Preparation method of amorphous-crystal mixed phase iron-manganese composite material and application thereof in adsorbing heavy metal arsenic

Abstract

This invention belongs to the field of arsenic pollution treatment technology, specifically relating to a method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material and its application in the adsorption of heavy metal arsenic. The invention first prepares a solution A containing FeCl3·6H2O and MnCl2, then prepares a solution B containing NaOH and Na2SO4. Solution B is then added dropwise to solution A, heated under reflux, centrifuged, washed, and dried to obtain the amorphous-crystalline mixed-phase iron-manganese composite material. This invention achieves controllable composite and synergistic effects of crystalline and amorphous structures through a specific preparation method, combining the high reactivity of the amorphous structure with the stability of the crystalline structure. Simultaneously, it innovatively introduces sulfate ions as a loading component, which not only enhances the material's adsorption capacity for arsenic but also avoids potential pollution from sulfur-containing toxic substances. The synthesis process of this invention is simple, the raw materials are readily available, and the cost is low, making it economically feasible for large-scale practical application and promotion.

Description

Technical Field

[0001] This invention belongs to the field of arsenic pollution treatment technology, specifically relating to a method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material and its application in the adsorption of heavy metal arsenic. Background Technology

[0002] With the widespread use of industrial technologies, particularly metallurgy, ore mining, fossil fuel combustion, and pesticides and fertilizers, large quantities of arsenic-containing wastewater are discharged into natural water bodies, causing serious arsenic pollution. Arsenic typically exists in water in trivalent and pentavalent forms; long-term exposure can cause damage to the nervous system and even cancer, seriously threatening the ecological environment and human health. Therefore, developing economical, efficient, stable, and reliable arsenic removal technologies is of great significance for ensuring water environmental safety and public health.

[0003] Currently, chemical precipitation is the main industrial method for treating arsenic-containing wastewater, especially using iron salts (such as ferrous sulfate and ferric chloride). The principle is based on the utilization of Fe... 3+ Arsenic reacts with arsenate to form a stable ferric arsenate precipitate, and arsenic removal is achieved through the flocculation effect of the ferric salt. This process can reduce the arsenic concentration in the effluent to below 10 μg / L, meeting national standards, but it has significant drawbacks: firstly, it generates a large amount of arsenic-containing iron sludge during the treatment process, which is difficult to dispose of; secondly, to achieve the ideal arsenic removal effect, the iron-arsenic dosage ratio usually needs to be higher than 3:1, resulting in excessive residual Fe in the effluent. 2+ / Fe 3+ This causes an increase in water color, often requiring secondary treatment. In addition, some processes use sulfide salts (such as sodium sulfide) to precipitate arsenic, which is fast-acting and has a low removal limit, but it easily releases sulfur ions and toxic hydrogen sulfide, posing secondary pollution and safety risks.

[0004] Adsorption is another commonly used arsenic removal technology. Common adsorbents include activated alumina, iron-based materials, modified activated carbon, and rare earth adsorbents. This method is simple to operate and produces good effluent quality, but the cost of adsorbents is generally high, especially for iron-based materials, whose adsorption capacity is typically low (usually below 60 mg / g). Existing iron-based materials are mostly structurally complete crystals, which, while exhibiting good stability, have limited adsorption capacity. Although some studies have attempted to improve performance through surface modification, doping, or pore formation, these often come at the cost of material stability, failing to fundamentally solve the problem of balancing high adsorption capacity and high stability. Therefore, there is an urgent need to develop an economical, high-capacity, stable, non-toxic, and harmless adsorbent material for the removal of arsenic from water. Summary of the Invention

[0005] To overcome existing technological bottlenecks, this invention provides a method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material and its application in the adsorption of the heavy metal arsenic. This material efficiently adsorbs arsenic and generates ferric arsenate precipitate, while its solid structure effectively avoids the release of dissolved iron ions, controlling the iron concentration in the effluent from the source and reducing the load on subsequent treatment processes. Unlike sulfide salt precipitation methods that may produce toxic sulfide byproducts, this invention innovatively introduces environmentally friendly sulfate ions as a loading component, improving the material's arsenic adsorption capacity while eliminating the risk of generating sulfur-based toxic substances.

[0006] The core of this invention lies in constructing an iron-manganese compound that combines amorphous and crystalline states: Amorphous phase: It provides an extremely high specific surface area and a large number of exposed iron active sites, which greatly improves its adsorption capacity and reaction efficiency for arsenic.

[0007] Crystalline phase: As a stable framework structure, it effectively enhances the overall mechanical strength and chemical stability of the material, ensuring its long-term effectiveness in practical applications.

[0008] Through this design, the present invention successfully achieves a synergistic balance between "high adsorption capacity" and "long-term stability," providing a new solution for developing efficient, stable, and environmentally friendly arsenic removal materials.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material, the method comprising the following steps: (1) Solution preparation: Using ultrapure water, prepare solution A containing FeCl3·6H2O and MnCl2, and solution B containing NaOH and Na2SO4; (2) Heating reaction: Add solution B dropwise to solution A, stir, transfer it to a reflux condenser, and heat the reaction in a water bath; (3) Washing and drying: After the reaction is complete, the solution is centrifuged, washed, and washed four times. Then it is dried to obtain the amorphous-crystalline mixed phase iron-manganese composite material.

[0010] Further, in step (1), the concentration of FeCl3·6H2O in solution A is 0.05-0.1 mol / L.

[0011] Further, in step (1), the concentration of MnCl2 in solution A is 0.15-0.3 mol / L.

[0012] Further, in step (1), the concentration of NaOH in solution B is 0.32-0.64 mol / L.

[0013] Furthermore, in step (1), the concentration of Na2SO4 is 0.1-0.2 mol / L.

[0014] Furthermore, in step (2), the heating temperature is 70 °C and the reaction time is 4 h.

[0015] Furthermore, in step (3), the centrifugation speed is 8000 rpm and the washing time is 5 min.

[0016] Furthermore, in step (3), the drying temperature is 60 °C and the drying time is 24 h.

[0017] A second aspect of the present invention provides an amorphous-crystalline mixed-phase iron-manganese composite material prepared by the above-described preparation method.

[0018] A third aspect of the present invention provides the application of the above-mentioned amorphous-crystalline mixed-phase iron-manganese composite material in the adsorption of heavy metal arsenic.

[0019] The principle of the amorphous-crystalline mixed-phase iron-manganese composite material of the present invention for adsorbing heavy metal arsenic is as follows: During the reaction stirring, amorphous iron and manganese compounds are rapidly dispersed in the water. Due to the amorphous nature of the material, a large number of iron, manganese, and sulfate ions are exposed on the surface and combine with arsenate ions in the water.

[0020] Ferric ions and manganese compounds have active sites on their surfaces, which combine with pentavalent arsenic to form insoluble arsenic compounds (such as ferric arsenate or manganese arsenate): Its chemical formula for the reaction is: Fe 3+ + H2AsO4 - → FeAsO4 (ferric arsenate precipitate); Mn 2+ + H2AsO4 - → Mn3(AsO4)2 (manganese arsenate precipitate); Mn 3+ + H2AsO4 - → MnAsO4 (manganese arsenate precipitate); In summary, the amorphous iron-manganese-sulfur compounds of the present invention can remove pentavalent arsenic pollution from wastewater through adsorption and complexation, significantly reducing the concentration and mobility of arsenic in water.

[0021] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material and its application in the adsorption of the heavy metal arsenic. Through a specific preparation method, controllable composite and synergistic effects of crystalline and amorphous structures are achieved.

[0022] Crystal structure components: mainly iron and manganese oxides and hydroxides (such as one or more of goethite, ferrihydrite, and manganese hydroxide). This component constitutes the stable framework of the material, ensuring the physical and chemical stability of the material in complex aquatic environments (such as different pH values ​​and interference from coexisting ions), preventing the dissolution of active components or structural collapse, and ensuring long-term arsenic removal capability.

[0023] The amorphous structural component mainly consists of amorphous iron and manganese oxides and hydroxide hydrated phases. This component has an extremely high specific surface area and abundant surface active sites, which can expose large amounts of iron (Fe), manganese (Mn), and supported sulfate (SO4). 2- These active sites interact strongly with arsenic (mainly As(V)) in water through various mechanisms such as ligand exchange, surface complexation, and co-precipitation, which is key to achieving high-capacity and rapid adsorption.

[0024] Sulfate (SO4 2- The function of sulfate ions: Sulfate ions are not only a dopant component, but also, when loaded onto the material surface and interface, they can further modify the surface charge, enhance the electrostatic attraction of negatively charged arsenate / arsenite ions, strengthen the immobilization effect of arsenic, and inhibit the secondary release of arsenic. Furthermore, sulfate ions can adsorb arsenic from water onto the material through ion exchange.

[0025] Specifically, it has the following advantages: 1. High adsorption capacity and excellent arsenic removal performance: This invention's material, through a unique design, combines the high reactivity of an amorphous structure with the stability of a crystalline structure. The amorphous phase exposes numerous highly reactive iron, manganese, and sulfur sites, significantly enhancing the contact and reaction efficiency with arsenic; the coexisting crystalline phase maintains the integrity of the overall material structure, ensuring continuous adsorption. Experiments show that this material achieves a maximum adsorption capacity of 104.99 mg / g for arsenic under neutral pH conditions, a value higher than most reported iron-based or manganese-based single-component adsorbents.

[0026] 2. Stable structure, long service life, and no risk of secondary pollution: The crystalline framework in the material effectively enhances its mechanical strength and chemical stability, and no significant decrease in adsorption capacity or instability in particle morphology has been observed during long-term use. Furthermore, the material exists in a solid state, effectively inhibiting the dissolution of metal ions such as iron and manganese, thus avoiding secondary pollution caused by increased metal ion concentrations in the water and ensuring the stability and safety of the effluent water quality.

[0027] 3. Environmentally friendly, safe and non-toxic, and low cost: This invention uses loaded sulfate ions as the modifying component. These anions are naturally occurring, non-toxic, and harmless, avoiding the use of other chemical modifiers (such as organic complexing agents) that may pose environmental risks. Furthermore, the material uses widely available and inexpensive iron and manganese as its main raw materials, resulting in a simple synthesis process, readily available raw materials, and significantly lower costs than many specialized adsorbent materials (such as rare earth materials and metal-organic frameworks). This makes it economically feasible for large-scale practical application and promotion. Attached Figure Description

[0028] Figure 1 The XRD patterns are those of the amorphous-crystalline mixed-phase iron-manganese composite material in Example 1, the completely amorphous iron compound obtained in Comparative Example 1 when iron is used as a precursor, and the well-crystallized manganese oxide obtained in Comparative Example 2 when manganese is used as a precursor.

[0029] Figure 2 The image shows the transmission electron microscopy (TEM) lattice fringes of the amorphous-crystalline mixed-phase iron-manganese composite material in Example 1.

[0030] Figure 3 This is a graph showing the adsorption capacity test results of the amorphous-crystalline mixed-phase iron-manganese composite material of the present invention for arsenic in different water bodies in Example 4. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0033] Example 1: Preparation of amorphous-crystalline mixed-phase iron-manganese composite material (1) Solution preparation: Using ultrapure water, prepare 100 mL of solution A containing 0.1 mol / L FeCl3·6H2O and 0.3 mol / L MnCl2, and prepare 100 mL of solution B containing 0.64 mol / L NaOH and 0.2 mol / L Na2SO4.

[0034] (2) Heating reaction: Slowly add solution B to solution A, stir rapidly, transfer it to a reflux condenser and heat it in a 70 ℃ water bath for 4 h.

[0035] (3) Washing and drying: The solution obtained in step (2) is centrifuged and washed at 8000 rpm for 5 min, and repeated four times. The obtained material is placed in a drying oven at 60 ℃ for drying. After drying for 24 h, the amorphous-crystalline mixed phase iron-manganese composite material is obtained.

[0036] Comparative Example 1: Preparation of completely amorphous iron compound adsorbents using iron as a precursor (1) Solution preparation: Using ultrapure water, prepare 100 mL of solution A containing 0.4 mol / L FeCl3·6H2O, and prepare 100 mL of solution B containing 0.64 mol / L NaOH and 0.2 mol / L Na2SO4.

[0037] (2) Heating reaction: Slowly add solution B to solution A, stir rapidly, transfer it to a reflux condenser and heat it in a 70 ℃ water bath for 4 h.

[0038] (3) Washing and drying: The solution obtained in step (2) is centrifuged and washed at 8000 rpm for 5 min, and repeated 4 times. The obtained material is placed in a drying oven at 60 ℃ for drying. After drying for 24 h, the completely amorphous iron compound adsorbent material is obtained.

[0039] Comparative Example 2: Preparation of well-crystallized manganese oxide adsorbents using manganese as a precursor (1) Solution preparation: Using ultrapure water, prepare 100 mL of solution A containing 0.4 mol / L MnCl2 and 100 mL of solution B containing 0.64 mol / L NaOH and 0.2 mol / L Na2SO4.

[0040] (2) Heating reaction: Slowly add solution B to solution A, stir rapidly, transfer it to a reflux condenser and heat it in a 70 ℃ water bath for 4 h.

[0041] (3) Washing and drying: The solution obtained in step (2) is centrifuged and washed at 8000 rpm for 5 min, and repeated four times. The obtained material is placed in a drying oven at 60 ℃ for drying. After drying for 24 h, the well-crystallized manganese oxide adsorbent material is obtained.

[0042] The XRD patterns of the amorphous-crystalline mixed-phase iron-manganese composite material prepared in Example 1, the completely amorphous iron compound adsorbent prepared in the comparative example, and the well-crystallized manganese oxide adsorbent prepared in Comparative Example 2 are shown in the figure. Figure 1 As shown in the figure, when iron is used as the precursor alone, the product obtained is a completely amorphous iron compound, and its XRD pattern only shows a broad diffuse diffraction pattern; while when manganese is used as the precursor alone, the product obtained is a well-crystallized manganese tetroxide oxide, and its XRD pattern shows sharp and clear diffraction peaks. Example 1, by combining iron and manganese in a specific ratio and process, produced a material whose XRD pattern simultaneously contained clear diffraction peaks from the manganese-based crystalline phase and broadened diffuse peaks from the iron-based amorphous phase. This indicates that the present invention successfully constructed a composite structure in which crystalline and amorphous states coexist. Figure 3 Transmission electron microscopy analysis revealed that the synthesized material is composed of both crystalline and amorphous regions. High-resolution images showed clear lattice fringes and amorphous regions coexisting, with some lattice defects and discontinuities, confirming that the material is a hybrid structure of crystalline and amorphous phases. This structure combines the good stability of the crystalline region with the high specific surface area and high reactivity of the amorphous region, demonstrating that the material is a composite adsorbent with a unique microstructure, existing between pure amorphous and fully crystalline materials.

[0043] Example 2: Maximum Adsorption Capacity Test 1) Take six 50 mL beakers as six reactors. Add 50 mL of a solution containing 100 mg / L As(V) to each beaker. Divide the six beakers into two groups: one group is the control group, which does not add any material, and the other group is the experimental group, which adds 50 mg of the amorphous-crystalline mixed phase iron-manganese composite material prepared in Example 1.

[0044] 2) Stir the reaction system to promote the adsorption and stabilization of arsenate ions in the water by the material.

[0045] 3) After 12 hours of reaction, initial and final water samples were taken, filtered, diluted tenfold, and the arsenic content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The maximum adsorption capacity data are shown in Table 1 below: Table 1 Adsorption performance results of different experimental groups Group 1 96.1 108.12 Group 2 100 103.53 Group 3 94.9 100.32 Since the As content in the control group without added materials remained almost unchanged, its data were not included. As shown in Table 1, the amorphous iron-manganese compound synthesized in this invention exhibits a high adsorption capacity for arsenic, reaching 108.12 mg / g, with an average adsorption capacity of 104.99 mg / g in several repeated experiments.

[0046] Example 3: Low-concentration adsorption effect test 1) Take six 50 mL beakers as six reactors. Add 50 mL of a solution containing 20 mg / L As (V) to each beaker. Divide the six beakers into two groups: one group is the control group, which does not add any material, and the other group is the experimental group, which adds 50 mg of the amorphous-crystalline mixed phase iron-manganese composite material prepared in Example 1.

[0047] 2) Stir the reaction system to promote the adsorption and stabilization of arsenate ions in the water by the material.

[0048] 3) After 12 hours of reaction, initial and final water samples were taken, filtered, diluted 10-fold, and the arsenic content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The obtained arsenic adsorption data are shown in Table 2 below: Table 2 Adsorption effect at low concentration Group 1 100 22.3 Group 2 100 22.65 Group 3 100 21.95 Since the As content in the control group without the added material remained almost unchanged, its data were not included. As shown in Table 2, the material synthesized in this invention can achieve 100% removal of arsenic pollutants at low concentrations, thus demonstrating good removal efficiency for low pollutant concentrations.

[0049] Example 4: Adsorption Tests in Different Water Bodies 1) Take 15 50 mL beakers as reactors and divide the 15 beakers into 5 groups. Group 1 is the control group, and 50 mL of pure water is added to each beaker; Group 2 is each beaker containing 100 mg / L As (V) prepared with 50 mL of pure water; Group 3 is each beaker containing 100 mg / L As (V) prepared with 50 mL of tap water; Group 4 is each beaker containing 100 mg / L As (V) prepared with 50 mL of Pearl River water; Group 5 is each beaker containing 100 mg / L As (V) prepared with 50 mL of seawater; and 50 mg of the amorphous-crystalline mixed-phase iron-manganese composite material prepared in Example 1 is added to each beaker.

[0050] 2) Stir the reaction system to promote the adsorption and stabilization of arsenate ions in the water by the material.

[0051] 3) After reacting for 12 hours, initial and final water samples were taken, filtered, diluted tenfold, and the arsenic content was detected using inductively coupled plasma atomic emission spectrometry (ICP-AES). The adsorption capacity test graphs of the amorphous-crystalline mixed-phase iron-manganese composite material of this invention for arsenic in different water bodies are shown below. Figure 3 As shown, the material of this invention maintains a high adsorption capacity for arsenic in complex water bodies (such as tap water and Pearl River water), exhibiting excellent anti-interference performance. Even in seawater environments with high ionic strength, although its adsorption capacity decreases somewhat, the attenuation is controlled at around 20%, and the overall removal efficiency remains high. These results demonstrate that the material of this invention not only possesses excellent arsenic adsorption performance but also exhibits good stability under different water quality conditions, possessing the potential to cope with complex real-world water environments.

[0052] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for producing an amorphous-crystalline mixed phase iron-manganese composite material, characterized by, The preparation method includes the following steps: (1) Solution preparation: Using ultrapure water, prepare solution A containing FeCl3·6H2O and MnCl2, and solution B containing NaOH and Na2SO4; (2) Heating reaction: Add solution B dropwise to solution A, stir, transfer it to a reflux condenser, and heat the reaction in a water bath; (3) Washing and drying: After the reaction is complete, the solution is centrifuged, washed, and washed four times. Then it is dried to obtain the amorphous-crystalline mixed phase iron-manganese composite material.

2. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (1), the concentration of FeCl3·6H2O in solution A is 0.05-0.1 mol / L.

3. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (1), the concentration of MnCl2 in solution A is 0.15-0.3 mol / L.

4. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (1), the concentration of NaOH in solution B is 0.32-0.64 mol / L.

5. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (1), the concentration of Na2SO4 is 0.1-0.2 mol / L.

6. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (2), the heating temperature is 70 °C and the reaction time is 4 h.

7. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (3), the centrifugation speed is 8000 rpm and the washing time is 5 min.

8. The method for preparing an amorphous-crystalline mixed-phase iron-manganese composite material according to claim 1, characterized in that, In step (3), the drying temperature is 60 °C and the drying time is 24 h.

9. An amorphous-crystalline mixed-phase iron-manganese composite material prepared by the preparation method according to any one of claims 1-8.

10. The application of the amorphous-crystalline mixed-phase iron-manganese composite material as described in claim 9 in the adsorption of heavy metal arsenic.

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