Method for measuring sulfate radicals in vanadium electrolyte by ICP (Inductively Coupled Plasma)

Abstract

The invention relates to a method for detecting the content of sulfate radicals, in particular to a method for determining the content of sulfate radicals in a vanadium electrolyte by using ICP (Inductively Coupled Plasma), which comprises the following steps: 1) preparing a sample solution: mixing excessive Ba < 2 + > solution with known Ba < 2 + > initial concentration with the vanadium electrolyte, and taking supernate after the reaction is finished; (2) drawing a standard curve: preparing a Ba < 2 + > standard solution according to the ratio of 50%-150% of the theoretical concentration of Ba < 2 + > in the supernatant obtained in the step (1), measuring the Ba < 2 + > standard solution by using ICP (Inductively Coupled Plasma), and drawing the Ba < 2 + > standard curve; and 3) sample detection and calculation: measuring the supernatant obtained in the step 1) by using ICP, substituting the measurement result into the Ba < 2 + > standard curve in the step 2) to determine the actual concentration of Ba < 2 + > in the supernatant, and subtracting the actual concentration of Ba < 2 + > in the supernatant from the initial concentration of Ba < 2 + > in the Ba < 2 + > solution in the step 1) to obtain the concentration of SO4 < 2-> in the vanadium electrolyte. According to the method, the step of measuring the concentration of SO4 < 2-> in the vanadium electrolyte through a precipitation gravimetric method is greatly simplified, the test time is shortened, and errors and potential safety hazards caused by manual operation are avoided.

Description

Technical Field

[0001] The invention relates to a method for detecting sulfate content, in particular to a method for measuring sulfate content in vanadium electrolyte by using ICP. Background Art

[0002] The main components of the electrolyte for all-vanadium liquid flow batteries (hereinafter referred to as vanadium electrolyte) are vanadium ions of different valence states and sulfate ions. Among them, the complex of pentavalent vanadium ions and sulfate can form trace precipitation under strong acid conditions. There may be a large amount of pentavalent vanadium ions in the positive electrolyte of all-vanadium liquid flow batteries. The commercially available 3.5-valent electrolyte may also produce a small amount of pentavalent vanadium ions due to some unexpected factors. The trace precipitation formed by it and sulfate will cause certain errors in the process of determining the sulfate content by precipitation method, thereby affecting the final result. Therefore, when determining the sulfate content in the vanadium electrolyte, oxalic acid is added to reduce the pentavalent vanadium ions to prevent the formation of pentavalent vanadium sulfate complexes. At the same time, a certain amount of hydrochloric acid is added to remove possible barium oxalate precipitates. At present, the determination of sulfate ion concentration generally adopts the weight method, that is, BaCl2 is used to precipitate SO4 2- , weigh the mass of the precipitate, and calculate the sulfate concentration in the original electrolyte according to the formula c=m / VM (m is the mass of the precipitate, V is the electrolyte sampling volume, and M is the molecular weight of barium sulfate). This method requires multiple washing, centrifugation, and pouring out of the supernatant of the BaSO4 precipitate. It is easy to mistakenly pour out a small amount of powdered precipitate, resulting in errors. In order to improve the accuracy of the test results, the precipitate needs to be burned at an extremely high temperature (often around 800°C) for a long time. The entire test process has complicated steps, a long time, and high energy consumption. It is difficult to detect a large number of samples in a short period of time, and there are certain safety hazards.

[0003] There are also some reports on the use of titration to determine sulfate. For example, after chelating vanadium ions with ETDA, the total hydrogen ion concentration in the solution is titrated with NaOH, and finally the sulfate concentration in the vanadium electrolyte is calculated. The calculation process of this scheme is relatively complicated, involving the estimation of the amount of hydrogen ions ionized by sulfuric acid, and the addition of multiple reagents. The amount of EDTA added will also affect the final result. Overall, it is still relatively cumbersome. The prior art also discloses a scheme for determining the sulfate concentration in the vanadium electrolyte by temperature titration. The temperature change caused by the endothermic process of BaSO4 precipitation formation is detected to determine SO4 2- This method is relatively simple, but it has high requirements on the ambient temperature during the entire test process, and a constant temperature water bath with slightly lower precision may affect the results.

[0004] The invention relates to a scheme for measuring the sulfate concentration in a vanadium electrolyte by using an inductively coupled plasma spectrometer (hereinafter referred to as ICP). The method is relatively simple and has high accuracy. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a method for determining sulfate in vanadium electrolyte by ICP, so as to solve the problems existing in the prior art.

[0006] To achieve the above object and other related objects, the present invention provides a method for determining sulfate in a vanadium electrolyte by ICP, comprising the following steps:

[0007] 1) Prepare sample solution: Add an excess of known Ba 2+ Initial concentration of Ba 2+ The solution is mixed with vanadium electrolyte, and the supernatant is taken after the reaction is completed;

[0008] 2) Draw a standard curve: According to the Ba in the supernatant of step 1) 2+ Ba was prepared at a ratio of 50% to 150% of the theoretical concentration. 2+

[0009] Standard solution; Ba prepared using ICP determination 2+ Standard solution, draw Ba 2+ Standard curve;

[0010] 3) Sample detection and calculation: Use ICP to measure the supernatant obtained in step 1) and substitute the measurement result into Ba in step 2) 2+ The standard curve was used to determine the Ba content in the supernatant. 2+ The actual concentration of Ba in step 1) 2+ Ba in solution 2+ The initial concentration minus the Ba in the supernatant 2+ The actual concentration of SO4 in vanadium electrolyte is obtained 2- concentration.

[0011] As described above, the present invention provides a method for ICP determination of sulfate in vanadium electrolyte, which has the following beneficial effects:

[0012] 1) The steps of gravimetric determination of sulfate concentration are greatly simplified, the test time is shortened, and errors and safety hazards caused by human operation are avoided;

[0013] 2) The Ba content in the supernatant after the precipitation reaction is determined by ICP, and the sulfate content in the original vanadium electrolyte is obtained by theoretical calculation. There are almost no requirements for the test environment, and the calculation process does not involve any estimates and assumptions that are not yet clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Shown are different concentrations of Ba in Example 1 of the present invention 2+ Linear relationship graph between standard solution and absorbance.

[0015] Figure 2 Shown are different concentrations of Ba in Example 2 of the present invention 2+ Linear relationship graph between standard solution and absorbance.

[0016] Figure 3 Shown are different concentrations of Ba in Example 3 of the present invention 2+ Linear relationship graph between standard solution and absorbance. DETAILED DESCRIPTION

[0017] The present invention provides a method for ICP determination of sulfate in vanadium electrolyte, comprising the following steps:

[0018] 1) Prepare sample solution: Add an excess of known Ba 2+ Initial concentration of Ba 2+ The solution is mixed with vanadium electrolyte, and the supernatant is taken after the reaction is completed;

[0019] 2) Draw a standard curve: According to the Ba in the supernatant of step 1) 2+ Ba was prepared at a ratio of 50% to 150% of the theoretical concentration. 2+

[0020] Standard solution; Ba prepared using ICP determination 2+ Standard solution, draw Ba 2+ Standard curve;

[0021] 3) Sample detection and calculation: Use ICP to measure the supernatant obtained in step 1) and substitute the measurement result into Ba in step 2) 2+ The standard curve was used to determine the Ba content in the supernatant. 2+ The actual concentration of Ba in step 1) 2+ Ba in solution 2+ The initial concentration minus the Ba in the supernatant 2+ The actual concentration of SO4 in vanadium electrolyte is obtained 2- concentration.

[0022] The method also includes directly using the sample information provided by the manufacturer or the weight method to estimate the SO4 2- The weight method is estimated to be the excess Ba 2+ After the solution is mixed and reacted with the vanadium electrolyte, the predicted concentration of SO4 in the vanadium electrolyte is calculated according to formula (1).

[0023] Specifically,

[0024] Excessive Ba 2+ After the solution is mixed with the vanadium electrolyte, the precipitate is filtered and weighed without washing, centrifugation, drying, burning and other steps. The concentration of sulfate in the vanadium electrolyte Calculate according to the following formula:

[0025]

[0026] Where m[BaSO4] represents the weight of the precipitate generated; M[BaSO4] represents the relative molecular mass of BaSO4; V 电解液 Represents the sample volume of the electrolyte.

[0027] In certain embodiments of the present invention, the Ba 2+ Provided by BaCl2 solution.

[0028] In certain embodiments of the present invention, in step 1), further comprising: 2+ With SO4 2- Before the reaction, the vanadium electrolyte is mixed with oxalic acid. Oxalic acid is used to reduce VO2 in the vanadium electrolyte. + to prevent trace precipitation of pentavalent vanadium.

[0029] In certain embodiments of the present invention, after the vanadium electrolyte and oxalic acid are mixed, the mixture is further subjected to a heating state of 70 to 100° C. for 5 to 10 minutes. The heating increases the reaction rate of oxalic acid and pentavalent vanadium to ensure complete reaction.

[0030] In certain embodiments of the present invention, after the vanadium electrolyte and oxalic acid are mixed, the mixture further comprises reacting in an oxygen-free state to prevent the pentavalent vanadium reduced by the oxalic acid from being oxidized again.

[0031] In certain embodiments of the present invention, the oxalic acid is solid or liquid.

[0032] In certain embodiments of the present invention, the amount of oxalic acid is excessive relative to the pentavalent vanadium ion. For example, the amount ratio of oxalic acid to the pentavalent vanadium ion in the vanadium electrolyte is (2-3):1. The remaining oxalic acid after the reaction is decomposed and removed under heating at 70-100°C.

[0033] The oxalic acid reduces VO2 in the vanadium electrolyte + When oxidized, the volume of water generated is recorded as ΔV[H2C2O4].

[0034] When the added oxalic acid is solid, ΔV[H2C2O4] is calculated according to the following formula:

[0035]

[0036] Where m[H2C2O4] represents the mass of oxalic acid added; M[H2C2O4] represents the molecular weight of oxalic acid, which is 90.034; M[H2O]

[0037] represents the molecular weight of water, which is 18.015; ρ[H2O] represents the volume of water at the experimental temperature, which is 0.997 at 25°C.

[0038] When the added oxalic acid is liquid, ΔV[H2C2O4] is calculated according to the following formula:

[0039]

[0040] Among them, c aq [H2C2O4] represents the concentration of oxalic acid in the added solution; V aq [H2C2O4] represents the volume of oxalic acid solution added.

[0041] In certain embodiments of the present invention, the method further includes adjusting the pH of the system after the vanadium electrolyte and oxalic acid are mixed to be less than 1. By controlling the pH value of the system, the generation of barium oxalate precipitation is prevented.

[0042] In certain embodiments of the present invention, the acid solution used to adjust the pH of the system after the vanadium electrolyte and oxalic acid are mixed is hydrochloric acid.

[0043] For example, hydrochloric acid with a mass concentration of 36%.

[0044] In certain embodiments of the present invention, in step 2), the supernatant contains Ba 2+ Theoretical concentration Calculate according to the following formula:

[0045]

[0046] Among them, b represents joining Ba 2+ The volume of Ba 2+ The concentration of vanadium electrolyte; a represents the volume of vanadium electrolyte; Represents the SO4 in the vanadium electrolyte calculated by the weight method 2- The predicted concentration; m represents the total volume of oxalic acid, hydrochloric acid and ΔV[H2C2O4]; n represents the dilution factor. If the undiluted sample is tested, the dilution factor is 1; where That is Ba 2+ The amount of substance relative to SO4 in vanadium electrolyte 2- The amount of substance is in excess.

[0047] In certain embodiments of the present invention, the dilution factor is 100 to 10000. The specific value may be determined according to the actual sample concentration and the detection limit of the ICP device.

[0048] In certain embodiments of the present invention, in step 2), the supernatant contains Ba 2+ 50% to 150% of the theoretical concentration

[0049]

[0050] In certain embodiments of the present invention, in step 3), the excitation wavelength when using ICP measurement is 455.40 nm.

[0051] In certain embodiments of the present invention, in step 3), the concentration of sulfate in the vanadium electrolyte is calculated according to the following formula:

[0052]

[0053] in, represents the concentration of sulfate in vanadium electrolyte, mol / L; Representative Ba 2+ The concentration of is in mg / L;

[0054] b represents joining Ba 2+ The volume of Ba 2+ a represents the volume of vanadium electrolyte; m represents the total volume of oxalic acid, hydrochloric acid and water generated by oxidation of oxalic acid; n represents the dilution factor. If the undiluted sample is tested, the dilution factor is 1.

[0055] In certain embodiments of the present invention, in step 3), the excitation wavelength is 455.40 nm when ICP is used for measurement.

[0056] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0057] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing the specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0058] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0059] Example 1

[0060] The sample was a blind sample that had not been touched, and its approximate sulfate concentration was unknown. The sulfate content was estimated to be 4.45 mol / L using a simplified gravimetric method.

[0061] The steps are as follows: ① Take 1 mL of electrolyte, add 8 mL of 1 mol / L BaCl2 solution to it, wait for the precipitate to precipitate, filter and weigh it; ② The precipitate weight m[BaSO4] is 1.0389 g, and the concentration of sulfate in the original electrolyte is calculated according to formula (1):

[0062]

[0063] The concentration of sulfate in the original vanadium electrolyte is 4.45 mol / L.

[0064] Take 1 mL of vanadium electrolyte sample, add 6.4 mL of 1 mol / L BaCl2 solution, centrifuge after the reaction is completed, take 1 mL of the supernatant, dilute it 1000 times with deionized water, and the Ba in the supernatant is 1000 times. 2+ Theoretical concentration Calculate according to formula (4):

[0065]

[0066] Refer to Ba 2+ The theoretical concentration of BaCl2 standard solution was prepared, and the concentrations were 15mg / L, 20mg / L, 30mg / L, 50mg / L, and 65mg / L. The standard curve is as follows Figure 1 As shown, the equation of the standard curve is y = 1176.93x + 152.08. After ICP testing, the Ba content in the diluted supernatant was obtained. 2+ The actual concentration It is 37.1mg / L.

[0067] The concentration of sulfate in the original vanadium electrolyte is calculated according to formula (5):

[0068]

[0069] The sulfate concentration in the original vanadium electrolyte was calculated to be 4.40 mol / L.

[0070] Example 2

[0071] The persulfate content of the sample was determined by the gravimetric method described in NBT42006-2013, and the result was 4.50 mol / L.

[0072] The determination steps are as follows: ① Take 1 mL of vanadium electrolyte and add 8 mL of 1 mol / L BaCl2 solution to it; ② After the precipitate is precipitated, it is centrifuged, washed and dispersed three times, then dried and burned in a tube furnace at 800°C to constant weight; ③ The weight of the crucible is 14.5089 g, and the weight of the crucible plus the precipitate is 15.5592 g. The net weight of the precipitate m[BaSO4] is 1.0503 g. The concentration of sulfate in the original electrolyte is calculated according to formula (1):

[0073]

[0074] The concentration of sulfate in the original vanadium electrolyte is 4.50 mol / L.

[0075] Take 1 mL of vanadium electrolyte sample, add 6.4 mL of 1 mol / L BaCl2 solution, centrifuge after the reaction is completed, take 1 mL of the supernatant, dilute it 10000 times with deionized water, and the Ba in the supernatant is 10000 times. 2+ Theoretical concentration Calculate according to formula (4):

[0076]

[0077] Refer to Ba 2+ The theoretical concentration of BaCl2 standard solution was prepared, and the concentrations were 1mg / L, 2mg / L, 3mg / L, 5mg / L, and 6mg / L. The standard curve is as follows Figure 2 As shown, the standard curve equation is y = 3424.48x + 83.18. After ICP test, the Ba content of the diluted supernatant was obtained. 2+ The actual concentration It is 3.55mg / L.

[0078] The concentration of sulfate in the original vanadium electrolyte is calculated according to formula (5):

[0079]

[0080] The calculated sulfate concentration in the original vanadium electrolyte was 4.49 mol / L, which was almost consistent with the result of gravimetric measurement.

[0081] Example 3

[0082] The sample was tested for persulfate content using the gravimetric method described in NBT42006-2013, and the result was 4.32 mol / L.

[0083] The determination steps are as follows: ① Take 1 mL of vanadium electrolyte and add 8 mL of 1 mol / L BaCl2 solution to it; ② After the precipitate is precipitated, it is centrifuged, washed and dispersed three times, then dried and burned in a tube furnace at 800°C to constant weight; ③ The weight of the crucible is 14.5656 g, and the weight of the crucible plus the precipitate is 15.5746 g. The net weight of the precipitate m[BaSO4] is 1.0092 g. The sulfate concentration in the original electrolyte is calculated according to formula (1):

[0084]

[0085] The concentration of sulfate in the original vanadium electrolyte is 4.32 mol / L.

[0086] It is the positive electrode electrolyte after charging is completed, in which the content of pentavalent vanadium ions exceeds 3 mol / L.

[0087] Take 1 mL of vanadium electrolyte sample, add 0.5 g of oxalic acid and 0.1 mL of hydrochloric acid (mass concentration is 36%), stir evenly, heat at 80°C for 5 min in an anaerobic state, and then return to room temperature. The volume change ΔV[H2C2O4] caused by the hydrolysis reaction of adding oxalic acid is calculated according to formula (2):

[0088]

[0089] The volume change caused by the addition of oxalic acid for hydrolysis was 0.1003 mL.

[0090] Add 6.4mL of 1mol / L BaCl2 solution and centrifuge after the reaction is complete. The total volume of the supernatant is 1 (电解液取样体积) +6.4 (BaCl2溶液体积) +0.1003 (草酸水解造成的体积变化) +0.1 (盐酸体积) =7.6003ml.

[0091] Take 1 mL of the supernatant and dilute it 10,000 times with deionized water. 2+ Theoretical concentration Calculate according to formula (4):

[0092]

[0093] Refer to Ba 2+ The theoretical concentration of BaCl2 standard solution was prepared, and the concentrations were 1mg / L, 2mg / L, 3mg / L, 5mg / L, and 6mg / L. The standard curve is as follows Figure 3As shown, the standard curve equation is y = 3614.37x-58.09. After ICP test, the Ba content of the diluted supernatant was obtained. 2+ The actual concentration It is 3.76mg / L.

[0094] The concentration of sulfate in the original vanadium electrolyte is calculated according to formula (5):

[0095]

[0096] The calculated sulfate concentration in the original vanadium electrolyte was 4.32 mol / L, which was consistent with the measurement result by the gravimetric method.

[0097] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limiting the present invention. In addition, the various modifications listed herein and the variations of the methods in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for determining sulfate in vanadium electrolyte by ICP, characterized in that: The method comprises the following steps: 1) Prepare sample solution: Add an excess of known Ba 2+ Initial concentration of Ba 2+ The solution is mixed with vanadium electrolyte, and the supernatant is taken after the reaction is completed; 2) Draw a standard curve: According to the Ba in the supernatant of step 1) 2+ Ba was prepared at a ratio of 50% to 150% of the theoretical concentration. 2+ Standard solution; Ba prepared using ICP determination 2+ Standard solution, draw Ba 2+ Standard curve; 3) Sample detection and calculation: Use ICP to measure the supernatant obtained in step 1) and substitute the measurement result into Ba in step 2) 2 + The standard curve was used to determine the Ba content in the supernatant. 2+ The actual concentration of Ba in step 1) 2+ Ba in solution 2+ The initial concentration minus the Ba in the supernatant 2+ The actual concentration of SO4 in vanadium electrolyte is obtained 2- concentration.

2. The method according to claim 1, characterized in that The Ba 2+ Provided by BaCl2 solution.

3. The method according to claim 1, characterized in that In step 1), an excess of Ba 2+ After the solution is mixed with the vanadium electrolyte, the SO4 in the vanadium electrolyte is calculated according to the following formula: 2- The predicted concentration of Where m[BaSO4] represents the weight of the precipitate generated; M[BaSO4] represents the relative molecular mass of BaSO4; V 电解液 Represents the sample volume of the electrolyte.

4. The method according to claim 1, characterized in that Step 1) also includes the following steps: 2+ Before the solution reacts with the vanadium electrolyte, the vanadium electrolyte is mixed with oxalic acid and then reacted.

5. The method according to claim 4, characterized in that The conditions for the reaction after the vanadium electrolyte and oxalic acid are mixed include one or more of the following conditions: 1) React in the absence of oxygen; 2) The reaction temperature is 70-100°C; 3) The reaction time is 5 to 10 minutes.

6. The method according to claim 4, characterized in that Step 1) also includes adjusting the pH of the system after the vanadium electrolyte and oxalic acid are mixed to less than 1.

7. The method according to claim 1, characterized in that In step 2), the supernatant contains Ba 2+ Theoretical concentration Calculate according to the following formula: Among them, b represents joining Ba 2+ The volume of Ba 2+ The concentration of vanadium electrolyte; a represents the volume of vanadium electrolyte; Represents the SO4 in vanadium electrolyte calculated by weight method 2- The predicted concentration; m represents the total volume of oxalic acid, hydrochloric acid and water generated by oxidized oxalic acid; n represents the dilution factor. If the undiluted sample is tested, the dilution factor is 1; where That is Ba 2+ The amount of substance relative to SO4 in vanadium electrolyte 2- The amount of substance is in excess.

8. The method according to claim 7, characterized in that The dilution multiple n is 100-10000.

9. The method according to claim 1, characterized in that: In step 3), the concentration of sulfate in the vanadium electrolyte is calculated according to the following formula: in, represents the concentration of sulfate in vanadium electrolyte, mol / L; Representative Ba 2+ The concentration is in mg / L; b represents the addition of Ba 2+ The volume of Ba 2+ a represents the volume of vanadium electrolyte; m represents the total volume of oxalic acid, hydrochloric acid and water generated by oxidation of oxalic acid; n represents the dilution factor. If the undiluted sample is tested, the dilution factor is 1.

10. The method according to claim 1, characterized in that In step 3), the excitation wavelength is 455.40 nm when ICP is used for measurement.

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