Vanadium precipitation mother liquor comprehensive utilization method

Abstract

The application discloses a comprehensive utilization method of vanadium precipitation mother liquor, and steps include: S1: vanadium and silicon in the vanadium precipitation mother liquor are removed first to obtain a decontamination liquid, vanadium precipitation and silicon residue, then the pH value of the decontamination liquid is adjusted and high-valence cations are precipitated and removed to obtain a purified liquid; S2: hexavalent chromium in the purified liquid is reduced to trivalent and precipitated to obtain chromium hydroxide and chromium precipitation mother liquor, and the chromium hydroxide precipitate is washed and calcined to obtain a chromium trioxide product; S3: hydrogen peroxide is added to the chromium precipitation mother liquor to oxidize excessive reducing agent, then heating evaporation is carried out to remove ammonia and decompose excessive hydrogen peroxide to obtain ammonia water and ammonia evaporation mother liquor; S4: the ammonia evaporation mother liquor is decomposed by adopting a bipolar membrane electrodialysis to obtain desalted water, sodium hydroxide solution and mixed acid solution of sulfuric acid and hydrochloric acid. The effect is that the chromium, vanadium and ammonia in the vanadium precipitation mother liquor can be recycled and utilized, the chromium trioxide product is obtained, and the resource utilization of the salt-containing wastewater can be realized.

Description

Technical Field

[0001] This invention relates to industrial wastewater treatment technology, specifically to a method for the comprehensive utilization of vanadium precipitation mother liquor. Background Technology

[0002] Vanadium slag obtained from vanadium-containing molten iron through converter blowing is the main raw material for vanadium extraction in my country. This vanadium slag undergoes a process of "oxidative roasting - purification and impurity removal - ammonium salt precipitation of vanadium," which yields ammonium polyvanadate but also generates a large amount of vanadium precipitation wastewater, known in the industry as vanadium precipitation mother liquor. The main components of vanadium precipitation mother liquor are sodium sulfate, ammonium sulfate, and small amounts of inorganic salts such as sodium chloride, as well as heavy metal ions such as chromium (VI) and vanadium (V). Due to its high salt and heavy metal content, vanadium precipitation mother liquor is difficult to reuse directly and falls far short of discharge standards, requiring proper treatment before reuse or discharge. Currently, production enterprises often use a "reduction to remove vanadium and chromium - deammoniation - MVR evaporation desalination" process to treat vanadium precipitation mother liquor. However, this process has the following drawbacks: 1. MVR evaporation desalination consumes a large amount of steam and is costly, and the evaporation produces mixed salts of sodium sulfate and sodium chloride, making subsequent recovery and utilization difficult; 2. Under acidic conditions, vanadium and chromium are simultaneously reduced by metabisulfite to obtain vanadium-chromium reduction slag, which is then selectively oxidized to extract and separate vanadium and chromium, resulting in a long, cumbersome, and costly process.

[0003] Currently, there are several patents addressing the recovery and utilization of vanadium and chromium from vanadium precipitation mother liquor. For example, patent 201910823295.5 uses an extraction method to simultaneously extract vanadium and chromium from the vanadium precipitation mother liquor. After calcium salt precipitation, the back-extraction liquid is concentrated by evaporation to obtain sodium chromate crystals. The vanadium-containing precipitate is mixed with the raffinate to dissolve the vanadium, which is then precipitated with ammonium salt to obtain ammonium metavanadate. This method can simultaneously recover vanadium and chromium from the vanadium precipitation mother liquor, but the process is relatively long. Patent 202110294130.0 discloses a method for comprehensive treatment of the liquid after vanadium slag extraction and vanadium precipitation using acidic ammonium salts. This method first heats to remove ammonia, then adds lead salts and iron salts or aluminum salts to precipitate chromium and vanadium in the solution after ammonia removal. Further treatment yields a vanadium-enriched product that can be used to produce vanadium pentoxide and a chromium-enriched liquid for the production of chromium chemical products. This method can recover vanadium and chromium from the vanadium precipitation mother liquor, but the added lead salts are toxic compounds, which can easily cause lead content in the wastewater to exceed the standard.

[0004] Therefore, there is an urgent need to develop a new technology for the resource utilization of vanadium precipitate mother liquor, which can recover valuable resources while reducing processing costs. Summary of the Invention

[0005] To address the problems mentioned in the background art, this invention provides a method for the comprehensive utilization of vanadium precipitate mother liquor, comprising the following steps:

[0006] S1. Purification of vanadium precipitation mother liquor: First, remove vanadium and silicon from the vanadium precipitation mother liquor to obtain impurity removal liquid, vanadium removal precipitate and silicon removal slag. Then, adjust the pH value of the impurity removal liquid and precipitate out high-valence cations to obtain purified liquid.

[0007] S2. Preparation of Chromium Trioxide Product: The hexavalent chromium in the purification solution is reduced to trivalent chromium and precipitated to obtain chromium hydroxide and chromium precipitation mother liquor. The chromium hydroxide precipitate is washed and calcined to obtain chromium trioxide product.

[0008] S3. Pretreatment of chromium precipitation mother liquor: Add hydrogen peroxide to the chromium precipitation mother liquor to oxidize the excess reducing agent, then heat and evaporate to remove ammonia and decompose the excess hydrogen peroxide to obtain ammonia water and ammonia-evaporated mother liquor.

[0009] S4. Electrodialysis treatment of ammonia stripping mother liquor: Bipolar membrane electrodialysis is used to decompose the ammonia stripping mother liquor to obtain demineralized water, sodium hydroxide solution and mixed acid solution of sulfuric acid and hydrochloric acid.

[0010] Optionally, in step S1, the pH of the vanadium precipitation mother liquor is first adjusted to 3-11, and the temperature is 25℃-95℃. Then, a vanadium and silicon removal precipitant is added and reacted for 10-60 minutes to precipitate and remove vanadium and silicon from the vanadium precipitation mother liquor.

[0011] Optionally, in step S1, vanadium removal and silicon removal precipitants are added in sequence and reacted for 10-30 minutes each, or vanadium removal and silicon removal precipitants are added simultaneously and reacted for 10-60 minutes.

[0012] Optionally, the vanadium-removing precipitant is one or more of ferric chloride, ferric sulfate, and calcium chloride, and the silicon-removing precipitant is one or more of magnesium chloride, magnesium sulfate, aluminum chloride, and aluminum sulfate.

[0013] Optionally, in step S2, the pH of the purification solution is first adjusted to 1-12 and the temperature is 0℃-100℃, and then a reducing agent is added and reacted for 30-120 minutes to reduce and precipitate hexavalent chromium.

[0014] Optionally, the reducing agent is one or more combinations of sodium sulfide, ammonium sulfide, sodium hydrosulfide, ammonium hydrogen sulfide, sodium sulfite, sodium metabisulfite, glucose, paraformaldehyde, and hydrazine hydrate.

[0015] Optionally, in step S2, water and chromium hydroxide are mixed at a ratio of 0.5 to 3:1 and stirred and washed at 25 to 75°C for 30 to 60 minutes; then the washed chromium hydroxide is calcined at 800 to 1200°C for 30 to 120 minutes.

[0016] Optionally, the heating and evaporation to remove ammonia and decompose excess hydrogen peroxide in step S3 refers to adjusting the pH value of the chromium precipitation mother liquor to 10-12, heating it to 80-95°C, and reacting for 30-180 minutes to evaporate and remove free ammonia and decompose excess hydrogen peroxide at high temperature.

[0017] Optionally, the use of bipolar membrane electrodialysis to decompose the ammonia-distilled mother liquor in step S4 refers to passing the ammonia-distilled mother liquor into the concentrate chamber of the bipolar membrane electrodialysis device, applying electricity and controlling the current density to be between 100 and 250 A / m. 2 Under the influence of an electric field, sodium ions in the ammonia stripping mother liquor migrate to the alkali chamber to obtain a 4-6 mol / L sodium hydroxide solution, while chloride and sulfate ions migrate to the acid chamber to obtain a 2-3 mol / L mixed solution of sulfuric acid and hydrochloric acid. After electrodialysis, the ammonia stripping mother liquor yields demineralized water with a flow rate of 0-15 ms / cm.

[0018] Optionally, the vanadium-free precipitate obtained in step S1 is recycled to the oxidative roasting process for vanadium extraction from vanadium slag, the demineralized water in step S4 is recycled back to the leaching process for vanadium extraction from vanadium slag, the sodium hydroxide solution is recycled back to adjust the pH of the vanadium precipitate mother liquor or sold externally, and the mixed acid solution of sulfuric acid and hydrochloric acid is sent to the pickling process of the steel rolling mill.

[0019] Compared with the prior art, the method for comprehensive utilization of vanadium precipitation mother liquor provided by the present invention has the following beneficial effects:

[0020] (1) Trivalent chromium can complex with ammonia to form [Cr(NH3)6]. 3+ This method can reduce the precipitation rate of chromium hydroxide and increase the ion rearrangement time, thereby reducing the amount of impurities adsorbed by chromium hydroxide. However, ammonia nitrogen in vanadium precipitation mother liquor usually needs to be removed by ammonia stripping under alkaline conditions. This invention organically combines the two, utilizing the existing ammonia in the vanadium precipitation mother liquor as a complexing agent. By reducing the precipitation rate of chromium hydroxide and reducing the adsorption and encapsulation of impurities during reduction, high-purity chromium trioxide can be prepared.

[0021] (2) The present invention can prepare chromium trioxide products from vanadium precipitation mother liquor through one reduction and calcination. Compared with the traditional process, which simultaneously reduces vanadium and chromium in vanadium precipitation mother liquor and then separates and extracts vanadium and chromium products from the vanadium-chromium reduction residue, the process is shorter, simpler to operate and has lower processing cost.

[0022] (3) This invention recovers vanadium and chromium from vanadium mother liquor by precipitation and removes high-valence cations. The relatively pure sodium sulfate and sodium chloride solution produced by ammonia evaporation is then used to prepare a mixed solution of sodium hydroxide and sulfuric acid and hydrochloric acid by bipolar membrane electrodialysis. Compared with the traditional MVR evaporation process, the processing cost is low and no difficult-to-treat sodium sulfate and sodium chloride impurities are produced. Attached Figure Description

[0023] Instruction manual illustrations

[0024] Figure 1 This is a process flow diagram of a method for comprehensive utilization of vanadium precipitation mother liquor disclosed in this invention.

[0025] Figure 2 The image shows the XRD pattern of chromium trioxide obtained in Example 1 of this invention.

[0026] Figure 3 The images show the SEM and XRD patterns of the chromium trioxide product obtained in Example 2 of this invention. Detailed Implementation

[0027] The present invention will now be described in detail through specific embodiments. It should be noted that these embodiments are only for further illustration and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description. Unless otherwise specified, all parts mentioned in the present invention are parts by weight, all percentages are mass percentages, and all concentrations are mass percentage concentrations.

[0028] like Figure 1 As shown, the present invention provides a method for comprehensive utilization of vanadium precipitation mother liquor, comprising the following steps:

[0029] S1. Purification of vanadium precipitation mother liquor: First, remove vanadium and silicon from the vanadium precipitation mother liquor to obtain impurity removal liquid, vanadium removal precipitate and silicon removal slag. Then, adjust the pH value of the impurity removal liquid and precipitate out high-valence cations to obtain purified liquid.

[0030] S2. Preparation of Chromium Trioxide Product: The hexavalent chromium in the purification solution is reduced to trivalent chromium and precipitated to obtain chromium hydroxide and chromium precipitation mother liquor. The chromium hydroxide precipitate is washed and calcined to obtain chromium trioxide product.

[0031] S3. Pretreatment of chromium precipitation mother liquor: Add hydrogen peroxide to the chromium precipitation mother liquor to oxidize the excess reducing agent, then heat and evaporate to remove ammonia and decompose the excess hydrogen peroxide to obtain ammonia water and ammonia stripping mother liquor.

[0032] S4. Electrodialysis treatment of ammonia stripping mother liquor: Bipolar membrane electrodialysis is used to decompose the ammonia stripping mother liquor to obtain demineralized water, sodium hydroxide solution and mixed acid solution of sulfuric acid and hydrochloric acid.

[0033] The significant effects of the present invention will be further illustrated below through specific implementation examples and comparative examples:

[0034] Example 1:

[0035] 1000 ml of vanadium pentoxide mother liquor (1.5 g / L, chromium 2.41 g / L, and silicon 0.47 g / L) was placed in a beaker. The pH of the mother liquor was adjusted to 4.5. 9.9 g of ferric sulfate was added, and the mixture was stirred at room temperature for 60 min. The mixture was filtered to obtain a vanadium-removed solution and ferric vanadate precipitate. The concentrations of vanadium, chromium, and silicon in the vanadium-removed solution were 0.06 g / L, 2.32 g / L, and 0.30 g / L, respectively, with precipitation rates of 94.7% and 36.2%, respectively. The pH of the vanadium-removed solution was adjusted to 9, and the mixture was heated to 90 °C. 4.3 g of magnesium chloride hexahydrate was added, and the mixture was stirred for 60 min. The mixture was filtered to obtain a silicon-removed solution and silicon-removed slag. The concentrations of vanadium, chromium, and silicon in the silicon-removed solution were... The concentrations were 0.045 g / L, 2.30 g / L, and 0.05 g / L, respectively, with a silicon removal rate of 83.3%. Sodium carbonate and ammonia were added to the silicon removal solution to adjust the pH to 12 and remove excess magnesium and iron ions. Then, 4.5 g of sodium sulfide was added, and the mixture was stirred at 90°C for 60 min. After standing, it was filtered to obtain 16.8 g of chromium precipitate residue and a chromium precipitation mother liquor. The chromium concentration in the chromium precipitation mother liquor was 0.005 g / L, and the chromium precipitation rate was 99.8%. The chromium precipitate residue and pure water were mixed at a solid-liquid ratio of 1:4 and stirred and washed at room temperature for 30 min. After filtration, it was vacuum dried to obtain chromium hydroxide. The chromium hydroxide was calcined at 950°C for 60 min to obtain chromium trioxide (XRD pattern shown). Figure 2 As shown in Table 1, 20 ml of 30% hydrogen peroxide was added to the chromium precipitation mother liquor and stirred at room temperature for 30 min. The pH of the solution was then adjusted to 11. Excess hydrogen peroxide in the solution was heated to decompose, and ammonia was evaporated to obtain ammonia water and ammonia-evaporized mother liquor. The cooled ammonia-evaporized mother liquor was pumped into the concentrate chamber of a bipolar membrane electrodialysis system. 500 ml of 0.05 mol / L sodium hydroxide and sulfuric acid solutions were added to the alkali and acid chambers, respectively. 500 ml of 0.05 mol / L sodium sulfate solution was used as the electrode solution. The bipolar membrane electrodialysis power supply was turned on, and the current density was adjusted to 150 A / m. 2 After 90 minutes of circulation, a sodium hydroxide solution with a hydroxide concentration of 4.1 mol / L was obtained in the alkali chamber, and a mixed solution of sulfuric acid and hydrochloric acid with a hydrogen ion concentration of 4.0 mol / L was obtained in the acid chamber. The conductivity of the original water decreased to 5.0 mS / cm.

[0036] Table 1: Composition of chromium trioxide obtained in this embodiment

[0037]

[0038] Example 2:

[0039] Take 1000 ml of vanadium precipitation mother liquor with a concentration of 1.41 g / L vanadium pentoxide, 6.89 g / L chromium, and 0.58 g / L silicon and place it in a beaker. Adjust the pH of the mother liquor to 10, add 3.5 g anhydrous calcium chloride and 8.1 g magnesium chloride hexahydrate, and stir the reaction at 90 °C for 90 min. Filter to obtain a purified liquor and a silicon-removed vanadium slag. The concentrations of vanadium, chromium, and silicon in the purified liquor are 0.08 g / L, 6.78 g / L, and 0.06 g / L, respectively. The vanadium and silicon precipitation removal rates are 90.1% and 89.7%, respectively. The obtained silicon-removed and vanadium slags can be returned for calcination roasting to extract vanadium. The calcination process involves adjusting the pH of the impurity-removing solution to 12 using sodium carbonate and ammonia to remove excess calcium and magnesium ions. Then, 9.4 g of ammonium sulfide is added, and the mixture is stirred at 95°C for 60 min. After settling, it is filtered to obtain 48.5 g of chromium precipitate residue and a chromium precipitation mother liquor. The chromium concentration in the chromium precipitation mother liquor is 0.006 g / L, and the chromium precipitation rate is 99.9%. The chromium precipitate residue and purified water are mixed at a solid-liquid ratio of 1:4 and stirred and washed at room temperature for 30 min. After filtration, it is vacuum dried to obtain chromium hydroxide. The chromium hydroxide is calcined at 1000°C for 40 min to obtain chromium trioxide (SEM and XRD images are shown below). Figure 3 (As shown); 58 ml of 30% hydrogen peroxide was added to the chromium precipitation mother liquor and stirred at room temperature for 30 min. Then, the excess hydrogen peroxide in the solution was decomposed by heating, and ammonia was evaporated to obtain ammonia water and ammonia-evaporized mother liquor. The cooled ammonia-evaporized mother liquor was pumped into the concentrate chamber of a bipolar membrane electrodialysis system. 500 ml of 0.05 mol / L sodium hydroxide solution and 500 ml of 0.05 mol / L sulfuric acid solution were added to the alkali chamber and acid chamber, respectively. The electrode solution was 500 ml of 0.05 mol / L sodium sulfate solution. The bipolar membrane electrodialysis power supply was turned on, and the current density was adjusted to 200 A / m. 2 After 90 minutes of circulation, a sodium hydroxide solution with a hydroxide concentration of 4.5 mol / L was obtained in the alkali chamber, and a mixed solution of sulfuric acid and hydrochloric acid with a hydrogen ion concentration of 4.3 mol / L was obtained in the acid chamber. The conductivity of the original water decreased to 3.3 mS / cm.

[0040] Example 3:

[0041] Take 1000 ml of vanadium pentoxide mother liquor (1.2 g / L, chromium 4.19 g / L, and silicon 0.51 g / L) and place it in a beaker. Adjust the pH of the mother liquor to 5.0, add 7.9 g of ferric sulfate and 9.31 g of aluminum sulfate, and react and stir at 80℃ for 60 min. Filter to obtain a purified liquid and a vanadium-silicon precipitate. The concentrations of vanadium, chromium, and silicon in the purified liquid are 0.03 g / L, 4.08 g / L, and 0.05 g / L, respectively, and the precipitation rates of vanadium and silicon are 97.5% and 90.2%, respectively. Adjust the pH of the purified liquid to 6.0 with sodium carbonate and ammonia to precipitate and remove excess iron and aluminum ions. Then, adjust the pH of the purified liquid back to 1.0. Add 20.31 g of sodium sulfite to reduce the hexavalent chromium ions in the purified liquid to trivalent ions. Then, slowly add ammonia to adjust the pH of the solution to 8.5, and stir and precipitate at 5℃ for 90 min. After standing, filter to obtain 3 chromium precipitate residues. 0.3g of chromium precipitation mother liquor was prepared, with a chromium concentration of 0.009g / L and a chromium precipitation rate of 99.79%. The chromium precipitate residue was mixed with purified water at a liquid-to-solid ratio of 1:3 and stirred and washed at 50℃ for 30min. After filtration, the mixture was vacuum dried to obtain chromium hydroxide. The chromium hydroxide was calcined at 1000℃ for 40min to obtain a product with a chromium trioxide content of 98.1%. 28ml of 30% hydrogen peroxide was added to the chromium precipitation mother liquor, and the mixture was stirred and reacted at room temperature for 30min. Then, excess hydrogen peroxide in the solution was heated to decompose the solution, and ammonia was evaporated to obtain ammonia water and ammonia-evaporated mother liquor. The cooled ammonia-evaporated mother liquor was pumped into the concentrate chamber of a bipolar membrane electrodialysis system. 500ml of 0.05mol / L sodium hydroxide and sulfuric acid solutions were added to the alkali and acid chambers, respectively. 500ml of 0.05mol / L sodium sulfate solution was used as the electrode solution. The bipolar membrane electrodialysis power supply was turned on, and the current density was adjusted to 100A / m³. 2 After 120 minutes of circulation, a sodium hydroxide solution with a hydroxide concentration of 3.8 mol / L was obtained in the alkali chamber, and a mixed solution of sulfuric acid and hydrochloric acid with a hydrogen ion concentration of 3.7 mol / L was obtained in the acid chamber. The conductivity of the original water decreased to 4.2 mS / cm.

[0042] Comparative example:

[0043] Take 1000 ml of vanadium pentoxide mother liquor (1.41 g / L, chromium 6.89 g / L, and silicon 0.58 g / L) and place it in a beaker. Adjust the pH of the mother liquor to 4.5, add 33.15 g of sodium metabisulfite, stir and react at room temperature for 60 min, and filter to obtain filtrate and vanadium-chromium precipitate residue. The vanadium-chromium precipitate residue contains 58.4 g of vanadium pentoxide, 31.94% chromium trioxide, and 0.8 mg / L chromium in the filtrate. The vanadium content is... 1.1 mg / L; After drying, the vanadium-chromium precipitate residue can be sold to chromium salt manufacturers as raw material for chromium extraction (price 200 yuan / t, drying cost 1000 yuan / t). Chromium green is prepared by "oxidative roasting-calcination-calcination-reduction precipitation of chromium". The pH of the filtrate is adjusted to 11, and ammonia nitrogen in the filtrate is removed by ammonia stripping. Then the pH of the filtrate is adjusted back to 7. Condensate and sodium sulfate-sodium chloride mixed salt are obtained by MVR evaporation. The condensate can be returned to production and the sodium sulfate-sodium chloride mixed salt is temporarily stored.

[0044] The comparison clearly shows that the method provided by this invention can recover and utilize chromium, vanadium, and ammonia from vanadium precipitation mother liquor to obtain chromium trioxide, and can also realize the resource utilization of saline wastewater. Specifically, Examples 1 and 2 demonstrate that by using vanadium precipitation mother liquor with different chromium concentrations, vanadium and silicon are removed beforehand, and high-quality chromium trioxide can be obtained by sodium sulfide reduction and high-temperature calcination under alkaline conditions in the presence of ammonia. The solution after chromium precipitation can be processed by ammonia stripping and bipolar membrane electrolysis to obtain sodium hydroxide solution and a sulfuric acid + hydrochloric acid mixed solution. Example 3 shows that by first removing vanadium and silicon from the vanadium precipitation mother liquor, reducing chromium with sodium sulfite under acidic conditions, and precipitating trivalent chromium in the presence of ammonia followed by calcination, high-quality chromium trioxide can also be obtained. The solution after chromium precipitation can also be processed by ammonia stripping and bipolar membrane electrolysis to obtain sodium hydroxide solution and a sulfuric acid + hydrochloric acid mixed solution. Compared with the comparative examples, Examples 1-3, through the process of "impurity removal-reduction of chromium-ammonia stripping-electrodialysis", can not only recover vanadium and chromium from the vanadium precipitation mother liquor, but also convert high-salt wastewater into sodium hydroxide solution and sulfuric acid + hydrochloric acid mixed solution, thus realizing the resource utilization of the vanadium precipitation mother liquor.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the comprehensive utilization of vanadium precipitation mother liquor, characterized in that, Includes the following steps: S1. Purification of vanadium precipitation mother liquor: First, adjust the pH of the vanadium precipitation mother liquor to 3-11 and the temperature to 25℃-95℃; then add the vanadium removal precipitant and silicon removal precipitant in sequence, reacting for 10-30 minutes each, to precipitate and remove vanadium and silicon from the vanadium precipitation mother liquor, obtaining a purified liquid, vanadium removal precipitate, and silicon removal slag; or add the vanadium removal precipitant and silicon removal precipitant simultaneously and react for 10-60 minutes, then filter to obtain a purified liquid and silicon removal vanadium slag; finally, adjust the pH of the purified liquid and precipitate to remove high-valence cations, obtaining a purified liquid; S2. Preparation of Chromium Trioxide: First, adjust the pH of the purification solution to 1-12 and the temperature to 0-100℃. Then, add a reducing agent and react for 30-120 minutes to reduce hexavalent chromium to trivalent chromium. Next, add ammonia to adjust the pH and form [Cr(NH3)6] through complexation of trivalent chromium and ammonia. 3+ The precipitation rate of chromium hydroxide is reduced, and chromium hydroxide and chromium precipitation mother liquor are obtained through precipitation. The chromium hydroxide precipitate is washed and calcined to obtain chromium trioxide product. S3. Pretreatment of chromium precipitation mother liquor: Add hydrogen peroxide to the chromium precipitation mother liquor to oxidize the excess reducing agent, then heat and evaporate to remove ammonia and decompose the excess hydrogen peroxide to obtain ammonia water and ammonia stripping mother liquor. S4. Electrodialysis treatment of ammonia stripping mother liquor: Bipolar membrane electrodialysis is used to decompose the ammonia stripping mother liquor to obtain demineralized water, sodium hydroxide solution and mixed acid solution of sulfuric acid and hydrochloric acid.

2. The method for comprehensive utilization of vanadium precipitation mother liquor according to claim 1, characterized in that: The vanadium removal precipitant is one or more of ferric chloride, ferric sulfate, and calcium chloride, and the silicon removal precipitant is one or more of magnesium chloride, magnesium sulfate, aluminum chloride, and aluminum sulfate.

3. The method for comprehensive utilization of vanadium precipitation mother liquor according to claim 1, characterized in that: The reducing agent is one or more combinations of sodium sulfide, ammonium sulfide, sodium hydrosulfide, ammonium hydrogen sulfide, sodium sulfite, sodium metabisulfite, glucose, paraformaldehyde, and hydrazine hydrate.

4. The method for comprehensive utilization of vanadium precipitation mother liquor according to claim 3, characterized in that: In step S2, water and chromium hydroxide are mixed at a ratio of 0.5 to 3:1 and stirred and washed at 25 to 75°C for 30 to 60 minutes; then the washed chromium hydroxide is calcined at 800 to 1200°C for 30 to 120 minutes.

5. The method for comprehensive utilization of vanadium-precipitated mother liquor according to claim 1, 3, or 4, characterized in that: The heating, evaporation, deammoniation, and decomposition of excess hydrogen peroxide mentioned in step S3 refers to adjusting the pH value of the chromium precipitation mother liquor to 10-12, heating it to 80-95℃, and reacting for 30-180 minutes to evaporate and remove free ammonia and decompose excess hydrogen peroxide at high temperature.

6. The method for comprehensive utilization of vanadium precipitation mother liquor according to claim 1, characterized in that: The step S4, which describes the use of bipolar membrane electrodialysis to decompose the ammonia-distilled mother liquor, refers to passing the ammonia-distilled mother liquor into the concentrate chamber of a bipolar membrane electrodialysis device, applying electricity, and controlling the current density to be between 100 and 250 A / m. 2 Under the influence of an electric field, sodium ions in the ammonia stripping mother liquor migrate to the alkali chamber to obtain a 4-6 mol / L sodium hydroxide solution, while chloride and sulfate ions migrate to the acid chamber to obtain a 2-3 mol / L mixed solution of sulfuric acid and hydrochloric acid. After electrodialysis, the ammonia stripping mother liquor yields demineralized water with a flow rate of 0-15 ms / cm.

7. The method for comprehensive utilization of vanadium precipitation mother liquor according to claim 1, characterized in that: The vanadium precipitate obtained in step S1 is transported to the oxidative roasting process for vanadium extraction from vanadium slag for reuse. The demineralized water in step S4 is returned to the leaching process for vanadium extraction from vanadium slag for reuse. The sodium hydroxide solution is returned to adjust the pH value of the vanadium precipitate mother liquor or sold externally. The mixed acid solution of sulfuric acid and hydrochloric acid is sent to the pickling process of the steel rolling mill.

Images