Three-dimensional reticular iron-manganese microsphere material as well as preparation method and application thereof

Abstract

The invention discloses a three-dimensional reticular iron-manganese microsphere material as well as a preparation method and application thereof, and belongs to the technical field of soil heavy metal pollution remediation. The preparation method of the three-dimensional reticular iron-manganese microsphere material comprises the following steps: dissolving a soluble manganese salt and an oxidizing agent in water together, then adding a solution containing ferrous ions, carrying out a heating reaction, and collecting an obtained solid product, so as to obtain the three-dimensional reticular iron-manganese microsphere material. The three-dimensional net-shaped ferro-manganese microsphere material provided by the invention shows remarkable aging repair performance in a soil environment: short-term rapid adsorption, middle-term stable deposition and long-term slow release maintenance; meanwhile, a relatively stable pH value and an ion balance environment can be maintained, obvious damage to physical and chemical properties of soil is avoided, and on the contrary, deep fixation of pollutants is promoted; and the mobility and toxicity release level of heavy metals in the soil can be effectively reduced under the dynamic environment condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil heavy metal pollution remediation, and particularly relates to a three-dimensional network iron-manganese microsphere material, a preparation method thereof, and an application thereof. Background Art

[0002] Heavy metals in soil have extremely strong accumulation, concealment, and persistence, which makes it extremely difficult to remediate soil once it is contaminated by heavy metals. Arsenic (As), lead (Pb), and cadmium (Cd) usually exist in the form of combined pollution, and different chemical forms have different toxicity levels. For example, As mainly exists in the anionic forms of As(III) (arsenite) and As(V) (arsenate) in soil, and the toxicity of arsenite is 25 to 60 times that of arsenate. Cd and Pb mainly exist in the form of divalent cations in soil and have relatively high mobility. In particular, the form of Cd in soil is easily affected by the pH value and has extremely strong mobility. Lead, due to its easy combination with organic matter, often exists in the form of insoluble lead sulfide or iron-manganese oxide.

[0003] The physical and chemical properties of these heavy metals pose challenges to the remediation work. In particular, the co-remediation of As, Pb, and Cd is complex because they exhibit very different chemical behaviors under different pH and redox conditions. In addition, the high persistence of heavy metals in soil means that even if the pollution source is eliminated, the pollutants can still exist for a long time, threatening the environment and health. For example, studies have found that Cd can still be detected in some untreated soils even after 30 years of treatment.

[0004] The combined pollution of arsenic, lead, and cadmium in soil is one of the most challenging areas in current environmental remediation. Due to the different chemical properties and toxicities of these heavy metals, they may coexist in multiple forms in soil, increasing the difficulty of remediating combined pollution. Summary of the Invention

[0005] In view of the current research and challenges in the remediation of combined soil pollution by arsenic, lead, and cadmium, the present invention provides a three-dimensional network iron-manganese microsphere material, a preparation method thereof, and an application thereof.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention: provides a preparation method of a three-dimensional network iron-manganese microsphere material, comprising the following steps:

[0008] Dissolve a soluble manganese salt and an oxidant in water together, then add a solution containing ferrous ions, heat and react, and collect the obtained solid product, which is the three-dimensional network iron-manganese microsphere material.

[0009] Optionally, the soluble manganese salt used is manganese sulfate.

[0010] Preferably, the oxidant is potassium persulfate.

[0011] More preferably, the molar ratio of manganese ions in the soluble manganese salt to the potassium persulfate is 1:1 to 1.1.

[0012] Preferably, the addition amount of ferrous ions is 1 / 6 to 1 / 4 of the molar amount of manganese ions in the soluble manganese salt.

[0013] Optionally, the source of the ferrous ions used is ferrous sulfate.

[0014] Preferably, the temperature of the heating reaction is 60 to 70 °C, and the time is 6 to 8 h.

[0015] Preferably, after collecting the solid product, it further includes washing and drying steps.

[0016] The second technical solution of the present invention: Provide a three-dimensional network iron-manganese microsphere material prepared by the preparation method of the above three-dimensional network iron-manganese microsphere material.

[0017] The third technical solution of the present invention: Provide an application of the above three-dimensional network iron-manganese microsphere material in repairing arsenic, lead and cadmium co-polluted soil.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] The three-dimensional network iron-manganese microsphere material provided by the present invention exhibits significant aging repair performance in the soil environment: rapid adsorption in the short term, stable deposition in the medium term, and slow release maintenance in the long term; at the same time, it can maintain a relatively stable pH value and ionic balance environment, and will not cause obvious damage to the physical and chemical properties of the soil, but instead promotes the deep fixation of pollutants; it can still effectively reduce the mobility and toxicity release level of heavy metals in the soil under dynamic environmental conditions.

[0020] The three-dimensional network iron-manganese microsphere material provided by the present invention can be used as a key material for the repair of composite contaminated sites, and has good engineering practical prospects and environmental safety guarantee capabilities. Description of the Drawings

[0021] Figure 1 It is the SEM diagram of the pure MnO2 sample and the Fe-MnO2 prepared in Example 1. Among them, a to c are the SEM diagrams of the pure MnO2 sample at different magnification multiples, and d to e are the SEM diagrams of Fe-MnO2 at different magnification multiples.

[0022] Figure 2 It is the stabilization repair performance of the Fe-MnO2 prepared in Example 1 and seven common stabilization materials in multi-metal contaminated soil.

[0023] Figure 3For the time-dependent changes in the contents of available As, Cd, and Pb in the Fe-MnO2 group and the CK group during the aging experiment, as well as the time-dependent changes in the fixation rates of available As, Cd, and Pb in the Fe-MnO2 group relative to the CK group. Among them, (a) shows the time-dependent changes in the content of available As in the Fe-MnO2 group and the CK group, (b) shows the time-dependent changes in the content of available Cd in the Fe-MnO2 group and the CK group, (c) shows the time-dependent changes in the content of available Pb in the Fe-MnO2 group and the CK group, and (d) shows the time-dependent changes in the fixation rates of available As, Cd, and Pb in the Fe-MnO2 group relative to the CK group.

[0024] Figure 4 For the time-dependent changes in the soil pH value and EC of the Fe-MnO2 group and the CK group during the aging experiment.

[0025] Figure 5 For the time-dependent changes in the TCLP concentrations of As, Cd, and Pb in the Fe-MnO2 group and the CK group, as well as the time-dependent changes in the decline rates of the TCLP concentrations of As, Cd, and Pb in the Fe-MnO2 group relative to the CK group. Among them, (a) shows the time-dependent changes in the TCLP concentration of As in the Fe-MnO2 group and the CK group, (b) shows the time-dependent changes in the TCLP concentration of Cd in the Fe-MnO2 group and the CK group, (c) shows the time-dependent changes in the TCLP concentration of Pb in the Fe-MnO2 group and the CK group, and (d) shows the time-dependent changes in the decline rates of the TCLP concentrations of As, Cd, and Pb in the Fe-MnO2 group relative to the CK group. Detailed implementation manners

[0026] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention.

[0027] It should be noted that the aspects not described in detail in the present invention are all conventional operation means in the art and are not the focus of the present invention.

[0028] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention.

[0030] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0031] In the embodiments of this invention, a three-dimensional network iron-manganese microsphere material is prepared by a one-pot in-situ redox reaction. Potassium persulfate (K2S2O8) is used as the oxidant, and the introduction of ferrous ions (Fe 2+ ) is used to regulate the structure and reactivity of manganese dioxide (MnO2). The synthesis mechanism can be divided into the following stages:

[0032] 1) Redox reaction stage

[0033] In the reaction system, K2S2O8 decomposes rapidly under heating conditions, generating sulfate radicals (SO4 - ·) with strong oxidizing properties and peroxymonoxide (O2 - ).

[0034] The sulfate radical (SO4 - ·) undergoes a redox reaction with the low-valent manganese ion (Mn 2+ ), generating manganese dioxide (MnO2):

[0035]

[0036] Meanwhile, Fe 2+ can also be oxidized to Fe 3+ , and part of it forms a composite structure with MnO2:

[0037]

[0038] 2) Crystal nucleus formation and aggregation stage

[0039] Under the oxidation conditions of K2S2O8, MnO2 and Fe 3+ generate a three-dimensional network-structured Fe-Mn composite oxide through coprecipitation or coordination complexation.

[0040] Fe 3+ 's introduction can regulate the crystal phase growth of MnO2, forming a more open three-dimensional network structure instead of simple flaky or needle-like particles. This structural feature can provide more active sites and adsorption channels, which is beneficial for the removal of heavy metals.

[0041] 3) Fe-Mn Synergistic Mechanism

[0042] Under the condition of Fe / Mn mass ratio of 1:5, there is a good synergistic effect between Fe 3+ and MnO2. Fe 3+ can form Fe-OH or Fe-O bonds on the material surface, forming a complementary adsorption environment with the surface functional groups of Mn oxides (such as Mn-O-Mn).

[0043] Example 1

[0044] Preparation of three-dimensional network iron-manganese microsphere material:

[0045] Dissolve 5 mmol of MnSO4·H2O and 5 mmol of K2S2O8 in 40 mL of deionized water to form a uniform metal ion mixed solution. Under continuous magnetic stirring, slowly add 10 mL of FeSO4·7H2O solution (100 mmol / L) to the above mixed solution to ensure full mixing of the reactants. The entire mixing process is carried out at room temperature until the solution shows a homogeneous state. Subsequently, transfer the mixed solution to a thermostatic heating magnetic stirrer, heat it to 60 °C, and continuously stir and react at this temperature for 8 hours. During the reaction process, the color of the system gradually changes from light yellow to brownish-yellow and then to blackish-brown, and very fine suspended particles gradually precipitate in the solution.

[0046] After the reaction is completed, wait for the system to cool naturally to room temperature, and collect the obtained solid product by centrifugation (8000 rpm, 10 min). The obtained precipitate is washed repeatedly with deionized water and absolute ethanol to remove unreacted ions and soluble impurities. The washed solid sample is placed in a vacuum drying oven at 60 °C and dried for 12 hours. After ensuring that the material is completely dry, a three-dimensional network iron-manganese microsphere material (denoted as Fe-MnO2) is obtained, collected and stored in a sealed container for subsequent research.

[0047] To study the effect of Fe doping on the microstructure and specific surface area of the material, the present invention combines scanning electron microscopy (SEM) and specific surface area measurement (BET) to conduct a comparative analysis on the undoped Fe MnO2 material and the three-dimensional network iron-manganese microsphere material with an Fe / Mn mass ratio of 20%.

[0048] Figure 1 Figure 26 shows the SEM images of the pure MnO2 sample and the Fe-MnO2 prepared in Example 1. Among them, a-c are the SEM images of the pure MnO2 sample at different magnifications, and d-e are the SEM images of Fe-MnO2 at different magnifications.

[0049] Figure 1Figures a - c show the SEM images of the pure MnO2 sample. Its overall structure is mainly composed of needle - shaped and flaky crystals, which are piled up in clusters. The surface structure is relatively dense, and the morphology is similar to that of a "cactus - like" aggregate. This morphology is a common crystal form during the synthesis of MnO2 under the condition of thermal - activated persulfate, reflecting the characteristics of strongly - oriented growth nuclei.

[0050] In contrast, the morphology of the Fe - MnO2 prepared in this invention shows significant differences. The surface of the material changes from the original flaky and needle - shaped structure to a loose three - dimensional grid - like structure microsphere. Its pore distribution is uniform, the particle size decreases, and the surface is significantly rougher, with typical porous - structure characteristics. In this invention, the introduction of Fe 3+ significantly inhibits the epitaxial growth and crystallization process of MnO2 crystals, changes the microscopic morphology and structural characteristics of the product, and thus affects the pore structure and specific surface area of the material. Fe 3+ partially replaces Mn at the octahedral sites 4+ and reduces the crystallinity of MnO2. At the same time, a certain degree of lattice strain and vacancy defects are introduced. These morphological and structural changes are the key factors affecting the adsorption and electrochemical properties of the material. This change in the structural morphology indicates that the introduction of Fe 3+ significantly affects the crystal growth path and aggregation mode, probably by regulating the nucleation rate and grain growth direction, inhibiting the accumulation of flaky structures, and promoting the formation of a more open and three - dimensional framework structure.

[0051] To evaluate the stabilization and remediation performance of Fe - MnO2 in Example 1 for multi - metal - contaminated soil, this invention uses the reduction rate of the available heavy - metal content as the evaluation index of the immobilization efficiency, and makes a systematic comparison of the Fe - MnO2 prepared in Example 1 and seven common stabilization materials, specifically Fe - MnO2, MnO2, FeSO4, Fe - Mg LDO (i.e., iron - manganese oxide), CaCO3, CaO, oyster - shell powder, and montmorillonite. The experimental results are as Figure 2 shown.

[0052] Figure 2The results show that different materials exhibit significant differences in the immobilization effects of Pb, Cd, and As, reflecting the complex interactions between the physicochemical properties of the materials and the soil environment. The Fe-MnO2 material shows the best performance in the immobilization of As and Pb, with immobilization rates of 46.02% and 80.03% respectively, which are significantly higher than those of the un-doped Fe MnO2 (20.44% and 76.78% respectively). The three-dimensional porous microsphere structure formed after doping with iron not only increases the specific surface area and the number of reaction sites, but also may optimize the electronic structure and surface complexation ability of the material through the Fe-Mn synergy, thereby enhancing the adsorption stability of heavy metals. Especially for As(III), the introduction of an appropriate amount of iron may promote the oxidation-complexation reaction, making it exist in a more stable form in the soil.

[0053] To systematically evaluate the long-term and medium-term stabilization effects of the prepared Fe-MnO2 on heavy metal pollution in the soil environment, the present invention sets up a 100-day aging experiment. Under the standard conditions of a constant temperature of 30 °C, a water content of 40 wt.%, and a dosing ratio of 3 wt.% Fe-MnO2 (Fe-MnO2 group), with no addition of Fe-MnO2 as the blank control group (CK group), samples are taken on the 3rd, 7th, 15th, 30th, 45th, 60th, and 100th days to dynamically monitor the changes in the available contents of three heavy metals, namely arsenic (As), cadmium (Cd), and lead (Pb). Combining with the changes in soil pH and electrical conductivity (EC), the reaction rate, durability performance of Fe-MnO2, and its impact on the soil physicochemical environment are comprehensively evaluated.

[0054] Figure 3 Figures show the changes in the available contents of As, Cd, and Pb over time in the Fe-MnO2 group and the CK group, as well as the changes in the immobilization rates of available As, Cd, and Pb in the Fe-MnO2 group relative to the CK group over time. Among them, (a) shows the changes in the available As content over time in the Fe-MnO2 group and the CK group, (b) shows the changes in the available Cd content over time in the Fe-MnO2 group and the CK group, (c) shows the changes in the available Pb content over time in the Fe-MnO2 group and the CK group, and (d) shows the changes in the immobilization rates of available As, Cd, and Pb in the Fe-MnO2 group relative to the CK group (the immobilization rate is the percentage reduction in the available content in the Fe-MnO2 group relative to the CK group) over time.

[0055] Figure 3The results show that in terms of the changes in the available heavy metal content, the Fe-MnO2 material exhibited strong reactivity within the first 7 days after application. The available concentrations of the three heavy metals decreased rapidly, and the short-term fixation rate was significant. Among them, the fixation rate of As was 60.89% on the 7th day, 75.53% for Cd, and 67.16% for Pb. This indicates that the active sites were fully exposed at the initial stage of material addition, with strong adsorption ability, capable of effectively capturing heavy metal ions existing in ionic or weakly bound states in the soil and rapidly reducing their bioavailability.

[0056] In the medium- to long-term stage (15 - 60 days), the fixation trends of each metal began to show differential evolution. The available content of As decreased continuously from 112.78 mg / kg to 15.51 mg / kg on the 60th day, corresponding to a fixation rate as high as 85.23%. Although it rebounded to 29.56 mg / kg on the 100th day, it still remained at a relatively low level, and the final fixation rate was 76.65%. This shows that Fe-MnO2 can complete the efficient fixation process of As within 60 days, and a relatively stable As-Fe / Mn composite structure may have formed on the material surface and inside the structure. The fixation process of Pb was the most stable. The available content decreased from 25.86 mg / kg to 1.41 mg / kg within 100 days, and the fixation rate was as high as 95.21%, indicating that the binding mechanism of the material to Pb is more stable and lasting, possibly involving multiple mechanisms such as precipitation, embedding, or mineral structure encapsulation. The change of Cd showed a trend of "rapid decrease - slow increase". The fixation rate was 67.96% on the 30th day, but then gradually decreased to 50.78% on the 100th day, suggesting that Fe-MnO2 mainly relies on the initial adsorption reaction for Cd, and later, due to site saturation or desorption of weakly bound states, a certain degree of Cd release occurred.

[0057] To further reveal the long-term stability of the material and its interaction with the soil environment, the monitored changes in pH and EC are shown in Figure 4 .

[0058] Figure 4 The results show that in the Fe-MnO2 remediation group, the soil pH value generally showed a slight downward trend: it slowly decreased from 5.95 on the 7th day to 5.70 on the 100th day, a decrease of about 0.3 units compared to the CK group. In contrast, the pH value of the CK group decreased from 6.39 to 6.10 within the same period, remaining in the slightly acidic range. The pH of the Fe-MnO2 remediation group stabilized in the weakly acidic range, indicating that the material released certain acidic components during the reaction, such as H + or SO4 2-, but did not cause strong acidification of the soil. Considering that the original pH of the soil in this experiment was 6.32, sourced from the southern region of Guangdong, it had good acid buffering capacity, and slightly acidic conditions were more conducive to the complexation and synergistic effects between the active functional groups (such as Fe-OH and Mn-OH) in Fe-MnO2 and anionic or neutral form pollutants such as As and Pb, which helped to stably continue the material's remediation effect.

[0059] In terms of electrical conductivity (EC), the Fe-MnO2 remediation group was higher than the CK group throughout the experiment. At the initial stage, on the 7th day, the EC was 0.613 ms / cm, significantly higher than 0.523 ms / cm of the CK group; thereafter, it showed a slow downward trend and dropped to 0.549 ms / cm on the 100th day, still higher than 0.413 ms / cm of the control group. The increase in EC can be attributed to the soluble ions (such as Fe 2+ 、Fe 3+ 、Mn 2+ etc.) gradually released by the Fe-MnO2 material in the soil, as well as the matrix ions such as Na + 、Ca 2+ etc. released during the ion exchange process between the material and the soil. These electrolytes entered the soil pore fluid, indicating that the material had a certain "slow release" characteristic. At the same time, the slow decrease in EC might indicate that the ion migration in the system gradually tended to dynamic equilibrium, and the effective components of the material gradually participated in adsorption, precipitation, or complexation reactions in the soil, forming a stable reaction interface to provide continuous chemical support for the long-term fixation of heavy metals. Therefore, this gentle and persistent ion regulation process not only extended the functional life of the material but also verified its adaptability and long-term reaction potential in the actual soil remediation environment.

[0060] Generally speaking, the Fe-MnO2 material demonstrated significant time-dependent remediation performance in the soil environment: rapid adsorption in the short term, stable deposition in the medium term, and slow release maintenance in the long term; at the same time, it could maintain a relatively stable pH and ion balance environment, did not cause obvious damage to the soil physical and chemical properties, but instead promoted the deep fixation of pollutants. Especially under the typical climate background of high temperature, high humidity, and slightly acidic soil in the Guangdong region, the performance of this material had strong environmental adaptability and promotion potential. Its high-efficiency and long-term remediation ability for Pb and As was particularly prominent. Although the Cd remediation was affected by time, it still had good control effects in the initial treatment, and could be compensated by compounding with other functional materials in the later stage. Therefore, Fe-MnO2 can be used as a key material for the remediation of composite polluted sites and has good engineering practical prospects.

[0061] To deeply evaluate the long-term control ability of Fe-MnO2 on the environmental risks of heavy metals, this invention carried out experiments based on the TCLP (Toxicity Characteristic Leaching Procedure) method.

[0062] The toxicity leaching method is widely used to evaluate the potential migration ability and bioavailability of heavy metals in soil under acidic conditions, and it is an important means to judge the effect of remediation and stabilization. In this invention, toxicity leaching experiments were carried out by simulating acidic conditions to analyze the environmental risk levels of As, Pb, and Cd in the remediated soil.

[0063] In the experiment, 1.00 g of air-dried and sieved soil samples were weighed into 50 mL polypropylene centrifuge tubes. The toxicity leaching solution was prepared by diluting glacial acetic acid, that is, 17.25 mL of glacial acetic acid (about 99%) was taken and diluted with deionized water to 1000 mL, and the pH of the obtained solution was controlled at 2.64 ± 0.05 and confirmed using a calibrated pH meter.

[0064] 20 mL of the toxicity leaching solution (solid-liquid ratio 1:20) was added to each tube. After sealing, it was placed at room temperature (20 - 25 °C) and oscillated at 200 rpm for 20 hours. After the reaction, the samples were centrifuged at 8000 rpm for 5 minutes, the supernatant was taken and filtered through a 0.45 μm filter membrane, and the filtrate was collected in a clean polyethylene centrifuge tube and stored refrigerated at 4 °C for testing. The concentrations of As, Pb, and Cd in the filtrate of each sample were determined by ICP-MS. Three parallel samples were set for the experiment, and the measured values were averaged for analysis.

[0065] The TCLP experiment uses an acetic acid buffer solution to simulate the release process of soil in an acidic environment (such as acid rain, leachate, etc.), and it is an important standard widely used in the international safety evaluation of solid waste and polluted soil. By monitoring the TCLP leaching concentrations of As, Pb, and Cd during different curing periods, the actual control effect of materials on the migration and bioavailability of pollutants can be effectively reflected.

[0066] Figure 5 Figures show the changes in the TCLP concentrations of As, Cd, and Pb over time in the Fe-MnO2 group and the CK group, as well as the changes in the decline rates of the TCLP concentrations of As, Cd, and Pb in the Fe-MnO2 group relative to the CK group over time. Among them, (a) shows the changes in the TCLP concentration of As over time in the Fe-MnO2 group and the CK group, (b) shows the changes in the TCLP concentration of Cd over time in the Fe-MnO2 group and the CK group, (c) shows the changes in the TCLP concentration of Pb over time in the Fe-MnO2 group and the CK group, and (d) shows the changes in the decline rates of the TCLP concentrations of As, Cd, and Pb in the Fe-MnO2 group relative to the CK group over time.

[0067] Figure 5The results showed that there were significant differences in the three heavy metals between the remediation group (Fe-MnO2 group) and the CK group. The TCLP concentration of arsenic (As) remained at a high level in the CK group, reaching 31.26 mg / kg on the 7th day of curing and rising to 36.28 mg / kg on the 30th day, indicating a strong tendency of re-release under acidic conditions. In contrast, the As concentration in the remediation group dropped to 0.95 mg / kg on the 7th day and remained between 1.1 and 2.4 mg / kg at subsequent time points, with the decline ratio always remaining above 93%, fully demonstrating that the Fe-MnO2 material has excellent short-term rapid fixation ability and long-term stability for As.

[0068] The trend of the toxic leaching of lead (Pb) was relatively complex. In the CK group, the TCLP concentration of Pb generally remained between 20 and 32 mg / kg and showed certain fluctuations; while the initial concentration in the remediation group was 9.67 mg / kg and then gradually decreased to 4.65 mg / kg on the 100th day, with the overall decline ratio stabilizing between 70% and 77%. Although the inhibitory effect on Pb leaching in the early stage of remediation was not as significant as that of As, with the extension of the reaction time, its release concentration gradually decreased and tended to be stable, indicating that Fe-MnO2 can gradually establish a stable inclusion, precipitation or complexation structure in the middle and later stages to effectively fix Pb and inhibit its toxic release.

[0069] The TCLP concentration of cadmium (Cd) also continued to rise under the unrepaired condition, reaching 2.68 mg / kg on the 100th day, while the remediation group showed a control process of "slow decline - tending to be stable". The Cd concentration on the 3rd day was 1.20 mg / kg and gradually decreased to 0.77 mg / kg after the 60th day, with a decline ratio of 71.3%. Although the immobilization rate of Cd was slower than that of As and Pb, there was no "redissolution" or rebound phenomenon in the material during the entire curing period, indicating that it also has good slow-release and steady-state transformation capabilities for Cd.

[0070] From the overall trend, during the 100-day natural curing process of the unrepaired soil, the toxic releases of the three heavy metals all increased to varying degrees, indicating that in-situ pollutants in the highly acidic environment have a strong risk of cumulative release. In contrast, the Fe-MnO2 material showed rapid stabilization of As, gradual inhibitory fixation of Pb, and continuous slow-release effect on Cd in the TCLP test, indicating that it can still effectively reduce the mobility and toxic release level of heavy metals in soil under dynamic environmental conditions and has good engineering application prospects and environmental safety guarantee capabilities.

[0071] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a three-dimensional network iron-manganese microsphere material, characterized in that, It includes the following steps: Dissolve soluble manganese salt and oxidant in water together, then add a solution containing ferrous ions, heat for reaction, and collect the obtained solid product, which is the three-dimensional network iron-manganese microsphere material.

2. The preparation method of the three-dimensional network iron-manganese microsphere material according to claim 1, wherein The oxidant is potassium persulfate.

3. The preparation method of the three-dimensional network iron-manganese microsphere material according to claim 2, characterized in that, The molar ratio of manganese ions in the soluble manganese salt to the potassium persulfate is 1:1 to 1.

1.

4. The preparation method of the three-dimensional network iron-manganese microsphere material according to claim 1, wherein The addition amount of the ferrous ions is 1 / 6 to 1 / 4 of the molar amount of manganese ions in the soluble manganese salt.

5. The preparation method of the three-dimensional network iron-manganese microsphere material according to claim 1, wherein, The temperature of the heating reaction is 60 to 70 °C, and the time is 6 to 8 h.

6. The preparation method of the three-dimensional network iron-manganese microsphere material according to claim 1, characterized in that, After collecting the solid product, it further includes the steps of washing and drying.

7. A three-dimensional network iron-manganese microsphere material prepared by the preparation method of the three-dimensional network iron-manganese microsphere material according to any one of claims 1 to 6.

8. Application of the three-dimensional network iron-manganese microsphere material according to claim 7 in repairing soil co-polluted by arsenic, lead and cadmium.

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