A method for preparing vanadyl sulfate crystal by room temperature crystallization

Abstract

The application discloses a method for preparing vanadyl sulfate crystals by room-temperature crystallization, which comprises the following steps: (1) preparing a vanadyl sulfate dilute solution; (2) preparing a vanadyl sulfate concentrated solution: under stirring, concentrated sulfuric acid is added into the vanadyl sulfate dilute solution prepared in the step (1), and then a mixture of dihydrate oxalic acid and vanadium pentoxide is continuously and uniformly added within 30-40 min after uniform stirring; then the solution is heated to 95-100 DEG C, and kept for 6-8 h, and vanadyl sulfate concentrated solution is obtained; (3) crystallization: the vanadyl sulfate concentrated solution is cooled to room temperature and then stirred to crystallize, and a slurry containing vanadyl sulfate crystals is obtained; solid-liquid separation is performed on the slurry, and a crystallization filtrate and vanadyl sulfate crystals are obtained; the vanadyl sulfate crystals are collected after washing and drying; the filtrate and washing liquid can be returned to the step (2) as the vanadyl sulfate dilute solution. The method can not only realize the room-temperature crystallization preparation of vanadyl sulfate, but also reduce waste liquid discharge and improve vanadium utilization.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, and in particular relates to a method for preparing vanadium oxysulfate crystals by room temperature crystallization. Background Technology

[0002] Vanadyl sulfate (VOSO4), an important vanadium intermediate, has wide applications in vanadium redox flow batteries, as a mordant, and a catalytic reducing agent. Particularly in all-vanadium redox flow batteries, the key active component of the electrolyte is typically an acidic solution of vanadium sulfate. However, vanadium sulfate in solution presents challenges in transportation and storage, high safety requirements, and its liquid state leads to high transportation costs. Therefore, developing an efficient and low-cost crystallization process for vanadium sulfate to transform the active material from a liquid state into a stable solid product is crucial for reducing storage and transportation costs and improving safety.

[0003] Patent application CN 119349636 A discloses a method for preparing vanadium oxysulfate. The method employs a stepwise synergistic reduction process using an organic reducing agent (oxalic acid) and inorganic reducing agents (sulfur dioxide, sulfurous acid, and vanadium trioxide) to reduce V₂O₅, yielding a vanadium oxysulfate solution. This solution is then concentrated by steam heating to obtain vanadium oxysulfate crystals. During the evaporation and concentration process of the vanadium oxysulfate solution, the solution viscosity continuously increases with the increase in the solid-liquid ratio of the slurry. This not only makes subsequent slurry filtration and separation difficult but also results in high energy consumption for evaporation, concentration, and crystallization, increasing the cost of vanadium oxysulfate crystallization.

[0004] Patent application CN 112607774 A uses high-purity vanadate (purity ≥ 99 wt%) slurry as raw material and employs a direct gas reduction-cooling crystallization method to obtain high-purity vanadium oxysulfate crystals (purity > 99.5 wt%). The entire preparation process requires no external heat source, has mild reaction conditions, and allows for the recycling of the mother liquor. However, the high-purity vanadate in this method is a sparingly soluble substance, and the reduction reaction time in the gas-liquid-solid three-phase system is long. The resulting vanadium oxysulfate crystals contain residual sulfate impurities. When washing with water to remove these impurities, the vanadium oxysulfate easily dissolves, leading to a significant decrease in recovery rate. Simultaneously, sulfate enters the wastewater, and when the wastewater is recycled more than twice, the purity of the vanadium oxysulfate product is difficult to meet the product specifications. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention aims to provide a method for preparing vanadium oxysulfate crystals by room temperature crystallization. This method not only allows for the preparation of vanadium oxysulfate crystals at room temperature, significantly reducing energy consumption, but also enables the recycling of the crystallization mother liquor, minimizing waste discharge and achieving the recycling of vanadium resources.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing vanadium oxysulfate crystals by room temperature crystallization includes the following steps: (1) Preparation of dilute vanadium oxysulfate solution: Add a mixture of oxalic acid dihydrate and vanadium pentoxide to an aqueous sulfuric acid solution, stir at room temperature for 1-2 h, heat to 95-100℃ and keep warm for 8-10 h, filter while hot to remove insoluble impurities, and let the filtrate cool naturally to room temperature to obtain the solution.

[0007] (2) Preparation of concentrated vanadium oxysulfate solution: Under stirring conditions, add concentrated sulfuric acid to the dilute vanadium oxysulfate solution prepared in step (1), stir evenly, and continuously and evenly add the mixture of oxalic acid dihydrate and vanadium pentoxide within 30~40 min; after the addition is completed, heat the solution to 95~100℃ and keep it at that temperature for 6~8 h to obtain the solution.

[0008] (3) Crystallization: After cooling the concentrated vanadium oxysulfate solution to room temperature, stir and crystallize to obtain a slurry containing vanadium oxysulfate crystals; perform solid-liquid separation on the slurry to obtain crystallized filtrate and vanadium oxysulfate crystals; collect the vanadium oxysulfate crystals after washing and drying; the filtrate and washing liquid can be returned to step (2) as a dilute vanadium oxysulfate solution.

[0009] Furthermore, in step (1) of the present invention, the molar ratio of oxalic acid dihydrate and vanadium pentoxide in the mixture is 1:1 to 1.05:1.

[0010] Further, in step (1) of the present invention, the concentration of vanadium oxysulfate in the dilute solution is 1.5~3 mol / kg water, preferably 1.5~2.5 mol / kg water; the concentration of the free sulfuric acid is 0.5~1.5 mol / kg water, preferably 0.7~1.3 mol / kg water.

[0011] Furthermore, the concentrated sulfuric acid in step (2) of this invention contains 93 wt% sulfuric acid.

[0012] Further, in step (2) of the present invention, the concentration of vanadium oxysulfate in the vanadium oxysulfate concentrated solution is 6.0~9.0 mol / kg water, preferably 7.5~8.8 mol / kg water; the concentration of the free sulfuric acid is 0.7~1.5 mol / kg water, preferably 0.8~1.2 mol / kg water.

[0013] Furthermore, in step (2) of the present invention, the molar ratio of oxalic acid dihydrate and vanadium pentoxide in the mixture is 1:1 to 1.02:1.

[0014] Furthermore, when the filtrate in step (3) of the present invention contains Na2O+K2O≥2.0 wt% or Fe≥1.2 wt%, it is collected as waste liquid and vanadium is recycled through a continuous operation of ammonium salt precipitation-calcination.

[0015] Furthermore, in step (3) of the present invention, the room temperature is 20~25℃, the stirring rate for stirring and crystallization is 200~350 r / min, preferably 250~320 r / min, and the crystallization time is 4~6 h, preferably 5~6 h.

[0016] The crystallinity of vanadium oxysulfate crystals prepared by the method of the present invention is 56.2-70.5%.

[0017] The inventive principle of this invention lies in: This invention employs a process route of first preparing a dilute vanadium oxysulfate solution, then synthesizing a concentrated solution, and finally cooling and crystallizing. The technical principle lies in using the dilute vanadium oxysulfate solution as a buffer medium for continuous feeding, thereby reducing the instantaneous reaction rate of the raw materials and avoiding the localized overheating phenomenon that easily occurs when directly preparing a concentrated vanadium oxysulfate solution. If a mixture of vanadium pentoxide and oxalic acid dihydrate is directly added to a concentrated sulfuric acid system, even with a significantly reduced feeding rate, the reduction reaction involving oxalic acid dihydrate competes with its decomposition reaction under acidic conditions the moment the solid particles come into contact with and are wetted by the concentrated acid, rapidly generating gases such as CO and CO2, which can easily lead to solution overflow.

[0018] Based on the above principles, this invention optimizes the addition amounts and rates of vanadium pentoxide, oxalic acid dihydrate, and sulfuric acid, enabling the materials to complete dissolution and further reduction reactions in a dilute vanadium oxysulfate solution environment. This effectively reduces the risk of solution overflow caused by the concentrated decomposition of oxalic acid dihydrate generating a large number of bubbles, successfully producing a concentrated vanadium oxysulfate solution. Subsequently, vanadium oxysulfate crystals are obtained by stirring and crystallizing at room temperature. The crystallization filtrate is returned to the reactor as a dilute solution for recycling in the preparation of the next batch of vanadium oxysulfate. When the impurity content in the filtrate reaches or exceeds a preset threshold, it is collected as waste liquid. The waste liquid is then treated sequentially through oxidation-ammonium salt precipitation-calcination and other continuous operations to obtain recyclable vanadium pentoxide raw material, thereby achieving vanadium recovery and utilization.

[0019] The beneficial technical effects of this invention are as follows: This invention utilizes a pre-prepared dilute vanadium oxysulfate solution as a reaction buffer medium. When vanadium pentoxide and oxalic acid dihydrate are subsequently added, this dilute solution effectively dilutes the instantaneous reaction concentration of the reactants, avoiding localized overheating that easily occurs when directly preparing concentrated vanadium oxysulfate solutions. It also reduces the risk of excessive bubbles and solution overflow caused by oxalic acid decomposition. Simultaneously, this dilute solution promptly dissolves the vanadium oxysulfate generated in the reaction, preventing it from forming a dense coating layer on the surface of unreacted raw material particles. This ensures that the redox reaction proceeds fully and thoroughly, resulting in a homogeneous vanadium oxysulfate solution.

[0020] Based on the above process, this invention uses room temperature stirred crystallization technology to replace traditional evaporation crystallization, significantly reducing process energy consumption. All mother liquor after crystallization is returned to the reactor and recycled as a dilute solution for the next batch preparation, achieving maximum wastewater reduction. When impurities in the circulating filtrate accumulate to a preset threshold, the wastewater undergoes a continuous directional recovery process involving oxidation, ammonium salt precipitation of vanadium, and calcination to convert the vanadium component into recyclable vanadium pentoxide raw material, thereby achieving efficient utilization of vanadium resources throughout the entire process and a green closed-loop process. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process for preparing vanadium oxysulfate crystals and recovering vanadium according to the present invention.

[0022] Figure 2 The image shows the vanadium oxysulfate product prepared by cooling crystallization in Example 1.

[0023] Figure 3 The XRD pattern of the standard card of vanadium oxysulfate and VOSO4·3H2O prepared by one cooling crystallization and the fourth recycling crystallization of the filtrate in Example 1 is shown. Detailed Implementation

[0024] To better understand the present invention, the invention is described in detail below with reference to specific embodiments. Example 1

[0025] A method for preparing vanadium oxysulfate crystals by room temperature crystallization, the process flow is as follows: Figure 1 Specifically, it includes the following steps: (1) Preparation of dilute vanadium oxysulfate solution: 100 mL of water and 16.12 mL of 93 wt% concentrated sulfuric acid were added sequentially to a double-walled glass reactor. Stirring was started. 13.65 g of vanadium pentoxide and 9.5 g of oxalic acid dihydrate were mixed evenly and added to the above sulfuric acid solution. The mixture was stirred at room temperature for 1 h. The solution was then heated to 95 °C and kept at that temperature for 8 h. The solution was filtered while hot to remove insoluble impurities. The filtrate was allowed to cool naturally to room temperature to obtain the solution. The concentration of vanadium oxysulfate in the dilute vanadium oxysulfate solution was 1.5 mol / kg water and the concentration of free sulfuric acid was 1.3 mol / kg water.

[0026] (2) Preparation of concentrated vanadium oxysulfate solution: Under stirring conditions, 25.91 mL of 93 wt% concentrated sulfuric acid was added to the above dilute vanadium oxysulfate solution. After stirring evenly, a mixture of 40.95 g of vanadium pentoxide and 28.7 g of oxalic acid dihydrate was continuously and evenly added over 40 min. The solution was heated to 99℃ and kept at that temperature for 6 h to obtain concentrated vanadium oxysulfate solution. The concentration of vanadium oxysulfate in the obtained concentrated vanadium oxysulfate solution was 6.0 mol / kg water, and the concentration of free sulfuric acid was 1.3 mol / kg water.

[0027] (3) Cooling and crystallization: The concentrated vanadium oxysulfate solution prepared in step (2) was transferred to a crystallization reactor, and stirring was started at a rate of 200 r / min. The temperature was then reduced to 25℃ at a rate of 5℃ / min and stirred for 4.5 h to obtain a slurry containing vanadium oxysulfate crystals. The filtrate and vanadium oxysulfate crystals were then separated by filtration. The vanadium oxysulfate crystals were collected after washing with water and drying. The crystallization rate was calculated to be 56.2%.

[0028] The filtrate and washing solution obtained in this step are mixed together to form a dilute vanadium oxysulfate solution. The sulfate and vanadium content in this solution is determined. Then, a concentrated vanadium oxysulfate solution is prepared by adding an appropriate amount of sulfuric acid, as well as premixed oxalic acid dihydrate and vanadium pentoxide solid. Subsequently, vanadium oxysulfate crystals, filtrate, and washing solution are obtained through cooling crystallization and filtration. The filtrate and washing solution are continuously circulated in this manner until the impurity content in the filtrate exceeds a set value. At this point, air can be introduced into the filtrate. After the tetravalent vanadium in the filtrate is oxidized to pentavalent, vanadium pentoxide is obtained through continuous operations such as ammonium salt precipitation and calcination, and is recycled for the preparation of vanadium oxysulfate solution.

[0029] The vanadium oxysulfate crystals prepared in this embodiment are as follows: Figure 2 As shown. By Figure 2 As can be seen, the prepared vanadium oxysulfate is in the form of blue granules. The vanadium oxysulfate crystals prepared in the other examples are the same as in Example 1, and will not be provided again.

[0030] The XRD pattern of the standard card for vanadium oxysulfate and VOSO4·3H2O prepared by the first cooling crystallization and the fourth cycle crystallization of the filtrate in this embodiment is shown below. Figure 3 As shown; by Figure 3 It can be seen that the XRD pattern of the prepared sample is consistent with the standard card of VOSO4·3H2O (PDF#27-0950), indicating that the method successfully prepared vanadium oxysulfate crystals. Example 2

[0031] A method for preparing vanadium oxysulfate crystals by room temperature crystallization, the process flow is as follows: Figure 1 Specifically, it includes the following steps: (1) Preparation of dilute vanadium oxysulfate solution: 100 mL of water and 18.43 mL of 93 wt% concentrated sulfuric acid were added sequentially to a double-walled glass reactor. Stirring was started. 15.47 g of vanadium pentoxide and 10.77 g of oxalic acid dihydrate were mixed evenly and added to the above sulfuric acid solution. The mixture was stirred at room temperature for 1 h. The solution was then heated to 96 °C and kept at that temperature for 8.5 h. The solution was filtered while hot to remove insoluble impurities. The filtrate was allowed to cool naturally to room temperature to obtain the solution. The concentration of vanadium oxysulfate in the dilute vanadium oxysulfate solution was 1.7 mol / kg water and the concentration of free sulfuric acid was 1.5 mol / kg water.

[0032] (2) Preparation of concentrated vanadium oxysulfate solution: Under stirring conditions, 39.16 mL of 93 wt% concentrated sulfuric acid was added to the above dilute vanadium oxysulfate solution. After stirring evenly, the mixture of 61.88 g of vanadium pentoxide and 43.3 g of oxalic acid dihydrate was continuously and evenly added within 35 min. After the addition was completed, the solution was heated to 95℃ and kept at that temperature for 7 h to obtain concentrated vanadium oxysulfate solution. The concentration of vanadium oxysulfate in the obtained concentrated vanadium oxysulfate solution was 8.5 mol / kg water, and the concentration of free sulfuric acid was 1.5 mol / kg water.

[0033] (3) Cooling and crystallization: The above-mentioned concentrated vanadium oxysulfate solution was transferred to a crystallization reactor, and stirring was started at a rate of 300 r / min. The temperature was then reduced to 20°C at a rate of 3°C / min. After stirring for 6 h, the solution was filtered to obtain the filtrate and vanadium oxysulfate crystals. The vanadium oxysulfate crystals were washed with water, dried, and collected. The crystallization rate was calculated to be 70.5%. The filtrate and washing liquid were collected and returned to the reactor as the next cycle of dilute vanadium oxysulfate solution for preparing concentrated vanadium oxysulfate solution. The filtrate recycling operation was the same as in Example 1. Example 3

[0034] A method for preparing vanadium oxysulfate crystals by room temperature crystallization, the process flow is as follows: Figure 1 Specifically, it includes the following steps: (1) Preparation of vanadium oxysulfate dilute solution: Under stirring conditions, 100 mL of water and 14.4 mL of 93 wt% concentrated sulfuric acid were added sequentially to a double-walled glass reactor, followed by the addition of a mixture of 18.2 g of vanadium pentoxide and 12.71 g of oxalic acid dihydrate; after stirring at room temperature for 1 h, the mixture was heated to 98 °C and kept at that temperature for 9 h, and the insoluble impurities were removed by filtration while hot. The filtrate was then allowed to cool naturally to room temperature to obtain the solution. The concentration of vanadium oxysulfate in the vanadium oxysulfate dilute solution was 2.0 mol / kg water, and the concentration of free sulfuric acid was 0.5 mol / kg water.

[0035] (2) Preparation of concentrated vanadium oxysulfate solution: Under stirring conditions, 35.7 mL of 93 wt% concentrated sulfuric acid was added to the above dilute vanadium oxysulfate solution. After stirring evenly, a mixture of 54.6 g of vanadium pentoxide and 38.03 g of oxalic acid dihydrate was continuously and evenly added over 30 min. After the addition was complete, the solution was heated to 95℃. At this time, due to the rapid addition rate of oxalic acid, a large amount of oxalic acid decomposed as the solution temperature increased, producing bubbles with a volume approximately twice that of the solution. However, as the solution was continuously stirred, the bubbles gradually disappeared. After maintaining the temperature for 8 h under these conditions, a concentrated vanadium oxysulfate solution was obtained. The concentration of vanadium oxysulfate in the obtained concentrated vanadium oxysulfate solution was 8.0 mol / kg water, and the concentration of free sulfuric acid was 0.7 mol / kg water.

[0036] (3) Cooling and crystallization: The above-mentioned concentrated vanadium oxysulfate solution was transferred to a crystallization reactor, and stirring was started at a rate of 350 r / min. The temperature was then reduced to 21°C at a rate of 3°C / min. After stirring for 5 h, the solution was filtered to separate the filtrate and vanadium oxysulfate crystals. The vanadium oxysulfate crystals were washed with water, dried, and collected. The crystallization rate was calculated to be 65.3%. The filtrate and washing liquid were collected and returned to the reactor as the next cycle of dilute vanadium oxysulfate solution for preparing concentrated vanadium oxysulfate solution. The filtrate recycling operation was the same as in Example 1. Example 4

[0037] A method for preparing vanadium oxysulfate crystals by room temperature crystallization, the process flow is as follows: Figure 1 Specifically, it includes the following steps: (1) Preparation of dilute vanadium oxysulfate solution: Under stirring conditions, 100 mL of water and 24.18 mL of 93 wt% concentrated sulfuric acid were added sequentially to a double-walled glass reactor. Then, a mixture of 27.3 g of vanadium pentoxide and 19.8 g of oxalic acid dihydrate was added. After stirring at room temperature for 1 h, the solution was heated to 99 °C and kept at that temperature for 10 h. The solution was filtered while hot to remove insoluble impurities. The filtrate was then allowed to cool naturally to room temperature. The concentration of vanadium oxysulfate in the obtained dilute vanadium oxysulfate solution was 3.0 mol / kg water and the concentration of free sulfuric acid was 1.2 mol / kg water.

[0038] (2) Preparation of concentrated vanadium oxysulfate solution: Under stirring conditions, 34.55 mL of 93wt% concentrated sulfuric acid was added to the above dilute vanadium oxysulfate solution; after stirring evenly, the mixture of 54.6 g of vanadium pentoxide and 38.6 g of oxalic acid dihydrate was continuously and evenly added within 30 min; after the addition was completed, the solution was heated to 99℃ and kept at that temperature for 8 h to obtain concentrated vanadium oxysulfate solution. The concentration of vanadium oxysulfate in the obtained concentrated vanadium oxysulfate solution was 9.0 mol / kg water and the concentration of free sulfuric acid was 1.2 mol / kg water.

[0039] (3) Cooling and crystallization: The above-mentioned concentrated vanadium oxysulfate solution was transferred to a crystallization reactor, and stirring was started at a rate of 280 r / min. The temperature was then reduced to 23°C at a rate of 5°C / min. After stirring for 4 h, the solution was filtered to obtain the filtrate and vanadium oxysulfate crystals. The vanadium oxysulfate crystals were washed with water, dried, and collected. The crystallization rate was calculated to be 68.7%. The filtrate and washing liquid were collected and returned to the reactor as the next cycle of dilute vanadium oxysulfate solution. The filtrate was used to prepare the concentrated vanadium oxysulfate solution, and the filtrate recycling operation was the same as in Example 1. Comparative Example 1

[0040] The preparation method of vanadium oxysulfate crystals in this comparative example is as follows: 100 mL of water and 50.1 mL of 93 wt% concentrated sulfuric acid were sequentially added to a double-walled glass reactor. Stirring was started. 72.8 g of vanadium pentoxide and 50.7 g of oxalic acid dihydrate were mixed thoroughly and continuously and uniformly fed into the sulfuric acid solution over 30 min. The mixture was stirred at room temperature for 1 h, then heated to 60 °C. At this temperature, the oxalic acid rapidly decomposed, producing bubbles approximately four times the volume of the solution. The number of bubbles increased continuously with rising temperature. Heating was stopped, and stirring continued for approximately 1.5 h until the bubbles disappeared. The temperature was then further increased to 95 °C and held for 6 h to obtain the vanadium concentration. =8.0 mol / kg water and free sulfuric acid concentration A vanadium oxysulfate solution with a concentration of 0.7 mol / kg water was prepared. This solution was transferred to a crystallization reactor, and stirring was started at a rate of 260 r / min. The temperature was then reduced to 25°C at a rate of 5°C / min, and stirring was continued for 7 h. Subsequently, the filtrate and vanadium oxysulfate crystals were separated by filtration. The crystallization rate of vanadium oxysulfate was 60.4%. The filtrate was collected and returned to the reactor as a dilute solution for the next cycle to synthesize a concentrated vanadium oxysulfate solution. The filtrate recycling operation was the same as in Example 1. Comparative Example 2

[0041] In this comparative example, the concentrated vanadium oxysulfate solution prepared in Example 2 was placed in a double-layer reactor and evaporated and crystallized at 80°C for 8 hours. As the solvent continued to evaporate, the viscosity of the solution increased, and finally the solution became a gel-like solid. The gel-like solid was taken out and placed in an oven at 60°C for another 6 hours to obtain solid vanadium oxysulfate.

[0042] The results of the comparative examples and embodiments show that when oxalic acid dihydrate and vanadium pentoxide raw materials are directly added to sulfuric acid solution to prepare vanadium oxysulfate concentrated solution, as the reaction temperature increases, oxalic acid decomposes violently and releases a large number of bubbles, posing a safety hazard of solution overflow. On the other hand, the evaporation crystallization method for preparing vanadium oxysulfate crystals has the problems of long crystallization cycle and high energy consumption, and the product obtained from the initial evaporation is a sticky solid that is not easy to collect.

[0043] The method for preparing vanadium oxysulfate crystals by room temperature crystallization proposed in this invention has been described through examples. Those skilled in the art should not modify or appropriately alter or combine the methods described in this invention to achieve the technical requirements of this invention. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered part of this invention.

Claims

1. A method for preparing vanadium oxysulfate crystals by room temperature crystallization, characterized in that, Includes the following steps: (1) Preparation of dilute vanadium oxysulfate solution: Add a mixture of oxalic acid dihydrate and vanadium pentoxide to an aqueous sulfuric acid solution, stir at room temperature for 1-2 h, heat to 95-100℃ and keep warm for 8-10 h, filter while hot to remove insoluble impurities, and let the filtrate cool naturally to room temperature to obtain the solution. (2) Preparation of concentrated vanadium oxysulfate solution: Under stirring conditions, add concentrated sulfuric acid to the dilute vanadium oxysulfate solution prepared in step (1), stir evenly, and then continuously and evenly add the mixture of oxalic acid dihydrate and vanadium pentoxide within 30~40 min; after the addition is completed, heat the solution to 95~100℃ and keep it at that temperature for 6~8 h to obtain the solution. (3) Crystallization: After cooling the concentrated vanadium oxysulfate solution to room temperature, stir and crystallize to obtain a slurry containing vanadium oxysulfate crystals; perform solid-liquid separation on the slurry to obtain crystallized filtrate and vanadium oxysulfate crystals; collect the vanadium oxysulfate crystals after washing and drying; the filtrate and washing liquid can be returned to step (2) as a dilute vanadium oxysulfate solution.

2. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, In step (1), the molar ratio of oxalic acid dihydrate to vanadium pentoxide in the mixture is 1:1 to 1.05:

1.

3. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, In step (1), the concentration of vanadium oxysulfate in the dilute solution is 1.5~3 mol / kg water, and the concentration of free sulfuric acid is 0.5~1.5 mol / kg water.

4. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, The concentrated sulfuric acid in step (2) contains 93 wt% sulfuric acid.

5. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, In step (2), the concentration of vanadium oxysulfate in the vanadium oxysulfate solution is 6.0~9.0 mol / kg water, and the concentration of free sulfuric acid is 0.7~1.5 mol / kg water.

6. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, In step (2), the molar ratio of oxalic acid dihydrate to vanadium pentoxide in the mixture is 1:1 to 1.02:

1.

7. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, When the filtrate in step (3) contains Na2O+K2O≥2.0 wt% or Fe≥1.2 wt%, it is collected as waste liquid and vanadium is recycled through a continuous operation of ammonium salt precipitation-calcination.

8. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, The room temperature in step (3) is 20~25℃, the stirring rate for crystallization is 200~350 r / min, and the crystallization time is 4~6 h.

9. The method for preparing vanadium oxysulfate crystals by room temperature crystallization according to claim 1, characterized in that, The crystallinity of vanadium oxysulfate crystals prepared by the method is 56.2-70.5%.

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