A method for in situ removal of vanadium from wastewater

Abstract

This invention provides a method for in-situ removal of vanadium from wastewater. The method involves first adjusting the pH to acidity and then alkalinity, thereby controlling the degree of vanadium hydrolysis and disrupting the stable form of (meta)vanadate in the wastewater, causing it to primarily exist as VO2(OH)2. ‑ Vanadium exists in the form of vanadium, and when Fe(II) is added, it undergoes a redox reaction with V(V) in the wastewater, effectively reducing vanadium(V) in the wastewater to V, which has lower toxicity and is relatively unstable. 2+ (VI) Reduce wastewater toxicity; then adjust to an alkaline environment, utilizing the interaction of hydroxide ions, iron, and vanadium to precipitate vanadium into VO2·H2O and Fe2O3·V2O5·H2O, thus achieving vanadium removal. The entire process of this invention is easy to control, has a high vanadium removal rate, and requires a small amount of reducing agent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment and relates to a method for removing vanadium from wastewater. BACKGROUND

[0002] Vanadium is an important alloying element, which is mainly used in steel, aerospace, chemical industry and other fields. With the increasing use of vanadium, the content of vanadium in the environment is continuously accumulating, which may pose a great threat to the health of humans, animals and plants. Vanadium mainly exists in two valence states in the environment, namely, tetravalent and pentavalent, and pentavalent vanadium is more toxic and has a certain stability. Therefore, it is necessary to eliminate excess vanadium in wastewater and reduce the valence state of vanadium before the wastewater containing vanadium is discharged into the environment system, in order to protect human health and the ecological system.

[0003] Currently, the commonly used methods for treating wastewater containing vanadium at home and abroad mainly include chemical precipitation, ion exchange, adsorption, electrolysis and biological methods. For example, Guan Hongliang et al. based on the generation of polyammonium polyvanadate precipitate from metavanadate and ammonium salt under weak acid conditions, and used ammonium chloride to remove vanadium from wastewater. Wang S. et al. used carboxymethyl chitosan as an adsorbent to remove vanadium from pipeline crude oil under the action of microwaves, and found that the amino group (-NH2) and carboxyl group (-COO-) on the adsorbent had good effect on the removal of vanadium. Adedayo Bello et al. used Fe extracted from sludge to modify kaolin, and the surface complexation of hydroxyl groups in the shell with Fe and V was the main mechanism for adsorbing metal vanadium in wastewater. This study has good removal effect on vanadium in wastewater, but the preparation steps of the adsorbent are complicated, which increases the process flow.

[0004] CN114835097A discloses a method for removing pentavalent vanadium from wastewater by adding phosphorus iron slag after acidification, reducing pentavalent vanadium through chemical reaction, and precipitating vanadium by adding alkali. The method achieves the conversion and resource utilization of phosphorus iron slag, and reduces the treatment cost. However, the method is mainly used for treating wastewater containing high-concentration vanadium (1g / L-2g / L), and the removal rate of vanadium in the wastewater can reach more than 99%, but the effluent still needs subsequent treatment, and it is difficult to directly meet the discharge standard.

[0005] CN110104834A discloses a method for treating vanadium and cadmium in wastewater, which adds ferrous sulfate to wastewater containing vanadium to react, adjusts the pH to generate iron vanadate precipitate, and uses amino phosphoric acid resin to adsorb and remove the chromium-containing solution. The invention effectively removes metal vanadium and nickel in wastewater, but the recovery rate is only about 90%, and the addition of ferrous sulfate leads to the residual of iron ions in the treated wastewater, causing secondary pollution.

[0006] CN102795721A discloses a kind of acidic vanadium precipitation wastewater treatment method, to wastewater is added solid sodium pyrosulfite reduction, with Fe (II) is reduced again, by adding lime powder, precipitate vanadium, cadmium, iron in wastewater.The invention has good removal effect on vanadium and cadmium in wastewater, but a large amount of reducing reagent needs to be added, which increases the cost of wastewater treatment. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a method for removing vanadium in wastewater in situ, which adjusts the existence form of vanadium in wastewater by adjusting the pH value of wastewater, then adds Fe (II), adjusts the pH value to make vanadium in wastewater react to form a precipitate, thereby achieving the purpose of removal.

[0008] The technical purpose of the present application is achieved by the following technical solutions:

[0009] A method for removing vanadium in wastewater in situ, comprising the following steps:

[0010] (1) first adjust the pH of vanadium-containing wastewater to 1-4, and adjust the pH to 5-8 by adding alkali at 30-60°C;

[0011] (2) add ferrous salt to the wastewater and react;

[0012] (3) adjust the pH of the wastewater to 8-10 by adding alkali, and form a precipitate after reaction.

[0013] In the above technical solution, the present application first adjusts the pH value of wastewater to change the existence form of vanadium in wastewater, so that it mainly exists in the form of VO2(OH)2-, then adds Fe (II) to react with V (V) in wastewater, and then adjusts to an alkaline environment to utilize the interaction of hydroxyl, iron and vanadium to make vanadium generate precipitates VO2·H2O and Fe2O3·V2O5·H2O. The reaction principle in the whole process is as follows:

[0014]

[0015]

[0016] VO 2+ +2OH - →VO2·H2O(s)

[0017] The vanadium-containing wastewater in the present application refers to wastewater containing a certain concentration of high-valence vanadium generated in industrial production process. The wastewater may also inevitably contain other metals and organic pollutants. In the present application, the wastewater treated is mainly polluted by metallic vanadium, and the concentration of other pollutants may be reduced during the treatment process to improve the efficiency of wastewater treatment.

[0018] Further, the strong acid or strong base used in step (1) to adjust the pH is sulfuric acid, sodium hydroxide solution or potassium hydroxide solution, and the mass concentration is 1-10%, preferably 5-8%.

[0019] Further, in step (1), the pH of the wastewater is adjusted to 2-3 with a strong acid to acidify the pollutants in the wastewater.

[0020] Further, the pH range for adding alkali in step (1) is preferably 6-7, which can effectively control the degree of vanadium hydrolysis at different pH values, destroy the stable form of (meta)vanadate in the wastewater, and convert it into VO2(OH)2 as much as possible. - .

[0021] Further, before adjusting the pH by adding alkali in step (1), the wastewater temperature is preferably adjusted to 40-50°C. The alkali is added slowly drop by drop while stirring to allow the vanadium to undergo sufficient hydrolysis reaction.

[0022] Further, in step (2), the ferrous salt is ferrous sulfate, and the addition amount is calculated according to the molar ratio of iron to vanadium of 0.25:1-1.25:1, preferably 0.4:1-1:1, and more preferably 0.5:1-0.7:1; the reaction time is 10-60 min, preferably 20-40 min.

[0023] In step (2), ferrous sulfate is added to the pretreated wastewater to undergo an oxidation-reduction reaction between iron and vanadium, part of the vanadium forms Fe2O3·V2O5·H2O precipitate, and part of the pentavalent vanadium is reduced to tetravalent, reducing its toxicity in water.

[0024] Further, in step (3), the pH of the wastewater is adjusted to 8.5-9, preferably using sodium hydroxide solution or potassium hydroxide solution, and sodium hydroxide solution is preferred, which makes OH - , iron and vanadium interact in the wastewater to form VO2·H2O and Fe2O3·V2O5·4H2O; at the same time, with the increase of pH, the residual iron ions in the wastewater react to form hydroxyl iron oxide, which has a certain adsorption effect on the residual vanadium in the wastewater based on electrostatic interaction, further improving the removal efficiency of vanadium.

[0025] Further, after adjusting the pH in step (3), a flocculating agent is preferably added to make the formed VO2·H2O and Fe2O3·V2O5·4H2O flocculate and settle, and then filtered. The flocculating agent is preferably polyacrylamide (PAM), and the addition amount is 30-60 mg / L, preferably 40-50 mg / L, based on the weight of the wastewater, and the mass concentration is 0.5%-3%, preferably 1%-2%, which improves the removal efficiency of vanadium in the wastewater and accelerates the settling speed of the precipitate in the wastewater.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] (1) The present application first controls the degree of hydrolysis of vanadium at different pH values to destroy the stable form of (meta)vanadate in the wastewater, facilitating the subsequent treatment of vanadium in the wastewater, and then divalent iron is added to effectively reduce vanadium (V) in the wastewater to VO 2+ (Ⅵ) which has lower toxicity and is relatively unstable, thereby reducing the toxicity of the wastewater; through the interaction between vanadium (V) and iron (II, III) in the wastewater, Fe2O3·V2O5·4H2O (s) and VO2·H2O (s) are co-precipitated to remove vanadium in the wastewater and reduce the use of reagents.

[0028] (2) As can be seen from the reaction principle of the present application, Fe (II) first reacts with VO2(OH)2 - , Fe (II) is oxidized to Fe (III), and Fe (III) can further consume VO2(OH)2 - in the wastewater to generate a precipitate, and the theoretical molar ratio of iron to vanadium is 0.5:1, and part of the vanadium is removed in the final flocculation stage, so the actual amount of iron used can be lower than the theoretical value, greatly reducing the amount of reducing agent added.

[0029] (3) Finally, by adding alkali, vanadium is removed while the excess Fe 3+ in the wastewater is also consumed, and the generated Fe(OH)3 also further adsorbs and removes vanadium in the wastewater through electrostatic action, thereby greatly improving the removal efficiency of vanadium in the wastewater while reducing the addition of reagents.

[0030] (4) The entire process of the present application is easy to control, and the removal rate of vanadium is high, even when treating wastewater containing vanadium at a lower concentration, the removal rate of vanadium can reach.

[0031] Other features and advantages of the present application will be described in detail in the following specific embodiments. DETAILED DESCRIPTION

[0032] The method of the present application will be further described in detail below through examples. The examples are implemented on the premise of the technical solution of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0033] In the following examples, the experimental methods are conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are purchased from conventional biochemical reagent stores unless otherwise specified.

[0034] The pH value in the present application is determined by the method of "Determination of pH Value of Water by Glass Electrode Method" (GB / T6920), and the metal ion is determined by the method of "Microwave Digestion / Inductively Coupled Plasma Mass Spectrometry" (ICP-MS).

[0035] Example 1

[0036] The vanadium-containing wastewater is taken from a chemical plant, the pH value is 6.2, the total vanadium content is 280 mg / L, and the wastewater may also contain a certain amount of other metals and organic pollutants.

[0037] (1) 500 mL of the wastewater is taken in a beaker, the pH value of the wastewater is adjusted to 2.5 by 5% sulfuric acid, the wastewater is heated to 45°C, and 5% NaOH solution is slowly added until the pH value is 6.

[0038] (2) Ferrous sulfate is added to the wastewater, the molar ratio of iron to total vanadium is 0.6:1, and the reaction is carried out for 30 minutes;

[0039] (3) The pH value of the wastewater is adjusted to 8.5 by 5% NaOH solution, 1 wt% polyacrylamide (PAM) solution is added at 40 mg / L, and after standing for 10 minutes, the supernatant is filtered, and the total vanadium content in the effluent is detected to be 0.075 mg / L, reaching the discharge standard (1 mg / L), and the total vanadium removal rate reaches 99.97%.

[0040] Example 2

[0041] The vanadium-containing wastewater is taken from a chemical plant, the pH value is 6.5, the total vanadium content is 264 mg / L, and the wastewater may also contain a certain amount of other metals and organic pollutants.

[0042] (1) 500 mL of the wastewater is taken in a beaker, the pH value of the wastewater is adjusted to 4 by 5% sulfuric acid, the wastewater is heated to 50°C, and 5% NaOH solution is slowly added until the pH value is 8.

[0043] (2) Ferrous sulfate is added to the wastewater, the molar ratio of iron to total vanadium is 0.6:1, and the reaction is carried out for 30 minutes;

[0044] (3) The pH value of the wastewater is adjusted to 8.5 by 5% NaOH solution, 1 wt% polyacrylamide (PAM) is added at 40 mg / L, and after standing for 10 minutes, the supernatant is filtered, and the total vanadium content in the effluent is detected to be 0.914 mg / L, reaching the discharge standard (1 mg / L), and the total vanadium removal rate reaches 99.65%.

[0045] Example 3

[0046] The vanadium-containing wastewater is taken from a chemical plant, the pH value is 6, the total vanadium content is 270 mg / L, and the wastewater may also contain a certain amount of other metals and organic pollutants.

[0047] (1) Take 500 mL of the wastewater in a beaker, adjust the pH of the wastewater to 2.2 with 5% sulfuric acid, heat the wastewater to 40°C, and slowly add 5% NaOH solution until the pH is 6.5.

[0048] (2) Add ferrous sulfate to the wastewater, with a molar ratio of iron to total vanadium of 0.25:1, and react for 30 minutes;

[0049] (3) Adjust the pH of the wastewater to 8.5 with 5% NaOH solution, add 2wt% polyacrylamide (PAM) at 35mg / L, let it stand for 10 minutes, then take the supernatant and filter it, and detect the total vanadium content in the effluent, which is 2.95mg / L (although it does not meet the discharge standard, but in this example, the amount of iron added is small, which proves that when the proportion of iron is significantly lower than the theoretical proportion, it can still play a role in removing vanadium, and its utilization rate is higher), and the total vanadium removal rate reaches 98.91%.

[0050] Example 4

[0051] The vanadium-containing wastewater is taken from a sewage treatment plant, with a pH of 6.8 and a total vanadium content of 285mg / L. The wastewater may also contain a certain amount of other metals and organic pollutants.

[0052] (1) Take 500 mL of the wastewater in a beaker, adjust the pH of the wastewater to 2.5 with 5% sulfuric acid, heat the wastewater to 45°C, and slowly add 5% NaOH solution until the pH is 6.

[0053] (2) Add ferrous sulfate to the wastewater, with a molar ratio of iron to total vanadium of 0.4:1, and react for 30 minutes;

[0054] (3) Adjust the pH of the wastewater to 8.5 with 5% NaOH solution, add 1wt% polyacrylamide (PAM) at 40mg / L, let it stand for 10 minutes, then take the supernatant and filter it, and detect the total vanadium content in the effluent, which is 0.837mg / L, meeting the discharge standard (1mg / L), and the total vanadium removal rate reaches 99.7%.

[0055] Example 5

[0056] The vanadium-containing wastewater is taken from a sewage treatment plant, with a pH of 7.4 and a total vanadium content of 1000mg / L. The wastewater may also contain a certain amount of other metals and organic pollutants.

[0057] (1) Take 500 mL of the wastewater in a beaker, adjust the pH of the wastewater to 2.5 with 5% sulfuric acid, heat the wastewater to 45°C, and slowly add 5% NaOH solution until the pH is 6.

[0058] (2) Add ferrous sulfate to the wastewater, with a molar ratio of iron to total vanadium of 0.7:1, and react for 30 minutes;

[0059] (3) Adjust the pH of the wastewater to 9 with 5% NaOH solution, add 1 wt% polyacrylamide (PAM) at 50 mg / L, let it stand for 10 minutes, then take the supernatant and filter it. The total vanadium content in the effluent is 0.89 mg / L, reaching the discharge standard (1 mg / L), and the total vanadium removal rate reaches 99.91%.

[0060] Comparative Example 1

[0061] The vanadium-containing wastewater is taken from a chemical plant, with a pH of 6.8 and a total vanadium content of 300 mg / L. The wastewater may also contain a certain amount of other metals and organic pollutants.

[0062] (1) Take 500 mL of the wastewater in a beaker, adjust the pH to 3 with 5% sulfuric acid, heat the wastewater to 40°C, and slowly add 5% NaOH solution until the pH is 9.

[0063] (2) Add ferrous sulfate to the wastewater, with a molar ratio of iron to total vanadium of 0.5:1, and react for 30 minutes.

[0064] (3) Adjust the pH of the wastewater to 8 with 5% NaOH solution, add 1 wt% polyacrylamide (PAM) at 45 mg / L, let it stand for 10 minutes, then take the supernatant and filter it. The total vanadium content in the effluent is 8.56 mg / L, and the total vanadium removal rate is 97.15%.

[0065] Comparative Example 2

[0066] The vanadium-containing wastewater is taken from a chemical plant, with a pH of 6.5 and a total vanadium content of 296 mg / L. The wastewater may also contain a certain amount of other metals and organic pollutants.

[0067] (1) Take 500 mL of the wastewater in a beaker, adjust the pH to 2.5 with 5% sulfuric acid, heat the wastewater to 45°C, and slowly add 5% NaOH solution until the pH is 6.5.

[0068] (2) Add ferrous sulfate to the wastewater, with a molar ratio of iron to total vanadium of 0.5:1, and react for 30 minutes.

[0069] (3) Adjust the pH of the wastewater to 7 with 5% NaOH solution, add 1 wt% polyacrylamide (PAM) at 40 mg / L, let it stand for 10 minutes, then take the supernatant and filter it. The total vanadium content in the effluent is 13.9 mg / L, and the total vanadium removal rate is 95.3%.

[0070] Comparative Example 3

[0071] A certain vanadium(Ⅴ)-containing wastewater, the vanadium(Ⅴ) content of which is 1000mg / L, is added with sulfuric acid(mass fraction 98%) in an amount of 8 times of the vanadium content; ground phosphorus-iron slag is added into the above wastewater in an amount of 1 times of the vanadium. After stirring and reacting at normal temperature for 2 hours, sodium hydroxide is added to adjust the pH value of the wastewater to 12. The obtained wastewater is aged for 24 hours, and the treated filtrate and filter residue are obtained by filtration. The removal rate of vanadium(Ⅴ) in the filtrate reaches 99%, but further deep treatment is still needed to reach the discharge standard.

Claims

1. A method for removing vanadium from wastewater in situ, comprising the following steps: (1) adjusting the pH of the wastewater containing vanadium to 1-4, and adjusting the pH to 6-7 by adding alkali at 40-50℃; (2) adding ferrous salt to the wastewater and reacting; (3) adjusting the pH of the wastewater to 8-10 by adding alkali, and forming precipitate after the reaction.

2. The method of claim 1, wherein, The strong acid or strong alkali is used to adjust the pH in step (1).

3. The method of claim 1, wherein, The strong acid or strong alkali is sulfuric acid, sodium hydroxide solution or potassium hydroxide solution, and the mass concentration is 1-10% in step (1).

4. The method of claim 1, wherein, The pH of the wastewater is adjusted to 2-3 by the strong acid in step (1).

5. The method of claim 1, wherein, The ferrous salt is ferrous sulfate, and the molar ratio of iron to vanadium is 0.25:1-1.25:1 in step (2).

6. The method of claim 1, wherein, The reaction time after adding the ferrous salt is 10-60 min in step (2).

7. The method of claim 1, wherein, The pH of the wastewater is adjusted to 8.5-9 in step (3).

8. The method of claim 1, wherein, The step of adding flocculant is included after adjusting the pH in step (3), so that the formed VO2·H2O and Fe2O3·V2O5·4H2O flocculate and settle, and then filtered.

Images