A method for repairing pesticide-polluted soil under dry-wet alternating condition by using ferrihydrite-biochar coupling activated hydrogen peroxide

Abstract

The present application belongs to the technical field of in-situ remediation of contaminated soil, and particularly relates to a method for remediation of pesticide-contaminated soil under dry-wet alternation by using ferrihydrite-biochar coupling activated hydrogen peroxide. To solve the problem that the existing iron mineral mediated Fenton-like remediation system has poor effect when used for remediation of pesticide-contaminated soil under dry-wet alternation, the present application provides a method for remediation of pesticide-contaminated soil under dry-wet alternation by using ferrihydrite-biochar coupling activated hydrogen peroxide. In the method, ferrihydrite and biochar are prepared respectively, and then the two are coupled to construct an iron-carbon interface. Relying on the electron buffering and shuttling effect of biochar, the iron coordination effect of oxygen-containing functional groups, and the spatial regulation effect of microorganisms, the Fe(III) / Fe(II) cycle is stabilized, hydroxyl radicals are continuously generated, so as to inhibit iron loss, delay system activity attenuation, intercept pesticides and reduce free radical invalid consumption, and promote in-situ remediation of periodically dry-wet alternation contaminated soil such as paddy field and farmland.

Description

Technical Field

[0001] This invention belongs to the field of in-situ remediation technology for contaminated soil, specifically relating to a method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrophosphate and biochar to activate hydrogen peroxide. Background Technology

[0002] Pesticides play a vital role in ensuring agricultural production and food security, but their long-term and extensive use can lead to pesticide residues in farmland soil. Under the influence of rainfall, irrigation, and soil pore water migration, these pesticide residues can further migrate into deeper soil layers and groundwater, increasing the risks to the ecological environment and human health. Currently, technologies for remediating pesticide-contaminated soil mainly include physical adsorption, biodegradation, and chemical oxidation. Physical adsorption struggles to achieve complete pollutant degradation, bioremediation has a long cycle and is easily affected by environmental conditions, while chemical oxidation, although highly efficient, often faces challenges in complex soil systems such as limited mass transfer, low oxidant utilization, and competitive consumption of oxidants by soil organic matter. Therefore, there is an urgent need to develop in-situ pesticide pollution remediation technologies suitable for farmland soil environments that combine high efficiency and stability.

[0003] Paddy soils and farmland soils undergoing seasonal wet-dry cycles exhibit distinct redox dynamics. In a flooded anaerobic environment, iron-reducing microorganisms and reducing organic matter in the soil drive the reduction reaction of Fe(III) minerals to generate Fe(II). Upon entering the drained aerobic stage, the accumulated Fe(II) in the soil can further activate oxidants (such as oxygen and hydrogen peroxide), generating hydroxyl radicals (•OH), thereby driving the oxidative degradation of organic pollutants. Constructing an iron mineral-mediated in-situ Fenton-like remediation system based on this reaction process can achieve the cyclical regeneration of active iron substances through the soil's own redox cycles, providing a potentially applicable green technology approach for the remediation of pesticide-contaminated soils.

[0004] However, existing iron mineral-hydrogen peroxide-based Fenton systems still have significant limitations in soils with alternating wet and dry conditions. On the one hand, the interfacial electron transfer efficiency in single iron mineral systems is limited, and the regeneration of active Fe(II) is unstable. On the other hand, repeated redox processes are prone to problems such as iron leaching, mineral passivation, and instantaneous free radical bursts, leading to a rapid decline in reactivity. In addition, phenols, humic substances, and other components released during soil organic matter transformation may competitively consume •OH, reducing the oxidation efficiency of target pesticides. Due to these limitations, traditional iron mineral-based Fenton systems cannot maintain stable remediation capabilities in dynamically changing soil environments over the long term. Therefore, there is an urgent need to develop an interfacial-regulated in-situ soil remediation method that can stabilize iron redox cycles, inhibit iron leaching, and improve free radical utilization efficiency. Summary of the Invention

[0005] To overcome the problems of slow interfacial electron transfer, unstable regeneration of active Fe(II), severe iron leaching, accumulation of free radical scavengers, and decreased reactivity in existing iron mineral-mediated Fenton remediation systems in alternating wet and dry soils, this invention provides a method for remediating pesticide-contaminated soils in alternating wet and dry conditions using a ferroalloy-biochar coupled activation of hydrogen peroxide (H2O2). This method constructs a ferroalloy-biochar iron-carbon interface in the contaminated soil, utilizing the electron buffering effect of biochar, the iron coordination effect of oxygen-containing functional groups, and the spatial regulation effect of microorganisms to stabilize the Fe(III) / Fe(II) cycle and promote the continuous generation of •OH, thereby improving the remediation stability of pesticide-contaminated soils and reducing the risk of pollutant leaching and migration.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for remediating pesticide-contaminated soil during alternating wet and dry periods using a combination of ferrohydrate and biochar-hydrogen peroxide activation. Specifically, biochar and ferrohydrate are added to the pesticide-contaminated soil to construct a stable iron-carbon reaction interface. During the wet anaerobic stage of the soil, biochar accelerates electron transfer between microorganisms, organic matter, and ferrohydrate, promoting the reduction and regeneration of Fe(II) by Fe(III). Furthermore, biochar's surface oxygen-containing functional groups fix active iron at the iron-carbon interface, inhibiting iron ion loss. During the dry aerobic stage of the soil, the interface-fixed Fe(II) and dissolved Fe(II) synergistically activate exogenous H2O2, continuously generating hydroxyl radicals, which then efficiently oxidize and degrade pesticide pollutants in the soil, achieving in-situ remediation of the contaminated soil.

[0007] The exogenous H2O2 includes H2O2 in the soil and / or artificially applied H2O2, with a total H2O2 concentration of 0.1–10 mmol·L. -1 If the H2O2 content in the soil is insufficient, an appropriate amount of H2O2 can be applied to ensure the remediation effect. The concentration of H2O2 added is 0.1–10 mmol / L. -1 The solution can be added to the soil all at once or in multiple applications.

[0008] A single remediation cycle consists of one wet anaerobic stage followed by one dry aerobic stage. The remediation cycle can be set to 1 to 10 cycles, and can be carried out in a single cycle or multiple cycles until the pesticide residue in the soil meets the standards.

[0009] The technical principle of this invention is as follows: the ferrohydrate-biochar coupling system can form a stable iron-carbon reaction interface in the soil. During the wet anaerobic stage, the quinone / phenolic groups and their electron exchange capacity in the biochar promote electron transfer between microorganisms, organic matter, and ferrohydrate, and act as an electron buffer, thereby improving the regeneration efficiency of Fe(III) to Fe(II). Simultaneously, the carboxyl, hydroxyl, and carbonyl functional groups on the biochar surface can coordinate or complex with Fe(II) / Fe(III), retaining some of the regenerated active iron species at the ferrohydrate-biochar interface and reducing their excessive release into the pore water. During the drained aerobic stage, in the presence of exogenous H2O2, the Fe(II) retained at the interface and an appropriate amount of dissolved Fe(II) can synergistically activate the exogenous H2O2, continuously generating hydroxyl radicals, thereby oxidizing and degrading pesticide pollutants such as atrazine. Biochar can also adsorb and retain target pollutants, shorten the mass transfer distance between pollutants and interfacial active sites, and promote the removal of phenolic free radical scavengers by improving microbial attachment and spatial distribution, while reducing their competitive quenching of •OH. Through the synergistic effects of electron buffering, interfacial iron retention, pollutant retention, and microbial regulation, this system can transform the transient free radical burst process driven by aqueous iron leaching in traditional iron mineral systems into a more stable interfacial-regulated Fenton-like reaction process.

[0010] Preferably, the pesticide-contaminated soil subjected to alternating wet and dry conditions includes farmland soil, wetland soil, and other similar pesticide-contaminated soil.

[0011] Preferably, the wet anaerobic stage of the pesticide-contaminated soil undergoing alternating wet and dry conditions is 5–90 days, and the dry aerobic stage is 1–10 days.

[0012] Preferably, the amount of biochar added is 0.1% to 10% of the dry weight of the contaminated soil, and more preferably 0.5% to 5%.

[0013] Preferably, the amount of ferrohydrate added is 0.05% to 5% of the dry weight of the contaminated soil, based on the iron content, and more preferably 0.1% to 2%.

[0014] Preferably, the mass ratio of biochar to ferrohydrate is 1:10 to 20:1, and more preferably 1:5 to 10:1.

[0015] Preferably, the pesticides include (but are not limited to) atrazine, simazine, promethazine, atrazine, diuron, isoproturon, metolachlor, acetochlor, and other organic pesticides that can be oxidized and degraded by hydroxyl radicals.

[0016] Preferably, the biochar preparation method is as follows: agricultural and forestry waste biomass raw materials are dried, crushed and sieved, then subjected to oxygen-limited pyrolysis under an inert atmosphere, cooled, taken out, ground and sieved to obtain biochar.

[0017] More preferably, the agricultural and forestry waste biomass raw materials include (but are not limited to) pine sawdust, rice husks, corn stalks, bamboo shavings, fruit shells (or other agricultural and forestry waste).

[0018] More preferably, the temperature of the oxygen-limited pyrolysis is 300–800°C, more preferably 500–700°C; the heating rate is 2–10°C / min. -1 The heat preservation time is 0.5 to 4 hours.

[0019] More preferably, the inert atmosphere is a nitrogen or argon atmosphere, and the gas flow rate is 0.2–2.0 L / min. -1 .

[0020] More preferably, in the preparation of biochar, after grinding, it is sieved through a sieve with a pore size of 0.05 to 2 mm.

[0021] Preferably, the preparation method of the ferrohydrate is as follows: iron salt is dissolved in water, and the pH of the system is adjusted to a weakly acidic to neutral range under stirring conditions, so that the iron salt undergoes a hydrolysis-precipitation reaction to form a ferrohydrate suspension. After the reaction, the precipitate is collected by standing and washed until the supernatant is close to neutral and the conductivity is stable, thus obtaining ferrohydrate.

[0022] More preferably, the iron salt includes (but is not limited to) ferric nitrate, ferric chloride, ferric sulfate, or their hydrates.

[0023] More preferably, the pH of the system is adjusted to 4.5 to 7.5 under stirring conditions, preferably 5.0 ± 0.5.

[0024] More preferably, the stirring rate is 100-500 rpm and the time is 0.5-4 h.

[0025] More preferably, the ferrohydrate is repeatedly washed with ultrapure water until the supernatant is nearly neutral and has a conductivity of less than 10 µs / cm before use, and can be stored in a wet state or after being dried at low temperature.

[0026] Compared with the prior art, the beneficial effects of the present invention are: This invention discloses a method for remediating pesticide-contaminated soils with alternating wet and dry conditions using a combination of ferrohydrate and biochar-activated hydrogen peroxide. The method involves first preparing ferrohydrate and agricultural / forestry waste-based biochar separately, then coupling them to construct an iron-carbon interface. Leveraging the electron buffering and shuttle effect of biochar, the coordination effect between oxygen-containing functional groups and iron, and the spatial regulation of microorganisms, the method promotes the Fe(III) / Fe(II) cycle and fixes the generated Fe(II), continuously generating hydroxyl radicals. This inhibits iron loss, delays the decline in system activity, retains pesticides, and reduces ineffective consumption by free radicals. This method uses readily available materials, is simple to prepare, produces no secondary pollution, and operates under mild reaction conditions, making it suitable for in-situ remediation of periodically wet-dry contaminated soils such as paddy fields and farmland.

[0027] Specifically, the present invention has the following advantages: (1) The water-iron ore-biochar coupling system constructed in this invention can promote Fe(III) / Fe(II) cycle in alternating wet and dry soil, improve the regeneration efficiency of active Fe(II), and reduce the runaway release of Fe(II) in pore water through interfacial coordination, thereby improving the stability of iron cycle.

[0028] (2) This invention utilizes the electron shuttle and electron buffering functions of biochar to alleviate the problem of rapid decay of the reactivity of traditional iron minerals in Fenton-like systems, making H2O2 activation and •OH generation more sustainable.

[0029] (3) Based on the interfacial retention effect of biochar on pesticide pollutants such as atrazine and the regulatory effect on phenolic free radical scavengers, this invention effectively reduces the risk of pollutant leaching and migration and reduces the competitive consumption of free radicals by non-target matrices, thereby improving the utilization efficiency of free radicals.

[0030] (4) The biochar used in this invention can be derived from agricultural and forestry waste. Hydrometallurgical ore is a common environmental iron mineral. The material sources are wide, the preparation method is simple, the environmental compatibility is good, and it is not easy to introduce secondary pollution.

[0031] (5) This invention is applicable to paddy soil, farmland soil and other polluted soil environments affected by periodic wet and dry cycles. The reaction conditions are mild and do not require high temperature, high pressure or strong acid conditions, and have good potential for in-situ remediation. Attached Figure Description

[0032] Figure 1 A schematic diagram of the process for remediating pesticide-contaminated soil through alternating wet and dry conditions using a combination of hydroiron ore and biochar-activated H2O2.

[0033] Figure 2 The figure shows the characterization results of the ferrohydrate and biochar materials prepared in Example 1, including the X-ray diffraction pattern of ferrohydrate (a), the surface functional group characterization results of biochar (b), and the electrochemical property analysis (c).

[0034] Figure 3 The diagram shows the remediation effect of the ferrophosphate-biochar-H2O2 system on atrazine-contaminated soil in Example 2; a: concentration change in pore water, b: residual amount in the soil after remediation.

[0035] Figure 4 The diagram shows the regulatory effect of the ferrous ore-biochar-H2O2 system on the iron redox cycle and the sustainability of hydroxyl radical generation in Example 3; a: bar chart of soil iron speciation distribution, b: bar chart of surface ferrous iron content.

[0036] Figure 5 This is the effect of hydrofer ore-biochar coupled activation of H2O2 on the remediation of various pesticides in soil in Example 4. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0039] Example 1: Preparation and Characterization of Hydroferroic Ore and Biochar Materials Preparation of ferrohydrate: 80 g of Fe(NO3)3·9H2O was dissolved in 600 mL of ultrapure water. The mixture was stirred at 300 rpm for 2 h. During stirring, 1 M NaOH solution was slowly added dropwise to adjust the pH of the system to 5.0 ± 0.5, allowing Fe(III) to undergo a hydrolysis-precipitation reaction (at room temperature) to form a ferrohydrate suspension. After the reaction was complete, the precipitate was collected after standing for 30 min and repeatedly washed with ultrapure water until the supernatant was nearly neutral, yielding the ferrohydrate material. X-ray diffraction was used to analyze the obtained ferrohydrate. The results are as follows: Figure 2 As shown in a, the prepared hydrometallurgical ore has the characteristics of low-crystallization iron minerals and belongs to the two-line hydrometallurgical ore.

[0040] Biochar preparation: Dried pine sawdust was used as the biomass raw material. The sawdust was pulverized and placed in a tube furnace for oxygen-limited pyrolysis under nitrogen protection. The nitrogen flow rate was controlled at 1.0 L / min during pyrolysis. -1 The heating rate is controlled at 5℃·min. -1The pyrolysis temperature was 550℃, and the holding time was 2 h. After cooling to room temperature, the material was removed, ground, and sieved through a 0.15 mm sieve to obtain biochar material. Fourier transform infrared spectroscopy was used for characterization, and the results are as follows: Figure 2 As shown in b, its surface contains oxygen-containing functional groups such as hydroxyl, carboxyl, and carbonyl groups, which can provide active sites for interfacial coordination and electron transfer of iron species. The electrochemical properties of the biochar were further evaluated using cyclic voltammetry and electron donation-acceptance testing. Specific testing methods are as follows: (1) Testing instrument: Huachen CHI-660 electrochemical workstation; (2) Test method: 1) Experimental reagents: The buffer solution used was a phosphate buffer solution, specifically a buffer solution of 0.1 M disodium hydrogen phosphate / sodium dihydrogen phosphate (pH=7) and 0.1 M KCl. The water used in the experiment was ultrapure water, deoxygenated with nitrogen.

[0041] 2) Preparation of biochar suspension: The ball-milled biochar was prepared into a biochar suspension of the appropriate concentration using the buffer solution described above as the solvent. The concentration of the biochar suspension used in this experiment was 1 g / L, and it was sonicated for 30 min to ensure uniform dispersion in the solution.

[0042] 3) The CHI electrochemical workstation was used for testing, and a constant voltage-it curve was generated, providing a constant voltage of 0.61 V (MEO) and -0.49 V (MER). This experiment employed a three-electrode testing system, with a glassy carbon electrode as the working electrode, a platinum wire electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The mediators were ABTS (MRO) and ZiV (MER), respectively.

[0043] 4) Test procedure: Set the constant voltage to 0.61 V (mediated oxidation) or -0.49 V (mediated reduction). Take 6 mL of buffer solution and inject it into the reactor through the feed port. Start the electrochemical test program and obtain the current-time curve. After the current reaches stability, take 100 μL of ABTS or ZiV (concentration of 10 mM) and inject it into the reactor through the feed port. When the reaction current returns to the baseline and reaches stability, it indicates that the mediator in the system has been completely oxidized / reduced. At this time, add a small amount of biochar suspension (100 μL, 200 μL, 300 μL) to obtain the test curve.

[0044] (3) Experimental results: Experimental results are as follows Figure 2 As shown in c, the synthesized biochar exhibits significant redox current response and electron donation and acceptance capabilities, and can serve as an electron buffer medium to participate in the regulation of the Fe(III) / Fe(II) cycle.

[0045] Example 2: Remediation effect of the ferrohydrate-biochar-H2O2 coupled system on atrazine-contaminated soil 300 g of contaminated paddy soil with an atrazine concentration of 10.33 mg / kg was packed into a soil column reactor. A blank control and a ferrophosphate-biochar-H2O2 treatment group were set up. The blank control group received no exogenous remediation materials or H2O2 and was operated according to the same flooding-drainage procedure. In the ferrophosphate-biochar-H2O2 treatment group, biochar and ferrophosphate were thoroughly mixed with the contaminated soil at 1.0% and 0.25% of the soil dry weight, respectively, and then packed into the soil column. During the experiment, 0.01 M CaCl2 solution (3 cm above the soil surface) was first added to the soil column to put the soil into a flooded anaerobic state to promote the reduction of Fe(III) in the ferrophosphate to Fe(II). After 10 days of anaerobic treatment, the overlying water was drained, and 40 mL of 0.5 mM H2O2 solution was added to the ferrophosphate-biochar treatment group for 8 days of oxidation, allowing the ferrophosphate-biochar to activate H2O2 to generate •OH, which degraded atrazine in the soil. The above-mentioned anaerobic flooding stage and aerobic drainage stage were repeated for two cycles to simulate the alternating wet and dry process of farmland soil.

[0046] The simulation principle is as follows: During alternating wet and dry operation, the ferrophosphate-biochar interface regulates the soil iron redox cycle and Fenton-like oxidation reaction. In the flooded anaerobic stage, biochar acts as an electron buffer and electron transfer medium, promoting electron transfer from microorganisms or soil organic matter to ferrophosphate Fe(III), accelerating the reduction of Fe(III) to Fe(II). In the drainage stage, under the presence of oxygen and H2O2, the Fe(II) retained at the interface activates H2O2 to produce •OH, achieving in-situ oxidative degradation of pollutants such as atrazine. Figure 1 ).

[0047] Soil pore water samples were collected periodically during operation to determine atrazine concentration. Results are as follows: Figure 3 As shown in Figure a, compared with the blank control group, the ferrohydrate-biochar-H₂O₂ system significantly promoted the attenuation of atrazine in pore water. In the first oxidation stage, the system achieved rapid kinetic initiation, with an apparent rate constant of 0.096 ± 0.022 d⁻¹. During continuous wet-dry cycles, the atrazine concentration in pore water continuously decreased, reaching a low level in the later stages of remediation. After remediation, the atrazine residue in the soil at different depths of the soil column was measured. The results are as follows: Figure 3 As shown in b, compared with the blank control group, the ferroalloy-biochar-H2O2 system significantly reduced the amount of atrazine residue in each soil layer, indicating that the technology can effectively reduce the accumulation of atrazine in the soil profile and reduce its risk of deep migration.

[0048] Example 3: Regulation of soil iron speciation and surface Fe(II) retention by a hydrofer ore-biochar-H2O2 coupled system To verify the regulatory effect of the ferrohydrate-biochar-H2O2 coupled system on the iron redox cycle in alternating wet and dry soil, a soil iron cycle simulation experiment was constructed. 300 g of paddy soil contaminated with atrazine at a concentration of 10 mg / kg was packed into a soil column reactor. A blank control group, a H2O2-only treatment group, and a ferrohydrate-biochar-H2O2 treatment group were set up. The blank control group did not contain any exogenous materials or H2O2; the H2O2-only treatment group only added H2O2 during the oxidation stage; the ferrohydrate-biochar-H2O2 treatment group contained 0.5% ferrohydrate and 1.5% biochar based on soil dry weight, and 50 mL of 1 mM H2O2 was added during the oxidation stage. The anaerobic period was 20 days, the oxidation period was 5 days, and a total of 3 flooded anaerobic-drained oxidation cycles were set up to simulate the alternating wet and dry process of farmland soil.

[0049] After the reaction, soil samples were collected from 1-2 cm, 4-5 cm, and 7-8 cm depths, respectively. The content of different iron forms, including exchangeable iron, surface-complexed / low-crystal iron, and high-crystal iron, was determined using a sequential extraction method. Simultaneously, X-ray photoelectron spectroscopy was used to analyze the Fe(II) content on the soil surface. The results are as follows: Figure 4 As shown. Compared with the H2O2 treatment group alone, the ferrihydrite-biochar-H2O2 system was able to maintain a higher content of solid active iron (including exchangeable iron and surface complex / low-crystalline iron) and increase the proportion of Fe(II) on the soil surface, indicating that the biochar-ferrihydrite interface helps to promote the solid-phase retention of active Fe(II) and the stability of the Fe(III) / Fe(II) cycle.

[0050] Example 4: Removal effect of the ferrophosphate-biochar-H2O2 coupled system on multiple pesticides in soil To verify the applicability of the method of this invention to soils contaminated with different types of pesticides, bensulfuron-methyl, imidacloprid, butachlor, and chlorpyrifos were selected as target pesticides, and remediation experiments were constructed for soils contaminated with various pesticides. 500 g of paddy soil contaminated with multiple pesticides (initial concentration of each pollutant was 5 mg / kg) was prepared, and 0.25% ferrophosphate and 1.0% biochar were added according to the dry weight of the soil and mixed thoroughly. Subsequently, a flooding anaerobic stage and a drainage oxidation stage were set up, with a flooding period of 10 days and an oxidation period of 2 days, for a total of 4 cycles, to simulate the alternating wet and dry process of farmland soil. In the oxidation stage, 100 mL of 0.4 mM H₂O₂ solution was added to the system to activate H₂O₂ at the biochar-ferrophosphate interface, generating •OH, thereby promoting the oxidative degradation of pesticides in the soil.

[0051] After the reaction, the residual concentrations of bensulfuron-methyl, imidacloprid, butachlor, and chlorpyrifos in the soil were measured, and their removal rates were calculated. The results are as follows: Figure 5As shown, the ferrophosphate-biochar-H2O2 system described in this invention exhibits good removal effects on various types of pesticides. Specifically, the removal rates of bensulfuron-methyl, imidacloprid, butachlor, and chlorpyrifos in the soil are approximately 70%, 82%, 88%, and 92%, respectively. These results demonstrate that the method of this invention is not only suitable for the remediation of atrazine-contaminated soil, but also for the remediation of soil contaminated with various pesticides such as sulfonylureas, neonicotinoids, amides, and organophosphates.

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

Claims

1. A method for remediating pesticide-contaminated soil through alternating wet and dry conditions using a combination of ferrous sulfate and biochar activation of hydrogen peroxide, characterized in that... Biochar and ferrophosphate were added to pesticide-contaminated soil during alternating wet and dry periods to construct a stable iron-carbon reaction interface. During the wet anaerobic stage of the soil, biochar accelerated electron transfer between microorganisms, organic matter, and ferrophosphate, promoting the reduction and regeneration of Fe(II) by Fe(III), and fixing active iron at the iron-carbon interface through its oxygen-containing functional groups, thus inhibiting iron ion loss. During the dry aerobic stage of the soil, the Fe(II) fixed at the interface and the dissolved Fe(II) activated exogenous H2O2, continuously generating hydroxyl radicals, which then efficiently oxidized and degraded pesticide pollutants in the soil, achieving in-situ remediation of contaminated soil. The exogenous H2O2 includes H2O2 in the soil and / or artificially applied H2O2, and the total concentration of H2O2 is 0.1-10 mmol / L -1 ; one wet anaerobic stage is matched with one dry aerobic stage as a single repair period, the repair period is set to 1-10, and the single period repair or multi-period cyclic treatment can be performed until the soil pesticide residue reaches the standard.

2. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrous ore and biochar activation, as described in claim 1, is characterized in that... The method for preparing biochar is as follows: agricultural and forestry waste biomass raw materials are dried, crushed and sieved, then subjected to oxygen-limited pyrolysis under an inert atmosphere, cooled, taken out, ground and sieved to obtain biochar.

3. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrous ore and biochar activation, as described in claim 1, is characterized in that... The preparation method of the ferrohydrate is as follows: iron salt is dissolved in water, and the pH of the system is adjusted to a weakly acidic to neutral range under stirring conditions, so that the iron salt undergoes a hydrolysis-precipitation reaction to form a ferrohydrate suspension. After the reaction, the precipitate is collected by standing and washed until the supernatant is close to neutral and the conductivity is stable, thus obtaining ferrohydrate.

4. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 1, is characterized in that... The soil contaminated by pesticides in alternating wet and dry conditions includes farmland soil or wetland soil; the wet anaerobic stage of the soil contaminated by pesticides in alternating wet and dry conditions is 5 to 90 days, and the dry aerobic stage is 1 to 10 days.

5. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 1, is characterized in that... The biochar dosage is 0.1% to 10% of the dry weight of the contaminated soil; the ferrophosphate dosage is 0.05% to 5% of the dry weight of the contaminated soil by mass; and the mass ratio of biochar to ferrophosphate is 1:10 to 20:

1.

6. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 1, is characterized in that... The pesticides mentioned include atrazine, simazine, prochloraz, atrazine, diuron, isoproturon, metolachlor, or acetochlor.

7. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 2, is characterized in that... The biomass raw materials from agricultural and forestry waste include pine sawdust, rice husks, corn stalks, bamboo shavings, or fruit shells.

8. The method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 2, is characterized in that... The oxygen-limited pyrolysis temperature is 300–800℃, and the heating rate is 2–10℃ / min. -1 The heat preservation time is 0.5 to 4 hours.

9. A method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 3, is characterized in that... The iron salts include ferric nitrate, ferric chloride, ferric sulfate, or their hydrates.

10. A method for remediating soil contaminated by alternating wet and dry pesticides using a combination of ferrohydrate and biochar activation, as described in claim 3, is characterized in that... The pH of the system was adjusted to 4.5–7.5 under stirring conditions.

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