Method for electrocatalytic synergistic sulfidation of zero-valent iron to reduce oxidized chemical wastewater

Abstract

The application discloses a method for reducing oxidized chemical industrial wastewater by electrocatalysis and sulfurized zero-valent iron, and belongs to the technical field of wastewater treatment. The method comprises the following steps: adding sulfurized zero-valent iron into the chemical industrial wastewater, reducing for 2-4 hours, adding an oxidizing agent, and simultaneously catalytically oxidizing for 2-6 hours by using an electrocatalysis system, so that the sulfurized zero-valent iron replaces Fe 0 The electrocatalysis and catalysis are used by taking advantage of the potential difference of iron ions with different valences in the reaction system, the pH applicable range is expanded, Fe 0 The probability of generating a passivation film on the surface of the zero-valent iron is reduced, and the reaction rate is greatly improved.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment technology, specifically relating to a method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide. Background Technology

[0002] Against the backdrop of rapid industrialization, my country's chemical industry has developed rapidly but extensively. While this has greatly improved people's material lives, it has also exacerbated environmental pollution and the deterioration of people's living environment. Wastewater from the chemical industry is characterized by its large volume, complex water quality, high toxicity, and difficulty in treatment, further increasing the pressure and difficulty of water pollution control.

[0003] Given the aforementioned governance pressures and difficulties, Fenton advanced oxidation technology (Fe... 2+ Fenton oxidation (H2O2) has gradually become a mainstream technology for treating chemical wastewater due to its numerous advantages, such as strong oxidizing power (the redox potential of hydroxyl radicals is as high as 2.79V), rapid reaction initiation (the reaction begins almost immediately after the reagent is added), wide applicability (it can react with 95% of organic matter), minimal secondary pollution from residual reagents (the only reagents used are ferrous sulfate and hydrogen peroxide), and simpler operation (compared to processes such as extraction). However, Fenton advanced oxidation technology also has certain limitations. For example, due to the Fe... 2+ A large amount was converted into Fe 3+ For example, the catalytic rate of hydroxyl radical oxidation of organic matter will be reduced, affecting the reaction efficiency and generating a large amount of iron sludge, which increases the operating cost of subsequent hazardous waste disposal. Furthermore, although the redox potential of hydroxyl radicals is as high as 2.79V, in engineering examples of chemical wastewater treatment, there are still some toxic organic substances in the wastewater with high redox potentials, resulting in poor oxidation effect and high reagent consumption of Fenton advanced oxidation technology.

[0004] Recent studies have pointed out the possibility of replacing Fe with zero-valent iron, i.e., iron powder. 2+ ZVI reduction oxidation technology (Fe) 0 / H2O2), during the reaction, Fe 0 It can be converted into Fe 2+ Meanwhile, as the reaction continues, Fe 0 To reduce Fe 3+ Fe is continuously regenerated 2+ This ensures the efficiency of the reaction while reducing the amount of Fe in the system. 3+ The amount of Fe reduced the system's iron sludge and the corresponding operating costs for subsequent hazardous waste disposal. Furthermore, due to Fe... 0 It has reducing properties, allowing it to first reduce and then oxidize substances with high oxidation-reduction potentials in wastewater, thus significantly improving the ZVI reduction-oxidation technology (Fe). 0Scope of application of / H2O2).

[0005] However, ZVI reduction oxidation technology (Fe 0 During application, it was found that H2O2 has a narrow applicable pH range, limited to weakly acidic and acidic conditions (pH value approximately 1-5), leading to increased operating costs associated with adjusting the pH value of wastewater; Fe 0 Passivation films (iron oxides) easily form on the surface, affecting the reaction rate, etc. Summary of the Invention

[0006] 1. The problem to be solved

[0007] This application addresses the shortcomings of existing ZVI reduction and oxidation technologies, such as narrow pH applicability and Fe... 0 One of the problems is that the surface easily forms a passivation film (iron oxide), which affects the reaction rate. To address this, a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater using zero-valent iron sulfide is proposed, replacing Fe with zero-valent iron sulfide. 0 Furthermore, by utilizing the potential difference between iron ions in different valence states within the reaction system, electrocatalysis was employed in synergistic catalysis, thereby expanding the applicable pH range and reducing Fe content. 0 The surface is more likely to form a passivation film, which greatly increases the reaction rate.

[0008] 2. Technical Solution

[0009] To solve the above problems, the technical solution adopted in this application is as follows:

[0010] This application provides a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater using zero-valent iron sulfide. The method includes: adding zero-valent iron sulfide to the chemical wastewater, initiating a reduction reaction for 2-4 hours, adding an oxidant, and simultaneously catalytically oxidizing the wastewater using an electrocatalytic system for 2-6 hours. The zero-valent iron sulfide added in this application acts as both a reducing agent and a catalyst, and after addition, Fe is gradually released into the system. 2 + The system reduces pollutants in wastewater; the electrocatalytic system significantly promotes electron migration while greatly catalyzing the oxidation of pollutants in wastewater by hydroxyl radicals. As the reaction continues, the Fe content in the wastewater is significantly increased. 0 and Fe 3 + Converted to Fe 2+ The rate.

[0011] Furthermore, the amount of the aforementioned zero-valent iron sulfide added is 0.025% to 0.55% (w / v).

[0012] Furthermore, the aforementioned oxidizing agent includes hydrogen peroxide.

[0013] Furthermore, the hydrogen peroxide mentioned above is 30% hydrogen peroxide, and the dosage ratio is 0.25% to 2% (v / v).

[0014] Furthermore, the treatment temperature for the aforementioned chemical wastewater is 0–45°C.

[0015] Furthermore, the pH of the aforementioned chemical wastewater is 3.5–8.5.

[0016] Furthermore, the pH of the aforementioned chemical wastewater is 6.5–8.5.

[0017] Furthermore, the anode and cathode of the aforementioned electrocatalytic system are composed of zero-valent iron and graphite, respectively. The zero-valent iron anode and graphite cathode form a current loop between the anode and cathode, which greatly promotes the migration of electrons in the system and significantly enhances the oxidation effect of hydroxyl radicals on pollutants in wastewater.

[0018] Furthermore, the current density of the above electrocatalytic system is ≥10 mA / cm². 2 .

[0019] Furthermore, the above-mentioned method for preparing zero-valent iron sulfide is a mechanical-physical method, which includes mixing elemental sulfur and micron-sized zero-valent iron (particle size 1-3 μm), followed by stirring, grinding, and sieving to obtain nano-sized Fe. 0 / FeS.

[0020] Furthermore, in the above-mentioned method for preparing zero-valent iron sulfide, the mass ratio of elemental sulfur to micron-sized zero-valent iron is 1:(1-5).

[0021] Furthermore, in the above-mentioned method for preparing zero-valent iron sulfide, the mass ratio of elemental sulfur to micron-sized zero-valent iron is 1:(1-2).

[0022] Furthermore, in the above-mentioned method for preparing zero-valent iron sulfide, stirring and grinding are carried out for 2 to 5 hours.

[0023] Furthermore, in the above-mentioned method for preparing zero-valent iron sulfide, the mixture is stirred, ground, and then filtered through a 100,000-mesh sieve.

[0024] 3. Beneficial effects

[0025] Compared with the prior art, the advantages of this application are as follows:

[0026] (1) The mechanical-physical method for preparing zero-valent iron sulfide provided in this application is simple and easy to operate, and yields zero-valent iron sulfide (Fe). 0 / FeS) can reach the nanoscale, significantly improving Fe 0 The contact area between FeS and wastewater is increased, thus correspondingly improving Fe... 0 / FeS utilization efficiency.

[0027] (2) This application provides a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide, in which zero-valent iron sulfide replaces Fe. 0 As a reducing agent and catalyst, zero-valent iron sulfide retains its own reducing effect on pollutants, while compared to Fe... 0 It has a more obvious and efficient effect on oxidizing pollutants with hydrogen peroxide, and is less likely to agglomerate or passivate, thus reducing its effectiveness.

[0028] (3) This application provides a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide. The anode and cathode of the electrocatalytic system are composed of zero-valent iron and graphite. The synergistic effect of the electrocatalytic system achieves a current density of 10 mA / cm². 2 In summary, the zero-valent iron anode and graphite cathode form a current loop between the anode and cathode. The materials are inexpensive, which not only greatly promotes the migration of electrons in the system, ensuring that the zero-valent iron sulfide in the system is not easily oxidized, but also enhances the oxidizing effect of hydroxyl radicals on pollutants in wastewater.

[0029] (4) This application provides a method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide, which significantly improves the Fe... 2+ The catalytic effect overcomes the limitations caused by Fe 0 The low catalytic efficiency of the H2O2 system causes hydrogen peroxide to decompose on its own without participating in the actual reaction, resulting in incomplete utilization of hydrogen peroxide and failing to achieve the ideal treatment effect. This only increases the consumption of hydrogen peroxide reagent, thus reducing the cost of treating chemical wastewater.

[0030] (5) The electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide provided in this application overcomes the problem of narrow pH range (pH value of about 1 to 5) in the application of existing ZVI reduction and oxidation technology. As shown in Examples 2 and 3, the COD removal rate reaches 95.7% and 87.3% when the wastewater pH is 6.5 and 8.5, respectively, which reduces the steps of adjusting the pH of the wastewater and saves operating costs. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the reaction apparatus described in Example 1.

[0032] Figure 2 This is a flowchart of the electrocatalytic synergistic reduction and oxidation method for chemical wastewater by zero-valent iron sulfide, as described in this application. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments.

[0034] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0036] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0037] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0038] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0039] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0040] In this application, electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide is used in, for example... Figure 1 The reaction is carried out in the shown reaction device, which is a closed box structure. The anode and cathode of the electrocatalytic system are composed of zero-valent iron and graphite, respectively. The zero-valent iron electrode group is inserted into the main body of the reaction device by human operation to participate in synergistic catalysis.

[0041] In this application, the flowchart of the method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide is as follows: Figure 2 As shown, the mass of zero-valent iron sulfide is calculated based on the wastewater quality, and the addition ratio is 0.025%–0.55% (w / v). This is added to the wastewater, and after a reduction reaction of 2–4 hours, the volume of hydrogen peroxide (30%), calculated based on the wastewater quality, is added at a ratio of 0.25%–2% (v / v). The electrocatalytic system is then activated (current density ≥10 mA / cm²). 2 After 2-6 hours of synergistic catalytic oxidation reaction, the effluent is discharged.

[0042] In this application, the preparation method of zero-valent iron sulfide is a mechanical-physical method, which includes mixing elemental sulfur and micron-sized zero-valent iron (particle size 1-3 μm), stirring and grinding for 2-5 hours, with the mass ratio of elemental sulfur to micron-sized zero-valent iron being 1:(1-5), and then filtering and sieving through a 100,000-mesh sieve to obtain nano-sized Fe. 0 / FeS.

[0043] Example 1

[0044] This embodiment provides a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide.

[0045] In this embodiment, the preparation method of zero-valent iron sulfide includes the following steps: elemental sulfur and micron-sized zero-valent iron (particle size 1-3 μm) are stirred and ground together for 2 hours, with a mass ratio of elemental sulfur to micron-sized zero-valent iron of 1:5. After stirring and grinding, the mixture is filtered and sieved through a 100,000-mesh sieve to obtain nano-sized FeO / FeS.

[0046] A highly concentrated and toxic industrial wastewater, with COD = 1000 mg / L, pH = 3.5, and temperature of 25℃, was treated by adding 25 g of zero-valent iron sulfide to 100 L of wastewater. After a reduction reaction of 2 hours, 260 mL of 30% hydrogen peroxide was added, and the electrocatalytic system was activated with a current density of 10 mA / cm². 2 After 2 hours of synergistic catalytic oxidation, no obvious agglomeration of FeO / FeS was observed. The COD was detected by the potassium dichromate method, and the results showed that the COD was reduced to 16.3 mg / L, with a COD removal rate of 98.4%.

[0047] Example 2

[0048] This embodiment provides a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide.

[0049] In this embodiment, the preparation method of zero-valent iron sulfide includes the following steps: elemental sulfur and micron-sized zero-valent iron (particle size 1-3 μm) are stirred and ground together for 3 hours, with a mass ratio of elemental sulfur to micron-sized zero-valent iron of 1:3. After stirring and grinding, the mixture is filtered through a 100,000-mesh sieve to obtain nano-sized Fe.0 / FeS.

[0050] A highly concentrated and toxic industrial wastewater, with COD = 7000 mg / L, pH = 6.5, and temperature of 35℃, was treated by adding 200 g of zero-valent iron sulfide to 100 L of wastewater. After a reduction reaction of 2 hours, 900 mL of 30% hydrogen peroxide was added, and the electrocatalytic system was activated with a current density of 15 mA / cm². 2 After 4 hours of synergistic catalytic oxidation reaction, Fe 0 FeS did not show obvious agglomeration. COD was detected by potassium dichromate method, and the results showed that COD was reduced to 302 mg / L, with a COD removal rate of 95.7%.

[0051] Example 3

[0052] This embodiment provides a method for the electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide.

[0053] In this embodiment, the preparation method of zero-valent iron sulfide includes the following steps: elemental sulfur and micron-sized zero-valent iron (particle size 1-3 μm) are stirred and ground together for 5 hours, with a mass ratio of elemental sulfur to micron-sized zero-valent iron of 1:1. After stirring and grinding, the mixture is filtered through a 100,000-mesh sieve to obtain nano-sized Fe. 0 / FeS.

[0054] A highly concentrated and toxic industrial wastewater, with COD = 20000 mg / L, pH = 8.5, and temperature of 45℃, was treated by adding 550 g of zero-valent iron sulfide to 100 L of wastewater. After a reduction reaction of 4 hours, 2000 mL of 30% hydrogen peroxide was added, and the electrocatalytic system was activated with a current density of 30 mA / cm². 2 After 6 hours of synergistic catalytic oxidation, no obvious agglomeration of FeO / FeS was observed. The COD was detected by the potassium dichromate method, and the results showed that the COD was reduced to 2532 mg / L, with a COD removal rate of 87.3%.

Claims

1. A method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide, characterized in that, The method includes: adding zero-valent iron sulfide to chemical wastewater, performing a reduction reaction for 2-4 hours, adding an oxidant, and simultaneously using an electrocatalytic system for catalytic oxidation for 2-6 hours; The electrocatalytic system has zero-valent iron as the anode and graphite as the cathode, and the current density of the electrocatalytic system is ≥10 mA / cm². 2 ; The amount of zero-valent iron sulfide added is 0.025%~0.55% (w / v); the preparation method of the zero-valent iron sulfide includes: mixing elemental sulfur and micron-sized zero-valent iron, stirring, grinding, and sieving to obtain nano-sized Fe. 0 / FeS; The mass ratio of elemental sulfur to micron-sized zero-valent iron is 1:(1~5); The pH of the chemical wastewater is 3.5 to 8.

5.

2. The method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide according to claim 1, characterized in that, The oxidant includes hydrogen peroxide, and the addition ratio of hydrogen peroxide is 0.25%~2% (v / v).

3. The method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide according to claim 2, characterized in that, The mass ratio of elemental sulfur to micron-sized zero-valent iron is 1:(1~2).

4. The method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide according to any one of claims 1-3, characterized in that, Stir and grind for 2-5 hours, then filter and sieve through a 100,000 mesh screen.

5. The method for electrocatalytic synergistic reduction and oxidation of chemical wastewater by zero-valent iron sulfide according to claim 4, characterized in that, The pH of the chemical wastewater is 6.5 to 8.5.

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