Preparation method of all-vanadium redox flow battery electrolyte

Abstract

The invention belongs to the field of redox flow batteries, and particularly relates to a preparation method of an all-vanadium redox flow battery electrolyte, which comprises the following steps: mixing and roasting vanadium slag, sodium carbonate and magnesium oxide, adding the roasted mixed material into dilute sulphuric acid, heating and stirring, and carrying out suction filtration to obtain a leachate; the pH of the leachate is adjusted to be acidic, solid-liquid separation is conducted, precipitates are added into a phosphoric acid type extraction agent, and extraction is conducted to obtain raffinate containing chromium and vanadium; adjusting the pH value of the chromium-vanadium-containing raffinate to be strongly acidic, adding an amine extracting agent, and extracting to obtain vanadium-containing raffinate; adjusting the pH value of the vanadium-containing raffinate to 2-4, and enabling the vanadium-containing raffinate to pass through ion exchange resin to obtain saturated ion exchange And analyzing the saturated ion exchange resin by using mixed acid of sulfurous acid and sulfuric acid to obtain the all-vanadium redox flow battery electrolyte. The electrolyte prepared by the method is high in purity and simple in step, and does not generate ammonia-nitrogen wastewater and waste gas.

Description

Technical Field

[0001] The present invention belongs to the field of liquid flow batteries, and in particular relates to a method for preparing an electrolyte for an all-vanadium liquid flow battery. Background Art

[0002] The rapid development of renewable energy sources such as wind and solar power has led to fluctuations in power generation, posing challenges to the stable operation of power systems and the balance of supply and demand. Long-duration energy storage, with its long lifespan and large capacity, can mitigate fluctuations in renewable energy generation over extended periods, ensuring power supply during seasonal and extreme weather conditions.

[0003] Energy storage technology is an effective way to address the volatility and intermittency of renewable energy systems, primarily wind and solar. It plays a key supporting role in establishing new power systems and is of great strategic significance. With the increase in installed capacity and power generation proportion of renewable energy, the requirements for energy storage duration are becoming increasingly stringent, and the demand for capacity-based energy storage is growing. There are many types of long-term energy storage technologies, including pumped hydro, compressed air storage, flow battery storage, heat and cold storage, and hydrogen storage. These technologies provide strong support for the large-scale utilization of renewable energy. Flow battery energy storage technology is relatively mature and basically meets the conditions for large-scale development. As the electrolyte of flow batteries, electrolyte plays a vital role in battery performance.

[0004] To enrich vanadium in vanadium extraction, solvent extraction or ion exchange are commonly used. For example, Cheng Qian (Using D201 Resin to Extract Vanadium from Acid Leaching Solution of Stone Coal Vanadium Ore [J]. Nonferrous Metals, 2022, 5:38-41) used D201 resin to adsorb pentavalent vanadium, which was then desorbed using a mixed solution of sodium hydroxide and sodium chloride to produce a sodium vanadate solution. This process requires multiple steps, including precipitation, roasting, dissolution, and reduction, to produce a vanadium electrolyte. This is a complex process and results in high production costs.

[0005] Chinese invention patent publication number CN114243042A discloses an ammonium-free, liquid-circulating vanadium extraction method for preparing a vanadium electrolyte. The vanadium source material undergoes sodium-based roasting and leaching to produce a vanadium-containing leachate. This leachate is then reduced by electrolytic current or by adding a reducing agent. The vanadium is then extracted and enriched, and stripped to produce an electrolyte. Electrolytic reduction consumes a high amount of energy, requires a large amount of additional reducing agent, and has a low utilization rate. Furthermore, the metallic reducing agent is prone to introducing impurities into the electrolyte, which can affect battery performance.

[0006] Chinese invention patent document CN119465181A discloses a method for preparing an all-vanadium electrolyte. Vanadium slag is leached with alkali and ammonium salt is precipitated to obtain vanadium oxide. The vanadium oxide is then dissolved and electrocatalytically reduced. This process produces ammonia nitrogen wastewater and is cumbersome. Impurities are also present during the vanadium precipitation process. At the same time, a large amount of ammonia gas is generated during the roasting of the vanadium oxide, causing environmental pollution. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing an electrolyte for an all-vanadium redox flow battery. The method utilizes a mixed acid of sulfurous acid and sulfuric acid for cyclic analysis to prepare an electrolyte with high purity and high concentration, simple steps, no need for the addition of an additional reducing agent, obvious economic benefits, and environmental friendliness.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing an all-vanadium redox flow battery electrolyte, comprising the following steps: (1) Mix and roast vanadium slag, sodium carbonate and magnesium oxide, add the roasted mixture into dilute sulfuric acid, heat and stir, and filter to obtain a leachate; (2) adjusting the pH of the leachate to acidic, separating the solid and liquid, adding a phosphoric acid-type extractant to the liquid, and extracting to obtain a chromium-vanadium-containing raffinate; (3) adjusting the pH of the chromium-vanadium raffinate to 0.5-1.5, adding an amine extractant, and extracting to obtain a vanadium-containing raffinate; (4) adjusting the pH of the vanadium-containing raffinate to 2-4 and passing it through an impregnated ion exchange resin to obtain a saturated ion exchange resin; (5) The saturated ion exchange resin is subjected to cyclic analysis using a mixture of sulfurous acid and sulfuric acid. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid is 1:0.5-0.6, and the molar ratio of sulfurous acid to sulfuric acid is 1:1-2, thereby obtaining an all-vanadium redox flow battery electrolyte.

[0009] Preferably, in step (1), the mass ratio of vanadium slag, sodium carbonate and magnesium oxide is 1:0.3 to 1:0.1 to 0.5; the roasting temperature is 600 to 750°C; the concentration of dilute sulfuric acid is 0.5 to 1 mol / L; and the mass ratio of the mixture to dilute sulfuric acid is 1:3 to 5.

[0010] Preferably, in step (2), the pH of the leaching solution is adjusted in the range of 1.8 to 3; and the phosphoric acid extractant is any one of P204, Cyanex 272, and P538.

[0011] Preferably, in step (3), the amine extractant is one of N1923 and O216.

[0012] Preferably, in step (4), the pH of the vanadium-containing raffinate is adjusted to a range of 2 to 3; and the ion exchange resin is one of D202, D453, and D301.

[0013] Preferably, in step (5), the desorption cycle is performed 4 to 6 times.

[0014] Preferably, in step (4), the preparation steps of the impregnated ion exchange resin are as follows: the ion exchange resin and the chelating extractant are placed in a reaction kettle and impregnated at a constant temperature to obtain the impregnated ion exchange resin.

[0015] More preferably, in step (4), the chelating extractant is one of LIX 63 and LIX 860; the volume ratio of the ion exchange resin to the chelating extractant is 1:1-2; the temperature is 60-90°C; and the immersion time is 6-12 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses an impregnated ion exchange resin to enrich vanadium, and then uses a mixed acid of sulfurous acid and sulfuric acid for cyclic desorption to prepare an electrolyte. During the desorption process, sulfurous acid acts as a reducing agent, reducing pentavalent vanadium on the ion exchange resin to tetravalent vanadium. It also serves as a supporting electrolyte, allowing for direct production of a vanadyl sulfate electrolyte. Compared to the prior art process of using alkaline solution desorption to prepare the electrolyte, this method eliminates the need for the addition of additional reducing agents, avoids the introduction of impurity ions, and offers a short process flow, simple operation, and low production costs. Furthermore, the cyclic desorption method significantly increases the vanadium concentration in the mixed acid solution. The inventors discovered that the sulfurous acid content in the mixed acid should not be too high, and the molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid should be controlled within a range of 1:0.5-0.6. This ensures complete reduction of the vanadium while preventing excess sulfurous acid from being present, thereby preventing trace impurity ions other than vanadium from being desorbed into the electrolyte.

[0017] The technology of the present invention obtains a high-purity vanadium electrolyte by separating impurity elements in stages. First, magnesium oxide is added during the roasting process to effectively inhibit the removal of impurity element silicon. Magnesium oxide reacts with silicon in vanadium slag to form magnesium silicate. The roasted mixture is then added to dilute sulfuric acid for acid leaching. During the acid leaching process, magnesium silicate reacts with sulfuric acid, and silicon element is converted into precipitate and removed by filtration to avoid being introduced into the electrolyte. The synthesis temperature of soluble vanadium compounds can be reduced, that is, the roasting temperature is reduced, thereby reducing roasting energy consumption and reducing the leaching of impurity elements. The element magnesium entering the leachate exists in the form of cations, and the phosphoric acid type extractant reacts with the magnesium through hydrogen ions. Ion exchange is carried out to remove 99.2% of the impurity magnesium; at the same time, a large amount of chromium (VI) element is introduced during the leaching process. The properties of chromium and vanadium are similar and difficult to separate. The pH of the chromium-vanadium extract is controlled to 0.5-1.5 in a strong acidic environment, and amine extractants are used to exchange anions with chromium to remove 99% of the impurity chromium; in the subsequent adsorption and analysis process, the content of sulfurous acid is strictly controlled to inhibit the analysis of impurity elements, which plays a role of secondary impurity removal. The dual effects of early impurity removal and sulfurous acid further improve the purity of the vanadium electrolyte.

[0018] The present invention utilizes an impregnated ion exchange resin and cyclic sulfurous acid desorption to produce a high-concentration vanadium electrolyte. First, an impregnated ion exchange resin is used to adsorb vanadium. The extractant has a chelating effect, binding to vanadium in the vanadium-containing raffinate and assisting in ion exchange between the ion exchange resin and the vanadium. This increases vanadium adsorption compared to conventional ion exchange resins. Furthermore, the dual combination of resin and extractant is applicable over a wider pH range. Circular sulfurous acid desorption further enhances vanadium desorption, resulting in a high-concentration vanadium electrolyte.

[0019] The present invention adopts a closed-loop design scheme to realize the comprehensive utilization of vanadium slag, not only obtaining high-concentration and high-purity vanadium electrolyte, but also obtaining products such as ferric oxide, magnesium sulfate, and chromium oxide, which has wide economic benefits.

[0020] (5) The existing technology uses alkaline leaching or oxidative roasting and acid leaching to precipitate vanadium compounds, which are then roasted to obtain vanadium oxides. The vanadium oxides are then electrochemically reduced or chemically reduced to obtain a vanadium electrolyte. Impurities are introduced during the vanadium precipitation process and enter the vanadium electrolyte during the reduction process. At the same time, a large amount of ammonia nitrogen wastewater is generated during the vanadium precipitation process, and the vanadium compound precipitate releases ammonia gas during the roasting process, polluting the environment. The present invention does not require the addition of ammonium salts to precipitate the vanadium compounds, so no ammonia nitrogen wastewater or waste gas is generated, which is environmentally friendly. The entire process is carried out in a liquid phase environment, and no additional reducing agent is required, which avoids the introduction of impurity ions. The process is simple and significantly reduces the production cost of the electrolyte. DETAILED DESCRIPTION

[0021] To make the purpose, technical solution, and effects of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] The vanadium content adsorbed by the saturated ion exchange resin is calculated as follows: first, the vanadium content in the vanadium raffinate is obtained by ICP-OES testing as n, and then the vanadium content in the aqueous phase remaining after the vanadium raffinate passes through the impregnated ion exchange resin is measured as m. The vanadium content adsorbed by the saturated ion exchange resin is nm. Example 1

[0023] Preparation of All-vanadium Redox Flow Battery Electrolyte 1 (1) Vanadium slag, sodium carbonate, and magnesium oxide were mixed in a mass ratio of 1:1:0.2, and calcined in a calciner at 750°C. The mixture was then mixed with 1 mol / L sulfuric acid in a mass ratio of 1:4, heated and stirred, and filtered to obtain a leachate. (2) Adjusting the pH of the leachate to 2.5, and performing solid-liquid separation; adding extractant P204 to extract magnesium to obtain a vanadium- and chromium-containing raffinate and a magnesium-loaded organic phase; (3) The pH of the chromium-vanadium raffinate was adjusted to 0.9, and an O216 extractant was added to extract the chromium element to obtain a vanadium-containing raffinate and a chromium-loaded organic phase. The vanadium content in the vanadium raffinate was determined to be 14 g / L by ICP-OES testing; (4) The total amount of vanadium in the vanadium extract was measured and the pH of the vanadium-containing raffinate was adjusted to 3. The vanadium was then adsorbed through a D202 resin impregnated with the extractant LIX 63 (impregnation temperature was 80°C for 10 h). A saturated ion exchange resin was obtained. The vanadium content in the remaining aqueous phase was measured to be 0.03 g / L, and the adsorption capacity of vanadium was calculated to be 13.97 g / L. (5) The saturated ion exchange resin was subjected to cyclic analysis 6 times using a mixed acid of sulfurous acid and sulfuric acid in a molar ratio of 1:1. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid was 1:0.5, and an all-vanadium redox flow battery electrolyte was obtained. Example 2

[0024] Preparation of All-vanadium Redox Flow Battery Electrolyte 2 (1) Vanadium slag, sodium carbonate, and magnesium oxide were mixed in a mass ratio of 1:0.6:0.3, and calcined in a calciner at 750°C. The mixture was then mixed with 0.5 mol / L sulfuric acid in a mass ratio of 1:5, heated and stirred, and filtered to obtain a leachate; (2) adjusting the pH of the leachate to 2, and performing solid-liquid separation; adding the extractant Cyanex 272 to extract the magnesium element, and obtaining a vanadium- and chromium-containing raffinate and a magnesium-loaded organic phase; (3) Testing the total amount of vanadium in the vanadium extract and adjusting the pH of the chromium-containing vanadium extract to 1.2, adding O216 extractant to extract the chromium element, obtaining a vanadium-containing extract and a chromium-loaded organic phase, and determining the vanadium content of the vanadium extract to be 13.5 g / L by ICP-OES testing; (4) The pH of the vanadium-containing raffinate was adjusted to 2.5, and the vanadium was adsorbed on a D301 resin impregnated with the extractant LIX 63 (impregnation temperature was 90°C, time was 6 h); a saturated ion exchange resin was obtained; the vanadium content in the remaining aqueous phase was measured to be 0.04 g / L, and the adsorption capacity of vanadium was calculated to be 13.46 g / L; (5) The saturated ion exchange resin was subjected to cyclic analysis 5 times using a mixed acid of sulfurous acid and sulfuric acid in a molar ratio of 1:2. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid was 1:0.6, and an all-vanadium redox flow battery electrolyte was obtained. Example 3

[0025] Preparation of All-vanadium Redox Flow Battery Electrolyte 3 (1) Vanadium slag, sodium carbonate, and magnesium oxide were mixed in a mass ratio of 1:0.6:0.5, and calcined in a calciner at 650°C. The mixture was then mixed with 0.6 mol / L sulfuric acid in a mass ratio of 1:3, heated and stirred, and filtered to obtain a leachate; (2) Adjusting the pH of the leachate to 1.8, and performing solid-liquid separation; adding extractant P538 to extract magnesium to obtain a vanadium- and chromium-containing raffinate and a magnesium-loaded organic phase; (3) The pH of the chromium-vanadium raffinate was adjusted to 1.5, and N1923 extractant was added to extract the chromium element to obtain a vanadium-containing raffinate and a chromium-loaded organic phase. The vanadium content in the vanadium raffinate was determined to be 13.2 g / L by ICP-OES testing. (4) The total amount of vanadium in the vanadium extract was tested and the pH of the vanadium-containing raffinate was adjusted to 2. The vanadium was then adsorbed through a D301 resin impregnated with the extractant LIX 860 (impregnation temperature was 60°C, time was 12 h); a saturated ion exchange resin was obtained; the vanadium content in the remaining aqueous phase was tested to be 0.05 g / L, and the adsorption capacity of vanadium was calculated to be 13.15 g / L; (5) The saturated ion exchange resin was subjected to cyclic analysis 4 times using a mixed acid of sulfurous acid and sulfuric acid in a molar ratio of 1:1. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid was 1:0.5 to obtain an all-vanadium redox flow battery electrolyte. Example 4

[0026] Preparation of All-vanadium Redox Flow Battery Electrolyte 4 (1) Mix vanadium slag, sodium carbonate and magnesium oxide in a mass ratio of 1:1:0.3, place them in a roasting furnace and roast them at 700°C, then mix the mixture with 1 mol / L sulfuric acid in a mass ratio of 1:5, heat and stir, and filter to obtain a leachate; (2) Adjust the pH of the leachate to 1.8 and separate the solid and liquid; (3) The pH of the chromium-vanadium raffinate was adjusted to 0.6, and N1923 extractant was added to extract the chromium element to obtain a vanadium-containing raffinate and a chromium-loaded organic phase. The vanadium content in the vanadium raffinate was determined to be 13.8 by ICP-OES testing; (4) The total amount of vanadium in the vanadium extract was measured and the pH of the vanadium-containing raffinate was adjusted to 2. The vanadium was then adsorbed on a D453 resin impregnated with the extractant LIX 860 (impregnation temperature was 70°C for 10 h). A saturated ion exchange resin was obtained. The vanadium content in the remaining aqueous phase was measured to be 0.04 g / L, and the adsorption capacity of vanadium was calculated to be 13.76 g / L. (5) The saturated ion exchange resin was subjected to cyclic analysis five times using a mixed acid (concentration of 5 mol / L) of sulfuric acid and sulfuric acid in a volume ratio of 1:1.5. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfuric acid was 1:0.6, and an all-vanadium redox flow battery electrolyte was obtained. Example 5

[0027] Preparation of All-vanadium Redox Flow Battery Electrolyte 5 (1) Vanadium slag, sodium carbonate, and magnesium oxide were mixed in a mass ratio of 1:0.3:0.4, and calcined in a calciner at 600°C. The mixture was then mixed with 0.8 mol / L sulfuric acid in a mass ratio of 1:5, heated and stirred, and filtered to obtain a leachate; (2) Adjusting the pH of the leachate to 2.5, and performing solid-liquid separation; adding extractant P204 to extract magnesium to obtain a vanadium- and chromium-containing raffinate and a magnesium-loaded organic phase; (3) The pH of the chromium-vanadium raffinate was adjusted to 1.2, and an O216 extractant was added to extract the chromium element to obtain a vanadium-containing raffinate and a chromium-loaded organic phase. The vanadium content in the vanadium raffinate was determined to be 13.2 g / L by ICP-OES testing. (4) The total amount of vanadium in the vanadium extract was measured and the pH of the vanadium-containing raffinate was adjusted to 2.8. The vanadium was then adsorbed through a D202 resin impregnated with the extractant LIX 63 (impregnation temperature was 80°C for 8 hours). A saturated ion exchange resin was obtained. The vanadium content in the remaining aqueous phase was measured to be 0.02 g / L, and the adsorption capacity of vanadium was calculated to be 13.18 g / L. (5) The saturated ion exchange resin was subjected to cyclic analysis 4 times using a mixed acid of sulfurous acid and sulfuric acid in a molar ratio of 1:1. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid was 1:0.5, and an all-vanadium redox flow battery electrolyte was obtained. Comparative Example 1

[0028] Preparation of All-vanadium Redox Flow Battery Electrolyte 6 Step (4) tests the total amount of vanadium in the vanadium extract and adjusts the pH of the vanadium-containing raffinate to 3, and passes it through a D202 resin for adsorption; the vanadium content in the remaining aqueous phase is tested to be 1.32 g / L, and the adsorption amount of vanadium is calculated to be 12.68 g / L; the remaining conditions and calculation method are the same as those in Example 1. Comparative Example 2

[0029] Preparation of All-vanadium Redox Flow Battery Electrolyte 7 Step (4) The total amount of vanadium in the vanadium extract was tested and the pH of the vanadium-containing raffinate was adjusted to 3, and extraction was performed using the extractant LIX 63; the vanadium content in the remaining aqueous phase was tested to be 1.29 g / L, and the vanadium extraction amount was calculated to be 12.71 g / L; the remaining conditions and calculation method were the same as in Example 1. Comparative Example 3

[0030] Preparation of All-vanadium Redox Flow Battery Electrolyte 8 The pH of the chromium-vanadium raffinate was adjusted to 0.3, and an O216 extractant was added to extract the chromium element to obtain a vanadium-containing raffinate and a chromium-loaded organic phase; the remaining conditions and calculation method were the same as those in Example 1. Comparative Example 4

[0031] Preparation of All-vanadium Redox Flow Battery Electrolyte 9 The pH of the chromium-vanadium raffinate was adjusted to 2.0, and an O216 extractant was added to extract the chromium element to obtain a vanadium-containing raffinate and a chromium-loaded organic phase; the remaining conditions and calculation method were the same as those in Example 1.

[0032] The physical parameter results of the all-vanadium redox flow battery electrolytes prepared in Examples 1 to 5 and Comparative Examples 1 to 4 are listed in Table 1.

[0033]

[0034] In Example 1, the vanadium leaching rate was 95%. In Example 4, the mass ratio of vanadium slag to sodium carbonate and the sulfuric acid concentration were the same as in Example 1, but the roasting temperature was lower, 700°C, resulting in a slightly lower content of soluble vanadium compounds and a leaching rate of 94%. The leaching rates of Examples 2 and 3 were similar. The mass ratio of vanadium slag to sodium carbonate was the same, 1:0.6. However, the slightly higher magnesium oxide content in Example 3 significantly reduced the leaching rate, even at a roasting temperature of 650°C, lower than that of Example 2. This indicates that the addition of magnesium oxide can reduce the roasting temperature.

[0035] In Comparative Example 1, vanadium adsorption was performed only through D202 resin, and in Comparative Example 2, vanadium extraction was performed only through extractant LIX 63. Therefore, the degree of vanadium enrichment was low, resulting in a low electrolyte concentration.

[0036] In Comparative Example 3, the pH of the chromium-vanadium raffinate was adjusted to 0.3, resulting in a low chromium removal rate. Consequently, some chromium was not removed, leading to a higher chromium content in the electrolyte. In Comparative Example 4, the pH of the chromium-vanadium raffinate was adjusted to 2, resulting in co-extraction of vanadium during chromium extraction, resulting in an electrolyte concentration lower than that in Comparative Example 3.

Claims

1. A method for preparing an all-vanadium redox flow battery electrolyte, characterized in that: The steps include: (1) Mix and roast vanadium slag, sodium carbonate and magnesium oxide, add the roasted mixture into dilute sulfuric acid, heat and stir, and filter to obtain a leachate; (2) adjusting the pH of the leachate to acidic, separating the solid and liquid, adding a phosphoric acid-type extractant to the liquid, and extracting to obtain a chromium-vanadium-containing raffinate; (3) adjusting the pH of the chromium-vanadium raffinate to 0.5-1.5, adding an amine extractant, and extracting to obtain a vanadium-containing raffinate; (4) adjusting the pH of the vanadium-containing raffinate to 2-4 and passing it through an impregnated ion exchange resin to obtain a saturated ion exchange resin; (5) The saturated ion exchange resin is subjected to cyclic analysis using a mixture of sulfurous acid and sulfuric acid. The molar ratio of vanadium adsorbed by the saturated ion exchange resin to sulfurous acid is 1:0.5-0.6, and the molar ratio of sulfurous acid to sulfuric acid is 1:1-2, thereby obtaining an all-vanadium redox flow battery electrolyte.

2. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, wherein: In the step (1), the mass ratio of vanadium slag, sodium carbonate and magnesium oxide is 1:0.3 to 1:0.1 to 0.5; the roasting temperature is 600 to 750°C; the concentration of dilute sulfuric acid is 0.5 to 1 mol / L; and the mass ratio of the mixture to the dilute sulfuric acid is 1:3 to 5.

3. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: In the step (2), the pH of the leaching solution is adjusted in the range of 1.8 to 3; the phosphoric acid extractant is any one of P204, Cyanex 272, and P538.

4. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, wherein: In the step (3), the amine extractant is one of N1923 and O216.

5. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, wherein: In the step (4), the pH of the vanadium-containing raffinate is adjusted to a range of 2 to 3; and the ion exchange resin is one of D202, D453, and D301.

6. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: In the step (5), the desorption is cyclically performed 4 to 6 times.

7. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: In the step (4), the impregnated ion exchange resin is prepared by the following steps: placing the ion exchange resin and the chelating extractant in a reaction kettle and impregnating them at a constant temperature to obtain the impregnated ion exchange resin.

8. The method for preparing an all-vanadium redox flow battery electrolyte according to claim 7, wherein: In the step (4), the chelating extractant is one of LIX 63 and LIX 860; the volume ratio of the ion exchange resin to the chelating extractant is 1:1-2, the temperature is 60-90°C; and the immersion time is 6-12 hours.

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