Method for recovering copper, lead and tin from waste photovoltaic welding strip

Abstract

The invention provides a method for recovering copper, lead and tin from a waste photovoltaic welding strip, and belongs to the technical field of resource regeneration and nonferrous metallurgy. According to the method, the waste photovoltaic welding strip serves as a cathode, an inert material serves as an anode, direct-current voltage of 2.5 V or above is applied to molten sodium hydroxide for an electrolytic reaction, lead-tin alloy on the surface of the photovoltaic welding strip is selectively stripped and deposited at the bottom of molten salt in the electrolytic process, and a copper matrix is kept complete. After electrolysis is finished, elemental lead powder and filtrate containing sodium stannate can be obtained through water dissolution treatment. The method has the advantages of being efficient, green, easy and convenient to operate, remarkable in separation effect and the like, the adaptability to the form and loading mode of the photovoltaic welding strip is high, the morphology difference of copper, lead and tin products is obvious, and follow-up extraction and resource utilization are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of resource recycling and nonferrous metal metallurgy, and in particular to a method for recovering copper, lead and tin from waste photovoltaic welding ribbons. Background Art

[0002] With the rapid development of the photovoltaic industry and the large-scale deployment of photovoltaic modules, the massive amount of waste generated by these modules at the end of their service life is placing a dual pressure on the environment and resources. The metal solder ribbons in scrapped photovoltaic modules, a crucial material for connecting the current paths of the solar cells, are a crucial component of resource recovery because they contain high-value metals such as copper, lead, and tin. Currently, most solder ribbons are made of a copper base coated with a lead-tin alloy. This metal composite structure poses significant challenges to their subsequent separation and extraction.

[0003] Traditional methods for recycling solder ribbons primarily include hydrometallurgy and pyrometallurgy. The wet metallurgy typically relies on highly corrosive acids such as nitric acid, hydrochloric acid, and hydrofluoric acid for leaching. This not only involves high reagent consumption, complex by-product handling, and severe equipment corrosion, but is also prone to secondary pollution. Pyrometallurgy, on the other hand, achieves metal extraction through high-temperature melting and thermal reduction. While highly efficient, it often requires significant energy input and is prone to producing harmful gases (such as lead-containing fumes), hindering the development of green processes. Furthermore, due to the excellent wettability of lead-tin alloys on the copper substrate, a continuous coating easily forms during traditional heat treatment, making it difficult to achieve effective interfacial separation between copper and lead-tin.

[0004] Existing molten salt electrolysis research focuses on the overall metal recovery of electronic waste. Currently, there is no mature process or system research on applying molten salt electrolysis methods to the separation of metals in micro-scale composite materials such as photovoltaic welding ribbons. The welding ribbon has a composite structure of copper matrix + lead-tin alloy coating. Its separation process involves the stripping behavior of the alloy, changes in interfacial wettability and multiphase reaction mechanism, which places high demands on the selectivity and stability of the electrolysis system. Based on this, the present invention develops a molten salt electrolysis method suitable for photovoltaic welding ribbons to achieve the green separation and recovery of copper, lead and tin, which has clear technical innovation value and practical application prospects. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention provides a method for recovering copper, lead, and tin from waste photovoltaic ribbons. This method utilizes a molten sodium hydroxide electrolysis system. By controlling reaction conditions, the lead-tin alloy layer on the surface of the photovoltaic ribbon is selectively stripped away through electrochemical and physical interactions, resulting in an intact copper matrix and a recyclable lead-tin product. This method is environmentally friendly, simple, and has high separation efficiency, making it suitable for resource recovery and utilization of photovoltaic ribbons.

[0006] To achieve the above object, the specific technical solutions of the present invention are as follows:

[0007] A method for recovering copper, lead and tin from waste photovoltaic ribbons comprises the following steps:

[0008] The electrolysis system is constructed by using waste photovoltaic ribbon as cathode and inert material as anode, which are inserted into molten sodium hydroxide (NaOH);

[0009] Applying DC voltage at 350 ~ 450 ℃, electrolysis reaction is carried out to recover copper, lead and tin.

[0010] Furthermore, the method further includes: after the electrolysis reaction is completed, mixing the reaction mixture with water for water dissolution treatment, whereby lead exists in the sediment in the form of elemental powder, and tin exists in the solution in the form of sodium stannate (Na2SnO3), separating the elemental lead and the sodium stannate by filtration, and recovering the tin by adjusting the pH of the filtrate or by evaporation and crystallization.

[0011] The method provided herein uses molten sodium hydroxide as the electrolyte system. First, molten sodium hydroxide has a moderate melting point (approximately 318°C) and exhibits good thermal stability within the required operating temperature range of 350-450°C, facilitating control of the electrolysis reaction process. Second, the strongly alkaline environment provided by sodium hydroxide facilitates the selective oxidation and desorption of metals such as tin and lead, or the formation of an intermediate alloy structure with sodium, thereby facilitating the effective separation of tin, lead, and other metals from the copper matrix. After the electrolysis reaction, some metals (such as tin) in the system can form soluble products such as sodium stannate, which facilitates subsequent separation and purification through water dissolution and filtration. Furthermore, sodium hydroxide is a common alkaline compound in industry, widely available, and inexpensive, making it suitable for large-scale industrial recovery processes. Therefore, the present invention's use of molten sodium hydroxide as the electrolyte system for the recovery of copper, lead, and tin from photovoltaic ribbons offers significant advantages in terms of reaction activity, operational stability, and cost-effectiveness.

[0012] Under the electrolysis conditions of the present invention, the lead-tin alloy layer on the surface of the photovoltaic ribbon can be stripped from the copper substrate to form a deposit, which can be recovered through water dissolution to obtain elemental lead and sodium stannate products. The method uses waste photovoltaic ribbon as the cathode and an inert material as the anode to perform an electrolytic reaction to recover copper, lead, and tin from the waste photovoltaic ribbon. Scrap PV ribbons can be fed whole or cut as needed, as long as the current path is not affected. Multiple ribbons can be wound or arranged side by side at the cathode end to ensure good conductivity. Effective electrical isolation between the cathode and anode is sufficient to prevent short circuits, without strict restrictions on the electrode spacing. After inserting the cathode and anode into molten sodium hydroxide to create an electrolysis system, a constant DC voltage is applied for the electrolysis reaction. The recommended voltage is 2.5 V or above, which can be adjusted based on the specifications and processing volume of the PV ribbons. The electrolysis reaction time depends on the number of ribbons processed and the thickness of the coating. For example, for a 30 cm long PV ribbon with a cross-sectional size of 0.16 mm × 1.8 mm, the complete stripping time is approximately 3 minutes and 30 seconds. When processing multiple PV ribbons, the electrolysis time can be extended or efficiency can be improved by connecting multiple electrodes in parallel.

[0013] In the early stage of the electrolytic reaction, obvious bubble release and color change appeared on the surface of the photovoltaic welding ribbon; as the electrolytic reaction progressed, the lead-tin alloy layer gradually peeled off from the copper substrate and deposited at the bottom of the reaction system in the form of granules, flakes or loose blocks; the copper substrate was porous or exposed to metallic luster, with an intact structure and no obvious corrosion; after the electrolytic reaction was completed, it was directly cooled and the reaction residue was dissolved with water. Lead was deposited in the form of a single substance powder, and tin was dissolved in water as sodium stannate. The two forms were clearly separated, making it easy to extract them separately.

[0014] Furthermore, the DC voltage is 2.3~4.5V.

[0015] Furthermore, the electrolysis reaction time is 2 to 30 minutes. The specific electrolysis reaction time is adjusted according to the size and quantity of the waste photovoltaic ribbons.

[0016] Furthermore, the electrolysis reaction time is 5 to 15 minutes.

[0017] Furthermore, the molten sodium hydroxide is obtained by heating sodium hydroxide to 350-450° C. In one example of the present invention, the molten sodium hydroxide is obtained by heating sodium hydroxide to 400° C.

[0018] Furthermore, the inert material includes an inert metal or an inert anode material having high temperature alkaline corrosion resistance.

[0019] Furthermore, the inert metal includes but is not limited to nickel.

[0020] Furthermore, the inert anode material having high temperature alkaline corrosion resistance includes but is not limited to metal oxides or graphite.

[0021] Specifically, the method for recovering copper, lead and tin from waste photovoltaic ribbons comprises the following steps:

[0022] (1) Place sodium hydroxide (analytical or industrial purity) in a corrosion-resistant crucible and heat it to 350-450°C to form a uniform, clear molten medium;

[0023] (2) Insert the waste photovoltaic ribbon as the cathode and the inert material as the anode into the molten sodium hydroxide system, and maintain effective electrical isolation between the two electrodes to avoid contact short circuit;

[0024] (3) Electrolysis was performed at 350-450°C with a DC voltage of 2.5-4.5 V.

[0025] (4) After the reaction is completed, the reaction mixture is cooled and the cathode is removed to recover the copper; the reaction mixture is dissolved in water to obtain the reaction residue and the lead and tin are recovered.

[0026] Compared with the prior art, the present invention is beneficial in that:

[0027] 1. The method provided by the present invention achieves interfacial desorption of composite structure metals by in-situ generation of low-wettability intermetallic compounds during electrochemical reactions;

[0028] 2. The method provided by the present invention does not use acidic or organic reagents, the system does not generate toxic byproducts, and the operation is safe;

[0029] 3. The method provided by the present invention has loose requirements on the shape of the photovoltaic welding ribbon and the electrode spacing, and is applicable to waste materials of various specifications;

[0030] 4. The product obtained by the separation method of the present invention has a clear morphology and a clear extraction path.

[0031] 5. The method provided by the present invention is a new metal recovery method based on alloy wettability regulation and electrolysis-induced stripping. It is suitable for the green and efficient extraction of valuable metals in photovoltaic ribbons and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the method for recycling copper, lead and tin in photovoltaic ribbons according to the present invention;

[0033] Figure 2 The copper substrate exposure of the welding strip at different reaction times in Example 1 of the present invention;

[0034] Figure 3The copper substrate of the welding strip is exposed under different voltage conditions in Example 1 of the present invention;

[0035] Figure 4 The copper substrate exposure of the welding strip under different temperature conditions in Example 1 of the present invention;

[0036] Figure 5 This is a photo of the metallic copper recovered in Example 2 of the present invention;

[0037] Figure 6 This is a photo of the metallic copper recovered in Example 3 of the present invention. DETAILED DESCRIPTION

[0038] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The present invention provides a method for recovering copper, lead and tin from waste photovoltaic ribbons (the flow diagram is as follows Figure 1 As shown in the figure, the anode is an inert metal as an example), including the following steps:

[0040] The electrolysis system is constructed by using waste photovoltaic ribbon as cathode and inert material as anode, which are inserted into molten sodium hydroxide.

[0041] Apply DC voltage at 350 ~ 450 ℃ to carry out electrolysis reaction;

[0042] After the electrolysis reaction is completed, the reaction mixture is mixed with water for water dissolution treatment. Lead exists in the sediment in the form of elemental powder, and tin exists in the solution in the form of sodium stannate (Na2SnO3). The lead element and sodium stannate are separated by filtration, and the tin is recovered by adjusting the pH of the filtrate or evaporating and crystallizing.

[0043] In some examples, the DC voltage is 2.3 to 4.5 V.

[0044] In some examples, the electrolysis reaction time is 2 to 30 minutes. The specific electrolysis reaction time is adjusted according to the size and quantity of the waste photovoltaic ribbons.

[0045] In some examples, the molten sodium hydroxide is obtained by heating sodium hydroxide to 350-450°C.

[0046] In some examples, the inert material includes an inert metal or an inert anode material having high temperature alkaline corrosion resistance; the inert metal includes but is not limited to nickel; the inert anode material having high temperature alkaline corrosion resistance includes but is not limited to metal oxide or graphite.

[0047] Example 1 Electrolytic Separation and Recovery of Copper, Lead, and Tin from Waste Photovoltaic Ribbons

[0048] 1. Raw Materials Preparation

[0049] Select solder ribbons from decommissioned photovoltaic modules. These ribbons are copper-based and coated with a lead-tin alloy, approximately 1.8 mm wide and 0.16 mm thick. Cut the ribbons into 30 cm sections or wrap them in bundles to ensure good conductivity. Completely unrolling or splitting the ribbons is not necessary. Clean the ribbon surface briefly with deionized water and a non-corrosive solvent to remove dust and organic impurities.

[0050] 2. Molten Salt Preparation

[0051] Weigh about 500 g of industrial-purity sodium hydroxide, place it in a high-temperature-resistant and alkali-resistant silica crucible, and heat it to 400 °C in a muffle furnace to form a clear and transparent molten sodium hydroxide system.

[0052] 3. Electrolysis device construction

[0053] A welding strip was used as the cathode and a nickel sheet with a size of 20 mm × 15 mm was used as the anode. The cathode and anode were inserted into molten sodium hydroxide, with the electrodes separated by about 3 cm to avoid contact. The electrodes were then connected to an adjustable constant voltage DC power supply.

[0054] 4. Electrolysis reaction process

[0055] 4.1 Study on electrolysis reaction time

[0056] At 400 °C, a constant voltage of 2.5 V was applied and the electrolysis reaction was started. The exposure of the copper substrate of the solder strip at different electrolysis reaction times in this embodiment is shown in FIG. Figure 2 Within approximately 5 seconds of the electrolytic reaction, the surface of the solder ribbon began to release gas, and the surface color gradually darkened. As the electrolytic reaction proceeded, the lead-tin alloy layer underwent electrochemical conversion to form NaSn and NaPb alloys. These alloys, due to their poor wettability with the copper substrate, spontaneously peeled off and gradually fell off and deposited on the bottom of the crucible.

[0057] For a single 30 cm long solder strip, under the above conditions, the lead-tin alloy layer can be observed to be basically detached after about 3 minutes and 30 seconds of reaction, and the copper substrate is clearly visible.

[0058] 4.2 Study on the voltage required for electrolysis reaction

[0059] Under the condition of 400℃, a constant voltage of 2, 2.5, 3 or 3.5 V was applied and the electrolysis reaction was carried out respectively. The copper substrate of the solder strip exposed under the electrolysis reaction under different voltage conditions in this embodiment is shown in FIG. Figure 3 As can be seen from the figure, it is difficult for the photovoltaic ribbon to effectively peel off the lead-tin alloy at a voltage of 2V.

[0060] 4.3 Study on electrolysis reaction temperature

[0061] A constant voltage of 2.5 V was applied at 400°C, 320°C, 350°C, 380°C or 400°C, and the electrolysis reaction was carried out respectively. The exposure of the copper substrate of the solder strip under the electrolysis reaction under different heating temperature conditions in this embodiment is shown in FIG. Figure 4 As can be seen from the figure, when the photovoltaic ribbon is heated at 320°C, the lead-tin alloy is peeled off slowly; when heated at 350°C, the lead-tin alloy can be effectively peeled off within 3 minutes.

[0062] 5. Post-reaction treatment

[0063] After disconnecting the power supply, the electrodes were removed and the molten salt was allowed to cool naturally to a solid state. The cooled molten salt and the bottom sediment were immersed in deionized water and vigorously stirred to dissolve the sodium hydroxide. Filtering yielded a dark gray powder and a clear liquid. XRD analysis revealed that the solid was elemental lead, while the tin in the liquid existed as Na2SnO3. Further tin recovery can be achieved by adjusting the pH or by evaporative crystallization.

[0064] Example 2 Electrolytic Separation and Recovery of Copper, Lead, and Tin from Bulk Waste Photovoltaic Ribbons

[0065] 1. Raw Materials Preparation

[0066] Twenty strips of solder ribbon, each approximately 30 cm long and 0.16 mm × 1.8 mm in cross-section, were obtained from decommissioned photovoltaic modules. The copper substrate was coated with a lead-tin alloy layer. After cleaning and drying, the ribbons were directly wound randomly around a stainless steel wire, connecting the entire ribbon as the cathode to the circuit. This ensured good electrical contact and stable conduction between the ribbons, without the need for further cutting or separation.

[0067] 2. Molten salt preparation and electrolysis device construction

[0068] Heat approximately 500 g of industrial-grade sodium hydroxide to 400°C, forming a transparent molten state. Place the anode in a high-temperature-resistant ceramic crucible. A standard-sized nickel sheet (20 mm × 15 mm) is used as the anode and inserted below the molten salt surface. Connect the cathode welding ribbon and anode sheet to the negative and positive terminals of a DC regulated power supply, respectively. Insert the anode into the molten salt, ensuring that the two electrodes do not touch.

[0069] 3. Electrolysis reaction process

[0070] At 400°C and a voltage of 2.8 V, after power was applied, significant bubble release was observed on the surface of the solder ribbon within seconds, along with color changes and the sedimentation of fine particles. The reaction lasted approximately 20 minutes, during which time the majority of the ribbon surface turned dark red or copper-red, with no visible lead-tin alloy adhered to the surface, indicating that the coating had essentially detached.

[0071] 4. Post-reaction treatment

[0072] After cutting off the power supply, remove the electrodes (see the photo of the recovered copper metal). Figure 5 The molten salt is naturally cooled to a solid state. The cooled molten salt and bottom sediment are immersed in deionized water and vigorously stirred to dissolve the sodium hydroxide. Filtering yields a dark gray powder and a clear liquid. XRD analysis reveals that the solid is elemental lead, while the tin in the liquid exists as Na2SnO3. Tin can be further recovered by adjusting the pH or by evaporative crystallization.

[0073] 5. Results

[0074] The experiment shows that multiple solder strips in a wound state can be effectively electrolytically stripped at one time without having to be unfolded and arranged; the anode area does not need to be specially enlarged to still maintain a stable reaction current; the copper in the product remains basically intact and the color is typical copper red.

[0075] Example 3 Simulated electrolysis treatment of a small section of discarded photovoltaic ribbon in a nickel foam bath

[0076] To further verify the adaptability of the present invention in processing waste photovoltaic ribbons of irregular sizes (such as recyclables after pre-crushing or cutting), the following experiments were conducted:

[0077] 1. Raw Materials Preparation

[0078] Solder ribbons removed from retired photovoltaic modules were cut into approximately 20 segments, each approximately 1 cm long, 1.8 mm wide, and 0.16 mm thick, coated with a lead-tin alloy. The segments were not unfolded to simulate actual breakage. The samples were rinsed with ethanol and deionized water and air-dried for later use.

[0079] 2. Electrolysis Device Construction

[0080] Take a 30 mm × 30 mm nickel foam sheet (porosity of about 95%), place a small section of welding tape in the groove made of the nickel foam sheet, so that it is conductive with the nickel foam to form an integral cathode. The anode is still made of nickel sheet, which is 2–3 cm away from the cathode and inserted into the molten sodium hydroxide formed at 400 °C.

[0081] 3. Electrolysis Conditions Setup

[0082] At 400 °C, a 2.5 V DC voltage was applied, and the initial current was about 1.8 A. During the reaction, a large number of bubbles were released from the nickel foam tank, accompanied by a darkening of the solder strip surface and the shedding of local granular matter.

[0083] 4. Reaction Observation and Results

[0084] After the reaction continued for 10 minutes, the power was turned off, and the foam nickel sheet was taken out as a whole and cooled. It was observed that the copper-red substrate of the small section of the welding strip was basically exposed, and the coating was obviously peeling off.

[0085] 5. Post-reaction treatment

[0086] After cutting off the power supply, remove the electrodes (see the photo of the recovered copper metal). Figure 6 The molten salt was naturally cooled to a solid state. The cooled molten salt and bottom sediment were immersed in deionized water and vigorously stirred to dissolve the sodium hydroxide. Filtering yielded a dark gray powder and a clear liquid. XRD analysis revealed that the dark gray powder solid was elemental lead, and the filtrate contained sodium stannate, demonstrating that the lead-tin alloy was successfully separated under this environment.

[0087] 6. Results

[0088] This embodiment shows that the method of the present invention is suitable for processing scenarios of weld strips with broken shapes and irregular sizes. By constructing a foam nickel tank as a cathode support, the reaction efficiency and metal stripping effect can be guaranteed, providing a feasible solution for the adaptation of industrial pre-crushing and recycling systems.

[0089] In summary, the present invention uses discarded photovoltaic welding ribbons as cathodes and inert materials as anodes, and applies a DC voltage of 2.5 V or more in molten sodium hydroxide to carry out an electrolysis reaction. During the electrolysis process, the lead-tin alloy on the surface of the photovoltaic welding ribbon is selectively stripped and deposited at the bottom of the molten salt, while the copper matrix remains intact. After the electrolysis is completed, elemental lead powder and a filtrate containing sodium stannate can be obtained by water dissolution treatment. The method of the present invention has the advantages of high efficiency, greenness, simple operation, and significant separation effect. It also has strong adaptability to the morphology and loading method of the photovoltaic welding ribbon. The product morphology is significantly different (i.e., the copper matrix of the welding ribbon, the black-gray powder of elemental lead, and sodium stannate), which facilitates subsequent extraction and resource utilization.

[0090] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details of the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

Claims

1. A method for recovering copper, lead and tin from waste photovoltaic ribbons, characterized in that: The following steps are involved: The electrolysis system is constructed by using waste photovoltaic ribbon as cathode and inert material as anode, which are inserted into molten sodium hydroxide. Applying DC voltage at 350 ~ 450 ℃, electrolysis reaction is carried out to recover copper, lead and tin.

2. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 1, characterized in that: The method further comprises: after the electrolysis reaction is completed, mixing the reaction mixture with water for water dissolution treatment.

3. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 1, characterized in that: The DC voltage is 2.3 to 4.5 V.

4. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 1, characterized in that: The electrolysis reaction time is 2 to 30 minutes.

5. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 1, characterized in that: The molten sodium hydroxide is obtained by heating sodium hydroxide to 350-450°C.

6. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 1, characterized in that: The inert material includes an inert metal or an inert anode material having high temperature alkaline corrosion resistance.

7. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 6, characterized in that: The inert metal includes, but is not limited to, nickel.

8. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 6, characterized in that: The inert anode material having high temperature alkaline corrosion resistance includes but is not limited to metal oxides or graphite.

9. The method for recovering copper, lead and tin from waste photovoltaic ribbons according to claim 1, characterized in that: The following steps are involved: (1) Place sodium hydroxide in a corrosion-resistant crucible and heat it to 350-450°C to form a uniform and clear molten medium; (2) Insert the waste photovoltaic ribbon as the cathode and the inert material as the anode into the molten sodium hydroxide system, and maintain effective electrical isolation between the two electrodes to avoid contact short circuit; (3) Electrolysis was performed at 350-450°C with a DC voltage of 2.5-4.5 V. (4) After the reaction is completed, the reaction residue is cooled and dissolved in water to recover copper, lead, and tin.

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