Wet purification process suitable for silicon and precious metal of waste photovoltaic laminated part

Abstract

The invention provides a wet purification process suitable for silicon and precious metal of a waste photovoltaic laminated piece, which comprises the following steps of: immersing a waste crystalline silicon battery piece into a NaOH solution, and removing an aluminum wire on the surface of the crystalline silicon battery piece to obtain a dealuminized crystalline silicon piece; the dealuminated crystal silicon wafer is subjected to acid pickling, and a silver-removed crystal silicon wafer and silver leaching liquid are obtained; removing impurities from the silver-removed crystal silicon wafer through a hydrofluoric acid solution to obtain a high-purity crystal silicon wafer; and extracting the silver elementary substance from the silver leachate through a hydrazine hydrate reduction method. According to the wet purification process, the waste crystalline silicon battery piece can be subjected to high-purity recovery, and the high-purity crystalline silicon wafer and the silver elementary substance can be obtained.

Description

Technical Field

[0001] This invention relates to the field of waste photovoltaic module recycling technology, and in particular to a wet purification process for silicon and precious metals in waste photovoltaic laminates. Background Technology

[0002] Generally, photovoltaic (PV) modules have a lifespan of 25 to 30 years. As they age, a large number of expired or damaged PV modules urgently require safe disposal. PV modules consist of an aluminum frame and a photovoltaic laminate, which primarily comprises tempered glass, solar cells, and organic materials (encapsulant film and backsheet). Currently, the recycling and processing of retired PV modules involves two main steps: first, module disassembly, primarily disassembling the aluminum frame and junction box, removing the EVA film, separating the backsheet and glass; second, component separation, mainly separating silicon, silver, and aluminum from the cells, and copper, tin, and lead from the solder strips. Silver is a precious metal. However, current methods for recycling silicon wafers and silver are typically complex, and the final purity is not very high. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a wet purification process for silicon and precious metals in waste photovoltaic laminates, which can improve the extraction purity of silicon wafers and silver, and the method is simple.

[0004] This invention proposes a wet purification process for silicon and precious metals in waste photovoltaic laminates, comprising the following steps:

[0005] S1. Immerse the waste crystalline silicon solar cells in NaOH solution to remove the aluminum wires on the surface of the crystalline silicon solar cells and obtain dealuminized crystalline silicon wafers;

[0006] S2. Acid washing is performed on the dealuminized silicon wafer to obtain desilvered silicon wafer and silver leaching solution;

[0007] S3. Remove impurities from the desilvered silicon wafers using hydrofluoric acid solution to obtain high-purity silicon wafers;

[0008] S4. Extract elemental silver from the silver leaching solution using the hydrazine hydrate reduction method.

[0009] In some embodiments, in step S1, the concentration of the NaOH solution is 25-35%, the solid-liquid ratio of the crystalline silicon solar cell to the NaOH solution is 1:50, the immersion time is 50-70 min, and the temperature is 70-90°C.

[0010] In some embodiments, in step S2, when the dealuated silicon wafer is acid-washed, it is soaked in a nitric acid solution with a concentration of 5 mol / L and a solid-liquid ratio of 1:50 between the dealuated silicon wafer and the nitric acid solution.

[0011] In some embodiments, in step S2, the soaking time is 90-110 min and the leaching temperature is 50-70°C.

[0012] In some embodiments, step S4, the hydrazine hydrate reduction method includes: mixing silver leaching solution with hydrochloric acid solution to convert it into silver chloride precipitate solution, evaporating the silver chloride precipitate solution to obtain silver chloride solid, and then mixing the silver chloride solid with hydrazine hydrate and NaOH solution to obtain elemental silver.

[0013] In some embodiments, during step S4, when the silver chloride precipitate solution is evaporated, the silver chloride precipitate solution is placed in an oil bath at 100°C and heated for 4 to 6 hours until all the liquid in the silver chloride precipitate solution is evaporated, and the resulting solid is silver chloride solid.

[0014] In some embodiments, in step S4, silver chloride solid is first mixed with NaOH solution, and then hydrazine hydrate is slowly added dropwise until the solution is clear and no bubbles are generated. Stirring is continued, and then solid-liquid separation is performed to obtain elemental silver.

[0015] In some embodiments, in step S4, the mass concentration of the NaOH solution is 10%, and the solid-liquid ratio of silver chloride solid to NaOH solution is 1:1.5.

[0016] In some embodiments, the stirring time in step S4 is 1 to 1.5 hours.

[0017] In some embodiments, in step S4, elemental silver is mixed with hydrochloric acid of mass concentration of 15%, stirred to remove impurities, and finally washed with deionized water and dried to obtain high-purity elemental silver. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0019] in:

[0020] Figure 1 This is a flowchart of a wet purification process for silicon and precious metals in waste photovoltaic laminates, as described in an embodiment of the present invention.

[0021] Figure 2 This is a front-view electron microscope scan of the high-purity silicon wafer recovered in an embodiment of the present invention.

[0022] Figure 3 The front energy dispersive spectrum of the high-purity crystalline silicon wafer recovered in this embodiment of the invention;

[0023] Figure 4 This is a back electron microscope scan of the high-purity crystalline silicon wafer recovered in an embodiment of the present invention;

[0024] Figure 5 The back-side energy dispersive spectrum of the high-purity crystalline silicon wafer recovered in this embodiment of the invention;

[0025] Figure 6 This is a photograph of the desilvered silicon wafer before the silicon nitride antireflective layer was removed in this embodiment of the invention.

[0026] Figure 7 This is a photograph of the desilvered silicon wafer after the silicon nitride antireflective layer has been removed in an embodiment of the present invention. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] The following describes, with reference to the accompanying drawings, a wet purification process for silicon and precious metals in waste photovoltaic laminates, according to embodiments of the present invention.

[0029] like Figure 1 As shown in the figure, this invention proposes a wet purification process for silicon and precious metals in waste photovoltaic laminates, comprising the following steps:

[0030] S1. Immerse the waste crystalline silicon solar cells in NaOH solution to remove the aluminum wires on the surface of the crystalline silicon solar cells and obtain dealuminized crystalline silicon wafers;

[0031] S2. Acid washing is performed on the dealuminized silicon wafer to obtain desilvered silicon wafer and silver leaching solution;

[0032] S3. Remove impurities from the desilvered silicon wafers using hydrofluoric acid solution to obtain high-purity silicon wafers;

[0033] S4. Extract elemental silver from the silver leaching solution using the hydrazine hydrate reduction method.

[0034] The wet purification process of this invention can recycle waste crystalline silicon solar cells with high purity, yielding crystalline silicon wafers and elemental silver with high purity. The purity of the crystalline silicon wafers can reach 99.999%, and the method is relatively simple.

[0035] This invention improves the purity of recycled silicon wafers by removing the Si3N4 antireflective layer on the desilvered silicon wafers using hydrofluoric acid solution. The chemical reaction involved is Si3N4 + 12HF = SiF4 + 4NH3.

[0036] In step S1, NaOH is used to remove the aluminum wires on the surface of the battery cell. The chemical reaction involved is 2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2↑.

[0037] Furthermore, experiments revealed that increasing the concentration of the HF solution facilitates the rapid dissolution of the anti-reflective layer on the desilvered silicon wafer. Considering the strong corrosiveness and volatility of the HF solution, a mass concentration of 20% was determined as the optimal dissolution concentration.

[0038] It should be noted that in step S1, in addition to obtaining aluminum-free crystalline silicon wafers by reacting with NaOH solution, aluminum leachate is also obtained. Since aluminum is not a precious metal, the collection of aluminum metal is not within the scope of this invention and will not be elaborated upon.

[0039] In some embodiments, in step S1, the concentration of the NaOH solution is 25-35%, preferably 30%, the solid-liquid ratio of the crystalline silicon solar cell to the NaOH solution is 1:50, the immersion time is 50-70 min, preferably 60 min, and the temperature is 70-90°C, preferably 80°C.

[0040] The concentration of the NaOH solution is preferably 30% because it reduces the consumption of NaOH and the high corrosiveness caused by high alkalinity.

[0041] Experiments showed that extending the leaching time is beneficial to increasing the concentration of aluminum ions in the leachate. However, when the leaching time reaches 60 minutes, there is basically no change in the effect on the aluminum leaching rate when the leaching time is further increased. Considering that better leaching effect can be achieved in the shortest possible time, the leaching time is preferably 60 minutes.

[0042] Increasing the temperature is beneficial for further dissolving crystalline silicon solar cells in NaOH, thereby increasing the aluminum leaching rate. However, once the temperature reaches 80℃, further increases have little effect on the aluminum leaching rate. Therefore, 80℃ is selected as the optimal leaching temperature.

[0043] In some embodiments, in step S2, when the dealuated silicon wafer is acid-washed, it is soaked in a nitric acid solution with a concentration of 5 mol / L and a solid-liquid ratio of 1:50 between the dealuated silicon wafer and the nitric acid solution.

[0044] The chemical reaction involved in the extraction of silver is 3Ag + 4HNO3 = 3AgNO3 + 2H2O + NO↑. AgNO3 is the silver leaching solution.

[0045] In some embodiments, in step S2, the soaking time is 90-110 min, preferably 100 min, and the leaching temperature is 50-70°C, preferably 60°C.

[0046] Experiments revealed that increasing the temperature facilitates further dissolution of the dealuded silicon wafers in nitric acid, thereby increasing the silver leaching rate. However, when the temperature exceeds 60℃, further increases actually decrease the silver leaching rate. This is because the leaching temperature of 70℃ is close to the boiling point of nitric acid, resulting in the volatilization of a small amount of nitric acid components. Therefore, 60℃ was chosen as the optimal leaching temperature.

[0047] In some embodiments, step S4, the hydrazine hydrate reduction method includes: mixing silver leaching solution with hydrochloric acid solution to convert it into silver chloride precipitate solution, evaporating the silver chloride precipitate solution to obtain silver chloride solid, and then mixing the silver chloride solid with hydrazine hydrate and NaOH solution to obtain elemental silver.

[0048] Hydrazine hydrate (N₂H₄·H₂O) is a strong reducing agent that can undergo a redox reaction with AgCl. Ammonia and hydrazine hydrate are commonly used to reduce silver to elemental form. However, if this reaction is carried out in an ammonia solution, wastewater treatment is difficult, and silver azide may be formed, which can easily cause an explosion. Therefore, replacing the ammonia solution with NaOH solution can also ensure the complete reduction reaction. The relevant chemical equation is:

[0049] 4AgCl+N2H4·H2O+4NaOH→4Ag↓+N2↑+4NaCl+5H2O.

[0050] In some embodiments, during step S4, when the silver chloride precipitate solution evaporates, the silver chloride precipitate solution is placed in an oil bath at 100°C and heated for 4 to 6 hours, preferably 5 hours, until all the liquid (such as nitric acid, hydrochloric acid, or water) in the silver chloride precipitate solution evaporates, and the resulting solid is silver chloride solid.

[0051] In some embodiments, in step S4, silver chloride solid is first mixed with NaOH solution, and then hydrazine hydrate is slowly added dropwise until the solution is clear and no bubbles are generated. Stirring is continued, and then solid-liquid separation is performed to obtain elemental silver.

[0052] In some embodiments, in step S4, the mass concentration of the NaOH solution is 10%, and the solid-liquid ratio of silver chloride solid to NaOH solution is 1:1.5.

[0053] In some embodiments, in step S4, the stirring time is 1 to 1.5 hours, preferably 1 hour.

[0054] In some embodiments, in step S4, elemental silver is mixed with 15% hydrochloric acid by mass, stirred to remove impurities, and finally washed with deionized water and dried to obtain high-purity elemental silver. The purity of the elemental silver can reach 99.7%.

[0055] Furthermore, during the mixing and stirring of elemental silver and hydrochloric acid, appropriate heating, such as 40-70℃, can help to remove impurities more thoroughly.

[0056] Furthermore, after stirring to remove impurities, the mixture is washed multiple times with deionized water to remove chloride ions as completely as possible.

[0057] The present invention will be further illustrated by specific embodiments below.

[0058] Example 1

[0059] like Figure 1 As shown, a wet purification process for silicon and precious metals in waste photovoltaic laminates includes the following steps:

[0060] S1. Immerse the waste crystalline silicon solar cells in a NaOH solution with a concentration of 30%, a solid-liquid ratio of crystalline silicon solar cells to NaOH solution of 1:50, an immersion time of 60 minutes, and a temperature of 80°C to remove the aluminum wires on the surface of the crystalline silicon solar cells and obtain dealuminized crystalline silicon wafers.

[0061] S2. The dealuated silicon wafers are immersed in a nitric acid solution for pickling. The concentration of the nitric acid solution is 5 mol / L, the solid-liquid ratio of the dealuated silicon wafers to the nitric acid solution is 1:50, the immersion time is 100 min, and the leaching temperature is 60℃, to obtain silver-free silicon wafers and silver leaching solution.

[0062] S3. The desilvered silicon wafers are purified by passing them through a 20% (w / w) HF solution to obtain high-purity silicon wafers.

[0063] S4. Mix the silver leaching solution with hydrochloric acid solution to convert it into a silver chloride precipitate solution. Heat the silver chloride precipitate solution in an oil bath at 100°C for 5 hours until all liquids (such as nitric acid, hydrochloric acid, and water) in the silver chloride precipitate solution evaporate, and the resulting solid is silver chloride solid. First, mix the silver chloride solid with a 10% NaOH solution at a solid-liquid ratio of 1:1.5. Then, slowly add hydrazine hydrate dropwise until the solution is clear and no bubbles are produced. Continue stirring for 1 hour, then separate the solid and liquid to obtain elemental silver. Mix the elemental silver with a 15% hydrochloric acid solution, heat and stir to remove impurities, and finally wash repeatedly with deionized water and dry to obtain high-purity elemental silver.

[0064] The following results were obtained from the testing:

[0065] Results of high-purity silicon recovery:

[0066] The silicon nitride antireflective layer on desilvered silicon wafers is typically blue (e.g., Figure 6As shown in the image, after treatment with a 20% HF solution, the blue silicon nitride antireflective layer was removed, revealing a silver-gray crystalline silicon body, as shown in the image. Figure 7 As shown.

[0067] Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was used to examine the front side of the recovered high-purity silicon wafers (e.g., ...). Figure 2 (as shown) and the back (as shown) Figure 4 The analysis (as shown) is performed to obtain more accurate purity parameters for the silicon wafer.

[0068] like Figure 3 , 5 As shown, the energy dispersive spectrum indicates that the silver electrode on the front side and the aluminum electrode on the back side of the solar cell have been completely removed, and only the energy peak of silicon is observed, confirming that the purity of silicon on the crystalline silicon wafers obtained under this recycling process is higher than 99.999%.

[0069] Accurately weigh 0.1g of the recovered elemental silver into an Erlenmeyer flask, add 10ml of HNO3 solution, and let stand for 1 hour until the elemental silver is completely dissolved. After further filtration, dilution, and bringing the volume to 100ml, ICP-MS analysis revealed an Ag concentration of 997mg / L. Therefore, the purity of the recovered silver is:

[0070] The purity of Ag = (ICP concentration * volume) / mass of dissolved Ag = (997 mg / L * 100 ml) / 0.1 g = 99.7%.

[0071] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A wet purification process for silicon and precious metals in waste photovoltaic laminates, characterized in that, Includes the following steps: S1. Immerse the waste crystalline silicon solar cells in NaOH solution to remove the aluminum wires on the surface of the crystalline silicon solar cells and obtain dealuminized crystalline silicon wafers; S2. The aluminum-removed silicon wafer is acid-washed to obtain a silver-removed silicon wafer and a silver leaching solution; S3. The desilvered silicon wafer is purified by passing it through a hydrofluoric acid solution to obtain a high-purity silicon wafer; S4. Extract elemental silver from the silver leachate using the hydrazine hydrate reduction method.

2. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 1, characterized in that, In step S1, the concentration of the NaOH solution is 25-35%, the solid-liquid ratio of the crystalline silicon solar cell to the NaOH solution is 1:50, the immersion time is 50-70 min, and the temperature is 70-90℃.

3. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 1, characterized in that, In step S2, when the dealuated silicon wafer is acid-washed, it is soaked in a nitric acid solution with a concentration of 5 mol / L, and the solid-liquid ratio of the dealuated silicon wafer to the nitric acid solution is 1:

50.

4. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 3, characterized in that, In step S2, the soaking time is 90–110 min and the leaching temperature is 50–70 °C.

5. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 1, characterized in that, In step S4, the hydrazine hydrate reduction method includes: mixing the silver leaching solution with hydrochloric acid solution to convert it into a silver chloride precipitate solution, evaporating the silver chloride precipitate solution to obtain silver chloride solid, and then mixing the silver chloride solid with hydrazine hydrate and NaOH solution to obtain elemental silver.

6. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 5, characterized in that, In step S4, when the silver chloride precipitate solution is evaporated, the silver chloride precipitate solution is placed in an oil bath at 100°C and heated for 4 to 6 hours until all the liquid in the silver chloride precipitate solution is evaporated, and the solid obtained is the silver chloride solid.

7. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 5, characterized in that, In step S4, the silver chloride solid is first mixed with NaOH solution, and then hydrazine hydrate is slowly added dropwise until the solution is clear and no bubbles are generated. Stirring is continued, and then solid-liquid separation is performed to obtain the elemental silver.

8. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 7, characterized in that, In step S4, the mass concentration of the NaOH solution is 10%, and the solid-liquid ratio of the silver chloride solid to the NaOH solution is 1:1.

5.

9. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 7, characterized in that, In step S4, the stirring time is 1 to 1.5 hours.

10. The wet purification process for silicon and precious metals in waste photovoltaic laminates according to claim 7, characterized in that, In step S4, the elemental silver is mixed with hydrochloric acid with a mass concentration of 15%, stirred to remove impurities, and finally washed with deionized water and dried to obtain high-purity elemental silver.

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