Selective recovery method for valuable metal in retired crystalline silicon cell photovoltaic solder strip

Abstract

The invention belongs to the technical field of metal resource recovery and reutilization, and particularly relates to a selective recovery method for valuable metal in a retired crystalline silicon cell photovoltaic welding strip. The method comprises the following steps: disassembling a photovoltaic solder strip from a retired crystalline silicon cell, and removing impurities from the photovoltaic solder strip to obtain a clean solder strip; adding the clean welding strip into an acetic acid solution, heating and stirring to fully react, and filtering to respectively obtain filter residues, copper strips and lead-containing filtrate; adding a precipitant into the lead-containing filtrate to carry out precipitation reaction, and after the reaction is finished, carrying out solid-liquid separation, washing and drying to obtain a lead sulfate product; washing and drying filter residues to obtain a tin dioxide crude product; and washing the copper bar with absolute ethyl alcohol, and drying to obtain the metal copper bar with the purity not lower than 99.0%. The method has the advantages of high metal separation efficiency, high recovery rate, low energy consumption, low acid and alkali consumption, difficulty in causing secondary environmental pollution and the like, and provides a feasible solution for selective separation and recovery of valuable metals of retired photovoltaic modules.

Description

Technical Field

[0001] This invention belongs to the field of metal resource recycling and reuse technology, and relates to a selective recycling method for valuable metals in retired crystalline silicon photovoltaic cell welding ribbons. Background Technology

[0002] The exponential growth of global industry has raised concerns about the depletion of existing fossil fuels and global warming. Photovoltaic power generation technology, as a clean and renewable energy solution, has been widely studied. Solar photovoltaic modules typically have a lifespan of only 20-30 years. With the rapid development and widespread application of solar photovoltaic technology, the number of retired photovoltaic modules will surge. The retirement process presents potential hazards and risks. Photovoltaic solder ribbon is an important component of photovoltaic modules, referring to a composite conductive material formed by coating a certain thickness of tin-lead based alloy onto the surface of a copper strip of a certain size. Copper and tin are widely used as key materials in technological industries, while lead poses a potential environmental hazard. When these alloys are processed, manufactured, or retired, heavy metal elements may be released into the environment in large quantities, causing pollution. Therefore, in order to process and recycle retired photovoltaic solder ribbon, there is an urgent need to invent an efficient and stable method to recover copper (Cu), tin (Sn), and lead (Pb) from photovoltaic solder ribbon, improve the metal resource recovery rate, and reduce environmental hazards.

[0003] Currently, the main processes for metal recovery from photovoltaic solder ribbons, both domestically and internationally, include heat treatment, electrolysis, and chemical leaching. Chinese Patent (Publication No.: CN101570826A) discloses a method for separating tin-lead alloys using multi-stage vacuum distillation. This method involves three-stage vacuum distillation of the raw tin-lead alloy in a vacuum furnace, controlling the vacuum level and distillation temperature at each stage to achieve tin and lead separation. This method has high processing costs, requires sophisticated equipment, and consumes a lot of energy due to the high temperature. Chinese Patent (Publication No.: CN102424983A) discloses a combined electrolysis method for high-impurity lead-tin alloys. This method first melts the tin-lead alloy into tin slag, then electrolyzes the tin slag to complete the tin-lead alloy separation. This method requires a high cell voltage during electrolysis, resulting in high energy consumption. Existing chemical leaching methods mostly use strong acid and strong alkali leaching systems, which have poor separation effects, corrode equipment, and easily generate secondary pollution.

[0004] Therefore, there is an urgent need to invent an environmentally friendly, green, and efficient technology for separating decommissioned photovoltaic welding ribbons. Summary of the Invention

[0005] To address the three major contradictions in the field of valuable metal recycling of photovoltaic modules: (1) the contradiction between high energy consumption and low carbon targets in high-temperature metallurgy (high-temperature reaction versus low-temperature reaction); (2) the contradiction between high pollution and environmental protection requirements in chemical leaching (strong acid and strong base reagents versus organic acid system); and (3) the contradiction between low selectivity and high purity requirements in metal separation (mixed leaching versus selective separation), an organic acid system was constructed. This invention solves the problems of high energy consumption and low purity in the existing methods of valuable metal recycling of photovoltaic modules, such as the use of heat treatment methods and the large amount of acid and alkali used in chemical leaching methods, which are prone to secondary pollution. The purpose of this invention is to provide a mild and efficient selective recycling method for valuable metals in the photovoltaic ribbons of retired crystalline silicon cells. This method can obtain high-purity copper, as well as tin and lead compounds. This invention has the advantages of high metal separation efficiency and high recovery rate, low energy consumption, low acid and alkali usage, and low risk of secondary environmental pollution. It can avoid the release of toxic metals into the environment and effectively recycle metal resources, providing a feasible solution for the selective separation and recycling of valuable metals in retired photovoltaic modules.

[0006] This invention constructs a green and simple acetic acid system for the selective recovery of valuable metals from retired crystalline silicon photovoltaic solder ribbons obtained through physical dismantling methods. This invention eliminates the need for external oxidants, relying solely on acetic acid solvent leaching. Utilizing the micro-galvanic corrosion effect within the tin-lead alloy, lead preferentially dissolves in the presence of dissolved oxygen, while tin undergoes oxidative hydrolysis to form SnO2 precipitate instead of tin powder. Copper remains stable and undissolved due to its potential and passivation effect, thus achieving highly selective separation of the three metals. Furthermore, lead ions are precipitated to PbSO4 using dilute sulfuric acid, achieving high recovery rates and purity, and the solution can be recycled. This invention avoids the use of strong oxidants and extractants, achieving higher resource utilization and environmental friendliness, making the process more suitable for industrial-scale promotion. The technical solution of this invention is described in detail below.

[0007] A method for selectively recovering valuable metals from retired crystalline silicon photovoltaic cell solder ribbons includes the following steps: (1) Disassemble the photovoltaic ribbon from the retired crystalline silicon cell and then remove impurities from the photovoltaic ribbon to obtain a clean ribbon; (2) Add the clean solder strip to the acetic acid solution, heat and stir to allow it to react fully. After the reaction is complete, filter to obtain filter residue, copper strip and lead-containing filtrate respectively. (3) Add a precipitant to the lead-containing filtrate obtained in step (2) to carry out a precipitation reaction. After the reaction is completed, filter, wash and dry to obtain lead sulfate product; (4) The filter residue and copper strips obtained in step (2) are washed and dried to obtain crude tin dioxide and metallic copper strips with a purity of not less than 99.0%.

[0008] In this invention, in step (1), the photovoltaic solder ribbon comprises the following components by weight fraction: tin 5.00%~6.10%, lead 5.50%~6.00%, copper 86.50%~87.90%, with the remainder being trace impurity elements, and the total mass satisfies 100%.

[0009] In this invention, in step (1), the impurity removal step is: the photovoltaic welding ribbon is completely immersed in anhydrous ethanol and ultrasonically treated in an ultrasonic cleaner at an ultrasonic frequency of 40~60Hz for 30~50min.

[0010] In this invention, in step (2), the concentration of acetic acid solution is 2~6 mol / L, the feeding ratio of welding strip to acetic acid solution is (1~3) g:60mL, the reaction temperature is 40~70 ℃, the reaction time is 180~360 min, and the stirring rate is 200~600 rpm.

[0011] In this invention, the concentration of acetic acid solution is 4~5 mol / L, the feeding ratio of solder ribbon to acetic acid solution is (1~1.5) g:60 mL, the reaction temperature is 50~70 ℃, and the reaction time is 270~330 min.

[0012] In this invention, in step (3), the precipitant is dilute sulfuric acid, and the concentration of dilute sulfuric acid is between 0.5 and 1.2 mol / L; the precipitation reaction is carried out at a temperature of 20 to 50 °C for a reaction time of 10 to 60 min; during the precipitation process, the pH of the system is maintained at 3.5-4.2, and the purity of the final lead sulfate product is not less than 98%.

[0013] In this invention, in step (3), the remaining solution obtained after the precipitation reaction is completed is returned to the leaching system of step (3) for recycling.

[0014] In this invention, in step (4), the solvent used for washing is water, and after washing, the product is dried at a temperature of 60-80°C for 6-12 hours.

[0015] The present invention also includes step (5): the crude tin dioxide obtained in step (4) is subjected to high-temperature calcination to purify it. After the reaction is completed, the solid is taken out to obtain tin dioxide with a purity of >98%; wherein: the calcination temperature is 500~600 ℃ and the reaction time is 0.5~1h.

[0016] In summary, compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes an acetic acid leaching process. By controlling key parameters such as acetic acid concentration, temperature, time, and solid-liquid ratio, selective leaching and separation of tin and lead can be achieved under mild and environmentally friendly conditions without the need for external oxidants. Simultaneously, copper remains stable and undissolved, thus selectively recovering copper, tin, and lead. Specifically, metallic tin is oxidized to tin dioxide precipitate for recovery; metallic lead dissolves in solution in ionic form and can be recovered using different reagents depending on the specific requirements. For example, dilute sulfuric acid can be used for reduction precipitation to obtain lead sulfate; and metallic copper is recovered as a high-purity (≥99%) copper strip.

[0017] 2. The lead-containing filtrate after acetic acid leaching can be reacted by adding dilute sulfuric acid as a precipitant. The solution after the reaction can be returned to the pre-leaching system for recycling. There is no waste liquid discharge during the process, which greatly improves resource utilization and environmental benefits.

[0018] 3. This invention does not rely on traditional pyrometallurgical treatments or strong acid / alkali wet leaching methods, resulting in low energy consumption, minimal acid / alkali usage, and avoidance of secondary environmental pollution. It provides a solution for the recycling and utilization of metal resources from decommissioned photovoltaic modules.

[0019] 4. In the development of lead ion precipitation processes, it was found that the type of precipitant has a significant regulatory effect on product morphology and recovery efficiency. Through systematic screening of different anion systems (SO4... 2- OH - CO3 2- Discovery: The mechanism of sulfate-directed precipitation: When 0.5-1.2 mol / L dilute sulfuric acid is added, lead ions preferentially form well-defined PbSO4 precipitates (XRD patterns perfectly match JCPDS 36-1461). This condition increases the ion product of lead precipitation (Q=[Pb...]). 2+ SO4 2- The solubility product (Ksp = 1.6 × 10⁻⁶) significantly exceeded its solubility product (Ksp = 1.6 × 10⁻⁶). -8 Meanwhile, the system pH is maintained at 3.5-4.2, ensuring precipitation efficiency and seamless integration with the pre-leaching process. Compared to other anionic systems, sulfate precipitation has significant advantages in process compatibility and operational economy.

[0020] 5. This invention achieves efficient and selective separation of three metals, Sn, Pb, and Cu, in a mild and green reaction system that utilizes only dissolved oxygen in the solution by controlling temperature and medium acidity conditions. It is suitable for the resource recovery of solder strip metal in decommissioned photovoltaic modules. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a reaction mechanism diagram of the present invention.

[0022] Figure 2 This is a SEM image of tin dioxide obtained after calcination.

[0023] Figure 3 The images show the XRD patterns of tin dioxide obtained before and after calcination.

[0024] Figure 4 The final SEM image of lead sulfate is shown.

[0025] Figure 5 The final XRD pattern of lead sulfate is shown. Detailed Implementation

[0026] The present invention will be described in detail below with reference to the embodiments. However, the embodiments are not intended to limit the present invention. Any similar methods and similar variations of the present invention should be included in the protection scope of the present invention.

[0027] This invention provides a method for selectively recovering valuable metals from retired crystalline silicon photovoltaic solder ribbons, comprising the following steps: (1) Disassemble the photovoltaic ribbon from the retired crystalline silicon cell and then remove impurities from the photovoltaic ribbon to obtain a clean ribbon; (2) Add the clean solder strip to the acetic acid solution, heat and stir to allow it to react fully. After the reaction is complete, filter to obtain filter residue, copper strip and lead-containing filtrate respectively. (3) Add a precipitant to the lead-containing filtrate obtained in step (2) to carry out a precipitation reaction. After the reaction is completed, filter, wash and dry to obtain lead sulfate product; (4) The filter residue and copper strips obtained in step (2) are washed and dried to obtain crude tin dioxide and metallic copper strips with a purity of not less than 99.0%.

[0028] like Figure 1 As shown, this invention achieves selective recycling of tin-lead alloy from decommissioned crystalline silicon photovoltaic solder ribbons by fully utilizing the differences in the electrochemical behavior of tin (Sn), lead (Pb), and copper (Cu) in acetic acid medium. This invention can induce a selective leaching reaction of Sn-Pb alloy solder ribbons under heating (40~70℃) without the need for external oxidants. The specific reaction process is described below: Sn first reacts with hydrogen ions provided by acetic acid in the solution to form soluble Sn. 2+ And release hydrogen gas; the Sn 2+ It is further oxidized to Sn by dissolved oxygen in the solution. 4+Subsequently, under weakly acidic conditions, it undergoes hydrolysis to generate the intermediate Sn(OH)4, which rapidly dehydrates to form an insoluble SnO2 precipitate, which is deposited in the leaching residue. Under the same conditions, Pb is directly oxidized to Pb. 2+ The lead (Sn) remains stable in the leachate. Due to the small but significant potential difference between Sn and Pb that can drive galvanic corrosion (Sn: -0.14 V, Pb: -0.13 V), lead dissolves first in the alloy as the anode, thus promoting the selective precipitation of Pb throughout the system and providing cathodic protection for Sn. Meanwhile, copper, due to its higher standard electrode potential (+0.34 V), remains stable in the weakly oxidizing environment of acetic acid, and its surface may form a Cu2O or CuO passivation film, exhibiting excellent leaching resistance and ultimately remaining stably in the solid residue.

[0029] The following are specific examples.

[0030] Example 1

[0031] In this embodiment, 1 g of decommissioned photovoltaic solder ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 60°C. 60 mL of a 4 mol / L acetic acid solution was slowly poured in, and a leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic solder ribbon to 60 mL of acetic acid solution. A mechanical stirrer was used for mechanical stirring at a speed of 500 rpm for 300 min. After the reaction was complete, the residue, copper strip, and filtrate were separated by filtration. The residue and copper strip were washed, dried, and their mass was measured. The filtrate was further processed. The final leaching rates were 96.7% for lead, 1.5% for tin, and 0.1% for copper.

[0032] A 0.5 mol / L sulfuric acid solution was added as a precipitant to the filtrate after leaching. Lead sulfate precipitate was obtained by heating at 50°C. The precipitate was then repeatedly washed with hot water at 80°C and dried. The final lead recovery rate was 96.3%, and the purity of lead sulfate was >90%.

[0033] The leached residue was washed and dried, then calcined in a muffle furnace at 500°C for 0.5 h. X-ray diffraction was used to scan the residue, and peaks that were consistent with those of tin oxide were found, indicating that the purity of tin oxide was high and impurities in the sample were removed. Figure 2The XRD patterns of tin oxide before and after calcination are shown. X-ray diffraction was used to scan the SnO2 powder. The calcined SnO2 powder was basically consistent with the standard SnO2 spectrum (PDF#46-1088), with the main diffraction peaks at 26.57°, 33.72°, and 51.76° corresponding to planes (110), (101), and (200), respectively. However, the peak values ​​of the calcined SnO2 powder were relatively weaker, possibly because some crystalline phases transformed into amorphous states during calcination, resulting in a relative decrease in crystalline phase content. After digestion analysis, the SnO2 obtained had a high purity of 98.2%, which fully demonstrates that the acetic acid system can selectively separate valuable metals within the photovoltaic ribbon and obtain SnO2 material with extremely high purity. A complete recovery system can be established by recovering Sn from the ribbon in the form of SnO2.

[0034] Example 2

[0035] In this embodiment, 1 g of decommissioned photovoltaic solder ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 60°C. 50 mL of a 4 mol / L acetic acid solution was slowly poured in, and a leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic solder ribbon to 50 mL of acetic acid solution. A mechanical stirrer was used for mechanical stirring at a speed of 500 rpm for 300 min. After the reaction was complete, the residue, copper strip, and filtrate were separated by filtration. The residue and copper strip were washed, dried, and their mass was measured. The filtrate was further processed. The final leaching rates were 93.3% for lead, 1.1% for tin, and 0.3% for copper.

[0036] Example 3

[0037] In this embodiment, 1 g of decommissioned photovoltaic solder ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 50°C. 50 mL of a 5 mol / L acetic acid solution was slowly poured in, and a leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic solder ribbon to 50 mL of acetic acid solution. A mechanical stirrer was used for mechanical stirring at a speed of 500 rpm for 300 min. After the reaction was complete, the residue, copper strip, and filtrate were separated by filtration. The residue and copper strip were washed, dried, and their mass was measured. The filtrate was further processed. The final leaching rates were 91.6% for lead, 5.5% for tin, and 0.1% for copper.

[0038] Example 4

[0039] In this embodiment, 1 g of decommissioned photovoltaic solder ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 70°C. 50 mL of a 5 mol / L acetic acid solution was slowly poured in, and a leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic solder ribbon to 50 mL of acetic acid solution. A mechanical stirrer was used for mechanical stirring at a speed of 500 rpm for 300 min. After the reaction was complete, the residue, copper strip, and filtrate were separated by filtration. The residue and copper strip were washed, dried, and their mass was measured. The filtrate was further processed. The final leaching rates were 94.4% for lead, 2.1% for tin, and 0.4% for copper.

[0040] The experimental results of Examples 1 to 4 are shown in Table 1: Table 1

[0041] Comparative Example 1 In this embodiment, 1 g of decommissioned photovoltaic solder ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 80°C. 50 mL of 7 mol / L acetic acid solution was slowly poured in, and a leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic solder ribbon to 50 mL of acetic acid solution. A mechanical stirrer was used for mechanical stirring at a speed of 500 rpm for 300 min. After the reaction was complete, the residue, copper strip, and filtrate were separated by filtration. The residue and copper strip were washed, dried, and their mass was measured. The filtrate was further processed. The final leaching rates were 98.3% for lead, 17.2% for tin, and 5.6% for copper.

[0042] Comparative Example 2 In this embodiment, 1 g of decommissioned photovoltaic welding ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 70°C. 40 mL of a 1 mol / L ammonium persulfate solution and a 0.4 mol / L sodium chloride solution were slowly poured in, and a leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic welding ribbon to 40 mL of leaching solution. A mechanical stirrer was added for mechanical stirring at a speed of 500 rpm for 180 min. After the reaction was complete, the residue and filtrate were separated by filtration. The filtrate was further processed. The final leaching rates were 9.82% for lead, 10.06% for tin, and 88.11% for copper. Metallic copper was leached into the solution, while the tin-lead leaching rates were low, indicating poor separation.

[0043] Comparative Example 3 In this embodiment, 1 g of decommissioned photovoltaic solder ribbon was weighed into a 250 mL thick-walled beaker, placed in a water bath, and heated and stirred. The reaction temperature was set to 70°C. 40 mL of a 3 mol / L citric acid solution was slowly poured in, and the leaching experiment was conducted according to a ratio of 1 g of decommissioned photovoltaic solder ribbon to 40 mL of leaching solution. A mechanical stirrer was added for mechanical stirring at a speed of 500 rpm for 180 min. After the reaction was complete, the residue and filtrate were separated by filtration. The filtrate was further processed. The final leaching rates were 71.82% for lead, 95.0% for tin, and 83.16% for copper. Most of the three metals were leached into the solution, making effective selective separation of the three metals impossible.

[0044] In summary, the selective recovery method for different metals in decommissioned crystalline silicon photovoltaic ribbons provided by this invention selectively separates tin-lead alloys by controlling reaction conditions. Tin is recovered as tin dioxide precipitate, lead exists in solution as ions (leaching rate > 95%), while copper retains > 99% due to surface passivation, achieving precise metal separation. The entire leaching system is green, environmentally friendly, and pollution-free, avoiding the use of traditional strong acid and alkali reagents. The filtrate can also be recycled back to the pre-leaching system by adding a precipitant. This invention has a high recovery rate, enabling effective reuse of metal resources and possessing significant environmental and economic benefits.

[0045] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for selectively recovering valuable metals from retired crystalline silicon photovoltaic cell solder ribbons, characterized in that, Includes the following steps: (1) Disassemble the photovoltaic ribbon from the retired crystalline silicon cell and then remove impurities from the photovoltaic ribbon to obtain a clean ribbon; (2) Add the clean solder strip to the acetic acid solution, heat and stir to allow it to react fully. After the reaction is complete, filter to obtain filter residue, copper strip and lead-containing filtrate respectively. (3) Add a precipitant to the lead-containing filtrate obtained in step (2) to carry out a precipitation reaction. After the reaction is completed, filter, wash and dry to obtain lead sulfate product; (4) The filter residue and copper strips obtained in step (2) are washed and dried to obtain crude tin dioxide and metallic copper strips with a purity of not less than 99.0%.

2. The selective recovery method according to claim 1, characterized in that, In step (1), the photovoltaic solder ribbon comprises the following components by weight fraction: tin 5.00%~6.10%, lead 5.50%~6.00%, copper 86.50%~87.90%, with the remainder being trace impurity elements, and the total mass meets 100%.

3. The selective recovery method according to claim 1, characterized in that, In step (1), the impurity removal step is as follows: the photovoltaic welding ribbon is completely immersed in anhydrous ethanol and ultrasonically treated in an ultrasonic cleaner at an ultrasonic frequency of 40~60Hz for 30~50min.

4. The selective recovery method according to claim 1, characterized in that, In step (2), the concentration of acetic acid solution is 2~6 mol / L, the ratio of welding strip to acetic acid solution is (1~3) g:60mL, the reaction temperature is 40~70 ℃, the reaction time is 180~360 min, and the stirring rate is 200~600 rpm.

5. The selective recycling method according to claim 4, characterized in that, The concentration of acetic acid solution is 4~5 mol / L, the ratio of solder ribbon to acetic acid solution is (1~1.5) g:60mL, the reaction temperature is 50~70 ℃, and the reaction time is 270~330 min.

6. The selective recovery method according to claim 1, characterized in that, In step (3), the precipitant is dilute sulfuric acid with a concentration between 0.5 and 1.2 mol / L; the precipitation reaction is carried out at a temperature of 20 to 50 °C for a reaction time of 10 to 60 min.

7. The selective recovery method according to claim 1, characterized in that, In step (3), the remaining solution obtained after the precipitation reaction is completed is returned to the leaching system of step (3) for recycling.

8. The selective recovery method according to claim 1, characterized in that, In step (4), the solvent used for washing is water, and after washing, the product is dried at a temperature of 60-80℃ for 6-12 hours.

9. The selective recycling method according to claim 1, characterized in that, It also includes step (5): the crude tin dioxide obtained in step (4) is subjected to high-temperature calcination to purify it. After the reaction is completed, the solid is taken out to obtain tin dioxide. The calcination temperature is 500~600 ℃ and the reaction time is 0.5~1h.

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