A method for removing lead and iron ions for electro-tinning electrolytic pickling

Abstract

The application discloses a method for removing lead and iron ions in electro-tinning electrolytic pickling, which comprises the following steps: determining the lead removal period t of the acid liquid in the current pickling tank; adding barium hydroxide to remove lead according to the lead ion concentration; settling and filtering after reaction; discharging the clear liquid into a membrane separation device to remove iron ions and lead ions in the acid liquid through the membrane separation device; calculating the required volume of sulfuric acid to be added; discharging the acid liquid after reaction into the pickling tank to adjust the temperature and pH of the plating solution in the pickling tank and detect the lead ion concentration in the pickling tank. The method removes most of the lead ions in the electrolytic pickling, avoids removing lead in the plating solution, and can avoid damaging the plating solution due to the simple composition of the pickling solution, and prevent the existence of impurity ions in the plating solution to cause problems in the surface quality of the tin-plated plate.

Description

Technical Field

[0001] This invention relates to the field of electrolytic pickling for tin plating, and particularly to a method for removing lead and iron ions by electrolytic pickling for tin plating. Background Technology

[0002] With the improvement of people's living standards, the demand for tinplate used in high-end packaging is also increasing. Globally, 13 million tons of tinplate are used annually in the food and beverage packaging industry. While the market generates a large demand for tinplate, it also places higher demands on its safety. To improve production efficiency and shorten pickling time, electrolytic pickling is generally used for rust removal and activation before tin plating. Currently, the electrodes used for electrolytic pickling of tinplate substrates in tin-plating production lines are all lead-tin alloys (Babbitt metal), which may cause lead residue on the substrate surface during the pickling process. This residual lead will be carried into the electroplating section, increasing the lead content of the tin-plated product. According to the EU standard BS EN10333:2005 "Packaging steel, flat steel products in contact with food, products and beverages for human and animal use, tin-plated sheets", the lead content in the tin plating layer of tinplate should not exceed 0.01%. The Chinese national standard GB / T2520 "Cold-rolled electroplated tin steel sheet and strip", which came into effect in 2017, also imposed strict restrictions on the content of harmful elements in the tin-plating substrate, tin-plating raw materials and tin-plating layer. The final regulation stipulates that the lead content in the tin-plating layer shall not exceed 0.01%, which is based on the mass fraction of the plating layer not exceeding 100 mg / kg.

[0003] Since lead and tin are elements in the same group, tin and lead co-plating naturally occurs during tin electroplating, resulting in excessive lead content in the plating layer. To produce low-lead-content tinplate, special purification processes are required, increasing the price of tin raw materials and significantly raising production costs. However, lead removal during the electroplating process can reduce the lead content in the plating layer and lower production costs. Barium hydroxide solution is used for lead removal. The principle of barium hydroxide in reducing lead is that barium hydroxide reacts with sulfuric acid in the plating solution to form barium sulfate, which then encapsulates lead ions in the plating solution, forming a co-precipitate.

[0004] In the prior art, patent document CN118164575A, "A Method for Enhancing the Adsorption of Lead Ions by Nano-Silica Gel Using Anionic Surfactants," provides a method for efficiently removing lead ions using nano-silica gel enhanced by anionic surfactants, suitable for neutral or weakly alkaline environments. However, this method is only applicable to lead removal in neutral and alkaline solutions. The patent "A Lead Removal Device for Electroplating Tin Solution" (Patent No.: CN202120238608.3) provides a novel lead removal device for electroplating tin solution. Patent document CN114277416A, "A Method and Equipment for Producing Low-Lead Content Tinplate with Methanesulfonic Acid Plating of Insoluble Anode," provides a method for producing low-lead content tinplate with methanesulfonic acid plating of insoluble anode. This method includes an alkaline washing process, comprising brushing and acid washing processes. After alkaline washing, the strip steel enters a chemical acid washing tank using a low-concentration sulfuric acid solution, which is sprayed onto the surface of the strip steel using a high-pressure jet device, and also includes a brushing process. In the electroplating process, low current density, high tin ion concentration, and high plating solution temperature are used to control the deposition of lead ions in the plating solution. Lead in the plating solution is removed through continuous external circulation. The lead content in the tin plating layer is controlled below 50 mg / kg, achieving stable production of low-lead content tinplate and meeting the safety requirements of food packaging materials. However, lead removal is costly and can damage the plating solution, affecting subsequent electroplating.

[0005] During electrolytic pickling, excessively high iron ion concentrations can lead to a series of problems. First, high iron ion concentrations accelerate the metal corrosion process because iron ions act as catalysts in electrochemical reactions, promoting redox reactions. This can cause surface damage, such as spots and pits, reducing the metal's corrosion resistance and mechanical strength. Second, high iron ion concentrations can also affect the properties of the electrolyte, such as reducing its conductivity. Excessive iron ions may form precipitates or scale in the electrolyte, clogging the electrode surfaces and slowing down the electrolytic reaction rate.

[0006] To reduce lead ions in the pickling solution and residual iron ions on the substrate surface after electrolytic pickling, a method for removing lead and iron ions from tin plating by electrolytic pickling is established. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is to provide a method for removing lead and iron ions by electrolytic pickling in tin plating, so as to reduce lead ions in the pickling solution and those remaining on the substrate surface, and to reduce iron ions in the pickling solution.

[0008] The technical solution of the present invention is a method for removing lead and iron ions during electrolytic pickling in tin plating, comprising the following steps:

[0009] A. Determine the current lead removal cycle t of the acid solution in the pickling tank;

[0010] B. Add barium hydroxide to remove lead based on the lead ion concentration:

[0011] After the electrolytic pickling process reaches its operating cycle t, the pickling solution is discharged into the reaction tank; based on the upper limit concentration of lead ions in the pickling solution... Add barium hydroxide, according to Ba 2+ With Pb 2+ Barium hydroxide is added at a molar ratio of N = 15-30; the formed barium sulfate precipitate adsorbs lead ions, thereby removing lead; the mass of sulfuric acid consumed is calculated, and the pH value after the reaction is detected;

[0012] C. After reaction, sedimentation and then filtration:

[0013] After the reaction, the acid solution flows into a settling tank, where the solids in the plating solution precipitate. The clear liquid after settling overflows into a membrane separation device, and the precipitates in the acid solution are pumped into a filter press by a sludge pump. The lead ion concentration in the clear liquid after reaction and precipitation is measured.

[0014] D. The clarified liquid is discharged into a membrane separation device to remove iron and lead ions from the acid solution; the membrane in the device is a corrosion-resistant reverse osmosis membrane; the operating pressure of the reverse osmosis membrane is 1-2 MPa.

[0015] E. Based on the mass of sulfuric acid consumed Density of sulfuric acid g / cm 3 Calculate the required volume V of sulfuric acid to be added. S L;

[0016] F. Drain the reacted acid solution into the pickling tank, adjust the temperature and pH of the plating solution in the pickling tank, and detect the lead ion concentration in the pickling tank; once all the circulating acid solution has been drained into the pickling tank, one round of lead removal and sulfuric acid replenishment is completed.

[0017] In step B, barium hydroxide reacts with sulfuric acid to form barium sulfate precipitate, and also reacts with ferric sulfate generated during electrolytic pickling to form barium sulfate precipitate and ferric hydroxide precipitate; the sulfuric acid here is from step A, and is the sulfuric acid in the pickling solution.

[0018] Adding too little barium hydroxide makes it difficult to remove large amounts of lead ions, while adding too much barium hydroxide results in poor water solubility, prolonged dissolution time, and high cost. Therefore, according to Ba... 2+ With Pb 2+ Barium ions are added at a molar ratio of N = (15-30).

[0019] In step C, the clarified liquid is sent to the membrane separation device via pressure filtration, while the sludge cake is discharged as solid waste. This step can remove large particulate matter sediment and suspended solids, preventing clogging of the membrane separation device.

[0020] In step D, because the ionic radii of iron and lead ions in the solution are small, a corrosion-resistant reverse osmosis membrane is selected for removal. The principle of reverse osmosis membranes is to force water molecules through under high pressure, while blocking metal ions outside the membrane. The operating pressure of the reverse osmosis membrane is selected to be 1-2 MPa based on the temperature and pH value of the acid solution. In step E, the volume of sulfuric acid is calculated and added in this step. In step F, sulfuric acid is added to adjust the pH value.

[0021] According to a method for removing lead and iron ions by electrolytic pickling in tin plating according to the present invention, preferably, in step A, the lead removal cycle t, in hours, is calculated using the following formula:

[0022]

[0023] In the formula, V is the volume of the pickling tank of the current pickling unit, in liters (L); S is the surface area of ​​the lead-tin alloy, in dm². 2 C pb D is the electrochemical equivalent of lead, in g / (A·h); D is the current density for acid washing, in A / dm³. 2 The upper limit of lead ion concentration in pickling solution is mg / L; η d For current efficiency; η c The electrodeposition efficiency is [value missing]; the highest electrolytic pickling temperature is 80℃, and the actual operating temperature is T1, ℃.

[0024] According to a method for removing lead and iron ions during electrolytic pickling of tin plating according to the present invention, preferably, in step B, barium hydroxide is added to a barium hydroxide adding device for dissolution. Ultrasonication, heating, or stirring can be used to accelerate the dissolution of barium hydroxide.

[0025] According to a method for removing lead and iron ions by electrolytic pickling in tin plating according to the present invention, preferably, in step B, the amount of barium hydroxide added is as follows:

[0026]

[0027] In the formula, M pb is the molar mass of lead, in g / mol; V represents the molar mass of barium hydroxide, in g / mol; V is the volume of the reaction vessel, in L.

[0028] According to a method for removing lead and iron ions by electrolytic pickling in tin plating according to the present invention, preferably, in step C, the sediment in the acid solution is periodically pumped into a filter press by a sludge pump.

[0029] According to a method for removing lead and iron ions during electrolytic pickling in tin plating according to the present invention, preferably, in step D, the reverse osmosis membrane is made of polyether nitrile (PES) material. This material is corrosion-resistant and not easily contaminated by Fe ions.

[0030] According to a method for removing lead and iron ions in electrolytic pickling for tin plating, as proposed by the present invention, in step D, the required effluent flow rate Q, L / h of the reverse osmosis membrane equipment is calculated based on the volume V, L of the pickling tank and the lead removal cycle t, h of the pickling solution.

[0031]

[0032] Based on the membrane flux J of the reverse osmosis membrane, L / (m 2 Given the solution's pH value (·h), solution temperature (T, °C), and the maximum allowable operating temperature for reverse osmosis (40 °C), calculate the required reverse osmosis membrane area (S). m m 2 :

[0033]

[0034] Calculate the required number of reverse osmosis membranes, n, based on the area of ​​a single reverse osmosis membrane. The value e above is a natural base, 2.71828.

[0035] According to a method for removing lead and iron ions in electrolytic pickling of tin plating according to the present invention, preferably, in step F, the concentration of lead ions in the pickling tank is detected, sulfuric acid is added to adjust the pH value according to the amount of barium hydroxide added, and then the lead ions are discharged into the pickling tank.

[0036] After pickling, the strip steel will enter the water rinsing tank 14, and the water pump 12 will pump the water in the water tank 13 into the water spray pipe 11. The water spray pipe will wash away the sulfuric acid on the surface of the strip steel through the water flow.

[0037] This invention first uses barium hydroxide to remove lead, and then uses a membrane separation device to remove the remaining lead. This method can essentially eliminate 99% of lead ions in the pickling solution, preventing excessive lead ion deposition on the tinplate surface during electrolytic pickling. It also removes iron ions from the acid solution, preventing excessive iron ion concentration from affecting the quality of the electrolytic pickling. Compared to other methods for reducing lead ions on the tinplate surface, this method removes most of the lead ions during electrolytic pickling, avoiding lead removal in the plating solution. Since the pickling solution has a simple composition, mainly sulfuric acid, only sulfuric acid needs to be added after lead removal, avoiding damage to the plating solution and preventing impurities in the solution from causing surface quality problems on the tinplate. Furthermore, the initial barium hydroxide lead removal process pre-treats the membrane separation device to remove iron ions and remaining lead ions, adjusting the pH value and removing precipitates and floating matter. Attached Figure Description

[0038] Figure 1 Schematic diagram of lead removal and sulfuric acid replenishment circulation in pickling solution.

[0039] Figure 2 Method flowchart.

[0040] In the diagram, 1. strip steel, 2. submerged roller, 3. pickling tank, 4. temperature control sensor, 5. pressure roller, 6. lead-tin alloy, 7. barium hydroxide addition device, 8. reaction tank, 9. settling tank, 10. filter press, 11. water spray pipe, 12. pump, 13. water tank, 14. water rinsing tank, 15. sulfuric acid replenishment tank, and 16. membrane separation equipment. Detailed Implementation

[0041] The application of the method for removing lead and iron ions by sulfuric acid electrolytic pickling of tin plating, as described in the present invention, will be further explained in detail below with reference to the accompanying drawings and embodiments.

[0042] Example 1:

[0043] A) The current pickling unit has a pickling tank volume V of 20000L and a lead-tin alloy surface area S of 3200dm². 2 Electrochemical equivalent C of lead pb The current density for pickling is 0.0376 g / (A·h); the current density D for pickling is 15 A / dm³. 2 The upper limit of lead ion concentration in pickling solution is The concentration is 1 mg / L; the current efficiency η is 0.8; the electrodeposition efficiency is 0.7; the actual operating temperature is 40℃; the lead removal cycle t of the pickling solution under the current pickling unit conditions is calculated to be 1.98 h.

[0044] B) Adding barium hydroxide forms barium sulfate precipitate, which adsorbs lead ions.

[0045] B1) After the current electrolytic pickling unit reaches its operating cycle of 1.98 hours, the pickling solution is discharged into the reaction tank to remove excess lead ions from the pickling solution. The upper limit of lead ion concentration in the pickling solution is... It is 1 mg / L, so according to Ba 2+ With Pb 2+ Barium ions are added at a molar ratio of N = 30. The molar mass of lead is M. pb It is 202.7 g / mol; the molar mass of barium hydroxide is The concentration is 171 g / mol; the volume V of the pickling tank is 20000 L. Calculate the amount of barium hydroxide that needs to be added. 495.17g. Barium hydroxide was added to a barium hydroxide addition device for dissolution, and after dissolution, it was transferred to a reaction tank for reaction.

[0046] B2) Based on the molar mass of sulfuric acid The molar mass of barium hydroxide is 98 g / mol. The concentration is 171 g / mol and the amount of barium hydroxide added. The amount is 495.17g. Calculate the mass of sulfuric acid consumed. The weight was 283.78g, and the pH value after the reaction was measured to be around 3.

[0047] C) The reacted acid solution flows into a settling tank, where solids in the plating solution precipitate. The clarified solution overflows into a membrane separation unit. The precipitates in the acid solution are periodically pumped into a filter press by a sludge pump. After filtration, the clarified solution goes to the membrane separation unit, and the sludge cake is discharged as solid waste. This step removes large particulate matter and suspended solids, preventing clogging of the membrane separation unit. The lead ion concentration in the clarified solution after reaction and precipitation is approximately 0.25 mg / L, indicating a lead removal rate of approximately 75% in this step.

[0048] D) Remove iron and lead ions from the acid solution using a membrane separation device. Based on the acid solution temperature of 40℃ and pH value of 3, the operating pressure of the reverse osmosis membrane is selected as 2MPa.

[0049] D1) Based on the pickling tank volume V being 20000L and the lead removal cycle t being 1.98h, the required water output Q for the reverse osmosis membrane equipment is calculated to be 10101.01L / h.

[0050] D2) Based on the reverse osmosis membrane flux J being 15 L / (m²), 2 Given a solution with a pH of 3 and a temperature T of 40℃, calculate the required reverse osmosis membrane area S. m It is 118.19m 2 .

[0051]

[0052] D3) Based on the area of ​​a single reverse osmosis membrane of 50m² 2 The required number of reverse osmosis membranes, n, is 3.

[0053] E) Based on the mass of sulfuric acid consumed 283.78g, sulfuric acid density 1.84g / cm³ 3 Calculate the required volume V of sulfuric acid to be added. S It is 0.154L.

[0054] F) The reacted acid solution is discharged into the pickling tank. The temperature and pH of the plating solution in the pickling tank are adjusted. The lead ion concentration in the pickling tank is measured to be 0.02 mg / L, and the lead removal rate reaches 98%. After all the circulating acid solution is discharged into the pickling tank, one round of lead removal and sulfuric acid replenishment is completed. The pickled strip steel will enter the water rinsing tank. The water pump will pump water from the water tank into the spray pipe, and the spray pipe will wash away the sulfuric acid on the surface of the strip steel through the water flow.

[0055] Example 2:

[0056] A) The current pickling unit has a pickling tank volume V of 25000L and a lead-tin alloy surface area S of 2800dm². 2 Electrochemical equivalent C of lead pb The current density for pickling is 0.0376 g / (A·h); the current density D for pickling is 20 A / dm³. 2 The upper limit of lead ion concentration in pickling solution is The concentration is 1 mg / L; the current efficiency η is 0.8; the electrodeposition efficiency is 0.7; the actual operating temperature is 40℃; the lead removal cycle t of the pickling solution under the current pickling unit conditions is calculated to be 2.12 h.

[0057] B) Adding barium hydroxide forms barium sulfate precipitate, which adsorbs lead ions.

[0058] B1) After the current electrolytic pickling unit reaches its operating cycle of 2.12 hours, the pickling solution is discharged into the reaction tank to remove excess lead ions from the pickling solution. The upper limit of lead ion concentration in the pickling solution is... It is 1 mg / L, so according to Ba 2+ With Pb 2+ Barium ions are added at a molar ratio of N = 25. The molar mass of lead is M. pb It is 202.7 g / mol; the molar mass of barium hydroxide is The concentration is 171 g / mol; the volume V of the pickling tank is 25000 L. Calculate the amount of barium hydroxide that needs to be added. 527.26g. Barium hydroxide was added to a barium hydroxide addition device for dissolution, and after dissolution, it was transferred to a reaction tank for reaction.

[0059] B2) Based on the molar mass of sulfuric acid The molar mass of barium hydroxide is 98 g / mol. The concentration is 171 g / mol and the amount of barium hydroxide added. The amount is 527.26g. Calculate the mass of sulfuric acid consumed. The amount was 302.17g, and the pH value after the reaction was measured to be around 3.2.

[0060] C) The reacted acid solution flows into a settling tank, where solids in the plating solution precipitate. The clarified solution overflows into a membrane separation unit. The precipitates in the acid solution are periodically pumped into a filter press by a sludge pump. After filtration, the clarified solution goes to the membrane separation unit, and the sludge cake is discharged as solid waste. This step removes large particulate matter and suspended solids, preventing clogging of the membrane separation unit. The lead ion concentration in the clarified solution after reaction and precipitation is approximately 0.18 mg / L, indicating a lead removal rate of approximately 82% in this step.

[0061] D) Remove iron and lead ions from the acid solution using a membrane separation device. Based on the acid solution temperature of 40℃ and pH value of 3.2, the operating pressure of the reverse osmosis membrane is selected as 2MPa.

[0062] D1) Based on the pickling tank volume V being 25000L and the lead removal cycle t being 2.12h, the required water output Q for the reverse osmosis membrane equipment is calculated to be 11792.45L / h.

[0063] D2) Based on the reverse osmosis membrane flux J being 12 L / (m²), 2 Given a solution with a pH of 3.2 and a temperature T of 40℃, calculate the required reverse osmosis membrane area S. m It is 219.14m 2 .

[0064] D3) Based on the area of ​​a single reverse osmosis membrane of 50m² 2 The required number of reverse osmosis membranes, n, is 5.

[0065] E) Based on the mass of sulfuric acid consumed 302.17g, sulfuric acid density 1.84g / cm³ 3 Calculate the required volume V of sulfuric acid to be added. S It is 0.164L.

[0066] F) The reacted acid solution is discharged into the pickling tank. The temperature and pH of the plating solution in the pickling tank are adjusted. The lead ion concentration in the pickling tank is measured to be 0.02 mg / L, and the lead removal rate reaches 98%. After all the circulating acid solution is discharged into the pickling tank, one round of lead removal and sulfuric acid replenishment is completed. The pickled strip steel will enter the water rinsing tank. The water pump will pump water from the water tank into the spray pipe, and the spray pipe will wash away the sulfuric acid on the surface of the strip steel through the water flow.

Claims

1. A method for removing lead and iron ions during electrolytic pickling in tin plating, characterized in that: Includes the following steps: A. Determine the current lead removal cycle t of the acid solution in the pickling tank; B. Add barium hydroxide to remove lead based on the lead ion concentration: After the electrolytic pickling process reaches its operating cycle t, the pickling solution is discharged into the reaction tank; based on the upper limit concentration of lead ions in the pickling solution... Add barium hydroxide, according to Ba 2+ With Pb 2+ Barium hydroxide is added at a molar ratio of N = 15-30; the formed barium sulfate precipitate adsorbs lead ions, thereby removing lead; the mass of sulfuric acid consumed is calculated, and the pH value after the reaction is detected; C. After reaction, sedimentation and then filtration: After the reaction, the acid solution flows into a settling tank, where the solids in the plating solution precipitate. The clear liquid after settling overflows into a membrane separation device, and the precipitates in the acid solution are pumped into a filter press by a sludge pump. The lead ion concentration in the clear liquid after reaction and precipitation is measured. D. The clarified liquid is discharged into a membrane separation device to remove iron and lead ions from the acid solution; the membrane in the device is a corrosion-resistant reverse osmosis membrane; the operating pressure of the reverse osmosis membrane is 1-2 MPa. E. Based on the mass of sulfuric acid consumed Density of sulfuric acid g / cm 3 Calculate the required volume V of sulfuric acid to be added. S L; F. Drain the reacted acid solution into the pickling tank, adjust the temperature and pH of the plating solution in the pickling tank, and detect the lead ion concentration in the pickling tank; Once all the circulating acid solution is discharged into the pickling tank, one round of lead removal and sulfuric acid replenishment is completed.

2. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step A, the lead removal period t, in hours, is calculated using the following formula: In the formula, V is the volume of the pickling tank of the current pickling unit, in liters (L); S is the surface area of ​​the lead-tin alloy, in dm². 2 C pb D is the electrochemical equivalent of lead, in g / (A·h); D is the current density for acid washing, in A / dm³. 2 The upper limit of lead ion concentration in pickling solution is mg / L; η d For current efficiency; η c The electrodeposition efficiency is [value missing]; the highest electrolytic pickling temperature is 80℃, and the actual operating temperature is T1, ℃.

3. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step B, barium hydroxide is added to the barium hydroxide adding device for dissolution.

4. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step B, the amount of barium hydroxide added is determined according to the following formula: In the formula, M pb is the molar mass of lead, in g / mol; V represents the molar mass of barium hydroxide, in g / mol; V is the volume of the reaction vessel, in L.

5. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step C, the sediment in the acid solution is periodically pumped into the filter press by a sludge pump.

6. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step D, the chemical material of the reverse osmosis membrane is polyether nitrile (PES).

7. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step D, based on the volume V, L of the pickling tank and the lead removal cycle t, h of the pickling solution, the required effluent flow rate Q, L / h for the reverse osmosis membrane equipment is calculated: Based on the membrane flux J of the reverse osmosis membrane, L / (m 2 Given the solution's pH value (·h), solution temperature (T, °C), and the maximum allowable operating temperature for reverse osmosis (40 °C), calculate the required reverse osmosis membrane area (S). m m 2 : Calculate the required number of reverse osmosis membranes, n, based on the area of ​​a single reverse osmosis membrane.

8. The method for removing lead and iron ions by electrolytic pickling in tin plating according to claim 1, characterized in that: In step F, the concentration of lead ions in the pickling tank is detected, and sulfuric acid is added to adjust the pH value according to the amount of barium hydroxide added before being discharged into the pickling tank.

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