A method for purifying vanadium oxide

Abstract

The application discloses a method for purifying vanadium oxide, which comprises the following steps: a, dissolving APV, V2O5 or red cake in ammonia water or ammonium carbonate or ammonium bicarbonate to obtain an AMV solution; b, performing crystallization separation on the AMV solution to obtain solid AMV and a first filtrate; if the impurity content in the solid AMV is qualified, vanadium oxide is prepared by calcination or reduction; if the impurity content in the solid AMV is unqualified, the step c is performed; c, heating and dissolving the solid AMV, adding an acidic solution to adjust the pH value to increase the dissolution amount of the solid AMV, cooling and adjusting the pH value when the vanadium concentration in the solution reaches a certain value to obtain a stable acidic vanadium solution, and filtering the acidic vanadium solution; d, heating and crystallizing the filtrate in the step c to obtain solid APV and a second filtrate; if the impurity content in the solid APV is qualified, vanadium oxide is prepared by calcination or reduction. The method is used for mutual conversion between APV and AMV, the impurities in the raw material are gradually removed in an acidic or weak alkaline environment, and the purity of the vanadium oxide is improved.

Description

Technical Field

[0001] This invention belongs to the field of vanadium oxide preparation, and particularly relates to a method for purifying vanadium oxide. Background Technology

[0002] Vanadium is a very rare metallic element, mainly used in the steel industry to improve the strength and toughness of steel products. Vanadium also has wide applications in the chemical, energy storage, and pharmaceutical fields, making it highly valuable economically. The main impurities in vanadium oxide products or intermediates used in their production are P, Si, Mn, Fe, Cr, Ca, Mg, K, and Na. Acidic precipitation of ammonium polyvanadate (APV) can reduce some cationic impurities, while weakly alkaline precipitation of ammonium metavanadate (AMV) can reduce some anionic impurities. Combining the properties of acidic APV and weakly alkaline AMV precipitation can effectively reduce various impurities in vanadium oxide products.

[0003] Patent document CN106044853B, "A Purification Method for Deep Removal of Silicon from Ammonium Metavanadate," discloses the following steps: a. Adding crude silicon-containing ammonium metavanadate to water, with an addition amount of 375-500 g / L; b. Acidifying to pH 2-3 with 50-98% sulfuric acid over 10 min-2 h, followed by stirring for 1-5 h to convert the ammonium metavanadate into ammonium polyvanadate, and filtering to obtain ammonium polyvanadate filter cake and ammonium sulfate solution; c. Adding ammonium polyvanadate to ammonia water, stirring, and adjusting the reaction endpoint pH to 7-9 using ammonia water to convert the ammonium polyvanadate into ammonium metavanadate; d. Filtering to obtain high-purity ammonium metavanadate and filtrate, with the filtrate returned to step a for use as ammonium metavanadate feed.

[0004] However, the above methods have the following problems:

[0005] (1) The filtrate of high-purity ammonium metavanadate is returned to the preparation of ammonium polyvanadate from ammonium metavanadate. The filtrate of ammonium metavanadate contains impurities such as P that will not enter ammonium metavanadate. However, the P in the filtrate will enter ammonium polyvanadate when ammonium metavanadate is prepared, resulting in a higher P content in ammonium polyvanadate.

[0006] (2) When ammonium metavanadate is directly added to acid, it reacts to generate ammonium polyvanadate. Under acidic conditions, solid ammonium metavanadate will directly react to generate a mixture of water, vanadium pentoxide and ammonium polyvanadate. This mixture will encapsulate impurities, which cannot be effectively separated when all of them are converted to ammonium polyvanadate in the future.

[0007] (3) The direction of the ammonium sulfate solution is unknown.

[0008] In summary, there is an urgent need in the field of vanadium oxide preparation for a method that produces vanadium oxide with high product quality, low cost, less waste liquid, and less solid waste. Summary of the Invention

[0009] Therefore, in order to overcome the shortcomings of existing methods for producing vanadium oxide, a purification method for vanadium oxide is provided. This method has the advantages of high-quality vanadium oxide product, low cost, less waste liquid, and less solid waste.

[0010] To achieve the above objectives, the following technical solution is adopted:

[0011] This invention provides a method for purifying vanadium oxide, comprising the following steps:

[0012] a. Dissolve APV, V2O5 or red cake in ammonia water or ammonium carbonate or ammonium bicarbonate and filter to obtain AMV solution;

[0013] b. Crystallize the AMV solution to obtain solid AMV and primary filtrate. If the impurity content of the primary filtrate does not exceed the standard, return to step a; if the impurity content in the solid AMV is qualified, calcine or reduce it to prepare vanadium oxide; if the impurity content in the solid AMV is unqualified, proceed to step c.

[0014] c. Solid AMV is heated and dissolved. During the dissolution process, an acidic solution is added to adjust the pH value to increase the amount of solid AMV dissolved. When the vanadium concentration in the solution reaches a certain level, the temperature is lowered and the pH value is adjusted to stabilize the solution, resulting in an acidic vanadium solution. The acidic vanadium solution is then filtered.

[0015] d. Heating the filtrate from step c to crystallize it yields solid APV and a secondary filtrate. If the impurity content of the secondary filtrate does not exceed the standard, it is neutralized and filtered before returning to step c. If the impurity content of the solid APV is within the acceptable range, it is calcined or reduced to prepare vanadium oxide. If the impurity content of the solid APV is not within the acceptable range, it proceeds to step a and repeats the above steps.

[0016] In some embodiments, NH4 is controlled during dissolution in step a. + The molar ratio of NH4 to V is 1:1. + / V = 1.5~4.0, dissolution pH is 7.0~10, dissolution temperature is 70℃~95℃, and solution V concentration is controlled at 20g / L~40g / L.

[0017] In some embodiments, the linear velocity of the outermost part of the agitator in step b during crystallization is controlled at 0.4 m / s to 3 m / s, the cooling rate during crystallization is controlled at 0.2 °C / min to 4 °C / min, the final crystallization temperature is 6 °C to 30 °C, and crystallization is carried out at the final temperature for 60 min to 300 min.

[0018] In some embodiments, the element used to determine whether the impurity content of the primary filtrate exceeds the standard in step b is P, and P ≤ 0.2 g / L is considered not to exceed the standard;

[0019] The acceptable impurity content standards in the solid AMV in step b are: P≤0.01g / L, S≤0.02g / L, As≤0.01g / L, K≤0.03g / L, Na≤0.50g / L, Si≤0.08g / L, Fe≤0.08g / L, Cr≤0.05g / L, Mn≤0.10g / L, and Ca≤0.05g / L.

[0020] In some embodiments, the solid AMV dissolution temperature in step c is 80°C to 99°C, and the pH value is adjusted to 6 to 8 using sulfuric acid at a volume ratio of 20% to 50%.

[0021] In some embodiments, in step c, "when the vanadium concentration in the solution reaches a certain level, the pH value is adjusted by cooling to obtain an acidic vanadium solution," the vanadium concentration in the solution is controlled to be 15 g / L to 40 g / L, and the cooling rate is 0.2 °C / min to 10 °C / min. The matching relationship between temperature and pH value during the cooling process is as follows:

[0022] At temperatures of 80℃~99℃, the pH value is 6~8; at temperatures of 60℃~80℃, the pH value is 4~6; at temperatures of 40℃~60℃, the pH value is 2.4~4; at temperatures of 20℃~40℃, the pH value is 1.5~4; and at temperatures <20℃, the pH value is 1.5~4.

[0023] In some embodiments, after cooling to a temperature of 20°C to 40°C in step c, a vanadate solution is obtained by filtration. The filter residue is washed once with 0.02 to 0.1 times the volume of the vanadate solution in clean water at a temperature of 20°C to 40°C. The filtrate from the wash water is then added to the vanadate solution.

[0024] In some embodiments, after the heating and crystallization in step d is completed, solid APV is obtained by filtration. The solid APV is washed once with acidic water or an ammonium-containing solution, and the wash water contains NH4. + The concentration of the washing solution is controlled at 0–10 g / L, the washing water temperature is 65–95°C, the washing water pH is 2.0–4.0, and the washing water volume is equal to the mass of solid AMV dissolved in step c. The washing filtrate is added to the secondary filtrate.

[0025] In some embodiments, the elements used to determine whether the impurity content of the secondary filtrate exceeds the standard in step d are S and Fe, where S≤50g / L and Fe≤0.06g / L.

[0026] The acceptable impurity content standards in the solid APV in step d are: P≤0.01g / L, S≤0.02g / L, As≤0.01g / L, K≤0.03g / L, Na≤0.50g / L, Si≤0.08g / L, Fe≤0.08g / L, Cr≤0.05g / L, Mn≤0.10g / L, and Ca≤0.05g / L.

[0027] In some embodiments, the heating crystallization process in step d, "heating and crystallizing the filtrate from step c to obtain solid APV and secondary filtrate", includes: adjusting the pH value to 2.0 to 2.5, the heating rate to 1℃ / min to 7℃ / min, the heating endpoint temperature to 85℃ to 95℃, the crystallization time to 30min to 120min, and controlling the outermost linear velocity of the stirring paddle to 0.4m / s to 3m / s during the crystallization process.

[0028] The present invention has the following beneficial technical effects:

[0029] The vanadium oxide purification method of this invention utilizes the interconversion between APV and AMV, allowing impurities in the raw materials to be gradually removed in an acidic or weakly alkaline environment, thereby improving the purity of vanadium oxide. During the conversion process, if the quality of APV or AMV does not meet the requirements, the cycle continues; if the quality of APV or AMV meets the requirements, the cycle is terminated for further vanadium oxide preparation. The method of this invention has the advantages of producing high-quality vanadium oxide, low cost, less waste liquid, and less solid waste. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic flowchart of a vanadium oxide purification method according to an embodiment of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0033] This invention utilizes APV, V₂O₅, red cake, or AMV as raw materials. Through the interconversion between APV and AMV, impurities in the raw materials are gradually removed in an acidic or weakly alkaline environment to improve the purity of vanadium oxide. APV, V₂O₅, and red cake are dissolved and filtered using one or more of ammonia, ammonium carbonate, or ammonium bicarbonate. The filtrate is cooled to crystallize AMV. If the AMV is unqualified, it is dissolved and acidified to obtain a stable acidic vanadium solution. After filtration, the filtrate is heated to crystallize APV. If the APV is unqualified, the above dissolution process is repeated to prepare AMV. If either AMV or APV is qualified, the dissolution process is stopped, and vanadium oxide is prepared using the qualified AMV or APV. The AMV supernatant produced during AMV crystallization (e.g., ...) is used to prepare vanadium oxide. Figure 1The filtrate 1 shown, if its impurities do not exceed the standard, can be returned to dissolve APV, V2O5, and red cake; the AMV supernatant produced during APV crystallization (such as...) Figure 1 If the impurities in the filtrate 2 shown are within acceptable limits, it can be returned to dissolve AMV after neutralization and filtration. If the impurities in the AMV supernatant or APV supernatant exceed acceptable limits, it should be removed from the system for further processing.

[0034] Red cake is a common intermediate product of vanadium precipitation. Due to its high water content, high impurities, and low vanadium content, red cake is basically not produced in the industrial production of vanadium pentoxide. However, red cake does not require deammoniation during the re-dissolution process, so it is more often used to prepare vanadium pentoxide with higher purity.

[0035] like Figure 1 This is a schematic flowchart of a vanadium oxide purification method according to an embodiment of the present invention. The method includes the following steps:

[0036] a. Dissolve APV, V2O5 or red cake in ammonia water or ammonium carbonate or ammonium bicarbonate and filter to obtain AMV solution;

[0037] b. Crystallize the AMV solution to obtain solid AMV and primary filtrate. If the impurity content of the primary filtrate is within the standard, return to step a; if the impurity content of the primary filtrate exceeds the standard, exit the system processing; if the impurity content in the solid AMV is within the standard, calcine or reduce to prepare vanadium oxide; if the impurity content in the solid AMV is not within the standard, proceed to step c.

[0038] c. Solid AMV is heated and dissolved. During the dissolution process, an acidic solution is added to adjust the pH value to increase the amount of solid AMV dissolved. When the vanadium concentration in the solution reaches a certain level, the temperature is lowered and the pH value is adjusted to stabilize the solution, resulting in an acidic vanadium solution. The acidic vanadium solution is then filtered.

[0039] d. Heating the filtrate from step c to crystallize it yields solid APV and a secondary filtrate. If the impurity content of the secondary filtrate does not exceed the standard, it is neutralized and filtered before returning to step c. If the impurity content of the secondary filtrate exceeds the standard, it is exited from the system processing. If the impurity content of the solid APV is qualified, it is calcined or reduced to prepare vanadium oxide. If the impurity content of the solid APV is unqualified, it is returned to step a and the above steps are repeated.

[0040] Preferably, the NH4 is controlled during dissolution in step a. + The molar ratio of NH4 to V is 1:1. + / V = 1.5~4.0, dissolution pH is 7.0~10, dissolution temperature is 70℃~95℃, solution V concentration is controlled at 20g / L~40g / L, the dissolution process adopts stirring dissolution method, and the outermost linear velocity of the stirring paddle is controlled at 1m / s~10mm / s.

[0041] Preferably, in step a, after complete dissolution, the solution is kept at the dissolution temperature for 5 min to 30 min, and then filtered to obtain an AMV solution; the filter residue is washed once with 0.02 to 0.1 times the volume of the AMV solution in clean water at a temperature of 70°C to 95°C, and the wash water is added to the AMV solution.

[0042] Preferably, in step b, the linear velocity of the outermost part of the stirring paddle during crystallization is controlled at 0.4 m / s to 3 m / s, the cooling rate during crystallization is controlled at 0.2℃ / min to 4℃ / min, the final crystallization temperature is 6℃ to 30℃, and crystallization is carried out at the final temperature for 60 min to 300 min.

[0043] Preferably, after crystallization in step b, the solid AMV is obtained by filtration. The solid AMV is then washed once with water or an ammonium-containing solution, and the wash water contains NH4. + The concentration should be controlled between 0 and 50 g / L, the washing water temperature between 6°C and 30°C, and the washing water volume should be the same as the mass of APV, V2O5, and red cake dissolved in step a. The washing filtrate should be combined with the primary filtrate (i.e., Figure 1 Filtrate 1 shown.

[0044] Preferably, in step b, the element used to determine whether the impurity content of the primary filtrate exceeds the standard is P, and P ≤ 0.2 g / L is considered within the standard;

[0045] The impurity content standard in solid AMV in step b shall be based on actual production needs. The impurity content standard in solid AMV can be adjusted according to different needs, but shall not exceed the upper limit shown in Table 1 below.

[0046] Table 1

[0047]

[0048] Preferably, in step c, the solid AMV is dissolved at a temperature of 80°C to 99°C, and the pH value is adjusted to 6 to 8 using sulfuric acid at a volume ratio of 20% to 50%. The dissolution process is carried out by stirring, and the linear velocity of the outermost part of the stirring paddle is controlled at 1 m / s to 10 mm / s.

[0049] Preferably, in step c, the vanadium concentration in the solution is controlled to be 15 g / L to 40 g / L, and the cooling rate is 0.2℃ / min to 10℃ / min. The matching relationship between temperature and pH value during the cooling process is shown in Table 2 below.

[0050] Table 2

[0051] temperature 80℃～99℃ 60℃～80℃ 40℃～60℃ 20℃～40℃ <20℃ pH 6～8 4～6 2.4～4 1.5～4 1.5～4

[0052] Preferably, in step c, after cooling to a temperature of 20℃~40℃, a vanadate solution is obtained by filtration. The filter residue is washed once with 0.02~0.1 times the volume of the vanadate solution in clean water at a temperature of 20℃~40℃, and the filtrate from the wash water is added to the vanadate solution.

[0053] Preferably, the heating crystallization process in step d, which involves "heating and crystallizing the filtrate from step c to obtain solid APV and secondary filtrate", includes: adjusting the pH value to 2.0 to 2.5, the heating rate to 1℃ / min to 7℃ / min, and the final heating temperature to 85℃ to 95℃; the crystallization time to 30min to 120min, and controlling the outermost linear velocity of the stirring paddle to 0.4m / s to 3m / s during the crystallization process.

[0054] Preferably, after the heating and crystallization in step d is completed, the solid APV is obtained by filtration. The solid APV is washed once with acidic water or an ammonium-containing solution, and the wash water contains NH4. + The concentration of the washing solution is controlled at 0–10 g / L, the washing water temperature is 65–95℃, the pH value of the washing water is 2.0–4.0, and the washing water volume is equal to the mass of solid AMV dissolved in step c. The washing filtrate is combined with the secondary filtrate (i.e., Figure 1 Filtrate 2 shown.

[0055] Preferably, in step d, the elements used to determine whether the impurity content of the secondary filtrate exceeds the standard are S and Fe, where S≤50g / L and Fe≤0.06g / L;

[0056] Preferably, in step d, when the impurities in the crystallized liquid (secondary filtrate) do not exceed the standard, the neutralized pH is 7-9, and one or more of ammonia, ammonium carbonate, or ammonium bicarbonate are used for neutralization, and then the process returns to step c.

[0057] Preferably, the impurity content standard of solid APV in step d is based on actual production needs. The impurity content standard of solid APV can be adjusted according to different needs, but shall not exceed the upper limit shown in Table 3 below.

[0058] Table 3

[0059]

[0060] Preferably, vanadium oxide is prepared by calcination or reduction of solid APV or solid AMV: the calcination temperature of solid AMV or solid APV is 500℃~550℃, the calcination time is 120min~300min, and the oxygen content in the calcination atmosphere is greater than 15%;

[0061] Solid AMV or solid APV is reduced using coke oven gas, carbon monoxide, or hydrogen at a reduction temperature of 850℃~1000℃ for 90min~300min, with a reducing gas consumption of 0.25m³ per kilogram of APV or AMV. 3 / h~0.60m3 / h.

[0062] The method of the present invention obtains a filtrate of ammonium metavanadate, which is then returned for the preparation of ammonium polyvanadate. This solves the problem that phosphorus in the filtrate will enter the polyvanadate during the preparation of ammonium polyvanadate from ammonium metavanadate, resulting in a high phosphorus content in the polyvanadate.

[0063] The method of the present invention dissolves ammonium metavanadate under heating conditions, adjusts the pH value during slow cooling to obtain a stable vanadate solution under acidic conditions, and then raises the temperature to prepare ammonium polyvanadate, thereby achieving effective separation of impurities.

[0064] The method of the present invention allows for the recycling of ammonium sulfate solution produced during the preparation of ammonium polyvanadate from ammonium metavanadate, provided that the concentration and impurities are not high.

[0065] Example

[0066] The composition of the raw material vanadium pentoxide is shown in Table 4 below:

[0067] Table 4

[0068] Element P Mn Fe Si Na <![CDATA[V2O5]]> content / % 0.068 0.44 0.39 0.32 0.10 97.4

[0069] Take 20.54 g of the above-mentioned vanadium pentoxide, dissolve it in 500 mL of water, and control the NH4 content. +With a molar ratio (V) of 2.0, 16.86 g of ammonium carbonate and 6.95 g of ammonium bicarbonate were mixed and dissolved (ammonium content in ammonium carbonate was 0.8%, and in ammonium bicarbonate it was 0.2%). The pH was controlled at 9.0, the dissolution temperature at 90℃, and the vanadium concentration at 22.4 g / L. The linear velocity of the outermost part of the agitator was controlled at 1 m / s during the dissolution process. After complete dissolution, the solution was kept at 90℃ for 10 min, and then filtered to obtain an AMV solution. The filter residue was washed once with 10 mL of water (0.02 times the volume of the AMV solution) at 90℃, and the wash water was added to the AMV solution. During the AMV crystallization process, the outermost linear velocity of the agitator was controlled at 0.4 m / s, the cooling rate was controlled at 1℃ / min, the final crystallization temperature was 20℃, and crystallization was carried out at the final temperature for 180 min. After crystallization, 21.40 g of solid AMV was obtained by filtration. The solid AMV was washed once with water at 20℃, and the washing water volume was 20.54 mL. The washing filtrate was added to the crystallization liquid (filtrate 1), totaling 499 mL. The phosphorus concentration (P) in the crystallization liquid (filtrate 1) was approximately 0.02 g / L. Since P ≤ 0.2 g / L, the process was repeated in step a. The Fe content in solid AMV was 0.1%, which is unacceptable. Solid AMV was dissolved in 300 mL of water at 80℃. During dissolution, the pH was adjusted to 7 using 50% (volume ratio) sulfuric acid, and the vanadium concentration in the solution was controlled at 30.67 g / L. The outermost linear velocity of the agitator was controlled at 2 m / s during dissolution. The cooling rate was 1℃ / min. After cooling to the final temperature (20℃), the solution was filtered to obtain a vanadate solution. The filter residue was washed once with 30 mL of water (0.1 times the volume of the vanadate solution) at 20℃. The wash water filtrate was added to the vanadate solution. The pH was adjusted to 2.0, the heating rate was 7℃ / min, and the final temperature was 90℃. The APV crystallization time was 60 min, and the outermost linear velocity of the agitator was controlled at 0.5 m / s during crystallization. After crystallization, solid APV was obtained. The solid was washed once with an acidic ammonium-containing solution, with NH4+ added to the wash water. + The concentration of vanadium pentoxide was controlled at 8 g / L, the washing water temperature was 80℃, the washing water pH was 2.0, and the washing water volume was 21.4 mL. The washing filtrate was added to the crystallization solution (filtrate 2). The crystallization solution (filtrate 2) had S≤50 g / L and Fe≤0.06 g / L. After neutralization, it was returned to step c, with a neutralization pH of 8, using ammonium bicarbonate for neutralization. The impurity content of the solid APV was qualified. It was then treated under the conditions of calcination temperature of 500℃, calcination time of 300 min, and oxygen content in the calcination atmosphere greater than 15% to obtain 16.43 g of high-quality vanadium pentoxide.

[0070] The vanadium oxide purification method of this invention utilizes the interconversion between APV and AMV, allowing impurities in the raw materials to be gradually removed in an acidic or weakly alkaline environment, thereby improving the purity of vanadium oxide. During the conversion process, if the quality of APV or AMV does not meet the requirements, the cycle continues; if the quality of APV or AMV meets the requirements, the cycle is terminated for further vanadium oxide preparation. The method of this invention has the advantages of producing high-quality vanadium oxide, low cost, less waste liquid, and less solid waste.

[0071] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0072] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for purifying vanadium oxide, characterized in that, Includes the following steps: a. Dissolve APV, V2O5 or red cake in ammonia water or ammonium carbonate or ammonium bicarbonate and filter to obtain AMV solution; b. Crystallize the AMV solution to obtain solid AMV and primary filtrate. If the impurity content of the primary filtrate does not exceed the standard, return to step a; if the impurity content in the solid AMV is qualified, calcine or reduce it to prepare vanadium oxide; if the impurity content in the solid AMV is unqualified, proceed to step c. c. Solid AMV is heated and dissolved. During the dissolution process, an acidic solution is added to adjust the pH value to increase the amount of solid AMV dissolved. When the vanadium concentration in the solution reaches 15g / L~40g / L, the pH value is adjusted by cooling at a rate of 0.2℃ / min~10℃ / min to form a stable acidic vanadium solution. The acidic vanadium solution is then filtered. d. Heating the filtrate from step c to crystallize it yields solid APV and a secondary filtrate. If the impurity content of the secondary filtrate does not exceed the standard, it is neutralized and filtered before returning to step c. If the impurity content of the solid APV is qualified, it is calcined or reduced to prepare vanadium oxide. If the impurity content of the solid APV is unqualified, it is proceeded to step a and the above steps are repeated. In step c, the matching relationship between temperature and pH value during the cooling process is as follows: At temperatures of 80℃~99℃, the pH value is 6~8; at temperatures of 60℃~80℃, the pH value is 4~6; at temperatures of 40℃~60℃, the pH value is 2.4~4; at temperatures of 20℃~40℃, the pH value is 1.5~4; and at temperatures <20℃, the pH value is 1.5~4.

2. The method for purifying vanadium oxide as described in claim 1, characterized in that, The amount of substance ratio of NH4 + and V is NH4 + / V=1.5~4.0, the dissolving pH is 7.0~10, the dissolving temperature is 70℃~95℃, and the solution V concentration is controlled at 20g / L~40g / L.

3. The method for purifying vanadium oxide as described in claim 1, characterized in that, In step b, the linear velocity of the outermost part of the agitator during the crystallization process is controlled at 0.4 m / s to 3 m / s, the cooling rate during crystallization is controlled at 0.2 ℃ / min to 4 ℃ / min, the final crystallization temperature is 6 ℃ to 30 ℃, and crystallization is carried out at the final temperature for 60 min to 300 min.

4. The method for purifying vanadium oxide as described in claim 1, characterized in that, In step b, the element used to determine whether the impurity content of the first filtrate exceeds the standard is P. P ≤ 0.2 g / L is considered within the standard. The acceptable impurity content in the solid AMV in step b is as follows: P ≤ 0.01 g / L, S ≤ 0.02 g / L, As ≤ 0.01 g / L, K ≤ 0.03 g / L, Na ≤ 0.50 g / L, Si ≤ 0.08 g / L, Fe ≤ 0.08 g / L, Cr ≤ 0.05 g / L, Mn ≤ 0.10 g / L, and Ca ≤ 0.05 g / L.

5. The method for purifying vanadium oxide as described in claim 1, characterized in that, In step c, the solid AMV is dissolved at a temperature of 80℃~99℃, and the pH value is adjusted to 6~8 using sulfuric acid at a volume ratio of 20%~50%.

6. The method for purifying vanadium oxide as described in claim 1, characterized in that, In step c, after cooling to a temperature of 20℃~40℃, filter to obtain a vanadate solution. Wash the filter residue once with 0.02~0.1 times the volume of the vanadate solution in clean water at a temperature of 20℃~40℃. The wash water filtrate is then added to the vanadate solution.

7. The method for purifying vanadium oxide as described in claim 1, characterized in that, After the heating and crystallization in step d is completed, solid APV is obtained by filtration. The solid APV is washed once with acidic water or an ammonium-containing solution, and the wash water contains NH4. + The concentration of the washing solution is controlled at 0–10 g / L, the washing water temperature is 65℃–95℃, the washing water pH value is 2.0–4.0, and the washing water volume is equal to the mass of solid AMV dissolved in step c. The washing filtrate is added to the secondary filtrate.

8. The method for purifying vanadium oxide as described in claim 1, characterized in that, In step d, the elements that determine whether the impurity content of the secondary filtrate exceeds the standard are S and Fe, with S≤50g / L and Fe≤0.06g / L; The acceptable impurity content in the solid APV in step d is as follows: P≤0.01g / L, S≤0.02g / L, As≤0.01g / L, K≤0.03g / L, Na≤0.50g / L, Si≤0.08g / L, Fe≤0.08g / L, Cr≤0.05g / L, Mn≤0.10g / L, and Ca≤0.05g / L.

9. The method for purifying vanadium oxide as described in claim 1, characterized in that, The heating crystallization process in step d, "heating the filtrate from step c to crystallize and obtain solid APV and secondary filtrate", includes: adjusting the pH value to 2.0~2.5, the heating rate to 1℃ / min~7℃ / min, the final heating temperature to 85℃~95℃; the crystallization time to 30min~120min, and controlling the outermost linear velocity of the stirring paddle to 0.4m / s~3m / s during the crystallization process.

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