A magnesium ferrite and ferrous ion coupled zero-valent iron biochar composite material, a preparation method and application thereof

Abstract

The application discloses a magnesium ferrite and ferrous ion coupled zero-valent iron biochar composite material and a preparation method and application thereof, and steps are as follows: (1) iron-rich sludge is dried and crushed; (2) anhydrous magnesium chloride is crushed and then added into the dried iron-rich sludge, and a sludge precursor is obtained after uniform stirring; and (3) the sludge precursor is pyrolyzed under the protection of inert gas and at a high temperature of not less than 700 DEG C, and a magnesium ferrite and ferrous ion coupled zero-valent iron biochar composite material is obtained after cooling. 0 In combination, the magnesium ferrite and the ferrous ion can effectively reduce the electrical resistance of Fe 0 Particles, thereby promoting the conduction of electrons from the Fe 0 Core to the surface-adsorbed pollutants; in addition, the Fe 2+ Can convert the basic iron oxide generated in the reaction process into Fe3O4, thereby slowing down the passivation of the Fe 0 Particles; and the preparation method of the application is simple in steps, does not need a reducing agent, and does not generate waste water, and is a green and environment-friendly preparation method.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation materials technology, and in particular to a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, its preparation method and application. Background Technology

[0002] Chromium exists primarily in the +3 and +6 valence states in the natural environment. Cr(III) is an essential trace element for the human body, while Cr(VI) is a typical harmful heavy metal ion, exhibiting strong mobility and high toxicity, carcinogenicity, and mutagenicity. Excessive Cr(VI) can seriously threaten aquatic environmental safety and human health; therefore, Cr(VI) pollution in water bodies is receiving increasing attention from all sectors of society.

[0003] Currently, the main methods for remediating Cr(VI) pollution include adsorption, membrane separation, and biological methods. The most effective method is to reduce it to the less toxic Cr(III). Zero-valent iron has strong reducing properties (E0). 0 =(Fe 2+ Zero-valent iron (ZV), with its abundant and inexpensive sources, is often used as an environmentally friendly functional material to adsorb Cr(VI) pollution in water. However, this remediation technology suffers from drawbacks such as easy agglomeration, deactivation, and passivation of ZV particles. For example, nano-ZV tends to aggregate due to its high surface energy and magnetism, reducing its activity and fluidity. During preparation and reaction, the surface of ZV is easily oxidized or accumulates iron (hydrogen) oxides, forming a passivation layer that hinders the transfer of electrons from the particle core to the surface, thus reducing its reactivity. To address these issues, two main methods are employed to modify ZV: 1) biochar loading method; 2) surface modification method. To maximize the reactivity of zero-valent iron (ZVFe), studies have combined the two modification methods mentioned above for dual modification. For example, CN 116240027 A discloses a method for preparing sulfide-doped ZVFe nano-biochar. This method involves pyrolyzing lotus stems / crop straw to obtain biochar, then adding it to a mixed solution of ferric salt and polyethylene glycol, continuously stirring and purging with nitrogen. Subsequently, a mixed solution of potassium borohydride and sodium dithionite is added dropwise, the black precipitate is collected and dried, and finally calcined in a tube furnace under a nitrogen atmosphere to obtain sulfide-doped ZVFe nano-biochar particles. However, this method involves many steps, requires large amounts of chemical reagents, and has harsh preparation conditions, generating large amounts of wastewater and causing secondary pollution. More seriously, hydrogen gas is generated during the reduction of iron salts by potassium borohydride, thus posing a certain degree of danger during the preparation process.

[0004] Therefore, how to obtain a modified zero-valent iron material that is efficient, low-cost, and highly reactive is an urgent problem to be solved in this field. Summary of the Invention

[0005] This invention aims to overcome the aforementioned problems in the prior art by providing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions, its preparation method, and its application. The method involves coupling MgFe₂O₄ with Fe... 0 Combining can effectively reduce Fe 0 The resistance of the particles promotes the movement of electrons from Fe. 0 Contaminants are conducted from the core to the surface adsorbed. Additionally, Fe... 2+ The basic iron oxide produced during the corrosion process can be converted into Fe3O4, thus slowing down the corrosion of Fe. 0 The particles have a passivating effect; moreover, the preparation method of the present invention is simple, requires no reducing agent, and does not generate wastewater, making it a green and environmentally friendly preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions, comprising the following steps: (1) Dry and crush the iron-rich sludge; (2) After anhydrous magnesium chloride is pulverized, it is added to the dried iron-rich sludge and stirred evenly to obtain the sludge precursor. (3) The sludge precursor was pyrolyzed under inert gas protection and at a high temperature of 700±50℃, and after cooling, the zero-valent iron biochar composite material of magnesium ferrite and ferrous ions was obtained.

[0007] The present invention contains MgFe2O4 and Fe 2+ Coupled Fe 0 The formation principle of @BC is: ① Redox reaction: After the organic matter in the iron-rich sludge decomposes, it produces reducing substances such as carbon, carbon monoxide, and hydrogen. However, these substances can only reduce some iron oxides to Fe at 700 ℃. 0 ② Chlorination reaction: MgCl2 decomposes into Cl2 and HCl during pyrolysis. Some iron oxides are directly chlorinated by magnesium chloride or indirectly chlorinated by Cl2 and HCl to generate FeCl2 / FeCl3. However, at a high temperature of 700 °C, FeCl3 has completely volatilized, and FeCl2 remains in the composite material in solid form. ③ Synthesis reaction: MgO formed by the decomposition of magnesium chloride reacts with iron oxides to generate MgFe2O4.

[0008] MgFe2O4 is a soft magnetic n-type semiconductor material with a spinel structure, in which Mg 2+ and Fe 3+The ions are located in the interstices of tetrahedrons and octahedrons, while oxygen atoms form a close-packed face-centered cubic structure with a narrow band gap (~2.0 eV). This structure has been applied in various technical fields such as heterogeneous catalysis, photocatalysis, sensors, and adsorption. This invention combines MgFe₂O₄ with Fe... 0 Combining can effectively reduce Fe 0 The resistance of the particles promotes the movement of electrons from Fe. 0 The contaminants are conducted from the core to the surface adsorbed. Additionally, Fe... 2+ The basic iron oxide (γ-FeOOH) produced during the corrosion process can be converted into Fe3O4, thus slowing down the corrosion of Fe. 0 The passivation effect of the particles significantly enhances the reactivity of zero-valent iron materials. MgFe2O4 can be prepared by high-temperature calcination of a mixture of MgO and Fe2O3, while FeCl2 can be generated through a chlorination reaction. This invention involves the pyrolysis of a mixture of iron-rich sludge and MgCl2. During this process, iron oxides undergo chlorination volatilization, redox reactions, and the synthesis of MgFe2O4. By controlling the reaction conditions, Fe2O3 is simultaneously generated. 0 MgFe₂O₄, FeCl₂, and biochar were used to prepare MgFe₂O₄ and FeCl₂. 2+ Co-activated Fe 0 @BC. The preparation method of this invention is simple, requires no reducing agent, and does not generate wastewater, making it a green and environmentally friendly preparation method.

[0009] Preferably, the iron-rich sludge in step (1) has an iron content of 25-35 wt%.

[0010] Preferably, in step (1), the iron-rich sludge is dried to constant weight at 70~100℃.

[0011] Preferably, in step (1), the dried iron-rich sludge is crushed to a particle size of no more than 100 mesh.

[0012] Preferably, the mass ratio of anhydrous magnesium chloride to iron-rich sludge in step (2) is 1.2~2.7:10.0. Insufficient addition of anhydrous magnesium chloride will prevent the production of the required MgFe2O4 and Fe. 2+ Adding too much will result in an excessively thick layer of MgFe2O4, affecting the Fe content. 0 The electron conduction efficiency.

[0013] Preferably, in step (2), anhydrous magnesium chloride is pulverized to a particle size of no more than 100 mesh.

[0014] Preferably, the flow rate of the inert gas during pyrolysis in step (3) is 200~600 mL / min. During pyrolysis, organic matter decomposes to produce CO and H2, and HCl and Cl2 produced during the pyrolysis of MgCl2 will enter the carrier gas. Therefore, changing the flow rate of the inert gas may change the properties of the composite material and thus affect the Cr(VI) removal efficiency.

[0015] Preferably, the pyrolysis time in step (3) is 15-60 min. The holding time during pyrolysis also affects the Fe... 0 The properties of @BC have an impact; the longer the residence time, the more Fe will be formed. 0 Furthermore, more FeCl2 will volatilize, thereby altering the properties of the composite material and the removal performance of Cr(VI).

[0016] Preferably, the heating rate during pyrolysis in step (3) is 2~4℃ / min.

[0017] Secondly, the present invention provides a zero-valent iron biochar composite material made by coupling magnesium ferrite and ferrous ions using the above-described preparation method.

[0018] Thirdly, the present invention provides an application of the zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled by the above preparation method in the removal of Cr(VI) pollution from water bodies.

[0019] Therefore, the present invention has the following beneficial effects: (1) Mix MgFe2O4 with Fe 0 Combining can effectively reduce Fe 0 The resistance of the particles promotes the movement of electrons from Fe. 0 The core conducts pollutants to the surface adsorbed, enhancing the reactivity; (2) Fe 2+ The basic iron oxide (γ-FeOOH) produced during the corrosion process can be converted into Fe3O4, thus slowing down the corrosion of Fe. 0 The passivation effect of particles; (3) The preparation method is simple, requires no reducing agent, and does not produce wastewater, making it a green and environmentally friendly preparation method. Attached Figure Description

[0020] Figure 1 These are the XRD patterns of the composite materials prepared in Examples 1-3 and Comparative Example 1.

[0021] Figure 2 These are test graphs of Cr(VI) removal of the composite materials prepared in Examples 1-3 and Comparative Examples 1-3 (dosage was 2 g / L, initial Cr(VI) concentration was 100 mg / L, initial pH=5).

[0022] Figure 3 These are the Tafel corrosion curves of the composite materials prepared in Examples 1-3 and Comparative Example 1.

[0023] Figure 4 These are the XRD patterns of the composite materials prepared in Example 2 and Comparative Examples 2 and 3.

[0024] Figure 5 These are the XRD patterns of the composite materials prepared in Examples 2, 4, and 5.

[0025] Figure 6 These are the Tafel corrosion curves of the composite materials prepared in Examples 2, 4, and 5.

[0026] Figure 7 These are the Cr(VI) removal efficiency curves of the composite materials prepared in Examples 2, 4 and 5 (dosage was 2 g / L, initial Cr(VI) concentration was 100 mg / L, initial pH=5).

[0027] Figure 8 These are the XRD patterns of the composite materials prepared in Examples 4, 6, and 7.

[0028] Figure 9 These are the Tafel corrosion curves of the composite materials prepared in Examples 4, 6, and 7.

[0029] Figure 10 These are the Cr(VI) removal efficiency curves of the composite materials prepared in Examples 4, 6 and 7 (dosage was 2 g / L, initial Cr(VI) concentration was 100 mg / L, initial pH=5).

[0030] Figure 11 These are SEM images of the composite materials prepared in Examples 2, 4, 7 and Comparative Example 1.

[0031] Figure 12 This is a TEM image of the composite material prepared in Example 7.

[0032] Figure 13 MBC700 under different coexisting ions 120 -400-30 Cr(VI) removal rate test chart.

[0033] Figure 14 MBC700 at different initial pH values ​​of solutions 120 -400-30 Cr(VI) removal rate test chart.

[0034] Figure 15 MBC700 at different dosages 120 -400-30 Test graph of Cr(VI) removal rate and removal amount. Detailed Implementation

[0035] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0036] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0037] In the following examples, the iron-rich sludge was taken from a pig farm in Yuhang District, Hangzhou City, Zhejiang Province (with an iron content between 25wt% and 32wt%), and the chemical reagents such as anhydrous MgCl2, potassium dichromate, sodium hydroxide, and hydrochloric acid were purchased from Yonghua Chemical Co., Ltd.

[0038] General Implementation Examples: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry and crush the iron-rich sludge; (2) After anhydrous magnesium chloride is pulverized, it is added to the dried iron-rich sludge and stirred evenly to obtain the sludge precursor. (3) The sludge precursor was pyrolyzed under inert gas protection and at a high temperature of 700±50℃, and after cooling, the zero-valent iron biochar composite material of magnesium ferrite and ferrous ions was obtained.

[0039] In one specific implementation, in step (1), the iron-rich sludge is dried to constant weight at 70~90℃.

[0040] In one specific implementation, in step (1), the dried iron-rich sludge is crushed to a particle size of no more than 100 mesh.

[0041] In one specific implementation, the mass ratio of anhydrous magnesium chloride to iron-rich sludge in step (2) is 1.2~2.7:10.0.

[0042] In one specific implementation, in step (2), anhydrous magnesium chloride is pulverized to a particle size of no more than 100 mesh.

[0043] In one specific implementation, the flow rate of the inert gas during pyrolysis in step (3) is 200~600 mL / min.

[0044] In one specific implementation, the inert gas used in step (3) during pyrolysis is nitrogen.

[0045] In one specific implementation, the heating rate during pyrolysis in step (3) is 2~4℃ / min, and the pyrolysis time is 15~60min.

[0046] Example 1: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.2g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 200 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 80 -200-60℃, store in a vacuum desiccator for later use.

[0047] Example 2: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 200 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 120 -200-60℃, store in a vacuum desiccator for later use.

[0048] Example 3: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 2.7g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 200 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 160-200-60℃, store in a vacuum desiccator for later use.

[0049] Example 4: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 400 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 120 -400-60°C, store in a vacuum desiccator for later use.

[0050] Example 5: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 600 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 120 -600-60°C, store in a vacuum desiccator for later use.

[0051] Example 6: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 400 mL / min and a heating rate of 3 °C / min, and held for 15 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 120 -400-15, store in a vacuum desiccator for later use.

[0052] Example 7: A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 400 mL / min and a heating rate of 3 °C / min, and held for 30 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC700. 120 -400-30°C, store in a vacuum desiccator for later use.

[0053] Comparative Example 1 (without anhydrous magnesium chloride): A method for preparing a zero-valent iron biochar composite material includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) The dried iron-rich sludge was placed in a tube furnace and heated to 700 °C at a constant nitrogen flow rate of 200 mL / min and a heating rate of 3 °C / min and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain zero-valent iron biochar composite material, denoted as MBC700-200-60, and stored in a vacuum desiccator for later use.

[0054] Comparative Example 2 (temperature 800 ℃): A method for preparing a zero-valent iron biochar composite material includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 800 °C at a constant nitrogen flow rate of 200 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC800. 120 -200-60℃, store in a vacuum desiccator for later use.

[0055] Comparative Example 3 (temperature 900 ℃): A method for preparing a zero-valent iron biochar composite material includes the following steps: (1) Dry the iron-rich sludge at 80°C to constant weight and then crush it to 100 mesh; (2) Grind anhydrous magnesium chloride to 100 mesh, weigh 1.9g of anhydrous MgCl2 and 10.0g of dried iron-rich sludge and stir them evenly to obtain sludge precursor; (3) The sludge precursor was placed in a tube furnace and heated to 900 °C at a constant nitrogen flow rate of 200 mL / min and a heating rate of 3 °C / min, and held for 60 min. Then it was naturally cooled to room temperature under nitrogen protection to obtain a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled together, denoted as MBC900. 120 -200-60℃, store in a vacuum desiccator for later use.

[0056] XRD analysis was performed on the composite materials prepared in Examples 1-3 and Comparative Example 1, and the results are as follows: Figure 1 As shown; from Figure 1 As can be seen from the results, after modification with MgCl2, the MBC700 prepared in Example 1... 80 -200-60, MBC700 prepared in Example 2 120 -200-60 and the MBC700 prepared in Example 3 160 The XRD diffraction pattern at -200-60° shows characteristic peaks of MgFe₂O₄ at 2θ = 30.2° and 35.5°, and also indicates the presence of γ-Fe. 0 (2θ=43.2°), but only MBC700 120 α-Fe appears at -200-60 0 The characteristic peak (2θ=44.6°) was observed, while the MBC700-200-60 prepared in Comparative Example 1 without the addition of anhydrous MgCl2 modification did not show the characteristic peak of MgFe2O4, but γ-Fe was present. 0 and α-Fe 0 The characteristic peak, and its intensity is higher than that of MBC700. 120The Cr(VI) removal effect of the composite materials in Examples 1-3 and Comparative Example 1 was compared and analyzed, and the results are as follows: Figure 2 As shown; from Figure 2 As can be seen from the data, the MBC700 prepared in Example 2... 120 The highest Cr(VI) removal rate was observed at -200-60, reaching 28.80 mg / g. Figure 3 The Tafel corrosion curves for Examples 1-3 and Comparative Example 1 show that MBC700 120 The corrosion potential at -200-60 is the lowest (-0.20 V), indicating that its electron transport rate is the highest.

[0057] To clarify the effect of pyrolysis temperature on the properties of zero-valent iron biochar composites and the amount of Cr(VI) removed, the MBC700 prepared in Example 2 was used... 120 -200-60 and the MBC800 prepared in Comparative Example 2 120 MBC900 prepared in -200-60 and Comparative Example 3 120 XRD analysis was performed at -200-60°C, and the results are as follows: Figure 4 As shown; from Figure 4 As can be seen, when the temperature rises to 800 ℃ and 900 ℃, iron oxides are further reduced to Fe. 0 α-Fe 0 The characteristic peak intensity increased significantly, while the characteristic peak of MgFe2O4 disappeared, but the characteristic peak of MgO appeared (2θ=43.2°, 62.3°). From Figure 2 As can be seen from this, the MBC800 prepared in Comparative Example 2... 120 MBC900 prepared from -200-60 and Comparative Example 3 120 -200-60 compared to the MBC700 prepared in Example 2 120 The removal of Cr(VI) at -200-60°C decreased significantly, mainly because the band gap (BG) of MgO is 7.8 eV, making its conductivity significantly lower than that of MgFe2O4 (BG=2.0 eV). In other words, although the Fe in the composite materials of Comparative Example 2 and Comparative Example 3... 0 The content of Cr is higher, but the surface conductivity is reduced, which prevents electrons from being effectively conducted to Cr(VI).

[0058] In Examples 4 and 5, the N2 flow rate was adjusted to 400 and 600 mL / min, respectively. Figure 5 XRD patterns of composite materials prepared at various N2 flow rates, from Figure 5 From this, we can know that α-Fe 0 The intensity of the characteristic peak increases with increasing airflow, but the intensity of the characteristic peak of MgFe2O4 decreases accordingly. Figure 6The Tafel corrosion curves of the composite materials prepared at various N2 flow rates are shown below. Figure 6 As can be seen from the example, the MBC700 prepared in Example 4... 120 The corrosion potential is lowest at -400-60 (-0.32 V). Figure 7 The change in the ratio of residual Cr(VI) (C) to the initial Cr(VI) concentration (C0) during the reaction process is described from... Figure 7 As can be seen from the example, the MBC700 prepared in Example 4... 120 The removal efficiency is highest at -400 to -60, reaching 70.36%.

[0059] The divalent iron salts in the composite materials prepared in the above examples and comparative examples were extracted with anhydrous ethanol, and the Fe content was determined. 2+ The content, and the results are shown in Table 1. As can be seen from the table, although Fe... 2+ The content of Cr(VI) increased with increasing airflow, but the removal efficiency of Cr(VI) did not increase accordingly, indicating that the α-Fe in the composite material still plays a decisive role in the removal efficiency of Cr(VI). 0 And the crystallinity of MgFe2O4.

[0060] Table 1: Fe in composite materials 2+ Content test results.

[0061] Example 1 Not detected Example 2 0.13 Example 3 Not detected Example 4 0.35 Example 5 0.79 Example 6 2.30 Example 7 0.99 Comparative Example 1 Not detected Comparative Example 2 Not detected Comparative Example 3 Not detected In Examples 6 and 7, the residence time during high-temperature pyrolysis was reduced (15 min and 30 min, respectively) to investigate the properties of the composite materials. Figure 8 XRD patterns of composite materials prepared at various residence times, from Figure 8 As can be seen, the intensity of the characteristic peaks of MgFe2O4 increases significantly with decreasing residence time, but α-Fe 0 The intensity of the characteristic peaks decreased significantly. Figure 9 The Tafel corrosion curves of the composite material at various residence times are shown below. Figure 9 As can be seen, the composite material has the lowest corrosion potential (-0.52 V) when the residence time is 30 min, which means that the MBC700 prepared in Example 7 has the lowest corrosion potential. 120 The electron conduction rate is highest at -400 to -30. Figure 10 The change in the ratio of residual Cr(VI) (C) to the initial Cr(VI) concentration (C0) during the reaction process is described from... Figure 10 As can be seen, the highest Cr(VI) removal efficiency (95.17%) was achieved when the residence time was 30 min, which is the same as that of the MBC700 prepared in Example 7. 120 The removal efficiency is optimal at -400-30. Table 1 shows that Fe... 2+The content increases as the residence time decreases, as seen in the MBC700 prepared in Example 6. 120 -400-15 Fe 2+ The content of α-Fe is the highest, but α-Fe 0 The content of Fe is the lowest in composite materials. 2+ It is easily oxidized to Fe after entering the solution. 3+ Ultimately, Fe(OH)3 is deposited on the surface of the composite material, making MBC700 120 -400-15 rapid inactivation.

[0062] The composite materials obtained in the above embodiments and comparative examples were subjected to SEM and TEM tests, and the results are as follows: Figure 11 and Figure 12 As shown. From Figure 11 As can be seen from the scanning electron microscope (SEM) image, the MBC700 prepared in Example 2... 120 The surface of the -200-60 medium formed near-spherical MgFe2O4 particles, which is significantly different from the unmodified MBC700-200-60 in Comparative Example 1. The MBC700 prepared in Example 4... 120 The spherical particles on the -400-60 surface aggregated to form larger polyhedral particles; while in Example 7, due to the shortened residence time, the MBC700 120 The surface morphology changes significantly at -400-30°, forming various lamellar structures; from Figure 12 The transmission electron microscopy (TEM) images show that the Fe in the composite material obtained in Example 7 is... 0 The particles appear to be encased in a shell containing MgFe2O4.

[0063] The analysis results from the above examples and comparative examples show that MgFe2O4 and Fe 2+ Synergistic effect improved the material's Cr(VI) removal efficiency.

[0064] Application Example 1: The MBC700 with the best test results 120 -400-30 Cr(VI) removal effect under the influence of different coexisting ions.

[0065] The test method is as follows: 10 mM Ca is added to a 100 mg / L Cr(VI) solution. 2+ NO3 - CO3 - and HCO3 - A solution without coexisting ions was used as a control; 0.1 g of MBC700 was added. 120 After -400-30, insert 25.0. +The device was oscillated at a constant temperature of 180 rpm for 24 hours on a constant temperature electric shaker at 0.5 ℃. The results are as follows: Figure 13 As shown, Ca 2+ The presence of NO3 has almost no effect on the removal of Cr(VI) from the composite material. - CO3 - and HCO3 - The presence of NO3 negatively impacted the Cr(VI) removal efficiency of the composite material. Compared to the control, NO3... - CO3 - and HCO3 - MBC700 120 The Cr(VI) removal efficiency of -400-30 decreased by 14.72%, 26.24%, and 12.90%, respectively, indicating that they compete with Cr(VI) for active sites on the composite material.

[0066] Application Example 2: The removal efficiency of Cr(VI) was tested at different initial pH values.

[0067] The test method is as follows: Using 0.1 mol / L hydrochloric acid and sodium hydroxide solutions, the initial pH of a 100 mg / L Cr(VI) solution was adjusted to 2, 4, 5, 6, 8, and 10, respectively. 0.1 g of MBC700 was then added. 120 -400-30, and at 25.0 + The device was subjected to uniform oscillation at 180 rpm on a 0.5 ℃ constant-temperature electric shaker for 24 hours. The results are as follows: Figure 14 As shown, MBC700 120 The removal efficiency of Cr(VI) at -400-30 decreased with increasing pH, from 99.72% (pH = 2) to 36.29% (pH = 10). Except for the initial pH = 10, the final pH of all other solutions increased compared to the initial value.

[0068] Application Example 3: The effect of different dosages on the Cr(VI) removal efficiency of composite materials was tested.

[0069] The test method is as follows: 0.02 g to 0.12 g of MBC700 is added to 50 mL of a 100 mg / L Cr(VI) solution with an initial pH of 5. 120 The removal efficiency / removal amount of Cr(VI) was tested at -400 to -30°C. The results are as follows: Figure 15 As shown, MBC700 120The Cr(VI) removal efficiency of MBC700120-400-30 increased with increasing dosage, reaching a minimum of 23.47% at 0.02 g and a maximum of 98.82% at 0.12 g. However, the removal efficiency of MBC700120-400-30 did not vary as drastically, fluctuating between 41.17 and 58.66 mg / g.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a zero-valent iron biochar composite material coupled with magnesium ferrite and ferrous ions, characterized in that, Includes the following steps: (1) Dry and crush the iron-rich sludge; (2) After crushing anhydrous magnesium chloride, add it to the dried iron-rich sludge and stir evenly to obtain the sludge precursor; the mass ratio of anhydrous magnesium chloride to iron-rich sludge is 1.2~2.7:10.0; (3) The sludge precursor was pyrolyzed under inert gas protection and at a high temperature of 700±50℃, and after cooling, the zero-valent iron biochar composite material of magnesium ferrite and ferrous ions was obtained.

2. The preparation method according to claim 1, characterized in that, The iron-rich sludge in step (1) has an iron content of 25-35 wt%.

3. The preparation method according to claim 1, characterized in that, In step (1), the iron-rich sludge is dried at 70~90℃ to constant weight.

4. The preparation method according to claim 1 or 3, characterized in that, In step (1), the dried iron-rich sludge is crushed to a particle size of no more than 100 mesh.

5. The preparation method according to claim 1 or 4, characterized in that, In step (2), anhydrous magnesium chloride is pulverized to a particle size of no more than 100 mesh.

6. The preparation method according to claim 1, characterized in that, In step (3), the flow rate of the inert gas during pyrolysis is 200~600 mL / min.

7. The preparation method according to claim 1, characterized in that, In step (3), the heating rate during pyrolysis is 2~4℃ / min, and the pyrolysis time is 15~60min.

8. A zero-valent iron biochar composite material made of magnesium ferrite and ferrous ions coupled using the preparation method described in any one of claims 1 to 7.

9. The application of a zero-valent iron biochar composite material of magnesium ferrite and ferrous ions coupled using the preparation method described in any one of claims 1 to 7 in the removal of Cr(VI) pollution from water bodies.

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