Method for detecting components of lead plaster of waste lead-acid storage battery

Abstract

The invention discloses a method for detecting lead plaster components of a waste lead-acid storage battery. The invention relates to the technical field of waste storage battery resourceful treatment and detection, the method comprises preparation and calibration of an EDTA standard solution, and continuous determination of the content of lead oxide, lead sulfate, metal lead and lead dioxide in lead plaster, through use of formic acid, ammonium carbonate and other reagents and combination of an ultrasonic-assisted extraction technology, the dissolution efficiency is significantly improved, and the content of lead oxide, lead sulfate, metal lead and lead dioxide in the lead plaster is determined. The reaction time is greatly shortened; the selective dissolution of the metal lead is realized by accurately controlling the low-temperature condition and the reaction time, and the interference of lead dioxide is effectively avoided; according to the method, by optimizing a reagent system and introducing ultrasonic-assisted extraction, the dosage of strong acid and the emission of toxic wastes are greatly reduced, the method is more environment-friendly while the result accuracy is ensured, and the method is clear in operation flow, good in reproducibility and suitable for rapid and reliable determination of the components of the lead paste in an industrial recovery scene.

Description

Technical Field

[0001] This invention relates to the field of resource utilization and testing technology for waste lead-acid batteries, specifically to a method for detecting the composition of lead paste from waste lead-acid batteries. Background Technology

[0002] Lead-acid batteries are widely used in key sectors of the national economy, such as transportation, power storage, and communication base stations, due to their mature technology, low cost, and high reliability. However, at the end of their service life, lead-acid batteries fail due to plate corrosion, softening of active materials, and sulfation, resulting in a large number of waste batteries. Statistics show that a huge number of waste lead-acid batteries are generated globally each year, and improper disposal will cause serious harm to the environment and human health.

[0003] The main components of spent lead-acid batteries include waste lead paste, grids, casing, and electrolyte. Waste lead paste has a complex composition, primarily containing PbSO4, PbO4, PbO, Pb, and small amounts of other metallic impurities. It is not only classified as hazardous solid waste but also an important secondary lead resource. Achieving efficient and clean recycling of waste lead paste is crucial for reducing lead pollution and promoting resource recycling. Accurate and rapid determination of the chemical composition of waste lead paste is a key prerequisite for optimizing recycling processes, improving lead recovery rates, and achieving green regeneration.

[0004] Currently, there is a lack of unified and efficient analytical methods for detecting the components of waste lead paste. Traditional methods suffer from problems such as cumbersome procedures, long cycles, or insufficient accuracy, making it difficult to meet the needs of rapid component identification and process control in large-scale recycling processes. Therefore, developing an accurate, efficient, and industrially applicable method for detecting the components of waste lead paste is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies, such as the large amount of reagents and long processing time in lead-acid battery plates (GB / T 23636-2017). This invention provides a method for detecting the composition of lead paste from waste lead-acid batteries. This invention relates to the field of waste battery resource utilization and testing technology. The method includes the preparation and calibration of EDTA standard solution, and the continuous determination of the content of lead oxide, lead sulfate, metallic lead, and lead dioxide in the lead paste. By using reagents such as formic acid and ammonium carbonate combined with ultrasonic-assisted extraction technology, the dissolution efficiency is significantly improved, and the reaction time is greatly shortened. By precisely controlling the low-temperature conditions and reaction time, selective dissolution of metallic lead is achieved, effectively avoiding interference from lead dioxide. This invention significantly reduces the amount of strong acid used and the emission of toxic waste by optimizing the reagent system and introducing ultrasonic-assisted extraction. While ensuring the accuracy of the results, it is also more environmentally friendly. The method has a clear operation process, good reproducibility, and is suitable for rapid and reliable determination of lead paste composition in industrial recycling scenarios.

[0006] To achieve the above technical effects, the following technical solution is adopted: A method for detecting the composition of lead paste from waste lead-acid batteries, the specific steps of which are as follows: Step S1: Preparation and standardization of EDTA standard solution Prepare a disodium EDTA solution and use lead nitrate as a reference. In an acetate-sodium acetate buffer system at pH 5.5, use xylenol orange as an indicator to standardize the solution and calculate the actual concentration of the EDTA standard solution and the titer of each target component. Step S2: Determination of lead oxide (PbO) content Accurately weigh the lead paste sample, use formic acid solution as the extractant, dissolve PbO under ultrasonic assistance and heating conditions, filter, take a portion of the test solution to adjust the pH value of the filtrate, use xylenol orange as an indicator, titrate with the EDTA standard solution obtained in step S1, and calculate the PbO content based on the volume of EDTA consumed. Step S3: Determination of lead sulfate (PbSO4) content The residue obtained in step S2 was converted and dissolved using ammonium carbonate solution as a conversion agent under ultrasonic assistance. After filtration, the filtrate was acidified, and a portion of the test solution was taken to adjust the pH value. Using xylenol orange as an indicator, the EDTA standard solution obtained in step S1 was titrated, and the PbSO4 content was calculated based on the volume of EDTA consumed. Step S4: Determination of lead (Pb) content The residue obtained in step S2 was subjected to selective dissolution of metallic lead with nitric acid solution under low temperature conditions. The reaction time and temperature were strictly controlled to avoid dissolution of lead dioxide. After filtration, a portion of the filtrate was taken to adjust the pH value. Using xylenol orange as an indicator, the solution was titrated with the EDTA standard solution obtained in step S1. The Pb content was calculated based on the volume of EDTA consumed. Step S5: Determination of lead dioxide (PbO2) content The residue obtained in step S4 was dissolved in nitric acid and ascorbic acid solution as reducing solvents under ultrasonic assistance to dissolve PbO2. The pH of the solution after the reaction was adjusted, and the solution was titrated with the EDTA standard solution obtained in step S1 using xylenol orange as an indicator. The PbO2 content was calculated based on the volume of EDTA consumed.

[0007] Furthermore, the specific steps for standardizing the EDTA standard solution in step S1 are as follows: Weigh the reference lead nitrate, dissolve it in water and boil it to remove nitrogen oxides, cool it and then add ammonia water dropwise until a precipitate is formed, then add nitric acid dropwise until the precipitate just dissolves to form a buffer system, add acetate-sodium acetate buffer solution and xylenol orange indicator, and titrate with the EDTA solution to be standardized until the solution changes from purple-red to bright yellow and does not fade for 30 seconds. The accurate concentration of EDTA is obtained by calculation, and the titer T1, T2, T3, and T4 for PbO, PbSO4, Pb, and PbO2 are further calculated.

[0008] Furthermore, in step S2, the extractant is a 5% formic acid solution, and the dissolution process is carried out in a 40°C water bath with the aid of ultrasound. The ultrasound power is 200W and the ultrasound time is 10 minutes. The pH value is 5.5.

[0009] Furthermore, in step S3, the conversion agent is a 25% ammonium carbonate solution, and the conversion process is carried out in a 40°C water bath with the aid of ultrasound. The ultrasound power is 200W and the ultrasound time is 10 minutes. After filtration, the washing liquid is tested with sodium sulfide solution until there is no lead ion reaction. The filtrate is acidified with formic acid, and the pH value is 5.5.

[0010] Furthermore, the selective dissolution conditions for metallic lead in step S4 are as follows: after cooling the residue in an ice-water bath, add a 50% nitric acid solution and stir the reaction for 15 minutes at room temperature ≤ 25°C. After the reaction is completed, immediately wash and filter with a cold 1% nitric acid solution. The pH value is 5.5.

[0011] Furthermore, in step S5, the reducing solvent is a mixture of nitric acid and ascorbic acid solution. The dissolution process is carried out in a 40°C water bath with the aid of ultrasound. The ultrasound power is 200W and the ultrasound time is 10 minutes. The pH value is 5.5.

[0012] Furthermore, the nitric acid concentration during the dissolution process is 50%; and the nitric acid concentration during the washing process is 1%.

[0013] Furthermore, the nitric acid has a mass concentration of 50%; the ascorbic acid has a mass concentration of 5%.

[0014] Furthermore, in steps S2, S3, S4 and S5, the pH value of the solution before titration is adjusted to 5.5 using sodium hydroxide solution or ammonia, and an acetate-sodium acetate buffer solution is added to maintain the stability of the system.

[0015] The above-mentioned detection method is used for rapid quantitative detection of lead paste components in the resource recycling and treatment process of waste lead-acid batteries.

[0016] The beneficial effects of this invention are as follows: 1. Ultrasonic-assisted treatment is introduced to shorten reaction time and improve extraction efficiency. In key dissolution steps (such as formic acid for PbO, ammonium carbonate for PbSO4, and ascorbic acid for PbO2), temperature-controlled ultrasonic-assisted treatment is innovatively introduced. The cavitation effect of ultrasound greatly promotes mass transfer and reaction rate, reducing the original 30-60 minute stirring and dissolution process to 10 minutes, while ensuring more thorough dissolution, thereby improving extraction efficiency and the accuracy of results.

[0017] 2. By precisely controlling the low temperature conditions and reaction time (15 minutes), the high selectivity of nitric acid in dissolving metallic lead was achieved, effectively inhibiting the co-dissolution of PbO2 in this step, solving the problem of core separation in continuous determination, and ensuring the accuracy of the results.

[0018] 3. In the determination of lead dioxide (PbO2) content, an innovative mixed system of nitric acid and ascorbic acid solution was used in conjunction with ultrasound to ensure accurate determination of lead dioxide (PbO2) content. Compared with a single dissolution system, the mixed system of nitric acid and ascorbic acid solution can achieve more accurate determination of PbO2 content.

[0019] 4. By reducing the amount of strong acid used, using milder reagents (such as formic acid and ascorbic acid), and optimizing the process to shorten the exposure time, the risk of generating toxic gases (such as nitrogen oxides) and causing violent reactions during the experiment was reduced, thus improving the safety of the experimental operation.

[0020] 5. The invention not only has significant advantages in terms of analysis speed, cost, and environmental friendliness, but also enables the analysis of multiple lead paste components in one go through technological innovation and process optimization. It is significantly superior to existing technical standards in terms of accuracy, reliability, safety, and operability, providing a more efficient and accurate analytical and testing method for the resource utilization of waste lead-acid battery lead paste. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 A process flow diagram of a method for detecting the composition of lead paste from waste lead-acid batteries provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the ultrasound-assisted extraction device according to an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0026] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0027] The following describes a method for detecting the composition of lead paste from waste lead-acid batteries provided by the present invention, with reference to specific embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0028] Example 1: This method optimizes the sample pretreatment and titration analysis process, enabling rapid, continuous, and accurate determination of lead oxide (PbO), lead sulfate (PbSO4), metallic lead (Pb), and lead dioxide (PbO2) in lead paste.

[0029] like Figure 1As shown, a method for detecting the composition of lead paste from waste lead-acid batteries includes the following steps: Step 1: First, weigh about 19g of disodium ethylenediaminetetraacetate and place it in a beaker. Add deionized water to dissolve it, then transfer it to a 1L volumetric flask and add deionized water to the mark. Shake well and store it in a hard glass bottle or polyethylene plastic bottle, avoiding contact with rubber stoppers, rubber tubing, etc.

[0030] Step 2: Weigh 0.64 g (accurate to 0.0001 g) of reference grade lead nitrate [Pb(NO3)2] into a 300 mL Erlenmeyer flask, add 50 mL of deionized water, and stir until completely dissolved. Boil the solution for 2 minutes to remove nitrogen oxides, and cool to room temperature. Add 50% ammonia solution dropwise until a white precipitate just appears and does not disappear. Then add 20% nitric acid solution dropwise, stirring thoroughly until the precipitate is just completely dissolved. Add 20 mL of pH 5.5 acetic acid-sodium acetate (HAc-NaAc) and three drops of 0.5% xylenol orange indicator. Titrate with the prepared standard EDTA solution until the solution changes from purple-red to bright yellow and the yellow color remains for 30 seconds without fading. Perform a blank test (without adding lead nitrate, keeping all other steps the same). Calculate the actual concentration of the EADT standard solution: ,in, To measure the mass (g) of lead nitrate. This refers to the volume of EDTA solution used (ml). The volume (ml) of EDTA solution used in the blank experiment. Calculate the titer of each substance in the lead paste: Titration of lead oxide: (g / mL); titer of lead sulfate : (g / mL); titer of lead dioxide : (g / mL); titer of metallic lead : (g / mL).

[0031] Step 3: Determination of PbO content. Accurately weigh approximately 3g of the sample (accurate to 0.0001g) that has passed through a 200-mesh sieve, record it as m, and place it in a 300 mL beaker. Add 60 mL of 5% (mass fraction) formic acid solution (HCOOH, which can improve dissolution efficiency). Figure 2As shown, place the beaker in a 40℃ water bath and sonicate for 10 minutes using an ultrasonic generator (VOSHIN-1500C, China, 200W). After the reaction is complete, slowly filter the solution into a 250 ml beaker using slow-speed quantitative filter paper. Carefully wash the original beaker and filter residue 5-6 times with 5 wt% formic acid solution, about 5 mL each time. (Be sure to retain all filter residue for subsequent determination of PbSO4 and Pb). Pipette 50 ml into a 250 ml Erlenmeyer beaker, add water to about 100 ml, and add 20 wt% sodium hydroxide solution dropwise while stirring vigorously to adjust the pH of the solution to 5-6. Then add 20 mL of HAc-NaAc buffer solution and 2 drops of 0.5 wt% xylenol orange indicator, and shake well. Titrate with the standardized EDTA standard solution until the solution color changes from purplish-red to bright yellow, and the yellow color remains unchanged for 30 seconds, which is the endpoint. Record the volume of EDTA standard solution consumed, V3. The mass fraction of PbO in the sample is: , in the formula, V3 is the titer of EDTA standard solution for lead oxide, in g / L; V3 is the volume of EDTA standard solution consumed in the titration, in mL; m is the mass of the sample, in g.

[0032] Step 4: Determination of PbSO4 content. Place the residue from the lead oxide determination in a clean, dry 300 mL beaker. Add 150 mL of 25 wt% ammonium carbonate ((NH4)2CO3) solution. Place the beaker in a 40°C water bath and sonicate for 10 minutes using an ultrasonic generator (200W). After the reaction is complete, filter quickly using slow-speed quantitative filter paper. Carefully wash the beaker and residue with 10 wt% ammonium carbonate washing solution, and test the effluent with sodium sulfide solution until no lead ion reaction is observed (the washing solution does not turn black). (Be sure to retain all filter residue for subsequent PbO2 determination). Add 5 mL of formic acid to the filtrate and shake well. Transfer the entire solution to a 250 mL volumetric flask, add distilled water to the mark, and shake well. Accurately pipette 25 mL of the above test solution into a 250 mL Erlenmeyer flask, dilute with water to approximately 100 mL, and adjust the pH of the solution to 5.5 with 20 wt% sodium hydroxide solution. Add 20 mL of HAc-NaAc buffer solution and 2 drops of 0.5 wt% xylenol orange indicator. Titrate with EDTA standard solution until the solution changes from purple-red to bright yellow, and the yellow color remains unchanged for 30 seconds; this is the endpoint. Record the volume of EDTA consumed, V4. The mass fraction of PbSO4 in the sample is: , in the formula, V4 is the titer of EDTA standard solution to lead sulfate, in g / mL; V4 is the volume of EDTA standard solution consumed in the titration, in mL; m is the mass of the sample, in g.

[0033] Step 5: Determination of Pb content. Take the residue from the lead oxide determination and place it in a dry, clean 100mL beaker. Cool the beaker in an ice-water bath for 2 minutes. Add 20 mL of 50% nitric acid solution to the cooled beaker and stir for 15 minutes at room temperature (≤25℃). (Using an ice bath and strictly controlling the reaction time (15 minutes) ensures that the nitric acid dissolves only metallic lead and not lead dioxide; this is one of the key factors for the success of the entire continuous determination process). After the reaction is complete, immediately filter rapidly using slow-speed quantitative filter paper. Wash the beaker and residue 3-4 times with cold 1wt% nitric acid solution. (Be sure to retain all filter residue for subsequent PbO2 determination). Transfer the filtrate and washings to a 250mL volumetric flask, add deionized water to the mark, and mix well. Accurately pipette 50 mL of the above filtrate into a 250 mL Erlenmeyer flask, dilute with water to 100 mL, then adjust the pH of the filtrate to 5–6 with 20 wt% sodium hydroxide solution. Add 20 mL of HAc-NaAc buffer solution and 2 drops of 0.5 wt% xylenol orange indicator. Titrate with EDTA standard solution until the solution changes from purple-red to bright yellow, and the yellow color remains unchanged for 30 seconds; this is the endpoint. Record the volume of EDTA consumed, V5. The mass fraction of Pb in the sample is: , in the formula, V5 is the titer of EDTA standard solution for lead, in g / L; V5 is the volume of EDTA standard solution consumed in the titration, in mL; m is the mass of the sample, in g.

[0034] Step 6: Determination of PbO2 content. Take the residue retained after determining the lead content and place it in a dry, clean 100mL beaker. Add 5 mL of 50% nitric acid and accurately add 50 mL of 5wt% ascorbic acid solution (or weigh approximately 2.5 g of solid ascorbic acid) using a pipette. Place the beaker in a 40℃ water bath and sonicate for 10 minutes using an ultrasonic generator (200W) to fully reduce and dissolve the PbO2 in the sample. After the reaction is complete, filter directly into a 250mL beaker using slow quantitative filter paper (if the solution is clear, filtration is not necessary). Wash the beaker and residue carefully with water 3-4 times, and combine all washings with the filtrate. Add 20 mL of HAc-NaAc buffer solution and 2 drops of 0.5wt% xylenol orange indicator to the solution and shake well. The solution should be purple-red at this point. Titrate with EDTA standard solution until the solution changes from purple-red to bright yellow, and the yellow color remains unchanged for 30 seconds; this is the endpoint. Record the volume of EDTA consumed, V6. The mass fraction of PbO2 in the sample is: , in the formula, V6 is the titer of EDTA standard solution for lead dioxide, in g / L; V6 is the volume of EDTA standard solution consumed in the titration, in mL; m is the mass of the sample, in g.

[0035] Example 2: Analysis of the lead paste content in used batteries from a certain electric bicycle: 1. Sample preparation and EDTA calibration Lead paste from a dismantled lead-acid battery of an electric vehicle was dried at 105℃, ground, and passed through a 200-mesh sieve. 3.0025 g (accurate to 0.0001 g) of this uniformly mixed, dried lead paste sample was accurately weighed and recorded as follows: Place it in a 300mL beaker for subsequent continuous determination.

[0036] Prepare the EDTA solution according to step 1 of the invention. Accurately weigh 0.6402 g of lead nitrate (Pb(NO3)2) according to step 2 for standardization, consuming EDTA volume V2 = 38.55 mL, with a blank volume V1 = 0.05 mL. Calculate the EDTA concentration. The titers of each substance were then calculated as follows: T1(PbO) = 0.01119 g / mL, T2(PbSO4) = 0.01520 g / mL, T3(Pb) = 0.01038 g / mL, and T4(PbO2) = 0.01198 g / mL.

[0037] 2. Determination of PbO content Add 60 mL of 5 wt% formic acid solution to a beaker containing the sample, and sonicate at 40 °C and 200 W for 10 minutes. After the reaction is complete, filter and wash, and bring the filtrate to a final volume of 250 mL. Transfer 50 mL of the filtrate, adjust the pH to 5.5, add buffer and indicator, and titrate with EDTA until a bright yellow endpoint is reached, consuming the required volume of EDTA. =12.50 mL. Calculate the PbO mass fraction: .

[0038] 3. Determination of PbSO4 content Transfer the residue after PbO determination to a new beaker, add 150 mL of 25 wt% ammonium carbonate solution, and sonicate at 40℃ and 200 W for 10 minutes. Filter, wash with 10 wt% ammonium carbonate until lead ions are removed (Na2S test), acidify the filtrate with formic acid, and bring the volume to 250 mL. Transfer 25.00 mL of the test solution, adjust the pH, and titrate, consuming the volume of EDTA consumed. =9.80 mL. Calculate the mass fraction of PbSO4: .

[0039] 4. Determination of Pb content Take another 3.0018 g sample of lead paste, reserved after PbO determination, cool it in an ice bath, add 20 mL of 50% HNO3, and react precisely at 25°C for 15 minutes. Filter immediately, wash with cold 1 wt% nitric acid, and dilute the filtrate to 250 mL. Transfer 50.00 mL of the solution, adjust the pH, and titrate, consuming the volume of EDTA consumed. =2.90 mL. Calculate the mass fraction of metallic Pb: .

[0040] 5. Determination of PbO2 content The residue after Pb determination was sonicated for 10 minutes at 40°C and 200W with 5 mL of 50% HNO3 and 50 mL of 5wt% ascorbic acid solution. After filtration and washing, the filtrates were combined, and the solution was titrated directly with buffer solution, consuming the required volume of EDTA. =4.8 mL. Calculation: .

[0041] 6. Results Analysis The total percentage is calculated as follows: 23.29% (PbO) + 49.61% (PbSO4) + 5.01% (Pb) + 19.15% (PbO2) = 97.06%. Since some metallic impurities have a percentage less than 100%, and the total is reasonable, this indicates that the calculations for each component are correct, confirming the effectiveness of the method.

[0042] Example 3: Analysis of the content of waste lead paste provided by Yunnan Xiangyun Feilong Recycling Technology Co., Ltd.: 1. Sample preparation and EDTA calibration Lead paste from a dismantled lead-acid battery of an electric vehicle was dried at 105℃, ground, and passed through a 200-mesh sieve. 3.0506 g of this uniformly mixed, dried lead paste sample was accurately weighed and recorded as follows: Place it in a 300mL beaker for subsequent continuous determination.

[0043] Prepare the EDTA solution according to step 1 of the invention. Accurately weigh 0.6217 g of lead nitrate (Pb(NO3)2) according to step 2 for standardization, consuming EDTA volume V2 = 37.45 mL, with a blank volume V1 = 0.05 mL. Calculate the EDTA concentration. The following values ​​were then calculated: T1(PbO) = 0.01120 g / mL, T2(PbSO4) = 0.01522 g / mL, T3(Pb) = 0.01040 g / mL, and T4(PbO2) = 0.01200 g / mL.

[0044] 2. Determination of PbO content Add 60 mL of 5 wt% formic acid solution to a beaker containing the sample, and sonicate at 40 °C and 200 W for 10 minutes. After the reaction is complete, filter and wash, and bring the filtrate to a final volume of 250 mL. Transfer 50 mL of the filtrate, adjust the pH to 5.5, add buffer and indicator, and titrate with EDTA until a bright yellow endpoint is reached, consuming the required volume of EDTA. =7.64 mL. Calculate the PbO mass fraction: .

[0045] 3. Determination of PbSO4 content Transfer the residue after PbO determination to a new beaker, add 150 mL of 25 wt% ammonium carbonate solution, and sonicate at 40℃ and 200 W for 10 minutes. Filter, wash with 10 wt% ammonium carbonate until lead ions are removed (Na2S test), acidify the filtrate with formic acid, and bring the volume to 250 mL. Transfer 25.00 mL of the test solution, adjust the pH, and titrate, consuming the volume of EDTA consumed. =12.22 mL. Calculate the mass fraction of PbSO4: .

[0046] 4. Determination of Pb content Take another 3.0009 g of lead paste sample retained after PbO determination, cool it in an ice bath, add 20 mL of 50% HNO3, and react precisely at 25℃ for 15 minutes. Filter immediately, wash with cold 1 wt% nitric acid, and dilute the filtrate to 250 mL. Transfer 50.00 mL of the solution, adjust the pH, and titrate, consuming the volume of EDTA consumed. =1.1 mL. Calculate the mass fraction of metallic Pb: .

[0047] 5. Determination of PbO2 content The residue after Pb determination was sonicated for 10 minutes at 40°C and 200W with 5 mL of 50% HNO3 and 50 mL of 5% ascorbic acid solution. After filtration and washing, the filtrates were combined, and the solution was titrated directly with buffer solution, consuming the required volume of EDTA. =5.4 mL. Calculate the mass fraction of PbO2: .

[0048] 6. Results Analysis The total is 14.02% (PbO) + 60.96% (PbSO4) + 1.91% (Pb) + 21.59% (PbO2) = 98.48%. The total error of the method compared with the waste lead paste content data (14.56%(PbO)+61.36%(PbSO4)+1.70%(Pb)+21.22%(PbO2)=98.84%, He P, Ouyang LA, Yang Y, et al. Energy-saving recovery of lead from waste lead paste via in-situ hydrometallurgical reduction and electrochemical mechanism[J]. Electrochimica Acta, 2023, 465:143021.) provided by Yunnan Xiangyun Feilong Recycling Technology Co., Ltd. was 0.36%, and the errors for individual chemical substances were 0.54%(PbO)+0.4%(PbSO4)+0.21%(Pb)+0.37%(PbO2), all within 1%, confirming the effectiveness of the method.

[0049] Example 4: Analysis of mixtures of pure substances: To verify the accuracy and reliability of this method, based on the typical component data of waste lead paste (PbO: 14.56%, PbSO4: 61.36%, Pb: 2.86%, PbO2: 21.22%) provided by Yunnan Xiangyun Feilong Recycling Technology Co., Ltd., a pure mixture of lead paste was simulated using high-purity reagents.

[0050] Accurately weigh: PbO (0.4368 g), PbSO4 (1.8408 g), Pb (0.0858 g), PbO2 (0.6366 g), mix evenly, totaling 3.0000 g, grind and mix this simulated sample thoroughly, and set aside for later use.

[0051] The standardization of the EDTA standard solution was the same as in Example 3, directly using the pre-calibrated concentration c=0.05019 mol / L and the corresponding titers: T1=0.01120 g / mL, T2=0.01522 g / mL, T3=0.01040 g / mL, T4=0.01200 g / mL.

[0052] 1. Determination of PbO content Accurately weigh 3.0000 g of the simulated sample and place it in a 300 mL beaker. Proceed as described in step 3 of the invention. Add 60 mL of 5 wt% formic acid solution and sonicate at 40°C and 200 W for 10 minutes. After the reaction is complete, filter and wash, and bring the filtrate to a final volume of 250 mL. Transfer 50.00 mL of the filtrate, adjust the pH to 5.5, and titrate with EDTA, consuming the required volume. =8.0 mL. Calculate the PbO mass fraction: (The error from the theoretical value of 14.56% is -0.37%).

[0053] 2. Determination of PbSO4 content The residue after PbO determination was processed according to step 4 of the invention. 150 mL of 25 wt% ammonium carbonate solution was added, and the mixture was sonicated at 40°C and 200 W for 10 minutes. The solution was filtered, washed until lead ions were removed, and the filtrate was acidified and brought to a final volume of 250 mL. 25.00 mL of the solution was transferred, the pH was adjusted, and titrated to determine the volume of EDTA consumed. = 12.1 mL. Calculate the mass fraction of PbSO4: (The error from the theoretical value of 61.36% is +0.99%).

[0054] 3. Determination of Pb content Take another 3.0000g sample and proceed according to step 5 of the invention. After cooling in an ice bath, add 20mL of 50% HNO3 and react precisely at 25°C for 15 minutes. After filtration and washing, bring the filtrate to a final volume of 250mL. Transfer 50.00mL of the solution, adjust the pH, and titrate, consuming the volume of EDTA. = 1.38 mL. Calculate the mass fraction of metallic Pb: (The error from the theoretical value of 2.86% is 0.61%).

[0055] 4. Determination of PbO2 content The residue after Pb determination was processed according to step 6 of the invention. 5 mL of 50% HNO3 and 50 mL of 5% ascorbic acid solution were added, and the mixture was sonicated at 40°C and 200W for 10 minutes. After the reaction was complete, the mixture was filtered, the pH was adjusted, and then directly titrated, consuming the required volume of EDTA. = 5.6 mL. Calculate the mass fraction of PbO2: (The error is 0.78% compared to the theoretical value of 21.22%).

[0056] Results analysis: This embodiment measures the content of a pure substance mixture with known precise concentrations, and the total concentration is calculated as 14.93% + 60.37% + 2.25% + 22.00% = 99.55%. The result has an error of 0.55% compared to the theoretical value, demonstrating a high degree of agreement between the measured result and the theoretical value (error <1%). This fully proves that the detection method provided by this invention has extremely high accuracy and reliability. In the continuous determination of PbO, PbSO4, Pb, and PbO2, this method exhibits minimal systematic error and can achieve precise quantification of the content of various lead compounds.

[0057] Example 5: The effect of ultrasound-assisted extraction on PbO content determination results (comparative experiment) 1. Sample preparation and EDTA calibration This embodiment uses the same homogeneous lead paste sample prepared in the same batch as Example 3 to ensure comparability. 3.0510 g of this dried lead paste sample was accurately weighed and recorded as follows: Place it in a 300mL beaker.

[0058] The preparation and standardization process of the EDTA standard solution was exactly the same as in Example 3. The pre-calibrated concentrations c=0.05019 mol / L and the corresponding titers were directly used: T1=0.01120 g / mL, T2=0.01522 g / mL, T3=0.01040 g / mL, T4=0.01200 g / mL.

[0059] 2. PbO content determination (ultrasound procedure omitted) Add 60 mL of 5 wt% formic acid solution to the beaker containing the sample. Place the beaker in a 40°C constant temperature water bath and stir magnetically for 10 minutes (ovenous assistance omitted). After the reaction is complete, filter and wash as in Example 3, and bring the filtrate to a final volume of 250 mL. Transfer 50 mL of the filtrate, adjust the pH to 5.5, add buffer and indicator, and titrate with EDTA to a bright yellow endpoint, consuming the required volume of EDTA. =6.50 mL. Calculate the PbO mass fraction:

[0060] Compared with the PbO content (14.02%) measured using ultrasound assistance in Example 3, the PbO content (11.92%) measured in this comparative example after omitting ultrasound was significantly lower, with an absolute deviation of -2.10% and a relative error as high as -15.0%. This result demonstrates that omitting the ultrasound assistance step significantly reduces the extraction efficiency of PbO by formic acid, and the reaction time of 10 minutes did not allow PbO to completely dissolve, thus introducing a large negative error.

[0061] Example 6: The effect of ultrasound-assisted treatment on the determination of lead sulfate (PbSO4) content (comparative experiment) 1. Samples, reagents, and titer This comparative experiment used the same homogeneous lead paste sample prepared in the same batch as Example 3 (the residue after PbO determination in Example 5), and employed the exact same EDTA standard solution (c=0.05019 mol / L) and titer (T2=0.01522 g / mL) to ensure that all differences stemmed solely from the omission of ultrasonic assistance in the PbSO2 determination step.

[0062] 2. Determination of lead sulfate (PbSO4) content (ultrasonic procedure omitted) The residue obtained after PbO determination was transferred to a dry, clean 300 mL beaker. 150 mL of 25 wt% ammonium carbonate solution was added, and the beaker was placed in a 40°C constant temperature water bath with magnetic stirring for 60 minutes (the ultrasonic-assisted step was omitted, and the reaction time was extended to 60 minutes to ensure complete reaction). After the reaction was complete, the solution was filtered, washed (tested for lead ions with Na₂S until no lead ions were found), acidified, and diluted to 250 mL in the same manner as in Example 3. 25.00 mL of the solution was transferred, the pH was adjusted to 5.5, and titration was performed, consuming the required volume of EDTA. =10.95 mL. Calculate the mass fraction of PbSO4:

[0063] Omitting the ultrasonic-assisted step, even with the reaction time extended to 60 minutes, resulted in a PbSO4 content of 54.62%, a significant absolute deviation (relative error -11.6%) compared to the accurate result (60.96%) in Example 3. This result confirms that omitting ultrasonic assistance significantly reduces the conversion and dissolution efficiency of lead sulfate (PbSO4) in ammonium carbonate solution. The reaction between ammonium carbonate and PbSO4 ((NH4)2CO3 + PbSO4 → PbCO3 + (NH4)2SO4) is a solid-liquid multiphase reaction, the rate of which is limited by the mass transfer process of reactants on the surface of solid particles. The ultrasonic cavitation effect can greatly enhance mass transfer, break up particles, and renew the surface, thus enabling the reaction to proceed rapidly and completely within 10 minutes. Omitting ultrasound and relying solely on magnetic stirring results in low mass transfer efficiency, leading to a large amount of PbSO4 remaining unconverted and undissolved even within a longer reaction time (60 minutes), thus introducing a significant negative error.

[0064] This comparative experiment powerfully demonstrates from the opposite perspective that the ultrasonic-assisted treatment introduced in step 3 of this invention is a key technical means to ensure the rapid and complete conversion of PbSO4. It not only significantly reduces the reaction time from 60 minutes to 10 minutes, but more importantly, it guarantees the completeness of the reaction, thereby ensuring the accuracy of the measurement results.

[0065] Example 7: Effects of reaction temperature and time on the determination of metallic lead (Pb) content (comparative experiment) 1. Samples, reagents, and titer This embodiment and Example 3 used the same homogeneous lead paste sample prepared in the same batch, and employed the exact same EDTA standard solution (c=0.05019 mol / L) and titer (T3=0.01040 g / mL) to ensure that all differences stemmed solely from changes in the Pb determination procedure.

[0066] 2. Determination of metallic lead (Pb) content (by varying reaction temperature and time) Accurately weigh 3.0015 g of lead paste sample from the same source as that used in the Pb determination in Example 6.

[0067] The key change was replacing "ice bath cooling" and "reaction at 25°C for 15 minutes" with "reaction in a 35°C water bath for 30 minutes." The remaining steps (addition of 20 mL of 50% HNO3, filtration, washing, volume adjustment, separation, titration, etc.) remained completely consistent with Example 3. Measurements were performed under these modified conditions, and the volume of EDTA consumed was recorded. =2.95 mL. Calculate the mass fraction of metallic Pb: .

[0068] When the reaction temperature was increased to 35°C and the reaction time was extended to 30 minutes, the measured "metallic lead" content reached 5.11%, which, compared to the true value of 1.91% in Example 3, resulted in an absolute deviation of +3.20% (relative error +168%), indicating a severely skewed and completely distorted result. This result confirms that increasing the temperature and extending the reaction time causes the lead dioxide (PbO2) in the sample to be partially dissolved by nitric acid. Nitric acid, which should only react with metallic lead, also attacked PbO2 (Pb) under more intense conditions. 4+ ), reduce it to Pb 2+ And dissolve (reaction: PbO2 + 4HNO3 → Pb(NO3)2 + 2H2O + 2NO2↑). This additional Pb produced 2+ The Pb content is included in the subsequent titration, which leads to an overestimation of the Pb content and will inevitably result in an underestimation of the PbO2 content in subsequent measurements.

[0069] This comparative experiment powerfully demonstrates from the opposite perspective that the selective dissolution of metallic lead achieved in step 4 of this invention through "ice-water bath cooling" and "strict control of reaction time (15 minutes)" is another indispensable core technical feature ensuring the accuracy of the entire continuous measurement process. These conditions strictly limit the redox activity of nitric acid, effectively inhibiting its dissolution of PbO2 and ensuring the specificity and accuracy of the measurement results for each component.

[0070] Example 8: The Influence of Different Conditions on the Determination of Lead Dioxide (PbO2) Content (Comparative Experiment Series) 1. Samples, reagents, and titer This series of comparative experiments used the same homogeneous lead paste sample (the residue retained after Pb determination) prepared in the same batch as Example 3, and employed the exact same EDTA standard solution (c=0.05019 mol / L) and titer (T4=0.01200 g / mL) to ensure that all differences stemmed solely from changes in the PbO2 determination procedure. 3.0000 g of this residue was weighed for each comparative example.

[0071] 2. Comparison of experimental design and results Comparative Experiment 8a: Ultrasound-assisted treatment omitted Modified conditions: Except for omitting the sonication step, all other steps (reagent types, amounts, reaction temperature, and time) were exactly the same as in Example 3. That is, after adding 5 mL of 50% HNO3 and 50 mL of 5wt% ascorbic acid solution, the mixture was magnetically stirred in a 40°C water bath for 30 minutes.

[0072] Measurement results: Volume of EDTA consumed =4.1 mL. Calculate the mass fraction of PbO2.

[0073] Deviation from Example 3: The absolute deviation from the result of Example 3 (21.59%) was -5.19%. This indicates that omitting ultrasound significantly reduced the reaction rate, and even over a longer period (30 min), the dissolution of PbO2 was still insufficient, resulting in a severely low measurement result.

[0074] Comparative Experiment 8b: Ascorbic acid alone (without nitric acid) Modified conditions: No nitric acid was added. Following Example 3, using 5 mL of 50% HNO3 (approximately 0.116 mol HNO3) and 50 mL of 5wt% ascorbic acid solution (approximately 0.014 mol ascorbic acid), to ensure comparable total reducing power, the volume of the 5wt% ascorbic acid solution was increased to approximately 450 mL (approximately 0.127 mol ascorbic acid), and an additional amount of water was added to maintain a total volume similar to that of Example 3. The mixture was sonicated at 40°C and 200W for 10 minutes.

[0075] Measurement results: Volume of EDTA consumed =3.8 mL.

[0076] Calculate the mass fraction of PbO2: W(PbO2) = (0.01200 × 3.8) / 3.0000 × 100% = 15.20%.

[0077]

[0078] Deviation from Example 3: The results were significantly lower (deviation -6.39%). Despite using sufficient reducing agent, the lack of an acidic environment (H+) provided by nitric acid resulted in an extremely slow reduction rate of ascorbic acid, failing to effectively reduce and dissolve PbO2 within 10 minutes. This demonstrates the crucial role of an acidic environment in the reduction reaction.

[0079] Comparative Experiment 8c: Nitric acid alone (to remove ascorbic acid) Changes to the conditions: Ascorbic acid was not added. To ensure the acidity was similar to that of Example 3, the amount of 50% HNO3 was increased to 55 mL (providing an HNO3 concentration approximately equivalent to "5 mL HNO3 + 50 mL 5wt% ascorbic acid solution" in Example 3). + (Concentration). Ultrasonic treatment was performed at 40℃ and 200W for 10 minutes.

[0080] Measurement results: Volume of EDTA consumed =0.9 mL.

[0081] Calculate the mass fraction of PbO2:

[0082] Deviation from Example 3: The result is extremely low (deviation -17.99%). Although nitric acid alone can slowly dissolve PbO2 at low temperatures (PbO2 + 4HNO3 → Pb(NO3)2 + 2H2O + 2NO2↑), the reaction rate is slow and incomplete. Furthermore, the generated NO2 gas encapsulates the sample, further hindering the reaction. This result demonstrates that without an effective reducing agent (ascorbic acid), PbO2 is difficult to convert rapidly and quantitatively to Pb. 2+ .

[0083] The results of Example 3 and the three comparative examples are summarized in the following table:

[0084] The results of the three comparative studies were significantly lower than those of Example 3, confirming that the synergistic effect of ultrasound assistance, an acidic environment (nitric acid), and a strong reducing agent (ascorbic acid) is indispensable for the accurate and rapid determination of PbO2 content.

[0085] This series of comparative experiments powerfully demonstrates from the opposite perspective that the "nitric acid + ascorbic acid + ultrasound" system used in the PbO2 determination step of this invention is an ingeniously designed, efficient, and necessary combination. Any attempt to omit or alter any of these elements will lead to serious distortion of the measurement results, thus further highlighting the rationality and superiority of the technical solution of this invention.

[0086] In all the above implementation cases, all reported experimental data are the average of three independent parallel experimental results.

[0087] In summary, this invention discloses a method for detecting the composition of lead paste from waste lead-acid batteries. This invention relates to the field of waste battery resource utilization and testing technology. The method includes the preparation and calibration of EDTA standard solution, and the continuous determination of the content of lead oxide, lead sulfate, metallic lead, and lead dioxide in the lead paste. By using reagents such as formic acid and ammonium carbonate combined with ultrasound-assisted extraction technology, the dissolution efficiency is significantly improved, and the reaction time is greatly shortened. By precisely controlling the low-temperature conditions and reaction time, selective dissolution of metallic lead is achieved, effectively avoiding interference from lead dioxide. This invention significantly reduces the amount of strong acid used and the emission of toxic waste by optimizing the reagent system and introducing ultrasound-assisted extraction. While ensuring the accuracy of the results, it is also more environmentally friendly. The method has a clear operation process, good reproducibility, and is suitable for rapid and reliable determination of lead paste composition in industrial recycling scenarios.

[0088] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A method for detecting the composition of lead paste from waste lead-acid batteries, characterized in that, The specific steps of the detection method are as follows: Step S1: Preparation and standardization of EDTA standard solution Prepare a disodium EDTA solution and use lead nitrate as a reference. In an acetate-sodium acetate buffer system at pH 5.5, use xylenol orange as an indicator to standardize the solution and calculate the actual concentration of the EDTA standard solution and the titer of each target component. Step S2: Determination of lead oxide (PbO) content Accurately weigh the lead paste sample, use formic acid solution as the extractant, dissolve PbO under ultrasonic assistance and heating conditions, filter, take a portion of the test solution to adjust the pH value of the filtrate, use xylenol orange as an indicator, titrate with the EDTA standard solution obtained in step S1, and calculate the PbO content based on the volume of EDTA consumed. Step S3: Determination of lead sulfate (PbSO4) content The residue obtained in step S2 was converted and dissolved using ammonium carbonate solution as a conversion agent under ultrasonic assistance. After filtration, the filtrate was acidified, and a portion of the test solution was taken to adjust the pH value. Using xylenol orange as an indicator, the EDTA standard solution obtained in step S1 was titrated, and the PbSO4 content was calculated based on the volume of EDTA consumed. Step S4: Determination of lead (Pb) content The residue obtained in step S2 was subjected to selective dissolution of metallic lead with nitric acid solution under low temperature conditions. The reaction time and temperature were strictly controlled to avoid dissolution of lead dioxide. After filtration, a portion of the filtrate was taken to adjust the pH value. Using xylenol orange as an indicator, the solution was titrated with the EDTA standard solution obtained in step S1. The Pb content was calculated based on the volume of EDTA consumed. Step S5: Determination of lead dioxide (PbO2) content The residue obtained in step S4 was dissolved in nitric acid and ascorbic acid solution as reducing solvents under ultrasonic assistance to dissolve PbO2. The pH of the solution after the reaction was adjusted, and the solution was titrated with the EDTA standard solution obtained in step S1 using xylenol orange as an indicator. The PbO2 content was calculated based on the volume of EDTA consumed.

2. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 1, characterized in that, The specific steps for standardizing the EDTA standard solution in step S1 are as follows: Weigh the reference lead nitrate, dissolve it in water and boil it to remove nitrogen oxides. After cooling, add ammonia water dropwise until a precipitate is formed, then add nitric acid dropwise until the precipitate just dissolves to form a buffer system. Add acetate-sodium acetate buffer solution and xylenol orange indicator. Titrate with the EDTA solution to be standardized until the solution changes from purple-red to bright yellow and does not fade for 30 seconds. Calculate the accurate concentration of EDTA and further calculate the titer T1, T2, T3, and T4 for PbO, PbSO4, Pb, and PbO2.

3. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 1, characterized in that, The extractant in step S2 is a 5% formic acid solution. The dissolution process is carried out in a 40°C water bath with the aid of ultrasound. The ultrasound power is 200W and the ultrasound time is 10 minutes. The pH value is 5.

5.

4. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 1, characterized in that, In step S3, the conversion agent is a 25% ammonium carbonate solution. The conversion process is carried out in a 40°C water bath with the aid of ultrasound. The ultrasound power is 200W and the ultrasound time is 10 minutes. After filtration, the washing solution is tested with sodium sulfide solution until there is no lead ion reaction. The filtrate is acidified with formic acid, and the pH value is 5.

5.

5. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 1, characterized in that, The selective dissolution conditions for metallic lead in step S4 are as follows: after cooling the residue in an ice-water bath, add a 50% nitric acid solution and stir the reaction for 15 minutes at room temperature ≤ 25°C. After the reaction is completed, immediately wash and filter with a cold 1% nitric acid solution. The pH value is 5.

5.

6. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 1, characterized in that, In step S5, the reducing solvent is a mixture of nitric acid and ascorbic acid solution. The dissolution process is carried out in a 40°C water bath with the aid of ultrasound. The ultrasound power is 200W and the ultrasound time is 10 minutes. The pH value is 5.

5.

7. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 5, characterized in that, The nitric acid concentration during the dissolution process is 50%; the nitric acid concentration during the washing process is 1%.

8. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 6, characterized in that, The nitric acid has a mass concentration of 50%; the ascorbic acid has a mass concentration of 5%.

9. The method for detecting the composition of lead paste from waste lead-acid batteries as described in claim 1, characterized in that, In steps S2, S3, S4 and S5, the pH value of the solution before titration is adjusted to 5.5 using sodium hydroxide solution or ammonia, and an acetate-sodium acetate buffer solution is added to maintain the stability of the system.

10. A method for detecting the composition of lead paste from waste lead-acid batteries as described in any one of claims 1-9, characterized in that, The detection method is used for rapid quantitative detection of lead paste components in the resource recycling and treatment process of waste lead-acid batteries.

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