FI122595B - Method of recycling metal by electrolysis and electrolysis system - Google Patents

Description

METHOD FOR ELECTROLYTIC METAL

RECOVERY AND ELECTROLYSIS SYSTEM

FIELD OF THE INVENTION

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The invention relates to a method as defined in the preamble of claim 1. The invention further relates to an electrolysis system as defined in the preamble of claim 11.

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BACKGROUND OF THE INVENTION

In electrolysis, the metal dissolved in the electrolyte is electrolytically recovered (electrowinning). Recovery occurs in an electrolysis pool if there are a plurality of anodes and a plurality of cathodes arranged alternately. When an electric current is introduced into the system by sulfate-based electrolysis, the metal precipitates on the cathode surface and is formed at the anodes by the decomposition of the acid and oxygen according to the reaction equations (1) and (2):

Anodic reaction: H 2 O 2 H + + ^ O 2 + 2e '(1)

Cathodic Reaction: Mez + + ze "Me 25 Me = metal, e.g. Ni, Co, Mn or Cu where z = metal ion charge cvj ^ Diat ragmat has been used in the electrolytic recovery of metals which are less noble than hydrogen in an electrochemical series .

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- metals such as nickel, cobalt and manganese have a higher potential for reduction than hydrogen, and therefore the evolution of hydrogen at low pH should be avoided by separating the anolyte and

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g 35 catholyte from each other in an electrolyte controlled passage through a material such as diaphragm fabric and the electrolyte must flow from the catholyte space to the anolyte space. Generally, the cathodes are placed in a diaphragm space for sulphate-based electrolysis.

When using anode pouches, each anode is arranged inside an anode pouch made of a material permeable to 5 electrolytes. The anode pouch defines the anodic space and the cathodes are in the free cathodic space surrounding the anode pouches. The anolyte in the anode bag has a lower pH due to acid formation (on the order of pH 1 or less) than the pH of the catholyte in the cathodic state (on the order of pH 3 to 4). The electrolyte is continuously flowing from the cathodic space inside the anode bag to the anodic space. The anolyte is the electrolyte surrounding the anode and the catholyte is the electrolyte surrounding the ka-15 fact. The electrolyte is fed to the cathodic space and discharged in an overflow. Anolyte is continuously removed from each anode bag. The flow of the electrolyte is achieved by a differential pressure between the anodic and cathodic states, including hydro-20 static pressure (caused by the height difference between the anolyte surface and the catholyte surface) and this prevents the protons from re-diffusing into the catholyte space.

Although anode bag technology has been commercially used for 25 short periods at Cawse Nickel Refinery in Australia, the nickel electrolytic recovery process used there is no longer operational. c \ j δ, at Anglo Platinum Base Metal Refinery, located in * 9 30 South Africa, the anode bag technology has been tested co i- ["Nickel Electrowinning Tankhouse Developments at Anglo

ϊ Platinum Base Metal Refinery "by LJ Bryson, NJ

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Graham, EP Bogosi, DL Erasmus proceedings of ALTA 2008 o - Nickel / Cobalt, Copper & Uranium Conference, June 16-

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§ 35 18 2008]. According to this article, the process criteria for anionic acid concentration are the main stumbling block in implementation. The anode bags operated under the reduced pressure needed to remove both the aerosols and the anolyte from the anode bag, causing the low acid concentration to be drawn through the anode bags, causing a further significant increase in the amount of recycled nickel electrolyte. In other words, due to the low concentration of anolyte acid, the anode bag technology tested at Anglo Platinum Base Metal Refinery was not economically attractive.

10 The production of nickel is more economical if the acid concentration of the anolyte is reached in an electrolytic nickel recovery process. The high acid content of the anolyte is useful in dissolution. A high concentration of anolyte acid can be achieved by appropriate selection of diaphragm fabric as well as by controlling process parameters, namely, electrolyte viscosity and permeability of the wall formed by a diaphragm fabric that is permeable to the anode bag, which depends on the electrolyte viscosity.

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The problem is that the correct choice of diaphragm fabric for the anode bag is difficult because manufacturers offer step by step fabrics of different permeabilities and report the permeability of the fabrics only as the permeability of water (a certain viscosity) and a certain pressure difference (a certain height of water column). On the basis of the above information, it is impossible to choose the right fabric to achieve a high anolyte acid content because it is not known what is the permeability of the fabric to the electrolyte? 30 le and how the electrolyte viscosity and the pressure difference across the co i fabric affect the permeability.

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PURPOSE OF THE INVENTION

The object of the invention is to eliminate the aforementioned disadvantages of § 35, o

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In particular, it is an object of the present invention to provide a method and system that allow the selection of an anodic pouch diaphragm fabric and adjusting process parameters based on the selected fabric so as to obtain the desired high anolyte acid concentration, which makes electrolytic metal recovery an economically viable business.

SUMMARY OF THE INVENTION

The process of the invention is characterized in what is set forth in claim 1. The electrolysis system of the invention is characterized in that set forth in claim 11.

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According to the invention, the process utilizes a substantially dense diaphragm fabric as an anode bag material, determines diaphragm fabric permeability dependencies on catholyte viscosity and applied pressure difference, and adjusts the it has an acid content of not less than 50 25 g / l.

According to the invention, the diaphragm fabric of the anode bag is selected from a group of diaphragm fabrics of various similarities with a substantially dense fabric whose permeability dependencies on the viscosity of the catholyte.

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f-viscosity and pressure difference used are known.

The anolyte removal rate is controlled by the current used.

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rim density, differential pressure, and viscosity of the catholyte so that the anolyte to be removed from the anode bag

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g 35 has an acid content of not less than 50 g / l.

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It is essential in the invention that the flow can be primarily determined by the density of the fabric, i.e. by the permeability of the electrolyte, which is determined not only by the properties of the fabric but also by the pressure difference and viscosity.

The concentration of the anolyte acid can be controlled by using a tighter fabric for the less viscous electrolyte, which reduces the flow rate from the cathodic volume within the anode bag to the anodic space, and vice versa, i.e. by using a less tight fabric for the most viscous electrolyte. The electrolyte viscosity, in turn, can be slightly adjusted by the concentration of the metal salt in the catholyte while other parameters remain constant. This adjustment is not necessarily relevant to the process. For example, the Ni content in the process can only vary by about 10 g / L. The concentration of the metal salt in the catholyte, in turn, can be controlled by adjusting the catholyte turnover rate. Figure 1 shows a block flow diagram of 20 processes.

Thus, the acid concentration settles to a certain level, which depends on the electrolyte removal rate (which is equal to the flow of the electrolyte to the anode bag) and the current used. For example, in a process where the total current fed to one of the 25 electrolysis pools is 16000 A and the total electrolyte flow into the anode bags is 0.33 m3 / h, the concentration of anolyte acid is about 80 g / L. In one embodiment of the method, the concentration of the metal salt in the catholyte and / or the catholyte is measured.

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1 viscosity, and the circulation rate of the catholyte is increased if the concentration of the metal salt in the catholyte is increased

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and / or the viscosity of the catholyte exceeds a predetermined threshold and the catholyte turnover rate is reduced if the concentration of the metal salt in the catholyte w and / or the catholyte viscosity is below a predetermined threshold.

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In one embodiment of the method, the pressure difference is controlled by varying the height difference between the liquid surfaces of the anolyte and the catholyte.

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In one embodiment of the method, the anolyte is removed from each anode pouch as an overflow flow so that the level of the surface of the anolyte is maintained below the level of the surface of the catholyte to provide hydrostatic pressure. This provides a sufficiently high hydrostatic pressure, which causes the electrolyte to flow from the catholyte side to the anode bags, preventing the protons from returning from the anolyte to the catholyte side, i.e. from the anode space to the cathode space.

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In one embodiment of the method, the anolyte is removed from each anode pouch by means of an overflow tube, the end of the overflow tube defining the surface height of the anolyte in the anode pouch. The position of the overflow tube head within the 20 anode bags determines very precisely the maximum surface height of the anolyte in the anode bag. Damage to the anode pouch is easy to detect because then the anolyte level in the anode pouch rises above normal and the anolyte flow into the overflow tube is exceptionally large, which is easy to detect and initiates corrective action.

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In one embodiment of the method, the anolyte is led from the overflow tubes to the manifold and further to the manifold. co ^ In one embodiment of the method,

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of each anode pouch by means of a first suction tube 0, uo 1 35 cm In one embodiment of the method, oxygen and / or acid mist is drawn from the anode pouch.

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In one embodiment of the method, oxygen and / or oxygen mist is aspirated from the anode bag through a first suction line, a second suction line, and / or an overflow line.

In one embodiment of the process, the metal to be recovered is nickel, cobalt or manganese, and the metal salt is the sulfate of the particular metal.

In one embodiment of the system, the system 10 includes means for measuring the concentration of the metal salt in the catholyte, and means for adjusting the circulation rate of the catholyte based on the measured concentration.

In one embodiment of the system, the means for removing the anolyte includes an overflow tube for each anode pouch, which opens in the region of the top of the anode pouch, determining the level of the anolyte in the anode pouch so that the surface of the anolyte is below the surface.

In one embodiment of the system, the system includes a manifold channel for receiving the anolyte collected by overflow tubes.

In one embodiment of the system, the system includes a collecting container for receiving the anolyte co-cm. .

f- collect from channel.

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<9 30 In one embodiment of the system,

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1- Bone first suction tube for sucking anolyte and possibly oxygen and / or acid mist from the anode pouch.

Q_ o In one embodiment of the system,

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g 35 another bone suction tube and possibly an anolyte for sucking oxygen and / or acid mist from the anode pouch.

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LIST OF FIGURES

In the following, the invention will be described in detail with reference to the accompanying drawings, with reference to the accompanying drawing, in which Fig. 1 shows a block flow diagram of the process; Fig. 2 is a schematic sectional view of an electrolysis tank according to one of the 10 embodiments of the electrolysis system according to the invention; permeability values for the first diaphragm fabric (Fabric 1) at three different heights of liquid surfaces (i.e., three different pressure pressures) at five different viscosity values for the catholyte, and viscosity 20 and permeability curves for the second diaphragm (Fig. 7-9). permeability values at five different viscosity values of the catholyte and dependence curves for wettability and permeability, c \ j S ^

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Fig. 10 of cp 30 shows the effect of the difference (pressure difference) of the liquid surfaces on the permeability of Fabric 1 and Fabric 2.

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DETAILED DESCRIPTION OF THE INVENTION

- «fr § Figure 1 shows a schematic overview of the electro-

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g 35 from a rolysis system suitable for recovering a metal such as nickel, cobalt or manganese from an electrolyte containing salts of said metal. An electrolyte is introduced into the electrolysis pool from the recirculation tank, and the catholyte is removed from the pool to the recirculation tank by overflow. A rich electrolyte is added to the recycling tank. From the electrolysis tank 5, the anolyte is removed from the inside of the anode bags and further led to dissolution. Oxygen and acid mist are removed from the anode bags for purification and oxygen is further directed to dissolution. In tanks using centrifugal cathodes and having a sufficient amount of recoverable metal deposited on the surface, the electrolysis pool is periodically removed, the metal is removed from the cathode surface, and the permanent cathodes are returned to the pool. In pots using seed plates and with sufficient deposited metal-15 deposition on the surface, the seed plates are periodically removed from the electrolysis tank and new seed plates are placed in the tank.

Figures 2 and 3 show a portion of one electrolysis vessel 20 1. The vessel 1 has a plurality of anodes 2 and a plurality of cathodes 3 arranged alternately. The anodes 2 are lead anodes, lead alloys, DSA (Dimensionally Stable Anode) or titanium anodes. Preferably, the cathodes 3 are permanent cathodes made of special acid-proof steel, titanium or special purpose nickel core plates.

Referring to Figure 3, the anodes 2 are contained within the anode bags 4, which are permeable to the electrolyte. The cathodes 3 co1 are freely indoors. The anode bag 4 delimits c inside the anodic space 5 and to the outside,

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a real state 6 with cathodes 3. Metal precipitates o on the surface of cathodes 3 and anodes 2 generate oxygen and

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§ 35 Acids, o

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The pH of the anolyte 7 in the anode bag 3 is lower (pH <1) than the pH of the catholyte 8 in the cathode space 6 (pH about 3-4). The electrolyte is continuously flowing from the cathodic state inside the anode bag to the anodic state 5 to the anolyte. The system includes means for feeding the catholyte to the cathodic space and removing it from the pool by overflow or suction (not shown).

To remove the anolyte separately from each anode pouch 10, an overflow tube 9 is provided for each anode pouch 4, the end 10 of which opens into the upper region of the anode pouch 4. The position of the head 10 determines the pin height of the anolyte in the anode pouch so that the level of the surface of the anolyte is a distance H below the level of the surface of the catholyte 15. The difference H of the catholyte and of the anolyte causes a differential pressure. The electrolyte flows through the diaphragm fabric at a flow rate depending on its permeability properties, which can be from 1 to 100 l / m 2 / h.

Figure 2 further shows that the anode bag 4 may include a first suction tube 12 for suction removal of the anolyte / oxygen / acid mist. Further, it may include a second second suction tube 13 from the anode bag of anolyte / oxygen / acid mist. The bag may be closed and not gas-permeable above the surface of the nes-25.

There are three arrangements for removing the anolyte, oxygen and acid mist from the anode pouch: (1) the anolyte is removed by an overflow 9 through an overflow pipe 9 and an oxygen and acid mist by the first co> suction pipe 12 or also through the overflow pipe 9 | 2) the anolyte is removed by a second suction pipe ^ 13, which also removes oxygen and acid mist; o 3) the anolyte is removed by a second suction pipe § 35 13 and the first suction pipe 12 is removed by both °. n.

anolyte that oxygen and acid mist.

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The diaphragm fabric material of the anode bag is selected for the process on the basis of the desired concentration of anolyte acid such that the diaphragm fabric permeability 5 X = f (Δρ, T) where Δρ is the pressure difference T is the catholyte viscosity 10

Correspondingly, the acid concentration of the anolyte is C = f (X, I) 15 where I is the amount of electric current used

A high concentration of anolyte acid and a suitable diaphragm can be selected for the process. In the process, an attempt is made to maintain the viscosity of the catholyte by adjusting the catholyte circulation.

The diaphragm fabric obtains the desired permeability with the dia-25 fragment fabric made of polymer or microfibre and with the right choice of yarns, weaving and coating. The electrolyte permeability can also be

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^ optimize by calendering. By selecting a suitable fabric, the desired acid content can be achieved; the other? 30 parameters cannot achieve high

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I - acid content, unless the fabric is sufficiently dense, 1

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EXAMPLE 1 To demonstrate that a high ano g concentration of lithic acid can be achieved, two bench-size electrolytic recovery tests for nickel were performed using anode pouch fabrics with different electrolyte permeabilities. Two diaphragm fabrics A and B with electrolyte permeabilities of 280 ml / h and B 2070 ml / h per anode bag for an electrolyte having a NiSO 4 concentration of about 70 g / l were used.

5 A cell with a volume of 27 liters was fitted with three anode bags (lead anodes) and two cathodes (seed plate). The anolyte was removed by an overflow and the catholyte overflow was adjusted to 30 and 20 mm hydrostatic pressure elevation differences H for bag fabrics A and 10 B, respectively. The catholyte was recycled and the same amount of fresh electrolyte was added to the container as the anolyte was removed from the anode bags. The electrolyte temperature was 57 ° C. The current density was 200 A / m 2, with cell currents at A 23 A and B 22 A. The catholyte rotation speed was 6 1 / h. For the electrolyte having a nickel concentration of 106 g / l, the total removal of the anolyte from the cell during the experiment was 0.34 l / h for bag cloth A and 3.4 l / h for bag cloth B. As a result, the anolyte acid concentrations were 122 g / l for A and 28 g / l for B at the end of the experiments. The experiment shows that a high concentration of anolyte acid can be achieved with the right process parameters.

Figures 4-6 show the measured diameters (i.e., three different pressure differences) of the liquid surfaces for two different fabrics, Fabric 1 and Fabric 2 (not the same fabric as in the example above).

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Viscosity and permeability curves were determined from five different viscosity values for the catholyte and based on the measured values.

co The curves show the electrolyte permeability (liters per hour and tr per square meter) as a function of viscosity (cP or ^ mPa / s). The curves are fitted to a damping exponential function g 35 having three parameters y0, a and b: o W f (1) = yo + ae ~ bri 13 η is the viscosity, i.e. the x-axis, and X is the permeability, i.e., the y-axis.

Parameter matching resulted in the following values for the parameters:

Fabric 1 H (cm) _10_15_19 y0 33.2 45.8 51.4 a 3709 3414 1116 _b_3 ^ _1_2_ / 7_1.7

Fabric 2 H (cm) _10_15_19 y0 7.9 13.6 15.0 a 102 290 228 _b_1J_2_lJ / 7_1.3 10

Figure 10 shows the effect of H (i.e. pressure difference) on the permeability at a given viscosity value of 2.99 cP at 87 g / l for the catholyte, for Canvas 1 and Canvas 2.

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The invention is not limited to the above embodiments only, but many modifications are possible within the scope of the inventive idea set forth in the claims.

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Claims (16)

A method for electrolytic recovery of metal from an electrolyte containing metal salt in an electrolysis pool (1), comprising a plurality of anodes (2) and a plurality of cathodes (3) arranged alternately with each anode (2) disposed within an anode strip ( 4), which anode strip consists of a material which is controlled by electrolyte passing through and which defines within it an anodic space (5) and outside a free cathodic space, where the cathodes (3) are located, whereby metal precipitates on the surface of the cathode and acid and oxygen rise on the anodes, and the permeability of hydrogen ions rising on the anode through a diaphragm material is prevented by a pressure differential, so that electrolyte flows continuously from the cathodic space to the anode space, and wherein catholyte is measured into the cathodic space in the electrolysis basin, is removed therefrom as overcurrent and is recirculated in the cathodic space, and anolyte is removed separately from each anode paste as overflow or with suction, characterized in that as a material for the anode paste, a diaphragm material is selected from a number of diaphragm fabrics with different permeability, the dependence of the diaphragm material's permeability, and the catholic surface's permeability. - the reference is defined, and on the basis of these defined dependencies, the anolyte's output velocity from the anode paste is regulated by the applied electrical density, the pressure difference and the viscosity of the catholyte to such a speed CO that the anolyte obtains an acid content which is at least 50 g / l. x tr CL 2. A process according to claim 1, characterized in that the concentration of metal salt in the catholyte mg (8) and / or the viscosity of the catholyte is measured, and the cathode c and / or viscosity exceeds a predetermined limit value, and the rate of circulation of the catholyte is reduced if the concentration of metal salt in the catholyte and / or the viscosity of the catholyte is below a predetermined limit value. 3. A method according to claim 1 or 2, characterized in that the pressure differential is controlled by changing the height difference between the liquid levels of the anolyte and the catholyte. 10 Method according to any one of claims 1-3, characterized in that anolyte (7) is removed from each anode strip (4) as an overflow, so that the surface level of the anolyte is poured lower than the surface level of the catholyte to achieve a hydrostatic pressure. Method according to claim 4, characterized in that anolyte (7) is removed from each anode bag (4) by means of an overflow tube (9), the end (10) of the overflow tube defining the surface level of the anolyte in the anode bag. Method according to any of claims 1-5, characterized in that anolyte (7) is guided from the overflow tubes (9) into a collecting duct (11). Method according to any of claims 1-6, characterized in that anolyte (7) is removed from each anode bag (4) by means of a first suction tube 9 (12). oo | r Method according to any of claims 1-7, characterized in that oxygen and / or oxygen mist are drawn from the anode bag (4). LO § 35 o <m Method according to claim 8, characterized in that oxygen and / or oxygen mist are sucked out of the anode bag (4) through a first suction pipe (12), a second suction pipe (13) and / or an overflow pipe (9). Process according to any of claims 1-9, 5, characterized in that the metal to be recovered is nickel, cobalt or manganese, and the metal salt is sulfate of the respective metal. An electrolysis system for recovering metal from an electrolyte containing metal salt, said system comprising electrolysis pools (1), wherein in each pool there are a plurality of anodes (2) and a plurality of cathodes (3) arranged alternately with each anode ( 2) disposed within an anode bag (4), said anode bag comprising a wall consisting of a diaphragm fabric controlled electrolyte delimiting an anodic space (5) and outside a cathodic space , including the cathodes (3), wherein metal is precipitated on the cathode surface and acid and oxygen build up on the anodes, and the permeability of hydrogen ions rising on the anode through the diaphragm is impeded by a pressure differential, so that electrolyte continuously flows from the cathode the space to the anodic space inside the anode stage, and whereby catholyte is measured to the cathodic space in the electrolyte basin, is removed therefrom as overflow and h is recirculated to the cathodic space, and the C1 anolyte is removed separately from each anode bag as overflow or suction, and the system includes means for feeding catholyte into the cathodic space, removing it as an overflow or with suction and to re-circulate it to the cathodic space, and means for removing anolyte separately from each anode piece, characterized by LO g having an aperture diaphragm fabric selected fabrics ^ among a number of diaphragm fabrics of different permeability, the dependence of the catholyte viscosity and the applied pressure difference known; and that the output rate of the anolyte is controlled by the applied electrical density, pressure difference, and viscosity of the catholyte, so that the anolyte removed from the anode paste will have an acid content of at least 50 g / l. 12. A system according to claim 11, characterized in that the system comprises means for measuring the concentration of metal salt in the catholyte, and means 10 for controlling the rate of circulation of the catholyte on the basis of the measured concentration. 13. A system according to claim 11 or 12, characterized in that the means for removing anolyte 15 (7) comprise an overflow tube (9) for each anode strip (4), which opens into the region of the upper part of the anode strip and defines the anolyte. surface level in the anode stage, such that the surface level of the anolyte is lower than the surface level of the catholyte. System according to any one of claims 11 - 13, characterized in that the system comprises a collection channel (11) for receiving anolyte (7) collected with the overflow tubes (9). System according to any one of claims 11 to 14, characterized in that the anode bag (4) comprises a first suction tube (12) for sucking anolyte, oxygen CM 2 and / or acid mist from the anode bag. CM? 30 System according to any one of claims 11 to 15, CO-r characterized in that the anode strip (4) comprises | a second suction tube (13) for sucking anolyte, oxygen and / or oxygen mist from the anode bag. o> o tn σ> o o CM