PCB desmear waste liquid recycling and copper-tin recovery method

Abstract

The application relates to a PCB desmear waste liquid recycling and copper-tin recovery method, and belongs to the technical field of energy saving and environmental protection. The technical points are as follows: S1, oxalic acid is added into nitric acid type desmear waste liquid as a precipitant, so that tin and copper in the waste liquid are precipitated in the form of oxalate and are separated together, and copper-tin mixed oxalate is obtained; S2, a tin-containing solution and copper hydroxide are obtained; S3, metal copper is recovered; S4, metal tin is recovered; and S5, nitric acid, iron nitrate, a desmear copper protective agent and citric acid are added into the primary separation liquid obtained in S1, and a regenerated desmear liquid is prepared. According to the scheme, copper and tin in the desmear waste liquid can be efficiently and synchronously recovered, the tin recovery rate is greater than or equal to 93%, the purity is greater than or equal to 99.5%, the copper recovery rate is greater than or equal to 80%, and the purity is greater than or equal to 98.5%.

Description

Technical Field

[0001] This invention patent relates to the production field of wastewater treatment, and in particular to a method for recycling and regenerating PCB tin stripping waste liquid and recovering copper and tin. Background Technology

[0002] Tin stripping solution is a key chemical material used in printed circuit board production to selectively dissolve tin plating, tin-lead alloy plating, and tin solder joints on electroplated copper layers.

[0003] Nitric acid-based solder stripping solution is currently the most widely used type of solder stripping agent in the PCB industry. It is mainly composed of nitric acid, ferric nitrate, copper corrosion inhibitor (copper protectant), surfactant, nitric acid inhibitor, complexing agent, etc. As the solder stripping process proceeds, the concentration of tin ions in the solder stripping solution continuously increases, while copper ions also continuously accumulate (mainly due to the trace amount of copper substrate being etched after solder stripping of the circuit board). When the tin concentration reaches 80-100 g / L, the solder stripping effect decreases significantly, and the solution becomes waste solder stripping solution.

[0004] Typical waste tin stripping solution contains approximately 15%–20% nitric acid, 80–100 g / L tin, 2–8 g / L copper, and 15–25 g / L iron ions, as well as various organic additives.

[0005] The existing methods for treating tin stripping waste liquid are mainly: (1) Conventional neutralization precipitation method (CN121537124A, CN121292617A): Alkali solution is added to co-precipitate heavy metal ions such as tin and copper into mixed sludge, which is then dewatered and outsourced for treatment. This method not only generates a large amount of hazardous waste sludge and ammonia nitrogen wastewater, causing secondary pollution, but also has high material consumption and wastewater treatment costs.

[0006] (2) Simple tin salt recovery method (CN120905539A): such as preparing barium stannate, metastannic acid and other products, but the copper in the waste liquid cannot be effectively recovered, and a large amount of acid and iron ions remain, causing secondary pollution.

[0007] (3) Copper-tin selective precipitation method (CN121250366A): Copper-tin precipitant (mostly oxalic acid) is added to allow most of the copper and tin in the waste liquid to precipitate out as tin sludge. After pressure filtration, the tin sludge is treated as hazardous waste by an external contractor. Although the regenerated liquid is recycled after being mixed, the tin sludge produced is hazardous waste. The external treatment causes secondary pollution, and most of the recovered products are metal salts rather than elemental metals, resulting in low added value.

[0008] Therefore, finding a new technical approach to treat tin stripping waste liquid is an urgent technical problem to be solved. Summary of the Invention

[0009] The purpose of this invention is to provide a method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin, so as to solve the problems existing in the background art.

[0010] The technical solution of this application is: A method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin includes the following steps: S1, Oxalic acid precipitation of copper and tin: Oxalic acid is added to the nitric acid-type tin stripping waste liquid as a precipitant, so that tin and copper in the waste liquid are precipitated together in the form of oxalate precipitate, and copper-tin mixed oxalate precipitate and primary separation liquid are obtained. S2, after washing the copper-tin mixed oxalate precipitate obtained in S1 with water, it is mixed with sodium hydroxide solution, so that the tin oxalate selectively dissolves into the solution and the copper oxalate is converted into copper hydroxide precipitate. After solid-liquid separation, a tin-containing solution and copper hydroxide are obtained. S3, copper hydroxide solid is washed with water and converted into copper sulfate, which is then electrolytically deposited to recover metallic copper; The tin-containing solutions obtained from S4 and S2 are mixed with the water washing solution from S3 and electrolytically deposited to recover metallic tin. S5, add nitric acid, ferric nitrate, copper stripping agent and citric acid to the primary separation solution obtained in S1 to prepare a regenerated tin stripping solution.

[0011] Furthermore, the precipitation reaction temperature of S1 is room temperature, and the reaction time is 60–90 min.

[0012] Furthermore, a flocculant is added to S1, wherein the flocculant is cationic polyacrylamide, and the addition amount is 5-25 mg per liter of waste liquid.

[0013] Furthermore, the sodium hydroxide concentration in S2 is 15-30%, the solid-liquid volume ratio is 1:4-1:8, the reaction temperature is 60°C-80°C, and the reaction time is 60-120 min.

[0014] Furthermore, S3 includes: mixing copper hydroxide with dilute sulfuric acid and reacting the resulting copper sulfate solution by electrolytic deposition to recover metallic copper.

[0015] Furthermore, the mass ratio of copper hydroxide to dilute sulfuric acid is 1:1 to 1:3, and the electrolytic copper extraction conditions are: current density 1.0 to 3.0 A / dm³. 2 The cell voltage is 1.5~2.5V, the electrolyte temperature is 40~60℃, and the electrolysis time is 2~8h.

[0016] Furthermore, the conditions for electrolytic tin extraction are as follows: the cathode material is a stainless steel plate or a titanium plate, the anode material is an inert anode, the electrolyte temperature is 30–50℃, the cell voltage is 2.0–4.0V, and the current density is 0.5–2.5A / dm³. 2The electrolysis time is 2 to 8 hours; sodium hydroxide solution needs to be added during the electrowinning process, and the concentration of sodium hydroxide should be controlled at 1 to 4%.

[0017] Furthermore, the concentration of nitric acid in the regenerated tin stripping solution in S5 is 4.0~6.5mol / L, and the concentration of iron ions is 15~25g / L; the tin stripping and copper protection agent is benzotriazole, and the addition amount is 2~6g per liter of separation solution.

[0018] Furthermore, the purity of the recovered tin is no less than 99%, and the tin recovery rate is no less than 93%; the purity of the recovered copper is no less than 98%, and the copper recovery rate is no less than 80%.

[0019] The beneficial effects of this application are as follows: (1) In the existing methods for treating tin stripping waste liquid, the conventional neutralization precipitation method co-precipitates heavy metal ions such as copper and tin into mixed sludge, which cannot achieve the separate recovery of copper and tin. The simple tin salt recovery method only focuses on the recovery of tin, and the copper in the waste liquid cannot be effectively recovered; although the copper-tin selective precipitation method can precipitate most of the copper and tin in the form of oxalate, the tin-copper separation effect is poor, and the precipitate is a mixed tin sludge, which is still treated as hazardous waste by outsourcing.

[0020] To address the aforementioned issues, this application employs the following techniques: "In step S1, oxalic acid is used as a co-precipitant, causing tin and copper ions in the waste liquid to co-precipitate as oxalate precipitates, resulting in a copper-tin mixed oxalate precipitate." "In step S2, the significant difference in the dissolution reactions of tin oxalate and copper oxalate in sodium hydroxide solution is utilized: tin oxalate reacts with sodium hydroxide to form soluble stannate which enters the solution, while copper oxalate is converted into the less soluble copper hydroxide precipitate, achieving selective separation of copper and tin." "Steps three and four involve electrolytic deposition of copper hydroxide and tin-containing solutions, respectively, to recover metallic copper and metallic tin." Through the synergistic combination of these techniques, efficient recovery of tin and copper is achieved: the recovered metallic tin has a purity of not less than 99%, and a tin recovery rate of not less than 93%; the recovered metallic copper has a purity of not less than 98%, and a copper recovery rate of not less than 80%.

[0021] (2) Although the existing copper-tin selective precipitation method can precipitate copper and tin in the form of oxalate, the precipitate is a mixed tin mud, which is costly to outsource.

[0022] To address the aforementioned issues, this application employs the following methods: "In step S2, tin-containing solution and copper hydroxide solid are selectively separated using sodium hydroxide solution," "In step S3, copper hydroxide solid is reacted with sulfuric acid to convert it into copper sulfate solution, which is then electrolytically deposited to obtain metallic copper," and "In step S4, the tin-containing solution is directly electrolytically deposited to obtain metallic tin." Through the synergistic combination of these techniques, efficient recovery of metallic tin and copper is achieved, rather than relying on traditional tin salts or mixed sludge.

[0023] (3) Conventional neutralization precipitation method requires a large amount of alkaline solution to neutralize waste acid, and the nitric acid in the tin stripping solution is completely wasted and cannot be recycled. The simple tin salt recovery method leaves a large amount of acid and iron ions, which also fails to achieve the recycling of tin stripping solution. This leads to high procurement costs of tin stripping solution and generates a large amount of waste liquid that needs to be treated.

[0024] To address the aforementioned issues, this application employs a method of "adding nitric acid, ferric nitrate, a tin-removing and copper-protecting agent, and citric acid to the primary separation solution obtained in S1 to prepare a regenerated tin-removing solution." Through this technique, nitric acid and ferric nitrate are retained to the maximum extent in the primary separation solution after oxalic acid precipitation. After component analysis and replenishment of missing components, the tin-removing performance can be restored. Verification through examples shows that the regenerated tin-removing solution can achieve a tin-removing rate of 11.5 μm / min and can continuously remove 2.7 μm of tin. 2 The solder plates meet the new solder stripping solution standards. This significantly reduces the procurement cost of the solder stripping solution and also reduces the amount of waste liquid discharged. Attached Figure Description

[0025] Figure 1 This is a flow chart of the PCB desoldering waste liquid recycling and copper-tin recovery method of this application. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0027] One liter of nitric acid-based tin stripping waste liquid from a circuit board factory in Guangdong was tested and found to be composed of: 16.5% nitric acid (mass fraction), 98 g / L tin, 3.8 g / L copper, 16 g / L iron, and a specific gravity of 1.35.

[0028] A method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin includes the following steps: S100, oxalic acid precipitates copper and tin: The waste liquid is introduced into a reaction beaker, and stirring is started. Oxalic acid solid powder is gradually added by reducing the amount of oxalic acid, and stirring is continued for about 10 minutes. Then it is allowed to stand. When no more precipitate is produced after adding oxalic acid to the supernatant, about 32g of oxalic acid is added and stirring is continued. At the same time, 15mg of polyacrylamide flocculant is added. The reaction is carried out at room temperature for 80 minutes. After standing, a large amount of white (slightly bluish) precipitate is observed to form S200, which is adsorbed by resin.

[0029] S200, Filtration and solid-liquid separation: The reaction mixture is filtered through a vacuum filter to obtain approximately 870 mL of primary separation liquid and approximately 180 g (wet weight) of copper-tin mixed oxalate precipitate.

[0030] S300, tin-copper mud water washing and filtration: Add about 100ml of water to the filtered tin-copper mud and wash and stir for about 15 minutes to dissolve the nitric acid, iron ions and other substances remaining in the tin-copper mud into the water and remove them from the solid; wash 3 times in sequence; after 3 water washing and filtration, about 171g of purified tin-copper mud is obtained.

[0031] S400, Copper-Tin Oxalate Separation: The copper-tin sludge obtained from water washing and filtration was mixed with 15% sodium hydroxide at a solid-liquid volume ratio of 1:5 and reacted. The mixture was heated to 65-70℃ and stirred for 80 minutes. Filtration yielded solid copper hydroxide (filter residue) and a tin-containing solution (filtrate). The filter residue was washed three times with 100 ml of water each time, then filtered, and the wash water was added to the filtrate. Analysis showed that the filter residue contained 3.3 g of copper and 0.1 g of tin; the tin-containing filtrate (including wash water) totaled 1130 mL; the tin content was approximately 95.4 g, and the copper content was 0.1 g.

[0032] S500, Copper hydroxide conversion and electrolytic copper extraction: (a) After washing, copper hydroxide and 30% sulfuric acid were mixed at a mass ratio of 1:1.5 and reacted for 30 min under stirring to obtain 200 mL of copper sulfate solution with a copper content of about 16 g / L. (b) Introduce copper sulfate solution into the electrolytic cell and control the current density at 2.0 A / dm³. 2 The cell voltage was 2.0V, the electrolyte temperature was 45℃, the electrolysis time was 4h, and metallic copper was deposited at the cathode. (c) The copper deposited at the cathode was collected, washed and dried to obtain approximately 3.2 g of metallic copper with a purity of 99.3%.

[0033] S600, tin-containing solution purification and electrolytic tin extraction: (a) The tin-containing solution obtained in step S400 is introduced into an electrolytic cell, with a stainless steel plate as the cathode and a titanium-based coated anode as the anode. The electrolyte temperature is controlled at 40°C, the cell voltage at 3.2V, the current density at 1.8A / dm², and the electrolysis time at 5h. (b) Metallic tin was deposited at the cathode, collected and washed, and then melted and cast at 400°C to obtain approximately 94g of tin ingots with a purity of 99.6%.

[0034] S700, primary separation solution regeneration preparation: The primary separation solution is introduced into the preparation tank, and the nitric acid content is detected to be approximately 18.8% and the iron ion content is 14.5 g / L; 110 mL of 68% nitric acid and 20 g of ferric nitrate are added, along with 3 g of copper protectant (benzotriazole) and 1 g of citric acid; the mixture is stirred for 30 minutes to obtain approximately 1000 mL of regenerated tin stripping solution with a specific gravity of 1.25.

[0035] The immersion method was used to conduct the tin stripping experiment. The temperature of the regenerated tin stripping solution was controlled at 30℃ and the tin stripping rate was 11.5μm / min. It can continuously strip 2.7㎡ of tin board, and the tin stripping performance meets the standard of fresh tin stripping solution.

[0036] In Example 1, the tin recovery rate was approximately 95.5%, and the copper recovery rate was approximately 83.6%. Example

[0037] One liter of nitric acid-based tin stripping waste liquid from a circuit board factory in Zhejiang was tested and found to be composed of: 18.5% nitric acid (mass fraction), 87 g / L tin, 5.8 g / L copper, 18 g / L iron, and a specific gravity of 1.35.

[0038] A method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin includes the following steps: S100, Oxalic Acid Precipitates Copper and Tin: Pour the waste liquid into a reaction beaker, start stirring, and gradually add oxalic acid solid powder using a decreasing method, stirring continuously for about 10 minutes. Then let it stand. When no more precipitate is produced after adding oxalic acid to the supernatant, add about 28g of oxalic acid and continue stirring. At the same time, add 15mg of polyacrylamide flocculant and react at room temperature for 80 minutes. After standing, a large amount of white (slightly bluish) precipitate is observed to be formed.

[0039] S200, Filtration and solid-liquid separation: The reaction mixture is filtered through a vacuum filter to obtain approximately 850 mL of primary separation liquid and approximately 172 g (wet weight) of copper-tin mixed oxalate precipitate.

[0040] S300, tin-copper mud water washing and filtration: Add about 100ml of water to the filtered tin-copper mud and wash and stir for about 15 minutes to dissolve the nitric acid, iron ions and other substances remaining in the tin-copper mud into the water and remove them from the solid; wash 3 times in sequence; after 3 water washing and filtration, about 160g of purified tin-copper mud is obtained.

[0041] S400, Copper-Tin Sludge Oxalate Separation: Copper-tin sludge obtained from water washing and filtration was mixed with 15% sodium hydroxide at a solid-liquid volume ratio of 1:5 and reacted. The mixture was heated to 75℃ and stirred for 80 minutes. Filtration yielded solid copper hydroxide (filter residue) and a tin-containing solution (filtrate). The filter residue was washed three times with 100 ml of water each time, then filtered. The wash water was added to the filtrate. The filter residue was found to contain 4.75 g of copper and 0.2 g of tin. The total tin-containing filtrate (including wash water) was approximately 1200 mL, with a tin content of approximately 82.1 g and a copper content of 0.15 g.

[0042] S500, Copper hydroxide conversion and electrolytic copper extraction: (a) After washing, copper hydroxide and 30% sulfuric acid were mixed at a mass ratio of 1:2 and reacted for 30 min under stirring to obtain 250 mL of copper sulfate solution with a copper content of about 18.5 g / L. (b) A copper sulfate solution was introduced into an electrolytic cell, and the current density was controlled at 2.2 A / dm², the cell voltage at 2.1 V, the electrolyte temperature at 40 °C, and the electrolysis time at 6.5 h. Metallic copper was deposited at the cathode. (c) The copper deposited at the cathode was collected, washed and dried to obtain approximately 4.7 g of metallic copper with a purity of 99.1%.

[0043] S600, tin-containing solution purification and electrolytic tin extraction: (a) Current density 1.5A / dm², cell voltage 3.0V, electrolyte temperature 38℃, electrolysis time 4.5h; (b) Approximately 81.4 g of metallic tin was obtained and melted at 400°C to obtain tin ingots with a purity of 99.4%.

[0044] S700, primary separation solution regeneration preparation: The primary separation solution is introduced into a mixing tank, and the nitric acid content is measured to be approximately 20.8%, with ferric ions at 15 g / L. 85 mL of 68% nitric acid and 15 g of ferric nitrate are added, along with 3 g of copper protectant (benzotriazole) and 1 g of citric acid. The mixture is stirred for 30 minutes to obtain 950 mL of regenerated tin stripping solution with a specific gravity of 1.25. The tin stripping test using the immersion method is successful.

[0045] In Example 2, the tin recovery rate was approximately 93%, and the copper recovery rate was approximately 80.3%.

[0046] The solution proposed in this application has the following advantages: (1) Simultaneous and efficient recovery of copper and tin: This invention is the first to use oxalic acid as a co-precipitant to precipitate tin and copper in tin stripping waste liquid into mixed oxalates in one step. Then, the significant difference in solubility between tin oxalate and copper oxalate in sodium hydroxide solution is used for selective separation, achieving efficient separation and separate recovery of tin and copper. The tin recovery rate can reach over 93%, and the copper recovery rate can reach over 80%. Both metals are recovered in high-purity elemental form, resulting in high economic value.

[0047] (2) Recycling of tin stripping solution: The primary separation liquid containing nitric acid and ferric nitrate after oxalic acid precipitation is directly returned to the tin stripping production line after component adjustment, realizing the recycling of tin stripping solution. The tin stripping performance can be restored to more than 95% of that of fresh tin stripping solution. This significantly reduces the procurement cost of tin stripping solution and the cost of hazardous waste disposal.

[0048] (3) Oxalic acid precipitation of tin and copper: Oxalic acid precipitation avoids the problem of generating a large amount of nitrate wastewater in the traditional neutralization precipitation method. Oxalic acid can be decomposed or recycled in subsequent processes.

[0049] (4) By precisely controlling the precipitation pH and temperature, the co-precipitation rate of tin oxalate and copper oxalate reaches more than 98%, and the precipitate particles are large and have good filtration performance.

[0050] (5) Innovations in copper and tin recycling: Through selective separation of copper and tin, and through dissolution to form copper salts and stannates, copper and tin are recycled in metallic form through electrolysis, which greatly improves economic and environmental benefits; The preferred embodiments of this aspect have been described in detail above. However, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to the invention. These equivalent forms also fall within the protection scope of the appended claims.

Claims

1. A method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin, characterized in that, Includes the following steps: S1, Oxalic acid precipitation of copper and tin: Oxalic acid is added to the nitric acid-type tin stripping waste liquid as a precipitant, so that tin and copper in the waste liquid are precipitated together in the form of oxalate precipitate, and copper-tin mixed oxalate precipitate and primary separation liquid are obtained. S2, after washing the copper-tin mixed oxalate precipitate obtained in S1 with water, it is mixed with sodium hydroxide solution, so that the tin oxalate selectively dissolves into the solution and the copper oxalate is converted into copper hydroxide precipitate. After solid-liquid separation, a tin-containing solution and copper hydroxide are obtained. S3, copper hydroxide solid is washed with water and converted into copper sulfate, which is then electrolytically deposited to recover metallic copper; The tin-containing solutions obtained from S4 and S2 are mixed with the water washing solution from S3 and electrolytically deposited to recover metallic tin. S5, add nitric acid, ferric nitrate, copper stripping agent and citric acid to the primary separation solution obtained in S1 to prepare a regenerated tin stripping solution.

2. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 1, characterized in that, The precipitation reaction temperature of S1 is room temperature, and the reaction time is 60-90 min.

3. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 2, characterized in that, S1 also contains a flocculant, which is a cationic polyacrylamide, added at a rate of 5-25 mg per liter of waste liquid.

4. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 1, characterized in that, The sodium hydroxide concentration in S2 is 15-30%, the solid-liquid volume ratio is 1:4-1:8, the reaction temperature is 60°C-80°C, and the reaction time is 60-120 min.

5. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 1, characterized in that, S3 includes: reacting copper hydroxide with dilute sulfuric acid, and then electrolyzing the resulting copper sulfate solution to recover metallic copper.

6. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 5, characterized in that, The mass ratio of copper hydroxide to dilute sulfuric acid is 1:1 to 1:

3. The conditions for electrolytic copper extraction are: current density 1.0 to 3.0 A / dm³. 2 The cell voltage is 1.5~2.5V, the electrolyte temperature is 40~60℃, and the electrolysis time is 2~8h.

7. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 6, characterized in that, The conditions for electrolytic tin extraction are as follows: the cathode material is stainless steel or titanium plate, the anode material is inert anode, the electrolyte temperature is 30–50℃, the cell voltage is 2.0–4.0V, and the current density is 0.5–2.5A / dm³. 2 The electrolysis time is 2 to 8 hours; sodium hydroxide solution needs to be added during the electrowinning process, and the concentration of sodium hydroxide should be controlled at 1 to 4%.

8. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 7, characterized in that, The concentration of nitric acid in the regenerated tin stripping solution in S5 is 4.0~6.5mol / L, and the concentration of iron ions is 15~25g / L; the tin stripping and copper protection agent is benzotriazole, and the addition amount is 2~6g per liter of separation solution.

9. The method for recycling and regenerating PCB desoldering waste liquid and recovering copper and tin according to claim 8, characterized in that, The purity of the recovered tin is not less than 99%, and the tin recovery rate is not less than 93%; the purity of the recovered copper is not less than 98%, and the copper recovery rate is not less than 80%.

Images