Method for detecting content of chloride ions in mixed acid-based all-vanadium electrolyte

Abstract

The application discloses a detection method of the content of chloride ions in mixed acid-based all-vanadium electrolyte, and relates to the field of batteries. The detection method comprises the following steps: providing a to-be-detected liquid, adding vanadium ion complexing agent, potassium permanganate and ascorbic acid into the to-be-detected liquid in sequence to obtain a pretreated liquid; adjusting the pH value of the pretreated liquid to be 6.5-10.5, adding a titration indicator, adding a silver nitrate standard solution dropwise, carrying out a titration reaction, and obtaining the volume V of the silver nitrate standard solution consumed; and calculating the content of chloride ions in the to-be-detected liquid according to the obtained volume V. In the technical scheme, the vanadium ion complexing agent is first added into the to-be-detected liquid, and then the vanadium ions in the to-be-detected liquid can be effectively and stably complexed in cooperation with potassium permanganate, so that vanadate is avoided from appearing when the pH value is adjusted subsequently, and thus the interference of vanadium ions on the detection of chloride ions is avoided, and the accuracy of the detection result of the content of chloride ions is ensured.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a method for detecting the chloride ion content in a mixed acid-based vanadium electrolyte. Background Technology

[0002] Vanadium redox flow batteries, as a large-scale electrochemical energy storage technology, are evolving towards higher energy density and wider temperature windows. To this end, the industry has recently proposed a "mixed-acid" electrolyte system, which introduces a second acid, such as hydrochloric acid (HCl aqueous solution), into the traditional sulfuric acid-based electrolyte. The mixed-acid system can significantly improve the solubility of vanadium ions and the stability of the electrolyte, and is one of the key technological routes for next-generation high-performance flow batteries.

[0003] However, accurate monitoring of chloride ion concentration in the electrolyte is crucial when using hydrochloric acid and chlorine-containing raw materials. This is because: firstly, to achieve the synergistic effect of mixed acids, the ratio of sulfate to chloride ions must be precisely controlled; secondly, if the chloride ion concentration is too low, the advantages of mixed acids cannot be realized; if the chloride ion concentration is too high, it will exacerbate corrosion of critical components (such as electrodes and current collectors). Currently, the industry commonly uses silver nitrate titration, ion chromatography, and potentiometric titration to detect the chloride ion concentration in mixed acid-based vanadium-containing electrolytes.

[0004] In the silver nitrate titration method, potassium chromate indicator is added to the system. After the chloride ions react with the silver ions, the silver ions react with the chromate ions to form a brick-red / reddish-brown precipitate, which is the titration endpoint. The chloride ion content in the system is calculated from the volume consumed by the silver nitrate titration. However, during the titration process, vanadate ions in the system react with the silver ions to form a brown silver vanadate precipitate. This causes silver vanadate to precipitate before all the chloride ions have reacted with the silver ions, prematurely consuming the silver nitrate titrant, affecting the accuracy of the test results, and making the endpoint color change less sharp (from yellow to brownish-red or directly the appearance of a brown precipitate), making it difficult to judge.

[0005] Ion chromatography typically uses a conductivity detector. If the system contains a high concentration of vanadium ions (especially polyvalent cations), after the sample enters the column, the various ions will undergo exchange reactions with the functional groups on the column packing material and be retained. However, the separation capacity (column capacity) of an ion chromatography column is limited. When high concentrations of vanadium ions (whether V³⁺, V...) are present... 4 ⁺ or V 5When chloride ions (⁺, all of which are polyvalent cations) enter the chromatographic column, they occupy a large number of exchange sites, causing the retention time of chloride ions to become unstable, either earlier or later, leading to inaccurate qualitative analysis. The chromatographic peak of chloride ions may become both broad and short (broadening), or exhibit abnormal shapes such as tailing or forward extension. Peak shape distortion directly results in the peak area or peak height used for quantification failing to accurately reflect the chloride ion content. Peak broadening makes area calculation difficult, while a decrease in peak height directly leads to negative errors.

[0006] If potentiometric titration is used, high concentrations of chloride ions will consume a large amount of silver nitrate titrant, resulting in a very weak or even undetectable titration endpoint jump for chloride ions. This leads to a sharp decrease in sensitivity and selectivity, affecting the accuracy of chloride ion detection. Summary of the Invention

[0007] The main objective of this application is to propose a method for detecting chloride ion content in mixed acid-based vanadium electrolyte, aiming to solve the problem of inaccurate detection results of existing detection methods for chloride ion content in mixed acid-based vanadium electrolyte.

[0008] Firstly, this application provides a method for detecting chloride ion content in a mixed acid-based vanadium electrolyte, comprising the following steps:

[0009] S1. Provide the test solution, and add vanadium ion complexing agent, potassium permanganate and ascorbic acid to the test solution in sequence to obtain the pretreatment solution;

[0010] S2. Adjust the pH of the pretreated solution obtained in step S1 to 6.5~10.5, add a titration indicator, add silver nitrate standard solution dropwise, and carry out the titration reaction until the silver nitrate standard solution reacts with the titration indicator to form a colored precipitate. The titration is then completed, and the volume V consumed by the silver nitrate standard solution is obtained.

[0011] S3. Calculate the chloride ion content in the test solution based on the volume V obtained in step S2.

[0012] In step S1, the molar ratio of vanadium ions to vanadium ion complexing agent in the test solution is 1:1, and the molar ratio of vanadium ion complexing agent, potassium permanganate and ascorbic acid is (0.5~1.5):(0.1~0.2):(0.3~0.6).

[0013] By employing the above technical solution, a vanadium ion complexing agent is first added to the test solution to complex most of the vanadium ions. A small portion of the vanadium ions remain in a free state. Potassium permanganate is then added to oxidize these free, low-valence vanadium ions into high-valence vanadium ions, promoting their complexation with the vanadium ion complexing agent and achieving stable complexation of vanadium ions in the test solution. This avoids the formation of vanadate ions during subsequent pH adjustment, thus preventing interference with chloride ion detection. Furthermore, the amount of potassium permanganate used is low, meaning the amount of manganese ions introduced is low and will not interfere with subsequent titration detection. Ascorbic acid is then added to eliminate the purple-developing effect of potassium permanganate, resulting in a colorless, clear, and transparent solution. This avoids misjudgment of the titration endpoint due to solution color, ensuring the accuracy of the titration detection.

[0014] If potassium permanganate is added first, followed by a vanadium ion complexing agent, all low-valence vanadium ions in the system will be in a free state. If the amount of potassium permanganate is insufficient, it cannot adequately oxidize these low-valence vanadium ions. Consequently, when the vanadium ion complexing agent is added, only a majority of the vanadium ions will be complexed, leaving some in a free state. At this point, there are almost no high-valence permanganate ions with oxidizing power, affecting the final vanadium ion complexing effect. During subsequent pH adjustment, the free vanadium ions can form vanadate ions, which then react with silver ions, affecting the accuracy of the titration results. If the amount of potassium permanganate is excessive, it can adequately oxidize the low-valence vanadium ions to high-valence vanadium ions. Adding a vanadium ion complexing agent then promotes vanadium ion complexation. However, excessive potassium permanganate means that too much ascorbic acid needs to be added to counteract its purple-developing effect, leading to higher raw material consumption. Furthermore, the introduction of a large amount of manganese ions can easily lead to the formation of manganese-containing precipitates during subsequent pH adjustments, interfering with the determination of the titration endpoint and affecting the accuracy of the test results.

[0015] After stabilizing the vanadium ions in the system, the pH of the resulting pretreatment solution is adjusted to 6.5–10.5 to ensure the effectiveness of subsequent titration and color development. Regarding the pH adjustment range, for example, when using potassium chromate indicator solution as the titration indicator, if the pH is too low, in an acidic medium, chromate ions will react with hydrogen ions to form acidic chromate ions, reducing the concentration of chromate ions in the solution. This will delay or even prevent the precipitation of silver chromate, affecting the accuracy of the titration results. Conversely, if the pH is too high, in a strongly alkaline medium, silver ions easily form silver oxide precipitate, also affecting the accuracy of the titration results.

[0016] After adjusting the pH, a titration indicator is added, followed by the addition of silver nitrate standard solution. Ag⁺ preferentially reacts with Cl⁻ to form a white AgCl precipitate. At this point, the concentration of Ag⁺ in the solution is low, insufficient to reach the solubility product of Ag₂CrO₄, so no color change is observed. When the chloride ions in the system are completely consumed, further addition of silver nitrate causes a rapid increase in the Ag⁺ concentration, reaching the solubility product of Ag₂CrO₄. The resulting Ag₂CrO₄ precipitate turns brick red / reddish-brown, marking the endpoint of the titration and the end of the titration reaction. The volume of silver nitrate standard solution consumed is known, and since the concentration of the silver nitrate standard solution is known, the chloride ion content in the test solution can be calculated.

[0017] It is understandable that "the molar amount of vanadium ions in the test solution" refers to the sum of the molar amounts of vanadium ions of different valences in the test solution. For example, if the test solution contains trivalent and tetravalent vanadium ions, then the molar amount of vanadium ions in the test solution is the sum of the molar amounts of trivalent and tetravalent vanadium ions.

[0018] Optionally, in step S1, a vanadium ion complexing agent is added to the test solution, stirred for 4-8 minutes, potassium permanganate is added, stirred for 5-15 minutes, ascorbic acid is added, and stirred until a colorless and clear pretreatment solution is obtained.

[0019] By adopting the above technical solution, adding the vanadium ion complexing agent and then stirring helps the vanadium ion complexing agent to dissolve quickly and completely, thus ensuring the subsequent complexing effect of vanadium ions. Adding potassium permanganate and stirring for a slightly longer time than when adding the vanadium ion complexing agent can not only quickly promote the dissolution of potassium permanganate, but also more fully oxidize a small portion of the uncomplexed low-valence vanadium ions, thereby effectively promoting the complexation of vanadium ions.

[0020] Optionally, in step S1, the temperature of the test solution is controlled at 35~50℃, a vanadium ion complexing agent is added to the test solution, and the mixture is stirred for 4~5 minutes. The temperature of the test solution is then reduced to 25~30℃ at a cooling rate of 1~5℃ / min. Potassium permanganate is added, and the mixture is stirred for 5~10 minutes. Ascorbic acid is then added.

[0021] By employing the above technical solution, controlling the temperature of the test solution at 35-50℃ accelerates ion diffusion / migration, promoting rapid and sufficient complexation of vanadium ions by the vanadium ion complexing agent. Subsequently, cooling is performed at a rate of 1-5℃ / min to maintain the stability of the complexation system and prevent imbalance caused by excessively slow or rapid cooling. Lowering the temperature to 25-30℃ ensures the activity of potassium permanganate and ascorbic acid, ultimately guaranteeing sufficient complexation of vanadium ions and a clear, transparent system, thus improving the accuracy of subsequent titration results.

[0022] Optionally, in step S1, the molar ratio of vanadium ion complexing agent to potassium permanganate is 1:(0.15~0.20).

[0023] By adopting the above technical solution, the dosage ratio of vanadium ion complexing agent and potassium permanganate is further optimized to ensure that vanadium ions are fully complexed.

[0024] Optionally, in step S1, the vanadium ion complexing agent is selected from at least one of disodium ethylenediaminetetraacetate, citric acid, and hydroxyethylethylenediaminetriacetic acid.

[0025] By adopting the above technical solution and using a specific vanadium ion complexing agent, the complexing effect of vanadium ions can be guaranteed, and the impact on the subsequent titration reaction can be avoided.

[0026] Optionally, in step S2, the pH value of the pretreatment solution obtained in step S1 is adjusted to 7.5~8.5.

[0027] Preferably, in step S2, the pH value of the pretreatment solution obtained in step S1 is adjusted to 8.0.

[0028] Optionally, in step S1, a test solution is provided and diluted to obtain a diluted solution. Vanadium ion complexing agent, potassium permanganate, and ascorbic acid are added sequentially to the diluted solution to obtain a pretreatment solution. In step S2, a volume V0 of the pretreatment solution is taken, and the pH value of the pretreatment solution is adjusted to 6.5~10.5 using sodium hydroxide solution and nitric acid solution.

[0029] By adopting the above technical solution and diluting the test solution, the amount of vanadium ion complexing agent, potassium permanganate, and ascorbic acid can be effectively reduced, thus lowering the cost.

[0030] Optionally, in step S2, the volume of the titration indicator added is V1, and V0:V1 = (20~30):(1~3).

[0031] By adopting the above technical solution, the titration indicator, as an indicator of the titration reaction, can better display the endpoint of the titration reaction by controlling the volume ratio of the titration indicator to the diluent.

[0032] Optionally, in step S3, the chloride ion content in the test solution is ρ(Cl... - ), ρ(Cl - The calculation formula for ) is as follows:

[0033] ρ(Cl) - = [C×V×M / V0]×1000×N,

[0034] In the formula, C is the molar concentration of the silver nitrate standard solution, in mol / L; V is in mL; M is the molar mass of chloride ions, in g / mol; V0 is in mL; N is the ratio of the volume of the diluent to the volume of the test solution; ρ(Cl - The unit is mg / L.

[0035] Optionally, in step S2, the titration indicator is a 5wt% potassium chromate indicator solution, and the concentration of the silver nitrate standard solution is 0.01~1mol / L.

[0036] In summary, this application includes at least one of the following beneficial technical effects:

[0037] 1. In the technical solution of this application, a vanadium ion complexing agent is first added to the test solution, and then, with the synergy of potassium permanganate, the vanadium ions in the test solution can be effectively and stably complexed, avoiding the formation of vanadate ions when adjusting the pH later, thereby avoiding interference of vanadium ions with the detection of chloride ion content and ensuring the accuracy of chloride ion content detection results.

[0038] 2. The amount of vanadium ion complexing agent was controlled to be the same as the amount of vanadium ions in the test solution, and a lower amount of potassium permanganate and ascorbic acid was used to avoid excessive reagent dosage from interfering with the stability of the system and to ensure the accuracy of chloride ion content detection results.

[0039] 3. After stabilizing the vanadium ions in the system by complexation, adjust the pH of the resulting pretreatment solution to 6.5~10.5 to avoid the formation of acidic chromate ions in the system due to excessively low pH, or the formation of silver oxide precipitate due to excessively high pH. Controlling the pH within a suitable range ensures the accuracy of the titration results. Detailed Implementation

[0040] The present application will be further described in detail below with reference to the embodiments. Example 1

[0041] A method for detecting chloride ion content in a mixed acid-based vanadium-based electrolyte, comprising the following steps:

[0042] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at 200 rpm for 6 min. Add 0.004 mol of potassium permanganate and stir at 200 rpm for 8 min. Add 0.012 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at 200 rpm until a colorless and clear pretreatment solution is obtained.

[0043] S2. Pipette 25.00 mL (V0) of the pretreatment solution obtained in step S1 into a 250 mL Erlenmeyer flask. Adjust the pH of the pretreatment solution obtained in step S1 to 8.0 using 0.8 mol / L sodium hydroxide solution and 20 wt% nitric acid solution. Add 2 mL of 5 wt% potassium chromate indicator solution (5 wt% potassium chromate, 95 wt% deionized water) and shake well. Use a brown acid burette to hold 0.1 mol / L silver nitrate standard solution and record the initial volume reading V. 初 Begin titration by continuously adding the solution while shaking the conical flask until a slightly reddish-brown precipitate appears in the solution and does not disappear after shaking. This is the titration endpoint. Immediately record the titration volume reading V. 终 , by V 初 and V 终 The difference was used to calculate the volume of silver nitrate standard solution consumed, V = 9.89 mL.

[0044] S3. Calculate the chloride ion content in the test solution using the following formula:

[0045] ρ(Cl) - = [C×V×M / V0]×1000×N,

[0046] In the formula, C is the molar concentration of the silver nitrate standard solution, in mol / L; V is in mL; M is the molar mass of chloride ions, in g / mol; V0 is in mL; N is the ratio of the volume of the diluent to the volume of the test solution; ρ(Cl - The unit is mg / L.

[0047] Specifically, in this embodiment, C = 0.1 mol / L, V = 9.89 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100. ρ(Cl) was calculated to be... - =140240.2mg / L. Example 2

[0048] This embodiment is based on Embodiment 1, the difference being that the amount of raw materials used in step S1 is different, while the other steps remain the same as in Embodiment 1. Specifically, step S1 of this embodiment is as follows:

[0049] S1: Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at 200 rpm for 6 min. Add 0.002 mol of potassium permanganate and stir at 200 rpm for 8 min. Add 0.006 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at 200 rpm until a colorless and clear pretreatment solution is obtained.

[0050] In this embodiment, C = 0.1 mol / L, V = 9.85 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 1 was used. The calculated ρ(Cl) - =139673mg / L. Example 3

[0051] This embodiment is based on Embodiment 1, the difference being that the amount of raw materials used in step S1 is different, while the other steps remain the same as in Embodiment 1. Specifically, step S1 of this embodiment is as follows:

[0052] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at 200 rpm for 6 min. Add 0.003 mol of potassium permanganate and stir at 200 rpm for 8 min. Add 0.009 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at 200 rpm until a colorless and clear pretreatment solution is obtained.

[0053] In this embodiment, C = 0.1 mol / L, V = 9.9 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 1 was used. The calculated ρ(Cl) - =140382mg / L. Example 4

[0054] This embodiment is based on Embodiment 3, the difference being that in step S2, the pH value of the pretreatment solution is adjusted differently, while the other steps remain the same as in Embodiment 3. Specifically, step S2 of this embodiment is as follows:

[0055] S2. Pipette 25.00 mL (V0) of the pretreatment solution obtained in step S1 and place it in a 250 mL Erlenmeyer flask. Adjust the pH of the pretreatment solution obtained in step S1 to 6.5 using 0.8 mol / L sodium hydroxide solution and 20 wt% nitric acid solution. Add 2 mL of 5 wt% potassium chromate indicator solution (5 wt% potassium chromate, 95 wt% deionized water) and shake well. Use a brown acid burette to hold 0.1 mol / L silver nitrate standard solution and record the initial volume reading V. 初 Begin titration by continuously adding the solution while shaking the conical flask until a slightly reddish-brown precipitate appears in the solution and does not disappear after shaking. This is the titration endpoint. Immediately record the volumetric reading V from the titration tube. 终 , by V 初 and V 终 The difference was used to calculate the volume of silver nitrate standard solution consumed, V = 10.25 mL.

[0056] In this embodiment, C = 0.1 mol / L, V = 10.25 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =145345mg / L. Example 5

[0057] This embodiment is based on Embodiment 3, the difference being that in step S2, the pH value of the pretreatment solution is adjusted differently, while the other steps remain the same as in Embodiment 3. Specifically, step S2 of this embodiment is as follows:

[0058] S2. Pipette 25.00 mL (V0) of the pretreatment solution obtained in step S1 into a 250 mL Erlenmeyer flask. Adjust the pH of the pretreatment solution obtained in step S1 to 10.5 using 0.8 mol / L sodium hydroxide solution and 20 wt% nitric acid solution. Add 2 mL of 5 wt% potassium chromate indicator solution (5 wt% potassium chromate, 95 wt% deionized water) and shake well. Use a brown acid burette to hold 0.1 mol / L silver nitrate standard solution and record the initial volume reading V. 初 Begin titration by continuously adding the solution while shaking the conical flask until a slightly reddish-brown precipitate appears in the solution and does not disappear after shaking. This is the titration endpoint. Immediately record the volumetric reading V from the titration tube. 终 , by V 初 and V 终The difference was used to calculate the volume of silver nitrate standard solution consumed, V = 9.75 mL.

[0059] In this embodiment, C = 0.1 mol / L, V = 9.75 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =138255mg / L. Example 6

[0060] This embodiment is based on Embodiment 3, the difference being that in step S1, heating and cooling operations are performed during the addition of raw materials; other steps remain the same as in Embodiment 3. Specifically, step S1 of this embodiment is as follows:

[0061] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 40℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at a stirring rate of 200 rpm for 4 min. Cool the diluted solution to 25℃ at a cooling rate of 2℃ / min. Add 0.004 mol of potassium permanganate and stir at a stirring rate of 200 rpm for 7 min. Add 0.012 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at a stirring rate of 200 rpm until a colorless and clear pretreatment solution is obtained.

[0062] In this embodiment, C = 0.1 mol / L, V = 10 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =141800mg / L. Example 7

[0063] This embodiment is based on Embodiment 3, the difference being that in step S1, heating and cooling operations are performed during the addition of raw materials; other steps remain the same as in Embodiment 3. Specifically, step S1 of this embodiment is as follows:

[0064] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 50℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at a stirring rate of 200 rpm for 4 min. Cool the diluted solution to 25℃ at a cooling rate of 2℃ / min. Add 0.004 mol of potassium permanganate and stir at a stirring rate of 200 rpm for 7 min. Add 0.012 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at a stirring rate of 200 rpm until a colorless and clear pretreatment solution is obtained.

[0065] In this embodiment, C = 0.1 mol / L, V = 10.05 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =142509mg / L. Comparative Example 1

[0066] This comparative example is based on Example 3, except that the amount of disodium ethylenediaminetetraacetate in step S1 is changed, and potassium permanganate and L-ascorbic acid are not included. The other steps remain the same as in Example 3. Specifically, step S1 of this comparative example is as follows:

[0067] S1. Provide 1 mL of the test solution (a commercially available standard sample with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃, add 0.024 mol of disodium ethylenediaminetetraacetate to the diluted solution, and stir at a stirring speed of 200 rpm for 6 min to obtain a pretreated solution.

[0068] In this embodiment, C = 0.1 mol / L, V = 10.5 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =148890mg / L. Comparative Example 2

[0069] This comparative example is based on Example 3, except that the amounts of potassium permanganate and L-ascorbic acid used in step S1 have changed, while the other steps remain the same as in Example 3. Specifically, step S1 of this comparative example is as follows:

[0070] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at 200 rpm for 6 min. Add 0.007 mol of potassium permanganate and stir at 200 rpm for 8 min. Add 0.021 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at 200 rpm until a colorless and clear pretreatment solution is obtained.

[0071] In this embodiment, C = 0.1 mol / L, V = 9.80 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =138964mg / L. Comparative Example 3

[0072] This comparative example is based on Example 3, except that the amounts of potassium permanganate and L-ascorbic acid used in step S1 have changed, while the other steps remain the same as in Example 3. Specifically, step S1 of this comparative example is as follows:

[0073] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃. Add 0.02 mol of disodium ethylenediaminetetraacetate to the diluted solution and stir at 200 rpm for 6 min. Add 0.001 mol of potassium permanganate and stir at 200 rpm for 8 min. Add 0.003 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at 200 rpm until a colorless and clear pretreatment solution is obtained.

[0074] In this embodiment, C = 0.1 mol / L, V = 9.70 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =137546mg / L. Comparative Example 4

[0075] This comparative example is based on Example 3, except that the order in which disodium ethylenediaminetetraacetate and potassium permanganate are added in step S1 has been adjusted; the other steps remain the same as in Example 3. Specifically, step S1 of this comparative example is as follows:

[0076] S1. Provide 1 mL of the test solution (commercially available standard sample, with a vanadium ion concentration of 2 mol / L and a chloride ion content of 141800 mg / L). Dilute the test solution to 100 mL with deionized water to obtain a diluted solution. Control the temperature of the diluted solution at 25℃. Add 0.004 mol of potassium permanganate to the diluted solution and stir at 200 rpm for 6 min. Add 0.02 mol of disodium ethylenediaminetetraacetate and stir at 200 rpm for 8 min. Add 0.012 mol of L-ascorbic acid (chemical formula C6H8O6) and stir at 200 rpm until a colorless and clear pretreatment solution is obtained.

[0077] In this embodiment, C = 0.1 mol / L, V = 9.35 mL, M = 35.45 g / mol, V0 = 25 mL, N = 100, and the same calculation formula as in Example 3 was used. The calculated ρ(Cl) - =132583mg / L.

[0078] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the principles of this application should be covered within the scope of protection of this application.

Claims

1. A method for detecting the content of chloride ions in a mixed acid-based all-vanadium electrolyte, characterized in that, The method comprises the following steps: S1, providing a to-be-tested liquid, adding a vanadium ion complexing agent, potassium permanganate and ascorbic acid into the to-be-tested liquid in sequence to obtain a pretreated liquid; S2, adjusting the pH value of the pretreated liquid obtained in the step S1 to be 6.5-10.5, adding a titration indicator, and adding a silver nitrate standard solution dropwise to perform a titration reaction until the silver nitrate standard solution reacts with the titration indicator to generate colored precipitates, the titration is ended, and the volume V of the silver nitrate standard solution consumed is obtained; S3, calculating the content of the chloride ion in the to-be-tested liquid according to the volume V obtained in the step S2; In the step S1, the molar ratio of the vanadium ion in the to-be-tested liquid to the vanadium ion complexing agent is 1:1, and the molar ratio of the vanadium ion complexing agent, the potassium permanganate and the ascorbic acid is (0.5-1.5):(0.1-0.2):(0.3-0.6). In the step S1, the vanadium ion complexing agent is added into the to-be-tested liquid, stirred for 4-8 min, the potassium permanganate is added, stirred for 5-15 min, and the ascorbic acid is added and stirred until the pretreated liquid is colorless and clear.

2. The method for detecting the content of chloride ions in a mixed acid-based all-vanadium electrolyte according to claim 1, characterized in that, In the step S1, the temperature of the to-be-tested liquid is controlled to be 35-50 ℃, the vanadium ion complexing agent is added into the to-be-tested liquid, stirred for 4-5 min, the temperature of the to-be-tested liquid is reduced to 25-30 ℃ at a cooling rate of 1-5 ℃ / min, the potassium permanganate is added, stirred for 5-10 min, and the ascorbic acid is added.

3. The method according to claim 1, wherein the method is characterized by, In the step S1, the molar ratio of the vanadium ion complexing agent to the potassium permanganate is 1:(0.15-0.20).

4. The method according to claim 1, wherein the method is characterized by, In the step S1, the vanadium ion complexing agent is disodium ethylenediaminetetraacetate.

5. The method according to claim 1, wherein the method is characterized by, In the step S2, the pH value of the pretreated liquid obtained in the step S1 is adjusted to be 7.5-8.

5.

6. The method of claim 1, wherein the mixed acid-based vanadium electrolyte is a mixed acid-based all-vanadium electrolyte. In the step S1, the to-be-tested liquid is provided and diluted to obtain a diluted liquid, the vanadium ion complexing agent, the potassium permanganate and the ascorbic acid are added into the diluted liquid in sequence to obtain the pretreated liquid; and in the step S2, the volume V0 of the pretreated liquid is taken, and the pH value of the pretreated liquid is adjusted by using a sodium hydroxide solution and a nitric acid solution.

7. The method according to claim 6, wherein the method is characterized by, In the step S2, the volume of the titration indicator added is V1, and V0:V1=(20-30):(1-3).

8. The method according to claim 6, wherein the method is characterized by, The content of the chloride ion in the liquid to be measured in the step S3 is ρ(Cl - ), and the calculation formula of ρ(Cl - ) is as follows: ρ(C1 - ) = [C x V x M / V0] x 1000 x N, In the formula, C is the molar concentration of the silver nitrate standard solution, with units of mol / L; V has units of mL; M is the molar mass of the chloride ion, with units of g / mol; V0 has units of mL; N is the ratio of the volume of the diluent to the volume of the sample to be measured; and p(Cl - ) has units of mg / L.

9. The method according to claim 1, wherein the method is characterized by, In the step S2, the titration indicator is a 5wt% potassium chromate indicator solution, and the concentration of the silver nitrate standard solution is 0.01-1 mol / L.