Method for recovering copper and tin from tin stripping waste liquid step by step

Abstract

The invention discloses a method for recovering copper and tin from tin stripping waste liquid step by step, which comprises the following steps: firstly, adding an alkaline regulator into the tin stripping waste liquid to control the pH value, then adding a precipitator to enable copper ions to form precipitates, and carrying out plate-frame pressure filtration after flocculation of PAC and PAM to obtain copper sludge and copper-removed liquid; adding excessive iron powder into the copper-removed liquid to reduce tin ions into sponge tin, and filtering to obtain a tin-iron mixture filter cake; and finally, mixing the tin-iron mixture with sodium hydroxide and sodium nitrate in proportion, carrying out a melting reaction, leaching with hot water, filtering and separating to obtain a sodium stannate solution and reduced iron powder, and respectively crystallizing and drying to obtain industrial-grade sodium stannate and reduced iron powder products.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste liquid resource treatment technology, specifically relating to a method for recovering and utilizing valuable metal components in nitric acid-type tin stripping waste liquid, particularly a resource treatment method for stepwise recovery of copper from tin stripping waste liquid and simultaneous preparation of sodium stannate and iron powder. Background Technology

[0002] In the printed circuit board (PCB) and electronic component manufacturing industry, nitric acid-based tin stripping solutions are widely used to etch and remove the tin plating layer from the substrate surface. As production progresses, the nitric acid in the stripping solution is continuously consumed, and the concentration of metal ions such as tin and copper gradually increases, leading to a decrease in stripping efficiency and ultimately forming waste stripping liquid. This waste liquid is highly acidic, with a tin content generally exceeding 90 g / L, a copper content of 5–10 g / L, and 15–20% nitric acid residue. It also contains heterocyclic compounds, polycyclic aromatic hydrocarbons, and polymers, making it highly corrosive and polluting. Direct discharge without proper treatment will inevitably cause serious pollution to water resources and the ecological environment. Furthermore, the tin-containing waste liquid has a high content of valuable metals such as tin and copper, making it highly valuable for recycling.

[0003] Currently, the main methods for treating tin stripping wastewater include the following: First, the simple neutralization-precipitation method, which involves adding alkaline solution to form hydroxide sludge from heavy metal ions. While simple to operate, this method generates a large amount of tin- and copper-containing sludge requiring hazardous waste disposal, failing to recover valuable resources and incurring high disposal costs. Second, single-metal recovery methods, such as electrolytic recovery of tin or copper. However, due to the coexistence of multiple metal ions in the wastewater, direct electrolysis results in low efficiency, poor product purity, and limited economic benefits. Third, solvent extraction, which can selectively separate and recover copper, but subsequent tin recovery processes are often independent and complex, with long processes and high extractant costs. Furthermore, existing technologies primarily focus on metal recovery, while paying insufficient attention to the resource utilization of large amounts of iron ions and nitrate ions in the wastewater, failing to achieve comprehensive conversion and high-value utilization of all components of the wastewater. Summary of the Invention

[0004] Technical problem to be solved: The technical problem to be solved by this invention is to overcome the shortcomings of existing tin stripping waste liquid treatment technology and provide an efficient, economical and environmentally friendly resource-based treatment method.

[0005] Technical solution: A method for stepwise recovery of copper and tin from tin stripping waste liquid, comprising the following steps: S1. Add an alkaline regulator to the waste tin stripping solution to control the pH value to 3.5~4.5. Add a precipitant while stirring to react and cause copper ions to form precipitates. Then add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. Finally, perform solid-liquid separation through a plate and frame filter press to obtain a copper sulfide / copper chelate filter cake with low water content and a clear copper-removed liquid. S2. Add excess iron powder to the copper-removed solution obtained in step S1, stir and react to reduce the remaining tin ions in the solution to sponge tin. After the reaction is completed, filter to obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate, and after melting reaction at high temperature, the melt product is leached with water, and separated by filtration to obtain sodium stannate solution and reduced iron powder; S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0006] Preferably, the precipitant in step S1 is one of sodium sulfide, TMT, DTCR, DDTC, and WY5, and the molar ratio of its dosage to copper ions is (0.8~2):1.

[0007] Preferably, the amount of iron powder added in step S2 is calculated as Fe:Sn = (1.5~2.5):1 based on the molar ratio with the remaining tin ions.

[0008] Preferably, the raw material ratio for the melting reaction in step S3 is: solid mixture: sodium hydroxide: sodium nitrate = 1:(0.8~1.2):(0.1~0.3), the reaction temperature is 500~700℃, and the reaction time is 1~2h.

[0009] Preferably, the alkaline regulator in step S1 is one or a mixture of sodium hydroxide solution and sodium carbonate.

[0010] Preferably, the dosage of PAC in step S1 is 50~200 mg / L, and the dosage of PAM is 1~10 mg / L.

[0011] Preferably, the iron powder mentioned in step S2 is reduced iron powder or cast iron shavings, with a particle size range of 100~300 mesh.

[0012] Preferably, the leaching operation in step S3 uses hot water at a temperature of 60~95℃, the leaching time is 0.5~1 h, and the liquid-solid ratio is (3~6):1.

[0013] Preferably, the operating pressure of the plate and frame filter press in step S1 is 0.4 to 0.8 MPa, and the moisture content of the resulting filter cake is less than 30%.

[0014] Beneficial effects: The method for stepwise recovery of copper and tin from tin stripping waste liquid of the present invention has the following advantages: 1. This invention utilizes highly efficient organic sulfur precipitants such as TMT and DTCR, which can form extremely stable chelate precipitates with copper ions in a weakly acidic environment with a pH of 3.5 to 4.5. This achieves highly selective separation of copper ions, effectively solving the problem of separating tin and copper ions and providing a guarantee for subsequent processes.

[0015] 2. This invention uses the addition of PAC and PAM for coagulation and flocculation, which rapidly forms dense flocs from fine precipitates and reduction products. Combined with plate and frame filtration, the moisture content of the filter cake is reduced to below 30%, which greatly reduces the loss of metal in the filtrate and improves the overall metal recovery rate.

[0016] 3. This invention uses excess reduced iron powder as a displacement agent, which not only completely reduces tin ions to sponge tin for enrichment, but also the ferrous ions generated by the dissolution of iron powder can reduce and remove residual nitrate ions in the waste liquid, avoiding nitrogen oxide pollution. At the same time, the excess iron powder becomes the raw material source for the subsequent preparation of iron powder, realizing the treatment of waste with waste.

[0017] 4. This invention utilizes a high-temperature molten system composed of sodium hydroxide and sodium nitrate to convert tin and its oxides into water-soluble sodium stannate on the one hand, and to stabilize metallic iron in a strongly alkaline oxidizing environment on the other hand. Finally, the sodium stannate and reduced iron powder can be efficiently separated by simple hot water leaching. The process route is short and the product has high added value.

[0018] 5. The process of this invention ultimately converts copper in the waste liquid into copper sludge, tin into sodium stannate, iron into reduced iron powder, and nitrate into sodium nitrate byproduct, thus basically achieving full element recovery of the tin stripping waste liquid and truly achieving the goal of harmless and resource-based treatment of hazardous waste. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate, or a mixture thereof, to the waste tin stripping solution to control the pH value to 3.5-4.5. Add a precipitant under stirring to react; the precipitant is one of sodium sulfide, TMT, DTCR, DDTC, or WY5, with a molar ratio of (0.8-2):1 to copper ions. This causes copper ions to precipitate. Then, add PAC to the system for coagulation, followed by PAM for flocculation, promoting the aggregation of fine precipitates into large flocs. The dosage of PAC is 50-200 mg / L, and the dosage of PAM is 1-10 mg / L. Finally, perform solid-liquid separation using a plate and frame filter press at a pressure of 0.4-0.8 MPa. Filtration yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. In the above steps, a slightly acidic environment with a pH of 3.5-4.5 is precisely controlled, and organic sulfur precipitants such as TMT are used to form stable chelate precipitates with copper ions. Under these conditions, tin ions remain stable in the liquid phase, thus achieving selective separation of copper. Subsequently, PAC and PAM flocculants are added, and through charge neutralization and adsorption bridging, the fine precipitate is agglomerated into dense flocs. This is then filtered through a plate and frame filter press to obtain copper sludge with low water content, greatly improving solid-liquid separation efficiency and copper recovery rate.

[0020] S2. Add 100-300 mesh iron powder with a molar ratio of Fe:Sn=(1.5~2.5):1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. In step S2 above, excess reduced iron powder is added to the copper-removed liquid, utilizing the difference in metal activity. This reduces tin ions to sponge tin through a displacement reaction. The excess iron powder completely eliminates residual nitrate ions in the waste liquid, preventing nitrogen oxide pollution, and simultaneously provides raw materials for subsequent iron powder products. After the reaction, filtration yields a tin-iron mixed solid, achieving efficient enrichment of tin.

[0021] S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:(0.8~1.2):(0.1~0.3). After melting reaction at a high temperature of 500~700℃ for 1~2h, the melt product is leached with warm water at a temperature of 60~95℃ for 0.5~1h. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is (3~6):1. In step S3 above, the tin-iron mixture is mixed with sodium hydroxide and sodium nitrate and then subjected to a high-temperature alkaline fusion reaction. In the oxidizing molten system, tin is converted into water-soluble sodium stannate, while iron forms a dense oxide layer under alkaline conditions to maintain its metallic state. Subsequently, through hot water leaching, the sodium stannate enters the solution, while the iron powder remains insoluble, and efficient separation can be achieved through simple filtration.

[0022] S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0023] Example 1

[0024] A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0025] Example 2

[0026] A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution, or a mixture thereof, to the waste tin stripping solution to control the pH value to 4. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 2:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, followed by PAM for flocculation, to promote the aggregation of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation using a plate and frame filter press at a pressure of 0.4 MPa to obtain a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0027] Example 3

[0028] A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 2.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0029] Example 4

[0030] A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:0.8:0.3. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0031] Example 5

[0032] A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 6:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0033] Comparative Example 1 A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution, or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is 0.5:1 molar ratio of TMT to copper ions, causing copper ions to form precipitates. Then, add PAC to the system for coagulation, followed by PAM for flocculation, to promote the aggregation of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation using a plate and frame filter press at a pressure of 0.4 MPa. Filtration yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0034] Comparative Example 2 A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 0.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0035] Comparative Example 3 A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:0.5:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0036] Comparative Example 4 A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 1:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0037] Comparative Example 5 A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 8. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 60℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0038] Comparative Example 6 A method for stepwise recovery of copper and tin from tin stripping waste liquid includes the following steps: S1. Add an alkaline regulator, such as sodium hydroxide solution or sodium carbonate solution or a mixture thereof, to the waste tin stripping solution to control the pH value to 3. Add a precipitant, such as one of TMT, under stirring to react. The precipitant is added at a molar ratio of 1:1 to copper ions to form a precipitate. Then, add PAC to the system for coagulation, and then add PAM for flocculation to promote the agglomeration of fine precipitates into large flocs. The dosage of PAC is 50 mg / L and the dosage of PAM is 1 mg / L. Finally, perform solid-liquid separation by using a plate and frame filter press at a pressure of 0.4 MPa. The filter press yields a copper sulfide / copper chelate filter cake with a water content of less than 30% and a clear copper-removed liquid. S2. Add 100-mesh iron powder with a molar ratio of Fe:Sn = 1.5:1 to the copper-removed solution obtained in step S1, stir the reaction, reduce the remaining tin ions in the solution to sponge tin, filter after the reaction is completed, and obtain a filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate. S3. The solid mixture filter cake obtained in step S2 is mixed with sodium hydroxide and sodium nitrate in a ratio of 1:1:0.1. After melting reaction at 500℃ for 1 hour, the melt product is leached with warm water at 25℃ for 0.5 hours. After filtration and separation, the liquid-solid ratio of sodium stannate solution and reduced iron powder is 3:1. S4. The sodium stannate solution obtained in step S3 is evaporated, concentrated, cooled and crystallized to obtain industrial-grade sodium stannate product. The resulting reduced iron powder is washed, dried and recycled as a product.

[0039] Performance testing: Copper recovery rate: The residual copper concentration in the solution after copper removal was determined by inductively coupled plasma spectroscopy and calculated by comparing it with the concentration of the original solution.

[0040] Tin reduction rate: The residual tin concentration in the filtrate was determined by ICP-OES and calculated by comparing it with the concentration of the filtrate after copper removal in step S1.

[0041] Sodium stannate conversion rate: The tin content of the sodium stannate solution obtained in step S3 was determined by chemical titration and calculated by comparing it with the total tin content in the filter cake of the solid mixture in step S2.

[0042] Iron powder quality: X-ray fluorescence was performed on the reduced iron powder obtained in step S3 to determine its main content and the content of key impurities.

[0043] Table 1 shows a comparison of the relevant recovery rates.

[0044] serial number Copper recovery rate Tin reduction rate Sodium stannate conversion rate Main components of reduced iron powder Example 1 98.5% 98.8% 96.2% Fe: 95.5%; Sn: 1.2% Example 2 99.9% 98.7% 96.0% Fe: 94.8%; Sn: 1.3%; S: 0.5% Example 3 98.4% 99.9% 95.8% Fe: 92.1%; Sn: 1.5% Example 4 98.6% 98.9% 78.5% Fe: 95.0%; Sn: 15.5% Example 5 98.5% 98.8% 97.5% Fe: 95.7%; Sn: 1.0% Comparative Example 1 75.3% - - - Comparative Example 2 98.5% 65.4% - - Comparative Example 3 98.4% 98.7% 45.2% Fe: 92.8%; Sn: 38.5% Comparative Example 4 98.3% 98.8% 82.1% Fe: 94.2%; Sn: 8.5% Comparative Example 5 - - - - Comparative Example 6 98.6% 98.9% 81.3% Fe: 95.1%; Sn: 9.8% As shown in Table 1, Example 1 achieved efficient copper precipitation, complete tin reduction, and high sodium stannate conversion. The iron powder quality was good. In Example 2, the copper recovery rate was extremely high, but sulfur impurities were introduced. Excessive TMT ensured complete copper precipitation, but excessive sulfurizing agent may lead to increased sulfur content in copper slag and subsequent iron powder, affecting product purity. In Example 3, tin reduction was complete, but the iron powder yield and quality were poor. Excessive iron powder ensured complete tin recovery, but a large amount of unreacted iron entered the product, diluting the purity of the iron powder and increasing the burden of subsequent washing. In Example 4, the conversion failed because insufficient NaOH led to incomplete melting reaction, and a large amount of tin was not converted into soluble sodium stannate, ultimately remaining in the iron powder, resulting in extremely high tin content in the iron powder and a sharp drop in tin product recovery rate. In Example 5, the conversion rate was high but the economics were poor. Increasing the water volume improved the leaching rate, but the concentration of the resulting sodium stannate solution was only 50% of the baseline group, and the energy consumption for evaporation and concentration was expected to increase by more than 200%. In Comparative Example 1, insufficient precipitant resulted in a large amount of copper remaining in the copper-removed liquid, which could not be effectively treated in subsequent steps, and the entire recovery process failed. In Comparative Example 2, insufficient iron powder led to... The following issues were identified: In Comparative Example 3, a large amount of tin ions remained in the S2 filtrate, resulting in ineffective tin recovery and resource waste. In Comparative Example 4, severe alkali deficiency prevented the main reaction from proceeding, and most of the tin remained unconverted, mixing with iron powder and failing to separate, thus failing to achieve the process objective. In Comparative Example 5, insufficient water led to oversaturation of the high-concentration sodium stannate solution and adsorption losses, resulting in a large amount of sodium stannate failing to dissolve and entering the solution, being lost with the iron powder slag, and incomplete leaching. In Comparative Example 5, incorrect pH adjustment caused a large amount of tin hydroxide precipitate to form in step S1, resulting in complete co-precipitation of copper and tin, making stepwise recovery impossible. In Comparative Example 6, slow leaching kinetics and low sodium stannate solubility meant that even with extended leaching time, up to 10% of the tin remained undissolved and unrecovered, resulting in low production efficiency.

[0045] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A process for the stepwise recovery of copper and tin from a desmearing waste solution, characterized in that, The method comprises the following steps: S1. Adding an alkaline regulator to the spent tin plating solution to control the pH value to 3.5-4.5, adding a precipitant under stirring to react and form a precipitate of copper ions, then adding PAC for coagulation and PAM for flocculation to promote the aggregation of fine precipitates into large alunite flowers, and finally performing solid-liquid separation by a plate-and-frame filter press to obtain a low-moisture copper sulfide / copper chelate filter cake and a clarified copper-removed solution; S2. Adding excess iron powder to the copper-removed solution obtained in step S1 to react and reduce the remaining tin ions in the solution into sponge tin, and then filtering to obtain a solid mixture filter cake rich in tin and iron and a filtrate mainly containing sodium nitrate; S3. Mixing the solid mixture filter cake obtained in step S2 with sodium hydroxide and sodium nitrate, performing a high-temperature melting reaction, leaching the melting product with water, and then filtering to obtain a sodium stannate solution and reduced iron powder; S4. Evaporating and concentrating the sodium stannate solution obtained in step S3, cooling and crystallizing to obtain an industrial-grade sodium stannate product, and washing and drying the reduced iron powder to obtain a product.

2. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, The precipitant in step S1 is one of sodium sulfide, TMT, DTCR, DDTC, and WY5, and the molar ratio of the addition amount to copper ions is (0.8-2):

1.

3. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, The addition amount of the iron powder in step S2 is Fe:Sn=(1.5-2.5):1 in terms of the molar ratio to the remaining tin ions.

4. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, In step S3, the raw material ratio of the melting reaction is solid mixture:sodium hydroxide:sodium nitrate=1:(0.8-1.2):(0.1-0.3), the reaction temperature is 500-700℃, and the reaction time is 1-2h.

5. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, The alkaline regulator in step S1 is one or a mixture of sodium hydroxide solution and sodium carbonate.

6. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, The addition amount of PAC in step S1 is 50-200 mg / L, and the addition amount of PAM is 1-10 mg / L.

7. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, The iron powder in step S2 is reduced iron powder or cast iron scrap, and the particle size range is 100-300 mesh.

8. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, In step S3, hot water is used for leaching, the temperature is 60-95℃, the leaching time is 0.5-1h, and the liquid-solid ratio is (3-6):

1.

9. A process for the stepwise recovery of copper and tin from a speltering waste solution as claimed in claim 1 wherein, In step S1, the operating pressure of the plate-and-frame filter press is 0.4-0.8 MPa, and the moisture content of the obtained filter cake is less than 30%.