Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
  • C25D21/14—Controlled addition of electrolyte components
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes

Definitions

• 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.
• the invention relates to an electrolytic tinning process insoluble anode metal strips in continuous scrolling and an installation for its implementation.
• 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:
• 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:
• 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.
• 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.
• 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:
• 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.
• the required membrane area severe hundred m 2 for tinning continuous steel strip installations
• 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.
• 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. + .
• the said method according to the invention provides that:
• the two alternating cycles of continuous sampling are defined by neighboring durations.
• 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.
• each of the two electrodes of the electro-dissolution reactor is provided of a soluble nature.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• CMX cationic membrane
• 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.
• FIG. 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
• the installation also includes:
• 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,
• 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.
• the two electrodes comprise conductive soluble elements, giving them identical properties of permutation from an anode type to a cathode type and vice versa.
• 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.
• 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 "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 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).
• 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.
• 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).
• 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.
• 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).
• 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).
• 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.
• the compartment (6a) of the electro-dissolution reactor is anodic and the compartment (6b) cathodic.
• 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.
• 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.
• 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:
• 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,
• 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
• 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.
• reservoirs such as buffer tanks
• 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.
• a catholyte tank (5) such as buffer tanks of the compartments of the electro-reactor. -dissolution.
• 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
• the installation also includes:
• 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,
• 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.
• the two electrodes comprise conductive soluble elements, giving them identical properties of permutation from an anode type to a cathode type and vice versa.
• 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.
• 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:
• 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 "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.
• 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).
• 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.
• 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.
• 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.
• 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).
• 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.
• 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).
• 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).
• 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.
• the compartment (6a) of the electro-dissolution reactor is anodic and the compartment (6b) cathodic.
• 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.
• a second 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 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).
• 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:
• 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 feed device for tin pellets serves hoppers (73) of all the baskets of the reactor.

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