Method for recycling metallic silver in waste solar cells

Abstract

The invention provides a method for recycling metallic silver in waste solar cells, which comprises the following steps: S1, preparing a chemical solvent, namely selecting and preparing a mixed solution of ammonia water, hydrogen peroxide and water according to the volume ratio of (0.5-2): (0.5-2): (2-6), the concentration of the ammonia water being 25-30%, and the concentration of the hydrogen peroxide being 30-35%; s2, soaking treatment: soaking the waste solar cells in the mixed solution at the soaking temperature of 30-60 DEG C for 1-3 hours; s3, carrying out high-temperature treatment, drying the soaked battery piece, heating the battery piece in an environment of 300-500 DEG C, and carrying out heat preservation for 20-60 minutes; and S4, collecting and separating, wherein high-purity metal silver is obtained through mechanical vibration, screening and ultrasonic cleaning separation. By means of the process, efficient separation of the silver electrode and the silicon substrate is achieved by means of the oxidation effect and the thermal expansion coefficient difference of the solvent. Compared with the prior art, the method is simple in process and high in selectivity, the metal silver recovery rate is larger than 90%, the purity is higher than 95%, and the method has remarkable economic benefits and environmental protection advantages and is suitable for industrial popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of silver electrode recovery, in particular to a method for recovering metallic silver from waste solar cells. Background Art

[0002] With the rapid development of the photovoltaic industry, a large number of waste solar cell modules are about to be retired. In particular, crystalline silicon photovoltaic cell modules at the end of their life have exerted considerable pressure on the environment. How to effectively recover high-value-added materials, such as metallic silver, has become a focus of attention in the industry. Silver is one of the most valuable materials in photovoltaic modules and is mainly found in the electrodes of solar cells for collecting photogenerated charges. However, existing methods for recovering silver from solar cells still have significant shortcomings in terms of efficiency, environmental friendliness, and ease of operation.

[0003] Currently, mainstream silver recovery methods are based on hydrometallurgical techniques, which typically use acidic or alkaline solutions to treat spent solar cells, dissolving the silver from the electrodes before separating it through precipitation, reduction, or extraction. While this method has some feasibility, it also suffers from the following drawbacks: complex processes, numerous steps, high chemical reagent consumption, severe environmental pollution, and low recovery efficiency. Furthermore, this technology struggles to recover high-purity silver and significantly damages the silicon substrate, resulting in a low material reuse rate.

[0004] Chinese patent application publication number CN114207164A proposes a method for recovering silver from photovoltaic cells through a multi-step chemical etching process. The main steps include: etching the anti-reflective layer using an acid solution (such as hydrofluoric acid); etching the doped silicon upper layer using an alkaline solution (such as sodium hydroxide), thereby separating the silver wires; and finally, extracting the solid silver wires through physical methods. While this method can achieve silver separation, its major drawbacks include high reliance on chemical reagents: the hydrofluoric acid and sodium hydroxide used in this method are highly corrosive and hazardous, posing a potential threat to the environment and operator safety. Furthermore, the wastewater treatment process is complex, making it difficult to meet environmental protection requirements. The operational process is complex: separate acid and alkaline etching processes are required, with precise control of temperature, solution concentration, and ultrasonic frequency, increasing the complexity and cost of the process. Material damage is severe: during the etching process, not only the anti-reflective layer and doped silicon layer are destroyed, but even the silicon substrate itself may be affected, resulting in a decrease in its purity and recyclability. Furthermore, the silver wires may partially dissolve under chemical action, reducing the purity and total amount of recovered silver. High equipment requirements: To improve process efficiency, this technology requires additional ultrasonic equipment to accelerate the etching and separation process, further increasing the cost and complexity of the recycling system.

[0005] Furthermore, a Chinese patent application with publication number CN118326166A proposes a method for recovering silver from waste photovoltaic cells using water or an aqueous solution combined with ultrasonic treatment. The core technology of this method is to accelerate the separation of silver by applying ultrasonic waves, and ultimately extract silver-containing solid particles through screening. Although this method effectively reduces reliance on hazardous chemicals, it still has the following drawbacks: the configuration and operation of ultrasonic equipment are complex. Especially in industrial recycling, the control requirements for parameters such as power, frequency, and tank size are high, making it difficult to maintain stable recovery efficiency. The method is less applicable to complex battery structures, especially batteries containing aluminum and other impurities. The separation effect is poor, resulting in certain limitations on the purity of the recovered silver. The recovered silver particles are prone to impurity adhesion, requiring additional subsequent processing to meet high-purity application requirements, thereby increasing the overall processing cost.

[0006] Chinese patent application publication number CN112662884A proposes a silver recovery method for crystalline silicon heterojunction solar cells. The method involves immersing the cells in an alkaline solution to separate the silver grid, followed by high-temperature heat treatment to remove impurities and obtain high-purity metallic silver. While this method offers certain advantages in reducing chemical pollution and process costs, it still presents several challenges: The method primarily targets crystalline silicon heterojunction cells and is less applicable to traditional photovoltaic cells and modules with diverse structures. Furthermore, the heat treatment process has high requirements for temperature and atmosphere, which, if improperly controlled, can lead to silver oxidation or a decrease in recovery rate. The overall process remains complex, and controlling the alkaline solution concentration and heat treatment conditions, particularly for large-scale industrial applications, requires higher equipment and management costs.

[0007] In summary, existing silver recycling technologies suffer from several shortcomings, including poor environmental performance, complex processes, severe material damage, and high equipment requirements. Therefore, there is an urgent need to develop an efficient, environmentally friendly, simple, and widely applicable silver recycling method for various types of waste solar cells, in order to improve resource utilization, reduce recycling costs, and meet increasingly stringent environmental protection requirements. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for recycling metallic silver from waste solar cells, so as to solve the problems existing in the prior art such as poor environmental protection, complex process, serious material damage and high equipment requirements.

[0009] To overcome the above defects of the prior art, the present invention provides a method for recovering metallic silver from waste solar cells, comprising the following steps:

[0010] S1: Chemical solvent preparation: Prepare a mixed solution of ammonia water, hydrogen peroxide and water in a volume ratio of ammonia water: hydrogen peroxide: water = (0.5-2): (0.5-2): (2-6), wherein the concentration of ammonia water is 25-30%, and the concentration of hydrogen peroxide is 30-35%;

[0011] S2: Immersion treatment: Immersing the waste solar cell in the chemical solvent of step S1;

[0012] S3: High temperature treatment: After the soaked solar cell is cleaned and dried, it is placed in a high temperature environment of 300-500°C for heat treatment for 20-60 minutes;

[0013] S4: Collection and separation: The detached silver electrode fragments and the silicon matrix are separated by mechanical vibration or ultrasonic cleaning, and the silicon matrix residues on the surface of the silver particles are further removed to obtain metallic silver.

[0014] The principles of the present invention include: the above-mentioned method of the present invention achieves efficient recovery of metallic silver from waste solar cells through a multi-step synergistic process combining chemical selective dissolution, heat treatment and physical separation. First, a chemical solvent system with strong oxidizing and complexing capabilities is constructed through the synergistic effect of ammonia and hydrogen peroxide. In the system, hydrogen peroxide generates hydroxyl radicals (·OH) in an alkaline environment, selectively oxidizing the silver-silicon alloy or aluminum-silicon alloy at the junction of the silver electrode. At the same time, the ammonia in the formula stabilizes the generated silver-ammonia complex through complexation, significantly weakening the bonding force between the silver electrode and the silicon substrate. Subsequently, high-temperature treatment (300-500°C) is used to further accelerate interfacial separation by leveraging the significant difference in thermal expansion coefficients between silver and silicon. Simultaneously, the gases (including ammonia and oxygen) generated by the thermal decomposition of the residual solvent further promote a micro-explosion effect, thereby accelerating the detachment of the silver electrode. On this basis, the large-particle silver electrode is separated from the silicon substrate by mechanical vibration, and the cavitation effect of ultrasonic cleaning is further used to remove silicon substrate residues on the surface of the silver particles, thereby obtaining high-purity metallic silver. The method of the present invention achieves efficient separation of silver electrodes and complete retention of the silicon substrate through the selective action of chemical solvents, physical stripping by heat treatment, and the strengthening effects of mechanical vibration and ultrasonic cleaning, significantly improving the recovery efficiency and purity, while reducing the use of chemical reagents and environmental pollution, and providing an environmentally friendly and efficient solution for the resource recycling of waste solar cells.

[0015] This application provides a method for recycling metallic silver from waste solar cells, which has the following significant advantages over the prior art:

[0016] Significantly improved environmental friendliness: The method of the present invention replaces the highly corrosive acidic solvent (such as hydrofluoric acid) in the prior art with a mild mixed solution of ammonia and hydrogen peroxide, greatly reducing the difficulty of waste liquid treatment and the harm to the environment; and the effect of the chemical solvent is limited to the bonding area of ​​the silver-silicon alloy or aluminum-silicon alloy, with almost no effect on the pure silver and the silicon substrate, so the silicon substrate can be reused.

[0017] Simplified operation process and improved efficiency: Traditional hydrometallurgical processes require dissolving silver from a solid state to a liquid state and then reducing it to a solid state. However, the present invention directly recovers silver particles through a combined physical and chemical process, avoiding complex chemical conversion steps. In the method of the present invention, high-temperature treatment utilizes differences in thermal expansion coefficients and solvent thermal decomposition to accelerate separation, significantly shortening the processing time.

[0018] High selectivity and high recovery rate: The synergistic effect of ammonia and hydrogen peroxide solution can selectively oxidize the silver-silicon alloy at the junction of the silver electrode without damaging the silicon substrate and pure silver, avoiding the material waste caused by chemical reagents damaging the silicon substrate in traditional methods. In the method of the present invention, the recovery rate of silver is as high as over 90%, and the purity reaches over 95%, far exceeding the existing technology.

[0019] Cost advantage: The method of the present invention has mild operating conditions and low energy consumption, and the equipment used is conventional laboratory or industrial equipment, without the need for expensive special equipment, thereby reducing the cost of industrial application.

[0020] High process safety: No need to use dangerous acidic solvents (such as hydrofluoric acid or concentrated nitric acid), which can harm operators and improve overall process safety.

[0021] In a possible implementation, in step S1, the volume ratio of the mixed solution is ammonia water: hydrogen peroxide: water = 1:1:3.

[0022] Compared with the existing technology, the above technical solution enhances the selectivity and reaction efficiency of the chemical solution by further optimizing the component ratio. The concentration of ammonia water and the ratio of hydrogen peroxide reach an optimal balance, so that ammonia water can more efficiently complex silver ions. At the same time, the ability of hydrogen peroxide to generate active oxygen (such as OH free radicals) in an alkaline environment is fully utilized, thereby achieving faster selective dissolution of the silver-silicon alloy and the aluminum-silicon alloy in the bonding area, while the impact on pure silver and the silicon substrate remains at an extremely low level, further improving the separation efficiency of the silver electrode and the silicon substrate.

[0023] In a possible embodiment, in step S2, the soaking temperature is 30-60° C. and the soaking time is 1-3 hours.

[0024] Compared with the existing technology, the above technical solution provides an ideal activation energy for the chemical reaction in the temperature range of 30-60°C, which can effectively enhance the efficiency of hydrogen peroxide in generating active oxygen in an alkaline environment and improve the complexation effect of ammonia on silver ions. At the same time, this temperature range avoids solvent decomposition caused by excessively high temperatures or a decrease in reaction rate caused by excessively low temperatures, thereby achieving an efficient dissolution reaction while protecting pure silver and silicon substrates. The immersion time of 1-3 hours ensures sufficient reaction at the interface between the chemical solution and the silver electrode, avoiding overreaction or underreaction.

[0025] In a possible implementation, in step S3, the heat treatment temperature is 400° C., and the holding time is 25 minutes.

[0026] Compared with the existing technology, the above technical solution and the selection of 400°C as the heat treatment temperature can achieve the optimal thermal decomposition effect of the chemical solvent, while avoiding the thermal damage to the silicon substrate or the silver electrode surface caused by excessively high temperatures. The 25-minute holding time provides sufficient reaction time to completely release the physical bonding force of the silver electrode joint, ensuring that the silver electrode falls off in the form of fragments without causing excessive thermal impact on the material.

[0027] In a possible embodiment, in step S4, after separating the detached silver electrode fragments and the silicon substrate, the step further includes screening the silver electrode fragments, specifically separating silver particles of different particle sizes through a sieve.

[0028] Compared with the existing technology, the above technical solution is used to screen the detached silver electrode fragments by setting an appropriate screen aperture, which can not only separate the silver particles from the silicon matrix fragments, but also classify the silver particles by particle size, thereby ensuring that the subsequent cleaning and purification process is more concentrated and uniform. By adding the screening step, the residual silicon matrix can be further reduced and the surface purity of the silver particles can be improved.

[0029] In a possible embodiment, in step S4, the further removal of silicon matrix residues on the surface of the silver particles is carried out by ultrasonically cleaning the surface of the silver particles for 20-30 minutes to remove the silicon matrix residues on the surface of the silver fragments.

[0030] Compared with the existing technology, the above technical solution can quickly and efficiently remove the silicon matrix residue attached to the surface of silver particles through ultrasonic cleaning, thereby obtaining silver particles with a cleaner surface. This not only reduces the interference of impurities in subsequent processing, but also further increases the purity of recovered silver to more than 95%. At the same time, the efficient effect of ultrasound reduces the demand for cleaning fluid or other chemical reagents during the cleaning process, reducing operating costs and environmental risks.

[0031] In a possible implementation, in step S4, the recovery rate of the metallic silver is greater than 90%, and the purity is greater than 95%.

[0032] Compared with the prior art, the above technical solution is adopted. Through the oxidation effect of the chemical solvents (ammonia water and hydrogen peroxide) of specific concentrations and ratios on the silver-silicon alloy or the aluminum-silicon alloy in the method of the present invention, combined with the difference in thermal expansion coefficients during high-temperature treatment, the bonding force between the silver electrode and the silicon substrate is destroyed, thereby achieving complete separation of the silver electrode. At the same time, through further optimization steps such as screening and ultrasonic cleaning, the silicon substrate residues on the surface of the silver particles are effectively removed, thereby ensuring the purity and recovery rate of the recovered silver. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Solar cell sheets processed by recycling metallic silver from waste solar cells;

[0034] Figure 2 It is a silver electrode obtained by separating the metallic silver from waste solar cells. DETAILED DESCRIPTION

[0035] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of the present application and are not intended to limit the scope of protection of the embodiments of the present application. Those skilled in the art may adjust them as needed to suit specific application scenarios.

[0036] The present invention provides a method for recovering metallic silver from waste solar cells, comprising the following steps:

[0037] S1: Chemical solvent preparation: Prepare a mixed solution of ammonia water, hydrogen peroxide and water in a volume ratio of ammonia water: hydrogen peroxide: water = (0.5-2): (0.5-2): (2-6), wherein the concentration of ammonia water is 25-30%, and the concentration of hydrogen peroxide is 30-35%;

[0038] S2: Immersion treatment: Immersing the waste solar cell in the chemical solvent of step S1;

[0039] S3: High temperature treatment: After the soaked solar cell is cleaned and dried, it is placed in a high temperature environment of 300-500°C for heat treatment for 20-60 minutes;

[0040] S4: Collection and separation: The detached silver electrode fragments and the silicon matrix are separated by mechanical vibration or ultrasonic cleaning, and the silicon matrix residues on the surface of the silver particles are further removed to obtain metallic silver.

[0041] The present invention utilizes the synergistic effect of ammonia (NH3·H2O) and hydrogen peroxide (H2O2) to produce a reaction system with strong oxidizing and complexing capabilities. Ammonia provides an alkaline environment and stabilizes the oxidized silver complex through complexation. Hydrogen peroxide decomposes in an alkaline environment to form hydroxyl radicals (·OH), a mild but highly effective oxidant.

[0042] H2O2+OH-→HO2 - -+H2O

[0043] In the above step S2, the solution can selectively oxidize the junction of the silver-silicon alloy or the aluminum-silicon alloy through the synergistic effect of hydroxide and peroxy radicals, while having little effect on the pure silver and the silicon substrate.

[0044] Selective oxidation of silver-silicon junction: During the reaction process of the above method of the present invention, the surface of the silver-silicon alloy or aluminum-silicon alloy at the junction of the silver electrode is gradually oxidized and dissolved into a complex. At the same time, due to the complexation of ammonia water, the generated silver ions (Ag + ) Silver-ammine complex stabilized in solution:

[0045] 2Ag+4NH3→[Ag(NH3)2]++e -

[0046] The selective dissolution mechanism in the present invention effectively weakens the bonding force between the silver electrode and the silicon substrate without damaging the pure silver and the silicon substrate, thereby ensuring selective recovery.

[0047] In step S3, during the high temperature treatment (300-500°C), the silver electrode and the silicon substrate have different thermal expansion coefficients (the thermal expansion coefficient of silver is about 19.2×10 -6 / ℃, while silicon is about 2.6×10 -6 / °C), interfacial separation occurs under thermal stress. This physical effect further weakens the bond between the silver electrode and the silicon substrate, promoting the shedding of silver particles. Under high temperature conditions, the residual chemical solvents (such as ammonia and hydrogen peroxide) decompose into gases (such as ammonia and oxygen), further promoting the peeling effect at the interface and accelerating the separation of the silver electrode. This process does not require the assistance of additional chemical reagents, significantly improving the separation efficiency.

[0048] In step S4, the mechanical vibration particle separation is set after high-temperature treatment, and the silver electrode has fallen off in the form of powder or fragments. Mechanical vibration can achieve efficient separation of large particles and silicon matrix. When an ultrasonic cleaning machine is further used for separation, the cavitation effect generated by high-frequency vibration (that is, the process of forming and collapsing microbubbles in the liquid) can be used to peel off the silicon matrix residues attached to the surface of the silver particles, significantly improving the purity of the silver particles while avoiding mechanical damage.

[0049] In summary, the core of the present invention lies in the synergistic effect of chemical and physical reactions: in steps S1 / S2, the chemical solvent weakens the binding force through selective dissolution, creating conditions for subsequent steps; the high-temperature treatment in step S3 further peels off the binding interface through thermal expansion differences; and the mechanical vibration and ultrasonic cleaning in step S4 effectively separate and purify the silver particles, improving the final recovery efficiency and purity. Through the synergistic effect of these multiple steps, the present invention achieves efficient and environmentally friendly recovery of metallic silver from waste solar cells while retaining the integrity of the silicon substrate, providing a cost-effective solution for resource recycling.

[0050] As a preferred solution, in step S1, the volume ratio of the mixed solution is ammonia water: hydrogen peroxide: water = 1:1:3.

[0051] As a preferred solution, in step S2, the soaking temperature is 30-60° C. and the soaking time is 1-3 hours.

[0052] As a preferred solution, in step S3, the heat treatment temperature is 400° C. and the holding time is 25 minutes.

[0053] As a preferred solution, in step S4, after separating the detached silver electrode fragments and the silicon substrate, the step of screening the silver electrode fragments is further included, specifically, separating silver particles of different particle sizes through a sieve.

[0054] As a preferred solution, in step S4, the method of further removing the silicon matrix residues on the surface of the silver particles is: ultrasonically cleaning the surface of the silver particles for 20-30 minutes to remove the silicon matrix residues on the surface of the silver fragments.

[0055] As a preferred solution, in step S4, the recovery rate of the metallic silver is greater than 90%, and the purity is greater than 95%.

[0056] The following provides specific embodiments combined with data in combination with the above-mentioned technical solutions to further expand the technical solutions of the present invention:

[0057] Example 1:

[0058] This embodiment provides a method for recovering metallic silver from waste solar cells, comprising the following steps:

[0059] S1: Chemical solvent preparation

[0060] Prepare a 1 L solution by mixing 28% ammonia, 33% hydrogen peroxide, and deionized water in a volume ratio of 1:1:3. Stir the solution thoroughly to ensure all components are thoroughly mixed.

[0061] S2: Infiltration treatment

[0062] Rinse the used solar cells with deionized water to remove surface dust and impurities. Then, completely immerse the cleaned cells in the chemical solution prepared in step S1. This immersion process is performed in a 50°C water bath for 2 hours to ensure that the solvent fully penetrates the interface between the silver electrode and the silicon substrate.

[0063] S3: High temperature treatment

[0064] After the immersion treatment in step S2, the solar cell is removed and thoroughly rinsed with deionized water to remove any residual chemical solvent. The cell is then air-dried in a well-ventilated environment or dried in a 60°C oven for 30 minutes to ensure complete dehydration. The dried cell is then placed in a muffle furnace preheated to 400°C and held at this temperature for 25 minutes. During this process, the silver electrode gradually separates from the silicon substrate by utilizing the difference in thermal expansion coefficients and the decomposition of residual chemical solvent.

[0065] S4: Collection and separation

[0066] After high-temperature treatment, the cell is placed in a vibrating screen, where mechanical vibration separates the detached silver electrode fragments from the silicon substrate. A 200-mesh screen is then used to further separate silver particles of varying sizes. The sieved silver particles are then transferred to an ultrasonic cleaner, where deionized water is added and ultrasonically cleaned for 25 minutes to remove any silicon substrate residue from the silver particle surface. The result is high-purity metallic silver with a recovery rate exceeding 92% and a purity of 97%.

[0067] Example 2

[0068] This embodiment provides a method for recovering metallic silver from waste solar cells, comprising the following steps:

[0069] S1: Chemical solvent preparation

[0070] Prepare a 1 liter solution by mixing 25% ammonia, 30% hydrogen peroxide, and deionized water in a volume ratio of 0.5:0.5:2. Stir thoroughly to ensure all components are thoroughly mixed.

[0071] S2: Infiltration treatment

[0072] Rinse the used solar cells with deionized water to remove surface dust and impurities. Then, completely immerse the cleaned cells in the chemical solution prepared in step S1. Set the immersion temperature to 30°C for 1 hour to ensure that the chemical solution effectively penetrates the interface between the silver electrode and the silicon substrate.

[0073] S3: High temperature treatment

[0074] After the immersion treatment in step S2, the solar cell is removed and thoroughly rinsed with deionized water to remove any residual chemical solvent. The cleaned cell is then air-dried in a well-ventilated environment or dried in a 50°C oven for 20 minutes to ensure complete dehydration. The dried cell is then placed in a muffle furnace preheated to 300°C and held at this temperature for 20 minutes. During this process, the silver electrode gradually separates from the silicon substrate due to differences in thermal expansion coefficients and the decomposition of residual chemical solvent.

[0075] S4: Collection and separation

[0076] After high-temperature treatment, the cell is placed in a mechanical vibrating screen, where mechanical vibration separates the detached silver electrode fragments from the silicon substrate. A 300-mesh screen is then used to further separate silver particles of varying sizes. The sieved silver particles are then transferred to an ultrasonic cleaner, where deionized water is added and ultrasonically cleaned for 20 minutes to remove any silicon substrate residue from the silver particle surface. This results in high-purity metallic silver with a recovery rate of 91% and a purity of 96%.

[0077] Example 3

[0078] This embodiment provides a method for recovering metallic silver from waste solar cells, comprising the following steps:

[0079] S1: Chemical solvent preparation

[0080] Prepare a 1 liter chemical solution by mixing 30% ammonia, 35% hydrogen peroxide, and deionized water in a volume ratio of 2:2:6. Stir the solution thoroughly to ensure that all components are thoroughly mixed.

[0081] S2: Infiltration treatment

[0082] Rinse the used solar cells with deionized water to remove surface dust and impurities. Then, completely immerse the cleaned cells in the chemical solution prepared in step S1. Set the immersion temperature to 60°C for 3 hours to ensure the chemical solvent fully acts on the silver electrode interface and decomposes the silver-silicon alloy and aluminum-silicon alloy.

[0083] S3: High temperature treatment

[0084] After soaking in step S2, the solar cell is removed and thoroughly rinsed with deionized water to remove any residual chemical solvent. The cleaned cell is then air-dried in a well-ventilated environment or dried in a 70°C oven for 40 minutes to ensure complete dehydration. The dried cell is then placed in a muffle furnace preheated to 500°C and held at this temperature for 60 minutes. This process accelerates the separation of the silver electrode from the silicon substrate by utilizing the difference in thermal expansion coefficients and the decomposition of residual chemical solvent.

[0085] S4: Collection and separation

[0086] After high-temperature treatment, the cell is placed in a mechanical vibrating screen, where mechanical vibration separates the detached silver electrode fragments from the silicon substrate. A 200-mesh screen is then used to further separate silver particles of varying sizes. The screened silver particles are then placed in an ultrasonic cleaner with deionized water and ultrasonically cleaned for 30 minutes to remove any silicon substrate residue from the silver particle surface. This results in high-purity metallic silver with a recovery rate exceeding 91% and a purity of 95%.

[0087] Figure 1 、 Figure 2 They are respectively a solar cell sheet processed by a method for recovering metallic silver from waste solar cells and a silver electrode obtained by separation by a method for recovering metallic silver from waste solar cells.

[0088] The above examples further demonstrate that the method of the present invention selectively dissolves the silver-silicon alloy and aluminum-silicon alloy in the region where the silver electrode and the silicon substrate are bonded, through the oxidation and complexation of a mixed solution of ammonia and hydrogen peroxide, while having little effect on pure silver and the silicon substrate. Further high-temperature treatment utilizes the difference in thermal expansion coefficients and the thermal decomposition of chemical solvents to further promote the detachment of the silver electrode. This combined process significantly improves the separation efficiency of the silver electrode and shortens the processing time. This method is simple and efficient, and is suitable for recycling silver electrodes from waste solar cells. Compared with the prior art, the present invention overcomes the problems of the prior art, such as the complex and time-consuming hydrometallurgical process, the large amount of chemical solvents used, and the potential for environmental pollution during the processing. In particular, the present invention avoids the tedious steps of treating the anti-reflective layer and the silicon substrate with multiple acidic and alkaline solutions, simplifying the recycling process. At the same time, the present invention significantly reduces the use of chemical solvents and improves the recovery purity of silver by selectively dissolving the silver-silicon alloy and aluminum-silicon alloy in the bonding interface area rather than completely dissolving the silver. Furthermore, the present invention does not require extensive use of ultrasonic-assisted separation, and can achieve efficient separation of silver electrodes only through the efficient oxidation of ammonia and hydrogen peroxide and high-temperature treatment, thereby reducing equipment requirements and operating costs, while further avoiding the problem of silicon substrate damage caused by excessive ultrasonic treatment. The present invention can not only separate silver electrodes under mild chemical conditions, but also ensure the purity of the recovered silver (reaching more than 95%) through further high-temperature treatment. The methods in the prior art may leave some organic matter and impurities due to insufficient alkaline solution treatment. The present invention improves the separation efficiency of silver electrodes and the purity of the final product by combining complete chemical and physical treatments.

[0089] This invention represents a significant advancement in technical solutions compared to existing technologies, achieving superior performance through the synergistic effect of multiple technical approaches. First, the invention has a wider scope of application, applicable to traditional crystalline silicon, polycrystalline silicon, and heterojunction solar cells, not limited to crystalline silicon heterojunction cells. Second, a mixed solution of ammonia and hydrogen peroxide creates a chemical system with strong oxidizing and complexing capabilities, selectively dissolving silver-silicon and aluminum-silicon alloys while leaving the silicon substrate and pure silver intact, achieving a highly selective and environmentally friendly chemical treatment. Furthermore, high-temperature treatment utilizes differences in thermal expansion coefficients and the thermal decomposition of residual chemical solvents to significantly accelerate the interfacial separation between the silver electrode and the silicon substrate. Subsequently, mechanical vibration and ultrasonic cleaning are combined to effectively remove silicon substrate residues from the surface of the silver particles. This synergistic process of chemical dissolution, high-temperature separation and physical purification significantly improves the recovery rate (>90%) and purity (>95%) of silver particles. Compared with CN112662884A, which relies on a single method of high-temperature strong alkaline solution and long-term heat treatment, the synergistic effect of the present invention makes the process more efficient, environmentally friendly, simple and safe, with obvious advantages in comprehensive performance and is more suitable for industrial applications.

[0090] In summary, the present invention demonstrates significant advantages in solving technical problems such as complex process flow, environmental pollution, high cost and low recycling efficiency in the prior art, and provides a new, efficient, environmentally friendly and economical solution for the recovery of metallic silver from waste solar cells. It has important industrial application value and broad market prospects.

[0091] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0092] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for recovering metallic silver from waste solar cells, characterized in that: The following steps are involved: S1: Chemical solvent preparation: preparing a mixed solution of ammonia water, hydrogen peroxide and water, wherein the volume ratio is ammonia water: hydrogen peroxide: water = (0.5-2): (0.5-2): (2-6), wherein the concentration of ammonia water is 25-30%, and the concentration of hydrogen peroxide is 30-35%; S2: Immersion treatment: soaking the waste solar cell in the chemical solvent of step S1; S3: High temperature treatment: After the soaked solar cell is cleaned and dried, it is placed in a high temperature environment of 300-500°C for heat treatment for 20-60 minutes; S4: Collection and separation: The detached silver electrode fragments and the silicon matrix are separated by mechanical vibration or ultrasonic cleaning, and the silicon matrix residues on the surface of the silver particles are further removed to obtain metallic silver.

2. The method for recovering metallic silver from waste solar cells according to claim 1, characterized in that: In the step S1, the volume ratio of the mixed solution is ammonia water: hydrogen peroxide: water = 1:1:

3.

3. The method for recovering metallic silver from waste solar cells according to claim 1, characterized in that: In the step S2, the soaking temperature is 30-60° C. and the soaking time is 1-3 hours.

4. The method for recovering metallic silver from waste solar cells according to claim 1, characterized in that: In step S3, the heat treatment temperature is 400° C. and the heat preservation time is 25 minutes.

5. The method for recovering metallic silver from waste solar cells according to claim 1, characterized in that: In the step S4, after the separation of the detached silver electrode fragments and the silicon substrate, the step of screening the silver electrode fragments is further included, specifically, separating silver particles of different particle sizes through a sieve.

6. The method for recovering metallic silver from waste solar cells according to claim 1, characterized in that: In the step S4, the method of further removing the silicon matrix residue on the surface of the silver particles is: ultrasonically cleaning the surface of the silver particles for 20-30 minutes.

7. The method for recovering metallic silver from waste solar cells according to claim 1, characterized in that: In step S4, the recovery rate of the metallic silver is greater than 90%, and the purity is greater than 95%.

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