METHOD FOR RECOVERING MONEY CONTAINED IN PARTICLES ORIGINATING, FOR EXAMPLE, FROM PHOTOVOLTAIC CELLS

Abstract

A process for recovering silver from particles, for example, from ground photovoltaic cells, the process comprising the following successive steps: i) immersing silver-containing particles in a solution comprising a deep eutectic solvent and a redox mediator, thereby forming silver ions in solution; ii) separating the particles from the solution containing the silver ions; iii) performing electrolysis of the solution, thereby reducing the silver ions and regenerating the redox mediator. Figure for the abstract: 1

Description

Title of the invention: METHOD FOR RECOVERING SILVER CONTAINED IN PARTICLES ORIGINATING, FOR EXAMPLE, FROM PHOTOVOLTAIC CELLS technical field

[0001] The present invention relates to the general field of photovoltaic panel recycling.

[0002] The invention relates more particularly to a method of recovering silver from a photovoltaic panel, containing for example crystalline silicon photovoltaic cells.

[0003] The invention is particularly interesting since it allows the silver present in photovoltaic cells to be recovered through green chemistry. PREVIOUS STATE OF THE ART

[0004] Currently, the recycling of photovoltaic (PV) panels has become a major issue since August 13, 2012, since on that date, the Directive on Waste Electrical and Electronic Equipment (WEEE) was extended to photovoltaic (PV) panels.

[0005] Today, 90% of existing panels are made of crystalline silicon (the remaining 10% are thin-film solar panels). A silicon photovoltaic module is mainly composed of glass (74% of the total weight), aluminum (10%), polymer (approximately 6.5%), and silicon (approximately 3%). Metals (zinc, lead, copper, and silver) represent only a negligible portion of the total mass of the photovoltaic panel.

[0006] The minimum objectives for recovery and recycling are therefore easily achieved by the recovery of the glass and the aluminum frame alone.

[0007] Current processes focus on dismantling modules by chemical or thermal means and then on recycling the different elements through specialized reprocessing methods.

[0008] Silver represents the metal with the highest added value (nearly 90% of the cell's value). Therefore, silver recovery is a major issue for ensuring the sustainability of the recycling sector.

[0009] Conventionally, photovoltaic cells in photovoltaic modules are chemically treated by total dissolution of the metallic elements (Cu, Ag, Sn, Pb, Al, etc.), the anti-reflective coatings, and the n-doped layer to recover the silicon. Dissolution can be carried out in treatment baths composed of various acids. concentrated in mixtures and often brought to a boil. However, these solutions are harmful and dangerous.

[0010] This is why the most recent work uses ionic liquids to dissolve and / or recover the elements.

[0011] For example, it has been shown that it is possible to recover silver by electrodeposition from solutions containing silver salts and chloroaluminate ionic liquids [1] or from choline chloride-type ionic liquids [2]. Silver is electrodeposited onto various substrates, such as Pt, Au, W or vitreous carbon (GC) substrates.

[0012] Regarding dissolution, few studies have focused on the leaching of silver and metals in ionic liquid media. Among these studies, one can cite the dissolution of silver (and various metals Au, Cu, Zn, Pb, Fe) from a chalcopyrite ore in ionic liquid media [3]. These studies deal with the leaching yield of gold and silver in an ionic liquid solution ([BMIM][HS04]) containing Fe3+ ions and thiourea.

[0013] More recently, the effects of leaching in a protic ionic liquid ([BMIM][HSO4]) mixed with water (on the same ore) were studied [4]. No results are reported for silver; only the dissolution yields of copper and iron are discussed. The results indicate an increase in the dissolution of these metals with increasing water content, which is explained by the combined increase in dissolved protons and dioxygen.

[0014] Recently, it has been demonstrated that it is possible to achieve the chemical dissolution and electrochemical recovery of silver in ionic liquids in the presence of a redox mediator using a two-step process [5]. In the first step, silver is dissolved in a solution comprising an ionic liquid and a redox mediator. This solution ensures the chemical dissolution of silver under atmospheric (air) conditions. In the second step, the silver is recovered by electrolysis in metallic form. Simultaneously with the silver deposition, the redox mediator is regenerated in the ionic liquid medium.

[0015] However, the process uses ionic liquids which are expensive and not biodegradable.

[0016] Currently, the processes implemented for the recovery of silver are complex, costly, reagent-intensive and / or dangerous and, consequently, induce a significant economic and environmental cost.

[0017] Thus, none of the current processes allows the dissolution and recovery of the money in a satisfactory manner. Description of the invention

[0018] An object of the present invention is to propose a method for recovering the silver present in a medium, for example a photovoltaic module to be recycled, the method being simple to implement, inexpensive and not requiring the use of any product toxic to the environment and / or to the health of the people implementing the method.

[0019] To this end, the present invention proposes a method for recovering silver contained in particles, originating, for example, from ground photovoltaic cells, the method comprising the following successive steps:

[0020] i) immersing particles containing silver in a solution comprising a deep eutectic solvent and a redox mediator, thereby forming silver ions in solution,

[0021] ii) separate the particles from the solution containing the silver ions,

[0022] iii) carry out an electrolysis of the solution, thereby reducing the silver ions and regenerating the redox mediator.

[0023] The invention is fundamentally distinguished from the prior art by the use of deep eutectic solvents (or DES for "Deep Eutectic Solvents" in English).

[0024] The properties of DES are extremely different from those of ionic liquids in terms of conductivity, viscosity, decomposition temperature, electrochemical window and oxide solubility.

[0025] DESs are solvents formed by mixing two or more compounds in a precise proportion that corresponds to the eutectic point. Most of these solvents are liquid at room temperature, which facilitates their use. DESs are non-volatile, non-flammable, and chemically stable at temperatures up to 200 °C.

[0026] The synthesis of DESs is easy and clean compared to that of ionic liquids, which require several steps of chemical synthesis and purification. DESs are obtained by simply mixing the components of the DES in the correct proportions, possibly with heating of the mixture, until a homogeneous and transparent liquid is obtained. DESs are formed from a pair comprising a hydrogen bond donor and a hydrogen bond acceptor.

[0027] The preparation of DES requires no chemical reaction and, consequently, the production yield is 100%. It is a simple mixing of the products composing the DES in the correct proportion with heating, until a homogeneous and transparent liquid is obtained.

[0028] DES allows silver to be dissolved and recovered by way of green chemistry, unlike processes using ionic liquids.

[0029] According to an advantageous embodiment, the deep eutectic solvent is formed from a choline chloride and a hydrogen bond donor, in particular a glycol such as ethylene glycol.

[0030] According to another advantageous embodiment, the deep eutectic solvent is a natural deep eutectic solvent (NADES). For example, it may be malic acid:glucose or citric acid:sucrose.

[0031] Advantageously, steps i), ii) and iii) are carried out in air at a temperature between 20°C and 100°C, preferably between 20°C and 80°C.

[0032] By between X and Y, we mean here and thereafter that the bounds X and Y are included in the interval.

[0033] Advantageously, the substrate is in particulate form.

[0034] Advantageously, the redox mediator has a concentration between 0.1 and 2 mol / L, preferably between 0.1 and 0.5 mol / L.

[0035] Advantageously, the redox mediator is chosen from iron, manganese, cobalt, chromium, vanadium, tin, silver, copper, ruthenium, chlorine, bromine, and iodine. In particular, the redox mediator will be chosen from among Mn27Mn3+, Co27Co3+, Cr27Cr3+, Cr37Cr6+, V27V3+, V47V5+, Sn27Sn4+, Ag7Ag2+, Cu7Cu2+, Ru47Ru8+, C1 / C13, Br2 / Br, I / I3, and Fe27Fe3+.

[0036] Advantageously, the redox mediator is a metallic salt, and more particularly an iron(III) salt or a copper(II) salt to obtain, respectively, Fe27Fe3+ and / or Cu7Cu2+. It may also be a mixture thereof.

[0037] Advantageously, the solution contains an additive, such as water, to improve transport conditions (viscosity, ionic conductivity).

[0038] Advantageously, the particles originate from a ground-up of crystalline silicon or polycrystalline silicon photovoltaic cells. The particles may also originate from an electrical connector containing silver.

[0039] Advantageously, the solution further contains water, the molar percentage of water relative to the deep eutectic solvent preferably being less than 50%.

[0040] Advantageously, prior to step i), the process further comprises the following steps:

[0041] a) supply a photovoltaic panel comprising cables, a junction box, a metal frame, photovoltaic cells encapsulated in a polymer layer and electrical connectors,

[0042] b) remove the cables, junction box and metal frame of the photovoltaic panel,

[0043] c) perform a thermal and / or chemical or mechanical treatment to remove the polymer layer encapsulating the photovoltaic cells,

[0044] d) to grind the photovoltaic cells and / or electrical connectors, so as to form particles containing silver,

[0045] e) preferably, carry out a dealuminization step on the particles containing silver, the dealuminization step being carried out in an acidic solution at a pH between 1 and 4.

[0046] The process has many advantages:

[0047] - the process makes it possible to couple, on the one hand, dissolution and, on the other hand, the electrodeposition of silver and the regeneration of the redox mediator in a single unit step,

[0048] - the redox mediator regenerates, unlike conventional reducing agents which degrade during the dissolution reaction (as is the case for example with HNO3 which leads to the generation and irreversible consumption of nitrates with the formation of NOx),

[0049] - since DES is an ionic conductor, there is no need to add an additional salt conductor to ensure ionic conduction during the electrolysis step,

[0050] - the use of DES makes it possible to overcome the problems of solubility and stability (chemical degradation) of the complexing agent (e.g., thiourea, thiosulfate, etc.) and to induce the active species at very high concentrations (between 0.1 and 2 mol.L*) favoring the dissolution kinetics of the metal,

[0051] - the redox mediator does not co-deposit with the silver, allowing recovery complete and pure silver,

[0052] - the redox mediator is regenerated without degradation and without pollution of the DES,

[0053] - the redox mediator is readily available commercially (especially salts with (based on Fe3+ and Cu2+),

[0054] - the process does not require the use of acidic solution or ionic liquid,

[0055] - the use of DES (and its possible reuse) makes it possible to eliminate the steps of solvent treatment, which reduces costs,

[0056] - DES are biodegradable, which reduces the constraints related to standards safety and / or environmental,

[0057] - the process does not release harmful gases and does not degrade the reaction medium,

[0058] - the process can be carried out under atmospheric conditions (under air),

[0059] - the process can be carried out at room temperature (typically 25°C), which avoids the supply of thermal energy,

[0060] - DES are inexpensive solvents, which reduces the costs of the process,

[0061] - DESs are easy to prepare and can therefore be prepared in situ.

[0062] Other features and advantages of the invention will become apparent from the following supplementary description.

[0063] It goes without saying that this additional description is given only as an illustration of the object of the invention and should in no case be interpreted as a limitation of this object. Brief description of the drawings

[0064] The present invention will be better understood by reading the description of examples of embodiments, given purely as an example and in no way limiting, with reference to the attached [Fig.1].

[0065] [Fig.1] represents an intensity-potential curve on a platinum electrode (50 mV s1) with a solution of Ethaline (1:2) and 0.25 mol kg FeCl3.6H20 after leaching of silver, according to a particular embodiment of the invention.

[0066] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0067] Subsequently, even though the description refers to the valorization of photovoltaic panels or modules; the invention is transferable to other substrates containing silver and in particular to waste electrical and electronic equipment (WEEE), to electronic boards.

[0068] The photovoltaic panel to be recycled includes cables, a junction box and a metal frame, a polymer layer (typically ethyl vinyl acetate (EVA)) and elements containing silver: photovoltaic cells and electrical connectors.

[0069] Photovoltaic cells can be made of crystalline silicon, polycrystalline silicon, or perovskite. The electrodes of the photovoltaic cells are, for example, made with a silver metallization paste. The connectors are, for example, formed of a copper core coated with Sn62Pb36Ag2.

[0070] The recycling process makes it possible to recover the silver contained in these items. The recycling process comprises the following steps:

[0071] a) provide a photovoltaic panel,

[0072] b) remove the cables, junction box and metal frame of the photovoltaic panel,

[0073] c) perform a thermal, chemical and / or mechanical treatment to remove the polymer layer encapsulating the photovoltaic cells and electrical connectors,

[0074] d) grind the silver-containing elements (photovoltaic cells and / or electrical connectors) so as to form silver-containing particles,

[0075] e) preferably, carry out a desaluminization step under mild conditions in a moderately acidic solution (pH between 1 and 4), containing at least one acid, thereby dissolving the aluminum present in the particles,

[0076] f) recovery of the silver contained in the particles, according to the following successive steps:

[0077] i) immersing particles containing silver in a solution comprising a deep eutectic solvent and a redox mediator, thereby forming silver ions in solution,

[0078] ii) separate the particles from the solution containing the silver ions,

[0079] iii) carry out an electrolysis of the solution, thereby simultaneously reducing the silver ions to the form of metallic silver and regenerating the redox mediator.

[0080] The process is described more specifically for a photovoltaic panel, but several photovoltaic panels could be treated simultaneously.

[0081] Steps b) and c) allow the photovoltaic cells and the silver-containing electrical connectors to be separated and decoupled from the other elements of the photovoltaic panel. Once the photovoltaic cells are decoupled, they are advantageously disconnected from each other and, optionally, from the non-silver-containing electrical connectors.

[0082] Following steps b) and c), the elements of interest from the photovoltaic panel were recovered.

[0083] In step d), a powder is formed consisting of particles containing silver. The silver is in solid form. The particles can have different dimensions depending on the chosen grinding conditions. They will nevertheless be small enough to have a large specific surface area and to dissolve more easily in the dissolving solution. Advantageously, they will be less than 1 centimeter in size. Size corresponds to the largest dimension of the particle, generally the diameter or the length.

[0084] Step e) removes the aluminum from the particles. To do this, the ground material is immersed in an acidic solution, having a pH ranging from 0 to 4, to dissolve the aluminum present in the photovoltaic cell and separate it from the ground material. The solid / liquid ratio is between 1% and 45%, and preferably between 1% and 30%. This ratio is denoted S / L. Preferably, the S / L ratio is on the order of 10%. By 10%, we mean 10% ± 1%. The solid phase corresponds to the aluminum to be dissolved. The liquid phase corresponds to the acidic solution. This ratio corresponds to the mass of solid, in grams, divided by the volume of the solution, in milliliters. Thus, a S / L ratio between 1% and 30% corresponds to a mass concentration of the metal oxide in the acidic solution between 0.01 g / mL and 0.3 g / mL. For S / L values ​​below 1%, the dissolution yield is also high.However, the amount of acid used is considerably high compared to the amount of metal to be dissolved, and the amount of reagents lost is significant. The temperature of the acid solution is advantageously between 15°C and 80°C, and preferably between 15°C and 40°C. For example, it is around 25°C to minimize toxicity and reduce the energy consumption of the process. Silver. is not, or only very slightly, dissolved in the acidic solution. The dissolution of silver is considered negligible at this stage.

[0085] During step e), the acid or acids used are preferably chosen from mineral acids, in particular sulfuric acid and hydrochloric acid.

[0086] A control system can be implemented to maintain the pH between 1 and 4.

[0087] This treatment makes it possible to dealuminize the powder of particles and thus improve the purity of the product obtained.

[0088] In step f), the particles are treated with a solution comprising a deep eutectic solvent and a redox mediator. This step leads to the dissolution of the silver, while avoiding the emission of gas (flammability, volatility) and / or degradation of the solution.

[0089] In general, DES can be grouped into 4 different families:

[0090] - Type I: Quaternary salt + Metal chloride

[0091] - Type II: Quaternary salt + Hydrated metal chloride

[0092] - Type III: Quaternary salt + Hydrogen bond donor

[0093] - Type IV: Hydrated metal chloride + Hydrogen bond donor

[0094] Deep eutectic solvents are, for example, based on mixtures of quaternary ammonium salts with hydrogen bond donors such as amines and carboxylic acids.

[0095] Advantageously, DES is formed from choline chloride in association with a hydrogen bond donor, advantageously of very low toxicity, such as glycerol, ethylene glycol, or urea. Such DES are non-toxic and obtained at very low cost.

[0096] Preferably, the DES cation is stable up to a cathodic potential sufficiently high to allow for electrochemical silver deposition. Its association meets the requirements for thermal (> 200 °C) and chemical (no hydrolysis) stability. It is liquid at or near room temperature (< 100 °C) with numerous associations.

[0097] According to an advantageous embodiment, DES is a natural deep eutectic solvent (or NADES for "Natural Deep Eutectic Solvents"). It is a subcategory of DES based on natural products that can be established; they are named for being prepared by mixing natural constituents. These mixtures include organic acids, sugars, choline, urea, and amino acids.

[0098] The solution may contain one or more redox mediators (for example, two redox mediators). A redox mediator is defined as an ion in solution capable of being reduced during the dissolution step and oxidized during electrolysis.

[0099] The redox mediator is advantageously Mn₂₇Mn³⁺, Co₂₇Co³⁺, Cr₂₇Cr³⁺, Cr₃₇Cr⁶⁺, V₂₇V³⁺, V₄₇V⁵⁺, Sn₂₇Sn⁴⁺, Ag₇Ag²⁺, Cu₇Cu²⁺, Ru₄₇Ru⁸⁺, C₁₇C₁³, Br₂ / Br, I₂ / I₃, or Fe₂₇Fe³⁺, and advantageously with Fe₂₇Fe³⁺ and / or Cu₇Cu²⁺. The redox mediator may be alone or in a mixture. These redox mediators are soluble in both their oxidation states, are non-toxic, do not degrade DES, and have suitable redox potentials.

[0100] Preferably, the redox mediator is a metal salt dissolved in solution. The metal salt is preferably an iron(III) salt, for example FeCl3, or a copper(II) salt, such as copper(II) sulfate.

[0101] These redox mediators have suitable redox potentials. By suitable, we mean that the redox potentials of the couples are sufficiently high. These redox mediators do not deposit with the silver during electrodeposition. They remain in solution, which allows for complete recovery of the silver in its pure form.

[0102] The introduction of the dealuminized powder into the DES results in the immediate dissolution of the silver by a redox mechanism with the mediator. The dissolution step is carried out at a temperature between 15°C and 80°C, and preferably between 15°C and 40°C, for example at room temperature, i.e., around 25°C. Advantageously, no thermal energy input is required to dissolve the silver. However, increasing the temperature can advantageously be done to improve the dissolution rate without degrading the medium (for temperatures between 15 and 80°C).

[0103] The solid / liquid ratio during the dissolution of silver is between 1% and 45%, and preferably between 1% and 30%. Preferably, this ratio is on the order of 10%. By 10%, we mean 10% ± 1%. The solid phase corresponds to the silver. The liquid phase corresponds to the solution.

[0104] Optionally, the solution may include a drying agent and / or an agent that promotes mass transport (viscosity, ionic conductivity). For example, this could be water. The percentage of water relative to the DES is advantageously less than 50 mol%, and preferably on the order of 10 mol%.

[0105] After the silver metal dissolves, the powder is extracted from the bath by solid / liquid separation, and the silver is recovered and the redox mediator regenerated by electrolysis. At the negative electrode, the silver is deposited in metallic form onto a substrate, which can be stainless steel, carbon, titanium, noble metals, or a silver electrode. Simultaneously, the redox mediator is oxidized and regenerated at the positive electrode. The electrode can be steel, carbon, or a noble metal electrode. The solution is then ready for further treatment.

[0106] The electrolysis step allows simultaneously the recovery of silver in metallic form and the regeneration of the medium (unit step).

[0107] The solution containing the DES and the regenerated redox mediator can then be used for a new treatment cycle.

[0108] Preferably, steps i) to iii) are carried out in air, at ambient pressure (1 bar) and / or at ambient temperature (25°C).

[0109] Illustrative and non-limiting examples of an embodiment j.

[0110] Test 1: Treatment of a silicon cell containing silver in DES - Ethalin medium with 0.5M iron and at 80°C

[0111] Silver is in contact with silicon. The treatment is carried out in an ethaline medium. (Choline chloride and ethylene glycol in a 1:2 molar ratio) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.5 mol / L*. A cell sample is immersed in the DES bath under agitation at 400 rpm. After treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 12.7 mg / cm² / h*.

[0112] Test 2: Treatment of a silicon cell containing silver in DES - Ethalin medium with 0.5M iron and at 23 °C

[0113] Silver is placed in contact with silicon. The treatment is carried out in Ethalin medium (choline chloride ethylene glycol with a molar ratio of 1:2) at 23 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.5 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 2.3 mg·cm²·h⁻¹.

[0114] Test 3: Treatment of a silicon cell containing silver in DES - Ethalin medium with 0.1 M iron and at 80°C

[0115] Silver is placed in contact with silicon. The treatment is carried out in Ethalin medium (choline chloride ethylene glycol with a molar ratio of 1:2) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.1 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 25.9 mg·cm²·h⁻¹.

[0116] Test 4: Treatment of a silicon cell containing silver in DES - Ethalin (1 / 3) medium with 0.5M iron and at 80°C

[0117] Silver is placed in contact with silicon. The treatment is carried out in Ethalin medium (choline chloride ethylene glycol with a molar ratio of 1 to 3) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.5 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 7.6 mg·cm²·h⁻¹.

[0118] Test 5: Treatment of a silicon cell containing silver in DES-Oxaline medium with 0.5 M iron and at 80°C

[0119] Silver is placed in contact with silicon. The treatment is carried out in Ethalin medium (equimolar choline chloride and oxalic acid dihydrate) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.5 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 4.7 mg·cm²·h⁻¹.

[0120] Test 6: Treatment of a silicon cell containing silver in DES-Reline medium with 0.5 M iron and at 80°C

[0121] Silver is placed in contact with silicon. The treatment is carried out in an ethalin medium (choline chloride and urea in a 1:2 ratio) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.5 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 11.9 mg·cm²·h⁻¹.

[0122] Test 7: Treatment of a silicon cell containing silver in DES - Ethalin medium with 0.2 M iron and at 80°C

[0123] Silver is placed in contact with silicon. The treatment is carried out in Ethalin medium (choline chloride and ethylene glycol in a 1:2 molar ratio) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.2 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 50 mg·cm²·h⁻¹.

[0124] Electrochemical recovery test after treatment of a silicon cell containing silver in DES-Ethaline medium with iron at 80°C and 0.2 M

[0125] Silver is placed in contact with silicon. The treatment is carried out in an Ethalin medium (choline chloride and ethylene glycol in a 1:2 molar ratio) at 80 °C for 2 hours, with a volume of 2.5 mL of DES. Ferric salt FeCl3·6H2O is introduced at a concentration of 0.2 mol·L⁻¹. A cell sample is immersed in the DES bath under stirring at 400 rpm. After the treatment, an elemental chemical analysis is performed to determine the amount of silver in solution. It is noted that 100% of the silver is dissolved at a rate of 50 mg·cm⁻¹.

[0126] Following this, an electrochemical potential scan is performed to define the potential range suitable for silver recovery ([Fig. 1]). Selective silver deposition can be achieved in the vicinity of -0.6 V vs. Fe2+ / 3+. A deposit is therefore made at this potential, by potentiostatic holding, at 400 rpm and 80°C. After 2 hours of treatment, the deposit is dissolved, and ICP analysis confirms the exclusive silver deposition. ANNEXES

[0127] [1] Xu, XH and CL Hussey, Electrodeposition of Silver on Metallic and Nonmetallic Electrodes from the Acidic Aluminum Chloride-1 -Methyl-3-Ethylimidazolium Chloride Molten-Salt. Journal of the Electrochemical Society, 1992. 139(5): p. 1295-1300.

[0128] [2] Abbott, AP, et al., Electroless deposition of metallic silver from a choline chloride-based ionic liquid: a study using acoustic impédance spectroscopy, SEM and atomic force microscopy. Physical Chemistry Chemical Physics, 2007. 9(28): p. 3735-3743.

[0129] [3] Whitehead, J.A., et al., Application of l-alkyl-3-methyl-imidazolium ionic liquids in the oxidative leaching of sulphidic copper, gold and silver ores. Hydrometallurgy, 2007. 88(1-4): p. 109-120.

[0130] [4] Dong, T.G., et al., Eeaching of chalcopyrite with Bronsted acidic ionic liquid. Hydrometallurgy, 2009. 99(1-2): p. 33-38.

[0131] [5] EP 3178576

Claims

Demands

1. A process for recovering silver contained in particles, for example from a photovoltaic cell grind, the process comprising the following successive steps: i) immersing silver-containing particles in a solution comprising a deep eutectic solvent, water and a redox mediator, thereby forming silver ions in solution, the deep eutectic solvent being formed from choline chloride and ethylene glycol, ii) separating the particles from the solution containing the silver ions, iii) carrying out electrolysis of the solution, thereby reducing the silver ions and regenerating the redox mediator.

2. A method according to claim 1, characterized in that steps i), ii) and iii) are carried out in air and at a temperature between 20°C and 100°C, preferably between 20°C and 80°C.

3. 3. A method according to any one of the preceding claims, characterized in that the redox mediator has a concentration between 0.1 and 2 mol / L, preferably between 0.1 and 0.5 mol / L.

4. 4. A process according to any one of the preceding claims, characterized in that the redox mediator is selected from iron, manganese, cobalt, chromium, vanadium, tin, silver, copper, ruthenium, chlorine, bromine and iodine.

5. 5. A process according to any one of the preceding claims, characterized in that the redox mediator is an iron (III) salt or a copper (II) salt, or a mixture thereof.

6. A method according to any one of the preceding claims, characterized in that the particles are derived from a ground-up of crystalline silicon or polycrystalline silicon photovoltaic cells.

7. A process according to any one of the preceding claims, characterized in that the molar percentage of water relative to the deep eutectic solvent is less than 50%.

8. A method according to any one of the preceding claims, characterized in that, prior to step i), the method further comprises the following steps: a) providing a photovoltaic panel comprising cables, a junction box, a metal frame, photovoltaic cells encapsulated in a polymer layer and electrical connectors, b) remove the cables, junction box and metal frame of the photovoltaic panel, c) perform a thermal, chemical and / or mechanical treatment to remove the polymer layer encapsulating the photovoltaic cells, d) grind the photovoltaic cells and / or electrical connectors, so as to form particles containing silver, e) carry out a desaluminization step on the particles containing silver, the desaluminization step being carried out in an acidic solution at a pH between 1 and 4.

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