Method for measuring acidity of all-vanadium electrolyte based on complexing mass difference method

Abstract

The invention is suitable for the application field of electrolyte acidity determination, and provides a method for determining the acidity of an all-vanadium electrolyte based on a complexing mass difference method, and the method comprises the following steps: taking the all-vanadium electrolyte, and diluting the all-vanadium electrolyte into a pretreated all-vanadium electrolyte with the concentration of 0.05-0.1 mol / L; adding 1.5-2mL of a complexing masking reagent with the molar concentration of 1.5-2mol / L, weighing, and recording as M1; stirring and titrating, weighing and recording as M2; a quantitative determination method of mass difference is used for calculation, and the formula is {(M2-M1)-0.05} / A * C. In conclusion, a mass difference quantitative determination method is adopted, the vanadium complexing masking reagent is added, the adding amount and the pH value of the vanadium complexing masking reagent are controlled, a stable complex is formed through the complexing masking reagent, vanadium ions and impurity ions, the oxidation-reduction reaction and the precipitation reaction of the complex and sodium hydroxide are inhibited, and the accuracy of the acidity value of the all-vanadium electrolyte is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolyte acidity determination, and particularly relates to a method for determining the acidity of a full vanadium electrolyte based on a complex mass difference method. BACKGROUND

[0002] In a full vanadium redox flow battery, the acidity of the electrolyte plays a crucial role in the performance and lifespan of the battery. Accurate determination of the acidity of the full vanadium electrolyte is of great significance for optimizing the operating conditions of the battery and improving the efficiency and stability of the battery.

[0003] In the prior art, the methods for determining the acidity of the electrolyte of a full vanadium redox flow battery are mainly based on instrumental analysis, including potentiometric titration and pH meter measurement. Both of these methods require the use of sodium hydroxide solution for titration. However, in the electrolyte of a full vanadium redox flow battery, vanadium ions themselves undergo redox reactions, leading to an increase in the amount of sodium hydroxide solution required for titration, resulting in significant fluctuations in the acidity determination results. Vanadium ions also undergo redox reactions with sodium hydroxide during the acid-base titration process, leading to an overestimation of the results. In addition, other impurity ions inevitably exist in the raw materials of the electrolyte of a full vanadium redox flow battery, which also react with sodium hydroxide, leading to an overestimation of the acidity measurement value.

[0004] Therefore, although the methods based on instrumental analysis in the prior art have high precision, they may be affected by vanadium ions and other impurity ions in the electrolyte in actual applications, leading to inaccurate determination results, and the calibration and maintenance of the instruments are required to be relatively high.

[0005] Patent No. CN 103454330 B discloses a method for detecting the acid radical of a full vanadium electrolyte. The amount of EDTA disodium added is 1.1-2 times the amount of vanadium substance to complex vanadium ions. An acid-base potentiometric titration electrode is used to obtain the total hydrogen ion concentration, which can accurately and quickly determine the acid radical concentration of the solution. Although this patent can indirectly measure the hydrogen ion concentration, it has two shortcomings: 1. Potentiometric titration is used to calculate the volume of sodium hydroxide consumed by the potential jump. First, the electrode needs to be calibrated and activated regularly, otherwise the precision will decrease. In addition, the electrode in the above technical solution is easily disturbed by experimental temperature, stirring speed, sodium hydroxide solution concentration, and strong oxidizing agent potassium permanganate, leading to potential drift and large fluctuations in potential jump, making the volume of sodium hydroxide calculated by potential jump inaccurate, resulting in inaccurate determination of the total hydrogen ion concentration; and the data consistency is poor in multiple experiments.

[0006] 2. The amount of EDTA disodium solution added is 1.2-1.5 times the amount of vanadium substance. The excess EDTA disodium solution releases hydrogen ions when complexing with metal cations, leading to inaccurate total hydrogen ion concentration data and inaccurate acidity determination results.

[0007] In summary, the prior art in practical use is obviously inconvenient and defective, so it is necessary to improve. SUMMARY

[0008] Therefore, the application provides a method for determining the acidity of a full vanadium electrolyte based on a complex mass difference method.

[0009] The technical solution of the application is as follows: The application provides a method for determining the acidity of a full vanadium electrolyte based on a complex mass difference method, comprising the following steps: Step one: taking the full vanadium electrolyte, uniformly oscillating and dispersing, and then diluting to obtain a pretreated full vanadium electrolyte with a molar concentration of 0.05-0.1 mol / L.

[0010] Step two: adding 1.5-2 mL of a complex masking reagent with a molar concentration of 1.5-2 mol / L to the pretreated full vanadium electrolyte, and weighing and recording as M1.

[0011] Step three: stirring the pretreated full vanadium electrolyte to which the complex masking reagent is added, then adding a standard sodium hydroxide solution dropwise to obtain a mixed solution, and weighing and recording as M2 after stopping titration.

[0012] Step four: calculating by using a quantitative determination method of mass difference, and the acidity calculation formula is {(M2-M1)-0.05} / AxC.

[0013] 0.05 is an error correction coefficient; A is the density of the standard sodium hydroxide solution, A=Cx1.01, 1.01 is an error correction coefficient; C is the molar concentration (mol / L) of the standard sodium hydroxide solution.

[0014] On the basis of the above technical solution, preferably, in step one, the method for uniformly oscillating and dispersing the full vanadium electrolyte is as follows: using an ultrasonic disperser with a vibration frequency of 30-40 Hz, oscillating and dispersing at 20-25℃ for 14-20 min; or using other mechanical dispersion methods, such as stirring to achieve dispersion.

[0015] On the basis of the above technical scheme, preferably, the pH value of the complex masking reagent is 5-8; the complex masking reagent comprises an aminocarboxylate, a hydroxyl-containing compound or an ethanolamine; the aminocarboxylate comprises EDTA (ethylenediaminetetraacetic acid), disodium EDTA and other derivatives of EDTA; the hydroxyl-containing compound comprises d-sorbitol and mannitol.

[0016] On the basis of the above technical scheme, preferably, the complex masking reagent is prepared as follows: the complex masking reagent solid is weighed in a volumetric flask, deionized water is added, then NaOH solid is added, and slow heating and stirring are performed until there are no obvious particles in the solution system, the pH value is adjusted to 6-7, and after dissolution is completed, deionized water is added to 100 ml.

[0017] On the basis of the above technical scheme, preferably, the stirring mode of the pretreated vanadium electrolyte to which the complex masking reagent is added is as follows: the pH value is monitored using a pH acidimeter, and stirring is performed at 20-25 DEG C and 500-600 r / min.

[0018] On the basis of the above technical scheme, preferably, the molar concentration C of the standard sodium hydroxide solution is 0.5-1 mol / L; when the titration is stopped, the pH value of the mixed solution is 2-4.

[0019] The method for determining the acidity of a vanadium electrolyte based on the complex mass difference method of the application has the following beneficial effects relative to the prior art: 1. The mass difference quantitative determination method is used to determine the acidity of the vanadium electrolyte, thereby avoiding the problem of decreased precision caused by not performing periodic calibration and activation of the electrode, and avoiding the problem of interference of the electrode by experimental temperature, stirring speed, concentration of the sodium hydroxide solution and the strong oxidizing agent potassium permanganate.

[0020] 2. Although the mass difference quantitative determination method can to some extent avoid the shortcomings of other methods, vanadium ions in the vanadium electrolyte are prone to redox reactions, which increases the titration amount of the sodium hydroxide solution and causes large fluctuations in the acidity determination results; after the sodium hydroxide solution is added to the vanadium electrolyte, the vanadium ions undergo redox reactions with the sodium hydroxide solution, which causes the acidity determination results to be too large. Therefore, the complex masking reagent is added to the vanadium electrolyte, the complex masking reagent has a complexing effect on the vanadium ions, which can avoid the redox reactions of the vanadium ions themselves and avoid large fluctuations in the acidity determination results; since the complex masking reagent has a complexing effect on the vanadium ions, it also avoids the redox reactions of the vanadium ions with the sodium hydroxide solution and avoids the acidity determination results being too small.

[0021] 3. In the preparation process of vanadium electrolyte, impurity ions are inevitably present in the raw materials. These impurity ions react with sodium hydroxide, resulting in a higher acidity measurement value. The complexing masking reagent added in this invention can react with the impurity ions to avoid side reactions of impurity ions in the vanadium electrolyte and prevent a higher acidity measurement value.

[0022] 4. Since it is necessary to form a complexation reaction with vanadium ions and other impurity ions, the complexation masking reagent of the present invention is selected from aminocarboxylate salts, hydroxyl-containing compounds, or ethanolamines.

[0023] 5. While complexing masking reagents can mitigate the impact of redox reactions on acidity results, in the process of carboxylic acid complexing metal cations, inaccurate control of the amount added can release hydrogen ions, affecting the final hydrogen ion concentration and thus the acidity measurement. This invention first dilutes the vanadium electrolyte in step one. Diluting the vanadium electrolyte reduces the amount of complexing masking reagent used, allowing for better control of its addition and preventing excessive release of hydrogen ions that would affect the final hydrogen ion concentration. Therefore, the dilution in step one synergistically with the addition of the complexing masking reagent in step two ensures that after complete complexation with vanadium ions and impurity ions, the remaining amount is ≤0.1 mL, minimizing the interference of hydrogen ion release on acidity measurement.

[0024] 6. The molar concentration of the diluted vanadium electrolyte is 0.05-0.1 mol / L. This allows for the control of the added complexing masking reagent at 1.5-2 mL. The molar concentration of the complexing masking reagent is 1.5-2 mol / L, ensuring that after the complexing masking reagent undergoes a complexation reaction with vanadium, the remaining reagent can also complex with impurity ions. Ultimately, the amount of remaining complexing masking reagent is very small, resulting in very little release of hydrogen ions and minimal impact on acidity measurements. If the molar concentration of the diluted vanadium electrolyte is too high, a larger amount of complexing masking reagent is required, which will have a greater impact on acidity measurements. If the concentration of the complexing masking reagent is too low, redox reactions cannot be completely prevented, and the acidity measurement results will remain inaccurate. If the concentration of the complexing masking reagent is too high, hydrogen ions will be released, affecting the final hydrogen ion concentration.

[0025] 7. By diluting the vanadium electrolyte and controlling the amount of complexing masking reagent added, the accuracy of hydrogen ion concentration measurement can be improved. It is also necessary to further control the pH value of the complexing masking reagent to 5-8. If the pH value is less than 5, more sodium hydroxide will be used during the titration process, resulting in a higher acidity measurement value. If the pH value is greater than 8, less sodium hydroxide will be used during the titration process, resulting in a lower acidity measurement value.

[0026] 8. The titration end point pH is 2-4, the acidity measurement value is slightly large, the acidity value of the all-vanadium electrolyte can be accurately obtained in the 2-4 interval, and the use amount of the standard sodium hydroxide solution is the least, the cost of the reagent consumables is the most saved; when greater than 4, the acidity value of the all-vanadium electrolyte can also be accurately obtained, but the use amount of the standard sodium hydroxide solution is large, and the cost of the reagent consumables is high.

[0027] 9. The mass difference quantitative determination method is used, the error correction coefficient is 0.05 which is obtained through a standard curve in the all-vanadium electrolyte acidity calculation process, and therefore the calculation formula of the all-vanadium electrolyte acidity is {(M2-M1)-0.05} / AxC. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] Embodiment 1 1. 50 mL of the all-vanadium electrolyte to be measured is taken, an ultrasonic disperser with a vibration frequency of 30 Hz is used, and the sample is shaken and dispersed at 20℃ for 14 min to make the sample uniformly shaken and dispersed. Then 0.8 mL of the uniformly shaken and dispersed all-vanadium electrolyte is taken into a 100 mL glass beaker, deionized water is added for pretreatment dilution, and a stirring magnet is put in for stirring and uniform mixing at a stirring speed of 500 r / min to obtain a pretreated all-vanadium electrolyte with a molar concentration of 0.05 mol / L.

[0030] 2. 1.5 mL of a complexing masking reagent EDTA which plays a complexing role on vanadium ions is added to the pretreated all-vanadium electrolyte, and the weight is recorded as M1.

[0031] The molar concentration of the complexing masking reagent is 1.5 mol / L, and the pH value is 5.

[0032] The preparation method of the complexing masking reagent is as follows: 14 g of EDTA solid is weighed into a volumetric flask, deionized water is added to 70 ml, NaOH solid is added, and the solution system is slowly heated and stirred until there are no obvious particles, the pH value is adjusted to 6, and after dissolution, deionized water is added to 100 ml.

[0033] 3. The pH value is monitored using a Mettler pH meter, stirring is carried out at 20°C and 500 r / min, during the stirring process, the solution in the beaker is kept from splashing and the liquid surface is in a small vortex shape, then the standard sodium hydroxide solution is added dropwise to obtain a mixed solution, the titration is stopped when the pH of the mixed solution is 2, and the weight is recorded as M2 and the volume V of the mixed solution; the molar concentration C of the standard sodium hydroxide solution is 0.5 mol / L.

[0034] 4. The acidity is calculated by the quantitative determination method of mass difference: {(M2-M1)-0.05} / AxC.

[0035] Example 2 1. 55 mL of the full-vanadium electrolyte to be measured is taken, an ultrasonic disperser with a vibration frequency of 35 Hz is used to disperse for 17 min at 22°C, the sample is uniformly dispersed by shaking, then 1 mL of the uniformly dispersed full-vanadium electrolyte is taken into a 100 mL glass beaker, deionized water is added for pretreatment dilution, and a stirring magnet is put in for stirring and uniform mixing, the stirring speed is 530 r / min, and a pretreated full-vanadium electrolyte with a molar concentration of 0.08 mol / L is obtained.

[0036] 2. 1.8 mL of a complexing masking agent mannitol which has a complexing effect on vanadium ions is added to the pretreated full-vanadium electrolyte, and the weight is recorded as M1.

[0037] The molar concentration of the complexing masking agent is 1.8 mol / L, and the pH value is 6.5.

[0038] The preparation method of the complexing masking agent is as follows: 14.5 g of mannitol solid is weighed into a volumetric flask, deionized water is added to 75 ml, NaOH solid is added, slow heating and stirring are carried out until there are no obvious particles in the solution system, the pH value is adjusted to 6.5, after dissolution, deionized water is added to 100 ml.

[0039] 3. The pH value is monitored using a Mettler pH meter, stirring is carried out at 23°C and 550 r / min, during the stirring process, the solution in the beaker is kept from splashing and the liquid surface is in a small vortex shape, then the standard sodium hydroxide solution is added dropwise to obtain a mixed solution, the titration is stopped when the pH of the mixed solution is 3, and the weight is recorded as M2; the molar concentration C of the standard sodium hydroxide solution is 0.8 mol / L.

[0040] 4. The acidity is calculated by the quantitative determination method of mass difference: {(M2-M1)-0.05} / AxC.

[0041] Example 3 1. Take 60 mL of the vanadium electrolyte to be tested and disperse it using an ultrasonic disperser with an oscillation frequency of 40 Hz at 25 °C for 20 min to ensure uniform dispersion. Then, take 1.5 mL of the uniformly dispersed vanadium electrolyte into a 100 mL glass beaker, add deionized water for pretreatment dilution, and place a magnetic stir bar to stir and mix at a stirring speed of 550 r / min to obtain a pretreated vanadium electrolyte with a molar concentration of 0.1 mol / L.

[0042] 2. Add 2 mL of ethanolamine, a complexing masking reagent that complexes vanadium ions, to the pretreated vanadium electrolyte and weigh it, recording the weight as M1.

[0043] The molar concentration of the complexing masking reagent was 2 mol / L, and the pH value was 8.

[0044] The preparation method of the complexing masking reagent is as follows: Weigh 15g of ethanolamine solid into a volumetric flask, add deionized water to 80ml, then add NaOH solid, slowly heat and stir until there are no obvious particles in the solution system, adjust the pH value to 7, after dissolution, add deionized water to 100ml.

[0045] 3. Use a Mettler pH meter to monitor the pH value. Stir at 25℃ and 600r / min. During stirring, keep the solution in the beaker from splashing and keep the liquid surface in a small vortex. Then add standard sodium hydroxide solution dropwise to obtain a mixed solution. Stop the titration when the pH of the mixed solution is 4. Weigh and record the weight as M2. The molar concentration C of the standard sodium hydroxide solution is 1 mol / L.

[0046] 4. Calculate using the quantitative determination method based on mass difference: Acidity = {(M2-M1)-0.05} / A×C.

[0047] Comparative Example 1 The acidity of the vanadium electrolyte was determined according to the pH meter measurement method in the national standard GB / T 6920-1986 Determination of pH value of water - Glass electrode method.

[0048] Comparative Example 2 The acidity of the vanadium electrolyte was determined by potentiometric titration according to the national standard GB / T 1668-2008 Determination of Acid Value and Acidity of Plasticizers.

[0049] Comparative Example 3 1. Sample preparation: Accurately transfer 5.00 mL of vanadium electrolyte into a 250 mL titration cup using a pipette, dilute with 150 mL of distilled water, add 10 mL of EDTA disodium solution (concentration of 1 mol / L), place the stir bar in the titrator, and place it on the stirring table of the titrator.

[0050] 2. Electrode calibration: Turn on the titrator, insert the electrode into the buffer solution with pH 6.86 for calibration, then use the buffer solution with pH 4.00 for calibration. After calibration, rinse the electrode with distilled water and dry the surface with filter paper.

[0051] 3. Titration operation: Insert the electrode into the sample solution, set the titration mode as "potential jump titration", and determine the end point as potential mutation (corresponding to pH about 7.0, at which point the hydrogen ions are completely neutralized). Start titration, and the instrument automatically adds sodium hydroxide standard solution (concentration of 0.1 mol / L) to record the real-time potential and titration volume.

[0052] Titrate the solution with a known concentration of sodium hydroxide solution to the end of the first potential jump, and obtain the total hydrogen ion concentration.

[0053] 4. Calculate the original hydrogen ion concentration from the vanadium valence and concentration.

[0054] Comparative Example 4 On the basis of Example 1, no complex masking agent is added in step 2 of pretreating the all-vanadium electrolyte, and the pretreated all-vanadium electrolyte is directly weighed. Other conditions are the same.

[0055] Comparative Example 5 On the basis of Example 1, the complex masking agent is replaced with citric acid, and other conditions are the same.

[0056] Comparative Example 6 On the basis of Example 1, step 1 is deleted, and the all-vanadium electrolyte is not diluted for pretreatment. Correspondingly, in step 2, 1.2-1.5 times the mass of the vanadium in the pretreated all-vanadium electrolyte is added with the complex masking agent, and other conditions are the same.

[0057] Comparative Example 7 On the basis of Example 1, after the all-vanadium electrolyte is diluted for pretreatment in step 1, the pretreated all-vanadium electrolyte with a molar concentration of 0.2 mol / L is obtained. Correspondingly, in step 2, 3 mL of the complex masking agent is added to the pretreated all-vanadium electrolyte, and other conditions are the same.

[0058] Comparative Example 8 On the basis of Example 2, in step 2, 1 mL of the complex masking agent that plays a complexing role on vanadium ions is added to the pretreated all-vanadium electrolyte, and other conditions are the same.

[0059] Comparative Example 9 On the basis of Example 2, in step 2, 3 mL of the complex masking agent that plays a complexing role on vanadium ions is added to the pretreated all-vanadium electrolyte, and other conditions are the same.

[0060] Comparative Example 10 On the basis of Example 2, in step 2, the pH value of the complex masking reagent is 3, and other conditions are consistent.

[0061] Comparative Example 11 On the basis of Example 2, in step 2, the pH value of the complex masking reagent is 10, and other conditions are consistent.

[0062] Comparative Example 12 On the basis of Example 3, in step 3, at the titration end point, the pH of the mixed solution is 1, and other conditions are consistent.

[0063] Comparative Example 13 On the basis of Example 3, in step 3, at the titration end point, the pH of the mixed solution is 5, and other conditions are consistent.

[0064] A full-vanadium electrolyte with an acidity of 4 is prepared, and the actual acidity of the full-vanadium electrolyte is determined by the methods of the above three examples and the methods of the comparative examples, and the error is calculated. Error = actual acidity - standard acidity. The determination results of each example and comparative example are shown in Table 1.

[0065]

[0066]

[0067] From the above data, it can be seen that the full-vanadium electrolyte acidity values measured by each example of the present application are very stable, and the error is small.

[0068] In Comparative Examples 1-3, the pH meter measurement method and the potentiometric titration method are used, and the error of the full-vanadium electrolyte acidity value is large.

[0069] In Comparative Example 4, the mass difference quantitative determination method of the present application is used, but no complex masking reagent is added, the error of the full-vanadium electrolyte acidity value is large, and the data is unstable after multiple measurements.

[0070] In Comparative Example 5, the complex masking reagent of the present application is not used, but citric acid is used instead. In acidic conditions, the carboxyl group is not dissociated, and the complexing ability is poor, which is equivalent to the failure of the complexing agent, the complexing is unstable, and the data fluctuates greatly.

[0071] In Comparative Example 6, the full-vanadium electrolyte is not diluted, and a large amount of complex masking reagent needs to be added. During the complexing reaction, hydrogen ions are released at the same time, which makes the actual acidity value measured too large.

[0072] In Comparative Example 7, the molar concentration of the diluted full-vanadium electrolyte is too large, which also makes the actual acidity value measured too large.

[0073] In Comparative Example 8, the amount of complex masking reagent added is relatively small, the complexing is not complete, and the determination result is unstable.

[0074] In the comparative example 9, the amount of complex masking agent added is relatively large, and the release of hydrogen ions will make the measured actual acidity value too large.

[0075] In the comparative example 10, the pH value of the complex masking agent is relatively small, the acidity of the whole solution is large, and the amount of sodium hydroxide used is large, which will make the measured actual acidity value too large.

[0076] In the comparative example 11, the pH value of the complex masking agent is relatively large, the acidity of the whole solution is small, and the amount of sodium hydroxide used is small, which will make the measured actual acidity value too small.

[0077] In the comparative example 12, the titration end point pH value is less than 2, and the acidity measurement value is too large.

[0078] In the comparative example 13, the titration end point pH value is greater than 4, and the vanadium electrolyte acidity value can be accurately obtained, but the amount of standard sodium hydroxide solution used is large, and the reagent consumable cost is high.

[0079] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for determining the acidity of a total vanadium electrolyte based on the complexometric mass difference method, characterized in that, The method comprises the following steps: Step one: taking the all-vanadium electrolyte, oscillating and dispersing uniformly, and then diluting to obtain a pretreated all-vanadium electrolyte with a molar concentration of 0.05-0.1 mol / L; Step two: adding 1.5-2 mL of a complex masking reagent with a molar concentration of 1.5-2 mol / L to the pretreated all-vanadium electrolyte, and recording the weight as M1; Step three: stirring the pretreated all-vanadium electrolyte to which the complex masking reagent is added, and then adding a standard sodium hydroxide solution dropwise to obtain a mixed solution; after the titration is stopped, the weight is recorded as M2; Step four: calculating by using the quantitative determination method of the mass difference, and the acidity calculation formula is {(M2-M1)-0.05} / AxC, wherein 0.05 is an error correction coefficient; A is the density of the standard sodium hydroxide solution, A=C*1.01, 1.01 is an error correction coefficient; and C is the molar concentration of the standard sodium hydroxide solution.

2. The method for determining the acidity of a total vanadium electrolyte based on the complexometric difference method according to claim 1, characterized in that, In the step one, the method for oscillating and dispersing the all-vanadium electrolyte uniformly is as follows: using an ultrasonic disperser with an oscillation frequency of 30-40 Hz, oscillating and dispersing at 20-25°C for 14-20 min.

3. The method for determining the acidity of a total vanadium electrolyte based on the complexometric difference method according to claim 1, characterized in that, The pH value of the complex masking reagent is 5-8.

4. The method for determining the acidity of a total vanadium electrolyte based on the complexometric difference method according to claim 1, characterized in that, The complex masking reagent comprises an aminocarboxylate, a hydroxyl-containing compound or an ethanolamine.

5. The method for determining the acidity of a total vanadium electrolyte based on the complexometric difference method according to claim 1, characterized in that, The preparation method of the complex masking reagent is as follows: weighing the complex masking reagent solid in a volumetric flask, adding deionized water, and then adding NaOH solid, slowly heating and stirring until there are no obvious particles in the solution system, adjusting the pH value to 6-7, and then adding deionized water to 100 ml after dissolution.

6. The method for determining the acidity of a total vanadium electrolyte based on the complexometric difference method according to claim 1, characterized in that, In the step three, the stirring mode of the pretreated all-vanadium electrolyte to which the complex masking reagent is added is as follows: using a pH acidimeter to monitor the pH value, and stirring at 20-25°C and 500-600 r / min.

7. The method for determining the acidity of a total vanadium electrolyte based on the complexometric difference method according to claim 1, characterized in that, The molar concentration C of the standard sodium hydroxide solution is 0.5-1 mol / L; and the pH of the mixed solution is 2-4 when the titration is stopped.

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