Method and system for removing vanadium from vanadium extraction wastewater and recovering ferric vanadate

Abstract

This invention discloses a method and system for vanadium extraction wastewater treatment and ferric vanadate recovery, belonging to the field of vanadium-containing wastewater treatment. The method includes: circulating wastewater into multiple equalization tanks; simultaneously adding precipitated sludge from a thickener and polyferric sulfate, and stirring the reaction; after stopping the injection, continuing to add polyferric sulfate to adjust the pH to weakly acidic, stirring, and allowing it to settle to form ferric vanadate precipitate; sending the supernatant from the equalization tanks to the reaction tank, adjusting the pH, adding flocculant, reacting, and then separating in the thickener; returning the precipitated sludge to the equalization tank currently used for vanadium extraction wastewater injection, and the supernatant entering subsequent processes; the ferric vanadate precipitate at the bottom of the equalization tank being filtered to obtain ferric vanadate filter sludge; the system includes at least two equalization tanks, one reaction tank, and one thickener. This invention achieves the recovery and utilization of ferric hydroxide by returning the precipitated sludge from the thickener, reducing the amount of polyferric sulfate added, significantly reducing operating costs, and increasing the ferric vanadate content in the filter sludge.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment of vanadium-containing wastewater, and in particular to a method and system for removing vanadium and recovering ferric vanadate from vanadium-extraction wastewater. Background Technology

[0002] Vanadium is an important rare metal element, often referred to as "industrial MSG." In vanadium extraction processes using vanadium-titanium magnetite as raw material, the ore undergoes blast furnace smelting and converter blowing to obtain chromium-vanadium slag. Subsequent processes such as sodium roasting and water leaching produce vanadium extraction wastewater. This wastewater is extremely toxic and cannot be directly discharged, but it also contains valuable vanadium, making it of significant recovery value. Among various vanadium recovery methods (ferric vanadate precipitation, ion exchange, solvent extraction, complexation separation, adsorption, electrolysis, etc.), ferric vanadate precipitation is one of the most commonly used methods in factories.

[0003] According to the process recommended by Yang Shaoli et al. in the "Comprehensive Utilization Technology Manual for Vanadium-Titanium Magnetite," the existing technology uses a stirred intermittent reactor for precipitation reaction. Specific conditions are: adding ferric sulfate to the wastewater and stirring evenly; controlling the final pH value to be 4.5-5.5 (usually adjusted to around 5); the molar ratio of iron to vanadium (n(Fe) / n(V)) to be 14-15; and the reaction temperature to be 60-80℃. After the precipitation reaction is complete, the addition of flocculant PAM to aid sedimentation can be determined experimentally, followed by pressure filtration and online washing of the filter cake. Leading domestic vanadium enterprises use this method to treat vanadium-precipitated wastewater, achieving a vanadium recovery rate of 80%-90%; the V2O5 content of the obtained "ferric vanadate" recovery product is generally 8%-17%, and the Fe2O3 content is generally 32%-43%. While the sludge generated from vanadium extraction wastewater can be used as a raw material for vanadium recovery, it contains not only ferric vanadate but also a large amount of ferric hydroxide. During the subsequent recovery of ferric vanadate, ferric hydroxide, as an impurity, needs to be removed through calcination, acid leaching, and alkali precipitation, resulting in significant waste of energy, acid, and alkali. Therefore, existing technologies suffer from the problems of high ferric sulfate consumption and high ferric hydroxide content in the resulting filter press sludge. Reducing the ferric hydroxide content in the sludge is of significant practical importance for environmental protection and cost reduction. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a method and system for recovering ferric vanadate from vanadium extraction wastewater, thereby addressing the technical issues of high ferric sulfate dosage and high ferric hydroxide content in the resulting filter press sludge in existing vanadium extraction wastewater treatment processes. This invention achieves the recovery and utilization of ferric hydroxide from the sludge by recirculating the sludge from the thickening tank to the equalization tank, and increases the vanadium content in the equalization tank by increasing the vanadium pentavalent (V2) content. 5+ ) and trivalent iron (Fe 3+This increases the concentration of ferric vanadate in the filter press mud obtained from the first sedimentation, reduces the proportion of impurity ferric hydroxide, reduces energy and reagent consumption in subsequent treatment processes, and improves environmental and economic benefits.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater includes the following steps: Step 1: Continuously inject vanadium extraction wastewater into a regulating tank until the liquid level reaches the predetermined value, then switch to the next regulating tank to continue injection, and repeat the cycle. Step 2: While injecting vanadium extraction wastewater into each equalization tank, add precipitated sludge from the thickening tank to the equalization tank, add polyferric sulfate, stir and mix thoroughly, and carry out the reaction. Adding ferric vanadate sludge from the thickener to the equalization tank increases the concentration of ferric vanadate, making it easier to precipitate, thus resulting in ferric vanadate precipitate in the equalization tank. The precipitate sludge from the thickener added to the equalization tank contains ferric hydroxide colloids, which, under acidic conditions, have already reacted to form Fe. 3+ Its existence reduces the amount of polyferric sulfate used, lowering operating costs. It can save over 50% on polyferric sulfate.

[0006] Step 3: After stopping the injection of vanadium extraction wastewater and the addition of sediment sludge from the thickening tank, continue to add polyferric sulfate to adjust the pH of the mixed solution in the adjustment tank to weak acidity. Then stir and mix, let it stand to precipitate, and generate ferric vanadate precipitate. Step 4: The supernatant after settling in the equalization tank is sent to the reaction tank, the pH is adjusted and flocculant is added to carry out flocculation reaction. The mixture after reaction enters the thickening tank and is separated to obtain precipitated sludge and supernatant. The precipitated sludge is returned to the equalization tank where vanadium extraction wastewater is currently being injected, and the supernatant enters the subsequent process. In existing technologies, the precipitated sludge (co-precipitated ferric hydroxide colloid and ferric vanadate) in the thickening tank directly enters the filter press, forming a vanadium-containing sludge cake, which then enters the recovery process. Ferric hydroxide, as an impurity, reduces the vanadium content of the vanadium-containing sludge cake, increasing the difficulty of recovery. In this invention, however, the flocculated precipitated sludge is used to recover Fe as an iron salt. 3+ This reduces the amount of polyferric sulfate used, thus lowering costs; it also reduces the sulfate concentration in wastewater, reducing the amount of sulfate to be treated subsequently, further lowering costs; the vanadium concentration in the supernatant is reduced to less than 1 mg / L, which meets the "Vanadium Industry Pollutant Emission Standard" (GB26452-2011).

[0007] Step 5: Send the ferric vanadate precipitate generated at the bottom of the equalization tank into a filter press to obtain ferric vanadate filter mud.

[0008] A further improvement to the technical solution of this invention lies in the following: In step 1, the pH of the vanadium extraction wastewater is controlled to be 2-3; if the original pH of the vanadium extraction wastewater is higher than 3, sulfuric acid is added to adjust it to 2-3. The sludge precipitated in the thickener is returned to the equalization tank to enrich V and Fe, and under pH 2-3 conditions, the ferric hydroxide colloid reacts again to Fe. 3+ This can reduce the amount of polyferric sulfate used; V 5+ As the iron is enriched and its concentration increases, ferric vanadate precipitates. The elemental content of Fe in the filter press mud is significantly reduced, while V is significantly increased.

[0009] A further improvement to the technical solution of this invention lies in: in steps 2 and 3, the reaction temperature in the regulating tank is 60℃~80℃; based on V in the vanadium extraction wastewater... 5+ The total amount of polyferric sulfate added is determined by the concentration of vanadium, and the molar ratio of iron to vanadium is controlled at 14–15. After stopping the injection of vanadium extraction wastewater into the equalization tank and the addition of precipitated sludge, the amount of polyferric sulfate added is then determined based on the V6 concentration in the vanadium extraction wastewater. 5+ The concentration of polyferric sulfate was used to determine the total amount added, ensuring that the pH and V values ​​in the equalization tank would not fluctuate due to changes in the influent water quality. 5+ Concentration fluctuations create a stable environment.

[0010] A further improvement to the technical solution of this invention lies in the following: In step 3, the pH of the mixed solution in the adjustment tank is adjusted to 3.5–4.5; and the mixture is allowed to settle for 6–24 hours. After the reaction, the pH of the adjustment tank is adjusted to a slightly acidic level, which can control the amount of Fe. 3+ Ferric hydroxide colloid and ferric vanadate form a complex, which then precipitates upon standing. Compared to the original process, the ferric vanadate content of this precipitate is significantly increased, with most of the Fe... 3+ The form still exists in the solution.

[0011] A further improvement of the technical solution of this invention lies in the fact that the number of equalization tanks is 2 to 4; the capacity of each equalization tank can meet the treatment requirements for continuous influent for 12 to 24 hours. During production, the influent, pH adjustment, settling, and effluent discharge are carried out in rotation, ensuring the effect of settling and sedimentation, and allowing the effluent from the equalization tank to remain stable for 12 to 24 hours. This solves the problem of large fluctuations in the quality and quantity of vanadium extraction wastewater and its difficulty in treatment, facilitating precise control of the dosage in subsequent production and reducing reagent waste.

[0012] A further improvement to the technical solution of this invention lies in: in step 4, the pH of the supernatant fed into the reaction tank is adjusted to 5-6, and then a flocculant is added. The supernatant in the adjustment tank carries some V... 5+ and Fe 3+ The mixture is introduced into the reaction tank, and liquid alkali is added to adjust the pH to 5-6. After flocculation reaction V... 5+ and Fe 3+ It transforms into ferric vanadate precipitate and ferric hydroxide colloid.

[0013] A further improvement of the technical solution of the present invention is that the flocculant is polyacrylamide.

[0014] A system for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater includes: At least two equalization tanks are provided, each equipped with an inlet, a stirring device, a dosing port, a sludge discharge port, and a supernatant outlet. The at least two equalization tanks are used to receive vanadium extraction wastewater in sequence and alternately. The reaction tank has its inlet connected to the supernatant outlet of each equalization tank. A concentration tank, the inlet of which is connected to the outlet of the reaction tank, is provided with a supernatant discharge outlet and a precipitate outlet; The return pipeline is connected at one end to the sediment outlet of the thickener and at the other end to the inlet of the equalization tank. The plate and frame filter press has its inlet connected to the sludge discharge port of each equalization tank.

[0015] A further improvement of the technical solution of the present invention is that: the front end of the regulating tank is provided with a mud-water mixing tank connected to the regulating tank, and the mud-water mixing tank is provided with a homogenizing stirrer.

[0016] A further improvement of the technical solution of the present invention is that the bottom of the equalization tank and the thickening tank are conical or sloping, and are equipped with a sludge scraper. This facilitates the collection of settled sludge.

[0017] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows: This invention achieves the recycling of ferric hydroxide by returning the secondary precipitate (mainly containing ferric hydroxide) in the concentration tank to the equalization tank, thereby effectively reducing the amount of polyferric sulfate added and significantly reducing operating costs.

[0018] Because the amount of polyferric sulfate used in this invention is reduced, the concentration of sulfate in the wastewater is correspondingly reduced, which in turn significantly reduces the power consumption in the subsequent MVR evaporation and crystallization process.

[0019] This invention employs an operation mode in which multiple equalization tanks alternately receive water, react, settle, and discharge water. This effectively overcomes the treatment challenges caused by large fluctuations in the quality and quantity of vanadium extraction wastewater, providing stable influent conditions for subsequent processes and reducing the waste of reagents.

[0020] This invention significantly improves the purity of ferric vanadate precipitate in the equalization tank through a reflux enrichment process, resulting in a higher ferric vanadate content in the obtained vanadium-containing sludge cake and effectively suppressing interference from impurity ferric hydroxide. After treatment by this invention, the V2O5 content in the recovered ferric vanadate product increases from the original 8%–17% to over 23%, while the Fe2O3 content decreases from the original 32%–43% to below 30%, demonstrating significant economic and environmental benefits. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a schematic diagram of a method and system for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater provided in an embodiment of the present invention; The components include: 1. Equalization tank; 1-1. Sludge-water mixing tank; 1-1-1. Homogenizer; 1-2. First sludge scraper; 2. Reaction tank; 2-1. Reaction agitator; 3. Thickening tank; 3-1. Second sludge scraper; 4. Filter; 5. Plate and frame filter press; 6. First transfer pump; 7. Second transfer pump; 8. Third transfer pump; 9. First sludge pump; 10. Second sludge pump. Detailed Implementation

[0022] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification, claims and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product or device.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: like Figure 1 As shown, the system used in the process of vanadium extraction wastewater vanadium removal and ferric vanadate recovery provided by the present invention includes four equalization tanks 1 (A, B, C, and D respectively), one reaction tank 2, and one concentration tank 3. Each equalization tank 1 is equipped with an inlet, a stirring device (not shown in the figure), a chemical dosing port, a sludge discharge port, and a supernatant outlet. The four equalization tanks are used to receive vanadium extraction wastewater in sequence. Each equalization tank 1 is connected to a sludge-water mixing tank 1-1 at its front end, and each sludge-water mixing tank 1-1 is equipped with a homogenizing stirrer 1-1-1.

[0024] The bottom of the equalization tank 1 is conical or sloping (to facilitate the collection of settled sludge) and is equipped with a first sludge scraper 1-2. A first sludge pump 9 is installed at the sludge discharge port of each equalization tank 1, and the first sludge pump 9 is connected to a plate and frame filter press 5 via a pipeline. A first transfer pump 6 is installed at the supernatant outlet of each equalization tank 1 to pump the supernatant into the reaction tank 2. A second transfer pump 7 is installed at the discharge port of the plate and frame filter press 5 to return the filtrate discharged from the plate and frame filter press 5 to the reaction tank 2. A sludge collection and discharge system is installed at the bottom of the equalization tank 1. The first sludge pump 9 can be directly connected to the plate and frame filter press 5, or it can be connected to the plate and frame filter press 5 after concentration. The settled sludge at the bottom of the equalization tank 1 is compressed by the plate and frame filter press 5 to obtain vanadium-containing sludge cake.

[0025] A reaction stirrer 2-1 is installed in reaction tank 2. The inlet of reaction tank 2 is connected to the supernatant outlet of each equalization tank 1. A third transfer pump 8 is installed at the outlet of reaction tank 2 to pump the reaction mixture in reaction tank 2 into concentration tank 3 for precipitation.

[0026] The thickener 3 is equipped with a second sludge scraper 3-1, the inlet of which is connected to the outlet of the reaction tank 2. The thickener 3 has a supernatant discharge outlet and a sediment outlet; a second sludge pump 10 is installed at the sediment outlet of the thickener 3 to pump the settled sludge in the thickener 3 into the return pipeline and back to the equalization tank 1. The bottom of the thickener 3 is conical or sloping.

[0027] One end of the return pipeline is connected to the sediment outlet of the thickener 3, and the other end is connected to the inlet of the equalization tank 1. A filter 4 is also installed on the return pipeline to filter the settled sludge before it is fed into the equalization tank 1, and the filtrate produced by filtration is returned to the thickener 3.

[0028] The composition analysis data of the vanadium extraction wastewater to be treated are as follows: V 5+ 0.12~0.15g / L, flow rate 50m³ 3 / h, pH 2~2.5, temperature 60~80℃.

[0029] A method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater includes the following: (1) The capacity of the four regulating tanks 1 (A, B, C, and D respectively) is 1000m³. 3 The vanadium extraction wastewater to be treated is injected in turn; the larger the capacity of the equalization tank 1 and the longer the water inlet time, the more stable the water quality, which solves the problem of difficult treatment and waste of reagents caused by large fluctuations in the water quality and quantity of vanadium extraction wastewater.

[0030] (2) First, continuously inject vanadium extraction wastewater into the A equalization tank for 12 hours (flow rate 50 m³ / h). 3 / h, pH 2~2.5), while adding sediment sludge from the thickener (flow rate 5m³ / h).3 (pH 6) and a small amount of polyferric sulfate.

[0031] (3) Stop injecting vanadium extraction wastewater into the A equalization tank and sedimentation sludge into the thickener tank, and measure V. 5+ Polyferric sulfate was precisely added after the concentration was determined, controlling the molar ratio of iron to vanadium in the mixture, n(Fe) / n(V), to be 14-15, and controlling the final pH value of the reaction to be 3.5-4.5. Monitoring and precise dosing were only carried out after stopping the addition of vanadium extraction wastewater to the A equalization tank and the sedimentation sludge from the thickener. This approach ensures that the pH and V values ​​in the equalization tank are not affected by fluctuations in the influent water quality. 5+ Concentration fluctuations create a stable environment.

[0032] The sludge from the thickener added to the equalization tank contains ferric hydroxide colloids. Under acidic conditions, the ferric hydroxide has already reacted to Fe. 3+ Its existence saves on the amount of polyferric sulfate used, reduces operating costs, and can save more than 50% on polyferric sulfate.

[0033] Adding ferric vanadate sludge from the thickening tank to the equalization tank increases the concentration of ferric vanadate, making it easier for it to precipitate, thus obtaining ferric vanadate precipitate in the equalization tank.

[0034] (4) The wastewater mixture in equalization tank A was stirred for 3 hours (the stirrer in the equalization tank is a standard configuration and is not shown in the figure), and then left to stand for 21 hours. A precipitate was obtained under weakly acidic conditions. The precipitate was mainly ferric vanadate (ferric hydroxide had already reacted to Fe). 3+ (It exists in the supernatant). The precipitate is pumped into a plate and frame filter press for filtration, and the filtration yields ferric vanadate filter mud with a high ferric vanadate content.

[0035] A sludge collection and discharge system is installed at the bottom of the equalization tank. The sludge discharge pump can be directly connected to a plate and frame filter press, or it can be connected to the plate and frame filter press after concentration. Vanadium-containing sludge cake is obtained. Compared to the original process, this vanadium-containing sludge cake has a higher ferric vanadate content.

[0036] The supernatant after settling in the equalization tank is sent to the reaction tank, and the drainage time is 12 hours.

[0037] (5) Perform the same operation on B, C and D in turn according to steps (2) to (4) to form a cyclic operation of A, B, C, D, A, B, C, D...

[0038] (6) In the reaction tank, the pH value is adjusted to about 5-6; after the precipitation reaction is completed, add anionic flocculant PAM (polyacrylamide, 0.60 kg / m³). 3The sediment is then precipitated and then enters a thickener to obtain thickener slurry and vanadium-removed supernatant. The thickener slurry is returned to the equalization tank where vanadium extraction wastewater is currently being injected, while the thickener supernatant enters the subsequent process.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater, characterized in that, Includes the following steps: Step 1: Continuously inject vanadium extraction wastewater into a regulating tank until the liquid level reaches the predetermined value, then switch to the next regulating tank to continue injection, and repeat the cycle. Step 2: While injecting vanadium extraction wastewater into each equalization tank, add precipitated sludge from the thickening tank to the equalization tank, add polyferric sulfate, stir and mix thoroughly, and carry out the reaction. Step 3: After stopping the injection of vanadium extraction wastewater and the addition of sediment sludge from the thickening tank, continue to add polyferric sulfate to adjust the pH of the mixed solution in the adjustment tank to weak acidity. Then stir and mix, let it stand to precipitate, and generate ferric vanadate precipitate. Step 4: The supernatant after settling in the equalization tank is sent to the reaction tank, the pH is adjusted and flocculant is added to carry out flocculation reaction. The mixture after reaction enters the thickening tank and is separated to obtain precipitated sludge and supernatant. The precipitated sludge is returned to the equalization tank where vanadium extraction wastewater is currently being injected, and the supernatant enters the subsequent process. Step 5: Send the ferric vanadate precipitate generated at the bottom of the equalization tank into a filter press to obtain ferric vanadate filter mud.

2. The method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to claim 1, characterized in that, In step 1, the pH of the vanadium extraction wastewater is controlled to be 2-3; if the original pH of the vanadium extraction wastewater is higher than 3, sulfuric acid is added to adjust it to 2-3.

3. The method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to claim 1, characterized in that, In steps 2 and 3, the reaction temperature in the regulating tank is 60℃~80℃; based on the V in the vanadium extraction wastewater... 5+ The total amount of polyferric sulfate added is determined by the concentration of iron, and the molar ratio of iron to vanadium is controlled to be 14-15.

4. The method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to claim 1, characterized in that, In step 3, the pH of the mixed solution in the adjustment tank is adjusted to 3.5-4.5; and the mixture is allowed to stand for 6-24 hours to settle.

5. The method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to claim 1, characterized in that, The number of equalization tanks is 2 to 4; the capacity of each equalization tank can meet the treatment requirements for continuous water intake for 12 to 24 hours.

6. The method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to claim 1, characterized in that, In step 4, the pH of the supernatant sent into the reaction tank is adjusted to 5-6, and then flocculant is added.

7. The method for removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to claim 1, characterized in that, The flocculant is polyacrylamide.

8. A system for the method of removing vanadium and recovering ferric vanadate from vanadium extraction wastewater according to any one of claims 1-7, characterized in that, include: At least two equalization tanks are provided, each equipped with an inlet, a stirring device, a dosing port, a sludge discharge port, and a supernatant outlet. The at least two equalization tanks are used to receive vanadium extraction wastewater in sequence and alternately. The reaction tank has its inlet connected to the supernatant outlet of each equalization tank. A concentration tank, the inlet of which is connected to the outlet of the reaction tank, is provided with a supernatant discharge outlet and a precipitate outlet; The return pipeline is connected at one end to the sediment outlet of the thickener and at the other end to the inlet of the equalization tank. The plate and frame filter press has its inlet connected to the sludge discharge port of each equalization tank.

9. The system according to claim 8, characterized in that, The regulating tank is connected to a mud-water mixing tank at its front end, and a homogenizing agitator is installed in the mud-water mixing tank.

10. The system according to claim 8, characterized in that, The bottom of the equalization tank and the concentration tank are conical or sloping, and are equipped with sludge scrapers.

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