PROCESS FOR RECOVERING INDIUM FROM A SUBTRATE COMPRISING INDIUM-TIN OXIDE AND A METAL LAYER BY GREEN CHEMISTRY

Abstract

A method for recovering indium contained in a substrate comprising an indium-tin oxide film locally covered by a metallic layer, made of silver or a platinum group metal, the method comprising a dissolution step during which the substrate is immersed in a dissolution solution comprising a deep eutectic solvent chosen from relin, malin and oxaline, whereby the indium-tin oxide is selectively dissolved, the dissolution of the indium-tin oxide leading to the release of the metallic layer. Figure for the abstract: 1B.

Description

Title of the invention: METHOD FOR RECOVERING INDIUM FROM A SUBTRATE COMPRISING INDIUM TIN OXIDE AND A METAL LAYER BY GREEN CHEMISTRY Technical field

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

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

[0003] The invention is particularly interesting since it makes it possible to recover the indium present in photovoltaic cells by means of green chemistry. STATE OF THE PRIOR ART

[0004] 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] Photovoltaic panels generally comprise several photovoltaic cells coated in a polymer, the whole being arranged between two plates, for example made of glass. Existing photovoltaic cells may, for example, be made of silicon. By way of illustration and not limitation, a heterojunction silicon cell (HJT) may comprise a monocrystalline silicon substrate covered, on both sides, by layers of amorphous silicon (P and N+). These layers are themselves covered with the transparent conductive oxide (TCO) film and then by a conductive grid.

[0006] Thus, a photovoltaic module with silicon photovoltaic cells is therefore 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 part of the total mass of the photovoltaic panel.

[0007] The minimum recovery and recycling objectives are therefore easily achieved by the recovery of the glass and the aluminum frame alone.

[0008] Current processes focus on the dismantling of modules by chemical or thermal means and then on the recycling of the different elements using methods specialized reprocessing.

[0009] Silver represents the metal constituting the highest added value (nearly 90% of the value of the cell). This is why silver recovery represents a major challenge for the sustainability of the recycling sector.

[0010] It is also interesting to recover the silicon plates and the metals from the conductive transparent oxide layers.

[0011] For this, conventionally, the photovoltaic cells of the photovoltaic modules are chemically treated by total dissolution of the metallic elements (Cu, Ag, Sn, Pb, Al, etc.), the anti-reflectors and the n-doped layer to recover the silicon. The dissolution can be carried out in treatment baths composed of various acids (for example, HF, HNO3, H2SO4) concentrated alone or in a mixture and often brought to a boil.

[0012] For example, document CN 102 343 352 A describes a multi-step process for recovering silicon wafers without damaging the anti-reflective layer or the PN junction. The process is divided into several steps. First, organic solvents such as ethanol, acetone or isopropyl alcohol are used to dissolve the organic part of the metallization and thus separate it from the silicon wafer. This step can be carried out under ultrasound. Next, nitric acid (concentration of 50 to 65% by mass) or sulfuric acid (concentration of 70 to 98% by mass) is used to remove the remaining metal and glass residues. Then hydrochloric acid is used to remove the metal ions. Finally, a final cleaning with hydrofluoric acid removes the remaining silicon oxide. Between each step, the cells are rinsed with water. Thus, the silicon wafer can be recycled.

[0013] Document US 2011 / 0083972 A1 describes an electrolytic process for recycling active elements, specifically aimed at removing the transparent conductive oxide coating, for example indium tin oxide (or ITO for 'indium tin oxide'). The substrate is immersed in an acidic (hydrochloric acid or sulfuric acid) or basic (sodium hydroxide or potassium hydroxide) bath. It is connected to a DC power source, on which a voltage is applied so that it acts as a cathode (negative electrode). The cathodic potential generates protons which cause the layer to dissolve. The system is closed with an anode immersed in the solution which is connected to the power source. This electrolytic process is not concerned with the recovery of silver.

[0014] However, these processes have many drawbacks, in particular due to the nature of the chemical baths and the complexity of the processes (numerous stages).

[0015] This is why the most recent work uses ionic liquids to dissolve and / or recover the elements.

[0016] Recently, it has been demonstrated that it is possible to carry out the chemical dissolution and electrochemical recovery of silver in ionic liquids in the presence of a redox mediator with a two-step process (EP 3178576 A1). In a first step, the silver is dissolved in a solution comprising an ionic liquid and a redox mediator. This solution ensures the chemical dissolution of the silver under atmospheric conditions (air). In a second step, the silver is recovered by electrolysis in metallic form. Simultaneously with the deposition of silver, the redox mediator is regenerated in the ionic liquid medium.

[0017] However, the process uses ionic liquids which are expensive and not biodegradable. In addition, this process does not disclose the recovery and valorization of indium.

[0018] Currently, the processes implemented for the recovery of silver are complex, expensive, reagent-intensive and / or dangerous and, consequently, induce a significant economic and environmental cost.

[0019] Thus, none of the current processes allows the recovery of silver and indium in a satisfactory manner. Statement of the invention

[0020] An aim of the present invention is to propose a method for recovering the indium present in a substrate containing indium-tin oxide and a metal layer made of a platinum group metal or silver, the substrate originating for example from a photovoltaic module to be recycled, the method having to be simple to implement, inexpensive and not requiring the use of a product toxic to the environment and / or to the health of the people implementing the method.

[0021] For this purpose, the present invention proposes a method for recovering the indium contained in a substrate comprising a film of indium-tin oxide locally covered by a metallic layer, made of silver or a platinum group metal, the method comprising a dissolution step during which the substrate is immersed in a dissolution solution comprising a deep eutectic solvent chosen from relin, malin and oxaline, whereby the indium-tin oxide is selectively dissolved, the dissolution of the indium-tin oxide leading to the release of the metallic layer.

[0022] The invention is fundamentally distinguished from the prior art by the use of deep eutectic solvents (or DES for "Deep Eutectic Solvents" in English). DES are solvents formed by mixing two or more compounds in an exact proportion which corresponds to the eutectic point. Most of these solvents are liquid at room temperature, which facilitates their use. DES are non- volatile, non-flammable and chemically stable at temperatures up to 200°C.

[0023] The synthesis of DES is easy and clean compared to that of ionic liquids which require several stages of chemical synthesis and purification. DES are obtained by simply mixing the products composing the DES in the right proportions, possibly with heating of the mixture, until a homogeneous and transparent liquid is obtained. DES are formed from a couple comprising a hydrogen bond donor and an acceptor of this bond.

[0024] The preparation of the solvents does not require any chemical reaction and, therefore, the production yield is 100%. It is a simple mixing of the products composing the DES in the right proportion with heating, until a homogeneous and transparent liquid is obtained.

[0025] DESs make it possible to dissolve the indium-tin oxide layer and recover the metal layer in solid form using green chemistry, unlike processes using ionic liquids.

[0026] According to a particularly advantageous embodiment, the deep eutectic solvent is oxaline.

[0027] Advantageously, the dissolution step is carried out at a temperature between 20°C and 120°C, and preferably between 50°C and 80°C.

[0028] Advantageously, the solid liquid ratio is between 1 and 40%, and preferably between 10% and 20%.

[0029] Advantageously, the dissolving solution further comprises water, the molar percentage of water relative to the deep eutectic solvent preferably being less than 50%.

[0030] According to a particularly advantageous embodiment, the metallic layer is silver.

[0031] Advantageously, the substrate further comprises a support, the indium-tin oxide film being arranged between the support and the metal layer, the support containing silicon or copper, indium and gallium selenide (CIGS).

[0032] Advantageously, the substrate is a photovoltaic cell or photovoltaic cell waste, for example a heterojunction cell or a CIGS cell. The metal layer, preferably silver, forms the current collectors. The method makes it possible to selectively dissolve the ITO layer of the photovoltaic cell, for example a heterojunction silicon cell (HJT), which separates the collectors from the body of the silicon cell, without dissolving elements other than the transparent conductive oxide layer of indium-tin oxide.

[0033] The process avoids non-selective dissolution of the elements and the use of concentrated and dangerous acids. Furthermore, this dissolution is carried out in a green solvent. which accepts numerous treatment cycles, increasing the economic and environmental benefits. This approach limits reagent consumption, avoids the use of various concentrated acids and reduces the number of steps.

[0034] According to an advantageous embodiment, the method comprises the following steps:

[0035] a) providing a photovoltaic panel comprising cables, a junction box, a metal frame, photovoltaic cells encapsulated in a polymer layer and electrical connectors,

[0036] b) remove the cables, the junction box and the metal frame of the photovoltaic panel,

[0037] c) carrying out a thermal, chemical and / or mechanical treatment to remove the polymer layer encapsulating the photovoltaic cells,

[0038] d) recovering the photovoltaic cells, the photovoltaic cells forming a substrate containing a film of indium tin oxide locally covered by a metallic layer, preferably silver,

[0039] e) implementing the indium recovery step as defined previously.

[0040] Advantageously, after the dissolution step, the method comprises a subsequent step during which the tin is recovered by, for example, implementing a first step of electrodeposition of the tin and then the indium is recovered by, for example, implementing a second step of electrodeposition of the indium.

[0041] The process has many advantages:

[0042] - the method does not require the use of an acid solution or ionic liquid,

[0043] - the use of DES (and its possible reuse) makes it possible to eliminate the steps of solvent treatment, which reduces costs,

[0044] - DES are biodegradable, which reduces the constraints linked to standards of safety and / or environmental,

[0045] - the process does not release harmful gases and does not degrade the reaction medium,

[0046] - the process can be carried out under atmospheric conditions (in air),

[0047] - the process can be carried out at room temperature (typically 25°C), which avoids the supply of thermal energy,

[0048] - DESs are inexpensive solvents, which reduces process costs,

[0049] - DES are easy to prepare and can therefore be prepared in situ,

[0050] - the silver is not dissolved and is thus easily recoverable.

[0051] Other characteristics and advantages of the invention will emerge from the additional description which follows.

[0052] It goes without saying that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject. Brief description of the drawings

[0053] The present invention will be better understood upon reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0054] [Fig.lA]

[0055] [Fig.lB]

[0056] [Fig.lC] are photographic images of a plate of a heterojunction cell (HJT), respectively, before, during and after treatment in Oxaline according to a particular embodiment of the invention.

[0057] [Fig.2] is a snapshot obtained using a scanning electron microscope on a plate of an HJT photovoltaic cell, before treatment in Oxaline.

[0058] [Fig.3] is EDX spectrum obtained on a plate of an HJT photovoltaic cell, before treatment in Oxaline; the EDX spectrum was carried out in the box of [Fig.2],

[0059] [Fig.4] is a snapshot obtained using a scanning electron microscope on a plate of an HJT photovoltaic cell, after treatment in Oxaline, according to another particular embodiment of the invention.

[0060] [Fig.5] is an EDX spectrum obtained on a plate of an HJT photovoltaic cell, after treatment in Oxaline, according to another particular embodiment of the invention; the EDX spectrum was carried out at the level of the area framed in [Fig.4].

[0061] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0062] Subsequently, even if the description refers to the recovery of photovoltaic panels or modules; the invention can be transposed to other substrates containing indium-tin oxide and a metallic layer of silver or a platinum group metal (PGM).

[0063] The process for recycling a photovoltaic panel to recover indium comprises the following steps:

[0064] a) provide a photovoltaic panel,

[0065] b) remove the cables, the junction box and the metal frame of the photovoltaic panel,

[0066] c) carrying out a thermal, chemical and / or mechanical treatment to remove the polymer layer encapsulating the photovoltaic cells and the electrical connectors,

[0067] d) recovering the photovoltaic cells, the photovoltaic cells forming a substrate containing a film of indium-tin oxide covered locally by a metallic layer, and more particularly by a layer containing silver,

[0068] e) implementing an indium recovery step.

[0069] The photovoltaic panel to be recycled includes cables, a junction box and a metal frame, a polymer layer (typically ethyl vinyl acetate (EVA)), electrical connectors and photovoltaic cells.

[0070] The method is more particularly described for a photovoltaic panel but several photovoltaic panels could be treated simultaneously.

[0071] The photovoltaic cell comprises a substrate with various recoverable elements. In particular, the substrate may successively comprise a support, a transparent conductive oxide (TCO) film, and a metallization layer partially covering the TCO. The TCO film is thus accessible for etching.

[0072] Hereinafter, we will describe more particularly a substrate comprising a support, a transparent conductive oxide film and a metal layer. However, the method can also be implemented for a substrate formed from a transparent conductive film and a metal layer.

[0073] The photovoltaic cells can be made of crystalline silicon, polycrystalline silicon, CIGS or even perovskite.

[0074] A heterojunction cell (HJT) will preferably be chosen.

[0075] By way of illustration and not limitation, the HJT cell may comprise a monocrystalline silicon substrate covered, on both sides, by layers of amorphous silicon (P and N+). The amorphous silicon layers may have a thickness of around ten nanometers. These layers are themselves covered with the conductive transparent oxide film and then by a conductive grid.

[0076] In the context of the invention, the TCO film is an indium-tin oxide (or ITO for “Indium Tin Oxide”) film. LTTO comprises, for example, 97% indium oxide (In2O3) and 3% tin oxide SnO2.

[0077] The metallization layer forms a conductive grid.

[0078] The metallization layer is a metallic layer made of a metal from the group of platinum or silver.

[0079] The platinum group metal is selected from ruthenium, rhodium, palladium, osmium, iridium and platinum. Preferably, it is platinum.

[0080] Preferably, the metal layer is silver. The metal layer contains at least 0.01% by mass of silver of the total mass, and preferably at least 0.035% by mass of silver.

[0081] The metallic layer may be made of pure silver (i.e. the layer contains at least 99% silver). It is, for example, made with a silver metallization paste.

[0082] Alternatively, it may contain one or more other elements, for example, selected from lead, tin and copper. The connectors are, for example, formed from a copper core coated with Sn62Pb36Ag2.

[0083] Steps b) and c) make it possible to separate and detach the photovoltaic cells. as well as the electrical connectors containing silver from the other elements of the photovoltaic panel. Once the photovoltaic cells are separated, they are advantageously disconnected from each other and, possibly, from the electrical connectors not containing silver.

[0084] At the end of steps b) and c), the elements of interest of the photovoltaic panel have been separated.

[0085] The photovoltaic cells are thus recovered (step d).

[0086] Each photovoltaic cell represents a substrate containing indium and silver to be recovered during step e).

[0087] In step e), a dissolution step is carried out during which the substrate is immersed in a dissolution solution. The dissolution solution comprises a deep eutectic solvent chosen from relin, malin and oxalin.

[0088] Generally speaking, DESs can be grouped according to IV different families:

[0089] - Type I: Quaternary salt + Metal chloride

[0090] - Type II: Quaternary salt + Hydrated metal chloride

[0091] - Type III: Quaternary salt + Hydrogen bond donor

[0092] - Type IV: Hydrated metal chloride + Hydrogen bond donor

[0093] Deep eutectic solvents are, for example, based on mixtures of quaternary ammonium salts with hydrogen bond donors such as amines and carboxylic acids.

[0094] Advantageously, the DES is choline chloride in association with an H-bond donor of very low toxicity, such as glycerol, ethylene glycol or urea, which guarantees a non-toxic and very low-cost DES.

[0095] Preferably, DES meets the requirements of thermal (> 200 °C) and chemical (no hydrolysis) stability. It is liquid at room temperature or near it (< 100 °C) with many associations.

[0096] According to an advantageous embodiment variant, the DES is a natural deep eutectic solvent (or NADES for "Natural Deep Eutectic Solvents"). This is a subcategory of DES based on natural products that can be established, they have the name being prepared by mixing natural constituents. We will find mixtures of the type organic acids, sugars, choline, urea, amino acids.

[0097] Acids such as oxalic acid, carboxylic acid, malonic acid, urea, phenylpropionic acid are preferred as hydrogen bond donors (HDB). They will advantageously be associated with a hydrogen bond acceptor (HBD) which may be a quaternary ammonium and more generally choline chloride (ChCl). The Oxaline system will be preferred, which is the ChCl / Oxalic acid mixture in a 1:1 proportion. The latter has excellent solubility for TITO.

[0098] Introduction of the substrate into the DES results in immediate dissolution of the oxide transparent conductor.

[0099] This step avoids the emission of gas (flammability, volatility) and / or the degradation of the solution.

[0100] 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. of the order of 25°C. There is, advantageously, no need to supply thermal energy to dissolve the TCO. However, an increase in temperature may advantageously be carried out to improve the dissolution rate without degradation of the medium (for temperatures between 15 and 80°C).

[0101] The solid / liquid ratio is between 1% and 45%, and preferably, the solid / liquid ratio is between 1% and 30%. This ratio is noted S / L. Preferably, the S / L ratio is of the order of 10%. By 10%, we mean 10%±1%. The solid phase corresponds to the quantity of material used during step e). The liquid phase corresponds to the deep eutectic solvent. This ratio corresponds to the mass of solid, in grams, divided by the volume of the solution, in milliliters. Thus, an S / L ratio between 1% and 30% corresponds to a mass concentration of the metal oxide in the acid solution between 0.01 g / mL and 0.3 g / mL. For S / L values ​​less than 1%, the dissolution efficiency 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 substantial.

[0102] Silver is not dissolved or is very little dissolved in the dissolution solution. The dissolution of silver is considered negligible during this step. The same applies to a platinum group metal.

[0103] Optionally, the solution may further comprise an additive. For example, it may be a drying agent, and / or an agent promoting the transport of matter (viscosity, ionic conductivity).

[0104] For example, the material transport promoting agent may be water. The percentage of water relative to the DES is advantageously less than 50 mol%, and preferably of the order of 10 mol%.

[0105] According to another embodiment variant, the additive may be gamma-butyrolactone.

[0106] The dissolution step may be carried out with stirring.

[0107] After dissolving the indium, the silver layer, in solid form, can also be easily extracted from the dissolution solution.

[0108] The tin dissolved in solution can be recovered, for example by a first electrodeposition step.

[0109] The indium dissolved in solution can be recovered by a second electrodeposition step.

[0110] Advantageously, the tin will be recovered first, then the indium.

[0111] A person skilled in the art may choose different separation / recovery techniques depending on the elements. For example, he may choose to implement: an ionic flotation step, screening, electrostatic separation, screening, liquid / liquid extraction with the use of a DES-insoluble solvent, more specifically solvents with low polarities, precipitation or even a zinc cementation step.

[0112] The dissolution solution can then be used for a new treatment cycle.

[0113] Alternatively, several substrates can be successively treated in the dissolution solution before carrying out the electrodeposition steps.

[0114] Illustrative and non-limiting examples of embodiments: Test 1: Dissolution of ITO in DES medium:

[0115] Dissolution tests were carried out for four DES: Reline, Maline, Ethaline and Oxaline. Dissolution is carried out at 70 °C. Unlike acidic aqueous media, this temperature is not restrictive with regard to the release of harmful species. The treatment duration is 24 hours with a solid / liquid ratio of 10%, with a mass of ITO powder (In2O3, SnO2) of 543 mg.

[0116] The following table lists the maximum concentrations of dissolved indium and tin from ITO for different DESs. The target concentration is a theoretical objective that assumes the treatment of HJT cells with a ratio of 15%.

[0117] Very significant dissolution is observed in Reline medium, in Maline medium and in Oxaline medium.

[0118] On the other hand, no dissolution of indium was observed for the Ethaline medium.

[0119] These results demonstrate the excellent solubility of the transparent layer in certain DES. The results with oxaline are remarkable.

[0120] It was possible to achieve:

[0121] - in Reline medium, the successive treatment of 10 batches of HJT cells,

[0122] - in Maline medium, the successive treatment of 45 batches of HJT cells,

[0123] - in Oxaline medium, the successive treatment of 149 batches of HJT cells. [Table 1] DES Nature Dissolved concentration (g / L) Target concentration for a HJT cell with S / L=15% (g / L) In Sn In Sn Reline (ChClAJrée) 1:2 4.2 8.7 0.420 0.167 Ethaline (ChCl / Ethylene Glycol) 1:2 0 8.5 0.420 0.167 Mali ne (ChCl / Mal onic acid) 1:1 19.3 8.6 0.420 0.167 Oxali ne (ChCl / Oxalic acid) 1:1 62.7 8.6 0.420 0.167

[0124] Test 2: Treatment of an HJT cell in DES medium - Oxaline:

[0125] The selective dissolution of 1TTO disposed between the silicon and the connectors in silver of HJT cells was studied. The treatment is carried out in Oxaline medium at 70 °C for 4 hours, with a volume of 10 mL of DES. A piece of HJT cell is immersed in the DES bath while stirring at 300 rpm. Before treatment the piece is intact ([Fig.lA]), during treatment we observe the detachment of the silver collectors ([Fig.lB]), and after treatment the absence of collectors ([Fig.lC]). The dissolution of the layer on which the silver rests causes the physical separation of silver and silicon. SEM-EDX measurements were carried out before and after treatment (Figures 2 to 4). Before treatment we measure the presence of indium (Figures 2 and 3), and its absence after treatment (Figures 4 and 5), which confirms the dissolution of 1TTO on the surface.

Claims

Claims

1. A method for recovering indium contained in a substrate comprising an indium-tin oxide film locally covered by a metallic layer, made of silver or a platinum group metal, the method comprising a dissolution step during which the substrate is immersed in a dissolution solution comprising a deep eutectic solvent chosen from relin, malin and oxaline, whereby the indium-tin oxide is selectively dissolved, the dissolution of the indium-tin oxide leading to the release of the metallic layer.

2. Method according to claim 2, characterized in that the deep eutectic solvent is oxaline.

3. Method according to one of claims 1 and 2, characterized in that the dissolution step is carried out at a temperature between 20°C and 120°C, and preferably between 50°C and 80°C.

4. Method according to any one of the preceding claims, characterized in that a solid liquid ratio is between 1 and 40%, and preferably between 10% and 20%.

5. A method according to any one of the preceding claims, characterized in that the dissolving solution further comprises water, the molar percentage of water relative to the deep eutectic solvent preferably being less than 50%.

6. Method according to any one of the preceding claims, characterized in that the metallic layer is silver.

7. A method according to any one of the preceding claims, characterized in that the substrate further comprises a support, the indium-tin oxide film being disposed between the support and the metal layer, the support further containing silicon or copper indium gallium selenide (CIGS).

8. A method according to any one of the preceding claims, characterized in that the substrate is a photovoltaic cell or photovoltaic cell waste, for example a heterojunction cell or a CIGS cell.

9. Method according to any one of the preceding claims, characterized in that it comprises the following steps: a) providing a photovoltaic panel comprising cables, a junction box, a metal frame, photovoltaic cells en- encapsulated in a polymer layer and electrical connectors, b) eliminate the cables, the junction box and the metal frame of the photovoltaic panel, c) carrying out a thermal, chemical and / or mechanical treatment to remove the polymer layer encapsulating the photovoltaic cells, d) recovering the photovoltaic cells, the photovoltaic cells forming a substrate containing a film of indium tin oxide covered locally by a metallic layer, preferably silver, e) implementing the indium recovery method as defined in one of claims 1 to 8.

10. Method according to any one of the preceding claims, characterized in that, after the dissolution step, the method comprises a subsequent step during which the tin is recovered by, for example, implementing a first step of electrodeposition of the tin and then the indium is recovered by, for example, implementing a second step of electrodeposition of the indium.

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