Composite repairing agent for synchronously removing heavy metal cadmium and neonicotinoid pesticides as well as preparation method and application of composite repairing agent

Abstract

The invention provides a composite repairing agent capable of synchronously removing heavy metal cadmium and neonicotinoid pesticides and a preparation method and application of the composite repairing agent. The composite repairing agent comprises a functional fungicide and iron minerals, and the ratio of the dry weight of the iron minerals to the volume of a fungicide liquid of the functional fungicide is 1: (1-10); the functional microbial agent is a viable bacterium culture of dissimilatory iron reducing bacteria, the thallus concentration of the functional microbial agent is not lower than 1 * 10 < 8 > CFU / mL, and the iron mineral is Fe2O3.nH2O. According to the method, an iron reducing bacteria-ferrihydrite mixed system formed by in-situ active minerals is constructed, efficient treatment of combined pollution is achieved through an adsorption-conversion-degradation synergistic mechanism, and ferrihydrite is converted into magnetite in situ within 24-72 hours through iron reducing bacteria in the iron reducing bacteria-ferrihydrite; the new magnetite shows excellent dual functions, and the removal rate of Cd can be increased to gt by crystal lattices of the new magnetite through obligate adsorption and coprecipitation; meanwhile, structural ferrous iron is used as a strong reducing agent and can efficiently attack nitryl in imidacloprid molecules, and gt, gt, gt, gt, gt, gt and gt are achieved; the degradation rate is 90%.

Description

Technical Field

[0001] This invention belongs to the field of environmental pollutant treatment technology, specifically relating to a composite remediation agent that simultaneously removes heavy metal cadmium and neonicotinoid pesticides, its preparation method, and its application. Background Technology

[0002] Paddy soil, as a typical anthropogenic soil, exhibits a unique alternating wet and dry tillage system, resulting in cyclical redox dynamics. Especially during flooding, the soil rapidly transitions from an oxidative state to an anaerobic environment. While this characteristic brings agricultural benefits, it also makes paddy fields a breeding ground and amplifier for combined pollution from neonicotinoid pesticides and the heavy metal cadmium, making remediation extremely difficult. Neonicotinoid insecticides (such as imidacloprid and thiamethoxam) are widely used for rice pest control due to their strong systemic properties, but their high water solubility and persistence lead to significant residues in paddy soil and water. Simultaneously, irrigation water, industrial emissions, and the long-term use of cadmium-containing phosphate fertilizers contribute to the widespread accumulation of cadmium in paddy fields. The coexistence of these two pollutants in the anaerobic paddy soil and water environment creates a complex compound pollution system that not only threatens rice quality and safety but also impacts the surrounding water environment through runoff and other means.

[0003] Most existing remediation technologies, particularly the highly efficient microbial agents or advanced oxidation technologies for degrading organic pesticides, rely on aerobic conditions. In the anaerobic environment of flooded paddy fields, their activity is severely inhibited or even completely ineffective. Adding chemical oxidants (such as persulfate) or H2O2 to paddy fields to degrade pesticides is not only costly but also drastically alters the soil's physicochemical properties, disrupts the paddy field's microecology, and its effects are difficult to sustain in the strongly reducing anaerobic environment. Furthermore, existing heavy metal passivation technologies may only focus on cadmium fixation, failing to address the coexisting pesticide residue problem; conversely, focusing solely on pesticide degradation cannot control the bioavailability of cadmium. Such single-function technologies cannot cope with the complex situation of "pesticide-heavy metal" coexistence in paddy fields. Existing remediation technologies are limited by the inherent effectiveness of mineral materials, lacking sufficient capacity for cadmium fixation and completely unable to degrade neonicotinoid pesticides, while also lacking long-term effectiveness due to performance degradation.

[0004] Therefore, it is necessary to provide a compound remediation agent and its application that can simultaneously remove heavy metal cadmium and neonicotinoid pesticides. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a composite remediation agent for the simultaneous removal of heavy metal cadmium and neonicotinoid pesticides, as well as its preparation method and application. It constructs an in-situ active mineral-forming "iron-reducing bacteria-hydrothermic mineral" mixed system, and achieves efficient treatment of composite pollution through a "adsorption-conversion-degradation" synergistic mechanism.

[0006] This invention provides the following technical solution:

[0007] This invention provides a composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides, comprising functional microbial agents and iron minerals, wherein the dry weight ratio of the iron minerals to the volume of the functional microbial agent is 1:1~10; the functional microbial agent is a live culture of dissimilatory iron-reducing bacteria, with a cell concentration of not less than 1×10⁻⁶. 8 CFU / mL, wherein the iron mineral is ferrohydrate Fe2O3·nH2O.

[0008] The dissimilar iron-reducing bacteria in the system convert ferrohydrate into magnetite in situ within 24-72 hours, which is equivalent to automatically generating a more active remediation material at the pollution site. The newly formed magnetite exhibits excellent dual functions. Its lattice can increase the removal rate of Cd²⁺ to >25% and achieve long-term stable fixation through specific adsorption and co-precipitation. At the same time, its structural divalent iron acts as a strong reducing agent, which can efficiently attack the nitro group in the imidacloprid molecule and achieve a degradation rate of >90%.

[0009] The present invention also provides a method for preparing the above-mentioned composite repair agent, comprising the following steps:

[0010] Provides iron ore;

[0011] Live bacterial cultures of dissimilatory iron-reducing bacteria;

[0012] The live bacterial culture of iron minerals and dissimilar iron-reducing bacteria is mixed in a ratio of 1:1 to 10 between the dry weight of iron minerals and the volume of functional bacterial agent.

[0013] Furthermore, the iron mineral is obtained by purchasing commercially available materials or by preparation. The preparation process is as follows: ferric nitrate nonahydrate is added to deionized water, KOH solution is continuously added dropwise until the pH reaches 7.4~7.6, the mixture is stirred and reacted for a period of time, the supernatant is removed by centrifugation, the resulting precipitate is washed, and the iron mineral is obtained after drying.

[0014] Furthermore, the ratio of ferric nitrate nonahydrate to deionized water is 2g:25mL, and the concentration of KOH solution is 1mol / L.

[0015] Further, the process of culturing live bacterial cultures of dissimilatory iron-reducing bacteria includes the following steps: taking out strain MR-1 and thawing it in a constant temperature water bath; activating MR-1 by incubation in LB medium under aerobic conditions; culturing the bacteria to the logarithmic growth phase; centrifuging to obtain MR-1 bacterial sediment; and then washing and resuspending it with buffered salt solution.

[0016] Furthermore, the centrifugation is performed at 4°C and 7000 rpm for 5 minutes.

[0017] Further, the buffer salt solution comprises 0.14 g L -1 KH2PO4, 0.2 g L-1 NaCl, 0.3 g / L -1 NH4Cl, 0.5 g L -1 MgSO4·7H2O and 0.1 g L -1 The pH of the buffer salt solution is 7, and the solution is CaCl2·2H2O.

[0018] The present invention also provides the application of the above-mentioned composite remediation agent in soil pollution remediation, wherein the composite remediation agent is added and dispersed in polluted soil or water to simultaneously remove heavy metal cadmium and neonicotinoid pesticides under anaerobic conditions.

[0019] Furthermore, the composite remediation agent is added to the contaminated soil or water at an inoculum of 5% (v / v) and reacted at a temperature of 25-35°C.

[0020] The present invention has the following beneficial effects:

[0021] 1. This invention achieves a self-driven, time-sequential remediation process by carefully designing the bacterial-mineral ratio and controlling environmental conditions: firstly, it utilizes the adsorption properties of ferrohydrate to rapidly fix Cd. 2+ Subsequently, through microbial-driven mineral phase transition, the adsorbent is transformed into a multifunctional material with both Cd fixation and pesticide degradation capabilities, thereby achieving synergistic removal of complex pollutants with a unified technical solution.

[0022] 2. This invention only requires a one-time addition of the bacterial-mineral mixture to achieve self-driving under anaerobic conditions, without the need for additional chemicals or complex equipment, and has significant advantages such as simple operation, low cost and environmental friendliness. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a TEM image of the ferrohydrite obtained in Example 1 of the present invention;

[0025] Figure 2 This is a diagram showing the N2 adsorption-desorption and pore size distribution of the ferrohydrate prepared in Example 1 of this invention;

[0026] Figure 3 Cd in Example 1 2+ Fitting curves of PFO and PSO kinetic models on ferrosilicon ore;

[0027] Figure 4For example, the adsorption of Cd by water iron ore in Example 1 2+ Langmuir and Freundlich isotherms;

[0028] Figure 5 The images show the XRD patterns of the ferrohydrate ore before and after the reaction in Example 1 of this invention.

[0029] Figure 6 This is a TEM image of the ferrous ore after reaction in Example 1 of the present invention;

[0030] Figure 7 The above is the Fe(II) formation kinetic curve during the reaction process in Example 1 of this invention;

[0031] Figure 8 Analysis of XPS Fe 2p spectra;

[0032] Figure 9 The degradation curve of imidacloprid;

[0033] Figure 10 For Cd 2+ Removal kinetics curves of imidacloprid and chlorpyrifos;

[0034] Figure 11 The reagents prepared in Example 1 and Comparative Examples 1-3 of this invention were introduced into the contamination system and then discharged as Cd. 2+ A comparison chart of degradation rates with imidacloprid. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention provides a composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides, comprising functional microbial agents and iron minerals, wherein the dry weight ratio of the iron minerals to the volume of the functional microbial agent is 1:1~10; the functional microbial agent is a live culture of dissimilatory iron-reducing bacteria, with a cell concentration of not less than 1×10⁻⁶. 8 CFU / mL, wherein the iron mineral is ferrohydrate Fe2O3·nH2O.

[0037] The technical principle behind this invention for simultaneously removing heavy metal cadmium and neonicotinoid pesticides lies in the precise control of a sequential phase transition process of iron minerals driven by microbial metabolism. This process comprises two closely linked stages: the first stage is adsorption and enrichment, where, after the composite remediation agent is added to an anaerobic environment, the ferrohydrate minerals with a large specific surface area rapidly adsorb and fix Cd in the solution through surface coordination.2+ This process makes Cd 2+ The pollutants are transferred from the liquid phase to the solid surface, achieving initial enrichment and concentration reduction. This stage mainly occurs within 0-12 hours after the reaction begins. The second stage is transformation and degradation, including Cd adsorption. 2+ The ferrohydrite underwent a biophase transition driven by functional bacteria. Dissimilatory iron-reducing bacteria, using sodium lactate as an electron donor, reduced Fe(III) in the ferrohydrite to Fe(II), initiating mineral dissolution. Under specific pH and ionic strength conditions, the dissolved Fe(II) and residual Fe(III) co-precipitated, directionally transforming into magnetite (Fe3O4) with an anti-spinel structure. For the heavy metal cadmium, the newly formed magnetite, through lattice substitution, absorbed surface-adsorbed Cd. 2+ It is fixed into its crystal structure, forming a stable Cd-Fe oxide solid solution, thus achieving long-term stabilization of Cd. Furthermore, the structural divalent iron in the magnetite lattice has strong reducing properties, which can directly donate electrons to the imidacloprid molecules adsorbed on the mineral surface, specifically attacking their electron-withdrawing groups such as nitro (-NO2), and achieving molecular bond breaking and degradation through reduction reaction.

[0038] This invention also provides a method for preparing the above-mentioned composite repair agent, comprising the following steps:

[0039] Provides iron ore;

[0040] Live bacterial cultures of dissimilatory iron-reducing bacteria;

[0041] The live bacterial culture of iron minerals and dissimilar iron-reducing bacteria is mixed in a ratio of 1:1 to 10 between the dry weight of iron minerals and the volume of functional bacterial agent.

[0042] In one specific embodiment, the iron mineral is purchased commercially or prepared by means of preparation. The preparation process is as follows: ferric nitrate nonahydrate is added to deionized water, KOH solution is continuously added dropwise until the pH reaches 7.4~7.6, the mixture is stirred and reacted for a period of time, the supernatant is removed by centrifugation, the resulting precipitate is washed, and the iron mineral is obtained after drying.

[0043] In one specific embodiment, the process of culturing a live culture of dissimilar iron-reducing bacteria includes the following steps: taking out strain MR-1 and thawing it in a constant temperature water bath; activating MR-1 by incubating it in LB medium under aerobic conditions; culturing the bacteria to the logarithmic growth phase; centrifuging to obtain MR-1 bacterial sediment; and then washing and resuspending it with buffered salt solution.

[0044] The present invention also provides the application of the above-mentioned composite remediation agent in soil pollution remediation, wherein the composite remediation agent is added and dispersed in polluted soil or water, and heavy metal cadmium and neonicotinoid pesticides are removed simultaneously under anaerobic conditions.

[0045] This composite remediation agent is added to the contaminated system at an inoculum rate of 5% (v / v) and reacted at a temperature of 25-35℃. The agent can be applied directly to contaminated soil or water, and a sequential remediation process can be initiated through natural mixing.

[0046] This system can be self-driven under anaerobic conditions with only a one-time addition of the bacterial-mineral mixture, without the need for additional chemicals and complex equipment. It has the significant advantages of simple operation, low cost and environmental friendliness.

[0047] The present invention will be further illustrated below through specific embodiments:

[0048] Example 1:

[0049] The preparation of the composite repair agent is as follows:

[0050] 40.0 g of ferric nitrate nonahydrate, Fe(NO3)3·9H2O, was dissolved in 500 mL of deionized water. 1 mol / L KOH solution was continuously added dropwise until the pH of the system stabilized in the range of 7.4 to 7.6. The reaction was carried out under vigorous stirring for 1 hour. The resulting colloidal solution was centrifuged for 12 minutes, and the supernatant was removed. The precipitate was repeatedly washed with deionized water. The above washing operation was repeated 5 times. Finally, the obtained product was dried under a constant temperature of 40 °C to obtain ferrohydrate.

[0051] The Fe(III)-reducing model bacterium *Shewanella oneidensis* strain MR-1 (ATCC No. 700550) was used.

[0052] (Purchased from Beijing Baozang Biotechnology Co., Ltd.) After amplification and preservation, the bacteria were removed from storage in an ultra-low temperature freezer (-80℃) and thawed in a constant temperature water bath at 37℃. MR-1 was activated by incubation in lysogeny broth (LB) medium under aerobic conditions. The bacteria were cultured to the logarithmic growth phase, and the medium was centrifuged at 7000 rpm for 5 minutes at 4℃ to obtain MR-1 bacterial sediment. The sediment was then diluted with a buffered salt solution (pH 7, 0.14 g / L). -1 KH2PO4, 0.2 g L -1 NaCl, 0.3 g L -1 NH4Cl, 0.5 gL -1 MgSO4·7H2O, 0.1 g L -1 Wash and resuspend the cells with CaCl2·2H2O, ensuring a cell concentration of at least 1×10⁻⁶. 8 CFU / mL.

[0053] The dry weight of ferrohydrate and the volume of bacterial culture were mixed at a ratio of 1:5, and then added to the contamination system at an inoculum volume of 5% (v / v). The reaction was carried out at a temperature of 25-35℃. Samples were taken on the third day, and the solid and liquid phases were separated by centrifugation and filtration. Then, ICP-MS was used to analyze the residual Cd in the supernatant. 2+ The concentration was quantitatively analyzed, and the IMI concentration was detected by high performance liquid chromatography.

[0054] Example 2:

[0055] The preparation of the composite repair agent is as follows:

[0056] 20 mg of iron oxide (Fe2O3, 99.95%) powder was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd. and placed in the reaction system as an iron source.

[0057] The preparation of the functional microbial agent is exactly the same as in Example 1.

[0058] The dry weight of ferrohydrate and the volume of the bacterial culture suspension were mixed at a ratio of 1:5, and the reaction was carried out according to the steps of Example 1. Test results showed that commercially purchased ferrohydrate and laboratory-made ferrohydrate exhibited similar effects in the simultaneous degradation of IMI and fixation of Cd. 2+ There was no significant difference in the final effectiveness.

[0059] Example 3:

[0060] The ferroalloy and functional bacteria required for the composite repair agent are exactly the same as those in Example 1.

[0061] The dry weight of ferrohydrate and the volume of the bacterial culture suspension were mixed at ratios of 1:1 and 1:10, respectively, and the subsequent experiments were conducted following the steps in Example 1. The results showed that both the 1:1 and 1:10 mixing systems could completely degrade IMI within 8 days, and both exhibited resistance to Cd. 2+ The removal efficiency of IMI is better at 1:10 than at 1:1, and Cd is also improved. 2+ The adsorption efficiencies are similar. However, both systems can ensure sufficient microbial biomass to drive the iron reduction process, promoting the rapid and complete conversion of ferrophosphate to magnetite, thereby achieving efficient removal of pollutants.

[0062] Comparative Example 1:

[0063] Weigh 20 mg of the ferrohydrate prepared in the same manner as in Example 1, and add it to 20 mL of Cd solution with an initial concentration of 200 mg / L. 2+ The reaction was carried out with 2 μM IMI solution. During the experiment, the pH value was adjusted to 7, and the experiment was carried out under constant temperature conditions of 25-35℃. The test procedure was the same as in Example 1.

[0064] Comparative Example 2:

[0065] The preparation of the functional microbial agent was the same as in Example 1. 5% of the agent was inoculated into the contaminated system to test the metabolic effects of MR-1 alone on IMI and its effect on Cd. 2+ Its removal effect.

[0066] Comparative Example 3:

[0067] The experimental setup for this comparative example is basically the same as that for Example 1, with the only difference being the bacterial-mineral ratio. In this comparative example, the dry weight of the ferrohydrate and the volume of the bacterial culture suspension are mixed at a ratio of 1:0.5.

[0068] Test Analysis:

[0069] After centrifuging, washing, and freeze-drying the solid samples before and after the reaction in Example 1, the morphology, size, and dispersion state of the iron (oxygen-hydrogen) oxides were determined using transmission electron microscopy. The specific operation was as follows: a small amount of dried powder sample was taken in anhydrous ethanol, dispersed by ultrasonication, and a small amount of suspension was aspirated onto an ultrathin carbon support film using a micropipette. After drying at room temperature, the film was placed in a sample holder to monitor its morphology.

[0070] X-ray diffraction was used to determine the crystal structure of iron (oxygen-hydrogen) oxides: A dry powder sample was finely ground in an agate mortar and placed in a grooved glass sample dish for X-ray diffraction analysis. The diffractometer was operated at below 40 kV and 40 mA. The scan range, step size, and speed parameters were set to 2−90, 0.02, and 2°min, respectively. Jade 6.0 software was used to qualitatively determine the components in the sample through peak matching.

[0071] X-ray photoelectron spectroscopy (XPS): Performed on a Thermo Scientific K-Alpha XPS spectrometer using a monochromatic Al Kα excitation source (hv = 1486.6 eV). Full-spectrum scans were performed in 1 eV steps at a binding energy of 150 eV. Narrow-spectrum scans were performed in 0.1 eV steps at a binding energy of 50 eV, with peak positions calibrated based on the C1s peak of amorphous carbon at a binding energy of 284.8 eV.

[0072] Results analysis and explanation:

[0073] from Figure 1 As can be seen, the ferrohydrate prepared in Example 1 exhibits irregular blocky and clump-like particles without a clearly regular crystal shape, consistent with the characteristics of a weakly crystalline structure of ferrohydrate. The particles are uneven in size and show significant agglomeration, forming large aggregates, indicating strong interparticle forces and the presence of voids between the aggregates, providing potential channels for material diffusion. High-magnification TEM images reveal its nanoscale granular structure and high dispersibility; this microstructure further increases the specific surface area of ​​the ferrohydrate.

[0074] Generally, IUPAC classifies adsorption pores into three categories: macropores (>50 nm); mesopores (2-50 nm); and micropores (<2 nm). For example... Figure 2 As shown, N2 adsorption-desorption isotherm analysis of ferrihydrite reveals a significant and rapid increase in adsorption capacity in the low relative pressure region (p / p° < 0.4). This phenomenon is primarily due to the micropore filling effect. When the relative pressure increases (p / p° > 0.4), a hysteresis loop with H3-type characteristics appears between the desorption and adsorption curves, confirming the presence of a mesoporous structure within the material. Pore size distribution testing reveals that the peak pore volume distribution of this material is in the 2-10 nm range, consistent with typical characteristics of mesoporous materials. The existence of this mesoporous-microporous composite pore structure is beneficial for improving the adsorption performance and mass transport efficiency of ferrihydrite.

[0075] Table 1 Surface structural characteristics of ferrohydra

[0076] As shown in Table 1, the SSA of ferrohydra is... BET It is 251.303 m 2 / g indicates that it has a high specific surface area. Secondly, the mesopore volume (V) of ferrohydrate meso ) as a percentage of total pore volume (V total The fact that more than half of the surface area of ​​ferrohydrite is greater than half indicates that the porosity of ferrohydrite is characterized by the coexistence of micropores and mesopores, with mesopores being the dominant structure. The high specific surface area and the coexistence of micropores and mesopores in ferrohydrite enable it to provide better adsorption conditions.

[0077] Figure 3 It can be observed that the ferroalloy of Example 1 is effective against Cd. 2+ The adsorption kinetics of Cd exhibit two distinct phases: rapid adsorption in the initial stage, followed by a gradual convergence to equilibrium over a period of 360 minutes. Table 2 shows the fitting results of the kinetic model, indicating that the correlation coefficient of the pseudo-second-order kinetic model is significantly higher than that of the pseudo-first-order kinetic model. This phenomenon confirms that the PSO model is more suitable for describing Cd. 2+ The adsorption behavior on the surface of ferrohydrate suggests that the adsorption process may be mainly dominated by a chemisorption mechanism.

[0078] Table 2. Cd obtained from PFO and PSO models 2+ Adsorption kinetic parameters on ferrohydride

[0079] in accordance with Figure 4 The experimental data presented show the effect of water iron ore on Cd.2+ The adsorption capacity of Cd exhibits a striking change with increasing initial equilibrium concentration: it rises rapidly in the initial stage, then the rate of increase gradually slows down and eventually tends towards a steady state. Table 3 shows the fitting results of the isothermal adsorption model, indicating that both the Langmuir and Freundlich models can effectively describe the adsorption of Cd. 2+ The adsorption process suggests that it may involve multiple mechanisms. Analysis of the data in Table 3 reveals that the Langmuir model has a higher correlation coefficient (R²). 2 The correlation coefficient R of the Langmuir model is greater than that of the Freundlich model, and the correlation coefficient R of the Langmuir model is greater. 2 The correlation coefficient reached 0.9863, indicating a significant correlation. This result confirms the existence of monolayer adsorption characteristics and provides strong evidence for the chemisorption mechanism, consistent with the conclusions of kinetic studies. The R-value calculated using the Langmuir model... L The values ​​are in the range of 0 to 1, verifying the effect of water-iron ore on Cd. 2+ The adsorption process is thermodynamically spontaneous.

[0080] Table 3. Cd obtained from Langmuir and Freundlich models 2+ Adsorption isotherm parameters on ferrohydra

[0081] To clarify the simultaneous adsorption of Cd during the microbial reduction of ferrophosphate in Example 1 2+ Regarding the effect of IMI degradation, the bacterial agent and minerals were prepared according to the experimental steps of Example 1, and a compound bacterial agent was made at a ratio of 1:5. 5% of the compound bacterial agent was added to the contaminated system, which included sterile water culture medium, 20 mg of ferrous sulfate, 2 μM IMI, and 200 mg / L of Cd. 2+ The mixture was oscillated at a constant speed at 30 °C for 24 hours. To monitor the adsorption process, samples were taken at different time points, and the solid and liquid phases were separated by centrifugation and filtration. Then, ICP-MS was used to analyze the residual Cd in the supernatant. 2+ The concentration was quantitatively analyzed, and the IMI concentration was detected by high performance liquid chromatography.

[0082] To investigate the influence of different oxygen-containing anions on the final mineral composition of the Fh transformation, the minerals from Example 1 before and after the reaction were characterized using XRD. Figure 5 As shown, crystalline iron ore (goethite) and mixed-valence (magnetite) iron solids can form in anoxic, neutral environments. MR-1 induces the formation of Gth and Magnetometallic oxide (GhN), with Magnetometallic oxide accounting for approximately 70% and Gth accounting for approximately 30%.

[0083]

[0084] Fh initially appears as a reddish-brown viscous liquid, but after freeze-drying, it becomes a reddish-brown powder, which is an amorphous crystal. The secondary mineral produced by Fh after the reaction is black magnetite. Figure 6 As shown, we used TEM to image the above samples to investigate the changes in Fh transformation. Unreacted ferrihydrite was an amorphous crystal, and no crystal form was observed overall. Goethite was needle-shaped or rod-shaped, with needle-shaped crystals growing along the C-axis and having sharp ends. Magnetite was a spherical aggregate (microspheres of 20-100 nm). Comparative spectral analysis showed that goethite after the reaction had (101) crystal planes, while magnetite had (311) crystal planes. Therefore, it can be concluded that ferrihydrite evolved from amorphous nanoparticles before the reaction into regular cubic magnetite nanoparticles.

[0085] like Figure 7 As shown, under anaerobic conditions, poorly crystallizable Fh can be reduced to produce abundant Fe(II). Even under anoxic conditions, Fe(II) will not be generated on the surface of ferrohydrate due to the lack of electron transfer. When MR-1 is added to the system, electrons generated by respiration reach the ferrohydrate interface and couple with protons for electron transfer. Over time, Fe(II) gradually accumulates in the solution, leading to an increase in concentration, directly demonstrating that the microorganisms in the mixed system have an active iron-reducing ability, while the sterile control group does not exhibit this phenomenon.

[0086]

[0087] The binding energies of Fe2p3 / 2 and Fe2p1 / 2 in ferrihydrite are 711 eV ± 0.2 eV and 724 eV ± 0.2 eV, respectively. Therefore, the difference between these lines is Δ = 13.29 eV, and the satellite exists at approximately 719.81 eV: this is typical of Fe(III) species. Figure 8 As shown, the fine spectrum of Fe 2p exhibits two typical characteristic peaks: Fe 2p3 / 2 at 710 eV ± 0.2 eV and Fe 2p1 / 2 at 724 eV ± 0.2 eV. The Fe 2p3 / 2 peak is decomposed into two peaks, associated with Fe(III) and Fe(II), respectively. Figure 8 As shown, the characteristic peak of Fe(III) predominates before the reaction, while the characteristic peak of Fe(II) appears after the reaction, confirming the formation of structural divalent iron.

[0088] The degradation process of imidacloprid exhibits significant two-stage kinetic characteristics. Figure 9Within the initial 0-12 hours of the reaction, the degradation rate was only 8%, indicating a significant degradation lag phase. This phase corresponds to the dissimilatory iron reduction process driven by iron-reducing bacteria in the system, where ferrohydrate is consumed as the main electron acceptor for microbial growth and metabolism, while simultaneously generating Fe(II).

[0089] Subsequently, imidacloprid rapidly degraded after 12 hours. From 12 to 72 hours, the total degradation rate of imidacloprid reached 91%. This rapid transformation coincided precisely with the formation of magnetic secondary minerals (such as magnetite) in the system. The efficient degradation at this stage was mainly attributed to the newly formed magnetite, which is rich in structural divalent iron. The Fe(II) in its crystal structure acts as a powerful reducing agent, directly attacking and reducing characteristic functional groups (such as nitro groups) in the imidacloprid molecule, leading to the breaking of its molecular bonds and thus achieving efficient degradation. This degradation kinetic curve visually confirms that microbial-driven mineral transformation is the fundamental reason for the efficient removal of imidacloprid in this system.

[0090] The "iron-reducing bacteria-hydrothermic mineral" mixed system described in this invention has a positive effect on Cd. 2+ The removal of imidacloprid exhibits a clear temporal synergistic characteristic, fully embodying the tandem reaction mechanism of "first adsorption and enrichment, then reduction and degradation and stabilization". Figure 10 ).

[0091] Therefore, it can be seen that the Cd²⁺ removal kinetics of the present invention exhibits two typical stages: in the initial 0-12 hours of the reaction, more than 60% of the Cd in the liquid phase is removed. 2+ The dextrose is rapidly removed. This stage is mainly attributed to rapid surface adsorption dominated by the ferrohydrate with its large specific surface area, which is in high agreement with the results of separate adsorption kinetic experiments. Subsequently, during the period from 12 hours until the end of the reaction, Cd is rapidly removed. 2+ The concentration remained stable at a low level with no desorption. XRD and TEM analyses indicated that the ferrihydrite had transformed into well-crystallized magnetite; XPS valence state analysis further confirmed the presence of structural Fe(II). This suggests that the Cd initially adsorbed on the surface of the ferrihydrite... 2+ During the mineral phase transformation process, it is further fixed in the newly formed and more stable magnetite lattice, realizing the transformation from "reversible adsorption" to "long-term fixation".

[0092] with cd 2+In stark contrast to the rapid removal of other pesticides, imidacloprid degradation exhibits a significant lag. In the initial 0-12 hours, its degradation rate is extremely low (<10%), indicating limited adsorption by ferrohydrate and its own degradative activity against the pesticide. However, after 12 hours, the concentration of imidacloprid begins to decrease sharply, while the Fe(II) concentration in the system increases significantly. Therefore, the efficient degradation of imidacloprid is not caused by the initial ferrohydrate, but rather by reductive degradation triggered by microbially generated magnetite rich in structural divalent iron.

[0093] The time-series removal data, along with mineral characterization and valence state analysis results, corroborate each other, forming a complete chain of evidence: the system first utilizes the physicochemical adsorption capacity of ferrohydrate to rapidly capture and enrich Cd. 2+ This prepares the ground for subsequent stabilization and solidification; subsequently, driven by iron-reducing bacteria, Cd is adsorbed. 2+ The in-situ transformation of ferrohydrate into magnetite, a process that, on the one hand, converts Cd... 2+ It is firmly fixed, and on the other hand, it generates an active component (structural Fe(II)) that can degrade imidacloprid, thereby initiating the deep removal of organic pollutants.

[0094] Application Examples:

[0095] The "iron-reducing bacteria-iron ore" mixed remediation agent of this invention has a direct and simple application prospect in the remediation of contaminated soil, especially in scenarios with natural or easily created anaerobic environments such as paddy fields, wetlands, and flooded farmland.

[0096] 1. Preparation of repair agent

[0097] Mix commercial or homemade ferrohydrate with high concentrations (~1×10⁻⁵) in a ratio (e.g., dry weight of ferrohydrate: volume of bacterial solution = 1:5). 8 A homogeneous microbial-mineral composite remediation agent is formed using an iron-reducing bacterium (Shewanella oneidensis MR-1) inoculum (CFU / mL). This remediation agent can be prepared as a slurry or an easily spreadable powder for convenient transportation and application.

[0098] 2. On-site application

[0099] The prepared remediation agent is evenly spread or mixed into the surface layer (usually the 0-20 cm tillage layer) of the target contaminated soil by manual or mechanical means. This is to ensure that the remediation agent comes into full contact with the contaminant.

[0100] 3. Process Maintenance

[0101] Immediately after application, the soil should be flooded to maintain a water layer of at least 3-5 cm. This aims to isolate the soil from air and, relying on the respiration of soil microorganisms and organic matter, rapidly create the anaerobic environment required by this invention within a few days. Throughout the entire remediation cycle (e.g., 30-60 days), the field must be kept flooded to ensure stable anaerobic conditions. Under these conditions, the remediation agent will automatically initiate and run the aforementioned sequential synergistic remediation process of "adsorption-conversion-degradation".

[0102] 4. Application conditions

[0103] Anaerobic conditions can be naturally and cost-effectively achieved through the aforementioned field flooding management. This is a fundamental characteristic of paddy fields and similar settings, requiring no additional energy input. The temperature range of 25-35℃ closely matches the natural field temperatures in most parts of my country from late spring to autumn, and can be easily met by selecting the appropriate season for construction, without the need for external heating. The pH value of most agricultural soils is between 6.5 and 7.5, which meets the requirements. If the soil is too acidic (pH < 6.0), a small amount of lime can be applied before remediation for gentle adjustment; if it is too alkaline, gypsum can be used for adjustment. In actual soil environments, soil organic matter (such as root exudates, organic fertilizers, and degradation products of straw returned to the field) can serve as a natural and continuous source of electron donors, providing nutrients for iron-reducing bacteria, requiring little or no additional chemicals.

[0104] The reagents prepared in Example 1 and Comparative Examples 1-3 were added to the same contamination system at an inoculum of 5% (v / v), and reacted at a temperature of 25-35°C. Group testing and observation were then conducted (each reagent corresponded to one group). Figure 11 As shown, all tests represent the degradation efficiency on the third day. Under the ratio of Example 1 (bacteria:minerals = 1:5), the system's degradation efficiency for Cd... 2+ The simultaneous adsorption and fixation rate reached 65%, and the degradation rate of imidacloprid reached 98.7%. This efficiency is significantly better than all single-component or improperly proportioned systems. The results of Comparative Example 1 show that a single mineral has a high Cd degradation rate. 2+ The adsorption capacity was limited, with a removal rate of only 27.9%, and it had almost no degradation effect on imidacloprid (degradation rate <1%), confirming the limitations of simple adsorption technology. Comparative Example 2 showed that, without the support of iron minerals, the bacterial agent had limited effect on Cd. 2+ While it had no fixed effect (0.1%), it could metabolize a certain amount of imidacloprid, with a degradation rate of 27.7%, both of which were at a low level, demonstrating the inadequacy of single-microbial technology. In Comparative Example 3, the ratio of bacteria to mineral was 1:0.5, meaning that the remediation efficiency of the excessive bacterial agent (Cd²⁺ removal rate 36.7%, imidacloprid degradation rate 63.5%) was actually lower than that of Example 1. This indicates that an excessively high proportion of bacterial agent can disrupt the system balance, possibly due to excessive consumption of substrate by microorganisms or the generation of steric hindrance, thus inhibiting mineral transformation and pollutant removal efficiency.

[0105] Comprehensive analysis demonstrates that only within a bacterial-mineral ratio of 1:1 to 1:10 (dry weight:volume) can the system achieve efficient synergistic removal of pollutants. First, ferrous sulfate acts as a highly efficient adsorbent, rapidly enriching Cd²⁺. Then, driven by functional bacteria, it transforms into magnetite. The newly formed magnetic mineral stabilizes and immobilizes the adsorbed cadmium while simultaneously utilizing its structural ferrous iron to efficiently degrade imidacloprid. This mechanism ensures that, under optimized ratios, this invention achieves simultaneous, efficient, and long-lasting remediation capabilities unattainable by any single technology.

[0106] The application scheme of this invention is highly compatible with existing agricultural production practices (such as paddy field flooding), and its core technical requirements can be met through simple agronomic operations (spreading and flooding). This technology does not require complex equipment installation or expensive energy consumption; the main cost is concentrated in the one-time addition of the remediation agent itself, demonstrating outstanding advantages such as ease of operation, low cost, and good environmental compatibility. It provides a green remediation path with great application potential for farmland soil, especially paddy fields with combined cadmium and pesticide pollution.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides, characterized in that, The mixture comprises functional microbial agents and iron minerals, wherein the dry weight ratio of the iron minerals to the volume of the functional microbial agent is 1:1~10; the functional microbial agent is a live culture of dissimilar iron-reducing bacteria, with a cell concentration of not less than 1×10⁻⁶. 8 CFU / mL, wherein the iron mineral is ferrohydrate Fe2O3·nH2O.

2. The preparation method of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 1, characterized in that, Includes the following steps: Provides iron ore; Live bacterial cultures of dissimilatory iron-reducing bacteria; The live bacterial culture of iron minerals and dissimilar iron-reducing bacteria is mixed in a ratio of 1:1 to 10 between the dry weight of iron minerals and the volume of functional bacterial agent.

3. The preparation method of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 2, characterized in that: The iron mineral is purchased commercially or prepared by means of preparation. The preparation process is as follows: ferric nitrate nonahydrate is added to deionized water, KOH solution is continuously added dropwise until the pH reaches 7.4-7.6, the mixture is stirred and reacted for a period of time, the supernatant is removed by centrifugation, the resulting precipitate is washed, and the iron mineral is obtained after drying.

4. The preparation method of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 3, characterized in that: The ratio of ferric nitrate nonahydrate to deionized water was 2g:25mL, and the concentration of KOH solution was 1 mol / L.

5. The preparation method of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 2, characterized in that: The steps for culturing live bacterial cultures of dissimilatory iron-reducing bacteria are as follows: take out strain MR-1 and thaw it in a constant temperature water bath; activate MR-1 by incubation in LB medium under aerobic conditions; after culturing the bacteria to the logarithmic growth phase, centrifuge to obtain MR-1 bacterial sediment, and then wash and resuspend it with buffered salt solution.

6. The preparation method of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 5, characterized in that: The centrifugation is performed at room temperature at 5000-7000 rpm for 5-10 minutes.

7. The preparation method of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 5, characterized in that: The buffer salt solution comprises 0.14 g / L -1 KH2PO4, 0.2 g L -1 NaCl, 0.3 g / L -1 NH4Cl, 0.5 g L -1 MgSO4·7H2O and 0.1 g L -1 The pH of the buffer salt solution is 7, and the solution is CaCl2·2H2O.

8. The application of the composite remediation agent for simultaneously removing heavy metal cadmium and neonicotinoid pesticides as described in claim 1 in soil pollution remediation, characterized in that: The compound remediation agent is added and dispersed in polluted soil or water to remove heavy metal cadmium and neonicotinoid pesticides simultaneously under anaerobic conditions.

9. The application as described in claim 8, characterized in that: The composite remediation agent is added to contaminated soil or water at an inoculum of 5% (v / v) and reacted at a temperature of 25-35℃.

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