Method for preparing high-concentration vanadium electrolyte by vanadate crystallization purification and chemical reduction

Abstract

The present invention provides a method for preparing a high-concentration vanadium electrolyte by vanadate crystallization purification - chemical reduction. Using vanadium-containing materials such as red vanadium, ammonium metavanadate, and crude V2O5 obtained from the vanadium slag roasting process as raw materials, they are dissolved in an alkali solution at 30 - 99 °C to obtain a saturated vanadate solution, which is cooled to 0 - 30 °C to obtain vanadate crystals. The alkali dissolution - cooling crystallization steps are repeated 2 - 6 times to obtain high-purity vanadate with a purity of over 99.9%. The high-purity vanadate is dissolved in dilute sulfuric acid, a reducing agent is added to reduce vanadium to +4 valence, the pH is adjusted to 4 - 14 with alkali, and after filtration, the filter cake is washed with dilute sulfuric acid or pure water. The filter cake is dissolved in sulfuric acid with a concentration of 2.5 - 5 mol / L to obtain a high-concentration vanadium electrolyte with a concentration of 1.5 - 3 mol / L. The whole process of the present invention is a wet process, using the physical method of recrystallization for purification, with simple operation and low cost. Moreover, no polluting and high-cost reagents such as ammonium salts, organic extractants, and inorganic impurity removal agents are required throughout the process. It is a low-cost and clean method for preparing a high-concentration vanadium electrolyte.

Description

Technical Field

[0001] The present invention relates to a method for preparing a high-concentration vanadium electrolyte by vanadate crystallization purification - chemical reduction, belonging to the field of vanadium batteries. Background Art

[0002] The all-vanadium redox flow battery is a new type of green and environmentally friendly large-scale energy storage system. Compared with traditional storage batteries, it has significant advantages such as safety, high efficiency, simple maintenance, and fast charge and discharge rate, and has great application prospects in the fields of green power storage, power grid "peak shaving and valley filling", and uninterruptible power supply. However, the cost issue has always been one of the key factors restricting the all-vanadium redox flow battery. As the core of the all-vanadium redox flow battery, the cost of vanadium electrolyte accounts for more than 50% of the total cost of the vanadium redox flow battery; on the other hand, the concentration of vanadium electrolyte is closely related to the capacity of the vanadium redox flow battery, directly affecting the long-term stability of the battery and the battery maintenance cost. Therefore, reducing the production cost of the electrolyte and increasing the electrolyte concentration are the two key points to promote the large-scale application of vanadium redox flow batteries.

[0003] Currently, vanadium electrolyte is mainly prepared by methods such as chemical reduction or electrolytic reduction of 99.5 - 99.9% high-purity vanadium pentoxide. However, the preparation of high-purity vanadium pentoxide requires multiple "dissolution - purification - ammonium precipitation - calcination" processes for ammonium metavanadate or crude vanadium pentoxide. This process not only has a complex process and high production cost, but also generates a large amount of ammonia nitrogen wastewater and ammonia gas that are difficult to treat, resulting in serious environmental pollution. In addition, some studies have used extraction processes to prepare vanadium electrolytes. Although this method has the advantages of a short process and low pollution, the prepared electrolyte has a high organic matter content and a low vanadium concentration, which greatly limits the performance of vanadium redox flow batteries.

[0004] Chinese Patent CN115196676A proposes a method for preparing high-purity vanadium pentoxide by combining two-stage impurity removal and cooling crystallization. The vanadium pentoxide product prepared by this method has high purity and meets the requirements for the raw material of the electrolyte. However, in the impurity removal step, impurity removers, reducing agents, oxidizing agents, etc. are required, resulting in high costs. In addition, the solubility of ammonium metavanadate is low, and the purification efficiency of cooling crystallization is low. Chinese Patent CN104477992A proposes a method for preparing high-purity vanadium pentoxide using ammonium polyvanadate as the raw material, through redissolution-crystallization-water dissolution-ammonium precipitation-calcination. However, this method has a single raw material, a low crystallization temperature (2-5°C), a long crystallization time (20-40h), and high energy consumption. Chinese Patent CN104495927 dissolves ammonium polyvanadate in a sodium hydroxide solution and adds ethanol as a crystallization agent to the sodium vanadate solution to crystallize sodium vanadate crystals. The sodium vanadate crystals are dissolved, ammonium-precipitated, and calcined to prepare vanadium pentoxide with a purity of over 99.9%. Although this method can achieve rapid crystallization (30-60min), the recycling and regeneration of the crystallization agent require means such as rectification, resulting in a complex production process and high energy consumption. In particular, the above methods still require ammonium precipitation and calcination steps, resulting in the problem of difficult-to-treat ammonia-nitrogen wastewater discharge.

[0005] In summary, the traditional repeated "dissolution-purification-ammonium precipitation-calcination" process has problems such as a long process flow and heavy pollution. The extraction process cannot prepare a high-concentration electrolyte, and the introduction of organic reagents limits the performance of the vanadium redox flow battery. Therefore, there is an urgent need to design and develop a low-cost and clean high-concentration vanadium electrolyte preparation technology. Summary of the Invention

[0006] The present invention provides a method for preparing a high-concentration vanadium electrolyte by vanadate crystallization purification-chemical reduction. Using red vanadium, crude V2O5, ammonium polyvanadate or ammonium metavanadate obtained from the vanadium slag roasting process as raw materials, the raw materials are leached with hot alkali solution. Utilizing the difference in the solubility of vanadate at different temperatures, vanadate is purified by multiple cooling crystallizations. The high-purity vanadate is subjected to reduction leaching, precipitation, and dissolution to obtain a high-concentration vanadyl sulfate electrolyte. The whole process is a wet process and does not require polluting and high-cost reagents such as ammonium salts, organic extractants, and inorganic impurity removers, which is a low-cost and clean method for preparing vanadium electrolyte.

[0007] To achieve the above object, the technical solution provided by the method of the present invention is as follows:

[0008] A method for preparing a high-concentration vanadium electrolyte by vanadate crystallization purification-reduction, the steps are as follows:

[0009] (1) Dissolve the vanadium-containing material in an alkali solution at 30-99 °C to obtain a saturated vanadate solution. Cool the vanadate solution at a rate of 1-10 °C / min to 0-30 °C, let it stand for 2-6 h, filter to obtain vanadate crystals, and re-dissolve the vanadate crystals after purifying and heating up the filtrate. Repeat the above dissolution-cooling crystallization steps 2-6 times for the vanadate crystals to obtain high-purity vanadate crystals with a purity greater than 99.9%;

[0010] (2) Dissolve the high-purity vanadate crystals in water, adjust the pH of the system to 0-4 with sulfuric acid, add a reducing agent at 1.1-1.5 times the theoretical reaction amount, react at 0-99 °C for 1-3 h to reduce vanadium to +4 valence; then add an alkali solution to adjust the pH to 5-13, carry out solid-liquid separation after reacting for 0.5-2 h; wash the filter cake 2-4 times with pure water or a dilute sulfuric acid solution with pH = 4-7 to obtain high-purity VO(OH)₂, and return the filtrate and washing solution to dissolve the high-purity vanadate; mix VO(OH)₂ with sulfuric acid at 2.5-5 mol / L to prepare a high-concentration vanadyl sulfate electrolyte at 1.5-3 mol / L, and the electrolyte meets the requirements for tetravalent electrolytes in vanadium redox flow batteries in GB / T 37204-2018.

[0011] Preferably, the vanadium-containing material in step (1) is one or more of red vanadium, crude V₂O₅, ammonium polyvanadate, and ammonium metavanadate.

[0012] Preferably, the red vanadium contains 0.5-5% of Na₂O, 80-90% of V₂O₅, and 0.2-3% of H₂O; the crude V₂O₅ refers to metallurgical-grade V₂O₅ with a purity of 98% obtained by sodium roasting-ammonium salt precipitation of vanadium slag-calcination, or chemical-grade V₂O₅ with a purity of 97%.

[0013] Preferably, the alkali solution in step (1) is one or more of NaOH and KOH solutions at 50-500 g / L.

[0014] Preferably, the reducing agent in step (2) is one or more of sodium sulfite, potassium sulfite, sulfur dioxide, sulfur, sodium sulfide, oxalic acid, oxalate, sucrose, glucose, and fructose.

[0015] Preferably, the alkali solution in step (2) is one or more of saturated NaOH and KOH.

[0016] Preferably, the vanadate in step (2) is one or more of sodium metavanadate, sodium pyrovanadate, sodium orthovanadate, potassium metavanadate, potassium pyrovanadate, and potassium orthovanadate.

[0017] Compared with the prior art, the advantages of the method of the present invention are as follows:

[0018] (1). The present invention utilizes the difference in the solubility of vanadate at different temperatures and uses the cooling crystallization method to purify vanadate. Compared with the purification processes such as dissolution-ammonium precipitation-calcination and extraction, the whole process does not require polluting and high-cost reagents such as ammonium salts, organic extractants, and inorganic impurity removal agents, does not introduce other impurities, is environmentally friendly, and has low costs.

[0019] (2). The whole process of the technology of the present invention is a wet process, physically crystallizing and purifying, without high-temperature reactions and calcination processes, with low energy consumption, easy to operate, no waste gas and waste residue generated, and the whole process liquid can be recycled, and the process is clean.

[0020] (3). After the high-purity vanadate obtained by the present invention is dissolved in water and reacts with a reducing agent, tetravalent vanadium can be prepared, which has a faster solid-liquid reaction rate with the reducing agent than that in the traditional method of vanadium pentoxide and the reducing agent, uses less sulfuric acid, and saves costs.

[0021] (4). The present invention first prepares VO(OH)2 and then uses sulfuric acid to dissolve it to prepare a vanadyl sulfate electrolyte, which can not only further remove impurities deeply, but also flexibly control the concentration of the electrolyte, and prepare a high-concentration vanadium electrolyte, which is beneficial to improving the storage capacity of the vanadium redox flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flow chart of the method of the present invention;

[0023] Figure 2 is a physical diagram of the vanadyl sulfate electrolyte. DETAILED DESCRIPTION OF THE INVENTION

[0024] To describe the present invention more clearly, the specific embodiments are described as follows:

[0025] Example 1:

[0026] Weigh 20 g of crude V2O5, leach the crude V2O5 with 200 ml of NaOH solution with a concentration of 250 g / L at 30 °C, with a stirring rate of 500 r / min and a leaching time of 1 h. Cool down to 5 °C at a rate of 1 °C / min, keep warm for 2 h, and filter to obtain sodium vanadate crystals; dissolve the sodium vanadate crystals in NaOH solution with a concentration of 330 g / L to saturation at 30 °C, cool down to 5 °C at a rate of 1 °C / min, and filter while it is hot. Repeat this cooling crystallization process 2 times to obtain 3.59 g of high-purity sodium vanadate with a purity of 99.9%; dissolve the obtained high-purity sodium vanadate in water, add sulfuric acid to adjust the pH to 0, with a temperature of 60 °C, add 2.8 g of anhydrous sodium sulfite, react for 1 h, add saturated sodium hydroxide solution to adjust the pH of the solution to 6, react for 0.5 h, filter to obtain VO(OH)2, wash it 3 times with dilute sulfuric acid with a pH of 6, and dissolve VO(OH)2 with 10 ml of 2.5 mol / L sulfuric acid to obtain a vanadyl sulfate electrolyte. The vanadium concentration of the electrolyte is 2.0 mol / L, and the sulfuric acid concentration is 2.3 mol / L, meeting the requirements for a tetravalent electrolyte in GB / T 37204-2018 "Electrolyte for All-Vanadium Redox Flow Battery".

[0027] Example 2

[0028] Weigh 200 g of crude V2O5, leach the crude V2O5 with 1000 ml of KOH solution with a concentration of 400 g / L at 90 °C, with a stirring rate of 500 r / min and a leaching time of 4 h. Cool down to 30 °C at a rate of 6 °C / min, keep warm for 6 h, and filter to obtain potassium vanadate crystals; dissolve the potassium vanadate crystals in KOH solution with a concentration of 400 g / L to saturation at 90 °C, cool down to 30 °C at a rate of 6 °C / min, and filter. Repeat this cooling crystallization process 6 times to obtain 46.4 g of high-purity potassium vanadate with a purity of 99.98%; dissolve the obtained high-purity potassium vanadate in water, add sulfuric acid to adjust the pH to 3, with a temperature of 30 °C, add 10 g of elemental sulfur, react for 3 h, add saturated potassium hydroxide solution to adjust the pH of the solution to 13, react for 2 h, filter to obtain VO(OH)2, wash VO(OH)2 with pure water, and dissolve VO(OH)2 with 100 ml of 5 mol / L sulfuric acid to obtain a vanadyl sulfate electrolyte. The vanadium concentration of the electrolyte is 2.5 mol / L, and the sulfuric acid concentration is 4.6 mol / L, meeting the requirements for a tetravalent electrolyte in GB / T 37204-2018 "Electrolyte for All-Vanadium Redox Flow Battery".

[0029] Example 3

[0030] Weigh 20 g of red vanadium oxide, leach the red vanadium oxide with 1000 ml of a KOH solution with a concentration of 50 g / L at 40 °C, with a stirring rate of 500 r / min and a leaching time of 3 h. Cool down to 10 °C at a rate of 3 °C / min, keep warm for 3 h, filter to obtain potassium vanadate crystals; dissolve the potassium vanadate crystals in a 50 g / L NaOH solution to saturation at 40 °C, cool down to 10 °C at a rate of 3 °C / min, filter, and repeat this cooling crystallization process 3 times to obtain 3.16 g of high-purity potassium vanadate with a purity of 99.92%; dissolve the obtained high-purity potassium vanadate in water, add dilute sulfuric acid to adjust the pH to 1, at a temperature of 60 °C, add 0.6 g of oxalic acid, react for 1 h, add saturated potassium hydroxide solution, adjust the pH of the solution to 8, react for 0.5 h, filter to obtain VO(OH)₂, and wash VO(OH)₂ with pure water; dissolve VO(OH)₂ with 10 ml of 2.5 mol / L sulfuric acid to obtain a vanadyl sulfate electrolyte, with the vanadium concentration in the electrolyte being 1.6 mol / L and the sulfuric acid concentration being 2.4 mol / L, meeting the requirements for a tetravalent electrolyte in GB / T 37204-2018 "Electrolyte for All-Vanadium Redox Flow Battery".

[0031] Example 4

[0032] Weigh 200 g of red vanadium oxide, leach the red vanadium oxide with 1000 ml of a NaOH solution with a concentration of 300 g / L at 80 °C, with a stirring rate of 500 r / min and a leaching time of 4 h. Cool down to 20 °C at a rate of 8 °C / min, keep warm for 5 h, filter to obtain sodium vanadate crystals; dissolve the sodium vanadate crystals in a 300 g / L NaOH solution to saturation at 80 °C, cool down to 20 °C at a rate of 8 °C / min, filter, and repeat this cooling crystallization process 4 times to obtain 63.2 g of high-purity sodium vanadate with a purity of 99.98%; dissolve the obtained high-purity sodium vanadate in water, add dilute sulfuric acid to adjust the pH to 1.5, at a temperature of 90 °C, add 27.7 g of anhydrous sodium sulfite, react for 3 h, add saturated sodium hydroxide solution, adjust the pH of the solution to 7, react for 2 h, filter to obtain VO(OH)₂, and wash VO(OH)₂ with pure water; dissolve VO(OH)₂ with 200 ml of 3.5 mol / L sulfuric acid to obtain a vanadyl sulfate electrolyte, with the vanadium concentration in the electrolyte being 1.7 mol / L and the sulfuric acid concentration being 3.3 mol / L, meeting the requirements for a tetravalent electrolyte in GB / T 37204-2018 "Electrolyte for All-Vanadium Redox Flow Battery".

[0033] Example 5

[0034] Weigh 50 g of ammonium metavanadate and leach it with 500 ml of a NaOH solution with a concentration of 200 g / L at 70 °C. The stirring rate is 500 r / min, and the leaching time is 1.5 h. Cool it to 10 °C at a rate of 3 °C / min, keep it warm for 3 h, and then filter to obtain sodium vanadate crystals. Dissolve the sodium vanadate crystals in a 200 g / L NaOH solution to saturation at 70 °C, cool it to 10 °C at a rate of 3 °C / min, and filter. Repeat this cooling crystallization process 3 times to obtain 12.64 g of high-purity sodium vanadate with a purity of 99.95%. Dissolve the obtained high-purity sodium vanadate in water, adjust the pH to 4, and the temperature to 50 °C. Then, introduce SO2 gas until the solution turns dark blue. Add saturated sodium hydroxide solution to adjust the pH of the solution to 10, react for 1 h, and filter to obtain VO(OH)2. Wash VO(OH)2 with pure water, dissolve VO(OH)2 with 30 ml of 5 mol / L sulfuric acid to obtain a vanadyl sulfate electrolyte. The vanadium concentration of the electrolyte is 2.3 mol / L, and the sulfate ion concentration is 4.8 mol / L, meeting the requirements for a tetravalent electrolyte in GB / T 37204-2018 "Electrolyte for All-Vanadium Redox Flow Battery".

[0035] Example 6

[0036] Weigh 50 g of ammonium metavanadate and leach it with 200 ml of a KOH solution with a concentration of 500 g / L at 60 °C. The stirring rate is 500 r / min, and the leaching time is 4 h. Cool it to 5 °C at a rate of 5 °C / min, keep it warm for 4 h, and then filter to obtain potassium vanadate crystals. Dissolve the potassium vanadate crystals in a 500 g / L KOH solution to saturation at 60 °C, cool it to 5 °C at a rate of 5 °C / min, and filter. Repeat this cooling crystallization process 3 times to obtain 9.7 g of high-purity potassium vanadate with a purity of 99.96%. Dissolve the obtained high-purity potassium vanadate in water, adjust the pH to 0, and the temperature to 10 °C. Add 1.1 g of sucrose and react for 3 h. Then, add saturated potassium hydroxide solution to adjust the pH of the solution to 5 and react for 1 h. Filter to obtain VO(OH)2. Wash VO(OH)2 with dilute sulfuric acid with a pH of 5, dissolve VO(OH)2 with 20 ml of 4 mol / L sulfuric acid to obtain a vanadyl sulfate electrolyte. The vanadium concentration of the electrolyte is 3 mol / L, and the sulfuric acid concentration is 3.9 mol / L, meeting the requirements for a tetravalent electrolyte in GB / T 37204-2018 "Electrolyte for All-Vanadium Redox Flow Battery".

[0037] It should be noted that according to the above embodiments of the present invention, those skilled in the art can fully implement the entire scope of the independent claims and dependent claims of the present invention. The implementation process and method are the same as those in the above embodiments; and the parts not elaborated in detail in the present invention belong to the well-known technology in the art. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those familiar with the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. Method for purifying vanadate crystals for preparing high-concentration vanadium electrolyte by chemical reduction, which is characterized by comprising the following steps: (1) Dissolve vanadium-containing materials in an alkaline solution at 30 99 °C to obtain a saturated vanadate solution, and cool it at a rate of 1 10 °C / min to 0 30 °C, let it stand for 2 6 h, filter to obtain vanadate crystals, and purify and heat up the filtrate to redissolve the vanadate crystals; repeat the dissolution cooling and crystallization steps 2 6 times to obtain high-purity vanadate crystals with a purity greater than 99.9%; (2) Dissolve the high-purity vanadate crystals in water, add sulfuric acid to adjust the pH of the system to 0 4, and add according to 1.1 of the theoretical reaction amount Add the reducing agent in an amount 1.5 times, and react at 0 99 °C for 1 3 h to reduce vanadium to +4 valence; then add an alkaline solution to adjust the pH to 5 13 and react for 0.5 2 h, then perform solid-liquid separation; wash the filter cake with pure water or dilute sulfuric acid solution with pH = 4 7 for 2 4 times to obtain high-purity VO(OH)2. The filtrate and washing solution are returned to dissolve high-purity vanadate; mix VO(OH)2 with 2.5 5 mol / L sulfuric acid to prepare 1.5 3 mol / L high-concentration vanadyl sulfate electrolyte, and the electrolyte meets the requirements of the 4-valence electrolyte for vanadium redox flow batteries in GB / T 37204 2018; The vanadium-containing material described in step (1) is one or more of red vanadium, crude V2O5, ammonium polyvanadate, and ammonium metavanadate; The lye in step (1) is one or more of 50 500 g / L NaOH, KOH solutions; The reducing agent described in step (2) is one or more of sodium sulfite, potassium sulfite, sulfur dioxide, elemental sulfur, sodium sulfide, oxalic acid, oxalate, sucrose, glucose, and fructose; The alkaline solution described in step (2) is one or more of saturated NaOH and KOH.

2. A method for purifying vanadate crystals according to claim 1 A method for preparing a high-concentration vanadium electrolyte by chemical reduction, characterized in that: The red vanadium contains 0.5 - 5% of Na2O, 80 - 90% of V2O5 and 0.2 - 3% of H2O; the crude V2O5 refers to the metallurgical grade V2O5 with a purity of 98% obtained by sodium roasting of vanadium slag, ammonium salt precipitation of vanadium calcination, or the chemical grade V2O5 with a purity of 97%.

3. A method for purifying vanadate crystallization according to claim 1 A method for preparing a high-concentration vanadium electrolyte by chemical reduction, characterized in that: The vanadate described in step (2) is one or more of sodium metavanadate, sodium pyrovanadate, sodium orthovanadate, potassium metavanadate, potassium pyrovanadate, and potassium orthovanadate.

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