EP2334846B1 - Method and installation for electrolytic tinning of a continuously running steel strip in an electrodeposition unit - Google Patents

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 with 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 soluble anode deposition processes that differ in 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 disadvantages perfectly described in the document US 4,181,580 which also proposes a variant using 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 → ½ 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 4,181,580 wherein an installation uses a circuit for recirculating the electrolyte in the bath by coupling the latter to a fluidized bed reactor into which the electrolyte, tin granules and an oxygen-rich gas stream are introduced. 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.

The document US5,312,539 proposes another method using an anionic membrane dialysis cell and a separate tin dissolving unit in which the tin is supplied as an oxide dissolved directly in the acid or as an anode in tin dissolved electrolytically. 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.

The document US 6,120,673 proposes a facility for dissolving and regenerating electrolyte in a trough with three compartments: one having a soluble anode tin, another in which is disposed an insoluble cathode and, in between, an "intermediate" compartment separated from the anode compartment by a cationic membrane passing therein Sn ⁺⁺ ions and separated from the cathode compartment by an anionic membrane passing through the acid ions A ^- . The intermediate compartment provides recombination of the electrolyte from the ions from the other two compartments. However, the surfaces of anionic and cationic membranes required are very different and make it very difficult to achieve an industrial installation.

The Applicant has herself experimented extensively with a variant of the processes already described by using an electrodeposition bath coupled to an electro-dissolution reactor, the soluble anode of 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 selective permeability it implements may be of modest area compared to the current densities 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 the document JP11-172496 which proposes to remedy this by periodically reversing 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 electrolyte of an electroplating unit and having in line an electrolytic reactor. dissolution for recharging the electrolyte tin ions, for which the continuity of recharging 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.

• les permutations attenantes et périodiques de la polarité d'alimentation en courant électrique de l'unité d'électro-dissolution et de circulation de l'électrolyte retournant à l'unité d'électrodéposition assurent un prélèvement continu de l'électrolyte par cycles alternatifs à partir d'un ou l'autre des deux compartiments en attribuant à un dit compartiment une fonction anodique d'électro-dissolution au moyen d'une électrode soluble tant pour l'anode pour un premier cycle que la cathode pour un second cycle et vice-versa,
• les deux cycles alternatifs de prélèvement continu sont définis par des durées avoisinées.

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 switching of each of the two electrodes, and
the control member providing, 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,
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 electroplating unit ensure a continuous withdrawal of the electrolyte by alternating cycles at from one or the other of the two compartments by attributing to one said compartment an anodic function of electro-dissolution by means of an electrode soluble for both the anode for a first cycle and the cathode for a second cycle and vice versa,
• the two alternative continuous sampling cycles are defined by neighboring durations.

So unlike the document JP11-172496 , the periodic inversion "go-and-return", that is to say on two consecutive cycles, the polarity of the dissolution current applied to the electrodes (anode / cathode) is no longer carried out over a very short time but by a "go" cycle and a "return" cycle of neighboring durations, themselves longer than an inversion 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 reloaded tin ions necessary for feeding the electroplating unit is taken from one or other of the compartments as long as this one is anodic.

1. a) Coupure de l'alimentation en courant électrique du réacteur d'électro-dissolution.
2. b) Arrêt de pompes de circulation de l'anolyte et du catholyte.
3. c) Ouverture de premières vannes d'entrée et de sortie de l'électrolyte du circuit catholyte et mise en route de la pompe de circulation de l'anolyte jusqu'à évacuation dans le réservoir de catholyte de l'électrolyte contenu dans les circuits liés aux dites premières vannes et au compartiment préalablement cathodique,
4. d) Ouverture de deuxièmes vannes d'entrée et de sortie de l'électrolyte du circuit anolyte et mise en route de la pompe de circulation du catholyte jusqu'à évacuation dans le réservoir d'anolyte de l'électrolyte contenu dans les circuits liés aux dites secondes vannes et au compartiment préalablement anodique,
5. e) Fermeture des vannes de sortie de l'électrolyte vers des réservoirs d'évacuation dès la fin de l'évacuation de l'anolyte et du catholyte vers des réservoirs correspondants,
6. f) Ouverture des vannes de sortie de l'électrolyte vers des circuits correspondant au nouveau mode de fonctionnement permuté,
7. g) Permutation et rétablissement du courant d'alimentation électrique.

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 of the electric power supply polarity are carried out according to the sequence which will be described later, and can be summarized as follows:

1. a) Disconnection of the power supply of the electro-dissolution reactor.
2. b) Stopping circulating pumps of the anolyte and the catholyte.
3. 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 said first valves and the previously cathodic compartment,
4. d) Opening of second inlet and outlet valves of the electrolyte of the anolyte circuit and starting of the circulation pump of the catholyte until evacuation in the anolyte reservoir of the electrolyte contained in the circuits related to say second valves and to the previously anodic compartment,
5. e) Closing of 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,
6. f) Opening of the electrolyte outlet valves to circuits corresponding to the new permuted mode of operation,
7. g) Permutation and restoration of the power supply current.

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 unit makes it possible to ensure in time real 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 soluble tin electrode of the electro-dissolution reactor, 99% pure tin elements (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 provides 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.

Figure 1 :

Schéma de principe d'une installation d'électrodéposition à anode insoluble,

Figure 2 :

Schéma général de circulation de l'électrolyte d'une installation d'étamage électrolytique selon l'invention,

Figure 3 :

Schéma d'une installation d'étamage électrolytique selon l'invention dans un premier mode de polarisation électrique du réacteur d'électro-dissolution,

Figure 4 :

Schéma d'une installation d'étamage électrolytique selon l'invention dans un second mode de polarisation électrique du réacteur d'électro-dissolution,

Figure 5 :

Schéma général de circulation de l'électrolyte d'une installation alternative d'étamage électrolytique selon l'invention,

Figure 6 :

Schéma d'une installation d'étamage électrolytique selon figure 5 dans un premier mode de polarisation électrique du réacteur d'électro-dissolution,

Figure 7 :

Schéma d'une installation d'étamage électrolytique selon figure 5 dans un second mode de polarisation électrique du réacteur d'électro-dissolution,

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

Figure 1 :

Schematic diagram of an insoluble anode electrodeposition plant,

Figure 2:

General flow diagram of the electrolyte of an electrolytic tinning installation according to the invention,

Figure 3:

Diagram of an electrolytic tinning installation according to the invention in a first electric polarization mode of the electro-dissolution reactor,

Figure 4:

Diagram of an electrolytic tinning installation according to the invention in a second electric polarization mode of the electro-dissolution reactor,

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 mode of electric polarization of the electro-dissolution reactor,

Figure 7:

Diagram of an electrolytic tinning installation according to figure 5 in a second mode of electric polarization of the electro-dissolution reactor,

The figure 1 discloses a schematic diagram of an installation comprising an insoluble anode electrodeposition: A strip of steel in flow and to be coated (1) plunges into an electroplating tank (2) by winding on two conductive rolls ( 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.

The figure 2 discloses a general flow diagram of the electrolyte of an installation according to the invention suitable for the electrolytic tinning of a steel strip in continuous running in an electrolytic insoluble anode plating unit (3) and disposing, 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 permutation 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.

• l'organe de commande active les permutations attenantes et périodiques de la polarité d'alimentation en courant électrique de l'unité d'électro-dissolution et de circulation de l'électrolyte retournant à l'unité d'électrodéposition en assurant un prélèvement continu de l'électrolyte par cycles alternatifs à partir d'un ou l'autre des deux compartiments en attribuant au dit compartiment une fonction anodique d'électro-dissolution au moyen d'une électrode soluble,
  • - l'organe de commande active séquentiellement chacun des deux cycles alternatifs en maintenant un prélèvement continu (c'est-à-dire ininterrompu) de l'électrolyte, les dits cycles étant définis par des durées avoisinées.

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 a continuous sampling 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,
  • 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.

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.

• Une zone inférieure « humide » constituée d'un matériau non conducteur d'électricité, un plastique ou une résine polyester armée ou un acier revêtu de polymère, complètement immergée dans l'électrolyte et comporte un treillis composé d'au moins un filet en plastique de maille adaptée à la granulométrie de l'étain soit entre 0,50 et 0,05 mm, préférentiellement entre 0,3 et 0,10 mm, ledit filet étant supporté par l'enveloppe du panier de dissolution qui présente des ouvertures de mise en contact avec l'électrolyte au moins 50 fois plus larges que les mailles dudit filet.
• Une zone médiane « humide » non immergée mais baignée par circulation de l'électrolyte et équipée d'une auge de récupération (72a, 72b) d'électrolyte régénéré, ladite auge étant alimentée par un treillis identique à celui de la zone inférieure, et en ce que l'ensemble treillis et auge est en matériau non conducteur d'électricité tel qu'un plastique ou une résine polyester armée ou un acier revêtu de polymère.
• Une zone supérieure « sèche » conductrice d'électricité libre de toute immersion ou en contact avec l'électrolyte, équipée d'une trémie métallique de remplissage (73) en granules d'étain et reliée à un des contacts de polarité du circuit d'alimentation (11) en courant électrique.

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 refillable with tin granules in which the electrolyte circulates from bottom to top of the column and has:

• A "wet" bottom zone consisting of a non-electrically conductive material, a reinforced plastic or polyester resin or a polymer coated steel, fully immersed in the electrolyte and comprising a mesh of at least one plastic net of mesh adapted to the granulometry of 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 for setting in contact with 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 fed with a lattice identical to that of the lower zone, and in that the trellis and trough assembly is of non-electrically conductive material such as a reinforced plastic or polyester resin or a polymer coated steel.
• An electrically conductive upper "dry" 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. power 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 pipes or branches (81 a, 81 b) 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 (91 a, 91 b) 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.

The figure 3 describes 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) to switch its polarities at outputs (121, 122) of generators. In the example of the figure 3 the electrode (122b) connected to the dissolution basket (7b) is connected to the positive pole and thus behaves as a soluble anode while the electrode (121a) connected to the dissolution basket (7a), thus connected to the negative pole, conducts itself 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 (91 b) 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.

The figure 4 describes 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 the figure 3 the electric power generator (11) is connected to a switching device (12) for switching polarities to the outputs (121) and (122). In the example of the figure 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, conducts itself 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.

• le circuit d'alimentation électrique en courant (11) du réacteur d'électro-dissolution comporte un inverseur de polarité (12) apte à assurer la permutation de l'alimentation électrique de chacune des électrodes (121 a, 122b) selon une polarité positive ou négative, chaque dite électrode étant en conséquence anode ou cathode suivant la séquence commandable de polarisation.
• un premier circuit est apte à assurer la circulation de l'électrolyte selon le schéma suivant :
  • Un électrolyte appauvri en étain et enrichi en acide est prélevé dans l'unité d'électrodéposition (3), soumis à une unité de dégazage de l'oxygène (4) puis introduit dans la zone inférieure d'un premier panier de dissolution (7a) des granules d'étain à une pression suffisante pour permettre un débordement dudit électrolyte dans l'auge de récupération (72a) de la zone médiane sans débordement dans la zone supérieure sèche.
  • Un électrolyte rechargé en ions d'étain lors de sa circulation dans le premier panier de dissolution (7a) du réacteur d'électro-dissolution est prélevé dans son auge de récupération (72a) en vue d'être réinjecté dans le bac de revêtement (2).
  • Un électrolyte prélevé dans le deuxième compartiment (6b) du réacteur d'électro-dissolution au voisinage de la membrane d'électrodialyse ou d'électrolyse (10), du côté opposé au premier panier de dissolution (7a), est soumis à un dégazage (5) de l'hydrogène puis réinjecté dans la même zone du compartiment du réacteur d'électro-dissolution.
• un second circuit est apte à assurer la circulation de l'électrolyte selon le schéma suivant :
  • Un électrolyte appauvri en étain et enrichi en acide est prélevé dans l'unité d'électrodéposition (3), soumis à une unité de dégazage de l'oxygène (4) puis introduit dans la zone inférieure du second panier de dissolution (7b) des granules d'étain à une pression suffisante pour permettre un débordement dudit électrolyte dans l'auge de récupération (72b) de la zone médiane sans débordement dans la zone supérieure sèche.
  • Un électrolyte rechargé en ions d'étain lors de sa circulation dans le second panier de dissolution (7b) du réacteur d'électro-dissolution est prélevé dans son auge de récupération (72b) en vue d'être réinjecté dans le bac de revêtement (2).
  • Un électrolyte prélevé dans le premier compartiment (6a) du réacteur d'électro-dissolution au voisinage de la membrane d'électrodialyse ou d'électrolyse (10), du côté opposé au second panier de dissolution (7b), est soumis à un dégazage de l'hydrogène (5) puis réinjecté dans la même zone du compartiment du réacteur.
• le circuit de circulation de l'électrolyte comprend un premier et un deuxième circuit de circulation, étant respectivement équipés d'un jeu de premières et deuxièmes vannes motorisées commandées à distance permettant de permuter séquentiellement sur le premier ou le deuxième circuit en relation avec la permutation des polarités électriques appliquées aux électrodes selon deux modes séquentiels :
  • Un mode d'ouverture du premier circuit et une fermeture corrélative du second circuit lorsque le premier compartiment lié au premier circuit est initialement anodique.
  • Un mode d'ouverture du second circuit et une fermeture corrélative du premier circuit lorsque le deuxième compartiment lié au deuxième circuit est initialement anodique.
• au moyen d'un circuit hydraulique (8) assurant la circulation de l'électrolyte d'un compartiment du réacteur d'électro-dissolution (6) en alimentation par un circuit anolyte (6b), vers l'unité d'électrodéposition (3) et un circuit catholyte (6a) en vue de devenir anolyte, les permutations attenantes de circulation de l'électrolyte et de la polarité d'alimentation en courant électrique sont réalisées selon une séquence bien définie mettant en jeu des moyens de dégazage de l'oxygène et de l'hydrogène avantageusement commutables sur les électrodes. Cette séquence sera décrite plus précisément dans le cadre des figures 5, 6 et 7.
• les vannes motorisées et un inverseur de polarité électriques appliquées aux électrodes sont commandés par un organe de commande qui délivre des ordres de permutation à partir de données concernant des teneurs en ions d'étain de chacun des compartiments (6a, 6b), lesdites teneurs étant délivrées à l'organe de commande par un organe d'analyse fonctionnant idéalement selon une technique de spectroscopie par ablation laser ou « Laser Induced Breakdown Spectroscopy »
• le réacteur d'électro-dissolution est constitué de plusieurs cellules d'électro-dissolution munis de circuits de circulation et d'alimentation en courant électrique montées en parallèle et comportant chacune :
  • Un premier panier de dissolution (7a) alternativement de type anode ou cathode,
  • Un second panier de dissolution (7b) alternativement de type cathode ou anode,
  • Une membrane d'électrodialyse ou d'électrolyse cationique séparant chaque cellule en une zone d'anolyte et une zone de catholyte en fonction de la polarisation des électrodes.
• le réacteur d'électro-dissolution est constitué de plusieurs cellules d'électro-dissolution dont les circuits de circulation et d'alimentation en courant électrique sont séparés et capables d'être permutés indépendamment les uns des autres. Ainsi, il peut être assurer qu' au moins un réacteur sera toujours en phase de régime actif d'électro-dissolution établi alors qu'un ou plusieurs autres réacteurs peuvent être en phase transitoire de permutation. Cela améliore une constance de régularité de composition de l'électrolyte.
• un dispositif automatique d'alimentation en granules d'étain dessert des trémies (73) de tous les paniers du réacteur.

In summary according to the figures 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 electro-dissolution reactor comprises a polarity inverter (12) adapted to ensure the switching of the electrical 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 tank (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 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 electroplating unit (3), subjected to an oxygen degassing unit (4) and then introduced into the lower zone of the second dissolving basket (7b). tin granules at a pressure sufficient to allow an overflow of said electrolyte into the recovery trough (72b) of the median 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 tank (7b), is subjected to degassing. hydrogen (5) and 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 specifically in the context of figures 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 analysis device 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 of circulation and power supply connected in parallel and each comprising:
  • A first dissolution basket (7a), alternatively of anode or cathode type,
  • A second dissolution basket (7b), alternatively 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.
• the electro-dissolution reactor consists of several electro-dissolution cells whose circulation and electrical power 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.

Figure 5 describes a general flow diagram of the electrolyte of an alternative electrolytic tinning installation according to the invention and presenting with respect to figures 2 , 3 and 4 an advantage in that two hydrogen and oxygen degassing poles (4, 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 the electro-dissolution reactor (6) as a function of a hydraulic permutation according to the imposed polarity switching and thus alternating anode / cathode alternate 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 reservoir (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 tin electrolyte 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 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.

• l'organe de commande active les permutations attenantes et périodiques de la polarité d'alimentation en courant électrique de l'unité d'électro-dissolution et de circulation de l'électrolyte retournant à l'unité d'électrodéposition en assurant un prélèvement continu de l'électrolyte par cycles alternatifs à partir d'un ou l'autre des deux compartiments en attribuant au dit compartiment une fonction anodique d'électro-dissolution au moyen d'une électrode soluble,
• l'organe de commande active séquentiellement chacun des deux cycles alternatifs en maintenant un prélèvement continu (c'est-à-dire ininterrompu) de l'électrolyte, les dits cycles étant définis par des durées avoisinées.

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 a continuous sampling 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,
• the controller sequentially activates each of the two reciprocating cycles by maintaining a continuous (i.e. uninterrupted) sampling of the electrolyte, said cycles being defined by neighboring times.

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 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.

• Une zone inférieure « humide » constituée d'un matériau non conducteur d'électricité, un plastique ou une résine polyester armée ou un acier revêtu de polymère, complètement immergée dans l'électrolyte et comporte un treillis composé d'au moins un filet en plastique de maille adaptée à la granulométrie de l'étain soit entre 0,50 et 0,05 mm, préférentiellement entre 0,3 et 0,10 mm, ledit filet étant supporté par l'enveloppe du panier de dissolution qui présente des ouvertures de mise en contact avec l'électrolyte au moins 50 fois plus larges que les mailles dudit filet.
• Une zone médiane « humide » non immergée mais baignée par circulation de l'électrolyte et équipée d'une auge de récupération (72a, 72b) d'électrolyte régénéré, ladite auge étant alimentée par un treillis identique à celui de la zone inférieure, et en ce que l'ensemble treillis et auge est en matériau non conducteur d'électricité tel qu'un plastique ou une résine polyester armée ou un acier revêtu de polymère.
• Une zone supérieure « sèche » conductrice d'électricité libre de toute immersion ou en contact avec l'électrolyte, équipée d'une trémie métallique de remplissage (73) en granules d'étain et reliée à un des contacts de polarité du circuit d'alimentation (11) en courant électrique.

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 refillable of tin pellets in which the electrolyte flows 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, fully immersed in the electrolyte and comprising a mesh of at least one plastic net of mesh adapted to the granulometry of 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 for setting in contact with 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 fed with a lattice identical to that of the lower zone, and in that the trellis and trough assembly is of non-electrically conductive material such as a reinforced plastic or polyester resin or a polymer coated steel.
• An electrically conductive upper "dry" 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. power 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 collected in an anolyte tank (4) where it is degassed oxygen, and then injected into the dissolution reactor (6) by two pipes or branches (81 a, 81 b) 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 (91 a, 91 b) equipped with remotely controlled motorized valves (92a, 92b) and able to collect the electrolyte in each of the two compartments of the electro-dissolution reactor to conduct it in the catholyte tank (5) where it is subjected to a degassing of hydrogen from which it leaves to be returned to the same compartment of the reactor 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). according to a polarity that can be swapped.

The figure 6 describes the diagram of an installation according to figure 5 in a first switchable mode of electrical polarity of the electro-dissolution reactor: a switch-mode electrical current generator (12) for permuting its polarities at the outputs (121, 122) of generators. In the example of the figure 3 , the electrode (122b) connected to the dissolution basket (7b) is connected to the positive pole and thus behaves as a soluble anode while the electrode (121a) connected to the dissolution basket (7a), thus connected to the negative pole , behaves 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.

The figure 7 describes the diagram of an installation according to figure 5 in a second mode of electrical polarity of the electro-dissolution reactor, said mode being permuted with respect to the figure 3 : the switchgear electrical power generator (12) for switching polarity to the outputs (121) and (122). In the example of the figure 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, conducts itself 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 (91 a) 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 reservoir (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 this polarization, the compartment (6a) of the electro-dissolution reactor is anodic and the compartment (6b) cathodic.

• le circuit d'alimentation électrique en courant du réacteur d'électro-dissolution (12) apte à assurer la permutation de l'alimentation électrique de chacune des électrodes (121a, 122b) selon une polarité positive ou négative, chaque dite électrode étant en conséquence anode ou cathode suivant la séquence commandable de polarisation.
• un premier circuit est apte à assurer la circulation de l'électrolyte selon le schéma suivant :
  • Un électrolyte (3) appauvri en étain et enrichi en acide est prélevé dans l'unité d'électrodéposition (2), recueilli dans un réservoir d'anolyte (4) où il est soumis à un dégazage de l'oxygène, puis introduit dans la zone inférieure d'un premier panier de dissolution (7a) des granules d'étain à une pression suffisante pour permettre un débordement dudit électrolyte dans l'auge de récupération (72a) de la zone médiane sans débordement dans la zone supérieure sèche.
  • Un électrolyte rechargé en ions d'étain lors de sa circulation dans le premier panier de dissolution (7a) du réacteur d'électro-dissolution est prélevé dans son auge de récupération (72a), en vue de retourner au réservoir (4) où il est soumis à un dégazage d'oxygène pour être réinjecté dans le bac de revêtement (2).
  • Un électrolyte prélevé dans le deuxième compartiment (6b) du réacteur d'électro-dissolution au voisinage de la membrane d'électrodialyse ou d'électrolyse (10), du côté opposé au premier panier de dissolution (7a), est recueilli dans un réservoir de catholyte (5) où il est soumis à un dégazage de l'hydrogène puis réinjecté dans la même zone du compartiment du réacteur d'électro-dissolution.
• un second circuit est apte à assurer la circulation de l'électrolyte selon le schéma suivant :
  • Un électrolyte (3) appauvri en étain et enrichi en acide est prélevé dans l'unité d'électrodéposition (2), recueilli dans un réservoir d'anolyte (4) où il est soumis à un dégazage de l'oxygène, puis introduit dans la zone inférieure du second panier de dissolution (7b) des granules d'étain à une pression suffisante pour permettre un débordement dudit électrolyte dans l'auge de récupération (72b) de la zone médiane sans débordement dans la zone supérieure sèche.
  • Un électrolyte rechargé en ions d'étain lors de sa circulation dans le second panier de dissolution (7b) du réacteur d'électro-dissolution est prélevé dans son auge de récupération (72b), en vue de retourner au réservoir (4) où il est soumis à un dégazage d'oxygène pour être réinjecté dans le bac de revêtement (2).
  • Un électrolyte prélevé dans le premier compartiment (6a) du réacteur d'électro-dissolution au voisinage de la membrane d'électrodialyse ou d'électrolyse (10), du côté opposé au second panier de dissolution (7b), est recueilli dans un réservoir de catholyte (5) où il est soumis à un dégazage de l'hydrogène puis réinjecté dans la même zone du compartiment du réacteur.
• le circuit de circulation de l'électrolyte comprend un premier et un deuxième circuit de circulation, étant respectivement équipés d'un jeu de premières et deuxièmes vannes motorisées commandées à distance permettant de permuter séquentiellement sur le premier ou le deuxième circuit en relation avec la permutation des polarités électriques appliquées aux électrodes selon deux modes séquentiels :
  • Un mode d'ouverture du premier circuit et une fermeture corrélative du second circuit lorsque le premier compartiment lié au premier circuit est initialement anodique.
  • Un mode d'ouverture du second circuit et une fermeture corrélative du premier circuit lorsque le deuxième compartiment lié au deuxième circuit est initialement anodique.
• au moyen d'un circuit hydraulique (8) assurant la circulation de l'électrolyte d'un compartiment du réacteur d'électro-dissolution (6) en alimentation par un circuit anolyte (6a), vers le réservoir d'anolyte (4) puis, de là, vers l'unité d'électrodéposition (2) et un circuit catholyte (6b) en vue de devenir anolyte, les permutations attenantes de circulation de l'électrolyte et de la polarité d'alimentation en courant électrique sont réalisées selon la séquence suivante :
  1. a) Coupure de l'alimentation en courant électrique du réacteur d'électro-dissolution.
  2. b) Arrêt de pompes de circulation (104, 105) de l'anolyte et du catholyte en sortie des réservoirs (4, 5) vers chacune des électrodes,
  3. c) Ouverture de premières vannes (82b, 92a) d'entrée et de sortie de l'électrolyte du circuit catholyte (6b), des vannes (82a, 84b) liées au circuit anolyte (6a) et une des vannes (94a) liée au circuit catholyte étant fermées, et mise en route de la pompe (104) jusqu'à évacuation dans le réservoir de catholyte (5) du catholyte contenu dans le réacteur de dissolution côté (6b) et des tubulures (81b, 91a) liées aux dites premières vannes et au compartiment précédemment cathodique (71 b),
  4. d) Ouverture de deuxièmes vannes (94b, 84a) d'entrée et de sortie de l'électrolyte du circuit anolyte (6a), des vannes (94a, 92b) liées au circuit catholyte (6b) et une des vannes (82a) liée au circuit anolyte, étant fermées, et mise en route de la pompe (105) jusqu'à évacuation dans le réservoir d'anolyte (4) de l'anolyte contenu dans le réacteur de dissolution côté (6a) et des tubulures (81 a, 83a) liées aux dites secondes vannes et au compartiment précédemment anodique (71 a),
  5. e) Fermeture d'une des premières et d'une des deuxième vannes (84a, 92a) dès la fin de l'évacuation de l'anolyte de (71 a) vers le réservoir d'anolyte (4) et de l'évacuation du catholyte de (71 b) vers le réservoir de catholyte (5)
  6. f) Ouverture de vannes (84b, 92b) de chacune des électrodes à un des réservoirs (4, 5),
  7. g) Permutation et rétablissement du courant d'alimentation électrique.
• les vannes motorisées et un inverseur de polarité électriques appliquées aux électrodes sont commandés par un organe de commande qui délivre des ordres de permutation à partir de données concernant des teneurs en ions d'étain de chacun des compartiments (6a, 6b), lesdites teneurs étant délivrées à l'organe de commande par un organe d'analyse fonctionnant idéalement selon une technique de spectroscopie par ablation laser ou « Laser Induced Breakdown Spectroscopy »
• le réacteur d'électro-dissolution est constitué de plusieurs cellules d'électro-dissolution munis de circuits de circulation et d'alimentation en courant électrique montées en parallèle et comportant chacune :
  • Un premier panier de dissolution (7a) alternativement de type anode ou cathode,
  • Un second panier de dissolution (7b) alternativement de type cathode ou anode,
  • Une membrane d'électrodialyse ou d'électrolyse cationique séparant chaque cellule en une zone d'anolyte et une zone de catholyte en fonction de la polarisation des électrodes.
• le réacteur d'électro-dissolution est constitué de plusieurs cellules d'électro-dissolution dont les circuits de circulation et d'alimentation en courant électrique sont séparés et capables d'être permutés indépendamment les uns des autres. Ainsi, il peut être assurer qu' au moins un réacteur sera toujours en phase de régime actif d'électro-dissolution établi alors qu'un ou plusieurs autres réacteurs peuvent être en phase transitoire de permutation. Cela améliore une constance de régularité de composition de l'électrolyte.
• un dispositif automatique d'alimentation en granules d'étain dessert des trémies (73) de tous les paniers du réacteur.

In summary according to the figures 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 electric current supply circuit of the electro-dissolution reactor (12) capable of ensuring the permutation of the electrical supply of each of the electrodes (121a, 122b) in a positive or negative polarity, each said electrode being consequently anode or cathode following the controllable polarization sequence.
• a first circuit is able to ensure the circulation of the electrolyte according to the following diagram:
  • An acid-depleted tin-enriched electrolyte (3) is withdrawn from the electroplating unit (2), collected in an anolyte tank (4) where it is degassed for oxygen, and then introduced into the the lower zone of a first dissolving basket (7a) of the tin granules at a pressure sufficient to allow an overflow of said electrolyte into 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 tank (7a) of the electro-dissolution reactor is taken from its recovery trough (72a), in order to return to the reservoir (4) where it is degassed with oxygen 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 side opposite to the first dissolution basket (7a), is collected in a reservoir of catholyte (5) where it is subjected to a degassing of hydrogen and then reinjected into the same zone of the compartment of the electro-dissolution reactor.
• a second circuit is able to ensure the circulation of the electrolyte according to the following diagram:
  • An acid-depleted tin-enriched electrolyte (3) is withdrawn from the electroplating unit (2), collected in an anolyte tank (4) where it is degassed for oxygen, and then introduced into the the lower zone of the second dissolving basket (7b) of the 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 reservoir (4) where it is degassed with oxygen 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 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 (6a), to the anolyte tank (4) from there, to the electroplating unit (2) and a catholyte circuit (6b) to become anolyte, the permutations for circulating the electrolyte and the power supply polarity are carried out according to the following sequence:
  1. a) Disconnection of the power supply of the electro-dissolution reactor.
  2. 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,
  3. c) Opening first electrolyte inlet and outlet valves (82b, 92a) 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 switching on the pump (104) until the catholyte reservoir (5) is discharged from the catholyte contained in the dissolution reactor (6b) and the tubings (81b, 91a) connected to the catholyte said first valves and the previously cathodic compartment (71 b),
  4. d) Opening second electrolyte input and output valves (94b, 84a) and the anolyte circuit electrolyte (6a), the 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 discharging into the anolyte tank (4) the anolyte contained in the dissolution reactor (6a) and the pipes (81a, 83a) connected to said second valves and the previously anodic compartment (71a),
  5. e) Closing of one of the first and one of the second valves (84a, 92a) as soon as the evacuation of the anolyte from (71 a) to the anolyte reservoir (4) and the evacuation from the catholyte of (71 b) to the catholyte reservoir (5)
  6. f) opening of valves (84b, 92b) of each of the electrodes to one of the reservoirs (4, 5),
  7. g) Permutation and restoration of the power supply current.
• 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 analysis device 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 of circulation and power supply connected in parallel and each comprising:
  • A first dissolution basket (7a), alternatively of anode or cathode type,
  • A second dissolution basket (7b), alternatively 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.
• the electro-dissolution reactor consists of several electro-dissolution cells whose circulation and electrical power 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 (26)

1. Method for 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 electrical current supply circuit (12) and a cathodic compartment (6a) comprising a second electrode (121a) connected to the negative terminal of the same electrical circuit,
   for which a control unit of the electrodissolution reactor engages a first change in the polarity of the electrical current supply of each of the two electrodes,
   the control unit providing for, in a manner adjoining the first change, a second change in the circulation of the electrolyte between each of the two compartments of the electrodissolution reactor and the electrodeposition unit,
   and characterised in that

   - the adjoining and periodic changes in the polarity of the electrical current supply of the electrodissolution unit and in the circulation of the electrolyte returning to the electrodeposition unit provide for continuous sampling of the electrolyte through 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 sampling are defined by similar durations.
2. Method according to claim 1, for which each of the two electrodes is linked with an electrically non-conducting dissolution bin (7a, 7b) and supplied with soluble conducting elements, providing the electrodes with identical anode/cathode type switching properties.
3. Method according to claim 2, for which the supply of soluble elements is provided by continuous or sequential addition of tin granules to each of the electrically non-conducting dissolution bins (7a, 7b), each of them being partially dipped in the electrolyte of one of the two said compartments.
4. Method according to one of the preceding claims for which the switching of the circulation of the electrolyte between each of the two compartments of the electrodissolution reactor is synchronously coupled to a switchable loop of a process for degassing hydrogen from the electrolyte.
5. Method according to one of the preceding claims 1-4, for which, by means of a hydraulic circuit (8) providing for the circulation of the electrolyte from a compartment of the electrodissolution reactor (6) currently being supplied by an anolyte circuit (6a) to the electrodeposition unit (3) and a catholyte circuit (6b) about to become anolyte, the changes in circulation of the electrolyte and in the polarity of the electrical current supply are performed in accordance with the following sequence:

   a) Cut off the electrical current supply to the electrodissolution reactor.

   b) Stop the anolyte and catholyte circulation pumps (104,105) at the outlet from the tanks (4, 5) to each of the electrodes.

   c) Open first electrolyte inlet and outlet valves (82b, 92a) of the catholyte circuit (6b), the valves (82a, 84b) connected to the anolyte circuit (6a) and one of the valves (94a) connected to the catholyte circuit being closed, and operate the pump (104) until the catholyte contained in one side of the dissolution reactor (6b) and the piping (81b, 91a) connected to said first valves and to the previously cathodic compartment (71b) is emptied into the catholyte tank (5).

   d) Open second electrolyte inlet and outlet valves (94b, 84a) of the anolyte circuit (6a), the valves (94a, 92b) connected to the catholyte circuit (6b) and one of the valves (82a) connected to the anolyte circuit being closed, and operate the pump (105) until the anolyte contained in one side of the dissolution reactor (6a) and the piping (81a, 83a) connected to said second valves and to the previously anodic compartment (71a) is emptied into the anolyte tank (4).

   e) Close one of the first and one of the second valves (84a, 92a) when the anolyte has been emptied from (71a) into the anolyte tank (4) and the catholyte has been emptied from (71b) into the catholyte tank (5).

   f) Open valves (84b, 92b) from each of the electrodes to one of the tanks (4, 5).

   g) Change and re-establish the electrical current supply.
6. Method according to one of the preceding claims, characterised in that an analysis unit capable of qualitatively and quantitatively measuring the chemical composition of each of the two compartments of the electrodissolution reactor (6) delivers to the control unit a signal corresponding to the content of tin ions in each of said compartments and that, as a function of an adjustable threshold for content of tin ions, said control unit provides for change in the polarity of the electrical current supply and change in the circulation of the electrolyte.
7. Method according to claim 6, characterised in that the control unit of the electrodissolution reactor is capable of providing for the control of dissolution current density as a function of the need for replenishment of the tin ions estimated according to at least the signal delivered by the analysis unit.
8. Method according to claim 6 or 7, characterised in that the analysis unit makes use of a spectroscopic analyser by laser ablation.
9. Method according to one of the preceding claims, characterised in that a sulphonic acid, for example methanesulphonic acid, is used as the electrolyte.
10. Method according to preceding claims, characterised in that the electrodialysis or electrolysis membrane separating the anolyte and catholyte compartments - anodic and cathodic - of the electrodissolution reactor is a cationic membrane with selective permeability making it possible to maintain a large fraction of the Sn++ tin ions in the anodic compartment and to transfer H+ hydrogen ions to the cathodic compartment and to transfer few Sn++ tin ions to this same cathodic compartment.
11. Method according to one of the preceding claims, characterised in that the two electrodes of the electrodissolution reactor are made of tin which is more than 99% pure.
12. Installation for electrolytic tinning of a continuously running steel strip in an electrodeposition unit (3) with an insoluble anode in an electrolyte and having, in line, an electrodissolution reactor (6) in a circuit 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 electrical current supply circuit (12) and a cathodic compartment (6a) comprising a second electrode (121a) connected to the negative terminal of the same electrical circuit,
    for which a control unit of the electrodissolution reactor engages a first change in the polarity of the electrical current supply (11) of each of the two electrodes,
    the control unit providing for, in a manner adjoining the first change, a second change in the circulation of the electrolyte between each of the two compartments of the electrodissolution reactor and the electrodeposition unit,
    and characterised in that

    - the control unit activates the adjoining and periodic changes in the polarity of the electrical current supply of the electrodissolution unit and in the circulation of the electrolyte returning to the electrodeposition unit, while providing for continuous sampling of the electrolyte through 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,

    - the control unit sequentially activates each of the two alternating cycles while maintaining continuous sampling of the electrolyte, said cycles being defined by similar durations.
13. Installation according to claim 12 for which the two electrodes comprise soluble conducting elements providing them with identical anode/cathode type change properties.
14. Installation according to claim 13, for which the soluble elements comprise tin granules capable of continuous or sequential filling of at least one of two electrically non-conducting dissolution bins (7a, 7b), each of said soluble elements being partially dipped in the electrolyte of one of the two said compartments.
15. Installation according to one of the preceding claims 12-14, for which the control unit comprises synchronous coupling of the change in the circulation of the electrolyte between each of the two compartments of the electrodissolution reactor with switching of a loop of a hydrogen degassing unit (5) 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 for which each dissolution bin (7a, 7b) is partially in the form of a vertical column so as to be able to be filled with tin granules in which the electrolyte circulates from bottom to top of the column and comprises:

    • A lower "wet" zone made from an electrically non-conducting material, a reinforced plastic or polyester resin or a steel covered with polymer, completely immersed in the electrolyte and comprising a lattice made up of at least one plastic net with a mesh matched to the grain size of the tin, i.e. between 0.50 and 0.05 mm, preferentially between 0.3 and 0.10 mm, said net being supported by the casing of the dissolution bin which has apertures to provide contact with the electrolyte at least 50 times larger than the mesh of said net.

    • A middle "wet" zone not immersed but washed by circulation of the electrolyte and fitted with a recovery trough (72a, 72b) for regenerated electrolyte, said trough being fed by a lattice identical to that of the lower zone, and in that the lattice and trough assembly is made from an electrically non-conducting material such as a reinforced plastic or polyester resin or a steel covered with polymer.

    • An electrically conducting upper "dry" zone free from any immersion in or contact with the electrolyte, fitted with a metal hopper (73) for filling with tin granules and connected to one of the polarity contacts of the electrical current supply circuit (11).
17. Installation according to one of claims 12-16, characterised in that the electrical current supply circuit (11) of the electrodissolution reactor comprises a polarity inverter (12) capable of changing the electrical supply of each of the electrodes (121a, 122b) according to a positive or negative polarity, each said electrode being consequently anode or cathode according to the switchable polarisation sequence.
18. Installation according to claim 16, characterised in that a first circuit is capable of providing for the circulation of the electrolyte according to the following pattern:

    • An electrolyte depleted of tin and 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 a first tin granule dissolution bin (7a) at a sufficient pressure to allow said electrolyte to overflow into the recovery trough (72a) of the middle zone without overflowing into the upper dry zone.

    • An electrolyte recharged with tin ions during its circulation in the first dissolution bin (7a) of the electrodissolution reactor is taken from its recovery trough (72a) and subjected to oxygen degassing (4) with a view to being reinjected into the coating vat (2).

    • An electrolyte taken from the second compartment (6b) of the electrodissolution reactor in the vicinity of the electrodialysis or electrolysis membrane (10), on the side opposite the first dissolution bin (7a), is subjected to hydrogen degassing (5) and then reinjected into the same zone of the compartment of the electrodissolution reactor.
19. Installation according to one of claims 16 or 18, characterised in that a second circuit is capable of providing for the circulation of the electrolyte according to the following pattern:

    • An electrolyte depleted of tin and 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 tin granule dissolution bin (7b) at a sufficient pressure to allow said electrolyte to overflow into the recovery trough (72b) of the middle zone without overflowing into the upper dry zone.

    • An electrolyte recharged with tin ions during its circulation in the second dissolution bin (7b) of the electrodissolution reactor is taken from its recovery trough (72b) and subjected to oxygen degassing (4) with a view to being reinjected into the coating vat (2).

    • An electrolyte taken from the first compartment (6a) of the electrodissolution reactor in the vicinity of the electrodialysis or electrolysis membrane (10), on the side opposite the second dissolution bin (7b), is subjected to hydrogen degassing (5) and then reinjected into the same zone of the compartment of the reactor.
20. Installation according to one of claims 18 or 19, characterised in that the oxygen (4) and hydrogen (5) degassing is carried out in an anolyte tank (4) or respectively a catholyte tank (5), such as buffer tanks of the compartments of the electrodissolution reactor.
21. Installation according to one of the preceding claims 12-20, for which, by means of a hydraulic circuit (8) providing for the circulation of the electrolyte from a compartment of the electrodissolution reactor (6) currently being supplied by an anolyte circuit (6a) to the electrodeposition unit (3) and a catholyte circuit (6b) about to become anolyte, the changes in circulation of the electrolyte and in the polarity of the electrical current supply are performed in accordance with the following sequence:

    a) Cut off the electrical current supply to the electrodissolution reactor.

    b) Stop the anolyte and catholyte circulation pumps (104,105) at the outlet from the tanks (4, 5) to each of the electrodes.

    c) Open first electrolyte inlet and outlet valves (82b, 92a) of the catholyte circuit (6b), the valves (82a, 84b) connected to the anolyte circuit (6a) and one of the valves (94a) connected to the catholyte circuit being closed, and operate the pump (104) until the catholyte contained in one side of the dissolution reactor (6b) and the piping (81b, 91a) connected to said first valves and to the previously cathodic compartment (71b) is emptied into the catholyte tank (5).

    d) Open second electrolyte inlet and outlet valves (94b, 84a) of the anolyte circuit (6a), the valves (94a, 92b) connected to the catholyte circuit (6b) and one of the valves (82a) connected to the anolyte circuit being closed, and operate the pump (105) until the anolyte contained in one side of the dissolution reactor (6a) and the piping (81a, 83a) connected to said second valves and to the previously anodic compartment (71a) is emptied into the anolyte tank (4).

    e) Close one of the first and one of the second valves (84a, 92a) when the anolyte has been emptied from (71a) into the anolyte tank (4) and the catholyte has been emptied from (71b) into the catholyte tank (5).

    f) Open valves (84b, 92b) from each of the electrodes to one of the tanks (4, 5).

    g) Change and re-establish the electrical current supply.
22. Installation according to one of claims 12 to 21, characterised in that the electrolyte circulation circuit comprises a first and a second circulation circuit, being respectively fitted with a set of first and second motorised, remotely controlled valves providing for changing sequentially to the first or the second circuit in line with the changes in the electrical polarities applied to the electrodes according to two sequential methods:

    • A method of opening of the first circuit and correlative closing of the second circuit when the first compartment connected to the first circuit is initially anodic.

    • A method of opening of the second circuit and correlative closing of the first circuit when the second compartment connected to the second circuit is initially anodic.
23. Installation according to one of claims 12 to 22, characterised in that the motorised valves and an inverter for the electrical polarity applied to the electrodes are controlled by a control unit which delivers change orders from data concerning the content of tin ions in each of the compartments (6a, 6b), said contents being delivered to the control unit by an analysis unit ideally operating in accordance with a method of spectroscopy by laser ablation or "Laser Induced Breakdown Spectroscopy".
24. Installation according to one of claims 12 to 23, characterised in that the electrodissolution reactor is made up of several electrodissolution cells fitted with circulation and electrical current supply circuits installed in parallel and each comprising:

    • A first dissolution bin (7a) alternatively of anode or cathode type.

    • A second dissolution bin (7b) alternatively of cathode or anode type.

    • A cationic electrodialysis or electrolysis membrane separating each cell in an anolyte zone and a catholyte zone depending on the polarisation of the electrodes.
25. Installation according to one of claims 12 to 24, characterised in that the electrodissolution reactor is made up of several electrodissolution cells the circulation and electrical current supply circuits of which are separate and capable of being changed independently of one another.
26. Installation according to one of claims 24 or 25, characterised in that an automatic tin granule supply device serves hoppers (73) for all the bins of the reactor.

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