EP3388555B1 - Process for selective recovery of silver in the presence of aluminium, electrochemically and in aqueous solution - Google Patents

Process for selective recovery of silver in the presence of aluminium, electrochemically and in aqueous solution Download PDF

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EP3388555B1
EP3388555B1 EP18166892.2A EP18166892A EP3388555B1 EP 3388555 B1 EP3388555 B1 EP 3388555B1 EP 18166892 A EP18166892 A EP 18166892A EP 3388555 B1 EP3388555 B1 EP 3388555B1
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Prior art keywords
silver
process according
positive electrode
negative electrode
electrode
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German (de)
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EP3388555A1 (en
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Emmanuel BILLY
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
    • C25C1/20—Electrolytic production, recovery or refining of metals by electrolysis of solutions of noble metals

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  • the present invention relates to a process for the selective recovery of silver in the presence of aluminum.
  • It relates more particularly to a process for the selective recovery of silver, electrochemically, and in aqueous solution.
  • the present invention finds particular application in the recycling and recovery of photovoltaic panels.
  • PV panels also called photovoltaic modules, are used to convert solar radiation into thermal or electrical energy.
  • the other photovoltaic panels are of the thin layer type (10%).
  • a crystalline silicon photovoltaic panel comprises several photovoltaic cells electrically connected to each other, encapsulated by transparent polymer layers, and arranged between glass plates, and an aluminum frame. Electrodes, for example made of copper or silver, make it possible to collect the electric current generated by the photovoltaic cells.
  • Each photovoltaic cell is, conventionally formed, of a silicon substrate, the front face of which is covered with silver metallizations and the rear face of which is covered with aluminum.
  • a silicon photovoltaic module is therefore mainly composed of glass (74% of the total weight), aluminum (10%), polymer (about 6.5%) and silicon (about 3%), metals (zinc, lead, copper and silver) representing only a negligible part of the mass.
  • the current processes consist in dismantling the modules by chemical and / or thermal means then in carrying out a series of treatments to dissolve the various metallic elements in solution, and finally to recover the silver.
  • the silver recovery process comprises the following stages: grinding of the cells, treatment of the powder obtained in a solution of H 2 SO 4 (15mol / L to 20mol / L) at a temperature ranging from 60 to 100 ° C. , recovery of the aluminum-containing filtrate and crystallization at 100-150 ° C to obtain metallic aluminum.
  • the powder residues containing silicon and silver are treated with HNO 3 (4 to 12 mol / L).
  • the silver-containing filtrate is recovered and the silver is reduced in the presence of hypophosphorous acid.
  • Treatment with boric acid at a temperature of 900-1100 ° C makes it possible to form silver ingots.
  • this silver recovery process is complex and requires the use of many acids at high concentrations and / or at high temperatures (above 100 ° C and up to 1100 ° C).
  • the document TW-A-200836850 proposes to remove silver and aluminum by contactless electrolysis by immersing a photovoltaic cell in a solution containing nitric acid, phosphoric acid, acetic acid and ferric chloride.
  • the anti-reflective layer of the cell is dissolved in phosphoric acid heated between 100 and 200 ° C.
  • the cell is rinsed with nitric acid to remove the last traces of silver. This process does not evoke the recovery of metals after dissolution by electrolysis. In addition, it uses many acids.
  • an object of the present invention to provide a simple method for recovering silver, making it possible to selectively and effectively dissolve silver, with respect to aluminum, bringing into play mild conditions in terms temperature, while limiting energy and reprocessing costs, so that it can be transposed to an industrial scale.
  • the substrate does not dissolve in the aqueous solution. It does not participate in electrochemical reactions.
  • the substrate has two main faces (the first face and the second face) parallel to each other. It is, for example, in the form of a plate.
  • the substrate does not come from a grinding operation. The process avoids a prior and energy-consuming grinding step.
  • Silver covers the first side of the substrate.
  • silver is present on the first face of the substrate. It is on the first face of the substrate and covers it at least partially.
  • the money is accessible so that it can be dissolved.
  • the money can be in the form of a continuous film, threads or even a grid. The same goes for aluminum.
  • the first face of the substrate forms a first positive electrode which acts as an anode.
  • the silver is oxidized and dissolved in solution.
  • the second face forms a first negative electrode which acts as a cathode.
  • an oxide is formed on the surface of aluminum, giving it cathodic protection and preventing its dissolution in the pH range of the electrolytic solution.
  • the process takes advantage of the presence of aluminum and silver, by simultaneously carrying out, in the same tank or container, the passivation of aluminum (reduction) and the oxidation of silver (oxidation). There is no need to protect, cover the aluminum before putting the substrate in solution.
  • step c) the aluminum is not dissolved in the acid electrolytic solution thanks to cathodic protection.
  • small quantities of aluminum may be found in solution, but these will be negligible quantities (less than 2% by mass and preferably less than 1% by mass relative to the mass of aluminum initially present).
  • the electrodes are connected to a device making it possible to control the potential of one of the two positive and negative electrodes and, more advantageously, to control the potential difference between the two positive and negative electrodes.
  • the device makes it possible to control the current of one of the two positive and negative electrodes and, more advantageously, to control the difference in current between the two positive and negative electrodes.
  • a potential or a current it is preferably meant a constant potential or a constant current.
  • the system further comprises a reference electrode, for example Ag / AgCl.
  • the potential applied to the first positive electrode ranges from -0.4 V to 0 V vs Ag / AgCl.
  • the complexing agent for example thiourea
  • the silver will be dissolved in the electrolytic solution, it will not be electrodeposited on the first negative electrode.
  • the choice of applied potential makes it possible to control the microstructure of the deposit.
  • the potential is applied to the first positive electrode for a period ranging from 30 minutes to 3 hours, and preferably from 30 minutes to 1 hour.
  • the process is easy to implement and makes it possible to control, via the application of a potential or a current, the rate of dissolution of silver.
  • Step f) makes it possible to deposit the silver on the second negative electrode and, at the same time, to regenerate the silver complexing agent.
  • the silver is recovered and the bath regenerated without dissolving the aluminum (cathodic protection).
  • steps a), b), c) can be repeated with another electrically conductive substrate, one side of which is covered with silver and the other side is covered with aluminum so as to selectively recover money.
  • the electrolytic solution can be the same.
  • the selective dissolution and silver recovery stages are advantageously carried out in the same tank, containing the electrolytic solution.
  • the solution does not need to be treated, to be transferred between the electrodissolution step and the electrodeposition step.
  • Different substrates can be recovered in the same electrolytic solution. This leads to a great simplification of the process, a greater compactness of the installations, a reduction in the number of pipes and other devices for conveying fluids and solids, etc.
  • the pH of the electrolytic solution ranges from -1 to 2, more advantageously from 0 to 1.
  • the method of the invention brings together the advantages of selectivity and of treatment efficiency. The lower the pH, the faster the dissolution of the silver in solution.
  • the acid is sulfuric acid H 2 SO 4 , nitric acid HNO 3 or one of their mixtures.
  • the complexing agent also called ligand or complexing agent, makes it possible to complex the dissolved silver element, in the form of a silver complex.
  • the complexing agent is chosen so as to be sufficiently complexing to favor the electrodissolution of the silver and facilitate the electrodeposition of the silver in the window of electrochemical stability of the solution.
  • the use of silver complexing agent makes it possible, via the formation of silver complex, to adjust the electrodeposition potential of silver.
  • the complexing agent must be soluble in the electrolytic solution and selective for silver. In addition, it should not degrade in the pH range used.
  • the complexing agent is thiourea or a derivative thereof.
  • Thiourea as complexing agent for the metal to be dissolved has many advantages in terms of chemistry, cost or process. It promotes the solubility and the stability of the complexing agent, while lowering the electrodeposition potential of the silver from 0.799 V to around 0.2 V. In addition, it is regenerated during the deposition of the silver. The process can be carried out in a closed cycle, thus limiting the release of chemicals, the cost of production and the environmental impact.
  • the concentration of complexing agent ranges from 0.01 mol / L to 1 mol / L, preferably from 0.05 mol / L to 1 mol / L, and even more preferably, is of the order of 0.5 mol / L.
  • concentrations make it possible to promote the kinetics of dissolution of the metal and the recovery of the silver.
  • This range of concentrations of complexing agent is particularly advantageous, since a concentration less than 0.01 mol / L decreases the complexing character, while a concentration greater than 1 mol / L generally corresponds to the saturation rate of the complexing agent solution. Even more advantageously, this concentration is equal to twice the stoichiometry of silver to be dissolved.
  • the solution also comprises an agent promoting the ion transport properties. It is, for example, a sulfate salt.
  • the sulfate salt can be any water-soluble salt of the sulfate ion [SO4 2- ], alone or as a mixture.
  • the sulfate salt is a water-soluble salt of the sulfate ion [SO4 2- ]. he can in particular be chosen from the group comprising Na 2 SO 4 , K 2 SO 4 and CaSO 4 .
  • the solution may include 0.001 to 1 mol / L of sulfate salt, preferably 0.1 to 0.5 mol / L. Salt does not intervene in electrode reactions and does not react with the solvent.
  • the agent promoting the ion transport properties may be an additional acid.
  • the substrate is made of silicon.
  • the silicon is electrochemically inert during the electrodissolution and electrodeposition stages.
  • the electrically conductive substrate comes from a photovoltaic cell and the silver forms the metallizations of the front face of the photovoltaic cell.
  • Aluminum covers the rear face of the cell.
  • the process is carried out at a temperature ranging from 15 ° C to 60 ° C, and preferably being of the order of 20-25 ° C. These conditions also make it possible to reduce the amount of energy required and to improve safety compared to the processes of the prior art which can use boiling acid solutions.
  • the process can be carried out at room temperature (20-25 ° C) facilitating its use in an industrial environment.
  • the process can be carried out in air. It is particularly advantageous not to work in a controlled atmosphere and not to use inert gases.
  • the process can be industrialized.
  • the silver recovery process described above and detailed below makes it possible to selectively obtain the electrochemical dissolution of the silver present on a substrate, which also includes aluminum, and its recovery in metallic form.
  • the method is described for recovering the silver contained in photovoltaic cells, advantageously in crystalline or polycrystalline silicon, and more particularly for recovering the silver, present on the front face of a cell, selectively with respect to the aluminum present on the back of the cell.
  • the process could be used for any type of electrically conductive substrate, which does not dissolve naturally in the electrolytic solution.
  • the cells Prior to the implementation of the process, the cells are removed from the photovoltaic panel and separated from the cables, junction boxes, and metal frames.
  • the cells are subjected to a heat treatment to remove, by calcination, the polymer encapsulation materials, such as ethylene vinyl acetate (EVA).
  • EVA ethylene vinyl acetate
  • the calcination step is, for example, carried out in an air oven.
  • the heat treatment is, for example, carried out at a temperature between 400 ° C. and 700 ° C, more preferably between 450 and 550 ° C.
  • the duration of this treatment can be between 30 and 120 minutes, more advantageously between 60 and 90 minutes.
  • the photovoltaic cell consists of an electrically conductive silicon substrate covered by one or more silver electrodes.
  • the silver electrodes are conventionally formed from a silver paste which may comprise a glass powder SiO 2 , B 2 O 3 , PbO and ZnO, silver and a binding agent.
  • the cells can also be separated from the electrical connectors.
  • the electrical connectors composed of a copper core coated with Sn 62 Pb 36 Ag 2 , for example, and silver can be valued with the method of the invention.
  • the different metals copper, lead, tin
  • the deposit on the first negative electrode will essentially be silver. It is therefore particularly advantageous to be selective with regard to money.
  • the choice of the temperature of the heat treatment can help promote the selective dissolution of silver.
  • the substrate is not ground to carry out the process. It can, for example, be cut in the form of a plate of a few cm 2 or dm 2 .
  • the substrate has a first face and a second face.
  • the first face corresponding to the front face of the photovoltaic cell, is covered with silver.
  • the money is, for example, in the form of a grid.
  • the second face corresponds to the rear face of the photovoltaic cell.
  • the second side is covered with aluminum.
  • Aluminum forms, for example, a continuous film.
  • the first face of the substrate, covered with silver, is electrically connected to the control device. It plays the role of anode.
  • all of the silver connectors (bus, bar) on the surface of the substrate are electrically connected to the potentiostat.
  • the second face of the substrate is also electrically connected to the control device. It plays the role of cathode.
  • the control device is a source of voltage or current, like a potentiostat.
  • the potentiostat is preferably used in potentiostatic mode. It could be used in galvanostatic mode.
  • the substrate is immersed, at least partially, in the electrolytic solution, so as to bring the two faces of the substrate into contact with the electrolytic solution.
  • a potential or a current is imposed on the first positive or negative electrode, which simultaneously generates the electro-dissolution of the silver present on the first positive electrode and the cathodic protection of the aluminum present on the first negative electrode.
  • a reference electrode for example Ag / AgCl, can also be added to the assembly.
  • the potential applied to the first positive electrode to dissolve the silver in the electrolytic solution and passivate the aluminum ranges from -0.4 V to 0 V vs Ag / AgCl, for example -0.2 V vs Ag / AgCl.
  • the potential is applied for a period of 30 minutes to 3 hours, and preferably for a period of 30 minutes to 1 hour.
  • the duration will, in particular, be chosen according to the amount of silver to be valorized, the pH and the potential (or current) applied. The more acidic the electrolyte solution, the faster the dissolution.
  • the silver can be electrodeposited on another electrode (cathode), using a two-electrode assembly (a second positive electrode and a second negative electrode) or three electrodes (a second positive electrode, a second negative electrode and a reference electrode).
  • a two-electrode assembly a second positive electrode and a second negative electrode
  • three electrodes a second positive electrode, a second negative electrode and a reference electrode.
  • the potential applied to the second negative electrode goes, for example, from -0.4 V to -1 V vs Ag / AgCl. For example, choose a potential of -0.5 V.
  • the acid treatment solution can therefore be reused, possibly by adjusting its pH, which reduces the consumption of reagents.
  • the electrodes are extracted from the electrolytic solution and it is possible to carry out a new treatment cycle with a new substrate containing silver to be recovered.
  • the electrolytic solution has a pH of -1 to 6, preferably of -1 to 2, and even more preferably of 0 to 1. It comprises at least one acid, a silver complexing agent and, optionally, a sulfate salt. to improve ion transport within the solution.
  • the acid used has a pKa of between - 7 and 3. It is a Brönsted acid, that is to say an acid capable of releasing at least one proton.
  • a Brönsted acid that is to say an acid capable of releasing at least one proton.
  • sulfuric acid, nitric acid or a mixture of these acids will be used.
  • the pH of the acid solution can be controlled and, optionally, adjusted to these values, by addition of acid.
  • the complexing agent is preferably thiourea (CAS number 62-56-6).
  • the electrolytic solution is preferably devoid of any solvent other than water.
  • the acid solution is preferably devoid of an oxidizing agent such as, for example, hydrogen peroxide or also metal salts (iron or copper sulphate for example).
  • the solution may naturally contain dissolved oxygen. We will not add oxygen in addition to that naturally present in solution.
  • the naturally occurring oxygen can also be removed from the solution by bubbling with another gas, such as argon.
  • the solution has a low viscosity and good ionic conductivity.
  • the process is advantageously carried out with mechanical stirring, for example between 200 and 1000 revolutions / minute.
  • silicon cells derived from conventional photovoltaic panels, are used.
  • the photovoltaic cells are subjected to a heat treatment in order to burn the layers of EVA encapsulation. This step takes place in an air oven at 500 ° C for 1 hour. The cells are also separated from the connectors.
  • the solution is stirred, in air at 20 ° C., at 400 rpm.
  • the electrodissolution is carried out in potentiostatic mode.
  • a constant potential of -0.25 V is applied to the first positive electrode, causing the silver from the first positive electrode to dissolve and, simultaneously, the cathodic protection of the aluminum from the first negative electrode.
  • the potential is maintained for 0.8 hours ( figure 1 ) allowing to extract 9 Coulombs, that is 98% of the silver available in the silicon cell.
  • the composition of the electrolytic solution was analyzed, after electrodissolution, by inductively coupled plasma spectrometry (ICP).
  • ICP inductively coupled plasma spectrometry
  • the electrolytic solution of the selective electrodissolution was then used to deposit silver on a glassy carbon electrode.
  • a three-electrode assembly is used with, this time, a glassy carbon working electrode.
  • the potential is maintained at -0.5 V for one hour (potentiostatic mode), which reduces the silver on the electrode.
  • a deposit is visible on the glassy carbon electrode. This deposit was analyzed by SEM and Dispersive Energy X-ray (EDX) to determine its chemical composition. Observations at the MEB highlighted the presence of a deposit of silver (light areas). The presence of silver was confirmed by microanalysis by EDX. The microstructure of the deposit is of the “cauliflower” type. Some sulfur impurities are present in the silver deposit. Tin is also present at 3 atomic% in the deposit. Tin is one of the elements that make up the silver solder (Cu, Sn, Pb and Ag) of the cells. The absence of copper confirms the selectivity of the deposit
  • the semi-quantitative analysis by EDX indicates that the silver content is greater than 94% to reach a higher grade after washing the elements trapped in the silver deposit.
  • These residual impurities essentially sulfur can be removed after washing the silver deposit in water in which the deposit is insoluble.
  • This example shows that it is possible to recover silver selectively, in the presence of aluminum, by electrochemical dissolution then electrodeposition, under an uncontrolled atmosphere such as air.

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Description

DOMAINE TECHNIQUE ET ÉTAT DE LA TECHNIQUE ANTÉRIEURETECHNICAL AREA AND PRIOR ART

La présente invention concerne un procédé de récupération sélective de l'argent en présence d'aluminium.The present invention relates to a process for the selective recovery of silver in the presence of aluminum.

Elle se rapporte plus particulièrement à un procédé de récupération sélective de l'argent, par voie électrochimique, et en solution aqueuse.It relates more particularly to a process for the selective recovery of silver, electrochemically, and in aqueous solution.

La présente invention trouve notamment une application dans le recyclage et la valorisation des panneaux photovoltaïques.The present invention finds particular application in the recycling and recovery of photovoltaic panels.

Les panneaux photovoltaïques (PV), aussi appelés modules photovoltaïques, sont utilisés pour convertir le rayonnement solaire en énergie thermique ou électrique. Aujourd'hui, environ 90% des panneaux photovoltaïques sont en silicium cristallin. Les autres panneaux photovoltaïques sont de type couche mince (10%).Photovoltaic (PV) panels, also called photovoltaic modules, are used to convert solar radiation into thermal or electrical energy. Today, around 90% of photovoltaic panels are made of crystalline silicon. The other photovoltaic panels are of the thin layer type (10%).

Typiquement, un panneau photovoltaïque en silicium cristallin comprend plusieurs cellules photovoltaïques électriquement connectées entre elles, encapsulées par des couches de polymère transparentes, et disposées entre des plaques de verre, et un cadre en aluminium. Des électrodes, par exemple en cuivre ou en argent, permettent de collecter le courant électrique généré par les cellules photovoltaïques.Typically, a crystalline silicon photovoltaic panel comprises several photovoltaic cells electrically connected to each other, encapsulated by transparent polymer layers, and arranged between glass plates, and an aluminum frame. Electrodes, for example made of copper or silver, make it possible to collect the electric current generated by the photovoltaic cells.

Chaque cellule photovoltaïque est, classiquement formée, d'un substrat en silicium, dont la face avant est recouverte de métallisations en argent et dont la face arrière est recouverte d'aluminium.Each photovoltaic cell is, conventionally formed, of a silicon substrate, the front face of which is covered with silver metallizations and the rear face of which is covered with aluminum.

Un module photovoltaïque en silicium est donc majoritairement composé de verre (74% du poids total), d'aluminium (10%), de polymère (environ 6,5%) et de silicium (environ 3%), les métaux (zinc, plomb, cuivre et argent) ne représentant qu'une part négligeable de la masse.A silicon photovoltaic module is therefore mainly composed of glass (74% of the total weight), aluminum (10%), polymer (about 6.5%) and silicon (about 3%), metals (zinc, lead, copper and silver) representing only a negligible part of the mass.

En raison du fort développement des panneaux photovoltaïques au cours des dernières années, la question de leur recyclage est fondamentale. Ainsi, depuis le 13 août 2012, la Directive relative aux Déchets d'Equipements Electriques et Electroniques (DEEE) a été étendue aux panneaux photovoltaïques (PV).Due to the strong development of photovoltaic panels in recent years, the question of their recycling is fundamental. Thus, since August 13, 2012, the Directive on Waste Electrical and Electronic Equipment (WEEE) has been extended to photovoltaic (PV) panels.

Les objectifs de valorisation et de recyclage de ces panneaux sont déjà aisément atteints par la seule récupération du verre et du cadre en aluminium des panneaux photovoltaïques.The recovery and recycling objectives for these panels are already easily achieved by simply recovering the glass and the aluminum frame of the photovoltaic panels.

La récupération des métaux (le cuivre, l'étain, le plomb, l'aluminium présent en face arrière de la cellule...), et plus particulièrement de l'argent, qui est le métal ayant la plus forte valeur ajoutée (près de 90% du prix de la cellule), représente un enjeu majeur pour pérenniser la filière de recyclage.The recovery of metals (copper, tin, lead, aluminum present on the back of the cell ...), and more particularly of silver, which is the metal with the highest added value (near of 90% of the price of the cell), represents a major stake to perpetuate the recycling sector.

Pour valoriser l'argent, les procédés actuels consistent à démanteler les modules par voie chimique et/ou thermique puis à réaliser une série de traitements pour dissoudre les différents éléments métalliques en solution, et finalement à récupérer l'argent.To recover the silver, the current processes consist in dismantling the modules by chemical and / or thermal means then in carrying out a series of treatments to dissolve the various metallic elements in solution, and finally to recover the silver.

La dissolution des métaux est, souvent, réalisée dans des solutions acides très concentrées et parfois portées à ébullition (HF, HNO3, H2SO4).The dissolution of metals is often carried out in very concentrated acid solutions and sometimes brought to a boil (HF, HNO 3 , H 2 SO 4 ).

Par exemple, dans le document TW-A-201328990 , le procédé de récupération de l'argent comprend les étapes suivantes : broyage des cellules, traitement de la poudre obtenue dans une solution de H2SO4 (15mol/L à 20mol/L) à une température allant de 60 à 100°C, récupération du filtrat contenant l'aluminium et cristallisation à 100-150°C pour obtenir de l'aluminium métallique. Les résidus de poudre contenant du silicium et de l'argent sont traités avec HNO3 (4 à 12 mol/L). Le filtrat contenant l'argent est récupéré et l'argent est réduit en présence d'acide hypophosphoreux. Un traitement avec de l'acide borique à une température de 900-1100°C permet de former des lingots d'argent. Cependant, ce procédé de récupération de l'argent est complexe et nécessite l'utilisation de nombreux acides à des concentrations et/ou à des températures élevées (supérieures à 100°C et jusqu'à 1100°C).For example, in the document TW-A-201328990 , the silver recovery process comprises the following stages: grinding of the cells, treatment of the powder obtained in a solution of H 2 SO 4 (15mol / L to 20mol / L) at a temperature ranging from 60 to 100 ° C. , recovery of the aluminum-containing filtrate and crystallization at 100-150 ° C to obtain metallic aluminum. The powder residues containing silicon and silver are treated with HNO 3 (4 to 12 mol / L). The silver-containing filtrate is recovered and the silver is reduced in the presence of hypophosphorous acid. Treatment with boric acid at a temperature of 900-1100 ° C makes it possible to form silver ingots. However, this silver recovery process is complex and requires the use of many acids at high concentrations and / or at high temperatures (above 100 ° C and up to 1100 ° C).

Le document TW-A-200836850 propose de retirer l'argent et l'aluminium par électrolyse sans contact en plongeant une cellule photovoltaïque dans une solution contenant de l'acide nitrique, de l'acide phosphorique, de l'acide acétique et du chlorure ferrique. La couche antireflet de la cellule est dissoute dans l'acide phosphorique chauffé entre 100 et 200°C. La cellule est rincée avec l'acide nitrique pour enlever les dernières traces d'argent. Ce procédé n'évoque pas la récupération des métaux après dissolution par électrolyse. De plus, il utilise de nombreux acides.The document TW-A-200836850 proposes to remove silver and aluminum by contactless electrolysis by immersing a photovoltaic cell in a solution containing nitric acid, phosphoric acid, acetic acid and ferric chloride. The anti-reflective layer of the cell is dissolved in phosphoric acid heated between 100 and 200 ° C. The cell is rinsed with nitric acid to remove the last traces of silver. This process does not evoke the recovery of metals after dissolution by electrolysis. In addition, it uses many acids.

Tous ces procédés de l'art antérieur nécessitent plusieurs étapes, avec parfois l'utilisation d'acides à fortes concentrations et /ou à des températures proches de la température d'ébullition. Cela conduit à des procédés complexes et/ou nécessitant un coût supplémentaire pour le traitement des déchets. De plus, aucun des procédés de recyclage des cellules photovoltaïques en silicium ne permet la dissolution et la récupération sélective de l'argent, vis-à-vis de l'aluminium.All these prior art processes require several stages, sometimes with the use of acids at high concentrations and / or at temperatures close to the boiling temperature. This leads to complex processes and / or requiring an additional cost for the treatment of waste. In addition, none of the processes for recycling photovoltaic cells into silicon allows the dissolution and the selective recovery of silver, with respect to aluminum.

EXPOSÉ DE L'INVENTIONSTATEMENT OF THE INVENTION

C'est, par conséquent, un but de la présente invention de proposer un procédé de récupération de l'argent simple, permettant de dissoudre sélectivement et efficacement l'argent, par rapport à l'aluminium, mettant en jeu des conditions douces en termes de température, tout en limitant les coûts énergétique et de retraitement, pour pouvoir être transposé à une échelle industrielle.It is, therefore, an object of the present invention to provide a simple method for recovering silver, making it possible to selectively and effectively dissolve silver, with respect to aluminum, bringing into play mild conditions in terms temperature, while limiting energy and reprocessing costs, so that it can be transposed to an industrial scale.

Ce but est atteint par un procédé de récupération sélective de l'argent d'un substrat électriquement conducteur, ledit procédé comprenant les étapes suivantes :

  1. a) fourniture d'un système comprenant :
    • ∘ un substrat électriquement conducteur, comprenant une première face recouverte par de l'argent et une seconde face recouverte par de l'aluminium, la première face formant une première électrode positive, et la seconde face formant une première électrode négative, et
    • ∘ un dispositif de contrôle, relié à la première électrode positive et à la première électrode négative, le dispositif de contrôle permettant de contrôler le potentiel ou le courant d'une électrode ;
  2. b) immersion de la première électrode positive et de la première électrode négative dans une solution électrolytique, la solution électrolytique étant une solution aqueuse comprenant au moins un acide et un agent complexant de l'argent, la solution électrolytique ayant un pH allant de -1 à 6 ; et
  3. c) application d'un potentiel ou d'un courant à la première électrode positive ou à la première électrode négative, de manière à dissoudre l'argent de la première électrode positive dans la solution électrolytique et à passiver l'aluminium de la première électrode négative.
This object is achieved by a process for the selective recovery of silver from an electrically conductive substrate, said process comprising the following steps:
  1. a) supply of a system comprising:
    • ∘ an electrically conductive substrate, comprising a first face covered with silver and a second face covered with aluminum, the first face forming a first positive electrode, and the second face forming a first negative electrode, and
    • ∘ a control device, connected to the first positive electrode and to the first negative electrode, the control device making it possible to control the potential or the current of an electrode;
  2. b) immersion of the first positive electrode and of the first negative electrode in an electrolytic solution, the electrolytic solution being an aqueous solution comprising at least one acid and a silver complexing agent, the electrolytic solution having a pH ranging from -1 to 6; and
  3. c) applying a potential or a current to the first positive electrode or to the first negative electrode, so as to dissolve the silver of the first positive electrode in the electrolytic solution and to passivate the aluminum of the first electrode negative.

Un procédé avec une telle succession d'étapes n'a pas été décrit dans l'art antérieur. Le procédé de l'invention est sélectif vis-à-vis de l'argent grâce à la protection cathodique de l'aluminium.A process with such a succession of steps has not been described in the prior art. The process of the invention is selective with regard to silver thanks to the cathodic protection of aluminum.

Le substrat ne se dissout pas dans la solution aqueuse. Il ne participe pas aux réactions électrochimiques. Le substrat comporte deux faces principales (la première face et la seconde face) parallèles entre elles. Il est, par exemple, sous la forme d'une plaque. Le substrat n'est pas issu d'une opération de broyage. Le procédé évite une étape de broyage préalable et énergivore.The substrate does not dissolve in the aqueous solution. It does not participate in electrochemical reactions. The substrate has two main faces (the first face and the second face) parallel to each other. It is, for example, in the form of a plate. The substrate does not come from a grinding operation. The process avoids a prior and energy-consuming grinding step.

L'argent recouvre la première face du substrat. Autrement dit, l'argent est présent sur la première face du substrat. Il est sur la première face du substrat et la recouvre au moins partiellement. L'argent est accessible pour pouvoir être dissous. L'argent peut être sous la forme d'un film continu, de fils ou encore d'une grille. Il en va de même pour l'aluminium.Silver covers the first side of the substrate. In other words, silver is present on the first face of the substrate. It is on the first face of the substrate and covers it at least partially. The money is accessible so that it can be dissolved. The money can be in the form of a continuous film, threads or even a grid. The same goes for aluminum.

La première face du substrat forme une première électrode positive qui joue le rôle d'anode. Lorsque le potentiel (ou le courant) est appliqué, l'argent est oxydé et dissous en solution. La seconde face forme une première électrode négative qui joue le rôle de cathode. Lorsque le potentiel (ou le courant) est appliqué, un oxyde se forme à la surface de l'aluminium, lui conférant une protection cathodique et empêchant sa dissolution dans la gamme de pH de la solution électrolytique. Le procédé tire profit de la présence de l'aluminium et de l'argent, en réalisant simultanément, dans une même cuve ou récipient, la passivation de l'aluminium (réduction) et l'oxydation de l'argent (oxydation). Il n'y a pas besoin de protéger, de couvrir l'aluminium avant de mettre le substrat en solution. Lors de l'étape c), l'aluminium n'est pas dissous dans la solution électrolytique acide grâce à la protection cathodique. Eventuellement, de faibles quantités d'aluminium peuvent se retrouver en solution, mais il s'agira de quantités négligeables (inférieures à 2% massique et de préférence inférieures à 1% massique par rapport à la masse d'aluminium présent initialement).The first face of the substrate forms a first positive electrode which acts as an anode. When the potential (or current) is applied, the silver is oxidized and dissolved in solution. The second face forms a first negative electrode which acts as a cathode. When the potential (or current) is applied, an oxide is formed on the surface of aluminum, giving it cathodic protection and preventing its dissolution in the pH range of the electrolytic solution. The process takes advantage of the presence of aluminum and silver, by simultaneously carrying out, in the same tank or container, the passivation of aluminum (reduction) and the oxidation of silver (oxidation). There is no need to protect, cover the aluminum before putting the substrate in solution. During step c), the aluminum is not dissolved in the acid electrolytic solution thanks to cathodic protection. Optionally, small quantities of aluminum may be found in solution, but these will be negligible quantities (less than 2% by mass and preferably less than 1% by mass relative to the mass of aluminum initially present).

Avec une telle gamme de pH, il est possible de dissoudre l'argent tout en évitant la dégradation de l'agent complexant de l'argent.With such a pH range, it is possible to dissolve the silver while avoiding the degradation of the silver complexing agent.

Les électrodes sont reliées à un dispositif permettant de contrôler le potentiel de l'une des deux électrodes positive et négative et, plus avantageusement, de contrôler la différence de potentiel entre les deux électrodes positive et négative.The electrodes are connected to a device making it possible to control the potential of one of the two positive and negative electrodes and, more advantageously, to control the potential difference between the two positive and negative electrodes.

Dans une variante de l'invention, le dispositif permet de contrôler le courant de l'une des deux électrodes positive et négative et, plus avantageusement, de contrôler la différence de courant entre les deux électrodes positive et négative.In a variant of the invention, the device makes it possible to control the current of one of the two positive and negative electrodes and, more advantageously, to control the difference in current between the two positive and negative electrodes.

Par application d'un potentiel ou d'un courant, on entend, de préférence, un potentiel constant ou un courant constant.By applying a potential or a current, it is preferably meant a constant potential or a constant current.

Avantageusement, le système comprend, en outre, une électrode de référence, par exemple Ag/AgCl.Advantageously, the system further comprises a reference electrode, for example Ag / AgCl.

Avantageusement, pour réaliser en une seule étape l'électrodissolution de l'argent et la protection cathodique de l'aluminium, le potentiel appliqué à la première électrode positive va de -0,4 V à 0 V vs Ag/AgCl. Dans cette gamme de potentiels, l'agent complexant, par exemple la thio-urée, ne sera pas dégradée et l'argent sera dissous dans la solution électrolytique, il ne sera pas électrodéposé sur la première électrode négative. Le choix du potentiel appliqué permet de contrôler la microstructure du dépôt.Advantageously, in order to carry out the electrodissolution of silver and the cathodic protection of aluminum in a single step, the potential applied to the first positive electrode ranges from -0.4 V to 0 V vs Ag / AgCl. In this range of potentials, the complexing agent, for example thiourea, will not be degraded and the silver will be dissolved in the electrolytic solution, it will not be electrodeposited on the first negative electrode. The choice of applied potential makes it possible to control the microstructure of the deposit.

Avantageusement, le potentiel est appliqué à la première électrode positive pendant une durée allant de 30 minutes à 3 heures, et de préférence, de 30 minutes à 1 heure.Advantageously, the potential is applied to the first positive electrode for a period ranging from 30 minutes to 3 hours, and preferably from 30 minutes to 1 hour.

Le procédé est facile à mettre en œuvre et permet de contrôler, via l'application d'un potentiel ou d'un courant, la vitesse de dissolution de l'argent.The process is easy to implement and makes it possible to control, via the application of a potential or a current, the rate of dissolution of silver.

Après la dissolution de l'argent dans la solution électrolytique, celui-ci peut être récupéré par précipitation, cémentation ou électrodéposition. Avantageusement, l'argent est récupéré par électrodéposition. Le procédé comprend les étapes ultérieures suivantes :

  • d) retrait de la première électrode positive et de la première électrode négative de la solution électrolytique, et déconnexion de la première électrode positive et de la première électrode négative du dispositif de contrôle ;
  • e) immersion d'une deuxième électrode positive et d'une deuxième électrode négative, reliées au dispositif de contrôle, dans la solution électrolytique ; et
  • f) application d'un potentiel ou d'un courant à la deuxième électrode positive ou à la deuxième électrode négative, de manière à électrodéposer l'argent, dissous dans la solution électrolytique, sur la deuxième électrode négative et à régénérer l'agent complexant de l'argent.
After the silver has dissolved in the electrolytic solution, it can be recovered by precipitation, carburizing or electrodeposition. Advantageously, the silver is recovered by electrodeposition. The process includes the following subsequent steps:
  • d) removing the first positive electrode and the first negative electrode from the electrolytic solution, and disconnecting the first positive electrode and the first negative electrode from the control device;
  • e) immersion of a second positive electrode and a second negative electrode, connected to the control device, in the electrolytic solution; and
  • f) applying a potential or a current to the second positive electrode or to the second negative electrode, so as to electrodeposit the silver, dissolved in the electrolytic solution, on the second negative electrode and to regenerate the complexing agent money.

L'étape f) permet de déposer l'argent sur la deuxième électrode négative et, en même temps, de régénérer le complexant de l'argent.Step f) makes it possible to deposit the silver on the second negative electrode and, at the same time, to regenerate the silver complexing agent.

En deux étapes électrochimiques, on réalise la récupération de l'argent et la régénération du bain sans mise en solution de l'aluminium (protection cathodique).In two electrochemical stages, the silver is recovered and the bath regenerated without dissolving the aluminum (cathodic protection).

Avantageusement, après l'étape f), les étapes a), b), c) peuvent être répétées avec un autre substrat électriquement conducteur dont une des faces est recouverte d'argent et l'autre face est recouverte d'aluminium de manière à récupérer sélectivement l'argent. La solution électrolytique peut être la même.Advantageously, after step f), steps a), b), c) can be repeated with another electrically conductive substrate, one side of which is covered with silver and the other side is covered with aluminum so as to selectively recover money. The electrolytic solution can be the same.

Les étapes de dissolution sélective et de récupération de l'argent sont, avantageusement, réalisées dans une même cuve, contenant la solution électrolytique. La solution n'a pas besoin d'être traitée, d'être transférée entre l'étape d'électrodissolution et l'étape d'électrodéposition. Différents substrats peuvent être valorisés dans la même solution électrolytique. Cela conduit à une grande simplification du procédé, à une plus grande compacité des installations, à une réduction du nombre des canalisations et autres dispositifs d'acheminement des fluides et des solides etc.The selective dissolution and silver recovery stages are advantageously carried out in the same tank, containing the electrolytic solution. The solution does not need to be treated, to be transferred between the electrodissolution step and the electrodeposition step. Different substrates can be recovered in the same electrolytic solution. This leads to a great simplification of the process, a greater compactness of the installations, a reduction in the number of pipes and other devices for conveying fluids and solids, etc.

Avantageusement, le pH de la solution électrolytique va de -1 à 2, plus avantageusement de 0 à 1. Avec de tels pH, le procédé de l'invention rassemble les avantages de la sélectivité et de l'efficacité de traitement. Plus le pH sera faible et plus la dissolution de l'argent en solution sera rapide.Advantageously, the pH of the electrolytic solution ranges from -1 to 2, more advantageously from 0 to 1. With such pHs, the method of the invention brings together the advantages of selectivity and of treatment efficiency. The lower the pH, the faster the dissolution of the silver in solution.

Avantageusement, l'acide est de l'acide sulfurique H2SO4, de l'acide nitrique HNO3 ou un de leurs mélanges.Advantageously, the acid is sulfuric acid H 2 SO 4 , nitric acid HNO 3 or one of their mixtures.

L'agent complexant, aussi appelé ligand ou complexant, permet de complexer l'élément argent dissous, sous la forme d'un complexe d'argent. Le complexant est choisi de manière à être suffisamment complexant pour favoriser l'électrodissolution de l'argent et faciliter l'électrodéposition de l'argent dans la fenêtre de stabilité électrochimique de la solution. L'utilisation d'agent complexant de l'argent permet, via la formation de complexe d'argent, d'ajuster le potentiel d'électrodéposition de l'argent. L'agent complexant doit être soluble dans la solution électrolytique et sélectif vis-à-vis de l'argent. En outre, il ne devra pas se dégrader dans la gamme de pH utilisée.The complexing agent, also called ligand or complexing agent, makes it possible to complex the dissolved silver element, in the form of a silver complex. The complexing agent is chosen so as to be sufficiently complexing to favor the electrodissolution of the silver and facilitate the electrodeposition of the silver in the window of electrochemical stability of the solution. The use of silver complexing agent makes it possible, via the formation of silver complex, to adjust the electrodeposition potential of silver. The complexing agent must be soluble in the electrolytic solution and selective for silver. In addition, it should not degrade in the pH range used.

Selon un mode de réalisation avantageux, l'agent complexant est la thio-urée ou un dérivé de celle-ci. La thio-urée comme complexant du métal à dissoudre présente de nombreux avantages en termes de chimie, de coût ou de procédé. Elle favorise la solubilité et la stabilité du complexant, tout en abaissant le potentiel d'électrodéposition de l'argent de 0,799 V à environ 0,2 V. De plus, elle est régénérée durant le dépôt de l'argent. Le procédé peut être réalisé en cycle fermé, limitant ainsi le rejet de produits chimiques, le coût de réalisation et l'impact environnemental.According to an advantageous embodiment, the complexing agent is thiourea or a derivative thereof. Thiourea as complexing agent for the metal to be dissolved has many advantages in terms of chemistry, cost or process. It promotes the solubility and the stability of the complexing agent, while lowering the electrodeposition potential of the silver from 0.799 V to around 0.2 V. In addition, it is regenerated during the deposition of the silver. The process can be carried out in a closed cycle, thus limiting the release of chemicals, the cost of production and the environmental impact.

Avantageusement, la concentration en agent complexant va de 0,01 mol/L à 1 mol/L, de préférence de 0,05 mol/L à 1 mol/L, et encore plus préférentiellement, est de l'ordre de 0,5 mol/L. De telles concentrations permettent de favoriser la cinétique de dissolution du métal et la récupération de l'argent. Cette gamme de concentrations d'agent complexant est particulièrement avantageuse, étant donné qu'une concentration inférieure à 0,01 mol/L diminue le caractère complexant, alors qu'une concentration supérieure à 1 mol/L correspond généralement au taux de saturation de la solution en agent complexant. De manière encore plus avantageuse, cette concentration est égale à deux fois stœchiométrie d'argent à dissoudre.Advantageously, the concentration of complexing agent ranges from 0.01 mol / L to 1 mol / L, preferably from 0.05 mol / L to 1 mol / L, and even more preferably, is of the order of 0.5 mol / L. Such concentrations make it possible to promote the kinetics of dissolution of the metal and the recovery of the silver. This range of concentrations of complexing agent is particularly advantageous, since a concentration less than 0.01 mol / L decreases the complexing character, while a concentration greater than 1 mol / L generally corresponds to the saturation rate of the complexing agent solution. Even more advantageously, this concentration is equal to twice the stoichiometry of silver to be dissolved.

Avantageusement, la solution comprend, en outre, un agent favorisant les propriétés de transport ionique. Il s'agit, par exemple, d'un sel de sulfate. Le sel de sulfate peut être tout sel hydrosoluble de l'ion sulfate [SO42-], seul ou en mélange. De manière générale, le sel de sulfate est un sel hydrosoluble de l'ion sulfate [SO42-]. Il peut notamment être choisi dans le groupe comprenant Na2SO4, K2SO4 et CaSO4. Par exemple, la solution peut comprendre 0,001 à 1 mol/L de sel de sulfate, de préférence de 0,1 à 0,5 mol/L. Le sel n'intervient pas dans les réactions aux électrodes et ne réagit pas avec le solvant.Advantageously, the solution also comprises an agent promoting the ion transport properties. It is, for example, a sulfate salt. The sulfate salt can be any water-soluble salt of the sulfate ion [SO4 2- ], alone or as a mixture. In general, the sulfate salt is a water-soluble salt of the sulfate ion [SO4 2- ]. he can in particular be chosen from the group comprising Na 2 SO 4 , K 2 SO 4 and CaSO 4 . For example, the solution may include 0.001 to 1 mol / L of sulfate salt, preferably 0.1 to 0.5 mol / L. Salt does not intervene in electrode reactions and does not react with the solvent.

Selon une variante, l'agent favorisant les propriétés de transport ionique peut être un acide additionnel.According to a variant, the agent promoting the ion transport properties may be an additional acid.

Avantageusement, le substrat est en silicium. Le silicium est inerte électrochimiquement lors des étapes d'électrodissolution et d'électrodéposition.Advantageously, the substrate is made of silicon. The silicon is electrochemically inert during the electrodissolution and electrodeposition stages.

Avantageusement, le substrat électriquement conducteur provient d'une cellule photovoltaïque et l'argent forme les métallisations de la face avant de la cellule photovoltaïque. L'aluminium recouvre la face arrière de la cellule.Advantageously, the electrically conductive substrate comes from a photovoltaic cell and the silver forms the metallizations of the front face of the photovoltaic cell. Aluminum covers the rear face of the cell.

Avantageusement, le procédé est réalisé à une température allant de 15°C à 60°C, et de préférence étant de l'ordre de 20-25°C. Ces conditions permettent également de diminuer la quantité d'énergie nécessaire et d'améliorer la sécurité par rapport aux procédés de l'art antérieur qui peuvent mettre en œuvre des solutions acides en ébullition. Le procédé peut être réalisé à température ambiante (20-25°C) facilitant son utilisation en milieu industriel.Advantageously, the process is carried out at a temperature ranging from 15 ° C to 60 ° C, and preferably being of the order of 20-25 ° C. These conditions also make it possible to reduce the amount of energy required and to improve safety compared to the processes of the prior art which can use boiling acid solutions. The process can be carried out at room temperature (20-25 ° C) facilitating its use in an industrial environment.

Le procédé peut être réalisé sous air. C'est particulièrement avantageux de ne pas travailler sous atmosphère contrôlée et de ne pas utiliser des gaz inertes. Le procédé est industrialisable.The process can be carried out in air. It is particularly advantageous not to work in a controlled atmosphere and not to use inert gases. The process can be industrialized.

D'autres caractéristiques et avantages de l'invention apparaîtront mieux à la lecture du complément de description qui suit, qui se rapporte à un essai de récupération, par dissolution électrochimique et électrodéposition, d'argent présent dans une cellule photovoltaïque au moyen d'une solution électrolytique conforme à l'invention.Other characteristics and advantages of the invention will appear better on reading the additional description which follows, which relates to an attempt to recover, by electrochemical dissolution and electrodeposition, of silver present in a photovoltaic cell by means of a electrolytic solution according to the invention.

Il est précisé que cette description détaillée, qui se réfère notamment aux figures 1 à 3 telles qu'annexées, n'est donnée qu'à titre d'illustration de l'objet de l'invention et ne constitue en aucun cas une limitation de cet objet.It should be noted that this detailed description, which refers in particular to Figures 1 to 3 as annexed, is only given as an illustration of the object of the invention and does not in any way constitute a limitation of this object.

En particulier, le procédé de récupération d'argent décrit ci-dessus et détaillé ci-après permet d'obtenir sélectivement la dissolution électrochimique de l'argent présent sur un substrat, qui comprend également de l'aluminium, et sa récupération sous forme métallique.In particular, the silver recovery process described above and detailed below makes it possible to selectively obtain the electrochemical dissolution of the silver present on a substrate, which also includes aluminum, and its recovery in metallic form.

BRÈVE DESCRIPTION DES DESSINSBRIEF DESCRIPTION OF THE DRAWINGS

La présente invention sera mieux comprise sur la base de la description qui va suivre et des dessins en annexe sur lesquels :

  • la figure 1 est une courbe courant-temps correspondant à l'étape d'électro-dissolution de connectiques en argent d'une des faces d'un substrat en silicium recouvert également, sur une autre face, par de l'aluminium, provenant d'une cellule photovoltaïque,
  • la figure 2 est un cliché obtenu par microscopie électronique à balayage, en électrons rétrodiffusés, du dépôt d'argent obtenu avec le procédé de l'invention, sur une électrode en carbone vitreux,
  • la figure 3 est un spectre d'une microanalyse par Energie Dispersive des rayons X de l'argent électrodéposé sur l'électrode en carbone vitreux.
The present invention will be better understood on the basis of the description which follows and of the appended drawings in which:
  • the figure 1 is a current-time curve corresponding to the electro-dissolution step of silver connectors on one side of a silicon substrate also covered, on another side, by aluminum, coming from a cell photovoltaic,
  • the figure 2 is a photograph obtained by scanning electron microscopy, in backscattered electrons, of the silver deposit obtained with the process of the invention, on a glassy carbon electrode,
  • the figure 3 is a spectrum of a Dispersive Energy microanalysis of X-rays of silver electrodeposited on the glassy carbon electrode.

EXPOSÉ DÉTAILLÉ DE MODES DE RÉALISATION PARTICULIERSDETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Par la suite le procédé est décrit pour récupérer l'argent contenu dans des cellules photovoltaïques, avantageusement en silicium cristallin ou polycristallin, et plus particulièrement pour récupérer l'argent, présent en face avant d'une cellule, sélectivement vis-à-vis de l'aluminium présent en face arrière de la cellule.Subsequently the method is described for recovering the silver contained in photovoltaic cells, advantageously in crystalline or polycrystalline silicon, and more particularly for recovering the silver, present on the front face of a cell, selectively with respect to the aluminum present on the back of the cell.

Le procédé pourrait être utilisé pour tout type de substrat électriquement conducteur, ne se dissolvant pas naturellement dans la solution électrolytique.The process could be used for any type of electrically conductive substrate, which does not dissolve naturally in the electrolytic solution.

Préalablement à la mise en œuvre du procédé, les cellules sont retirées du panneau photovoltaïque et séparées des câbles, boîtes de jonction, et cadres métalliques. Les cellules sont soumises à un traitement thermique pour éliminer, par calcination, les matériaux d'encapsulation en polymère, tel que l'éthylène-acétate de vinyle (EVA). L'étape de calcination est, par exemple, réalisée dans un four sous air. Le traitement thermique est, par exemple, réalisé à une température comprise entre 400°C et 700°C, plus avantageusement entre 450 et 550°C. La durée de ce traitement peut être comprise entre 30 et 120 minutes, plus avantageusement entre 60 et 90 minutes.Prior to the implementation of the process, the cells are removed from the photovoltaic panel and separated from the cables, junction boxes, and metal frames. The cells are subjected to a heat treatment to remove, by calcination, the polymer encapsulation materials, such as ethylene vinyl acetate (EVA). The calcination step is, for example, carried out in an air oven. The heat treatment is, for example, carried out at a temperature between 400 ° C. and 700 ° C, more preferably between 450 and 550 ° C. The duration of this treatment can be between 30 and 120 minutes, more advantageously between 60 and 90 minutes.

A l'issue de ce prétraitement, la cellule photovoltaïque consiste en un substrat électriquement conducteur en silicium recouvert par une ou plusieurs électrodes d'argent. Les électrodes d'argent sont classiquement formées à partir d'une pâte d'argent qui peut comprendre une poudre de verre SiO2, B2O3, PbO et ZnO, de l'argent et un agent liant.At the end of this pretreatment, the photovoltaic cell consists of an electrically conductive silicon substrate covered by one or more silver electrodes. The silver electrodes are conventionally formed from a silver paste which may comprise a glass powder SiO 2 , B 2 O 3 , PbO and ZnO, silver and a binding agent.

Les cellules peuvent être, également, séparées des connecteurs électriques. Selon une variante, les connecteurs électriques, composés d'un cœur en cuivre enrobé de Sn62Pb36Ag2, par exemple, et l'argent peuvent être valorisés avec le procédé de l'invention. Les différents métaux (cuivre, plomb, étain) formant des complexes très stables avec l'agent complexant et/ou étant en quantité minime et/ou n'étant pas dissous et/ou n'étant pas électrodéposés avec le potentiel utilisé dans le procédé, le dépôt sur la première électrode négative sera essentiellement de l'argent. Il est donc particulièrement avantageux d'être sélectif vis-à-vis de l'argent. Le choix de la température du traitement thermique pourra aider à favoriser la dissolution sélective de l'argent.The cells can also be separated from the electrical connectors. According to a variant, the electrical connectors, composed of a copper core coated with Sn 62 Pb 36 Ag 2 , for example, and silver can be valued with the method of the invention. The different metals (copper, lead, tin) forming very stable complexes with the complexing agent and / or being in minimal quantity and / or not being dissolved and / or not being electrodeposited with the potential used in the process , the deposit on the first negative electrode will essentially be silver. It is therefore particularly advantageous to be selective with regard to money. The choice of the temperature of the heat treatment can help promote the selective dissolution of silver.

Le substrat n'est pas broyé pour mettre en œuvre le procédé. Il peut, être, par exemple, découpé sous forme d'une plaque de quelques cm2 ou dm2.The substrate is not ground to carry out the process. It can, for example, be cut in the form of a plate of a few cm 2 or dm 2 .

Le substrat comporte une première face et une seconde face. La première face, correspondant à la face avant de la cellule photovoltaïque, est recouverte par de l'argent. L'argent est, par exemple, sous la forme d'une grille. La seconde face correspond à la face arrière de la cellule photovoltaïque. La seconde face est recouverte par de l'aluminium. L'aluminium forme, par exemple, un film continu.The substrate has a first face and a second face. The first face, corresponding to the front face of the photovoltaic cell, is covered with silver. The money is, for example, in the form of a grid. The second face corresponds to the rear face of the photovoltaic cell. The second side is covered with aluminum. Aluminum forms, for example, a continuous film.

La première face du substrat recouverte d'argent, est électriquement connectée au dispositif de contrôle. Elle joue le rôle d'anode. Avantageusement, la totalité des connectiques d'argent (bus, bar) en surface du substrat est électriquement connectée au potentiostat.The first face of the substrate, covered with silver, is electrically connected to the control device. It plays the role of anode. Advantageously, all of the silver connectors (bus, bar) on the surface of the substrate are electrically connected to the potentiostat.

La seconde face du substrat est également électriquement connectée au dispositif de contrôle. Elle joue le rôle de cathode.The second face of the substrate is also electrically connected to the control device. It plays the role of cathode.

Le dispositif de contrôle est une source de tension ou de courant, comme un potentiostat. Le potentiostat est utilisé, de préférence, en mode potentiostatique. Il pourrait être utilisé en mode galvanostatique.The control device is a source of voltage or current, like a potentiostat. The potentiostat is preferably used in potentiostatic mode. It could be used in galvanostatic mode.

Le substrat est plongé, au moins partiellement, dans la solution électrolytique, de manière à mettre les deux faces du substrat en contact avec la solution électrolytique.The substrate is immersed, at least partially, in the electrolytic solution, so as to bring the two faces of the substrate into contact with the electrolytic solution.

On impose un potentiel ou un courant à la première électrode positive ou négative, ce qui génère simultanément l'électro-dissolution de l'argent présent sur la première électrode positive et la protection cathodique de l'aluminium présent sur la première électrode négative.A potential or a current is imposed on the first positive or negative electrode, which simultaneously generates the electro-dissolution of the silver present on the first positive electrode and the cathodic protection of the aluminum present on the first negative electrode.

Une électrode de référence, par exemple Ag/AgCl, peut également être ajoutée au montage.A reference electrode, for example Ag / AgCl, can also be added to the assembly.

Le potentiel appliqué à la première électrode positive pour dissoudre l'argent dans la solution électrolytique et passiver l'aluminium va de -0,4 V à 0 V vs Ag/AgCl, par exemple -0,2 V vs Ag/AgCl.The potential applied to the first positive electrode to dissolve the silver in the electrolytic solution and passivate the aluminum ranges from -0.4 V to 0 V vs Ag / AgCl, for example -0.2 V vs Ag / AgCl.

Avantageusement, le potentiel est appliqué pendant une durée de 30 minutes à 3 heures, et de préférence pendant une durée de 30 minutes à 1 heure. La durée sera, notamment, choisie en fonction de la quantité d'argent à valoriser, du pH et du potentiel (ou du courant) appliqué. Plus la solution électrolytique sera acide et plus la dissolution sera rapide.Advantageously, the potential is applied for a period of 30 minutes to 3 hours, and preferably for a period of 30 minutes to 1 hour. The duration will, in particular, be chosen according to the amount of silver to be valorized, the pH and the potential (or current) applied. The more acidic the electrolyte solution, the faster the dissolution.

Une fois que l'argent est dissous en solution, l'argent peut être électrodéposé sur une autre électrode (cathode), en utilisant un montage à deux électrodes (une deuxième électrode positive et une deuxième électrode négative) ou à trois électrodes (une deuxième électrode positive, une deuxième électrode négative et une électrode de référence). Pour électrodéposer l'argent, le potentiel appliqué à la deuxième électrode négative va, par exemple, de -0,4 V à -1 V vs Ag/AgCl. On choisira par exemple un potentiel de -0,5 V.Once the silver is dissolved in solution, the silver can be electrodeposited on another electrode (cathode), using a two-electrode assembly (a second positive electrode and a second negative electrode) or three electrodes (a second positive electrode, a second negative electrode and a reference electrode). For electrodepositing silver, the potential applied to the second negative electrode goes, for example, from -0.4 V to -1 V vs Ag / AgCl. For example, choose a potential of -0.5 V.

À l'issue de l'électrodéposition, l'agent complexant est régénéré. La solution acide de traitement peut donc être réutilisée, éventuellement en ajustant son pH, ce qui réduit la consommation de réactifs.After the electroplating, the complexing agent is regenerated. The acid treatment solution can therefore be reused, possibly by adjusting its pH, which reduces the consumption of reagents.

Après électro-dissolution/électrodéposition du métal argent, les électrodes sont extraites de la solution électrolytique et il est possible de procéder à un nouveau cycle de traitement avec un nouveau substrat contenant de l'argent à récupérer.After electro-dissolution / electrodeposition of the silver metal, the electrodes are extracted from the electrolytic solution and it is possible to carry out a new treatment cycle with a new substrate containing silver to be recovered.

La solution électrolytique a un pH de -1 à 6, de préférence, de -1 à 2, et encore plus préférentiellement de 0 à 1. Elle comprend au moins un acide, un agent complexant l'argent et, éventuellement un sel de sulfate pour améliorer le transport ionique au sein de la solution.The electrolytic solution has a pH of -1 to 6, preferably of -1 to 2, and even more preferably of 0 to 1. It comprises at least one acid, a silver complexing agent and, optionally, a sulfate salt. to improve ion transport within the solution.

Selon un mode de réalisation particulier, l'acide utilisé présente un pKa compris entre - 7 et 3. Il s'agit d'un acide de Brönsted, c'est-à-dire un acide apte à libérer au moins un proton. On utilisera par exemple de l'acide sulfurique, de l'acide nitrique ou un mélange de ces acides.According to a particular embodiment, the acid used has a pKa of between - 7 and 3. It is a Brönsted acid, that is to say an acid capable of releasing at least one proton. For example, sulfuric acid, nitric acid or a mixture of these acids will be used.

Lors de la mise en œuvre du procédé selon l'invention, le pH de la solution acide peut être contrôlé et, éventuellement, ajusté à ces valeurs, par addition d'acide.During the implementation of the method according to the invention, the pH of the acid solution can be controlled and, optionally, adjusted to these values, by addition of acid.

L'agent complexant est, de préférence, la thio-urée (numéro CAS 62-56-6).The complexing agent is preferably thiourea (CAS number 62-56-6).

La solution électrolytique est, de préférence, dépourvue de solvant autre que l'eau. La solution acide est, de préférence, dépourvue d'agent oxydant tel que, par exemple, le peroxyde d'hydrogène ou encore des sels métalliques (sulfate de fer ou de cuivre par exemple).The electrolytic solution is preferably devoid of any solvent other than water. The acid solution is preferably devoid of an oxidizing agent such as, for example, hydrogen peroxide or also metal salts (iron or copper sulphate for example).

La solution peut contenir naturellement de l'oxygène dissous. On ne rajoutera pas d'oxygène en plus de celui naturellement présent en solution. L'oxygène naturellement présent peut également être évacué de la solution par bullage avec un autre gaz, tel que l'argon.The solution may naturally contain dissolved oxygen. We will not add oxygen in addition to that naturally present in solution. The naturally occurring oxygen can also be removed from the solution by bubbling with another gas, such as argon.

La solution présente une faible viscosité et une bonne conductivité ionique.The solution has a low viscosity and good ionic conductivity.

Le procédé est avantageusement réalisé sous agitation mécanique, par exemple entre 200 et 1000 tours/minute.The process is advantageously carried out with mechanical stirring, for example between 200 and 1000 revolutions / minute.

Les différentes étapes du procédé sont, avantageusement, réalisées sous air.The various stages of the process are advantageously carried out in air.

•Exemple illustratif et non limitatif d'un mode de réalisation :• Illustrative and non-limiting example of an embodiment :

Dans cet exemple, des cellules en silicium, issues de panneaux photovoltaïques conventionnels, sont utilisées.In this example, silicon cells, derived from conventional photovoltaic panels, are used.

Dans un premier temps, les cellules photovoltaïques sont soumises à un traitement thermique afin de brûler les couches d'encapsulation en EVA. Cette étape a lieu dans un four sous air à 500°C pendant 1h. Les cellules sont également séparées des connecteurs.Initially, the photovoltaic cells are subjected to a heat treatment in order to burn the layers of EVA encapsulation. This step takes place in an air oven at 500 ° C for 1 hour. The cells are also separated from the connectors.

Le système électrochimique utilisé dans le cadre de cette étude comprend trois électrodes :

  • une première électrode positive : la face avant de la cellule photovoltaïque recouverte par les métallisations en argent,
  • une première électrode négative : la face arrière de la cellule photovoltaïque recouverte par un film en aluminium,
  • une électrode de référence Ag/AgCl.
The electrochemical system used in this study includes three electrodes:
  • a first positive electrode: the front face of the photovoltaic cell covered by silver metallizations,
  • a first negative electrode: the rear face of the photovoltaic cell covered with an aluminum film,
  • an Ag / AgCl reference electrode.

Les électrodes sont plongées dans une solution aqueuse de 200 mL comprenant 10-1 mol.L-1 d'acide sulfurique (pH=1) et 0,5 mol.L-1 de thio-urée. La solution est agitée, sous air à 20°C, à 400 tours/min.The electrodes are immersed in an aqueous solution of 200 ml comprising 10 -1 mol.L -1 of sulfuric acid (pH = 1) and 0.5 mol.L -1 of thiourea. The solution is stirred, in air at 20 ° C., at 400 rpm.

L'électrodissolution est réalisée en mode potentiostatique. Un potentiel constant de -0,25 V est appliqué à la première électrode positive, provoquant la dissolution de l'argent de la première électrode positive et, simultanément, la protection cathodique de l'aluminium de la première électrode négative. Le potentiel est maintenu pendant 0,8 heures (figure 1) permettant d'extraire 9 Coulombs, soit 98% de l'argent disponible dans la cellule de silicium.The electrodissolution is carried out in potentiostatic mode. A constant potential of -0.25 V is applied to the first positive electrode, causing the silver from the first positive electrode to dissolve and, simultaneously, the cathodic protection of the aluminum from the first negative electrode. The potential is maintained for 0.8 hours ( figure 1 ) allowing to extract 9 Coulombs, that is 98% of the silver available in the silicon cell.

La composition de la solution électrolytique a été analysée, après l'électrodissolution, par spectrométrie à plasma à couplage inductif (ICP). Les résultats confirment que, avec la protection cathodique, l'argent est dissous et la concentration en aluminium en solution est résiduelle (∼1% de l'aluminium). Il s'agit bien d'une dissolution sélective de l'argent vis-à-vis de l'aluminium.The composition of the electrolytic solution was analyzed, after electrodissolution, by inductively coupled plasma spectrometry (ICP). The results confirm that, with cathodic protection, the silver is dissolved and the concentration of aluminum in solution is residual (∼1% of aluminum). It is indeed a selective dissolution of silver vis-à-vis aluminum.

Cette composition a été comparée avec un substrat identique, comprenant sur une de ses faces de l'argent et sur l'autre face de l'aluminium, plongé dans la même solution électrolytique. La dissolution a été réalisée sans protection cathodique. Les résultats sont regroupés dans le tableau ci-dessous. Sans protection cathodique, on observe une très forte dissolution de l'aluminium et une très faible dissolution de l'argent. Résultats ICP Procédé Ag (mg/L) Al (mg/L) Electrodissolution sélective 105,6 9,5 Dissolution sans protection cathodique 0,4 868,3 This composition was compared with an identical substrate, comprising on one of its faces silver and on the other face of aluminum, immersed in the same electrolytic solution. The dissolution was carried out without cathodic protection. The results are collated in the table below. Without cathodic protection, we observe a very strong dissolution of aluminum and a very weak dissolution of silver. ICP results Process Ag (mg / L) Al (mg / L) Selective electrodissolution 105.6 9.5 Dissolution without cathodic protection 0.4 868.3

La solution électrolytique de l'électrodissolution sélective a, ensuite, servi pour faire un dépôt d'argent sur une électrode de carbone vitreux. Un montage à trois électrodes est utilisé avec, cette fois-ci, une électrode de travail en carbone vitreux. Le potentiel est maintenu à -0,5 V pendant une heure (mode potentiostatique), ce qui permet de réduire l'argent sur l'électrode.The electrolytic solution of the selective electrodissolution was then used to deposit silver on a glassy carbon electrode. A three-electrode assembly is used with, this time, a glassy carbon working electrode. The potential is maintained at -0.5 V for one hour (potentiostatic mode), which reduces the silver on the electrode.

A la fin du procédé, un dépôt est visible sur l'électrode de carbone vitreux. Ce dépôt a fait l'objet d'analyses par MEB et Energie Dispersive de rayon X (EDX) afin d'en déterminer la composition chimique. Les observations au MEB ont mis en évidence la présence d'un dépôt d'argent (zones claires). La présence d'argent a été confirmée par microanalyse par EDX. La microstructure du dépôt est de type « choux fleurs ». Quelques impuretés de soufre sont présentes dans le dépôt d'argent. L'étain est également présent à hauteur de 3% atomique dans le dépôt. L'étain est un des éléments qui composent la soudure argent (Cu, Sn, Pb et Ag) des cellules. L'absence de cuivre confirme la sélectivité du dépôtAt the end of the process, a deposit is visible on the glassy carbon electrode. This deposit was analyzed by SEM and Dispersive Energy X-ray (EDX) to determine its chemical composition. Observations at the MEB highlighted the presence of a deposit of silver (light areas). The presence of silver was confirmed by microanalysis by EDX. The microstructure of the deposit is of the “cauliflower” type. Some sulfur impurities are present in the silver deposit. Tin is also present at 3 atomic% in the deposit. Tin is one of the elements that make up the silver solder (Cu, Sn, Pb and Ag) of the cells. The absence of copper confirms the selectivity of the deposit

Avant lavage, l'analyse semi-quantitative par EDX indique que la teneur en argent est supérieure à 94% pour atteindre un grade supérieur après lavage des éléments piégés dans le dépôt d'argent. Ces impuretés résiduelles (soufre essentiellement) peuvent être retirées après un lavage du dépôt d'argent dans de l'eau dans lequel le dépôt est insoluble.Before washing, the semi-quantitative analysis by EDX indicates that the silver content is greater than 94% to reach a higher grade after washing the elements trapped in the silver deposit. These residual impurities (essentially sulfur) can be removed after washing the silver deposit in water in which the deposit is insoluble.

Cet exemple montre qu'il est possible de récupérer l'argent de manière sélective, en présence d'aluminium, par dissolution électrochimique puis électrodéposition, sous une atmosphère non contrôlée telle que l'air.This example shows that it is possible to recover silver selectively, in the presence of aluminum, by electrochemical dissolution then electrodeposition, under an uncontrolled atmosphere such as air.

Claims (14)

  1. A process for selectively recovering silver from an electrically conducting substrate, said process comprising the following successive steps of:
    a) providing a system comprising:
    ∘ an electrically conducting substrate, comprising a first face covered with silver and a second face covered with aluminium, the first face forming a first positive electrode and the second face forming a first negative electrode, and
    ∘ a control device, connected to the first positive electrode and to the first negative electrode, the control device enabling the potential or current of an electrode to be controlled;
    b) dipping the first positive electrode and the first negative electrode into an electrolyte solution, the electrolyte solution being an aqueous solution comprising at least one acid and a silver complexing agent, the electrolyte solution having a pH ranging from -1 to 6; and
    c) applying a potential or a current to the first positive electrode or to the first negative electrode, so as to dissolve silver from the first positive electrode in the electrolyte solution and to passivate aluminium from the first negative electrode.
  2. The process according to claim 1, characterised in that the process comprises the following subsequent steps of:
    d) withdrawing the first positive electrode and the first negative electrode from the electrolyte solution, and disconnecting the first positive electrode and the first negative electrode from the control device;
    e) dipping a second positive electrode and a second negative electrode, connected to the control device, into the electrolyte solution; and
    f) applying a potential or a current to the second positive electrode or the second negative electrode, so as to electrodeposit silver, dissolved in the electrolyte solution, onto the second negative electrode and regenerate the silver complexing agent.
  3. The process according to claim 2, characterised in that, after step f), steps a), b), c) can be repeated with another electrically conducting substrate.
  4. The process according to any of claims 1 to 3, characterised in that the system further comprises a reference electrode, for example Ag/AgCl.
  5. The process according to claim 4, characterised in that the potential applied to the first positive electrode ranges from -0.4V to 0V vs Ag/AgCI.
  6. The process according to claim 5, characterised in that the potential is applied to the first positive electrode for a duration ranging from 30 minutes to 3 hours, and preferably, from 30 minutes to 1 hour.
  7. The process according to any of claims 1 to 6, characterised in that the aqueous solution has a pH ranging from -1 to 2, and preferably from 0 to 1.
  8. The process according to any of claims 1 to 7, characterised in that the acid is sulphuric acid, nitric acid or a mixture thereof.
  9. The process according to any of claims 1 to 8, characterised in that the concentration of complexing agent ranges from 0.01 to 1mol/L, preferably from 0.05mol/L to 1mol/L, and even more preferentially, is in the order of 0.5mol/L.
  10. The process according to any of claims 1 to 9, characterised in that the complexing agent is thio-urea.
  11. The process according to any of claims 1 to 10, characterised in that the solution further comprises a sulphate salt, preferably selected from Na2SO4, CaSO4 and K2SO4.
  12. The process according to any of claims 1 to 11, characterised in that the process is performed at a temperature ranging from 15°C to 60°C, and preferably, being in the order of 20-25°C.
  13. The process according to any of claims 1 to 12, characterised in that the electrically conducting substrate is of silicon.
  14. The process according to any of claims 1 to 13, characterised in that the substrate comes from a photovoltaic cell, silver forming metallisations of the front face of the photovoltaic cell.
EP18166892.2A 2017-04-12 2018-04-11 Process for selective recovery of silver in the presence of aluminium, electrochemically and in aqueous solution Active EP3388555B1 (en)

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FR3127760A1 (en) * 2021-10-01 2023-04-07 Commissariat A L'energie Atomique Et Aux Energies Alternatives METHOD FOR RECOVERING THE SILVER CONTAINED IN THE PARTICLES ORIGINATING, FOR EXAMPLE, FROM PHOTOVOLTAIC CELLS

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US3616332A (en) * 1969-12-17 1971-10-26 Texas Instruments Inc Process for recovering silver from scrap materials and electrolyte composition for use therein
DE2025211A1 (en) * 1970-05-23 1971-12-02 Kraft J Selective anodic recovery of silver - from scrap by electro - -deposition from aq soln
US4606797A (en) * 1985-09-12 1986-08-19 Engelhard Corporation Method for recovery of high grade gold alloy from karat gold-clad base metal substrates
JP2017506702A (en) * 2014-02-26 2017-03-09 グリーン リヨン グループ, インコーポレーテッドGreene Lyon Group, Inc. Recovery of gold and / or silver from scrap
FR3028433B1 (en) * 2014-11-18 2016-11-11 Commissariat Energie Atomique PROCESS FOR RECOVERING METALS CONTAINED IN A SILICON SUBSTRATE

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