A process for the recovery of vanadium, chromium and sodium from a solution containing sodium vanadate and sodium chromate

Abstract

This invention provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution: (1) Adjusting the pH value of the vanadium-chromium sodium salt solution, adding a chromium precipitation agent and performing a first hydrothermal reaction to obtain chromium hydroxide product and chromium precipitation mother liquor; sequentially performing a first washing and a first heat treatment on the chromium hydroxide product to obtain chromium oxide product; (2) Adjusting the pH value of the chromium precipitation mother liquor, adding a vanadium precipitation agent and performing a second hydrothermal reaction to obtain vanadium dioxide product and vanadium precipitation mother liquor; sequentially performing a second washing and a second heat treatment on the vanadium dioxide product to obtain vanadium pentoxide product; (3) Mixing the first washing residue from step (1), the second washing residue from step (2), and the vanadium precipitation mother liquor, and evaporating and crystallizing the resulting sodium-containing solution to obtain sodium carbonate product. This method avoids the introduction of sulfur and ammonia nitrogen from the source, generates no chromium-containing solid waste, and has a short process, clean process, and low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy, and more particularly to a method for recovering vanadium, chromium and sodium from a vanadium-chromium sodium salt solution. Background Technology

[0002] Vanadium is an important metallic resource in my country, often referred to as the "MSG of industry." Its main products include vanadium pentoxide, vanadium trioxide, vanadium-nitrogen alloys, ferrovanadium alloys, and vanadium-aluminum alloys, which are widely used in steel, chemical, defense, electronics, manufacturing, energy storage, pharmaceutical, and catalysis industries. Chromium, as a key strategic metal and industrial element, holds an extremely important position in modern society. It is not only the "soul component" of stainless steel but also the cornerstone of many high-performance alloys, corrosion-resistant coatings, and functional materials, directly supporting several pillar industries such as construction, automobiles, energy, chemicals, and aerospace. Currently, my country's dependence on imports exceeds 90%.

[0003] Vanadium oxide, as an important vanadium product, is traditionally prepared by methods that involve the addition of large amounts of sulfuric acid and ammonium sulfate during the preparation of the intermediate product ammonium vanadate. This results in the generation of substantial amounts of high-salt wastewater and waste salts, and chromium is exported as heavy metal solid waste, making it ineffective for utilization. Therefore, traditional methods not only cause severe pollution from wastewater, waste gas, and solid waste, but also result in the ineffective utilization of metallic chromium and a significant waste of resources. In summary, the key to solving these problems lies in two aspects: firstly, achieving efficient separation of vanadium and chromium; and secondly, ensuring that the preparation processes of vanadium and chromium products avoid the introduction of these three waste elements.

[0004] The extraction and separation method for vanadium and chromium uses organic ammonium as an extractant to extract and separate vanadium and chromium. Vanadium is then back-extracted to obtain a sodium vanadate solution, which is then used to precipitate vanadium, while the raffinate precipitates chromium. This method is related to patents CN101121962A / CN100497675C. This method is technically mature and is currently the main method for preparing most high-purity ammonium metavanadate. However, it does not deviate from the traditional ammonium salt precipitation process and cannot avoid the generation of high-salt and high-ammonia nitrogen wastewater. It is suitable for small-scale high-purity product applications.

[0005] Other methods for separating vanadium and chromium involve separation from acidic leaching solutions. The vanadium precipitation does not deviate from the traditional ammonium salt precipitation. A large amount of acid and alkali is added during the process, thus achieving the clean preparation of vanadium and chromium products. The patents involved include CN101121962A, CN107312942B, CN101538652A, CN111041205A, and CN112011688A.

[0006] In addition, the main methods for preparing vanadium oxide by direct liquid-phase reduction of vanadium-containing solutions include: preparing vanadium trioxide by high-pressure, high-temperature hydrothermal hydrogen reduction of sodium vanadate solution. The relevant patents include CN201610321176.6, CN201610322604.7, CN201610321154.X, CN201610322651.1, CN201710674292.0, and CN201710674293.5. This method uses hydrogen as a reducing agent, with a reaction temperature of around 300℃, making the operating conditions very harsh and extremely dangerous. Furthermore, sulfuric acid needs to be added during this process to neutralize the hydroxide ions generated by vanadium hydrolysis, thus not fundamentally solving the problem of high-salinity wastewater in the vanadium industry.

[0007] In summary, traditional methods for separating vanadium and chromium from vanadium and chromium-containing raw materials and for preparing vanadium and chromium products do not avoid the introduction of waste elements such as ammonia nitrogen and sulfur, and cannot solve the problem of pollution from these three wastes. Therefore, it is of great significance to study methods for the efficient separation of vanadium and chromium sodium from vanadium and chromium-containing sodium solutions and for the clean preparation of products. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for recovering vanadium, chromium and sodium from a vanadium-chromium sodium salt solution, realizing the separation and recovery of chromium, vanadium and sodium products, avoiding the introduction of ammonia nitrogen and sulfur and other waste elements. It is a method for efficient separation and product preparation of vanadium-chromium sodium with short process, low energy consumption and clean process.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, the method comprising the following steps:

[0011] (1) Adjust the pH value of the sodium vanadium chromium salt solution, add a chromium precipitation agent and carry out a first hydrothermal reaction to obtain chromium hydroxide product and chromium precipitation mother liquor; subject the chromium hydroxide product to a first washing and a first heat treatment in sequence to obtain chromium oxide product;

[0012] (2) Adjust the pH value of the chromium precipitation mother liquor and add vanadium precipitation agent to carry out a second hydrothermal reaction to obtain vanadium dioxide product and vanadium precipitation mother liquor; subject the vanadium dioxide product to a second washing and a second heat treatment in sequence to obtain vanadium pentoxide product;

[0013] (3) Mix the first washing residue in step (1), the second washing residue in step (2) and the vanadium precipitation mother liquor to obtain a sodium-containing solution; evaporate and crystallize the sodium-containing solution to obtain sodium carbonate product, and return the condensate generated by evaporation and crystallization to step (1) and step (2) as washing water.

[0014] This invention achieves effective acid-base control of vanadium-chromium sodium solutions and utilizes the differences in redox reactions of vanadium and chromium under different pH conditions to achieve the distribution, precipitation, and separation of vanadium and chromium. Furthermore, it leverages the charge characteristics of chromium hydroxide at different pH levels to achieve efficient separation of vanadium and chromium. The prepared vanadium product contains ≥99% V₂O₅, ≤0.2% Na₂O + K₂O, and Cr levels below the detection limit, meeting or exceeding the standard requirements of YB / T 5304-2017 for powdered vanadium (V₂O₅ 99-P). The prepared chromium product contains ≥98% Cr₂O₃, ≤0.5% V, and ≤0.5% Na₂O + K₂O. This technology not only solves the problems of complex processes, severe waste pollution, and substandard chromium products associated with traditional vanadium-chromium separation processes, but also offers significant technical advantages compared to conventional reduction-based vanadium oxide preparation technologies, including shorter processes, lower operating temperatures, milder reaction conditions, improved operational safety, and lower system energy consumption.

[0015] The sodium-containing solution described in this invention can also be directly returned to the upstream process of the sodium vanadium-chromium solution for leaching.

[0016] As a preferred embodiment of the present invention, the chromium salt in the vanadium-chromium sodium salt solution includes sodium chromate.

[0017] Preferably, the vanadium salt in the vanadium-chromium sodium salt solution includes sodium vanadate.

[0018] Preferably, the sodium vanadate includes any one or a combination of at least two of sodium orthovanadate, sodium pyrovanadate, or sodium metavanadate. Typical but non-limiting combinations include combinations of sodium orthovanadate and sodium pyrovanadate, combinations of sodium pyrovanadate and sodium metavanadate, etc.

[0019] Preferably, the sodium salt in the vanadium-chromium sodium salt solution includes any one or a combination of at least two of the following: chromium sodium salt, vanadium sodium salt, sodium carbonate, sodium bicarbonate, or sodium hydroxide.

[0020] As a preferred technical solution of the present invention, the pH value of the vanadium chromium sodium salt solution in step (1) is adjusted to 9-11, for example, it can be 9, 10 or 11, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Before adding the chromium precipitation agent, the pH value of the sodium vanadium chromium salt solution is adjusted to 9-11. If the pH value is too low, the chromium hydroxide is positively charged, and a large amount of vanadate anions are adsorbed, resulting in the loss of vanadium and the chromium product failing to meet the requirements. If the pH value is too high, the chromium hydroxide particles will be washed, resulting in high viscosity, difficulty in filtration, and high water content, thus failing to meet the product quality requirements.

[0022] Preferably, the acid-base regulator used to adjust the pH value in step (1) includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, CO2, or sodium hydroxide.

[0023] As a preferred embodiment of the present invention, the chromium precipitation agent comprises any one or a combination of at least two of formaldehyde, methanol, formic acid, sodium formate, glucose, sucrose, glycerol, hydrazine hydrate, or starch. Typical but non-limiting combinations include combinations of formaldehyde and methanol, formsaldehyde and sodium formate, sodium formate and sucrose, hydrazine hydrate and starch, etc.; the temperature of the first hydrothermal reaction satisfies the following conditions:

[0024] (1) When the chromium precipitation agent contains hydrazine hydrate, the reaction temperature is 90-220℃, for example, it can be 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃ or 220℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] (2) When the chromium precipitation agent is any one or a combination of at least two of formaldehyde, methanol, formic acid or sodium formate, and does not contain hydrazine hydrate, the reaction temperature is 190-220℃, for example, it can be 190℃, 200℃, 210℃ or 220℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] (3) When the chromium precipitation agent is any one or a combination of at least two of glucose, sucrose, glycerol or starch, and does not contain hydrazine hydrate, the reaction temperature is 120-220℃, for example, it can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃ or 220℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] As a preferred technical solution of the present invention, the amount of chromium precipitation agent added satisfies the following condition: the total amount of electron transfer provided by it is 1-1.5 times the total amount of electron transfer required for the complete reduction of chromium salt in the sodium vanadium chromium salt solution to chromium hydroxide product. For example, it can be 1 time, 1.1 times, 1.2 times, 1.3 times, 1.4 times or 1.5 times, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the time for the first hydrothermal reaction is 2-6 hours, for example, it can be 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the aging and crystallization time after the first hydrothermal reaction is 1-4 h, for example, it can be 1 h, 2 h, 3 h or 4 h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the first washing includes: the volume ratio of washing water to the mass of the chromium hydroxide product is (3-5):1, for example, it can be 3:1, 4:1, or 5:1; countercurrent washing is performed 1-3 times by a pulping washing method, for example, once, twice, or three times; the washing temperature is ≥70℃; and the washing time for a single wash is 0.5-1h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, or 1.0h, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the temperature of the first heat treatment is 800-1300℃, for example, it can be 800℃, 900℃, 1000℃, 1100℃, 1200℃ or 1300℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0032] Preferably, the first heat treatment time is 3-4 hours, for example, it can be 3 hours, 3.5 hours or 4 hours, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] As a preferred technical solution of the present invention, the pH value of the chromium precipitation mother liquor in step (2) is adjusted to 7-9, for example, it can be 7, 8 or 9, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] In this invention, the pH value of the vanadium chromium sodium salt solution is adjusted to 7-9 before adding the vanadium precipitation agent. If the pH value is too low, the vanadium product particles will be small, the precipitation rate will be less than 80%, the single-pass efficiency will be low, and the product quality will be unqualified. If the pH value is too high, the vanadium cannot be effectively precipitated.

[0035] Preferably, the acid-base regulator used to adjust the pH value in step (2) includes CO2 and / or organic acids.

[0036] Preferably, the organic acid includes any one or a combination of at least two of formic acid, oxalic acid, or acetic acid. Typical but non-limiting combinations include combinations of formic acid and oxalic acid, combinations of formic acid and acetic acid, combinations of oxalic acid and acetic acid, etc.

[0037] As a preferred technical solution of the present invention, the vanadium precipitation agent includes any one or a combination of at least two of hydrazine hydrate, glycerol, sucrose, glucose or starch. Typical but non-limiting combinations include combinations of hydrazine hydrate and glycerol, combinations of hydrazine hydrate and sucrose, combinations of sucrose and starch, etc.

[0038] Preferably, the amount of chromium precipitation agent added satisfies the following condition: the total amount of electron transfer it provides is 1.2-1.5 times the total amount of electron transfer required for the complete reduction of vanadium salt in the sodium vanadium chromium salt solution to vanadium dioxide product. For example, it can be 1.2 times, 1.3 times, 1.4 times or 1.5 times, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] As a preferred technical solution of the present invention, the temperature of the second hydrothermal reaction is 130-190℃, for example, it can be 130℃, 140℃, 150℃, 160℃, 170℃, 180℃ or 190℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0040] Preferably, the second hydrothermal reaction time is 3-6 h, for example, it can be 3 h, 4 h, 5 h or 6 h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] As a preferred technical solution of the present invention, the temperature of the second heat treatment is 200-500℃, for example, it can be 200℃, 300℃, 400℃ or 500℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] Preferably, the second heat treatment time is 2-4 hours, for example, it can be 2 hours, 3 hours or 4 hours, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the second heat treatment is carried out in an oxidizing atmosphere.

[0044] As a preferred technical solution of the present invention, the sodium carbonate product in step (3) can be applied to the sodium vanadium extraction process.

[0045] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0046] (1) Clean and environmentally friendly: It avoids the introduction of ammonia nitrogen, sulfur and other three waste elements, fundamentally solves the problem of three waste pollution, and realizes the cleanliness of vanadium-chromium separation and product preparation process;

[0047] (2) Simple and efficient process: short process, low energy consumption, mild reaction conditions, high operation safety, overall technical and economic efficiency is better than conventional methods, and has higher operation safety;

[0048] (3) Excellent product indicators: The vanadium product obtained has a V2O5 content ≥99% and a Na2O+ content ≥99%. K2O≤0.2%, Cr is below the detection limit, meeting the requirements of standard YB / T 5304-2017 for vanadium powder V2O599-P and above; the chromium product prepared contains Cr2O3≥98%, V≤0.5%, and Na2O+K2O≤0.5%. Detailed Implementation

[0049] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0050] It should be noted that any use of the process provided in the embodiments of the present invention or any substitution or change of conventional data falls within the protection and disclosure scope of the present invention.

[0051] Example 1

[0052] This embodiment provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, the method comprising the following steps:

[0053] Take a solution containing sodium vanadium chromium, wherein the composition of sodium vanadium chromium is: V: 30 g / L, Cr: 2 g / L, Na: 35 g / L; add sodium bicarbonate to the solution to adjust the pH of the solution to 9.5;

[0054] Then, glycerol was added to the solution at 1.5 times the total amount of electron transfer required for the complete reduction of chromium salt to chromium hydroxide product, and the first hydrothermal reaction was carried out at 130°C for 3 hours. After the reaction, the liquid and solid were separated to obtain chromium precipitate mother liquor and chromium hydroxide. The chromium hydroxide was washed countercurrently at a liquid-to-solid volume-to-mass ratio of 4:1. After washing, the chromium hydroxide was calcined at 800°C for 4 hours to prepare chromium oxide product. The chromium oxide product obtained by calcination has a main content of greater than or equal to 98%, which meets the metallurgical requirements.

[0055] Formic acid was added to adjust the pH of the chromium precipitation mother liquor to 8. Hydrazine hydrate was added to the chromium precipitation mother liquor, and the amount of hydrazine hydrate added was calculated as 1.2 times the total amount of electron transfer required for the complete reduction of vanadium salt to vanadium dioxide product. Then the solution was added to the reaction vessel and carried out a second hydrothermal reaction at 150°C for 3 hours. After the reaction was completed, vanadium dioxide and vanadium precipitation mother liquor were obtained by liquid-solid separation.

[0056] Vanadium dioxide is dried at 300℃ for 2 hours in an oxidizing atmosphere. The dried vanadium dioxide is powdered V2O5 with V2O5 ≥ 99%, and the product quality meets the standard requirements of powdered vanadium V2O5 99-P and above.

[0057] The washing residue and the vanadium precipitation mother liquor are mixed to obtain a sodium-containing solution; the sodium-containing solution is evaporated and crystallized to obtain sodium carbonate product, and the condensate generated during evaporation and crystallization is returned to the above steps as washing water.

[0058] Example 2

[0059] This embodiment provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, the method comprising the following steps:

[0060] Take a solution containing sodium vanadium chromium, wherein the composition of sodium vanadium chromium is: V: 5 g / L, Cr: 90 g / L, Na: 80 g / L; add sodium bicarbonate to the solution to adjust the pH of the solution to 10;

[0061] Then, glucose was added to the solution at a rate of 1 times the total amount of electron transfer required for the complete reduction of chromium salt to chromium hydroxide product, and the first hydrothermal reaction was carried out at 130°C for 3 hours. After the reaction, the liquid and solid were separated to obtain chromium precipitate mother liquor and chromium hydroxide. The chromium hydroxide was washed countercurrently at a liquid-to-solid volume-to-mass ratio of 3:1. After washing, the chromium hydroxide was calcined at 900°C for 3 hours to prepare chromium oxide product. The chromium oxide product obtained by calcination had a main content of greater than or equal to 98%, which met the metallurgical requirements.

[0062] Oxalic acid was added to adjust the pH of the chromium precipitation mother liquor to 7. Glycerol was added to the chromium precipitation mother liquor, and the amount of glycerol added was calculated as 1.1 times the total amount of electron transfer required for the complete reduction of vanadium salt to vanadium dioxide product. The solution was then added to the reaction vessel and subjected to a second hydrothermal reaction at 160°C for 3 hours. After the reaction was completed, vanadium dioxide and vanadium precipitation mother liquor were obtained by liquid-solid separation.

[0063] Vanadium dioxide is dried at 200℃ for 3 hours in an oxidizing atmosphere. The dried vanadium dioxide is powdered V2O5 with V2O5 ≥ 99%, and the product quality meets the standard requirements of powdered vanadium V2O5 99-P and above.

[0064] The washing residue and the vanadium precipitation mother liquor are mixed to obtain a sodium-containing solution; the sodium-containing solution is evaporated and crystallized to obtain sodium carbonate product, and the condensate generated during evaporation and crystallization is returned to the above steps as washing water.

[0065] Example 3

[0066] This embodiment provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, the method comprising the following steps:

[0067] Take a solution containing sodium vanadium chromium, wherein the composition of sodium vanadium chromium is: V: 25 g / L, Cr: 3 g / L, Na: 10 g / L; add sodium hydroxide to the solution to adjust the pH of the solution to 9.5;

[0068] Sodium formate was then added to the solution at 1.3 times the total amount of electrons transferred required for the complete reduction of chromium salts to chromium hydroxide. The first hydrothermal reaction was carried out at 210°C for 3 hours. After the reaction, the liquid and solid were separated to obtain chromium precipitate mother liquor and chromium hydroxide. The chromium hydroxide was washed countercurrently at a liquid-to-solid volume-to-mass ratio of 5:1. After washing, the chromium hydroxide was calcined at 900°C for 3 hours to prepare chromium oxide. The chromium oxide product obtained by calcination had a main content of greater than or equal to 98%, which met the metallurgical requirements.

[0069] Formic acid was added to adjust the pH of the chromium precipitation mother liquor to 9. Glucose was added to the chromium precipitation mother liquor, and the amount of glucose added was calculated as 1.5 times the total amount of electron transfer required for the complete reduction of vanadium salt to vanadium dioxide product. The solution was then added to the reaction vessel and subjected to a second hydrothermal reaction at 190°C for 3 hours. After the reaction was completed, vanadium dioxide and vanadium precipitation mother liquor were obtained by liquid-solid separation.

[0070] Vanadium dioxide is dried at 250°C for 3.5 hours in an oxidizing atmosphere. The dried vanadium dioxide is powdered V2O5 with V2O5 ≥ 99%, and the product quality meets the standard requirements of powdered vanadium V2O5 99-P and above.

[0071] The washing residue and the vanadium precipitation mother liquor are mixed to obtain a sodium-containing solution; the sodium-containing solution is evaporated and crystallized to obtain sodium carbonate product, and the condensate generated during evaporation and crystallization is returned to the above steps as washing water.

[0072] Example 4

[0073] This embodiment provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, the method comprising the following steps:

[0074] Take a solution containing sodium vanadium chromium, wherein the composition of sodium vanadium chromium is: V: 30 g / L, Cr: 2 g / L, Na: 35 g / L; add CO2 to the solution to adjust the pH of the solution to 9;

[0075] Then, glycerol was added to the solution in an amount equal to the total amount of electron transfer required for the complete reduction of chromium salt to chromium hydroxide product, and the first hydrothermal reaction was carried out at 130°C for 2 h. After the reaction, the liquid and solid were separated to obtain chromium precipitate mother liquor and chromium hydroxide. The chromium hydroxide was washed countercurrently twice at a liquid-to-solid volume mass ratio of 3:1. After washing, the chromium hydroxide was calcined at 800°C for 3 h to prepare chromium oxide product.

[0076] Formic acid was added to adjust the pH of the chromium precipitation mother liquor to 7. Sucrose was then added to the chromium precipitation mother liquor, with the amount of sucrose added calculated as 1.1 times the total amount of electrons transferred required for the complete reduction of vanadium salt to vanadium dioxide product. The solution was then added to a reaction vessel and subjected to a second hydrothermal reaction at 130°C for 3 hours. After the reaction, liquid-solid separation was performed to obtain vanadium dioxide and vanadium precipitation mother liquor. The vanadium dioxide was then dried at 200°C for 4 hours under an oxidizing atmosphere.

[0077] The washing residue and the vanadium precipitation mother liquor are mixed to obtain a sodium-containing solution; the sodium-containing solution is evaporated and crystallized to obtain sodium carbonate product, and the condensate generated during evaporation and crystallization is returned to the above steps as washing water.

[0078] Example 5

[0079] This embodiment provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, the method comprising the following steps:

[0080] Take a solution containing sodium vanadium chromium, wherein the composition of sodium vanadium chromium is: V: 30 g / L, Cr: 2 g / L, Na: 35 g / L; add sodium hydroxide to the solution to adjust the pH of the solution to 11;

[0081] Then, starch was added to the solution at 1.5 times the total amount of electron transfer required for the complete reduction of chromium salt to chromium hydroxide product, and the first hydrothermal reaction was carried out at 130°C for 6 hours. After the reaction, the liquid and solid were separated to obtain chromium precipitate mother liquor and chromium hydroxide. The chromium hydroxide was washed countercurrently at a liquid-to-solid volume mass ratio of 5:1. After washing, the chromium hydroxide was calcined at 1300°C for 4 hours to prepare chromium oxide product.

[0082] CO2 was added to adjust the pH of the chromium precipitation mother liquor to 9. Glucose was then added to the chromium precipitation mother liquor, with the amount of glucose added being 1.5 times the total amount of electrons transferred required for the complete reduction of vanadium salt to vanadium dioxide product. The solution was then added to a reaction vessel and subjected to a second hydrothermal reaction at 190°C for 6 hours. After the reaction, liquid-solid separation was performed to obtain vanadium dioxide and vanadium precipitation mother liquor. The vanadium dioxide was dried at 500°C for 2 hours under an oxidizing atmosphere.

[0083] The washing residue and the vanadium precipitation mother liquor are mixed to obtain a sodium-containing solution; the sodium-containing solution is evaporated and crystallized to obtain sodium carbonate product, and the condensate generated during evaporation and crystallization is returned to the above steps as washing water.

[0084] Example 6

[0085] This embodiment provides a method for recovering vanadium, chromium and sodium from a vanadium-chromium sodium salt solution. The only difference between this method and Example 1 is that sodium bicarbonate is added to the vanadium-chromium sodium salt solution to adjust the pH value to 8. All other aspects are the same as in Example 1.

[0086] Example 7

[0087] This embodiment provides a method for recovering vanadium, chromium and sodium from a vanadium-chromium sodium salt solution. The only difference between this method and Example 1 is that sodium bicarbonate is added to the vanadium-chromium sodium salt solution to adjust the pH value to 12, while the rest is the same as in Example 1.

[0088] Example 8

[0089] This embodiment provides a method for recovering vanadium, chromium and sodium from a vanadium-chromium sodium salt solution. The only difference between this method and Example 1 is that the pH of the chromium precipitation mother liquor is adjusted to 6, while the rest is the same as in Example 1.

[0090] Example 9

[0091] This embodiment provides a method for recovering vanadium, chromium and sodium from a vanadium-chromium sodium salt solution. The only difference between this method and Example 1 is that the pH of the chromium precipitation mother liquor is adjusted to 10, while the rest is the same as in Example 1.

[0092] Comparative Example 1

[0093] This comparative example provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution. The only difference between this method and Example 1 is that sodium bicarbonate is not added to the vanadium-chromium sodium salt solution to adjust the pH value, and a chromium precipitating agent is directly added and a first hydrothermal reaction is carried out. All other aspects are the same as in Example 1.

[0094] Comparative Example 2

[0095] This comparative example provides a method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution. The only difference between this method and Example 1 is that the pH value of the chromium precipitation mother liquor is not adjusted, and hydrazine hydrate is directly added for a hydrothermal reaction. All other aspects are the same as in Example 1.

[0096] Performance testing

[0097] The products obtained by the methods for recovering vanadium, chromium and sodium from vanadium-chromium sodium salt solutions provided in the examples and comparative examples were subjected to performance tests in accordance with the test methods for vanadium, chromium and sodium in YB / T5328-2009. The results are shown in Table 1.

[0098]

[0099] In Table 1, "-" indicates that there is no relevant data.

[0100] A comprehensive comparison of Examples 1 and 6-9 shows that if the pH of the chromium precipitation solution is too low, the chromium oxide product quality will fail to meet requirements due to the adsorption of a large amount of vanadium; if the pH is too high, the resulting chromium oxide particles will be too fine, have a high water content, and carry many impurities, thus reducing product quality. If the mother liquor pH of the chromium precipitation solution is too high, vanadium cannot be effectively precipitated, and the vanadium product cannot be prepared; if the pH is too low, the resulting product particles will be too fine, have a high water content, and the product quality will not meet requirements.

[0101] A comprehensive comparison of Example 1 and Comparative Examples 1-2 shows that if the pH of the sodium vanadium chromium solution is not adjusted, the pH will be too high and impurities will be carried in, or too low and vanadium will be adsorbed, ultimately resulting in the chromium oxide product failing to meet the standard quality requirements.

[0102] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering vanadium, chromium, and sodium from a vanadium-chromium sodium salt solution, characterized in that, The method includes the following steps: (1) Adjust the pH value of the sodium vanadium chromium salt solution, add a chromium precipitation agent and carry out a first hydrothermal reaction to obtain chromium hydroxide product and chromium precipitation mother liquor; subject the chromium hydroxide product to a first washing and a first heat treatment in sequence to obtain chromium oxide product; (2) Adjust the pH value of the chromium precipitation mother liquor and add vanadium precipitation agent to carry out a second hydrothermal reaction to obtain vanadium dioxide product and vanadium precipitation mother liquor; subject the vanadium dioxide product to a second washing and a second heat treatment in sequence to obtain vanadium pentoxide product; (3) Mix the first washing residue in step (1), the second washing residue in step (2) and the vanadium precipitation mother liquor to obtain a sodium-containing solution; evaporate and crystallize the sodium-containing solution to obtain sodium carbonate product, and return the condensate generated by evaporation and crystallization to step (1) and step (2) as washing water.

2. The method according to claim 1, characterized in that, The chromium salt in the vanadium-chromium sodium salt solution includes sodium chromate. Preferably, the vanadium salt in the vanadium-chromium sodium salt solution includes sodium vanadate; Preferably, the sodium vanadate includes any one or a combination of at least two of sodium orthovanadate, sodium pyrovanadate, or sodium metavanadate; Preferably, the sodium salt in the vanadium-chromium sodium salt solution includes any one or a combination of at least two of the following: chromium sodium salt, vanadium sodium salt, sodium carbonate, sodium bicarbonate, or sodium hydroxide.

3. The method according to claim 1 or 2, characterized in that, In step (1), the pH value of the sodium vanadium chromium salt solution is adjusted to 9-11; Preferably, the acid-base regulator used to adjust the pH value in step (1) includes any one or a combination of at least two of sodium carbonate, sodium bicarbonate, CO2, or sodium hydroxide.

4. The method according to any one of claims 1 to 3, characterized in that, The chromium precipitation agent comprises any one or a combination of at least two of formaldehyde, methanol, formic acid, sodium formate, glucose, sucrose, glycerol, hydrazine hydrate, or starch; the temperature of the first hydrothermal reaction satisfies the following condition: (1) When the chromium precipitation agent contains hydrazine hydrate, the reaction temperature is 90-220℃; (2) When the chromium precipitation agent is any one or a combination of at least two of formaldehyde, methanol, formic acid or sodium formate, and does not contain hydrazine hydrate, the reaction temperature is 190-220℃. (3) When the chromium precipitation agent is any one or a combination of at least two of glucose, sucrose, glycerol or starch, and does not contain hydrazine hydrate, the reaction temperature is 120-220℃.

5. The method according to any one of claims 1 to 4, characterized in that, The amount of chromium precipitation agent added satisfies the following condition: the total amount of electron transfer it provides is 1-1.5 times the total amount of electron transfer required for the complete reduction of chromium salt in the sodium vanadium chromium salt solution to chromium hydroxide product; Preferably, the first hydrothermal reaction takes 2-6 hours; Preferably, the aging and crystallization time after the first hydrothermal reaction is 1-4 hours; Preferably, the first washing includes: the volume ratio of washing water to the mass of the chromium hydroxide product is (3-5):1, countercurrent washing is performed 1-3 times using a pulping washing method, the washing temperature is ≥70℃, and the washing time for each wash is 0.5-1h; Preferably, the temperature of the first heat treatment is 800-1300℃; Preferably, the first heat treatment time is 3-4 hours.

6. The method according to any one of claims 1 to 5, characterized in that, In step (2), the pH of the chromium precipitation mother liquor is adjusted to 7-9; Preferably, the acid-base regulator used to adjust the pH value in step (2) includes CO2 and / or organic acids; Preferably, the organic acid includes any one or a combination of at least two of formic acid, oxalic acid, or acetic acid.

7. The method according to any one of claims 1 to 6, characterized in that, The vanadium precipitation agent includes any one or a combination of at least two of hydrazine hydrate, glycerol, sucrose, glucose, or starch; Preferably, the amount of vanadium precipitating agent added satisfies the following condition: the total amount of electron transfer it provides is 1.1-1.5 times the total amount of electron transfer required for the complete reduction of vanadium salt in the sodium vanadium chromium salt solution to vanadium dioxide product.

8. The method according to any one of claims 1 to 7, characterized in that, The temperature of the second hydrothermal reaction is 130-190℃; Preferably, the second hydrothermal reaction takes 3-6 hours.

9. The method according to any one of claims 1 to 8, characterized in that, The temperature for the second heat treatment is 200-500℃; Preferably, the second heat treatment time is 2-4 hours; Preferably, the second heat treatment is carried out in an oxidizing atmosphere.

10. The method according to any one of claims 1 to 9, characterized in that, The sodium carbonate product described in step (3) can be used in the sodium vanadium extraction process.

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