Method for stepwise precipitation of vanadium from vanadium-containing chromium wastewater

Abstract

The application provides a method for step-by-step precipitation and recovery of vanadium from vanadium-containing chromium wastewater, and belongs to the technical field of industrial wastewater treatment and metal resource recovery. The method comprises the following steps: mixing acid vanadium-containing chromium wastewater with sulfur dioxide hydride, placing the mixture under ultraviolet light to perform photocatalytic reduction reaction, and obtaining wastewater containing divalent vanadium and trivalent chromium; adjusting the pH of the wastewater containing divalent vanadium and trivalent chromium to a first alkalinity, performing solid-liquid separation, and obtaining trivalent chromium hydroxide precipitate and divalent vanadium-containing filtrate; adjusting the pH of the divalent vanadium-containing filtrate to a second alkalinity, performing solid-liquid separation, and obtaining divalent vanadium hydroxide precipitate. The application uses ultraviolet light to excite sulfur dioxide hydride, reduces vanadium and chromium in the acid vanadium-containing chromium wastewater into divalent vanadium and trivalent chromium, and realizes the recovery of vanadium through step-by-step precipitation by utilizing the pH difference of the precipitates.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and metal resource recovery technology, and in particular to a method for stepwise precipitation and recovery of vanadium from vanadium-chromium-containing wastewater. Background Technology

[0002] Vanadium is an important strategic metal, widely used in high-end steel, aerospace, and new energy batteries. During vanadium smelting and processing, a large amount of vanadium-containing wastewater is generated annually, with pentavalent vanadium (vanadium(V)) concentrations reaching tens to hundreds of mg / L, and often accompanied by even higher concentrations of hexavalent chromium (chromium(VI)). Due to the similar chemical properties of vanadium(V) and chromium(VI), effective separation is difficult to achieve using traditional treatment processes.

[0003] Currently, the mainstream industrial method for treating vanadium-chromium-containing wastewater is the ferrous reduction-lime neutralization method. This method reduces both vanadium (V) and chromium (VI) to trivalent forms. Under conditions of approximately pH 8, trivalent vanadium (vanadium (III)) and trivalent chromium (chromium (III)) simultaneously form hydroxide precipitates, resulting in a complex mixed sludge. The vanadium content in this type of sludge is usually less than 3%, making it difficult to efficiently separate and recover vanadium, thus causing resource waste.

[0004] Numerous attempts have been made to address these issues. For example, an improved precipitation method, employing sulfur dioxide reduction followed by sodium carbonate neutralization, was used to attempt to increase the vanadium content in the sludge. However, due to the co-precipitation of chromium, the vanadium content in the sludge could only be increased to 6%-8%, failing to achieve efficient vanadium-chromium separation. Another approach, microemulsion extraction, while capable of directly extracting vanadium from wastewater, suffers from a lengthy and complex process that generates large amounts of high-salinity wastewater, making it difficult to promote and apply in practical engineering projects.

[0005] Therefore, there is an urgent need to develop a method for recovering vanadium from vanadium-chromium-containing wastewater. Summary of the Invention

[0006] In view of this, in order to at least partially solve the aforementioned technical problems, the present invention provides a method for recovering vanadium from vanadium-chromium-containing wastewater through stepwise precipitation.

[0007] According to one aspect of the present invention, a method for stepwise precipitation recovery of vanadium from vanadium-chromium-containing wastewater is provided, comprising: mixing acidic vanadium-chromium-containing wastewater with thiourea dioxide, subjecting it to a photocatalytic reduction reaction under ultraviolet light to obtain wastewater containing divalent vanadium and trivalent chromium; adjusting the pH of the wastewater containing divalent vanadium and trivalent chromium to a first alkaline state, and performing solid-liquid separation to obtain a trivalent chromium hydroxide precipitate and a filtrate containing divalent vanadium; adjusting the pH of the filtrate containing divalent vanadium to a second alkaline state, and performing solid-liquid separation to obtain a divalent vanadium hydroxide precipitate.

[0008] According to embodiments of the present invention, unlike traditional methods that reduce both vanadium and chromium to trivalent states, this invention, under acidic conditions and using ultraviolet light to excite thiourea dioxide, achieves for the first time in the treatment of vanadium- and chromium-containing wastewater the selective reduction of vanadium to divalent vanadium and chromium to trivalent chromium. This utilizes the difference in precipitation pH between divalent and trivalent vanadium to achieve efficient direct separation and recovery of vanadium from vanadium- and chromium-containing wastewater. This invention offers significant advantages in vanadium recovery rate and product purity, solving the problem of difficult vanadium recovery using traditional methods. Simultaneously, the process flow is short, with less secondary pollution, reducing treatment costs and environmental risks. By controlling the valence state to achieve separation, this invention provides more technical pathways for the resource-based treatment of wastewater containing similar heavy metals. Attached Figure Description

[0009] Figure 1 This is a process flow diagram of the stepwise precipitation and recovery of vanadium from vanadium-chromium-containing wastewater according to the present invention. Detailed Implementation

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0011] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0012] Improved precipitation and microemulsion extraction methods have failed to overcome the core bottleneck: the lack of techniques to achieve differential reduction of vanadium (V) and chromium (VI), thus hindering efficient separation by leveraging the differences in their subsequent chemical behaviors. Existing processes either introduce vanadium into low-grade mixed sludge, leading to recovery difficulties, or, while achieving direct separation, the process is complex and poses secondary pollution problems. Therefore, there is an urgent need to develop a direct recovery method that can achieve clean and efficient separation of vanadium and chromium by controlling the reduction pathway.

[0013] In the process of realizing this invention, it was discovered that by using ultraviolet light to excite thiourea dioxide, controlling the differential reduction pathways of vanadium and chromium in acidic vanadium-chromium-containing wastewater, and then controlling the pH during the precipitation process, efficient separation of vanadium and chromium can be achieved. This invention solves the problem of vanadium entering the mixed slag and being difficult to recover in the above methods. At the same time, the method of this invention has a short process flow, does not generate high-salt wastewater, and has a higher vanadium recovery rate than the above methods, enabling the high-value recovery of the strategic metal vanadium.

[0014] Figure 1 This is a process flow diagram of the stepwise precipitation and recovery of vanadium from vanadium-chromium-containing wastewater according to the present invention.

[0015] like Figure 1 As shown, the method for stepwise precipitation recovery of vanadium from vanadium-chromium-containing wastewater according to the present invention includes: mixing acidic vanadium-chromium-containing wastewater with thiourea dioxide, and subjecting it to photocatalytic reduction under ultraviolet light to obtain wastewater containing divalent vanadium and trivalent chromium; adjusting the pH of the wastewater containing divalent vanadium and trivalent chromium to the first alkaline state, and performing solid-liquid separation to obtain trivalent chromium hydroxide precipitate and divalent vanadium-containing filtrate; adjusting the pH of the filtrate containing divalent vanadium to the second alkaline state, and performing solid-liquid separation to obtain divalent vanadium hydroxide precipitate.

[0016] According to an embodiment of the present invention, under acidic conditions, by using ultraviolet light to excite the thiourea dioxide reduction system, vanadium in vanadium-chromium-containing wastewater can be simultaneously reduced to divalent vanadium (vanadium(II)) and chromium to trivalent chromium. This allows for the direct separation and recovery of vanadium from the vanadium-chromium-containing wastewater by utilizing the difference in precipitation pH between divalent and trivalent vanadium. In the ultraviolet light-excited thiourea dioxide reduction system, because the CS bond length in the thiourea dioxide molecular structure is greater than the SO bond length and CN bond length, the CS bond is more easily excited under ultraviolet light irradiation, breaking and releasing hyposulfate (SO2). 2- SO2 2- Further excited by ultraviolet light to produce SO2• - Free radicals and hydrated electrons (e aq - These highly reducing active species can directly reduce vanadium to divalent vanadium and chromium to trivalent chromium, thereby utilizing the pH difference between the precipitates of divalent vanadium and trivalent chromium to achieve vanadium recovery.

[0017] In some implementations, the pH of the acidic vanadium-chromium-containing wastewater is 1.5-2.5, for example, 1.5, 2.0, or 2.5. The acidic vanadium-chromium-containing wastewater includes pentavalent vanadium and hexavalent chromium. The aforementioned pH value can enhance the activity of reactive species (such as SO2•). - The generation of free radicals further enhances the reduction ability of vanadium, which helps to reduce pentavalent vanadium to divalent vanadium and hexavalent chromium to trivalent chromium, thereby enabling stepwise precipitation and recovery of vanadium.

[0018] In some implementations, the molar ratio of thiourea dioxide to pentavalent vanadium is 1.5-3.0:1, for example, 1.5:1, 2.0:1, 2.5:1, or 3.0:1. This setting helps to fully reduce vanadium to divalent vanadium and chromium to trivalent chromium, thereby improving the vanadium-chromium separation selectivity. If the molar ratio is too low (e.g., less than 1.5:1), the reduction of vanadium and chromium will be incomplete, resulting in poor subsequent precipitation separation and reduced vanadium recovery. If the molar ratio is too high (e.g., greater than 3.0:1), it may lead to over-reduction, resulting in decreased vanadium-chromium separation selectivity and increased costs.

[0019] In some implementations, the wavelength of the ultraviolet light is 254-365 nm, for example, 254 nm, 270 nm, 310 nm, 350 nm, or 365 nm. The illuminance is 10-100 mW / cm². 2 For example, it can be 10mW / cm 2 50mW / cm 2 60mW / cm 2 Or 100mW / cm 2 This configuration helps to stably generate active species during the activation of thiourea dioxide, thereby improving the reduction capacity of vanadium and ensuring the separation effect of vanadium and chromium.

[0020] In some implementations, the photocatalytic reduction reaction time is 10-60 min, for example, 10 min, 15 min, 30 min, 45 min, or 60 min. This setting helps to fully reduce vanadium and chromium to divalent vanadium and trivalent chromium, further improving the separation efficiency of vanadium and chromium.

[0021] In some implementations, the initial alkaline pH is 7.5-8.5, for example, 7.5, 8.0, or 8.5. This setting helps to efficiently convert trivalent chromium into a stable hydroxide precipitate while also facilitating its separation from divalent vanadium. A pH of 7.5-8.5 is the preferred precipitation range for trivalent chromium hydroxide, enabling the separation and enrichment of trivalent chromium from wastewater. Simultaneously, this pH value reduces the co-precipitation of divalent vanadium, preventing vanadium from contaminating the chromium precipitate.

[0022] In some implementations, the pH of the second alkaline environment is 9.5-10.5, for example, 9.5, 10.0, or 10.5. This setting helps to promote the efficient conversion of divalent vanadium into stable hydroxide precipitates. A pH of 9.5-10.5 is the preferred precipitation range for divalent vanadium hydroxide, enabling the separation and enrichment of divalent vanadium from wastewater.

[0023] In some implementations, the agents used to adjust the pH to the first and second alkalinity include sodium hydroxide or sodium carbonate. Using sodium hydroxide to adjust pH is fast and responsive, introduces few impurity ions into the system, and produces no solid residue, thus helping to maintain system purity. Using sodium carbonate to adjust pH is a gentler process with strong buffering properties, allowing for a slow increase in system alkalinity.

[0024] In some implementation schemes, the method for stepwise precipitation recovery of vanadium from vanadium-chromium-containing wastewater further includes calcining the divalent vanadium hydroxide precipitate to obtain vanadium pentoxide. The calcination temperature is 500-600℃, for example, 500℃, 550℃, or 600℃. The time is 1-3 hours, for example, 1 hour, 2 hours, or 3 hours. Calcination causes dehydration, oxidation, and crystal transformation of the divalent vanadium hydroxide precipitate, ultimately yielding high-purity vanadium pentoxide. The calcination process effectively removes bound water, hydroxyl groups, and adsorbed impurities from the divalent vanadium hydroxide precipitate, improving the stability and purity of vanadium pentoxide. Controlling the calcination temperature and time helps to fully dehydrate and dehydroxylate the divalent vanadium hydroxide precipitate, as well as fully convert it to vanadium pentoxide, thereby improving the purity of vanadium pentoxide and ensuring that the final product is vanadium pentoxide with a uniform phase and stable properties.

[0025] The technical solution of the present invention will be further illustrated below through specific embodiments. It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of the present invention is not limited thereto.

[0026] Unless otherwise specified, all test conditions in the examples are as follows: the total concentration of vanadium and chromium in the wastewater is quantitatively detected according to the People's Republic of China National Environmental Protection Standard "Determination of 32 Elements in Water by Inductively Coupled Plasma Atomic Emission Spectrometry" (HJ 776-2015); the purity of vanadium pentoxide is determined by digestion according to the People's Republic of China National Environmental Protection Standard "Digestion of Total Metal Elements in Soil and Sediments by Microwave Digestion" (HJ 832-2017), and then detected according to the People's Republic of China National Environmental Protection Standard "Determination of 32 Elements in Water by Inductively Coupled Plasma Atomic Emission Spectrometry" (HJ 776-2015).

[0027] Example 1

[0028] Take 1 L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Thiourea dioxide is added at a dosage 2.0 times the molar concentration of vanadium (V). Under ultraviolet light (254 nm, light intensity 50 mW / cm²), the concentration is determined. 2After reacting for 30 minutes, the pH was first adjusted to 8.0 with NaOH solution to precipitate chromium(III). After solid-liquid separation, the pH of the filtrate was adjusted to 10.0 to precipitate vanadium(II). The vanadium(II) hydroxide was then calcined at 550℃ for 2 hours to precipitate. The final chromium precipitation rate was 99.5%, the vanadium pentoxide product purity was 97.5%, and the vanadium recovery rate was 95.2%.

[0029] Example 2

[0030] Take 1L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Thiourea dioxide is added at a dosage 2.5 times the molar concentration of vanadium (V). Under ultraviolet light (365nm, light intensity 50mW / cm²), the concentration is determined. 2 The reaction was carried out for 45 minutes. Subsequent steps were the same as in Example 1. The final measured chromium precipitation rate was 99.3%, the vanadium pentoxide product purity was 97.1%, and the vanadium recovery rate was 94.8%.

[0031] Example 3

[0032] Take 1L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Thiourea dioxide is added at a dosage 3.0 times the molar concentration of vanadium (V). Under ultraviolet light (mixed light of 254nm and 365nm, total light intensity 60mW / cm²), the concentration is determined. 2 The reaction was carried out for 15 minutes. Subsequent steps were the same as in Example 1. The final measured chromium precipitation rate was 99.1%, the vanadium pentoxide product purity was 96.8%, and the vanadium recovery rate was 94.5%.

[0033] Example 4

[0034] Take 1 L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Thiourea dioxide is added at a dosage 1.2 times the molar concentration of vanadium (V). Under ultraviolet light (254 nm, light intensity 50 mW / cm²), the concentration is determined. 2 The reaction was carried out for 30 minutes. Subsequent steps were the same as in Example 1. The final measured chromium precipitation rate was 98.0%, the vanadium pentoxide product purity was 92.0%, and the vanadium recovery rate was 85.5%.

[0035] Example 5

[0036] Take 1 L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Thiourea dioxide is added at a dosage 2.0 times the molar concentration of vanadium (V). Under ultraviolet light (254 nm, light intensity 50 mW / cm²), the concentration is determined. 2 The reaction was carried out for 5 minutes. Subsequent steps were the same as in Example 1. The final measured chromium precipitation rate was 97.5%, the vanadium pentoxide product purity was 90.5%, and the vanadium recovery rate was 82.0%.

[0037] Example 6

[0038] Take 1 L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Thiourea dioxide is added at a dosage 2.0 times the molar concentration of vanadium (V). Under ultraviolet light (254 nm, light intensity 50 mW / cm²), the concentration is determined. 2 After reacting for 30 minutes, the pH was first adjusted to 9.0 with NaOH solution to precipitate chromium(III). After solid-liquid separation, the pH of the filtrate was adjusted to 10.0 to precipitate vanadium(II). Subsequent steps were the same as in Example 1. The final chromium precipitation rate was 99.0%, the purity of the vanadium pentoxide product was 93.5%, and the vanadium recovery rate was 88.0%.

[0039] Comparative Example 1

[0040] 1 L of simulated wastewater was taken and the pH was adjusted to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater was 50 mg / L, and the concentration of chromium (VI) was 500 mg / L. Thiourea dioxide was added at a dosage 3.0 times the molar concentration of vanadium (V). The reaction was mechanically stirred for 60 min under light-protected conditions at 40°C. Subsequent steps were the same as in Example 1. A mixed neutralized residue was finally obtained, and the vanadium content was only 2.9%, failing to achieve vanadium separation and recovery.

[0041] Comparative Example 2

[0042] Take 1 L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50 mg / L, and the concentration of chromium (VI) is 500 mg / L. Add sodium sulfite with the same molar sulfur content as in Example 1. Under ultraviolet light (254 nm, light intensity 50 mW / cm²), [the process is repeated]. 2 The reaction was carried out for 30 minutes. Subsequent steps were the same as in Example 1. In the end, vanadium(III) and chromium(III) precipitated simultaneously, and the vanadium content in the resulting mixed slag was 4.5%, failing to achieve the separation and recovery of vanadium.

[0043] Comparative Example 3

[0044] One L of simulated wastewater was taken and the pH was adjusted to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this wastewater was 50 mg / L, and the concentration of chromium (VI) was 500 mg / L. 10 g of ferrous sulfate was added, and after stirring and reduction for 2 hours, the pH was adjusted to 8.5 with lime slurry for co-precipitation. The final mixed neutralized residue showed a vanadium content of only 2.8%, failing to achieve vanadium separation and recovery.

[0045] Comparative Example 4

[0046] Take 1L of simulated wastewater and adjust the pH to 2.0 to obtain acidic vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this acidic vanadium-chromium-containing wastewater is 50mg / L, and the concentration of chromium (VI) is 500mg / L. Add thiourea in an amount equal to that of thiourea dioxide from Example 1. Under ultraviolet light (254nm, light intensity 50mW / cm²),... 2 The reaction was carried out for 30 minutes. Subsequent steps were the same as in Example 1. The final mixed neutralized residue was tested and found to contain only 2.7% vanadium, failing to achieve vanadium separation and recovery.

[0047] Comparative Example 5

[0048] One L of simulated wastewater was taken and the pH was adjusted to 9.0 with sodium hydroxide to obtain alkaline vanadium-chromium-containing wastewater. The concentration of vanadium (V) in this alkaline vanadium-chromium-containing wastewater was 50 mg / L, and the concentration of chromium (VI) was 500 mg / L. Subsequent steps were the same as in Example 1. Finally, a mixed neutralization residue was obtained, and the vanadium content was only 2.9%, failing to achieve vanadium separation and recovery.

[0049] In summary, the parameters and effects of Examples 1-6 and Comparative Examples 1-5 are compared in Table 1.

[0050] Table 1. Parameters and Effects of Examples and Comparative Examples

[0051]

[0052] As shown in Table 1, vanadium recovery was successfully achieved in Examples 1-6, proving the feasibility of the technical solution of the present invention. In Examples 1-3, the vanadium recovery rate was higher than 94%, and the purity of vanadium pentoxide was higher than 96%, achieving excellent and stable technical results. Examples 4-6 showed decreased performance due to insufficient reducing agent, short reaction time, and deviation in precipitation pH control, but the vanadium recovery rate was still significantly higher than that of Comparative Examples 1-5. Comparative Examples 1-5, however, failed to achieve vanadium separation and recovery at all, forming a stark contrast to the technical effect of the present invention.

[0053] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering vanadium from vanadium-chromium-containing wastewater through stepwise precipitation, comprising: Acidic vanadium-chromium-containing wastewater was mixed with thiourea dioxide and subjected to photocatalytic reduction under ultraviolet light to obtain wastewater containing divalent vanadium and trivalent chromium. The pH of the wastewater containing divalent vanadium and trivalent chromium was adjusted to the first alkaline state, and after solid-liquid separation, trivalent chromium hydroxide precipitate and filtrate containing divalent vanadium were obtained. The pH of the filtrate containing divalent vanadium was adjusted to the second alkaline state, and after solid-liquid separation, divalent vanadium hydroxide precipitate was obtained.

2. The method for stepwise precipitation recovery of vanadium from vanadium-chromium-containing wastewater according to claim 1, wherein, The acidic vanadium-chromium-containing wastewater has a pH value of 1.5-2.5 and includes pentavalent vanadium and hexavalent chromium.

3. The method for recovering vanadium from vanadium-chromium-containing wastewater according to claim 2, wherein, The molar ratio of thiourea dioxide to the pentavalent vanadium is 1.5-3.0:

1.

4. The method for stepwise precipitation recovery of vanadium from vanadium-chromium-containing wastewater according to claim 1, wherein, The ultraviolet light has a wavelength of 254-365nm and an illuminance of 10-100mW / cm². 2 .

5. The method for recovering vanadium from vanadium-chromium-containing wastewater by stepwise precipitation according to claim 1, wherein, The photocatalytic reduction reaction takes 10-60 minutes.

6. The method for recovering vanadium from vanadium-chromium-containing wastewater by stepwise precipitation according to claim 1, wherein, The pH value of the first alkaline solution is 7.5-8.

5.

7. The method for recovering vanadium from vanadium-chromium-containing wastewater by stepwise precipitation according to claim 1, wherein, The second alkaline pH value is 9.5-10.

5.

8. The method for recovering vanadium from vanadium-chromium-containing wastewater by stepwise precipitation according to claim 1, wherein, The agents used to adjust the pH to the first alkalinity and the second alkalinity include sodium hydroxide or sodium carbonate.

9. The method for recovering vanadium from vanadium-chromium-containing wastewater by stepwise precipitation according to any one of claims 1-8, further comprising: The precipitate of divalent vanadium hydroxide was calcined to obtain vanadium pentoxide.

10. The method for recovering vanadium from vanadium-chromium-containing wastewater by stepwise precipitation according to claim 9, wherein, The calcination temperature is 500-600℃, and the time is 1-3 hours.

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