A method for preparing ultra-high purity lead by electrolysis

Abstract

This invention belongs to the field of wet electrolytic refining technology for recycled lead, and provides a method for electrolytically preparing ultra-high purity lead. It involves constructing a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed layer on the cathode plate surface, combined with a bypass impurity removal unit to continuously remove impurity ions from the electrolyte, and then using staged current density electrolysis to ensure uniform nucleation and stable deposition of lead on the cathode surface. The resulting cathode lead has a purity of not less than 99.996 wt%, and the deposited layer is dense, flat, and has a low risk of inclusions. This method solves the problems of difficulty in balancing high-throughput deposition and ultra-high purity, as well as the difficulty in synchronizing seed layer adhesion stability and pollution control in existing processes. It is suitable for the high-value preparation of recycled lead from waste lead-acid batteries.

Description

Technical Field

[0001] This invention relates to the field of wet electrolytic refining technology for recycled lead, and specifically to a method for electrolytically preparing ultra-high purity lead. Background Technology

[0002] In the process of preparing ultra-high purity lead from recycled crude lead through electrolysis, the cathode deposition behavior, solution impurity state, flow field conditions, and surface interface structure are coupled and directly determine whether the final product can simultaneously achieve high purity, dense and smooth deposition layer, and stable peeling properties. Especially when recycled crude lead from waste lead-acid batteries is used as the anode source, fluctuations in raw material composition and the amplification effect of electrolyte circulation exacerbate these contradictions: the cathode surface needs more controllable initial nucleation conditions to avoid localized rapid growth leading to coarsening and dendrite tendencies; simultaneously, the electrolyte must maintain a low level of impurity interference during continuous operation; and the seed layer must not become unstable or detach under fluid scouring, otherwise uneven deposition, inclusion introduction, and increased burden on subsequent washing and drying are likely. Therefore, how to match interface nucleation control, impurity bypass purification, and current regime to form an overall solution that balances deposition quality, process throughput, and continuous stability has become a key technical problem urgently needing to be solved in this field.

[0003] Currently, several improvement approaches exist for the electrolytic refining of crude lead. For example, Chinese patent CN102618883A discloses a method for direct electrolytic refining of crude lead, focusing on improving anodic dissolution and cathodic electrodeposition through perchloric acid-lead perchlorate electrolyte and various additives. Another example is Chinese patent CN108950600A, which discloses an electrolyte and electrolysis method for crude lead electrolytic refining, emphasizing the enhancement of the electrolysis process through a lead acetate-acetic acid system and pulsed current. However, these solutions primarily improve process control from the perspective of electrolyte system replacement or current regime optimization. For simultaneously addressing the controllability of initial cathode nucleation, the adhesion stability of the seed layer under flow field scouring, and the risk of inclusion contamination caused by the continuous accumulation of bismuth, copper, antimony, and iron in a lead hexafluorosilicate-free fluorosilicic acid system, a comprehensive solution that couples interface seeding construction with bypass impurity removal is still lacking. Therefore, under high-throughput deposition conditions, achieving both dense and smooth deposition layers with ultra-high purity remains a significant challenge. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing ultra-high purity lead by electrolysis, which solves the current problems of difficulty in achieving both high-throughput electrodeposition and dense, flat cathode deposits with ultra-high purity in the process of ultra-high purity lead electrolysis, as well as the difficulty in balancing high seed layer loading and high adhesion stability with avoiding contamination by external impurities.

[0005] This invention provides a uniform nucleation interface for lead ion reduction by pre-constructing a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed layer on the cathode plate surface. It also utilizes 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres to continuously purify bismuth, copper, antimony, and iron in the circulating electrolyte. Combined with staged current density control, it achieves a synergistic match between cathode deposition morphology, seed layer stability, and electrolyte cleanliness, thus balancing high-throughput deposition with the preparation of ultra-high purity lead.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing ultra-high purity lead by electrolysis includes the following steps: S1. The waste lead-acid battery is crushed and sorted to separate the lead-containing components, and the lead-containing components are melted and cast into recycled crude lead anode plates; S2. An aqueous suspension of 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate is coated onto the surface of a cathode plate and dried, such that the loading amount of 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate on the cathode plate surface is 0.20-2.00 g / m². 2 ; S3. The electrolyte is introduced into the electrolytic cell, using the regenerated crude lead anode plate obtained in step S1 as the anode and the cathode plate obtained in step S2 as the cathode. A bypass impurity catching unit is led out from the main circulation pipeline of the electrolyte. The flow rate of the electrolyte flowing through the bypass impurity catching unit is 2-10% of the total flow rate of the main circulation of the electrolyte. The bypass impurity catching unit is filled with 3-aminopropyltriethoxysilane modified silica impurity catching microspheres. The bypass impurity catching unit is put into operation before the start of electrolysis and runs continuously throughout the entire electrolysis process. S4. First use 50-100A / m 2 Electrolysis at an initial current density of 5-20 min, followed by 140-220 A / m 2 Electrolysis is performed at a working current density to cause lead to deposit on the surface of the cathode plate; S5. The precipitated lead is stripped off, washed, and dried to obtain ultra-high purity lead with a purity of not less than 99.996 wt%.

[0007] In this process, after the electrolyte is introduced into the electrolytic cell, it flows out from the cell outlet and returns to the cell inlet via the main circulation pump and main circulation pipeline. The main circulation pipeline connects the cell's outlet and inlet, forming the main circulation loop for the electrolyte. A bypass outlet is installed on the main circulation pipeline between the cell outlet and inlet. This bypass outlet is connected to the inlet of a bypass impurity removal unit via a bypass pipeline. The outlet of the bypass impurity removal unit is connected to the downstream main circulation pipeline or the front end of the cell inlet via a return pipeline, allowing the impurity-treated electrolyte to rejoin the main circulation. Flow meters are installed on both the main circulation pipeline and the bypass pipeline. A regulating valve is installed on the bypass pipeline to control the electrolyte flow through the bypass impurity removal unit to be 2-10% of the total main circulation flow rate.

[0008] Furthermore, in step S1, the lead content in the recycled crude lead anode plate is 96-99.5 wt%, the antimony content is 0.30-1.20 wt%, and the sum of the lead content and the antimony content is not greater than 100 wt%.

[0009] Furthermore, in step S2, the concentration of the aqueous suspension of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate is 1-10 g / L. The drying process is vacuum drying, with a drying temperature of 40-80℃ and a drying time of 0.5-2 hours.

[0010] Furthermore, in step S2, the cathode plate is a 304 stainless steel plate or a titanium plate, and the ratio of the effective area of ​​the recycled crude lead anode plate to the effective area of ​​the cathode plate is 1.0-1.5:1.

[0011] Furthermore, the preparation method of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate includes the following steps: A1. Disperse 100 parts by weight of lead carbonate in deionized water to form a lead carbonate dispersion, and add a modifying solution, wherein the total amount of deionized water used in the lead carbonate dispersion and the modifying solution is 300-800 parts by weight, and the modifying solution contains 0.20-2.00 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.05-0.50 parts by weight of sodium carbonate; A2. Stir at 25-50℃ for 0.5-2.0h, and adjust the pH of the reaction system to 6.5-8.5; A3. After filtration, wash with deionized water 2-4 times, and then dry at 60-90℃ for 4-12h to obtain 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate.

[0012] Further, in step A1, the modified solution is prepared by dissolving 0.20-2.00 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.05-0.50 parts by weight of sodium carbonate in 50-150 parts by weight of deionized water, and the lead carbonate dispersion is 100 parts by weight of lead carbonate dispersed in 250-650 parts by weight of deionized water; The initial average particle size D50 of the lead carbonate is 0.20-0.80 μm, or it is wet-milled before dispersion to an average particle size D50 of 0.20-0.80 μm.

[0013] Furthermore, in step A2, the reaction system is carried out under mechanical stirring at 200-500 rpm. The pH value of the reaction system is adjusted to 6.5-8.5 by adding 1.0 mol / L sodium hydroxide solution dropwise. If the pH exceeds 8.5, it is finely adjusted to 6.5-8.5 by adding 0.5 mol / L hydrochloric acid solution dropwise. The pH is monitored online by a pH meter with an accuracy of ±0.01.

[0014] Furthermore, in step S3, the electrolyte flowing through the bypass impurity trapping unit has an empty bed residence time of 5-30 minutes in the bypass impurity trapping unit to trap impurity ions in the electrolyte. The impurity ions include bismuth ions, copper ions, antimony ions, and iron ions. The total concentration of bismuth, copper, antimony, and iron in the electrolyte before entering the electrolytic cell is not greater than 50 mg / L.

[0015] Furthermore, the preparation method of the 3-aminopropyltriethoxysilane modified silica impurity-trapping microspheres includes the following steps: B1. Disperse 100 parts by weight of silica microspheres with an average particle size D50 of 20-150 μm in 300-1000 parts by weight of deionized water, and add 5-15 parts by weight of 3-aminopropyltriethoxysilane. B2. Under industrial nitrogen protection, react at 60-80℃ for 2-6 hours, and maintain the pH of the reaction system at 8.0-10.0; B3. After filtration, wash with deionized water 2-5 times, and then dry at 70-110℃ for 2-8 hours to obtain 3-aminopropyltriethoxysilane modified silica impurity-trapping microspheres.

[0016] Furthermore, in step S3, the electrolyte is a lead hexafluorosilicate-free fluorosilicic acid system, wherein the lead ion concentration in the electrolyte (Pb) is 80-130 g / L and the concentration of free fluorosilicic acid is 60-100 g / L.

[0017] Furthermore, in step S4, electrolysis is carried out under the conditions of a bath temperature of 28-38℃, an electrode spacing of 40-90mm, and an electrolyte linear velocity of 0.2-0.8m / s.

[0018] Further, in step A1, the lead carbonate dispersion is mechanically stirred at 200-500 rpm for 30 min, and the modified liquid is added to the lead carbonate dispersion at a rate not exceeding 5 mL / min.

[0019] Furthermore, the aqueous suspension of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate is ultrasonically dispersed at a frequency of 20 kHz using a probe-type ultrasonic device and prepared under conditions where the temperature is controlled in an ice bath not exceeding 30°C.

[0020] Furthermore, the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate is loaded onto the surface of the cathode plate by dip coating, spraying or brushing.

[0021] Furthermore, the bypass impurity removal unit determines the regeneration timing by detecting the total concentration of bismuth, copper, antimony and iron in the outlet liquid, and is regenerated by elution with hydrochloric acid and rinsing with deionized water before being put back into operation.

[0022] Further, in step B1, the silica microspheres are mechanically stirred and dispersed at 200-400 rpm for 30 min, and the 3-aminopropyltriethoxysilane is added dropwise to the silica microsphere dispersion at a rate not exceeding 1.0 mL / min, while keeping the system temperature not higher than 30°C.

[0023] Furthermore, in step B2, the purity of industrial nitrogen is not less than 99.5%, and the reaction system is reacted at 60-80℃ and 200-400rpm after being purged with industrial nitrogen. The pH value is adjusted and maintained at 8.0-10.0 by adding 1.0mol / L sodium hydroxide solution dropwise.

[0024] As a concept of this invention, the present invention employs a design that constructs a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal layer on the cathode plate surface and coordinates it with a bypass impurity trapping and purification system. This design primarily enhances the uniform nucleation capacity, the density and smoothness of the deposited layer, and the impurity repulsion capability during the ultra-high purity lead electrolytic deposition process. The modified lead carbonate seed crystal intermediate provides a nucleation interface compatible with lead deposition in the initial stage of cathode deposition, reducing dendrite growth and rough deposition tendencies caused by local nucleation imbalances. The bypass impurity trapping unit continuously weakens the accumulation and co-deposition risk of impurities such as bismuth, copper, antimony, and iron in the circulating electrolyte, mitigating inclusions and surface contamination. Combined with a phased switching from an initial low current density to the operating current density, nucleation, growth, and flow field stability can be matched, thereby achieving ultra-high purity, morphological controllability, and continuous process stability of the cathode lead without sacrificing flux.

[0025] The focus of 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediates is on regulating the microstructure of the cathode interface. Its phosphorus-modified surface layer improves particle dispersion and interfacial compatibility with the cathode substrate and lead ions, shifting initial lead deposition from random nucleation to more uniform directional nucleation, thereby enhancing the density and smoothness of the deposited layer. The focus of 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres is on regulating the solution environment. Their surface amino sites have adsorption and trapping capabilities for impurity ions such as bismuth, copper, antimony, and iron, reducing impurity enrichment and inclusion at the cathode interface. The former stabilizes the deposition starting point, while the latter purifies the deposition environment; their synergistic effect simultaneously inhibits rough growth, particle shedding, and impurity contamination, resulting in a simultaneous improvement in deposition quality and final purity at high current densities.

[0026] Beneficial technical effects 1. By pre-constructing a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal layer on the cathode plate surface, a more uniform nucleation interface can be provided for the initial reduction of lead ions, reducing the tendency of coarse grains and dendrites caused by local current concentration, and improving the compactness, smoothness and subsequent peeling stability of the cathode deposition layer from the interface level.

[0027] 2. By setting up a bypass impurity trapping unit filled with 3-aminopropyltriethoxysilane-modified silica impurity trapping microspheres, the accumulation of impurities such as bismuth, copper, antimony and iron in the circulating electrolyte can be continuously reduced without interrupting the main electrolysis process. This reduces the probability of impurity co-deposition and inclusion introduction, which is beneficial for the stable acquisition of high-purity cathode lead.

[0028] 3. By adopting a staged electrolysis method that switches from low initial current density to working current density, and by coordinating the control of electrode spacing and electrolyte linear velocity, the initial nucleation and subsequent crystal growth processes can be better matched, thereby increasing the throughput while reducing the risk of deposition layer instability, thus balancing electrolysis efficiency and deposition quality.

[0029] 4. By using lead-containing components from waste lead-acid batteries as the anode source and combining seed crystal layer construction, bypass impurity removal and purification, and electrolysis process control, this invention forms a complete process chain for the high-value utilization of recycled lead. It can balance product purity, operational continuity, and process feasibility in a resource recycling scenario, and has good prospects for industrial application. Attached Figure Description

[0030] Figure 1 High-resolution X-ray photoelectron spectra of the P 2p cathode seed layer in Examples 1, 1, and 2.

[0031] Figure 2 The high-resolution X-ray photoelectron spectra of the cathode seed layer O 1s in Examples 1, 1, and 2 are shown.

[0032] Figure 3 The graph shows the phosphorus content on the surface of the cathode seed layer in Example 1, Comparative Example 1, and Comparative Example 2.

[0033] Figure 4 The figures are current-time curves of the cathode plate constant potential timing for Example 1, Comparative Example 1, and Comparative Example 8.

[0034] Figure 5 The image shows the normalized nucleation fitting diagrams of the cathode plates in Example 1, Comparative Example 1, and Comparative Example 8.

[0035] Figure 6 This is a dynamic transmission diagram of bismuth ions, copper ions, antimony ions, and iron ions in the bypass trapping unit of Example 1.

[0036] Figure 7 The image shows the dynamic transmission diagrams of bismuth, copper, antimony, and iron ions in the bypass trapping unit of Comparative Example 4.

[0037] Figure 8 The image shows the dynamic transmission diagrams of bismuth, copper, antimony, and iron ions in the bypass trapping unit of Comparative Example 5.

[0038] Figure 9 This is a comparison chart of lead ion loss rates after bypass impurity collection in Example 1, Comparative Example 4, and Comparative Example 5.

[0039] Figure 10 The N 1s high-resolution X-ray photoelectron spectra of the impurity-trapping microspheres after adsorption in Example 1 and Comparative Example 4 are shown.

[0040] Figure 11 High-resolution X-ray photoelectron spectra of Bi 4f trapping microspheres after adsorption in Example 1 and Comparative Example 4.

[0041] Figure 12 High-resolution X-ray photoelectron spectra of Sb 3d3 / 2 trapping microspheres after adsorption in Example 1 and Comparative Example 4.

[0042] Figure 13 The graph shows the ratio of N to metal atoms in the impurity-trapping microspheres after adsorption in Examples 1 and 4.

[0043] Figure 14 The X-ray diffraction patterns of lead cathode deposits in Example 1, Comparative Example 6, and Comparative Example 8 are shown.

[0044] Figure 15 Scanning electron microscope image of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate prepared in Example 1.

[0045] Figure 16 Transmission electron microscopy (TEM) image of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate prepared in Example 1.

[0046] Figure 17 Macroscopic optical photograph of the ultra-high purity cathode lead product prepared in Example 1.

[0047] Figure 18 The image shown is a scanning electron microscope (SEM) image of the ultra-high purity cathode lead product prepared in Example 1.

[0048] Figure 19 Transmission electron microscope image of the ultra-high purity cathode lead product prepared in Example 1. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0050] Example 1

[0051] This embodiment provides a method for preparing ultra-high purity lead by electrolysis, including the following steps: S1. The waste lead-acid batteries are crushed and sorted to separate the lead-containing components, and the lead-containing components are melted and cast into recycled crude lead anode plates. In this embodiment, the recycled crude lead anode plate has a lead content of 97.5 wt% and an antimony content of 0.75 wt%, with the sum of the lead and antimony contents being 98.25 wt%.

[0052] S2. A cathode plate and a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate are provided. In this embodiment, the cathode plate is made of 304 stainless steel. An aqueous suspension of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate with a concentration of 5 g / L is prepared and sprayed onto the surface of the cathode plate. After spraying, it is vacuum dried at 60°C for 1.2 h. By repeating the spraying and drying operations and weighing with an accuracy of ±0.1 mg, the loading of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate on the cathode plate is controlled to be 1.00 g / m³. 2 A cathode seed layer was obtained. In this embodiment, the aqueous suspension was specifically prepared by ultrasonic dispersion at a frequency of 20 kHz using a probe-type ultrasonic device, and the temperature was controlled in an ice bath at a temperature not exceeding 30°C.

[0053] In this embodiment, the ratio of the effective area of ​​the recycled crude lead anode plate to the effective area of ​​the cathode plate is 1.25:1.

[0054] The 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate of this embodiment was prepared according to the following steps: A1. 100 parts by weight of lead carbonate with an initial average particle size D50 of 0.50 μm were dispersed in 450 parts by weight of deionized water to form a lead carbonate dispersion. The dispersion was mechanically stirred at 350 rpm for 30 min. The modified solution was then added to the lead carbonate dispersion at a rate of 2.5 mL / min. The modified solution was prepared by dissolving 1.10 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.28 parts by weight of sodium carbonate in 100 parts by weight of deionized water.

[0055] A2. The reaction was carried out at 37℃ with mechanical stirring at 350 rpm for 1.2 h. The pH of the reaction system was adjusted to 7.5 by adding 1.0 mol / L sodium hydroxide solution dropwise, and the pH of the reaction system was maintained at 7.5 by online monitoring with a pH meter with an accuracy of ±0.01.

[0056] A3. After filtration, wash three times with deionized water, using 400 parts by weight of deionized water each time. Then dry at 75°C for 8 hours to constant weight to obtain the intermediate.

[0057] The surface phosphorus content of the intermediate was determined by X-ray photoelectron spectroscopy, confirming successful modification, thus obtaining 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate.

[0058] S3. Preparation of lead hexafluorosilicate-free fluorosilicic acid electrolyte: Based on 1L of electrolyte, add lead hexafluorosilicate to about 600mL of deionized water and stir to dissolve. The amount of lead hexafluorosilicate is 177.1g based on anhydrous PbSiF6. When using hydrate or commercial solution, adjust according to the Pb content. Then slowly add fluorosilicic acid aqueous solution. The amount of fluorosilicic acid is 80.0g based on H2SiF6. When using 40wt% fluorosilicic acid aqueous solution, adjust to 200.0g. After cooling to room temperature, make up to 1L with deionized water so that the lead ion concentration in the electrolyte of this example is 105g / L based on Pb and the concentration of free fluorosilicic acid is 80g / L.

[0059] Electrolyte is introduced into the electrolytic cell, with the regenerated crude lead anode plate obtained in step S1 as the anode and the cathode plate obtained in step S2 as the cathode. Electrolyte flows out from the outlet of the electrolytic cell and returns to the inlet of the electrolytic cell via the main circulation pump and the main circulation pipeline. A bypass impurity removal unit is led out from the main circulation pipeline of the electrolyte. The bypass impurity trapping unit is filled with 3-aminopropyltriethoxysilane-modified silica impurity trapping microspheres for trapping bismuth, copper, antimony, and iron. The flow rate of the electrolyte flowing through the bypass impurity trapping unit is 6% of the total flow rate of the main electrolyte circulation, and the empty bed residence time is 17 min. In this embodiment, the bypass impurity trapping unit is put into operation before the start of electrolysis and operates continuously throughout the entire electrolysis process. The total amount of bismuth, copper, antimony, and iron in the electrolyte of this embodiment before entering the electrolytic cell is 25 mg / L.

[0060] The 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres of this embodiment were prepared according to the following steps: B1. 100 parts by weight of silica microspheres with an average particle size D50 of 85 μm were placed in 650 parts by weight of deionized water and dispersed by mechanical stirring at 300 rpm for 30 min. Then, 10 parts by weight of 3-aminopropyltriethoxysilane were added. 3-Aminopropyltriethoxysilane was added dropwise to the silica microsphere dispersion at a rate of 0.5 mL / min, while maintaining the system temperature not higher than 30 °C.

[0061] B2. The reaction was carried out under industrial nitrogen protection at 70°C and mechanical stirring at 300 rpm for 4 hours. The industrial nitrogen used in this example had a purity of 99.8%. The reaction system was purged with industrial nitrogen, and the pH was adjusted and maintained at 9.0 by adding 1.0 mol / L sodium hydroxide solution dropwise.

[0062] B3. After filtration, wash three times with deionized water, using 400 parts by weight of deionized water each time. Then dry at 90°C for 5 hours under vacuum at an absolute pressure of 2.5 kPa until constant weight is obtained, thus obtaining 3-aminopropyltriethoxysilane modified silica impurity-trapping microspheres.

[0063] S4. Electrolysis is carried out under the conditions of a bath temperature of 33℃, an electrode spacing of 65mm, and an electrolyte linear velocity of 0.5m / s, initially using 75A / m. 2 The initial current density was electrolyzed for 12 minutes, and then switched to 180 A / m. 2 Electrolysis is performed using the operating current density to deposit lead on the surface of the cathode plate in this embodiment.

[0064] S5. The precipitated lead is stripped, washed, and dried to obtain cathode lead (ultra-high purity lead) with a purity of 99.998 wt%, which is not less than 99.996 wt%, meeting the technical requirements for ultra-high purity lead.

[0065] Example 2

[0066] This embodiment provides a method for preparing ultra-high purity lead by electrolysis, including the following steps: S1. The waste lead-acid batteries are crushed and sorted to separate the lead-containing components, and the lead-containing components are melted and cast into recycled crude lead anode plates. In this embodiment, the recycled crude lead anode plate has a lead content of 98.5 wt% and an antimony content of 0.50 wt%, with the sum of the lead and antimony contents being 99.0 wt%.

[0067] S2. A cathode plate and a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate are provided. In this embodiment, a titanium plate is used as the cathode plate. An aqueous suspension of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate with a concentration of 7.5 g / L is prepared and dip-coated onto the surface of the cathode plate. After dip-coating, it is vacuum dried at 70°C for 1.5 h. By repeating the dip-coating and drying operations and weighing with an accuracy of ±0.1 mg, the loading of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate on the cathode plate is controlled to be 1.50 g / m³. 2 A cathode seed layer was obtained. In this embodiment, the aqueous suspension was ultrasonically dispersed at a frequency of 20 kHz using a probe-type ultrasonic device and prepared under conditions where the temperature was controlled in an ice bath not exceeding 30°C.

[0068] In this embodiment, the ratio of the effective area of ​​the recycled crude lead anode plate to the effective area of ​​the cathode plate is 1.35:1.

[0069] The 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate of this embodiment was prepared according to the following steps: A1. 100 parts by weight of lead carbonate with an initial average particle size D50 of 0.35 μm were dispersed in 530 parts by weight of deionized water to form a lead carbonate dispersion. The dispersion was mechanically stirred at 400 rpm for 30 min. The modified solution was then added to the lead carbonate dispersion at a rate of 3.5 mL / min. The modified solution was prepared by dissolving 1.50 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.35 parts by weight of sodium carbonate in 120 parts by weight of deionized water.

[0070] A2. The reaction was carried out at 42℃ with mechanical stirring at 400 rpm for 1.5 h. The pH of the reaction system was adjusted to 7.8 by adding 1.0 mol / L sodium hydroxide solution dropwise, and the pH of the reaction system was maintained at 7.8 by online monitoring with a pH meter with an accuracy of ±0.01.

[0071] A3. After filtration, wash four times with deionized water, using 450 parts by weight of deionized water each time. Then dry at 80°C for 9 hours to constant weight to obtain the intermediate.

[0072] The surface phosphorus content of the intermediate was determined by X-ray photoelectron spectroscopy, confirming successful modification, thus obtaining 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate.

[0073] S3. Preparation of lead hexafluorosilicate-free fluorosilicic acid electrolyte: Based on 1L of electrolyte, add lead hexafluorosilicate to about 600mL of deionized water and stir to dissolve. The amount of lead hexafluorosilicate is 202.3g based on anhydrous PbSiF6. When using hydrate or commercial solution, adjust according to the Pb content. Then slowly add fluorosilicic acid aqueous solution. The amount of fluorosilicic acid is 90.0g based on H2SiF6. When using 40wt% fluorosilicic acid aqueous solution, adjust to 225.0g. After cooling to room temperature, make up to 1L with deionized water so that the lead ion concentration in the electrolyte of this example is 120g / L based on Pb and the concentration of free fluorosilicic acid is 90g / L.

[0074] Electrolyte is introduced into the electrolytic cell, with the regenerated crude lead anode plate obtained in step S1 as the anode and the cathode plate obtained in step S2 as the cathode. Electrolyte flows out from the outlet of the electrolytic cell and returns to the inlet of the electrolytic cell through the main circulation pipeline. A bypass impurity removal unit is led out from the main circulation pipeline of the electrolyte. The bypass impurity trapping unit is filled with 3-aminopropyltriethoxysilane-modified silica impurity trapping microspheres for trapping bismuth, copper, antimony, and iron. The flow rate of the electrolyte flowing through the bypass impurity trapping unit is 8% of the total flow rate of the main electrolyte circulation, and the empty bed residence time is 22 min. In this embodiment, the bypass impurity trapping unit is put into operation before the start of electrolysis and runs continuously throughout the entire electrolysis process. The total amount of bismuth, copper, antimony, and iron in the electrolyte of this embodiment before entering the electrolytic cell is 35 mg / L.

[0075] The 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres of this embodiment were prepared according to the following steps: B1. Disperse 100 parts by weight of silica microspheres with an average particle size D50 of 110 μm in 800 parts by weight of deionized water. After mechanically stirring at 350 rpm for 30 min, add 12 parts by weight of 3-aminopropyltriethoxysilane. Add 3-aminopropyltriethoxysilane dropwise to the silica microsphere dispersion at a rate of 0.7 mL / min, while maintaining the system temperature not exceeding 30 °C.

[0076] B2. The reaction was carried out under industrial nitrogen protection at 75°C and mechanical stirring at 350 rpm for 5 hours. The industrial nitrogen used in this example had a purity of 99.8%. The reaction system was purged with industrial nitrogen, and the pH was adjusted and maintained at 9.5 by adding 1.0 mol / L sodium hydroxide solution dropwise.

[0077] B3. After filtration, wash four times with deionized water, using 450 parts by mass of deionized water each time. Then dry at 100℃ for 6 hours under vacuum drying conditions of 2.0 kPa absolute pressure until constant weight is obtained, thus obtaining 3-aminopropyltriethoxysilane modified silica impurity-trapping microspheres.

[0078] In this embodiment, the bypass impurity removal unit determines the regeneration timing by detecting the total concentration of bismuth, copper, antimony, and iron in the outlet liquid, and then regenerates and puts it back into operation by elution with hydrochloric acid and rinsing with deionized water.

[0079] S4. Electrolysis is carried out under the conditions of a bath temperature of 30℃, an electrode spacing of 55mm, and an electrolyte linear velocity of 0.65m / s, initially using 85A / m. 2 Electrolysis was performed at an initial current density of 15 min, and then switched to 200 A / m. 2 Electrolysis is performed using the operating current density to deposit lead on the surface of the cathode plate in this embodiment.

[0080] S5. The precipitated lead is stripped, washed, and dried to obtain cathode lead with a purity of 99.997 wt%, which is not less than 99.996 wt%, meeting the technical requirements for ultra-high purity lead.

[0081] Example 3

[0082] This embodiment provides a method for preparing ultra-high purity lead by electrolysis, including the following steps: S1. The waste lead-acid batteries are crushed and sorted to separate the lead-containing components, and the lead-containing components are melted and cast into recycled crude lead anode plates. In this embodiment, the recycled crude lead anode plate has a lead content of 96.8 wt% and an antimony content of 1.00 wt%, with the sum of the lead and antimony contents being 97.8 wt%.

[0083] S2. A cathode plate and a 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate are provided. In this embodiment, the cathode plate is made of 304 stainless steel. An aqueous suspension of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate with a concentration of 2.5 g / L is prepared and brushed onto the surface of the cathode plate. After brushing, it is vacuum dried at 50°C for 0.8 h. By repeating the brushing and drying operations and weighing with an accuracy of ±0.1 mg, the loading of the 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate on the cathode plate is controlled to be 0.50 g / m³. 2 A cathode seed layer was obtained. In this embodiment, the aqueous suspension was ultrasonically dispersed at a frequency of 20 kHz using a probe-type ultrasonic device and prepared under conditions where the temperature was controlled in an ice bath not exceeding 30°C.

[0084] In this embodiment, the ratio of the effective area of ​​the recycled crude lead anode plate to the effective area of ​​the cathode plate is 1.10:1.

[0085] The 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate of this embodiment was prepared according to the following steps: A1. 100 parts by weight of lead carbonate with an average particle size D50 of 0.65 μm were dispersed in 330 parts by weight of deionized water to form a lead carbonate dispersion. The dispersion was mechanically stirred at 250 rpm for 30 min. The modified solution was then added to the lead carbonate dispersion at a rate of 1.5 mL / min. The modified solution was prepared by dissolving 0.50 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.15 parts by weight of sodium carbonate in 70 parts by weight of deionized water.

[0086] A2. The reaction was carried out at 45℃ with mechanical stirring at 250 rpm for 1.6 h. The pH of the reaction system was adjusted to 7.2 by adding 1.0 mol / L sodium hydroxide solution dropwise, and the pH of the reaction system was maintained at 7.2 by online monitoring with a pH meter with an accuracy of ±0.01.

[0087] A3. After filtration, wash three times with deionized water, using 350 parts by weight of deionized water each time. Then dry at 85°C for 10 hours to constant weight to obtain the intermediate.

[0088] The surface phosphorus content of the intermediate was determined by X-ray photoelectron spectroscopy, confirming successful modification, thus obtaining 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate.

[0089] S3. Preparation of lead hexafluorosilicate-free fluorosilicic acid electrolyte: Based on 1L of electrolyte, add lead hexafluorosilicate to about 600mL of deionized water and stir to dissolve. The amount of lead hexafluorosilicate is 151.7g based on anhydrous PbSiF6. When using hydrate or commercial solution, adjust according to the Pb content. Then slowly add fluorosilicic acid aqueous solution. The amount of fluorosilicic acid is 70.0g based on H2SiF6. When using 40wt% fluorosilicic acid aqueous solution, adjust to 175.0g. After cooling to room temperature, make up to 1L with deionized water so that the lead ion concentration in the electrolyte of this example is 90g / L based on Pb and the concentration of free fluorosilicic acid is 70g / L.

[0090] Electrolyte is introduced into the electrolytic cell, with the regenerated crude lead anode plate obtained in step S1 as the anode and the cathode plate obtained in step S2 as the cathode. Electrolyte flows out from the outlet of the electrolytic cell and returns to the inlet of the electrolytic cell through the main circulation pipeline. A bypass impurity removal unit is led out from the main circulation pipeline of the electrolyte. The bypass impurity trapping unit is filled with 3-aminopropyltriethoxysilane-modified silica impurity trapping microspheres for trapping bismuth, copper, antimony, and iron. The flow rate of the electrolyte flowing through the bypass impurity trapping unit is 4% of the total flow rate of the main electrolyte circulation, and the empty bed residence time is 10 min. In this embodiment, the bypass impurity trapping unit is put into operation before the start of electrolysis and operates continuously throughout the entire electrolysis process. The total amount of bismuth, copper, antimony, and iron in the electrolyte of this embodiment before entering the electrolytic cell is 15 mg / L.

[0091] The 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres of this embodiment were prepared according to the following steps: B1. 100 parts by weight of silica microspheres with an average particle size D50 of 50 μm were dispersed in 450 parts by weight of deionized water. After mechanically stirring at 250 rpm for 30 min, 7 parts by weight of 3-aminopropyltriethoxysilane were added. 3-Aminopropyltriethoxysilane was added dropwise to the silica microsphere dispersion at a rate of 0.3 mL / min, while maintaining the system temperature not exceeding 30 °C.

[0092] B2. The reaction was carried out under industrial nitrogen protection at 65°C and mechanical stirring at 250 rpm for 3 hours. The industrial nitrogen used in this example had a purity of 99.6%, not lower than 99.5%. The reaction system was purged with industrial nitrogen, and the pH was adjusted and maintained at 8.5 by adding 1.0 mol / L sodium hydroxide solution dropwise.

[0093] B3. After filtration, wash three times with deionized water, using 350 parts by mass of deionized water each time. Then dry at 80°C for 4 hours under vacuum at an absolute pressure of 3.5 kPa until constant weight is obtained, thus obtaining 3-aminopropyltriethoxysilane modified silica impurity-trapping microspheres.

[0094] S4. Electrolysis is carried out under the conditions of a bath temperature of 36℃, an electrode spacing of 75mm, and an electrolyte linear velocity of 0.3m / s, initially using 60A / m 2 The initial current density was electrolyzed for 8 minutes, and then switched to 155 A / m. 2 Electrolysis is performed using the operating current density to deposit lead on the surface of the cathode plate in this embodiment.

[0095] S5. The precipitated lead is stripped, washed, and dried to obtain cathode lead with a purity of 99.997 wt%, which is not less than 99.996 wt%, meeting the technical requirements for ultra-high purity lead.

[0096] Comparative Example 1: The experiment was basically the same as in Example 1, except that the seed crystal material loaded on the surface of the cathode plate was replaced with lead carbonate that was not modified with 1-hydroxyethylidene-1,1-diphosphonic acid, while other conditions remained unchanged.

[0097] Comparative Example 2: The method is essentially the same as in Example 1, except that the loading of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate on the cathode plate surface is 0.10 g / m². 2 All other conditions remain unchanged.

[0098] Comparative Example 3: The method is basically the same as in Example 1, except that the loading of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate on the cathode plate surface is 2.50 g / m². 2 All other conditions remain unchanged.

[0099] Comparative Example 4: The process is basically the same as in Example 1, except that the material packed in the bypass impurity trapping unit is changed to silica microspheres that are not modified with 3-aminopropyltriethoxysilane, while other conditions remain unchanged.

[0100] Comparative Example 5: The process is basically the same as in Example 1, except that the electrolyte flow rate through the bypass impurity trapping unit is 1% of the total electrolyte main circulation flow rate, and the empty bed residence time is still controlled at 17 minutes. Except for adjusting the loading volume of the bypass impurity trapping unit to maintain this empty bed residence time, other electrolysis conditions remain unchanged.

[0101] Comparative Example 6: The process is basically the same as in Example 1, except that the operating current density in step S4 is 240 A / m. 2 All other conditions remain unchanged.

[0102] Comparative Example 7: It is basically the same as Example 1, except that the electrolyte linear velocity in step S4 is 0.10 m / s, while other conditions remain unchanged.

[0103] Comparative Example 8: The method is basically the same as in Example 1, except that 75A / m is not set after step S4 begins. 2 In the initial current density stage, it directly reaches 180 A / m 2 Electrolysis is carried out, with other conditions remaining unchanged.

[0104] Performance testing: (1) Cathode lead purity and impurity content test. The obtained cathode lead was digested by microwave in an ultrapure nitric acid system, and trace element analysis was performed by inductively coupled plasma mass spectrometry to determine the contents of bismuth, copper, antimony, iron, and common impurity elements such as silver, arsenic, tin, nickel, zinc, and cadmium. Three batches of samples were selected for each experiment, and three parallel samples were taken from each batch. After digestion, volume adjustment, and matrix matching dilution, the internal standard method was used for determination. The purity of cathode lead was calculated by subtracting the difference in the total mass fraction of the measured impurity elements, that is, the purity of cathode lead is 100% - Σwi, where Σwi is the sum of the mass fractions of the measured impurity elements. In Table 1, "total bismuth + copper + antimony + iron in cathode lead" is the sum of the mass concentrations of the four target impurity elements.

[0105] (2) Current efficiency test. The mass of lead deposited at the cathode was weighed before and after electrolysis, and the theoretical mass of deposited lead was calculated based on the electrolysis current and electrolysis time. The current efficiency was calculated as η = m_actual / m_theoretical × 100%, where the lead deposition reaction was based on Pb. 2+ The calculation involves gaining two electrons and reducing the metal to lead.

[0106] (3) Characterization of surface modification of seed crystal intermediates. X-ray photoelectron spectroscopy was used to perform full-spectrum scanning and P 2p narrow-region high-resolution scanning on the dry powder samples to characterize the phosphorus-containing modification features on their surfaces.

[0107] (4) Initial nucleation behavior test. The cathode plate with the seed layer loaded was subjected to a potentiostatic chronoamperometry test under the same free fluorosilicic acid concentration and temperature conditions as in the example. A three-electrode system was used for the test, with the cathode plate loaded with the seed layer as the working electrode, the lead plate as the counter electrode, and the Ag / AgCl electrode or equivalent reference electrode as the reference electrode. The peak current, peak time, and normalized nucleation curve were obtained from the chronoamperometry curve to compare the initial nucleation behavior of different cathode interfaces.

[0108] (5) Bypass impurity removal performance and lead ion loss rate test. The bypass impurity removal unit was evaluated using a fixed-bed dynamic adsorption method. The influent composition was consistent with the electrolyte in the corresponding embodiment. The unit was operated according to the set bypass flow rate and empty bed residence time. Inlet and outlet liquid samples were collected periodically, and the concentrations of bismuth, copper, antimony, iron, and lead were determined by inductively coupled plasma mass spectrometry. The target impurity removal rate was calculated by subtracting the total concentrations of bismuth, copper, antimony, and iron in the inlet and outlet liquids. The lead ion loss rate was calculated by L... Pb =(C Pb,in- C Pb,out ) / C Pb,in Calculated by multiplying by 100%.

[0109] (6) Seed layer adhesion retention rate test. The cathode plate loaded with seed crystal layer was placed in a simulated electrolyte with the same free fluorosilicic acid concentration, temperature and linear velocity as in the example for rinsing treatment. After rinsing, it was washed, dried and weighed respectively. The seed layer adhesion retention rate was calculated according to the ratio of the remaining mass of the seed crystal layer to the mass of the seed crystal layer before rinsing.

[0110] (7) Test of cathodic deposited lead phase and surface morphology. After stripping, washing and drying, the cathodic deposited lead was analyzed by X-ray diffraction with a scanning range of 10°-90°; the surface morphology of the deposited layer was observed by scanning electron microscopy; the surface roughness Ra was measured by stylus profilometer, with no less than 5 profilometer lines measured for each sample, covering the central and edge areas, and the average value and standard deviation were calculated.

[0111] To verify the interface construction effect of the modified seed crystal layer in this embodiment, the elemental composition and chemical state of the cathode seed crystal layer surface were first analyzed. Figure 1High-resolution X-ray photoelectron spectra of the P 2p cathode seed layers in Examples 1, 1, and 2. Figure 1 It is evident that the P 2p characteristic signal is more pronounced in Example 1, indicating that the 1-hydroxyethylidene-1,1-diphosphonic acid modified component can be stably introduced into the surface of the lead carbonate seed crystal intermediate and form a recognizable phosphorus-containing interface structure in the cathode seed crystal layer. Compared with the comparative example that has not undergone effective phosphonic acid modification or has insufficient modification, the enhanced phosphorus signal in Example 1 indicates that the phosphonic acid groups are not merely present in a physical mixture form, but are more stably distributed on the surface of the seed crystal layer, thereby improving the interfacial compatibility between the seed crystal layer and the cathode substrate, electrolyte, and subsequent lead deposition.

[0112] Based on the confirmation of the chemical state of phosphorus, the chemical environment of oxygen on the surface of the seed crystal layer was further characterized. Figure 2 The images show the O 1s high-resolution X-ray photoelectron spectra of the cathode seed layers in Examples 1, 1, and 2. Figure 2 It can be seen that Example 1 exhibits a more reasonable distribution of oxidative states, indicating that carbonate, hydroxyl, and phosphonic acid-related oxygen-containing functional groups form a more harmonious interfacial chemical environment on the seed crystal layer surface. This result shows that the introduction of 1-hydroxyethylidene-1,1-diphosphonic acid not only increases the number of phosphorus-containing functional groups on the surface but also regulates the distribution of oxygen-containing groups on the seed crystal layer surface, making the seed crystal layer interface more favorable for the adsorption, migration, and nucleation of lead ions in the initial stage of electrolysis.

[0113] Figure 3 This is a statistical chart showing the phosphorus content on the surface of the cathode seed layer in Example 1, Comparative Example 1, and Comparative Example 2. Figure 3 It can be seen that the phosphorus content on the surface of the crystal layer in Example 1 is significantly higher than that in the comparative examples, further proving that under the modification conditions used in Example 1, the phosphonic acid modified component can be effectively loaded onto the surface of the lead carbonate seed crystal intermediate. Combined with... Figure 1 and Figure 2 It can be seen that Example 1 not only has a more distinct P 2p characteristic signal, but also a more suitable surface oxidation state, indicating that its surface modification degree is within an optimal range. This type of crystal layer can provide a sufficient number and uniformly distributed nucleation induction sites for the cathode surface, thereby laying the foundation for the subsequent formation of uniform lead deposition and dense deposition layers.

[0114] To further verify the influence of the modified seed layer on the initial electrodeposition behavior, the lead nucleation and growth processes under different cathode conditions were compared using the constant potential chronoamperometry method. Figure 4 The figures show the potentiostatic chronoamperometry current-time curves of the cathode plates in Example 1, Comparative Example 1, and Comparative Example 8. Figure 4It can be seen that Example 1 exhibits more coordinated peak current and peak time changes in the initial electrodeposition stage, indicating that its nucleation process starts at a moderate pace and that the matching between nucleation and subsequent growth is better. In contrast, in the comparative examples, due to the lack of an effective modified seed layer or unreasonable electrochemical control conditions, the initial lead deposition process is more prone to local rapid nucleation or uneven growth, which is not conducive to the formation of a continuous, dense, and uniform cathode lead deposition layer.

[0115] Figure 5 This is a normalized nucleation fitting graph for the cathode plates of Example 1, Comparative Example 1, and Comparative Example 8. This graph compares the normalized curves obtained from the potentiostatic chronoamperometry test with the theoretical nucleation model to determine the nucleation behavior in the early stages of lead deposition. Figure 5 It can be seen that the normalized nucleation curve of Example 1 is closer to the uniform nucleation characteristics, indicating that the modified seed layer can provide more uniform initial nucleation sites on the cathode surface, and transform lead deposition from local growth of a small number of active sites to multi-site synergistic nucleation and uniform growth. Combined with... Figure 4 The results show that the modified seed layer and the staged current density control in Example 1 have a synergistic effect, which can effectively suppress dendrite, nodule and local coarsening growth, and improve the structural uniformity of the cathode deposition layer.

[0116] In addition to the regulation of nucleation at the cathode interface, the continuous control of impurity ions in the electrolyte is also a key factor in the preparation of ultra-high purity cathode lead. Figure 6 This is a dynamic transmittance diagram of bismuth, copper, antimony, and iron ions in the bypass trapping unit of Example 1. A fixed-bed dynamic adsorption experiment was conducted, combined with inductively coupled plasma mass spectrometry (ICP-MS) to monitor the concentration of target impurity ions in the effluent. Figure 6 It can be seen that the overall penetration time of each impurity ion in Example 1 is delayed, indicating that the 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres have a good continuous trapping ability for impurity ions such as Bi, Cu, Sb, and Fe. This dynamic penetration behavior shows that under bypass circulation conditions, the modified impurity-trapping microspheres can maintain a high impurity retention efficiency for a longer operating time, thereby reducing the risk of impurity ions entering the cathode deposition layer.

[0117] Figure 7 This is a dynamic transmittance diagram of bismuth, copper, antimony, and iron ions in the bypass trapping unit of Comparative Example 4. Comparative Example 4 uses unmodified silica microspheres as the trapping material. Figure 7 It can be seen that the impurity ions penetrated earlier than in Example 1, indicating that the unmodified silica microspheres mainly rely on weak interaction sites such as surface silanol groups for adsorption, making it difficult to form stable and effective selective binding to various metal impurity ions. Figure 6 The comparison shows that the amino functional group introduced by 3-aminopropyltriethoxysilane plays a key role in enhancing the complexing ability and dynamic adsorption capacity of the impurity-trapping microspheres.

[0118] Figure 8 This is a dynamic transmittance diagram of bismuth, copper, antimony, and iron ions in the bypass trapping unit of Comparative Example 5. Comparative Example 5 was used to investigate the bypass purification effect under low processing flow conditions. Figure 8 The significantly earlier penetration of impurity ions indicates that when the bypass treatment flow rate is too low, the amount of electrolyte entering the impurity trapping unit per unit time is insufficient, making it difficult to reduce the concentration of impurity ions in the main electrolysis system in a timely manner. This result demonstrates that the bypass impurity trapping unit not only needs highly efficient adsorption materials but also requires a suitable circulation flow rate to maintain stable impurity control during continuous electrolysis.

[0119] Figure 9 This is a comparison of lead ion loss rates after bypass impurity trapping in Examples 1, 4, and 5. The change in lead ion concentration during the purification process was simultaneously monitored using inductively coupled plasma mass spectrometry to evaluate the retention capacity of the impurity trapping unit for the bulk lead ions. Figure 9 It can be seen that Example 1 maintains a high impurity removal capacity while exhibiting a low lead ion loss rate, indicating that the 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres have a more preferential binding capacity for impurity ions such as Bi, Cu, Sb, and Fe, while exhibiting weaker non-target adsorption of high-concentration Pb ions in the electrolyte. This result demonstrates that the bypass impurity-trapping design of this embodiment can balance impurity purification efficiency with the retention of the main lead component, avoiding fluctuations in electrolyte composition or increased production costs due to excessive lead ion adsorption.

[0120] To elucidate the mechanism of action of the impurity-trapping microspheres, the elemental state of the surface of the adsorbed microspheres was further characterized. Figure 10 The images show the N 1s high-resolution X-ray photoelectron spectra of the impurity-trapping microspheres after adsorption in Examples 1 and 4 (Comparative Example 4). Figure 10 It can be seen that Example 1 still retains a significant nitrogen-containing signal after adsorption, and the N 1s chemical environment changes, indicating that the amino sites on the surface of the modified microspheres participate in the binding process of impurity ions. In contrast, Comparative Example 4 did not introduce effective nitrogen-containing functional groups, and its surface lacks active sites that can form stable coordination or complexation with metal impurities, thus exhibiting weaker dynamic impurity-trapping performance. This result demonstrates the necessity of amino-functionalization modification for improving impurity-trapping performance from a surface chemistry perspective.

[0121] Figure 11 High-resolution X-ray photoelectron spectra of Bi₄f in Bi4f after adsorption in Example 1 and Comparative Example 4. Figure 11It can be seen that the bismuth signal on the surface of the microspheres after adsorption in Example 1 is more prominent, indicating that the modified impurity-trapping microspheres can effectively fix bismuth ions in the electrolyte. Since bismuth impurities have a significant impact on product purity and subsequent application performance in the preparation of high-purity lead, the enhancement of the Bi 4f signal in Example 1 indicates that the bypass impurity-trapping unit can effectively remove key impurities, thereby reducing the migration and entrainment of bismuth into the cathode lead deposition layer.

[0122] Figure 12 High-resolution X-ray photoelectron spectra of Sb 3d3 / 2 in Example 1 and Comparative Example 4 after adsorption of impurity-trapping microspheres. Figure 12 It can be seen that a clearer antimony-related signal appeared in Example 1, indicating that the 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres also have an effective trapping effect on antimony ions. Combined with... Figure 11 It can be seen that the modified impurity-catching material is not only effective against a single impurity, but can also synergistically remove multiple metal impurity ions in the electrolyte that affect the purity of lead.

[0123] Figure 13 This is a statistical graph showing the ratio of nitrogen (N) to metal atoms on the surface of the impurity-trapping microspheres after adsorption in Examples 1 and 4 (Comparative Example 4). This graph quantitatively compares the correspondence between surface amino sites and adsorbed metals using X-ray photoelectron spectroscopy peak areas. Figure 13 It can be seen that Example 1 exhibits a more reasonable N / metal atom ratio, indicating that the nitrogen-containing sites in its surface functional layer can provide stable and effective binding sites for impurity metal ions. This result is consistent with... Figures 10 to 12 The evidence corroborates each other, proving that the amino functional layer is the core structural basis for achieving selective impurity capture and dynamic purification.

[0124] After verifying the effects of nucleation regulation and impurity purification, the crystal phase structure of cathode deposited lead obtained under different electrolysis conditions was analyzed. Figure 14 X-ray diffraction patterns of lead cathode deposition in Examples 1, 6, and 8 are shown. Figure 14 It can be seen that the main diffraction peak of the deposited lead in Example 1 is clearer and the diffraction intensity distribution is more concentrated, indicating that its deposited layer has a more complete crystal structure and a more ordered crystal orientation. In contrast, the crystal integrity of the deposited layers in Comparative Examples 6 and 8 is poor due to insufficient control of electrolysis parameters or cathode interface. This result shows that, under the combined effect of modified seed crystal layer, staged current density, and bypass impurity removal and purification, lead ions can be reduced and deposited on the cathode surface in a more uniform manner, thereby forming a metallic lead layer with a clear crystal phase and dense structure.

[0125] Figure 15 Scanning electron microscope (SEM) images of the modified lead carbonate seed crystal intermediate prepared in Example 1. Figure 15It can be seen that the powder is well dispersed overall, with particles exhibiting a near-spherical to quasi-spherical morphology. The particle size is mainly distributed in the range of 0.40–0.65 μm, with a smooth and dense surface. The particles are loosely packed in a point-contact manner, without any obvious hard agglomerates. Combined with the aforementioned X-ray photoelectron spectroscopy results, it can be seen that a continuous or near-continuous phosphonic acid-modified layer is formed on the particle surface. This result indicates that under the conditions of a 1-hydroxyethylidene-1,1-diphosphonic acid to lead carbonate mass ratio of 0.011:1 and a reaction pH of 7.5, uniform surface modification of lead carbonate particles can be achieved while maintaining good powder dispersibility and submicron particle size characteristics. This microstructure is conducive to the stable adhesion of seed crystal intermediates on the cathode surface and to achieving moderate dissolution and continuous induced nucleation in the electrolyte.

[0126] Figure 16 Transmission electron microscopy (TEM) images of the modified lead carbonate seed crystal intermediate prepared in Example 1, wherein, Figure 16 a is the bright field diagram. Figure 16 b is a magnified view of a portion of the image. Figure 16 c is a high-resolution transmission electron microscope image. Figure 16 d represents the selected area electron diffraction pattern. (From...) Figure 16 a and Figure 16 As can be seen from b, the seed crystals have a solid and dense structure with relatively uniform internal lining; from Figure 16 c shows locally short-range ordered lattice fringes with a spacing of approximately 0.32 nm, corresponding to the low-index crystal planes of lead carbonate. Figure 16 The selected area electron diffraction (SID) pattern in d shows weak and diffuse diffraction rings, indicating that the seed crystal intermediate as a whole has weak crystalline to amorphous characteristics and contains localized nanocrystalline structures. These results demonstrate that the seed crystal intermediate prepared at 37 ℃ in a liquid phase without high-temperature calcination has suitable crystallinity, maintaining a moderate dissolution rate in an electrolyte with a free fluorosilicic acid concentration of 80 g / L, and providing effective nucleation induction for initial lead deposition at the cathode.

[0127] Based on the verification of seed crystal layer construction, nucleation behavior regulation, impurity capture and deposition crystal phase, the morphology and purity of the finally prepared ultra-high purity cathode lead product were evaluated. Figure 17 This is a macroscopic optical photograph of the ultra-high purity cathode lead product prepared in Example 1. (From...) Figure 17 It can be seen that the obtained sample is in the form of thin flakes or small blocks of silver-gray to light blue-gray metal. The freshly peeled surface has a high metallic luster and reflectivity. The overall surface is flat and has a mirror or semi-mirror finish. The edges are natural fractures formed during the peeling process, and no obvious cracks, holes or inclusions are observed.

[0128] Figure 18 This is a scanning electron microscope (SEM) image of the ultra-high purity cathode lead product prepared in Example 1. Figure 18It is evident that the cathode lead surface is formed by a large number of densely packed, micron-sized polyhedral grains, with uniform overall coverage. No obvious pores, cracks, or loose areas were observed. The grain boundaries are clear, exhibiting concave or convex morphologies, and no second-phase particles or inclusions were found on the surface of individual grains. This result indicates that the operating current density is 180 A / m. 2 Forced convection conditions with an electrolyte linear velocity of 0.5 m / s promote uniform mass transfer of lead ions and avoid rough deposition caused by local concentration polarization. Simultaneously, the electrolyte composition of 80 g / L free fluorosilicic acid and 105 g / L lead ion concentration matches the seed layer-induced nucleation effect, enabling the formation of a high-purity lead deposition layer with relatively uniform grain size and dense structure on the cathode surface.

[0129] Figure 19 Transmission electron microscopy (TEM) images of the ultra-high purity cathode lead product prepared in Example 1, wherein, Figure 19 a is the bright field diagram. Figure 19 b is a magnified view of a portion of the image. Figure 19 c is a high-resolution transmission electron microscope image. Figure 19 a and Figure 19 As can be seen from b, the cathode lead exhibits a typical polycrystalline metallic structure with clear grain boundaries and no obvious inclusions observed within the grains; therefore, Figure 19 Clear and continuous lattice fringes are visible, and the interplanar spacing d111 is approximately 0.286 nm and d200 is approximately 0.248 nm, consistent with the standard data for lead face-centered cubic structures. This result indicates that, using recycled crude lead anode plates with a lead content of 97.5 wt% and an antimony content of 0.75 wt% as raw material, the purity of the cathode deposition layer can be increased to 99.998 wt% after electrolytic refining according to this embodiment. This is because the 3-aminopropyltriethoxysilane-modified silica impurity-trapping microspheres in the bypass impurity-trapping unit can efficiently remove impurity ions such as Bi, Cu, Sb, and Fe. Simultaneously, combined with the difference in deposition potential between impurity elements and lead elements during electrochemical separation, the risk of impurity co-deposition and entrainment is significantly reduced. This demonstrates that this embodiment can achieve efficient purification from recycled crude lead to ultra-high purity cathode lead, and the resulting product can meet the raw material preparation requirements of high-value-added fields such as electronic-grade lead materials, lead for superconducting materials, and nuclear shielding materials.

[0130] The performance of the examples and comparative examples is summarized in Table 1.

[0131] As can be seen from the performance of the examples and comparative examples in Table 1, Examples 1-4 are generally superior to all comparative examples in terms of cathode lead purity, current efficiency, surface roughness of the deposited layer, seed layer adhesion retention rate, and impurity removal rate after bypass impurity trapping. Among them, Example 1 has the best overall performance, indicating that there is a significant synergistic effect between the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed layer, the 3-aminopropyltriethoxysilane modified silica impurity trapping microspheres, and the segmented current process. Eliminating the seed modification or deviating from the appropriate loading will weaken uniform nucleation and increase roughness; weakening the bypass impurity trapping unit will lead to a decrease in impurity removal rate and lower cathode lead purity; excessively high operating current density or eliminating the low current initial stage will more easily induce surface instability and increase inclusions, verifying the necessity and rationality of this process window.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for electrolytically preparing ultra-high purity lead, characterized in that, Includes the following steps: S1. The waste lead-acid battery is crushed and sorted to separate the lead-containing components, and the lead-containing components are melted and cast into recycled crude lead anode plates; S2. An aqueous suspension of 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate is coated onto the surface of a cathode plate and dried, such that the loading amount of 1-hydroxyethylidene-1,1-diphosphonic acid-modified lead carbonate seed crystal intermediate on the cathode plate surface is 0.20-2.00 g / m². 2 ; S3. The electrolyte is introduced into the electrolytic cell, with the regenerated crude lead anode plate obtained in step S1 as the anode and the cathode plate obtained in step S2 as the cathode. A bypass impurity removal unit is led out from the main circulation pipeline of the electrolyte, and the flow rate of the electrolyte flowing through the bypass impurity removal unit is 2-10% of the total flow rate of the main circulation of the electrolyte. The bypass impurity trapping unit is filled with 3-aminopropyltriethoxysilane-modified silica impurity trapping microspheres; S4. First use 50-100A / m 2 Electrolysis at an initial current density of 5-20 min, followed by 140-220 A / m 2 Electrolysis is performed at a working current density to cause lead to deposit on the surface of the cathode plate; S5. The precipitated lead is stripped off, washed, and dried to obtain ultra-high purity lead with a purity of not less than 99.996 wt%.

2. The method according to claim 1, characterized in that, In step S1, the lead content in the recycled crude lead anode plate is 96-99.5 wt%, the antimony content is 0.30-1.20 wt%, and the sum of the lead content and the antimony content is not greater than 100 wt%.

3. The method according to claim 1, characterized in that, In step S2, the concentration of the aqueous suspension of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate is 1-10 g / L. The drying process is vacuum drying, with a drying temperature of 40-80℃ and a drying time of 0.5-2 hours. The cathode plate is made of 304 stainless steel or titanium, and the ratio of the effective area of ​​the recycled crude lead anode plate to the effective area of ​​the cathode plate is 1.0-1.5:

1.

4. The method according to claim 1, characterized in that, The preparation method of the 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate includes the following steps: A1. Disperse 100 parts by weight of lead carbonate in deionized water to form a lead carbonate dispersion, and add a modifying solution, wherein the total amount of deionized water used in the lead carbonate dispersion and the modifying solution is 300-800 parts by weight, and the modifying solution contains 0.20-2.00 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.05-0.50 parts by weight of sodium carbonate; A2. Stir at 25-50℃ for 0.5-2.0h, and adjust the pH of the reaction system to 6.5-8.5; A3. After filtration, wash with deionized water 2-4 times, and then dry at 60-90℃ for 4-12h to obtain 1-hydroxyethylidene-1,1-diphosphonic acid modified lead carbonate seed crystal intermediate.

5. The method according to claim 4, characterized in that, In step A1, the modified solution is prepared by dissolving 0.20-2.00 parts by weight of 1-hydroxyethylidene-1,1-diphosphonic acid and 0.05-0.50 parts by weight of sodium carbonate in 50-150 parts by weight of deionized water, and the lead carbonate dispersion is 100 parts by weight of lead carbonate dispersed in 250-650 parts by weight of deionized water; The initial average particle size D50 of the lead carbonate is 0.20-0.80 μm, or it is wet-milled before dispersion to an average particle size D50 of 0.20-0.80 μm.

6. The method according to claim 4, characterized in that, In step A2, the reaction system is carried out under mechanical stirring at 200-500 rpm. The pH value of the reaction system is adjusted to 6.5-8.5 by adding 1.0 mol / L sodium hydroxide solution dropwise. If the pH exceeds 8.5, it is finely adjusted to 6.5-8.5 by adding 0.5 mol / L hydrochloric acid solution dropwise. The pH is monitored online by a pH meter with an accuracy of ±0.

01.

7. The method according to claim 1, characterized in that, In step S3, the electrolyte flowing through the bypass impurity trapping unit has an empty bed residence time of 5-30 min in the bypass impurity trapping unit in order to trap impurity ions in the electrolyte, including bismuth ions, copper ions, antimony ions and iron ions. The total concentration of bismuth, copper, antimony and iron in the electrolyte before it enters the electrolytic cell is not greater than 50 mg / L.

8. The method according to claim 1, characterized in that, The preparation method of the 3-aminopropyltriethoxysilane modified silica impurity trapping microspheres includes the following steps: B1. Disperse 100 parts by weight of silica microspheres with an average particle size D50 of 20-150 μm in 300-1000 parts by weight of deionized water, and add 5-15 parts by weight of 3-aminopropyltriethoxysilane. B2. Under industrial nitrogen protection, react at 60-80℃ for 2-6 hours, and keep the pH of the reaction system at 8.0-10.0; B3. After filtration, wash with deionized water 2-5 times, and then dry at 70-110℃ for 2-8 hours to obtain 3-aminopropyltriethoxysilane modified silica impurity-trapping microspheres.

9. The method according to claim 1, characterized in that, In step S3, the electrolyte is a lead hexafluorosilicate-free fluorosilicic acid system electrolyte, wherein the lead ion concentration in the electrolyte (Pb) is 80-130 g / L and the concentration of free fluorosilicic acid is 60-100 g / L.

10. The method according to claim 1, characterized in that, In step S4, electrolysis is carried out under the conditions of a bath temperature of 28-38℃, an electrode spacing of 40-90mm, and an electrolyte linear velocity of 0.2-0.8m / s.

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