embodiment of the flotation method according to the invention, the suspension is subjected to at least four primary flotation stages, or 3-10 primary flotation stages, or 4-7 primary flotation stages. In one embodiment of the flotation method, the slurry is subjected to at least two stages of secondary flotation, or 2-10 stages of secondary flotation, or 4-7 stages of secondary flotation. In one embodiment of the flotation method, the primary overflow from 1-3 stages of rougher flotation, or from 1-2 stages of rougher flotation is directed to a secondary flotation stage. In one embodiment of the flotation method, the primary overflow from at least one additional rougher flotation stage, and the secondary overflow from the additional secondary flotation stage are directed to an additional secondary flotation stage of secondary flotation. In a further embodiment of the flotation method, primary overflow from a first rougher flotation stage is directed to a first secondary flotation stage, and primary overflow from at least two additional rougher flotation stages is directed to the additional secondary flotation stage. In one embodiment of the flotation method, bottom reflux from a secondary flotation stage is directed to primary flotation at the latter of the at least one rougher flotation stage from which the primary overflow was received, or to a rougher flotation stage downstream of the latter of the at least one rougher flotation stage from which the primary overflow was received. In one embodiment of the flotation method, froth flotation is employed in at least one primary flotation stage and / or at least one secondary flotation stage. In one embodiment of the flotation method, overflow flotation is employed in the first rougher flotation stage, or in the first rougher flotation stage and in a second rougher flotation stage. Brief Description of the Drawings The accompanying drawings, which are included to provide a better understanding of the present disclosure and which constitute part of this description, illustrate embodiments of the disclosure and, together with the description, help explain the principles of the present disclosure. In the drawings: Fig. 1a is a flowchart illustration for an embodiment of the invention. Fig. 1b is a flowchart illustration for an embodiment of the invention. Fig. 2 is a flowchart illustration for an embodiment of the invention. Fig. 3 is a flowchart illustration for an embodiment of the invention. Fig. 4a is a flowchart illustration for a detail of the embodiment of Fig. 1a. Fig. 4b is a simplified schematic perspective projection for the realization of Fig. 4a. Fig. 4c is a flowchart illustration for an alternative detail of the embodiment of Fig. 1a. Fig. 5a is a flow diagram illustration for another detail of the flotation arrangement. Fig. 5b is a simplified schematic perspective projection for the realization of Fig. 5a. Fig. 5c is a simplified illustration showing the relative vertical location of the flotation cells viewed from the direction of the secondary flotation cells in Fig. 5a. Fig. 6a is a flowchart illustration for a detail of an embodiment of the invention. Fig. 6b is a simplified schematic perspective projection for the realization of Fig. 6a. Fig. 6c is a simplified illustration showing the relative vertical location of the flotation cells viewed from the direction of the secondary flotation cells in Figure 6a. Fig. 7 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 8 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 9 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 10 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 11 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 12 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 13 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 14 is a flowchart illustration for a detail of an embodiment of the invention. Fig. 15 is a flow diagram illustration for one embodiment of a flotation plant according to the invention. Fig. 16 is a simplified schematic perspective projection of a flotation tank. Detailed Description of Preferred Modalities Reference will now be made in detail to embodiments of the present disclosure, an example of which is illustrated in the attached drawing. The following description discloses some embodiments in such detail that a person skilled in the art would be able to utilize the arrangement, layout, and method based on the disclosure. Not all steps of the embodiments are discussed in detail, as many of the steps will be obvious to a person skilled in the art based on this disclosure. For reasons of simplicity, the element numbers will be retained in the following exemplary embodiments in the case of repeated components. The accompanying Figures 1a-14 illustrate a flotation arrangement 1 or detail parts A, B of the flotation arrangement 1, and Figure 15 illustrates a flotation plant 9 schematically. Figure 16 presents a flotation cell in some detail. The figures are not drawn in proportion, and many of the components of the flotation cell, flotation arrangement 1, and flotation plant 9 are omitted for clarity. In order to fit a figure on a single drawing page, some of the connections between flotation cells, waterlines, or flotation arrangements are presented as graphic lines of disproportionate lengths rather than connections of actual dimensions in proportion. The direction of advance of the slurry flows is shown in the figures by arrows. Although flotation is disclosed in the following examples with reference primarily to froth flotation, it should be noted that the principles according to the invention may be implemented independently of the specific type of flotation, i.e. the flotation technique may be any of the flotation techniques known per se, such as froth flotation, dissolved air flotation or induced gas flotation. The basic operating principle of the float arrangement 1 is presented in Figures 1a-b, 2, 3, and 4a-c. The following description should be read primarily in conjunction with those figures, unless otherwise indicated. A first, rougher primary flotation cell 111a of a primary flotation line 10 receives a slurry flow, i.e., a slurry inlet 100 comprising ore particles, water, and in some cases flotation chemicals such as collector chemicals and non-collecting flotation reagents to separate the slurry into an underflow 40 and an overflow 51a. Figure 16 shows a typical flotation cell 111, 112, 210, 300. The flotation cell may comprise a mixer 78 in the form of a mechanical stirrer as shown in Figure 16, or any other suitable mixer to promote collisions between the flotation gas bubbles and the ore particles. In one embodiment, flotation gas may be fed or introduced into the flotation cell where the slurry is separated into an overflow and underflow.In one embodiment, the flotation gas may be introduced into a part of the flotation cell in which a mixer is arranged, i.e. into a preparation flotation cell preceding a flotation cell in which the metal ore particles float and are thus separated into overflow and underflow. In a flotation process using conventional flotation with flotation chemicals, a process similar to froth flotation is carried out: chemical collector molecules adhere to the surface areas of the ore particles containing the valuable mineral through a process of adsorption. The valuable mineral acts as the adsorbent, while the chemical collector acts as the adsorbent. The chemical collector molecules form a film on the valuable mineral areas on the surface of the ore particles. The chemical collector molecules have a non-polar and a polar portion. The polar portions of the collector molecules adsorb to the surface areas of the ore particles containing valuable minerals. The non-polar portions are hydrophobic, repelling water.The repulsion causes the hydrophobic tails of the collector molecules to adhere to the flotation gas bubbles. An example of a flotation gas is atmospheric air pumped into the flotation cell. A sufficient amount of collector molecules adsorbed on sufficiently large surface areas of valuable mineral on a mineral particle can cause the mineral particle to adhere to a flotation gas bubble. It is also conceivable that the flotation process can be carried out without flotation chemicals. It is also possible to carry out the flotation process as reverse flotation. In the following, most examples are disclosed in relation to conventional flotation, unless indicated that the examples specifically relate to reverse flotation. All embodiments and examples given can, however, also be carried out in a reverse flotation process. The ore particles coalesce or adhere to gas bubbles to form agglomerates of ore particles with gas bubbles. These agglomerates rise to the surface of the flotation cells 111, 112, 210, 300 at the top of the cell due to the buoyancy of the gas bubbles, as well as the continuous upward flow of suspension, which can be induced both by mechanical agitation and by the entry of suspension into the cell 111, 112, 210, 300. The gas bubbles can form a froth layer. The froth collected on a suspension surface in the flotation cell 111, 112, 210, 300, comprising the particle agglomerates with gas bubbles, is allowed to flow out of the flotation cell 111, 112, 210, 300, over a trough spout 76 and into a trough 75. It is also conceivable that the flotation cells are used as so-called overflow flotation cells, where a coherent, continuous froth layer does not form on the suspension surface, but the suspension comprising metal ore particles with valuable minerals floating in the flotation cell is forced over the trough spout 76. From the slurry surface at the top of a rougher primary flotation cell 111a, 111b, ore particles containing valuable mineral overflow the tundish spout 76 of the flotation cell to be collected in the tundish 75. In the case of reverse flotation, ore particles not containing valuable mineral are naturally collected in the overflow, while ore particles containing valuable mineral are recovered through a lower reflux. This fraction of the suspension is referred to as the primary overflow 51a, 51b. From a secondary flotation cell 210a, 210b, the overflow 50a, 50b is collected in the same manner. The trough spout 76 refers to the peripheral edge of a flotation cell 111, 112, 210, 300 at the top of the cell, over which the froth overflow containing valuable material particles flows into the trough 75. The overflow 50a, 50b from the secondary waterline 20 is recovered as a first concentrate 81. The first concentrate 81 of metalliferous ore particles comprising valuable mineral is in the form of a fluid which is conducted towards other waterlines or stages according to embodiments of the invention, or to further treatment according to solutions known in the art. From the area located near the bottom of a flotation cell 71, a gangue or a part of the suspension containing metalliferous ore particles that do not rise to the surface of the suspension is expelled from the rougher primary flotation cell 111a as bottom reflux 40. The bottom reflux 40 is conducted to a subsequent rougher primary flotation cell 111b which receives the bottom reflux 40 as an input from the previous rougher primary flotation cell 111a. The suspension is treated in the subsequent rougher primary flotation cell 111b in a similar manner as in the first rougher primary flotation cell 111a, in a manner well known to one skilled in the art. The primary flotation line 10 comprises a rougher part 11 with at least two rougher primary flotation cells 111a, 111b connected in series and arranged in fluid communication, followed by a scrubber part 12 with at least two scrubber primary flotation cells 112a, 112b connected in series and arranged in fluid communication. The last rougher primary flotation cell 111e is connected in series and arranged in fluid communication with the first scrubber primary flotation cell 112a, the rougher primary flotation cells 111 of the rougher part 11 and the scrubber primary flotation cells 112 of the scrubber part 12, thus comprising a continuous treatment line. The overflow 51a from the rougher first primary flotation cell 111a may be arranged to flow directly to a secondary flotation line 20, 30. The overflow 52 from the primary scrubbing flotation cells 112a-d is arranged to flow back to a rougher flotation cell 111af (see Figure 3). Alternatively, the overflow 52 from the primary scrubbing flotation cells 112a-d may be arranged to flow to a grinding stage 64 and then to a cleaner scrubbing flotation line (see Figures 1a, 1b, 2). The primary overflow 52 of at least one scrubber primary flotation cell 112 may be arranged to flow directly to a regrind stage 64. In one embodiment, the combined primary overflow of the scrubber primary flotation cells 112 of the scrubber portion 12 may be arranged to flow directly to a regrind stage 64. The primary line 10 may comprise at least four primary flotation cells 111, 112. Alternatively, the primary flotation line 10 may comprise 4-10 primary flotation cells 111, 112. Alternatively, the primary flotation line 10 may comprise 4-7 primary flotation cells 111, 112. The rougher part 11 may comprise at least two rougher primary flotation cells 111a, 11b. Alternatively, the rougher part 11 may comprise 2-6 rougher primary flotation cells 111 af. Alternatively, the rougher part 11 may comprise 2-4 rougher primary flotation cells 111a-d. The scrubber part 12 may comprise at least two scrubber primary flotation cells 112a-b. Alternatively, the scrubber part 12 may comprise 2-6 primary scrubber flotation cells 112a-d. Alternatively, the scrubber part 12 may comprise 2-4 primary scrubber flotation cells 112a-d.Embodiments of the invention, comprising different numbers of primary flotation cells in the primary waterline 10 are introduced in the “Examples” section of this disclosure. The rougher and / or scrubber primary flotation cells 111 af, 112a-d are connected in series. The fluid connection may be made by a conduit 500 (pipe or tube, as shown in the figures) so that the following primary flotation cells 111a-f, 112a-d are arranged at a distance from each other. Alternatively, any two adjacent or subsequent primary flotation cells 111a-f, 112a-d may be arranged in direct connection with the cell so that a separate conduit between the two flotation cells 111ae, 112a-e is not necessary (not shown in the figures). In embodiments of the invention, where the primary flotation line 10 comprises more than two rougher primary flotation cells 111 af, all adjacent or subsequent primary flotation cells 111 af, 112a-d may be arranged in fluid connection with conduits 500 arranged between the flotation cells to direct an underflow 40 from one flotation cell to the next flotation cell. Alternatively, all of the flotation cells 111 af, 112a-d may be arranged in direct cell connection with adjacent flotation cells. Alternatively, some of the adjacent flotation cells 111 af, 112a-d may be arranged in direct cell connection with neighboring flotation cells, while other adjacent flotation cells may have a conduit 500 to make the fluid connection.The layout and design of the primary flotation line 10 may depend on the overall process requirements and the physical location of the flotation arrangement 1. Furthermore, the first secondary flotation cell 210a of the secondary flotation line 20 as well as a further secondary flotation cell 210b of the secondary flotation line 20 may be arranged in direct fluid connection with the rougher first primary flotation cell 111a, 111b from which the secondary flotation cell 210a, 210b receives the overflow 51a, 51b, i.e. no further processing steps such as a grinding step or a conditioning step are arranged between the primary flotation line 10 and the secondary flotation line 20. From the last primary scrubber flotation cell 112d of the waterline 10, the bottom reflux 40' (which may be rejected in normal flotation, or accepted in reverse flotation) is expelled from the flotation arrangement 1 as a tailings flow 83 which may be further treated in any suitable manner known in the art. The first rougher primary flotation cell 111a may have a volume of at least 150 m3. Alternatively, the first rougher primary flotation cell 111a may have a volume of at least 500 m3. Alternatively, the first rougher primary flotation cell 111a may have a volume of at least 2000 m3. The second rougher primary flotation cell 111b, or any subsequent rougher primary flotation cells 111 bf downstream of the first rougher primary flotation cell 111a, may have at least 100 m3 of volume. Alternatively, the second rougher primary cell 111b, or any subsequent rougher primary flotation cells 111 bf downstream of the first rougher primary flotation cell 111a, may have at least 300 m3 of volume. Alternatively, the second rougher primary cell 111b, or any subsequent rougher primary flotation cells 110b-f downstream of the first rougher primary flotation cell 111a, may have at least 500 m3 of volume. In embodiments of the invention, the second primary flotation cell 111b, some of the subsequent rougher primary flotation cells 111bf downstream of the first rougher primary flotation cell 111a, or all of the subsequent rougher primary flotation cells 111bf downstream of the first rougher primary flotation cell 111a, may have the same volume as the first rougher primary flotation cell 111a (see Figure 1). In embodiments of the invention, the second primary flotation cell 111b, some of the subsequent rougher primary flotation cells 111bf downstream of the first rougher primary flotation cell 111a, or all of the subsequent rougher primary flotation cells 111bf downstream of the first rougher primary flotation cell 111a, may have a smaller volume than the first primary flotation cell 111a (see Figure 11). The primary overflow 51a from the first rougher primary flotation cell 111a is directed to a first secondary flotation cell 210a of the secondary flotation line 20. The first secondary flotation cell 210a is arranged in direct fluid communication with at least one first rougher primary flotation cell 111a. The first secondary flotation cell 210a is arranged to receive the primary overflow 51 from the at least one rougher primary flotation cell 111a as input, for the recovery of a first concentrate 81 containing metalliferous ore particles with valuable mineral(s). The first secondary flotation cell 210a, as well as any other secondary flotation cells, operates under standard flotation principles, as described earlier in this disclosure.An overflow 50a from the first secondary flotation cell 210a is collected as the first concentrate 81, which may be conducted to any suitable further processing step known in the art. The secondary flotation line 20 comprises at least two secondary flotation cells 210a in fluid communication. In one embodiment, the secondary flotation line 20 may comprise 2-10 secondary flotation cells 210a-210j in fluid communication. In one embodiment, the secondary flotation line 20 may comprise 4-7 secondary flotation cells 210a-g. In another embodiment, the secondary flotation line 20 may comprise three secondary flotation cells 210a-c. In the secondary flotation line 20, the first secondary flotation cell 210a is arranged in fluid communication with at least one rougher primary flotation cell 111a, and arranged to receive the primary overflow 51a from the at least one rougher primary flotation cell 111a for recovery of a first concentrate 81. Another secondary flotation cell 210b is arranged in fluid communication with at least one further rougher primary flotation cell 111b, and arranged to receive the primary overflow 51b from the at least one further rougher primary flotation cell 111b for recovery of a first concentrate 81. The further secondary flotation cell 210b is arranged in fluid communication with a prior secondary flotation cell 210a. The additional secondary flotation cells 210b-c of a secondary waterline 20 may be arranged in direct cell connection with one another, or they may be arranged in fluid connection with one another through a conduit or conduits 500. In one embodiment, all of the adjacent secondary flotation cells 210b-c of a secondary waterline 20 may be arranged in direct cell connection with one another; alternatively, all of the adjacent secondary flotation cells 210b-c may be arranged in fluid connection through conduits 500; alternatively, some of the adjacent secondary flotation cells 210b-c may be arranged in direct cell connection, while others may be arranged to have a conduit 500 therebetween, similar to what has been described in relation to the primary waterline 10. In one embodiment as shown in Figure 4a, the secondary bottom reflux 42a from the first secondary flotation cell 210a may be arranged to flow to a further secondary flotation cell 210b. Alternatively, the bottom reflux 42a from the first secondary flotation cell 210a may be arranged to be combined with the secondary bottom reflux 42b from the further secondary flotation cell 210b (not shown in the figures). The first secondary flotation cell 210a of the secondary flotation line 20 in fluid communication with a rougher primary flotation cell 111a is 100-1000 m3 in volume. Alternatively, the first secondary flotation cell 210a of the secondary flotation line 20 in fluid communication with a rougher primary flotation cell 111a may be 400-1000 m3 in volume. The volume of the first secondary flotation cell 210a of the secondary flotation line 20 in fluid communication with the at least one rougher primary flotation cell 111a is 2 to 50% of the aggregate volume of the at least one rougher primary flotation cell 111a. Alternatively, the volume of the first secondary flotation cell 210a of the secondary flotation line 20 in fluid communication with the at least one rougher primary flotation cell 111a may be 3-30% of the aggregate volume of the at least one rougher primary flotation cell 111a (see FIG. 4a). By aggregate volume is meant the combined volume of the rougher primary flotation cells 111a from which the first additional secondary flotation cell 210a receives the overflow 51a. For example, the first additional secondary flotation cell 210a may receive overflows 51a from more than one rougher primary flotation cell 111 of the primary line 10. In that case, the aggregate volume is the combined volume of the rougher primary flotation cells 111. At least one further secondary flotation cell 210b is disposed downstream of the first secondary cell 210b. The further secondary flotation cell 210b is disposed in direct fluid communication with at least one further rougher primary flotation cell 111b of the primary flotation line 10. The further secondary flotation cell 210b of the secondary flotation line 20 is arranged to receive a primary overflow 51b from the at least one further rougher primary flotation cell 111b. The further secondary flotation cell 210b is arranged to receive the primary overflow 51b from the at least one further rougher primary flotation cell 111b as an inflow, for the recovery of a first concentrate 81, comprising metal ore particles with valuable mineral(s).The additional secondary flotation cell 210b, as well as any other secondary flotation cells 210, operate according to standard flotation principles, as described earlier in this description. An overflow 50b from the secondary flotation cell 210b is collected as the first concentrate 81, which may then be conducted to any suitable further processing step known in the art. The number of secondary flotation cells 210 in series on the secondary waterline 20 may be equal to the number of rougher primary flotation cells 111 on the primary waterline 10. In some embodiments, the number of secondary flotation cells 210 on the secondary waterline 22 may be less than the number of rougher primary flotation cells 111 on the primary waterline 10. A secondary flotation cell 210a, 210b may be arranged to receive primary overflow 51a, 51b from 1-3 rougher primary flotation cells 111. In one embodiment, a secondary flotation cell 210a, 210b may be arranged to receive primary overflow 51a, 51b from 1-2 rougher primary flotation cells 111a, 111b. In one embodiment, a secondary flotation cell 210a, 210b may be arranged to receive primary overflow 51a, 51b from at most two rougher primary flotation cells 111a, 111b. In one embodiment, a secondary flotation cell 210a may be arranged to receive primary overflow 51a from a single rougher primary flotation cell 111a. Alternatively or additionally, the additional secondary flotation cell 210b may be arranged to receive the primary overflow 51b, 51c from at least two rougher primary flotation cells 111b, 111c (see Figure 12). The additional secondary flotation cell 210b may be arranged to receive the primary overflow bd from 1-4 rougher primary flotation cells 111 bd. In one embodiment, the additional secondary flotation cell 210b may be arranged to receive the primary overflow 51 bd from 1-2 rougher primary flotation cells 111 bc. An embodiment where the additional secondary flotation cell 210b receives the primary overflow 51b from one rougher primary flotation cell 111b is shown, for example, in Figures 1a-b and 2a-c. The bottom reflux 42b of the further secondary flotation cell 210b may be arranged to flow back to the rougher part 11 of the primary waterline 10 at a point downstream of the rougher primary flotation cell 111b from which the further secondary flotation cell 210b is arranged to receive the primary overflow 51b (see Figure 1a). In one embodiment, the bottom reflux 42b of the further secondary flotation cell 210b is arranged to flow back to a further rougher primary flotation cell 110c downstream of the first rougher primary flotation cell 111b from which the further secondary flotation cell 210b is arranged to receive the primary overflow 51b (see Figures 6a, 9).In one embodiment, the lower reflux 42b from the further secondary flotation cell 210b is arranged to be combined into overflow 51 from at least one further rougher primary flotation cell 111c downstream of the rougher primary flotation cell 111b from which the further secondary flotation cell 210b is arranged to receive the primary overflow 51b (see Figure 1b). In one embodiment, the bottom reflux 42c from a further secondary flotation cell 210c of the secondary flotation line 20 may be arranged to be combined with the overflow 52a of a scrubbing primary flotation cell 112a, or combined overflows 52a-d from two or more scrubbing primary flotation cells 112a-d of the scrubbing part 12, as shown in Figure 2 (solid line). This is because the quality in the sense of quantity of valuable mineral particles still present in the bottom reflux 42c is close to or similar to that of the overflow(s) 52 of the scrubbing line 12, and therefore the two streams can be conducted to further treatment, for example, joint re-grinding 64. This can increase the efficiency of the flotation arrangement 1 and also lead to savings in energy consumption, since the number of individual additional treatment stages can be reduced. Alternatively, depending on the mineralogy of the bottom reflux 42c, it may also be conducted to the scrubber part 12 of the flotation arrangement 1 to be treated in the scrubber flotation. The bottom reflux 42c may be conducted to a scrubber primary flotation cell 112a, either directly to the flotation cell, or to a conduit between two primary flotation cells 111, 112. Figure 2 shows an embodiment where the bottom reflux 42c is conducted to the conduit between the last, rougher primary flotation cell 111e and the first, scrubber primary flotation cell 112a to be combined with the bottom reflux 40 from the rougher part 11 (dashed line). It is conceivable that the overflow 42c may also be conducted to a conduit between two primary purifying flotation cells 112a-d to be treated in a primary purifying flotation cell.The above embodiments may be especially beneficial, if the quality of the lower reflux 42c of the secondary float line 20 is such that it requires additional flotation to efficiently recover valuable metalliferous ore particles from the slurry flow. The additional secondary flotation cell 210b of the secondary flotation line 20 in direct fluid communication with a rougher primary flotation cell 111, for example the primary flotation cell 111b, has a volume of 100-1000 m3. Alternatively, the additional secondary flotation cell 210b of the secondary flotation line 20 in direct fluid communication with a rougher primary flotation cell 111, for example the primary flotation cell 111b, may have a volume of 300-1000 m3. The volume of the additional secondary flotation cell 210b of the secondary flotation line 20 in fluid communication with the at least one rougher primary flotation cell is 2-50% of the aggregate volume of the at least one primary flotation cell 111. Alternatively, the volume of the additional secondary flotation cell 210b of the secondary flotation line 20 in fluid communication with the at least one rougher primary flotation cell is 3-30% of the aggregate volume of the at least one primary flotation cell 111 (see Figure 4c). By aggregate volume is meant the combined volume of the primary flotation cells 110 from which the secondary flotation cell 210b receives the overflow 51. For example, the additional secondary flotation cell 210b may receive overflows 51b, 51c from the primary flotation cells 111b, 111c of the primary line 10 (see FIG. 12). In that case, the aggregate volume is the combined volume of the primary flotation cells 111b, 111c. In one embodiment, the first secondary flotation cell 210a of the secondary flotation line 20 has a larger volume than the additional secondary flotation cell 210b of the secondary line 20. In one embodiment, the additional secondary flotation cell 210b of the secondary waterline 20 has a larger volume than the first flotation cell 210a of the secondary waterline 20. The subsequent additional secondary flotation cells 210b, 210c of a secondary flotation line 20 may be arranged in direct cell connection with one another, or may be arranged in fluid connection with one another via a conduit or conduits 500. In one embodiment, all adjacent secondary flotation cells 210 of the secondary flotation line 20 may be arranged in direct cell connection with one another; alternatively, all adjacent secondary flotation cells 210 may be arranged in fluid connection via conduits 500; alternatively, some of the adjacent secondary flotation cells 210 may be arranged in direct cell connection, while others may be arranged to have a conduit 500 therebetween, similar to what has been described in relation to the primary flotation line 10. From the area located near the bottom of a flotation cell 71, a gangue or a portion of the slurry containing metalliferous ore particles that do not rise to the surface of the slurry is expelled from the first secondary flotation cell 210a as bottom reflux 42a. The bottom reflux 42a is conducted to a further or subsequent primary flotation cell 210b which receives the bottom reflux 42a as an input from the previous primary flotation cell 210a. The slurry is treated in the further or subsequent secondary flotation cell 210b in a similar manner as in the first secondary flotation cell 210a, in a manner well known to one skilled in the art. In one embodiment, the lower reflux 42b from the further secondary flotation cell 210b is arranged to flow into the latter of the at least one rougher primary flotation cell 111 from which the primary overflow 51b was received, or into a rougher primary flotation cell 110c (see FIGS. 6a-c, 9) downstream of the latter of the at least one rougher primary flotation cell 51b from which the primary overflow 51b was received. The lower reflux 42b can be directed to a conduit 500 preceding the rougher primary flotation cell 111 into which the lower reflux 42b must be conducted (see figure 1b), or to a collecting conduit 510 collecting the overflow from several rougher primary flotation cells 111 (see figure 1 a), or directly to the rougher primary flotation cell (see for example figure 6a). In one embodiment, the lower flowback 42' from the last secondary flotation cell of the secondary flotation line 20 may be arranged to flow out of the further secondary flotation cell 210b as a tailings flow 83. In one embodiment, the underflow 42b may be arranged to flow to a rougher primary flotation cell 111c downstream of the rougher primary flotation cell 111b from which the primary overflow 51b was received. The underflow 42b may be arranged to flow directly into the rougher primary flotation cell 111b, 111c, or into the conduit 500 preceding the rougher primary flotation cell 111b, 111c. In one embodiment, the primary overflow 51a from a primary flotation cell 111a may be arranged to flow into two parallel secondary flotation cells 210a. This embodiment is not shown in the figures. Such an embodiment could be readily conceivable, for example, in the embodiment presented in Figure 5a, by arranging a second first secondary flotation cell 210a next to or in the vicinity of the single secondary flotation tank 210a at the secondary waterline 20, and by directing the overflow 51a through a collecting duct 510 into the two parallel secondary flotation cells 210a.A first concentration 81 as overflow 50a from both of the first two parallel secondary flotation cells 210a would be collected separately and directed further, while overflows from both of the first two parallel secondary flotation cells 210a could be collected and directed downstream to the further secondary flotation cell 210b through a collecting conduit 510 similar to that shown in Figure 7, for example. The slurry flows, both the underflows 40, 42 and the overflows 50, 51, 52, may be arranged to be gravity-driven. That is, any flow between at least two flotation cells at the fluid connection may be gravity-driven. For example, slurry flow between the first, rougher primary flotation cell 111a and a further rougher primary flotation cell 111b may be gravity-driven. Alternatively or additionally, slurry flow between a first, scrubber primary flotation cell 112a and a scrubber primary flotation cell 112b may be gravity-driven. Alternatively or additionally, slurry flow between a rougher primary flotation cell 111e and a scrubber flotation cell 112a may be gravity-driven.Alternatively or additionally, slurry flow between the first secondary flotation cell 210a and a further secondary flotation cell 210b may be gravity driven. Alternatively or additionally, slurry flow between a rougher primary flotation cell and a secondary flotation cell in fluid communication with each other may be gravity driven. For example, slurry flow between the first rougher primary flotation cell 111a of the primary waterline 10 and the first secondary flotation cell 210a of the secondary waterline 20 may be gravity driven. For example, slurry flow between a further rougher primary flotation cell 111b of the primary waterline 10 and a further secondary flotation cell 210b of the secondary waterline 20 may be gravity driven. To facilitate gravity movement of the slurry flows, at least some of the flotation cells 111, 112, 210, 300 may be arranged in a staggered manner relative to the ground level on which the flotation arrangement is established (see Figures 5c and 6c). Alternatively, the trough spouts 76 of the flotation cells, for example the primary flotation cells 111a-c, may be arranged at different heights. As can be seen in Figures 5c and 6c, a step carried out between any adjacent flotation cell causes a difference in the surface level of the suspension 70 of the two adjacent flotation cells. In this case, the step is arranged between the rougher primary flotation cells 111 of the primary waterline 10, as well as between the two secondary flotation cells 210a, 210b of the secondary waterline 20.It is likewise conceivable that the stage may be arranged between a rougher primary flotation cell 111 of a primary waterline and at least one secondary flotation cell 210a of the secondary waterline 20 or a further secondary flotation cell 210b; or between adjacent secondary flotation cells 210a, 210b of the secondary waterline 20; or between the last rougher primary flotation cell 111 and the first scrubbing primary flotation cell 112a; or between two scrubbing primary flotation cells 112a of the scrubbing portion 12 of the primary waterline 10. It is obvious to a person skilled in the art that the vertical placement of the different flotation cells 111, 112, 210, 300 can be carried out in the best possible way taking into account the requirements of the flotation process and the construction location of the flotation arrangement 1. The gravitational flow of suspension is achieved by the hydraulic gradient between two flotation cells with different surface levels of the suspension, carried out with a stage between the bottoms of the flotation cell 71, as can be seen in Figures 5c and 6c, or with a stage between the heights of the trough peaks, as explained above in the summary of this disclosure. Alternatively or additionally to the above-described form of gravity-driven slurry flows, the slurry flows may be driven, in the same configuration as the flotation cells, by one or more low-head pumps arranged between two adjacent flotation cells, either in the conduit or conduits 500, or directly between the adjacent flotation cells in case the adjacent cells are arranged in direct cell connection with each other. Pumping may be required when the flotation cells or some of the flotation cells are arranged in a uniplanar manner, i.e. having the cell bottoms 70 at a single level relative to the ground level, where the slurry surface level of two adjacent flotation cells may be more or less the same and a hydraulic gradient is now created, at least not sufficient to drive the slurry flow by gravity.In one embodiment, slurry flows may be driven by gravity between some of the adjacent flotation cells, and by a low head pump or pumps between some of the adjacent flotation cells in the flotation arrangement 1. The flotation arrangement 1 may also comprise a further processing stage 62. For example, the overflow 51 c from at least one rougher primary flotation cell 111 c may be directed to flow to this further processing stage 62. In one embodiment, the combined overflows from the at least one rougher primary flotation cell 111 c, and that of at least one further rougher primary flotation cell 111 d downstream of the rougher primary flotation cell 111 c, may be directed to flow to the further processing stage 62. Figure 15 shows a flotation arrangement 1 b, where the overflows 51 c, 51 d from the rougher primary flotation cells 111 c, 111 d of a primary flotation line 10 b are combined and conducted to the further processing stage 62 through a collecting conduit. 510.The further processing step 63 in this example is a cleaning flotation, performed in a cleaning flotation line. Alternatively or additionally, the combined secondary overflows 50a, 50b from the at least two secondary flotation cells 210a, 210b may be arranged to flow to a subsequent processing stage 62. The bottom reflux 40' from the last primary flotation cell of the primary waterline 10, i.e. the last scrubber primary flotation cell 112d, may be arranged to flow to a subsequent processing stage 62, or may be arranged to leave the flotation arrangement 1 as tailings 83. Additionally or alternatively, the bottom reflux 42' from the last secondary flotation cell 210b of the secondary waterline 20 may be arranged to flow to a subsequent processing stage 62, or may be arranged to leave the flotation arrangement 1 as tailings 83. The subsequent processing step 62 may comprise, for example, a grinding step. Alternatively or additionally, the subsequent processing step 62 may comprise a conditioning step. Alternatively or additionally, the subsequent processing step 62 may comprise a flotation step, such as a cleaning flotation step. In other words, the subsequent processing step 62 may also comprise several individual process steps in combination. The flotation arrangement 1 may further comprise an additional secondary flotation line 30 comprising at least one additional secondary flotation cell 300 in fluid communication with at least one rougher primary flotation cell 111 and arranged to receive the primary overflow 51 from at least one additional rougher primary flotation cell 111 (see, for example, Figures 7 and 8). The additional secondary flotation cell 300 operates in essentially the same manner as the other secondary flotation cells 210, as described earlier in this specification. The further secondary flotation cell 300 is arranged to receive the primary overflow 51b from at least one rougher primary flotation cell 111, and the overflow 42 from the further secondary flotation cell 210b. The underflow 42' from the further secondary flotation cell 300 is arranged to leave the flotation arrangement 1 as a tailings flow 83. Alternatively or additionally, the underflow 42' from the further secondary flotation cell 300 may be directed to a subsequent processing stage 62. In one embodiment, the first secondary flotation cell 210a may be arranged to receive the primary overflow 51a from the first rougher primary flotation cell 111a, and the further secondary flotation cell 300 is arranged to receive the primary overflow 51b, 51c from at least two further rougher primary flotation cells 111. In one embodiment, the additional secondary flotation cell 300 may be arranged to receive the primary overflow 51b, 51c from at least two rougher primary flotation cells 110b, 110c (this embodiment is not shown in the figures). In one embodiment, the additional secondary flotation cell 300 may be a conventional cleaner cell 300, arranged to receive the primary overflow 51c, 51d, 51e from at least three rougher primary flotation cells 111c, 111d, 111e (see for example figure 9). In one embodiment, the additional secondary flotation cell 300 may be arranged in a downstream position of the at least one first secondary flotation cell 210a and / or the at least one additional secondary flotation cell 210b (see, for example, Figures 7, 8 and 10). According to one embodiment of the invention, the flotation arrangement 1 may comprise two primary flotation lines 10a, 10b. The first secondary flotation line 210a of the secondary line 20 may receive the overflow 51a, 52a from the first rougher primary flotation cells 111a, 121a of both primary lines 10a, 10b (see Figure 13). In one embodiment, the secondary flotation line 20 may comprise two further secondary flotation cells 300a, 300b which are arranged to receive combined overflows from the further rougher primary flotation cells 111b-e and 121b-e, respectively, of both primary flotation lines 10a and 10b. The secondary overflow 42 from the first secondary flotation cell 210a may be arranged to flow to the two further secondary flotation cells 300a, 300b, as can be seen in Figure 13.The bottom refluxes 42' may be arranged to flow to a subsequent processing stage 62 in a manner similar to that described above, either separately, or the two streams may be combined; or arranged to leave the flotation arrangement 1 as tailings 83, separately from the two additional secondary flotation cells 300a, 300b. The tailings stream 83 from the additional secondary flotation cells 300a, 300b may also be combined and then conducted to leave the flotation arrangement as a combined tailings stream 83. At least one of the rougher primary flotation cells 111a-f, and / or at least one of the secondary flotation cells 210a-b, 300 may comprise a froth flotation cell, or a so-called conventional flotation cell, the operation of which has been described in the Summary of this disclosure. In one embodiment, a third rougher primary flotation cell 111c of the primary waterline 10 comprises a froth flotation cell. Furthermore, any subsequent rougher primary flotation cell 111df after the third rougher primary flotation cell 111c may comprise a froth flotation cell. In one embodiment, the first rougher primary flotation cell 111a and a second rougher primary flotation cell 111b of the primary waterline 10 may be operated as overflow flotation cells, details of which have also been described in the Summary of this disclosure. Additionally or alternatively to the two previous embodiments, the secondary flotation line 20 may comprise at least one cleaning cell, that is, one or more of the secondary flotation cells 210a-b, 300 may act as rougher cleaning cells, and therefore the secondary flotation line 20 may be understood, or operated, as a rougher cleaning line or circuit. In one embodiment, the flotation gas may enter the flotation cell where the suspension is separated into overflow and underflow. The flotation cell into which the flotation gas enters may comprise a mixer. Alternatively, the flotation gas may enter a preparation flotation cell 115 in which a mixer is provided. The flotation arrangement 1 described herein is particularly suitable for, but is not limited to, use in the recovery of minerals containing valuable minerals, wherein the ore particles comprise copper (Cu), zinc (Zn), iron (Fe), pyrite, or a metal sulfide such as gold sulfide. The flotation arrangement is suitable for use in the recovery of ore particles comprising a valuable mineral, particularly low-grade ore. Ore particles comprising other valuable minerals such as Pb, Pt, PGMs (platinum group metals Ru, Rh, Pd, Os, Ir, Pt), oxide ore, industrial minerals such as L¡ (i.e., spodumene), petalite, and rare earth minerals may also be recovered, in accordance with the different aspects of the present invention.The flotation arrangement is suitable for use in the recovery of metal ore particles comprising valuable mineral, particularly low grade. The flotation system is particularly suitable for the recovery of Cu-containing ore particles from low-grade ore. The flotation system is also suitable for the recovery of Fe-containing ore particles by reverse flotation. An embodiment of the use of a flotation arrangement according to this disclosure may utilize, in the flotation arrangement, a first, rougher primary flotation cell 111a having at least 150 m3 of volume, and gravity to drive slurry flow. An embodiment of the use of a flotation arrangement according to this disclosure may utilize, in the flotation arrangement, a first, rougher primary flotation cell 111a having at least 500 m3 of volume, and gravity to drive slurry flow. An embodiment of the use of a flotation arrangement according to this disclosure may utilize, in the flotation arrangement, a first, rougher primary flotation cell 111a having at least 2000 m3 of volume, and gravity to drive slurry flow. An embodiment of the use of a flotation arrangement according to this disclosure may alternatively or additionally utilize a second, rougher primary flotation cell 111b having at least 100 m3 of volume, and gravity to drive slurry flow. An embodiment of the use of a flotation arrangement according to this disclosure may utilize a second, rougher primary flotation cell 111b having at least 300 m3 of volume, and gravity to drive slurry flow. An embodiment of the use of a flotation arrangement according to this disclosure may utilize a second, rougher primary flotation cell 111b 111b which has at least 500 m3 of volume, and gravity to drive the suspension flow. An embodiment of the use of a flotation arrangement according to this disclosure may alternatively or additionally utilize gravity to drive slurry flow between the rougher primary flotation cells 111 af. An embodiment of the use of a flotation arrangement according to this disclosure may alternatively or additionally utilize gravity to drive slurry flow between the secondary flotation cells 210a-b, 300. An embodiment of the use of a flotation arrangement according to this disclosure may alternatively or additionally utilize gravity to drive slurry flow between a rougher primary flotation cell 111 and a secondary flotation cell 210, the two flotation cells having a fluid connection to one another. An embodiment of the use of a flotation arrangement according to this disclosure may utilize gravity to drive slurry flow between the first rougher primary flotation cell 111a and the first secondary flotation cell 210a. Alternatively or additionally, a further embodiment of the use of a flotation arrangement according to this disclosure may utilize gravity to drive slurry flow between a further rougher primary flotation cell 110b-f and a further secondary flotation cell 210b or a further secondary flotation cell 300. According to a further aspect of the invention, a flotation plant 9 comprises a flotation arrangement 1 according to this specification. In one embodiment, the flotation plant 9 may comprise at least two flotation arrangements 1. In one embodiment, the flotation plant 9 may comprise at least three flotation arrangements 1. In one embodiment, the flotation plant 9 may comprise at least a first flotation arrangement 1a for the recovery of a first concentrate 81, and at least a second flotation arrangement 1b for the recovery of a second concentrate 82 (see Figure 15). In one embodiment, the primary flotation cells 111, 112 of the primary flotation line 10a of the at least one first flotation arrangement 1a for the recovery of the first concentrate 81 and the primary flotation cells 111, 122 of the primary flotation line 10b of the at least one second flotation arrangement 1b for the recovery of the second concentrate 82 are arranged in series (see figure 15). The flotation plant 9 may comprise a flotation arrangement 1 arranged to recover Cu. Alternatively or additionally, the flotation plant 9 may comprise a flotation arrangement 1 arranged to recover Zn. Alternatively or additionally, the flotation plant 9 may comprise a flotation arrangement 1 arranged to recover pyrite. Alternatively or additionally, the flotation plant 9 may comprise a flotation arrangement 1 arranged to recover a metal from a sulfide, such as gold. According to a further embodiment of the invention, the flotation plant 9 may comprise a flotation arrangement 1 arranged to recover metalliferous ore particles comprising Cu from low-grade ore. According to one embodiment of the invention, the flotation plant 9 may comprise a flotation arrangement 1 arranged to recover Fe by reverse flotation. The flotation plant 9 may further comprise an arrangement for further treating the suspended ore particles such that the second concentrate 82 is different from the first concentrate 81. In one embodiment, the arrangement for further treating the ore particles may be a grinding stage 62 arranged between a first flotation arrangement 1a and a second flotation arrangement 1b. In one embodiment, the arrangement for further treating the ore particles may be an arrangement 65 for adding flotation chemicals, arranged between a first flotation arrangement 1a and a second flotation arrangement 1b. According to another aspect of the invention, a flotation method is provided for treating metal ore particles suspended in suspension. In the method, the slurry is subjected to primary flotation 10 comprising at least two rougher flotation stages 111a and 111b in series and in fluid communication to separate the slurry into primary inflow 40 and primary overflow 51a and 51b, and further comprising at least two scrubber flotation stages 112a and 112b in series and in fluid communication to separate the slurry into underflow 40 and primary overflow 52a and 52b. Primary bottom reflux 40 from a prior primary flotation stage 111a may be directed to a subsequent primary flotation stage 111b. Primary overflow 51a from at least a first primary flotation stage 110a is directed to a first secondary flotation stage 210a of secondary flotation 20 for recovery of a first concentrate 81, the secondary flotation 20 comprising at least two secondary flotation stages 210a, 210b in series and in fluid communication. The at least first rougher flotation stage 110a and the first secondary flotation stage 210a are arranged in series and in fluid communication.Furthermore, according to the method, in secondary flotation 20, primary overflow 51b from at least one further rougher flotation stage 111b is directed to a further secondary flotation stage 210b arranged in series and in fluid communication with at least one further rougher flotation stage 111b, for recovery of a first concentrate 81, and underflow 42a from the preceding secondary flotation stage 210a is directed to the further secondary flotation stage 210b. Alternatively, underflow 42a from a preceding secondary flotation stage 210a may be combined with underflow 42b from the further secondary flotation stage 210b. The primary overflow 52a, 52b from the scrubber flotation stages 112a, 112b is directed back to a rougher flotation stage 111a, 111b, or to a grinder 64 and then to a cleaner flotation. The slurry may be subjected to at least four stages of primary flotation. In one embodiment, the slurry may be subjected to 4-10 stages of primary flotation. In one embodiment, the slurry may be subjected to 4-7 stages of primary flotation. Alternatively or additionally, the slurry may be subjected to at least two stages of secondary flotation. In one embodiment, the slurry may be subjected to 2-10 stages of secondary flotation. In one embodiment, the slurry may be subjected to 4-7 stages of secondary flotation. In one embodiment, primary overflow 51c-e from 1-3 rougher flotation stages 111c-e may be directed to a secondary flotation stage 210b. In one embodiment, primary overflow 51bc from 1-2 rougher flotation stages 111bc may be directed to a secondary flotation stage 210b. In one embodiment, primary overflow 51c from at least one additional rougher flotation stage 111c, and secondary underflow 42 from additional secondary flotation stage 210b may be directed to an additional secondary flotation stage 300 of secondary flotation. In one embodiment, primary overflow 51a from a first rougher flotation stage 111a may be directed to a first secondary flotation stage 210a, and primary overflow 51bc from at least two further rougher flotation stages 110b-c may be directed to further secondary flotation stage 300. In one embodiment, a secondary flotation stage 210a may receive primary overflow 51a, 51b from at most two rougher flotation stages 111a, 111b. In another embodiment, a secondary flotation stage 210a may receive primary overflow 51a from only one rougher flotation stage 111a. In one embodiment, additionally or alternatively, a further secondary stage 210b may receive primary overflow 51b, 51c from at most two rougher flotation stages 110b, 110c. In one embodiment, the bottom reflux 42b from a secondary flotation stage 210b may be directed to the primary flotation 10 at the latter of the at least one rougher flotation stage 111b from which the primary overflow 51b was received, or at a rougher flotation stage 111c-e downstream of the latter of the at least one rougher flotation stage 111b from which the primary overflow 51b was received. Froth flotation may be employed in at least one rougher flotation stage 111a and / or at least one secondary flotation stage 210a. Additionally or alternatively, overflow flotation may be employed in the first rougher flotation stage 111a. In one embodiment, overflow flotation may be employed in the first rougher flotation stage 111a and in a second rougher flotation stage 111b. Examples The suspension flows (overflow, underflow) between the different flotation cells (primary flotation cells and / or secondary flotation cells) can be arranged in any suitable manner depending on the requirements of the flotation process and the physical characteristics of the site where the flotation arrangement is to be established. Examples of possible embodiments are given below. Examples 1-10 describe in more detail the slurry flows in and between the rougher part 11 of the primary waterline 10 and the secondary waterline 20, i.e. the part of the flotation arrangement 1 marked with the letter “B” in Figure 1a. Example 11 describes a flotation plant 9 according to the invention. It is obvious to a person skilled in the art that other combinations are possible within the scope of the invention. Different embodiments can be combined to obtain suitable arrangements. Embodiments of the invention are presented below in conjunction with the figures. Example 1 In one embodiment of the invention as shown in Figures 5a-c, a slurry inlet 100 is led to a flotation arrangement 1 comprising a primary flotation line 10 with a rougher first primary flotation cell 111a to separate into a lower reflux 40 and an overflow 51a. For the sake of clarity, in Figures 5a-c, only part B of the entire flotation arrangement 1 is shown. The bottom reflux 40, which may comprise a quantity of metalliferous ore particles comprising valuable mineral, from the first rougher primary flotation cell 111a is directed to an adjacent second primary flotation cell 111b, connected in series with the first rougher primary flotation cell 110a, through a conduit 500, to be separated into a bottom reflux 40 and an overflow 51b. The bottom reflux 40, which may still comprise a quantity of metalliferous ore particles comprising valuable mineral, from the second rougher primary flotation cell 111 b is directed towards an adjacent third rougher primary flotation cell 111 c, connected in series with the second rougher primary flotation cell 111 b, through a conduit 500, to be separated into a bottom reflux 40 and an overflow 51 c. It should be understood that after the last, rougher primary flotation cell 111c shown in the figures, the bottom reflux 40 is directed to a further primary flotation cell, which may be a further rougher primary flotation cell 111, or a scrubber primary flotation cell 112; and that after the last secondary flotation cell 210b shown in the figures, the bottom reflux 42b is directed to the primary flotation line 10, to a further secondary flotation cell 210, or to a further secondary flotation cell 300 according to the invention as described above. This applies to all examples presented here. The overflow 51c is collected as a first concentrate 81 for further treatment in any suitable manner known in the art. The arrangement thus far is typical for conventional froth flotation. The overflow 51a from the rougher first primary flotation cell 111a is directed to a first secondary flotation line 21, comprising a secondary flotation cell 210a, through a conduit 500 to separate into an overflow 50 and an underflow 42a in the secondary flotation cell 210a. The overflow 50 is directed out of the first secondary flotation line 20 as a first concentrate 81, to be further treated in any suitable manner. This part of the flotation circuit is similar to any conventional froth flotation arrangement. However, unlike a conventional cascade flotation process, the bottom reflux 42a, which may comprise an amount of ore particles comprising valuable ore, from the first secondary flotation cell 210a is directed to a further primary flotation cell 210b for further treatment to recover any remaining ore particles comprising valuable ore, thereby increasing the recovery rate for such ore within the flotation arrangement 1. This is very advantageous in the recovery of ore particles comprising valuable ore from slurries comprising low grade ores. Similarly, the overflow 51 b from the rougher second primary flotation cell 111 b is directed to the secondary waterline 20, more specifically to an additional secondary flotation cell 210 b via a conduit 500, to be separated into an overflow 50 b and an underflow 42 b in the secondary flotation cell 210 b. The overflow 50 b is directed off the secondary waterline 20 as a first concentrate 81, to be further treated in any suitable manner. The concentrates 81 from the secondary waterline 20 may be combined prior to further treatment. The lower reflux 42b from the additional secondary flotation cell 210b may be directed in the manner described above. The rougher primary flotation cells 111a, 111b and 111c are arranged in a staggered manner such that there is a difference in the surface level of the slurry 70 between each subsequent rougher primary flotation cell 111a, 111b, 111c. In this particular example, as shown in FIG. 5c, each subsequent rougher primary flotation cell 111b, 111c has a bottom 71 arranged at a lower level than the preceding rougher primary flotation cell 111a, 111b, creating a stage between the flotation cells. The difference in the surface level of the suspension 70 can, of course, be noticed by arranging the trough peaks 76 of each subsequent rougher primary flotation cell 111a, 111b, 111c at a different height. At the same time, a similar stage may be arranged between the secondary flotation cells 210a, 210b, as well as between the first rougher primary flotation cell 111a and the secondary flotation cell 210a, and the second rougher primary flotation cell 111b and the secondary flotation cell 210b. Due to the stages, the surface levels of the slurry 70 in each subsequent downstream flotation cell are lower than the surface level of the slurry 70 in the previous flotation cell, in the slurry flow direction, creating adequate space between cells to allow gravity-driven slurry flows. This can lead to energy savings, as pumping energy is not required. The construction of the flotation arrangement can also be simplified. Example 2 Figures 6a-c show a detail of part B of another embodiment of the flotation arrangement 1. In the embodiment otherwise similar to that of Example 1, the secondary flotation cells 210a, 210b have a smaller volume than the rougher primary flotation cells 111a, 111b, 111c, and the underflow 42b of the further secondary flotation cell 210b is arranged to flow into the third rougher primary flotation cell 111c, to be treated again in the rougher part 11 of the primary waterline 10. By utilizing secondary flotation cells of smaller volume than the rougher primary flotation cells from which the secondary cells receive the overflow 51, the secondary flotation line 20 may be more efficient at recovering particles that contain less valuable mineral, i.e., are harder to drive to the surface and froth layer to be recovered in the overflow, leading to a higher grade concentration 81. This would further increase the recovery rate of the flotation arrangement 1. Unlike a conventional cascade flotation process, the bottom reflux 42b, which may still comprise an amount of ore particles comprising valuable minerals, from the further secondary flotation cell 210b is directed to the third, rougher primary flotation cell 111c for further treatment to recover any remaining ore particles containing valuable minerals, thereby increasing the recovery rate of that mineral within the flotation arrangement 1. This so-called short-connected flotation is very advantageous for the recovery of ore particles containing valuable minerals from slurries containing low-grade minerals. Example 3 In one embodiment of the flotation arrangement 1 as shown in detail in Figure 7, a suspension inlet 100 is led to the rougher part 11 of a primary flotation line of a flotation arrangement, comprising a first rougher primary flotation cell 111a, which will separate into a lower reflux 40 and an overflow 51a. The bottom reflux 40, which may comprise an amount of metalliferous ore particles comprising valuable mineral, from the first rougher primary flotation cell 111a is directed to an adjacent second rougher primary flotation cell 111b, connected in series with the first rougher primary flotation cell 111a, through a conduit 500, to be separated into a bottom reflux 40 and an overflow 51b. The bottom reflux 40, which may still comprise a quantity of metalliferous ore particles comprising valuable mineral, from the second rougher primary flotation cell 111 b is directed towards an adjacent third rougher primary flotation cell 111 c, connected in series with the second rougher primary flotation cell 111 b, through a conduit 500, to be separated into a bottom reflux 40 and an overflow 51 c. The bottom reflux 40, which may still comprise a quantity of metalliferous ore particles comprising valuable mineral, from the third rougher primary flotation cell 111c is directed to an adjacent fourth rougher primary flotation cell 111d, connected in series with the third rougher primary flotation cell 111c, through a conduit 500, to be separated into a bottom reflux 40 and an overflow 51d. The bottom reflux 40, which may still comprise a quantity of metalliferous ore particles comprising valuable mineral, from the fourth rougher primary flotation cell 111d is directed to an adjacent fifth rougher primary flotation cell 111e, connected in series with the fourth rougher primary flotation cell 111d, through a conduit 500, to be separated into a bottom reflux 40 and an overflow 51e. The lower reflux 40 from the fifth rougher primary flotation cell 111e is directed to a further primary flotation cell in the primary flotation line 10, which may be an even rougher flotation cell 111 of a scrubber primary flotation cell 112 in a scrubber portion 12 of the primary line 10. The overflow 51a from the rougher first primary flotation cell 111a is directed to a secondary waterline 20 with a first secondary flotation cell 210a through a conduit 500 to separate into an overflow 50 and an underflow 42a in the first secondary flotation cell 210a. The secondary flotation cell 210a may have a smaller volume than the rougher first primary flotation cell 111a. The overflow 50 is directed off the secondary waterline 20 as a first concentrate 81, to be further treated in any suitable manner. The bottom reflux 42a, which may comprise an amount of metalliferous ore particles comprising valuable ore, from the first secondary flotation cell 210a is directed to a further secondary flotation cell 300 for further treatment to recover any remaining ore particles comprising valuable ore, thereby increasing the recovery rate of the flotation arrangement 1 for that ore within the flotation arrangement 1. The bottom reflux 42a may be returned by gravity alone, as shown in Figure 7, by a low head pump60, which may decrease the energy consumption of the flotation process. The overflows 51b, 51c, 51d, 51e from the additional rougher primary flotation cells 111b, 111c, 111d, 111e are first collected in a collecting duct 510 and are directed together as an inlet into a further secondary flotation cell 300 to be separated into an overflow 50 and a bottom reflux 42'. The lower 42' flowback is arranged to exit the secondary flotation line 20 as tailings 83. The overflow 50 is directed out of the additional secondary flotation cell 300 as a first concentrate 81, to be further treated in any suitable manner. The concentrates 81 from the secondary flotation line 20 may be combined for further treatment. The volume of the additional secondary flotation cell is chosen to accommodate the added volume of the overflows 51b, 51c, 51d, 51e from the rougher portion 11 of the primary waterline 10, as well as the lower reflux 42a of the first secondary flotation cell 210a. However, it may be smaller in volume than the added volume of the rougher primary flotation cells 111b, 111c, 111d, 111e. The rougher primary flotation cells 111a, 111b, 111c, 111d, and 111e are arranged in a staggered manner, as described above. Similarly, the secondary flotation cell 210a is one stage above the rougher primary flotation cell 111b to which the underflow 42a is directed. There is also a stage between the further secondary flotation cell 300 and at least some of the rougher primary flotation cells 111b, 111c, 111d. Thus, gravity can be used to drive slurry flows between these flotation cells. In the event that it is not possible to arrange the different flotation cells in a staggered manner, or is only partially possible, one or more low-head pumps 60 may be used to drive the suspension flow between two flotation cells that have fluid connection with each other, but that do not have enough difference in their respective suspension surface levels to allow gravitational propulsion of the suspension flow only. Example 4 Figure 8 shows a slightly different embodiment than that presented above. The bottom reflux 42a from the first secondary flotation cell 210a is directed to a further secondary flotation cell 210b, which also receives primary overflow 51b from the rougher second primary flotation cell 111b. From the further secondary flotation cell 210b, the bottom reflux 42b is directed to the further secondary flotation cell 300, which receives overflow 51 from the rougher part 11 of the primary waterline 10, although only from three rougher primary flotation cells 111c, 111d, 111e. Otherwise, the process is carried out similarly to Example 3. Example 5 An embodiment as shown in Figure 9 combines the advantageous configurations of Figures 6a and 5: the rougher part 11 of a primary flotation line 10 comprises five rougher primary flotation cells 110a-e connected in series, and the underflows 40 are treated in a similar manner to what has been presented above in relation to Examples 3 and 4. The secondary flotation line 20 is similar to that of Example 4, having a first secondary flotation cell 210a receiving overflow 51a from the first rougher primary flotation cell 111a, and another secondary flotation cell 210b receiving primary overflow 51b from another rougher primary flotation cell 111b and secondary underflow 42a from the first secondary flotation cell 210a. However, contrary to the embodiment of Example 4, the bottom reflux 42b from the further secondary flotation cell 210b is arranged to flow back towards the rougher part 10, more specifically, towards a third rougher primary flotation cell 111c. It is equally conceivable that the bottom reflux 42b may be conducted to a conduit 500 between the second rougher primary flotation cell 111b and the third rougher primary flotation cell 111c to be combined with the bottom reflux 40 from the second rougher primary flotation cell 111b (see Figure 1b). The overflows 50a, 50b are collected as a first concentrate 81, as described above. By directing the bottom reflux 42b, which may still comprise a quantity of metalliferous ore particles comprising valuable ore, from the further secondary flotation cell 210b towards the rougher part 11 of the primary line 10, more specifically, towards the third rougher primary flotation cell 111c for further treatment, any remaining ore particles comprising valuable ore may be efficiently recovered, thereby increasing the recovery rate for that ore within the flotation arrangement 1. Furthermore, a further secondary flotation cell 300 is arranged to receive overflows 51c, 51d, 51e from the third, fourth and fifth rougher primary flotation cells 111c, 111d, 111e. These primary overflows 51ce are first collected in a collecting duct 510 and directed together as an inlet into the further secondary flotation cell 300 to separate them into an overflow 50 and a lower reflux 42'. The volume of the first and further secondary flotation cells 210a, 210b may be less than the volume of the rougher primary flotation cells 111a, 111b, as described above. The volume of the additional secondary flotation cell 300 is chosen to accommodate the added volume of overflows 51c, 51d, 51e. However, it may be smaller in volume than the aggregate volume of the rougher primary flotation cells 111c, 111d, 111e. The slurry flow may be driven by one or more low-head pumps, while the other flows may be gravity driven if suitable stages are arranged between adjacent flotation cells in fluid connection with each other (not shown in Figure 9). The overflow 50 is directed out of the additional secondary flotation cell 300 as a first concentrate 81, to be further treated in any suitable manner. The concentrates 81 from the secondary flotation line 20 and the additional secondary flotation cell 300 may be combined for further treatment. Example 6 Figure 10 shows detail B of a new embodiment. In this variation, the secondary flotation line 20 comprises three secondary flotation cells 210a, 210b, 210c arranged in series. In this embodiment, primary overflow 51a from the rougher first primary flotation cell 111a is directed to the first secondary flotation cell 210a, and primary overflow 51b from the rougher second primary flotation cell 111b is directed to a first additional secondary cell 210b. Secondary underflow 42a from the first secondary flotation cell 210a is directed to the first additional secondary flotation cell 210b. Secondary underflow 42b from that flotation cell is directed to a second additional secondary flotation cell 210c in fluid communication with the prior secondary flotation cell 210b. Thereafter, the secondary underflow 42c is further directed to the additional secondary flotation cell 300. The secondary overflows 50a, 50b, 50c and 50c from the respective secondary flotation cells 210a, 210b, 210c and 300 are recovered as first concentrates 81.The final secondary bottom reflux 42' is carried out of the additional secondary flotation cell 300 as tailings 83. The primary overflows 51c, 51d, 51e from the third, fourth and fifth primary rougher flotation cells 111c, 111d, 111e are first collected in a collecting duct 510 and directed together as an inlet into the further secondary flotation cell 300 which separates them into an overflow 50 and a lower reflux 42', as in Examples 5 and 6. Example 7 In one embodiment of the invention, detail B is shown in Figure 11, the rougher part 11 of a primary waterline 10 also comprises five rougher primary flotation cells 111a, 111b, 111c, 111d, 111e. The first two rougher primary flotation cells 111a, 111b have a larger volume than the last three rougher primary flotation cells 111c, 111d, 111e. The flotation process in the rougher part 11 of the primary waterline 10 is, however, similar to that described in connection with the previous examples. The secondary flotation line 20 comprises three secondary flotation cells 210a, 210b, 300 that operate in a similar manner to that described above. The volume of the secondary flotation cells 210a, 210b is smaller than the volume of the first two rougher primary flotation cells 111a, 111b. The additional secondary flotation cell 300 is arranged to receive the combined overflows 51c, 51d, 51e of the last three rougher primary flotation cells 111c, 111d, 111e through a collecting duct 510. Since the aggregate volume of the last three primary flotation cells 111b, 111c, 111d is smaller in this embodiment, the volume of the additional secondary flotation cell 300 may also be smaller, as can be seen in Figure 11. The secondary bottom reflux 42' from the additional secondary flotation cell 300 is carried out of the flotation arrangement 1 as tailings flow 83, which may be combined with the tailings flow 83 from the primary flotation line 10. The combined tailings flow may, for example, be conducted to another flotation arrangement 1 for the recovery of a second concentrate 82. The secondary overflow 50, 50a, 50b comprises a recovered first concentrate 81, which will be processed in a similar manner to what has been described in relation to the other examples and embodiments. Example 8 Figure 12 shows detail B of another embodiment of the flotation arrangement 1. In this embodiment, the rougher part 11 of a primary line 10 comprises six rougher primary flotation cells 111a, 111b, 111c, 111d, 111e, 111f. The flotation process in the rougher part 11 is similar to that described in relation to the previous examples. The overflow 51a from the rougher first primary flotation cell 111a is directed to a first secondary flotation cell 210a through a conduit 500 to be separated into an overflow 50a and an underflow 42a in the secondary flotation cell 210a. The secondary flotation cell 210a may be smaller in volume than the rougher first primary flotation cell 111a. The overflow 50a is directed out of the first secondary flotation cell 210a as a first concentrate 81, to be suitably further treated. The secondary bottom reflux 42a from the first secondary flotation cell 210a, which bottom reflux 42a may comprise an amount of mineral particles comprising valuable ore, is directed to another secondary flotation cell 210b for further treatment to recover any remaining mineral particles comprising valuable ore, thereby increasing the recovery rate of that mineral within the flotation arrangement 1. The primary overflows 51 b, 51 c from the second and third rougher primary flotation cells 111 b, 111 c are first collected in a collecting duct 510 and directed together as an inlet to the secondary flotation cell 210 b to be separated into a secondary overflow 50 b and a secondary underflow 42 b. The volume of the secondary flotation cell 210 b may be less than the aggregate volume of the two rougher primary flotation cells 111 b, 111 c from which it received the overflows 51 b, 51 c. The secondary overflow 50b from the secondary flotation cell 210b is collected as a first concentrate 81, and the secondary overflow 42b is arranged to flow to an additional secondary flotation cell 300 for further treatment. The additional secondary flotation cell 300 is arranged to receive the combined overflows 51 d, 51 e, 51 f from the last three rougher primary flotation cells 111 d, 111 e, 111 f through a collecting duct 510. The lower reflux 42' from the additional secondary flotation cell 300 is carried out of the flotation arrangement 1 as a tailings flow 83, which may be combined with the tailings flow 83 from the primary flotation line 10 (not shown in Figure 12). The combined tailings flows 83 may, for example, be conducted to another flotation arrangement 1 for the recovery of a second concentrate. The overflow 50 of the additional secondary flotation cell 300 comprises a recovered first concentrate 81, which will be further processed in a similar manner to what has been described in relation to the other examples and embodiments. Example 9 Figure 13 shows detail B of another embodiment of the flotation arrangement 1. In the embodiment, there are two primary flotation lines, both comprising a rougher part 11a and 11b. Both rougher parts 11a, 11b comprise five rougher primary flotation cells 111a-e, 121a-e, respectively. The primary flotation lines are arranged to treat the slurry flow in a similar manner to that described in relation to, for example, Examples 3 and 4. However, the primary overflows 51a, 53a from the first rougher primary flotation cells 111a, 121a of the two rougher portions 11a, 11b are arranged to flow into a single secondary flotation cell 210a. The secondary overflow 50a from the secondary flotation cell 210a is recovered as a first concentrate 81. The secondary bottom reflux 42 is directed downstream in two separate flows (i.e., the secondary bottom reflux 42 from the first secondary flotation cell 210a is divided into two separate flows within the first secondary flotation cell 210a, or the bottom reflux 42 may be separated into two flows downstream of the first secondary flotation cell 210a) in two further secondary flotation cells: a first further secondary flotation cell 300a, arranged to receive the combined overflows 51b, 51c, 51d, 51e from the last four rougher primary flotation cells 111b, 111c, 111d, 111e from the rougher portion 10a of the first primary flotation line via a collecting conduit 510;and a second additional secondary flotation cell 300b, arranged to receive the combined overflows 53b, 53c, 53d, 53e of the last four rougher primary flotation cells 121b, 121c, 121d, 121e from the rougher part 10b of the second primary flotation line via a collecting conduit 520.; In a similar manner to what has been described in connection with Example 8, the underflows 42' from the additional secondary flotation cells 300a, 300b are carried out of the flotation arrangement 1 as tailings flows 83, which may be combined with the tailings flow 83 from the primary flotation lines (not shown in the figure). The overflows 50b from the additional secondary flotation cells 300a, 300b comprise a recovered first concentrate 81, which will be further processed in a similar manner to what has been described in connection with the other examples and embodiments. Example 10 Figure 14 shows detail B of another embodiment of the flotation arrangement 1. It comprises essentially the same construction details as the arrangement of Example 8 (see Figure 12), but instead of individual flotation cells 111, 210, where the slurry is aerated and separated into two fractions (overflow and underflow) in a single cell, each flotation line 10, 20 comprises a first preparatory flotation cell 115, 215 and a flotation cell 111, 210 adjacent to the preparation flotation cell 115, 215 through a hydraulic conduit 41. In the preparation flotation cell 115, 215 the slurry flow is aerated either by an agitator equipped with gas inlet or by a spray type aeration device.The adjacent flotation cell 111, 210 operates as a flotation cell without mechanical agitation to ensure the stability of the ore particle agglomerates with gas bubbles and the formation of an undisturbed froth layer. The scrubbing portion of the primary flotation line may also comprise a similar combination of flotation cell and preparatory flotation cell, although this is not shown in Figure 14. The incoming slurry flow 100 is first conducted to the rougher portion 11, a primary waterline of the flotation arrangement. More specifically, the slurry is conducted to a preparation flotation cell 115a to be treated as disclosed above. From the preparation flotation cell 115a, the slurry flow is directed through a hydraulic conduit 41 to a rougher primary flotation cell 111a, from which the overflow 51a is directed to a first secondary waterline 20 comprising a similar preparation flotation cell 215a and an adjacent flotation cell 210a through a hydraulic conduit 41. The primary bottom reflux 40 from a rougher primary flotation cell 111 a of the primary flotation line 10 is carried downstream to be treated in a similar manner as in the preparation of additional flotation cells 115 and rougher primary flotation cells 111 of the rougher part 11 until the primary bottom reflux 40 from the last flotation cell 111 f is carried to a scrubber part in a similar manner as in the other embodiments of this invention. The secondary underflow 42a from the flotation cell 210a of the secondary flotation line 20 is directed downstream to be similarly treated in another secondary preparation cell 215b and another flotation cell 210b. The combined primary overflows 51b, 51c from the rougher primary flotation cells 111b, 111c, both also preceded by a preparatory flotation cell 115b, 115c, are directed to the preparation cell 215b of the further secondary flotation cell 210b through a collecting conduit 510. The underflow 42b from the further secondary flotation cell 210b is directed downstream to a preparation cell 315 of a further secondary flotation cell 300. The secondary overflow 50a from the first secondary flotation cell 210a and the secondary overflow 50b from the further secondary flotation cell 210b are directed off the secondary waterline 20 as a first concentrate 81. The combined overflows 51 d, 51 e, 51 f from further rougher primary flotation cells 111 d, 111 e, 111 f are directed to the preparation flotation cell 305 of the further secondary flotation cell 300 through a collection conduit 510. The overflow 50 from the further secondary flotation cell 300 comprises the recovered first concentration 81. The lower flowback 42' from the further secondary flotation line 23 may be directed out of the flotation arrangement 1 as tailings flow 83. Example 11 Figure 15 shows an embodiment of a flotation plant 9 according to the invention. The flotation plant 9 comprises two flotation arrangements 1a, 1b, which resemble the type described in Example 4, but which may also be of any of the types presented in the previous examples. A first flotation arrangement 1a is intended for the recovery of a first concentrate 81, and a second flotation arrangement 1b is intended for the recovery of a second concentrate 82. The rougher primary flotation cells 111a-e of a rougher part 11a of the first flotation arrangement 1a and the rougher primary flotation cells 121a-e of a rougher part 11a of the second flotation arrangement 1b are arranged in series. Since the functions and flow arrangement of the float arrangements 1a, 1b have already been discussed in detail in connection with the previous examples, the details of the float arrangements 1a, 1b are not explained again here. The lower reflux 40' from the last primary scrubber flotation cell 112b of a scrubber portion 12a of the primary line 10a of the first flotation arrangement 1a is directed to a suitable arrangement for further treatment of the mineral particles suspended in the suspension. In one embodiment, the arrangement may be a grinding stage 62 or, in another embodiment, an arrangement 65 for adding flotation chemicals. (In FIG. 15, this arrangement is shown for exemplary purposes only, and it should be understood that the box may represent a grinding stage 62 or an arrangement 65 for adding flotation chemicals, depending on the embodiment.) In an embodiment where the arrangement comprises a grinding step 62, the second concentrate 82 recovered in the second flotation arrangement 1b contains metalliferous ore particles comprising the same valuable mineral as the first concentrate 81 recovered in the first flotation arrangement 1a (i.e. the two concentrates have the same or similar mineralization), but the particle size distribution of the second concentrate 82 is different due to the grinding step 62. Alternatively, the further processing step may comprise reconditioning the slurry stream collected as underflow 40' from the first flotation arrangement 1a, i.e. treating the slurry with further flotation chemicals to prepare the slurry inlet 11b for recovery of a second concentrate 82. In that case, the second concentrate 82 recovered in the second flotation arrangement 1b contains metalliferous ore particles comprising a different valuable mineral than the first concentrate 81 recovered in the first flotation arrangement 1a. The two concentrates therefore have different mineralogy. In one embodiment, the second concentrate 82 collected as primary overflows 51c-e from the last two rougher primary flotation cells 111c-d of the second primary flotation line 10b of the rougher part 11b may be combined and directly conducted to further treatment, which may be, instead of an additional secondary flotation cell 300 as in the first flotation line 10a, any other suitable further processing process or operation known in the art, for example, an additional cleaner flotation operation in a cleaner, rougher flotation line.The overflow 52a, 52b from the primary scrubber flotation cells 112a, 112b of both flotation arrangements 1a, 1b may be treated as described earlier in this specification, either by directing the overflows to a grinding stage 64 and a cleaner scrubber flotation line; or by directing the overflows back to the primary flotation line (see Figure 3). The embodiments described above may be used in any combination with one another. Several of the embodiments may be combined together to form a further embodiment. An arrangement, method, plant, or use, to which the disclosure relates, may comprise at least one of the embodiments described above. It is obvious to one 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, therefore, are not limited to the examples described above; instead, they may vary within the scope of the claims.

Claims

1. A flotation method for treating suspended metalliferous mineral particles in flotation stages, wherein the suspension is separated by underflow and overflow with the aid of flotation gas, wherein the suspension is subjected to primary flotation (10) comprising at least two coarser flotation stages (111a and 111b) in series and in fluid communication, primary overflow from a first coarser stage directed to secondary flotation (20, 30), comprising at least two scrubber flotation stages (112a and 112b) in series and in fluid communication, primary overflow from the scrubber stages directed back to a coarser flotation stage, or to grinding and then to cleaner flotation,and wherein the primary overflow from a previous flotation stage is directed to a subsequent flotation stage; and wherein the slurry is further subjected to secondary flotation (20) comprising at least two secondary flotation stages (210a, 210b) in fluid communication, wherein the primary overflow from at least a first coarser flotation stage is directed to a first secondary flotation stage for the recovery of a first concentrate, the at least first coarser flotation stage and the first flotation stage being in series and in direct fluid communication, characterized in that in the secondary flotation the primary overflow from at least one additional coarser flotation stage is directed to another secondary flotation stage in series and in direct fluid communication with the at least one other coarser flotation stage, for the recovery of a first concentrate,wherein the at least one other rougher flotation stage and the other secondary flotation stage are in series and in fluid communication, the at least one other rougher flotation stage being different from the at least one rougher flotation stage from which the primary overflow is directed to the first secondary flotation stage, the other secondary flotation stage and a previous secondary flotation stage are in fluid communication, and the underflow from the first secondary flotation stage is directed to the other secondary flotation stage, or is combined with the secondary underflow from the other secondary flotation stage.

2. The flotation method according to claim 1, wherein the suspension is subjected to at least four primary flotation stages, or 4-10 primary flotation stages, or 4-7 primary flotation stages.

3. The flotation method according to claim 1 or 2, wherein the suspension is subjected to at least two secondary flotation stages, or 2-10 secondary flotation stages, or 4-7 secondary flotation stages.

4. The flotation method according to any of claims 1-3, wherein the primary overflow from at least 1-3 coarser flotation stages, or from 1-2 coarser flotation stages, is directed to a secondary flotation stage.

5. The flotation method according to any of claims 1-4, wherein the primary overflow from at least one other coarser flotation stage and the overflow from the other secondary flotation stage are directed to an additional secondary flotation stage.

6. The flotation method according to claim 5, wherein the primary overflow from a first coarser flotation stage is directed to a first secondary flotation stage, and the primary overflow from at least two additional coarser flotation stages is directed to the additional secondary flotation stage.

7. The flotation method according to any of claims 1-6, wherein the lower reflux from a secondary flotation stage is directed to the primary flotation in the last of the at least one coarser flotation stage from which the primary overflow was received, or to a coarser flotation stage downstream of the last of the at least one coarser flotation stage from which the primary overflow was received.

8. The flotation method according to any of claims 1-7, wherein froth flotation is employed in at least one primary flotation stage and / or at least one secondary flotation stage.

9. The flotation method according to any of claims 1-8, wherein overflow flotation is employed in the first rougher flotation stage, or in the first rougher flotation stage and in a second rougher flotation stage.