EP2334846A1

EP2334846A1 - Method and installation for electrolytic tinning of a continuously running steel strip in an electrodeposition unit

Info

Publication number: EP2334846A1
Application number: EP08877379A
Authority: EP
Inventors: Philippe Barbieri
Original assignee: Siemens VAI Metals Technologies SAS
Current assignee: Clecim SAS
Priority date: 2008-10-14
Filing date: 2008-10-31
Publication date: 2011-06-22
Anticipated expiration: 2028-10-31
Also published as: RU2476630C2; CN102187017A; WO2010043774A1; ES2400474T3; EP2334846B1; RU2011119502A; WO2010043776A1; CN102187017B

Abstract

The present invention describes a method for the electrolytic tinning of a continuously running steel strip (1) in an electrodeposition unit (3) with an insoluble anode (23) in an electrolyte and having, in line, an electrodissolution reactor (6) intended to recharge the electrolyte with tin ions by selective separation through an electrodialysis or electrolysis membrane (10) which divides said electrodissolution reactor (6) into an anodic compartment (6b) comprising a first electrode (122b) connected to the positive terminal of an electric current supply circuit (12) and a cathodic compartment (6a) comprising a second electrode (121a) connected to the negative terminal of the same electric circuit, and for which a control member of the electrodissolution reactor engages a first change in the polarity of the electric current supply of each of the two electrodes, the control member ensuring, in a manner adjoining the first change, a second change of the circulation of the electrolyte between each of the two compartments of the electrodissolution reactor and the electrodeposition unit, the adjoining and periodic changes in the polarity of the electric current supply of the electrodissolution unit and of the circulation of the electrolyte returning to the electrodeposition unit ensure a continuous withdrawal of the electrolyte via alternating cycles from one or the other of the two compartments by attributing to said compartment an anodic electrodissolution function by means of a soluble electrode, two alternating cycles of continuous withdrawal are defined by similar durations. An installation that implements this electrolytic tinning method is also presented. A major objective of the invention is for the continuity in the recharging of the electrolyte to be effectively ensured.

Description

Method and installation of electrolytic tinning of a continuous strip of steel in an electroplating unit

The present invention relates to a method and an electrolytic tinning installation of a continuous steel strip in an electroplating unit according to the preambles of claims 1 and 12.

In particular, the invention relates to an electrolytic tinning process insoluble anode metal strips in continuous scrolling and an installation for its implementation.

The lack of tin toxicity and the excellent corrosion protection that tin provides to steel have long led to the use of tin-plated mild steel in the food packaging field where it is used. known as "tinplate"

The general cycle of manufacture of tinplate from hot-rolled mild or ultra-soft steel coils comprises cold rolling to obtain strips of a few tenths of a millimeter thick. These strips are then annealed, "skin" -passed, degreased, stripped and tinned. This cycle is followed by finishing operations such as coating remelting, passivation, oiling, etc.

The tinning operation is performed electrochemically, the transfer of tin ions is made to the steel strip to be coated in a tinning bath (or electrodeposition unit) according to the reaction:

Sn, 2 ^ + + 2e -> Sn deposited

This reaction involves the availability of stannous ions in the bath. In addition to these stannous ions, the bath comprises an acid for lowering the pH and increasing the electrical conductivity in said bath. It also contains additives that contribute, among other things, to stabilize the stannous ions by preventing them from oxidizing which would lead to the formation of stannous oxide sludge. Two tinning processes can be implemented:

- With soluble anode:

The majority of electrolytic tinning plants use a high purity (at least 99.85%) tin anode which dissolves during electrolysis and charges the Sn ++ stannous ion bath.

There are several methods of deposition with soluble anode which differ by the electrolyte used. In all cases, the reactions developed are of the type:

At the soluble anode: Sn + 2A ^" -" SnA ₂ + 2e ^" On the band (cathode): SnA ₂ + 2e ^" -_> Sn + 2A ^"

Soluble anode processes have several drawbacks that are fully described in US Pat. No. 4,181,580, which also proposes a variant that uses an insoluble anode.

- With insoluble anode:

The process involves replacing the tin anode with an anode consisting of, for example, titanium coated with a platinum family metal. The tin ions necessary for the coating are, in this case, derived from an electrolyte bath itself in the form SnA ₂ , A being an acid radical. The reactions are of the type:

At the insoluble anode: H ₂ O - ^ VT. O ₂ + 2H ⁺ + 2e ^" On the band (cathode): SnA ₂ + 2e -" Sn + 2A ^"

In the absence of a soluble anode capable of continuously supplying tin ions, the coating operation causes an increase in the acid concentration of the bath in correlation with its depletion of tin. These continuous changes require a constant replenishment of the tin bath. Several possibilities have been envisaged, including that described in document US Pat. No. 4,181,580, in which an installation uses a circuit for recirculating the electrolyte in the bath by coupling the latter with a fluidized bed reactor into which the electrolyte is introduced. tin granules and a gas stream rich in oxygen. This process effectively regenerates the electrolyte and solves some of the problems posed by the use of soluble electrodes but promotes the production of quadrivalent tin ions by reaction:

Sn + O ₂ + 4H ⁺ Sn ⁴⁺ + 2H ₂ O These Sn ⁴⁺ ions precipitate in the form of sludge which needs to be regularly recovered, which greatly reduces the interest of the process.

US 5,312,539 proposes another method using an anionic membrane dialysis cell and a separate tin dissolving unit in which the tin is supplied as an oxide directly dissolved in the acid or anode in Tin electrolytically dissolved. Such a method has certain disadvantages such as the cost of tin oxide or the need to create a strong concentration gradient across the membrane, which requires the implementation of a concentration control unit. On the other hand, even with a strong concentration gradient, the required membrane area (several hundred m ² for tinning continuous steel strip installations) makes the industrial application very problematic to achieve.

US 6,120,673 proposes an electrolyte dissolution and regeneration plant in a three-compartment tank: one having a soluble tin anode, another in which is disposed an insoluble cathode and, in between, a compartment " intermediate "separated from the anode compartment by a cationic membrane passing therein Sn ⁺⁺ ions and separated from the cathode compartment by an anionic membrane passing acid ions A. ^" The intermediate compartment ensures the recombination of the electrolyte from However, the anionic and cationic membrane surfaces required are very different and make it very difficult to construct an industrial installation.

The Applicant has herself experimented extensively with a variant of the processes already described by implementing an electroplating bath coupled to an electro-dissolution reactor whose soluble anode in tin granules and the cathode are separated by a simple cationic electrodialysis or electrolysis membrane. This process essentially solves the problems posed since it makes it possible to avoid the formation of quadrivalent tin ions and thus of sludge, that it does not require a concentration gradient in the electrolyte and that the cationic membranes with selective permeability that it implements can be of modest surface area compared to the densities of current used. However, experiments have shown that the cationic membranes available on the market can not be totally impermeable to Sn ⁺⁺ ions and that the accumulation of these in a catholyte compartment can lead to a large deposition of tin on the cathode and other disadvantages such as those described in JP11-172496 which proposes to remedy this periodically reverse the polarity of the dissolution current applied to the electrodes (anode / cathode) for a very short time, which is not without disadvantages on the continuity of recharging of the electrolyte.

An object of the present invention is to provide a method and an electrolytic tinning installation of a steel strip in continuous travel in an electrolytic unit of an electroplating unit and having in line a reactor of electro-dissolution for charging the electrolyte with tin ions, for which the continuity of recharging of the electrolyte is effectively ensured. More particularly, the invention must provide for preserving all the advantages of electro-dissolution with a reactor provided with an electrodialysis or electrolysis cationic membrane separation while solving the aforementioned problem of permeability to Sn ⁺ ions. ⁺ .

For this purpose, a method and an electrolytic tinning installation are presented through the contents of claims 1 and 12.

From a method of electrolytic tinning of a continuous steel strip in an electrode-insoluble anode electrodeposition unit and having in line an electro-dissolution reactor for recharging the electrolyte tin-ion electrolyte by selective separation through an electrodialysis or electrolysis membrane which divides said electro-dissolution reactor into an anode compartment having a first electrode connected to the positive pole of a circuit of power supply and a cathode compartment having a second electrode connected to the negative pole of the same electrical circuit, for which a control member of the electro-dissolution reactor engages a first power supply polarity changeover of each of the two electrodes, and the control member providing, adjacent to the first permutation, a second permutation of the circulat ion of the electrolyte between each of the two compartments of the electro-dissolution reactor and the electroplating unit,

The said method according to the invention provides that:

- The adjoining and periodic permutations of the power supply polarity of the electro-dissolution and circulation unit of the electrolyte returning to the electrodeposition unit ensure a continuous withdrawal of the electrolyte by alternating cycles. from one or the other of the two compartments by attributing to an said compartment an anodic function of electro-dissolution by means of soluble trode both for the anode for a first cycle and the cathode for a second cycle and vice versa,

the two alternating cycles of continuous sampling are defined by neighboring durations.

Thus, unlike JP11-172496, the periodic inversion "round-trip", that is to say on two consecutive cycles, of the polarity of the dissolution current applied to the electrodes (anode / cathode) s It does not perform on a very short time, but by a "go" cycle and a "return" cycle of neighboring durations, themselves longer than a reversal from one cycle to another. The continuity of recharging of the electrolyte is thus advantageously ensured, because even if a transition of short duration during the permutation of polarity takes place, it does not affect the overall latency imposed by the sequential cycles of recharging.

In particular, each of the two electrodes of the electro-dissolution reactor is provided of a soluble nature. Thus, according to a simple example of embodiment, each electrode may be associated with an electrically non-conductive dissolution basket and supplied with conductive soluble elements, providing each of the electrodes with identical anode / cathode type permutation properties. In other words, the soluble electrodes of the anode and cathode type can become respectively cathode and anode after polarity permutation. The compartments of the electro-dissolution reactor, their components and their two modes of operation (anolyte / catholyte) for each of the alternative cycles are thus perfectly symmetrical with respect to the electrodialysis or electrolysis membrane.

The desired supply of soluble elements is accomplished by simply filling (continuously or at least sequentially depending on the type of a granule leveling and filling device) tin granules in each of the dissolving baskets. electrically conductive, each of them being partially immersed in the electrolyte of one of said two compartments.

The permutation of the flow of the electrolyte between each of the two compartments of the electro-dissolution reactor is synchronously coupled to a switchable loop (on the anolyte compartment) of a hydrogen degassing process of the electrolyte. This therefore allows the electrolyte reloaded tin ions necessary for feeding the electrodeposition unit is taken from one or other of the compartments as long as it is anodic. The method according to the invention also provides a hydraulic circuit means so that the electrolyte recharged with tin ions necessary for feeding the electroplating unit is taken from one or the other of the compartments as long as the it is anodic.

Said hydraulic circuit thus ensures an alternating circulation of the electrolyte of a compartment of the electro-dissolution reactor currently fed by an anolyte circuit, to the electroplating unit and a catholyte circuit in order to become anolyte, according to which the Adjacent permutations of circulation of the electrolyte and the polarity of supply of electric current are carried out according to the sequence which will be described later, and can be summed up in this way: a) Shutdown of the power supply of the reactor electro-dissolution. b) Stopping circulating pumps of the anolyte and the catholyte. c) Opening of the first electrolyte inlet and outlet valves of the catholyte circuit and starting of the anolyte circulation pump until the electrolyte contained in the connected circuits is discharged into the catholyte reservoir to the said first valves and to the previously cathodic compartment, d) Opening of the second inlet and outlet valves of the electrolyte of the anolyte circuit and starting of the circulation pump of the catholyte until discharging into the anolyte reservoir the electrolyte contained in the circuits connected to the said second valves and the previously anodic compartment, e) Closing the electrolyte outlet valves to the evacuation tanks as soon as the evacuation of the anolyte and the catholyte has been completed to corresponding reservoirs, f) Opening of the electrolyte outlet valves to circuits corresponding to the new permuted operating mode, g) Permutation and recovery of the power supply.

These chronological stages of switching of the hydraulic circuit ensure a dynamic flow of the electrolyte in excellent phase with the adjacent permutation of polarity, thus finally ensuring a better continuity of recharging of the electrolyte.

The method according to the invention makes use of an analysis device capable of qualitatively and quantitatively measuring the chemical composition of each of the two compartments of the electro-dissolution reactor. signal corresponding to the content of tin ions in each of said compartments and that, depending on an adjustable threshold of tin ion contents, said control member ensures the permutation polarity supply of electrical power and the permutation of the electrolyte circulation. The recharging of the electrolyte is thus advantageously regulated in a continuous and precise manner. In addition, the control member of the electro-dissolution reactor is preferably capable of providing a dissolution current density control as a function of the need for renewal of tin ions evaluated according to at least the signal delivered by the body of analysis. In this sense, the analysis unit can make use of a laser ablation spectroscopic analyzer also known under the name of "Laser Induced Breakdown Spectroscopy" or LIBS, in which case the analysis device makes it possible to ensure in real time the qualitative and quantitative measurement of the chemical composition of each of the two compartments of the reactor. Therefore, the method according to the invention allows the analysis member to deliver to the control member a status signal of each of the two compartments at a high rate, which can, as needed, reach more than one signal. per second.

The method uses, as the soluble tin electrode of the electro-dissolution reactor, tin elements that are more than 99% pure (in the ideal form of tin granules contained in dissolution baskets). and as an electrolyte a sulfonic acid such as, for example, methanesulfonic acid which has, compared with other acids such as phenol-sulfonic acid, the advantage of being biodegradable.

The method according to the invention recommends making use of an electrodialysis or electrolysis membrane separating the compartments (alternately anodic and cathodic) from the electro-dissolution reactor which is a cationic membrane, for example the reference membrane " CMX "of the company TOKUYAMA SODA, having a selective permeability allowing maintenance of a large fraction of tin ions Sn ⁺⁺ in the anode compartment and a transfer of hydrogen ions H ⁺ to the cathode compartment and a weak transfer of Sn ⁺⁺ tin ions to this same cathode compartment.

Finally, the invention also proposes an electrolytic tinning installation for implementing the method according to the invention presented above. This installation will be presented more precisely with the help of figures that will follow. A set of subclaims also has advantages of the invention.

Examples of implementation and application are provided using the figures described:

Figure 1: Schematic diagram of an insoluble anode electroplating installation, Figure 2: Schematic diagram of electrolyte circulation of an electrolytic tinning installation according to the invention, Figure 3: Schematic diagram of an electroless plating installation electrolytic tinning according to the invention in a first mode of electric polarization of the electro-dissolution reactor, FIG. 4: Diagram of an electrolytic tinning installation according to the invention in a second mode of electric polarization of the electro-reactor -dissolution, Figure 5: General flow diagram of the electrolyte of an alternative electrolytic tinning installation according to the invention, Figure 6: Diagram of an electrolytic tinning installation according to Figure 5 in a first electric polarization mode of the electro-dissolution reactor, FIG. 7: Diagram of an electrolytic tinning installation according to FIG. 5 in a second mode of electric polarization of the reactor r electro-dissolution,

FIG. 1 depicts a block diagram of an installation comprising an insoluble anode electroplating unit: A running steel strip and to be coated (1) plunges into an electroplating tank (2) by winding up on two conducting rollers (21), which supply said strip with electric current, as well as on a bottom roller (22). Insoluble electrodes (23) are immersed in the tank comprising an electrolyte (3) and arranged on either side of descending strands and mounting tape in the tray. The strip is connected to the negative pole and the insoluble anodes connected to the positive pole of an electric power generator. The anodes are partially immersed in an electrolyte (3). A dissolution reactor (6) loop-coupled to an outlet and an inlet of the electroplating tank (2) regenerates the electrolyte by drawing it, regenerating it and returning it to said tank.

FIG. 2 depicts a general flow diagram of the electrolyte of an installation according to the invention suitable for the electrolytic tinning of a strip of steel in continuous flow in an electrodeposition unit (3) with anode insoluble in an electrolyte having, by in-line coupling (8, 83a, 83b, 85), an electro-dissolution reactor (6) in a line circuit (8, 83a, 83b, 85) for recharging the electrolyte in tin ions by selective separation through an electrodialysis or electrolysis membrane (10) which divides said electro-dissolution reactor (6) into an anode compartment (6b) having a first electrode (122b ) connected to the positive pole of a supply circuit (still not shown) in electric current and a cathode compartment (6a) having a second electrode (121a) connected to the negative pole of the same electrical circuit, for which a control member ( not shown) of the electro-dissolution reactor engages a first polarity inversion of the electric power supply circuit (11) of each of the two electrodes, the control member providing, adjacent to the first permutation, a second permutation of the flow of the electrolyte between each of the two compartments of the electro-dissolution reactor and the electroplating unit.

The installation also includes:

the control member activates the adjoining and periodic permutations of the power supply polarity of the electro-dissolution and circulation unit of the electrolyte returning to the electroplating unit, ensuring continuous sampling alternately cycling the electrolyte from one or the other of the two compartments by attributing to said compartment an anodic function of electro-dissolution by means of a soluble electrode,

the control member sequentially activates each of the two alternative cycles by maintaining a continuous (i.e. uninterrupted) sampling of the electrolyte, said cycles being defined by neighboring durations.

According to the invention, the two electrodes comprise conductive soluble elements, giving them identical properties of permutation from an anode type to a cathode type and vice versa. For this purpose, the soluble elements may advantageously comprise tin granules capable of filling (continuous or sequential) at least one of two electrically non-conductive dissolving baskets (7a, 7b), each of said soluble elements being partially immersed in the electrolyte of one of said two compartments.

Said control member comprises a synchronous coupling of the permutation of the flow of the electrolyte between each of the two compartments of the electro-dissolution reactor with a commutation of a loop of a degassing unit (5) of hydrogen for the electrolyte, said loop being switchable between one of the compartments and the degassing unit. Finally, the plant according to the invention provides that each dissolution basket (7a, 7b) is partially in the form of a vertical column so as to be filled with tin granules in which the electrolyte circulates from bottom to top of the column and comprises:

• A "wet" bottom zone consisting of a non-electrically conductive material, a reinforced plastic or polyester resin or a polymer-coated steel, completely immersed in the electrolyte and comprising a trellis composed of at least one net plastic mesh adapted to the particle size of the tin is between 0.50 and 0.05 mm, preferably between 0.3 and 0.10 mm, said net being supported by the envelope of the dissolution basket which has openings of contacting the electrolyte at least 50 times wider than the mesh of said net.

A "wet" median zone not immersed but bathed by circulation of the electrolyte and equipped with a recovery trough (72a, 72b) of regenerated electrolyte, said trough being supplied with a trellis identical to that of the lower zone, and in that the lattice and trough assembly is of non-electrically conductive material such as a reinforced plastic or polyester resin or a polymer coated steel.

• A "dry" electrically conductive upper zone free of any immersion or in contact with the electrolyte, equipped with a metal filler hopper (73) made of tin granules and connected to one of the polarity contacts of the circuit. supply (11) with electric current.

The electrolyte (3) depleted of tin ions in the electroplating unit (2) and taken from a sampling circuit (8) where it is first subjected to degassing of oxygen in a tank of degassing (4). The sampling circuit (8) is divided into two conduits or branches (81a, 81b) equipped with controlled motorized valves (82a, 82b) remotely. Each of these branches is capable of injecting the electrolyte into the lower zone (71) of one of the two dissolution baskets (7a) and (7b) serving as electrodes for the electro-dissolution reactor (6). During its crossing of the lower zone then of the median zone (72) of the dissolution basket, the electrolyte is charged with Sn ⁺⁺ ions before being recovered in the trough of the median zone by the two pipes or branches (83a , 83b) of the circuit equipped with two motorized valves (84a, 84b) controlled remotely. It is then reinjected into the electrodeposition unit (2).

A second electrolyte circulation circuit (9) ensures degassing of the hydrogen. It comprises two pipes or branches (91a, 91b) equipped with valves motorized remote control (92a, 92b) and able to collect the electrolyte in each of the two compartments of the electro-dissolution reactor to take it into the degassing tank (5) from which it leaves to be returned in the same reactor compartment by one of the two branches (93a, 93b) equipped with motorized valves (94a, 94b) remotely controlled.

The dissolution reactor (6) is here divided by a cationic electrodialysis membrane (10) into two compartments each containing a dissolution basket and which can be, depending on the polarity of the current applied to the electrodes, an anode compartment or a cathode compartment.

Each of the two dissolution baskets (7a) and (7b) is filled with tin granules and their upper dry zone (73) is connected to a circuit and a power source (not shown) in a polarity which may be swapped.

FIG. 3 depicts the diagram of an installation according to the invention in a first switchable mode of electrical polarity of the electro-dissolution reactor: an electric current generator (11) is connected to a switching device (12) making it possible to to switch its polarities to outputs (121, 122) of generators. In the example of FIG. 3, the electrode (122b) connected to the dissolving basket (7b) is connected to the positive pole and thus conducts itself in a soluble anode while the electrode (121a) connected to the dissolution basket (7a) ), thus connected to the negative pole, is conducted as a cathode.

The electrolyte (3) depleted of tin ions is taken from the electroplating unit (2) by a sampling circuit (8) which first transfers it to a degassing tank of dissolved oxygen (4). ). The motorized valve (82b) is open, the valve (82a) being closed, and allows the electrolyte to be injected into the lower zone (71b) of the dissolution basket (7b). During its crossing of the lower zone then of the median zone (72b) of the dissolution basket, the electrolyte is charged with Sn ⁺⁺ ions before being recovered in the trough of the median zone by the branch (83b) of the circuit whose motorized valve (84b) is open, the valve (84a) being closed, thus allowing the electrolyte to be reinjected into the electroplating unit (2).

The branch (91b) of the second electrolyte circulation circuit (9) whose motorized valve (92b) is open, the valve (92a) being closed, ensures the removal of the electrolyte in the cathode compartment to conduct it in the degassing tank (5) from which it leaves to be returned to the same cathode compartment of the electro-dissolution reactor by the branch (93b) whose motorized valve (94b) is open, the valve (94a) being closed. In this polarization, the compartment (6b) of the electro-dissolution reactor is anodic and the compartment (6a) cathodic.

FIG. 4 depicts the diagram of an installation according to the invention in a second mode of electrical polarity of the electro-dissolution reactor, said mode being permuted with respect to FIG. 3: the electric current generator (11) is connected a switching device (12) for switching polarity to the outputs (121) and (122). In the example of FIG. 4, the electrode (121a) connected to the dissolving basket (7a) is connected to the positive pole and thus conducts itself as a soluble anode while the electrode (122b) connected to the dissolution basket (7b) ), thus connected to the negative pole, is conducted as a cathode.

The electrolyte (3) depleted of tin ions is taken from the electroplating unit (2) by a sampling circuit (8) which first transfers it to an oxygen degassing tank (4). . The motorized valve (82a) is open, the valve (82a) being closed, and allows the electrolyte to be injected into the lower zone (71a) of the dissolution basket (7a). During its crossing of the lower zone and the middle zone (72a) of the dissolution basket, the electrolyte is charged with Sn ⁺⁺ ions before being recovered in the trough of the median zone by the branch (83a) of the circuit whose motorized valve (84a) is open, the valve (84b) being closed, thus allowing the electrolyte to be reinjected into the electroplating unit (2).

The branch (91a) of the second electrolyte circulation circuit (9) whose motorized valve (92a) is open, the valve (92b) being closed, ensures the removal of the electrolyte in the cathode compartment to conduct it in the degassing tank (5) from which it leaves to be returned to the same cathode compartment of the electro-dissolution reactor by the branch (93a) whose motorized valve (94a) is open, the valve (94b) being closed.

In this polarization, the compartment (6a) of the electro-dissolution reactor is anodic and the compartment (6b) cathodic.

In summary according to FIGS. 2, 3 and 4, there is presented a method according to the invention associated with an installation for implementing it and for which:

- The current supply circuit (11) of the electrolysis reactor comprises a polarity inverter (12) adapted to ensure the permutation of the power supply of each of the electrodes (121a, 122b) in a positive polarity or negative, each said electrode being accordingly anode or cathode according to the controllable sequence of polarization. a first circuit is able to ensure the circulation of the electrolyte according to the following diagram:

• A tin-depleted electrolyte enriched in acid is taken from the electroplating unit (3), subjected to an oxygen degassing unit (4) and then introduced into the lower zone of a first dissolving basket ( 7a) tin granules at a pressure sufficient to allow an overflow of said electrolyte in the recovery trough (72a) of the central zone without overflow in the upper dry zone.

• An electrolyte recharged with tin ions during its circulation in the first dissolution basket (7a) of the electro-dissolution reactor is taken from its recovery trough (72a) in order to be reinjected into the coating tank. (2).

An electrolyte taken from the second compartment (6b) of the electro-dissolution reactor in the vicinity of the electrodialysis or electrolysis membrane (10), on the opposite side to the first dissolution basket (7a), is subjected to a degassing (5) hydrogen and then reinjected into the same zone of the electro-dissolution reactor compartment.

a second circuit is able to ensure the circulation of the electrolyte according to the following diagram:

• A tin-depleted electrolyte enriched in acid is taken from the electrodeposition unit (3), subjected to an oxygen degassing unit (4) and then introduced into the lower zone of the second dissolution basket (7b). tin granules at a pressure sufficient to allow an overflow of said electrolyte into the recovery trough (72b) of the central zone without overflow in the upper dry zone.

• An electrolyte recharged with tin ions during its circulation in the second dissolution tank (7b) of the electro-dissolution reactor is taken from its recovery trough (72b) in order to be reinjected into the coating tank. (2).

An electrolyte taken from the first compartment (6a) of the electro-dissolution reactor in the vicinity of the electrodialysis or electrolysis membrane (10), on the opposite side to the second dissolution basket (7b), is subjected to a degassing of the hydrogen (5) then reinjected into the same zone of the reactor compartment. the electrolyte circulation circuit comprises a first and a second circulation circuit, respectively being equipped with a set of first and second remote-controlled motorized valves for sequentially switching on the first or the second circuit in relation to the permutation. electrical polarities applied to the electrodes in two sequential modes:

• An opening mode of the first circuit and a correlative closure of the second circuit when the first compartment connected to the first circuit is initially anodic.

• An opening mode of the second circuit and a correlative closure of the first circuit when the second compartment connected to the second circuit is initially anodic.

by means of a hydraulic circuit (8) ensuring the circulation of the electrolyte of a compartment of the electro-dissolution reactor (6) fed by an anolyte circuit (6b), to the electroplating unit (3 ) and a catholyte circuit (6a) in order to become anolyte, the adjacent permutations of circulation of the electrolyte and of the power supply polarity are made in a well-defined sequence involving degassing means of the oxygen and hydrogen advantageously switchable on the electrodes. This sequence will be described more precisely in the context of FIGS. 5, 6 and 7.

the motorized valves and an electrical polarity inverter applied to the electrodes are controlled by a controller which issues permutation commands from tin ion content data of each of the compartments (6a, 6b), said contents being delivered to the control member by an analyzer operating ideally according to a technique of laser ablation spectroscopy or "Laser Induced Breakdown Spectroscopy"

the electro-dissolution reactor consists of a plurality of electro-dissolution cells provided with circuits for circulating and supplying electric current connected in parallel and each comprising:

A first dissolution basket (7a) alternately of anode or cathode type,

A second dissolution basket (7b) alternately of cathode or anode type, An electrodialysis or cationic electrolysis membrane separating each cell into an anolyte zone and a catholyte zone according to the polarization of the electrodes.

the electro-dissolution reactor consists of several electro-dissolution cells whose circulation and electrical current supply circuits are separated and capable of being exchanged independently of one another. Thus, it can be ensured that at least one reactor will always be in the active electro-dissolution active phase while one or more other reactors may be in a transient phase of permutation. This improves a regularity of composition of the electrolyte.

- an automatic feeding device in tin granules serves hoppers

(73) of all the baskets of the reactor.

FIG. 5 depicts a general electrolyte circulation diagram of an alternative electrolytic tinning installation according to the invention and having, with respect to FIGS. 2, 3 and 4, an advantage in that two hydrogen and oxygen degassing poles (FIG. , 5) are now provided in the form of reservoirs such as buffer tanks in order to effectively degass the electrolyte (anolyte or catholyte) passing through each of the electrodes of the electro-dissolution reactor (6) according to a permutation hydraulic according to the polarity switching imposed and thus alternating anode / cathode function of said electrodes. In other words, the degassing of the oxygen and of the hydrogen is carried out in an anolyte tank (4) or respectively a catholyte tank (5), such as buffer tanks of the compartments of the electro-reactor. -dissolution. This distribution in several reservoirs makes it possible to draw from a stable anolyte reservoir to recharge the electroplating tank (2) whatever the state of the hydraulic circuits during the permutations and commutations over-month.

Thus, this plant is suitable for the electrolytic tinning of a steel strip running continuously in an electrode-insoluble anode plating unit (2) and having, by in-line coupling (8, 85), an anolyte tank (4) itself coupled in line or loop (81a, 81b, 83a, 83b) to the soluble electrodes of the electro-dissolution reactor (6) in a line circuit for recharging the electrolyte tin ions by selective separation through an electrodialysis or electrolysis membrane (10) which divides said electro-dissolution reactor (6) into a anode compartment (6b) having a first electrode (122b) connected to the positive pole of a supply circuit (still not shown) in electrical current and a cathode compartment (6a) having a second electrode (121a) connected to the negative pole of same electrical circuit, for which a control member (not shown) of the electro-dissolution reactor engages a first polarity permutation of the electric power supply circuit (12) of each of the two electrodes, the control member assuring , next to the first permutation, a second permutation of the flow of the electrolyte between each of the two compartments of the electro-dissolution reactor and the electroplating unit.

The installation also includes:

the control member sequentially activates each of the two alternative cycles by maintaining a continuous (that is to say uninterrupted) sampling of the electrolyte, said cycles being defined by neighboring durations.

Said control member comprises a synchronous coupling of the permutation of the flow of the electrolyte between each of the two compartments of the electro-dissolution reactor with a switching of a loop of a catholyte reservoir (5) in which is degassing the hydrogen, said loop being switchable between one of the compartments and the catholyte reservoir.

Finally, the installation according to the invention provides that each dissolution basket (7a, 7b) is partially in the form of a vertical column so as to be filled in. ble of tin pellets in which the electrolyte flows from bottom to top of column and comprises:

The electrolyte (3) depleted of tin ions in the electroplating unit (2) and taken from a sampling circuit (8) where it is first collected in an anolyte tank (4) where it is degassed oxygen, and then injected into the dissolution reactor (6) by two pipes or branches (81a, 81b) equipped with controlled motorized valves (82a, 82b) remotely. Each of these branches is capable of injecting the electrolyte into the lower zone (71) of one of the two dissolution baskets (7a) and (7b) serving as electrodes for the electro-dissolution reactor (6). During its crossing of the lower zone then of the median zone (72) of the dissolution basket, the electrolyte is charged with Sn ⁺⁺ ions before being recovered in the trough of the median zone by the two pipes or branches (83a , 83b) of the circuit equipped with two motorized valves (84a, 84b) controlled remotely. It is then collected by the tank (4) and then reinjected into the electrodeposition unit (2).

A second electrolyte circulation circuit (9) ensures the recovery of H + ions and thus a degassing of hydrogen. It comprises two pipes or branches (91a, 91b) equipped with remote-controlled motorized valves (92a, 92b) and able to take the electrolyte in each of the two compartments of the electro-reactor. dissolution to conduct it in the catholyte tank (5) where it is subjected to a degassing hydrogen from which it leaves to be returned to the same compartment of the reactor by one of the two branches (93a, 93b) equipped valves motorized actuators (94a, 94b) controlled remotely.

Each of the two dissolution baskets (7a) and (7b) is filled with tin granules and their upper dry zone (73) is connected to a circuit and a power source (not shown). according to a polarity that can be swapped.

FIG. 6 depicts the diagram of an installation according to FIG. 5 in a first switchable mode of electrical polarity of the electro-dissolution reactor: a switch-mode electrical current generator (12) allowing its polarities to be switched to outputs ( 121, 122) of generators. In the example of FIG. 3, the electrode (122b) connected to the dissolving basket (7b) is connected to the positive pole and thus conducts itself in a soluble anode while the electrode (121a) connected to the dissolution basket (7a) ), thus connected to the negative pole, is conducted as a cathode.

The electrolyte (3) depleted of tin ions is taken from the electroplating unit (2) by a sampling circuit (8) which transfers it to an anolyte reservoir (4) where it is subjected to degassing of oxygen, the motorized valve (82b) is open, the valve (82a) being closed, and allows the electrolyte to be injected into the lower zone (71b) of the dissolution basket (7b). During its crossing of the lower zone then of the median zone (72b) of the dissolution basket, the electrolyte is charged with Sn ⁺⁺ ions before being recovered in the trough of the median zone by the branch (83b) of the circuit whose motorized valve (84b) is open, the valves (84a) and (92a) being closed, thus allowing the electrolyte to return to the reservoir (4) to be reinjected into the electroplating unit (2).

The branch (91b) of the second electrolyte circulation circuit (9) whose motorized valve (92b) is open, the valve (92a) being closed, ensures the removal of the electrolyte in the cathode compartment to conduct it in the catholyte tank (5) where it is subjected to a degassing of hydrogen and from which it leaves to be returned to the same cathode compartment of the electro-dissolution reactor by the branch (93b) whose motorized valve (94b) ) is open, the valves (94a) and (82a) being closed. In this polarization, the compartment (6b) of the electro-dissolution reactor is anodic and the compartment (6a) cathodic.

FIG. 7 depicts the diagram of an installation according to FIG. 5 in a second mode of electrical polarity of the electro-dissolution reactor, said mode being switched with respect to FIG. 3: the electrical generator with a switching device (12 ) for switching the polarities to the outputs (121) and (122). In the example of FIG. 4, the electrode (121a) connected to the dissolving basket (7a) is connected to the positive pole and thus conducts itself as a soluble anode while the electrode (122b) connected to the dissolution basket (7b) ), thus connected to the negative pole, is conducted as a cathode.

The electrolyte (3) depleted of tin ions is taken from the electroplating unit (2) by a sampling circuit (8) in an anolyte tank (4) where it is subjected to degassing of the The motorized valve (82a) is open, the valve (82b) being closed, and allows the electrolyte to be injected into the lower zone (71a) of the dissolution basket (7a). During its crossing of the lower zone and the middle zone (72a) of the dissolution basket, the electrolyte is charged with Sn ⁺⁺ ions before being recovered in the trough of the median zone by the branch (83a) of the circuit whose motorized valve (84a) is open, the valves (84b) and (92b) being closed, thus allowing the electrolyte to return to the reservoir (4) to be reinjected into the electroplating unit (2).

The branch (91a) of the second electrolyte circulation circuit (9) whose motorized valve (92a) is open, the valve (92b) being closed, ensures the removal of the electrolyte in the cathode compartment to conduct it in the catholyte tank (5) where it is subjected to a degassing of hydrogen and from which it leaves to be returned to the same cathode compartment of the electro-dissolution reactor by the branch (93a) whose motorized valve (94a) is open, the valves (94b) and (82b) being closed.

In summary according to FIGS. 5, 6 and 7, there is presented a method according to the invention associated with an alternative installation for implementing it and for which:

- The current supply circuit of the electro-dissolution reactor (12) adapted to ensure the permutation of the power supply of each of the electrodes (121a, 122b) in a positive or negative polarity, each said electrode being in consequence anode or cathode following the controllable sequence of polarization. a first circuit is able to ensure the circulation of the electrolyte according to the following diagram:

An acid-enriched tin-rich electrolyte (3) is withdrawn from the electroplating unit (2), collected in an anolyte tank (4) where it is subjected to oxygen degassing, and then introduced in the lower zone of a first dissolving basket (7a) tin granules at a pressure sufficient to allow an overflow of said electrolyte in the recovery trough (72a) of the central zone without overflow in the upper dry zone.

• An electrolyte recharged with tin ions during its circulation in the first dissolution basket (7a) of the electro-dissolution reactor is taken from its recovery trough (72a), in order to return to the reservoir (4) where it is subjected to a degassing of oxygen to be reinjected into the vat

(2).

An electrolyte taken from the second compartment (6b) of the electro-dissolution reactor in the vicinity of the electrodialysis or electrolysis membrane (10), on the opposite side to the first dissolution basket (7a), is collected in a catholyte tank (5) where it is subjected to a degassing of hydrogen and then reinjected into the same zone of the electro-dissolution reactor compartment.

An acid-enriched tin-rich electrolyte (3) is withdrawn from the electroplating unit (2), collected in an anolyte tank (4) where it is subjected to oxygen degassing, and then introduced in the lower zone of the second dissolving basket (7b) tin granules at a pressure sufficient to allow an overflow of said electrolyte in the recovery trough (72b) of the central zone without overflow in the upper dry zone.

• An electrolyte recharged with tin ions during its circulation in the second dissolution tank (7b) of the electro-dissolution reactor is taken from its recovery trough (72b), in order to return to the tank (4) where it is subjected to oxygen degassing to be reinjected into the coating tank (2).

An electrolyte taken from the first compartment (6a) of the electro-dissolution reactor in the vicinity of the electrodialysis membrane or electrode (10), on the side opposite the second dissolution basket (7b), is collected in a catholyte tank (5) where it is subjected to a degassing of hydrogen and then reinjected into the same zone of the reactor compartment .

the circuit for circulating the electrolyte comprises a first and a second circulation circuit, respectively being equipped with a set of first and second remote-controlled motorized valves making it possible to switch sequentially on the first or the second circuit in relation to the permutation of the electric polarities applied to the electrodes in two sequential modes:

by means of a hydraulic circuit (8) ensuring the circulation of the electrolyte of a compartment of the electro-dissolution reactor (6) fed by an anolyte circuit (6a), to the anolyte reservoir (4). ) then from thence to the electroplating unit (2) and a catholyte circuit (6b) to become anolyte, the adjacent permutations of electrolyte circulation and electric power polarity are realized according to the following sequence: a) Disconnection of the power supply of the electrolysis reactor. b) Stopping circulating pumps (104, 105) of the anolyte and the catholyte at the outlet of the reservoirs (4, 5) towards each of the electrodes, c) Opening of first inlet and outlet valves (82b, 92a) electrolyte of the catholyte circuit (6b), valves (82a, 84b) connected to the anolyte circuit (6a) and one of the valves (94a) connected to the catholyte circuit being closed, and starting of the pump (104) until with discharge into the catholyte reservoir (5) of the catholyte contained in the dissolution reactor (6b) and the pipes (81b, 91a) connected to said first valves and the previously cathodic compartment (71b), d) Opening of second valves (94b, 84a) for entering and leaving the electrolyte of the anolyte circuit (6a), valves (94a, 92b) connected to the catholyte circuit (6b) and one of the valves (82a) connected to the anolyte circuit, being closed, and starting of the pump (105) until evacuation in the anolyte tank (4) of the anolyte contained in the dissolution reactor on the side (6a) and the pipes (81a, 83a) connected to the said second valves and the previously anodic compartment (71a), e) Closure of one of the first and one of the second valves (84a, 92a) at the end of the evacuation of the anolyte from (71a) to the anolyte reservoir (4) and the evacuation of the catholyte from (71b) to the catholyte reservoir (5) f ) Opening of the valves (84b, 92b) of each of the electrodes to one of the reservoirs (4, 5), g) Switching and restoration of the power supply current.

A first dissolution basket (7a) alternately of anode or cathode type,

A second dissolution basket (7b) alternately of cathode or anode type,

An electrodialysis or cationic electrolysis membrane separating each cell into an anolyte zone and a catholyte zone according to the polarization of the electrodes.

the electro-dissolution reactor consists of several electro-dissolution cells whose circulation and electrical current supply circuits are separated and capable of being exchanged independently of one another. Thus, it can be ensured that at least one reactor will always be in the active electro-dissolution active phase while one or more other reactors may be in a transient phase of permutation. This improves a regularity of composition of the electrolyte. an automatic feed device for tin pellets serves hoppers (73) of all the baskets of the reactor.

Claims

claims

1. Method of electrolytically tinning a steel strip (1) in continuous travel in an insoluble anode electrodeposition unit (3) (23) in an electrolyte and having in line a reactor of electro-dissolution device (6) for charging the electrolyte with tin ions by selective separation through an electrodialysis or electrolysis membrane (10) which divides said electro-dissolution reactor (6) into a compartment anode (6b) having a first electrode (122b) connected to the positive pole of a power supply circuit (12) and a cathode compartment (6a) having a second electrode (121a) connected to the negative pole of the same electrical circuit , for which a control member of the electro-dissolution reactor engages a first power supply polarity switching of each of the two electrodes, the control member ensuring, adjacent to the first permutation, a second permutation of the flow of the electrolyte between each of the two compartments of the electro-dissolution reactor and the electroplating unit, and characterized in that

- The adjoining and periodic permutations of the power supply polarity of the electro-dissolution and circulation unit of the electrolyte returning to the electrodeposition unit ensure a continuous withdrawal of the electrolyte by alternating cycles. from one or the other of the two compartments by attributing to said compartment an anodic function of electro-dissolution by means of a soluble electrode,

two alternating cycles of continuous sampling are defined by neighboring durations.

2. Method according to claim 1, wherein each of the two electrodes is associated with a dissolution basket (7a, 7b) electrically non-conductive and supplied with conductive soluble elements, providing the electrodes with identical anode / cathode type permutation properties.

3. Method according to claim 2, for which the supply of soluble elements is carried out by continuous or sequential filling of tin granules in each of the electrically non-conductive dissolving baskets (7a, 7b), each of them being partially immersed in the electrolyte of one of said two compartments.

4. Method according to one of the preceding claims wherein the permutation of the flow of electrolyte between each of the two compartments of the electro-dissolution reactor is synchronously coupled to a switchable loop of a hydrogen degassing process. the electrolyte.

5. Method according to one of the preceding claims 1-4, for which by means of a hydraulic circuit (8) ensuring the flow of electrolyte from a compartment of the electro-dissolution reactor (6) currently fed by a circuit anolyte (6a), to the electrodeposition unit (3) and a catholyte circuit (6b) to become anolyte, the permutations of circulation of the electrolyte and the power supply polarity are carried out according to the following sequence: a) Disconnection of the power supply of the electrolysis reactor. b) Stopping circulating pumps (104, 105) of the anolyte and the catholyte at the outlet of the reservoirs (4, 5) towards each of the electrodes, c) Opening of first inlet and outlet valves (82b, 92a) electrolyte of the catholyte circuit (6b), valves (82a, 84b) connected to the anolyte circuit (6a) and one of the valves (94a) connected to the catholyte circuit being closed, and starting of the pump (104) until with discharge into the catholyte reservoir (5) of the catholyte contained in the dissolution reactor (6b) and the pipes (81b, 91a) connected to said first valves and the previously cathodic compartment (71b), d) Opening of second valves (94b, 84a) for entering and leaving the electrolyte of the anolyte circuit (6a), valves (94a, 92b) connected to the catholyte circuit (6b) and one of the valves (82a) connected to the anolyte circuit, being closed, and starting of the pump (105) until discharge into the anolyte reservoir (4) of the anolyte contained in the sheave dissolver (6a) and tubings (81a, 83a) connected to said second valves and the previously anodic compartment (71a), e) Closing one of the first and one of the second valves (84a, 92a) as soon as the end of the evacuation of the anolyte from (71a) to the anolyte reservoir (4) and the evacuation of the catholyte from (71b) to the catholyte reservoir (5) f) Opening of the valves (84b, 92b) from each of the electrodes to one of the reservoirs (4, 5), g) Permutation and restoration of the power supply current.

6. Method according to one of the preceding claims, characterized in that an analysis member capable of measuring qualitatively and quantitatively the chemical composition of each of the two compartments of the electro-dissolution reactor (6) delivers to the control member a signal corresponding to the content of tin ions in each of said compartments and that as a function of an adjustable threshold of tin ion contents, said control member ensures the permutation polarity supply of electric current and as the permutation of the electrolyte circulation.

7. Method according to claim 6, characterized in that the control member of the electro-dissolution reactor is capable of providing a control of the dissolution current density as a function of the need for renewal of tin ions evaluated according to less the signal delivered by the analysis organ.

8. Method according to claim 6 or 7, characterized in that the analysis member makes use of a spectroscopic analyzer by laser ablation.

9. Method according to one of the preceding claims, characterized in that a sulphonic acid, for example methanesulfonic acid, is used as the electrolyte.

10. Method according to the preceding claims, characterized in that the electrodialysis or electrolysis membrane separating the anode and cathode compartments of anolyte and catholyte from the electro-dissolution reactor is a cationic membrane _τ having a selective permeability. allowing the retention of a large fraction of Sn ⁺⁺ tin ions in the anode compartment as well as a transfer of H ⁺ hydrogen ions to the cathode compartment and a low tin ion transfer Sn ⁺⁺ to this same cathode compartment.

11. Method according to one of the preceding claims, characterized in that the two electrodes of the electro-dissolution reactor consist of tin greater than 99% pure.

12. An electrolytic tinning installation of a continuous steel strip in an electrolyte-insoluble anode plating unit (3) having an electro-dissolution reactor (6) in line in an electroless plating unit (6). circuit for charging the electrolyte with tin ions by selective separation through a mem- an electrodialysis or electrolysis brane (10) which divides said electro-dissolution reactor (6) into an anode compartment (6b) having a first electrode (122b) connected to the positive pole of a supply circuit ( 12) in electrical current and a cathode compartment (6a) having a second electrode (121a) connected to the negative pole of the same electrical circuit, for which a control member of the electro-dissolution reactor engages a first polarity permutation of the circuit d supplying electric current (11) to each of the two electrodes, the control member providing, adjacent to the first permutation, a second permutation of the flow of the electrolyte between each of the two compartments of the electro-reactor. dissolution and the electroplating unit, and characterized in that

- The control member activates sequentially each of the two reciprocating cycles by maintaining a continuous removal of the electrolyte, said cycles being defined by neighboring times.

13. Installation according to claim 12 for which the two electrodes comprise conductive soluble elements, providing them with identical properties of anode / cathode type switching.

14. Apparatus according to claim 13, wherein the soluble elements comprise tin granules capable of continuous or sequential filling of at least one of two electrically non-conductive dissolving baskets (7a, 7b), each of said soluble elements. being partially immersed in the electrolyte of one of the two said compartments.

15. Installation according to one of the preceding claims 12-14, wherein the control member comprises a synchronous coupling of the permutation of the flow of the electrolyte between each of the two compartments of the electrolysis reactor with a switching of a loop of a degassing unit (5) hydrogen for the electrolyte, said loop being switchable between one of the compartments and the degassing unit.

16. Installation according to one of the preceding claims 14-15 wherein each dissolution basket (7a, 7b) is partially in the form of a vertical column so as to be filled with tin granules in which the electrolyte flows from bottom to top of column and has:

17 / installation according to one of claims 12-16, characterized in that the power supply circuit current (11) of the electro-dissolution reactor comprises a polarity inverter (12) adapted to ensure the switching of the power supply electrically of each of the electrodes (121a, 122b) in a positive or negative polarity, each said electrode being accordingly anode or cathode according to the controllable polarization sequence.

18 / Apparatus according to claims 16, characterized in that a first circuit is adapted to ensure the circulation of the electrolyte according to the following diagram: • A tin-depleted and acid-enriched electrolyte is withdrawn from the electroplating unit (3), subjected to an oxygen degassing unit (4) and then introduced into the lower zone of a first dissolving basket ( 7a) tin granules at a pressure sufficient to allow an overflow of said electrolyte in the recovery trough (72a) of the central zone without overflow in the upper dry zone.

• An electrolyte recharged with tin ions during its circulation in the first dissolution basket (7a) of the electro-dissolution reactor is taken from its recovery trough (72a), is subjected to oxygen degassing (4). ) to be reinjected into the coating pan (2).

19 / installation according to one of claims 16 or 18, characterized in that a second circuit is adapted to ensure the circulation of the electrolyte according to the following diagram:

• An electrolyte recharged with tin ions during its circulation in the second dissolution tank (7b) of the electro-dissolution reactor is taken from its recovery trough (72b), is subjected to oxygen degassing (4). ) to be reinjected into the coating pan (2).

An electrolyte taken from the first compartment (6a) of the electro-dissolution reactor in the vicinity of the electrodialysis or electrolysis membrane (10), on the opposite side to the second dissolution basket (7b), is subjected to a degassing of the hydrogen (5) then reinjected into the same zone of the reactor compartment.

20 / Apparatus according to one of claims 18 or 19, characterized in that the degassing of oxygen (4) and hydrogen (5) is carried out in a reservoir anolyte (4) or respectively a catholyte reservoir (5), such as buffer tanks of the compartments of the electro-dissolution reactor.

21 / installation according to one of the preceding claims 12-20, wherein by means of a hydraulic circuit (8) ensuring the circulation of the electrolyte of a compartment of the electro-dissolution reactor (6) currently fed by a circuit anolyte (6a), to the electrodeposition unit (3) and a catholyte circuit (6b) to become anolyte, the permutations of circulation of the electrolyte and the power supply polarity are carried out according to the following sequence: a) Disconnection of the power supply of the electrolysis reactor. b) Stopping circulating pumps (104, 105) of the anolyte and the catholyte at the outlet of the reservoirs (4, 5) towards each of the electrodes, c) Opening of first inlet and outlet valves (82b, 92a) electrolyte of the catholyte circuit (6b), valves (82a, 84b) connected to the anolyte circuit (6a) and one of the valves (94a) connected to the catholyte circuit being closed, and starting of the pump (104) until with discharge into the catholyte reservoir (5) of the catholyte contained in the dissolution reactor (6b) and the pipes (81b, 91a) connected to said first valves and the previously cathodic compartment (71b), d) Opening of second valves (94b, 84a) for entering and leaving the electrolyte of the anolyte circuit (6a), valves (94a, 92b) connected to the catholyte circuit (6b) and one of the valves (82a) connected to the anolyte circuit, being closed, and starting of the pump (105) until discharge into the anolyte reservoir (4) of the anolyte contained in the sheave dissolver (6a) and tubings (81a, 83a) connected to said second valves and the previously anodic compartment (71a), e) Closing one of the first and one of the second valves (84a, 92a) as soon as the end of the evacuation of the anolyte from (71a) to the anolyte reservoir (4) and the evacuation of the catholyte from (71b) to the catholyte reservoir (5) f) Opening of the valves (84b, 92b) from each of the electrodes to one of the reservoirs (4, 5), g) Permutation and restoration of the power supply current.

22 / installation according to one of claims 12 to 21, characterized in that the electrolyte circulation circuit comprises a first and a second circulation circuit, being respectively equipped with a set of first and second valves motorized remote actuators for sequentially switching on the first or the second circuit in relation to the permutation of the electrical polarities applied to the electrodes in two sequential modes:

23 / Apparatus according to one of claims 12 to 22, characterized in that the motorized valves and an electric polarity inverter applied to the electrodes are controlled by a control member which issues permutation commands from data concerning levels of ion ions. each of the compartments (6a, 6b), said contents being delivered to the control member by an analysis member operating ideally according to a technique of laser ablation spectroscopy or "Laser Induced Breakdown Spectroscopy"

24 / Apparatus according to one of claims 12 to 23, characterized in that the electro-dissolution reactor consists of several electro-dissolution cells provided with circuits of circulation and power supply connected in parallel and comprising each :

A first dissolution basket (7a) alternately of anode or cathode type,

A second dissolution basket (7b) alternately of cathode or anode type,

An electrodialysis or cationic electrolysis membrane separating each cell into an anolyte zone and a catholyte zone depending on the polarization of the electrodes.

25 / Apparatus according to one of claims 12 to 24, characterized in that the electro-dissolution reactor consists of several electro-dissolution cells whose circuits of circulation and supply of electric current are separated and capable of be permuted independently of each other. 26 / Apparatus according to one of claims 24 or 25, characterized in that an automatic feed device tin pellets serves hoppers (73) of all baskets of the reactor.