In-situ recovery method of fenton iron mud in wastewater treatment

Abstract

This invention provides an in-situ recovery method for Fenton iron sludge from wastewater treatment, belonging to the field of resource recovery technology. The in-situ recovery method of this invention includes: subjecting wastewater to a Fenton reaction or a Fenton-like reaction to obtain a reaction solution; adding a regulator solution and a sodium hydroxide solution to the reaction solution to obtain a mixed solution; subjecting the mixed solution to ultrasonic treatment; and then performing magnetic separation, thus defining the composition of the regulator. This in-situ recovery method of the present invention can directionally convert and recover iron from Fenton iron sludge in situ, eliminating the need for sludge separation, transportation, and treatment steps; the compound regulator of cysteine ​​and citric acid can partially recover Fe from the Fenton or Fenton-like reaction solution. 3+ Reduced to Fe 2+ and with Fe 3+ and Fe 2+ Complex formation; sodium hydroxide solution creates an alkaline environment, allowing the complexed Fe to form a complex. 3+ and Fe 2+ With OH ‑ The reaction produces Fe3O4 functionalized with magnetic cysteine ​​and citric acid, which has excellent environmental remediation function.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, and in particular to an in-situ recovery method for Fenton iron sludge in wastewater treatment. Background Technology

[0002] Fenton and Fenton-like oxidation processes are highly efficient advanced oxidation technologies widely used in the treatment of organic wastewater. Fenton and Fenton-like oxidation processes utilize Fe... 2+ / Fe 3+ Fenton and Fenton-like reactions react with oxidants such as hydrogen peroxide, persulfate, or perdisulfate to generate highly reactive species with strong oxidizing properties, such as hydroxyl radicals and sulfate radicals, effectively degrading organic pollutants in wastewater. However, the Fenton and Fenton-like reactions require the addition of large amounts of iron ions, ultimately producing a large amount of iron-containing sludge (i.e., Fenton iron sludge), mainly composed of Fe(OH)3 and unreacted iron salts. Traditional methods involve landfilling or incinerating Fenton iron sludge as solid waste, resulting in a waste of iron resources and potentially causing secondary pollution. Therefore, researching how to recycle and utilize Fenton iron sludge is crucial.

[0003] Currently, the main methods for recycling Fenton iron sludge include acid leaching to recover iron, preparation of iron-based catalysts, and iron-based magnetic materials. Acid leaching requires large amounts of acid and reducing agents, and the catalytic activity of the recovered iron sludge is affected by residual organic matter or changes in crystal structure, leading to decreased degradation efficiency when reused in the Fenton system. Preparing iron-based catalysts involves calcining Fenton iron sludge to produce Fe2O3 catalysts; however, calcination is energy-intensive, and the catalytic activity of Fe2O3 catalysts is significantly affected by impurities in the iron sludge. Recycling Fenton iron sludge by reacting it with a reducing agent (such as NaBH4) to generate nano-zero-valent iron is costly and complex, making large-scale application difficult. Patent CN114349296A discloses a comprehensive resource recovery method for Fenton iron sludge, which involves mixing Fenton iron sludge with a carbon source, nitrogen source, and template agent, grinding it into powder, calcining it under a protective atmosphere, and obtaining Fe through magnetic separation and acid washing. 3+The method involves using an acidic solution and a nitrogen-doped carbon-supported Fe single-atom catalyst. This method is complex, with high energy consumption from high-temperature calcination and high recovery costs, but the resource recovery rate is low. Patent CN120364915A discloses a method for the resource utilization of Fenton iron sludge, using a citric acid-ascorbic acid composite solution to soak the Fenton iron sludge, followed by hydrothermal liquefaction in an inert reducing system to reduce ferric iron to ferrous iron. The resulting ferrous iron solution can be directly combined with hydrogen peroxide to form a Fenton system and reused in the Fenton reaction. While this method can recover iron relatively completely, hydrothermal liquefaction requires specialized equipment and has high energy consumption. Furthermore, the degradation efficiency of the reused ferrous iron solution decreases, limiting its widespread application. In summary, current Fenton iron sludge recycling technologies mainly suffer from low resource recovery efficiency, complex processes, high costs, and unstable reuse effects. The fundamental reason lies in the high chemical stability of the iron in Fenton iron sludge (amorphous Fe(OH)3), making direct reuse difficult. None of the above methods achieve in-situ transformation of iron, requiring additional separation and processing, and they also lack targeted regulation methods for iron species.

[0004] Therefore, there is an urgent need to develop efficient and low-cost in-situ recovery methods for Fenton iron sludge to realize the recycling of iron resources and improve the economy and sustainability of Fenton and Fenton-like oxidation technologies. Summary of the Invention

[0005] The purpose of this invention is to provide an in-situ recovery method for Fenton iron sludge in wastewater treatment, addressing the shortcomings of existing technologies.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides an in-situ recovery method for Fenton iron sludge in wastewater treatment, comprising the following steps:

[0008] 1) The wastewater is subjected to a Fenton reaction or a Fenton-like reaction to obtain a reaction solution;

[0009] 2) Add a regulator solution and sodium hydroxide solution to the reaction solution to obtain a mixture;

[0010] 3) The mixture is subjected to ultrasonic treatment and then magnetic separation to obtain the magnetic functionalized material;

[0011] The regulator in the regulator solution contains cysteine ​​and citric acid.

[0012] Preferably, the concentration of the regulator in the mixture in step 2) is 150–500 mmol / L, the concentration of the sodium hydroxide solution is 0.5–5 mol / L, and the pH value of the mixture is >11;

[0013] The molar ratio of cysteine ​​to citric acid in the regulator is 1 to 10:1.

[0014] Preferably, the dropping rate in step 2) is 1-10 mL / min, and the reaction solution is subjected to ultrasonication and stirring during the dropping process.

[0015] The acoustic energy density of the ultrasound is 0.5–10 W / cm². 3 The stirring speed is 50 to 250 rpm.

[0016] Preferably, the acoustic energy density of the ultrasonic treatment in step 3) is 0.5–10 W / cm². 3 The ultrasonic treatment time is 15 to 240 minutes.

[0017] Preferably, after the magnetic separation in step 3), the magnetic material is further subjected to vacuum drying to obtain a magnetically functionalized material.

[0018] The vacuum drying process involves a vacuum degree of 10–60 Pa, a vacuum drying temperature of -80–25°C, and a vacuum drying time of 12–48 hours.

[0019] Preferably, the process of carrying out the Fenton reaction or Fenton-like reaction on the wastewater in step 1) includes: sequentially adding ferrous salt and oxidant to the wastewater to obtain a reaction system; and stirring the reaction system.

[0020] Preferably, the ferrous salt comprises one or more of ferrous sulfate, ferrous nitrate and ferrous chloride;

[0021] The oxidant includes hydrogen peroxide or persulfate.

[0022] Preferably, Fe in the reaction system 2+ The concentration of the oxidant is 100–500 mmol / L, and the concentration of the oxidant in the reaction system is 100–250 mmol / L.

[0023] Preferably, the stirring speed is 100-500 rpm and the stirring time is 30-240 min.

[0024] The beneficial effects of this invention are:

[0025] The in-situ recovery method for Fenton iron sludge in wastewater treatment of the present invention can directionally convert and recover iron in Fenton iron sludge in situ, eliminating the need for sludge separation, transportation, and treatment steps. The method is simple, has a short process flow, and a fast recovery speed. A regulator composed of cysteine ​​and citric acid in a specific ratio can be used to partially recover Fe from Fenton or Fenton-like reaction solutions. 3+ Reduced to Fe 2+ and with Fe 3+ and Fe 2+The formation of complexes; the addition of sodium hydroxide solution creates an alkaline environment and, on the other hand, allows the complexed Fe to form a complex. 3+ and Fe 2+ With OH - The reaction generates Fe3O4 functionalized with magnetic cysteine ​​and citric acid, which has excellent environmental remediation function and can be applied to many fields such as advanced oxidation technology catalysts, pollutant adsorbents, magnetic powder for magnetic coagulation processes, and soil heavy metal passivation agents. Attached Figure Description

[0026] Figure 1 This is a diagram of separating magnetic materials using a magnet in Example 1;

[0027] Figure 2 This is an image of the magnetic functionalized material obtained in Example 1. Detailed Implementation

[0028] This invention provides an in-situ recovery method for Fenton iron sludge in wastewater treatment, comprising the following steps:

[0029] 1) The wastewater is subjected to a Fenton reaction or a Fenton-like reaction to obtain a reaction solution;

[0030] 2) Add a regulator solution and sodium hydroxide solution to the reaction solution to obtain a mixture;

[0031] 3) The mixture is subjected to ultrasonic treatment and then magnetic separation to obtain the magnetic functionalized material;

[0032] The regulator in the regulator solution contains cysteine ​​and citric acid.

[0033] In this invention, the concentration of the regulator in the mixture in step 2) is preferably 150–500 mmol / L, more preferably 200–400 mmol / L, and even more preferably 250–300 mmol / L; the concentration of the sodium hydroxide solution is preferably 0.5–5 mol / L, more preferably 1–4 mol / L, and even more preferably 2–3 mol / L; the pH value of the mixture is preferably >11, more preferably >12, and even more preferably >13.

[0034] The molar ratio of cysteine ​​to citric acid in the regulator is preferably 1 to 10:1, more preferably 3 to 8:1, and even more preferably 5 to 7:1.

[0035] In this invention, the dropping rate in step 2) is preferably 1-10 mL / min, more preferably 3-8 mL / min, and even more preferably 5 mL / min; the reaction solution is preferably subjected to ultrasonication and stirring simultaneously with the dropping.

[0036] The acoustic energy density of the ultrasound is preferably 0.5–10 W / cm².3 Further preferred is 3-8 W / cm 3 More preferably 4-7 W / cm 3 The stirring speed is preferably 50-250 rpm, more preferably 100-200 rpm, and even more preferably 150 rpm.

[0037] In this invention, the preferred method for adding the regulator solution and sodium hydroxide solution to the reaction solution in step 2) includes simultaneously adding the regulator solution and sodium hydroxide solution, sequentially adding the regulator solution and sodium hydroxide solution, or adding a mixed solution of regulator and sodium hydroxide.

[0038] In this invention, the acoustic energy density of the ultrasonic treatment in step 3) is preferably 0.5–10 W / cm². 3 Further preferred is 3-8 W / cm 3 More preferably 4-7 W / cm 3 The ultrasonic treatment time is preferably 15-240 min, more preferably 60-200 min, and even more preferably 100-150 min.

[0039] In this invention, after the magnetic separation described in step 3), it is preferable to further perform vacuum drying on the magnetic material to obtain a magnetically functionalized material.

[0040] The vacuum degree of the vacuum drying is preferably 10-60 Pa, more preferably 20-50 Pa, and even more preferably 30-40 Pa; the vacuum drying temperature is preferably -80-25℃, more preferably -50-0℃, and even more preferably -20℃; the vacuum drying time is preferably 12-48 h, more preferably 20-40 h, and even more preferably 24-32 h.

[0041] In this invention, the process of carrying out the Fenton reaction or Fenton-like reaction of the wastewater in step 1) preferably includes: adding ferrous salt and oxidant to the wastewater in sequence to obtain a reaction system; and stirring the reaction system.

[0042] In this invention, the ferrous salt preferably comprises one or more of ferrous sulfate, ferrous nitrate and ferrous chloride;

[0043] The oxidant preferably comprises hydrogen peroxide or persulfate.

[0044] In this invention, the persulfate preferably comprises permonosulfate and / or perdisulfate;

[0045] The persulfate preferably comprises one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and calcium persulfate;

[0046] The persulfate preferably comprises one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and calcium persulfate.

[0047] In this invention, Fe in the reaction system 2+ The concentration of the oxidant is preferably 100-500 mmol / L, more preferably 150-400 mmol / L, and even more preferably 200-300 mmol / L; the concentration of the oxidant in the reaction system is preferably 100-250 mmol / L, and even more preferably 150-200 mmol / L.

[0048] In this invention, the pH value of the reaction system is preferably 2 to 11, more preferably 3 to 9, and even more preferably 5 to 7.

[0049] In this invention, the concentration of the regulator in the mixture in step 2) is preferably the same as the concentration of Fe in the reaction system. 2+ The concentrations are the same.

[0050] In this invention, the stirring speed is preferably 100-500 rpm, more preferably 200-400 rpm, and even more preferably 300 rpm; the stirring time is preferably 30-240 min, more preferably 100-200 min, and even more preferably 130-180 min.

[0051] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0052] The wastewater used in the embodiments of the present invention is coking wastewater generated by the Ningdong Energy and Chemical Base.

[0053] Example 1

[0054] At 25℃, a 1 mol / L ferrous sulfate solution was added to coking wastewater while stirring the wastewater at 300 rpm. Simultaneously, a 1 mol / L sodium persulfate (PS) solution was added to form a reaction system containing Fe. 2+ / PS. Reaction system Fe 2+ / PS in Fe 2+ The concentration of the active ingredient was 150 mmol / L, the concentration of PS was 100 mmol / L, and the pH of the reaction system was 5. The reaction system was stirred at 300 rpm for 180 min to obtain a reaction solution containing Fenton iron sludge.

[0055] The reaction liquid was subjected to an acoustic energy density of 3 W / cm². 3The mixture was subjected to ultrasonic treatment in an ultrasonic generator while being stirred at 150 rpm. During the ultrasonic treatment, a regulator solution (in which the molar ratio of cysteine ​​to citric acid was 3:1) and a 1 mol / L sodium hydroxide solution were added dropwise to the reaction solution at a rate of 5 mL / min to obtain a mixture. The total concentration of cysteine ​​and citric acid in the mixture was 150 mmol / L, and the pH of the mixture was 12. The mixture was then further subjected to ultrasonic treatment at an acoustic energy density of 3 W / cm². 3 The material was subjected to ultrasonic treatment for 60 minutes using an ultrasonic generator. During the ultrasonic treatment, the Fenton iron sludge gradually transformed into a black precipitate. After the ultrasonic treatment, the magnetic material was separated using a magnet and then vacuum-dried at 30 Pa and -20 °C for 24 hours to obtain the magnetic functionalized material.

[0056] Figure 1 This is a diagram illustrating the separation of magnetic materials using a magnet in Example 1. (From...) Figure 1 It can be seen that after the magnet separates the magnetic material, the mixture becomes clear, indicating that the Fenton iron sludge is recovered in situ.

[0057] Figure 2 This is an image of the magnetic functionalized material obtained in Example 1.

[0058] Example 2

[0059] At 25℃, a 1.5 mol / L ferrous chloride solution was added to coking wastewater while stirring the wastewater at 100 rpm. Simultaneously, a 2 mol / L sodium persulfate (PS) solution was added to form a reaction system containing Fe. 2+ / PS. Reaction system Fe 2+ / PS in Fe 2+ The concentration of the active ingredient was 500 mmol / L, the concentration of PS was 250 mmol / L, and the pH of the reaction system was 7. The reaction system was stirred at 100 rpm for 240 min to obtain a reaction solution containing Fenton iron sludge.

[0060] The reaction liquid was subjected to an acoustic energy density of 10 W / cm². 3 The mixture was subjected to ultrasonic treatment in an ultrasonic generator while being stirred at 250 rpm. During the ultrasonic treatment, a regulator solution (in which the molar ratio of cysteine ​​to citric acid was 1:1) and a 4 mol / L sodium hydroxide solution were added dropwise to the reaction solution at a rate of 3 mL / min to obtain a mixture. The total concentration of cysteine ​​and citric acid in the mixture was 500 mmol / L, and the pH of the mixture was 13. The mixture was then further subjected to ultrasonic treatment at an acoustic energy density of 10 W / cm². 3The Fenton iron sludge was subjected to ultrasonic treatment for 200 minutes in an ultrasonic generator. During the ultrasonic treatment, the Fenton iron sludge gradually transformed into a black precipitate. After the ultrasonic treatment, the magnetic material was separated using a magnet and then vacuum-dried at 20 Pa and -50 °C for 36 hours to obtain the magnetic functionalized material.

[0061] Example 3

[0062] At 25℃, a 2 mol / L ferrous nitrate solution was added to coking wastewater, and the wastewater was stirred at 500 rpm. Simultaneously, a 1.5 mol / L sodium persulfate (PS) solution was added to form a reaction system containing Fe. 2+ / PS. Reaction system Fe 2+ / PS in Fe 2+ The concentration of the active ingredient was 300 mmol / L, the concentration of PS was 200 mmol / L, and the pH of the reaction system was 7. The reaction system was stirred at 500 rpm for 100 min to obtain a reaction solution containing Fenton iron sludge.

[0063] The reaction liquid was subjected to an acoustic energy density of 7 W / cm². 3 The mixture was subjected to ultrasonic treatment in an ultrasonic generator while being stirred at 100 rpm. During the ultrasonic treatment, a regulator solution (in which the molar ratio of cysteine ​​to citric acid was 7:1) and a 2 mol / L sodium hydroxide solution were added dropwise to the reaction solution at a rate of 10 mL / min to obtain a mixture. The total concentration of cysteine ​​and citric acid in the mixture was 300 mmol / L, and the pH of the mixture was 13. The mixture was then further subjected to ultrasonic treatment at an acoustic energy density of 7 W / cm². 3 The Fenton iron sludge was subjected to ultrasonic treatment for 150 minutes in an ultrasonic generator. During the ultrasonic treatment, the Fenton iron sludge gradually transformed into a black precipitate. After the ultrasonic treatment, the magnetic material was separated using a magnet and then vacuum-dried at 10 Pa and -80°C for 48 hours to obtain the magnetic functionalized material.

[0064] In Examples 2 and 3, after the magnetic material was separated by the magnet, the mixture became clear, indicating that the Fenton iron sludge was recovered in situ.

[0065] Comparative Example 1

[0066] The molar ratio of cysteine ​​to citric acid in Example 1 was modified to 0.5:1, and all other aspects remained the same as in Example 1.

[0067] Comparative Example 2

[0068] The molar ratio of cysteine ​​to citric acid in Example 1 was modified to 12:1, and all other aspects remained the same as in Example 1.

[0069] In Comparative Examples 1 and 2, after the magnetic substances were separated by magnets, the clarity of the mixture was not as good as in Examples 1-3. This result indicates that the ratio of cysteine ​​to citric acid in the regulator was unreasonable and could not enable the in-situ recovery of Fenton iron sludge.

[0070] As can be seen from the above embodiments, the present invention provides an in-situ recovery method for Fenton iron sludge in wastewater treatment. By adding a regulator and sodium hydroxide under ultrasonic conditions, the regulator contains a compound of cysteine ​​and citric acid. By reasonably controlling the ratio of the two, the iron in Fenton iron sludge is directionally converted into magnetic Fe3O4, thereby achieving in-situ recovery of Fenton iron sludge with high recovery efficiency.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for in-situ recovery of Fenton iron sludge from wastewater treatment, characterized in that, It includes the following steps: 1) The wastewater is subjected to a Fenton reaction or a Fenton-like reaction to obtain a reaction solution; 2) Add a regulator solution and sodium hydroxide solution to the reaction solution to obtain a mixture; 3) The mixture is subjected to ultrasonic treatment and then magnetic separation to obtain the magnetic functionalized material; The regulator in the regulator solution contains cysteine ​​and citric acid; The molar ratio of cysteine ​​to citric acid in the regulator is 1~10:

1.

2. The in-situ recovery method according to claim 1, characterized in that, Step 2) The concentration of the regulator in the mixture is 150~500 mmol / L, the concentration of the sodium hydroxide solution is 0.5~5 mol / L, and the pH value of the mixture is >11.

3. The in-situ recovery method according to claim 1 or 2, characterized in that, Step 2) The dropping rate is 1~10 mL / min, and the reaction solution is subjected to ultrasonication and stirring during the dropping process; The acoustic energy density of the ultrasound is 0.5~10W / cm². 3 The stirring speed is 50~250 rpm.

4. The in-situ recovery method according to claim 3, characterized in that, Step 3) The acoustic energy density of the ultrasonic treatment is 0.5~10 W / cm². 3 The ultrasonic treatment time is 15~240 min.

5. The in-situ recovery method according to claim 4, characterized in that, Step 3) After the magnetic separation, the magnetic material is further subjected to vacuum drying to obtain a magnetically functionalized material. The vacuum drying process involves a vacuum degree of 10~60 Pa, a vacuum drying temperature of -80~25℃, and a vacuum drying time of 12~48 h.

6. The in-situ recovery method according to claim 1, characterized in that, Step 1) The process of carrying out the Fenton reaction or Fenton-like reaction in the wastewater includes: adding ferrous salt and oxidant to the wastewater in sequence to obtain a reaction system; and stirring the reaction system.

7. The in-situ recovery method according to claim 6, characterized in that, The ferrous salt comprises one or more of ferrous sulfate, ferrous nitrate and ferrous chloride; The oxidant includes hydrogen peroxide or persulfate.

8. The in-situ recovery method according to claim 6 or 7, characterized in that, Fe in the reaction system 2+ The concentration of the oxidant is 100~500 mmol / L, and the concentration of the oxidant in the reaction system is 100~250 mmol / L.

9. The in-situ recovery method according to claim 8, characterized in that, The stirring speed is 100~500 rpm, and the stirring time is 30~240 min.

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