Centralized recovery treatment process for nitric acid type system tin stripping liquid

Abstract

The invention discloses a nitric acid type system tin stripping liquid centralized recovery treatment process which comprises the following steps: firstly, adding a cationic coagulant into a nitric acid type tin stripping waste liquid, filtering through a 5-micron filter membrane, discharging into a reaction kettle, and adding a H2O2 solution with the concentration of 5-10%; the pH is adjusted to 2.0-2.5, and copper is removed under the condition of 40-50 DEG C; when the pH value is increased from 2.5 to 3.0-3.5, iron is removed; adjusting the pH value to 13.0-13.5, heating to remove aluminum, and separating to obtain a filtrate containing Na2SnO3; adjusting the pH value of the filtrate to 6.0-6.5, heating to 70-75 DEG C for reaction, and then carrying out gradient cooling to room temperature to generate Sn (OH) 4 precipitate; and centrifugally separating the mixed solution to obtain a tin-containing solid and a tin stripping regenerated solution, and firing the tin-containing solid to obtain a tin dioxide solid. Compared with a traditional process, copper is removed firstly, then iron is removed, aluminum is finally removed, and directional removal is achieved through the difference of precipitation conditions.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, and particularly relates to the treatment of tin stripping solution, specifically a centralized recycling and treatment process for tin stripping solution in a nitric acid-based system. Background Technology

[0002] In the production of printed circuit boards (PCBs), nitric acid-based tin-containing solutions are commonly used to remove the tin plating layer from the circuit boards. When the tin-containing solution's ability to erode tin decreases, it becomes tin stripping wastewater. Tin stripping wastewater is an acidic wastewater with a pH between 1 and 2. It contains 90-150 g / L of tin, 5-30 g / L of copper, 5-20 g / L of iron, 1-10 g / L of aluminum, 15-20% residual nitric acid, and some negatively charged colloidal particles, such as photoresist fragments.

[0003] Prior research, CN120138633A, discloses a method for tin extraction and regeneration from tin-removing waste liquid in a nitric acid-based system, such as... Figure 1 As shown, industrial nitric acid is added to the tin stripping waste liquid in the nitric acid-based system to increase H2O. + Concentration, filtration; heat the filtrate to 65-70℃ and react for 1-2 hours, filter to obtain tin mud and regenerated tin stripping solution, the regenerated tin stripping solution is returned to the production line for continued use; add alkaline solution to the tin mud until the pH is above 13, heat to completely dissolve it, introduce CO2 until pH < 9, filter to obtain sodium stannate solid, calcine the sodium stannate solid at 300-350℃ to obtain tin dioxide solid.

[0004] The actual tin recovery rate of the above process can reach over 90%, but the following problems have also been found in its application: (1) Oxidizing Sn by supplementing nitric acid 2+ It will generate NO2, which will exacerbate corrosion and toxicity, and directly supplementing with concentrated nitric acid will adjust the H2O. + The concentration may be excessive in some areas, leading to the decomposition of nitric acid, which reacts with reducing impurities in the waste liquid, increasing the difficulty of recovery.

[0005] (2) The process does not remove impurities such as copper, iron, aluminum, and polymers, and the process relies on the addition of industrial nitric acid to maintain the pH level. + Concentration leads to impurities in the waste liquid (such as matrix metal ions Cu) during the recycling process. 2+ Fe 2+ Fe 3+ Al 3+ As impurities accumulate, they not only affect the purity of the tin recovered from the tin stripping solution, but also hinder the recycling and reuse of the tin stripping solution.

[0006] (3) The tin loss rate of this process is relatively large, and the purity of tin dioxide is about 90%. 4+The hydrolysis reaction to produce Sn(OH)4 is reversible, and the H+ is maintained by supplementing with industrial nitric acid. + Hydrolysis was incomplete under acidic conditions after reaching a certain concentration, and some Sn was lost. 4+ It will remain in the tin stripping solution, causing tin loss; after Sn(OH)4 is generated, it dissolves and regenerates sodium stannate. After being dissolved by alkali, it is completely lost by insoluble impurities and adsorbed sodium stannate solution, further leading to tin loss.

[0007] (4) This process obtains carbon dioxide by burning sodium stannate solid, and sodium compounds will be generated regardless of whether it is in air or an inert gas atmosphere.

[0008] Currently, the process of recovering tin dioxide from tin stripping waste liquid is relatively mature. Some methods also use calcination with metastannic acid to obtain tin dioxide products. However, the calcination temperature of this method is relatively high, usually reaching 600-950℃. During the process of calcining from metastannic acid to tin dioxide, the residual impurities in the early stage will remain in the final product. Affected by the residual impurities, the purity of tin dioxide is usually between 90% and 95%. Summary of the Invention

[0009] The purpose of this invention is to provide a centralized recycling process for nitrate-based tin stripping solutions to solve the problems in the background art.

[0010] The present invention achieves the above objectives through the following technical solutions: This invention provides a centralized recycling process for tin stripping solution in a nitric acid-based system, comprising the following steps: (1) Add cationic coagulant to the nitric acid-type tin stripping waste liquid discharged from the production line, filter it through a 5μm filter membrane, discharge the filtrate into the reaction vessel, and add H2O2 solution with a concentration of 5%-10%; the main impurities in the tin stripping waste liquid are copper, iron and aluminum; (2) Add NaOH solution to adjust the pH of the filtrate to 2.0-2.5, add Na2S solution at 40-50℃, react to form a black precipitate, and filter to separate; (3) Continue to add NaOH solution to the filtrate to raise the pH from 2.5 to 3.0-3.5. The reaction at room temperature produces a reddish-brown precipitate, which is then separated by filtration. (4) Add NaOH solution to the filtrate to adjust the pH to 13.0-13.5. After reacting at 60-70℃, a white precipitate is generated. Filter while hot to separate the filtrate containing Na2SnO3. (5) Adjust the pH of the filtrate containing Na2SnO3 to 6.0-6.5, heat it to 70-75℃ for reaction, and then gradually cool it to room temperature to generate Sn(OH)4 precipitate; (6) Centrifuge the mixture obtained in step (5) to obtain tin-containing solid and tin stripping regeneration solution. The tin stripping regeneration solution is directly transported to the production line for reuse. The tin-containing solid is calcined to obtain tin dioxide solid.

[0011] As a further optimization of the above invention, in step (1), the cationic coagulant is polyaluminum chloride or cationic polyacrylamide, the addition amount is 0.5-1g / L, the stirring rate is 150-200rpm, and the reaction time is 10-20min.

[0012] As a further optimization of the above invention, in step (2), the pH is adjusted by using 1-5% NaOH, the amount of Na2S added is 6.8-40.6 g / L, the reaction time is 10-30 min, the filter is filtered by a 0.5 μm filter membrane, the filter residue is washed twice with dilute nitric acid at pH=2.0, and the washing liquid is returned to the reaction system.

[0013] As a further optimization of the above invention, in step (3), the pH is adjusted by using NaOH with a mass concentration of 1-5%, the reaction time is 10-20 min, and a 0.5 μm filter membrane is used.

[0014] As a further optimization of the above invention, in step (4), a NaOH solution with a mass concentration of 25-30% is used to adjust the pH, the reaction time is 10-20 min, and a 0.5 μm filter membrane is used for filtration.

[0015] As a further optimization of the above invention, in step (5), dilute nitric acid is used to adjust the pH, the reaction time is 30-60 min, and the gradient cooling rate is 2-5℃ / min.

[0016] As a further optimization of the above invention, in step (5), after the pH is adjusted to 6.0-6.5 and before the heating reaction begins, 0.05%-0.1% of nonionic polyacrylamide is added.

[0017] As a further optimization of the above invention, in step (6), the centrifugal separation speed is 4000-5000 rpm, the centrifugation time is 10-25 min, and the tin-containing solid is washed after centrifugation, and the washing liquid is returned to the heating vessel in step (5).

[0018] As a further optimization of the above invention, in step (6), the calcination temperature is 300-350℃ and the time is 1-2h.

[0019] The present invention also provides an application of the tin dioxide obtained by the above process in the preparation of tin dioxide-doped fluorine materials.

[0020] As a further optimization of the above invention, tin dioxide and tin fluoride are used as raw materials to obtain tin dioxide-doped fluorine materials by high-temperature sintering.

[0021] The beneficial effects of this invention are as follows: (1) The process of the present invention adopts the order of removing copper first, then iron, and finally aluminum. It utilizes the differences in precipitation conditions of each ion to achieve targeted removal. The impurity removal rate reaches more than 99%, which solves the problem of impurity accumulation affecting the performance of regenerated liquid in traditional processes.

[0022] (2) By optimizing the tin enrichment conditions, the total tin recovery rate can be increased to over 99%, and the purity of tin dioxide can also reach over 99.5%. The regenerated liquid after deep treatment has low impurity content and can be recycled multiple times, reducing the consumption of fresh tin stripping liquid.

[0023] (3) The steps are well-connected, the pH adjustment is consistent, and there is no need for frequent adjustments, which reduces reagent consumption and operational complexity, making it suitable for large-scale centralized processing. It realizes the resource utilization of tin stripping waste liquid, reduces pollutant emissions, and is in line with the development direction of green manufacturing. Attached Figure Description

[0024] Figure 1 This is a flow chart of the existing tin stripping solution process; Figure 2 This is a flow chart of the centralized recycling process for the nitric acid-based tin stripping solution in this invention. Detailed Implementation

[0025] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0026] At least one embodiment of the present invention discloses a centralized recycling process for tin stripping solution in a nitric acid-based system, comprising the following steps: (1) Add a cationic coagulant to the nitric acid-type tin stripping waste liquid discharged from the production line. The organic colloids (such as photoresist fragments and resin particles) in the tin stripping waste liquid are mostly negatively charged. The cationic coagulant neutralizes the charge, causing the colloidal particles to lose stability and aggregate into flocs. After filtration through a 5μm filter membrane, the filtrate is discharged into the reaction vessel, and a 5%-10% H2O2 solution is added. The oxidizing property of H2O2 under acidic conditions is used to help maintain the tin stripping ability (H2O2 + 2 ... + +2e - →2H2O), reducing nitric acid consumption, making the reaction milder, and also reducing the conversion of ferrous iron to ferric iron in molten tin; (2) Add NaOH solution to adjust the pH of the filtrate to 2.0-2.5, add Na2S solution at 40-50℃, react to form a black precipitate, and filter to separate; (3) Continue to add NaOH solution to the filtrate to raise the pH from 2.5 to 3.0-3.5. The reaction at room temperature produces a reddish-brown precipitate, which is then separated by filtration. (4) Add NaOH solution to the filtrate to adjust the pH to 13.0-13.5. After reacting at 60-70℃, a white precipitate is generated. Filter while hot to separate the filtrate containing Na2SnO3. (5) Adjust the pH of the filtrate containing Na2SnO3 to 6.0-6.5, heat it to 70-75℃ to react, and then gradually cool it to room temperature to generate Sn(OH)4 precipitate; (6) Centrifuge the mixture obtained in step (5) to obtain tin-containing solid and tin stripping regeneration solution. The tin stripping regeneration solution is directly transported to the production line for reuse. The tin-containing solid is calcined to obtain tin dioxide solid.

[0027] In step (1), the cationic coagulant is polyaluminum chloride or cationic polyacrylamide, the addition amount is 0.5-1g / L, the stirring rate is 150-200rpm, and the reaction time is 10-20min.

[0028] In step (2), the pH is adjusted by using 1-5% NaOH, the amount of Na2S added is 6.8-40.6 g / L, the reaction time is 10-30 min, the filter is filtered with a 0.5 μm filter membrane, the filter residue is washed twice with dilute nitric acid at pH=2.0, and the washing liquid is refluxed back into the reaction system.

[0029] In step (3), the pH is adjusted by using 1-5% NaOH, the reaction time is 10-20 min, and a 0.5 μm filter membrane is used.

[0030] In step (4), the pH is adjusted using a NaOH solution with a mass concentration of 25-30%, the reaction time is 10-20 min, and a 0.5 μm filter membrane is used for filtration.

[0031] In step (5), dilute nitric acid is used to adjust the pH, the reaction time is 30-60 min, and the gradient cooling rate is 2-5℃ / min.

[0032] In step (6), the centrifugation speed is 4000-5000 rpm and the centrifugation time is 10-25 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5).

[0033] In step (6), the calcination treatment temperature is 300-350℃ and the time is 1-2h.

[0034] At least one embodiment of the present invention discloses the application of tin dioxide obtained by the above process in the preparation of tin dioxide fluoride-doped materials, using tin dioxide and tin fluoride as raw materials, and obtaining tin dioxide fluoride-doped materials by high-temperature sintering.

[0035] 1. Explanation The composition of the tin stripping solution in this invention is shown in Table 1.

[0036] Table 1. Composition of the desoldering solution tin copper iron aluminum colloidal particles 90-150g / L 5-30g / L 5-20g / L 1-10g / L 0.1-1％ Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products, and all instruments used are conventional instruments known to those skilled in the art.

[0037] 2. Methods

[0038] Example 1 like Figure 2 As shown, the centralized recycling process for nitrate-based stripping solution in this embodiment includes the following steps: (1) Add cationic polyacrylamide to the nitric acid-type tin stripping waste liquid discharged from the production line. The addition amount is 0.5 g / L, the stirring rate is 200 rpm, and after 20 min, filter it through a 5 μm filter membrane and discharge the filtrate into the reaction vessel. Add a 5% H2O2 solution to the reaction vessel. (2) Add 1% NaOH solution to the reaction vessel at a rate of 1 mL / min, adjust the pH of the filtrate to 2.5, and add Na2S (10.2 g / L) at 45℃, first quickly and then slowly. The reaction time is 15 min. The reaction produces a black precipitate CuS. After it stops forming, filter it with a 0.5 μm filter membrane. Wash the filter residue twice with dilute nitric acid at pH=2.0, and reflux the washing liquid back into the reaction system. (3) Continue to add 1% NaOH solution to the filtrate at a rate of 1 mL / min to raise the pH from 2.5 to 3.0. The reaction produces a reddish-brown precipitate Fe(OH)3 at room temperature for 20 min. The filtrate is then filtered and separated using a 0.5 μm filter membrane. (4) Add 25% NaOH solution to the filtrate to adjust the pH to 13.0. After reacting at 70℃, a white precipitate NaAlO2·H2O is generated. The reaction time is 20 min. Filter the solution while it is hot using a 0.5 μm filter membrane to separate the filtrate containing Na2SnO3. (5) The pH of the filtrate containing Na2SnO3 was adjusted to 6.2 using 20% ​​dilute nitric acid, heated to 70°C for 60 min, and then gradually cooled to room temperature at a rate of 2°C / min to generate Sn(OH)4 precipitate. (6) The mixture obtained in step (5) is centrifuged at a speed of 4000 rpm for 15 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5). The tin-regenerated liquid obtained by centrifugation is directly transported to the production line for reuse. The tin-containing solid is calcined at 300℃ for 1.5 h (spread calcination, thickness < 1 cm) to obtain tin dioxide solid. After grinding, white tin dioxide powder is obtained.

[0039] Example 2 like Figure 2 As shown, the centralized recycling process for nitrate-based stripping solution in this embodiment includes the following steps: (1) Add cationic polyacrylamide to the nitric acid-type tin stripping waste liquid discharged from the production line. The addition amount is 0.5 g / L, the stirring rate is 200 rpm, and after 20 min, filter it through a 5 μm filter membrane and discharge the filtrate into the reaction vessel. Add a 5% H2O2 solution to the reaction vessel. (2) Add 1% NaOH solution to the reaction vessel at a rate of 1 mL / min, adjust the pH of the filtrate to 2.5, and add Na2S (11.5 g / L) at a rate of 100-200°C. The reaction time is 16 min. The reaction produces a black precipitate CuS. After the precipitate no longer forms, filter the filtrate with a 0.5 μm filter membrane. Wash the filter residue twice with dilute nitric acid at pH 2.0. Reflux the washing liquid back into the reaction system. (3) Continue to add 1% NaOH solution to the filtrate at a rate of 1 mL / min to raise the pH from 2.5 to 3.0. The reaction produces a reddish-brown precipitate Fe(OH)3 at room temperature for 20 min. The filtrate is then filtered and separated using a 0.5 μm filter membrane. (4) Add 25% NaOH solution to the filtrate to adjust the pH to 13.0. After reacting at 70℃, a white precipitate NaAlO2·H2O is generated. The reaction time is 20 min. Filter the solution while it is hot using a 0.5 μm filter membrane to separate the filtrate containing Na2SnO3. (5) The pH of the filtrate containing Na2SnO3 was adjusted to 6.5 using 20% ​​dilute nitric acid, and 0.08% (total system) of nonionic polyacrylamide was added. The mixture was heated to 70°C and reacted for 30 min. Then the mixture was gradually cooled to room temperature at a rate of 2°C / min to generate Sn(OH)4 precipitate. (6) The mixture obtained in step (5) is centrifuged at a speed of 4000 rpm for 15 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5). The tin-regenerated liquid obtained by centrifugation is directly transported to the production line for reuse. The tin-containing solid is calcined at 300℃ for 1.5 h (spread calcination, thickness of 2.5 cm) to obtain tin dioxide solid. After grinding, white tin dioxide powder is obtained.

[0040] Comparative Example 1 The centralized recycling process for the nitric acid-based tin stripping solution in this comparative example includes the following steps: (1) After filtering the nitric acid-type tin stripping waste liquid discharged into the production line through a 5μm filter membrane, the filtrate is discharged into the reaction vessel, and a 5% H2O2 solution is added to the reaction vessel; (2) Add 1% NaOH solution to the reaction vessel at a rate of 1 mL / min, adjust the pH of the filtrate to 2.5, and add Na2S (10.4 g / L) at a rate of 1 mL / min first and then slowly at 45 °C. The reaction time is 20 min. The reaction produces black precipitate CuS and some suspended black flocculent matter. Filter the mixture using a 0.45 μm filter membrane. Wash the filter residue twice with dilute nitric acid at pH 2.0. Reflux the washing liquid back into the reaction system. (3) Continue to add 1% NaOH solution to the filtrate at a rate of 1 mL / min to raise the pH from 2.5 to 3.0. At room temperature, a reddish-brown precipitate Fe(OH)3 is formed, but the color is uneven. The reaction time is 30 min. Filter and separate the filtrate using a 0.45 μm filter membrane. (4) Add 25% NaOH solution to the filtrate to adjust the pH to 13.0. After reacting at 70℃, a white precipitate NaAlO2·H2O is generated, mixed with black dots. The reaction time is 25 min. Filter the solution while hot using a 0.45 μm filter membrane to separate the filtrate containing Na2SnO3. (5) The pH of the filtrate containing Na2SnO3 was adjusted to 6.5 using 20% ​​dilute nitric acid, and 0.08% (total system) of nonionic polyacrylamide was added. The mixture was heated to 70°C and reacted for 50 min. Then the mixture was gradually cooled to room temperature at a rate of 2°C / min to generate Sn(OH)4 precipitate. (6) The mixture obtained in step (5) is centrifuged at a speed of 4000 rpm for 15 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5). The tin-regenerated liquid obtained by centrifugation is directly transported to the production line for reuse. The tin-containing solid is calcined at 300℃ for 1.5 h (spread calcination, thickness of 2.5 cm) to obtain tin dioxide solid. After grinding, gray-white tin dioxide powder is obtained.

[0041] Comparative Example 2 The centralized recycling process for the nitric acid-based tin stripping solution in this comparative example includes the following steps: (1) Add cationic polyacrylamide to the nitric acid-type tin stripping waste liquid discharged from the production line. The addition amount is 0.5 g / L, the stirring rate is 200 rpm, and after 20 min, filter it through a 5 μm filter membrane and discharge the filtrate into the reaction vessel. Add a 5% H2O2 solution to the reaction vessel. (2) Add 1% NaOH solution to the reaction vessel at a rate of 1 mL / min to raise the pH from 2 to 3.5. The reaction produces a reddish-brown precipitate Fe(OH)3 at room temperature for 20 min. The precipitate is separated by filtration using a 0.5 μm filter membrane. (3) Add a 5% dilute nitric acid solution to the reactor and adjust the pH of the filtrate to 2.5. Add Na2S (11.1 g / L) quickly and slowly at 45°C for 15 min. The reaction produces a black precipitate CuS. Filter the precipitate using a 0.5 μm filter membrane. Wash the filter residue twice with dilute nitric acid at pH 2.0 and return the washing liquid to the reaction system. (4) Add 25% NaOH solution to the filtrate to adjust the pH to 13.0. After reacting at 70℃, a white precipitate NaAlO2·H2O is generated. The reaction time is 20 min. Filter the solution while it is hot using a 0.5 μm filter membrane to separate the filtrate containing Na2SnO3. (5) The pH of the filtrate containing Na2SnO3 was adjusted to 6.5 using 20% ​​dilute nitric acid, and 0.08% (total system) of nonionic polyacrylamide was added. The mixture was heated to 70°C and reacted for 30 min. Then the mixture was gradually cooled to room temperature at a rate of 2°C / min to generate Sn(OH)4 precipitate. (6) The mixture obtained in step (5) is centrifuged at a speed of 4000 rpm for 15 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5). The tin-regenerated liquid obtained by centrifugation is directly transported to the production line for reuse. The tin-containing solid is calcined at 300℃ for 1.5 h (spread calcination, thickness of 2.5 cm) to obtain tin dioxide solid. After grinding, white tin dioxide powder is obtained.

[0042] Comparative Example 3 The centralized recycling process for the nitric acid-based tin stripping solution in this comparative example includes the following steps: (1) Add cationic polyacrylamide to the nitric acid-type tin stripping waste liquid discharged from the production line. The addition amount is 0.5 g / L, the stirring rate is 200 rpm, and after 20 min, filter it through a 5 μm filter membrane and discharge the filtrate into the reaction vessel. Add a 5% H2O2 solution to the reaction vessel. (2) Add 1% NaOH solution to the reaction vessel at a rate of 1 mL / min, adjust the pH of the filtrate to 2.5, and add Na2S (11.7 g / L) at 45℃ first quickly and then slowly. The reaction time is 17 min. The reaction produces a black precipitate CuS. After it stops forming, filter it with a 0.5 μm filter membrane. Wash the filter residue twice with dilute nitric acid at pH=2.0, and reflux the washing liquid back into the reaction system. (3) Continue to add 1% NaOH solution to the filtrate at a rate of 1 mL / min to raise the pH from 2.5 to 3.0. The reaction produces a reddish-brown precipitate Fe(OH)3 at room temperature for 20 min. The filtrate is then filtered and separated using a 0.5 μm filter membrane. (4) Add 25% NaOH solution to the filtrate to adjust the pH to 13.0. After reacting at 70℃, a white precipitate NaAlO2·H2O is generated. The reaction time is 20 min. Filter the solution while it is hot using a 0.5 μm filter membrane to separate the filtrate containing Na2SnO3. (5) The pH of the filtrate containing Na2SnO3 was adjusted to 6.5 using 20% ​​dilute nitric acid, and 0.08% (total system) of nonionic polyacrylamide was added. The mixture was heated to 70°C and reacted for 30 min. Then it was allowed to cool down naturally to generate Sn(OH)4 precipitate. (6) The mixture obtained in step (5) is centrifuged at a speed of 4000 rpm for 15 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5). The tin-regenerated liquid obtained by centrifugation is directly transported to the production line for reuse. The tin-containing solid is calcined at 300℃ for 1.5 h (spread calcination, thickness of 2.5 cm) to obtain tin dioxide solid. After grinding, white tin dioxide powder is obtained.

[0043] Comparative Example 4 like Figure 1 As shown, the treatment steps for the tin stripping waste liquid in the nitric acid type system in this comparative example are as follows: (1) Add 40% industrial nitric acid to the nitric acid-based tin stripping waste liquid discharged from the production line to make H + The concentration was 4.8 mol / L; after filtration. (2) The filtrate is heated to 70°C and reacted for 2 hours. After filtration, tin mud and regenerated tin stripping solution are obtained. (3) Add alkaline solution to tin mud until pH is 14, heat to dissolve completely, filter out the remaining insoluble matter, and then pass CO2 into the solution to make pH 8.5. Filter to obtain solid, and calcine the solid at 350℃ to obtain tin dioxide solid. After grinding, obtain white tin dioxide powder.

[0044] Comparative Example 5 The method for recovering tin dioxide using stripping solution in this comparative example includes the following steps: (1) The tin stripping waste liquid discharged from the production line is heated at a temperature of 70°C and a pressure of 10. 5 The mixture was subjected to vacuum distillation. Na2SO4 was added to the distillate at a dosage of 30 g / L. After sedimentation was complete, the mixture was filtered under pressure. The filter cake was washed and then pressed dry. (2) Neutralize the filtrate and washing liquid obtained in step (1) with alkali, control the pH value of the solution to 6, add sodium sulfide solution until no more precipitate is formed, filter, the filter cake is copper sulfide, and the filtrate is sent to the sewage treatment system. (3) The filter cake obtained in step (1) is sent into the reactor, and solid NaOH with a molar ratio of 1:2 to the filter cake is added. The temperature is raised to 90°C under stirring and kept at 2h to convert α-stannic acid and β-stannic acid into sodium stannate. Then water with a mass ratio of 1:3 to sodium stannate is added, stirred, and kept at 90°C for 4h. After filtration, the filter cake is sent to the iron recovery system. (4) Heat and concentrate the filtrate obtained in step (3) until crystals appear, then stop heating, allow it to cool naturally to crystallize, filter, and dry the filter cake to obtain sodium stannate; (5) Neutralize the mother liquor obtained after filtration in step (4) with acid, centrifuge, filter, and wash to obtain stannic acid, calcine the stannic acid at 600℃ to obtain tin dioxide, and grind it to obtain tin dioxide powder.

[0045] Comparative Example 6 The method for recovering tin dioxide from tin stripping waste liquid in this comparative example includes the following steps: (1) Neutralize the tin stripping waste liquid discharged from the production line to pH 6 with sodium carbonate solution, filter, add water and sodium hydroxide to the filter cake, the molar ratio of tin to sodium hydroxide is 1:7, the amount of water added is to make the weight ratio of water to dried filter cake 2-4, boil for 2 hours, continue to add water and stir for 30 minutes, and filter. (2) Pass carbon dioxide into the filtrate and stir until the tin is completely precipitated. Filter, wash, and dry the filter cake to obtain metastannic acid powder. (3) The stannic acid powder was calcined at 650°C for 3 hours to obtain white tin dioxide powder.

[0046] test ① The tin recovery rate and tin dioxide purity in Examples 1-2 and Comparative Examples 1-6 were determined, and the results are shown in Table 2: Table 2. Tin recovery rate and tin dioxide purity Group Tin recovery rate Tin dioxide purity Example 1 99.6% ≥99.5% Example 2 99.8% ≥99.5% Comparative Example 1 99.8% 98.7% Comparative Example 2 98.9% 99.5% Comparative Example 3 99.8% 99.0% Comparative Example 4 99.1% 93.2% Comparative Example 5 99.5% 90.4% Comparative Example 6 96.1% 85.8% The data above shows that existing tin stripping waste liquid processes can generally achieve a tin recovery rate of over 95%, but the purity of tin dioxide fluctuates significantly. Examples 1 and 2 achieve the optimal balance between high tin recovery rate (>99.5%) and high tin dioxide purity (≥99.5%), while the comparative examples show varying degrees of decrease in purity or recovery rate. Specifically: The purity of Comparative Example 1 decreased significantly to 98.7%, and subsequent steps revealed suspended black flocculent matter, uneven color (possibly due to complex formation), and black specks. This indicates that the initial flocculation and filtration step is crucial for removing colloidal and fine impurity particles (potentially carbon, organic matter, or other insoluble substances). Even with multiple membrane filtrations in subsequent processes, some nanoscale polymer impurities can still be incorporated into the tin dioxide product, leading to a decrease in tin dioxide purity and a grayish color.

[0047] Comparative Example 2, where the pH was first raised to 3.5 to remove iron, did not show a decrease in purity, indicating that the order of the reaction has little impact on the final purity, but it does affect the stability of the recovery rate. Furthermore, subsequently switching back to acidic conditions to remove copper results in a repetitive process and low efficiency.

[0048] The purity of Comparative Example 3 decreased to 99.0%, possibly because gradient cooling controls the generation and growth rate of Sn(OH)4 crystal nuclei, which helps to form a precipitate with uniform, dense particles that is easy to filter and wash. Rapid natural cooling results in fine, uneven precipitate particles, the formation of colloids, or the encapsulation of impurities, making them difficult to remove completely during subsequent washing, thus leading to a decrease in purity.

[0049] Comparative Example 4 is a prior research result. In step (3), it was originally thought that Fe 3+ Al 3+ It will be completely converted into sparingly soluble hydroxides (Fe(OH)3, Al(OH)3), Cu 2+ This will produce Cu(OH)₂ precipitate. However, in practice, stronger H₂O will... + Concentration affects metal impurities. Metal impurities (Cu, Fe, Al) may co-precipitate with tin, and the resulting tin sludge is a mixture of various metal hydroxides, which naturally reduces its purity.

[0050] The process of Comparative Example 5 is complex, involving high-temperature alkali melting, and in step (5), acid is added to the mother liquor for neutralization, which may cause impurities to co-precipitate again. Moreover, the lack of targeted removal of aluminum components may be one of the main reasons for the low purity.

[0051] In Comparative Example 6, the initial pH was 1-2, which was neutralized to pH 6. At this point, Fe 3+ Al 3+ Cu 2+ Both will form hydroxides and Sn(OH)4 to precipitate together, resulting in low purity of the final product. The failure to remove aluminum is also a reason for the low purity. Its recovery rate is the lowest, which may also be due to the loss caused by precipitation, encapsulation and adsorption.

[0052] ② The removal rates of copper, iron, and aluminum in Examples 1-2 and Comparative Examples 1-6 were measured, and the results are shown in Table 3: Table 3. Removal rates of copper, iron, and aluminum Group copper iron aluminum Example 1 ＞99.9% ＞99.9% ＞99.5% Example 2 ＞99.9% ＞99.9% ＞99.5% Comparative Example 1 99.5% 99.0% 97.5% Comparative Example 2 ＞99.9% ＞99.9% ＞99.5% Comparative Example 3 ＞99.9% ＞99.9% ＞99.5% Comparative Example 4 90.5% 90.5% 87.3% Comparative Example 5 99.2% 90.7% 76.2% Comparative Example 6 83.9% 85.4% 76.5% Examples 1 and 2 employed a progressive purification process: first, copper was removed (pH=2.5 to form CuS), then iron (pH=3.0 to form Fe(OH)3), and finally aluminum (pH=13.0 to form NaAlO2·H2O). This ensured that each metal ion precipitated under optimal pH conditions, avoiding mutual interference. Furthermore, cationic polyacrylamide was added in the early stages to remove suspended particles and colloidal substances through flocculation, improving filtration and providing a clean filtrate for the subsequent precipitation step. Comparative Example 1 lacked this step, resulting in ineffective removal of fine particles and colloidal substances from the waste liquid, affecting the subsequent precipitation reaction. Comparative Example 2 changed the order of copper and aluminum removal, but the data showed that the order of iron and copper removal did not affect the removal rates of copper and iron.

[0053] In Comparative Example 4, the process only involves adding nitric acid and heating, without specific precipitation steps for copper, iron, and aluminum. Impurity metals may be partially removed in the form of co-precipitation, but the efficiency is low. In step 3, CO2 is introduced to pH=8.5 to precipitate tin, but aluminum and iron may not be completely precipitated, resulting in a low removal rate.

[0054] In Comparative Example 5, the process only includes partial impurity removal. Step 2, with the addition of Na₂S, removes copper efficiently, but there are no dedicated steps for iron and aluminum removal. Step 3, the filter cake treatment, primarily targets tin recovery; iron may be partially removed as ferric hydroxide, but aluminum is not effectively treated. While processes involving distillation and the addition of Na₂SO₄ are involved, the lack of optimized conditions for iron and aluminum results in low removal rates, especially for aluminum.

[0055] In Comparative Example 6, there was no impurity removal step for copper, iron, and aluminum. Impurity metals may remain in the filtrate or co-precipitate, but the removal is incomplete.

[0056] ③ The tin dioxide powder and sintering aid (ZnO) obtained in Examples 1-2 and Comparative Examples 1-6 were pressed into tablets and sintered at high temperature (1250℃) into dense discs (1 cm thick). The conductivity was tested at room temperature using the four-probe method. The results are shown in Table 4.

[0057] Tin dioxide powder and tin fluoride (SnF2) obtained in Examples 1-2 and Comparative Examples 1-6 were mixed with a sintering aid (ZnO) at a doping concentration of 1%. Anhydrous ethanol was added as a medium, and the mixture was ball-milled for 6 hours. The resulting slurry was thoroughly dried in an oven at 80°C, sieved, granulated, and pressed into tablets (1 cm thick). The pressed wafers were placed in an alumina crucible and heated first at a low temperature (400°C) and then at a high temperature (1300°C) for 4 hours to obtain tin dioxide-doped fluorine material. The conductivity was tested at room temperature using the four-probe method. The results are shown in Table 4.

[0058] Table 4. Conductivity of pure tin dioxide and fluorine-doped tin dioxide (S / m) Group The conductivity of pure tin dioxide Tin dioxide doped with fluorine has high conductivity. Example 1 0.84 x 10 2 ]] 8.38 x 10 2 ]]> Example 2 0.85 x 10 2 ]]> 10.51 x 10 2 ]]> Comparative Example 1 0.79 x 10 2 ]]> 8.01 x 10 2 ]]> Comparative Example 2 0.84 x 10 2 ]] 10.26 x 10 2 ]]> Comparative Example 3 0.81 x 10 2 ]] 7.24 x 10 2 ]]> Comparative Example 4 0.71 x 10 2 ]] 6.37 x 10 2 ]] Comparative Example 5 0.70 x 10 2 ]] 6.13 x 10 2 ]] Comparative Example 6 0.65 x 10 2 ]] <![CDATA[5.62×10 2 ]]> The conductivity of tin dioxide obtained by processes in Examples 1 and 2 is not much different. The pure samples themselves have high purity, while Example 2 is superior. During preparation, nonionic polyacrylamide is added to optimize the precipitation effect. Moreover, during calcination, it turns into a gas to increase the porosity of the sintered block, resulting in more uniform sintering. After fluorine doping, the carrier transport is smoother.

[0059] Comparative Example 3 used natural cooling, resulting in a poor Sn(OH)4 precipitation structure and uneven grain size. A possible reason is that this poor microstructure was retained after sintering and severely affected the efficiency of subsequent fluorine doping, indicating that the physical structure of the precursor has a crucial impact on the final performance.

[0060] In Comparative Examples 4-6, the raw material purity was lowest due to the lack of an effective impurity removal step in the process itself. Even with fluorine doping, the large amount of residual acceptor impurities (Cu, Fe, Al) compensated for by the presence of fluorine. - The free electrons provided significantly reduce the doping effect, resulting in the lowest conductivity.

[0061] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A centralized recycling process for tin stripping solution in a nitric acid-based system, characterized in that, Includes the following steps: (1) Add cationic coagulant to the nitric acid-type tin stripping waste liquid discharged from the production line, filter it through a 5μm filter membrane, discharge the filtrate into the reaction vessel, and add H2O2 solution with a concentration of 5%-10%; (2) Add NaOH solution to adjust the pH of the filtrate to 2.0-2.5, add Na2S solution at 40-50℃, react to form a black precipitate, and filter to separate; (3) Continue to add NaOH solution to the filtrate to raise the pH from 2.5 to 3.0-3.

5. The reaction at room temperature produces a reddish-brown precipitate, which is then separated by filtration. (4) Add NaOH solution to the filtrate to adjust the pH to 13.0-13.

5. After reacting at 60-70℃, a white precipitate is generated. Filter while hot to separate the filtrate containing Na2SnO3. (5) Adjust the pH of the filtrate containing Na2SnO3 to 6.0-6.5, heat it to 70-75℃ for reaction, and then gradually cool it to room temperature to generate Sn(OH)4 precipitate; (6) Centrifuge the mixture obtained in step (5) to obtain tin-containing solid and tin stripping regeneration solution; the tin stripping regeneration solution is directly transported to the production line for reuse, and the tin-containing solid is calcined to obtain tin dioxide solid.

2. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (1), the cationic coagulant is polyaluminum chloride or cationic polyacrylamide, the addition amount is 0.5-1g / L, the stirring rate is 150-200rpm, and the reaction time is 10-20min.

3. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (1), the amount of H2O2 solution added is 2%-5% of the volume of waste liquid, and after addition, the reaction is carried out at 25-40℃ for 10-30 minutes.

4. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (2), the pH is adjusted by using 1-5% NaOH, the amount of Na2S added is 6.8-40.6 g / L, the reaction time is 10-30 min, the filter is filtered with a 0.5 μm filter membrane, the filter residue is washed twice with dilute nitric acid at pH=2.0, and the washing liquid is refluxed back into the reaction system.

5. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (3), the pH is adjusted by using 1-5% NaOH, the reaction time is 10-20 min, and a 0.5 μm filter membrane is used.

6. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (4), the pH is adjusted using a NaOH solution with a mass concentration of 25-30%, the reaction time is 10-20 min, and a 0.5 μm filter membrane is used for filtration.

7. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (5), dilute nitric acid is used to adjust the pH, the reaction time is 30-60 min, and the gradient cooling rate is 2-5℃ / min.

8. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 7, characterized in that, In step (5), after adjusting the pH to 6.0-6.5, before the heating reaction begins, add 0.05%-0.1% of nonionic polyacrylamide.

9. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (6), the centrifugation speed is 4000-5000 rpm and the centrifugation time is 10-25 min. After centrifugation, the tin-containing solid is washed and the washing liquid is returned to the heating vessel in step (5).

10. The centralized recycling process for tin stripping solution in a nitric acid-based system according to claim 1, characterized in that, In step (6), the calcination treatment temperature is 300-350℃ and the time is 1-2h.

11. The application of tin dioxide obtained by the centralized recycling process of tin stripping solution in a nitric acid-based system as described in any one of claims 1-10 in the preparation of tin dioxide-doped fluorine materials.

12. The application according to claim 11, characterized in that, Using the aforementioned tin dioxide and tin fluoride as raw materials, tin dioxide doped with fluorine is obtained by high-temperature sintering.

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