Recycling method of failure all-vanadium redox flow battery electrolyte

Abstract

The invention provides a recycling method of a failed all-vanadium redox flow battery electrolyte, which comprises the following steps: taking an auxiliary electrolyte as an anolyte and a failed positive electrolyte as a catholyte, electrolyzing to obtain a VOSO4 solution, evaporating, crystallizing and filtering to obtain VOSO4 crystals and a VOSO4 mother solution; taking the auxiliary electrolyte as anolyte and the invalid cathode electrolyte as catholyte, electrolyzing to obtain a V2 (SO4) 3 solution, evaporating and crystallizing, and filtering to obtain V2 (SO4) 3 crystals and V2 (SO4) 3 mother liquor; and respectively carrying out vanadium recovery, sulfuric acid recovery and waste liquid recovery on the V2 (SO4) 3 mother liquor. According to the method, an electrolytic method and an evaporative crystallization method are combined, VOSO4 crystals and V2 (SO4) 3 crystals are prepared in situ, and efficient and direct recovery of the electrolyte of the invalid all-vanadium redox flow battery is achieved; and the prepared crystal is large in particle size and high in purity. According to the invention, the purposes of green and environment-friendly recycling of the invalid all-vanadium redox flow battery electrolyte, cost reduction and efficiency improvement are realized.

Description

Technical Field

[0001] The invention relates to an electrolyte recovery technology, and in particular to a method for recovering and utilizing electrolyte of a failed all-vanadium liquid flow battery. Background Art

[0002] The global energy structure is undergoing revolutionary changes, and my country's energy structure adjustment is also deepening. After decades of research and exploration, the liquid flow battery technology system has been continuously developed and improved. In particular, the all-vanadium liquid flow battery system, the iron-chromium liquid flow battery system, the zinc-bromine liquid flow battery system, etc. Among all the liquid flow battery technologies that have been researched and developed, the all-vanadium liquid flow battery system is the most mature, commercially applied and industrialized. Its safety, long life, and green environmental protection characteristics have been verified in practice at home and abroad. However, due to the limited crustal content of vanadium resources and the complexity of the current vanadium extraction process, the subsequent low-cost and high-efficiency recovery of liquid flow battery electrolytes for reuse has also become one of the hot spots that schools, research institutes and enterprises are focusing on. At present, the main methods for treating failed vanadium electrolytes are:

[0003] CN 117142519 B discloses a method, device and application for recovering vanadium oxyhydroxide from waste vanadium electrolyte. The method comprises the following steps: subjecting waste low-valent vanadium electrolyte to bipolar membrane electrodialysis to obtain low-valent vanadium hydroxide and / or vanadium oxyhydroxide, oxidizing the low-valent vanadium hydroxide to obtain vanadium oxyhydroxide; wherein the low-valent vanadium is V 2+ 、V 3 + 、V 4+ This method can effectively recover vanadium ions in spent electrolyte, but the valence ratio of vanadium in the obtained product is uncertain, and the low-temperature instability of low-valence vanadium easily leads to product deterioration.

[0004] CN 116130692 A discloses a method for recycling electrolyte of waste vanadium battery, belonging to the technical field of all-vanadium liquid flow battery, for mixed acid system vanadium electrolyte, by adding calculated amount of vanadium sulfate, vanadyl sulfate and corresponding acid, the electrolyte of the whole system is recycled in batches, solving the problem of distinguishing positive and negative electrode treatment of electrolyte of existing failed vanadium battery. The method can effectively solve the problem of troublesome recycling of mixed acid system vanadium electrolyte and avoid the problem of ion pollution caused by the introduction of other ions, but the raw materials added to the failed electrolyte cannot be dissolved quickly, and the insoluble crystals are easy to cause crystal precipitation of the electrolyte, which impairs the electrochemical performance.

[0005] CN 110994061 B discloses a method for recovering vanadium electrolyte, wherein the average valence of vanadium in the vanadium electrolyte is adjusted to not less than 4.9 by charging the positive electrode or adding an oxidant, and then the vanadium electrolyte is diluted with water and an alkaline substance is added to adjust the pH of the solution, and red vanadium is obtained by filtering and washing, and then an alkaline substance is added to heat and dissolve, and then a precipitant is added, stirred, and filtered to obtain high-purity ammonium metavanadate. Although this method can obtain a high-purity ammonium metavanadate product, a large amount of alkaline substances and ammonium salts are added during the recovery process, and a large amount of ammonia nitrogen wastewater is generated, and the auxiliary material cost and wastewater treatment cost are high.

[0006] The publication number is "CN 201210514078", and the name of the invention is "A method for preparing vanadium oxysulfate using electrolyte for failed vanadium batteries". It discloses a method of charging the positive electrode of vanadium electrolyte with different concentrations under nitrogen protection conditions to charge the vanadium valence state to 5, adjusting the solution pH to 47, heating to 90°C constant temperature, adding a precipitant, stirring for 1 hour, stopping heating and continuing to stir for 2 hours. The precipitate is left standing for 24 hours, and the reducing agent (ethanol, acetic acid, acetaldehyde) is added for reduction and then left standing for 24 hours, and the centrifuge is 5000r / min for 20 minutes to obtain vanadium oxysulfate crystals with a recovery rate of >90%. The recovery rate of vanadium electrolyte in this method is high, but the process is complicated, the process is long, the cost is high, and it cannot meet the requirements of large-scale production.

[0007] In summary, the current domestic research process on the recycling technology of flow battery electrolytes generally has problems such as complex process, high cost, low recovery rate, new impurities in the recycling process, high cost of packaging and transportation, and inability to meet the requirements of large-scale production. Therefore, it is of great practical significance to develop a vanadium electrolyte recycling technology that has wider applicability, avoids long-distance transportation, has simple process, high product purity, and can be directly reused. Summary of the invention

[0008] The purpose of the present invention is to propose a method for recycling spent all-vanadium liquid flow battery electrolyte in response to the problems of existing electrolyte recovery methods, such as complex process, high cost, low recovery rate, introduction of new impurities in the recovery process, high transportation cost of packaging boxes and inability to meet the requirements of large-scale production. The method uses spent all-vanadium liquid flow battery electrolyte as vanadium source, does not require high-temperature roasting to prepare vanadium oxide, and can prepare VOSO4 crystals and V2(SO4)3 crystals in situ only by electrolysis and evaporation crystallization, thereby realizing efficient and direct recovery of spent all-vanadium liquid flow battery electrolyte; the VOSO4 crystals and V2(SO4)3 crystals prepared by the present invention have large particle size, high product purity and low impurity content, thus saving raw material and equipment costs, solving the problem of transportation radius of spent all-vanadium liquid flow battery electrolyte, and realizing the purpose of green and environmentally friendly recycling and cost reduction and efficiency improvement.

[0009] It should be noted that, in the present invention, unless otherwise specified, the specific meaning of "including" in relation to composition limitations and descriptions includes both open-ended "including", "comprising", etc. and similar meanings, as well as closed-ended "composed of", "composed of", etc. and similar meanings.

[0010] To achieve the above object, the technical solution adopted by the present invention is: a method for recycling the electrolyte of a spent all-vanadium liquid flow battery, comprising the following steps:

[0011] Step 1: using the auxiliary electrolyte (A1) as the anolyte and the spent positive electrolyte (A2) as the catholyte, reducing the valence of vanadium ions in the catholyte to 4.0±0.1 by electrolysis to obtain a VOSO4 solution (A4);

[0012] Step 2: Evaporate and crystallize the VOSO4 solution (A4), and filter to obtain VOSO4 crystals and VOSO4 mother liquor;

[0013] Step 3: using the auxiliary electrolyte (A1) as the anolyte and the spent negative electrolyte (B1) as the cathode, electrolyzing the valence of vanadium ions in the cathode to 3.0±0.1 to obtain a V2(SO4)3 solution (B2);

[0014] Step 4: Evaporate and crystallize the V2(SO4)3 solution (B2), and filter to obtain V2(SO4)3 crystals and V2(SO4)3 mother liquor;

[0015] Step 5: recovering vanadium, sulfuric acid and waste liquid from the V2(SO4)3 mother liquor respectively;

[0016] The auxiliary electrolyte (A1) in step 1 and step 3 is a vanadium-containing sulfuric acid solution, such as a sulfuric acid solution containing VOSO4.

[0017] Furthermore, in the auxiliary electrolyte (A1) described in step 1 and step 3, the vanadium ion concentration is 1.5 mol / L to 1.8 mol / L, the vanadium ion valence is 4.0±0.1, and the sulfate concentration is 4.0 mol / L to 5.0 mol / L.

[0018] Furthermore, a reducing agent is added to the auxiliary electrolyte after electrolysis in step 1 and step 3 to reduce the valence of vanadium ions in the auxiliary electrolyte to 3.9 to 4.1 (i.e., restore to the state before electrolysis), thereby preparing an auxiliary electrolyte (A1), which is returned to step 1 and / or step 3 for recycling.

[0019] Furthermore, the reducing agent is one or more of citric acid, oxalic acid, formic acid, acetic acid, sulfite and hydrogen peroxide.

[0020] Furthermore, in the spent positive electrode electrolyte (A2) in step 1, the vanadium ion concentration is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence is 4.3 to 4.8, and the sulfate concentration is 4.0 mol / L to 5.0 mol / L.

[0021] Furthermore, in the spent negative electrode electrolyte (B1) in step 3, the vanadium ion concentration is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence is 3.0 to 4.0, and the sulfate concentration is 4.0 mol / L to 5.0 mol / L.

[0022] Furthermore, the electrolysis parameters of step 1 and step 3 are: the current density is 80 mA / cm 2 ~120mA / cm 2 , the voltage is greater than 0V and less than 62V.

[0023] Furthermore, the evaporation crystallization temperature in step 2 is 50°C to 100°C.

[0024] Furthermore, the evaporation crystallization temperature in step 5 is 60°C to 100°C.

[0025] Furthermore, the VOSO4 mother liquor in step 2 is mixed with the spent negative electrode electrolyte (B1), and the mixed liquor is used as the cathode liquid in step 3. The vanadium ion content in the VOSO4 mother liquor is low, so in order not to waste the mother liquor, it is directly added to the next process.

[0026] Furthermore, the vanadium recovery in step 5 is to extract vanadium ions in the V2(SO4)3 mother liquor by extraction or ion exchange.

[0027] Furthermore, in step 5, the sulfuric acid recovery is to first remove soluble impurity ions (such as vanadium, iron, zinc, etc.) from the obtained sulfuric acid solution through an ion exchange resin or a nanofiltration membrane; and then further remove organic impurities and color through activated carbon adsorption. Then, the sulfuric acid solution is adjusted to a target concentration (about 1 mol / L to 3 mol / L) by evaporation or dilution, and recovered according to the ratio requirements of the flow battery electrolyte.

[0028] Furthermore, step 1 adopts a first electrolysis system for electrolysis, in which the anolyte and the cathode liquid circulate in the entire electrolysis process; step 3 adopts a second electrolysis system for electrolysis, in which the anolyte and the cathode liquid circulate in the entire electrolysis process.

[0029] Furthermore, the first electrolysis system and the second electrolysis system both include a cathode liquid storage tank, an anode liquid storage tank, a cathode pump, an anode pump, a fuel cell stack device, a pipe connecting the cathode liquid storage tank and the fuel cell stack, and a pipe connecting the anode liquid storage tank and the fuel cell stack. The cathode pump is arranged on the pipe connecting the cathode liquid storage tank and the fuel cell stack, and the anode pump is arranged on the pipe connecting the anode liquid storage tank and the fuel cell stack. The cathode liquid circulates between the cathode liquid storage tank and the fuel cell stack through the cathode pump, and the anode liquid circulates between the anode liquid storage tank and the fuel cell stack through the anode pump.

[0030] Furthermore, the first electrolysis system also includes a VOSO4 mother liquor storage tank, a liquid transfer pump, and a pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank. The liquid transfer pump is arranged on the pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank, and the VOSO4 mother liquor is transferred to the cathode liquid storage tank through the liquid transfer pump.

[0031] Furthermore, the anode pump and the cathode pump are centrifugal pumps, magnetic pumps, axial flow pumps, vacuum pumps or magnetic levitation pumps.

[0032] Furthermore, the electrolysis devices of the first electrolysis system and the second electrolysis system are both tank electrolysis devices.

[0033] Furthermore, the diaphragm of the battery stack device is a Nafion membrane doped with inorganic nanoparticles, an organic polymer / Nafion composite membrane, a Daramic membrane or a Selemion CMV membrane.

[0034] Furthermore, the bipolar plate is a carbon-plastic composite bipolar plate, a flexible graphite plate or an electrode-bipolar plate.

[0035] Furthermore, the material of the trough equipment is HEPE, PP, UPVC or PTFE.

[0036] Furthermore, filtering devices are provided in the anode liquid storage tank and cathode liquid storage tank of the first electrolysis system and the second electrolysis system.

[0037] The method for recycling the electrolyte of the spent all-vanadium liquid flow battery of the present invention has the following advantages compared with the prior art:

[0038] 1) The present invention uses spent all-vanadium liquid flow battery electrolyte as the vanadium source. There is no need for high-temperature roasting to prepare vanadium oxide. VOSO4 crystals and V2(SO4)3 crystals can be prepared in situ only by electrolysis and evaporation crystallization, thus realizing short-process, efficient and direct recovery of spent all-vanadium liquid flow battery electrolyte.

[0039] 2) The method for recovering vanadium electrolyte of all-vanadium liquid flow battery of the present invention can make the vanadium recovery rate in vanadium electrolyte greater than or equal to 95%, and the prepared VOSO4 crystals and V2(SO4)3 crystals have low impurity content.

[0040] 3) The present invention uses electrolysis and distillation crystallization to directly recover the spent all-vanadium liquid flow battery electrolyte, saving raw material and equipment costs, solving the problem of the transportation radius of the spent all-vanadium liquid flow battery electrolyte, and achieving the purpose of green and environmentally friendly recycling and cost reduction and efficiency improvement.

[0041] 4) The present invention uses V2(SO4)3 mother liquor as the sulfuric acid source, and recovers the sulfuric acid solution in the mother liquor by evaporation or dilution without going through a high-temperature reduction or toxic and harmful gas process, thereby obtaining industrial sulfuric acid that meets the standards for all-vanadium liquid flow battery electrolytes, thereby achieving direct recycling of a large amount of sulfuric acid waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a process flow chart of the method for recycling the electrolyte of spent all-vanadium liquid flow battery.

[0043] Figure 2 This is a particle size analysis diagram of VOSO4 crystals prepared in Example 1;

[0044] Figure 3 This is a particle size analysis diagram of the V2(SO4)3 crystals prepared in Example 1;

[0045] Figure 4 XRD pattern of VOSO4 crystal prepared in Example 2;

[0046] Figure 5 XRD pattern of V2(SO4)3 crystal prepared in Example 2;

[0047] Figure 6 This is a charge and discharge efficiency diagram of the vanadium battery electrolyte prepared in Example 3;

[0048] Figure 7 This is an energy efficiency diagram of the vanadium battery electrolyte prepared in Example 3;

[0049] Figure 8 This is the energy density diagram of the vanadium battery electrolyte prepared in Example 3. DETAILED DESCRIPTION

[0050] The present invention is further described below with reference to the examples. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0051] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0052] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0053] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0054] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0055] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0056] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 15-25°C.

[0057] In this manual, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0058] Unless otherwise specified, % in the present invention refers to mass percentage.

[0059] In Examples 1 to 3, the first electrolysis system (the system used for S2 electrolysis) and the second electrolysis system (the system used for S5 electrolysis) both include a cathode liquid storage tank, an anode liquid storage tank, a cathode pump, an anode pump, and a battery stack device; the battery stack device includes a bipolar plate, a cathode cell, a diaphragm, an anode cell, a carbon felt, a plate frame, a single-cell voltage detector, and 40 single cells; each electrolysis system includes a pipe connecting the cathode liquid storage tank and the battery stack and a pipe connecting the anode liquid storage tank and the battery stack; the cathode pump is arranged on the pipe connecting the cathode liquid storage tank and the battery stack, and the anode pump is arranged on the pipe connecting the anode liquid storage tank and the battery stack; valves are arranged on each inlet and outlet of the battery stack device, the anode liquid storage tank, the cathode liquid storage tank, the anode pump, and the cathode pump.

[0060] The anode pump and cathode pump are magnetic pumps; the electrolysis devices of the electrolysis system are all cell-type electrolysis devices; the diaphragm of the stack device is a Nafion membrane doped with inorganic nanoparticles; the bipolar plate is a carbon-plastic composite bipolar plate; the material of the cell-type equipment is PTFE; and filtering devices are installed in the anode liquid storage tank and cathode liquid storage tank of each electrolysis system.

[0061] Example 1

[0062] This embodiment discloses a method for recycling spent all-vanadium liquid flow battery electrolyte. Figure 1 As shown, the following steps are included:

[0063] S1: Add 650 g of VOSO4 crystals to 500 mL of pure water, add 200 mL of concentrated sulfuric acid, and then add pure water to dilute to 1.5 L to obtain auxiliary electrolyte A1.

[0064] S2: The spent positive electrolyte A2 with a vanadium ion concentration of 1.70 mol / L and a vanadium ion valence of 4.85 was used as the cathode liquid, and the auxiliary electrolyte A1 obtained in S1 was used as the anode liquid. 2 The electrolysis was carried out at a current density of , and the cathode liquid after electrolysis was precisely filtered through a filter to obtain 1L of VOSO4 solution. The average valence of vanadium ions in the solution was 4.0, and the solution was a mixture of VOSO4 and sulfuric acid.

[0065] S3: The 1L VOSO4 solution obtained in S2 was evaporated and crystallized at 80°C for 6h, and then solid-liquid separation was performed to obtain 261g VOSO4 crystals and 213mL VOSO4 mother liquor.

[0066] S4: The VOSO4 mother liquor obtained in S3 is transferred to the spent negative electrode electrolyte to obtain 1L spent negative electrode electrolyte B1 with a vanadium ion concentration of 3.10 mol / L and a vanadium ion valence of 3.6; 250g of citric acid is added to the auxiliary electrolyte obtained in S2 for sufficient reaction to obtain 1.5L of auxiliary electrolyte A1.

[0067] S5: The spent negative electrode electrolyte B1 obtained in S4 is used as the cathode liquid, and the auxiliary electrolyte A1 obtained in S4 is used as the anode liquid, 120 mA / cm 2 The electrolysis was carried out at a current density of , and the cathode liquid after electrolysis was precisely filtered to obtain 1L of V2(SO4)3 solution. The average valence of vanadium ions in the solution was 3.0, and the solution was a mixture of V2(SO4)3 and sulfuric acid.

[0068] S6: The 1L V2(SO4)3 solution obtained in S5 was evaporated and crystallized at 70°C for 8 hours, and then solid-liquid separation was performed to obtain 1147g of V2(SO4)3 crystals and 255mL of V2(SO4)3 mother liquor.

[0069] S7: Add 50 mL of ion exchange resin to the V2(SO4)3 mother liquor obtained in S6, and extract vanadium ions and other soluble impurity metal ions in the V2(SO4)3 mother liquor by ion exchange. Then add a certain amount of activated carbon to the solution to remove organic impurities and color in the solution, and obtain 265 mL of SO4 2- Sulfuric acid solution with a concentration of 6.5 mol / L.

[0070] S8: Add 0.88L of pure water to the sulfuric acid solution obtained in S7 to obtain 1.15L of SO4 2- A dilute sulfuric acid solution with a concentration of 1.5 mol / L.

[0071] Example 2

[0072] This embodiment discloses a method for recycling spent all-vanadium liquid flow battery electrolyte, comprising the following steps:

[0073] S1: Add 650 g of VOSO4 crystals to 500 mL of pure water, add 250 mL of concentrated sulfuric acid, and then add pure water to dilute to 1.5 L to obtain auxiliary electrolyte A1.

[0074] S2: The spent positive electrolyte A2 with a vanadium ion concentration of 1.64 mol / L and a vanadium ion valence of 4.75 was used as the cathode liquid, and the auxiliary electrolyte A1 obtained in S1 was used as the anode liquid. The electrolyte was charged at 100 mA / cm 2 The electrolysis was carried out at a current density of , and the cathode liquid after electrolysis was precisely filtered through a filter to obtain 1L of VOSO4 solution. The average valence of vanadium ions in the solution was 4.05, and the solution was a mixture of VOSO4 and sulfuric acid.

[0075] S3: The 1L VOSO4 solution obtained in S2 was evaporated and crystallized at 70°C for 6h, and then solid-liquid separation was performed to obtain 267g VOSO4 crystals and 205mL VOSO4 mother liquor.

[0076] S4: The VOSO4 mother liquor obtained in S3 is transferred to the spent negative electrode electrolyte to obtain 1L spent negative electrode electrolyte B1 with a vanadium ion concentration of 3.13 mol / L and a vanadium ion valence of 3.55; 250g of citric acid is added to the auxiliary electrolyte obtained in S2, and the reaction is fully reacted to obtain 1.5L of auxiliary electrolyte A1.

[0077] S5: The spent negative electrode electrolyte B1 obtained in S4 is used as the cathode liquid, and the auxiliary electrolyte A1 obtained in S4 is used as the anode liquid, 100 mA / cm 2 The electrolysis was carried out at a current density of , and the cathode liquid after electrolysis was precisely filtered to obtain 1L of V2(SO4)3 solution. The average valence of vanadium ions in the solution was 3.05, and the solution was a mixture of V2(SO4)3 and sulfuric acid.

[0078] S6: The 1L V2(SO4)3 solution obtained in S5 was evaporated and crystallized at 70°C for 12 hours, and then solid-liquid separation was performed to obtain 1160g of V2(SO4)3 crystals and 230mL of V2(SO4)3 mother liquor.

[0079] S7: Add 50 mL of ion exchange resin to the V2(SO4)3 mother liquor obtained in S6, and extract vanadium ions and other soluble impurity metal ions in the V2(SO4)3 mother liquor by ion exchange. Then add a certain amount of activated carbon to the solution to remove organic impurities and color in the solution, and obtain 235 mL of SO4 2- Sulfuric acid solution with a concentration of 6.35 mol / L.

[0080] S8: Add 0.77L of pure water to the sulfuric acid solution obtained in S7 to obtain 1L of SO4 2- A dilute sulfuric acid solution with a concentration of 1.49 mol / L.

[0081] Example 3

[0082] This embodiment discloses a method for recycling spent all-vanadium liquid flow battery electrolyte, comprising the following steps:

[0083] S1: Add 620 g of VOSO4 crystals to 500 mL of pure water, add 225 mL of concentrated sulfuric acid, and then add pure water to dilute to 1.5 L to obtain auxiliary electrolyte A1.

[0084] S2: The spent positive electrolyte A2 with a vanadium ion concentration of 1.55 mol / L and a vanadium ion valence of 4.95 was used as the cathode liquid, and the auxiliary electrolyte A1 obtained in S1 was used as the anode liquid. 2 The electrolysis was carried out at a current density of , and the cathode liquid after electrolysis was precisely filtered through a filter to obtain 1L of VOSO4 solution. The average valence of vanadium ions in the solution was 4.1, and the solution was a mixture of VOSO4 and sulfuric acid.

[0085] S3: The 1L VOSO4 solution obtained in S2 was evaporated and crystallized at 80°C for 8h, and then solid-liquid separation was performed to obtain 270g VOSO4 crystals and 195mL VOSO4 mother liquor.

[0086] S4: The VOSO4 mother liquor obtained in S3 is transferred to the spent negative electrode electrolyte to obtain 1L spent negative electrode electrolyte B1 with a vanadium ion concentration of 2.95 mol / L and a vanadium ion valence of 3.46; 250g of citric acid is added to the auxiliary electrolyte obtained in S2, and the reaction is fully reacted to obtain 1.5L of auxiliary electrolyte A1.

[0087] S5: The spent negative electrode electrolyte B1 obtained in S4 is used as the cathode liquid, and the auxiliary electrolyte A1 obtained in S4 is used as the anode liquid, 80 mA / cm 2 The electrolysis was carried out at a current density of , and the cathode liquid after electrolysis was precisely filtered to obtain 1L of V2(SO4)3 solution. The average valence of vanadium ions in the solution was 3.10, and the solution was a mixture of V2(SO4)3 and sulfuric acid.

[0088] S6: The 1L V2(SO4)3 solution obtained in S5 was evaporated and crystallized at 60°C for 12 hours, and then solid-liquid separation was performed to obtain 1158g of V2(SO4)3 crystals and 210mL of V2(SO4)3 mother liquor.

[0089] S7: Add 50 mL of ion exchange resin to the V2(SO4)3 mother liquor obtained in S6, and extract vanadium ions and other soluble impurity metal ions in the V2(SO4)3 mother liquor by ion exchange. Then add a certain amount of activated carbon to the solution to remove organic impurities and color in the solution, and obtain 215 mL of SO4 2- Sulfuric acid solution with a concentration of 6.66 mol / L.

[0090] S8: Add 0.68L of pure water to the sulfuric acid solution obtained in S7 to obtain 0.9L of SO4 2- A dilute sulfuric acid solution with a concentration of 1.6 mol / L.

[0091] The VOSO4 crystal and V2(SO4)3 crystal of Examples 1-3 were tested respectively, and the test results are as follows:

[0092] Figure 2 The particle size analysis diagram of VOSO4 crystals prepared in Example 1; Figure 2 It can be seen that the particle sizes of the VOSO4 crystals prepared in Example 1 are Dv(10):46.3μm, Dv(50):125μm, Dv(90):447μm, and Dv(97):612μm. The VOSO4 crystals have large particle sizes and high crystallinity.

[0093] Figure 3 The particle size analysis diagram of the V2(SO4)3 crystal prepared in Example 1; Figure 3 It can be seen that the particle sizes of the V2(SO4)3 crystals prepared in Example 1 are Dv(10): 8.10μm, Dv(50): 21.5μm, Dv(90): 40.2μm, and Dv(97): 49.8μm. The V2(SO4)3 crystals have high crystallinity, small particle size, and uniform size.

[0094] Figure 4 is the XRD pattern of VOSO4 crystal prepared in Example 2; Figure 4 It can be seen that the VOSO4 crystals prepared in Example 2 do not have impurity characteristic peaks, and are consistent with the characteristic peaks of the standard card 01-072-0912. Therefore, the main existing form of the VOSO4 crystals prepared in Example 2 is VOSO4·3H2O.

[0095] Figure 5 XRD pattern of V2(SO4)3 crystal prepared in Example 2; Figure 5 It can be seen that the V2(SO4)3 crystals prepared in Example 2 do not have characteristic peaks of impurities, and are consistent with the characteristic peaks of standard card 00-023-0723. Therefore, the main form of the V2(SO4)3 crystals prepared in Example 2 is V2(SO4)3.

[0096] The ICP test results of the VOSO4 crystal prepared in Example 3 are shown in the following table:

[0097] Element Type K Na Fe Al Mo Cr Mn Ca W Mg <![CDATA[VOSO4 crystal]]> 0.0005 0.0005 0.0002 0.0006 0.0003 0.0001 0.0000 0.0003 0.0002 0.0001 Element Type B Pb Cu Bi Ti Co Zn Si Ni <![CDATA[VOSO4 crystal]]> 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0016 0.0000

[0098] From the ICP test results of the VOSO4 crystal prepared in the above Example 3, it can be seen that the impurity ion contents of K, Na, Fe, Al, Mo, Cr, Ca, W, Mg and Si in the VOSO4 crystal prepared in Example 3 all meet the national standard requirements for first-level products.

[0099] The ICP test results of the V2(SO4)3 crystals prepared in Example 3 are shown in the following table:

[0100] Element Type K Na Fe Al Mo Cr Mn Ca W Mg <![CDATA[V2(SO4)3 crystal]]> 0.0008 0.0004 0.0002 0.0007 0.0002 0.0002 0.0000 0.0001 0.0001 0.0001 Element Type B Pb Cu Bi Ti Co Zn Si Ni <![CDATA[V2(SO4)3 crystal]]> 0.0000 0.0000 0.0001 0.0000 0.0001 0.0000 0.0000 0.0011 0.0000

[0101] From the ICP test results of the V2(SO4)3 crystals prepared in the above Example 3, it can be seen that the impurity ion contents of K, Na, Fe, Al, Mo, Cr, Ca, W, Mg, Cu, Ti and Si in the V2(SO4)3 crystals prepared in Example 3 all meet the national standard requirements for first-level products.

[0102] Electrochemical performance test

[0103] Take the VOSO4 crystal and V2(SO4)3 crystal prepared in Example 3 to prepare a standard sulfuric acid system electrolyte with a vanadium concentration of 1.65 mol / L and a sulfate concentration of 4.10 mol / L, and heat the electrolyte at 30°C at 48 cm 2 Carbon felt area, 80Ma / cm 2 The electrochemical performance was tested under the conditions of current density and cut-off voltage of 1.55V. The test results are as follows Figure 6 to Figure 8 As shown:

[0104] Figure 6 This is a charge and discharge efficiency diagram of the vanadium battery electrolyte prepared in Example 3; Figure 7 This is an energy efficiency diagram of the vanadium battery electrolyte prepared in Example 3; Figure 8 This is the energy density diagram of the vanadium battery electrolyte prepared in Example 3. Figure 6 to Figure 8 The electrochemical test results show that when the temperature is 30℃, 48cm 2 Carbon felt area, 80mA / cm 2 Under the conditions of current density and cut-off voltage of 1.55V, the electrolyte is charged and discharged in a constant current + constant voltage mode, and the current is reduced to 40mA / cm at a constant voltage. 2The current density of the electrolyte was maintained at 87% and CE at 95.7% after 50 cycles. The highest energy density was 26Wh / L, and the energy retention rate was above 70% after 50 cycles. It can be seen that the VOSO4 crystals and V2(SO4)3 crystals prepared in Example 3 have good electrochemical properties and meet the raw material standards for preparing all-vanadium liquid flow battery electrolytes.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling spent all-vanadium redox flow battery electrolyte, characterized in that: The following steps are involved: Step 1: using the auxiliary electrolyte as the anolyte and the spent positive electrolyte as the cathode liquid, reducing the valence of vanadium ions in the cathode liquid to 4.0±0.1 by electrolysis to obtain a VOSO4 solution; the auxiliary electrolyte is a vanadium-containing sulfuric acid solution; Step 2: Evaporate and crystallize the VOSO4 solution, and filter to obtain VOSO4 crystals and VOSO4 mother liquor; Step 3: using the auxiliary electrolyte as the anolyte and the spent negative electrode electrolyte as the cathode liquid, electrolyzing the valence state of vanadium ions in the cathode liquid to 3.0±0.1 to obtain a V2(SO4)3 solution; the auxiliary electrolyte is a vanadium-containing sulfuric acid solution; Step 4: evaporate and crystallize the V2(SO4)3 solution, and filter to obtain V2(SO4)3 crystals and V2(SO4)3 mother liquor; Step 5: Recover vanadium and sulfuric acid from the V2(SO4)3 mother liquor respectively.

2. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: In the auxiliary electrolyte described in step 1 and step 3, the vanadium ion concentration is 1.5 mol / L to 1.8 mol / L, the vanadium ion valence is 4.0±0.1, and the sulfate concentration is 4.0 mol / L to 5.0 mol / L. And / or, the vanadium ion concentration in the spent positive electrode electrolyte in step 1 is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence is 4.3 to 4.8, and the sulfate concentration is 4.0 mol / L to 5.0 mol / L; And / or, the vanadium ion concentration in the spent negative electrode electrolyte in step 3 is 1.5 mol / L to 1.85 mol / L, the vanadium ion valence is 3.0 to 4.0, and the sulfate concentration is 4.0 mol / L to 5.0 mol / L.

3. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 2, characterized in that: A reducing agent is added to the auxiliary electrolyte after electrolysis in step 1 and step 3 to reduce the valence of vanadium ions in the auxiliary electrolyte to 3.9 to 4.1, thereby preparing an auxiliary electrolyte, which is returned to step 1 and / or step 3 for recycling.

4. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 3, characterized in that: The reducing agent is one or more of citric acid, oxalic acid, formic acid, acetic acid, sulfite and hydrogen peroxide.

5. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: The electrolysis parameters of step 1 and step 3 are: current density is 80 mA / cm 2 ~120mA / cm 2 , the voltage is greater than 0V and less than 62V.

6. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: The evaporation crystallization temperature in step 2 is 50°C to 100°C; And / or, the evaporation crystallization temperature in step 5 is 60°C to 100°C.

7. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: The VOSO4 mother liquor of step 2 is mixed with the spent negative electrode electrolyte, and the mixed liquor is used as the cathode liquid of step 3.

8. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: The vanadium recovery in step 5 is to extract vanadium ions in the V2(SO4)3 mother liquor by extraction or ion exchange; And / or, the sulfuric acid recovery in step 5 is to first remove soluble impurity ions from the obtained sulfuric acid solution through an ion exchange resin or a nanofiltration membrane; then further remove organic impurities and color through activated carbon adsorption; and then adjust the sulfuric acid solution to the target concentration through evaporation or dilution, and recover it according to the ratio requirements of the liquid flow battery electrolyte.

9. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 1, characterized in that: Step 1: electrolysis is performed using a first electrolysis system, wherein an anolyte and a catholyte in the first electrolysis system circulate throughout the electrolysis process; Step 3 uses a second electrolysis system for electrolysis, in which the anolyte and the cathode liquid circulate in the entire electrolysis process.

10. The method for recycling spent all-vanadium redox flow battery electrolyte according to claim 9, characterized in that: The first electrolysis system and the second electrolysis system both comprise a cathode liquid storage tank, an anode liquid storage tank, a cathode pump, an anode pump, a stack device, a pipeline connecting the cathode liquid storage tank and the stack, and a pipeline connecting the anode liquid storage tank and the stack, wherein the cathode pump is arranged on the pipeline connecting the cathode liquid storage tank and the stack, and the anode pump is arranged on the pipeline connecting the anode liquid storage tank and the stack, the cathode liquid circulates between the cathode liquid storage tank and the stack through the cathode pump, and the anode liquid circulates between the anode liquid storage tank and the stack through the anode pump; And / or, the first electrolysis system further includes a VOSO4 mother liquor storage tank, a liquid transfer pump, and a pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank, wherein the liquid transfer pump is arranged on the pipeline connecting the cathode liquid storage tank and the VOSO4 mother liquor storage tank, and the VOSO4 mother liquor is transferred to the cathode liquid storage tank through the liquid transfer pump.

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