Method for preparing vanadium electrolyte by sodium polyvanadate extraction method

Abstract

The invention provides a method for preparing a vanadium electrolyte through a sodium polyvanadate extraction method, and belongs to the technical field of vanadium electrolyte preparation, and the method comprises the steps that S1, sodium polyvanadate is dissolved in alkali liquor to remove impurity metal ions and insoluble substances, and a vanadium-containing alkaline solution is obtained; s2, a reducing agent is added into the vanadium-containing alkaline solution, the pH of the solution is adjusted to be strongly acidic, pentavalent vanadium is reduced into tetravalent vanadium, then alkali is added, the pH is adjusted to be within the optimal extraction pH range, and a tetravalent vanadium reducing solution is obtained; s3, extracting the tetravalent vanadium reduction solution by using an organic phase to obtain a loaded organic phase; s4, washing the loaded organic phase with a dilute sulfuric acid solution; s5, after washing is finished, reverse extraction is carried out with a sulfuric acid solution, and an organic phase-containing electrolyte is obtained; and S6, removing the organic phase in the electrolyte containing the organic phase through adsorption treatment to obtain the vanadium electrolyte. The method has the characteristics of short process, high efficiency and low-cost preparation potential of the vanadium electrolyte, can realize short-process preparation of the vanadium battery electrolyte, and greatly reduces the preparation cost of the electrolyte.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of vanadium electrolyte preparation, and particularly relates to a method for preparing vanadium electrolyte by sodium polyvanadate extraction. BACKGROUND

[0002] New power systems mainly based on renewable energy sources have become the focus of attention, and wind power and photovoltaic power as representatives of green energy have also attracted much attention. However, wind power and photovoltaic power both have problems such as intermittency and randomness, and it is difficult to control them artificially, while large-scale energy storage technology can effectively solve the above problems, realize continuous and stable power output, and ensure the safety of the power grid. According to the needs of different application scenarios, researchers have developed various forms of energy storage technology. Among them, all-vanadium redox flow battery (hereinafter referred to as vanadium battery) has the advantages of flexible design, long service life, good charge-discharge performance, high safety, and high energy efficiency, and is one of the most suitable technical solutions for large-scale energy storage, and has a broad application prospect in the field of large-scale energy storage.

[0003] The vanadium battery uses porous carbon felt or graphite felt as the electrode, which has good electrical conductivity and large specific surface area, and can provide sufficient reaction sites for electrochemical reaction. A separation membrane is placed between the two electrodes, which has selective permeability and only allows specific ions such as hydrogen ions to pass through, preventing vanadium ions in the positive and negative electrolytes from mixing, and ensuring the normal operation of the battery. The electrolyte and the electrode are connected by a pump and a pipeline, so that the electrolyte can flow on the surface of the electrode. Among them, the vanadium electrolyte is the core material in the vanadium battery, which directly affects the energy density and electrochemical performance of the battery, and at the same time, the cost of the electrolyte accounts for 40% of the total cost of the vanadium battery. Therefore, its preparation process is crucial to the development of vanadium batteries.

[0004] The national standard (GB / T37204-2018) for vanadium electrolyte makes clear requirements for vanadium ions, sulfate ions and impurity ions in the vanadium electrolyte. Impurity ions have a significant impact on the electrochemical performance, ion transport performance and stability of the electrolyte, so in the preparation process of the electrolyte, not only the concentrations of vanadium ions and sulfate ions should meet the standard, but also the concentration of impurity ions should not be greater than the requirement of the national standard.

[0005] Early vanadium electrolyte is prepared by dissolving high-purity VOSO4 in sulfuric acid solution directly, but VOSO4 is expensive, and such preparation method is high in cost and poor in process economy. Therefore, researchers begin to seek other efficient and low-cost ways to prepare vanadium electrolyte. At present, the mainstream preparation method of vanadium electrolyte is reduction method and electrolysis method. The raw material for the reduction method is V2O5 or NH4VO3. V2O5 or NH4VO3 is difficult to dissolve in sulfuric acid solution, and a reducing agent needs to be added to prepare vanadium electrolyte through oxidation-reduction reaction. The reducing agent has the following choices: oxalic acid, ethanol, tartaric acid, formic acid and acetic acid; H2S; SO2. In addition, H2O2, V2O3 and the like are also used as reducing agents for vanadium electrolyte preparation experiments. The reduction method, as the main process for the production of electrolyte in the industry at present, has the advantages of large scale and high efficiency, but the reducing agent easily introduces impurities, affecting the energy storage performance of the electrolyte. The electrolysis method uses V2O5 or NH4VO3 and sulfuric acid suspension as the reaction solution, and passes direct current to make vanadium ions on the electrode surface undergo oxidation-reduction reaction, so as to realize the generation and dissolution of vanadium ions in different valence states, and then prepare the required vanadium electrolyte. Skyllas-Kazacos M et al. prepared electrolyte by electrolyzing V2O5 and sulfuric acid suspension, which can meet the requirements of vanadium battery electrolyte in the laboratory. Johnson et al. added H2SO4 to the positive electrode of the electrolytic cell with a diaphragm, and added NH4VO3-containing H2SO4 of the same concentration to the negative electrode, and prepared high-performance vanadium electrolyte by electrolysis. When the electrolysis method is used to prepare electrolyte, the introduction of impurity elements can be effectively controlled, part of the heavy metal ions in the raw material can be removed, and the valence state of vanadium ions can be accurately controlled. However, the production efficiency is low, the energy consumption is high, and the equipment requirements are strict, which cannot meet the needs of industrial production.

[0006] The existing preparation process uses high-purity vanadium oxide as raw material, and industrial-grade vanadium oxide needs to be treated by ammonium salt vanadium precipitation (impurity ion removal) and high-temperature calcination for multiple times. This process not only leads to high energy consumption, low chemical reagent utilization rate and environmental pollution, but also significantly increases the cost of preparing vanadium electrolyte.

[0007] Some researchers have proposed a research idea of preparing vanadium electrolyte by extraction method, that is, by adding a specific extractant into a vanadium-containing solution, vanadium ions are selectively transferred to the extraction phase, and then through back extraction and other operations, vanadium ions are transferred to the back extraction solution, and after further treatment, vanadium electrolyte is obtained. In a method, a leaching solution obtained by blank roasting and acid leaching of stone coal decarburization slag is used as raw material, an amine extractant is used to extract vanadium, and sodium carbonate is used for back extraction to obtain an alkaline vanadium-rich solution, and then vanadium is precipitated, calcined to obtain V2O5, and after reduction, VOSO4 solution is obtained. In another method, vanadium precipitation wastewater from vanadium-titanium magnetite is used as raw material, an amine extractant is used to extract vanadium, and sodium hydroxide is used as a back extraction agent, and after multi-stage countercurrent back extraction, a vanadium-rich solution is obtained, and after hydrolysis, vanadium is precipitated, calcined to obtain V2O5, and after reduction, vanadium electrolyte is obtained. Although the above methods both use solvent extraction to prepare vanadium electrolyte, but still need to reduce vanadium once to obtain vanadium electrolyte, and cannot directly prepare high-concentration vanadium electrolyte by one-step extraction-back extraction. In a method, a two-stage acid leaching solution of vanadium slag calcification roasting is used as raw material, an amine extractant is used for extraction and sodium carbonate is used for back extraction to obtain an alkaline pentavalent vanadium-rich solution, and then the pentavalent vanadium-rich solution is treated with Na2SO3 as a reducing agent, extracted by a phosphorus extractant, back extracted by H2SO4 to obtain a tetravalent vanadium-rich back extraction solution, and then evaporated and concentrated to obtain vanadium electrolyte. This method avoids the step of reducing vanadium after back extraction, but needs two-step extraction, and the pH value needs to be adjusted in the middle, which is complicated.

[0008] In another method, vanadium-containing chloride solution is used as raw material, P507 is used as extractant, and sulfuric acid is used as back extraction agent, vanadium is separated by one extraction-back extraction, and vanadium, iron and aluminum are separated by five times of sulfate solution extraction-back extraction, and finally high-purity vanadium sulfate oxide solution is obtained, which contains 76.5g / L of vanadium and less than 50mg / L of impurities. This method does not need to adjust the pH value and evaporate and concentrate during the whole process, and liquid-liquid preparation of vanadium electrolyte is realized, but the extraction needs to go through two extraction-back extraction cycles, and the steps are relatively complicated.

[0009] Therefore, it is still a core problem to be solved for promoting large-scale application of all-vanadium redox flow batteries to develop a vanadium electrolyte preparation technology with simplified process and controllable cost. SUMMARY

[0010] In order to solve the problems of high cost, complex steps and poor process economy existing in the preparation technology of vanadium electrolyte, the present application provides a method for preparing vanadium electrolyte by sodium polyvanadate extraction, which has the characteristics of short process, high efficiency and low cost for preparing vanadium electrolyte, and can realize short process preparation of vanadium battery electrolyte and greatly reduce the preparation cost of electrolyte.

[0011] The present application is realized by the following technical scheme:

[0012] The present application provides a method for preparing vanadium electrolyte by sodium polyvanadate extraction, which comprises:

[0013] S1. Dissolving sodium polyvanadate in lye to remove impurity metal ions and insoluble substances, obtaining a vanadium-containing alkaline solution;

[0014] S2. Adding a reducing agent to the vanadium-containing alkaline solution and adjusting the pH of the solution to strong acidity to reduce pentavalent vanadium to tetravalent vanadium, and then adding alkali to adjust the pH to an optimal extraction pH range, obtaining a tetravalent vanadium reduction solution;

[0015] S3. Extracting the tetravalent vanadium reduction solution with an organic phase to obtain a loaded organic phase;

[0016] S4. Washing the loaded organic phase with a dilute sulfuric acid solution;

[0017] S5. After washing, stripping with a sulfuric acid solution to obtain an organic phase-containing electrolyte;

[0018] S6. Removing the organic phase from the organic phase-containing electrolyte by adsorption treatment to obtain a vanadium electrolyte;

[0019] The reducing agent includes any one of Na2SO3, Na2S2O5 and CaSO3.

[0020] The organic phase is formed by mixing an acidic phosphorus type extractant (main extractant), a phase separation agent (auxiliary extractant) and a diluent;

[0021] The acidic phosphorus type extractant includes any one of P204 (di(2-ethylhexyl) phosphoric acid), P507 (2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester) and Cyanex272 (bis(2,4,4-trimethylpentyl) phosphonic acid), the phase separation agent includes TBP (tributyl phosphate), and the diluent includes 260# solvent oil.

[0022] Further, step S1 specifically includes:

[0023] Dissolving sodium polyvanadate in a NaOH solution at 50-80°C to precipitate impurity metal ions and insoluble substances, and obtaining a vanadium-containing alkaline solution through solid-liquid separation;

[0024] The concentration of VO2 + in the vanadium-containing alkaline solution is 1-40 g / L, and the pH value of the vanadium-containing alkaline solution is 8-12.

[0025] Preferably, the concentration of VO2 + in the vanadium-containing alkaline solution is 10-30 g / L, the pH value of the vanadium-containing alkaline solution is 8-10, the temperature of the NaOH solution is preferably 65-75°C, the sodium polyvanadate dissolution time is 0.5-2.5 h, and is preferably 1-1.5 h.

[0026] Further, step S2 specifically includes:

[0027] adding a reducing agent and concentrated sulfuric acid to the vanadium-containing alkaline solution, controlling the reaction end-point pH value to be 0.5-1.5 to reduce the pentavalent vanadium to tetravalent vanadium, and adding sodium hydroxide to adjust the pH to 1.8-2.6 after the reduction is completed to obtain a tetravalent vanadium reduction solution;

[0028] wherein the amount of the reducing agent is 1.2-1.5 times the theoretical amount (i.e., the molar ratio of (SO3 2- ) in the reducing agent to (2VO2 + ) in the vanadium-containing alkaline solution is 1.2-1.5).

[0029] Preferably, the reducing agent is Na2SO3, and the amount of the reducing agent is 1.2-1.3 times the theoretical amount.

[0030] Preferably, the reducing agent and concentrated sulfuric acid are added to the vanadium-containing alkaline solution, and the reaction end-point pH value is controlled to be 0.8-1.2.

[0031] Further, step S3 specifically comprises:

[0032] carrying out multi-stage countercurrent extraction of the tetravalent vanadium reduction solution with the organic phase to obtain a loaded organic phase;

[0033] wherein the volume percentage of the acidic phosphorus-type extractant in the organic phase is 10-40%, the volume percentage of the phase splitter in the organic phase is 10%, and the volume percentage of the diluent in the organic phase is 50-80%.

[0034] Preferably, the acidic phosphorus-type extractant is P204, and the volume percentage of the acidic phosphorus-type extractant in the organic phase is 20-30%.

[0035] Further, in the multi-stage countercurrent extraction, the pH of the tetravalent vanadium reduction solution is 1.8-2.6, the extraction stage number is 4-6, and the volume ratio of the organic phase to the aqueous phase (the aqueous phase refers to the tetravalent vanadium reduction solution) is 1:3-3:1.

[0036] In the multi-stage countercurrent extraction, the volume ratio of the acidic phosphorus-type extractant, the phase splitter, and the diluent in the organic phase is (2-4):1:(7-5), the extraction mixing time is 4-12 min, and the clarification time is 4-12 min.

[0037] Preferably, the volume ratio of the organic phase to the aqueous phase is (2-3):1, the volume ratio of the acidic phosphorus-type extractant, the phase splitter, and the diluent in the organic phase is 3:1:6, the extraction mixing time is 8-10 min, and the clarification time is 6-8 min.

[0038] Further, step S4 specifically comprises:

[0039] The loaded organic phase is washed by a multi-stage countercurrent washing with a dilute sulfuric acid solution at 0.1-0.5 mol / L;

[0040] The volume ratio of the loaded organic phase to the dilute sulfuric acid solution (phase ratio (O / A)) is (1-10):1.

[0041] The washing mixing time is 6-14 min, and the clarification time is 6-14 min.

[0042] Preferably, the volume ratio of the loaded organic phase to the dilute sulfuric acid solution is 5:1, the washing mixing time is 10-12 min, and the clarification time is 8-10 min.

[0043] Further, step S5 specifically comprises:

[0044] After the washing, a multi-stage countercurrent stripping is performed with a sulfuric acid solution at 4.6-6 mol / L to obtain a VO 2+ The organic phase electrolyte has a concentration of 1.6-2.0 mol / L.

[0045] The stripping mixing time is 4-12 min, and the clarification time is 4-12 min.

[0046] Preferably, the stripping mixing time is 10-12 min, and the clarification time is 8-10 min.

[0047] Further, step S6 specifically comprises:

[0048] The activated carbon is sequentially soaked in a H2O2 solution and a H2SO4 solution, and then washed with water and dried to obtain an adsorbent.

[0049] The adsorbent is added to the organic phase electrolyte, and the obtained mixture is stirred and subjected to solid-liquid separation to obtain a vanadium electrolyte.

[0050] The carbon-to-liquid ratio of the adsorbent in the mixture is 0.03±0.01 g / mL.

[0051] Further, step S6 specifically comprises:

[0052] The activated carbon is soaked in a 4-6% H2O2 solution for 2±0.5 h, and then transferred to a 3±0.5 mol / L H2SO4 solution, and stirred at a constant temperature of 40-50°C for 2-4 h. The activated carbon is then washed with water several times, and dried at 120±10°C for 18-24 h to obtain an adsorbent.

[0053] The organic phase electrolyte is heated to 55-65 DEG C and kept for 30+ / -5 min, then the adsorbent is added into the organic phase electrolyte, and magnetic stirring is carried out at 25-30 DEG C for 4+ / -0.5 h, and then 0.45 mu m filter membrane is used for suction filtration to obtain the vanadium electrolyte.

[0054] Based on the same inventive concept, the application provides an application of a method for preparing vanadium electrolyte by sodium polyvanadate extraction method in preparation of a full vanadium liquid flow battery.

[0055] The one or more technical solutions in the embodiments of the application have at least the following technical effects or advantages:

[0056] 1. A method for preparing vanadium electrolyte by sodium polyvanadate extraction method, which uses sodium polyvanadate, a by-product of chromium extraction, as raw material, and prepares vanadium electrolyte by extraction technology, realizes separation of vanadium and impurity elements by optimizing the extraction process, has the characteristics of short process, high efficiency and low cost in preparation of vanadium electrolyte, has low raw material cost and easy access to extractant, and can avoid problems such as ammonia-nitrogen wastewater and high energy consumption in the current preparation process of vanadium battery electrolyte, and can realize short process preparation of vanadium battery electrolyte by solvent extraction method, greatly reduce the preparation cost of electrolyte, and solve the problems of high preparation cost, complex steps and poor process economy of the current vanadium electrolyte preparation.

[0057] 2. A method for preparing vanadium electrolyte by sodium polyvanadate extraction method, which can obtain national standard vanadium electrolyte from sodium polyvanadate, a by-product of chromium extraction, by a series of steps of leaching-reduction-extraction-washing-back extraction-removal of organic phase, to meet the energy storage demand of full vanadium liquid flow battery, specifically: first, preliminary impurity removal is carried out by alkali solution control of pH; second, impurity removal is carried out while vanadium ions are enriched by controlling related parameters such as extraction-washing; third, the concentration of back extraction agent and the phase ratio are controlled to make the vanadium concentration in the back extraction liquid directly reach the demand range of electrolyte; and finally, activated carbon adsorption is used to remove the organic phase, so that the effect of the electrolyte prepared by extraction method is consistent with that of the commercial vanadium electrolyte, and compared with the traditional method, the preparation, dissolution and re-dispersion of vanadium oxide intermediates are omitted, the production cost is effectively reduced while the stability of electrolyte components is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0059] Figure 1 The flow chart of the method for preparing vanadium electrolyte by sodium polyvanadate extraction method.

[0060] Figure 2 Cyclic voltammogram comparison chart of CG and EG.

[0061] Figure 3 Nyquist curve comparison chart of CG and EG.

[0062] Figure 4 First charge-discharge voltage curve of CG and EG.

[0063] Figure 5 Extraction method electrolyte prepared under different current densities and national standard vanadium electrolyte: (a) coulomb efficiency comparison chart; (b) voltage efficiency comparison chart; (c) energy efficiency comparison chart.

[0064] Figure 6 Morphological characteristics of sodium polyvanadate raw material. DETAILED DESCRIPTION

[0065] The advantages and various effects of the present application will be more clearly presented hereinafter in conjunction with specific embodiments and examples. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present application, rather than limit the present application.

[0066] Throughout the specification, unless otherwise specifically indicated, the terms used herein are to be understood in the manner as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. If there is a conflict, the present specification takes precedence.

[0067] Unless otherwise specifically indicated, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0068] The technical principle of the present application is as follows:

[0069] The chromium-containing by-product sodium polyvanadate is dissolved in an alkaline solution to form a vanadium-containing alkaline solution, and vanadium exists in the form of pentavalent. Since the raw material contains impurities such as iron, chromium, silicon and aluminum, the alkaline solution of sodium hydroxide can form hydroxide precipitate with them, so preliminary impurity removal can be carried out by suction filtration. After impurity removal, a reducing agent sodium sulfite is added and the pH of the solution is adjusted to about 1, the pentavalent vanadium solution is reduced to tetravalent vanadium reducing solution, and the metal impurities in the solution which are easy to co-extract with vanadium such as iron and chromium are reduced to reduce the co-extraction rate. The reaction equations are shown as (1), (2) and (3):

[0070]

[0071] According to formula (1), 1 mole of Na2SO3 reducing agent can reduce 2 moles of pentavalent vanadium ion (VO2 +). But in the actual reaction, excess reducing agent is added, so the amount of reducing agent is 1.2-1.5 times of the theoretical amount. In the reaction formula (1), the reduction reaction consumes hydrogen ions, so the reduction of pentavalent vanadium needs to be carried out in an acidic solution.

[0072] P204 (molecular formula C 16 H 35 O4P), TBP and 260# solvent oil are mixed in a certain proportion to obtain an organic phase. The organic phase is mixed with a reducing solution according to a given volume ratio (phase ratio (O / A)), multi-stage countercurrent extraction is carried out, and after standing and phase separation, a loaded organic phase and a lean reducing solution are obtained respectively. The reaction occurring in the extraction process is:

[0073] VO 2+ +(H(C8H 17 )2PO4) 2(o) =VO[(C8H 17 )2PO4] 2(o) +2H +

[0074] The washing solution is mixed with the reducing solution according to a given volume ratio (phase ratio (O / A)), multi-stage countercurrent washing is carried out, and after standing and phase separation, a purified loaded organic phase and a washing solution are obtained respectively.

[0075] According to the concentration of the loaded organic phase and the target vanadium electrolyte concentration, the volume ratio (phase ratio (O / A)) is calculated, the required sulfuric acid concentration is determined according to the national standard requirements of the vanadium electrolyte, multi-stage countercurrent washing is carried out, and after standing and phase separation, a vanadium electrolyte containing a small amount of organic phase and a lean organic phase are obtained. The stripping process is the reverse reaction of the extraction reaction, that is:

[0076] VO[(C8H 17 )2PO4] 2(o) +H2SO4=VOSO4+(H(C8H 17 )2PO4) 2(o)

[0077] The stripping solution inevitably contains organic matter. The activated carbon is subjected to oxidation pretreatment, surface organic impurities are removed by immersion in a hydrogen peroxide solution, and then acidification and activation treatment are carried out in a sulfuric acid solution. After being washed with deionized water to neutralization, the activated carbon is dried for standby use. The pretreated activated carbon is mixed with the electrolyte to be purified in a certain proportion, dynamic adsorption is carried out under constant temperature stirring, and finally solid-liquid separation is realized by vacuum filtration through a microporous filter membrane, so that a vanadium battery special electrolyte with a qualified organic impurity content is obtained.

[0078] Specifically, the present application provides a method for preparing a vanadium electrolyte by sodium polyvanadate extraction, which comprises:

[0079] S1. Dissolving sodium polyvanadate in lye to remove impurity metal ions and insoluble substances, obtaining a vanadium-containing alkaline solution;

[0080] S2. Adding a reducing agent to the vanadium-containing alkaline solution and adjusting the pH of the solution to strong acidity to reduce pentavalent vanadium to tetravalent vanadium, and then adding alkali to adjust the pH to an optimal extraction pH range, obtaining a tetravalent vanadium reduction solution;

[0081] S3. Extracting the tetravalent vanadium reduction solution with an organic phase to obtain a loaded organic phase;

[0082] S4. Washing the loaded organic phase with a dilute sulfuric acid solution;

[0083] S5. After washing, stripping with a sulfuric acid solution to obtain an organic phase-containing electrolyte;

[0084] S6. Removing the organic phase from the organic phase-containing electrolyte by adsorption treatment to obtain a vanadium electrolyte;

[0085] The reducing agent includes any one of Na2SO3, Na2S2O5 and CaSO3.

[0086] The organic phase is mixed by an acidic phosphorus type extractant, a phase separation agent and a diluent.

[0087] The acidic phosphorus type extractant includes any one of P204, P507 and Cyanex272, the phase separation agent includes TBP (tributyl phosphate), and the diluent includes 260# solvent oil.

[0088] In the present application, the reducing agent is Na2SO3, Na2S2O5 or CaSO3, which has strong reducing property. Since the alkali solution is used to remove impurities, NaOH is introduced, and therefore a reducing agent containing Na + is also required to avoid introducing new impurities. Therefore, the most preferred reducing agent is Na2SO3. The organic phase is mixed by an acidic phosphorus type extractant, a phase separation agent and a diluent, which can synergistically enhance the extraction and phase separation capacity: the extractant dominates the selectivity (P204): specifically binds to tetravalent vanadium ions (VO 2+ ), realizes high selective extraction and inhibits the co-extraction of metal impurity ions; the phase separation agent optimizes separation (TBP): reduces the interfacial tension of two phases, speeds up the separation and reduces emulsification. The diluent adjusts the physical properties (260# solvent oil): reduces the viscosity and density of the system, improves the flowability, promotes mass transfer, and at the same time avoids phase change or crystallization of the extractant due to too high concentration.

[0089] In the present invention, the advantages of using P204, P507 or Cyanex272 as the acidic phosphorus extractant are high single-stage extraction rate, low circulation cost, high vanadium enrichment, thorough impurity removal, and convenient operation; the phase separator uses TBP, which can effectively reduce the interfacial tension between the aqueous phase and the organic phase, promote rapid separation of the two phases, reduce emulsification and entrainment, and thus improve separation efficiency; the diluent uses 260# solvent oil, which has a moderate viscosity and can effectively reduce the viscosity of the system after mixing with the extractant (P204), improve fluidity, and promote mass transfer efficiency.

[0090] Furthermore, step S1 specifically includes:

[0091] Dissolve sodium polyvanadate in a NaOH solution at 50-80°C to precipitate impure metal ions and insoluble matter, and obtain a vanadium-containing alkaline solution through solid-liquid separation;

[0092] Wherein, the VO2 in the vanadium-containing alkaline solution + The concentration is 1-40 g / L, and the pH value of the vanadium-containing alkaline solution is 8-12.

[0093] Furthermore, step S2 specifically includes:

[0094] Adding a reducing agent and concentrated sulfuric acid to the vanadium-containing alkaline solution, controlling the pH value at the reaction end point to be 0.5-1.5 to reduce pentavalent vanadium to tetravalent vanadium, and then adding sodium hydroxide to adjust the pH to 1.8-2.6 to obtain a tetravalent vanadium reduction solution;

[0095] Wherein, the dosage of the reducing agent is 1.2 to 1.5 times the theoretical dosage.

[0096] In the present invention, the purpose of controlling the pH value of the reaction end point to 0.5-1.5 is that the reduction experiment must be carried out in an acidic environment, and the extraction pH is required to be maintained at 1.8-2.6. However, it was found in the experiment that when concentrated sulfuric acid was added to adjust the pH of the solution to 1±0.5, the color of the solution changed within tens of seconds. After testing with a spectrophotometer, it was found that VO2 + Has basically been restored to VO 2+ The reduction rate is 99.50%, so excess acid can accelerate the reduction, that is, the pH value at the end of the reaction is 0.5-1.5, and then a small amount of NaOH solid is added to adjust the pH to the optimal extraction pH range of 1.8-2.6.

[0097] Furthermore, step S3 specifically includes:

[0098] Performing multi-stage countercurrent extraction on a tetravalent vanadium reduction solution using an organic phase to obtain a loaded organic phase;

[0099] The volume percentage of the acidic phosphorus-based extractant in the organic phase is 10-40%, the volume percentage of the phase separation agent in the organic phase is 10%, and the volume percentage of the diluent in the organic phase is 50-80%.

[0100] In the present invention, the volume percentage of the acidic phosphorus extractant in the organic phase is 10-40%. The advantage is that the higher the concentration of the extractant, the higher the vanadium extraction rate. However, when the concentration of the extractant is too high, it will cause phase separation difficulties, the organic phase viscosity is too high, the fluidity is poor, and emulsification is likely to occur. At the same time, the extraction cost rises sharply. Considering the VO 2+ 、Fe 2+ The economic balance between the separation efficiency of impurity ions and the cost of reagents was finally determined to be 10-40%, at which point the extraction effect and economic balance were better.

[0101] Furthermore, in the multi-stage countercurrent extraction, the pH of the tetravalent vanadium reduction solution is 1.8 to 2.6, the number of extraction stages is 4 to 6, and the volume ratio of the organic phase to the aqueous phase is 1:3 to 3:1;

[0102] In the multi-stage countercurrent extraction, the volume ratio of the acidic phosphorus extractant, the phase separator and the diluent in the organic phase is (2-4):1:(7-5), the extraction mixing time is 4-12 minutes, and the clarification time is 4-12 minutes.

[0103] In the present invention, the pH of the tetravalent vanadium reducing solution is 1.8 to 2.6. 2+ In terms of P204 extraction, it is a cation exchange process, and the extractant releases H + With VO 2+ A coordination reaction occurs, forming a neutral complex that enters the organic phase. According to the principle of chemical equilibrium, the initial pH value of the aqueous phase of the extractant molecules directly affects the direction of the reaction: under low pH conditions, high concentrations of H + It will inhibit the dissociation of P204 and hinder the extraction process. Properly increasing the pH value can promote the dissociation of the extractant and push the reaction towards the product. However, when the pH exceeds the critical value, the trace metal impurity ions in the solution undergo hydrolysis reaction, and the resulting colloidal precipitation will cause VO4 to be adsorbed. 2+ The extraction rate decreased, while Fe 2+ Impurity ions such as ions occupy dimer sites, resulting in a significant increase in the co-extraction rate of impurity ions. Therefore, in the actual process, the optimal pH needs to be determined through systematic experiments. Finally, the pH was determined to be 1.8-2.6 through experiments. 2+The volume ratio of the organic phase to the aqueous phase is 1:3-3:1, which has the advantages of low phase ratio, although it is beneficial to the enrichment of vanadium, and the utilization rate of the unit organic phase is also higher, but the extraction rate of vanadium is relatively low; while the high phase ratio is beneficial to the extraction of vanadium, but the utilization rate of the unit organic phase is low, and it will lead to the reduction of the concentration of VO 2+ In the organic phase, the volume ratio of the acidic phosphorus type extractant, the phase separation agent and the diluent is (2-4):1:(7-5), which has the advantages that the higher the extractant concentration, the higher the extraction rate of vanadium, but when the extractant concentration is too large, it will cause phase separation difficulty, the viscosity of the organic phase is too large, the flowability is poor, and the emulsification phenomenon is easy to occur, at the same time, the extraction cost increases linearly, and the economic balance of the separation efficiency of metal impurity ions and the cost of reagents is considered, and the volume ratio is determined to be (2-4):1:(7-5) through experiments. 2+ The economic balance of the separation efficiency of metal impurity ions and the cost of reagents is considered, and the volume ratio is determined to be (2-4):1:(7-5) through experiments.

[0104] Further, step S4 specifically comprises:

[0105] The loaded organic phase is subjected to multi-stage countercurrent washing with a dilute sulfuric acid solution of 0.1-0.5 mol / L;

[0106] The volume ratio of the loaded organic phase to the dilute sulfuric acid solution is (1-10):1.

[0107] The washing mixing time is 6-14 min, and the clarification time is 6-14 min.

[0108] In the present application, the purpose of multi-stage countercurrent washing of the loaded organic phase with a dilute sulfuric acid solution of 0.1-0.5 mol / L is to remove part of the impurity ions co-extracted in the organic phase and part of the impurity ions (such as Na + ) entrained by the organic phase, and the dilute sulfuric acid solution is selected because SO42- in the dilute sulfuric acid reacts with Na + to generate Na2SO4, and since the solubility of Na2SO4 in dilute sulfuric acid is high, the generated Na2SO4 can be dissolved in the washing solution, thereby removing sodium ions by flushing, and through experiments, it is determined that a dilute sulfuric acid solution of 0.1-0.5 mol / L can remove as much Na + as possible while retaining VO 2+ , and the volume ratio of the loaded organic phase to the dilute sulfuric acid solution is (1-10):1, so that the volume of the loaded organic phase is larger and the volume of the dilute sulfuric acid solution is smaller, and thus the volume ratio (phase ratio O / A) is (1-10):1.

[0109] Further, step S5 specifically comprises:

[0110] After washing, the VO 2+ The organic phase electrolyte has a concentration of 1.6-2.0 mol / L.

[0111] The stripping mixing time is 4-12 min, and the clarification time is 4-12 min.

[0112] In the present application, the concentration of the sulfuric acid solution is 4.6-6 mol / L. According to the national standard and the production requirements of the vanadium electrolyte, the target vanadium electrolyte concentration is not less than 1.6 mol / L, and the sulfate concentration is not less than 4.6 mol / L. Therefore, the concentration of the stripping liquid sulfuric acid is 4.6-6 mol / L.

[0113] Further, the step S6 specifically comprises:

[0114] The activated carbon is sequentially soaked in H2O2 solution and H2SO4 solution, and then washed with water and dried to obtain the adsorbent.

[0115] The adsorbent is added to the organic phase electrolyte, and the obtained mixture is stirred and subjected to solid-liquid separation to obtain the vanadium electrolyte.

[0116] The carbon liquid ratio of the adsorbent in the mixture is 0.03±0.01 g / mL.

[0117] The method for preparing the vanadium electrolyte by the sodium polyvanadate extraction method will be described in detail below with reference to the examples and experimental data.

[0118] Example 1

[0119] The present application provides a method for preparing a vanadium electrolyte by a sodium polyvanadate extraction method, which specifically comprises the following steps:

[0120] (1) Dissolve the chromium extraction by-product sodium polyvanadate in a 70℃ NaOH solution to precipitate impurity metal ions Fe 2+ , Fe 3+ , Cr 3+ , Ca 2+ , Al 3+ , etc. and insoluble substances, and remove the impurities by suction filtration to obtain a vanadium-containing alkaline solution.

[0121] The 5.755g sodium polyvanadate sample is weighed into a 100ml beaker, an appropriate amount of deionized water is added, and the solution is fully stirred and heated to dissolve. The water bath heating temperature is 70℃, 0.59g of 98% sodium hydroxide solid is added, and heating is continued for 1.5h. At this time, the solution pH is 8. After the alkaline solution is cooled to room temperature, it is transferred to a 50ml volumetric flask and made up to volume. The VO2 +The concentration is controlled at 23.74 g / L, and the pH value of the vanadium-containing alkaline solution is controlled at 8.

[0122] (2) Add 1.80 g of 98% Na2SO3 to the alkaline vanadium-containing solution, and add concentrated sulfuric acid to adjust the pH of the solution to 1 at the end of the reaction. In a short time, the pentavalent vanadium is reduced to tetravalent vanadium to obtain a tetravalent vanadium reduction solution. At this time, VO 2+ The concentration was controlled at 23.62 g / L (99.50% reduction efficiency). After the reduction was complete, 0.19 g of 98% solid sodium hydroxide was added to adjust the solution pH to 2.2, the optimal pH for extraction. Testing (ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer, Agilent 5800)) revealed the following impurities (ppm): Ca 9.46; Cr 194.43; Fe 25.56; Na 29996.81; Si 48.74. All other impurities were less than 5 ppm.

[0123] (3) 1 L of the above-mentioned tetravalent vanadium reduction solution was prepared, and the solution was subjected to multi-stage countercurrent extraction with an organic phase to obtain a loaded organic phase.

[0124] In the multi-stage countercurrent extraction, the reducing solution had a pH of 2.2, the number of extraction stages was 5, the organic phase / aqueous phase volume ratio (phase ratio (O / A)) was 2:1, the organic phase volume ratio was 3:1:6 (P204:TBP:260# solvent oil), the extraction mixing time was 8 minutes, the settling time was 8 minutes, and the extraction yield was 96.32%. The organic phase was formed by mixing P204, TBP, and 260# solvent oil in a volume ratio of 3:1:6.

[0125] (4) The loaded organic phase was washed with a 0.1 mol / L dilute sulfuric acid solution at a volume ratio of 5:1 (O / A) using four countercurrent wash stages. The washing mixing time was 12 min, and the settling time was 8 min.

[0126] (5) After washing, multi-stage countercurrent stripping was performed with 4.6 mol / L sulfuric acid solution. The stripping volume ratio (phase ratio (O / A)) was 8:1, and the stripping rate of vanadium was 97.12%. VO was obtained. 2+ The organic phase electrolyte (also known as the vanadium strip solution) was 1.71 mol / L and contained 2.89 mol / L H₂SO₄. The total impurity content (including Si, Al, Fe, Cr, Mg, and Ca) was less than 50 ppm. The stripping mixing time was 10 minutes, and the clarification time was 8 minutes. The organic phase content in the electrolyte was measured at this time to be 500 μL / L.

[0127] (6) The activated carbon is soaked in 5% H2O2 solution for 2h, then transferred to 3 mol / L H2SO4 solution, stirred at constant temperature of 40℃ for 3h, washed with water for several times, and dried at 120℃ for 24h to obtain the adsorbent;

[0128] The organic phase electrolyte is heated to 55℃ and kept for 30min, and then cooled and placed to make the micro oil droplets in the electrolyte coagulate on the liquid surface to form floating oil. After the floating oil is separated, the adsorbent is added to the organic phase electrolyte, and then stirred at 25-30℃ for 4h. Then, the vanadium electrolyte is obtained by using a 0.45μm filter membrane to perform suction filtration.

[0129] In the vanadium electrolyte, the measured organic phase content is less than 2.5μL / L, which meets the requirements through physicochemical property analysis, charge and discharge test, cyclic voltammetry test and electrochemical impedance spectrum test, and a qualified vanadium electrolyte is prepared. In this embodiment, the raw material sodium polyvanadate used in step (1) is a chromium extraction by-product of a factory in Sichuan (Sichuan Tianfu Energy Storage Technology Co., Ltd.). The raw material is a dark red-brown soil solid, and the main component is vanadium element, and it also contains metal impurities such as iron, chromium, sodium and calcium, and non-metallic impurities such as silicon, and the solid component is unknown. The composition of the tetravalent vanadium reducing solution is shown in Table 1, and the morphological characteristics are shown in Figure 6 .

[0130] Table 1 Analysis Table of Reducing Solution Composition (unit: ppm)

[0131]

[0132] Example 2

[0133] In this embodiment, the performance of the vanadium electrolyte prepared in Example 1 is tested, and the specific steps are as follows:

[0134] 1. Physicochemical property analysis

[0135] AR grade V2O5 is dissolved in sulfuric acid solution to prepare a 1.6mol / L VOSO4+3mol / L H2SO4 standard electrolyte sample by oxalic acid reduction heating as a control group (CG), and the conductivity and viscosity of the electrolyte are compared with the electrolyte prepared by extraction method diluted to 1.6mol / L VOSO4+3mol / L H2SO4 (EG). The conductivity and viscosity of the electrolyte will affect the electrode reaction kinetics, reversibility and impedance of the electrolyte, thereby affecting the charge transfer and diffusion of the reactants. The results are shown in Table 2. The conductivities of EG and CG are 321.3ms / cm and 334.6ms / cm respectively, and the viscosities of EG and CG are 5.24mm 2 / s and 5.02mm 2 / s respectively, and overall they are relatively close. The electrolyte prepared by extraction method can meet the basic requirements.

[0136] Table 2 Comparison of physical properties of CG and EG

[0137]

[0138]

[0139] 2. Cyclic voltammetry test

[0140] Figure 2 The cyclic voltammetry curves of EG and CG vanadium electrolytes at a scan rate of 25 mA / s are shown in Table 3. The important parameters given in Table 3 include the oxidation peak current density ( pa ), reduction peak current density (j pc ) and redox peak potential difference (ΔE p ).

[0141] Table 3 Main data of cyclic voltammetry curves of CG and EG

[0142]

[0143] The peak current density of CG oxidation (j pa )0.38A / cm 2 Slightly higher than EG's 0.36A / cm 2 , reduction peak current density (j pc )0.36 is slightly higher than EG's 0.34A / cm 2 , indicating that CG has higher activity or efficiency in both anodic and cathodic reactions. The anodic potential of CG is 1.42V, which is higher than that of EG (1.37V), which means that CG requires a higher potential to drive the reaction in the anodic reaction. The cathodic potential of CG is 0.59V, which is lower than that of EG (0.62V), which means that CG requires a lower potential in the cathodic reaction and its reaction kinetics is slower. The redox peak potential difference of CG (ΔE p )0.83V is slightly larger than EG's 0.75V, which indicates that the battery of CG requires a higher potential difference to maintain the reaction, which affects the efficiency of the battery. pa / j pc The ratio is 1.06, which indicates that the current density of the anode and cathode is comparable in these two samples, and the battery has good symmetry. Overall, the cyclic voltammetry test results show that EG has similar characteristics to CG.

[0144] 3. Electrochemical Impedance Spectroscopy

[0145] The electrode reaction kinetics of EG and CG cathode electrolytes were further studied by AC impedance test. The Nyquist curves of EG and CG obtained by AC impedance test are shown in Figure 2. Figure 3 shown.

[0146] From Figure 3 It can be seen that the Nyquist curves of EG and CG are both composed of a semicircle in the high frequency region and a straight line in the low frequency region, which indicates that the electrode reactions of the two electrolytes are controlled by high-frequency charge transfer process and low-frequency diffusion process. The semicircle in the high frequency region represents the charge transfer process, and the size of the charge transfer resistance can be represented by the size of the semicircle. The larger the diameter of the semicircle, the larger the charge transfer resistance of the vanadium electrolyte, and the poorer the reversibility. As can be seen from the Nyquist diagram, the diameter of the semicircle of EG is slightly larger than that of CG, indicating that the reversibility of the electrolyte prepared by extraction method is lower than that of the electrolyte prepared by reduction method, which is consistent with the subsequent charge and discharge test results.

[0147] 4. Battery charge and discharge test

[0148] As Figure 4 shown, in the charging stage, the voltage of the two curves rises rapidly at the beginning of charging, and then the voltage rise slows down until the highest voltage is reached, but the initial charging voltage of CG is slightly lower than that of EG, which means that under the same charging conditions, CG can accept charges faster, so it starts charging at a lower voltage. In the discharging process, the voltage drop trend of CG and EG is similar, but the voltage drop of CG is slightly flatter, which means that CG has better stability and higher energy density during discharging. Overall, the charge and discharge characteristics of EG are similar to CG, and both have consistent charge and discharge characteristics.

[0149] As the active material of vanadium battery, the performance of electrolyte will also affect the charge and discharge efficiency of vanadium battery. Therefore, EG needs to be evaluated by battery performance test to determine whether the vanadium electrolyte prepared by this method can be used for vanadium battery. Therefore, the cyclic charge and discharge test was carried out at current densities of 160 mA / cm 2 , 200 mA / cm 2 and 240 mA / cm 2 . The performance differences between the electrolyte after organic phase removal and the national standard vanadium electrolyte were compared by data comparison. The coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of CG and EG under three different current densities are shown in Figure 5 .

[0150] Table 4 Comparison of charge and discharge parameters of electrolyte prepared by extraction method and national standard vanadium electrolyte under different current densities

[0151]

[0152] As shown in Table 4, when the current density is 160 mA / cm 2 , the utilization efficiency of CG is 67.60%, and the utilization efficiency of EG is 63.12%; when the current density is 200 mA / cm 2The CG utilization efficiency is 62.85%, and the EG utilization efficiency is 58.49%; the current density is 240 mA / cm 2 The CG utilization efficiency is 55.20%, and the EG utilization efficiency is 52.46%. It is found that the utilization rate of CG electrolyte is higher than that of EG. At the same time, the coulombic efficiency is close under different current densities, but the voltage efficiency and energy efficiency have a difference of 1-2%, and CG shows better performance, excluding the interference of the content of organic phase. It is guessed that the difference in impurity content leads to the difference in charge and discharge performance. CG is prepared by high-purity V2O5, H2SO4 dissolution, oxalic acid reduction and heating. The impurity content is extremely low. Although the impurity content of EG meets the requirements of GB / T37204-2018, the total amount of impurities is still higher than that of CG. The difference in impurity content will obviously affect the performance of the battery. Therefore, it is judged that the difference in impurity content leads to the change of parameters.

[0153] Through the multi-dimensional analysis of the comprehensive performance, electrochemical characteristics and battery running efficiency, EG is highly consistent with CG in key performance indicators, which proves that the vanadium electrolyte prepared by extraction method can basically meet the practical application requirements of vanadium battery.

[0154] Finally, it should be noted that the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or equipment including a series of elements not only include those elements, but also include other elements not explicitly listed or inherent to such processes, methods, articles or equipment.

[0155] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0156] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A method for preparing vanadium electrolyte by sodium polyvanadate extraction, characterized in that: The method comprises: S1. dissolving sodium polyvanadate in an alkaline solution to remove impurity metal ions and insoluble matter to obtain a vanadium-containing alkaline solution; S2. A reducing agent is added to the vanadium-containing alkaline solution and the pH of the solution is adjusted to a strongly acidic state to reduce pentavalent vanadium to tetravalent vanadium, and then a base is added to adjust the pH to the optimal extraction pH range to obtain a tetravalent vanadium reduction solution; S3. Extraction with an organic phase containing tetravalent vanadium was performed to obtain a loaded organic phase; S4. The loaded organic phase is washed with a dilute sulfuric acid solution; S5. After washing, stripping is performed with a sulfuric acid solution to obtain an electrolyte containing an organic phase; S6. removing the organic phase from the organic phase-containing electrolyte by adsorption treatment to obtain a vanadium electrolyte; Wherein, the reducing agent includes any one of Na2SO3, Na2S2O5 and CaSO3; The organic phase is formed by mixing an acidic phosphorus-type extractant, a phase separation agent and a diluent; The acidic phosphorus extractant includes any one of P204, P507 and Cyanex272, the phase separation agent includes TBP, and the diluent includes 260# solvent oil.

2. The method for preparing vanadium electrolyte by a sodium polyvanadate extraction method according to claim 1, wherein: Step S1 specifically includes: Dissolve sodium polyvanadate in a NaOH solution at 50-80°C to precipitate impure metal ions and insoluble matter, and obtain a vanadium-containing alkaline solution through solid-liquid separation; Wherein, the VO2 in the vanadium-containing alkaline solution + The concentration is 1-40 g / L, and the pH value of the vanadium-containing alkaline solution is 8-12.

3. The method for preparing vanadium electrolyte by a sodium polyvanadate extraction method according to claim 1, characterized in that: Step S2 specifically includes: Adding a reducing agent and concentrated sulfuric acid to the vanadium-containing alkaline solution, controlling the pH value at the reaction end point to be 0.5-1.5, so as to reduce pentavalent vanadium to tetravalent vanadium, and adding sodium hydroxide after the reduction is completed to adjust the pH to 1.8-2.6 to obtain a tetravalent vanadium reduction solution; Wherein, the dosage of the reducing agent is 1.2 to 1.5 times the theoretical dosage.

4. The method for preparing vanadium electrolyte by sodium polyvanadate extraction according to claim 1, wherein: Step S3 specifically includes: Performing multi-stage countercurrent extraction on a tetravalent vanadium reduction solution using an organic phase to obtain a loaded organic phase; The volume percentage of the acidic phosphorus-based extractant in the organic phase is 10-40%, the volume percentage of the phase separation agent in the organic phase is 10%, and the volume percentage of the diluent in the organic phase is 50-80%.

5. The method for preparing vanadium electrolyte by sodium polyvanadate extraction according to claim 4, characterized in that: In the multi-stage countercurrent extraction, the pH of the tetravalent vanadium reduction solution is 1.8 to 2.6, the number of extraction stages is 4 to 6, and the volume ratio of the organic phase to the aqueous phase is 1:3 to 3:1; In the multi-stage countercurrent extraction, the volume ratio of the acidic phosphorus extractant, the phase separator and the diluent in the organic phase is (2-4):1:(7-5), the extraction mixing time is 4-12 minutes, and the clarification time is 4-12 minutes.

6. The method for preparing vanadium electrolyte by sodium polyvanadate extraction according to claim 1, characterized in that: Step S4 specifically includes: The loaded organic phase is subjected to multi-stage countercurrent washing with a 0.1-0.5 mol / L dilute sulfuric acid solution; Wherein, the volume ratio of the loaded organic phase to the dilute sulfuric acid solution is (1-10):1; The washing and mixing time is 6 to 14 minutes, and the clarification time is 6 to 14 minutes.

7. The method for preparing vanadium electrolyte by sodium polyvanadate extraction according to claim 1, characterized in that: Step S5 specifically includes: After washing, 4.6-6 mol / L sulfuric acid solution was used for multi-stage countercurrent stripping to obtain VO 2+ An organic phase electrolyte having a concentration of 1.6 to 2.0 mol / L; The stripping mixing time is 4 to 12 minutes, and the clarification time is 4 to 12 minutes.

8. The method for preparing vanadium electrolyte by sodium polyvanadate extraction according to claim 1, characterized in that: Step S6 specifically includes: The activated carbon is sequentially soaked in H2O2 solution and H2SO4 solution, then rinsed with water and dried to obtain an adsorbent; adding the adsorbent to the organic phase electrolyte, stirring the resulting mixed solution and subjecting the mixture to solid-liquid separation to obtain a vanadium electrolyte; Wherein, the carbon-liquid ratio of the adsorbent in the mixed liquid is 0.03±0.01 g / mL.

9. The method for preparing vanadium electrolyte by sodium polyvanadate extraction according to claim 8, characterized in that: Step S6 specifically includes: The activated carbon was placed in a 4-6% H2O2 solution and soaked for 2±0.5 hours, then transferred to a 3±0.5 mol / L H2SO4 solution, stirred at a constant temperature of 40-50°C for 2-4 hours, then rinsed with water several times, and dried at 120±10°C for 18-24 hours to obtain an adsorbent; The organic phase electrolyte is heated to 55-65° C. and kept warm for 30±5 minutes, then the adsorbent is added to the organic phase electrolyte, magnetically stirred at 25-30° C. for 4±0.5 hours, and then filtered using a 0.45 μm filter membrane to obtain a vanadium electrolyte.

10. Use of the method for preparing vanadium electrolyte by sodium polyvanadate extraction according to any one of claims 1 to 9 in preparing all-vanadium redox flow batteries.

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