Green stripping solution for photovoltaic solder strip and separation and recovery method of valuable metals

Abstract

The invention discloses a green deplating solution for a photovoltaic welding strip and a valuable metal separation and recovery method. The deplating solution is an aqueous solution, and solutes comprise a main oxidizing agent, a green acidic auxiliary agent, a complexing cosolvent and a copper special corrosion inhibitor; the main oxidant is selected from sodium persulfate, ammonium persulfate and ferric nitrate; the green acidic auxiliary agent is selected from sulfamic acid, methanesulfonic acid, tartaric acid and citric acid; the complexing cosolvent is selected from sodium chloride, ammonium chloride and thiourea; and the corrosion inhibitor is selected from benzotriazole, methyl benzotriazole and 2-mercapto benzimidazole. The waste welding strip is subjected to an immersion reaction at the temperature of 20-60 DEG C, tin, lead and / or silver enter the solution in the form of complex ions, and a copper substrate is kept bright and clean; and after solid-liquid separation, gradient recovery of silver extraction by replacement, lead separation by temperature difference crystallization and tin precipitation by hydrolysis can be adopted, or total replacement recovery by adding excessive zinc-based displacer can be adopted. The separation and recovery method is rapid in deplating, free of white films, low in copper loss and suitable for silver-containing and silver-free solder strips.

Description

Technical Field

[0001] This invention relates to the field of crystalline silicon photovoltaic module recycling, and more specifically, to a method for separating and recycling valuable metals from green stripping solution used in photovoltaic solder ribbons. Background Technology

[0002] With the rapid development of the photovoltaic industry, the installed capacity of photovoltaic modules continues to expand, and early-used photovoltaic modules are gradually entering the concentrated retirement phase. Photovoltaic solder ribbon, as a crucial material used for electrical connection of solar cells in photovoltaic modules, is typically tin-coated copper ribbon. Its interior is a copper substrate covered with a tin-lead alloy plating, and some ribbons also contain precious metals such as silver. Therefore, how to efficiently and environmentally recover valuable metals from photovoltaic solder ribbon during the retirement process has significant economic and environmental implications.

[0003] Existing technologies for recovering metals from photovoltaic solder ribbons mainly include high-temperature heat treatment, physical-mechanical separation, and chemical leaching. High-temperature heat treatment is energy-intensive, requires sophisticated equipment, and is prone to metal oxidation loss. Physical-mechanical separation struggles to achieve complete separation of the coating metal from the copper substrate, limiting both the purity and recovery rate of the recovered metal. Therefore, chemical leaching has attracted attention due to its relatively mild processing conditions, but it still has many shortcomings in practical applications.

[0004] Chinese patent application CN120866640A discloses a method for selectively recovering valuable metals from decommissioned crystalline silicon photovoltaic solder ribbons using an acetic acid system. This method uses acetic acid leaching to allow lead to enter the solution, while tin undergoes oxidation and hydrolysis during the reaction to form tin dioxide precipitate, thus achieving the separation of tin, lead, and copper. However, this type of method essentially belongs to the recovery path of "tin conversion to solid-phase precipitation," which has a long reaction time and easily forms a dense deposition layer on the solder ribbon surface during the stripping process, hindering subsequent reactions and resulting in low stripping efficiency and a relatively complex process. Furthermore, this method has limited adaptability to silver-containing solder ribbons and is difficult to effectively solve the problem of stable dissolution and recovery of silver in the system. Chinese patent application CN119433222A discloses a metal recovery method for photovoltaic solder ribbons treated with strong acid or strong oxidizing system. This type of method relies on strong oxidizing ability to achieve rapid dissolution of the solder ribbon coating metal. Although the reaction speed is fast, it is easy to cause significant corrosion to the copper substrate in actual operation, causing some copper to enter the solution. This not only reduces the quality of copper recovery but also increases the difficulty of subsequent separation of multiple metals in the solution. At the same time, the use of strong acid or strong oxidizing agent increases safety risks and environmental burden, which is not conducive to green and sustainable industrial applications.

[0005] Furthermore, when processing silver-containing photovoltaic solder ribbons, existing chemical leaching systems generally lack effective means to dissolve and stabilize silver. In chlorine-containing environments or under inappropriate reaction conditions, silver is easily precipitated in the form of silver chloride or metallic silver and adheres to the surface of the solder ribbon or deposits in the reaction system. This not only causes the loss of silver resources but also causes problems such as blackening of the solder ribbon surface, further affecting the stripping effect and subsequent metal recovery process.

[0006] In summary, existing photovoltaic solder stripping and valuable metal recycling technologies still have significant shortcomings in terms of stripping efficiency, copper substrate protection, silver-containing solder strip treatment, and environmental friendliness, and are still unable to simultaneously meet the comprehensive requirements of rapid stripping, high-value metal recycling, and green environmental protection. Summary of the Invention

[0007] One of the technical problems to be solved by the present invention is to provide a green stripping solution for photovoltaic solder ribbons, so as to overcome the problems of easy formation of tin precipitates, incomplete stripping, easy corrosion of copper substrate, and difficulty in effectively dissolving and recovering silver in silver-containing solder ribbons in the existing chemical stripping methods.

[0008] To overcome the shortcomings of the prior art, the present invention provides a green stripping solution for photovoltaic solder ribbons, wherein the stripping solution is an aqueous solution and its solute components include: Main oxidant, green acidic additive, complexing solubilizer and copper-specific corrosion inhibitor; The primary oxidant is selected from one or more of sodium persulfate, ammonium persulfate, and ferric nitrate. The green acidic additive is selected from one or more of aminosulfonic acid, methanesulfonic acid, tartaric acid, and citric acid; The complexing co-solvent is selected from one or more of sodium chloride, ammonium chloride, and thiourea; The copper-specific corrosion inhibitor is selected from one or more of benzotriazole, methylbenzotriazole, and 2-mercaptobenzimidazole.

[0009] Compared with existing technologies, the green stripping solution for photovoltaic solder ribbons provided by this invention has the following advantages: The green stripping solution for photovoltaic solder ribbons provided by this invention, through the combined use of a main oxidant, a green acidic additive, a complexing co-solvent, and a copper-specific corrosion inhibitor, allows tin, lead, and silver in the solder ribbon coating to enter the solution in a dissolved state during the stripping process. This avoids the hydrolysis of tin ions during the reaction process, preventing the formation of a white film covering the solder ribbon surface during stripping, ensuring the continuous stripping reaction and achieving complete coating removal. Simultaneously, the introduction of a copper-specific corrosion inhibitor effectively protects the copper substrate under stripping conditions, reducing copper dissolution loss and maintaining a good surface condition for the recovered copper ribbon. Furthermore, the introduction of thiourea in the complexing co-solvent promotes the stable dissolution of silver in the stripping solution, preventing silver from depositing as silver chloride or metal, thus solving the problems of blackening of the solder ribbon and difficulty in silver recovery during the stripping process of silver-containing photovoltaic solder ribbons. The stripping solution of this invention can complete the stripping treatment of photovoltaic solder ribbons in a short time and provides favorable conditions for subsequent recovery of valuable metals using cascade separation or displacement methods.

[0010] As a preferred embodiment, the mass concentration ranges of each component in the stripping solution are as follows: Primary oxidant: 50-200 g / L; Green acidic additive: 30-120g / L; Complexing co-solvent: 20-100 g / L; Copper-specific corrosion inhibitor: 0.1-2.0 g / L.

[0011] Compared with existing technologies, this method achieves stable oxidation, dissolution, and complexation processes of the solder strip coating metal during stripping by synergistically limiting the concentration ranges of the main oxidant, acidic additive, complexing flux, and corrosion inhibitor. The main oxidant concentration of 50-200 g / L ensures continuous oxidation and dissolution of tin, lead, and silver without insufficient reaction. The green acidic additive, within the range of 30-120 g / L, maintains the system's acidity and inhibits metal ion hydrolysis. The complexing flux, within the range of 20-100 g / L, promptly complexes the generated metal ions, preventing their precipitation. The copper-specific corrosion inhibitor, within the range of 0.1-2.0 g / L, forms a stable adsorption layer on the copper substrate surface without affecting the dissolution of the plating metal. This embodiment, through the synergistic setting of the above concentration ranges, achieves a stable and continuous stripping process, avoids white film formation, and effectively reduces copper loss while ensuring stripping efficiency, ultimately achieving complete removal of the solder strip coating and effective protection of the copper substrate.

[0012] As a preferred embodiment, the mass concentration ranges of each component in the stripping solution are as follows: The main oxidant is sodium persulfate, with a concentration of 100-150 g / L; The green acidic additive is aminosulfonic acid, with a concentration of 70-100 g / L; The complexing solubilizer is a mixture of sodium chloride and thiourea, wherein the concentration of sodium chloride is 30-50 g / L and the concentration of thiourea is 5-15 g / L; The copper-specific corrosion inhibitor is benzotriazole, with a concentration of 0.3-1.0 g / L.

[0013] Compared with existing technologies, the above technical solution utilizes sodium persulfate and sulfamic acid to construct an oxidizing acidic system, enabling the tin, lead, and silver in the solder strip coating to be continuously oxidized and dissolved under relatively mild conditions. Furthermore, the chloride ions provided by sodium chloride, together with thiourea, act as complexing and solubilizing components, allowing the generated metal ions to exist in a stable complexed state in the solution, thus avoiding the hydrolysis of tin ions to form insoluble precipitates. Benzotriazole, within the above concentration range, can form a dense protective film on the copper substrate surface, significantly inhibiting the dissolution and corrosion of copper.

[0014] As a preferred embodiment, the complexing co-solvent includes thiourea, and the concentration of thiourea is not less than 5 g / L.

[0015] Compared with existing technologies, the above technical solution allows thiourea to play a dual role in the stripping system when processing silver-containing photovoltaic solder ribbons. As a highly effective silver complexing agent, thiourea can form stable thiourea-silver complexes with silver ions, transforming silver, which is prone to forming silver chloride or metallic silver deposits, into a soluble complex state. This prevents the formation of gray-black deposits on the solder ribbon surface or in the reaction system, ensuring that silver enters the stripping waste liquid in liquid phase, facilitating efficient recovery via displacement. Furthermore, thiourea can weakly adsorb onto the copper surface, synergistically reducing the copper's dissolution tendency during stripping with a copper-specific corrosion inhibitor. Limiting the thiourea concentration to no less than 5 g / L significantly improves the stripping stability of silver-containing solder ribbons, preventing blackening and silver loss, and achieving effective dissolution and recovery of silver from silver-containing photovoltaic solder ribbons.

[0016] Another technical problem to be solved by the present invention is to provide a method for separating and recovering valuable metals, so as to solve the problems of incomplete metal dissolution during the stripping process, easy precipitation leading to difficulties in subsequent separation, easy corrosion of copper substrate, and single recovery path with poor adaptability in the prior art.

[0017] To overcome the shortcomings of the prior art, the present invention provides a method for separating and recovering valuable metals using the above-mentioned stripping solution, comprising the following steps: S1: Full dissolution plating removal: Waste photovoltaic solder ribbons are immersed in stripping solution for reaction. Under the action of main oxidant, complexing flux and copper-specific corrosion inhibitor, all tin, lead and / or silver in the solder ribbon coating enter the solution in the form of soluble complex ions. At the same time, the copper substrate remains insoluble and forms a smooth surface, resulting in stripping waste solution. S2: Solid-liquid separation step: The stripping waste liquid is separated from the copper substrate to obtain stripping waste liquid rich in valuable metal ions and recycled copper strip.

[0018] Compared with existing technologies, the present invention provides a method for separating and recovering valuable metals, which has the following advantages: The method introduces an oxidation, complexation, and complete dissolution stripping process in step S1, allowing tin, lead, and silver in the solder strip coating to enter the solution as soluble complex ions during the stripping stage. This prevents the metal from forming insoluble precipitates or covering films during the stripping process, thus ensuring the continuity and thoroughness of the stripping process. Simultaneously, through the action of a copper-specific corrosion inhibitor, the stripping reaction mainly occurs in the solder strip coating metal, while the copper substrate remains insoluble and forms a coating during the reaction. A smooth surface allows for simultaneous stripping and copper recovery. In step S2, all valuable metals in the stripping waste liquid exist in a dissolved state. Depending on the system characteristics, a stepwise separation method can be selected to achieve the partial recovery of silver, lead, and tin, or a displacement method can be used for overall recovery. This improves the flexibility and adaptability of the recovery process. Based on the above method, the separation and recovery method of this invention can complete the stripping and separation pretreatment processes in a short time, providing stable and controllable conditions for the efficient recovery of subsequent valuable metals. This solves the problems of incomplete stripping, difficulty in metal separation, and easy damage to the copper substrate in the prior art.

[0019] As a preferred embodiment, in step S1, the reaction is carried out under stirring at a temperature of 20-60°C for 10-30 minutes.

[0020] Compared with existing technologies, by controlling the reaction temperature and time under stirring conditions, the stripping solution is allowed to fully contact the solder strip surface, which is beneficial to the uniform dissolution of the solder strip coating metal. Within a temperature range of 20-60°C, the oxidation reaction rate of the main oxidant on tin, lead, and / or silver can be guaranteed, avoiding excessive corrosion of the copper substrate or system instability caused by excessively high temperatures. Controlling the reaction time to within 10-30 minutes can avoid unnecessary copper loss caused by prolonged reactions while ensuring complete removal of the coating. This embodiment, through the combined setting of the above conditions, can stably complete the full dissolution and stripping in a short time, providing a uniform and stable stripping waste solution for subsequent metal separation and recovery.

[0021] As a preferred embodiment, step S2 includes: S21: Silver extraction by displacement: A copper-based displacement agent is added to the stripping waste liquid, and after the displacement reaction, solid-liquid separation is performed to obtain metallic silver; S22: Temperature difference crystallization of lead: The filtrate obtained in step S21 is heated, concentrated, and then cooled to crystallize lead chloride. After solid-liquid separation, lead chloride crystals and lead-poor tin-rich mother liquor are obtained. S23: Hydrolysis and Tin Precipitation: The pH value of the lead-poor and tin-rich mother liquor is adjusted to 1.5-2.5, and the temperature is raised to 70-90℃ to carry out a hydrolysis reaction. After solid-liquid separation, a tin-containing compound precipitate is obtained.

[0022] Compared with existing technologies, this embodiment achieves targeted recovery of multiple metals by separating valuable metals in the stripping waste liquid in sequence according to the differences in chemical behavior of silver, lead, and tin: In step S21, the potential difference between copper and silver is used to preferentially reduce silver ions in the solution to metallic silver through a displacement reaction, thereby achieving selective recovery of silver; In step S22, lead is concentrated by heating and then cooled, causing lead to crystallize out as lead chloride at 5-10°C, thereby effectively separating lead from the solution; In step S23, the pH of the lead-poor and tin-rich mother liquor is adjusted to 1.5-2.5 and the temperature is raised to 70-90°C, causing tin to undergo a hydrolysis reaction to form a precipitate, thereby achieving tin recovery; By setting the above-mentioned step-by-step separation sequence, the simultaneous deposition or mixing of multiple metals is avoided, improving the selectivity and purity of each metal recovery, and making it suitable for applications involving the high-value separation of silver, lead, and tin.

[0023] As a preferred embodiment, in step S21, the copper-based replacement agent is sponge copper powder.

[0024] As a preferred embodiment, in step S22, the crystallization temperature is 5-10℃.

[0025] Compared with existing technologies, the above-mentioned technical solution allows sponge copper powder to have a large specific surface area and high reactivity. When in contact with stripping waste liquid, it can quickly undergo a displacement reaction with silver ions, causing silver to precipitate in a metallic state. When the filtrate is cooled to 5-10°C, the solubility of lead chloride is significantly reduced, which is conducive to the full precipitation of lead from the solution in crystal form. The crystallization rate is moderate, and the resulting lead chloride crystals have a large particle size and stable morphology, which facilitates solid-liquid separation operations.

[0026] As a preferred embodiment, step S2 includes: adding an excess of zinc-based displacement agent to the stripping waste liquid, reducing tin, lead, silver and / or copper ions in the solution to mixed metal sludge in one step through a displacement reaction, obtaining the mixed metal sludge after solid-liquid separation, and using the mixed metal sludge as a smelting raw material for subsequent metal recovery treatment.

[0027] Compared with existing technologies, this embodiment adds an excess of zinc-based displacement agent, causing multiple metal ions in the solution to undergo a displacement reaction simultaneously and be reduced to their metallic state. This avoids the need for step-by-step adjustment of conditions and multiple separation operations. This method is particularly suitable for stripping waste liquid systems containing iron or with complex compositions that are difficult to separate in stages. Through a one-pot recovery path, the process can be simplified, the operational complexity reduced, and multiple valuable metals can be centrally converted into mixed metal sludge for centralized processing as smelting raw materials, thereby improving the overall recovery efficiency and process adaptability. Attached Figure Description

[0028] Figure 1 This is a photograph of the copper strip recovered in Example 1. Detailed Implementation

[0029] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0030] This invention provides a green stripping solution for photovoltaic ribbons and a method for removing the coating of photovoltaic ribbons and recovering valuable metals using the stripping solution.

[0031] The stripping solution is an aqueous solution, and its solute components include a main oxidant, a green acidic additive, a complexing co-solvent, and a copper-specific corrosion inhibitor. The main oxidant is selected from sodium persulfate, ammonium persulfate, and / or ferric nitrate; the green acidic additive is selected from aminosulfonic acid, methanesulfonic acid, tartaric acid, and / or citric acid; the complexing co-solvent is selected from sodium chloride, ammonium chloride, and / or thiourea; and the copper-specific corrosion inhibitor is selected from benzotriazole, methylbenzotriazole, and / or 2-mercaptobenzimidazole.

[0032] In a preferred embodiment, the main oxidant in the stripping solution has a mass concentration of 50–200 g / L, the green acidic additive has a mass concentration of 30–120 g / L, the complexing co-solvent has a mass concentration of 20–100 g / L, and the copper-specific corrosion inhibitor has a mass concentration of 0.1–2.0 g / L. More preferably, the main oxidant is sodium persulfate (100–150 g / L), the green acidic additive is aminosulfonic acid (70–100 g / L), the complexing co-solvent is a mixture of sodium chloride and thiourea, wherein the sodium chloride has a mass concentration of 30–50 g / L, the thiourea has a mass concentration of 5–15 g / L, and the copper-specific corrosion inhibitor is benzotriazole (0.3–1.0 g / L), and the concentration of thiourea is not less than 5 g / L.

[0033] The method for separating and recovering valuable metals includes the following steps: S1: Full dissolution stripping The waste photovoltaic solder ribbon is completely immersed in the stripping solution. Under stirring conditions, the reaction temperature is controlled at 20℃~60℃, and the reaction time is 10~30 minutes. During the stripping process, the main oxidant causes the tin, lead, and / or silver coating on the surface of the solder ribbon to oxidize and dissolve. The chloride ions and / or thiourea provided by the complexing co-solvent form stable complexes with the generated metal ions, thereby inhibiting the hydrolysis of metal ions to form precipitates. At the same time, the copper-specific corrosion inhibitor is adsorbed and forms a film on the exposed copper substrate surface, reducing the dissolution tendency of copper during the stripping process. After the solder ribbon coating is completely dissolved, solid-liquid separation is performed to obtain a clean-surfaced recycled copper ribbon and a stripping waste liquid rich in valuable metal ions.

[0034] Step S2: Solid-liquid separation and recovery of valuable metals The stripping waste liquid obtained in step S1 is subjected to solid-liquid separation with the recycled copper strip to obtain stripping waste liquid rich in valuable metal ions and recycled copper strip.

[0035] Valuable metals in the stripping waste liquid can be treated using one of the following two recovery pathways, depending on the recovery requirements and system composition: Recycling Path 1: Cascade Separation and Recycling Path This process involves the stepwise separation and recovery of silver, lead, and tin, including the following steps: Step S21: Replacement and Silver Extraction When the stripping waste liquid contains silver ions, a copper-based displacement agent is added to the stripping waste liquid to carry out a displacement reaction. Preferably, the copper-based displacement agent is sponge copper powder. Under stirring conditions, the silver ions are reduced to metallic silver and precipitated. The silver product is obtained by solid-liquid separation.

[0036] Step S22: Lead separation by temperature difference crystallization After removing silver in step S21, the filtrate is heated, concentrated, and then cooled. Preferably, the crystallization temperature is controlled at 5℃ to 10℃, so that dissolved lead precipitates in the form of lead chloride crystals. After solid-liquid separation, lead chloride crystals and lead-poor tin-rich mother liquor are obtained.

[0037] Step S23: Hydrolysis of tin plating The lead-poor and tin-rich mother liquor obtained in step S22 is heated to 70℃~90℃, and the pH value of the solution is adjusted to 1.5~2.5 to cause tin to undergo a hydrolysis reaction to generate a precipitate. The tin-containing compound precipitate is obtained by solid-liquid separation. The precipitate can be washed and calcined to obtain tin dioxide product.

[0038] Recovery Pathway Two: Zinc-Based Replacement Overall Recovery Pathway This approach is suitable for situations where stepwise separation is not required or the system composition is complex, and includes the following steps: An excess of zinc-based displacement agent is added to the stripping waste liquid, and the tin, lead, silver and / or copper ions in the solution are reduced to mixed metal sludge in one step through the displacement reaction. The mixed metal sludge is obtained by solid-liquid separation and is used as a smelting raw material for subsequent metal recovery treatment.

[0039] Compared with existing technologies, this invention constructs a fully dissolving stripping system with complexation as the core, allowing tin, lead, and silver in the photovoltaic solder ribbon coating to enter the solution in a dissolved state during the stripping stage. This avoids the problem in existing technologies where tin forms a capping layer due to the in-situ generation of insoluble hydrolysis products such as tin dioxide during stripping, thus ensuring continuous stripping and significantly shortening the stripping time. Simultaneously, by introducing a copper-specific corrosion inhibitor into the stripping system, the dissolution corrosion of the copper substrate under strong oxidizing conditions is effectively suppressed, enabling selective removal of the coating metal and obtaining a smooth-surfaced recovered copper strip. Furthermore, this invention employs a stepped separation path of displacement silver extraction, temperature-differential crystallization lead separation, and decomplexing hydrolysis tin deposition, allowing for the selective recovery of silver, lead, and tin sequentially. This avoids the mixed deposition of multiple metals, improving the recovery purity and utilization value of each metal. The temperature-differential crystallization method directly recovers lead chloride crystals without introducing new impurity ions, which is beneficial for the subsequent treatment and utilization of the mother liquor. Furthermore, the green acidic additives and persulfate system used in this invention avoid the generation of nitrogen oxide gas during the traditional nitric acid stripping process, improving the working environment. The overall process has significant advantages in terms of stripping efficiency, copper substrate protection, high-value recovery of valuable metals, and environmental friendliness.

[0040] The following are embodiments and comparative examples incorporating specific data to further illustrate the above-described technical solutions of the present invention: In the following examples and comparative examples, the raw materials used are all waste photovoltaic welding ribbons from the dismantling and cleaning of retired crystalline silicon photovoltaic modules, including: Raw material A (containing silver solder): Composition approximately Sn 62%, Pb 36%, Ag 2%; Raw material B (ordinary solder strip): Composition is approximately 60% Sn and 40% Pb.

[0041] Example 1 This embodiment provides a green stripping solution and valuable metal separation and recycling method for photovoltaic solder ribbons. Specifically, the method is an iron-free, environmentally friendly method for the high-value separation of silver, lead, and tin for valuable metal recycling.

[0042] The composition and preparation method of the stripping solution are as follows: Take 1 L of deionized water and add the following in sequence: 120 g of sodium persulfate (Na2S2O8), 80 g of aminosulfonic acid (NH2SO3H), 40 g of sodium chloride (NaCl), 10 g of thiourea (CH4N2S), and 0.5 g of benzotriazole (BTA). Stir until completely dissolved to obtain the stripping solution.

[0043] The separation and recovery method is as follows: S1: Full dissolution stripping Take 500 g of raw material A (containing silver solder ribbon, with a composition of approximately 62% Sn, 36% Pb, and 2% Ag) and immerse it in the stripping solution at 40°C for reaction. After 15 min of reaction, the solder ribbon coating is completely dissolved, and the solution is clear with no precipitate.

[0044] S2: Solid-liquid separation The stripped solder was removed and subjected to solid-liquid separation to obtain recycled copper strip and stripping waste liquid rich in valuable metal ions. The recycled copper strip had a bright, reddish metallic surface, and the copper loss rate was measured to be only 0.04%.

[0045] S21: Replacement Silver Add 2 g of sponge copper powder to the stripping waste liquid, stir for 30 min, and utilize the displacement reaction (Cu + 2Ag) + →Cu 2+ + 2Ag) precipitates metallic silver powder, and silver powder is obtained by solid-liquid separation with a silver recovery rate of ≥98%.

[0046] S22: Lead separation by temperature difference crystallization The filtrate obtained from S21 was heated and concentrated, then rapidly cooled to 5°C to crystallize out lead chloride (PbCl2). Solid-liquid separation yielded lead chloride crystals and a lead-poor, tin-rich mother liquor.

[0047] S23: Hydrolytic Tin Plating The lead-poor tin-rich mother liquor was heated to 80°C and the pH was adjusted to 2.0, causing tin to precipitate out as tin dioxide (SnO2). Solid-liquid separation was performed to obtain tin-containing compound precipitates.

[0048] This embodiment uses sodium persulfate as the main oxidant and aminosulfonic acid as a green acidic additive. With the synergistic effect of complexing co-solvent and copper-specific corrosion inhibitor, the complete dissolution and stripping of the solder strip coating is achieved. Furthermore, a stepped separation path sequentially completes the high-value recovery of silver, lead, and tin, verifying the stripping efficiency and metal separation effect of this invention in a completely green system. Figure 1 The copper strip recovered in Example 1 has a bright surface, which further verifies the technical effect of the present invention.

[0049] Example 2 This embodiment provides a method for separating and recovering valuable metals from green stripping solution used in photovoltaic solder ribbons. The method is a low-cost formulation and a simple recovery method. The main method path is a one-pot approach using an excess zinc-based displacement agent.

[0050] The composition and preparation method of the stripping solution are as follows: Measure 1 L of deionized water and add: 100 g of ferric nitrate Fe(NO3)3·9H2O, 60 g of tartaric acid C4H6O6, 60 g of ammonium chloride NH4Cl, and 1.0 g of benzotriazole BTA. Stir until dissolved to obtain the stripping solution.

[0051] The separation and recovery method is as follows: S1: Full dissolution stripping Take 500 g of raw material B (ordinary solder strip, composition approximately Sn 60% and Pb 40%), put it into the stripping solution at room temperature (25℃) and react for 25 min until the coating is completely removed; due to the addition of ammonium chloride and tartaric acid, no white precipitate appeared in the system.

[0052] S2: Solid-liquid separation Solid-liquid separation yields recovered copper strip and stripping waste liquid. The recovered copper strip has a smooth surface and is reduced in one step using an excess zinc-based displacement agent. Given that this system contains a high concentration of iron ions (Fe... 3+ / Fe 2+ Therefore, a stepwise pH-adjusting precipitation method is not suitable. In this embodiment, an excess of zinc powder is added to the stripping waste liquid, and the tin, lead, copper and silver ions in the solution are reduced to mixed metal sludge in one step through a displacement reaction. The mixed metal sludge is filtered to achieve solid-liquid separation, and the resulting mixed metal sludge is sold to the smelter as a crude raw material. The filtrate is discharged after simple treatment. The copper loss rate of the recovered copper strip is measured to be 0.09%.

[0053] This embodiment uses ferric nitrate as the main oxidant and tartaric acid as a green acidic additive to construct a low-cost stripping system. Under the premise of ensuring rapid and complete dissolution of the solder strip coating and preventing corrosion of the copper substrate, and considering the characteristic that iron-containing systems are not suitable for step-by-step pH adjustment precipitation, an excess zinc-based replacement agent is used for one-pot recovery, realizing the simultaneous reduction and recovery of multiple metal ions in the stripping waste liquid, and verifying the compatibility of the method of this invention with different recovery process routes.

[0054] Example 3 This embodiment provides a green stripping solution and a method for separating and recovering valuable metals for photovoltaic solder ribbons. The method uses methanesulfonic acid as a green acidic additive and ammonium persulfate as the main oxidant in the stripping system, and achieves the recovery of valuable metals such as silver, lead, and tin through a cascade separation path.

[0055] The composition and preparation method of the stripping solution are as follows: Take 1 L of deionized water and add: 100 g of ammonium persulfate (NH4)2S2O8, 60 g of methanesulfonic acid (MSA), 50 g of sodium chloride (NaCl), 5 g of thiourea, and 0.3 g of methylbenzotriazole (TTA). Stir until dissolved to obtain the stripping solution.

[0056] S1: Full dissolution stripping Raw material A (containing silver solder strip) was treated at 50°C. The reaction was extremely rapid, and the coating completely dissolved within 10 minutes.

[0057] S2: Solid-liquid separation Solid-liquid separation yields recovered copper strip and stripping waste liquid.

[0058] S21~S23: Cascaded Recycling The subsequent steps for recovering silver, lead, and tin from the stripping waste liquid are the same as those in Example 1: S21 silver removal by displacement, S22 lead separation by temperature difference crystallization, and S23 tin precipitation by hydrolysis.

[0059] The surface of the recycled copper strip obtained in step S2 is in a bright metallic state. The copper loss rate of the recycled copper strip is measured to be 0.08%. In the subsequent cascade recycling process, silver is recovered by liquid phase displacement.

[0060] In this embodiment, ammonium persulfate is used as the main oxidant and methanesulfonic acid is used as a green acidic additive to construct another green stripping system. Under high reaction rate conditions, the rapid and complete dissolution and stripping of the solder strip coating is achieved, and the separation and recovery of silver, lead and tin are completed by following the stepwise separation path. This further proves the adaptability of the stripping solution system of this invention to different combinations of oxidants and acidic additives.

[0061] Comparative Example 1 Comparative Example 1 also provides a stripping solution and recovery method for photovoltaic solder ribbons. The difference from Example 1 is that the stripping solution formula is the same as that of Example 1, but sodium chloride and thiourea are not added as complexing co-solvents during the full dissolution stripping process in step S1.

[0062] During the recycling process, in step S1, after 5 minutes of reaction, the surface of the solder strip was coated with a dense layer of white powder (tin oxide), which hindered the stripping reaction; after another 60 minutes of reaction, the solder strip coating was still not completely dissolved. In the subsequent step S2, the copper strip surface was covered with residues that were difficult to clean, making it impossible to achieve effective recovery of valuable metals.

[0063] Comparative Example 2 Comparative Example 2 also provides a stripping solution and recycling method for photovoltaic solder ribbons. The difference from Example 1 is that the stripping solution formula is the same as that in Example 1, but copper-specific corrosion inhibitor BTA is not added during the full dissolution stripping process in step S1.

[0064] During the recycling process, in step S1, although the solder strip coating can be dissolved quickly, the solution turns blue rapidly during the stripping process, indicating that the copper substrate has dissolved. In step S2, the surface of the recycled copper strip is rough, dark, and significantly thinner. The copper loss rate is measured to be as high as 4.52%, which seriously affects the quality of the copper strip and the purity of the stripping waste liquid.

[0065] Comparative Example 3 Comparative Example 3 also provides a stripping solution and recycling method for photovoltaic solder ribbons. The difference from Example 1 is that the stripping solution formula is the same as that in Example 1, but thiourea is not added in the full dissolution stripping process in step S1. Only sodium chloride is added as a complexing co-solvent.

[0066] During the recovery process, in step S1, when processing the silver-containing solder strip, a large amount of gray-black slag appeared on the surface of the solder strip and at the bottom of the reaction vessel. This slag was a mixture of silver chloride (AgCl) and silver powder. In the subsequent step S21, during the silver removal process, most of the silver was lost in the filter residue and could not be efficiently recovered by liquid-phase displacement. Furthermore, the surface of the recovered copper strip obtained in step S2 was blackened due to silver residue. Upon testing, obvious abnormalities appeared on the surface of the solder strip about 18 minutes after the reaction in step S1, and the copper loss rate of the recovered copper strip obtained in step S2 was about 0.05%.

[0067] The overall test and comparison of the stripping solutions and recovery methods of Examples 1-3 and Comparative Examples 1-3 were conducted, and the results are as follows: Table 1: Summary of Effect Data for Each Example and Comparative Example The test results from the combined examples and comparative examples show that the present invention, by constructing a synergistic stripping system of a main oxidant, a green acidic additive, a complexing flux, and a copper-specific corrosion inhibitor, achieves rapid oxidation and dissolution of the solder strip coating metal (tin, lead, and silver in silver-containing solder strips) in step S1. The high concentration of ligands (chloride ions and / or thiourea) provided by the complexing flux stabilizes the generated metal ions into highly soluble complexes, thereby inhibiting the hydrolysis of tin ions and the formation of insoluble precipitates, thus avoiding the formation of a white passivation layer. Meanwhile, the copper-specific corrosion inhibitor adsorbs onto the copper substrate surface to form a film, significantly inhibiting copper dissolution and corrosion. This results in the recovered copper strip obtained after solid-liquid separation in step S2 maintaining a good appearance and a low copper loss rate (0.04%, 0.09%, and 0.08% in Examples 1-3, respectively). In contrast, Comparative Example 1, lacking the complexing co-solvents (sodium chloride and thiourea) in S1, rapidly formed a white film of stannic acid, hindering the stripping process. Even with prolonged processing, complete stripping remained difficult, demonstrating that the strong complexing and complete dissolution mechanism in this invention is crucial for rapid and thorough stripping. Comparative Example 2, lacking the corrosion inhibitor in S1, exhibited a blue solution and a rough, thin copper strip, with the copper loss rate increasing to 4.52%, indicating that the corrosion inhibitor in this invention is indispensable for copper substrate protection. Furthermore, Comparative Example 3, lacking thiourea in S1, produced AgCl / silver powder-like gray-black slag on the silver-containing solder strip, making subsequent liquid-phase displacement silver extraction inefficient and causing the copper strip to blacken (despite a copper loss rate of approximately 0.05%), indicating the complexation effect of thiourea on silver. The solubilizing effect can prevent silver from depositing in the form of sparingly soluble salts and ensure that silver can be effectively recovered in the liquid phase. The above-mentioned Examples 1 and 3 of the present invention verify that the present invention can achieve silver displacement recovery, lead temperature difference crystallization recovery and tin hydrolysis precipitation recovery in S21 to S23 by using a stepwise separation path. Example 2 proves that in the case of iron-containing systems and other conditions where stepwise precipitation is not suitable, multi-metal simultaneous recovery can still be achieved through a one-pot path with an excess of zinc-based displacement agent, which reflects the compatibility and industrial applicability of the method of the present invention with different formulation systems and recovery routes. The present invention has the advantages of fast stripping speed, no surface passivation layer, strong protection of copper substrate, no blackening of silver-containing solder strips and efficient recovery of silver, and flexible selection of metal recovery path.

[0068] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example 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.

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A green stripping solution for photovoltaic solder ribbons, characterized in that: The stripping solution is an aqueous solution, and its solute components include: Main oxidant, green acidic additive, complexing solubilizer and copper-specific corrosion inhibitor; The primary oxidant is selected from one or more of sodium persulfate, ammonium persulfate, and ferric nitrate. The green acidic additive is selected from one or more of aminosulfonic acid, methanesulfonic acid, tartaric acid, and citric acid; The complexing co-solvent is selected from one or more of sodium chloride, ammonium chloride, and thiourea; The copper-specific corrosion inhibitor is selected from one or more of benzotriazole, methylbenzotriazole, and 2-mercaptobenzimidazole.

2. The green stripping solution for photovoltaic solder ribbons according to claim 1, characterized in that, The mass concentration ranges of each component in the stripping solution are as follows: Primary oxidant: 50-200 g / L; Green acidic additive: 30-120g / L; Complexing co-solvent: 20-100 g / L; Copper-specific corrosion inhibitor: 0.1-2.0 g / L.

3. The green stripping solution for photovoltaic solder ribbons according to claim 2, characterized in that, The mass concentration ranges of each component in the stripping solution are as follows: The main oxidant is sodium persulfate, with a concentration of 100-150 g / L; The green acidic additive is aminosulfonic acid, with a concentration of 70-100 g / L; The complexing solubilizer is a mixture of sodium chloride and thiourea, wherein the concentration of sodium chloride is 30-50 g / L and the concentration of thiourea is 5-15 g / L; The copper-specific corrosion inhibitor is benzotriazole, with a concentration of 0.3-1.0 g / L.

4. The green stripping solution for photovoltaic solder ribbons according to claim 1, characterized in that, The complexing co-solvent includes thiourea, and the concentration of thiourea is not less than 5 g / L.

5. A method for separating and recovering valuable metals using the stripping solution according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Full dissolution plating removal: Waste photovoltaic solder ribbons are immersed in stripping solution for reaction. Under the action of main oxidant, complexing flux and copper-specific corrosion inhibitor, all tin, lead and / or silver in the solder ribbon coating enter the solution in the form of soluble complex ions. At the same time, the copper substrate remains insoluble and forms a smooth surface, resulting in stripping waste solution. S2: Solid-liquid separation step: The stripping waste liquid is separated from the copper substrate to obtain stripping waste liquid rich in valuable metal ions and recycled copper strip.

6. The method for separating and recovering valuable metals from the stripping solution according to claim 5, characterized in that, In step S1, the reaction is carried out under stirring at a temperature of 20-60°C for 10-30 minutes.

7. The method for separating and recovering valuable metals from the stripping solution according to claim 5, characterized in that, Step S2 includes: S21: Silver extraction by displacement: A copper-based displacement agent is added to the stripping waste liquid, and after the displacement reaction, solid-liquid separation is performed to obtain metallic silver; S22: Temperature difference crystallization of lead: The filtrate obtained in step S21 is heated, concentrated, and then cooled to crystallize lead chloride. After solid-liquid separation, lead chloride crystals and lead-poor tin-rich mother liquor are obtained. S23: Hydrolysis and Tin Precipitation: The pH value of the lead-poor and tin-rich mother liquor is adjusted to 1.5-2.5, and the temperature is raised to 70-90℃ to carry out a hydrolysis reaction. After solid-liquid separation, a tin-containing compound precipitate is obtained.

8. The method for separating and recovering valuable metals from the stripping solution according to claim 7, characterized in that, In step S21, the copper-based replacement agent is sponge copper powder.

9. The method for separating and recovering valuable metals from the stripping solution according to claim 7, characterized in that, In step S22, the crystallization temperature is 5-10℃.

10. The method for separating and recovering valuable metals from the stripping solution according to claim 5, characterized in that, Step S2 includes: adding an excess of zinc-based displacement agent to the stripping waste liquid, reducing tin, lead, silver and / or copper ions in the solution to mixed metal sludge in one step through displacement reaction, obtaining the mixed metal sludge after solid-liquid separation, and using the mixed metal sludge as a smelting raw material for subsequent metal recovery treatment.

Images