Method for preparing sulfurized nano zero-valent iron (S-nZVI) based on low-sulfite rheological phase reaction and application of S-nZVI in heavy metal wastewater treatment

Abstract

The invention belongs to the technical field of environmental functional material preparation and heavy metal pollution control, and particularly relates to a method for preparing sulfurized nano zero-valent iron (S-nZVI) based on low-sulfite rheological phase reaction and application of the S-nZVI in heavy metal wastewater treatment. The method comprises the following steps: mixing and grinding an iron source and a low sulfite solid according to a certain molar ratio to form a rheological phase precursor; in the presence of inert atmosphere and trace water, heating in a closed reactor to perform rheological phase reduction reaction, so that S-S bonds in the low sulfite are broken to release electrons, iron ions are reduced into Fe (0) cores, iron sulfide layers are synchronously formed on the surfaces of the Fe (0) cores, and after the reaction is finished, cooling, washing and drying are performed to obtain the S-nZVI with the core-shell structure. The material has the characteristics that the specific surface area is high (greater than or equal to 85 m / g), the Fe (0) core size is 5-20 nm, and the outer layer is an amorphous iron sulfide layer, and has efficient adsorption capacity on heavy metal ions such as Cr (VI), As (III), Pb (II), Cd (II) and the like. The method is simple in process, green, efficient and low in cost, and a new scheme is provided for heavy metal wastewater treatment and recycling.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional material preparation and heavy metal pollution control technology. Specifically, it is a method for preparing sulfide nano-zero valent iron (S-nZVI) based on low sulfite rheotropic phase reaction and its application in heavy metal wastewater treatment and resource utilization. Background Technology

[0002] Nano-zero valent iron (nZVI) has shown great potential in the treatment of heavy metal wastewater due to its high reactivity and wide availability of raw materials. Sulfide-modified nano-zero valent iron (S-nZVI) can further improve its adsorption capacity, selectivity, and material stability for specific heavy metal ions. Currently, the mainstream synthesis method for S-nZVI is the NaBH4 reduction method, which suffers from problems such as high reducing agent costs and potential secondary pollution from reaction byproducts (such as borates). Other synthesis methods, such as carbothermal reduction and mechanical ball milling, generally suffer from high energy consumption, complex processes, and difficulty in precisely controlling the morphology and structure of the product.

[0003] Low-sulfites (such as sodium dithionite) are inexpensive and environmentally friendly potential reducing agents, and theoretically can be used for Fe. 3+ / Fe 2+ However, in conventional liquid-phase reaction systems, the electron release efficiency of sulfites is low, the formation rate of Fe(0) is limited, and the products are prone to aggregation and oxidation, which restricts their practical application in the efficient synthesis of S-nZVI. Therefore, developing a new method that can fully utilize the reduction potential of sulfites to achieve efficient, controllable, and green synthesis of high-performance sulfide nano-zero-valent iron (S-nZVI) materials has important scientific value and practical significance. Summary of the Invention

[0004] This invention provides a method for preparing sulfide nano-zero valent iron (S-nZVI) based on low sulfite rheo-phase reaction and its application in heavy metal wastewater treatment, in order to solve the problems mentioned in the background art.

[0005] To address the existing problems, this invention provides a method for preparing sulfide nano-zero valent iron (S-nZVI), comprising the following steps:

[0006] S1. The iron source and the low-sulfite solid powder are physically mixed and ground at a predetermined molar ratio to form a rheological phase precursor;

[0007] S2. The precursor is placed in a closed reactor and subjected to a rheological phase reduction reaction at a certain temperature in the presence of an inert atmosphere and trace amounts of water. This causes the SS bonds in the low sulfite to break and release electrons, reducing the iron ions in the iron source to Fe(O) nuclei and simultaneously forming an iron sulfide layer on its surface.

[0008] S3. After the reaction is complete, the product is cooled, washed and dried under a protective atmosphere to obtain core-shell structured sulfide nano-zero valent iron (S-nZVI) material.

[0009] Furthermore, the low-sulfite is selected from one or more of sodium dithionite, potassium dithionite, sodium sulfite, potassium sulfite, and ammonium sulfite.

[0010] Furthermore, the iron source is selected from one or more of FeSO4, FeCl2, FeCl3, and Fe(NO3)3.

[0011] Furthermore, the molar ratio of the iron source to the low-sulfite is 1:1 to 1:3.

[0012] Furthermore, the rheological phase reaction is carried out under a nitrogen or argon atmosphere, at a reaction temperature of 80°C to 150°C, at a reaction pressure of atmospheric pressure to 0.5 MPa, and for a reaction time of 2 to 8 hours.

[0013] Furthermore, the trace water is introduced by pre-humidifying the precursor or by introducing a protective gas containing water vapor, and the molar ratio of water to iron source is 0.05:1 to 0.5:1.

[0014] Furthermore, the molar ratio of water to iron source is 0.1:1.

[0015] The present invention also provides a sulfide nano-zero valent iron (S-nZVI) material prepared according to a method for preparing sulfide nano-zero valent iron (S-nZVI), the material having a core-shell structure, the core being crystalline Fe(O) particles and the outer shell being an amorphous sulfide iron layer, the size of the Fe(O) particles being 5-20 nm, and the specific surface area of ​​the material being not less than 85 m² / g.

[0016] This invention also provides the application of sulfide nano-zero valent iron (S-nZVI) materials in the treatment of heavy metal wastewater, wherein the heavy metals include one or more of As(III), Se(IV), Cr(VI), Pb(II), Cd(II), and Cu(II).

[0017] Furthermore, the dosage of the sulfurized nano-zero valent iron (S-nZVI) material is 0.1-0.5 g / L. The sulfurized nano-zero valent iron (S-nZVI) derivative material after adsorbing heavy metals can recover heavy metals through acid washing, electrolysis or pyrolysis, or be used as a precursor to prepare energy storage materials or catalytic materials.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. This invention uses low-sulfite (such as sodium dithionite) as a reducing agent and sulfur source. The raw materials are inexpensive, readily available, and environmentally friendly, avoiding the problems of high cost and potential secondary pollution caused by byproducts (borates) in the traditional NaBH4 reduction method. Through an innovative "rheological phase" reaction system, reduction and sulfidation are completed simultaneously under trace amounts of water and mild heating conditions, simplifying the process, reducing energy consumption, and ensuring controllable product morphology and structure.

[0020] 2. The sulfide nano-zero-valent iron (S-nZVI) prepared in this invention has a clear and uniform core-shell structure, with crystalline Fe(O) cores effectively coated by an amorphous sulfide iron layer. This structure endows the material with a high specific surface area (up to 85.3 m² / g, significantly higher than the ~35.2 m² / g of traditional nZVI), high reactivity, and excellent antioxidant and anti-agglomeration stability, which is beneficial to the exposure and maintenance of active sites.

[0021] 3. The sulfide nano-zero valent iron (S-nZVI) material prepared by this invention exhibits adsorption capacity, removal rate and selectivity far superior to traditional nZVI for a variety of heavy metal ions (such as Cr(VI), As(III), Se(IV), Pb(II), Cd(II), Cu(II), etc.), and has outstanding advantages in treating complex heavy metal wastewater.

[0022] 4. The sulfide nano-zero-valent iron (S-nZVI) derivative material after adsorbing heavy metals according to the present invention is no longer a hazardous waste that needs to be disposed of. Instead, it can recover valuable heavy metals through acid washing, electrolysis, etc., or be transformed into functional materials with good electrochemical performance (such as for lithium-ion battery anodes) or catalytic activity through simple heat treatment.

[0023] 5. The entire preparation process of this invention is carried out in a closed reactor under mild conditions (80-150°C, atmospheric pressure to 0.5MPa), simple to operate, and does not require high-end equipment. Furthermore, the product performance can be optimized by adjusting parameters such as the iron-sulfur ratio, water content, and temperature, and it has good process repeatability and scale-up potential. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the core process of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The core process of this invention can be summarized into three consecutive stages:

[0027] 1. Precursor preparation stage: Solid iron salt and solid low-sulfite are physically mixed and ground to form a uniform "rheological phase" precursor.

[0028] 2. Rheological phase reaction stage: The precursor undergoes a solid / quasi-solid phase reaction in a closed, temperature-controlled, and humidity-controlled inert atmosphere. Low sulfite decomposes to release electrons to reduce iron ions and simultaneously construct a sulfide shell.

[0029] 3. Product purification stage: After the reaction, the product is washed and dried under protection to obtain the final sulfide nano-zero valent iron (S-nZVI) product.

[0030] Example 1: Preparation of sulfide nano-zero valent iron (S-nZVI) under standard conditions and its performance in treating Cr(VI).

[0031] step:

[0032] 1. Weigh 0.03 mol (8.11 g) of FeCl3·6H2O and 0.06 mol (10.47 g) of Na2S2O4 (iron-sulfur molar ratio = 1:2) and place them in a mortar. Grind and mix for 20 minutes to obtain a light yellow uniform precursor.

[0033] 2. Transfer the precursor to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and purge the air with high-purity nitrogen for 5 minutes.

[0034] 3. Use a microsyringe to precisely inject 0.054 mL of deionized water (molar ratio of water to iron is 0.1:1) into the precursor, and seal the reaction vessel.

[0035] 4. Place the reactor in an oven preheated to 120°C and react for 4 hours (the pressure generated inside the reactor during the reaction is about 0.2 MPa).

[0036] 5. After the reaction is complete, allow it to cool naturally to room temperature, and remove the black product in a nitrogen glove box. Wash it three times with anhydrous ethanol, and dry it in a vacuum drying oven at 60°C for 12 hours to obtain the target product, denoted as S-nZVI-1.

[0037] Material characterization results:

[0038] Morphology and Structure: Transmission electron microscopy revealed that the S-nZVI-1 particles were approximately spherical with a narrow particle size distribution and a clear core-shell structure. The core consisted of crystalline Fe(O) with a size between 5 and 20 nm, surrounded by a uniformly thick layer of amorphous iron sulfide (FeS). X The shell layer has good particle dispersion and no obvious hard agglomeration.

[0039] Phase analysis: The X-ray diffraction pattern showed a distinct α-Fe characteristic diffraction peak at 44.9°, confirming the successful formation of Fe(0) nuclei. No obvious characteristic peaks of iron oxides such as Fe2O3 or Fe3O4 were detected, indicating that the sulfide shell provided effective antioxidant protection for the core.

[0040] Surface chemical states: X-ray photoelectron spectroscopy analysis showed a characteristic Fe(0) peak at 706.7 eV in the Fe 2p spectrum, and a peak near 707.5 eV attributed to the Fe-S bond. In the S 2p spectrum, a distinct sulfide (S) group appeared at 161.5 eV. 2- The characteristic peaks together confirm the successful construction of the sulfide layer on the material surface.

[0041] Specific surface area (BET): The specific surface area of ​​S-nZVI-1 was determined to be 85.3 m² / g by nitrogen adsorption-desorption test.

[0042] Comparative Example 1 (Traditional NaBH4 Reduction Method):

[0043] Ordinary nZVI was prepared according to the literature method: 0.03 mol FeCl3·6H2O was dissolved in 100 mL of deoxygenated water, and 200 mL of 0.15 mol / L NaBH4 solution was slowly added dropwise under nitrogen protection and vigorous stirring. After the addition was complete, the reaction was continued for 30 minutes. The resulting black precipitate was washed successively with ethanol and deoxygenated water, and then dried under vacuum. The specific surface area of ​​this nZVI was measured to be only 35.2 m² / g.

[0044] Application Example 1: Treatment of simulated wastewater containing Cr(VI)

[0045] Simulated wastewater with pH=5.0 and an initial Cr(VI) concentration of 50 mg / L was prepared. 100 mL of the wastewater was placed in an Erlenmeyer flask, and S-nZVI-1 prepared in Example 1 and nZVI prepared in Comparative Example 1 were added, both at a dosage of 0.1 g / L. The flasks were then placed in a constant-temperature shaker at 25℃ and 150 rpm for the adsorption reaction.

[0046] S-nZVI-1 performance: After 30 minutes of reaction, the removal rate of Cr(VI) reached over 99.5%; adsorption equilibrium was reached after 120 minutes of reaction, with a final removal rate exceeding 99.8%. Calculations show that its saturated adsorption capacity for Cr(VI) is as high as 248.6 mg / g.

[0047] Traditional nZVI performance: Within the same 120-minute reaction time, traditional nZVI only achieves a Cr(VI) removal rate of 78.2%.

[0048] Conclusion: The adsorption rate and capacity of S-nZVI-1 prepared by the method of this invention for Cr(VI) are significantly better than those of nZVI prepared by the traditional method.

[0049] Example 2: Investigating the effect of trace water content (water / iron ratio)

[0050] With the iron-sulfur molar ratio fixed at 1:2, the reaction temperature at 120℃, and the reaction time at 4 hours, the amount of deionized water injected in the steps was changed to make the water / iron molar ratio 0.05:1, 0.1:1, 0.2:1, and 0.5:1, respectively. A series of S-nZVI samples were prepared according to the same steps as in Example 1, and their adsorption performance for Cr(VI) was tested.

[0051] Table 1

[0052]

[0053] Results analysis:

[0054] When the water / iron ratio is 0.1:1, the prepared S-nZVI material has moderate crystallinity, the largest specific surface area, and the best adsorption performance for Cr(VI).

[0055] When the water / iron ratio is too low (0.05:1), the reaction system lacks sufficient water to promote the decomposition of low sulfites and ion migration, resulting in incomplete reduction reaction and low Fe(0) formation.

[0056] When the water / iron ratio is too high (0.2:1, 0.5:1), excessive water may cause the reaction system to approach the liquid phase, which will aggravate the oxidation of Fe(0) cores and the agglomeration of particles, resulting in a decrease in the specific surface area of ​​the material and a reduction in adsorption performance.

[0057] Example 3: Investigating the effect of the iron-sulfur molar ratio

[0058] With FeCl3·6H2O fixed at 0.03 mol, reaction temperature at 120℃, and water / iron ratio at 0.1:1 (using water of crystallization without additional water addition), the amount of Na2S2O4 was varied to achieve iron-sulfur molar ratios of 1:1, 1:2, and 1:3. Materials were prepared following similar procedures, and their adsorption performance for As(III) was tested (initial concentration 10 mg / L, pH=7, dosage 0.2 g / L).

[0059] Results analysis:

[0060] When the iron-sulfur molar ratio is 1:2, the resulting sulfide nano-zero valent iron (S-nZVI) material exhibits the highest adsorption capacity for As(III), reaching 68.5 mg / g.

[0061] When the sulfur ratio is too low (1:1), the resulting sulfide layer is too thin or incomplete, which does not provide sufficient protection for the Fe(0) core. The material is less stable in air or aqueous solution, which affects its long-term adsorption capacity.

[0062] When the sulfur ratio is too high (1:3), the resulting sulfide layer is too thick, which may hinder the transfer of electrons from the internal Fe(0) nuclei to the surface. At the same time, it will occupy some surface active sites, which is not conducive to the mass transfer and adsorption of heavy metal ions, resulting in a decrease in adsorption capacity.

[0063] Application Example 2: Resource Utilization of Adsorption Materials

[0064] The S-nZVI-1 material saturated with Cr(VI) adsorbed in Application Example 1 was collected, dried, and then calcined at 600°C for 2 hours under an argon protective atmosphere to obtain a composite material composed of iron oxide and chromium oxide.

[0065] The composite material was used as the negative electrode active material for lithium-ion batteries and assembled into CR2032 button batteries for electrochemical performance testing.

[0066] Test results:

[0067] The derived material achieved an initial discharge specific capacity of 1120 mAh / g at a current rate of 0.1C (1C = approximately 1000 mA / g).

[0068] After 100 charge-discharge cycles, its discharge specific capacity retention rate is still 82.3%.

[0069] The results show that the waste material after adsorbing heavy metals can be successfully transformed into an energy storage material with good electrochemical performance through simple heat treatment, realizing the upgrade and transformation from an environmental remediation byproduct to a high-value-added functional material, and demonstrating the outstanding advantages of the technical route of this invention in resource recycling.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing nano-zero valent iron sulfide (S-nZVI), characterized in that, Includes the following steps: S1. The iron source and the low-sulfite solid powder are physically mixed and ground at a predetermined molar ratio to form a rheological phase precursor; S2. The precursor is placed in a closed reactor and subjected to a rheological phase reduction reaction at a certain temperature in the presence of an inert atmosphere and trace amounts of water. This causes the SS bonds in the low sulfite to break and release electrons, reducing the iron ions in the iron source to Fe(O) nuclei and simultaneously forming an iron sulfide layer on its surface. S3. After the reaction is complete, the product is cooled, washed and dried under a protective atmosphere to obtain core-shell structured sulfide nano-zero valent iron (S-nZVI) material.

2. The preparation method according to claim 1, characterized in that: The low-sulfite is selected from one or more of sodium dithionite, potassium dithionite, sodium sulfite, potassium sulfite, and ammonium sulfite.

3. The preparation method according to claim 1, characterized in that: The iron source is selected from one or more of FeSO4, FeCl2, FeCl3, and Fe(NO3)3.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the iron source to the low-sulfite is 1:1 to 1:

3.

5. The preparation method according to claim 1, characterized in that: The rheological phase reaction is carried out under a nitrogen or argon atmosphere, at a reaction temperature of 80°C to 150°C, at a reaction pressure of atmospheric pressure to 0.5 MPa, and for a reaction time of 2 to 8 hours.

6. The preparation method according to claim 1, characterized in that: The trace water is introduced by pre-humidifying the precursor or by introducing a protective gas containing water vapor, and the molar ratio of water to iron source is 0.05:1 to 0.5:

1.

7. The preparation method according to claim 6, characterized in that: The molar ratio of water to iron source is 0.1:

1.

8. A sulfide nano-zero-valent iron (S-nZVI) material prepared by the method according to any one of claims 1 to 7, characterized in that: The sulfide nano-zero valent iron (S-nZVI) material has a core-shell structure, with a core of crystalline Fe(O) particles and an outer shell of amorphous iron sulfide layer. The size of the Fe(O) particles is 5-20 nm, and the specific surface area of ​​the material is not less than 85 m² / g.

9. The application of the sulfide nano-zero valent iron (S-nZVI) material as described in claim 8 in the treatment of heavy metal wastewater, characterized in that: The heavy metals include one or more of As(III), Se(IV), Cr(VI), Pb(II), Cd(II), and Cu(II).

10. The application according to claim 9, characterized in that: The dosage of the sulfurized nano-zero valent iron (S-nZVI) material is 0.1-0.5 g / L. The sulfurized nano-zero valent iron (S-nZVI) derivative material after adsorbing heavy metals can recover heavy metals through acid washing, electrolysis or pyrolysis, or be used as a precursor to prepare energy storage materials or catalytic materials.

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