A method for preparing FeVO4 by equal pH precipitation method and producing VO2 by using the same

Abstract

The present invention discloses a method for preparing iron vanadate by an isophasic pH precipitation method and using the same to produce vanadium dioxide, which relates to the technical field of hydrometallurgy for vanadium extraction. The method comprises the following steps: 1) heating a vanadium-containing acid solution to a set temperature and oxidizing it; 2) simultaneously adding the vanadium-containing acid solution, an iron salt solution and dilute alkali into the system at a certain flow rate respectively, and keeping the pH of the slurry unchanged; 3) separating the solid and liquid of the above slurry, washing the precipitate with hot dilute alkali to obtain an iron hydroxide precipitate and a vanadate alkaline solution; 4) adjusting the above alkaline solution to be acidic and adding a reducing agent; 5) adjusting the pH of the above vanadium-containing acidic solution to neutral to obtain a vanadium hydroxide precipitate, and calcining the precipitate without oxygen to obtain vanadium dioxide. The present invention provides a method for preparing iron vanadate by an isophasic pH precipitation method and using the same to produce vanadium dioxide, which can realize the recovery of vanadium in the vanadium-containing acid solution and the preparation of vanadium dioxide, and has the advantages of short production process, high vanadium precipitation rate, high recovery rate and pure vanadium dioxide.

Description

Technical Field

[0001] The present invention belongs to the technical fields of hydrometallurgy and vanadium chemical engineering, and relates to a method for preparing iron vanadate by an isophasic precipitation method and using the same to produce vanadium dioxide Background Art

[0002] Vanadium is called "the industrial monosodium glutamate". Vanadium dioxide is one of the most reported and widely used vanadium oxides at present, and has multiple allotropes. Due to the unique phase change properties and excellent performance of vanadium dioxide, it has been widely used in smart glass, optical storage, laser radiation protection films, lithium battery electrodes and other aspects in recent years

[0003] Regarding the resource utilization of vanadium in vanadium-containing minerals and vanadium-containing tailings, an acid leaching process is often used to leach the vanadium into the solution and then enrich it. Regarding the vanadium enrichment method, there are mainly solvent extraction method and ion exchange method. Due to the complex components in vanadium-containing tailings or minerals and the large number of impurity components in the acid leaching solution, the extraction method and ion exchange method are not applicable. Among the methods for recovering vanadium such as ammonium salt precipitation method, calcium salt precipitation method, and iron salt vanadium precipitation method, the ammonium salt and calcium salt precipitation methods have certain requirements for the vanadium concentration in the solution, and the vanadium precipitation efficiency is low. Calcium salt vanadium precipitation will produce a large amount of calcium slag, and ammonium salt vanadium precipitation will bring problems of sewage treatment. Therefore, in comparison, iron salt vanadium precipitation is simple and easy as a means of vanadium enrichment and recovery

[0004] CN108383165A discloses a method for preparing iron vanadate and using the same to produce vanadium pentoxide. The vanadium in vanadium-containing tailings is leached by water leaching, and the pH is adjusted to 6.5-8 to prepare iron vanadate. The iron vanadate is mixed and roasted with low-calcium tailings and ammonium salt vanadium precipitation is carried out to finally obtain vanadium pentoxide. This method can obtain iron vanadate precipitation, but for the acid solution with complex components, when adjusted to neutrality, the obtained components are complex and a variety of metal ions have precipitated at this time, resulting in a high content of impurity ions in the iron vanadate precipitation. In addition, when preparing vanadium pentoxide with this vanadium iron, calcium chloride, ammonium chloride, etc. need to be added, the process is cumbersome, and the post-treatment is complex

[0005] The conventional iron salt vanadium precipitation method is to slowly add iron salt to the vanadium-containing solution, while monitoring and adjusting the acidity change of the system. Due to the difficult control of the reaction process, obvious fluctuations, large supersaturation of the precipitation, and too fast precipitation nucleation rate, the crystals cannot grow, resulting in difficult filtration

[0006] In the process of separating vanadium from iron in the enriched vanadium iron precipitation, although alkali dissolution is the most commonly used method, due to the conversion into iron hydroxide colloid, it is difficult to filter, and it is difficult to achieve simple, rapid and effective separation. At the same time, in the conventional methods for generating vanadium pentoxide, other impurity ions are often introduced, resulting in cumbersome treatment processes and impure products

[0007] Therefore, due to the importance and utilization value of vanadium, it is urgent to develop a method for preparing easily filterable iron vanadate from vanadium-containing tailings or acid leaching solutions of vanadium-containing minerals for vanadium enrichment, and thereby achieve vanadium refining and effectively realize the resource utilization of vanadium slag and vanadium-containing minerals. Summary of the Invention

[0008] Aiming at the above deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing iron vanadate by the equal pH precipitation method and using it to produce vanadium dioxide. This method is simple to operate, has a short process flow, the precipitate is easy to filter and wash, the vanadium recovery rate is high, and the purity of vanadium dioxide is high.

[0009] To achieve the above invention purpose, according to a method for preparing iron vanadate by the equal pH precipitation method and using it to produce vanadium dioxide of the present invention, the method specifically includes the following steps:

[0010] (1) Oxidation of low-valent vanadium: Heat the vanadium-containing acid solution to a set temperature, and add an oxidant thereto to oxidize the low-valent vanadium to pentavalent vanadium.

[0011] (2) Equal pH precipitation: Under the condition of rapid stirring, add the vanadium-containing acid solution, iron salt solution, and dilute alkali solution into the system at a certain flow rate simultaneously, and keep the pH of the slurry system unchanged during the process. The iron vanadate precipitate slurry is obtained by the equal pH precipitation method.

[0012] (3) Alkaline washing to separate iron and vanadium: Filter the reaction slurry in step (2) to obtain iron vanadate, and perform high-temperature alkaline washing of the iron vanadate with dilute alkali solution to obtain a slurry containing iron hydroxide precipitate and vanadate alkaline solution, and this slurry is easy to filter.

[0013] (4) Reduction reaction: First, add acid to the alkali solution in step (3) to adjust the pH to 5-7; then add a reducing agent to the obtained vanadate acidic solution for reduction to reduce the pentavalent vanadium therein to tetravalent vanadium.

[0014] (5) Preparation of vanadium dioxide: Under the condition of a hot solution, add the above-reduced acidic vanadium solution and dilute alkali solution into the solution at different flow rates simultaneously, and keep the pH of the solution at 6-8 unchanged during the process. After reacting for a period of time, a uniform granular vanadium hydroxide precipitate is obtained, and this precipitate is subjected to anaerobic calcination to obtain vanadium dioxide.

[0015] The method provided by the present invention: First, the vanadium-containing solution is oxidized to oxidize the low-valent vanadium in the solution to a high-valent state. The vanadium-containing acid solution, iron salt solution, and dilute alkali solution are simultaneously added to the system at a certain flow rate, and the pH of the slurry system is kept unchanged during the process, so that the pH of the solution is stabilized at 2.0 - 2.5, thereby controlling the supersaturation and nucleation rate of iron vanadate. At this time, the generated iron vanadate precipitate is easy to filter and wash. The obtained iron vanadate precipitate is alkali-washed with a hot dilute alkali solution. On the one hand, the dissolution rate of vanadium is relatively high under this high-temperature condition. On the other hand, in this hot dilute alkali solution, the iron in iron vanadate will slowly convert into iron hydroxide, and the slowly generated iron hydroxide has a certain crystal structure at high temperature and is easy to filter. For the alkaline sodium vanadate solution obtained after alkali-washing, the pH is first adjusted to ensure the stability of the reduced tetravalent vanadium, and then vanadium hydroxide is prepared by the precipitation method, and then vanadium dioxide products are obtained by anaerobic calcination.

[0016] Meanwhile, the whole technological process of the present invention has a short process flow, the precipitate in the solid-liquid separation process is easy to filter and wash, the vanadium recovery rate is high, and the purity of vanadium dioxide is high.

[0017] In step (1), the oxidant is one or a combination of at least two of hydrogen peroxide, sodium chlorate, sodium hypochlorite, and sodium chlorite. The oxidation method of vanadium is a conventional technical means in the art, so it will not be elaborated here.

[0018] In step (1), the oxidation temperature of the oxidant is 70 - 100 °C, which is a conventional technical means in the art, so it will not be elaborated here.

[0019] In step (1), the addition amount of the oxidant is 1 - 1.5 times of the theoretical addition amount;

[0020] The following are the preferred technical solutions of the present invention, but not the limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

[0021] As a preferred technical solution of the present invention, in step (2), the dilute alkali solution is one or a combination of at least 2 of sodium carbonate solution, magnesium hydroxide solution, or calcium hydroxide solution.

[0022] As a preferred technical solution of the present invention, in step (2), the iron salt is one or a combination of at least 2 of ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, ferric nitrate, and polyferric sulfate.

[0023] As a preferred technical solution of the present invention, in step (2), the molar ratio of the addition amount of the iron salt to the vanadium in the solution is 1 ≤ iron / vanadium ≤ 10; for example, iron / vanadium is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., but not limited to the listed values, and other unlisted data within this range are equally applicable;

[0024] As a preferred technical solution of the present invention, in step (2), the pH of the system is 1.5 to 3.0; for example, the pH is adjusted to 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, etc., but is not limited to the listed values, and other unlisted data within this range are equally applicable. Further preferably, it is 2.0 to 2.5;

[0025] As a preferred technical solution of the present invention, in step (2), the flow rates of the iron salt solution, vanadium-containing acid solution, and dilute alkali solution are related to the actual iron / vanadium molar ratio, the concentration of the iron salt solution, and the concentration of the vanadium solution. In the actual process, pH stability is used as the control standard.

[0026] As a preferred technical solution of the present invention, in step (2), the precipitation rate of vanadium during the formation of iron vanadate precipitate is ≥98.5%, such as 98.5%, 99%, 99.5%, 100%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] As a preferred technical solution of the present invention, in step (3), the dilute alkali solution is one or a combination of several of sodium carbonate, sodium bicarbonate, and sodium hydroxide solutions.

[0028] As a preferred technical solution of the present invention, in step (3), the pH of the dilute alkali solution is 8.5 to 11, such as pH 8.5, 9, 9.5, 10, 10.5, 11, etc., but is not limited to the listed values, and other unlisted data within this range are equally applicable. Further preferably, the pH is 9 to 10;

[0029] As a preferred technical solution of the present invention, in step (3), the high-temperature alkali washing temperature is 130 to 240 °C, such as the alkali washing temperature is 130 °C, 150 °C, 170 °C, 190 °C, 200 °C, 220 °C, 240 °C, etc., but is not limited to the listed values, and other unlisted data within this range are equally applicable. Further preferably, the alkali washing temperature is 130 to 150;

[0030] As a preferred technical solution of the present invention, in step (3), the alkali washing time is 2 to 5 h, such as the alkali washing time is 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, etc., but is not limited to the listed values, and other unlisted data within this range are equally applicable. Further preferably, the alkali washing time is 3 h.

[0031] As a preferred technical solution of the present invention, in step (4), the reducing agent is one or a combination of at least two of sulfur dioxide, methanol, formic acid, hydrazine hydrate, etc.;

[0032] As a preferred technical solution of the present invention, in step (4), the reducing agent dosage is 1.5 to 3 times the theoretical addition amount, such as 1.5, 2, 2.5, 3 times, etc., but is not limited to the listed values, and other unlisted data within this range are equally applicable;

[0033] As a preferred technical solution of the present invention, in step (5), the dilute alkali solution is one or a combination of at least two of the solutions such as sodium carbonate, sodium bicarbonate, sodium hydroxide, magnesium hydroxide, etc.;

[0034] As a preferred technical solution of the present invention, in step (5), adjusting the pH to neutral is pH 7 ± 0.5, such as adjusting the pH to 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, etc., but is not limited to the listed values, and other unlisted data within this range are equally applicable.

[0035] As a preferred technical solution of the present invention, in step (5), the temperature of the hot solution is 80 - 90 °C.

[0036] As a preferred technical solution of the present invention, for the vanadium dioxide obtained in step (5), its recovery rate ≥ 97 wt%, such as 97%, 98%, 99%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] As a preferred technical solution of the present invention, in step (5), the purity of the prepared vanadium dioxide ≥ 98.5 wt%, such as 98.5%, 98.8%, 99.9%, 99.5%, 99.9%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] The method of the present invention has a short process flow, mild and easy - to - control conditions, a high vanadium precipitation rate, easy solid - liquid separation of the precipitate, easy washing and filtration, a high vanadium recovery rate, a high purity of vanadium dioxide, and is easy to implement industrially.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention provides a method for preparing iron vanadate by the equal - pH precipitation method and using it to produce vanadium dioxide. By the equal - pH precipitation method, the pH of the reaction slurry is accurately controlled, making the generated iron vanadate precipitate easy to filter and wash.

[0041] (2) After the iron vanadate precipitate in the present invention is washed with hot alkali, the iron hydroxide solid and the vanadate solution are easy to filter and separate.

[0042] (3) In the present invention, vanadium dioxide is prepared from the vanadate alkaline solution through acid adjustment - reduction - precipitation - calcination. The recovery rate of vanadium is high, greater than 95%, and the purity of vanadium dioxide is greater than 98.5%.

[0043] (4) The entire technological process of the present invention is simple, easy to operate, easy to control, and easy to promote industrially. Detailed implementation manners

[0044] The following further elaborates on the present invention in conjunction with specific embodiments, so that those skilled in the art can implement it with reference to the description. However, the following embodiments are merely simple examples of the present invention and do not represent or limit the scope of the claimed rights of the present invention. The scope of protection of the present invention is subject to the claims.

[0045] Example 1

[0046] This example provides a method for preparing iron vanadate by the equal - pH precipitation method and using it to produce vanadium dioxide. The vanadium - containing acid solution is the acid - leaching solution of stone coal, and the concentration of V in it is 1.92 g / L. The method includes the following steps:

[0047] (1) Heat the vanadium - containing acid solution to 70 °C, and add sodium chlorate in an amount of 1 times the theoretical amount to oxidize the low - valence vanadium to pentavalent vanadium.

[0048] (2) Under the condition of rapid stirring, add the vanadium - containing acid solution, iron salt solution, and dilute sodium carbonate solution into the system simultaneously at a certain flow rate. After adding the iron salt, the molar ratio of iron to vanadium in the solution is 1, and keep the pH of the slurry system stable at about 3.0 during the process. Obtain the iron vanadate precipitation slurry by the equal - pH precipitation method.

[0049] (3) Alkaline dissolution and separation of iron and vanadium: Filter the reaction slurry in step (2) to obtain the iron vanadate precipitate. The precipitation rate of vanadium is 99.2%. The solid - liquid separation suction filtration pressure is 0.1 MPa, and the filtration time is 4 min when the filter cake thickness is 1 cm. Subject the iron vanadate to high - temperature alkaline washing with sodium hydroxide solution with a pH of 10 at a temperature of 130 °C for 2 h. After filtering the alkaline washing solution, obtain the iron hydroxide precipitate and the vanadate alkaline solution. The suction filtration pressure of this precipitate is 0.1 MPa, and the filtration time is 6 min when the filter cake thickness is 1 cm.

[0050] (4) Reduction reaction: Add sulfuric acid to the vanadate alkaline solution in step (3) to adjust the pH to 5, and add sodium sulfite in an amount of 1.5 times the theoretical amount for reduction to reduce the pentavalent vanadium in the solution to tetravalent vanadium.

[0051] (5) Preparation of vanadium dioxide: Using dilute sodium hydroxide solution as the alkali source, adjust the pH of the reduced tetravalent vanadium alkaline solution in step (4) to 7.5, and react for 1 h to obtain vanadium hydroxide precipitate. Subject this precipitate to anaerobic calcination to obtain pure vanadium dioxide. The recovery rate of vanadium is 98.9%, and the purity of vanadium dioxide is 98.7%.

[0052] Example 2

[0053] This example provides a method for preparing iron vanadate by the equal-pH precipitation method and using it to produce vanadium dioxide. The vanadium-containing acid solution is the acid leaching solution of stone coal, and the concentration of V in it is 2.32 g / L. The method includes the following steps:

[0054] (1) Heat the vanadium-containing acid solution to 95 °C, and add 1.2 times the theoretical amount of sodium chlorate to oxidize the low-valent vanadium to pentavalent vanadium.

[0055] (2) Under the condition of rapid stirring, add the vanadium-containing acid solution, iron salt solution, and dilute alkali solution into the system simultaneously at a certain flow rate. After adding the iron salt, the molar ratio of iron to vanadium in the solution is 6. Keep the pH of the slurry system stable at about 2.3 during the process, and obtain the iron vanadate precipitate slurry by the equal-pH precipitation method.

[0056] (3) Alkaline dissolution and separation of iron and vanadium: Filter the reaction slurry in step (2) to obtain iron vanadate precipitate. The precipitation rate of vanadium is 98.5%. The pressure for solid-liquid separation by suction filtration is 0.1 MPa, and the filtration time is 5 min when the thickness of the filter cake is 1.1 cm. Subject this iron vanadate to high-temperature alkaline washing with sodium carbonate solution at pH 9 and a temperature of 150 °C for 2.5 h. After filtering the alkaline washing solution, obtain iron hydroxide precipitate and sodium vanadate alkaline solution. The pressure for suction filtration of this precipitate is 0.1 MPa, and the filtration time is 5 min when the thickness of the filter cake is 1 cm.

[0057] (4) Reduction reaction: Add sulfuric acid to the sodium vanadate alkaline solution in step (3) to adjust the pH to 4, and add 3 times the theoretical amount of sulfur dioxide for reduction to reduce the pentavalent vanadium in the solution to tetravalent vanadium.

[0058] (5) Preparation of vanadium dioxide: Using dilute sodium carbonate solution as the alkali source, adjust the pH of the reduced tetravalent vanadium alkaline solution in step (4) to 7.0, and react for 1.5 h to obtain vanadium hydroxide precipitate. Subject this precipitate to anaerobic calcination to obtain pure vanadium dioxide. The recovery rate of vanadium is 97.5%, and the purity of vanadium dioxide is 98.9%.

[0059] Example 3

[0060] This example provides a method for preparing iron vanadate by the equal-pH precipitation method and using it to produce vanadium dioxide. The vanadium-containing acid solution is the acid leaching solution of stone coal, and the concentration of V in it is 3.5 g / L. The method includes the following steps:

[0061] (1) Heat the vanadium-containing acid solution to 85 °C, and add sodium chlorate at 1.5 times the theoretical amount thereto to oxidize the low-valent vanadium to pentavalent vanadium.

[0062] (2) Under the condition of rapid stirring, add the vanadium-containing acid solution, the iron salt solution and the dilute alkali solution to the system at a certain flow rate simultaneously. After the addition of the iron salt, the molar ratio of iron to vanadium in the solution is 10. Keep the pH of the slurry system stable at about 2.0 during the process, and obtain the iron vanadate precipitation slurry by the isoelectric precipitation method.

[0063] (3) Alkaline dissolution and separation of iron and vanadium: Filter the reaction slurry in step (2) to obtain the iron vanadate precipitate, in which the precipitation rate of vanadium is 99.5%. The solid-liquid separation suction filtration pressure is 0.1 MPa, and the filtration time is 5.5 min when the filter cake thickness is 1 cm. Wash the iron vanadate with a sodium bicarbonate solution with a pH of 8.5 at 130 °C for 3 h by high-temperature alkali washing. After filtering the alkali washing solution, obtain the iron hydroxide precipitate and the sodium vanadate alkaline solution. The precipitation suction filtration pressure is 0.1 MPa, and the filtration time is 6 min when the filter cake thickness is 1 cm.

[0064] (4) Reduction reaction: Add sulfuric acid to the sodium vanadate alkaline solution in step (3) to adjust the pH to 6, and add methanol at 3 times the theoretical amount for reduction to reduce the pentavalent vanadium in the solution to tetravalent vanadium.

[0065] (5) Preparation of vanadium dioxide: Use dilute magnesium hydroxide solution as the alkali source, adjust the pH of the tetravalent vanadium alkaline solution after reduction in step (4) to 7.0, react for 2.5 h to obtain the vanadium hydroxide precipitate, and calcine the precipitate without oxygen to obtain pure vanadium dioxide. The recovery rate of vanadium is 98.9%, and the purity of vanadium dioxide is 99.1%.

[0066] Example 4

[0067] This example provides a method for preparing iron vanadate by the isoelectric precipitation method and using it to produce vanadium dioxide. The vanadium-containing acid solution is the acid leaching solution of stone coal, and the concentration of V therein is 3.5 g / L. The method includes the following steps:

[0068] (1) Heat the vanadium-containing acid solution to 100 °C, and add sodium chlorate at 1.0 times the theoretical amount thereto to oxidize the low-valent vanadium to pentavalent vanadium.

[0069] (2) Under the condition of rapid stirring, add the vanadium-containing acid solution, the iron salt solution and the dilute alkali solution to the system at a certain flow rate simultaneously. After the addition of the iron salt, the molar ratio of iron to vanadium in the solution is 3. Keep the pH of the slurry system stable at about 2.6 during the process, and obtain the iron vanadate precipitation slurry by the isoelectric precipitation method.

[0070] (3) Alkaline solution separation of iron vanadate: Filter the reaction slurry in step (2) to obtain iron vanadate precipitate, where the precipitation rate of vanadium is 99.3%. The suction filtration pressure for solid-liquid separation is 0.1 MPa, and the filtration time is 4.5 min when the filter cake thickness is 1 cm. Wash the iron vanadate with sodium carbonate solution at pH 9 at 150 °C for 3 h. After filtering the alkaline washing solution, iron hydroxide precipitate and sodium vanadate alkaline solution are obtained. The suction filtration pressure for this precipitate is 0.1 MPa, and the filtration time is 5.5 min when the filter cake thickness is 1 cm.

[0071] (4) Reduction reaction: Add sulfuric acid to the sodium vanadate alkaline solution in step (3) to adjust the pH to 5.5, and add 3 times the theoretical amount of sulfur dioxide for reduction to reduce pentavalent vanadium in the solution to tetravalent vanadium.

[0072] (5) Preparation of vanadium dioxide: Using dilute sodium carbonate solution as the alkali source, adjust the pH of the tetravalent vanadium alkaline solution after reduction in step (4) to 7.5, and react for 2 h to obtain vanadium hydroxide precipitate. Calcinate this precipitate under anaerobic conditions to obtain pure vanadium dioxide. The recovery rate of vanadium is 98.8%, and the purity of vanadium dioxide is 98.7%.

[0073] Comparative Example 1

[0074] This example provides a method for preparing iron vanadate by equal pH precipitation method and using it to produce vanadium dioxide. In this method, except that in step (2), the vanadium-containing solution and the iron salt solution are directly mixed, and then the pH of the solution is adjusted to 3.0 with dilute alkali solution, other materials and processes are the same as those in Example 1. The vanadium precipitation rate is 85.6%. The suction filtration pressure for solid-liquid separation in step (6) is 0.1 MPa, and the filtration time is 85 min when the filter cake thickness is 1 cm. After the iron vanadate is subjected to alkali washing - acid adjustment - reduction - precipitation - anaerobic calcination, the recovery rate of vanadium is 70.5%, and the purity of vanadium dioxide is 98.2%.

[0075] Comparative Example 2

[0076] This example provides a method for preparing crystalline iron vanadate by pH slow-release method of vanadium-containing acid solution. In this method, except that the pH value of the slurry in step (2) is 7.0, other materials and processes are the same as those in Example 2. The vanadium precipitation rate is 95.1%. The suction filtration pressure for solid-liquid separation in step (6) is 0.1 MPa, and the filtration time is 160 min when the filter cake thickness is 1 cm. After the iron vanadate is subjected to alkali washing - acid adjustment - reduction - precipitation - anaerobic calcination, the recovery rate of vanadium is 68.8%, and the purity of vanadium dioxide is 98.1%.

[0077] Comparative Example 3

[0078] This example provides a method for preparing crystalline iron vanadate by pH slow-release method of vanadium-containing acid solution. Except that in step (3), the iron vanadate is subjected to high-temperature alkali washing with 20% sodium hydroxide solution, other materials and processes are the same as those in Example 3. The filtration pressure for solid-liquid separation by alkali washing and recovery of vanadium is 0.1 MPa, and the filtration time is 145 min when the filter cake thickness is 1 cm. After the sodium vanadate solution is subjected to acid adjustment - reduction - precipitation - anaerobic calcination, the recovery rate of vanadium is only 62.5%, and the purity of vanadium dioxide is 98.2%.

[0079] Comparative Example 4

[0080] This example provides a method for preparing crystalline iron vanadate by pH slow-release method of vanadium-containing acid solution. Except that in step (4), the sodium vanadate solution after alkali washing is directly reduced with 3 times sulfur dioxide without acid adjustment, other materials and processes are the same as those in Example 4. After the sodium vanadate solution after alkali washing is directly reduced - precipitated - anaerobically calcined, the recovery rate of vanadium is only 72.5%, and the purity of vanadium dioxide is 98.1%.

[0081] Table 1 Vanadium precipitation rate and filtration rate

[0082]

[0083]

[0084] It can be seen from Table 1 that in Examples 1 to 4 of the present invention, the precipitation rate of vanadium is greater than or equal to 98.5%. When the filter cake thickness is 1 cm at a pressure of 0.1 MPa for the precipitation of iron vanadate, the filtration time is less than or equal to 5.5 min; the filtration time for solid-liquid separation after alkali washing is less than or equal to 6 min, the recovery rate of vanadium is greater than or equal to 97.5%, and the purity of vanadium dioxide is greater than or equal to 98.7%.

[0085] In Comparative Example 1, compared with Example 1, the equal-pH precipitation method is not used in Comparative Example 1, which will result in too high supersaturation during the vanadium precipitation process, fast nucleation rate, and difficult crystal growth, thus resulting in slow filtration rate of iron vanadate. When the filter cake thickness is 1 cm at a pressure of 0.1 MPa, the filtration time is greater than or equal to 85 min, and the vanadium precipitation rate is only 85.6%; and for this form of iron vanadate, due to small particles, viscous slurry and mutual wrapping during the alkali washing process, the dissolution of vanadium is affected, so that the recovery rate of vanadium in vanadium dioxide obtained after alkali washing - acid adjustment - reduction - precipitation - anaerobic calcination of iron vanadate is lower than 70.5%, and the purity of vanadium dioxide is not affected.

[0086] Comparative Example 2. Compared with Example 2, although the equal pH precipitation method was used in Comparative Example 2, the pH of the precipitation was too high, which would lead to too high precipitation rate of iron during the vanadium precipitation process and it existed in the form of iron hydroxide. The precipitates wrapped each other, resulting in too slow filtration rate of iron vanadate. The suction filtration time was 160 min when the filter cake with a thickness of 1 cm was under a pressure of 0.1 MPa. In these two cases, for the vanadium dioxide obtained after alkali washing - acid adjustment - reduction - precipitation - anaerobic calcination, the recovery rate of vanadium was lower than 70.5%, and the purity of vanadium dioxide was not affected.

[0087] Comparative Example 3. Compared with Example 3, a high - concentration alkali was used during the alkali washing process, which led to too fast nucleation rate of iron hydroxide while vanadium in iron vanadate was dissolved out. The precipitation conversion particles were small and easy to wrap, resulting in low vanadium dissolution rate, difficult solid - liquid separation, a suction filtration time of 145 min, and the recovery rate of vanadium was only 62.5%.

[0088] Comparative Example 4. Compared with Example 4, the sodium vanadate solution recovered after alkali washing was directly reduced without acidification. Due to the stability of tetravalent vanadium under alkaline conditions, the reduction efficiency of vanadium was reduced, resulting in part of vanadium still existing in the form of pentavalent vanadium, and the effective recovery rate of vanadium was only 72.5.

[0089] It can be seen from the data in Table 1 that the iron vanadate obtained by the equal pH precipitation method has a high vanadium precipitation rate, is easy to filter, and the alkali dissolution effect of the iron vanadate prepared by this method is good, and the recovery rate of vanadium is high.

[0090] Based on the results of Examples 1 - 4 and Comparative Examples 1 - 4, the present invention provides a method for preparing iron vanadate by equal pH precipitation and using it to produce vanadium dioxide. The oxidation - equal pH precipitation method is used to prepare iron vanadate that is easy to filter, and the vanadium in it is recovered and vanadium dioxide is prepared by the method of dilute alkali hot washing - acid adjustment - reduction - precipitation - anaerobic calcination using this iron vanadate as the raw material. The whole process of this method is simple to operate, has a high vanadium precipitation rate, fast solid - liquid separation speed, is easy to control, and can be promoted industrially.

[0091] The applicant declares that the present invention uses the above - mentioned examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above - mentioned detailed method, that is, it does not mean that the present invention must rely on the above - mentioned detailed method to be implemented. Those skilled in the art should understand that the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing vanadium dioxide by equal pH precipitation method, characterized in that, It includes the following steps: (1) Low-valent vanadium oxidation: Heat the vanadium-containing acid solution to a set temperature, and add an oxidant thereto to oxidize the low-valent vanadium to pentavalent vanadium; (2) Equal-pH precipitation: Under the condition of rapid stirring, add the vanadium-containing acid solution, the iron salt solution and the dilute alkali solution into the system at a certain flow rate simultaneously, and keep the pH of the slurry system unchanged during the process, and obtain a vanadium ferrite precipitation slurry by the equal-pH precipitation method; (3) Alkaline washing to separate iron and vanadium: Filter the reaction slurry in step (2) to obtain vanadium ferrite, and perform high-temperature alkaline washing on the vanadium ferrite with a dilute alkali solution to obtain a slurry containing iron hydroxide precipitate and a vanadate alkaline solution, and this slurry is easy to filter; (4) Reduction reaction: First, add an acid to the alkaline solution in step (3) to adjust it to acidic; then add a reducing agent to the obtained acidic vanadate solution for reduction to reduce the pentavalent vanadium therein to tetravalent vanadium; (5) Preparation of vanadium dioxide: Under the condition of a hot solution, add the above-reduced acidic vanadium solution and the dilute alkali solution into the solution at different flow rates simultaneously, and keep the pH of the solution stable at 7±0.5 during the process. After reacting for a period of time, a vanadium hydroxide precipitate with uniform particles is obtained, and this precipitate is subjected to anaerobic calcination to obtain vanadium dioxide; In step (2), the molar ratio of the iron salt added to vanadium in the solution is 1≤Fe / V≤10; In step (2), the pH of the system is 1.5 - 3.0; In step (3), the precipitation rate of vanadium in the vanadium ferrite is ≥98.5%; In step (3), the pH of the dilute alkali solution is 8.5 - 11; the high-temperature alkaline washing temperature is 130 - 240°C; In step (4), the reducing agent is one or at least two combinations of sulfur dioxide, sodium sulfite and methanol; the amount of the reducing agent added is 1.5 - 3 times the theoretical addition amount; In step (5), the temperature of the hot solution is 80 - 90°C; In step (5), the recovery rate of the prepared vanadium dioxide is ≥97.5wt%, and the purity is ≥98.7wt%.

2. The method for preparing vanadium dioxide by the equal pH precipitation method according to claim 1, characterized in that, In step (2), the dilute alkali solution is one or at least two combinations of sodium carbonate solution, sodium bicarbonate solution, magnesium hydroxide solution and basic magnesium carbonate solution.

3. The method for preparing vanadium dioxide by the equal pH precipitation method according to claim 1, characterized in that, In step (3), the dilute alkali solution is one or several combinations of sodium carbonate solution, sodium bicarbonate solution and sodium hydroxide solution.

4. The method for preparing vanadium dioxide by the equal pH precipitation method according to claim 1, characterized in that, In step (3), the time of the high-temperature alkaline washing is 2 - 5h.

5. The method for preparing vanadium dioxide by the equal pH precipitation method according to claim 1, characterized in that, In step (5), the dilute alkali solution is one or at least two combinations of sodium carbonate solution, sodium bicarbonate solution, sodium hydroxide solution and magnesium hydroxide solution.

Images