Iron-manganese sulfide composite filling particles for chlorobenzene removal in low flow rate groundwater, and preparation method and application in permeable reactive wall

Abstract

This invention relates to the field of groundwater remediation technology, and discloses an iron-manganese sulfide composite filler particle for chlorobenzene removal in low-flow-rate groundwater, its preparation method, and its application in permeable reactive barriers. The filler particle comprises an iron-manganese sulfide-corn stalk biochar composite material, bentonite, and an inorganic binder network. The iron-manganese sulfide-corn stalk biochar composite material includes corn stalk biochar and iron-manganese sulfide particles loaded thereon via in-situ chemical precipitation. The inorganic binder network consists of a silica framework formed by the dehydration and condensation of silica sol and layered bentonite mutually supporting each other. The iron-manganese sulfide-corn stalk biochar composite material is dispersed in the gaps of the inorganic binder network, forming a granular entity with a multi-level porous structure. This invention can significantly improve the long-term catalytic activity and physical structural stability of the material.

Description

Technical Field

[0001] This invention relates to the field of groundwater remediation technology, and in particular to an iron-manganese sulfide composite filler particle for the removal of chlorobenzene from low-flow-rate groundwater, its preparation method, and its application in permeable reactive barriers. Background Technology

[0002] The remediation of organic pollution in groundwater is a major challenge in the field of environmental engineering. Chlorobenzene (C6H5Cl), a typical halogenated organic pollutant, is widely found in groundwater from industrial sites such as chemical, pharmaceutical, and pesticide manufacturing facilities. Due to its strong chemical stability and biotoxicity, chlorobenzene is difficult to degrade in underground environments and easily causes widespread water pollution through seepage, posing a serious threat to human health and ecological safety.

[0003] Currently, permeable reactive barriers (PRBs) are considered an economical and efficient in-situ groundwater remediation technology. The core of a PRB lies in its reactive material, the performance of which directly determines the removal efficiency of contaminants and the service life of the barrier. In the remediation of low-flow-rate groundwater, persulfate (PDS) advanced oxidation technology has attracted widespread attention due to its strong oxidation capacity and good stability.

[0004] Currently, existing activated persulfate materials face numerous challenges in the remediation of low-flow-rate groundwater using permeable reactive barrier (PRB) technology: First, the surface of the catalytic material is prone to generating inert oxide or hydroxide layers due to redox reactions, leading to rapid passivation and failure of active sites; second, under low-flow-rate conditions, reaction products easily deposit on the material surface and within the pores, causing pore blockage or structural collapse, which not only weakens the effective reaction interface but may also interfere with the groundwater flow field by altering the permeability coefficient; furthermore, the rapid dissolution of active components such as iron and manganese not only shortens the material's lifespan but may also lead to the risk of secondary pollution such as excessive heavy metal ions; finally, existing materials often struggle to achieve efficient "adsorption-enrichment-catalysis" synergy under low-flow-rate conditions, resulting in insufficient long-term removal capacity for pollutants. Summary of the Invention

[0005] This invention addresses the technical problems in existing remediation materials in low-flow-rate groundwater environments, such as easy oxidation and passivation, rapid coverage of active sites, easy pore blockage, and excessive loss of active components. It provides an iron-manganese sulfide composite filler particle for chlorobenzene removal in low-flow-rate groundwater, its preparation method, and its application. Through a specific multi-scale spatial confinement structure design, this invention enables the filler particles to exhibit unexpected "pore self-evolution" characteristics during the reaction process, thereby significantly improving the long-term catalytic activity and physical structural stability of the material.

[0006] The present invention solves the above-mentioned technical problems through the following technical means: In a first aspect, the present invention provides an iron-manganese sulfide composite filler particle for the removal of chlorobenzene from low-flow-rate groundwater, the filler particle comprising an iron-manganese sulfide-corn straw biochar composite material, bentonite and an inorganic binder network; The iron-manganese-sulfur-corn straw biochar composite material includes corn straw biochar and iron-manganese-sulfur particles loaded thereon by in-situ chemical precipitation. The inorganic bonding network is composed of a silica skeleton formed by the dehydration and condensation of silica sol and layered bentonite supporting each other. The iron-manganese-sulfur-corn stalk biochar composite material is dispersed in the gaps of the inorganic bonding network, forming a particulate entity with a multi-level porous structure.

[0007] Preferably, the composite filler particles comprise the following raw materials in parts by weight: 24-28 parts of iron-manganese-sulfur-corn straw biochar composite material, 8-10 parts of bentonite, and 12-15 parts of deoxysilica sol with a mass fraction of 30%.

[0008] Preferably, the atomic ratio of iron, manganese, and sulfur in the iron-manganese-sulfur-corn straw biochar composite material satisfies: Fe:Mn:S=1:(0.8-1.2):(1.2-1.5).

[0009] Secondly, the present invention provides a method for preparing iron-manganese sulfide composite filler particles for chlorobenzene removal in low-flow-rate groundwater, the method comprising: S1. Mix corn straw biochar, soluble ferrous salt and soluble manganese salt in deoxygenated deionized water, add sodium sulfide nonahydrate solution dropwise under nitrogen atmosphere, and carry out hydrothermal reaction at 140-160℃ to obtain iron-manganese-sulfur-corn straw biochar composite material. S2. The composite material is mixed with bentonite, silica sol is added and kneaded until smooth, and then extruded through a 2mm sieve to form a mold; S3. The molding material is vacuum static curing and vacuum dried at 40-60℃, and powder with a particle size of less than 0.5mm is sieved out.

[0010] Preferably, in step S1, the corn stalk biochar is a porous biochar obtained by pyrolysis at 800-1000℃ and activation by steam.

[0011] Preferably, the weight ratio of the corn straw biochar, soluble ferrous salt, soluble ferrous manganese salt, and sodium sulfide nonahydrate is 0.5:(1.1-1.3):(1.1-1.3):(2.8-3.2), wherein the soluble ferrous salt includes ferrous chloride tetrahydrate, and the soluble ferrous manganese salt includes manganese chloride tetrahydrate.

[0012] Preferably, in step S1, the hydrothermal reaction is carried out in a polytetrafluoroethylene-lined high-pressure reactor for 12-18 hours.

[0013] Thirdly, the present invention provides an application of the aforementioned composite filler particles in the construction of a permeable reactive wall.

[0014] Preferably, the filler particles serve as an activator for sodium persulfate to remove chlorobenzene from groundwater.

[0015] During the preparation process, Fe 2+ and Mn 2+ First, it is adsorbed and anchored onto the surface and pores of corn straw biochar through electrostatic interactions, coordination interactions, and pore confinement. Then, S is introduced... 2- with Fe 2+ Mn 2+ An in-situ precipitation reaction occurs, generating iron-manganese sulfides (FMS) on the surface and within the pores of the biochar. Due to the abundant functional groups and hierarchical porous structure of the biochar, the FMS are loaded onto it in a highly dispersed and tightly adhered form, avoiding severe agglomeration of the metal sulfides. The freeze-drying process further preserves the pore structure and specific surface area of ​​the material, giving FMS@SBC a porous, rough composite structure rich in active sites, providing a good structural basis for subsequent reactions.

[0016] After FMS@SBC was mixed with bentonite and silica and granulated, the material was transformed from a powder state into filled particles with certain mechanical strength and macroscopic size. The layered structure of bentonite and the inorganic framework formed by silica sol cross-linked with each other, allowing the iron-manganese-sulfur-biochar composite to be stably embedded within it. This significantly improved the structural stability of the material under hydraulic scouring and long-term operating conditions while ensuring that the reactivity was not significantly lost. This multiphase composite structure ensured permeability at the macroscopic scale and preserved the active reaction interface at the microscopic scale, providing a stable carrier for continuous reaction.

[0017] In the reaction system, iron, manganese, and sulfur are the main activating components of sodium persulfate (PDS). Iron and manganese, in their lower valence states within the sulfide structure, can undergo electron transfer reactions with PDS, promoting the activation of S₂O₈. 2- Fractionation generates reactive species with strong oxidizing capabilities. During the reaction, Fe and Mn may have a synergistic effect; the cyclic transformation of different metal valence states improves electron transfer efficiency, allowing PDS to be continuously activated under relatively mild conditions. Sulfur acts as an electron buffer and structural stabilizer, reducing the rapid dissolution of metal ions and contributing to maintaining the long-term activity of the system.

[0018] In this system, biochar not only serves as a carrier but also directly participates in the pollutant removal process. Its abundant mesopores and high specific surface area effectively adsorb chlorobenzene molecules, enriching pollutants on the material surface and within the pores, thereby shortening the diffusion distance between them and reactive free radicals. Furthermore, the oxygen-containing functional groups and defect structures on the biochar surface act as electron transport channels, promoting the reaction between iron, manganese, sulfur, and persulfate, and improving the generation efficiency of active species. As the reaction proceeds, the further development of the biochar's pore structure also helps to increase the overall reaction interface area, enabling the adsorption and oxidation processes to proceed synergistically.

[0019] In this system, bentonite primarily functions as a structural regulator and reaction buffer. Its excellent water absorption and ion exchange capacity help regulate the local reaction environment, slowing the rapid release of iron and manganese ions and preventing excessive loss of active components. Simultaneously, bentonite possesses a certain physical adsorption capacity for organic pollutants, which can extend the residence time of chlorobenzene in the reaction zone to some extent, allowing it to participate more fully in the oxidation reaction. Furthermore, the presence of bentonite improves the overall stability and homogeneity of the packing material, contributing to the maintenance of reaction performance under long-term operating conditions.

[0020] In this composite filler material, although iron, manganese, and sulfur (Fe, M, and S) are thermodynamically readily oxidized, their oxidation failure process is significantly slowed down through structural design. Fe, M, and S are loaded in situ onto the surface and within the pores of biochar. The porous structure of biochar provides significant spatial confinement, limiting direct contact between Fe, M, and S and dissolved oxygen and other oxidizing agents. Simultaneously, the conjugated carbon structure and surface functional groups of biochar act as electron buffers at the microscale, helping to stabilize the low valence states of iron and manganese and reducing their conversion rates to inert oxides or hydroxides. After further preparation into filler particles, the Fe, M, and S-biochar composite is fixed within a porous framework formed by bentonite and silica. Macroscopically, this reduces the mass transfer rate of oxygen and water to active sites, while microscopically, the water absorption and buffering capacity of bentonite stabilize the local reaction environment. This transforms the oxidation process of Fe, M, and S from a rapid, uncontrollable surface reaction into a relatively slow, diffusion-controlled structural evolution process. This multi-scale synergistic protection allows Fe, M, and S to maintain their reactivity in the reaction system for a longer period without rapid failure.

[0021] In the packed particle system, the removal of chlorobenzene is not a single process, but rather the result of a synergistic effect of adsorption, enrichment, and oxidation. Chlorobenzene is first adsorbed and enriched on the surface and within the pores of the material by biochar and bentonite, and then undergoes bond breaking and gradual oxidation under the action of strongly oxidizing active species generated by iron-manganese-sulfur activated PDS. The porous structure and multiphase interface inside the material significantly improve the contact efficiency between pollutants and active species, thereby achieving efficient degradation of chlorobenzene.

[0022] The beneficial effects of this invention are: (1) Because the iron-manganese sulfides are confined in situ within the pores of the biochar and coated with an inorganic framework, the reaction products are distributed in situ within the particles without blocking the main pores. Instead, they induce further pore development through interfacial reconstruction. Experiments have shown that the specific surface area of ​​the filling material after the reaction increased from the initial approximately 113.48 m². 2 / g increased to 151.67m 2 / g, the average adsorption pore size decreased, indicating that the material structure is "evolvable rather than degenerate" during operation, effectively maintaining long-term permeability.

[0023] (2) The present invention significantly delays oxidation passivation. The porous structure of biochar and the inorganic network framework form a multi-scale spatial confinement, which reduces the diffusion rate of oxygen and water to the active sites, and transforms the oxidation process of iron and manganese sulfides from a rapid surface reaction to a diffusion-controlled slow process, thus significantly extending the catalytic lifetime.

[0024] (3) The ion exchange capacity of bentonite and the adsorption effect of biochar synergistically limited the rapid dissolution of iron and manganese ions. The total iron dissolution was measured to be less than 0.15 mg / L. There was also a balance between the release and refixation of manganese ions, which ensured the environmental safety of the remediation process. Attached Figure Description

[0025] Figure 1 This describes the change in the degradation rate of chlorobenzene in the effluent over time. Figure 2 It shows the change in pH of the effluent over time; Figure 3 It shows the change in sodium persulfate concentration in the effluent over time; Figure 4 It is the total iron ion concentration in the effluent over time; Figure 5 It is the change in the total manganese ion concentration in the effluent over time; Figure 6 These are SEM images of the prepared iron-manganese-sulfur-corn straw biochar composite material (FMS@SBC), the unreacted filler material, and the reacted filler material; Figure 7 The images show SEM images and principal element distribution diagrams of the prepared iron-manganese-sulfur-corn straw biochar composite material (FMS@SBC), the unreacted filler material, and the reacted filler material. Figure 8 These are the FTIR spectra of the filling material before and after the reaction; Figure 9 These are the N2 adsorption-desorption curves of the filling material before and after the reaction; Figure 10 This is a comparison chart of the degradation rates of chlorobenzene by different materials; Figure 11 This is a comparison chart of the degradation rates of chlorobenzene by different materials in cyclic testing; Figure 12 This is a graph showing the changes in total manganese ion concentration in different materials during cyclic testing. Figure 13 This is a graph showing the changes in total iron ion concentration in different materials during cyclic testing. Figure 14 The graph shows the quenching experimental results under the action of different quenching agents. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1: Preparation of iron-manganese sulfide composite filler particles (1) Preparation of iron-manganese-sulfur-corn straw biochar composite material (FMS@SBC): 5g of corn stalk biochar (made by pyrolyzing corn stalks at 800-1000℃ for 2-4 hours and activating with steam) was placed in 276 mL of deionized water and sonicated for 10 minutes to ensure thorough dispersion. Then, 12g of FeCl2·4H2O and 12g of MnCl2·4H2O were added, and the mixture was vigorously stirred under a continuous nitrogen atmosphere until a homogeneous solution was formed. Using a peristaltic pump, 30g of Na2S·9H2O (pre-dissolved in 92 mL of deoxygenated deionized water) was slowly added dropwise to the mixture over 1 hour. After the addition was complete, the entire mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor and heated at 150℃ for 15 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting product was washed three times with a mixture of ethanol and water, centrifuged, and then freeze-dried. Finally, the dried material was sieved to obtain a powdered iron-manganese-sulfur-corn stalk biochar composite material (FMS@SBC). Throughout the entire synthesis process, including the water used for dissolution and washing, deoxygenated deionized water treated with nitrogen gas was used to avoid oxidation side reactions and the formation of iron / manganese (oxygen) hydroxides.

[0027] (2) Molding and preparation of composite filler particles: Weigh 26g of the prepared FMS@SBC material and 10g of bentonite into a beaker. Stir thoroughly with a magnetic stirrer until the mixture is homogeneous and free of significant agglomeration. Then, add a total of 13.3g of 30% deoxysilica sol in portions, kneading thoroughly by hand or with a tool after each addition to ensure the wet material is evenly mixed and forms a ball. Extrude the wet material ball through a 2mm sieve to form cylindrical wet granules with a diameter of approximately 2mm. Wrap the formed wet granules in plastic wrap and allow them to solidify under vacuum at room temperature for 12 hours. Afterward, place the material in a vacuum drying oven and dry at 40-60℃ until constant weight. Finally, sieve out fine powder with a particle size less than 0.5mm to obtain the final iron-manganese sulfide composite filler particles.

[0028] Example 2: Performance testing of composite filler particles in a simulated permeable reactive barrier (PRB) The chlorobenzene degradation experiment was conducted in a transparent quartz glass sand tank (simulating a PRB reaction vessel) measuring 10 cm long, 1 cm wide, and 10 cm high. The reaction vessel was filled from top to bottom as follows: a 2 cm thick layer of quartz sand as a buffer layer, a 5 cm thick layer of composite filler particles prepared in Example 1 (as the core medium of the reaction wall), and a 2 cm thick layer of quartz sand as a lower buffer layer. Organic filter sheets were used to separate and fix the filler particles from the quartz sand layer to prevent particle loss. After filling, the reaction column was flushed from bottom to top with a background solution (0.01 mol / L NaCl, pH=7.0) at a low flow rate until the effluent was clear and free of significant turbidity.

[0029] A simulated contaminated groundwater sample containing 20 mg / L chlorobenzene and 1 mM sodium persulfate (PDS) and an oxidant (using the background solution as a solvent) was prepared. The contaminated water sample was continuously passed through the reaction wall from top to bottom at a constant flow rate of 2 mL / min. Samples were taken from the effluent on days 1, 3, 6, 9, 12, and 15 of the reaction. Each time, 1 mL of the water sample was immediately added to a sample vial containing 0.2 g NaCl, 4 mL n-hexane, and 1 mL of quencher (12410 mg / L sodium thiosulfate pentahydrate) for gas chromatography to determine the residual concentration of chlorobenzene. Simultaneously, another 1 mL water sample was taken at the same time point to determine the pH, total iron ion concentration, and total manganese ion concentration of the effluent. After the experiment, the packed particulate material before and after the reaction was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), specific surface area (BET), and Fourier transform infrared spectroscopy (FTIR) to analyze the material's structural evolution. This experiment set up two parallel experiments, and set up a blank experiment without adding filler particles (only filled with quartz sand) as a control.

[0030] Test methods (1) Chlorobenzene detection MCB concentration was determined using an automated gas chromatograph (GC, PerkinElmer, Clarus 690) with an HP-5MS column (30 m × 0.25 mm × 0.25 μm) and a flame ionization detector (FID). The column temperature program was as follows: initial temperature 50 °C held for 2 min, then increased to 155 °C at a rate of 15 °C / min and held for 2 min, and finally increased to 200 °C at a rate of 30 °C / min and held for 0.5 min.

[0031] (2) Detection of degradation products Chlorobenzene degradation products in the FMS / PDS system were identified using GC-MS (PerkinElmer, Clarus 690-SQ8T, USA). The instrument used high-purity He as the carrier gas at a flow rate of 1 mL / min. The injection port temperature was 280 °C, the injection volume was 1 μL, and there was no split flow. The mass spectrometry conditions were: ionization voltage 70 eV, ion source temperature 230 °C, transfer line temperature 280 °C, mass spectrum scan range 35–450 amu, and the NIST20 mass library.

[0032] (3) Persulfate (PDS, S2O8) 2- ) detection Weigh 4.98 g of KI and 0.252 g of NaHCO3 and dissolve them in 150 mL of deionized water to obtain a mixed solution (buffer solution) of 0.2 M KI (166) and 0.02 M NaHCO3 (84) in a brown light-proof bottle. Take the corresponding PDS standard solutions in sequence, quickly add 8 mL of the mixed solution, dilute to 30 mL with deionized water, shake well and let stand for 15 min. Measure the absorbance at a wavelength of λ = 400 nm and plot the PDS concentration standard curve. Filter 0.8 mL of the reaction solution with a filter, add 7.2 mL of the mixed solution of 0.2 M KI (166) and 0.02 M NaHCO3 (84), and dilute 10 times for testing.

[0033] (4) Detection of iron ions Total dissolved iron ions: determined by inductively coupled plasma mass spectrometry.

[0034] (5) Manganese ion detection Total dissolved manganese ions: determined by inductively coupled plasma mass spectrometry.

[0035] Test results: (1) Chlorobenzene degradation effect: such as Figure 1 As shown, the experimental group (filled particles) achieved a degradation rate of 98.55% for chlorobenzene in the initial stage of the reaction (days 1 and 3), indicating strong initial activity of the material. As the reaction progressed, the degradation rate gradually decreased, reaching 91.21%, 85.02%, 75.28%, and 52.63% on days 6, 9, 12, and 15, respectively, demonstrating sustained degradation capability. In contrast, the degradation rate of the blank control group remained only between 23% and 26% throughout the experiment, showing a gradual change, indicating limited natural decay of chlorobenzene. The main degradation effect originated from the filled particles, while the removal in the blank control group mainly came from non-catalytic factors such as volatilization, weak adsorption, and PDS auto-oxidation.

[0036] (2) Changes in system parameters: Figure 2The changes in pH of the reaction system over time are shown. In the initial stage (days 1-3), the pH remained near neutral (approximately 7.0-7.2), indicating a strong buffering capacity in the initial reaction phase. As the reaction progressed, the pH decreased to approximately 4.0 on days 6 and 9, due to the generation of acidic intermediates during persulfate activation and chlorobenzene degradation. Subsequently, the pH slightly recovered on days 12 and 15 and stabilized between 4.2 and 4.4, indicating that the system gradually reached a new acid-base equilibrium. Overall, the pH changes were relatively gradual, without drastic fluctuations.

[0037] Depend on Figure 3 It can be seen that in the initial stage of the reaction, the residual concentration of sodium persulfate in the effluent is close to 0 mg / L, indicating that the PDS entering the reaction zone can be rapidly activated and consumed by the filling particles. As the running time increases, the residual concentration of PDS in the effluent gradually increases, indicating that the active sites are consumed to a certain extent or mass transfer is limited, and the PDS is not completely activated; however, the system still maintains a certain chlorobenzene degradation capacity within 15 days, indicating that the material has the ability to continuously activate PDS.

[0038] like Figure 4 As shown, the total iron ion concentration in the solution remained at a low level throughout the reaction process. Initially (day 1), the iron ion concentration was approximately 0.05 mg / L, rising to approximately 0.15 mg / L by day 6. It then decreased to near the detection limit on days 9 and 12, before slightly increasing again on day 15. These results indicate that iron primarily participates in the reaction in its solid phase, with only a small amount of iron ions dissolving into the solution. Furthermore, the dissolution behavior exhibited a phased change without a sustained upward trend.

[0039] Figure 5 The changes in total manganese ion concentration in the system over time are shown. In the initial stages of the reaction (days 1-3), the manganese ion concentration was low, less than 1 mg / L. As the reaction proceeded, the manganese ion concentration increased to approximately 3 mg / L on day 6, reaching higher levels (approximately 13 mg / L) on days 9 and 12, before slightly decreasing on day 15. These changes in manganese ion concentration indicate that manganese underwent a certain degree of dissolution during the reaction, which is related to manganese participation in persulfate activation and the redox cycle. The later decrease in concentration suggests that the release and refixation of manganese may have occurred simultaneously in the system.

[0040] (3) Evolution of material structure: From Figure 6As can be seen, FMS@SBC exhibits a distinctly rough and porous structure, composed of irregularly stacked blocky and flocculent particles, with a surface covered by numerous fine particles. The well-developed and interconnected pores indicate that biochar, as a carrier, provides abundant attachment sites for the loading of iron and manganese sulfides. The surface structure of the unreacted filler material is relatively loose, with the sheet-like material mainly consisting of bentonite lamellar structures, interspersed with iron, manganese, and sulfide particles. Large voids exist in some areas, indicating that its internal structure has not yet undergone reaction reconstruction. In contrast, the surface of the reacted filler material becomes significantly denser, with more tightly bound bentonite particles, while still retaining most of the micropores and mesopores. This morphological change from loose to dense indicates that some material deposition or structural reorganization occurred on the material surface during the reaction, with reaction products covering or filling some of the original pores, reflecting that the filler material participated in interfacial reactions and underwent structural evolution during the reaction. However, the micropore and mesopore framework of the reacted filler particles did not collapse, indicating that the filler material can reduce the leaching of reaction products and maintain continuous permeability.

[0041] Figure 7 EDS (Energy Dispersive Spectroscopy) and elemental distribution results showed that C and O were uniformly distributed in FMS@SBC, indicating that the biochar framework structure remained intact. Meanwhile, Fe, Mn, and S elements exhibited relatively consistent distribution characteristics on the material surface, without obvious agglomeration, indicating that iron and manganese sulfides were uniformly loaded on the biochar surface or in the pores. The filler material had high O and Si contents, and the elemental distribution showed significant regional differences. This was due to the silica framework formed by silica sol and the incorporation of bentonite, which also reduced the distribution of Fe and Mn. After the reaction, the overall content and uniformity of Fe and Mn distribution in the filler material changed, with the overall elemental distribution becoming more dispersed. Simultaneously, the S element signal increased, indicating that Fe, Mn, and S recombinated or transformed during the reaction, forming a new sulfur-containing phase. The contents of C, Si, and S in the post-reaction filler material all increased, while the Mn content decreased significantly due to the leaching effect of the reaction.

[0042] Depend on Figure 8 It can be seen that the pre-reaction packing material is at 3416 cm⁻¹ -1 There is a distinct broad peak at 1000-1100 cm⁻¹, corresponding to the -OH stretching vibration. -1 Nearby (approximately 1036 cm) -1 The absorption peak indicates the presence of a large number of hydroxyl groups or adsorbed water on the material surface; the peak at 1334 cm⁻¹ before the reaction... -1 The weak peak at 727 cm⁻¹ is related to the CH / S- vibration in the organic functional group. This peak disappears in the reacted material, possibly due to oxidation altering the functional group. -1d The absorption peaks mainly represent the stretching vibrations of Fe-S and Mn-S. The low wavenumber regions are 469, 518, and 797 cm⁻¹.-1 The peak intensities did not change significantly, and these peaks are mainly related to the Si-O vibrations in bentonite and silica. Overall, the absorption peaks of H₂O and Si-O in the FTIR spectra before and after the reaction did not change much, indicating that the structures of bentonite and silica did not change much during the reaction. However, the CH / S- bonds weakened, indicating that the degradation of chlorobenzene mainly depends on the oxidation effect of iron-manganese-sulfur materials and the activation effect of biochar.

[0043] Depend on Figure 9 According to BET analysis results, the specific surface area of ​​the unreacted filler material is 113.4848 m². 2 / g, which is within the common range for engineering-grade load-bearing composite materials, can provide sufficient reaction interfaces while ensuring structural stability. The specific surface area of ​​the filler material increases to 151.6692 m² after the reaction. 2 The / g indicates that the reaction did not cause pore structure collapse, and the active components were not completely blocked or deactivated, demonstrating that the material structure is "evolvable rather than degenerate" during operation. The adsorption-desorption isotherms of both materials exhibit typical Type IV characteristics, accompanied by a significant hysteresis loop, indicating that their pore structure is predominantly mesopores. Compared to the unreacted sample, the nitrogen adsorption capacity of the reacted material increased across the entire relative pressure range, especially in the medium-to-high relative pressure region, reflecting further development of the pore structure. In terms of pore size parameters, the average BET adsorption pore size of the reacted material decreased from 6.9213 nm to 6.1331 nm, and the average desorption pore size decreased from 5.9256 nm to 5.1183 nm, indicating that some large mesopores were refined during the reaction, while potentially forming more numerous but smaller mesopore structures.

[0044] Example 3: Comparison of chlorobenzene removal effects of different materials Weigh 8 mg of the catalyst material (SBC, FMS, FMS@SBC, and composite material; wherein the composite material is the composite filler particle prepared in Example 1, with 10.7 mg of composite material containing approximately 8 mg of FMS@SBC) and add it to a 40 mL brown screw-top glass bottle. Add 40 mL of a mixed solution containing 20 mg / L chlorobenzene and 1 mM PDS to the bottle. React on a rotary mixer for 12 h, and determine the concentrations of chlorobenzene, total iron ions, and total manganese ions in the solution after the reaction according to the sampling and testing method in Example 2. Simultaneously, control experiments were conducted with chlorobenzene + SBC (without PDS) and chlorobenzene + PDS (without catalyst material).

[0045] In addition, a cyclic experiment was conducted. 40 mg of material (53 mg for the composite material) was weighed and added to a 40 mL brown screw-top glass bottle. 40 mL of a mixed solution containing 20 mg / L chlorobenzene and 1 mM PDS was added, and the mixture was reacted for 12 hours before sampling. The solution was centrifuged to separate the solid material, and then fresh mixed solution was added. The reaction and sampling were repeated for a total of 5 cycles. Using the same detection method as in Example 2, the concentrations of chlorobenzene, total iron, and total manganese in the sample were determined after each cycle.

[0046] Test Results (1) Chlorobenzene removal effect like Figure 10 As shown, the four materials—"bentonite," "SBC+PDS," "FMS+PDS," and "FMS@SBC+PDS"—exhibited different removal effects on chlorobenzene. Bentonite or PDS alone showed low removal efficiency, indicating limited adsorption capacity of bentonite. PDS, without a catalyst, exhibited weak degradation ability for chlorobenzene. SBC achieved a chlorobenzene removal rate of 68.82%, demonstrating strong adsorption capacity. The combined use of SBC and PDS further increased the removal rate to 76.59%, indicating that SBC has a certain catalytic effect on the degradation of chlorobenzene by PDS. Adding the FMS catalyst increased the removal rate to 92.52%, confirming the excellent catalytic performance of FMS for persulfate. The FMS@SBC+PDS combination achieved a chlorobenzene removal rate of 92.95%, indicating that the synergistic effect of adsorption and catalysis on SBC loaded onto FMS resulted in better degradation of chlorobenzene. The molded filler particles showed the highest degradation rate of chlorobenzene, reaching 94.16%. This is because, in addition to the adsorption and catalytic effects of the FMS@SBC material, the small amount of bentonite contained in the filler material also has a certain adsorption capacity for chlorobenzene.

[0047] The degradation results of chlorobenzene in the cyclic experiment are as follows: Figure 11 As shown, the degradation efficiency of all four materials for chlorobenzene gradually decreased with increasing cycle number. Overall, the cyclic removal efficiency of the materials was: composite material + PDS > SBC > FMS@SBC + PDS > FMS + PDS. The composite material exhibited the highest and most stable removal efficiency in multiple cycle experiments, demonstrating excellent cycle stability and continuous catalytic ability, making it suitable for repeated use in practical engineering.

[0048] (2) Changes in total manganese and iron ion concentrations The results of the total manganese ion concentration change in the cyclic experiment are as follows: Figure 12As shown in the figure, the total manganese ion concentration gradually decreases with increasing experimental cycles. This is because the manganese in the catalytic material reacts to form manganese ions which dissolve in the water. With increasing cycle count, oxidation of the material gradually weakens its catalytic ability against persulfate, leading to a gradual decrease in the total manganese ion concentration. Comparing the three catalytic materials, the leaching of total manganese ions from the filler material is consistently lower than that from FMS@SBC and FMS. This is due to the adsorption of manganese ions by the biochar and bentonite components in the composite material.

[0049] Changes in total iron ion concentration as follows Figure 13 As shown in the diagram, in the first cycle experiment, almost no iron ion leaching occurred in the reactions of the three materials. From the second cycle onwards, the total iron ion concentration increased, reaching its maximum in the FMS@SBC and FMS reaction groups by the end of the third cycle. This indicates that manganese in the catalytic materials first catalyzes persulfate degradation, followed by iron. In the catalytic material experimental group, the total iron ion concentration was consistently lower than that of the other two groups, with a maximum concentration not exceeding 1 mg / L. This is attributed to the adsorption effect of biochar and bentonite in the packing particles. The results of total manganese and iron ion concentrations demonstrate that the composite particles, as a catalytic material for the degradation of chlorobenzene by persulfate, not only exhibit good catalytic effects but also adsorb the leaching of manganese and iron ions during the reaction, reducing secondary pollution to groundwater.

[0050] Example 4 Quenching Experiment Weigh 10.7 mg of the composite material into a 40 mL brown screw-top glass bottle. Add 40 mL of a mixed solution containing 20 mg / L chlorobenzene, 1 mM MPDS, and different quenchers (quenchers being 500 mM methanol, 500 mM tert-butanol, 50 mM furfuryl alcohol, 50 mM p-benzoquinone, 5 mM sodium oxalate, and 5 mM silver nitrate, respectively). React on a rotary mixer for 12 h, and determine the concentration of chlorobenzene in the solution after the reaction according to the sampling and testing method in Example 2.

[0051] Test Results Quenching experiment results under different quenching agents are as follows Figure 14 As shown. Generally, tert-butanol is commonly used to quench H₂O•; methanol is commonly used to quench SO₄•− and H₂O•; p-benzoquinone can be used as a quencher for O₂•−; and furfuryl alcohol can be used as a detection agent. 1 Sodium oxalate is an effective quencher for O2. In the quenching of high-valence metal species, many chelating agents with specific functional groups (such as oxalates) can interact with high-valence Fe or Mn to form metal carboxyl complexes (Fe-OA or Mn-OA) due to high steric hindrance and coordination effects, thereby inhibiting the formation of HVMS in the activation system. Therefore, sodium oxalate can be a good choice for verifying high-valence metal interactions. AgNO3 has high electron quenching ability, but poor PDS activation performance, and is often used as a quencher for studying electron transfer in catalytic processes. Without the addition of a quencher, the degradation rate of chlorobenzene reached 94.16%. Figure 10 ).like Figure 14 As shown, the addition of methanol and tert-butanol reduced the chlorobenzene removal rate to 32.7% and 5.44%, respectively, indicating that SO4•− and HO• play a major role in the system. After the addition of furfuryl alcohol and p-benzoquinone, the degradation rate of chlorobenzene decreased to 47.35% and 35.28%, respectively, further demonstrating the role of organic free radicals O2•− and... 1 O2 contributes to the degradation process. The addition of sodium oxalate also reduced the chlorobenzene removal rate to 43%, indicating that high-valence metal species are generated and play an important role in degradation within the reaction system. The addition of silver nitrate reduced the chlorobenzene degradation rate to 34.27%, demonstrating the importance of electron transfer in the degradation process. Therefore, in the synergistic degradation of chlorobenzene by composite materials and PDS, both strong oxidizing free radicals such as SO4•− and HO• are dominant, while some reducing and electron transfer mechanisms are also involved, with multiple oxidation / reduction channels synergistically promoting the efficient degradation of chlorobenzene.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A composite filler particle made of iron and manganese sulfides for the removal of chlorobenzene from low-flow-rate groundwater, characterized in that, The filler particles include an iron-manganese-sulfur-corn straw biochar composite material, bentonite, and an inorganic binder network; The iron-manganese-sulfur-corn straw biochar composite material includes corn straw biochar and iron-manganese-sulfur particles loaded thereon by in-situ chemical precipitation. The inorganic bonding network is composed of a silica skeleton formed by the dehydration and condensation of silica sol and layered bentonite supporting each other. The iron-manganese-sulfur-corn stalk biochar composite material is dispersed in the gaps of the inorganic bonding network, forming a particulate entity with a multi-level porous structure.

2. The composite filler particles according to claim 1, characterized in that, The composite filler particles comprise the following raw materials in parts by weight: 24-28 parts of iron-manganese-sulfur-corn straw biochar composite material, 8-10 parts of bentonite, and 12-15 parts of deoxysilica sol with a mass fraction of 30%.

3. The composite filler particles according to claim 2, characterized in that, The atomic ratio of iron, manganese, and sulfur in the iron-manganese-sulfur-corn straw biochar composite material satisfies: Fe:Mn:S=1:(0.8-1.2):(1.2-1.5).

4. A method for preparing iron-manganese sulfide composite filler particles for chlorobenzene removal in low-flow-rate groundwater, used to prepare the iron-manganese sulfide composite filler particles for chlorobenzene removal in low-flow-rate groundwater as described in any one of claims 1-3, characterized in that, The preparation method includes: S1. Mix corn straw biochar, soluble ferrous salt and soluble manganese salt in deoxygenated deionized water, add sodium sulfide nonahydrate solution dropwise under nitrogen atmosphere, and carry out hydrothermal reaction at 140-160℃ to obtain iron-manganese-sulfur-corn straw biochar composite material. S2. The composite material is mixed with bentonite, silica sol is added and kneaded until smooth, and then extruded through a 2mm sieve to form a mold; S3. The molding material is vacuum static curing and vacuum dried at 40-60℃, and powder with a particle size of less than 0.5mm is sieved out.

5. The preparation method according to claim 4, characterized in that, In step S1, the corn stalk biochar is a porous biochar obtained by pyrolysis at 800-1000℃ and activation by steam.

6. The preparation method according to claim 4, characterized in that, The weight ratio of the corn straw biochar, soluble ferrous salt, soluble ferrous manganese salt, and sodium sulfide nonahydrate is 0.5:(1.1-1.3):(1.1-1.3):(2.8-3.2), wherein the soluble ferrous salt includes ferrous chloride tetrahydrate, and the soluble ferrous manganese salt includes manganese chloride tetrahydrate.

7. The preparation method according to claim 4, characterized in that, In step S1, the hydrothermal reaction is carried out in a polytetrafluoroethylene-lined high-pressure reactor for 12-18 hours.

8. The application of the composite filler particles according to claim 1 in the construction of a permeable reactive wall.

9. The application according to claim 8, characterized in that, The filler particles, acting as an activator for sodium persulfate, are used to remove chlorobenzene from groundwater.

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