Method for recovering metallic silver from retired crystalline silicon photovoltaic cell

Abstract

The invention provides a method for recovering metallic silver from a decommissioned crystalline silicon photovoltaic cell, which comprises the following steps: immersing the decommissioned crystalline silicon cell in a hydrochloric acid solution with the mass concentration of 15-25% for 30-60 minutes, carrying out solid-liquid separation, taking a solid to obtain a dealuminated cell, washing the dealuminated cell with deionized water, immersing the washed dealuminated cell in a mixed solution of an oxidant aqueous solution and a complexing agent aqueous solution, washing the washed dealuminated cell with deionized water, and drying the washed dealuminated cell to obtain the metallic silver from the decommissioned crystalline silicon photovoltaic cell. The preparation method comprises the following steps: adding a silver source into a reaction kettle, reacting at 30-50 DEG C for 20-50 minutes, carrying out solid-liquid separation after the reaction is finished, taking liquid to obtain a silver-containing leaching solution, adding a chlorine source into the leaching solution, reacting for 20-40 minutes, carrying out solid-liquid separation, taking precipitate, and drying to obtain silver chloride powder; silver chloride powder is added into an ammonia water solution with the concentration being 22-30 wt%, stirring is conducted at the temperature of 35-50 DEG C till silver chloride is completely dissolved, a silver-ammonia solution is obtained, a reducing agent is added, stirring reaction is conducted for 30-60 min, filtering is conducted to obtain metal silver sediment, and silver powder is obtained through aftertreatment; according to the method, the damage of nitrogen oxides generated in the nitric acid reaction process to the environment is avoided, and the toxicity of the system is greatly reduced by adopting cheap and green glucose as a reducing agent.

Description

Technical Field

[0001] This invention belongs to the field of rare and precious metal recycling technology, specifically relating to a method for recovering metallic silver from retired crystalline silicon photovoltaic cells. Background Technology

[0002] As a crucial component of clean energy, the photovoltaic (PV) industry plays a vital role in addressing climate change and the energy crisis, as well as building a low-carbon society. However, with the lifespan of PV modules (25-30 years) nearing its end, a concentrated wave of retirements is expected in 2030, with the total amount of retired PV modules (EOL) reaching 8 million tons. This figure is projected to increase rapidly at an annual growth rate of 30%, exceeding 80 million tons by 2050, with China accounting for more than a quarter of the total. Silver, a key conductive material, accounts for only 0.2-0.9% of the module's weight, but its economic value exceeds 40%. Traditional methods for recovering silver from retired PV modules primarily employ nitric acid leaching, which suffers from low efficiency, heavy pollution, and low-quality recovery. Uniform micron-sized spherical silver powder, due to its unique physicochemical properties, has broad application prospects in PV silver extraction, catalysis, and composite material preparation. Therefore, developing a technology for recycling silver resources from retired PV modules that is both highly efficient and environmentally friendly, while also enhancing product value, can not only reduce environmental pollution and alleviate dependence on primary silver mine resources but also meet market demand for high-value silver powder conversion.

[0003] Existing technologies mostly employ hydrometallurgical methods, using leaching solutions to dissolve silver from crystalline silicon solar cells, followed by reduction to elemental silver powder. For example, Chinese patent document CN106629738B discloses a method for extracting silver from crystalline silicon solar panels. This method uses sodium hydroxide to remove aluminum, then leaches silver with organic acids and hydrogen peroxide, followed by electrolytic reduction to obtain silver powder. However, this patent uses sodium hydroxide to dissolve aluminum, rendering the solution unusable for other purposes and inevitably imposing a burden on subsequent environmental treatment. Secondly, to ensure efficient silver extraction, hydrogen peroxide is added in excess, leading to preferential decomposition of hydrogen peroxide at the cathode during silver electrodeposition, resulting in increased energy consumption and hindering large-scale industrial applications. Chinese patent document CN120555756A discloses a method for recovering metallic silver from waste crystalline silicon solar cells, using hydrogen peroxide and organic acids to leach silver, followed by reduction with ammonia and ascorbic acid to obtain silver powder. The patented silver extraction process requires a long extraction time and a high reaction temperature. At the same time, the process still has the problem of how to deal with the aluminum-containing alkaline solution after aluminum removal by sodium hydroxide.

[0004] It is evident that existing technologies cannot simultaneously achieve high efficiency and environmental friendliness in the silver recovery process from retired crystalline silicon solar cells, and they do not fully consider the high-value utilization of byproducts in the silver recovery process. This leads to significant uncertainties in the scaling up and practical application of such technologies. Therefore, developing more efficient, environmentally friendly, and sustainable silver recovery technologies from retired crystalline silicon photovoltaic cells is extremely necessary. Summary of the Invention

[0005] The purpose of this invention is to address the problems of low efficiency, poor environmental protection, and lack of sustainability in current technologies for recycling silver from retired crystalline silicon solar cells. This invention provides a method for recovering silver from retired crystalline silicon solar cells, achieving a silver recovery rate of over 98% and a purity of over 99.9%, while obtaining silver powder in the form of uniformly shaped micron-sized silver spheres.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for recovering silver from retired crystalline silicon photovoltaic cells includes the following steps: (1) Immerse the retired crystalline silicon solar cell in a hydrochloric acid solution with a mass concentration of 15-25% for 30-60 minutes. After solid-liquid separation, an aluminum-containing solution and a solid are obtained. Take the solid to obtain a dealuminized solar cell (the liquid after solid-liquid separation can be recycled for the preparation of polyaluminum chloride). (2) The aluminum-dealuminized battery cell described in step (1) is washed with deionized water and then immersed in a mixed solution of an oxidant aqueous solution and a complexing agent aqueous solution. The mixture is reacted at 30-50°C for 20-50 minutes. After the reaction, the liquid is separated by solid-liquid separation to obtain a silver-containing extract. The oxidant is hydrogen peroxide or peracetic acid (preferably hydrogen peroxide). The complexing agent is ethylenediaminetetraacetic acid, aminotriacetic acid, or N,N-dihydroxymethyl-L-glutamate sodium salt (preferably ethylenediaminetetraacetic acid). The initial concentration of the oxidant in the mixed solution is 5-15 wt%, and the molar ratio of the oxidant in the oxidant aqueous solution to the complexing agent in the complexing agent aqueous solution is (10-30):1. (3) Add a chlorine source to the silver-containing extract in step (2) and react for 20-40 minutes (preferably 30 minutes). Separate the solid and liquid, and obtain the separated liquid and precipitate. Take the precipitate and dry it to obtain silver chloride powder. The chlorine source is sodium chloride or potassium chloride. The ratio of the amount of chloride ions in the chlorine source to the amount of silver ions measured in the silver-containing extract is 1-1.2:1. (4) Add the silver chloride powder mentioned in step (3) to a concentration of 22~30wt%. In a (preferably 25wt%) ammonia solution, the mixture is stirred at 35-50°C until silver chloride is completely dissolved to obtain a silver ammonia solution. The mass ratio of the silver chloride powder to the ammonia solution is 1:25-35. (5) Add a reducing agent to the silver ammonia solution in step (4), stir and react for 30-60 minutes, filter to obtain metallic silver precipitate, and obtain silver powder after post-treatment; the molar ratio of the reducing agent to the silver chloride powder in step (4) is 1:1-2. Furthermore, in step (2), the mass ratio of the dealuminized battery cell to the mixed solution of the oxidant aqueous solution and the complexing agent aqueous solution is 1:6.

[0007] Furthermore, the mass ratio of the decommissioned crystalline silicon solar cell to the hydrochloric acid solution in step (1) is 1:1-4 (preferably 1:1.5).

[0008] Furthermore, the oxidant mentioned in step (2) is hydrogen peroxide.

[0009] Furthermore, the complexing agent in step (2) is ethylenediaminetetraacetic acid.

[0010] Furthermore, the aluminum-containing solution in step (1) is used to prepare polyaluminum chloride.

[0011] Furthermore, the separated liquid from step (3) is recovered and added to the reaction system in step (2) of the next cycle reaction for recycling.

[0012] Furthermore, the reducing agent in step (4) is ascorbic acid or glucose.

[0013] Furthermore, the post-processing described in step (5) involves washing the precipitated metallic silver with deionized water and then vacuum drying it to obtain the silver powder.

[0014] Furthermore, the method is as follows: (1) The retired crystalline silicon solar cell was immersed in a hydrochloric acid solution with a mass concentration of 18% for 50 minutes. After solid-liquid separation, an aluminum-containing solution and a solid were obtained. The solid was taken to obtain a dealuminized solar cell. The mass ratio of the retired crystalline silicon solar cell to the hydrochloric acid solution was 1:1-4. (2) The aluminum-dealuminized battery cell described in step (1) is washed with deionized water and then immersed in a mixed aqueous solution of hydrogen peroxide and ethylenediaminetetraacetic acid. The reaction is carried out at 45°C for 40 min. After the reaction is completed, a silver-containing extract is obtained by solid-liquid separation. The initial concentration of hydrogen peroxide in the mixed aqueous solution is 3-10 wt% (more preferably 3.5 wt%), and the molar ratio of hydrogen peroxide to ethylenediaminetetraacetic acid is 20:1. (3) Add sodium chloride to the silver-containing extract in step (2) and react for 30 min. Separate the solids to obtain the separated liquid and precipitate. Take the precipitate and dry it to obtain silver chloride powder. The molar ratio of chloride ions in the sodium chloride to the silver ions measured in the silver-containing extract is 1.1:1. The separated liquid is recovered and added to the reaction system in step (2) of the next cycle reaction for recycling as a silver extraction agent. (4) Add the silver chloride powder described in step (3) to a 25wt% ammonia solution and stir at 45°C until the silver chloride is completely dissolved to obtain a silver ammonia solution; the mass ratio of the silver chloride powder to the ammonia solution is 1:30. (5) Add glucose to the silver ammonia solution in step (4), stir and react for 60 min, filter to obtain metallic silver precipitate, wash with deionized water and vacuum dry to obtain silver powder; the molar ratio of glucose to silver chloride powder in step (4) is 1:2.

[0015] According to the method provided by the present invention, the micron-sized spherical silver powder prepared has a uniform morphology and a particle size of about 1.5 micrometers.

[0016] In this invention, a mixture of complexing agent and oxidizing agent is used instead of traditional nitric acid extraction. This extract is recyclable, thus avoiding the environmental damage caused by nitrogen oxides generated during the nitric acid reaction. Furthermore, inexpensive and environmentally friendly glucose is used as a reducing agent instead of the traditional reducing agent hydrazine hydrate in the preparation of silver powder, significantly reducing the toxicity of the system. Attached Figure Description

[0017] Figure 1 A schematic diagram of the process flow of the method described in this invention is shown; Figure 2 The SEM images of the morphology of the silver powder obtained in Example 1 are shown. Figure 3 The SEM images of the morphology of the silver powder obtained in Example 2 are shown. Figure 4 The SEM image of the morphology of the silver powder obtained in Example 3 is shown; Detailed Implementation

[0018] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments of the invention are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments described herein.

[0019] In the examples, unless otherwise specified, the conditions were performed under standard conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the examples are assumed to be commercially available.

[0020] Example 1: Methods for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells, such as Figure 1 The flowchart shown includes the following steps: (1) Select retired crystalline silicon solar cells separated from the welding strip as raw materials. First, take 10g of retired crystalline silicon solar cells and soak them in 15g of 18wt% hydrochloric acid aqueous solution for 50min. After solid-liquid separation, aluminum-containing solution and dealuminized solar cells are obtained. The aluminum content in the aluminum-containing solution is 2.3 wt%. Polyaluminum chloride can be directly prepared by conventional slow drip alkali method. (2) Take 10g of dealuminized battery cell, wash and dry it with deionized water, and immerse it in a mixed solution (60g) containing aqueous solution of ethylenediaminetetraacetic acid and aqueous solution of hydrogen peroxide (hydrogen peroxide concentration is 5 wt%, molar ratio of hydrogen peroxide and ethylenediaminetetraacetic acid is 20:1). React at 45℃ for 40 minutes. After solid-liquid separation, silver-containing filtrate (silver-containing leaching solution) and dealuminized battery cell are obtained. (3) The concentration of Ag in the silver-containing filtrate was determined to be 1000 mg / L using an inductively coupled plasma spectrometer. 0.325 g NaCl was added to 600 ml of silver-containing filtrate. After reacting for 30 minutes, the precipitate was filtered and dried to obtain 0.13 g of silver chloride powder. The filtrate obtained was added to the reaction system of step (2) of the next cycle reaction for recycling.

[0021] (4) Add the obtained 0.13g silver chloride powder (0.000907 mol) to 3.9g 25wt% ammonia solution and stir at 45℃ until completely dissolved to obtain silver ammonia solution; (5) Add glucose solution dropwise to silver ammonia solution. At this time, the molar ratio of glucose to silver ions is 1:2. React at room temperature for 60 minutes to generate metallic silver powder precipitate. (6) The silver powder was filtered and washed three times with deionized water, and then dried in a vacuum drying oven at 70°C for 8 hours to obtain 0.0991 g of high-purity silver powder with a silver recovery rate of 99.1%.

[0022] Figure 2 The image shows the morphology of the spherical silver powder obtained in Example 1. The particle size is about 1.5 micrometers and the purity reaches 99.88%.

[0023] Example 2: Methods for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells, such as Figure 1 The flowchart shown includes the following steps: (1) Select retired crystalline silicon solar cells separated from the welding strip as raw materials. First, take 10g of retired crystalline silicon solar cells and soak them in 15g of 24wt% hydrochloric acid aqueous solution for 50min. After solid-liquid separation, aluminum-containing solution and dealuminized solar cells are obtained. The aluminum content in the aluminum-containing solution is 2.3 wt%. Polyaluminum chloride can be directly prepared by conventional slow drip alkali method. (2) Take 10g of dealuminized battery cell, wash and dry it with deionized water, and immerse it in a mixed solution (60g) containing aqueous solution of nitric acid and aqueous solution of hydrogen peroxide (hydrogen peroxide concentration is 10 wt%, and the molar ratio of hydrogen peroxide to nitric acid is 10:1). React at 45℃ for 40 minutes. After solid-liquid separation, silver-containing filtrate (silver-containing extract) and dealuminized battery cell are obtained. (3) The concentration of Ag in the silver-containing filtrate was determined to be 1000 mg / L using an inductively coupled plasma spectrometer. 0.325 g NaCl was added to 600 ml of silver-containing filtrate. After reacting for 30 minutes, the precipitate was filtered and dried to obtain 0.13 g of silver chloride powder. The filtrate obtained was added to the reaction system of step (2) of the next cycle reaction for recycling.

[0024] (4) Add the obtained 0.13g silver chloride powder (0.000907 mol) to 3.9g 25wt% ammonia solution and stir at 45℃ until completely dissolved to obtain silver ammonia solution; (5) Add glucose solution dropwise to silver ammonia solution. At this time, the molar ratio of glucose to silver ions is 1:2. React at room temperature for 60 minutes to generate metallic silver powder precipitate. (6) The silver powder was filtered and washed three times with deionized water, and then dried in a vacuum drying oven at 70°C for 8 hours to obtain 0.0988 g of high-purity silver powder with a silver recovery rate of 98.8%.

[0025] Figure 3 The image shows the morphology of the spherical silver powder obtained in Example 2. The particle size is about 1.5 micrometers and the purity reaches 99.79%.

[0026] Example 3: A method for recovering metallic silver from retired crystalline silicon photovoltaic cells includes the following steps: (1) Select retired crystalline silicon solar cells separated from the welding strip as raw materials. First, take 10g of retired crystalline silicon solar cells and soak them in 15g of 24wt% hydrochloric acid aqueous solution for 50min. After solid-liquid separation, aluminum-containing solution and dealuminized solar cells are obtained. The aluminum content in the aluminum-containing solution is 2.3 wt%. Polyaluminum chloride can be directly prepared by conventional slow drip alkali method. (2) Take 10g of dealuminized battery cell, wash and dry it with deionized water, and immerse it in a mixed solution (60g) containing N,N-dihydroxymethyl-L-glutamate sodium salt aqueous solution and hydrogen peroxide aqueous solution (hydrogen peroxide concentration is 10 wt%, and the molar ratio of hydrogen peroxide and nitric acid is 10:1). React at 35℃ for 45 minutes. After solid-liquid separation, silver-containing filtrate (silver-containing extract) and dealuminized battery cell are obtained. (3) The concentration of Ag in the silver-containing filtrate was determined to be 1000 mg / L using an inductively coupled plasma spectrometer. 0.39 g NaCl was added to 600 ml of silver-containing filtrate. After reacting for 30 minutes, the precipitate was filtered and dried to obtain 0.13 g of silver chloride powder. The filtrate obtained was added to the reaction system of step (2) of the next cycle reaction for recycling.

[0027] (4) Add the obtained 0.13g silver chloride powder (0.000907 mol) to 3.9g 25wt% ammonia solution and stir at 45℃ until completely dissolved to obtain silver ammonia solution; (5) Add glucose solution dropwise to silver ammonia solution. At this time, the molar ratio of glucose to silver ions is 1:1.5. React at room temperature for 60 minutes to generate metallic silver powder precipitate. (6) The silver powder was filtered and washed three times with deionized water, and then dried in a vacuum drying oven at 70°C for 8 hours to obtain 0.0984 g of high-purity silver powder with a silver recovery rate of 98.4%.

[0028] Figure 4 The image shows the morphology of the spherical silver powder obtained in Example 3. The particle size is about 1.5 micrometers and the purity reaches 99.91%.

[0029] Table 1. Test data of silver powder and polyaluminum chloride products obtained in each example.

[0030] The experimental results show that uniform micron-sized spherical silver powder with a particle size of about 1.5 micrometers was obtained in each embodiment, with a silver recovery rate of over 98% and a purity of over 99.5%. Furthermore, the method of this invention, while producing high-purity silver powder, also prepares high-quality polyaluminum chloride from aluminum dissolved in hydrochloric acid, solving the problem of byproduct disposal and avoiding the emission of toxic and harmful gases, thus achieving a green silver extraction method that is efficient, environmentally friendly, and sustainable.

[0031] The above embodiments are merely exemplary and not exhaustive, and the present invention is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. A method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells, characterized in that, The method is as follows: (1) Immerse the retired crystalline silicon solar cell in a hydrochloric acid solution with a mass concentration of 15-25% for 30-60 minutes. After solid-liquid separation, an aluminum-containing solution and a solid are obtained. Take the solid to obtain a dealuminized solar cell. (2) The aluminum-dealuminized battery cell described in step (1) is washed with deionized water and then immersed in a mixed solution of an oxidant aqueous solution and a complexing agent aqueous solution. The mixture is reacted at 30-50°C for 20-50 minutes. After the reaction is completed, the liquid is separated by solid-liquid separation to obtain a silver-containing extract. The oxidant is hydrogen peroxide or peracetic acid. The complexing agent is ethylenediaminetetraacetic acid, aminotriacetic acid, or N,N-bis(hydroxymethyl)-L-glutamate sodium salt. The initial concentration of the oxidant in the mixed solution is 5-15 wt%, and the molar ratio of the oxidant in the oxidant aqueous solution to the complexing agent in the complexing agent aqueous solution is (10-30):

1. (3) Add a chlorine source to the silver-containing extract in step (2) and react for 20-40 min. Separate the solid and liquid to obtain the separated liquid and precipitate. Take the precipitate and dry it to obtain silver chloride powder. The chlorine source is sodium chloride or potassium chloride. The ratio of the amount of chloride ions in the chlorine source to the amount of silver ions measured in the silver-containing extract is 1-1.2:

1. (4) Add the silver chloride powder described in step (3) to an ammonia solution with a concentration of 22~30wt%, and stir at 35~50℃ until the silver chloride is completely dissolved to obtain a silver ammonia solution. The mass ratio of the silver chloride powder to the ammonia solution is 1:25-35. (5) Add a reducing agent to the silver ammonia solution in step (4), stir and react for 30-60 minutes, filter to obtain metallic silver precipitate, and obtain silver powder after post-treatment; the molar ratio of the reducing agent to the silver chloride powder in step (4) is 1:1-2.

2. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The mass ratio of the dealuded battery cell to the mixed solution of the oxidant aqueous solution and the complexing agent aqueous solution in step (2) is 1:

6.

3. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The mass ratio of the decommissioned crystalline silicon solar cell to the hydrochloric acid solution in step (1) is 1:1-4.

4. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The oxidant mentioned in step (2) is hydrogen peroxide.

5. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The complexing agent mentioned in step (2) is ethylenediaminetetraacetic acid.

6. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The aluminum-containing solution in step (1) is used to prepare polyaluminum chloride.

7. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The separated liquid from step (3) is recycled and added to the reaction system in step (2) of the next cycle reaction for reuse.

8. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The reducing agent mentioned in step (5) is ascorbic acid or glucose.

9. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The post-processing described in step (5) involves washing the precipitated silver metal with deionized water and then vacuum drying it to obtain the silver powder.

10. The method for recovering metallic silver from decommissioned crystalline silicon photovoltaic cells as described in claim 1, characterized in that, The method is as follows: (1) The retired crystalline silicon solar cell was immersed in a hydrochloric acid solution with a mass concentration of 18% for 50 minutes. After solid-liquid separation, an aluminum-containing solution and a solid were obtained. The solid was taken to obtain a dealuminized solar cell. The mass ratio of the retired crystalline silicon solar cell to the hydrochloric acid solution was 1:1-4. (2) The aluminum-dealuminized battery cell described in step (1) is washed with deionized water and then immersed in a mixed aqueous solution of hydrogen peroxide and ethylenediaminetetraacetic acid. The reaction is carried out at 45°C for 40 min. After the reaction is completed, a silver-containing extract is obtained by solid-liquid separation. The initial concentration of hydrogen peroxide in the mixed aqueous solution is 3-10 wt%, and the molar ratio of hydrogen peroxide to ethylenediaminetetraacetic acid is 20:

1. (3) Add sodium chloride to the silver-containing extract in step (2) and react for 30 min. Separate the solid to obtain the separated liquid and precipitate. Take the precipitate and dry it to obtain silver chloride powder. The molar ratio of chloride ions in the sodium chloride to the amount of silver ions measured in the silver-containing extract is 1.1:

1. The separated liquid is recovered and added to the reaction system in step (2) of the next cycle reaction for recycling as a silver extraction agent; (4) Add the silver chloride powder described in step (3) to a 25wt% ammonia solution and stir at 45°C until the silver chloride is completely dissolved to obtain a silver ammonia solution; the mass ratio of the silver chloride powder to the ammonia solution is 1:

30. (5) Add glucose to the silver ammonia solution described in step (4), stir and react for 60 min, filter to obtain metallic silver precipitate, wash with deionized water and vacuum dry to obtain silver powder; The molar ratio of glucose to silver chloride powder in step (4) is 1:2.

Images