A method for directional extraction of silver in photovoltaic cells based on a deep eutectic solvent

Abstract

The present application relates to the technical field of green recycling of metal resources from waste photovoltaic modules, and particularly relates to a method for directional extraction of silver from photovoltaic cells based on a eutectic solvent. The method uses a eutectic solvent of tetramethylammonium chloride-lactic acid and a chlorosalt as a leaching agent to leach the pretreated photovoltaic cells. Through coordination of chloride ions and redox synergy, silver forms a stable complex. Subsequently, water is added to the leaching solution and the pH is adjusted to be acidic. After standing and filtering, silver chloride precipitates. Finally, the filtrate is evaporated to remove water, and the obtained leaching agent can be recycled. In the method, tetramethylammonium chloride provides chloride ions to form a complex with silver, and lactic acid acts as a hydrogen bond donor to adjust the structure and polarity of the solvent and optimize the silver dissolution environment. The present application replaces the traditional strong acid / alkali-strong oxidant system with a reaction system of tetramethylammonium chloride-lactic acid and an oxidizing agent, and realizes directional extraction of noble metal silver from retired crystalline silicon photovoltaic cells in a green and mild reaction system.

Description

Technical Field

[0001] This invention relates to the field of green recycling technology for metal resources from waste photovoltaic modules, specifically to a method for the targeted extraction of silver from photovoltaic cells based on a eutectic solvent. Background Technology

[0002] With the global energy structure transformation, the photovoltaic power generation industry has developed rapidly, and a large number of early-installed crystalline silicon photovoltaic modules are about to enter the retirement stage. Retired photovoltaic cells are rich in high-value-added elements such as silicon, silver, aluminum, and copper. Silver, mainly distributed on the conductive grid lines on the front of the cell, accounts for only about 0.05% to 0.15% of the total mass, but its economic value accounts for more than 40% of the total metal value of the module. Therefore, how to efficiently recover silver resources from the cells has become a key technological aspect in the recycling of retired photovoltaic modules.

[0003] Existing silver recovery processes mainly include pyrometallurgical methods, electrochemical methods, and chemical leaching methods. Pyrometallurgical methods separate the metal through high-temperature melting, but are energy-intensive and produce harmful gas emissions. Electrochemical methods rely on complex electrode systems, making large-scale application difficult. Chemical leaching offers advantages due to its mild reaction conditions, but traditional systems often use nitric acid, cyanide, or strong acids and alkalis, leading to equipment corrosion and secondary pollution. Furthermore, current silver extraction technologies from retired photovoltaic cells mostly involve the simultaneous leaching of aluminum and silver, and significant dissolution of the silicon matrix and other metals in the photovoltaic cells also occurs. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for the targeted extraction of silver from photovoltaic cells based on a eutectic solvent. Using a eutectic solvent (DES) and oxidant system as the leaching medium, silver undergoes complexation transformation under mild conditions through an ionic liquid system formed by hydrogen bond acceptors and donors. The chemical equilibrium of the system is then altered by adding water to achieve targeted precipitation and separation of silver. This method solves the problems of high energy consumption, heavy pollution, and low recovery rates associated with traditional silver recovery processes. The entire process is green and environmentally friendly, requiring no strong acids, strong oxidants, or toxic chemicals. The resulting solvent can be recycled, and both the silver leaching and precipitation rates are above 98%, achieving efficient and clean recovery of the precious metal silver and providing a new green process for the resource utilization of retired photovoltaic modules.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The purpose of this invention is to provide a method for the targeted extraction of silver from photovoltaic cells based on a eutectic solvent, comprising the following steps: S1. A mixture of a eutectic solvent and an oxidant is used as a leaching agent to leach photovoltaic cells. Through the synergistic effect of chloride ion coordination and redox reaction, silver forms a complex to obtain a leachate. The eutectic solvent is composed of tetramethylammonium chloride and lactic acid.

[0006] S2. Water is then added to the leachate to adjust the pH to 3-5, and a precipitation reaction is carried out to achieve the directional extraction of silver from the photovoltaic cells. The filtrate after the precipitation reaction is then evaporated to obtain the leachate.

[0007] In a preferred embodiment of the present invention, the eutectic solvent is obtained by mixing tetramethylammonium chloride and lactic acid in a molar ratio of 1:1 to 3, and the mixing temperature is 60°C to 90°C.

[0008] In a preferred embodiment of the present invention, the concentration of the oxidant in the leaching agent is 0.05 mol / L to 0.2 mol / L, and the oxidant is ferric chloride or copper dichloride.

[0009] In a preferred embodiment of the present invention, the mass-to-volume ratio of photovoltaic cell to leaching agent is 1g:50mL~100mL.

[0010] In a preferred embodiment of the present invention, the leaching temperature is 70℃~120℃ and the leaching time is 45min~100min.

[0011] In a preferred embodiment of the present invention, the volume ratio of water to leachate is 1 to 5:1.

[0012] In a preferred embodiment of the present invention, the pH is adjusted using at least one of nitric acid, hydrochloric acid, and sulfuric acid.

[0013] In a preferred embodiment of the present invention, the photovoltaic cell is a crystalline silicon cell obtained by pre-processing a retired crystalline silicon photovoltaic module. The crystalline silicon cell comprises the following components by mass percentage: 90.00%~91.50% silicon, 7.50%~9.00% aluminum, 0.30%~0.45% silver, and impurity elements, totaling 100%.

[0014] In a preferred embodiment of the present invention, the precipitation reaction time is 30 min to 120 min.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a method for the targeted extraction of silver from photovoltaic cells based on a eutectic solvent. A mixture of a eutectic solvent and an oxidant is used as the leaching agent to leach the photovoltaic cells. Through the synergistic effect of chloride ion coordination and redox reaction, silver forms a stable complex in the system, yielding a leachate and a filter residue. The eutectic solvent is composed of tetramethylammonium chloride and lactic acid. Water is then added to the leachate and the pH is adjusted to initiate a precipitation reaction, resulting in silver chloride precipitate and a filtrate, thus achieving the targeted extraction of silver from the photovoltaic cells. Finally, the filtrate is evaporated to obtain the leaching agent, which can be recycled. This invention utilizes a tetramethylammonium chloride / lactic acid system as a eutectic solvent to achieve efficient recovery of silver from decommissioned crystalline silicon solar cells. Tetramethylammonium chloride provides chloride ions to form a stable complex with silver for targeted extraction, while lactic acid acts as a hydrogen bond donor to adjust the solvent structure and polarity, optimizing the silver dissolution environment. Furthermore, it avoids the use of hazardous chemicals such as nitric acid and cyanide; the reaction system is non-toxic and biodegradable, significantly reducing the risk of environmental pollution. In addition, the extraction and precipitation of silver are carried out at low temperatures and normal pressures, requiring no complex equipment. The process is safe, controllable, and energy-efficient, making it suitable for large-scale applications.

[0016] 2. The method provided by this invention regulates the chemical equilibrium through chloride ion coordination and water addition disturbance, enabling the directional conversion of silver and the precipitation of high-purity silver chloride. The total silver recovery rate can reach over 98%, with selectivity superior to traditional chemical leaching methods. Furthermore, after the reaction, the eutectic solvent can be reused after treatment in a rotary evaporator, resulting in minimal solvent loss. The overall process is green, efficient, and low-cost, showing promising prospects for industrial application. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention.

[0018] Figure 2 The images show the SEM and EDS spectra of the AgCl product from Example 1 of this invention. Figure 2 Figure (a) is a SEM image, and Figure (b) is an EDS spectrum.

[0019] Figure 3 The image shows the XRD pattern of the AgCl product from Example 1 of this invention.

[0020] Figure 4 The images shown are SEM and EDS images of the photovoltaic silicon wafer before and after leaching in Example 1 of the present invention. Figure 4 Figure (a) shows the SEM morphology of the front side of the photovoltaic silicon wafer before leaching, Figure (b) shows the EDS distribution of Ag elements before leaching, Figure (c) shows the EDS surface distribution of Si elements before leaching, Figure (d) shows the SEM morphology of the front side of the photovoltaic silicon wafer after leaching, Figure (e) shows the EDS surface distribution of Ag elements after leaching, and Figure (f) shows the EDS surface distribution of Si elements after leaching. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0023] This invention provides a method for the directional extraction of silver from photovoltaic cells based on deep eutectic solvents (DES), such as... Figure 1 As shown, it includes the following steps: (1) The retired crystalline silicon solar cell was subjected to sample harmless pretreatment to obtain crystalline silicon solar cell: The aluminum frame and junction box of the retired crystalline silicon photovoltaic module were manually disassembled, and the ethylene-vinyl acetate copolymer (EVA) encapsulation layer and backsheet layer were removed by pyrolysis to separate the silicon wafer sample containing silver conductive grid lines; the sample was ultrasonically cleaned and dried with ethanol to obtain a clean solar cell sample to be processed.

[0024] (2) Tetramethylammonium chloride is mixed with lactic acid and stirred under heating conditions to form a uniform transparent liquid, thus obtaining the eutectic solvent DES; then chloride salt (oxidant) is added and fully dissolved to form DES leaching agent.

[0025] (3) Add the crystalline silicon solar cell sample obtained in step (1) to the DES leaching agent obtained in step (2), stir and leach under heating conditions, and after leaching, filter to obtain leaching liquid and filter residue.

[0026] (4) Add the leachate obtained in step (3) to deionized water and stir until precipitation is complete. Adjust the pH value to 3-5 during stirring. After the precipitation is complete at room temperature, filter to obtain silver chloride precipitate and filtrate.

[0027] (5) Remove the water from the filtrate obtained in step (4) by rotary evaporator, and the remaining leachate can be recycled.

[0028] It should be noted that the core concept of this invention lies in constructing a synergistic system of tetramethylammonium chloride-lactic acid eutectic solvent (DES) and chloride salts to achieve green, highly selective, and directional extraction of silver from retired crystalline silicon photovoltaic cells, replacing the traditional strong acid / strong alkali-strong oxidant system. During the extraction process, chloride ions complex with silver, and combined with the mild redox effect of the eutectic solvent system, silver is transformed from its metallic state into a soluble complex, achieving preferential dissolution of silver. Simultaneously, substrate elements such as silicon and aluminum, as well as trace impurities (such as tin and lead), are almost unaffected. Subsequently, by adding water to the leachate and adjusting it to acidity, the silver complex destabilizes and precipitates as silver chloride. The eutectic solvent in the filtrate can be recycled after evaporation, thus constructing a closed-loop green process. Compared with existing technologies, this invention has advantages such as being mild, environmentally friendly, highly selective, and allowing for the recycling of the leachate, effectively reducing corrosiveness and secondary pollution, while achieving efficient and directional recovery of precious metal silver from retired photovoltaic cells.

[0029] The aforementioned eutectic solvent, as a novel ionic liquid system, possesses advantages such as low vapor pressure, high designability, biodegradability, and environmental friendliness, attracting widespread attention in the field of waste metal recycling. Furthermore, the DES system containing halide anions can achieve selective dissolution of precious metals through chloride ion coordination and redox reactions, and the system is recyclable without the need for external strong acids or toxic oxidants, exhibiting both green and high-efficiency characteristics.

[0030] In step (1), the pretreated crystalline silicon solar cell is obtained through the following steps: first, the aluminum frame and junction box are disassembled manually, then the photovoltaic module is cut, and then the obtained sample is placed in a muffle furnace for heat treatment to remove EVA, thus obtaining the crystalline silicon solar cell; the obtained crystalline silicon solar cell is completely immersed in anhydrous ethanol to form a uniform impurity removal system, and the photovoltaic ribbon is placed in a 40Hz~60Hz ultrasonic cleaner for ultrasonic treatment for 30min~50min to ensure that impurities are thoroughly removed.

[0031] The crystalline silicon solar cells obtained from the pretreatment of retired crystalline silicon photovoltaic modules, by mass percentage, comprise the following components: 90.00%~91.50% silicon, 7.50%~9.00% aluminum, 0.30%~0.45% silver, and contain trace impurity elements (tin, lead), totaling 100%.

[0032] In step (2), a eutectic solvent is prepared by mixing tetramethylammonium chloride and lactic acid in a molar ratio of 1:1 to 3 and heating to 60°C to 90°C while stirring to form a uniform and transparent liquid. The preferred molar ratio is 1:2, and the preferred temperature is 80°C. In this invention, the tetramethylammonium chloride-lactic acid system is chosen to construct the eutectic solvent (DES) system mainly because tetramethylammonium chloride can provide abundant chloride ions, forming a stable complex with silver to achieve targeted extraction. Lactic acid, as a hydrogen bond donor, can adjust the solvent structure and polarity, optimize the dissolution environment of silver, and ensure that the system is mild, green, low-corrosion, and thermally stable, and can be recycled. Thus, while highly selectively extracting silver, it avoids the high corrosiveness and secondary pollution of traditional strong acid / strong alkali systems.

[0033] In step (3), the ratio of crystalline silicon solar cell to leaching agent is 1:50 g / mL to 100 g / mL, the leaching temperature is 70℃ to 120℃, the leaching time is 45 min to 100 min, and the chloride salt concentration in the leaching agent is 0.05 mol / L to 0.2 mol / L. The chloride salt is CuCl2, ferric chloride, etc., and is used as an oxidizing agent. The ratio of crystalline silicon solar cell to leaching agent, leaching temperature, leaching time, and chloride concentration in the leaching agent all directly affect the leaching efficiency and selectivity of silver. A suitable ratio (1:5 g / mL to 100 g / mL) ensures sufficient chloride ions and lactic acid in the DES system for adequate silver complexation, while also considering solvent economy. A temperature of 70℃ to 120℃ accelerates the redox and complexation reactions of silver without compromising the stability of the DES. A leaching time of 45 min to 100 min ensures complete silver dissolution while avoiding excessively long processing times and energy consumption. A chloride concentration of 0.05 mol / L to 0.2 mol / L provides sufficient Cl⁻ to form stable complexes and also acts as an oxidant to promote Ag⁻ leaching. 0 Convert to Ag + It maintains system selectivity and green circularity while achieving high leaching efficiency.

[0034] In step (3), the volume ratio of deionized water to leaching agent is 1~5:1.

[0035] In step (3), the pH is adjusted using one or more of nitric acid, hydrochloric acid, and sulfuric acid, preferably dilute nitric acid. The reason for adjusting the pH to 3-5 is to inhibit the secondary complexation and oxidation reactions of silver, and to promote the combination of silver ions and chloride ions to form pure silver chloride precipitate. The concentration of the dilute nitric acid is 3 mol / L.

[0036] In step (4), the precipitation reaction time at room temperature is 30 min to 120 min, and then silver chloride precipitate and filtrate are obtained by vacuum filtration device.

[0037] In step (5), the filtrate obtained in step (4) is dehydrated by a rotary evaporator at a temperature of 60°C for 45 minutes, thereby recycling the eutectic solvent and eliminating waste liquid discharge during the process.

[0038] This invention uses a combination of a eutectic solvent and a chloride salt as the leaching agent, and through the synergistic effect of chloride ion coordination and redox reaction, it removes silver (Ag) from the photovoltaic cell. 0 A stable metal complex is formed in the system, and the chemical equilibrium of the system is changed by adding water to induce the formation of silver chloride (AgCl) precipitate and achieve recovery.

[0039] The following specific examples will provide further explanation.

[0040] In this invention, the abbreviation for tetramethylammonium chloride is TMAC, and the abbreviation for eutectic solvent is DES.

[0041] Example 1 A method for targeted extraction of silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0042] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker. Place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES. Then, add CuCl2 oxidant with a concentration of 0.05 mol / L to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.05 mol / L CuCl2 in tetramethylammonium chloride and lactic acid (molar ratio 1:2).

[0043] S3. Weigh 0.2g of decommissioned crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 80℃ with magnetic stirring at 500rpm for 60min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product, thus achieving targeted extraction of silver from photovoltaic cells.

[0044] Example 2 A method for targeted extraction of silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0045] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker, place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES; then add 0.1 mol / L of oxidant CuCl2 to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.1 mol / L CuCl2 in tetramethylammonium chloride-lactic acid (molar ratio 1:2).

[0046] S3. Weigh 0.2g of decommissioned crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 100℃ with magnetic stirring at 500rpm for 60min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product, thus achieving the targeted extraction of silver from photovoltaic cells.

[0047] Example 3 A method for targeted extraction of silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0048] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker, place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES; then add 0.1 mol / L of oxidant CuCl2 to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.1 mol / L CuCl2 in tetramethylammonium chloride-lactic acid (molar ratio 1:2).

[0049] S2. Weigh 0.2g of decommissioned crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 120℃ with magnetic stirring at 500rpm for 60min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product, thus achieving the targeted extraction of silver from photovoltaic cells.

[0050] Example 4 A method for targeted extraction of silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0051] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker. Place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES. Then, add CuCl2 oxidant with a concentration of 0.05 mol / L to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.05 mol / L CuCl2 in tetramethylammonium chloride and lactic acid (molar ratio 1:2).

[0052] S3. Weigh 0.2g of decommissioned crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 100℃ with magnetic stirring at 500rpm for 90min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product, thus achieving the targeted extraction of silver from photovoltaic cells.

[0053] Comparative Example 1 A method for extracting silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0054] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker, place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES; then add 0.1 mol / L of oxidant CuCl2 to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.1 mol / L CuCl2 in tetramethylammonium chloride-lactic acid (molar ratio 1:2).

[0055] S3. Weigh 0.2g of retired crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 60℃ with magnetic stirring at 500rpm for 60min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product. Weighing the product shows that the amount of precipitate is small, and the solution color shows almost no significant change.

[0056] Comparative Example 2 A method for extracting silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0057] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker, place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES; then add 0.1 mol / L of oxidant CuCl2 to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.1 mol / L CuCl2 in tetramethylammonium chloride-lactic acid (molar ratio 1:2).

[0058] S2. Weigh 0.8g of retired crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:25). Leach at 60℃ with magnetic stirring at 500rpm for 60min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product. Weighing the product shows that the amount of precipitate is small, and the solution color shows almost no significant change.

[0059] Comparative Example 3 A method for extracting silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0060] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker, place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES; then add CuCl2 oxidant with a concentration of 0.3 mol / L to DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.3 mol / L CuCl2 in tetramethylammonium chloride-lactic acid (molar ratio 1:2).

[0061] S3. Weigh 0.2g of retired crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 80℃ with magnetic stirring at 500rpm for 60min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain the AgCl product.

[0062] Comparative Example 4 A method for extracting silver from photovoltaic cells based on a eutectic solvent includes the following steps: S1. First, the aluminum frame and junction box of the retired crystalline silicon photovoltaic module are manually disassembled. Then, the photovoltaic module is cut and placed in a muffle furnace for heat treatment at 500°C to remove EVA, thus obtaining crystalline silicon cells. The crystalline silicon cells are completely immersed in 50mL of anhydrous ethanol to form a uniform impurity removal system. Then, they are placed in a 40Hz ultrasonic cleaner for ultrasonic treatment for 30 minutes to ensure that impurities are completely removed, thus obtaining retired crystalline silicon photovoltaic cells.

[0063] S2. First, accurately weigh TMAC and lactic acid in a molar ratio of 1:2 into a beaker, place the beaker on a magnetic stirrer and heat and stir until a uniform and clear liquid is formed, thus obtaining DES; then add 0.1 mol / L of oxidant CuCl2 to the DES and continue stirring until fully dissolved to obtain a leaching agent containing 0.1 mol / L CuCl2 in tetramethylammonium chloride-lactic acid (molar ratio 1:2).

[0064] S3. Weigh 0.2g of retired crystalline silicon photovoltaic cells and dissolve them in 20mL of leaching agent (solid-liquid ratio 1:100). Leach at 80℃ with magnetic stirring at 500rpm for 30min. After leaching, cool to room temperature, add 40mL of deionized water to the leachate, stir at room temperature, and let stand for 60min until precipitation is complete. During stirring, add 3mol / L dilute nitric acid to adjust the pH to 5. After complete precipitation, filter, and wash and dry the precipitate to obtain AgCl product. Weighing the product shows that the amount of precipitate is small, and the solution color shows almost no significant change.

[0065] The silver content in the methods of Examples 1 to 4 and Comparative Examples 1 to 4 described above was calculated. The specific process is as follows:

[0066] S1. Dispose of waste photovoltaic silicon wafers in their original state: The original sample was ground evenly, and 0.1 g of the sample was accurately weighed and placed in a polytetrafluoroethylene digestion vessel. 6 mL of analytical grade nitric acid and 2 mL of analytical grade hydrofluoric acid were added as digestion solution. The vessel was sealed and placed in a microwave digestion apparatus. The temperature program was set to maintain the solution at 180℃ for 60 min to achieve complete matrix digestion. After the digestion vessel cooled to room temperature, the acid in the digestion solution was reduced to 1 mL. Finally, the digestion solution was transferred with 2 wt.%~5 wt.% dilute nitric acid and diluted to a 50 mL volumetric flask. After mixing, the silver content in the solution was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) to obtain the silver content (C0) in the original silicon wafer. 原样 ).

[0067] S2. Digest the leached waste photovoltaic silicon wafer samples: The dried leaching residue was ground evenly, and 0.1 g of sample was accurately weighed and placed in a polytetrafluoroethylene digestion vessel. 6 mL of high-purity nitric acid and 2 mL of high-purity hydrofluoric acid were added as digestion solution. The vessel was sealed and placed in a microwave digestion apparatus. The temperature program was set to maintain the solution at 180℃ for 60 min to achieve complete matrix digestion. After the digestion vessel cooled to room temperature, the acid in the digestion solution was reduced to 1 mL. Finally, the digestion solution was transferred with 2%–5% dilute nitric acid and diluted to a 50 mL volumetric flask. After mixing, the silver content in the solution was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) to obtain the silver content (C0) in the silicon wafer after leaching. 残余 ).

[0068] S3. Calculate the silver leaching rate η: η=(1−C 原样 / C 残余 )×100%.

[0069] Among them, C 原样 C represents the silver content in the original silicon wafer. 残余 This represents the silver content in the silicon wafer after leaching.

[0070] Table 1. Silver leaching rates of Examples 1-4 and Comparative Examples 1-4 Table 1 shows the silver leaching rates of Examples 1-4 and Comparative Examples 1-4. As shown in Table 1, the silver leaching rates of Examples 1-4 were 98.9%-99.3%, while the silver leaching rate of Comparative Example 1 was 58.7%. This result indicates that at 60°C, the eutectic solvent system had high viscosity, limited diffusion, and insufficient redox kinetics, leading to a decrease in the dissolution rate and complexation reaction rate of silver, thus significantly reducing the overall leaching rate. The silver leaching rate of Comparative Example 2 was 34.7%. This result indicates that when the solid-liquid ratio was 1:25, insufficient solvent in the system led to a decrease in the concentration of effective complexing agents such as chloride ions and lactic acid, resulting in insufficient contact at the reaction interface and limited mass transfer. This made it easy for a passivation layer to form or redeposit on the silver surface, comprehensively leading to a significant decrease in the silver leaching rate. The silver leaching rate of Comparative Example 3 was 87.1%. This result indicates that when the concentration of copper dichloride increased to 0.3 mol / L, the Cu in the system... 2+ Excessive amounts will cause an increase in solution viscosity and a shift in complexation equilibrium, with some Cu... + / Cu 2+ During the reaction, Cl - Competitive complexation or precipitation formation inhibits the effective dissolution of silver, leading to a decrease in the leaching rate. The silver leaching rate in Comparative Example 4 was 25.7%. This result indicates that at a leaching time of only 30 min, the reaction kinetics are not fully developed and mass transfer is limited, resulting in a decrease in the leaching rate of Ag. 0 It cannot be fully oxidized / complexed and enter the solution, resulting in a low leaching rate.

[0071] Figure 2 The images show the SEM and EDS spectra of the AgCl product from Example 1 of this invention. Figure 2 Image (a) is a SEM image, and image (b) is an EDS image. (From...) Figure 2 It can be seen that the product is mainly silver, and its main components and contents are: silver (Ag) 83.24% and chlorine (Cl) 16.76%.

[0072] Figure 3 This is the XRD pattern of the AgCl product from Example 1 of the present invention. Figure 3 It can be seen that the product matches the standard spectrum of silver chloride.

[0073] Figure 4 The images shown are SEM and EDS images of the photovoltaic silicon wafer before and after leaching in Example 1 of the present invention. Figure 4 Figure (a) shows the SEM morphology of the front side of the photovoltaic silicon wafer before leaching; Figure (b) shows the EDS distribution of Ag before leaching; Figure (c) shows the EDS surface distribution of Si before leaching; Figure (d) shows the SEM morphology of the front side of the photovoltaic silicon wafer after leaching; Figure (e) shows the EDS surface distribution of Ag after leaching; and Figure (f) shows the EDS surface distribution of Si after leaching. Figure 4 It can be seen that the silver grid lines in the photovoltaic silicon wafer before leaching are metallic silver, while the silver grid lines become lighter after leaching, confirming that the silver has been effectively leached out.

[0074] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0075] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for targeted extraction of silver from photovoltaic cells based on a eutectic solvent, characterized in that, Includes the following steps: A mixture of a eutectic solvent and an oxidant is used as the leaching agent to leach photovoltaic cells. Through the synergistic effect of chloride ion coordination and redox reaction, silver forms a complex to obtain the leachate. The eutectic solvent is composed of tetramethylammonium chloride and lactic acid. Water was then added to the leachate to adjust the pH to 5, and a precipitation reaction was carried out to achieve the targeted extraction of silver from the photovoltaic cells. The filtrate after the precipitation reaction was then evaporated to obtain the leachate. The photovoltaic cell is a crystalline silicon cell obtained by pre-processing retired crystalline silicon photovoltaic modules. The crystalline silicon cell comprises the following components by mass percentage: silicon 90.00%~91.50%, aluminum 7.50%~9.00%, silver 0.30%~0.45%, and impurity elements, totaling 100%. The eutectic solvent is obtained by mixing tetramethylammonium chloride and lactic acid in a molar ratio of 1:1 to 3, with a mixing temperature of 60℃ to 90℃. The concentration of the oxidant in the leaching agent is 0.05 mol / L to 0.1 mol / L, and the oxidant is copper dichloride; The mass-to-volume ratio of photovoltaic cells to leaching agent is 1g:50mL~100mL; The leaching temperature is 70℃~120℃, and the leaching time is 45min~100min; The volume ratio of water to leachate is 1~5:1; pH is adjusted using at least one of nitric acid, hydrochloric acid, and sulfuric acid. The precipitation reaction time is 30 min to 120 min.

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