A method for separating silicon-based waste double-glass photovoltaic modules and recycling metallic silver

Abstract

The application discloses a method for separating silicon-based waste double-glass photovoltaic modules by microwave heating and recycling metal silver. The method can enhance the reaction by using microwave heating, and can completely separate the metal silver from the module matrix by using a nitric acid solution containing disodium ethylenediaminetetraacetate (EDTA-2Na). The application can efficiently separate the plastic film and recycle the silver, and has the advantages of short process, simple operation, low cost, high silver recovery rate and the like.

Description

Technical Field

[0001] This invention relates to a method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver, belonging to the field of resource recycling technology. Background Technology

[0002] With the rapid development of the photovoltaic industry, the use of silicon-based double-glass photovoltaic modules is increasing. Over time, the disposal and recycling of these modules has become a significant issue. Silicon-based waste double-glass photovoltaic modules mainly consist of glass, plastic film (ethylene-vinyl acetate copolymer or polyvinyl butyral, etc.), and solar cells. The plastic film acts as an adhesive, fixing the solar cells to the glass backsheet; therefore, separating the plastic film is a crucial step in the recycling process. Furthermore, these modules contain the precious metal silver, an important metal resource with high economic value. Therefore, silver recovery is also essential in the recycling of these silicon-based waste double-glass photovoltaic modules.

[0003] Currently, common methods for separating plastic films mainly include physical crushing, chemical dissolution, and conventional thermal decomposition. These methods suffer from low processing efficiency, high energy consumption, and severe environmental pollution. Therefore, developing an efficient and environmentally friendly method for separating plastic films is of great significance. Similarly, for the recovery of silver from waste photovoltaic modules, commonly used methods include conventional acid leaching and electrolytic recovery. These methods often employ traditional heating methods, which suffer from low efficiency, high energy consumption, long processes, and low silver leaching rates. Therefore, developing a method for separating and recovering silver from double-glass photovoltaic modules that features rapid heating, quick reaction, short process, and low cost is of great importance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver. This method can efficiently separate plastic film and recover silver, and has the advantages of short process, simple operation, low cost and high silver recovery rate.

[0005] To solve the above technical problems, the present invention adopts the following technical solution: A method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver comprises the following steps: (1) Disassemble the silicon-based waste double-glass photovoltaic module, remove the frame and junction box, and obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The substrate of the silicon-based waste double-glass photovoltaic module is heated by microwave to melt the plastic film and separate it from the glass plate. Then it is rapidly cooled to make the plastic film shrink and crack. The plastic film is removed by water rinsing and vibration to obtain waste silicon-based solar cells. (3) Add disodium ethylenediaminetetraacetate to the nitric acid solution and stir until homogeneous to obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cells into a plastic container containing EDTA-2Na-nitric acid solution, control the liquid-to-solid volume ratio, and use microwave to intermittently heat the solution system to dissolve the silver. Filter out the silicon wafers and their fragments to obtain a silver-containing solution. (5) Add the metal iron powder to the silver-containing solution, use microwave to intermittently heat the solution system so that the silver is reduced by the metal iron powder, filter to obtain the silver-containing precipitate, wash the silver-containing precipitate repeatedly with dilute hydrochloric acid solution to remove the unreacted iron powder, wash it with water and dry it at low temperature to obtain metal silver particles.

[0006] In step (2) above, the microwave heating conditions are 2450MHz microwave, the heating time is 120-360S, the heating temperature is 120-300℃, the cooling method is ice bath cooling, and the cooling time is 5-40min.

[0007] Specifically, in step (2) above, the microwave heating conditions are 2450MHz microwaves, the heating time is 150-300S, the heating temperature is 150-250℃, the cooling method is ice bath cooling, and the cooling time is 10-30min.

[0008] In step (3) above, disodium ethylenediaminetetraacetate is added to a 3-40% nitric acid solution. The mass fraction ratio of disodium ethylenediaminetetraacetate to the 3-40% nitric acid solution is 0.1-5:100. The mixture is stirred until homogeneous to obtain an EDTA-2Na-nitric acid solution.

[0009] Specifically, in step (3) above, disodium ethylenediaminetetraacetate is added to a 5-30% nitric acid solution, with the mass fraction ratio of disodium ethylenediaminetetraacetate to the 5-30% nitric acid solution being 1-4:100. The mixture is stirred until homogeneous to obtain an EDTA-2Na-nitric acid solution.

[0010] In step (4) above, the waste silicon-based solar cell is placed in a plastic container containing EDTA-2Na-nitric acid solution. The volume ratio of the waste silicon-based solar cell to the EDTA-2Na-nitric acid solution is 2-6:1. The intermittent heating is performed 2-6 times under 2450MHz microwave conditions, with an interval of 3-15 minutes between each heating and a heating time of 10-100 seconds.

[0011] Specifically, in the aforementioned step (4), the waste silicon-based solar cells are placed in a plastic container containing EDTA-2Na-nitric acid solution. The volume ratio of the waste silicon-based solar cells to the EDTA-2Na-nitric acid solution is 3-5:1. The intermittent heating is performed 3-5 times under 2450MHz microwave conditions, with an interval of 5-10 minutes between each heating and a heating time of 15-80 seconds.

[0012] In the aforementioned step (5), according to the mass fraction ratio, the amount of iron powder added is 1-2.5 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The intermittent heating is performed 3-8 times under 2450MHz microwave conditions, with an interval of 3-15 minutes and a heating time of 5-90 seconds each time. The concentration of the dilute hydrochloric acid solution is 0.5%-30%, the number of cleaning cycles is 3-15, and the drying temperature is 40-100℃.

[0013] Specifically, in the aforementioned step (5), according to the mass fraction ratio, the amount of iron powder added is preferably 1.1-2 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The intermittent heating is performed 4-5 times under 2450MHz microwave conditions, with an interval of 5-10 minutes and a heating time of 10-60 seconds each time. The concentration of the dilute hydrochloric acid solution is 3-20%, the number of cleaning cycles is 5-10, and the drying temperature is 50-80℃.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Compared with existing technologies, the microwave heating method used in this invention has the advantages of fast heating speed, high selectivity, ability to heat polar molecular materials, no thermal effect on non-polar molecular substances, and the ability to heat plastic film layers through glass. In a solution containing metal particles, the metal will generate eddy currents under the action of an alternating electromagnetic field. These eddy currents will generate a large amount of heat, causing localized overheating of the solution. This overheating can promote chemical reactions and is beneficial for the dissolution and reduction of silver.

[0015] This method can efficiently separate plastic films and recover silver, with a silver recovery rate of up to 93.8%. It also has the advantages of short process, simple operation, low cost and high silver recovery rate. Attached Figure Description

[0016] Figure 1 Scanning electron microscope image of the recovered silver. Detailed Implementation

[0017] To better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0018] Example 1 The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver is carried out according to the following steps: (1) A certain type of silicon-based waste double-glass photovoltaic module is mechanically disassembled, and the frame and junction box are removed to obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The silicon-based waste double-glass photovoltaic module substrate is heated by an industrial microwave heating device with a frequency of 2450MHz for 120s to reach a temperature of 120℃. After removal, the glass plate is mechanically separated from the silicon substrate material. Then, the heated module is rapidly cooled in an ice bath for 5 minutes. After mechanical vibration and high-pressure water rinsing, the plastic film is removed to obtain the waste silicon-based solar cell. (3) Add disodium ethylenediaminetetraacetate to a 3% nitric acid solution, with a mass fraction ratio of disodium ethylenediaminetetraacetate to nitric acid solution of 0.1:100, stir well to obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cell into the prepared EDTA-2Na nitric acid solution with a liquid-to-solid volume ratio of 2:1. Use a 2450MHz industrial microwave heating device to heat the solution system twice at intervals, with an interval of 3 minutes each time and a heating time of 10 seconds each time. After cooling, remove the silicon wafers and fragments to obtain a silver-containing solution. (5) Add metallic iron powder with a particle size of about 150 micrometers to the silver-containing solution. According to the mass fraction ratio, the amount of iron powder added is 1 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The solution system is heated three times at intervals using an industrial microwave heating device of 2450MHz, with each heating time being 5 seconds every 3 minutes. After cooling, the solution is filtered to obtain a silver-containing precipitate. The silver-containing precipitate is then washed three times repeatedly with a 0.5% dilute hydrochloric acid solution to remove unreacted iron powder. After being washed with clean water, the solution is dried in a drying oven at 40°C for 24 hours to obtain metallic silver. The silver recovery rate reaches 80.2%.

[0019] Example 2 The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver is carried out according to the following steps: (1) The same silicon-based waste double-glass photovoltaic module as in Example 1 was mechanically disassembled, and the frame and junction box were removed to obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The silicon-based waste double-glass photovoltaic module substrate is heated by an industrial microwave heating device with a frequency of 2450MHz for 150 seconds and the temperature reaches 146℃. After taking it out, the glass plate is mechanically separated from the silicon substrate material. Then, the heated module is rapidly cooled in an ice bath for 10 minutes. After mechanical vibration and high-pressure water rinsing, the plastic film is removed to obtain the waste silicon-based solar cell. (3) Add disodium ethylenediaminetetraacetate to a 5% nitric acid solution, with a mass ratio of disodium ethylenediaminetetraacetate to nitric acid solution of 1:100, stir well to obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cell into the prepared EDTA-2Na-nitric acid solution with a liquid-to-solid volume ratio of 3:1. Use a 2450MHz industrial microwave heating device to heat the solution system three times at intervals, with an interval of 5 minutes each time and a heating time of 15 seconds each time. After cooling, remove the silicon wafers and fragments to obtain a silver-containing solution. (5) Add metallic iron powder with a particle size of about 150 micrometers to the silver-containing solution. According to the mass fraction ratio, the amount of iron powder added is 1.1 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The solution system is heated 4 times at intervals using an industrial microwave heating device of 2450MHz, with each heating time being 10 seconds every 5 minutes. After cooling, the solution is filtered to obtain a silver-containing precipitate. The silver-containing precipitate is then washed 5 times with a 3% dilute hydrochloric acid solution to remove unreacted iron powder. After being washed with clean water, the solution is dried in a drying oven at 50°C for 24 hours to obtain metallic silver. The silver recovery rate reaches 85.6%.

[0020] Example 3 The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver is carried out according to the following steps: (1) The same silicon-based waste double-glass photovoltaic module as in Example 1 was mechanically disassembled, and the frame and junction box were removed to obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The silicon-based waste double-glass photovoltaic module substrate is heated by an industrial microwave heating device with a frequency of 2450MHz for 200s and the temperature reaches 194℃. After taking it out, the glass plate is mechanically separated from the silicon substrate material. Then the heated module is rapidly cooled in an ice bath for 20min. After mechanical vibration and high-pressure water rinsing, the plastic film is removed to obtain the waste silicon-based solar cell. (3) Add disodium ethylenediaminetetraacetate to a 20% nitric acid solution. The mass fraction ratio of disodium ethylenediaminetetraacetate to nitric acid solution is 3:100. Stir well to obtain EDTA-2Na-nitric acid solution. (4) Place the waste silicon-based solar cell into the prepared EDTA-2Na-nitric acid solution with a liquid-to-solid volume ratio of 4:1. Use a 2450MHz industrial microwave heating device to heat the solution system 4 times at intervals, with an interval of 8 minutes each time and a heating time of 50 seconds each time. After cooling, remove the silicon wafers and fragments to obtain a silver-containing solution. (5) Add metallic iron powder with a particle size of about 150 micrometers to the silver-containing solution. According to the mass fraction ratio, the amount of iron powder added is 1.5 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The solution system is heated 5 times at intervals using an industrial microwave heating device of 2450MHz, with each heating time being 40 seconds after 8 minutes. After cooling, the solution is filtered to obtain a silver-containing precipitate. The silver-containing precipitate is then repeatedly washed with a 10% dilute hydrochloric acid solution to remove unreacted iron powder 8 times. After being cleaned with water, the solution is dried in a drying oven at 70°C for 24 hours to obtain metallic silver. The silver recovery rate reaches 91.7%.

[0021] Example 4 The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver is carried out according to the following steps: (1) The same silicon-based waste double-glass photovoltaic module as in Example 1 was mechanically disassembled, and the frame and junction box were removed to obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The silicon-based waste double-glass photovoltaic module substrate is heated by an industrial microwave heating device with a frequency of 2450MHz for 300s and the temperature reaches 258℃. After taking it out, the glass plate is mechanically separated from the silicon substrate material. Then, the heated module is rapidly cooled in an ice bath for 30min. After mechanical vibration and high-pressure water rinsing, the plastic film is removed to obtain the waste silicon-based solar cell. (3) Add disodium ethylenediaminetetraacetate to a 30% nitric acid solution, with a mass ratio of disodium ethylenediaminetetraacetate to nitric acid solution of 4:100, stir well to obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cell into the prepared EDTA-2Na-nitric acid solution with a liquid-to-solid volume ratio of 5:1. Use a 2450MHz industrial microwave heating device to heat the solution system 5 times at intervals, with an interval of 10 minutes each time and a heating time of 80 seconds each time. Then remove the silicon wafers and fragments to obtain a silver-containing solution. (5) Add metallic iron powder with a particle size of about 150 micrometers to the silver-containing solution. According to the mass fraction ratio, the amount of iron powder added is twice the theoretical amount required to neutralize excess nitric acid and reduce silver. The solution system is heated 5 times at intervals using an industrial microwave heating device of 2450MHz, with each heating time being 60 seconds for every 10 minutes. After heating, the solution is filtered to obtain a silver-containing precipitate. The silver-containing precipitate is then washed 10 times with a 20% dilute hydrochloric acid solution to remove unreacted iron powder. After being washed with clean water, the solution is dried in a drying oven at 80°C for 24 hours to obtain metallic silver. The silver recovery rate reaches 93.8%.

[0022] Example 5 The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver is carried out according to the following steps: (1) The same silicon-based waste double-glass photovoltaic module as in Example 1 was mechanically disassembled, and the frame and junction box were removed to obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The silicon-based waste double-glass photovoltaic module substrate is heated by an industrial microwave heating device with a frequency of 2450MHz for 360s and the temperature reaches 300℃. After taking it out, the glass plate is mechanically separated from the silicon substrate material. Then, the heated module is rapidly cooled in an ice bath for 40min. After mechanical vibration and high-pressure water rinsing, the plastic film is removed to obtain the waste silicon-based solar cell. (3) Add disodium ethylenediaminetetraacetate to a 40% nitric acid solution, with a mass ratio of disodium ethylenediaminetetraacetate to nitric acid solution of 5:100, stir well to obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cell into the prepared EDTA-2Na-nitric acid solution with a liquid-to-solid volume ratio of 6:1. Use a 2450MHz industrial microwave heating device to heat the solution system 6 times at intervals, with an interval of 15min each time and a heating time of 100s each time. After cooling, remove the silicon wafers and fragments to obtain a silver-containing solution. (5) Add metallic iron powder with a particle size of about 150 micrometers to the silver-containing solution. According to the mass fraction ratio, the amount of iron powder added is 2.5 times that of the silver-containing solution. The solution system is heated 8 times at intervals using an industrial microwave heating device of 2450MHz. The heating time is 90 seconds every 15 minutes. After cooling, the solution is filtered to obtain a silver-containing precipitate. The silver-containing precipitate is then repeatedly washed with a 30% dilute hydrochloric acid solution to remove unreacted iron powder 15 times. After being cleaned with water, the solution is dried in a drying oven at 100℃ for 24 hours to obtain metallic silver. The silver recovery rate reaches 93.5%.

[0023] Comparative Example 1 The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver is carried out according to the following steps: (1) The same silicon-based waste double-glass photovoltaic module as in Example 1 was mechanically disassembled, and the frame and junction box were removed to obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The silicon-based waste double-glass photovoltaic module substrate is heated by an industrial microwave heating device with a frequency of 2450MHz for 300s and the temperature reaches 256℃. After taking it out, the glass plate is mechanically separated from the silicon substrate material. Then the heated module is rapidly cooled in an ice bath for 30min. After mechanical vibration and high-pressure water rinsing, the plastic film is removed to obtain the waste silicon-based solar cell. (3) Add disodium ethylenediaminetetraacetate to a 30% nitric acid solution, with a mass ratio of disodium ethylenediaminetetraacetate to nitric acid solution of 4:100, stir well to obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cell into the prepared EDTA-2Na-nitric acid solution with a liquid-to-solid volume ratio of 5:1, heat it to 80°C in a water bath, keep it warm for 1 hour, and after cooling, remove the silicon wafers and fragments to obtain a silver-containing solution. (5) Add metallic iron powder with a particle size of about 150 micrometers to the silver-containing solution. According to the mass fraction ratio, the amount of iron powder added is twice the theoretical amount required to neutralize excess nitric acid and reduce silver. Heat the solution to 80°C in a water bath and keep it at that temperature for 1 hour. After cooling, filter the solution to obtain a silver-containing precipitate. Wash the silver-containing precipitate repeatedly 10 times with a 20% dilute hydrochloric acid solution to remove unreacted iron powder. After washing it with clean water, dry it in a drying oven at 80°C for 24 hours to obtain metallic silver. The silver recovery rate reached 74.2%.

Claims

1. A method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver, characterized in that, Follow these steps: (1) Disassemble the silicon-based waste double-glass photovoltaic module, remove the frame and junction box, and obtain the silicon-based waste double-glass photovoltaic module substrate; (2) The substrate of the silicon-based waste double-glass photovoltaic module is heated by microwave to melt the plastic film and separate it from the glass plate. Then it is rapidly cooled to make the plastic film shrink and crack. The plastic film is removed by water rinsing and vibration to obtain waste silicon-based solar cells. (3) Add disodium ethylenediaminetetraacetate to a 3-40% nitric acid solution, with a mass fraction ratio of disodium ethylenediaminetetraacetate to 3-40% nitric acid solution of 0.1-5:100, stir until homogeneous, and obtain EDTA-2Na-nitric acid solution; (4) Place the waste silicon-based solar cells into a plastic container containing EDTA-2Na-nitric acid solution, control the liquid-to-solid volume ratio, and use microwave to intermittently heat the solution system to dissolve the silver. Filter out the silicon wafers and their fragments to obtain a silver-containing solution. (5) Add the metal iron powder to the silver-containing solution, use microwave to intermittently heat the solution system so that the silver is reduced by the metal iron powder, filter to obtain the silver-containing precipitate, wash the silver-containing precipitate repeatedly with dilute hydrochloric acid solution to remove the unreacted iron powder, wash it with water and dry it at low temperature to obtain metal silver particles.

2. The method for separating silicon-based waste double-glass photovoltaic modules and recovering metallic silver according to claim 1, characterized in that: In step (2), the microwave heating conditions are 2450MHz microwave, the heating time is 120-360S, the heating temperature is 120-300℃, the cooling method is ice bath cooling, and the cooling time is 5-40min.

3. The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver according to claim 2, characterized in that: In step (2), the microwave heating conditions are 2450MHz microwave, the heating time is 150-300S, the heating temperature is 150-250℃, the cooling method is ice bath cooling, and the cooling time is 10-30min.

4. The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver according to claim 1, characterized in that: In step (3), disodium ethylenediaminetetraacetate is added to a 5-30% nitric acid solution. The mass fraction ratio of disodium ethylenediaminetetraacetate to the 5-30% nitric acid solution is 1-4:

100. The mixture is stirred until homogeneous to obtain an EDTA-2Na-nitric acid solution.

5. The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver according to claim 1, characterized in that: In step (5), according to the mass fraction ratio, the amount of iron powder added is 1-2.5 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The intermittent heating is performed 3-8 times under 2450MHz microwave conditions, with an interval of 3-15 minutes and a heating time of 5-90 seconds each time. The concentration of the dilute hydrochloric acid solution is 0.5%-30%, the number of cleaning cycles is 3-15, the drying temperature is 40-100℃, and the drying time is 24 hours.

6. The method for separating waste silicon-based double-glass photovoltaic modules and recovering metallic silver according to claim 5, characterized in that: In step (5), according to the mass fraction ratio, the amount of iron powder added is 1.1-2 times the theoretical amount required to neutralize excess nitric acid and reduce silver. The intermittent heating is performed 4-5 times under 2450MHz microwave conditions, with an interval of 5-10 minutes and a heating time of 10-60 seconds each time. The concentration of the dilute hydrochloric acid solution is 3-20%. The number of cleaning cycles is 5-10 times. The drying temperature is 50-80℃ and the drying time is 24 hours.

Images